FR3095597A1 - PHOTOCATALYTIC DECONTAMINATION PROCESS OF A GASEOUS MEDIUM IN THE PRESENCE OF AN EXTERNAL ELECTRIC FIELD - Google Patents

Abstract

The invention describes a photocatalytic process for treating a gaseous feed comprising volatile organic compounds (VOCs) and dioxygen, using a photocatalyst in the presence of an external electric field, it being understood that the photocatalyst is not in operation. electrical contact with the field generating electrodes. Said process being carried out by contacting said load containing VOCs and dioxygen with said photocatalyst, then subjecting the photocatalyst to an external electric field and irradiating the photocatalyst.

Description

METHOD FOR PHOTOCATALYTIC DECONTAMINATION OF A GAS MEDIUM IN THE PRESENCE OF AN EXTERNAL ELECTRIC FIELD

The field of the invention is that of the decontamination of a gaseous medium comprising volatile organic compounds by means of a photocatalytic process.

Prior art

Currently, there are many processes allowing the decontamination of a gaseous medium, in particular air, likely to contain volatile organic compounds.

A first way consists in bringing the gaseous medium into contact with an adsorbent (also called here capture mass) consisting mainly of activated carbon. However, the disadvantage of this type of adsorbent is that it must be replaced periodically to ensure the efficiency of the system. Another way proposed to eliminate volatile organic compounds (VOCs) in a gaseous medium, in particular air, consists of the photocatalytic degradation of these compounds. Today, the devices used, mainly comprising titanium dioxide (TiO2) as the active phase, have the disadvantage of not completely mineralizing these volatile organic compounds, which can lead to the release of these potentially harmful compounds into the the gaseous medium.

Photocatalysis is based on the principle of activating a semiconductor or a set of semiconductors such as a photocatalyst, using the energy provided by irradiation. Photocatalysis can be defined as the absorption of a photon, whose energy is greater than the forbidden band width or "bandgap" according to the Anglo-Saxon terminology between the valence band and the conduction band, which induces the formation of an electron-hole pair in the case of a semiconductor. We therefore have the excitation of an electron at the level of the conduction band and the formation of a hole on the valence band. This electron-hole pair will allow the formation of free radicals which will either react with compounds present in the medium, in order to initiate oxidation-reduction reactions, or else recombine according to various mechanisms. A semiconductor is characterized by its forbidden band or “bandgap”, i.e. the energy difference between its conduction band and its valence band, specific to it. Any photon with energy above its band gap can be absorbed by the semiconductor. Any photon with energy below its band gap cannot be absorbed by the semiconductor.

Methods for the photocatalytic decontamination of a gaseous medium are known in the state of the art, in particular in the publications by Y. Boyjoo et al., Chemical Engineering Journal, 310, p. 537-559, 2017; W.X. Zou et al., Chemosphere, 218, p. 845-859, 2019.

Photocatalytic processes in the presence of an electric field are also known in the state of the art.

Z.Jiang et al. (Chemosphere, 56, p. 503-508, 2004) implemented the photocatalytic degradation under an electric field of the red organic pigment X-3B by a semiconductor based on TiO2 deposited on a conductive aluminum plate electrically connected to one of the two electrodes. This implementation allows a deposition rate of 0.3 to 4 gTiO2/m2 depending on the number of deposits made, which corresponds to a loading rate relative to the total electrode surface of less than 2 g/m2.

C.M. Tank et al. (Solid State Science, 13, p. 1500-1504, 2011) implemented the photocatalytic degradation under an electric field of methylene blue by a TiO2-based semiconductor deposited on porous silicon serving as an electrode. This implementation has low photocatalyst loading rates relative to the total electrode surface.

S.C. Xu et al. (ACS Sustainable Chem. Eng., 4, p. 6887-6893) have implemented the reduction of Chromium VI contained in water contaminated with chromium III by photocatalysis under an electric field under the action of a semiconductor based on of TiO2 deposited on a titanium grid serving as an electrode. The use of a fine-mesh grid makes it possible to achieve photocatalyst loading rates relative to the total electrode surface of up to 250 g/m2.

