CN105749914B - A kind of method of symmetrical difunctional photochemical catalyst, dual chamber Photoreactor and photocatalytic reduction of carbon oxide - Google Patents

Abstract

The invention discloses a symmetrical double-function photocatalyst and a corresponding double-chamber photoreactor, belonging to the technical field of comprehensive utilization of carbon dioxide, wherein the symmetrical double-functional photocatalyst includes a graphene intermediate electron transport layer deposited on a double-sided _TiO2 nanotube array substrate , and then deposited narrow-bandgap semiconductor nanoparticles as photosensitizers. The symmetrical photocatalyst provided by the present invention expands the photoresponse of the ternary composite photocatalyst to the visible light region through the introduction of the electron transport layer and the photosensitizer component, and at the same time promotes the effective separation of photogenerated electron-hole pairs, and enhances the photosensitivity of the composite catalyst. The ability of catalytic reduction of CO ₂ ; the double-sided symmetric ternary composite catalyst is matched with a dual-chamber photoreactor, so that the photocatalytic water oxidation and CO ₂ reduction reactions are carried out in separate areas, reducing the occurrence of reverse reactions and further improving the photocatalytic performance. Catalytic _CO2 reduction efficiency.

Description

A symmetrical bifunctional photocatalyst, dual-chamber photoreactor and photocatalytic reduction of dioxygen carbonization method

technical field

The invention belongs to the technical field of comprehensive utilization of carbon dioxide, and in particular relates to a symmetrical double-function photocatalyst, a double-chamber photoreactor and a method for photocatalytically reducing carbon dioxide.

Background technique

Energy shortage and the greenhouse effect caused by carbon dioxide (CO ₂ ) have become the main problems threatening social development and people's daily life, but at the same time, because the abundant CO ₂ itself is also an important chemical raw material, how to convert it efficiently and extensively Utilization presents challenges and opportunities for people. However, since _CO2 itself is chemically stable, additional energy input is required to activate and convert it into useful compounds. Solar energy is a clean, cheap, and widely distributed renewable energy. Using solar photocatalysis technology to reduce _CO2 to solar fuel is of great significance for alleviating energy shortage and improving the ecological environment.

Current research on photocatalytic reduction of _CO2 mainly focuses on two aspects: the construction of photocatalysts and the design of reactors. Among the currently applied photocatalysts, powder-type catalysts are more commonly studied. Although the preparation method of powder-type catalyst is simple and the product has good dispersibility, there are disadvantages such as difficult recovery, inconvenient separation of products, easy recombination of photogenerated charges, and low photocatalytic efficiency. Therefore, the research on immobilization of powder photocatalysts and film-based catalysts is becoming a hot spot. Photoelectrocatalysis has been widely studied because it can greatly enhance the _CO2 reduction efficiency. However, the biggest shortcoming of photocatalytic technology is the need for external electric energy input, which increases the overall energy consumption and equipment cost. At the same time, under the action of an external electric field, the membrane electrode itself may also cause side reactions, which have a great impact on the stability of the catalyst. In view of the above problems, finding a kind of efficient and stable film-based photocatalyst is the key to the industrial application of photocatalytic _CO2 reduction technology.

