Method for enhancing photocatalytic seawater hydrogen production performance of nano-composite structure by using polymethyl methacrylate coating

Abstract

The invention relates to a method for enhancing the photocatalytic seawater hydrogen production performance of a nano-composite structure coated with polymethyl methacrylate, in particular to titanium dioxide (TiO2) loaded with platinum (Pt) particles, wherein the titanium dioxide (TiO2) grows in situ on vacant amorphous molybdenum disulfide (MoS2 + x) coated with polymethyl methacrylate (PMMA) through a reprecipitation method, and the titanium dioxide (TiO2) grows in situ on the vacant amorphous molybdenum disulfide (MoS2 + x). The Pt / TiO2 (at) MoS2 + x (at) PMMA is used for a stable and efficient photocatalytic hydrogen production system. The invention belongs to the technical field of catalytic energy. The PMMA used in the invention can effectively protect the catalyst, prevent surface reconstruction of the photocatalyst induced by salt ions and protect catalytic active sites, thereby improving the stability of the photocatalyst. The smooth implementation of the patent provides a simple, convenient and efficient strategy for improving the photocatalytic hydrogen production rate, solves the problem that the catalyst is unstable, and provides greater possibility for industrialization of photocatalytic marine water hydrogen production.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic energy, and particularly relates to a method for enhancing the photocatalytic hydrogen production performance of a nano-composite structure by coating with polymethyl methacrylate. This method uses polymethyl methacrylate as the coating material, and forms a polymer coating layer on the surface of Pt / TiO2@MoS 2+x through a reprecipitation method, thereby constructing an efficient photocatalytic hydrogen production system. This technical solution can significantly improve the hydrogen production efficiency and stability of the photocatalyst, providing a new solution for the development of clean energy. Background Art

[0002] Under the urgent needs of the global energy structure transformation and ecological environment protection, the development of renewable alternative energy has become the consensus of the international community. The increasing scarcity of traditional fossil fuels and the continuous environmental deterioration caused by greenhouse gas emissions have made new clean energy systems represented by hydrogen energy highly concerned. As a secondary energy carrier with zero carbon emissions, hydrogen energy shows broad application prospects in fields such as transportation power and industrial metallurgy due to its high calorific value and the advantage of non-polluting combustion products. The realization of hydrogen production by water splitting through semiconductor photocatalytic technology is regarded by the academic community as the most sustainable hydrogen production route due to its mild reaction conditions and direct utilization of solar energy. Currently, most of the research on photocatalytic hydrogen production focuses on pure water systems, which is obviously in contradiction with the distribution characteristics of the earth's water resources. According to the UNESCO water resources report, the global fresh water reserves only account for 2.53% of the total water volume, while the abundant seawater resources have not been effectively utilized for a long time. This research orientation is mainly due to the severe challenges posed by the complex components of seawater to the catalytic system: electrode corrosion caused by high-concentration chloride ions, catalyst deactivation caused by calcium and magnesium precipitation, and the recombination effect of salt on photo-generated carriers, which jointly restrict the energy conversion efficiency and long-term operation stability of the seawater photocatalytic system.

[0003] Pt / TiO2 shows significant advantages in promoting charge separation due to its unique Schottky barrier effect. The introduction of transition metal sulfides can further enhance the light absorption ability by reconstructing the energy band structure. However, these modification methods often encounter serious photo-induced degradation problems in seawater media - the high-salt environment not only accelerates the passivation of active sites on the catalyst surface, but also triggers an irreversible chloride erosion process. Therefore, how to enhance the corrosion resistance of materials while improving the catalytic activity has become the key to the breakthrough of seawater hydrogen production technology. Through the surface modification of the Pt / TiO2@MoS 2+x nano-composite catalyst with polymethyl methacrylate (PMMA), the synergistic optimization of catalytic performance and stability is achieved. Summary of the Invention

