Method for enhancing photocatalytic hydrogen production reaction by wrapping polymer on photocatalyst

Abstract

The invention relates to a method for enhancing photocatalytic hydrogen production reaction by wrapping a polymer on a photocatalyst, in particular to an efficient photocatalytic hydrogen production system synthesized by wrapping polymethyl methacrylate on the surface of the photocatalyst through a reprecipitation method, and belongs to the technical field of catalytic energy. According to the preparation method disclosed by the invention, polymethyl methacrylate (PMMA) is used, and the surface of graphite phase carbon nitride (Pt / g-C3N4) loaded with platinum particles is coated with the PMMA through a reprecipitation method, so that PMMA-wrapped Pt / g-C3N4 is formed. Under illumination, the local heat effect of polymethyl methacrylate and the polarization electric field on the surface can promote high catalytic activity in the photocatalyst HER. After different photocatalysts are replaced, the HER activity of PMMA wrapping is obviously enhanced. The smooth implementation of the patent provides a universal, simple, convenient and efficient strategy for regulating and controlling the efficiency of the photocatalytic hydrogen production reaction, solves the problem of unstable structure of the previous system, and provides greater possibility for industrialization in the field of photocatalytic hydrogen production.

Description

Technical Field

[0001] The present invention relates to a method for enhancing photocatalytic hydrogen production reaction by wrapping a polymer on a photocatalyst, and particularly to a method for synthesizing an efficient photocatalytic hydrogen production system by wrapping polymethyl methacrylate on the surface of a photocatalyst through a reprecipitation method, belonging to the technical field of catalytic energy. Background Art

[0002] As a clean energy source with high energy density, hydrogen energy shows great potential in solving global energy and environmental problems. The large-scale application of hydrogen energy urgently requires the development of simple and efficient new hydrogen production technologies. Among them, photocatalytic hydrogen evolution reaction (HER) has attracted much attention because it can directly utilize solar energy to drive chemical reactions. The core lies in the development of high-performance photocatalysts. Traditional photocatalysts achieve energy conversion through the synergistic effect of the photoelectron effect and the photothermal effect. However, there are still significant bottlenecks in the synergistic enhancement of these two effects in the existing technical systems.

[0003] In terms of optimizing the photoelectron effect, the existing technologies mainly focus on strategies such as band engineering, element doping, defect regulation, and heterostructure construction of semiconductor materials. For example, the separation of photogenerated carriers is promoted through the heterojunction electric field, or the carrier migration path is regulated through crystal plane engineering. However, such methods have limited improvement in the separation efficiency of photogenerated charges and are difficult to avoid the energy loss caused by carrier recombination. On the other hand, the photothermal effect can accelerate the reaction kinetics by increasing the local temperature. However, due to the high thermal conductivity of semiconductor materials themselves, the heat generated by photoexcitation is easily diffused rapidly to the liquid-phase reaction system, resulting in a weak local temperature rise effect and being difficult to effectively increase the reaction rate.

[0004] For the enhancement of the photothermal effect, the existing technologies mostly use plasmonic resonance materials (such as noble metal nanostructures) to enhance the photothermal conversion efficiency. However, the hot carriers generated by plasmons have extremely short lifetimes (usually in the femtosecond range), and their contribution to the photoelectron effect is severely limited. In addition, such materials are costly and lack stability, making it difficult to achieve industrial applications. Moreover, the photoelectron-photothermal synergistic mechanism of existing photocatalysts is not clear, and there is a lack of general technical means to synchronously enhance the two effects.

[0005] In the current technology system, both semiconductor-based photocatalysts and plasma photocatalysts have the inherent defect that the photoelectron effect and the photothermal effect are difficult to optimize synergistically: the former is limited by the insufficient temperature rise caused by heat dissipation and the high thermal conductivity of semiconductor materials in the liquid reaction system leads to rapid diffusion of photogenerated heat and limited local temperature rise; the latter is subject to energy loss caused by rapid recombination of hot carriers. Therefore, the development of a photocatalyst modification strategy that can simultaneously enhance the photoelectron effect and the photothermal effect and has universal applicability has become a technical problem that needs to be solved in this field. Based on this, the present invention proposes a new method for simultaneously enhancing the photoelectric effect and the photothermal effect by wrapping a layer of thermal insulation material polymethyl methacrylate (PMMA) on the surface of a semiconductor-based photocatalyst. This method is highly versatile and can be applied to a variety of photocatalyst systems, providing a simple and effective way to develop efficient and stable photocatalysts. Summary of the invention

[0006] The technical problem solved by the present invention is: a method for wrapping a polymer on a photocatalyst to enhance the photocatalytic hydrogen production reaction. The HER rate of the PMMA-wrapped Pt / g-C3N4 under visible light illumination is as high as 8.81mmol g -1 h -1 , PMMA wrapping can enhance light absorption capacity and broaden the scope of solar energy utilization; inhibit photogenerated carrier recombination and improve charge separation efficiency; optimize local photothermal effect and accelerate reaction kinetics; improve the cycle stability of the catalyst; and realize the versatility of the method in a variety of photocatalytic systems. The catalytic activity and stability of the photocatalyst PMMA-wrapped Pt / g-C3N4 of the present invention are better than the latest catalysts reported so far.

