WO2016034253A1

WO2016034253A1 - Photocatalytic reactor

Info

Publication number: WO2016034253A1
Application number: PCT/EP2014/069011
Authority: WO
Inventors: Luka SUHADOLNIK; Matic KRIVEC; Miran Ceh; Kristina Zagar; Goran DRAZIC
Original assignee: Jozef Stefan Institute
Priority date: 2014-09-05
Filing date: 2014-09-05
Publication date: 2016-03-10
Also published as: SI24802A

Abstract

Described herein is a reactor comprising: a housing defining a chamber therein; an inlet channel and an outlet channel running through the housing into the chamber; and a support positioned within the chamber; the support having a surface comprising a semiconductor material. Also described are methods of making reactors, methods of using reactors, and related uses and products.

Description

PHOTOCATALYTIC REACTOR

Technical Field The present invention applies to the field of reactor technology. It may be applied to the field of microreactor technology, for example photocatalytic microreactor technology.

It applies to reactors useful for, for example, wastewater treatment, gas treatment, determination of chemical oxygen demand or synthesis of organic molecules.

Background

Catalytic oxidation with, for example, a T1O2 photocatalyst is considered to be a suitable choice for relatively cheap and efficient elimination of organic pollutants from a variety of media, such as wastewater, polluted groundwater, toxic industrial wastes and polluted air (M.R. Hoffmann, S . Martin, W. Choi, D.W. Bahnemann, Chemical Reviews 95 (1995) 69- 96). Furthermore, catalysis with, for example, T1O2 can be successfully applied as an efficient route for the selective synthesis of a number of organic molecules, used in the food, pharmaceutical, and cosmetic industries (G. Palmisano, V. Augugliaro, M. Pagliaro, L.

Palmisano, Chem. Commun. (2007) 3425-3437).

Slurry reactors with suspended T1O2 particles have a uniform catalyst distribution and a high photocatalytic surface-to-volume ratio (H. de Lasa, B. Serrano, M. Salaices, Photocatalytic Reaction Engineering, Springer Science + Business Media, New York, 2005). However, there are problems with designing a continuous process and scale-up from laboratory to production is necessary for processing larger volumes of polluted media. Additionally, the T1O2 particles have to be separated from the products and recycled, which is an expensive and time-consuming process. In most cases, it is impossible to completely remove all of the T1O2 nanoparticles from the liquid. Furthermore, the penetration depth of the ultraviolet (UV) light is rapidly decreased due to the strong absorbing properties of the suspended T1O2 particles and other organic molecules.

In recent years, reactor technologies such as microreactor technology have become a valuable tool for the chemical industry and mobile applications of chemical systems.

Microreactor technology enables efficient and highly controlled photocatalytic processes based on, for example, T1O2 nanoparticles. Nanoparticles are immobilized on surfaces inside the microreactor. With very small dimensions of the microreactor, where at least one dimension is smaller than 1 millimetre, these systems have large surface to volume ratio, where surface is defined as free surface of T1O2 nanoparticles and volume is defined as free volume of microreactor's channel.

Microreactors also allow simple conduction of continuous processes. Scale-up is replaced by simple numbering-up of the microreactors developed on laboratory scale to meet industrial needs. In this way, capacity of microreactor system for water treatment is simply magnified by adding additional units to the existing system (R. Gorges, S. Meyer, G. Kreisel, Journal of Photochemistry and Photobiology A: Chemistry 167 (2004) 95-99). Similarly, using several microreactors in parallel, 'numbering-up', provides the possibility for the continuous industrial production of photocatalyzed products (D.M. Roberge, L. Durcy, N. Bieler, P. Cretton, B. Zimmermann, Chem. Eng. Technol. 28 (2005) 318-323).

There are several known methods for depositing ΤΊΟ2 as (for example) nanoparticles on surfaces inside a microreactor. For example, wash-coating (B.-C. Choi, L.-H. Xu, H.-T. Kim, D.W. Bahnemann, J. Ind. Eng. Chem. 5 (2006) 663-672; E.V. Rebrov, A. Berenguer-Murcia,

H.E. Skelton, B.F. Johnson, A.E. Wheatley, J.C. Schouten, Lab Chip 9 (2009) 503-506), continuous flow of a colloidal ΤΊΟ2 suspension through the microreactor (H. Lindstrom, R.

Wootton, A. lies, AIChE Journal 53 (2007) 695-702), spin-coating with titanium tetra- isopropoxide solution (Y. Matsushita, T. Ichimura, N. Ohba, S. Kumada, K. Sakeda, T.

Suzuki, H. Tanibata, T. Murata, Pure Appl. Chem. 79 (2007) 1959-1968), and anodization of a titanium foil to produce T1O2 nanotube arrays (K. Shankar, G.K. Mor, H.E. Prakasam, S.

Yoriya, M. Paulose, O.K. Varghese, C.A. Grimes, Nanotechnology 18 (2007) 65707-65718;

L. Sun, S. Zhang, X. Sun, X. He, J. Nanosci. Nanotechnol. 10 (2010) 4551-4561 ; A. Ghicov,

P. Schmuki, Chem. Commun. 20 (2009) 2791 -2808).

Patent applications JP 2003/301295 A, JP 2007/270213 A and JP 2012/161727 A, refer to anodic oxidation process for preparation of oxidized layers on metal substrate as a part of microreactor manufacturing process. Patent application EP 1 415 707 describes a microreactor with a T1O2 catalytic layer sprayed on the inner walls of microchannels. M. Krivec, K. Zagar, L. Suhadolnik, M. Ceh, G. Drazic, Appl. Mater. Interfaces 5 (2013) 9088-9094 describes the fabrication and properties of a titanium photomicroreactor with immobilized T1O2 photocatalyst and an integrated UV-LED light source. A two-step synthesis with anodization and subsequent thermal treatment, was applied for the preparation of a double-layered, anatase T1O2 film. General Notes

A number of patents and publications are cited herein in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Each of these references is incorporated herein by reference in its entirety into the present disclosure, to the same extent as if each individual reference was specifically and individually indicated to be incorporated by reference.

Throughout this specification, including the claims which follow, unless the context requires otherwise, the word "comprise" and variations such as "comprises" and "comprising," will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a surface layer formation step" includes combinations of two or more such surface layer formation steps, and the like.

Ranges may be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent "about," it will be understood that the particular value forms another embodiment. This disclosure includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art. Summary of the Invention

The present invention seeks to address the problems associated with known reactors as described above, and to improve upon them. In particular, the present invention seeks to provide reactors which demonstrate improvements in prolonging the undiminished photocatalytic activity to a larger number of cycles or longer period of operating time; in reducing production costs with utilization of more accessible and less expensive materials; and in increasing catalytic efficacy. In a first aspect, the present invention provides a reactor comprising: a housing defining a chamber therein; an inlet channel and an outlet channel running through the housing into the chamber; and a support positioned within the chamber; the support having a surface comprising a semiconductor material.

The support surface comprises a semiconductor material. In some embodiments, this surface comprising a semiconductor is present in the form of a layer partially or completely covering or encasing the support. In some embodiments, the support is itself formed of material comprising a semi-conductor material; therefore, the surface of the support comprises a semi-conductor material.

The chamber inside the housing is defined by walls. Those walls are effectively internal walls of the housing. The inlet and outlet channels may be through holes which create a fluid communication path between the chamber and the exterior of the housing. That is, the channels are conduits through which fluid can flow. Suitably, fluid flows into the chamber through the inlet channel and out of the chamber through the outlet channel; it will of course be recognised that the direction of fluid flow may be reversed. The channels are not necessarily enclosed in the present invention, that is, the channels may be entirely or partially in the form of an open trough. Suitably, however, the channels are in the form of sealed conduits.

The inlet channel is fluidically coupled with the outlet channel by the chamber. Therefore, in use, an inlet stream may flow through the inlet channel into the chamber and from there flow through the outlet channel as an outlet stream to exit the reactor.

Generally, the support is positioned in the chamber so that, when fluid flows through the reactor as described above, the fluid contacts the surface of the support. Depending on the exact configuration of the support and its surface, as well as the configuration of the chamber and the inlet and outlet channels, the extent and nature of that contact may vary.

