A type with N 3+ / P 3+ -Vacancy-Ti 3+ Preparation of structured suboxide titanium nanotube materials and their application in photoelectrocatalytic efficient degradation of organic pollutants

Abstract

A type with N 3+ / P 3+ ‑Vacancy‑Ti 3+ The present invention relates to the preparation of titanium dioxide nanotube materials and their application in photoelectrocatalytic efficient degradation of organic pollutants. 2‑x Nanotube array process, using NH3 and PH3 as reducing agents, on TiO 2‑x Oxygen vacancies are formed in the lattice, and P is introduced 3+ and N 3+ , construct a 3+ / P 3+ ‑Vacancy‑Ti 3+ Structured photoanode. N 3+ / P 3+ ‑Vacancy‑Ti 3+ The structure can adjust the electronic structure of the material, broaden its spectral absorption range, and have visible light catalytic properties. 3+ / P 3+ With Ti 3+ An electron migration channel is formed between Ti and 3+ The site maintains a high catalytic activity +3 valence state, significantly enhancing its service life and effectively avoiding the traditional TiO 2‑x Ti in materials 3+ The sites are easily oxidized, leading to electrode inactivation.

Description

Technical Field

[0001] The present invention belongs to the field of photoelectrocatalytic wastewater treatment, and particularly relates to a method having N 3+ / P 3+ -Vacancy-Ti 3+ Preparation of structured suboxide titanium nanotube materials and their application in photoelectrocatalytic efficient degradation of organic pollutants. Background Art

[0002] Photoelectrocatalysis is a new type of chemical treatment technology with the advantages of high mineralization rate and fast degradation rate in removing refractory organic pollutants. Anatase titanium dioxide nanotube arrays are widely used in photoanodes for water splitting and pollution degradation due to their simple preparation and excellent performance, but their wide band gap and low conductivity limit their practical applications. For example, the articles "TiO2 nanotubes with open channels as deactivation-resistant photocatalyst for the degradation of volatile organic compounds" and "Direct observation of oxygen vacancy self-healing on TiO2 photocatalysts for solar water splitting" mentioned the introduction of oxygen vacancies (O v ) to generate defect sites to form Ti with higher catalytic activity 3+ , forming defective titanium dioxide (TiO 2-x ). Usually, TiO 2-x There are two steps in the formation of TiO. First, amorphous TiO is prepared in situ on the surface of the titanium plate by electrochemical etching. 2-x Then, annealing is carried out in air atmosphere to transform the amorphous phase into polycrystalline anatase phase. 2-x Poor stability, Ti 3+ Under the action of highly electronegative oxygen atoms, they are easily oxidized, causing the electrode to become inactive and showing a clear irreversible trend. This seriously affects the application of this type of electrode material in actual wastewater degradation processes.

[0003] In order to improve its stability, researchers have adopted many strategies, such as coordination modulation, vacancy control, and band gap state engineering of doping elements. Among them, metal element doping can generally produce a stronger metal-support interaction and improve stability, but hinder the catalytic activity and have no obvious effect on the light utilization rate of the material. Non-metallic doping can change the coordination environment of the active site, form doping energy levels in the band gap, narrow the band gap width, and increase the spectral absorption range. Studies have found that during the calcination process, compared with other elements, N and P elements can hinder the phase transition from anatase to rutile and inhibit the growth of particles. In addition, the increase in N and P content is conducive to the effective chemical adsorption of oxygen, maintaining thermal stability, and effectively capturing conduction band electrons. As mentioned in the article "Phosphoruscontaining materials for photocatalytichydrogen evolution", N and P play an important role in improving the performance of TiO 2-x It has potential application value in terms of stability because it has lower electronegativity than O, which can inhibit the trend of the active center metal atom to transform into a high valence state. At the same time, the article "Phosphorus doped TiO2asoxygen sensor withlow operating temperature and sensing mechanism" mentioned that the doping of non-metallic elements in the coordination environment can effectively adjust the electronic structure in the system and improve the photocatalytic performance. The simultaneous doping of N and P can construct different catalytic active sites in the system. The synergistic effect of the two can effectively reduce the reaction energy barrier of the catalytic production of active oxidative species (hydroxyl radicals, superoxide radicals, etc.), accelerate the reaction rate, and significantly improve the oxidative degradation ability of the system. Therefore, N and P co-doped TiO2 is prepared by appropriate methods. 2-x , which can be used as a potential functional photoanode material. Summary of the Invention

[0004] For TiO with oxygen vacancies 2-x Ti exists at the anode 3+ The active sites are easily oxidized, which leads to electrode inactivation. 2-x In the process of transforming from amorphous to anatase crystal structure, NH3 and PH3 with strong reducing properties are used as precursors to simultaneously perform nitridation and phosphiding reactions, forming oxygen vacancies while introducing N into the lattice. 3+ and P 3+ . N 3+ and P 3+ Doping can effectively adjust the 2-xThe electronic structure of the material broadens the spectral absorption range, which makes the material have visible light catalytic properties, constructs an efficient and low-consumption photoelectric synergistic catalytic degradation system for pollutants, and promotes the effective removal of difficult-to-degrade organic pollutants.

