WO2015110117A2

WO2015110117A2 - Method for producing a polymeric carbon nitride catalyst

Info

Publication number: WO2015110117A2
Application number: PCT/DE2015/000046
Authority: WO
Inventors: Kevin Jablonka
Original assignee: Kevin Jablonka
Priority date: 2014-01-23
Filing date: 2015-01-20
Publication date: 2015-07-30
Also published as: DE102014000888B4; WO2015110117A3; DE102014000888A1; WO2015110117A9

Abstract

The invention relates to a method for producing a polymeric carbon nitride catalyst for improving the efficiency of catalysis, particularly during photochemical cleavage of water to obtain hydrogen. The invention also relates to a device in which a catalyst is used that was produced according to said method. The catalyst is preferably attached to drops/fibres of a water-insoluble carrier polymer the diameters and preferably thicknesses of which lie in the nanometre to micrometre range, and which form a mechanically-coherent structure. This mechanically-coherent structure is preferably produced by means of a so-called electrospinning, preferably electrospray, method.

Description

description

Process for the preparation of a polymeric carbon nitride catalyst

The invention relates to a method according to the preamble of patent claim 1, and an apparatus for using the product produced by this method.

Such processes are known, for example, from ZHANG, Y. & ANTONIETTI, M .: Photovoltaic generation by polymeric carbon nitride solids: an initial step towards a novel photovoltaic system. Chem. Asian J. 5: 1307-11 (2010) or YANG, F. ET AL. : Solar hydrogen evolution using metal-free photocatalytic polymeric carbon nitride / CuInS ₂ com- posites as photocathodes. J. Mater. Chem. A 1, 6407-6415 (2013). While in the former method only a small photocurrent can be measured, can be measured with the second method already a significant evolution of hydrogen. However, indium necessary for the presentation of this catalyst, which is a relatively expensive to others also under environmental aspects of concern. Both methods have the disadvantage that their efficiency is very low.

From Xu, J. , WANG, Υ. & ZHU, Y .: Nanoporous Graphitic Carbon Nitride with Enhanced Photocatalytic Performance. Langmuir 29, 10566-10572 (2013), an improved such a method is known, but still has a low efficiency and is also expensive to manufacture.

It was therefore an object of the invention to improve a method according to the preamble of claim 1 so that it has a significantly higher efficiency based on the production of larger amounts of hydrogen, and this for a relatively broad spectrum of the light used. Furthermore, it was an object of the invention to improve the process so that it can be inexpensively, environmentally friendly and implemented on a large scale.

Another object of the invention was to provide a device for the photochemical decomposition of water for the production of hydrogen, in which a catalyst with significantly increased efficiency is used.

These objects are achieved by the characterizing features of patent claims 1 and 12, respectively.

Polymeric carbon nitride can also be used for organic reactions. To name would be the oxidation of alkanes, olefins, alcohols, heteroaromatics, the direct oxidation of benzene to phenol and the degradation of contaminants by Oxidation, hydrogenation and, for example, the activation of π bonds and aromatic systems (see also WANG, Y., WANG, X. & ANTONIETTI, M .: Graphite carbonitride as a heterogeneous organocatalyst: from photochemistry to viekwec catalysis Sustainable Chemistry, Angew. Chemie 124, 70-92 (2012).). Due to this multiple use, the ejfindungsgemäfie catalyst, which in itself already consists of cost-effective materials, could become even cheaper due to production on a larger scale.

Carbon nitride also has the advantage over other catalysts that it is very stable thermally and chemically. It can also be chemically modified with relatively simple means.

The treatment of carbon nitride in a high voltage field is easy to accomplish and can be done without environmentally damaging or rare chemicals. This can be achieved with a few process steps and very inexpensive and environmentally friendly an improvement in the efficiency in terms of hydrogen production.

The fact that carbon nitride fibers or droplets whose thickness in the nano to micrometer range hangs, attaches (claim 2), there is the advantage that the active surface of the carbon nitride and thus also increases the efficiency of hydrogen production becomes. Thus, the method of the invention allows the direct conversion of light energy into storable chemical energy on a technically usable scale.

In addition, no much greater effort is required for the preparation of the catalyst than in the known methods. The preparation of the carrier polymer is very inexpensive.

