Cu-CdS-NRs photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalysts, in particular to a Cu-CdS-NRs photocatalyst as well as a preparation method and application thereof. A preparation method of a Cu-CdS-NRs photocatalyst comprises the following steps: S1, mixing and stirring cadmium chloride, water, copper nitrate and sodium diethyldithiocarbamate according to a certain ratio, standing, collecting white precipitate, washing and drying to obtain a brown precursor; s2, the precursor is dissolved in ethylenediamine for a hydrothermal reaction, centrifugal washing and drying are carried out, and the Cu-CdS-NRs photocatalyst is obtained. The Cu-CdS-NRs photocatalyst is used for selectively reducing and substituting nitrobenzene through photocatalysis, has high catalytic efficiency and has high selectivity on a corresponding product.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, and in particular to a Cu-CdS-NRs photocatalyst, its preparation method, and its application. Background Technology

[0002] The selective reduction of nitrobenzene to the corresponding aniline compounds is a crucial reaction in the synthesis of fine chemicals, pharmaceuticals, and pesticides. Aniline, as a key chemical intermediate, is widely used in the production of polyurethanes, rubber additives, dyes, and pharmaceuticals.

[0003] Currently, research on photocatalysts for the selective reduction of nitrobenzene mainly focuses on the following categories: Noble metal-based catalysts include semiconductor materials supported on gold (Au), palladium (Pd), and platinum (Pt), such as TiO2. These catalysts exhibit good activity and selectivity for aniline under specific conditions. However, the scarcity and high cost of noble metals severely limit their large-scale industrial application. Furthermore, noble metal particles are prone to agglomeration or leaching during photocatalytic cycling, leading to catalyst deactivation and unsatisfactory cycle stability.

[0004] Non-precious metal semiconductor catalysts, such as pure-phase TiO2, CdS, and g-C3N4, are relatively inexpensive, but they generally suffer from low visible light utilization efficiency (e.g., TiO2), high photogenerated carrier recombination rates, and weak adsorption and activation capabilities for nitrobenzene, resulting in generally low photocatalytic reduction activity. More importantly, these catalysts lack selectivity control, easily generating various intermediates such as nitrosobenzene and phenylhydroxylamine during the reaction, making it difficult to obtain the target product aniline with high selectivity, and the byproducts may cause catalyst poisoning.

[0005] Modified semiconductor catalysts: Performance is improved by doping the aforementioned semiconductors with metals / non-metals, constructing heterojunctions, or surface modification. For example, constructing heterojunctions (such as TiO2 / g-C3N4) promotes charge separation, or introducing defect sites such as oxygen vacancies enhances reactant adsorption. These improvement strategies enhance activity to some extent, but precise control of selectivity remains a challenge. Meanwhile, the complex preparation process and the structural stability of catalysts under photothermal-chemical environments remain prominent issues. Many modified catalysts experience loss of active components, phase transformation, or surface passivation after continuous cycling, leading to a significant decline in catalytic performance.

[0006] In summary, the common bottleneck faced by existing photocatalytic reduction technologies for nitrobenzene lies in how to develop a photocatalyst that simultaneously possesses excellent visible light response, efficient photogenerated charge separation and transport capabilities, near-specific selectivity for the nitro-to-amino transition, and maintains structural and chemical stability during long-term cyclic use, without the use of expensive precious metals. Currently, few photocatalytic systems have been reported that can effectively balance and resolve these three key issues of activity, selectivity, and stability. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of the prior art by proposing a Cu-CdS-NRs photocatalyst, its preparation method, and its application.

[0008] The first objective of this invention is to provide a method for preparing Cu-CdS-NRs photocatalyst, comprising the following steps: S1. Cadmium chloride, water, copper nitrate, and sodium diethyldithiocarbamate were mixed and stirred in a certain proportion. After standing, the white precipitate was collected, washed, and dried to obtain a brown precursor. S2. The precursor is dissolved in ethylenediamine and subjected to hydrothermal reaction. After centrifugation, washing and drying, the Cu-CdS-NRs photocatalyst is obtained.

[0009] Further, in step S1, the molar ratio of cadmium chloride, copper nitrate, and sodium diethyldithiocarbamate is 1-x:x:2, where x is 0.001 to 0.007.

[0010] Further, in step S1, after washing with deionized water, the product is dried at 50-70 °C for 12-14 h.