Another factor affecting the photoreduction of _CO2 technology is the design of the reactor. High-efficiency film-based photocatalysts require the cooperation of photoreactors optimized for their structures, so that the formed photocatalytic system can maximize its ability to reduce CO ₂ . Compared with the traditional single-chamber photocatalytic reactor, the double-chamber reactor can effectively generate redox products independently, reduce the occurrence of reverse reactions and side reactions, and improve the photocatalytic _CO2 reduction efficiency. At present, dual-chamber reactors are mostly used in photocatalytic systems, and there are few patent reports on _CO2 reduction using only photocatalytic processes. Chinese patent CN103348039A discloses a method for photocatalytic reduction of _CO2 in a double-chamber reactor, using a nitride semiconductor stack as the anode, indium or indium compound as the cathode, and two separate photochemical electrodes are connected by external wires. However, in this invention, due to the existence of external wires, the structure of the entire device is complicated, and the light conversion efficiency is reduced due to the voltage drop of the wires and thermal effects. Chinese patent CN103898548A discloses a method for photocatalytic reduction using graphene and _TiO2 nanotubes, in which Pt-doped graphene is loaded on nickel foam as an electric cathode, and the _TiO2 nanotube array is used as a photoanode, and they are respectively pasted on The two sides of the Nafion proton exchange membrane are made of catalyst electrodes, which are placed between the double-chamber reactors. At the same time, an external voltage is applied to the cathode and anode for the application of photoelectric catalytic reduction of CO ₂ . Also in this invention, due to the existence of the external circuit, even if the energy input of the whole reaction increases, energy loss may occur during the electron transfer process.

Contents of the invention

The purpose of the present invention is to provide a symmetrical double-functional photocatalyst and a corresponding double-chamber photoreactor, and to provide a method for photocatalytic reduction of carbon dioxide is another purpose of the present invention.

Based on the above purpose, the present invention adopts the following technical scheme: a symmetrical bifunctional photocatalyst, including a double-sided _TiO2 nanotube array (TNA) film substrate prepared from pure titanium by a two-step anodic oxidation method, and graphite is electrodeposited on the surface of the substrate Graphene layer, the graphene layer is the electron transport layer, by adjusting the electrochemical parameters to change the thickness of the graphene deposition layer, adjust the transmission of electrons in the composite symmetrical bifunctional photocatalyst, improve the recombination probability of photoelectron-hole pairs; Narrow bandgap semiconductor nanoparticles were deposited on the olefin layer as photosensitizers.

Preferably, the narrow bandgap semiconductor nanoparticles are one or a mixture of two or more of cuprous oxide, copper oxide, cadmium sulfide, zinc oxide, lead sulfide, and lead oxide.

Preferably, the electrodeposition method is cyclic voltammetry, constant current deposition or constant potential deposition.

Preferably, the method for depositing narrow-bandgap semiconductor nanoparticles on the graphene layer is electrochemical deposition, wet chemical deposition, hydrothermal deposition, solvothermal deposition or photochemical deposition.

The dual-chamber photoreactor adopting the above-mentioned symmetrical bifunctional photocatalyst includes symmetrically arranged anode reaction cells and cathode reaction cells, two connection ports are arranged between the cathode reaction cell and the anode reaction cell, and a Nafion proton is fixed in the middle of a connection port The exchange membrane is fixed with a substrate made of symmetrical bifunctional photocatalyst in the middle of the other connection port, the top of the cathode reaction pool and the anode reaction pool are equipped with air inlets and outlets, and the side wall of the anode reaction pool is equipped with a light window.

Further, the anode reaction pool and the cathode reaction pool are water or an electrolyte solution, and the electrolyte solution of the anode reaction pool is one or a mixture of two or more of Na ₂ SO ₄ , NaCl, and Na ₂ SO ₃ solutions; the cathode reaction The electrolyte solution of the cell is one or a mixture of two or more of NaHCO ₃ , Na ₂ CO ₃ , NaOH, KOH, K ₂ CO ₃ solutions.

Further, a liquid intake port is provided on the side wall of the cathode reaction cell, and the liquid or gas phase reduction product yield is detected and analyzed by gas chromatography through the liquid intake port or the gas outlet.