[0007] In order to solve the above technical problems, the technical solution proposed by the present invention is: a method for encapsulating a polymer on a photocatalyst to enhance the photocatalytic hydrogen production reaction, using a reprecipitation method to encapsulate the polymer on the surface of the photocatalyst to form a polymer-encapsulated photocatalyst system, and under light, the method of encapsulating the polymer on the surface of the photocatalyst to promote the photocatalyst catalytic efficient hydrogen production reaction is as follows: dissolving different masses of polymer powder in 1mL DMF to obtain a solution with a polymer to catalyst mass ratio of 0.02:1 to 5:1, adding 2mg of photocatalyst to the polymer solution, and then ultrasonically dispersing and quickly injecting into ultrapure water to form a polymer-encapsulated photocatalyst composite material. The photocatalytic hydrogen production experiment was carried out in a 40mL reactor, and hydrogen was produced under irradiation with a xenon lamp.

[0008] Preferably, the preparation process of the PMMA-wrapped Pt / g-C3N4 catalyst: Dissolve 1 mg of PMMA in 1 mL of DMF, add 2 mg of Pt / g-C3N4 and disperse evenly, quickly inject it into 19 mL of water under ultrasonic action, and then continue ultrasonic dispersion for 15 minutes to obtain PMMA-wrapped Pt / g-C3N4.

[0009] Preferably, g-C3N4 is prepared by the thermal oxidation etching method using urea.

[0010] Preferably, the specific preparation method of g-C3N4 is: Place 20 g of urea in a ceramic crucible, then use a muffle furnace to heat it to 500 °C at a rate of 5 °C / min in an air atmosphere, keep it warm for 4 hours, and then grind it to obtain g-C3N4 nanosheets.

[0011] Preferably, the preparation process of the Pt / g-C3N4 catalyst: Disperse 50 mg of g-C3N4 in a mixture of 20 mL of methanol and 10 mL of water, add 0.25 mL of 20 μM H2PtCl6, irradiate with a xenon lamp for 2 hours, and then centrifuge and wash.

[0012] Preferably, the process of the photocatalytic hydrogen production experiment is: Take 20 mL of the above-prepared PMMA-wrapped Pt / g-C3N4, add 1 mL of triethanolamine as the sacrificial agent and a magnetic stir bar, adjust the constant-temperature magnetic stirrer to a rotation speed of 450 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.).

[0013] Preferably, the stability test process of the photocatalytic hydrogen production experiment is: 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.

[0014] The beneficial effects of the present invention:

[0015] 1. The encapsulation of PMMA can improve the light absorption of Pt / g-C3N4. The encapsulation of PMMA does not affect the light absorption edge of the catalyst itself, but can enhance the light absorption within the light absorption range of the catalyst. Due to the presence of PMMA electric dipoles, the photoelectric effect of Pt / g-C3N4 can also be enhanced, promoting its charge separation. In addition, the poor thermal conductivity of PMMA can limit the local photothermal generation of Pt / g-C3N4, prevent the dissipation of photothermal generation, and promote the photothermal effect of Pt / g-C3N4.

[0016] 2. The method of PMMA wrapping is very simple and convenient, making this composite material have great potential value in many practical applications. The successful implementation of this patent will provide a simple and efficient strategy for enhancing the photocatalytic hydrogen production reaction of photocatalysts, and solve the problem of unstable system structure in the past, providing the possibility for efficient and stable photocatalytic hydrogen production reaction.

[0017] 3. The PMMA-wrapped Pt / g-C3N4 prepared by this patent has a HER rate as high as 8.84 mmol g -1 h -1 . In addition, this photocatalytic system is stable after 10 hours of catalytic cycle, greatly improving the stability of the original photocatalyst. The catalytic activity and stability of our composite photocatalyst are superior to the reported g-C3N4 catalysts.

[0018] 4. The method of this patent has strong versatility and is applicable to systems such as Pt / TiO2, Au / CdS, MoS2 / ZnIn2S4, etc., and the hydrogen production rate is increased by 5%-93%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with the accompanying drawings.