By using an electrospinning / spraying method (claim 3), the structure is significantly more variable with respect to the structure of the macroscopic coherent structure as compared with another spinning method such as melt spinning. For example, by changing parameters, one can first choose between the shape of the fibers and the droplets. In the first case, both the fiber structure, diameter and surface can be varied, as well as their orientation, while in the second case, the distribution of the droplets and their diameter can be changed.

[013] The characterizing features of claim 4 result in a more uniform distribution of the polymer fibers or droplets and thus a slight Further processing. A rotating collector (claim 5) allows easy controllable orientation and distribution of polymer fibers or droplets, whereby the risk of their clumping is significantly reduced. At a higher rotation speed ■ of the collector, this danger is steadily reduced further. In this way, the efficiency can be further increased. By moving the collector along the axis of rotation, larger areas of a thin film can be produced in a shorter time. This makes the process even more efficient.

For the parameters in the electrospinning / spraying method, the broad range of values has been established according to claim 5, whereby a considerable range of fiber and droplet shapes and orientations can be produced. Thus, by controlling the pumping speed, the thickness of the fibers or droplets, as well as the speed of their production can be controlled, which can also be achieved via the control of the voltage, the fiber or droplet thickness. Furthermore, by changing the voltage, it is possible to regulate the charge density and thus control whether predominantly electrospinning or electrospraying takes place. By controlling the distance between the needle and the collector, the fiber thickness can be controlled. Finally, the change in the distance between needle and collector allows further control of the fiber or droplet thickness.

The development of the invention according to claim 6 allows an environmentally friendly and inexpensive production of the macroscopically related structure. Due to the easy vaporizability of acetic acid fibers of less soluble substances such as carbon nitride can be easily and quickly produced even at lower voltages between needle and collector.

[016] If the method according to claim 7 is further developed, there is the advantage that, due to their large surface area, films allow high efficiency and can be easily transported and processed further. In addition, I LEVERAGING films ^"are particularly easily prepared by the electrospinning / spraying- method.

The development of the invention according to claim 8 enables the production of Pölymerfasern or droplets in the nanometer to micrometer range with very inexpensive and very environmentally friendly means. In addition, the production is simplified by the good solubility of cellulose acetate in acids. Due to the water insolubility of cellulose acetate heterogeneous catalysis and thus a very simple use of the catalyst is possible. The foil can thus be easily removed from the reaction mixture and reused. Forming the invention of claim 9 further, results in a very easy and inexpensive way of synthesizing polymeric carbon nitride id. This synthesis is thus easier to implement on an industrial scale, since, apart from the heating, no further process steps are necessary. Furthermore, dicyandiamide is a chemical that is very cheap.

[019] The development of the invention according to claim 10 allows a further increase in the efficiency, since the substances mentioned improve the absorption of light and the charge separation, whereby an increase of the photocurrent occurs.

Since the carbon nitride modified with the stated substances can be processed in the same way as the unmodified carbon nitride, the use of these modifications does not involve a higher production outlay. In addition, their use is inexpensive and environmentally friendly.

The development of the invention according to claim 11 allows a further increase in the efficiency of the method according to the invention by enlarging the catalytically active surface.

In the following, an embodiment of the invention will be described in more detail. [022]

FIG. 1 shows the synthesis of the graphitic carbon nitride starting from dicyandiamide, FIG.

{024] Fig. 2 schematically shows a structure for carrying out a high-shear treatment;

FIG. 3 schematically shows the structure for carrying out the electrospinning / spraying method, FIG.

[026] FIG. 4 shows a measurement of the H ₂ production of high-voltage-treated carbon nitride and carbon nitride according to the invention according to the prior art,

5 shows a characterization of the carbon nitride and cellulose acetate film according to the invention produced by means of the electrospinning process as carrier material and of the carbon nitride according to the prior art by means of electron spin resonance,

6 shows a characterization of the high-stress treated carbon nitride according to the invention, the carbon nitride according to the invention which has been processed by means of an electrospinning method to form a film with the carrier polymer cellulose acetate in comparison with carbon nitride according to the prior art,

Fig. 7 shows a measurement of the photocurrent in a film produced by electrospraying according to the invention, which consists of cellulose acetate fibers with attached graphitic carbon nitride and

[030] FIG. 8 shows a structural detail of a modified graphitic carbon nitride molecule, according to the prior art.