[0004] The technical problem solved by the present invention is: a method for enhancing the photocatalytic hydrogen production performance of a nanocomposite structure by coating with polymethyl methacrylate. The Pt / TiO2@MoS of the present invention 2+x @PMMA has a HER rate as high as 3.77 mmol g -1 h -1 under visible light illumination, and the catalytic activity and stability of this PMMA-coated catalyst in seawater are improved simultaneously. In addition, this PMMA coating effectively enhances the catalytic stability of Pt / TiO2@MoS 2+x , which is a key issue in photocatalytic seawater. The improvement of photocatalysis in seawater is attributed to the improvement of interfacial charge transfer and local heating, as well as the prevention of photocorrosion of the catalyst in seawater. In summary, the PMMA coating not only improves the efficiency of photocatalytic hydrogen evolution, but also significantly improves the stability and lifespan of the catalyst, making it very suitable for practical applications in seawater environments.

[0005] The present invention provides a method for enhancing the photocatalytic hydrogen production performance of a nanocomposite structure by coating with polymethyl methacrylate. The technical solution is as follows: Polymethyl methacrylate (PMMA) is coated on the surface of the Pt / TiO2@MoS 2+x photocatalyst by the reprecipitation method to form a Pt / TiO2@MoS 2+x @PMMA photocatalytic seawater hydrogen evolution system. The method for promoting its efficient and stable photocatalytic hydrogen evolution of seawater by coating PMMA on the surface of Pt / TiO2@MoS 2+x under light is as follows: First, different masses of the polymer are dissolved in 1 mL of DMF solvent, and the mass ratio of the polymer to the catalyst is adjusted within the range of 0.02:1 to 5:1; then 2 mg of the photocatalyst is added to this solution, and after ultrasonic dispersion, it is quickly injected into ultrapure water to obtain a polymer-coated photocatalyst composite. This composite material can achieve efficient photocatalytic hydrogen production under irradiation by a xenon lamp in a 40 mL reactor.

[0006] Preferably, the preparation process of the Pt / TiO2@MoS 2+x @PMMA catalyst: 1 mg of PMMA is dissolved in 1 mL of DMF, 2 mg of Pt / TiO2@MoS 2+x is added and dispersed evenly, and it is quickly injected into 19 mL of water under ultrasonic action, and then ultrasonic dispersion is continued for 15 minutes to obtain Pt / TiO2@MoS 2+x @PMMA.

[0007] Preferably, the preparation process of the Pt / TiO2 catalyst: 50 mg of TiO2 powder is dispersed in a solvent mixture of 60 mL of deionized water and 20 mL of ethanol, 80 μL of 0.1 M H2PtCl6 is added, and the mixture is purged with nitrogen for 15 minutes to form an inert atmosphere to eliminate dissolved oxygen, irradiated with a xenon lamp for 2 hours, and then centrifuged and washed.

[0008] Preferably, Pt / TiO2@MoS 2+x The preparation process of the catalyst: 50 mg of Pt / TiO2 nanoparticles are dispersed in 80 mL of a water-ethanol mixed solvent, and 130 μL of 0.2 M (NH4)2MoS4 solution is added to the suspension. The mixture is stirred at room temperature for 12 hours under a nitrogen atmosphere to promote the formation of sulfur-rich amorphous MoS 2+x . After washing 5-6 times alternately with deionized water and ethanol, it is dried in a vacuum oven at 50 °C for 12 hours.

[0009] Preferably, the process of the photocatalytic hydrogen production experiment is as follows: Take 20 mL of the above-prepared Pt / TiO2@MoS 2+x @PMMA, add 1 mL of triethanolamine as a sacrificial agent and a magnetic stir bar, adjust the constant temperature magnetic stirrer to a rotation speed of 400 rpm, irradiate the solution under a 300 W xenon lamp, and perform gas analysis every 0.5 h on an off-line gas chromatograph (GC-9860 5CNJ, Nanjing Haerpu Analytical Equipment Co., Ltd.).