The method for photocatalytic reduction of carbon dioxide using the above-mentioned dual-chamber photoreactor comprises the following steps: adding water or an electrolyte solution to the anode reaction cell and the cathode reaction cell of the dual-chamber photoreactor; clamping the catalyst substrate and the Nafion proton exchange membrane respectively On the two connection ports of the reactor, the anode reaction cell and the cathode reaction cell are not directly connected to each other, and only protons can flow between the two cells through the Nafion membrane; the light is injected into the anode reaction cell through the light window and directly irradiates on the substrate. High-purity N ₂ and CO ₂ gases are respectively passed into the electrolyte solution of the anode reaction cell and the cathode reaction cell through the inlet ports, and the gas phase products are discharged from the reactor through the gas outlet along with the carrier gas, forming a continuous feeding, open photocatalytic Reduction of CO ₂ reaction system; light source (including ultraviolet light, visible light or full-spectrum light source) excites the photosensitizer on the substrate to generate photoelectron-hole pairs on the anode surface, and the electrons go to the On the cathode side, the holes and electrons migrate to the anode and cathode sides of the photocatalyst, respectively, and participate in the photooxidation of water and the reduction of _CO2 in a separate reaction cell.

Further, the CO ₂ reduction product is one or a mixture of two or more of alcohols, hydrocarbons, and carbon monoxide.

The present invention uses _TiO2 nanotube array (TNA) as the substrate, which is convenient for direct application, recycling and replacement. By introducing the electron transport layer and photosensitizer components, the photoresponse of the ternary composite photocatalyst is extended to the visible light region, and at the same time it promotes The effective separation of photogenerated electron-hole pairs enhances the ability of the composite catalyst to photocatalytically reduce _CO2 ; after matching the double-chamber photocatalytic reactor, the oxidation-reduction reactions are carried out in independent areas, which reduces the occurrence of reverse reactions and further improves Photocatalytic _CO2 reduction efficiency. In addition, the present invention does not require external electric energy input, thereby reducing energy consumption.

At the same time, the present invention uses a double-sided symmetric dual-function photocatalyst directly as the isolation film of the dual-chamber photoreactor, eliminating the need for external circuit connections, and efficiently separating photogenerated charges through the formation of multiple heterojunction interfaces in the catalyst to improve the reduction of _CO2 Efficiency, the literature using this system for photoreduction of _CO2 has not been reported yet.

Description of drawings

Fig. 1 is the preparation flowchart of symmetrical bifunctional photocatalyst;

Figure 2 is the scanning electron microscope image of the sample prepared in Example 1, in which (a) is the electron microscope scanning surface image of TNA; (b) is the electron microscope scanning surface image of G/TNA; (c) is Cu ₂ O/G/TNA SEM surface image of ; (d) SEM cross-sectional image of Cu ₂ O/G/TNA;

Fig. 3 is the front view of double-chamber photocatalytic reactor;

Fig. 4 is the top view of double-chamber photocatalytic reactor;

Fig. 5 is the left side view of dual-chamber photocatalytic reactor;

Figure 6 is a _schematic diagram of the photocatalytic reduction of CO by a symmetrical bifunctional photocatalyst in a dual-chamber photoreactor;

Fig. 7 is Cu ₂ O/G/TNA, CdS/G/TNA, PbO ₂ /G/TNA, ZnO/G/TNA prepared in embodiment 1, 6, 7, 8 in the reaction shown in Fig. 3 ~ 5 Methanol production from photocatalytic reduction of _CO2 in a device.

Detailed ways

Below in conjunction with embodiment the present invention is further described and explained.

Example 1

1. Preparation of symmetrical bifunctional Cu ₂ O/G/TNA film photocatalyst

A symmetrical bifunctional photocatalyst, including a double-sided TiO ₂ nanotube array (TNA) film substrate prepared from pure titanium by a two-step anodic oxidation method, and a graphene layer is electrodeposited on the surface of the substrate, and the graphite can be changed by adjusting the electrochemical parameters The thickness of the graphene deposition layer can be adjusted to regulate the transport of electrons in the compound symmetrical bifunctional photocatalyst and improve the recombination probability of photoelectron-hole pairs; As shown in Figure 1, the following steps are included:

(1) Preparation of TNA film substrate: After physical grinding and ultrasonic cleaning, the pure titanium foil was soaked in chemical pickling solution for chemical polishing; then the titanium foil was placed in ethylene glycol with a mass fraction of 0.25% NH ₄ F -In the water mixed solution, wherein the volume ratio of ethylene glycol to water is 49:1, after using the three-electrode system to carry out anodic oxidation twice under the same conditions, wash and dry with deionized water, place in a muffle furnace, and air Baking at 500 ^o C for 2 h, the double-sided symmetrical TNA film substrate was finally obtained. The surface image scanned by the electron microscope is shown in Figure 2(a). From the figure, it can be seen that the surface layer of the TNA membrane substrate has a regular appearance and uniform pore size, and the bottom layer is a nanotube array with a pore size of about 30 nm and a tube length of about 500 nm;

(2) Preparation of G/TNA substrate (deposited graphene): In a three-electrode system with TNA film substrate as the working electrode, graphene sheets were deposited on the graphene oxide aqueous dispersion by cyclic voltammetry. On the surface of the TNA film, the scanning voltage range is -1.5 to +1 V, and the number of scanning cycles is 20, that is, the TNA film substrate (G/TNA) deposited with graphene is obtained. Its electron microscope scanning surface image is shown in Figure 2(b). From the figure, it can be seen that the characteristic folded structure of graphene and the surface morphology of TNA under its coverage prove that a thin layer of graphene with a certain thickness is deposited. to the TNA surface;

(3) Preparation of Cu ₂ O/G/TNA substrate (deposition of narrow-bandgap semiconductor nanoparticles on G/TNA substrate): Cu ₂ O nanoparticles were deposited on the surface of G/TNA by electrochemical deposition, and Cu ₂ The electrolyte of O is CuSO ₄ lactic acid aqueous solution, the concentration of CuSO ₄ is 0.4 mol/L, the concentration of lactic acid is 3 mol/L, the pH value is adjusted to 10 by 5 mol/L NaOH, and the deposition voltage is -0.4 V, The deposition time was 600 s. After the deposition was completed, it was washed with deionized water and dried to obtain a double-sided symmetric Cu ₂ O/G/TNA film photocatalyst, which was designated as sample 1. The surface image scanned by electron microscope is shown in Figure 2(c). It can be seen from the figure that Cu ₂ O nanoparticles are uniformly distributed on the surface of the graphene layer, with a particle size of about 80 nm; ), it can be seen from the figure that the graphene layer and Cu ₂ O nanoparticles were successively deposited on the surface of TNA and formed a ternary composite photocatalyst Cu ₂ O/G/TNA.

． Dual Chamber Photoreactor

The structure of the double-chamber photoreactor is shown in Figures 3 to 5, including an anode reaction pool A and a cathode reaction pool B. Add 1 mol/L Na ₂ SO ₄ and NaHCO ₃ solutions into the anode reaction pool A and the cathode reaction pool B respectively as electrolytes, and the connection port 7 between the anode reaction pool A and the cathode reaction pool B is sandwiched between Nafion proton exchange Membrane, so that the anode reaction cell and the cathode reaction cell are directly isolated from each other, and only protons can flow between the two cells through the Nafion membrane; the substrate made of Cu ₂ O/G/TNA film photocatalyst is clamped in the middle of the connection port 6; The top of the anode reaction pool A is equipped with a first air inlet 1 and a first air outlet 2, and the side wall of the anode reaction pool A is provided with a light window 8; the top of the cathode reaction pool B is equipped with a second air inlet 3 and a second air outlet. Two air outlets 4, and a liquid intake port 5 is arranged on the side wall.