The support is positioned within the chamber. That is, it is suitably mounted therein. While it may have a connection with the chamber, it is not integral with the chamber. This means that the present invention differs from known reactors in which a semiconductor material is immobilised on walls of the chamber.

This configuration has several advantages. The fluid flowing in the reactor has greater access to the semiconductor material of the surface of the support. Therefore, the useful surface area of the support is increased. Accordingly, more effective and more space- efficient reactors can be made. Put another way, the reactors of the present invention suitably have a high surface-to-volume ratio, leading to increased efficiency.

Furthermore, the present reactors can be made more easily because the surface on the support can be formed without the constrictions of the reactor housing. This allows separate, or parallel, processing of the housing and the support, saving time and costs. If the semiconductor material is to be deposited on the walls of the housing, the housing must of course be in hand first. The support surface comprises a semiconductor material. As explained below, certain such materials are preferred. The surface may contain a material which has some catalytic activity. That is, the material may have activity to alter (for example, increase) the rate of certain chemical reactions. It is apparent that, depending on the reaction to be carried out in the reactor, the material can be selected accordingly. The catalytic material may be a "photocatalyst", in that it catalyses a reaction which proceeds by absorption of light. In such embodiments, the present reactors can be described as photocatalytic reactors.

In a second aspect, the present invention provides a method of making a reactor, the method comprising: providing a support; forming a surface layer comprising a semiconductor material on a support; and positioning the support in the chamber provided in the housing.

In a third aspect, the present invention provides a reactor obtainable by the method of the second aspect. The present invention provides a reactor obtainable by a method which includes the method of the second aspect.

In a fourth aspect, the present invention provides a use of a reactor according to the first or third aspect for wastewater treatment, gas treatment, determination of chemical oxygen demand or synthesis of organic molecules. As mentioned above, depending on the intended use of the reactor a suitable semiconductor material for inclusion in the surface of the support can be selected.

In a fifth aspect, the present invention provides a method of using a reactor according to the first or third aspect, comprising: passing a fluid through the inlet channel into the chamber and then out of the chamber through the outlet channel.

Accordingly, reactors used in such a method may be described as flow reactors. Support

The support is positioned within the chamber of the reactor. The support has a surface which is discussed in more detail below. A support which has a high surface area is especially suitable. It may be, for example, at least partially in the form of a coil or a mesh. It has been found that such supports give a high improvement in the performance of the reactors.

As used herein, a coil refers to a structure having a joined sequence of turns, rings or loops. That is, a structure which is broadly helical. The turns, loops or rings may vary in diameter. The space between turns may also vary.

As used herein, a mesh refers to a structure having a group or an interwoven, or otherwise crossed, network of threads or strands which define spaces between them. The size, shape and spacing of the spaces may vary.

Where the support is a coil, it may have an outer diameter (width of the coils) of about 50 to 10000 μηη, for example about 2000 to 5000 μηη. The coil density (number of coils in a given length of the coil) maybe be about 1 to 20 coils per mm, for example about 2 to 10 coils per mm, for example about 3 to 5 coils per mm.

Where the coil is made from a wire, the coil density may range from the maximum value (that is, a space of 0 between turns or coils) to a lower value where the space between turns or coils is about equal to the diameter of the wire used. That is, with reference to the diameter of wire used to form the coil, the space between coils or turns may be from about 0 to about 1 times the diameter of the wire used, for example about 0.2 to 0.8 times the diameter of the wire used, for example about 0.4 to 0.6 times the diameter of the wire used.

Where the support is a mesh, it may be formed from individual pieces of wire/thread or from a single piece of wire/thread. The mesh may have a single mesh layer or multiple layers.

It is noted that while the word "wire" is used herein, it is not intended to be limited to metal items. That is, a "wire" making up a coil or mesh, for example, may be of plastics material etc. as set out herein. The word "thread" is also used herein to refer to a strand of material. It too is not intended to imply any particular property of the material such as its composition or malleability.

The support may be a broadly planar, sheet-like mesh, of a single layer. Multiple layers of such a mesh may be stacked, with or without a space between the layers. For example, a mesh might have a honeycomb structure. In some embodiments, the mesh may be in the form of, for example, a tube or tubular mesh. In some embodiments it may be cylindrical. The mesh may be formed in that way, or may be formed as a sheet and then bent or shaped to form the tubular mesh.

It will be recognised that multiple tubular meshes can also be stacked as set out above, with or without spaces between the layers. Such stacking can form a series of approximately concentric tubes or cylinders. It will be recognised that where multiple meshes are present, for example in a stack, one or more of them may be seen as the present "support". It is contemplated in the present invention that multiple supports as defined herein may be positioned within one chamber. This is not limited to the case where the support is a mesh. As mentioned above, the mesh may have a single mesh layer or multiple layers. In the or each layer, the mesh may have, for example, about 1 to 10 holes per cm², for example about 3 to 7 holes per cm², for example about 5 to 6 holes per cm².

Where the support is a mesh, in some preferred embodiments the mesh density may be as high as possible. The wire may be as thin as possible. The interval of the mesh (distance between the wires/threads making up the mesh) may be 37 to 1400 μηη, that is, 400 Mesh to 14 Mesh, for example 74 to 400 μηη, that is, 200 Mesh to 40 Mesh.

The support may have an area of about 5 to 200 cm².

Where the support is a coil, it may have an area of about 10 to 200 cm², for example about 30 to 100 cm², for example about 40 to 60 cm².

Where the support is a mesh, it may have an area of about 5 to 50 cm², for example about 10 to 40 cm², for example about 20 to 30 cm².

If the support is formed of a wire or thread (metal or non-metal), or a structure formed from such a wire or wires, thread or threads, it may have a diameter of about 0.005 to 5 mm, for example about 0.01 to 1 mm, for example about 100 to 500 μηη, for example about 200 to 400 μηη, for example about 250 μηη to about 350 μηη.

Larger diameters may not be preferred because then the specific area is reduced, limiting the efficacy of the reactor, and costs increase. The support may be formed from, for example, a metal or a plastics material. It may be formed from a metal so that a semiconductor material can be formed as a surface layer on the support by anodizing. It may also be formed from a plastics material. Such a plastics material may have, for example, a coating of a metal in the form of, for example, a foil. In an anodizing process, then, the metal foil can have its surface modified so that a semiconductor material is formed thereon.

The term "anodizing" as used herein refers to a passivation step, used to increase the thickness of the natural oxide layer on the surface of a metal.

In some embodiments, the support is formed from a metal such as titanium (Ti), iron (Fe) or Nickel (Ni). It is preferably formed from Ti. Under anodizing conditions, such a support will develop a T1O2 surface layer. T1O2 is a useful catalyst in certain photoreactions. In other embodiments, the support may be formed from an alloy. Such alloy may contain Ti, Fe and/or Ni. The alloy may be stainless steel. The alloy may be, for example, one of the Inconel family of alloys. These are nickel-chromium-based alloys. They may contain nickel as the major component, with chromium as the secondary major component. The support may be formed from a glass, or T1O2 polymer composites such as a

polypropylene-Ti02 nanocomposite or a combination of T1O2 with a polymer such as polyvinyl alcohol), partially hydrolysed polyvinyl acetate), polyvinylpyrrolidone, or poly(4- vinylpyridine). In such cases, T1O2 acts as the surface layer of the support. The chamber within which the support is positioned has an inner surface. In certain embodiments, the support is positioned or mounted in the chamber so that there is a gap or space between the outer surface of the support and the inner surface of the chamber. That is, the support is spaced from the surface of the chamber rather than being in contact with it. This allows greater flow of a fluid around the support in the chamber. The chamber may have a shape which encourages turbulent flow of a fluid through the reactor. The

configuration of the chamber, the inlet and outlet channels, and the support may also be such that turbulent flow of fluid through the reactor is encouraged. This increases contact between the surface of the support and the fluid (in particular 'unreacted' or 'fresh' fluid), further increasing the efficacy of the present reactors.