[0010] Preferably, the stability test process of the photocatalytic hydrogen production experiment is as follows: Take the above-prepared reaction solution, irradiate it under a 300 W xenon lamp, and perform gas analysis every 1 h on an off-line gas chromatograph (GC-9860 5CNJ, Nanjing Haerpu Analytical Equipment Co., Ltd.) for a total of ten hours.

[0011] The beneficial effects of the present invention:

[0012] 1. The PMMA coating layer has multiple synergistic effects on the Pt / TiO2@MoS 2+x photocatalyst: In terms of optical properties, while maintaining the original light absorption edge of the catalyst, PMMA significantly enhances its light capture ability within the effective spectral range; in terms of charge separation, the electric dipole characteristics in PMMA molecules effectively promote the separation of photo-generated electron-hole pairs; in terms of thermal effect regulation, the low thermal conductivity characteristics of PMMA can effectively limit the diffusion of local heat of the catalyst, and significantly improve the photothermal effect by constructing a thermal insulation layer. The triple composite synergistic mechanism enables the PMMA-coated Pt / TiO2@MoS 2+x system to exhibit excellent photocatalytic performance.

[0013] 2. The PMMA coating technology proposed by the present invention has prominent advantages such as simple operation and low cost, providing a highly promising solution for the practical application of photocatalytic hydrogen production technology. This technology can construct a stable polymer protective layer on the catalyst surface through a simple reprecipitation method, which not only significantly improves the light absorption capacity, charge separation efficiency and photothermal effect of the Pt / TiO2@MoS 2+x system, but also fundamentally solves the technical problem of the unstable structure of traditional photocatalysts in complex environments.

[0014] 3. Due to the high salinity of seawater, it will cause serious photocorrosion, salt corrosion and surface attachment of insoluble salts of the catalyst. All these effects will limit the photocatalytic efficiency and stability of the photocatalyst in seawater decomposition. The PMMA coating technology proposed by the present invention can effectively prevent the surface reconstruction of the photocatalyst induced by salt ions, thereby protecting the catalytic active sites from inactivation during the reaction process. The prepared Pt / TiO2@MoS 2+x @PMMA has a HER rate as high as 3.77 mmol g -1 h -1 under visible light illumination. In addition, the photocatalytic system is stable after 10 hours of catalytic cycling, greatly improving the stability of the original photocatalyst. The catalytic activity and stability of our composite photocatalyst are superior to the reported TiO2 catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described below with reference to the accompanying drawings.

[0016] Figure 1 is a schematic diagram of the highly efficient hydrogen evolution of Pt / TiO2@MoS 2+x @PMMA nanostructures.

[0017] Figure 2 is the structural characterization of Pt / TiO2@MoS 2+x @PMMA. (a) SEM image of Pt / TiO2@MoS 2+x . (b) TEM image of Pt / TiO2@MoS 2+x @PMMA. (c) XRD patterns of C1s of Pt / TiO2, Pt / TiO2@MoS 2+x , and Pt / TiO2@MoS 2+x @PMMA. (d) EDS mapping of Pt / TiO2@MoS 2+x @PMMA.

[0018] Figure 3 is Pt / TiO2 and Pt / TiO2@MoS 2+x and Pt / TiO2@MoS 2+xXPS spectra of @PMMA. a) Ti 2p, (b) O 1s, (c) Pt 4f, (d) Mo 3d, (e) S 2p, and (f) C 1s.

[0019] Figure 4 is Pt / TiO2@MoS 2+x compared with Pt / TiO2@MoS 2+x Hydrogen evolution efficiency diagram of @PMMA photocatalysis for 10 cycles.

