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

Abstract

This invention discloses a CdS / GQDs composite photocatalyst with visible light response and its preparation method, belonging to the field of photocatalytic materials technology. The preparation method includes: preparing a diluted solution of GQDs aqueous dispersion; preparing a precursor solution; hydrothermal reaction; sample post-treatment: naturally cooling the hydrothermal reactor to room temperature, removing the reaction product and washing it repeatedly with anhydrous ethanol and deionized water, centrifuging to obtain a solid sample, and drying the solid sample to obtain the product. The composite photocatalyst of this invention exhibits significant morphological differences; the hexagonal CdS has two crystal faces. Under visible light irradiation, the electron transfer channel formed between the two crystal faces promotes the effective separation of photogenerated electrons and holes, thereby accelerating Hg... 0 The catalytic oxidation removal rate of Hg in flue gas. This composite photocatalyst [is effective in removing Hg from flue gas]. 0 It exhibits high efficiency and stability, indicating its broad application potential. This significantly improves photocatalytic efficiency.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, specifically to a CdS / GQDs composite photocatalyst with visible light response and its preparation method. Background Technology

[0002] Mercury pollution from flue gas emissions poses a serious and undeniable threat to the natural environment and human health. Photocatalytic mercury removal technology, like a green sword, shines brightly in the environmental protection field due to its superior removal efficiency. Not only is the operation clean and pollution-free, but it also boasts low energy consumption, making it a leader in mercury removal technologies and demonstrating unparalleled advantages. The essence of photocatalysis lies in the research and development and preparation of novel and highly efficient photocatalysts.

[0003] Cadmium sulfide (CdS) is a narrow bandgap semiconductor material with a bandgap of approximately 2.4 eV, exhibiting excellent visible light response and effectively utilizing the visible light portion of the solar spectrum. However, the high recombination rate of photogenerated electron-hole pairs in CdS severely limits its practical application in photocatalysis. On the other hand, graphene quantum dots (GQDs), as a novel carbon-based nanomaterial, possess high conductivity, a wide spectral absorption range (from ultraviolet to near-infrared), and excellent photoelectric properties. GQDs can serve as highly efficient electron transport media, significantly suppressing the recombination of photogenerated carriers, thereby improving the overall performance of photocatalytic materials. Existing research on CdS / GQDs composite materials has provided relatively complex preparation methods or requires specific procedures, and they have not elucidated the reaction mechanisms.

[0004] Therefore, a method for applying elemental mercury (Hg) in flue gas is provided. 0 The efficient removal of CdS / GQDs, high visible light utilization, low recombination rate of photogenerated carriers, and the preparation method of such CdS / GQDs composite photocatalysts with visible light response are problems that urgently need to be solved by those skilled in the art. Summary of the Invention

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

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

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

[0008] (1) Preparation of dilution of GQDs aqueous dispersion: Add GQDs aqueous dispersion to deionized water and stir evenly to obtain dilution of GQDs aqueous dispersion.

[0009] (2) Preparation of precursor solution: Cd(NO3)2·4H2O and thiourea are dissolved in the diluted solution of the GQDs aqueous dispersion obtained in step (1), and then stirred evenly to obtain a mixed solution;

[0010] (3) Hydrothermal reaction: The obtained mixed solution is transferred to a hydrothermal reactor, and the hydrothermal reactor is sealed and placed in an oven for hydrothermal reaction;

[0011] (4) Sample post-processing: The hydrothermal reactor was naturally cooled to room temperature. The reaction product was taken out and washed repeatedly with anhydrous ethanol and deionized water. The solid sample was obtained by centrifugation and then dried in an oven to obtain the above CdS / GQDs composite photocatalyst.

[0012] The beneficial effects of this invention are as follows: Uniformly dispersed hexagonal layered CdS is formed in the graphene quantum dot-induced composite photocatalyst, which stacks into hexagonal prisms and self-assembles into nanospheres. The key lies in the two crystal faces of the hexagonal CdS. Under visible light irradiation, a Z-shaped heterojunction is formed between the two crystal faces inside the CdS, constructing a highly efficient electron transfer channel. This is crucial for effectively suppressing the rapid recombination of photogenerated carriers within CdS, thereby significantly improving the photocatalytic oxidation of Hg. 0 The efficiency of the composite material prepared by the method of this invention is significantly different from that of pure CdS. This morphological difference has a significant impact on the photocatalytic performance of the material. Therefore, by focusing on its morphology, this invention reveals the efficient and stable visible light photocatalytic oxidation of Hg by the composite material. 0 The mechanism.