Of course, it will be recognised that not the entirety of the support surface must be spaced from the surface of the chamber. That is, it is contemplated that some of the surface of the support may be in contact with the inner surface of the chamber and some not. In some embodiments, less than about 50%, for examples less than about 20%, for example less than about 5% of the surface of the support is in contact with the inner surface of the chamber. In certain embodiments, the distance between the surface of the support and the surface of the chamber (that is, the maximum distance which can be measured between the inner surface of the chamber and a part of the surface of the support) is about 0.001 to 10 mm, for example about 0.01 to 10 mm, for example about 0.01 to 0.3 mm or about 0.1 to 1 mm. In embodiments where the support is a coil, the distance may be about 0.01 to 10 mm. It may be about 0.1 to 1 mm.

In embodiments where the support is a mesh, the distance may be about 0.001 to 10 mm. It may be about 0.01 to 0.3 mm.

The support itself may have a length of about 1 to 10000 mm, for example about 1 to 100 mm. If the support is a coil, a length of about 1 to 100 mm is preferred, for example about 20 to 80 mm, for example about 40 to 60 mm. The support may have a length of about 10 to 10000 mm, for example about 100 to 2000 mm, for example about 500 to 1500 mm.

The support may be formed around a template. In embodiments where the support is a coil, the support coil may be wound around the template. In embodiments where the support is a mesh, the mesh may be for example wrapped around the template to form a mesh over the surface of the template.

As used herein, template describes a structure that facilitates formation of the support and/or positioning of the support within the chamber. For example, the template may be a template rod; that is, the chamber may contain a rod having the support affixed to and/or wound around the surface of the rod. Suitably, the support is wound around the rod, the rod thereby holding the support in place within the chamber. In some embodiments, the support may be a coil wound around the rod. The template may be affixed to the housing, or may be a discrete separable feature. For example, the template may be a rod affixed at either end of the rod to the housing. If a template is used, it preferably does not conduct electricity. In some uses described herein, the support and/or the surface layer of the support acts as an anode in a cell. If a template is used in such embodiments, a non-conductive template is particularly preferred. As used herein, non-conductive means that the object in question does not substantially conduct electricity. That is, it is an electrical insulator or electrically insulative material.

In some uses described herein, the chamber is illuminated with ultraviolet (UV) light. The ultraviolet light may be introduced at least partially through the template. At least part of the template may be translucent and/or transparent to ultraviolet light. In this way ultraviolet light in the chamber can reach the greatest surface area of the support. This increases the efficacy of the reactor, for example the catalytic activity of the surface of the support.

It is noted that, as used herein, transparent/translucent are intended to mean that light passes through the material in question. There is not intended to be a limitation to a particular level of, for example, scattering of the light.

Where the term ultraviolet (UV) light is used herein, it preferably refers to light of wavelength from about 159 to 400 nm, particularly 200 to 400 nm.

The template may be formed from, for example, a glass such as lime-stone glass or quartz glass, a polymer such as polyethylene, polypropylene, poly (methyl methacrylate), a polycarbonate polymer, or polytetrafluoroethylene, calcium fluoride or magnesium fluoride. Surface of Support

The surface of the support comprises a semiconductor material. As explained above that material may have catalytic activity. It may be integral to the support, or may take the form of an additional coating or layer on top of the support. For example, the support may have a metal foil coating which is anodized to form the semiconductor material as the surface layer of the support.

The surface of the support is preferably porous. That is, the surface has a microstructure which includes a number of pores, depressions and holes therein. This porosity serves to increase the surface area available to make contact with fluid in the reactor. Furthermore, the pores can act as anchor points for molecules or materials in the fluid flown through the reactor, yet further improving the activity of the reactor. Such surface adsorption is particularly preferred in embodiments where reaction or treatment of organic molecules is wanted. The support surface preferably comprises a metal chalcogenide, such as a metal oxide (for example T1O2, ZnO or SrTiOs), CdS or CdSe. In preferred embodiments, one or more metal chalogenides are provided as a layer on the support. They may be provided as part of a polymer composite. In preferred embodiments the support surface comprises T1O2, for example, a layer of T1O2.

In certain embodiments, the T1O2 of the surface of the support comprises T1O2 nanotubes. These may be formed by anodizing the support, thereby forming a surface layer, for example if the support is made from Ti or has a Ti foil as a coating. The nanotubes accordingly form a porous surface layer on the support. The nanotubes may form an array.

T1O2 nanotubes of this type can be further enhanced by immobilizing or forming additional T1O2 particles on them. This improves the absorption and reaction of pollutants or other molecules in the fluid which is flown through the reactor.

The nanotubes suitably have an aspect ratio of 1 or more. The nanotubes may have or form holes with a diameter of about 10 to 1000 nm, for example about 25 to 250 nm, for example about 50 to 200 nm. Where the support is a coil, the nanotubes preferably have holes of a diameter of about 25 to 250 nm. Where the support is a mesh, the nanotubes preferably have holes of a diameter of about 25 to 250 nm.

The nanotubes may have or form holes with a depth of 1 to 100000 nm. Where the support is a coil, the nanotubes preferably have holes of a depth of, for example, about 10000 to 30000 nm. Where the support is a mesh, the nanotubes preferably have holes of a depth of about 1 to 100000 nm, preferably about 10000 to 30000 nm.

The nanotubes may have or form holes such that the lateral distance between holes is 1 mm or less. The lateral distance between holes may be about 1 to 1000 nm, for example about 1 to 200 nm.

As used herein the term 'hole' with respect to nanotubes is used to describe the bore, pit or through hole in the centre of the nanotube (that is, the space which is not part of the tubular wall). The nanotubes are preferably vertically aligned. That it, the nanotubes have a length along the axis of their holes and the axes of the nanotubes are aligned with one another, generally in the directed perpendicular to the surface of the support. Housing

The housing defines a chamber therein. That is, in the housing, there is a chamber defined by internal walls of the housing. The support is positioned inside that chamber in the reactor of the present invention. The housing also has channels running from the outside the housing into the chamber. Those channels are, as explained herein, referred to as the inlet channel and the outlet channel.

In certain embodiments there may be more than one inlet channel and/or more than one outlet channel. That is, there may be multiple inlet channels and/or multiple outlet channels. There may be more than two channels connecting the chamber to the exterior of the housing. For example, there may be three, four, five or six such channels.

The channels provide fluidic connections between the chamber and the exterior of the chamber. They may be located anywhere around the chamber, but an inlet channel and an outlet channel are suitably approximately opposite to one another across the chamber.

In some embodiments, the chamber has an elongate shape. In such embodiments, at least one inlet channel and at least one outlet channel may be located at opposite ends of the chamber. This increases the residence time of a fluid within the reactor.

In certain embodiments, the housing comprises at least one portion which allows ultraviolet light to pass through it into the chamber. Indeed, the entire housing may allow ultraviolet light to pass through it. In embodiments where the reactor is used for a photoreaction this allows the highest amount of light to reach the chamber, increasing the efficacy of the reactor.

In particular, where the support has an anodized surface layer, for example of T1O2, a housing which is transparent to ultraviolet radiation means that the surface layer of the support can be maximally irradiated. The ultraviolet light directed to the chamber is not disrupted by, for example, the presence of immobilised particles on the chamber walls. By using a support as in the present invention, the area of the support which is exposed to ultraviolet light and which is in contact with the fluid when the reactor is in use is maximised.

Suitable materials for a portion of the housing, or the entire housing, include, for example, poly(methyl methacrylate), fluorinated ethylene propylene, a perfluoroalkoxy alkane, quartz glass, CaF₂, MgF₂ and sapphire.

The reactor may comprise means for exposing the chamber to ultraviolet light. That might be a UV light generation means. The housing may have one or more UV light sources mounted thereon and arranged such that the UV light emitted from them passes into the chamber to illuminate the surface of the support. This is particularly useful where the support surface includes a material such as T1O2 which catalyses photoreactions. Depending on the construction of the reactor, the light may pass through the housing to the chamber or through a gap or hole. In certain embodiments the light may be optically routed before entering the chamber.

In some embodiments it may be preferable to include a UV light source within the chamber. This or these may be instead of or in addition to any UV light sources mounted on the exterior of the housing. The internal UV light source may be located, for example, within a template around which the support is formed. Indeed, the light source itself might form the template. It may be located within a tubular support, for example a tubular mesh support. If multiple meshes are stacked, the internal UV light source may be positioned between layers of the stack, for example between concentric tubes if tubular meshes are stacked

concentrically or between individual planar meshes in a stack of those.

