CN111359630A

CN111359630A - Composite material and preparation method thereof

Info

Publication number: CN111359630A
Application number: CN201811593150.2A
Authority: CN
Inventors: 马松; 黎瑞锋; 钱磊; 曹蔚然; 刘文勇
Original assignee: TCL Research America Inc
Current assignee: TCL Corp; TCL Research America Inc
Priority date: 2018-12-25
Filing date: 2018-12-25
Publication date: 2020-07-03

Abstract

The invention discloses a composite material and a preparation method thereof, wherein the preparation method comprises the following steps: CdS nanosheet with WS bonded to the surface thereof₂Quantum dots and L-cysteine. The CdS nanosheet with the thickness of 1-10nm can shorten a carrier transmission path, so that the internal recombination probability of photo-generated electron hole pairs is reduced, and the CdS nanosheet with the thickness of 1-10nm has a large specific surface area, increases active sites and is beneficial to enhancing the photocatalytic activity; l-cysteine is combined on the surface of the CdS nano-sheet,s is slowly released in the process of illumination^2‑Ions can reduce the photo-corrosion phenomenon of the CdS nanosheets and improve the photocatalytic stability; the quantum dots are used as the material of the catalyst, have quantum restriction and edge effects, can provide more hydrogen production active sites due to the large specific surface area of the quantum dots, accelerate the reduction reaction, and obviously improve the catalytic hydrogen production performance.

Description

Composite material and preparation method thereof

Technical Field

The invention relates to the field of quantum dot composite materials, in particular to a photocatalytic material.

Background

Hydrogen energy is the most attractive clean and carbon-free energy source and is considered an ideal alternative to fossil fuels, but current industrial technologies are not suitable for producing hydrogen for fuel use. The conversion of solar energy into hydrogen by utilizing a photocatalytic technology is considered to be one of the most promising hydrogen production approaches, and is expected to fundamentally solve the problems of energy shortage and environmental pollution.

The photocatalytic reaction is a reaction process for converting solar energy into chemical energy of high energy density and storing the chemical energy in a chemical bond by using the structural characteristics of a semiconductor. The semiconductor material has a discontinuous energy band structure, i.e., contains an empty Conduction Band (CB) with high energy and a full Valence Band (VB) with low energy. And the energy band gaps at the bottom of the conduction band and the top of the valence band are called forbidden bands, the forbidden band width is expressed by Eg, electrons on the valence band are unstable, and when the semiconductor is irradiated by light with energy larger than the forbidden band width, the electrons on the valence band absorb energy and jump to the conduction band, leaving photo-generated holes (h +) on the valence band. The photoproduction electrons on the conduction band have strong reducibility and can convert H⁺Reduction of ions to H₂The photogenerated holes in the valence band have strong oxidizing properties and can oxidize water to O₂。

The key of semiconductor photocatalytic water decomposition hydrogen production is to select a proper photocatalyst. However, early photocatalysts such as TiO₂Most of the plants are responsive to ultraviolet light (ultraviolet light accounts for 5% of the energy of sunlight, and visible light accounts for about 46% of the energy of sunlight), and the utilization of sunlight is realizedThe rate is too low, the potentials of a valence band and a conduction band are difficult to simultaneously meet the potential requirements of various catalytic reactions, and the defects of high cost, easy recombination of a photoproduction electron-hole pair, low quantum efficiency and the like exist.

To date, none of the inexpensive and commercially available materials satisfies all the conditions of high visible light quantum efficiency, stability, safety, and cheapness. Therefore, in order to overcome such challenges, the development of efficient and stable visible light-responsive photocatalysts becomes a key problem to be solved urgently, and is also a key for realizing industrial application.

The forbidden band width of cadmium sulfide (CdS) is about 2.4 eV, so that the cadmium sulfide (CdS) not only has strong absorption to visible light, but also has conduction band and valence band potentials meeting the conditions of photocatalytic water decomposition, and is considered as an ideal visible light response photocatalyst. However, in the absence of any modification, the photocatalytic quantum efficiency of the narrow-bandgap semiconductor is not ideal due to the problems that the photogenerated electron-hole pairs are easy to recombine, the redox capability of the photogenerated electron and hole is weak, the number of surface active sites is small, and the like. Cd element and S element in CdS are combined in an ionic bond form, and after long-time illumination, strong-oxidizing photo-generated holes can combine S^2-The ions are oxidized into S simple substances, the catalytic life of the CdS photocatalyst is shortened due to the severe photo-corrosion phenomenon, and the activity and stability of photocatalytic hydrogen production are greatly reduced.

