CdS / GQDs composite photocatalyst with visible light response and preparation method of CdS / GQDs composite photocatalyst

Abstract

The invention discloses a CdS / GQDs composite photocatalyst with visible light response and a preparation method of the CdS / GQDs composite photocatalyst, and belongs to the technical field of photocatalytic materials. The preparation method comprises the following steps: preparing a diluent of a GQDs aqueous dispersion; preparing a precursor solution; carrying out hydrothermal reaction; sample post-treatment: naturally cooling the hydrothermal reaction kettle to room temperature, taking out a reaction product, washing with absolute ethyl alcohol and deionized water for multiple times, performing centrifugal separation to obtain a solid sample, and drying the solid sample to obtain the product. The composite photocatalyst disclosed by the invention has obvious difference in morphology, the hexagonal CdS has two crystal faces, and an electron transfer channel formed between the two crystal faces promotes effective separation of photo-induced electrons and holes under the irradiation of visible light, so that the catalytic oxidation removal rate of Hg < 0 > is accelerated. The composite photocatalyst shows high efficiency and stability in the aspect of removing Hg < 0 > in flue gas, and the wide application potential of the composite photocatalyst is indicated. Therefore, the photocatalytic efficiency is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalytic materials, and in particular to a CdS / GQDs composite photocatalyst with visible light response and a preparation method thereof. Background Art

[0002] Mercury pollution in flue gas emissions poses a serious hazard to the natural environment and human health and safety that cannot be ignored. Photocatalytic mercury removal technology is like a green sword. With its excellent removal efficiency, it shines in the field of environmental protection. Not only is the operation process clean and pollution-free, but it also consumes low energy. It has become a leader in mercury removal technology and has shown incomparable advantages. The essence of photocatalytic technology lies in the research and development and preparation of novel and high-efficiency photocatalysts.

[0003] Cadmium sulfide (CdS) is a narrow bandgap semiconductor material with a bandgap width of about 2.4 eV. It has excellent visible light response performance and can effectively utilize the visible light part of the solar spectrum. However, the recombination rate of photogenerated electron-hole pairs in CdS is high, which seriously limits its practical application in photocatalytic efficiency. On the other hand, graphene quantum dots (GQDs), as a new type of carbon-based nanomaterial, have high conductivity, wide spectral absorption range (from ultraviolet to near infrared) and excellent photoelectric properties. GQDs can act as an efficient electron transport medium, significantly inhibiting the recombination of photogenerated carriers, thereby improving the overall performance of photocatalytic materials. The preparation methods provided by existing CdS / GQDs composite material research are relatively complicated or require specific methods, and they do not explain the reaction mechanism.

[0004] Therefore, a method for treating elemental mercury (Hg 0 ), high visible light utilization rate, and low photogenerated carrier recombination rate, and a CdS / GQDs composite photocatalyst with visible light response and a preparation method thereof are issues that technicians in this field are in urgent need of solving. Summary of the invention

[0005] In view of this, the present invention provides a CdS / GQDs composite photocatalyst with visible light response and a preparation method thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for preparing a CdS / GQDs composite photocatalyst with visible light response comprises the following steps:

[0008] (1) Preparation of a dilution of the GQDs aqueous dispersion: adding the GQDs aqueous dispersion into deionized water and stirring uniformly to obtain a dilution of the GQDs aqueous dispersion;

[0009] (2) Preparation of precursor solution: Cd(NO 3 ) 2 ·4H 2 O and thiourea are dissolved in the dilution of the GQDs aqueous dispersion obtained in step (1), and then stirred to obtain a mixed solution;

[0010] (3) hydrothermal reaction: transferring the obtained mixed solution into a hydrothermal reaction kettle, sealing the hydrothermal reaction kettle and placing it in an oven for hydrothermal reaction;

[0011] (4) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature, the reaction product was taken out and washed with anhydrous ethanol and deionized water for multiple times, and a solid sample was obtained by centrifugation. The solid sample was placed in an oven to dry to obtain the above-mentioned CdS / GQDs composite photocatalyst.