[0011] Furthermore, in step S2, the hydrothermal reaction temperature is 160-180 ℃, and the time is 20-24 h.

[0012] Furthermore, in step S2, the mass-to-volume ratio of the precursor to ethylenediamine is 0.7-0.9 g: 40 mL.

[0013] Further, the sample was washed several times by centrifugation with anhydrous ethanol and deionized water, and then dried at 50-70 °C for 12-14 h.

[0014] A second objective of this invention is to provide a Cu-CdS-NRs photocatalyst prepared using the above-described preparation method.

[0015] A third objective of this invention is to provide an application of the Cu-CdS-NRs photocatalyst as described above, which is used for the photocatalytic selective reduction of substituted aromatic nitro compounds to corresponding amines under illumination in an aqueous phase.

[0016] Furthermore, the molar ratio of Cu-CdS-NRs photocatalyst to aromatic nitro compound is 4-6 mg : 5 mmol.

[0017] Furthermore, aromatic nitro compounds are , , , , , One of them.

[0018] The significant advantages of this invention are: (1) The Cu single atoms introduced into Cu-CdS nanorods by the present invention not only enhance the migration efficiency of photogenerated carriers, but also suppress the recombination of photogenerated electrons and holes, effectively prolonging the lifetime of photogenerated carriers; moreover, the introduction of Cu sites also introduces a large number of sulfur vacancies S. V S-shaped band gaps will form accordingly. V Impurity energy levels, as intermediate energy levels between the valence band and conduction band, participate in the migration process of photogenerated carriers and promote the separation of electron-hole pairs.

[0019] (2) The present invention uses Cu-CdS-NRs photocatalyst for photocatalytic selective reduction of substituted nitrobenzene, which has high catalytic efficiency and high selectivity for the corresponding product.

[0020] (3) It is simple to prepare. It uses light energy as the driving energy and water as the solvent to replace the selective reduction of nitrobenzene, which is conducive to the sustainable development of environment and energy.

[0021] (4) Cu-CdS-NRs photocatalysts have high photocatalytic activity and selectivity, good cycle performance, low production cost, simple production process, can be prepared macroscopically, are environmentally friendly and easy to recycle. Attached Figure Description

[0022] Figure 1 These are XRD patterns of CdS and a series of Cu-CdS-NRs with different Cu doping concentrations; Figure 2 These are SEM images and mapping images of the Cu-CdS-5 sample; Figure 3 This is a graph showing the photocatalytic hydrogenation activity of the samples prepared in the comparative examples and embodiments; Figure 4 The results are from a cyclic experiment on the selective reduction of p-nitroaniline using Cu-CdS-5. Figure 5 The transient photocurrent response curves, EIS impedance, and PL spectra of CdS-NRs and Cu-CdS-5 are shown. Figure 6Electron spin resonance (EPR) spectra of CdS and Cu-CdS-5; Figure 7 This is a spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of Cu-CdS-5. Detailed Implementation

[0023] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0024] Cadmium chloride (CdCl2), copper nitrate (Cu(NO3)2·3H2O), sodium diethyldithiocarbamate (C5H) 10 The reagents used were NNaS2·3H2O and ethylenediamine (C2H8N2). Deionized water was used in the experiments. The main instruments included a Bruker D8 X-ray powder diffractometer (Bruker GmbH, Germany), a UV-1800PC UV-Vis-NIR spectrophotometer (Shanghai Meipuda Instrument Co., Ltd.), a SU8010 scanning electron microscope (Hitachi, Japan), a transmission electron microscope (Thermo Scientific, USA), and a CHI 760 electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.).

[0025] Example 1 (1) 1.142 g of cadmium chloride (CdCl2) and 0.015 g of copper nitrate (Cu(NO3)2·3H2O), and 2.253 g of sodium diethyldithiocarbamate (C5H) 10 The NNaS2·3H2O was dissolved in 200 mL of deionized water, stirred for 1 min, and then sonicated for 5 min. After standing for 30 min, the white precipitate was collected, washed with deionized water, and dried at 70 °C for 12 h to obtain the brown precursor.

[0026] (2) Dissolve 0.843 g of the precursor in 30 mL of ethylenediamine, stir for 30 min and then sonicate for 5 min. Perform hydrothermal reaction at 180 °C for 24 h, wash several times with anhydrous ethanol and deionized water by centrifugation, and dry at 70 °C for 12 h to obtain a pale yellow Cu-CdS-NRs photocatalyst, denoted as Cu-CdS-1.