In these embodiments, additional UV radiation can be provided to the surface of the support. In particular, in certain embodiments UV radiation can illuminate the surface of the support from within, further increasing the efficacy of the reactor.

The housing itself may be formed in pieces. That is, the housing may comprise at least two separable parts. The different parts of the housing can be assembled to form the reactor housing. This allows for easier manufacturing and assembly of the reactors. The various channels and chambers described herein are formed within the housing material. They may be formed by known method, such as by molding the housing suitably or drilling or cutting the housing material. Where the housing comprises at least two separable parts, 'sections' of the channels and chamber may be included on the various parts. That is, one or more of the parts of the housing may have one or more depressions or indented shapes thereon or therein, which form channels and chambers when the parts of the housing are assembled. The inscribed depressions or indented shapes of the various parts may correspond to depressions or indented shapes on other of the parts of the housing. This can assist assembly and manufacture of the present reactors. Alternatively, there may be certain parts of the housing which have no depressions or indentations on their surfaces.

It will be understood that each part of the housing may have one or more UV light sources of the type described above mounted thereon. In some embodiments each part of the housing has one or more UV light sources mounted thereon and positioned such that the UV light emitted from them reaches the surface of the support. In other embodiments there may be parts of the housing which do not have a UV light source mounted thereon.

Reactor

The support is positioned within the chamber of the housing. The housing has an inlet channel and an outlet channel which provide a path for fluid to flow from the exterior of the housing, into and through the chamber and out again.

Suitably, the support is positioned in the fluid flow path between the location where the inlet channel and the outlet channel met the chamber. In this way the support is fluidically between the inlet channel and the outlet channel. Accordingly, when fluid flows through the reactor it contacts the surface of the support. Since the support surface may be active, this increases the efficacy of the reactor. The present inventors have found that it is preferable to include two or more electrodes within the chamber. When suitably connected to an electrical source, such as a DC power source, to provide a potential difference, an anode and a cathode are formed. By variation of the potential difference between the anode and the cathode, reaction of a fluid inside the chamber can be enhanced. For example, the present inventors have found that a potential of about 0 to 8 V, for example 2 to 6 V, for example about 4 V, is useful in the reactors described herein. The DC power source can be adjusted to provide the desired potential.

Accordingly, provided here is a reactor, comprising: a housing defining a chamber therein; an inlet channel and an outlet channel running through the housing into the chamber; and a support positioned within the chamber; and a one cathode positioned in the chamber; the support and the cathode each being connectable to an electrical source (for example a DC power source) to create a potential difference between the support and the cathode, such that the support functions as an anode. It will be recognised that the features discussed herein with respect to the support, housing, channels and chamber can be applied here as well.

Where the anode is the support or a surface layer of the support as described herein, the reactor can further comprise at least one cathode positioned within the chamber. The anode and cathode(s) can be electrically connected to a power source to create a potential difference between them. Electrical connectors may run, for example, from the anode and cathode through the housing via through holes. Those connectors may link the anode and cathode to respective anode and cathode terminals on the exterior of the housing. Then, those terminal can be connect to, for example, an electrical source. Since the support or the support surface layer described herein may conduct electricity it can function as the anode in such configurations without additional modification. If the support is formed on a template, as discussed above, it is preferable that the template does not conduct electricity.

It will be understood that one or more such anodes and cathodes may be present in the chamber. For example, there may be two cathodes. The relationship between the number of cathodes and the number of anodes is not fixed. For example, there may be one anode and one cathode, or one anode and two cathodes.

The cathode may be formed from any suitable material. For example, it may be a metal, such as Ti, Cu or Pt. It may be a metal loaded on, for example, a carbon carrier, such as Pt on a carbon carrier. It may be an alloy such as stainless steel. It may be an oxidised metal such as CuO or CU2O, which are p-type semiconductors. Other such semiconductors may be useful as the cathode material.

In certain embodiments at least one cathode is a coil of wire. As explained above, this is a similar form to that which is taken by the support in some embodiments. Like the support, the cathode may be formed on a template. Similar considerations apply. If the anode and the cathode (that is, the support and the cathode) are both on a template, they may be on the same template. That is, for example, an anode coil and a cathode coil may be formed on the same template rod.

Preferably, each cathode is separated from the anode by a non-conductive spacer which prevents direct contact between the anode and the cathode.

In some embodiments, both the anode (support) and the cathode can be formed on a single piece of material. This can be achieved by, for example, selectively anodizing or otherwise coating only a part of the material. It will be recognised that the anode and cathode cannot be electrically connected by the material on which they are formed. So, in these

embodiments the material is non-conductive of electricity. For example, if the material is a non-conductive material such a plastics material, separate regions can be coated with a foil or other coating to form the cathode and, separately, a foil or other coating to form the anode. The anode and cathode in such circumstances can of course have the other properties described herein. The present invention is also directed to reactors with multiple chambers. In particular, there are described reactors comprising two or more of the reactors generally described above, those individual reactors being fluidically coupled. They may be coupled in series. That is, fluid may flow into a first reactor through the inlet channel, undergo a reaction or process, then exit the first reactor via the outlet channel to flow into a second reactor for a further reaction or process before exiting the second reactor via its outlet channel. This can continue through an arbitrary number of reactors, which may be the same or different.

Alternatively or additionally, one or more reactors may be provided in parallel. That is, for example, a fluid stream may be partitioned into multiple streams, each of which flows through an inlet channel into the chamber of a reactor, where it undergoes a reaction or process before exiting said chamber via the respective outlet channels. The nascent streams of fluid may be re-combined. Using multiple reactors in parallel may permit larger volumes of fluid to be processed. It is apparent that by designing a system of multiple reactors, which may be the same or different, in series and/or parallel complex reaction or processing systems can be created.

Method of Making

A reactor can be made by a method comprising: providing a support; forming a surface layer comprising a semiconductor material on a support (a surface layer formation step); and positioning the support in a chamber provided in a housing (a mounting step), there being an inlet channel and an outlet channel running through the housing into the chamber. This method can be used to make the reactors described herein.

The surface layer formation step may be carried out before or after the mounting step. It is suitable carried out before the mounting step. The method may also include a step of forming a mesh or coil which is the support (a support formation step). That step may include, for example, a coil being formed by winding a metal wire around a template.

The support formation step may be carried out before or after the surface layer formation step. Suitably it is carried out before the surface layer formation step.

In some embodiments, in the surface layer formation step the surface layer is not formed on all of the support. That is, the surface layer may not cover the entire surface of the support. The surface layer formation step may suitably include anodizing the support to form a layer of semiconductor material on the surface of the support (an anodizing step). In some embodiments, it includes a step of anodizing a metal support or a support having a metal coating to form a layer of semiconductor material on the surface of the support.

The support having a metal coating may, as described above, be a metal or non-metal item on which a foil is present, for example a foil wrapped around the item.

Optional features relating to the support, surface layer of the support, housing, channels and so on described above apply equally in the presently described methods. For example, the metal of the support or of the coating may preferably be titanium. That is, the support may be formed from or coated with Ti. In such embodiments, the anodizing step forms a T1O2 layer on the support. That layer may have the properties described above. In embodiments where an anodizing step is carried out, the anodizing step suitably includes anodic oxidation of the support for a time between about 20 minutes and 8 hours. It suitably includes anodic oxidation of the support at an anodizing voltage of between about 60 and 120 V. It suitably includes anodic oxidation of the support at an anodizing temperature of about 5 to 50°C. By performing the anodizing step, an anodized support is formed. The anodizing process is able to straightforwardly form a suitable surface layer on the support. For example, a T1O2 layer can easily be formed on a support which is made from Ti or which has a Ti coating (for example a foil).

The method may further include a thermal treatment step of heating the support. This may be carried out after the anodizing step, to heat the anodized support. The thermal treatment step may suitably include heating the support to a temperature of about 400 to 600°C. It may suitably include heating the support in, for example, an air atmosphere or an oxygen atmosphere. It may suitably include heating the support for a time of about 10 to 300 minutes, for example about 120 to 240 minutes.