[0020] Figure 1 is a schematic diagram of efficient hydrogen evolution of PMMA-wrapped Pt / g-C3N4 nanostructures.

[0021] Figure 2 is the structural characterization of PMMA-wrapped Pt / g-C3N4. (a) TEM image of Pt / g-C3N4. (b) TEM image of PMMA-wrapped Pt / g-C3N4. (c) EDS mapping of PMMA-wrapped Pt / g-C3N4. (d) C1s XPS spectra of g-C3N4, Pt / g-C3N4, and PMMA-wrapped Pt / g-C3N4. (e) N1s XPS spectra of g-C3N4, Pt / g-C3N4, and PMMA-wrapped Pt / g-C3N4.

[0022] Figure 3 is (a) FTIR spectra of Pt / g-C3N4 and PMMA-wrapped Pt / g-C3N4. (b) TGA curve of PMMA-wrapped Pt / g-C3N4.

[0023] Figure 4is the stability of efficient and stable hydrogen evolution. (a) Hydrogen production rates of Pt / g-C3N4 and PMMA-wrapped Pt / g-C3N4 after 10 h of photocatalysis. (b) Stabilities of Pt / g-C3N4 and PMMA-wrapped Pt / g-C3N4.

[0024] Figure 5 are the photocatalytic hydrogen evolution performances of different catalysts before and after PMMA coating and the corresponding enhancement factors. The reaction conditions of the PMMA-wrapped catalyst are the same as those of the non-wrapped catalyst.

[0025] Figure 6 are (a) the water contact angles of PVDF, PS, ABS, and PMMA polymers. (b) The effects of different polymer coatings on the hydrogen evolution rate of Pt / g-C3N4.

[0026] Figure 7 is the photocatalytic hydrogen evolution efficiency of PMMA-wrapped Pt / g-C3N4 at different PMMA coating amounts. Detailed implementation manners

[0027] Example 1

[0028] First, place urea in a covered ceramic crucible and heat it to 500 °C at a rate of 5 °C·min -1 and hold for 4 h. After cooling, grind to obtain g-C3N4 powder. Subsequently, disperse 50 mg of g-C3N4 in a mixed solution of 20 mL of methanol and 10 mL of water, add 0.25 mL of 20 mM chloroplatinic acid solution, irradiate with a 300 W xenon lamp in an ice-water bath for 2 h, and obtain a Pt / g-C3N4 heterojunction with a Pt loading of 2% after centrifugation and washing.

[0029] In the polymer coating process, dissolve 40 mg of PMMA in 40 mL of DMF, stir for 60 min to form a homogeneous solution, disperse 2 mg of Pt / g-C3N4 in 1 mL of this solution, ultrasonically mix and quickly inject it into 19 mL of ultrapure water, and obtain a PMMA-coated Pt / g-C3N4 suspension after centrifugation and washing 3 times.

[0030] Our process of photocatalytic hydrogen production is as follows:

[0031] Polymer powders of different qualities were dissolved in 1 mL of DMF to obtain solutions with a polymer-to-catalyst mass ratio ranging from 0.02:1 to 5:1. 2 mg of photocatalyst was added to the polymer solution. After ultrasonic dispersion, it was quickly injected into ultrapure water to form a polymer-wrapped photocatalyst composite. Take the catalyst solution prepared above, 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 450 rpm, and then irradiate it under a 300 W xenon lamp. Gas analysis was performed every 1 h on an off-line gas chromatograph (GC-9860 5CNJ, Nanjing Haerpu Analytical Equipment Co., Ltd.).

[0032] As Figure 1 It is a schematic diagram of PMMA-wrapped Pt / g-C3N4 enhancing HER. PMMA improves the HER efficiency of Pt / g-C3N4 by synergistically enhancing the photoelectric effect and the photothermal effect.

[0033] As Figure 2 It is the structural characterization of PMMA-wrapped Pt / g-C3N4. First, we characterized the obtained PMMA-wrapped Pt / g-C3N4 catalyst by TEM, EDS, and XPS spectra. Transmission electron microscopy (TEM) and elemental mapping images showed that Pt / g-C3N4 was uniformly coated with PMMA polymer. Energy-dispersive spectroscopy (EDS) imaging confirmed this PMMA coating, where O and C elements from PMMA were observed in the Pt / g-C3N4 region. Then, X-ray photoelectron spectroscopy (XPS) measurements were carried out to further study the surface chemical composition and electronic state of the prepared samples. After PMMA coating, the binding energy of sp 2 hybrid carbon shifted to a higher binding energy by 0.5 eV. This shift might be caused by the introduction of carbon atoms in PMMA or the charge transfer between PMMA and g-C3N4. The N 1s spectrum showed that after PMMA coating, the N1s binding energies of sp 2 hybrid nitrogen and tertiary nitrogen in Pt / g-C3N4 shifted further to higher energies by 0.4 and 0.2 eV, respectively, further confirming the electron transfer from g-C3N4 to PMMA.