[0005] The technical solution of the present invention:

[0006] A type with N 3+ / P 3+ -Vacancy-Ti 3+ The preparation method of structured suboxide titanium nanotube material comprises the following steps:

[0007] Step 1: Etch the titanium plate with ammonium fluoride using the electrochemical etching method described in “Removal of aqueous triclosan using TiO2 nanotube arrays reactive membrane by sequential adsorption and electrochemical degradation” to obtain a titanium plate with in situ growth of titanium oxide nanotubes on the surface.

[0008] Step 2: Place the etched titanium plate in the downwind direction of the tube furnace, and place a porcelain boat containing 1-10g NaH2PO2 and 1-10g dicyandiamide at 40mm and 20mm away from the titanium plate in the upwind direction respectively; use N2 as the carrier gas, and heat up at a rate of 2-5℃ / min to 300-450℃, and maintain for 1-2h. After the reaction is completed, cool it naturally to room temperature; take out the electrode, rinse it with deionized water, and then charge it at 1-4mA / cm 2 The product was reduced in 1 mol / L (NH4)2SO4 solution for 5 to 10 min to obtain 3+ / P 3+ -Vacancy-Ti 3 + Structural suboxide titanium nanotube material, that is, with P / N-vacancy-Ti 3+ Active site photoelectrocatalytic anode (NP-NTA).

[0009] The NP-NTA prepared by the above preparation method was used as a photoanode, and a pure titanium plate was used as a cathode. The distance between the anode and the cathode was 20 to 30 mm. The anode was placed on the side of a quartz glass with high light transmittance. The outer wall of the anode side of the reactor was 100 mm away from the light source. The light source used was a 420 to 450 nm wavelength LED light source. A photoelectrocatalytic degradation system was constructed under the operating conditions of a constant current of 0.5 to 5 mA / cm 2 , which can efficiently degrade the difficult-to-degrade organic wastewater discharged from the printing and dyeing and drug synthesis processes.

[0010] In step 2, NaH2PO2 and dicyandiamide are used as phosphorus source and nitrogen source respectively, and are decomposed by heating to release PH3 and NH3. The reaction temperature is in the range of 300-450℃. Below 300℃, the phosphorus source and nitrogen source cannot be fully decomposed. Above 450℃, the phosphorus source and nitrogen source will decompose too quickly and cannot react evenly on the electrode surface. Only at the appropriate temperature can N3 be formed on the electrode. 3+ / P 3+ -Vacancy-Ti 3+ Active site.

[0011] The electrode after calcination in step 2 needs to undergo an electrocatalytic reduction process to make the Ti on the electrode surface 3+ The structure is stable, which enables the photoelectrocatalytic performance to reach the optimal level.

[0012] Beneficial effects of the present invention: In the present invention, the anatase phase of TiO is formed by calcining 2- In the process of x nanotube array, NH3 and PH3 are used as reducing agents and reaction precursors of doping N and P non-metallic elements. 2-x Oxygen vacancies are formed in the lattice structure, and P and N are introduced simultaneously to successfully construct a unique N / P-Ov-Ti 3+ Active catalytic sites. Compared with the traditional method to form Ti 3+ -Ov-Ti 3+ Catalytic site, P at the catalytic site in NP-NTA 3+ The 3s orbital and N in the M shell 3+ The L shell 2s orbitals of the TiO2O3O4 ... 3+ The valence electrons in the 3d orbital activate Ti 3+ 3d orbitals and inhibit the Ti 3+ Towards a high valence state (Ti 4+ ) transformation trend. In addition, P 3+ and N 3+ Doping can effectively adjust the 2-x The electronic structure of the material is modified, forming defect energy levels in the band gap and forming multi-photon absorption channels, which can significantly broaden the spectral absorption range of the material. At the same time, the original band gap width will not be changed, which can ensure the material's original strong photocatalytic redox ability. This makes the material have visible light catalytic performance, thus providing a solid foundation for the construction of an efficient and low-cost photoelectric synergistic catalytic degradation system for pollutants. 3+ / P 3+ -Ov-Ti 3+ The unique structure can be 3+ / P 3+ With Ti 3+ A stable and effective electron migration channel is formed between Ti and 3+The site maintains a highly catalytically active +3 valence state, significantly enhancing its service life. 3+ / P 3+ -Ov-Ti 3+ The synergistic effect of sites in the photoelectrocatalytic process can significantly increase the production of active oxidative species on the electrode surface, thereby effectively enhancing its ability to degrade and mineralize difficult-to-degrade organic pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the photoelectrocatalytic reactor of the present invention;