[0020] Figure 5 is Pt / TiO2@MoS 2+x Study on the improvement of photocatalytic stability of @PMMA. (a - b) Pt / TiO2@MoS 2+x SEM images before (a) and after (b) photocatalytic reaction. (c) TEM image of Pt / TiO2@MoS after photocatalytic reaction 2+x (d - e) SEM images of Pt / TiO2@MoS 2+x before (d) and after (e) photocatalytic reaction. (f) TEM image of Pt / TiO2@MoS 2+x after photocatalytic reaction. (g - h) TEM images of Pt / TiO2@MoS 2+x and (h) Pt / TiO2@MoS 2+x Particle size distribution of Pt nanoparticles in @PMMA. (i) Pt / TiO2@MoS 2+x and Pt / TiO2@MoS 2+x Comparison of electrochemically active surface area (ECSA) of Pt / TiO2@MoS before and after photocatalytic reaction.

[0021] Figure 6 is the photocatalytic hydrogen evolution efficiency of Pt / TiO2@MoS 2+x under different PMMA wrapping amounts. Detailed implementation methods

[0022] Example 1

[0023] First, dissolve 50 mg of TiO2 powder in a solvent mixture containing 60 mL of deionized water and 20 mL of ethanol. Ultrasonically treat the solution for 15 minutes to achieve uniform dispersion of TiO2 nanoparticles. Subsequently, add 80 μL of 0.1 M H2PtCl6 (HAuCl4 / RhCl3) solution to the TiO2 suspension. Purge the mixture with nitrogen for 15 minutes to form an inert atmosphere to eliminate dissolved oxygen, and then seal the system. Irradiate the sealed solution under a 300 W xenon lamp for 1 hour to promote the photodeposition of Pt / Au / Rh nanoparticles on the surface of TiO2, thereby forming a heterojunction structure.

[0024] Polymer wrapping method, the synthesized Pt / TiO2@MoS 2+x particles were dispersed in N,N-dimethylformamide (DMF) solvent to prepare a suspension with a concentration of 2 mg / mL. Meanwhile, polymethyl methacrylate (PMMA) was dissolved in DMF to obtain a PMMA solution with a concentration of 2 mg / mL. Take 1 mL of the PMMA solution and 1 mL of Pt / TiO2@MoS 2+x suspension and mix them, and perform ultrasonic treatment for 15 minutes to achieve uniform mixing. Subsequently, the PMMA-Pt / TiO2@MoS 2+x mixture was quickly injected into 2 mL of ultrapure water through a syringe to initiate the reprecipitation of PMMA on the surface of Pt / TiO2@MoS 2+x particles. The obtained suspension was continuously ultrasonically treated for 15 minutes to form uniform Pt / TiO2@MoS 2+x @PMMA particles, and finally the preparation was completed by washing three times with deionized water.

[0025] Our photocatalytic hydrogen production experimental process is as follows:

[0026] The above photocatalyst was dispersed in a simulated seawater system at a concentration of 2 mg / mL. A typical reaction system contains 1 mL of catalyst suspension, 2 mL of triethanolamine (TEOA), 584 mg of sodium chloride, and 20 mL of water. The photocatalytic hydrogen evolution experiment was carried out in a 40 mL reactor, and the light source was a 300 W xenon lamp equipped with a long-pass filter (λ≥400 nm, UV400CUT). During the reaction process, a magnetic stirrer was continuously used to stir (400 r / min) to maintain the homogeneity of the system, and the gas products were analyzed by a gas chromatograph (GC-9860 5CNJ, Nanjing Hop Analysis Instrument Co., Ltd.) every 0.5 hours. In the cyclic test, after each round of catalysis, the system was degassed and left standing in the dark for 1 hour. In some experiments, the reaction temperature was controlled by a constant temperature water bath.

[0027] As Figure 2 is the structural characterization of Pt / TiO2@MoS 2+x @PMMA. First, we characterized the obtained Pt / TiO2@MoS 2+x @PMMA catalyst by TEM, EDS, XRD and other spectra. Transmission electron microscopy (TEM) and elemental mapping images showed that Pt / TiO2@MoS 2+x was uniformly coated with PMMA polymer. Energy dispersive spectroscopy (EDS) imaging confirmed this PMMA wrapping, and the O and C elements from PMMA were observed in the Pt / TiO2@MoS 2+x region.