[0034] Subsequently, the presence of PMMA was further characterized, such as Figure 3As shown, we characterized the obtained PMMA-wrapped Pt / g-C3N4 catalyst by TGA and FTIR. Fourier transform infrared spectroscopy (FT-IR) further confirmed the encapsulation of PMMA. In the PMMA-wrapped Pt / g-C3N4 sample, characteristic peaks of PMMA were observed at 1733 and 2997 - 2952 cm-1, attributed to C=O and C-H stretching, respectively. Thermogravimetric analysis (TGA) was also conducted to study the PMMA-wrapped Pt / g-C3N4. When the mass ratio of PMMA to Pt / g-C3N4 was 0.5:1, PMMA completely decomposed at approximately 430 °C, representing a weight loss of about 34%. This value was highly consistent with the amount of PMMA used for encapsulation, confirming the successful PMMA encapsulation of Pt / g-C3N4.

[0035] The stability test process of this photocatalytic hydrogen production experiment was as follows: The prepared reaction solution was taken and irradiated under a 300 W xenon lamp. Gas analysis was performed every 1 h on an off-line gas chromatograph (GC-9860 5CNJ, Nanjing Haerpu Analytical Equipment Co., Ltd.) for a total of ten hours.

[0036] As Figure 4 shown, we found that after 10 h of cyclic photocatalytic hydrogen evolution testing, the PMMA-wrapped Pt / g-C3N4 nanostructure could maintain stable catalytic activity, and during this period, the catalytic performance hardly changed. TEM images showed that the morphology of PMMA-wrapped Pt / g-C3N4 hardly changed after 10 h of photocatalytic reaction, confirming the high morphological stability during the photocatalytic reaction. However, the flaky structure of Pt / g-C3N4 without PMMA encapsulation was damaged, indicating that PMMA encapsulation contributed to stabilizing the morphology and catalytic performance of the Pt / g-C3N4 composite.

[0037] The universality study process of this system was as follows: As Figure 5 shown, several widely used heterostructure-based photocatalysts were synthesized, including Pt / TiO2, Au / CdS, MoS2 / CdS, Pt / ZnIn2S4, and MoS2 / ZnIn2S4, and then encapsulated with PMMA to improve photocatalytic hydrogen production. The research showed that PMMA encapsulation could improve the photocatalytic performance of all these catalysts, even though the catalytic enhancement percentages of these systems were different (from 5% to 93%). These results indicated that the polymer encapsulation strategy was universal in catalytic enhancement and could be applied to various photocatalytic systems.

[0038] Comparative Example 1

[0039] Since the hydrophilicity and hydrophobicity of the polymer can affect the adsorption of water molecules by the photocatalyst, we expect that it is feasible to regulate the enhancement of the photocatalytic hydrogen evolution rate by controlling the hydrophilicity and hydrophobicity of the polymer. The hydrophilicity and hydrophobicity of the polymer are highly correlated with the surface energy of the polymer. Four commonly used polymers with different surface energies (including PVDF, PS, ABS, and PMMA) were selected to study the effect of different polymers on the catalytic enhancement of Pt / g-C3N4. These four polymers were coated on the surface of Pt / g-C3N4 using a similar precipitation method. All four polymers are thermal insulators, and their thermal conductivities are in the narrow range of 0.16–0.25 W m -1 K -1 . Therefore, all four of these polymers can limit the generation of heat, and their contributions to catalytic enhancement should be similar. As Figure 6 shown, the HER rate and catalytic enhancement are positively correlated with the surface energy of the coated polymer. It is worth noting that PVDF has the lowest surface energy, and Pt / g-C3N4 coated with PVDF exhibits the lowest HER rate, even lower than that of uncoated Pt / g-C3N4. Among the four selected polymers, PMMA has the highest surface energy, and Pt / g-C3N4 coated with PMMA exhibits the highest HER rate of 8.84 mmol g -1 h -1 and the highest catalytic enhancement of 1.5 times. The higher surface energy of the polymer coating may be beneficial for the surface adsorption of water molecules on the catalyst surface, which is beneficial for HER. Water contact angle measurements also confirm this advantage of water adsorption. It was observed that PMMA has the smallest contact angle of 68.2° among the four polymers, while PVDF has the largest contact angle of 103.6°. According to Young's equation, the contact angle is inversely proportional to the surface energy, which means that a larger contact angle corresponds to a lower surface energy.