[0013] Graphene quantum dots (GQDs), with their strong electron affinity, act as efficient electron acceptors, capturing and transferring photogenerated electrons migrating to the CdS surface. This significantly promotes the rapid separation of photogenerated carriers and effectively suppresses electron-hole recombination. Incorporating GQDs into CdS for recombination fully leverages the optical properties of both materials: CdS, as the primary light absorber, provides a strong visible light response; while GQDs, acting as electron transport channels, not only broaden the light absorption range but also significantly improve the separation efficiency of photogenerated carriers. This synergistic effect results in a significantly enhanced photocatalytic performance of the composite photocatalyst under visible light irradiation, providing a new approach for the development of highly efficient photocatalytic materials.

[0014] The doping of GQDs effectively suppressed the photocorrosion problem of CdS, and the composite material catalytically oxidized Hg under visible light irradiation. 0 The efficiency reached 95.82%, which is 42% higher than that of pure CdS. At the same time, it significantly enhanced the photocatalytic stability and durability of the composite material. After 5 cycles of experiments, the removal rate of mercury by the catalyst was still higher than 90%, showing excellent stability.

[0015] Existing research on CdS / GQDs composite materials provides relatively complex preparation methods. This invention simply involves mixing an appropriate amount of GQDs with a CdS precursor via hydrothermal reaction. Through deep hydrothermal reaction, cadmium sulfide and graphene quantum dots achieve a tight bond, thus successfully synthesizing a cadmium sulfide-graphene quantum dot composite photocatalyst. The preparation method of this invention is simple, convenient to operate, and suitable for widespread production and application.

[0016] Photogenerated holes migrating to the surface of a material possess sufficient energy to generate hydroxyl radicals (·OH). Photogenerated electrons migrating to the CdS surface further transfer to GQDs with strong electron affinity, combining with O2 in the simulated gas to generate superoxide radicals (·O2-). ·OH and ·O2-, as common reactive oxygen species, can rapidly decompose elemental mercury (Hg). 0 It is oxidized to mercuric oxide (HgO).

[0017] Specifically, the visible light photocatalytic oxidation of Hg by CdS / GQDs composite photocatalysts 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) +H2O / 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 GQDs aqueous dispersion to 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 effects of adopting the above-mentioned further technical solution are: it enables GQDs to be fully mixed with water and GQDs to be uniformly doped into CdS.

[0029] Furthermore, the molar ratio of Cd(NO3)2·4H2O, thiourea and GQDs in step (2) 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 effects of adopting the above-mentioned further technical solution are: GQDs and CdS precursor materials 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℃, and the time of the hydrothermal reaction is 3-8h.

[0033] Furthermore, in step (4), the centrifugation speed is 8000 r / min, the centrifugation time is 3 min, the drying temperature is 80℃, 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 visible light responsive CdS / GQDs composite photocatalyst for the removal of elemental mercury from flue gas. Attached Figure Description

[0036] Figure 1 Flowchart of the hydrothermal method for preparing CdS / GQDs composite photocatalysts.

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

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

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

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

[0041] Figure 6 In the figures, Figure a shows the instantaneous photocurrent (it) of CdS and CdS / GQDs in Example 1 and Comparative Example 1, Figure b shows the photoluminescence spectra (PL) of the two catalysts in Example 1 and Comparative Example 1, and Figure c shows the electrochemical impedance (EIS) spectra of Example 1 and Comparative Example 1. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1

[0044] A method for preparing a CdS / GQDs composite photocatalyst with visible light response includes the following steps:

[0045] (1) Preparation of dilution of GQDs aqueous dispersion: 2 mL of GQDs aqueous dispersion with a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was magnetically stirred until homogeneous. The stirring speed was 1000 r / min and the stirring time was 10 minutes to obtain the dilution of GQDs aqueous dispersion.

[0046] (2) Preparation of precursor solution: Dissolve 0.308g Cd(NO3)2·4H2O and 2.28g thiourea in the diluted solution of the GQDs aqueous dispersion obtained in step (1), and then stir magnetically until uniform. The stirring speed is 1000r / min and the stirring time is 30 minutes to obtain a mixed solution.

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

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

[0049] Example 2

[0050] A method for preparing a CdS / GQDs composite photocatalyst with visible light response includes the following steps:

[0051] (1) Preparation of dilution of GQDs aqueous dispersion: 4 mL of GQDs aqueous dispersion with a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was magnetically stirred until homogeneous. The stirring speed was 1000 r / min and the stirring time was 10 minutes to obtain the dilution of GQDs aqueous dispersion.

[0052] (2) Preparation of precursor solution: Dissolve 0.308g Cd(NO3)2·4H2O and 2.28g thiourea in the diluted solution of the GQDs aqueous dispersion obtained in step (1), and then stir magnetically until uniform. The stirring speed is 1000r / min and the stirring time is 30 minutes to obtain a mixed solution.