[0012] Beneficial effects of the present invention: Graphene quantum dot doping induces the formation of uniformly dispersed hexagonal lamellar CdS in the composite photocatalyst, which is stacked into hexagonal prisms and self-assembled into nanospheres. The key lies in the two crystal faces of the hexagonal CdS. Under visible light irradiation, a Z-type heterojunction is formed between the two crystal faces inside the CdS, which constructs an efficient electron transfer channel and is the key to effectively inhibiting the rapid recombination of the photogenerated carriers of CdS itself, thereby significantly improving the photocatalytic oxidation of Hg 0 The composite material prepared by the method of the present invention has a large difference in morphology compared with pure CdS. The morphology difference has a great influence on the photocatalytic performance of the material, so the invention reveals that the composite material can efficiently and stably catalyze the oxidation of Hg under visible light. 0 mechanism.

[0013] Graphene quantum dots (GQDs) with strong electron affinity act as efficient electron acceptors, which can capture and transfer photogenerated electrons that migrate to the surface of CdS, thereby significantly promoting the rapid separation of photogenerated carriers and effectively inhibiting electron-hole recombination. GQDs are doped into CdS for recombination, which can give full play to the advantages of the optical properties of both: CdS, as a light absorption host, provides a strong visible light response capability; while GQDs, as an electron transmission channel, not only broadens the light absorption range, but also significantly improves the separation efficiency of photogenerated carriers. This synergistic effect enables the composite photocatalyst to exhibit significantly enhanced photocatalytic performance under visible light irradiation, providing a new idea for the development of efficient photocatalytic materials.

[0014] The doping of GQDs effectively suppressed the photocorrosion problem of CdS. Under visible light irradiation, the composite material catalyzed the oxidation of Hg 0 The efficiency is as high as 95.82%, which is 42% higher than that of pure CdS. At the same time, the photocatalytic stability and durability of the composite material are significantly enhanced. After 5 cycle experiments, the mercury removal rate of the catalyst is still higher than 90%, showing excellent stability.

[0015] The preparation methods provided by existing CdS / GQDs composite material research are relatively complicated. The present invention only requires a proper amount of GQDs to be mixed with a CdS precursor for hydrothermal reaction to obtain the GQDs. Through deep hydrothermal reaction, cadmium sulfide and graphene quantum dots are tightly combined, thereby successfully synthesizing a cadmium sulfide-graphene quantum dot composite photocatalyst. The preparation method of the present invention is simple, easy to operate, and suitable for wide production and application.

[0016] The photogenerated holes that migrate to the surface of the material have enough energy to generate hydroxyl radicals (·OH). The photogenerated electrons that migrate to the surface of CdS are further transferred to the GQDs with strong electron affinity and react with O in the simulated gas. 2 Combined with superoxide radicals (·O 2 -), ·OH and ·O 2 -As a common reactive oxygen species, it can quickly convert elemental mercury (Hg 0 ) is oxidized to mercuric oxide (HgO).

[0017] Specifically, CdS / GQDs composite photocatalyst catalytically oxidizes Hg under visible light 0 The specific reaction pathway is as follows:

[0018] CdS-{001-100}+hv→CdS-{001}(e - +h + ) / CdS-{100}(e - +h + ) (1)

[0019] e - -CdS-{001} (CB )→h + -CdS-{100} (VB) (2)

[0020] h + -CdS-{001} (VB) +H 2 O / OH - → OH (3)

[0021] e ― -CdS-{100} (VB) →e - -GQDs (4)

[0022]

[0023]

[0024]

[0025] Furthermore, in step (1), the concentration of graphene quantum dots in the GQDs aqueous dispersion is 0.25 g / L.

[0026] Furthermore, in step (1), the volume ratio of the GQDs aqueous dispersion and deionized water is (2-4):60.