[0040] Comparative Example 2

[0041] The amount of polymer coating and the choice of polymer may also affect the catalytic enhancement effect of Pt / g-C3N4 in the photocatalytic hydrogen evolution reaction (HER). As Figure 7 shown, we studied the effect of the amount of PMMA coating on the photocatalytic performance. When the ratio of PMMA to Pt / g-C3N4 was 0.02:1, the PMMA coating was already able to effectively accelerate HER, and a 20% catalytic enhancement effect was observed. Increasing the amount of PMMA coating can further increase the HER rate. When the ratio of PMMA to Pt / g-C3N4 was 0.5:1, an optimized HER rate of 8.84 mmol g -1h-1 and a 50% catalytic enhancement effect. This trend of catalytic enhancement may be related to the photothermal effect caused by PMMA encapsulation. When the ratio of PMMA to the catalyst is 0.02, the temperature of the catalytic system slightly increases compared to the unencapsulated Pt / g-C3N4. When the ratio of PMMA to the catalyst is 0.5:1, the fastest temperature rise is observed, which is consistent with the catalytic enhancement effect. Further increasing the ratio of PMMA to the catalyst instead leads to a decrease in the temperature rise, and this trend is also consistent with the decrease in the catalytic enhancement effect observed in this catalytic system. Therefore, the photothermal effect significantly promotes the catalytic enhancement effect in PMMA-encapsulated Pt / g-C3N4.

[0042] 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 scope of protection required by the present invention.

Claims

1. A method for encapsulating a polymer on a photocatalyst to enhance the photocatalytic hydrogen production reaction, characterized in that : The polymer is wrapped on the surface of the photocatalyst by the reprecipitation method to form a polymer-wrapped photocatalyst system. The method of wrapping the polymer on the surface of the photocatalyst to promote the efficient hydrogen production reaction catalyzed by the photocatalyst under light is as follows: different masses of polymer powder are dissolved in 1 mL of DMF to obtain a solution with a polymer to catalyst mass ratio of 0.02:1 to 5:1, 2 mg of photocatalyst is added to the polymer solution, and after ultrasonic dispersion, it is quickly injected into ultrapure water to form a polymer-wrapped photocatalyst composite material. The photocatalytic hydrogen production experiment is carried out in a 40 mL reactor, and hydrogen is produced under irradiation with a xenon lamp.

2. The method of claim 1 for enhancing photocatalytic hydrogen production by encapsulating a polymer on a photocatalyst, characterized in that: Take 1 mL of the polymer solution, add 2 mg of the photocatalyst, and quickly inject it into ultrapure water under the action of ultrasound. The reaction is carried out under the irradiation of a 300 W xenon lamp.

3. The method of claim 1 for enhancing photocatalytic hydrogen production by encapsulating a polymer on a photocatalyst, characterized in that: The polymer was coated on the surface of the photocatalyst by reprecipitation method.

4. The method of claim 1 for enhancing photocatalytic hydrogen production by encapsulating a polymer on a photocatalyst, characterized in that: The specific method for preparing the polymer-encapsulated photocatalyst by the reprecipitation method is as follows: first, 0.04 to 10 mg of the polymer is added to 1 mL of DMF for ultrasonic dissolution, and then the photocatalyst is added. After ultrasonic dispersion for 30 minutes, a uniformly dispersed solution is obtained. Subsequently, a 1 mL disposable syringe is used to quickly inject the solution into a 40 mL glass bottle containing 19 mL of water under ultrasonic action, and ultrasonic dispersion is continued for 15 minutes to disperse the solution evenly, and then the solution is allowed to stand for storage.

5. The method of claim 1 for enhancing photocatalytic hydrogen production by wrapping a polymer on a photocatalyst, characterized in that: The polymer is PMMA, PS, ABS or PVDF.

6. The method of claim 1 for enhancing photocatalytic hydrogen production by wrapping a polymer on a photocatalyst, characterized in that: The semiconductor is g-C3N4, TiO2, CdS or ZnIn2S4, and the metal is Pt, Au or MoS2.

7. The method of claim 1 for enhancing photocatalytic hydrogen production by wrapping a polymer on a photocatalyst, characterized in that: The experimental process of photocatalytic hydrogen production is: take the catalyst solution prepared above, add 1 mL of sacrificial agent triethanolamine and a stirrer, adjust the constant temperature magnetic stirrer to 450 rpm, then irradiate under a 300 W xenon lamp, and perform gas analysis every 1 hour on an offline gas chromatograph.

Images