Method of Use

The reactors described herein can be used for, for example, wastewater treatment, gas treatment, determination of chemical oxygen demand or synthesis of organic molecules. Suitably the reactors are useful for wastewater treatment.

The reactors can be used by a method comprising passing a fluid through the inlet channel into the chamber and then out of the chamber through the outlet channel (a flowing step). In this way, as described herein, the fluid can contact the surface of the support. There it can undergo reaction, treatment etc. The fluid may be a liquid or a gas. For example, it may be a solution of various components such as wastewater. The fluid may enter the chamber through the inlet channel, flow through it and exit the chamber through the outlet channel in a continuous steam. Alternatively, aliquots of fluid may be held in the chamber for a period of time in order to allow reaction or other treatment to occur for a prolonged period. It may be preferable to expose fluid in the chamber to ultraviolet light, for example while fluid is flowing through the chamber. This is particularly the case where the reactor is being used for a photoreaction. For example, when the surface of the support comprises T1O2 and is used for a photoreaction, exposure of the chamber (and thereby the support surface) to ultraviolet light greatly increases catalysis.

It may also be preferable to set a potential difference between an anode and cathode as described herein, for example while fluid is flowing through the chamber. This yet further increases the catalytic effects of the reactors. In particular, a potential of about 0 to 8 V, for example about 2 to 6 V, for example about 4 V.

The following numbered paragraphs describe without limitation certain embodiments of the present invention.

(1 ) A reactor comprising: a housing defining a chamber therein; an inlet channel and an outlet channel running through the housing into the chamber; and a support positioned within the chamber; the support having a surface comprising a semiconductor material; optionally, wherein the support has a surface layer comprising a semiconductor material.

(2) A reactor according to (1 ), wherein the support is a coil or a mesh.

(3) A reactor according to (1 ) or (2), wherein the support is formed from a metal or a plastics material.

(4) A reactor according to (3), wherein the support is formed from an alloy containing Ti, Fe and/or Ni; stainless steel; or Inconel.

(5) A reactor according to (3), wherein the support is formed from Ti.

(6) A reactor according to any one of (1 ) to (5), wherein the support is spaced from the surface of the chamber.

(7) A reactor according to (6), wherein the distance between the support and the surface of the chamber is 0.001 to 10 mm.

(8) A reactor according to (7), wherein the distance between the support and the surface of the chamber is 0.01 to 10 mm. (9) A reactor according to (8), wherein the distance between the support and the surface of the chamber is 0.01 to 0.3 mm.

(10) A reactor according to (8), wherein the distance between the support and the surface of the chamber is 0.1 to 1 mm.

(1 1 ) A reactor according to any one of (1 ) to (10), wherein the support has a length of 10 to 10000 mm.

(12) A reactor according to (1 1 ), wherein the support has a length of 1 to 100 mm.

(13) A reactor according to any one (1 ) to (12), wherein the support is a coil wound around a template.

(14) A reactor according to (13), wherein the template is formed from a material which does not conduct electricity and/or which allows ultraviolet light to pass through it.

(15) A reactor according to (14), wherein the template is formed from lime-stone glass, quartz glass, polyethylene, polypropylene, poly (methyl methacrylate), a polycarbonate polymer, or polytetrafluoroethylene.

(16) A reactor according to any one (1 ) to (15), wherein the support surface is porous.

(17) A reactor according to any one (1 ) to (16), wherein the support surface comprises a metal chalcogenide.

(18) A reactor according to (17), wherein the support surface comprises ΤΊΟ2, ZnO or SrTiC .

(19) A reactor according to (17), wherein the support surface comprises CdS or CdSe.

(20) A reactor according to (18), wherein the support surface comprises ΤΊΟ2.

(21 ) A reactor according to (20), wherein the ΤΊΟ2 is a porous ΤΊΟ2 comprising ΤΊΟ2 nanotubes.

(22) A reactor according to (21 ), wherein the nanotubes have an aspect ratio of 1 or more.

(23) A reactor according to (21 ) or (22), wherein the nanotubes have holes with a diameter of 10 to 1000 nm.

(24) A reactor according to (23), wherein the nanotubes have holes with a diameter of 25 to 250 nm.

(25) A reactor according to (24), wherein the nanotubes have holes with a diameter of 50 to 200 nm.

(26) A reactor according to any one of (21 ) to (25), wherein the nanotubes have holes with a depth of 1 to 100000 nm.

(27) A reactor according (26), wherein the nanotubes have holes with a depth of 10000 to 30000 nm.

(28) A reactor according to (26), wherein the nanotubes have holes with a depth of 10 to 10000 nm.

(29) A reactor according to (28), wherein the nanotubes have holes with a depth of 200 to 2000 nm.

(30) A reactor according to any one of (21 ) to (29), wherein the nanotubes have holes with a lateral distance between them of 1 mm or less. (31 ) A reactor according to (30), wherein the nanotubes have holes with a lateral distance between them of 1 to 1000 nm.

(32) A reactor according to (31 ), wherein the nanotubes have holes with a lateral distance between them of 1 to 200 nm.

(33) A reactor according to any one of (1 ) to (32), wherein the housing comprises at least one portion which allows ultraviolet light to pass through it into the chamber.

(34) A reactor according to (33), wherein a portion of the housing is formed from poly(methyl methacrylate), fluorinated ethylene propylene, a perfluoroalkoxy alkane, quartz glass, CaF₂, MgF2, or sapphire.

(35) A reactor according to any one of (1 ) to (34), wherein the housing has one or more UV light sources mounted thereon and arranged such that the UV light emitted from them passes into the chamber to illuminate the surface of the support.

(36) A reactor according to any one of (1 ) to (35), wherein the housing comprises at least two separable parts.

(37) A reactor according to any one (1 ) to (36), wherein the reactor comprises a cathode positioned in the chamber; the support and the cathode each being connectable to an electrical source to create a potential difference between the support and the cathode, such that the support functions as an anode.

(38) A reactor according to (37), wherein two cathodes are positioned in the chamber.

(39) A reactor according to (38), wherein the or each cathode is formed from Ti, Cu, stainless steel, platinum, or a carbon carrier loaded with platinum.

(40) A reactor according to any one of (37) to (39), wherein at least one cathode is a coil of wire.

(41 ) A reactor according to any one of (37) to (40), wherein the or each cathode is separated from the anode by a non-conductive spacer which prevents direct contact between the anode and the cathode.

(42) A reactor comprising two or more reactors according to any one of (1 ) to (41 ) fluidically coupled.

(43) A method of making a reactor according to any one of (1 ) to (42), the method

comprising: providing a support; forming a surface layer comprising a semiconductor material on a support; and positioning the support in the chamber provided in the housing.

(44) A method according to (43), wherein the method further includes a step of forming a mesh or coil which is the support.

(45) A method according to (44), wherein the support is formed by winding a metal wire around a template rod to form a coil.

(46) A method according to any one of (43) to (45), wherein the surface does not cover the entire surface of the support. (47) A method according to any one of (43) to (46), wherein the step of forming the surface layer includes anodizing the support to form a layer of semiconductor material on the surface of the support.

(48) A method according to (47), wherein support is formed from or coated with titanium. (49) A method according to (47) or (48), wherein the anodizing is carried out for a time between 20 minutes and 8 hours.

(50) A method according to any one of (47) to (49), wherein the anodizing is carried out at an anodizing voltage of between 60 and 120 V.

(51 ) A method according to any one of (47) to (50), wherein the anodizing is carried out at an anodizing temperature of 5 to 50°C.

(52) A method according to any one of (47) to (51 ), wherein the method further includes a thermal treatment step of heating the anodized support.

(53) A method according to (52), wherein in the thermal treatment step the support is heated to a temperature of 400 to 600°C.

(54) A method according to (52) or (53), wherein in the thermal treatment step the support is heated in an air atmosphere or an oxygen atmosphere.

(55) A reactor formed according to a method comprising the method of any one of (43) to

(54) .

(56) Use of a reactor according to any one of (1 ) to (42) or according to (55) for wastewater treatment, gas treatment, determination of chemical oxygen demand or synthesis of organic molecules.