[0028] As Figure 3As shown, we performed X-ray photoelectron spectroscopy (XPS) measurements to further investigate the surface chemical composition and electronic state of the prepared samples. The XPS Ti 2p peaks are located at 459.4 and 465.1 eV in the Pt / TiO2 sample, and these two peaks shift to lower binding energies of 459.1 and 464.8 eV respectively in the Pt / TiO2@MoS 2+x sample. Similar shifts are also observed in the XPS O 1s peak. The XPS Pt 4f peaks are located at 71.3 and 74.6 eV in the Pt / TiO2 sample, and these two peaks shift to higher binding energies of 71.6 and 74.9 eV respectively in the Pt / TiO2@MoS 2+x sample, indicating that electrons transfer from MoS 2+x to Pt / TiO2 and form an interfacial electric field pointing from MoS 2+x to Pt / TiO2. In the PMMA-coated MoS 2+x sample, these two peaks shift back to 71.5 and 74.8 eV respectively, indicating the existence of interfacial electron transfer from PMMA to Pt / TiO2@MoS 2+x . Similar lower binding energy shifts are also observed in the XPS Mo 3d and S2p spectra after PMMA coating, double confirming the electron transfer from PMMA to Pt / TiO2@MoS 2+x .

[0029] The stability test process of this photocatalytic hydrogen production experiment is as follows: Take the above-prepared reaction solution, irradiate it under a 300 W xenon lamp, and perform gas analysis every 1 h on an off-line gas chromatograph (GC-9860 5CNJ, Nanjing Haerpu Analytical Equipment Co., Ltd.) for a total of ten hours.

[0030] As Figure 4 shown, we found that after 10 h of cyclic photocatalytic hydrogen evolution testing, the Pt / TiO2@MoS 2+x @PMMA nanostructure can maintain stable catalytic activity, and during this period, the catalytic performance hardly changes. TEM images show that the morphology of Pt / TiO2@MoS 2+x @PMMA hardly changes after 10 cycles of photocatalytic reaction, confirming the high morphological stability during the photocatalytic reaction.

[0031] Comparative Example 1

[0032] Due to the high salinity of seawater, it will cause serious photocorrosion, salt corrosion and surface attachment of insoluble salts of the catalyst. All these effects will limit the photocatalytic efficiency and stability of the photocatalyst in seawater decomposition. We expect that it is feasible to hinder seawater corrosion by polymer coating. We studied Pt / TiO2@MoS 2+x@PMMA and Pt / TiO2@MoS 2+x Morphology changes before and after photocatalytic hydrogen evolution from seawater. As Figure 5 shown, similar phenomena were also observed in the uncoated Pt / TiO2@MoS 2+x sample: the size of TiO2 nanoparticles was 91.5 ± 18.9 nm before the photocatalytic reaction and 91.3 ± 24.9 nm after the reaction; while in the PMMA-coated Pt / TiO2@MoS 2+x @PMMA sample, the size of TiO2 nanoparticles was 92.7 ± 18.7 nm before the reaction and 92.9 ± 18.4 nm after the reaction. These data indicate that the overall size of TiO2 nanoparticles remains basically unchanged before and after the reaction. These results show that PMMA coating can effectively prevent the surface reconstruction of the photocatalyst induced by salt ions, thus protecting the catalytic active sites from inactivation during the reaction.