Disclosure of Invention

In view of the defects of the prior art, the invention aims to provide a composite material and a preparation method thereof, wherein the composite material is suitable for the field of photocatalysis and has good visible light photocatalysis hydrogen production activity and stability.

The technical scheme of the invention is as follows:

a composite material, comprising: the CdS nanosheet is combined with quantum dots and L-cysteine on the surface.

The invention provides a composite photocatalyst with quantum dots and L-cysteine combined on the surface of a CdS nanosheet. The CdS nanosheet with the thickness of 1-10nm can shorten a carrier transmission path, so that the interior of a photo-generated electron hole pair is reducedThe compound probability is high, and the CdS nanosheets with the thickness of 1-10nm have large specific surface areas, so that active sites are increased, and the photocatalytic activity is enhanced; l-cysteine is combined on the surface of the CdS nanosheet, and S can be slowly released in the illumination process^2-Ions can reduce the photo-corrosion phenomenon of the CdS nanosheets and improve the photocatalytic stability; the quantum dots are used as the material of the catalyst, have quantum restriction and edge effects, can provide more hydrogen production active sites due to the large specific surface area of the quantum dots, accelerate the reduction reaction, and obviously improve the catalytic hydrogen production performance.

A method of making a composite material, comprising:

providing a first CdS nanosheet;

under the alkaline condition, mixing the first CdS nanosheet with L-cysteine, and carrying out ultrasonic stripping to obtain a second CdS nanosheet with L-cysteine combined on the surface;

and mixing the second CdS nanosheet with the L-cysteine combined on the surface and the quantum dot, and performing ultrasonic treatment to obtain the composite material.

The first CdS nanosheets are subjected to ultrasonic treatment through L-cysteine, then the second CdS nanosheets with the thickness of 1-10nm are obtained through stripping, the carrier transmission path can be shortened through the second CdS nanosheets with the thickness of 1-10nm obtained through stripping, so that the internal recombination probability of photo-generated electron hole pairs is reduced, the second CdS nanosheets with the thickness of 1-10nm have large specific surface areas, active sites are increased, and the photocatalytic activity is enhanced; l-cysteine is combined on the surface of the second CdS nanosheet and can slowly release S in the illumination process^2-Ions can reduce the photo-corrosion phenomenon of the second CdS nanosheet and improve the photocatalytic stability; the quantum dots are used as the material of the catalyst, have quantum restriction and edge effects, can provide more hydrogen production active sites due to the large specific surface area of the quantum dots, accelerate the reduction reaction, and obviously improve the catalytic hydrogen production performance.

Drawings

Fig. 1 is a schematic diagram illustrating a mechanism of improving hydrogen production activity and stability of a composite light material under irradiation of visible light in an embodiment of the present invention.

Detailed Description

Embodiments of the present invention first provide a composite material comprising: the CdS nanosheet is combined with quantum dots and L-cysteine on the surface.

The invention provides a composite photocatalyst with quantum dots and L-cysteine combined on the surface of a CdS nanosheet. The CdS nanosheet with the thickness of 1-10nm can shorten a carrier transmission path, so that the internal recombination probability of photo-generated electron hole pairs is reduced, and the CdS nanosheet with the thickness of 1-10nm has a large specific surface area, increases active sites and is beneficial to enhancing the photocatalytic activity; l-cysteine is combined on the surface of the CdS nanosheet, and S can be slowly released in the illumination process^2-Ions can reduce the photo-corrosion phenomenon of the CdS nanosheets and improve the photocatalytic stability; the quantum dots are used as the material of the catalyst, have quantum restriction and edge effects, can provide more hydrogen production active sites due to the large specific surface area of the quantum dots, accelerate the reduction reaction, and obviously improve the catalytic hydrogen production performance.