[0027] Furthermore, in step (1), the stirring speed is 1000 r / min and the stirring time is 10 minutes.

[0028] The beneficial effect of adopting the above further technical solution is that the GQDs are fully mixed with water and the GQDs are uniformly doped with CdS.

[0029] Furthermore, in step (2), Cd(NO 3 ) 2 ·4H 2 The molar ratio of O, thiourea and GQDs in step (1) is 1:30:(0.002-0.004).

[0030] Furthermore, in step (2), the stirring speed is 1000 r / min and the stirring time is 30 minutes.

[0031] The beneficial effect of adopting the above further technical solution is that the GQDs and the CdS precursor material are fully mixed to obtain a uniformly composite CdS / GQDs photocatalyst.

[0032] Furthermore, in step (3), the temperature of the hydrothermal reaction is 180-220° C., and the time of the hydrothermal reaction is 3-8 h.

[0033] Furthermore, in step (4), the centrifugal speed is 8000 r / min, the centrifugal time is 3 min, the drying temperature is 80° C., and the drying time is 12 hours.

[0034] The present invention also provides a CdS / GQDs composite photocatalyst with visible light response prepared by the above method.

[0035] The present invention also provides an application of the CdS / GQDs composite photocatalyst with visible light response in removing elemental mercury from flue gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Experimental flow chart of the hydrothermal preparation of CdS / GQDs composite photocatalyst.

[0037] Figure 2In the figure, Figure a is the SEM of the pure CdS catalyst prepared in Comparative Example 1, Figure b is the SEM of the CdS / GQDs composite photocatalyst prepared in Example 1 at 1 μm, and Figure c is the SEM of the CdS / GQDs composite photocatalyst prepared in Example 1 at 500 nm.

[0038] Figure 3 In the figure, Figure a shows the visible light mercury removal efficiency of catalysts with different GQDs contents prepared in Example 1, Example 2 and Comparative Example 1, Figure b shows the visible light mercury removal efficiency of catalysts prepared at different hydrothermal temperatures in Example 3 and Example 4, and Figure c shows the mercury removal efficiency of materials prepared at different hydrothermal times in Example 5 and Example 6.

[0039] Figure 4 In the figure, Figure a is the stability test of visible light mercury removal of CdS / GQDs composite materials of Example 1 and Comparative Example 1, and Figure b is the durability test of visible light mercury removal of Example 1 and Comparative Example 1.

[0040] Figure 5 Figure a shows the UV-visible diffuse reflectance spectra of pure CdS and CdS / GQDs in Example 1 and Comparative Example 1, and Figure b shows the two-photon energy (eV) of the two catalysts in Example 1 and Comparative Example 1. 2 )picture.

[0041] Figure 6 In the figure, Figure a is the instantaneous photocurrent (it) diagram of CdS and CdS / GQDs in Example 1 and Comparative Example 1, Figure b is the photoluminescence spectrum (PL) diagram of the two catalysts in Example 1 and Comparative Example 1, and Figure c is the electrochemical impedance spectroscopy (EIS) diagram of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Example 1

[0044] The preparation method of a CdS / GQDs composite photocatalyst with visible light response comprises the following steps:

[0045] (1) Preparation of a dilution of the GQDs aqueous dispersion: 2 mL of a GQDs aqueous dispersion having a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was stirred evenly by magnetic stirring at a stirring speed of 1000 r / min for 10 minutes to obtain a dilution of the GQDs aqueous dispersion;

[0046] (2) Preparation of precursor solution: 0.308 g Cd(NO 3 ) 2 ·4H 2 O and 2.28g thiourea were dissolved in the dilution of the GQDs aqueous dispersion obtained in step (1), and then magnetically stirred evenly at a stirring speed of 1000r / min for 30 minutes to obtain a mixed solution;

[0047] (3) Hydrothermal reaction: The obtained mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure hydrothermal reactor, which was sealed and placed in an oven for hydrothermal reaction. The hydrothermal reaction temperature was 200° C. and the hydrothermal reaction time was 5 h.