Fig. 1 shows schematically the reactions in the synthesis of graphitic carbon nitride (4) starting from dicyandiamide (1). Dicyandiamide (1) condenses on heating with elimination of ammonia (5) to give N2- (4,6-diamino-l, 3,5-triazin-2-yl) -l, 3 ₎ 5-triazine-2,4, 6-triamine, which is also called melam (2). If it is further heated, melam condenses with elimination of ammonia (5) to triamino-s-triazine (l, 3,4,6,7,9,9b-heptaazaphenalen-2,5,8-triamine), which also Meiern ( 3) is called. This condenses on further heating up to 560 ° C to yellow graphitic carbon nitride, which is a polymer of k tri-s-triazine units. This synthesis can be carried out on a small scale, for example, simply in a muffle furnace with programmed temperature profile. All intermediates have no hazardous material classification and are therefore harmless. The measurement of ammonia production makes it easy to check the progress of the synthesis. The graphitic carbon nitride prepared by the condensation reaction can now be dissolved with a carrier polymer, such as cellulose acetate, in an easily evaporable acid, such as concentrated acetic acid, by stirring or sonication. This solution should be slightly viscous for use in a so-called electrospinning / spraying process.

Fig. 2 shows schematically a possible structure for the high-voltage treatment of polymeric carbon nitride. Here, graphitic carbon nitride is first dissolved in glacial acetic acid in the ultrasonic bath. By protonation it is thus possible to bring individual layers of carbon nitride in the ultrasonic bath in solution. This solution is drawn into a syringe and then pumped into a needle by a pump through a tube attached in a tube guide which allows for easy adjustment of the distance between collector and needle. The positive pole of a DC high voltage source is connected to the needle. Below the needle is an ITO glass, which is mounted on a bracket and grounded. After the start of pumping, a high voltage - in the order of magnitude of the field between collector approximately 4 kV cm ^-1 - is applied between the needle and the collector. As a result, the acetic acid evaporates and carbon nitride is deposited on the ITO glass, which can be removed from the ITO glass after drying. The pumping speed is an important factor controlling the intensity of the high voltage treatment. The entire structure is embedded in a housing to minimize disturbances of the process.

Fig. 3 shows schematically the structure of the electrospinning / spraying method. In order to shield the experiment against external influences and to protect the experimenter from the high voltage, the area in which high voltage is applied is housed in a housing (6) of polyethylene (PE) panels with the dimensions of 800 cm (height) to 800 cm ( Width) to 400 cm (depth). For further protection, the syringe (10) filled with the polymer is located outside the housing. The syringe is connected by means of a so-called LuerLock connection to a transparent plastic tube (11), which is passed via a plastic tube (12) into the housing (6). As a further safeguard measure, a series resistor (19) can be interposed in order to make the current as low as possible and thus harmless in the event of a possible electric shock. The plate for the holder of the collector (17) is mounted on blocks of wood (7), which are fastened by means of large plastic screws in the bottom plate of the housing (6). In the bottom plate of the housing (6) holes are drilled at intervals of -5 cm. The plate for the holder of the collector is also made of PE and is attached above plastic plugs.

By the sliding plastic tube as a hose guide (12) and by attaching the .Sammlerplatte about blocks (7), which are fastened by screws to the bottom plate, a quick and easy conversion of the electrospinning / spraying construction is possible.

[035] The rotary collector (15) is made of an aluminum tube having an inner diameter of 2.1 cm and an outer diameter of 2.5 cm. The pipe is fastened via flanges with turned-up shafts at angles of aluminum, which are fixed to the support plate (17). The two shafts of the collector (15) are mounted by means of ball bearings to reduce the noise and to allow a smooth running of the collector (15). One of the two shafts has a bore to fix the motor shaft of a 12V DC motor (16) driving the collector tube therein by means of a screw. The DC motor (16) is also fixed to an angle at which the tube (15) is fixed, and can be driven by a laboratory power supply (8). By regulating the current intensity, it is possible to control its rotational speed.