By WS₂For example, quantum dots can easily excite electrons from Valence Band (VB) to Conduction Band (CB) of CdS nanosheet under illumination, and then react with H⁺Ion reaction to H₂. However, the conventional CdS nanosheet has relatively low photocatalytic hydrogen production activity caused by the problems of easy recombination of photo-generated electron-hole pairs, severe photo-corrosion and the like. On the contrary, for the composite material of the embodiment of the invention, the CdS nanosheet with the thickness of 1-10nm can shorten the carrier transmission path, so that the internal recombination probability of photo-generated electron hole pairs is reduced, and the CdS nanosheet with the thickness of 1-10nm has a large specific surface area, so that the active sites are increased, and the photocatalytic activity is favorably enhanced; l-cysteine is combined on the surface of the CdS nanosheet, and S can be slowly released in the illumination process^2-Ions can reduce the photo-corrosion phenomenon of the CdS nanosheets and improve the photocatalytic stability; the quantum dots are used as the material of the catalyst, have quantum restriction and edge effect, can provide more hydrogen production active sites due to the large specific surface area of the quantum dots, accelerate the reduction reaction and catalyze the productionThe hydrogen performance will be significantly improved.

In some embodiments, the quantum dots have a conductivity of 10^-2-10^-3Scm^-1The quantum dots can improve the electron utilization rate, accelerate the electron consumption, promote the electron hole separation of the CdS nanosheet surface and reduce the hydrogen production overpotential of the CdS nanosheet surface. In some embodiments, the quantum dots are selected from WS₂Quantum dots, MoS₂One or more of quantum dots and carbon quantum dots. In some embodiments, the quantum dots have a particle size of 2 to 3.5 nm.

Mechanism shown in FIG. 1, as WS₂Quantum dots are taken as a cocatalyst for example, the CdS nanosheets with the thickness of 1-10nm shorten the migration path of carriers, so that the internal recombination of photo-generated electron-hole pairs is weakened, and the electron utilization rate is improved. In some embodiments, the CdS nanosheets have a thickness of 2.5-4nm and a lateral dimension of 200-300 nm. Due to WS₂The quantum dots have high conductivity and low overpotential for electrocatalytic hydrogen production, so that photo-generated electrons can pass through CdS and WS₂Fast transfer of tight interfaces between quantum dots to WS₂And on the quantum dots, the effective separation of photon-generated electron-hole pairs and the prolonging of the service life of carriers are realized. WS of large specific surface area₂The quantum dots have more hydrogen production active sites, so that the reduction reaction can be accelerated, and the hydrogen production activity of the composite photocatalyst is further enhanced. At the same time, the photogenerated hole at the position of the CdS valence band can be released by L-cysteine^2-And the photo-corrosion phenomenon is weakened, so that the hydrogen production stability of the composite photocatalyst is improved, and the catalytic life is prolonged.

In some embodiments, the quantum dots comprise 7-15% by weight of the composite material. Through comparative research, the hydrogen production performance in the range is better by loading the composite material with quantum dots with different mass percentages.

Further, an embodiment of the present invention also provides a method for preparing a composite material, wherein the method comprises the steps of:

s01 providing a first CdS nanosheet;

s02, mixing the first CdS nanosheet with L-cysteine, and carrying out ultrasonic stripping to obtain a second CdS nanosheet with L-cysteine combined on the surface;

s03, mixing the second CdS nanosheet with the L-cysteine combined on the surface with the quantum dots, and performing ultrasonic treatment to obtain the composite material.

After the first CdS nanosheets are sonicated with L-cysteine, in some embodiments, the first CdS nanosheets have a thickness of 25-35nm and a lateral dimension of 400-. And stripping to obtain second CdS nanosheets with the thickness of 1-10nm, wherein in some embodiments, the second CdS nanosheets have the thickness of 2.5-4nm and the transverse dimension of 200-300 nm. The stripped second CdS nanosheet with the thickness of 1-10nm can shorten a carrier transmission path, so that the internal recombination probability of photo-generated electron hole pairs is reduced, and the second CdS nanosheet with the thickness of 1-10nm has a large specific surface area, so that active sites are increased, and the photocatalytic activity is enhanced; l-cysteine is combined on the surface of the second CdS nanosheet and can slowly release S in the illumination process^2-Ions can reduce the photo-corrosion phenomenon of the second CdS nanosheet and improve the photocatalytic stability; the quantum dots are used as the material of the catalyst, have quantum restriction and edge effects, can provide more hydrogen production active sites due to the large specific surface area of the quantum dots, accelerate the reduction reaction, and obviously improve the catalytic hydrogen production performance.