[0048] (4) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature, the reaction product was taken out and washed alternately with anhydrous ethanol and deionized water for three times, and the solid sample was obtained by centrifugation at a speed of 8000 r / min and a centrifugation time of 3 min. The solid sample was placed in an oven for drying at a drying temperature of 80°C and a drying time of 12 h to obtain a CdS / GQDs composite photocatalyst, which was recorded as CdS-G2.

[0049] Example 2

[0050] The preparation method of a CdS / GQDs composite photocatalyst with visible light response comprises the following steps:

[0051] (1) Preparation of a dilution of the GQDs aqueous dispersion: 4 mL of a GQDs aqueous dispersion having a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was stirred evenly by magnetic stirring at a stirring speed of 1000 r / min for 10 minutes to obtain a dilution of the GQDs aqueous dispersion;

[0052] (2) Preparation of precursor solution: 0.308 g Cd(NO 3 ) 2 ·4H 2 O and 2.28g thiourea were dissolved in the dilution of the GQDs aqueous dispersion obtained in step (1), and then magnetically stirred evenly at a stirring speed of 1000r / min for 30 minutes to obtain a mixed solution;

[0053] (3) Hydrothermal reaction: The obtained mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure hydrothermal reactor, which was sealed and placed in an oven for hydrothermal reaction. The hydrothermal reaction temperature was 200° C. and the hydrothermal reaction time was 5 h.

[0054] (4) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature, the reaction product was taken out and washed alternately with anhydrous ethanol and deionized water for three times, and the solid sample was obtained by centrifugation at a speed of 8000 r / min and a centrifugation time of 3 min. The solid sample was placed in an oven for drying at a drying temperature of 80°C and a drying time of 12 h to obtain a CdS / GQDs composite photocatalyst, which was recorded as CdS-G4.

[0055] The difference from Example 1 is that the amount of GQDs aqueous dispersion added is 4 mL.

[0056] Example 3

[0057] The preparation method of a CdS / GQDs composite photocatalyst with visible light response comprises the following steps:

[0058] (1) Preparation of a dilution of the GQDs aqueous dispersion: 2 mL of a GQDs aqueous dispersion having a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was stirred evenly by magnetic stirring at a stirring speed of 1000 r / min for 10 minutes to obtain a dilution of the GQDs aqueous dispersion;

[0059] (2) Preparation of precursor solution: 0.308 g Cd(NO 3 ) 2 ·4H 2 O and 2.28g thiourea were dissolved in the dilution of the GQDs aqueous dispersion obtained in step (1), and then magnetically stirred evenly at a stirring speed of 1000r / min for 30 minutes to obtain a mixed solution;

[0060] (3) Hydrothermal reaction: The obtained mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure hydrothermal reactor, which was sealed and placed in an oven for hydrothermal reaction at a temperature of 180° C. for 5 h.

[0061] (4) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature, the reaction product was taken out and washed alternately with anhydrous ethanol and deionized water for three times, and the solid sample was obtained by centrifugation at a speed of 8000 r / min and a centrifugation time of 3 min. The solid sample was placed in an oven for drying at a drying temperature of 80°C and a drying time of 12 h to obtain a CdS / GQDs composite photocatalyst.

[0062] The difference from Example 1 is that the hydrothermal reaction condition is changed to 180° C. for 5 h.