(57) A method of using a reactor according to any one of (1 ) to (42) or according to (55), comprising: passing a fluid through the inlet channel into the chamber and then out of the chamber through the outlet channel.

(58) A method according to (57), wherein fluid within the chamber is exposed to ultraviolet light.

(59) A method according to (57) or (580, wherein the reactor comprises a cathode positioned in the chamber; the support and the cathode each being connected to an electrical source to create a potential difference between the support and the cathode, such that the support functions as an anode, and wherein the potential between the anode and the cathode is set to 0 to 8 V.

Brief Description of the Figures The invention will now be described, without limitation, in the following discussion of embodiments of the invention and with reference to the accompanying Figures, in which:

Figure 1 shows a side view of a part of a reactor according to one embodiment of the present invention. Figure 2 shows an SEM micrograph of an anodized titanium coil of the type described herein. Figure 3 shows an exploded view of a reactor according to one embodiment of the present invention.

Figure 4 shows an exploded view of the reactor shown in Figure 3, from a different angle. Figure 5 shows a longitudinal cross-sectional view of a reactor of the type shown in Figures 3 and 4.

Figure 6 shows a perpendicular cross-sectional view of a reactor of the type shown in Figures 3 and 4.

Figure 7 shows a partial cut-away exploded view of a reactor according to another embodiment of the present invention.

Figure 8 shows an exploded view of a reactor of the type shown in Figure 7.

Figure 9 shows an SEM micrograph of an anodized titanium mesh of the type described herein.

Figure 10 shows a graph showing a comparison of the performance a reactor according to one embodiment of the present invention as compared with a reference reactor.

Figure 11 shows a graph showing a comparison of the performance a reactor according to another embodiment of the present invention as compared with a reference reactor.

First Embodiment

A first embodiment of the invention will be explained with reference to Figures 1 to 6. Figure 1 shows a basic unit 1 of a photocatalytic microreactor with a photocatalytically active anode coil 2 in the middle and two additional cathode coils 3 on a glass rod 4.

The active anode coil 2 corresponds to the support discussed above. The cathode coils 3 correspond to the cathode discussed above. The glass rod 4 corresponds to the template discussed above. The active anode coil 2 is, in this embodiment, an anodized titanium coil. In this embodiment, the support is formed of titanium with a layer of T1O2 on its surface. In the present embodiment, due to the anodizing process used, the T1O2 layer is mainly in the form of nanotubes. It will be recognised that in some embodiments the surface of the T1O2 nanotube array can be further modified by, for example, immobilising T1O2 particles thereon.

In the present embodiment, to form the basic unit, a titanium coil is anodized in a viscous organic electrolyte which results in the formation of immobilized T1O2 nanotubes on the surface of the titanium wire (an SEM micrograph showing such surface is Figure 2).

The processing times of anodic oxidation are short, lasting from 20 min to 8 h, depending on the electrolyte composition. The anodization voltage is adjusted between 60 and 120 V and the anodization temperature is held in the range from 5 to 50 °C. Several coils can be anodized simultaneously. The dimensions of T1O2 nanotubes, e.g. wall thickness, surface roughness, tube length, the diameter and the spacing between individual nanotubes, can be altered by changing the process parameters during anodic oxidation.

After anodizing, the anodized titanium coil is additionally thermally treated at elevated temperatures ranging from 400 to 600 °C in an air atmosphere. Processing parameters of anodic oxidation and thermal treatment of the titanium coil can be controlled in order to get the highest photocatalytic activity of the T1O2 nanotube layer.

After the thermal treatment, the anodized titanium coil is wrapped around the glass rod 4. Of course, it will be recognised the coil can be anodized and thermally treated as a coil, or can be anodized and even thermally treated in an 'uncoiled' form, effectively as a plain wire, and then formed into a coil after anodizing or thermal treatment.

In the present embodiment, after wrapping the anodized titanium coil 3 around the glass rod template 4, there is some length of the glass rod remaining at either end. This gives space for wrapping or positioning the cathode coils 3 of the present embodiment.

In this embodiment, the cathode coils 3 are formed of metal, for example non-anodized titanium, platinum, copper or stainless steel. Of course, such metals can be used in other embodiments of the present invention. In this embodiment they are separate from the active anode coil 2. In the present embodiment, inert, non-conductive spacers 5 prevent direct contact between the anode and the cathodes. This prevents a short circuit occurring between the anode and cathodes. The glass rod is also non-conductive and inert, that is, it does not conduct electricity and does not undergo chemical reaction with the fluids intended to be used in the reactor. The glass rod is also substantially transparent to UV light. It will be appreciated that, as explained above, templates which are not transparent to UV light can be used in other embodiments.

Figure 2 is an SEM micrograph of the active anode coil, which in this embodiment is an anodized titanium coil. The titanium coil itself corresponds to the support discussed above, while the T1O2 layer formed by the anodizing process corresponds to the surface layer of the support.

Figures 3 shows the basic unit 1 in context, as part of a photocatalytic microreactor 6 having top and bottom parts (7 and 8, respectively) of the housing with one basic unit. The basic unit is placed inside a chamber 9 within and ultraviolet LED sources 10 are placed on the top and the bottom of the photocatalytic microreactor. Figure 4 shows the same microreactor from an alternative angle. In this case, the basic unit is not shown.

In this embodiment the housing is made from a material which is transparent to ultraviolet light. Accordingly, light emitted from the ultraviolet LED sources shines into the chamber and onto the active anode coil 2 positioned in the chamber. The glass rod 4 on which the active anode coil is held is transparent to ultraviolet light, and so the irradiation of the active anode coil is further enhanced.

In this embodiment, the chamber 9 is a microchannel. The basic unit 1 is positioned within the chamber 9. In this embodiment, the chamber is defined by portions inscribed in each of a top and bottom part of the housing (7 and 8, respectively). That is, both the top part 7 and the bottom part 8 of the housing have a depression therein. When the top and bottom parts are brought together, the respective depressions align to define the chamber 9. This is also true for the inlet and outlet channels (1 1 and 12, respectively) in this embodiment, explained below. This can be seen in, for example, Figures 5 and 6.

The housing has an inlet channel 1 1 for fluid to flow into the chamber. In this embodiment, the inlet channel is in the form of a tube which communicates one end of the chamber with the exterior of the top part of the housing through an opening 13. The housing also has an outlet channel 12 for fluid to flow out of the chamber. In this embodiment, the outlet channel is in the form of a tube which communicates one end of the chamber with the exterior of the top part of the housing through an opening 14. The inlet and outlet channels are in this embodiment defined by portions inscribed in the top and bottom parts of the housing. This is shown in, for example, Figure 5. However, of course, it will be appreciated that the inlet and outlet channel may be formed in other ways. These conduits, which allow fluid to flow through them, fluidically communicate the interior chamber of the housing with the exterior of the housing. How that communication is achieved is not necessarily limited in the present invention.

Accordingly, it will be recognised that the inlet and outlet channels are in fluidic

communication (fluidically coupled) with one another by way of the chamber. In this embodiment, the inlet channel and the outlet channel run into the chamber at opposite ends of that chamber.

In the present embodiment, the support (that is, the anode coil in the basic unit) is positioned within the chamber and fluidically between the inlet channel and the outlet channel. The mounting of the basic unit, and thereby the support, within the chamber is shown in more detail in Figures 5 and 6.

As can be seen in Figure 5, the basic unit is mounted within the chamber between the location where the inlet channel connects to the chamber and the location where the outlet channel connects to the chamber. The active anode coil (the support) lies within the fluid path from the inlet channel to the outlet channel. Accordingly, when an inlet stream of fluid is flown to the chamber through the inlet channel, it will flow over, past and around the support on its way to the outlet channel.

Figure 6 shows an alternative cross section of the present embodiment along the line A-A of Figure 5. It can be seen that, in this embodiment, the chamber provides retaining sections which are adapted to hold ends of the template rod. This assures strong mounting of the basic unit without interfering with the active anode coil or the cathodes. Such retention is facilitated by the template (in this embodiment the glass rod), which as shown in Figure 1 has some extension beyond the area occupied by the cathode and anode coils. This bare portion, on which no support is present, allows easier handling of the basic unit and facilitates the secure mounting of the support within the chamber.