In step S01, the first CdS nanosheet may be prepared by a conventional method. For example, in one embodiment, Cd (Ac) is added to 60 mL of Ethylenediamine (EDA)₂·2H₂O (2-3 mmol) and SC (NH2)₂(6-9 mmol), stirring for 25-35 min, transferring to an autoclave with a polytetrafluoroethylene lining, and heating at 85-110 deg.C for 6-9 h. After the reaction is finished, the reaction solution is naturally cooled to room temperature, and the light yellow precipitate is centrifugally collected at 2800-. And drying for 8h at 60 ℃ in a vacuum drying oven to obtain the first CdS nanosheet.

In the embodiment of the invention, in the step S02, in a specific embodiment, after the first CdS nanosheet is mixed with L-cysteine under an alkaline condition, the ultrasonic treatment is continued for 2 to 4 hours under the condition that the ultrasonic power is 150-. The supernatant was centrifuged for 30 minutes (9000-. In some embodiments, according to the mass ratio of the first CdS nanosheet to L-cysteine of 0.5-2:1, after the first CdS nanosheet and the L-cysteine are mixed, the CdS nanosheet is negatively charged under an alkaline condition, the L-cysteine is positively charged, the L-cysteine is electrostatically adsorbed and combined on the surface of the second CdS nanosheet under the assistance of ultrasound after mixing and is inserted into the layered structure, and the second CdS nanosheet with the thickness of about 2.5-4nm and the transverse dimension of 400-600nm is obtained through intercalation and spalling. The alkaline condition may be provided by adding Ethylenediamine (EDA), ammonia, etc., but is not limited thereto, as a weakly alkaline substance to the mixed system, and in some embodiments, the alkaline condition refers to an environment having a pH of 9 to 11.

In an embodiment of the present invention, in the step S03, the quantum dot may be prepared by a conventional method, and in some embodiments, the particle size of the quantum dot is 2 to 3.5 nm. In a specific embodiment, WS₂Quantum dots can be exfoliated by employing ultrasound in surfactant solvent₂Preparing quantum dots (2-3.5 nm) from the powder. In some embodiments, the surfactant is F108 (HO- (C)₂H₄O)₁₄₁(C₃H6O)₄₄₍C₂H₄O)₁₄₁H) However, sodium cholate, cetyltrimethylammonium bromide, and the like are not limited thereto. Let WS be₂Adding the powder into an F108 solution (with the concentration of 0.1-0.5 mol/L), performing ultrasonic treatment for 3-6 h under the condition of ice-water bath at 200W, performing centrifugal separation on the non-peeled powder at a low rotation speed (7000 rpm), then performing centrifugal collection on quantum dots at a high rotation speed (10000-15000 rpm), washing the quantum dots for several times by deionized water, and finally dispersing the quantum dots in the deionized water for storage.

In some embodiments of the present invention, in the step S03, the quantum dots may be electrostatically adsorbed to the surfaceThe second CdS nanosheet combined with L-cysteine is combined, meanwhile, holes of about 7-10 nanometers exist on the surface of the second CdS nanosheet in some embodiments of the invention, and the quantum dots can also be combined into the holes. In a specific embodiment, the second CdS nanosheet with L-cysteine bound to its surface is combined with WS₂And mixing the quantum dots, carrying out ultrasonic treatment, and continuing the ultrasonic treatment for 3-6 hours under the condition that the ultrasonic power is 150-300W to obtain the composite material. In some embodiments, as said WS₂The mass ratio of the quantum dots to the second CdS nanosheets combined with the L-cysteine on the surfaces is 7:93-15:85, and the second CdS nanosheets combined with the L-cysteine on the surfaces and WS are₂The quantum dots are mixed and sonicated.

The following is a detailed description of specific examples.