[0033] Comparative Example 2

[0034] The amount of polymer wrapping may also affect the catalytic enhancement effect of Pt / TiO2@MoS 2+x @PMMA in photocatalytic hydrogen evolution from seawater. As Figure 6 shown, when the mass ratio of PMMA to Pt / TiO2@MoS 2+x increased from 0:1 to 1:1, the photocatalytic hydrogen production activity increased significantly from 2482 μmol g -1 h -1 to 3769 μmol g -1 h -1 . This PMMA-induced activity enhancement may be due to the promoted interfacial charge transfer by the coating layer. When the PMMA ratio was further increased to 5:1, the stability of the hydrogen evolution reaction (HER) only showed a slight increase, but the catalytic activity decreased significantly from 3769 μmol g -1 h -1 to 3390 μmol g -1 h -1 . This indicates that excessive PMMA coating inhibits the mass transfer process of water molecules - because the PMMA layer coated on the surface of Pt / TiO2@MoS 2+x particles hinders the transport of reactants (water molecules), resulting in a decrease in the local reactant concentration, thus causing a decrease in catalytic activity at a high PMMA ratio (5:1).

[0035] The present invention is not limited to the specific technical solutions described in the above embodiments. Any technical solutions formed by equivalent replacement are within the protection scope required by the present invention.

Claims

1. A method for enhancing the photocatalytic hydrogen production performance of a nano-composite structure by coating with polymethyl methacrylate, characterized in that: Polymethyl methacrylate (PMMA) was encapsulated on the surface of the Pt / TiO2@MoS 2+x photocatalyst by reprecipitation method to form a Pt / TiO2@MoS 2+x @PMMA photocatalytic seawater hydrogen evolution system. The method for promoting its efficient and stable photocatalytic seawater hydrogen evolution by encapsulating PMMA on the surface of Pt / TiO2@MoS 2+x under light irradiation is as follows: First, dissolve different masses of the polymer in 1 mL of DMF solvent, and adjust the mass ratio of the polymer to the catalyst in the range of 0.02:1 to 5:1; then add 2 mg of the photocatalyst to this solution, and quickly inject it into ultrapure water after ultrasonic dispersion to obtain a polymer-coated photocatalyst composite. The composite material can achieve efficient photocatalytic hydrogen production under the irradiation of a xenon lamp in a 40 mL reactor.

2. The method for enhancing the photocatalytic hydrogen production performance of a seawater by using a polymethyl methacrylate-coated reinforced nanostructure according to claim 1, wherein: Take 1 mL of the polymer solution, add 2 mg of the photocatalyst, inject it rapidly into ultrapure water after ultrasonic treatment, and carry out the catalytic reaction under the illumination of a 300 W xenon lamp.

3. The method for enhancing the photocatalytic hydrogen production performance of a seawater by using a polymethyl methacrylate-coated reinforced nanostructure according to claim 1, wherein: The polymer is coated on the surface of the photocatalyst by the reprecipitation method.

4. The method for enhancing the photocatalytic hydrogen production performance of the polymethyl methacrylate-coated reinforced nanocomposite structure according to claim 1, characterized in that: The specific preparation process of the reprecipitation method is as follows: Dissolve 0.04 - 10 mg of the polymer in 1 mL of DMF by ultrasonic dissolution, add the photocatalyst and disperse it ultrasonically for 30 minutes to form a homogeneous solution; then quickly inject this solution into a 40 mL glass bottle containing 19 mL of ultrapure water with a 1 mL syringe, continue to disperse it for 15 minutes under ultrasonic assistance, and finally store it statically to obtain the polymer-coated photocatalyst composite.

5. The method for enhancing the photocatalytic hydrogen production performance of a seawater by using a polymethyl methacrylate-coated reinforced nanocomposite structure according to claim 1, characterized in that: The specific operation of the photocatalytic hydrogen production experiment is as follows: Take an appropriate amount of the prepared catalyst solution, add 1 mL of triethanolamine as a sacrificial agent and put in a magnetic stir bar, irradiate it with a 300 W xenon lamp light source under the condition of constant temperature magnetic stirring at 400 rpm, and quantitatively analyze the generated gas by an off-line gas chromatograph every 1 hour.

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