[0014] In the figure: 1 reactor; 2 anode; 3 cathode; 4 quartz glass; 5 stirrer; 6 water inlet; 7 water outlet; 8 power supply; 9 light source. DETAILED DESCRIPTION

[0015] The specific implementation of the present invention is described in detail below in conjunction with the technical solutions and drawings.

[0016] Example 1

[0017] Photoanode preparation: Prepare an electrochemically etched titanium plate by referring to the method of "Removal of aqueous triclosan using TiO2 nanotubearrays reactive membrane by sequential adsorption and electrochemical degradation". The specific method is as follows:

[0018] A pure titanium plate (1 mm thick) with an effective area of 50 × 50 mm² was used as a substrate and immersed in acetone, ethanol, and deionized water for 10 minutes, respectively, to remove surface impurities. An electrolyte containing ethylene glycol, ammonium fluoride, and deionized water (mass ratio of 94.5:0.5:5) was prepared. The titanium plate was placed as the anode between two cathode plates, with a distance of 30 mm between the anode and cathode. The anode titanium plate was oxidatively etched using a DC regulated power supply at 60 V for 6 hours. After the reaction, the etched anode titanium plate was immersed in methanol for 4 hours to displace organic matter, such as ethylene glycol, from the electrode surface. The electrode was then rinsed with deionized water and dried at 60°C. The etched titanium plate was placed downwind in a tube furnace. 1 g of NaH₂PO₂ and 2 g of dicyandiamide were placed upwind, 40 mm and 20 mm from the titanium plate. Using N2 as carrier gas, the temperature was raised to 400℃ at a rate of 2℃ / min and maintained for 2h. After the reaction was completed, the electrode was naturally cooled to room temperature. The electrode was removed and washed with deionized water. After that, the electrode was heated at 2mA / cm 2 The TiO2 with N / P-vacancy was obtained by reduction in 1 mol / L (NH4)2SO4 solution for 10 min. 3+Active site photoanode (NP-NTA12).

[0019] Preparation of reference group samples: Since N and P doping have a significant impact on the performance of suboxide titanium nanotubes, NP-NTA with different N and P doping amounts were selected as the reference group for subsequent performance comparison.

[0020] The dosages of NaH2PO2 and dicyandiamide were selected as 1g and 0g, 0g and 2g, 2g and 2g, and 1g and 4g, respectively, to prepare a series of NP-NTA photoelectrodes, which were numbered NP-NTA10, NP-NTA02, NP-NTA22, and NP-NTA14.

[0021] Example 2

[0022] Photoanode accelerated life test: The NP-NTA series prepared in Example 1 was used as the photoanode and the pure titanium plate of the same size was used as the cathode. The test was carried out in a photoelectrocatalytic reactor. The electrolyte was 1 mol / L sodium perchlorate aqueous solution. The electrolyte was 20 mA / cm 2 and 10mA / cm 2 The electrode life was tested twice with a constant current, and the electrode deactivation standard was set at a photoanode potential of 10 V. The formula for the ultimate life is as follows:

[0023] T1×i1 n =T2×i2 n

[0024] T1 and T2 are the electrode lifespan (h) at two different currents, i1 and i2 are the electrode lifespan (mA / cm 2 ), n is the coefficient.

[0025] 20mA / cm 2 and 10mA / cm 2 Substitute the maximum life under these conditions into the formula to obtain the n value. Then select the current value required by the NP-NTA photoanode during normal operation to obtain the service life of the electrode under these conditions. By testing the n value, it is estimated that 1mA / cm 2 Under constant current conditions, the theoretical service life of NP-NTA12 is about 42,000 hours, which is 210 times the service life of pure NTA photoelectrode prepared by the traditional method in the article "Removal of aqueoustriclosan using TiO2 nanotube arrays reactive membrane by sequential adsorption and electrochemical degradation".