Example 1:

preparing CdS nanosheets: 60 mL of Ethylenediamine (EDA) was charged with Cd (Ac)₂·2H₂O (2.0 mmol) and SC (NH2)₂(6.0 mmol), stirred for 30 min, transferred to a 100mL Teflon lined autoclave and heated at 100 ℃ for 8 h. After the reaction, the mixture was naturally cooled to room temperature, centrifuged at 3000rpm to collect a pale yellow precipitate, and then washed three times with ethanol and deionized water to remove the organic solvent and impurities. Finally, the mixture is dried for 8 hours in a vacuum drying oven at 60 ℃.

Preparing an ultrathin CdS nanosheet: and adding 100mg of prepared CdS nanosheet and 1mL of EDA into 50mL of deionized water, ultrasonically dispersing for 30 minutes, adding 75 mgL-cysteine, ultrasonically treating for 2 hours again, centrifuging at 5000rpm, taking supernatant, and removing the un-peeled yellow precipitate at the bottom layer. The supernatant was centrifuged at 9000rpm for 30 minutes, and a pale yellow precipitate was collected and dispersed in deionized water for storage (5 mg/mL).

WS₂Preparing quantum dots: the WS2 powder is ultrasonically peeled off in a surfactant solvent to synthesize the quantum dot. The surfactant is F108 (HO- (C)₂H₄O)₁₄₁(C₃H₆O)₄₄(C₂H₄O)₁₄₁H)。50mg WS₂Powder additionIn 100mL of F108 solution (0.3 mol/L), ultrasonic treatment is carried out for 4h under the condition of ice-water bath at 200W, firstly, the unexfoliated powder is centrifugally separated at a low rotating speed (7000 rpm), then, the quantum dots are centrifugally collected at a high rotating speed (10000 rpm), are washed for a plurality of times by deionized water, and finally are dispersed in the deionized water for storage (0.2 mg/mL).

Preparing a composite photocatalyst: the composite photocatalyst is synthesized by an ultrasonic adsorption method. According to the concentration of the solution, taking 10mL of ultrathin CdS nanosheet solution and 20 mLWS₂The quantum dot solution is placed in a three-neck flask, the three-neck flask is sealed by a silicon rubber plug, and nitrogen is continuously introduced. Then mixing and ultrasonic processing for 2h, stirring for 6h, centrifuging at 8000rpm, removing supernatant, and washing precipitate with anhydrous ethanol for three times to obtain the composite photocatalyst (WS)₂Loading 8 wt%).

Hydrogen production activity test sample	Hydrogen production (mmol) at first hour	Hydrogen production (mmol) at first hour	Hydrogen production (mmol) at first hour	Average hydrogen production rate (mmol/h)
					CdS-5%WS₂	4.62	4.43	3.9	4.32
CdS-8%WS₂	5.56	5.94	5.77	5.76
					CdS-10%WS₂	4.88	4.71	4.35	4.65

Hydrogen production stability test	Average hydrogen production rate of 1-3 h （mmol/h）	Average hydrogen production rate of 4-6 h （mmol/h）	Average hydrogen production rate of 7-9 h （mmol/h）	Average hydrogen production rate of 10-12 h （mmol/h）
					CdS-8%WS₂	5.76	5.64	5.31	4.83

Example 2:

preparing CdS nanosheets: in 60 mL of ethylenediamine(EDA) adding Cd (Ac)₂·2H₂O (2.0 mmol) and SC (NH2)₂(6.0 mmol), stirred for 30 min, transferred to a 100mL Teflon lined autoclave and heated at 100 ℃ for 8 h. After the reaction, the mixture was naturally cooled to room temperature, centrifuged at 3000rpm to collect a pale yellow precipitate, and then washed three times with ethanol and deionized water to remove the organic solvent and impurities. Finally, the mixture is dried for 8 hours in a vacuum drying oven at 60 ℃.

Preparing an ultrathin CdS nanosheet: and adding 100mg of prepared CdS nanosheet and 1mL of EDA into 50mL of deionized water, ultrasonically dispersing for 30 minutes, adding 120mg of L-cysteine, ultrasonically treating for 3 hours again, centrifuging at 5000rpm, taking supernatant, and removing the un-peeled yellow precipitate on the bottom layer. The supernatant was centrifuged at 11000rpm for 30 minutes, and a pale yellow precipitate was collected and dispersed in deionized water for storage (8 mg/mL).