[0063] Example 4

[0064] The preparation method of a CdS / GQDs composite photocatalyst with visible light response comprises the following steps:

[0065] (1) Preparation of a dilution of the GQDs aqueous dispersion: 2 mL of a GQDs aqueous dispersion having a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was stirred evenly by magnetic stirring at a stirring speed of 1000 r / min for 10 minutes to obtain a dilution of the GQDs aqueous dispersion;

[0066] (2) Preparation of precursor solution: 0.308 g Cd(NO 3 ) 2 ·4H 2 O and 2.28g thiourea were dissolved in the dilution of the GQDs aqueous dispersion obtained in step (1), and then magnetically stirred evenly at a stirring speed of 1000r / min for 30 minutes to obtain a mixed solution;

[0067] (3) Hydrothermal reaction: The obtained mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure hydrothermal reactor, which was sealed and placed in an oven for hydrothermal reaction. The hydrothermal reaction temperature was 220° C. and the hydrothermal reaction time was 5 h.

[0068] (4) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature, the reaction product was taken out and washed alternately with anhydrous ethanol and deionized water for three times, and the solid sample was obtained by centrifugation at a speed of 8000 r / min and a centrifugation time of 3 min. The solid sample was placed in an oven for drying at a drying temperature of 80°C and a drying time of 12 h to obtain a CdS / GQDs composite photocatalyst.

[0069] The difference from Example 1 is that the hydrothermal reaction conditions are changed to 220° C. for 5 h.

[0070] Example 5

[0071] The preparation method of a CdS / GQDs composite photocatalyst with visible light response comprises the following steps:

[0072] (1) Preparation of a dilution of the GQDs aqueous dispersion: 2 mL of a GQDs aqueous dispersion having a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was stirred evenly by magnetic stirring at a stirring speed of 1000 r / min for 10 minutes to obtain a dilution of the GQDs aqueous dispersion;

[0073] (2) Preparation of precursor solution: 0.308 g Cd(NO 3 ) 2 ·4H 2O and 2.28g thiourea were dissolved in the dilution of the GQDs aqueous dispersion obtained in step (1), and then magnetically stirred evenly at a stirring speed of 1000r / min for 30 minutes to obtain a mixed solution;

[0074] (3) Hydrothermal reaction: The obtained mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure hydrothermal reactor, which was sealed and placed in an oven for hydrothermal reaction. The hydrothermal reaction temperature was 200° C. and the hydrothermal reaction time was 3 h.

[0075] (4) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature, the reaction product was taken out and washed alternately with anhydrous ethanol and deionized water for three times, and the solid sample was obtained by centrifugation at a speed of 8000 r / min and a centrifugation time of 3 min. The solid sample was placed in an oven for drying at a drying temperature of 80°C and a drying time of 12 h to obtain a CdS / GQDs composite photocatalyst.

[0076] The difference from Example 1 is that the hydrothermal reaction conditions are changed to 200° C. for 3 h.

[0077] Example 6

[0078] The preparation method of a CdS / GQDs composite photocatalyst with visible light response comprises the following steps:

[0079] (1) Preparation of a dilution of the GQDs aqueous dispersion: 2 mL of a GQDs aqueous dispersion having a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was stirred evenly by magnetic stirring at a stirring speed of 1000 r / min for 10 minutes to obtain a dilution of the GQDs aqueous dispersion;

[0080] (2) Preparation of precursor solution: 0.308 g Cd(NO 3 ) 2 ·4H 2 O and 2.28g thiourea were dissolved in the dilution of the GQDs aqueous dispersion obtained in step (1), and then magnetically stirred evenly at a stirring speed of 1000r / min for 30 minutes to obtain a mixed solution;

[0081] (3) Hydrothermal reaction: The obtained mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure hydrothermal reactor, which was sealed and placed in an oven for hydrothermal reaction. The hydrothermal reaction temperature was 200° C. and the hydrothermal reaction time was 8 h.

[0082] (4) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature, the reaction product was taken out and washed alternately with anhydrous ethanol and deionized water for three times, and the solid sample was obtained by centrifugation at a speed of 8000 r / min and a centrifugation time of 3 min. The solid sample was placed in an oven for drying at a drying temperature of 80°C and a drying time of 12 h to obtain a CdS / GQDs composite photocatalyst.

[0083] The difference from Example 1 is that the hydrothermal reaction conditions are changed to 200° C. for 8 h.