In addition, the rotary collector (16) can move on an axis (A). After filling the syringe (10) with a previously prepared solution of cellulose acetate carrier and graphitic carbon nitride in acetic acid and the tube (11) the latter is passed through the plastic tube (12) and a needle (13), in the size Gauge 20th , connected to the hose. Thereafter, the distance between needle (13) and collector (15) can be adjusted. Once this has been done, the needle (13) can be connected to the positive pole of the high voltage source (18). The collector (15) is placed on earth. Once this has taken place, the pumping rate can be regulated by means of the syringe pump (9). The ^" pump speed control ^" allows fiber thickness control and is the most important parameter to influence the speed of the manufacturing process.

After starting the pump, the collector (15) is switched on. Once a drop has formed on the needle (13), the high voltage is applied. In this case, this voltage is adjusted so that there is a stable jet of fibers or droplets between the needle (13) and collector (15). Due to the applied high voltage and the resulting ionization of the particles of the solution, there is repulsion between the particles of the solution in the needle (13). In an interaction between electrostatic repulsion, air pressure, gravity and surface tension, a so-called Taylor cone. From which forms a jet of polymer fibers / droplets (14), which are drawn over their time of flight to the collector (15) and dried. The duration of the flight time and thus the thickness of the fiber or the diameter of the droplets depends on the distance between the needle (13) and collector (1-5) and on the applied high voltage.

To end the process, first the high voltage and then the pump (9) and the collector (15) is turned off. After grounding of all parts, the film, which is now on the collector (15), for example, with a scalpel, simply durchgesch n i tten and thus be removed

Fig. 4 shows the H ₂ production of high voltage treated carbon nitride (dashed, a) according to the invention compared to prior art carbon nitride when illuminated by a solar simulator and triethanolamine as electron donor and H ₂ PtCl ₆ as co-catalyst in FIG H ₂ 0. Over time, gas production was monitored by pressure, and gas composition was determined by headspace gas chromatography at the end of the experiment. Although high-tension treated carbon nitride contaminated according to the invention was used for this measurement with graphitic carbon nitride, a clear increase in the catalytic activity and thus in the efficiency of the catalyst according to the invention can be observed.

Fig. 5 shows a characterization of the inventive film (dotted b)), which was prepared by means of the electrospinning method and cellulose acetate as a carrier polymer, from known graphite carbonitride powder (a)) and a reference sample (painted and dotted , c)) by electron spin resonance at 6.2 Kelvin. The reference sample was obtained by wiping out the electrospinning solution and then freeze-drying. It is known that a peak at a g-factor of ~ 2.0034 is due to unpaired holes in aromatic systems. An increase in the intensity of this peak is attributed to increased local stress and lattice defects. An extremely high density of unpaired hole electrons is found in literature known carbon nitride (a)). It is clear that the film (b) according to the invention by processing by the electrospinning method has a significantly lower density of defects. In addition, the reference sample (c)) shows that this effect is not due to any matrix effects of the carrier polymer matrix. FIG. 3 shows a characterization of high-stress treated carbon nitride according to the invention (dotted, b)), of a film according to the invention (deleted and scores, c)), which was prepared by means of the electrospinning method and cellulose acetate as a carrier polymer and of literature-known graphitic carbon nitride (a)) by means of ATR infrared spectroscopy. In all spectra, it is possible to detect carbon-nitride characteristic vibrations, such as the s-triazine respiratory vibration at 810 cm ^-1 , for the polymeric tri-s-triazine units. Furthermore, it can be seen that there are bonds between carbon and nitrogen in the analyzed structures. The bands for the double bond (1690 cm ^-1 to 1630 cm ^-1 ) and the single bond between carbon and nitrogen can be recognized (1590 cm ^-1 to 1030 cm ^-1 ).

FIG. 7 shows the measured photocurrent for a film according to the invention. The film (about 1 cm ² ) was here by means of poly-3, -ethylenedioxythiophen-poly (styrenesulfonate) (PEDOT: PSS) attached to ITO (indium-tin-oxide) - glass. The coating was dried at room temperature and sealed at 115 ° C. The current was measured against an Ag / AgCl electrode in a 0.1 mol L ^-1 KCl solution. The on / off cycles were generated by dimming and illuminating with an LED that has a similar light spectrum as daylight. Compared to 2.5 μΑ of the known carbon nitride (see, for example, ZHANG, Y. & ANTONIETTI, M .: Photocurrent generation by Polymeric Carbon Nitride Solids: An Initial Step Towards a Novel Photovoltaic System., Chem. Asian J. 5, 1307-11 (2010)), the photocurrent of the film according to the invention is significantly increased.