MoS₂Preparing quantum dots: MoS synthesis by hydrothermal method₂Quantum dots with the particle size of 2-3 nm. Under ice-water bath conditions, 25mmol of ammonium molybdate and 30 mmol of N-acetylcysteine were dissolved in 80mL of deionized water. The precursor solution was stirred continuously and 50mmol of thiourea was added. The mixed solution was then transferred to a 100mL Teflon stainless steel reaction vessel and heated at 200 ℃ for 4 h. After completion of the reaction, it was rapidly cooled to room temperature with water. The final product was purified by silica gel column chromatography using water as eluent. The product was finally stored dispersed in deionized water (0.6 mg/mL).

Preparing a composite photocatalyst: the composite photocatalyst is synthesized by an ultrasonic adsorption method. According to the concentration of the solution, taking 10mL of ultrathin CdS nanosheet solution and 16 mL of MoS₂The quantum dot solution is placed in a three-neck flask, the three-neck flask is sealed by a silicon rubber plug, and nitrogen is continuously introduced. Then, the composite photocatalyst can be obtained after mixing and ultrasonic treatment for 4h, stirring for 8h, centrifuging at 9000rpm, removing supernatant, and then washing the precipitate for three times by using absolute ethyl alcohol (MoS 2 quantum dot loading is 12 wt%).

Hydrogen production activity test sample	Hydrogen production (mmol) at first hour	Hydrogen production (mmol) at first hour	Hydrogen production (mmol) at first hour	Average hydrogen production rate (mmol/h)
					CdS-8%MoS₂	3.62	3.73	3.55	3.63
CdS-12%MoS₂	5.14	5.67	5.29	5.37
					CdS-18%MoS₂	4.52	4.58	4.07	4.39

Hydrogen production stability test	Average hydrogen production rate of 1-3 h （mmol/h）	Average hydrogen production rate of 4-6 h （mmol/h）	Average hydrogen production rate of 7-9 h （mmol/h）	Average hydrogen production rate of 10-12 h （mmol/h）
					CdS-12%MoS₂	5.37	5.21	4.94	4.7

Example 3:

preparing CdS nanosheets: 60 mL of Ethylenediamine (EDA) was charged with Cd (Ac)₂·2H₂O (2.0 mmol) and SC (NH)₂)₂(6.0 mmol), stirred for 30 min, transferred to a 100mL Teflon lined autoclave and heated at 100 ℃ for 8 h. After the reaction, the mixture was naturally cooled to room temperature, centrifuged at 3000rpm to collect a pale yellow precipitate, and then washed three times with ethanol and deionized water to remove the organic solvent and impurities. Finally, the mixture is dried for 8 hours in a vacuum drying oven at 60 ℃.

Preparing an ultrathin CdS nanosheet: and adding 100mg of prepared CdS nanosheet and 1mL of EDA into 50mL of deionized water, ultrasonically dispersing for 30 minutes, adding 200mg of L-cysteine, ultrasonically treating for 4 hours again, centrifuging at 5000rpm, taking supernatant, and removing the un-peeled yellow precipitate on the bottom layer. The supernatant was centrifuged at 12000rpm for 30 minutes, and a pale yellow precipitate was collected and dispersed in deionized water for storage (12.5 mg/mL).

Preparing a carbon quantum dot: the carbon quantum dots (particle size) are synthesized by a one-step microwave method. 15 mL of 20% glucoseWith 4 mL of 1mol/L NaH₂PO₄Mixing, ultrasonically dispersing, and heating in a microwave oven (750W) for 12 min. And finally, purifying and diluting the color-changing solution by using water, wherein the concentration of the carbon quantum dot solution is 1.3 mg/mL.

Preparing a composite photocatalyst: the composite photocatalyst is synthesized by an ultrasonic adsorption method. According to the concentration of the solution, 8mL of ultrathin CdS nanosheet solution and 5.4 mL of carbon quantum dot solution are placed in a three-neck flask, the three-neck flask is sealed by a silicon rubber plug, and nitrogen is continuously introduced. Then, the mixture is subjected to ultrasonic treatment for 4 hours, stirred for 12 hours, centrifuged at 10000rpm, the supernatant is removed, and then the precipitate is washed with absolute ethyl alcohol for three times to obtain the composite photocatalyst (the carbon quantum dot loading is 7 wt%).