Also, US 2018/0185785 describes an air purification process comprising the use of an electric field prior to the photocatalytic reaction to cause the precipitation of pollutants. The method also claims the coupled use of a photocatalytic material and an absorbent material. The photocatalytic material is brought into contact with at least one of the two electrodes generating the electric field.

Known implementations of the prior art reveal that the photocatalyst is in electrical contact with at least one of the electrodes generating the electric field, this implementation involves the consumption of at least some of the electrons supplied by the electric generator by the reagents, and thus an additional energy consumption due to the passage of an electric current.

Object of the invention

The object of the invention is to propose a new and more efficient way of photocatalytic decontamination of a gaseous medium using an external electric field, implementing a photocatalyst. The photocatalytic decontamination process according to the invention makes it possible to achieve improved performance, in particular with better VOC mineralization.

The state of the art concerning photocatalytic processes in the presence of an electric field differs from the invention in that there is an electric contact of the photocatalytic active species with at least one of the electrodes used to generate the electric field, this induces a consumption of electric current between the electrodes. In addition, this implementation does not allow a high charging rate per unit of electrode surface, which has the particular disadvantage of having to use very large electrode surfaces to improve the efficiency of the systems, and therefore represents a cost and significant bulk of the systems. The method according to the invention allows a higher charging rate per unit of electrode surface than the known methods of the state of the art.

Without being bound to any theory, the presence of an external electric field allows a better separation of the electron-hole pairs generated after the absorption of photons by the photocatalyst.

On the other hand, none of the documents of the prior art discloses a process for the photocatalytic decontamination of a gaseous medium under irradiation, implementing a photocatalyst in the presence of an external electric field and in which the photocatalytic active species n is not in electrical contact with the electrodes generating the electric field.

More particularly, the invention describes a photocatalytic process for treating a gaseous charge containing one or more volatile organic compounds and oxygen, said process comprising the following steps:

a) a gaseous charge containing one or more volatile organic compounds and dioxygen is brought into contact with a photocatalyst,

b) the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating said electric field,

c) the photocatalyst is irradiated by at least one radiation source producing at least one wavelength which can be absorbed by said photocatalyst so as to degrade the volatile organic compounds into carbon dioxide.

Definitions and abbreviations

The following terms are defined within the scope of the present invention for a better understanding:

In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief D.R. Lide, 81st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification.

The textural and structural properties of the photocatalysts described below are determined by characterization methods known to those skilled in the art.

The total pore volume and the pore distribution are determined by nitrogen porosimetry as described in the book “Adsorption by powders and porous solids. Principles, methodology and applications” written by F. Rouquérol, J. Rouquérol and K. Sing, Academic Press, 1999.

The term "specific surface" means the BET specific surface (SBET in m2/g) determined by nitrogen adsorption in accordance with the ASTM D 3663-78 standard established from the BRUNAUER-EMMETT-TELLER method described in the periodical " The Journal of American Society", 1938, 60, 309.

The maximum wavelength absorbable by a semiconductor is calculated using the following equation:

With λmax the maximum wavelength absorbable by a semiconductor (in m), h Planck's constant (4.13433559.10-15 eV.s), c the speed of light in vacuum (299 792 458 ms-1) and Eg the forbidden band width or “bandgap” of the semiconductor (in eV).

By “external electric field”, we mean a voltage applied to an electrical system, without generation of current and therefore without circulation of electrons from the anode to the cathode. The applied voltage leads to the creation of a potential, by the localized accumulation of medium electrons on the anode and the localized defect of medium electrons on the cathode, without current passing between the two electrodes. Ohmic losses, intrinsic to any system, are not considered as an electric current.

The term "reaction medium" means the mixture formed by the charge containing one or more volatile organic compounds (VOC) and dioxygen.