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

[0054] (4) Sample post-treatment: The hydrothermal reactor was naturally cooled to room temperature. The reaction product was taken out and washed three times with anhydrous ethanol and deionized water alternately. The solid sample was obtained by centrifugation at a speed of 8000 r / min for 3 min. The solid sample was placed in an oven to dry at a temperature of 80℃ for 12 hours to obtain the CdS / GQDs composite photocatalyst, denoted 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] A method for preparing a CdS / GQDs composite photocatalyst with visible light response includes the following steps:

[0058] (1) Preparation of dilution of GQDs aqueous dispersion: 2 mL of GQDs aqueous dispersion with a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was magnetically stirred until homogeneous. The stirring speed was 1000 r / min and the stirring time was 10 minutes to obtain the dilution of GQDs aqueous dispersion.

[0059] (2) Preparation of precursor solution: Dissolve 0.308g Cd(NO3)2·4H2O and 2.28g thiourea in the diluted solution of the GQDs aqueous dispersion obtained in step (1), and then stir magnetically until uniform. The stirring speed is 1000r / min and the stirring time is 30 minutes to obtain a mixed solution.

[0060] (3) Hydrothermal reaction: The obtained mixed solution was transferred to a 100mL stainless steel high-pressure hydrothermal reactor lined with polytetrafluoroethylene. After sealing the hydrothermal reactor, it was placed in an oven for hydrothermal reaction. The temperature of the hydrothermal reaction was 180℃ and the time of the hydrothermal reaction was 5h.

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

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

[0063] Example 4

[0064] A method for preparing a CdS / GQDs composite photocatalyst with visible light response includes the following steps:

[0065] (1) Preparation of dilution of GQDs aqueous dispersion: 2 mL of GQDs aqueous dispersion with a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was magnetically stirred until homogeneous. The stirring speed was 1000 r / min and the stirring time was 10 minutes to obtain the dilution of GQDs aqueous dispersion.

[0066] (2) Preparation of precursor solution: Dissolve 0.308g Cd(NO3)2·4H2O and 2.28g thiourea in the diluted solution of the GQDs aqueous dispersion obtained in step (1), and then stir magnetically until uniform. The stirring speed is 1000r / min and the stirring time is 30 minutes to obtain a mixed solution.

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

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

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

[0070] Example 5

[0071] A method for preparing a CdS / GQDs composite photocatalyst with visible light response includes the following steps:

[0072] (1) Preparation of dilution of GQDs aqueous dispersion: 2 mL of GQDs aqueous dispersion with a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was magnetically stirred until homogeneous. The stirring speed was 1000 r / min and the stirring time was 10 minutes to obtain the dilution of GQDs aqueous dispersion.

[0073] (2) Preparation of precursor solution: Dissolve 0.308g Cd(NO3)2·4H2O and 2.28g thiourea in the diluted solution of the GQDs aqueous dispersion obtained in step (1), and then stir magnetically until uniform. The stirring speed is 1000r / min and the stirring time is 30 minutes to obtain a mixed solution.

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

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

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

[0077] Example 6

[0078] A method for preparing a CdS / GQDs composite photocatalyst with visible light response includes the following steps:

[0079] (1) Preparation of dilution of GQDs aqueous dispersion: 2 mL of GQDs aqueous dispersion with a graphene quantum dot concentration of 0.25 g / L was added to 60 mL of deionized water, and the mixture was magnetically stirred until homogeneous. The stirring speed was 1000 r / min and the stirring time was 10 minutes to obtain the dilution of GQDs aqueous dispersion.

[0080] (2) Preparation of precursor solution: Dissolve 0.308g Cd(NO3)2·4H2O and 2.28g thiourea in the diluted solution of the GQDs aqueous dispersion obtained in step (1), and then stir magnetically until uniform. The stirring speed is 1000r / min and the stirring time is 30 minutes to obtain a mixed solution.

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

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

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

[0084] Comparative Example 1

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

[0086] (1) Preparation of precursor solution: Dissolve 0.308g Cd(NO3)2·4H2O and 2.28g thiourea in 60mL of water, then stir magnetically until homogeneous. The stirring speed is 1000r / min and the stirring time is 30 minutes to obtain a mixed solution.

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

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

[0089] The difference from Example 1 is that GQDs are not added.

[0090] Figure 1 Experimental procedure flowchart for preparing CdS / GQDs composite materials

[0091] Figure 2 In 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 bulk with a lattice spacing of 0.335 nm, corresponding to the {111} crystal plane of cubic CdS. Figures b (1 μm) and c (500 nm) are SEM images of the CdS / GQDs composite photocatalyst prepared in Example 1. The CdS / GQDs composite formed by doping with GQDs presents as uniformly dispersed nanospheres. The nanospheres are formed by the ordered self-assembly of hexagonal prisms, which are formed by the stacking of hexagonal nanosheets.