Fig. 8 shows a section of a graphitic carbon nitride molecule modified with metal cations such as zinc and iron. The "R" stands for more tri-s-triazine units, and the metal cation is mainly held between the tri-s-triazine units through N-M bonds.Zinc-modified graphitic carbon nitride can be prepared, for example, by using carbon nitride in the The mixture is allowed to stir for several hours and then the methanol is evaporated off, the residue is then dried, or the metal cations can be introduced into the carbon nitride with dicyandiamide by analogy with dicyandiamide To the solution is added a salt with the desired cation, then the solvent is evaporated off and the residue is dried.The dried residue can be processed by the method already described by heating to 560 ° C. to graphitic carbon nitride, which then with Metallka is modified.

The preparation of mesoporous graphitic carbon nitride is described in KWON, K., SA, YJ, CHEON, JY & Joo, SH: Ordered mesoporous carbon nitrides with graphitic frameworks as metal-free, highly durable, methanol-tolerant Langmuir 28, 991-6 (2012). described.

LIST OF REFERENCE NUMBERS

Number designation

1 dicyandiamide

2 Melam

3 Meiern

4 graphitic carbon nitride

5 ammonia

6 PE housings

7 bracket for center plate

8 laboratory power supply

9 syringe pump

10 syringes with LuerLock connection

11 Hose with LuerLock m / w

12 hose guide

13 needle

14 fibers / droplet spray

15 rotating collectors

16 12 V DC motor

17 plate made of PE for collector's attitude

18 high voltage source

19 resistor

20 ITO glass

21 Holder of the ITO glass

Claims

claims

1. A process for the preparation of a preferably for the photochemical cleavage of

Hydrogen from water with simultaneous oxidation of another substance suitable polymeric carbon nitride catalyst, characterized in that the polymeric carbon nitride (4) is exposed to increase its catalytic activity in suspended or dissolved form a stationary high voltage field of at least about 3 kV cm ^_1 .

2. The method according to claim 1, characterized in that the polymeric carbon nitride (4) is attached to fibers or droplet-shaped particles of a water-insoluble, a macroscopically coherent structure forming carrier polymer having a fiber thickness or a droplet diameter in the nanometer to micrometer range.

3. The method according to claim 2, characterized in that an electrospinning / spraying method is used in a homogeneous liquid mixture of polymeric carbon nitride (4) and the carrier polymer by means of a needle (13) fed through a high voltage field to a so-called collector (15) becomes.

4. The method according to claim 3, characterized in that for the electrospinning / spraying method, a so-called rotating collector (15) is used, which in addition to the rotation about its axis (A) even along this axis (A) moves.

5. The method according to claim 3, characterized in that at a distance of

l up to 20 cm between needle (13) and collector (15) of the electrospinning / spraying plant the voltage applied in the range of 15 kV to 40 kV is selected and that the pumping speed with which the homogeneous liquid mixture of polymeric carbon nitride and Carrier polymer is pressed by a pump (9) through the needle (13), a pumping capacity between 0.005 mL h ^-1 to 1.5 mL h ^-1 corresponds.

6. The method according to claim 3, characterized in that the electrospinning / spraying method polymeric carbon nitride (4) is processed together with the dissolved in a readily volatile acid, preferably concentrated acetic acid, carrier polymer.

7. The method according to claim 2, characterized in that the mechanically coherent structure has the shape of a film.

8. The method according to claim 2, characterized in that the carrier polymer fibers or droplets consist of cellulose acetate.

9. The method according to claim 1, characterized in that the polymeric carbon nitride (4) is prepared by heating dicyandiamide (1) to 560 ° C with a ramp of 2.5 ° C min ^-1 .

10. The method according to claim 1, characterized in that the polymeric carbon nitride used as catalyst material (4) with a few percent by weight of co-catalyst such as platinum, zinc oxide or a chromophore is modified.

11. The method according to claim 1, characterized in that the polymeric carbon nitride (4) in a mold with an enlarged surface - for example in mesoporous or monolayer form - is used.

12. A device for photochemical cleavage of hydrogen from water with simultaneous oxidation of another substance by means of a polymeric Korilenstoffnitrid- catalyst (4), characterized in that the catalyst is prepared according to one or more methods described in the preceding claims.