The term "volatile organic compounds (VOC)", according to European Council Directive 1999/13/EC, means any compound containing at least the element carbon and one or more of the following elements: hydrogen, halogen, oxygen, sulphur, phosphorus, silicon or nitrogen, excluding carbon dioxide, and having a vapor pressure of 0.01 kPa or more at a temperature of 273.15 K.

Detailed description of the invention

Within the meaning of the present invention, the various embodiments presented can be used alone or in combination with each other, without limitation of combination.

The invention describes a photocatalytic process for treating a gaseous feed containing one or more volatile organic compounds and dioxygen, said process comprising the following steps:

a) a gaseous charge containing one or more volatile organic compounds and dioxygen is brought into contact with a photocatalyst,

b) the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating said electric field,

c) the photocatalyst is irradiated by at least one radiation source producing at least one wavelength which can be absorbed by said photocatalyst so as to degrade the volatile organic compounds into carbon dioxide.

Step a) of bringing a gaseous charge containing one or more volatile organic compounds and oxygen into contact with a photocatalyst

According to step a) of the process according to the invention, a photocatalyst is brought into contact with a gaseous charge containing one or more volatile organic compounds and oxygen.

Load

The feed treated according to the process is in gaseous form, and contains volatile organic compounds, as well as oxygen. Preferably, the load treated according to the process is air, preferably air containing up to 10,000 ppm of volatile organic compounds.

The volatile organic compounds are chosen from halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, aldehydes, ketones, alone or as a mixture.

A gaseous diluent fluid may be present in the reaction medium. The presence of a diluent fluid is not required for carrying out the invention, however it may be useful to add it to the filler to ensure the dispersion of the filler in the reaction medium, the control of the adsorption reagents/products on the photocatalyst, the dilution of the products to limit their recombination and other parasitic reactions of the same order. The presence of a gaseous diluent fluid also allows control of the temperature of the reaction medium, thus being able to compensate for the possible exo/endo-thermicity of the photocatalyzed reaction. The nature of the diluent fluid is chosen in such a way that its influence is neutral on the reaction medium or that its possible reaction does not harm the achievement of the desired reaction of degradation of the volatile organic compounds. Advantageously, the gaseous diluent fluid is chosen from N2, O2, or air.

The photocatalyst

The photocatalyst is composed of one or more inorganic, organic or organic-inorganic semiconductors. The wavelengths of the photons absorbable by said photocatalysts are between 310 nm and 1000 nm (i.e. a band gap for inorganic, organic or organic-inorganic hybrid semiconductors generally between 1.24 and 4 eV).

- According to a first variant, the semiconductor is chosen from inorganic semiconductors. The inorganic semiconductors can be selected from one or more group IVA elements, such as silicon, germanium, silicon carbide or silicon-germanium. They can also be composed of elements of groups IIIA and VA, such as GaP, GaN, InP and InGaAs, or of elements of groups IIB and VIA, such as CdS, ZnO and ZnS, or of elements of groups IB and VIIA, such as CuCl and AgBr, or elements of groups IVA and VIA, such as PbS, PbO, SnS and PbSnTe, or elements of groups VA and VIA, such as Bi2Te3 and Bi2O3, or elements of groups IIB and VA, such as Cd3P2, Zn3P2 and Zn3As2, or group IB and VIA elements, such as CuO, Cu2O and Ag2S, or group VIIIB and VIA elements, such as CoO, PdO, Fe2O3 and NiO, or elements from groups VIB and VIA, such as MoS2 and WO3, or elements from groups VB and VIA, such as V2O5 and Nb2O5, or elements from groups IVB and VIA, such as TiO2 and HfS2, or d elements of groups IIIA and VIA, such as In2O3 and In2S3, or elements of groups VIA and lanthanides, such as Ce2O3, Pr2O3, Sm2S3, Tb2S3 and La2S3, or elements of groups VIA and actinides, such as UO2 and UO3. Preferably, the semiconductor is chosen from TiO2, Bi2O3, CdO, Ce2O3, CeO2, CeAlO3, CuO, Fe2O3, FeTiO3, ZnFe2O3, V2O5, ZnS, ZnO, WO3 and ZnFe2O4, alone or as a mixture.