[0027] Example 2 1.142 g of cadmium chloride and 0.045 g of copper nitrate were used, and the other processes were the same as in Example 1, to obtain a pale yellow Cu-CdS-NRs photocatalyst, denoted as Cu-CdS-3.

[0028] Example 3 1.142 g of cadmium chloride and 0.075 g of copper nitrate were used, and the other processes were the same as in Example 1, to obtain a pale yellow Cu-CdS-NRs photocatalyst, denoted as Cu-CdS-5.

[0029] Example 4 1.142 g of cadmium chloride and 0.105 g of copper nitrate were used, and the other processes were the same as in Example 1, to obtain a pale yellow Cu-CdS-NRs photocatalyst, denoted as Cu-CdS-7.

[0030] Comparative Example 1 In Example 1, copper nitrate was not added, but everything else was the same as in Example 1, resulting in CdS nanorods.

[0031] Figure 1 The figures show the XRD patterns of CdS and Cu-CdS-NRs samples with different Cu doping levels. From the figures, we can see characteristic peaks at 24.9, 26.5, 28.2, 43.8, and 52.0°, corresponding to the (100), (002), (101), (110), and (112) crystal planes of hexagonal CdS, respectively. The entire Cu-CdS series of samples perfectly matches the hexagonal CdS (JCPDS 06-0314) crystal phase after doping, with no impurity peaks and good crystallinity. With increasing doping concentration, the main diffraction peaks of the samples did not show significant shifts, indicating that this doping scheme did not significantly change the crystal phase of CdS itself.

[0032] Figure 2 These are the SEM images and EDS elemental distribution maps of the Cu-CdS-5 sample. From the images, we can see that Cu-CdS-NRs have a nanorod shape, and we can see the Cu element signal distributed on the nanorod sample, indicating that Cu was successfully incorporated into CdS.

[0033] Figure 7 This is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of Cu-CdS-5 with spherical aberration correction. Due to differences in scattering angle and atomic radius, Cd atoms with larger atomic radii are brighter than Cu and S atoms. Dark spots (marked with red lines) can indeed be seen on the doped Cu-CdS-5 surface. Based on the above inferences, it is believed that Cu replaces Cd lattice sites on CdS, existing in the sample in a single-atom state. Figure 7 a. Intensity distribution map of the highlighted yellow area ( Figure 7 b) Cu single-atom sites can be seen occupying Cd atomic sites, showing smaller lattice fringes. Figure 7 A partial magnification and color transformation can yield... Figure 7c. The figure clearly distinguishes Cd sites (marked by green lines) and Cu substitution sites (marked by yellow lines) by the size of the color blocks, further confirming the above inference.

[0034] The photocatalytic hydrogenation activity test process is as follows: (1) A white LED (λ>420 nm) was used as the excitation source. 50 mL of 10 ppm 4-NA solution was added to the reactor, along with 5 mg of semiconductor photocatalyst. The mixture was sonicated for 5 min to ensure uniform dispersion of the catalyst in the substrate solution. Then, 10 μL of 80% hydrazine hydrate was added as a hole sacrificial agent. The reactor was placed in the reaction system and stirred at a fixed speed for 30 min in the dark to establish the adsorption-desorption equilibrium between the catalyst and the substrate. (2) After the dark reaction is complete, turn on the light source and take 3 mL of solution at fixed intervals. The light source must be turned off when taking samples. (3) The absorbance of the clear solution of the sample is measured by a UV-Vis spectrophotometer.

[0035] Figure 3 The photocatalytic hydrogenation activity of CdS nanorods and Cu-CdS nanorods with different Cu doping amounts under these conditions is shown. It can be seen that the Cu-CdS nanorods exhibit the highest reactivity within 8 minutes of illumination. Furthermore, the Cu-doped Cu-CdS nanorods all demonstrate superior hydrogenation reduction performance compared to pure-phase CdS. The most outstanding example is Cu-CdS-5, which achieves a reduction rate of 97.1% for 4-NA. Meanwhile, the remaining samples with different doping amounts, Cu-CdS-1, Cu-CdS-3, and Cu-CdS-7, achieved reduction rates of 85.5%, 94.7%, and 96.7% respectively within 8 minutes of illumination, while the reduction rate of pure-phase CdS-NRs was only 74.1%.