[0026] Comparative Example 1: Using the same testing method as Example 2, the theoretical lifespans of the NP-NTA10, NP-NTA02, NP-NTA22, and NP-NTA14 photoanodes were 30,000, 8,200, 22,000, and 14,000 hours, respectively. This demonstrates that simply doping with appropriate amounts of P and N can improve electrode lifespan. When both N and P are doped simultaneously, excessive P or N doping can destroy the excess vacancy structure on the NTA surface, thereby affecting electrode stability.

[0027] Example 3

[0028] Photoanode degradation test of simulated wastewater containing anticancer drugs: Capecitabine was the target pollutant, the photoanode was NP-NTA, and the cathode was a pure titanium plate and a saturated calomel electrode as the reference electrode, placed in a photoelectrocatalytic reactor. The electrolyte was a Na2SO4 solution (20 mmol / L) containing capecitabine (10 mg / L). The light source was a 420-450 nm wavelength LED light source. The constant current was 1 mA / cm 2 After 40 minutes of reaction, the removal rate of capecitabine reached 100%. After 1 hour of reaction, the TOC removal rate reached 80%.

[0029] Comparative Example 2: Using the same test method as Example 3, the degradation performance of NP-NTA10, NP-NTA02, NP-NTA22, NP-NTA14, and pure NTA photoanode was tested. After 40 minutes of reaction, the removal rates of capecitabine by this series of photoelectrodes were 85%, 60%, 52%, 68%, and 72%, respectively. This shows that simply doping with an appropriate amount of P can improve the performance of the photoelectrode in generating active oxidative species, and thus the capecitabine removal rate is higher than that of the pure NTA photoelectrode. When N and P are doped at the same time, excessive P and excessive N doping will affect the surface structure of the NTA photoelectrode, reducing Ti 3+ , thus affecting the degradation performance of the photoelectrode.

[0030] Example 4

[0031] Photoanode degradation test of actual pharmaceutical wastewater: The photoanode is NP-NTA, and the cathode is a pure titanium plate, placed in a photoelectrocatalytic reactor. The target pollutant is wastewater from a pharmaceutical factory, with a TOC concentration of 500 ppm. The light source is a 420-450 nm wavelength LED. The constant current is 2 mA / cm 2 After 2 hours of reaction, the TOC removal rate reached 90%. After that, the treated wastewater was discharged through the reactor outlet, and new wastewater was pumped in, continuously treating the wastewater in an intermittent manner. After the degradation system operated for 200 hours, there was no significant attenuation of the photoanode degradation performance.

Claims

1. A method with N 3+ / P 3+ -Vacancy-Ti 3+ The application of structured suboxide titanium nanotube materials in photoelectrocatalytic efficient degradation of organic pollutants is characterized by: The N 3+ / P 3+ -Vacancy-Ti 3+ The preparation method of structured suboxide titanium nanotube material comprises the following steps: Step 1: using ammonium fluoride to etch a titanium plate using an electrochemical etching method to obtain a titanium plate with titanium oxide nanotubes in situ grown on the surface; Step 2: Place the titanium plate obtained in step 1 in the downwind direction of the tube furnace, and place porcelain boats containing NaH2PO2 and dicyandiamide at 40 mm and 20 mm away from the titanium plate in the upwind direction respectively; use N2 as the carrier gas, increase the temperature at a rate of 2-5 ° C / min to 300-450 ° C, and maintain it for 1-2 hours. After the reaction is completed, cool it naturally to room temperature; take out the titanium plate, rinse it with deionized water, and place it at 1-4 mA / cm 2 The product was reduced in 1 mol / L (NH4)2SO4 solution for 5-10 min to obtain 3+ / P 3+ -Vacancy-Ti 3+ Structural suboxide titanium nanotube material, that is, with P / N-vacancy-Ti 3+ Photoelectrocatalytic anode NP-NTA with active sites; The specific application is as follows: NP-NTA is used as the photoanode, a pure titanium plate is used as the cathode, the distance between the anode and the cathode is 20-30 mm, the anode is placed on the side of the quartz glass with high light transmittance, the outer wall of the anode side of the reactor is 100 mm away from the light source, and the light source uses a 420-450 nm wavelength LED light source to construct a photoelectrocatalytic degradation system. The operating conditions are a constant current of 0.5-5 mA / cm 2 , and efficiently degrade the difficult-to-degrade organic wastewater discharged from the printing and dyeing and drug synthesis processes.

2. The use according to claim 1, characterized in that The filling amounts of NaH2PO2 and dicyandiamide are both 1~10 g.

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