- According to another variant, the semiconductor is chosen from organic semiconductors. Said organic semiconductors can be tetracene, anthracene, polythiophene, polystyrenesulfonate, phosphyrenes, fullerenes and carbon nitrides.

- According to another variant, the semiconductor is chosen from organic-inorganic semiconductors. Among the organic-inorganic semiconductors, mention may be made of crystallized solids of the MOF type (for Metal Organic Frameworks according to the Anglo-Saxon terminology). MOFs are made up of inorganic subunits (transition metals, lanthanides, etc.) connected to each other by organic ligands (carboxylates, phosphonates, imidazolates, etc.), thus defining crystallized, sometimes porous, hybrid networks.

Preferably, the photocatalyst is composed of one or more inorganic semiconductors.

The semiconductors of said photocatalyst can optionally be doped with one or more ions chosen from metal ions, such as for example ions of V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti, non-metallic ions, such as for example C, N, S, F, P, or by a mixture of metallic and non-metallic ions.

The constituent semiconductors of said photocatalyst may contain particles comprising one or more element(s) in the metallic state chosen from an element of groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA and VA of the periodic table of the elements. Said particles comprising one or more element(s) in the metallic state are in direct contact with said semiconductor. Said particles can be composed of a single element in the metallic state or of several elements in the metallic state capable of forming an alloy. The term "element in the metallic state" (not to be confused with "metallic element") means an element belonging to the family of metals, said element being in the zero oxidation state (and therefore in the form of a metal). Preferably, the element or elements in the metallic state are chosen from a metallic element of groups VIIB, VIIIB, IB and IIB of the periodic table of the elements, and in a particularly preferred manner, from platinum, palladium, gold , nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium. Said particles comprising one or more element(s) in the metallic state are preferentially in the form of particles of size between 0.5 nm and 1000 nm, very preferably between 0.5 nm and 100 nm and even more preferably between 1 and 20 nm.

The constituent semiconductors of said photocatalyst can be surface-sensitized with any organic molecules capable of absorbing photons.

The photocatalyst preparation method can be any preparation method known to those skilled in the art and suitable for the desired photocatalyst.

The photocatalyst used in the process according to the invention can be in different forms (nanometric powder, nanoobjects with or without cavities, etc.) or shaped (films, monolith, balls of micrometric or millimetric size, etc.). The photocatalyst advantageously comes in the form of a nanometric powder.

Contact

Bringing the gaseous charge containing one or more volatile organic compounds and dioxygen into contact with said photocatalyst can be done by any means known to those skilled in the art. Preferably, the contacting of the gaseous charge containing one or more volatile organic compounds and dioxygen with said photocatalyst, can be done in a traversed fixed bed or in a licking fixed bed. The photocatalyst can also be deposited directly on optical fibers.

When the contacting is in a traversed fixed bed, said photocatalyst is preferentially fixed within the reactor, and the gaseous charge containing one or more volatile organic compounds and oxygen is sent through the photocatalytic bed.

When the contacting is in a licking fixed bed, said photocatalyst is preferably fixed within the reactor, and the gaseous charge containing one or more volatile organic compounds and oxygen is sent to the photocatalytic bed. The photocatalyst can also be deposited directly on optical fibers.

When the contacting is in a fixed bed or in a licking bed, the implementation can be done continuously or in a closed reactor.

Step b) of subjecting the photocatalyst to an external electric field

According to step b) of the method according to the invention, the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating the field.

According to a preferred embodiment, the photocatalyst is not in electrical contact, nor in physical contact with the electrodes generating said field.

The device for generating the electric field can be placed within the reaction medium or outside. The location of the device will be adapted to the implementation of the process (fixed bed, licking bed, etc.).