Photocatalytic reduction of _CO2 experiments

Using a 300 W xenon lamp with a 400 nm UV cut-off filter as the light source (λ>400 nm), after the reaction starts, high-purity N enters the anode reaction cell A from the first gas inlet ₁ , and is discharged from the first gas outlet 2. _CO2 enters the cathode reaction cell B from the second air inlet 3, and is discharged from the second air outlet 4. The light source excites the photosensitizer on the substrate to generate photoelectron-hole pairs on the anode surface, and the electrons pass through the matching energy level arrangement and The role of the electron transport layer is transmitted to the cathode surface, and the holes and electrons migrate to the anode and cathode surfaces of the photocatalyst, respectively, and participate in the photooxidation of water and the reduction of CO ₂ in an independent reaction cell, and the photocatalytic reduction of CO ₂ The schematic diagram of the process is shown in Figure 6. Every 1 h, 10 μL of the reaction solution was taken out from the liquid extraction port 5, and samples were taken 6 times, and the product was analyzed and detected by gas chromatography equipped with a flame ion detector. The yields were 67.5, 125, 148, 180, 223 and 275 μmol/cm ² , respectively, and the specific results are shown in Figure 7.

Example 2~5

Examples 2, 3, 4, and 5 The method for preparing TNA film substrates is the same as that of Example 1, and the process for preparing G/TNA substrates and _Cu2O /G/TNA substrates refers to Example 1. For specific process parameters, see In Table 1, the corresponding Cu ₂ O/G/TNA substrates are marked as sample 2, sample 3, sample 4, and sample 5 in sequence.

Sample 2, sample 3, sample 4, sample 5 are respectively clamped in the middle of the connection port 6 of the double-chamber photoreactor of embodiment 2, 3, 4, 5, and the type of electrolyte solution injected in the anode reaction pool A and the cathode reaction pool B See Table 1.

Examples 2, 3, 4, 5 The photocatalytic reduction of CO ₂ The process of producing methanol experiment is the same as that of Example 1.

The technological parameter table of table 1 embodiment 1～5

Example 6

The preparation process of the G/TNA film substrate is the same as that of Example 1.

CdS is deposited on the surface of G/TNA by hydrothermal precipitation method. The process is: respectively prepare cadmium chloride aqueous solution and thiourea aqueous solution with a concentration of 0.004mol/L, according to cadmium chloride aqueous solution: thiourea aqueous solution (mass ratio ) in a ratio of 1:3 and mixed evenly. The G/TNA membrane substrate was placed vertically in a high-pressure reactor, and a mixed solution of cadmium chloride and thiourea was added, and the sealed reactor was placed in an oven at 170 °C for 6 h. After the reaction, the sample was taken out, washed with distilled water, and then heat-treated at 400 °C for 3 h in an Ar atmosphere to prepare a CdS/G/TNA film substrate.

The CdS/G/TNA film substrate is clamped in the middle of the connection port 6 of the double-chamber photoreactor, and the photocatalytic reduction of CO is used to prepare _methanol . The specific product detection and analysis process is the same as in Example 1, and the calculated methanol yields are 52 and 78, respectively. , 110, 130, 151, and 170 μmol/cm ² , see Figure 7 for specific results.

Example 7

The preparation process of the G/TNA film substrate is the same as that of Example 1.

ZnO was deposited on the surface of G/TNA by photochemical deposition. The process was as follows: a zinc nitrate aqueous solution with a concentration of 0.5 mol/L was prepared, the G/TNA film substrate was vertically immersed in the zinc nitrate solution, and both sides of the substrate were simultaneously treated under an ultraviolet lamp. After irradiating for 15 min, take it out, wash it with deionized water, dry it in vacuum at 100 °C, and then heat-treat it in Ar atmosphere at 450 °C for 1 h, then the ZnO/G/TNA film substrate prepared by photochemical deposition method is obtained.

The ZnO/G/TNA film substrate is clamped in the middle of the connection port 6 of the double-chamber photoreactor, and the photocatalytic reduction of CO is used to prepare _methanol . The specific product detection and analysis process is the same as in Example 1, and the calculated methanol production is 12.5, 20, respectively. , 26, 29, 30, 31 μmol/cm ² , the specific results are shown in Figure 7.

Example 8

The preparation process of the G/TNA film substrate is the same as that of Example 1.