Hydrogen production activity test sample	Hydrogen production (mmol) at first hour	Hydrogen production (mmol) at first hour	Hydrogen production (mmol) at first hour	Average hydrogen production rate (mmol/h)
					CdS-5%C	3.44	3.23	3.25	3.31
CdS-7%C	4.36	4.59	4.12	4.36
					CdS-10%C	2.97	2.86	2.53	2.79

Hydrogen production stability test	Average hydrogen production rate of 1-3 h （mmol/h）	Average hydrogen production rate of 4-6 h （mmol/h）	Average hydrogen production rate of 7-9 h （mmol/h）	Average hydrogen production rate of 10-12 h （mmol/h）
					CdS-7%C	4.36	4.11	3.84	3.43

The hydrogen production activity and stability of the composite photocatalyst are tested by adopting the following method:

(1) the visible light hydrogen production activity of a sample is tested by using a Beijing Bofelea water photolysis hydrogen production device, and the hydrogen produced in the reaction process is detected on line by using a (GC-9500) type gas chromatograph. The method comprises the following steps: 50 mg of sample was added to the reactor, along with 100mL of 0.5M aqueous Na 2S-Na 2SO3 (10 vol% lactic acid) solution as a sacrificial agent. After 30 min of ultrasonic dispersion, the reactor was sealed, the entire reaction system was evacuated to-0.1 MPa with a vacuum pump, continuous visible light irradiation with a xenon lamp (PLS-CHF, 300W,. lambda. >420 nm) was carried out with uninterrupted magnetic stirring, and the reaction was carried out for a total of 3 hours with sampling once per hour. The stability test method was as above, and the test was continued for 12 hours.

Claims

1. A composite material, comprising: the CdS nanosheet is combined with quantum dots and L-cysteine on the surface.

2. The composite material of claim 1, wherein the quantum dots have an electrical conductivity of 10^-2-10^-3Scm^-1(ii) a And/or the presence of a gas in the gas,

the thickness of the CdS nanosheet is 1-10 nm.

3. The composite material of claim 1, wherein the quantum dots are selected from WS₂Quantum dots, MoS₂One or more of quantum dots and carbon quantum dots.

4. The composite of claim 1, wherein the CdS nanosheets are 2.5-4nm thick; and/or the presence of a gas in the gas,

the transverse size of the CdS nanosheet is 200-300 nm.

5. The composite material of claim 1, wherein the mass ratio of the quantum dots to the CdS nanosheets is 7:93-15: 85.

6. The composite material according to claim 1, which is used as a photocatalyst for hydrogen production.

7. A method of making a composite material, comprising:

providing a first CdS nanosheet;

and mixing the second CdS nanosheets with quantum dots, and performing ultrasonic treatment to obtain the composite material.

8. The preparation method according to claim 6, wherein the first CdS nanosheet is mixed with L-cysteine under an alkaline condition, and then is subjected to ultrasonic treatment for 2-4 h under the condition that the ultrasonic frequency is 150-300W to obtain a second CdS nanosheet with L-cysteine combined on the surface; and/or the presence of a gas in the gas,

mixing the second CdS nanosheet with the L-cysteine combined on the surface with the quantum dots, and carrying out ultrasonic treatment for 3-6 h under the condition that the ultrasonic frequency is 150-300W to obtain the composite material; and/or the presence of a gas in the gas,

and mixing the first CdS nanosheet with L-cysteine under the condition that the pH value is 9-11, and carrying out ultrasonic stripping to obtain a second CdS nanosheet with L-cysteine combined on the surface.

9. The preparation method according to claim 6, wherein the first CdS nanosheet and L-cysteine are mixed according to a mass ratio of 0.5-2:1, and then subjected to ultrasonic stripping to obtain a second CdS nanosheet with L-cysteine combined on the surface.

10. The preparation method according to claim 6, wherein the second CdS nanosheet with the L-cysteine combined on the surface and the WS nanosheet are mixed according to the mass ratio of the quantum dots to the CdS nanosheets being 7:93-15:85₂The quantum dots are mixed and sonicated.