The shape and size of the electrodes generating the electric field can be of any kind, adapted to the device and to the implementation of the method.

The electric field generating electrodes comprise at least one conductive compound, such as steel, copper.

The device for generating the electric field is such that the photocatalyst is subjected to an electric field of between 10 V/m and 100 kV/m, preferably, the electric field is between 100 V/m and 10 kV/m.

According to a variant, step c) is carried out before step b).

Stage c) of irradiation of the photocatalyst

According to step c) of the method according to the invention, the photocatalyst is irradiated by at least one irradiation source producing at least one wavelength which can be absorbed by the photocatalyst (i.e. less than the forbidden band width of the semiconductor constituent of said photocatalyst according to the variant where the photocatalyst is composed of at least one semiconductor) so as to degrade the volatile organic compounds into carbon dioxide by photocatalysis.

A photocatalyst composed of one or more semiconductors can be activated by the absorption of at least one photon.

In the case of semiconductors, the absorbable photons are those whose energy is greater than the forbidden band width, the "bandgap". In other words, the photocatalysts can be activated by at least one photon of a wavelength corresponding to the energy associated with the forbidden band widths of the semiconductors constituting the photocatalyst or of a lower wavelength.

Any irradiation source emitting at least one wavelength suitable for the activation of said photocatalyst, that is to say absorbable by the photocatalyst, can be used according to the invention. The source of irradiation can be both natural by solar irradiation and artificial such as laser, Hg, incandescent lamp, fluorescent tube, plasma or light-emitting diode (LED, or LED in English for Light-Emitting Diode). Preferably, the source of irradiation is natural by solar irradiation.

The irradiation source produces radiation of which at least some of the wavelengths are less than the maximum absorbable wavelength (λmax) by the constituent semiconductors of the photocatalyst according to the invention. When the irradiation source is solar irradiation, it generally emits in the ultraviolet, visible and infrared spectrum, that is, it emits a wavelength range of 280 nm to 2500 nm approximately (according to ASTM G173-03). Preferably, the source emits at least one wavelength range above 280 nm, very preferably between 315 nm and 800 nm, which includes the UV spectrum and/or the visible spectrum.

The irradiation source supplies a flux of photons which irradiates the reaction medium containing the photocatalyst. The interface between the reaction medium and the light source varies according to the applications and the nature of the light source.

The radiation source is an artificial or natural radiation source. In a preferred mode when it comes to artificial irradiation, the irradiation source is located outside the reactor and the interface between the two can be an optical window in pyrex, quartz, organic glass or any other interface allowing the photons absorbable by the photocatalyst according to the invention to diffuse from the external environment within the reactor.

The realization of said process is conditioned by the absorption capacity of said photocatalyst as well as by the supply of photons adapted to the photocatalytic system for the reaction envisaged, and for this reason is not limited to a specific range of pressure or temperature outside those ensuring the stability of the product or products. The temperature range employed for the photocatalytic production of dihydrogen is generally from -10°C to +200°C, preferably from 0 to 150°C, and very preferably from 0 to 50°C. The pressure range used for the process is generally from 0.01 MPa to 70 MPa (0.1 to 700 bar), preferably from 0.1 MPa to 5 MPa (1 to 50 bar), and even more preferably from 0.1 MPa to 2 MPa (1 to 20 bar).

The process according to the invention can be carried out with a dry or wet gas up to 100% relative humidity, preferably the gas to be treated contains from 0 to 60% relative humidity.

The following examples illustrate the invention without limiting its scope.

Examples

Example 1: Photocatalyst A - Quartzel ®

Material A is a commercial material consisting of TiO2 nanoparticles supported by quartz fibers sold under the name QuartzelTM by the company Saint Gobain®. QuartzelTM is known by those skilled in the art for its excellent photocatalytic properties in air purification.

Example 2: Photocatalyst B - TiO2

Photocatalyst B is a commercial TiO2-based semiconductor (Aeroxide® P25, Aldrich™, purity > 99.5%). The particle size of the photocatalyst is 21 nm and the specific surface measured by the BET method is equal to 52 m2/g.