Such a configuration, in which the chamber has retaining sections which hold the support within the chamber, can of course be adopted in other embodiments. Figure 6 shows how, in this embodiment, the support is held within the chamber such that flow spaces exist between the support coil and the walls of the chamber. The housing in the present embodiment includes additional through holes 15. In the present embodiment those are located in the top part of the housing. These electrical connection holes mean that, in the present embodiment, the anode and cathode can be connected electrically to external sources. In particular, in the present embodiment, the anode and cathode have electrical connectors attached to them. These connecters pass through the electrical connection holes to the exterior of the housing. There, the anode electrical connection and the cathode electrical connection can be individually connected to circuits. It will of course be understood that in the present embodiment there are two cathode coils, and one or both of them may be electrically connected in the way discussed herein. For example, the anode and cathode may be connected to a DC power source by their respective electrical connectors.

This means that, for example, a potential can be applied between the anode and the cathode. This can be done while fluid flows through the reactor in order to further increase the catalytic activity of the reactor.

In this embodiment, paraffin film is used as a sealant for sealing the housing. Of course, other suitable sealants may be used. The top and bottom parts of the housing are held together by, for example, screws.

Second Embodiment

A second embodiment of the invention will be explained with reference to Figures 7 to 9.

Figure 7 shows a photocatalytic reactor 16 with a photocatalytically active anode wire mesh 17 in the middle and two cathode plates 18 at either end of the chamber formed within the housing of the reactor. The housing has top and bottom parts (19 and 20, respectively) which, as in the first embodiment, are made from a material which is transparent to ultraviolet light. Ultraviolet LED sources 10 are placed on the top and the bottom of the photocatalytic reactor, meaning that light emitted from the ultraviolet LED sources shines into the chamber and onto the active anode wire mesh positioned in the chamber.

The active anode wire mesh 17 corresponds to the support discussed above. The cathode plates 18 correspond to the cathode discussed above. In this second embodiment, there is no template as discussed above. The active anode wire mesh 17 is, in this embodiment, an anodized titanium wire mesh. In this embodiment, the support is of titanium with a layer of ΤΊΟ2 on its surface. The titanium mesh itself corresponds to the support discussed above, while the T1O2 layer formed by the anodizing process corresponds to a surface layer of the support.

In the present embodiment, due to the anodizing process used, the T1O2 layer is mainly in the form of nanotubes. It will be recognised that in some embodiments the surface of the T1O2 nanotube array can be further modified by, for example, immobilising T1O2 particles thereon.

In the present embodiment, a titanium wire mesh is anodized in a viscous organic electrolyte which results in the formation of immobilized titania nanotubes on the surface of the titanium wire mesh. The processing times of anodic oxidation are short, lasting from 20 min to 5 h, depending on the electrolyte composition. The anodization voltage is adjusted between 60 and 120 V and the anodization temperature is held in the range from 5 to 50 °C. Several meshes can be anodized simultaneously. The dimensions of T1O2 nanotubes, e.g. wall thickness, surface roughness, tube length, the diameter and the spacing between individual nanotubes, can be altered by changing the process parameters during anodic oxidation.

After anodizing, the anodized titanium wire mesh is additionally thermally treated at elevated temperatures ranging from 400 to 600 °C in an air atmosphere. Processing parameters of anodic oxidation and thermal treatment of the titanium mesh can be controlled in order to get the highest photocatalytic activity of the T1O2 nanotube layer.

Figure 9 is an SEM micrograph of the active anode mesh, which in this embodiment is an anodized titanium mesh. The titanium mesh itself corresponds to the support discussed above, while the T1O2 layer formed by the anodizing process corresponds to a surface layer of the support.

Of course, it will be recognised the mesh can be anodized and thermally treated as a mesh, or can be anodized and even thermally treated as a plain wire which is then formed into a mesh after anodizing or thermal treatment.

After the thermal treatment, the anodized titanium mesh is placed inside the chamber 21 created in the housing material. On both sides of the wire mesh the cathodes 18 are placed into the chamber. It will be recognised that the order in which the electrodes are placed into the housing is not limited. In this embodiment, the cathode plates 18 are of platinum. For example, a pure platinum cathode can be used. Alternatively, platinum on a carbon carrier can be used as the cathode. In general, though, any suitable conductive material can be used, such as a metal, for example non-anodized titanium, platinum, copper or stainless steel.

The anode wire mesh 17 is positioned within the chamber. In this embodiment, the chamber 21 is defined by portions inscribed in each of a top and bottom part of the housing. The top and bottom portions have hollows or shapes cut, drilled or molded into them. When the housing is assembled, by bringing the top and bottom parts together in this embodiment, the various hollows in the parts combine to form the channels and chambers described herein.

Of course, depending on the exact configuration of channels and chambers desired, the various parts of the housing may have other designs in other embodiments. For example, some parts of the housing may have no hollows or shapes present.

The housing can be made by, for example, molding, cutting or drilling the material to form the desired shape and parts. The housing has an inlet channel for fluid to flow into the chamber. In this embodiment, the inlet channel 22 is in the form of a tube which communicates one end of the chamber, proximal one of the cathodes, with the exterior of the top part of the housing through a hole 24. The housing also has an outlet channel 23 for fluid to flow out of the chamber. In this embodiment, the outlet channel is in the form of a tube which communicates one end of the chamber, proximal the other of the cathodes, with the exterior of the top part of the housing through a hole 25. The inlet and outlet channels are in this embodiment defined by portions inscribed in the top and bottom parts of the housing, as explained above. However, of course, it will be appreciated that the inlet and outlet channel may be formed in other ways. These conduits, which allow fluid to flow through them, fluidically communicate the interior chamber of the housing with the exterior of the housing. How that communication is achieved is not necessarily limited in the present invention.

Accordingly, it will be recognised that the inlet 22 and outlet channels 23 are in fluidic communication (fluidically coupled) with one another by way of the chamber 21. In this embodiment, the inlet channel and the outlet channel run into the chamber at opposite ends of that chamber.

In the present embodiment, the support (that is, the titanium mesh anode) is positioned within the chamber 21 and fluidically between the inlet channel and the outlet channel. The mounting of the cathodes 18 and the anode mesh 17, within the chamber is shown in more detail in Figures 7 and 8.

As can be seen in Figures 7 and 8, the anode mesh 17 is mounted within the chamber 21 between the location where the inlet channel connects to the chamber and the location where the outlet channel connects to the chamber. The active anode mesh (the support) lies within the fluid path from the inlet channel to the outlet channel. Accordingly, when an inlet stream of fluid is flown to the chamber through the inlet channel, it will flow over, past and around the support on its way to the outlet channel.

The housing in present embodiment includes additional through holes 26. In the present embodiment those are located in the top part of the housing. These electrical connection holes 26 mean that, in the present embodiment, the anode and cathodes can be connected electrically to external sources. In particular, in the present embodiment, the anode and cathodes have electrical connectors 27 attached to them. These connecters pass through the electrical connection holes to the exterior of the housing. There, the anode electrical connection and the cathode electrical connections can be individually connected to circuits. It will of course be understood that in the present embodiment there are two cathode plates, and one or both of them may be electrically connected in the way discussed herein.

For example, the anode and cathodes may be connected to a DC power source by their respective electrical connectors.

This means that, for example, a potential can be applied between the anode and the cathodes. This can be done while fluid flows through the reactor in order to further increase the catalytic activity of the reactor.

Methods of Use

Next follows some description of the use of the reactors of the present invention. At their most basic, the present reactors can be used by flowing a fluid for treatment through the reactor. In more detail, an inlet stream is flown into the chamber of the reactor through the inlet channel. The fluid passes over, around, through and, for example, past the support which is positioned in the chamber. Accordingly the catalytic activity of the surface of the support acts on the fluid. This can lead to, for example, decomposition of compounds within the fluid.

The fluid, have flown past the support, flows out from the chamber as an outlet stream through the outlet channel. From there the outlet stream may, for example, continue on to further processing. That might be an additional reactor of the present invention, for example.