[0092] Figure 3 Figure a shows the visible light mercury removal efficiency of composite materials with different GQDs contents prepared in Examples 1, 2, and Comparative Example 1. Without GQDs, the visible light mercury removal efficiency of pure CdS is 53.8%. When 2 mL of GQDs is added, the photocatalytic performance of the composite material reaches its highest level of 95.82%. Further increasing the GQDs doping amount to 4 mL reduces the mercury removal efficiency to 76.51%. Adding an appropriate amount of graphene quantum dots enables the visible light photocatalytic oxidation of Hg by CdS. 0While efficiency is improved, excessive doping will negatively impact the excellent photocatalytic performance of the composite material. Figure b shows the visible light mercury removal efficiency of the photocatalysts prepared at different hydrothermal temperatures in Examples 1, 3, and 4. The composite material prepared at a hydrothermal temperature of 200℃ exhibits the highest photocatalytic mercury removal efficiency of 95.82%. Photocatalysts prepared at excessively low or high hydrothermal temperatures show a decrease in photocatalytic performance. Figure c shows the visible light catalytic 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 shows the best mercury removal efficiency, reaching 95.82%. Excessively high or low hydrothermal temperatures are not conducive to the visible light catalytic oxidation of Hg. 0 The optimal material.

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

[0094] Figure 5 In the figure, Figure a shows the UV-Vis diffuse reflectance spectra of CdS / GQDs prepared in Example 1 and CdS prepared in Comparative Example 1; Figure b shows the corresponding two-photon energies (eV). 2 As shown in the figures, both figures demonstrate that both materials have the ability to respond to visible light. The CdS-G2 photocatalytic composite material formed after doping with GQDs exhibits a red shift in the absorption wavelength of light, thus improving its ability to respond to visible light.

[0095] Figure 6 In the figure, Figure a shows the photocurrent density of the CdS / GQDs composite photocatalyst prepared in Example 1. The photocurrent intensity of CdS-GQDs is much higher than that of CdS, about 8 times that of pure CdS in Comparative Example 1. Figure b shows its corresponding photoluminescence spectrum. After doping with GQDs, the luminescence intensity of CdS drops significantly, indicating that its nano-hybrid structure effectively suppresses photogenerated electron-hole recombination. Figure c shows the electrochemical impedance spectroscopy of the composite material. The radius of the arc of CdS-GQDs is smaller than that of CdS. Doping with GQDs reduces impedance and improves carrier separation rate.

[0096] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those 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 invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Application of a CdS / GQDs composite photocatalyst with visible light response in removal of elemental mercury in flue gas, characterized in that, The preparation method of the CdS / GQDs composite photocatalyst with visible light response comprises the following steps: (1) Preparation of a dilution of a GQDs aqueous dispersion: GQDs aqueous dispersion is added to deionized water, and stirred to obtain a dilution of the GQDs aqueous dispersion; (2) Preparation of a precursor solution: Cd(NO3)2.4H2O and thiourea are dissolved in the dilution of the GQDs aqueous dispersion obtained in step (1), and then stirred 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 then placed in an oven for hydrothermal reaction; (4) Sample post-processing: the hydrothermal reaction kettle is naturally cooled to room temperature, the reaction product is taken out and washed with anhydrous ethanol and deionized water for multiple times, centrifugal separation is performed to obtain a solid sample, the solid sample is placed in an oven for drying, and the CdS / GQDs composite photocatalyst is obtained. In step (2), the molar ratio of Cd(NO3)2.4H2O, thiourea and GQDs in step (1) is 1:30:(0.002-0.004).

2. The use of the CdS / GQDs composite photocatalyst with visible light response for removing elemental mercury in flue gas 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 use of the CdS / GQDs composite photocatalyst with visible light response for removing elemental mercury in flue gas according to claim 1, characterized in that, In step (1), the volume ratio of the GQDs aqueous dispersion to deionized water is (2-4):

60.

4. The use of the CdS / GQDs composite photocatalyst with visible light response for removing elemental mercury in flue gas 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 use of the CdS / GQDs composite photocatalyst with visible light response according to claim 1 for removing elemental mercury in flue gas, characterized in that, In step (2), the stirring speed is 1000 r / min, and the stirring time is 30 minutes.

6. The use of a CdS / GQDs composite photocatalyst with visible light response for removing elemental mercury in flue gas according to claim 1, characterized in that, In step (3), the hydrothermal reaction temperature is 180-220 DEG C, and the hydrothermal reaction time is 3-8 h.

7. The use of the CdS / GQDs composite photocatalyst with visible light response according to claim 1 for removing elemental mercury in flue gas, characterized in that, In step (4), the centrifugal speed is 8000 r / min, the centrifugal time is 3 min, the drying temperature is 80 DEG C, and the drying time is 12 hours.

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