Example 3: Photocatalyst C - Pt/TiO2

0.0712 g of H2PtCl6.6H2O (37.5% by mass of metal) is inserted into 500 ml of distilled water. 50 ml of this solution are withdrawn and inserted into a jacketed glass reactor. 3 ml of methanol then 250 mg of TiO2 (Aeroxide® P25, Aldrich™, purity > 99.5%) are then added with stirring to form a suspension.

The mixture is then left with stirring and under UV radiation for two hours. The lamp used to provide the UV radiation is a 125W HPK™ mercury vapor lamp.

The mixture is then centrifuged for 10 minutes at 3000 revolutions per minute in order to recover the solid. Two washes with water are then carried out, each of the washes being followed by centrifugation. The recovered powder is finally placed in an oven at 70° C. for 24 hours.

We then obtain the photocatalyst C Pt/TiO2. The Pt element content is measured by plasma source atomic emission spectrometry (or inductively coupled plasma atomic emission spectroscopy “ICP-AES” according to the English terminology) at 0.93% by mass.

Example 4: Photocatalyst D - ZnO

Photocatalyst D is a commercial ZnO-based semiconductor (Lotus Synthesis™). The specific surface measured by the BET method is equal to 50 m2/g.

Example 5: Photocatalyst E - CeO2

30.04 g of Ce(NO3)3 (Aldrich ®, 98%) are dissolved in 150 mL of distilled water with stirring. A 1M solution of ammonia is prepared from a stock solution of ammonium hydroxide (Aldrich ®, 28-30%). The 1M ammonia solution is added with stirring to the solution containing Ce(NO3)3 until a pH approximately equal to 10 is reached. Stirring is maintained for 3 hours.

The mixture is then centrifuged for 10 minutes at 3000 revolutions per minute in order to recover the solid. Two washes with water are then carried out, each of the washes being followed by centrifugation. The recovered powder is finally placed in an oven at 100° C. for 12 hours. The recovered solid then underwent a calcination treatment in air at a flow rate of 1 L/g/h at 150° C. for 1 hour then at 450° C. for 2 hours with a temperature rise of 5° C./min.

The photocatalyst E CeO2 is then obtained. An analysis by X-ray diffraction shows the presence of CeO2 phase in a majority way. By transmission electron microscopy, the average size of the particles is evaluated at 8 nm.

Example 6: Implementation of photocatalysts in adsorption and photooxidation of toluene

Photocatalysts A, B, C, D and E are subjected to a toluene photooxidation test in the gas phase in a continuous through-bed reactor fitted with a quartz optical window with a surface area of 5.3.10-4 m2 and of a frit in front of the optical window on which the material is deposited.

Two copper electrodes of a shape adapted to the reactor and spaced on average by 2.4 cm are placed inside the device. The electrodes are surrounded by a Teflon ® film such that the photocatalyst is not in direct contact, and connected to a generator (Keysight, E36106A) so as to apply an electric field in the area where the photocatalyst is located.

About 100 mg of photocatalyst are deposited on the sinter. Before each test, the photocatalysts were conditioned by thermodesorption at 115° C. for 12 hours. The tests are carried out at ambient temperature under atmospheric pressure by passing dry air containing 70 ppmV of toluene at a flow rate of 60 mL/min. The residual toluene content and the production of carbon dioxide gas produced from the photooxidation of toluene are monitored by analyzing the effluent every 7 minutes by gas phase chromatography (GC FID / methaniser FID). The UV-Visible irradiation source is supplied by a Xe-Hg lamp (Asahi™, MAX302™). The irradiation power is always maintained at 30 W/m2 measured for a wavelength range between 315 and 400 nm. The overall duration of each test is approximately 100 hours. The tests are carried out in two stages: a first stage of balancing without irradiation, a second stage of photooxidation under irradiation which makes it possible to estimate the photocatalytic performances.