[0036] We also investigated the stability of the Cu-CdS-NRs samples, and performed cyclic testing on the Cu-CdS-5 sample from Example 3. Figure 4 The results of the medium-cycle experiment show that the Cu-CdS-5 sample in Example 3 has good stability, which lays a foundation for the application of the catalyst.

[0037] The photocatalytic reduction activity of the Cu-CdS-5 catalyst in Example 3 for different aromatic nitro compounds was tested. Add 5 mg of catalyst to 50 mL of an aromatic nitro compound solution with a concentration of 15 ppm, and add 5 μL of 80% hydrazine hydrate as a sacrificial agent. Stir for 30 min in the dark, then irradiate with light at a wavelength >420 nm. Take 3 mL samples of the solution at fixed intervals, with the light source turned off during sampling. Measure the absorbance of the supernatant of the sample solution using a UV-Vis spectrophotometer. The test results are shown in Table 1. As can be seen from Table 1, the catalyst prepared in this invention has certain photocatalytic reduction properties for different aromatic nitro compounds, and all show a certain degree of improvement compared to pure CdS.

[0038]

[0039] Mechanism of photocatalytic reaction Figure 5 The transient photocurrent response curves, EIS impedance, and PL spectra of CdS and Cu-CdS-5 are shown. It can be concluded that the Cu single atoms introduced by doping in Cu-CdS nanorods not only enhance the migration efficiency of photogenerated carriers but also suppress the recombination of photogenerated electrons and holes, effectively extending the lifetime of photogenerated carriers. This is the reason why Cu-CdS-5 exhibits excellent photocatalytic performance.

[0040] Figure 6 The electron spin resonance (EPR) spectra of CdS and Cu-CdS-5 were obtained. It was found that Cu-CdS-5 exhibits S at a g-factor of 2.003. V The symmetrical signal peaks confirmed that the introduction of Cu sites also introduced a large number of sulfur vacancies (S). V S-shaped band gaps will form accordingly. V The impurity energy levels, as intermediate energy levels between the valence band and the conduction band, participate in the migration process of photogenerated carriers and promote the separation of electron-hole pairs. This is another major reason why Cu-CdS-5 has excellent photocatalytic performance.

[0041] For any points not covered above, existing technologies shall apply.

[0042] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a Cu-CdS-NRs photocatalyst, characterized in that, Includes the following steps: S1. Cadmium chloride, water, copper nitrate, and sodium diethyldithiocarbamate were mixed and stirred in a certain proportion. After standing, the white precipitate was collected, washed, and dried to obtain a brown precursor. S2. The precursor is dissolved in ethylenediamine and subjected to hydrothermal reaction. After centrifugation, washing and drying, the Cu-CdS-NRs photocatalyst is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of cadmium chloride, copper nitrate, and sodium diethyldithiocarbamate is 1-x:x:2; where x is 0.001 to 0.

007.

3. The preparation method according to claim 1, characterized in that, In step S1, after washing with deionized water, the product is dried at 50-70 ℃ for 12-14 h.

4. The preparation method according to claim 1, characterized in that, In step S2, the hydrothermal reaction temperature is 160-180 ℃ and the time is 20-24 h.

5. The preparation method according to claim 1, characterized in that, In step S2, the mass-to-volume ratio of the precursor to ethylenediamine is 0.7-0.9 g: 40 mL.

6. The preparation method according to claim 1, characterized in that, Wash several times by centrifugation with anhydrous ethanol and deionized water, and dry at 50-70 ℃ for 12-14 h.

7. A Cu-CdS-NRs photocatalyst prepared by the preparation method according to any one of claims 1-6.

8. The application of the Cu-CdS-NRs photocatalyst as described in claim 7, characterized in that, Cu-CdS-NRs photocatalysts are used in aqueous phases under light irradiation for the photocatalytic selective reduction of substituted aromatic nitro compounds to obtain the corresponding amines.

9. The application as described in claim 8, characterized in that, The molar ratio of Cu-CdS-NRs photocatalyst to aromatic nitro compounds is 4-6 mg : 5 mmol.

10. The application as described in claim 8, characterized in that, Aromatic nitro compounds are , , , , , One of them.

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