The residence time of the fluid in the reactor (that is, the time between the inlet stream entry into the reactor and the outlet stream exit from the reactor) can of course be varied as desired by adjusting, for example, the flow rate of the inlet stream. During the residence time, the fluid is in contact with the surface of the support.

In some embodiments the reactors of the present invention are configured to have an anode and a cathode in the chamber of the housing. Two such embodiments are described in detail above. In reactors where an anode and a cathode are present in the chamber, the present inventors have found that by setting a potential difference between the anode and the cathode during fluid flow through the reactor catalytic activity can be further increased. The potential between the anode and the cathode may suitably be 0 to 8 V.

In reactors where the surface of the support has photocatalytic activity, illumination of the surface of the support with, for example, ultraviolet light during fluid flow through the reactor can also greatly enhance the catalytic activity of the reactor. Two such embodiments are described in detail above.

Combinations

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The same is true for features described in the context of products and methods. Any one or more of the aspects of the present invention may be combined with any one or more of the other aspects of the present invention. Similarly, any one or more of the features and optional features of any of the aspects may be applied to any one of the other aspects. Thus, the discussion herein of optional and preferred features may apply to some or all of the aspects. Furthermore, optional and preferred features associated with a method or use may also apply to a product and vice versa.

The options, features, preferences and so on mentioned herein apply both independently and in any combination, except where such a combination is expressly prohibited or clearly impermissible.

Examples

Example 1

The following example describes the photocatalytic activity of one embodiment of a reactor for the degradation of caffeine.

A reactor was assembled broadly as shown in Figures 1 and 3 to 6 and as set out above. That is, an anodized titanium coil was formed and positioned in the chamber of a housing made in two parts. A caffeine solution was flown as an inlet stream into the reactor.

The caffeine concentration at the inlet (Co) and the outlet (C) was characterized by UV-VIS- IR spectrometer for different volumetric flow rates and continuous flow. The initial concentration of caffeine was 50 mg/L. The area of anodized titanium coils was approximately 65 cm², while the area of the cathodes was approximately 2.5 cm². The potential between the electrodes was set to 4 V. The electrical conductivity of the caffeine solution in deionized water was adjusted to 0.38 mS with the addition of NaCI. The solution was continuously pumped through the reactor.

This resulted in 85 % degradation of the initial caffeine, calculated as 100% x C/Co, at a volumetric flow rate of 150 μΙ_/Γηίη and in 57 % degradation at a volumetric flow rate of 600 μΙ_/Γπίη . For comparison, a reference reactor according to Krivec, M. et al, "Highly Efficient T1O2-

Based Microreactor for Photocatalytic Applications", Appl. Mater. Interfaces, 5, (2013), 9088- 9094, was tested. In the reference reactor, T1O2 is bound to the walls of the 'chamber' of the reactor housing. By using the same flow conditions for the reference reactor and the reactor of the present invention, the comparison can be made.

Figure 10 shows the result of the comparison. The ratio C/Co illustrates the amount of caffeine remaining in the outlet stream after the caffeine solution has passed through the reactor (the reciprocal value of how much caffeine has been oxidised).

The initial caffeine concentration Co was the same for the two reactors tested. Accordingly, the improvement given by the present invention can be clearly seen. At equivalent flow rates, the reactor of the present invention provides a significantly lower level of caffeine in the outlet stream [that is, C/Co is much lower]. The level of caffeine oxidation is much higher in the reactor according to the present invention. Example 2

A reactor was assembled broadly as shown in Figures 7 and 8 and as set out above. That is, an anodized titanium mesh was formed and positioned in the chamber of a housing made in two parts. A caffeine solution was flown as an inlet stream into the reactor.

The caffeine concentration at the inlet (Co) and the outlet (C) was characterized by UV-VIS- IR spectrometer for different volumetric flow rates and continuous flow.

The initial concentration of caffeine was 25 mg/L. The area of anodized titanium wire mesh was approximately 23 cm², while the area of the cathodes was approximately 0.6 cm². The potential between the electrodes was set to 4 V. The electrical conductivity of the caffeine solution in deionized water was adjusted to 0.275 mS with the addition of NaCI. The solution was continuously pumped through the reactor.

This resulted in 100 % degradation of the initial caffeine, calculated as 100% x C/Co, at a volumetric flow rate of 48 μΙ_/Γηίη and in 53 % degradation at a volumetric flow rate of 960 μΙ_/Γπίη .

For comparison, a reference reactor according to Krivec, M. et al, "Highly Efficient T1O2- Based Microreactor for Photocatalytic Applications", Appl. Mater. Interfaces, 5, (2013), 9088- 9094, was tested. In the reference reactor, T1O2 is bound to the walls of the 'chamber' of the reactor housing. By using the same flow conditions for the reference reactor and the reactor of the present invention, the comparison can be made. Figure 11 shows the result of the comparison. The ratio C/Co illustrates the amount of caffeine remaining in the outlet stream after the caffeine solution has passed through the reactor (the reciprocal value of how much caffeine has been oxidised).

The initial caffeine concentration Co was the same for the two reactors tested.

Accordingly, the improvement given by the present invention can be clearly seen. At equivalent flow rates, the reactor of the present invention provides a significantly lower level of caffeine in the outlet stream [that is, C/Co is much lower]. The level of caffeine oxidation is much higher in the reactor according to the present invention.

Claims

I . A reactor comprising:

a housing defining a chamber therein;

an inlet channel and an outlet channel running through the housing into the chamber; and

a support positioned within the chamber;

the support having a surface comprising a semiconductor material.

2. A reactor according to claim 1 , wherein the support is a coil or a mesh.

3. A reactor according to claim 2, wherein the support is formed from an alloy containing Ti, Fe and/or Ni; stainless steel; or Inconel.

4. A reactor according to claim 2, wherein the support is formed from Ti.

5. A reactor according to any one of the preceding claims, wherein the support is spaced from the surface of the chamber.

6. A reactor according to claim 5, wherein the distance between the support and the surface of the chamber is 0.001 to 10 mm.

7. A reactor according to any one of the preceding claims, wherein the support is a coil wound around a template.

8. A reactor according to claim 7, wherein the template is formed from a material which does not conduct electricity and/or which allows ultraviolet light to pass through it.

9. A reactor according to claim 8, wherein the template is formed from lime-stone glass, quartz glass, polyethylene, polypropylene, poly (methyl methacrylate), a polycarbonate polymer, or polytetrafluoroethylene.

10. A reactor according to any one of the preceding claims, wherein the support surface comprises a metal chalcogenide.

I I . A reactor according to claim 10, wherein the support surface comprises ΤΊΟ2, ZnO or SrTiC ; or wherein the support surface comprises CdS or CdSe.

12. A reactor according to claim 1 1 , wherein the support surface comprises ΤΊΟ2 which is a porous ΤΊΟ2 layer comprising ΤΊΟ2 nanotubes.

13. A reactor according to any one of the preceding claims, wherein the reactor comprises a cathode positioned in the chamber;

the support and the cathode each being connectable to an electrical source to create a potential difference between the support and the cathode, such that the support functions as an anode.

14. A method of making a reactor according to any one of the preceding claims, the method comprising:

providing a support;

forming a surface layer comprising a semiconductor material on a support; and positioning the support in the chamber provided in the housing.

15. A method according to claim 14, wherein the step of forming the surface includes anodizing the support to form a layer of semiconductor material on the surface of the support.

16. A method according to claim 14 or 15, wherein support is formed from or coated with titanium.

17. A reactor formed according to a method comprising the method of any one of claims 14 to 16.

18. Use of a reactor according to any one of claims 1 to 13 or according to claim 17 for wastewater treatment, gas treatment, determination of chemical oxygen demand or synthesis of organic molecules.

19. A method of using a reactor according to any one of claims 1 to 13 or according to claim 17, comprising: passing a fluid through the inlet channel into the chamber and then out of the chamber through the outlet channel.

20. A method according to claim 19, wherein the reactor comprises a cathode positioned in the chamber;

the support and the cathode each being connected to an electrical source to create a potential difference between the support and the cathode, such that the support functions as an anode,

and wherein the potential between the anode and the cathode is set to 0 to 8 V.