[0084] Comparative Example 1

[0085] The preparation method of CdS photocatalyst comprises the following steps:

[0086] (1) Preparation of precursor solution: 0.308 g Cd(NO 3 ) 2 ·4H 2 O and 2.28 g of thiourea were dissolved in 60 mL of water, and then magnetically stirred at a stirring speed of 1000 r / min for 30 minutes to obtain a mixed solution;

[0087] (2) Hydrothermal reaction: The obtained mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure hydrothermal reactor, which was sealed and placed in an oven for hydrothermal reaction. The hydrothermal reaction temperature was 200° C. and the hydrothermal reaction time was 5 h.

[0088] (3) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature, the reaction product was taken out and washed alternately with anhydrous ethanol and deionized water for three times, and the solid sample was obtained by centrifugation at a speed of 8000 r / min and a centrifugation time of 3 min. The solid sample was placed in an oven for drying at a drying temperature of 80°C and a drying time of 12 h to obtain a CdS photocatalyst, which was recorded as CdS.

[0089] The difference from Example 1 is that no GQDs are added.

[0090] Figure 1 Experimental operation flow chart for preparing CdS / GQDs composite materials

[0091] Figure 2In the figure, Figure a is the SEM image of the sample prepared in comparative example 1. Pure CdS is formed by highly disordered aggregation of nanoparticles to form an amorphous block with a lattice spacing of 0.335nm, corresponding to the {111} crystal plane of cubic CdS. Figure b (1μm) and Figure c (500nm) are SEM images of the CdS / GQDs composite photocatalyst prepared in Example 1. The CdS / GQDs complex formed by doping GQDs appears as uniformly dispersed nanospheres. The nanospheres are orderly self-assembled by hexagonal prisms, and the hexagonal prisms are formed by layered stacking of hexagonal nanosheets.

[0092] Figure 3 In the figure, a shows the visible light mercury removal efficiency of the composite materials with different GQDs contents prepared in Example 1, Example 2 and Comparative Example 1. When GQDs are not doped, the visible light mercury removal efficiency of pure CdS is 53.8%. When the amount of GQDs added is 2 mL, the photocatalytic performance of the composite material reaches a maximum of 95.82%. When the doping amount of GQDs is further increased to 4 mL, the mercury removal efficiency is reduced to 76.51%. Adding an appropriate amount of graphene quantum dots can make CdS visible light catalytic oxidation of Hg 0 The efficiency is improved, but too much doping will be detrimental to the excellent photocatalytic performance of the composite material. Figure b is a graph of the visible light mercury removal efficiency of the photocatalysts prepared at different hydrothermal temperatures in Examples 1, 3, and 4. The photocatalytic mercury removal efficiency of the composite material prepared at a hydrothermal temperature of 200°C is as high as 95.82%. The photocatalytic performance of the photocatalysts prepared at too low or too high a hydrothermal temperature is reduced. Figure c is the visible light catalytic mercury oxidation effect of the composite catalysts prepared at different hydrothermal times in Examples 1, 5, and 6. The composite material prepared at a hydrothermal time of 5 hours has the best mercury removal efficiency, reaching 95.82%. Too high or too low a hydrothermal temperature does not produce visible light catalytic Hg 0 The best material.

[0093] Figure 4 Figure a shows the stability test of visible light mercury removal of CdS / GQDs composite material prepared in Example 1. The first two cycles of mercury removal of CdS prepared in Comparative Example 1 0 The efficiency exceeded 50%, but it dropped significantly after the third time and was only 36.31% after the fifth time. However, CdS-G2 still exceeded 90% after five cycles, indicating that CdS / GQDs has good photocatalytic stability. Figure b shows the photocatalytic oxidation of Hg 0 Durability experimental tests showed that the efficiency of CdS / GQDs dropped below 90% after 26 hours of visible light reaction, and the composite material exhibited excellent visible light catalytic oxidation stability.