The PbO ₂ /G/TNA film substrate was prepared by electrochemical deposition, the process is: first prepare the electroplating solution: the concentration of lead nitrate in the electroplating solution is 20.5 mol/L, the concentration of nitric acid is 0.1 mol/L, and the concentration of sodium fluoride The concentration was 0.04 mol/L, and then the G/TNA substrate was placed in the electroplating solution, and a three-electrode system was used to perform pulse electrodeposition at a temperature of 333 K, a stirring speed of 300r/min, and electrodeposition for 10 min to obtain β- PbO ₂ modified G/TNA substrate, that is, PbO ₂ /G/TNA film substrate.

The _PbO2 /G/TNA membrane substrate is clamped in the middle of the connection port 6 of the double-chamber photoreactor, and the photocatalytic reduction of _CO2 prepares methanol. The specific product detection and analysis process is the same as that of Example 1, and the calculated methanol production is 40, 51, 55, 68, 73, 75 μmol/cm ² , see Figure 7 for specific results.

Claims (8)

1. using the dual chamber Photoreactor of symmetrical difunctional photochemical catalyst, it is characterised in that the symmetrical difunctional photochemical catalyst Including TiO₂Nano-tube array substrate, substrate surface electro-deposition have graphene layer, and being deposited on graphene layer has low-gap semiconductor Nano particle is as photosensitizer；It is anti-including symmetrically arranged anode reaction pond and cathode reaction pond, cathode reaction pond and anode Two connectors are provided between Ying Chi, Nafion PEMs are fixed among a connector, in another connector Between be fixed with the substrate made of symmetrical difunctional photochemical catalyst, be equipped with air inlet at the top of cathode reaction pond and anode reaction pond Mouth and gas outlet, anode reaction pond side wall are provided with light window.

2. dual chamber Photoreactor according to claim 1, it is characterised in that the low-gap semiconductor nano particle is oxygen Change the mixing of one or both of cuprous, cupric oxide, cadmium sulfide, zinc oxide, vulcanized lead, lead oxide and the above.

3. dual chamber Photoreactor according to claim 1 or 2, it is characterised in that the method for the electro-deposition lies prostrate for circulation An Fa, galvanostatic deposition method or potentiostatic electrodeposition method.

4. dual chamber Photoreactor according to claim 3, it is characterised in that low-gap semiconductor is deposited on graphene layer The method of nano particle is that electrochemical deposition, wet chemistry method deposition, hydro-thermal method deposition, solvent-thermal method deposition or photochemical method sink Product.

5. according to the dual chamber Photoreactor described in claim 1 or 2 or 4, it is characterised in that anode reaction pond and cathode reaction pond In be water or electrolyte solution, the electrolyte solution in anode reaction pond is Na₂SO₄、NaCl、Na₂SO₃One kind in solution or two The mixture of kind and the above；The electrolyte solution in cathode reaction pond is NaHCO₃、Na₂CO₃、NaOH、KOH、K₂CO₃One in solution Kind or two kinds and the above mixture.

6. dual chamber Photoreactor according to claim 5, it is characterised in that the side wall in cathode reaction pond is provided with and takes liquid Mouthful.

7. using the method for the dual chamber Photoreactor photocatalytic reduction of carbon oxide described in claim 6, it is characterised in that：Double The anode reaction pond of room Photoreactor and cathode reaction pond add water or electrolyte solution；Light injects anode reaction by light window Direct irradiation is on substrate behind pond, high-purity N₂、CO₂Gas is each passed through anode reaction pond, cathode reaction pond by air inlet respectively Electrolyte solution in, enter photooxidation and the CO of water-filling₂Reduction reaction；Gas-phase product is discharged with carrier gas by gas outlet to react Device.

8. the method for photocatalytic reduction of carbon oxide according to claim 7, it is characterised in that CO₂Reduzate be alcohol The mixture of one or both of class, hydro carbons, carbon monoxide and the above.