The mineralization rates calculated as the percentage of measured CO2 compared to the theoretical quantity of CO2 resulting from the photooxidation of toluene are given in table 1 below (a value of 100% will indicate that no carbonaceous product other than CO2 is formed during the reaction). Photocatalyst Without electric field Electric field 800 V/m
(Implementation according to the invention) Electric field
4kV/m
(Implementation according to the invention) Toluene mineralization rate (%) AT Quartzel® 23 42 67 B TiO2 7 25 53 VS Pt/TiO2 32 49 78 D ZnO 4 12 27 E CeO2 3 8 19

Table 1 – Results of the mineralization rate of toluene for the different photocatalysts according to the electric field applied

The toluene mineralization rate values are significantly higher for an implementation according to the invention regardless of the photocatalysts used.

Claims (11)

Photocatalytic process for treating a gaseous feed containing one or more volatile organic compounds and dioxygen, said process comprising the following steps:
a) a gaseous charge containing one or more volatile organic compounds and oxygen is brought into contact with a photocatalyst,
b) the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating said electric field,
c) the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength absorbable by said photocatalyst so as to degrade the volatile organic compounds into carbon dioxide. Process according to Claim 1, in which the treated feed is air, preferably air containing up to 10,000 ppm of volatile organic compounds. Process according to any one of the preceding claims, in which the volatile organic compounds are chosen from halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, aldehydes, ketones, alone or as a mixture. A method according to any preceding claim, wherein a gaseous diluent fluid is present in the reaction medium. A method according to any preceding claim, wherein the photocatalyst is composed of one or more inorganic, organic or organic-inorganic semiconductors. Process according to Claim 5, in which the photocatalyst is an inorganic semiconductor selected from one or more elements of group IVA, such as silicon, germanium, silicon carbide or silicon-germanium, compounds of elements of groups IIIA and VA, such as GaP, GaN, InP and InGaAs, or elements of groups IIB and VIA, such as CdS, ZnO and ZnS, or elements of groups IB and VIIA, such as CuCl and AgBr , or elements of groups IVA and VIA, such as PbS, PbO, SnS and PbSnTe, or elements of groups VA and VIA, such as Bi2Te3 and Bi2O3, or elements of groups IIB and VA, such as Cd3P2 , Zn3P2 and Zn3As2, or elements of groups IB and VIA, such as CuO, Cu2O and Ag2S, or elements of groups VIIIB and VIA, such as CoO, PdO, Fe2O3 and NiO, or elements of groups VIB and VIA, such as MoS2 and WO3, or elements of groups VB and VIA, such as V2O5 and Nb2O5, or elements of groups IVB and VIA, such as TiO2 and HfS2, or elements of groups IIIA and VIA, such as In2O3 and In2S3, or elements of groups VIA and lanthanides, such as Ce2O3, Pr2O3, Sm2S3, Tb2S3 and La2S3, or elements of groups VIA and actinides, such as UO2 and UO3 . Preferably, the semiconductor is chosen from TiO2, Bi2O3, CdO, Ce2O3, CeO2, CeAlO3, CuO, Fe2O3, FeTiO3, ZnFe2O3, V2O5, ZnS, ZnO, WO3 and ZnFe2O4, alone or as a mixture. A method according to claim 5, wherein the photocatalyst is an organic semiconductor selected from tetracene, anthracene, polythiophene, polystyrenesulfonate, phosphyrenes, fullerenes and carbon nitrides. Process according to Claim 5, in which the photocatalyst is an organic-inorganic semiconductor chosen from crystalline solids of MOF type. A method according to any preceding claim, wherein the photocatalyst is subjected to an electric field between 10 V / m and 100 kV / m. Process according to any one of the preceding claims, in which the process is carried out with dry or wet gas up to 100% relative humidity, preferably the gas to be treated contains 0 to 60% relative humidity. A method according to any preceding claim, wherein step c) is performed before step b).