[0094] Figure 5 In the figure, Figure a is the UV-visible diffuse reflectance spectra of CdS / GQDs prepared in Example 1 and CdS prepared in Comparative Example 1, and Figure b is the corresponding two-photon energy (eV2 ) Figure 2 shows that both materials have the ability to respond to visible light. The absorption wavelength of light in the CdS-G2 photocatalytic composite material formed after doping with GQDs is red-shifted, which improves the ability to respond to visible light.

[0095] Figure 6 In the figure, Figure a is the photocurrent density diagram of the CdS / GQDs composite photocatalyst prepared in Example 1. The photocurrent intensity of CdS-GQDs is much higher than that of CdS, which is about 8 times that of pure CdS in Example 1; Figure b is its corresponding photoluminescence spectrum diagram. After doping with GQDs, the luminescence intensity of CdS is greatly reduced, indicating that its nano-hybrid structure effectively inhibits the recombination of photogenerated electrons and holes; Figure c is the electrochemical impedance diagram of the composite material. The arc radius of CdS-GQDs is smaller than that of CdS, GQDs doping reduces impedance, and the carrier separation rate is improved.

[0096] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a CdS / GQDs composite photocatalyst with visible light response, characterized in that: The following steps are involved: (1) Preparation of a dilution of the GQDs aqueous dispersion: adding the GQDs aqueous dispersion into deionized water and stirring uniformly to obtain a dilution of the GQDs aqueous dispersion; (2) Preparation of precursor solution: dissolving Cd(NO3)2·4H2O and thiourea in the diluted solution of the GQDs aqueous dispersion obtained in step (1), and then stirring to obtain a mixed solution; (3) hydrothermal reaction: the obtained mixed solution is transferred to a hydrothermal reaction kettle, the hydrothermal reaction kettle is sealed and placed in an oven for hydrothermal reaction; (4) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature, the reaction product was taken out and washed with anhydrous ethanol and deionized water for multiple times, and a solid sample was obtained by centrifugation. The solid sample was placed in an oven for drying to obtain the CdS / GQDs composite photocatalyst.

2. The method for preparing a CdS / GQDs composite photocatalyst with visible light response according to claim 1, characterized in that: In step (1), the concentration of graphene quantum dots in the GQDs aqueous dispersion is 0.25 g / L.

3. The method for preparing a CdS / GQDs composite photocatalyst with visible light response according to claim 1, characterized in that: In step (1), the volume ratio of the GQDs aqueous dispersion and deionized water is (2-4):

60.

4. The method for preparing a CdS / GQDs composite photocatalyst with visible light response according to claim 1, characterized in that: In step (1), the stirring speed is 1000 r / min and the stirring time is 10 minutes.

5. The method for preparing a CdS / GQDs composite photocatalyst with visible light response according to claim 1, characterized in that: The molar ratio of Cd(NO3)2·4H2O, thiourea and GQDs in step (1) is 1:30:(0.002-0.004) in step (2).

6. The method for preparing a CdS / GQDs composite photocatalyst with visible light response according to claim 1, characterized in that: In step (2), the stirring speed is 1000 r / min and the stirring time is 30 minutes.

7. The method for preparing a CdS / GQDs composite photocatalyst with visible light response according to claim 1, characterized in that: In step (3), the temperature of the hydrothermal reaction is 180-220° C., and the time of the hydrothermal reaction is 3-8 h.

8. The method for preparing a CdS / GQDs composite photocatalyst with visible light response according to claim 1, characterized in that: In step (4), the centrifugal speed is 8000 r / min, the centrifugal time is 3 min, the drying temperature is 80° C., and the drying time is 12 hours.

9. A CdS / GQDs composite photocatalyst with visible light response prepared by the method according to any one of claims 1 to 8.

10. Use of the CdS / GQDs composite photocatalyst with visible light response as claimed in claim 9 in removing elemental mercury from flue gas.

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