A preparation method of S-type indium hydroxide / cadmium sulfide heterostructure based on one-step hydrothermal method and application thereof in catalytic reduction of hexavalent chromium

Abstract

This invention belongs to the field of functional materials preparation, specifically relating to a one-step hydrothermal method for synthesizing S-type indium hydroxide / cadmium sulfide heterostructures and their application in the catalytic reduction of hexavalent chromium. This invention reports for the first time the controllable preparation of highly efficient 3D / 1D heterostructure composite photocatalysts by in-situ growth of In(OH)3 NCs on CdS NWs via a one-step hydrothermal method. This material achieves a synergistic enhancement of Cr(VI) reduction performance and ultra-high structural stability under visible light through an S-type interfacial charge transfer pathway.

Description

Technical Field

[0001] This invention belongs to the field of functional materials preparation, specifically relating to a method for preparing S-type indium hydroxide / cadmium sulfide heterostructures based on a one-step hydrothermal method and its application in the catalytic reduction of hexavalent chromium. Background Technology

[0002] Hexavalent chromium (Cr(VI)) is a heavy metal ion that is widely present in wastewater, mainly originating from industries such as dye production, petroleum refining, electroplating, and leather processing. It is highly toxic to human health and the ecological environment and has attracted widespread global attention.

[0003] Photocatalysis, as a green and sustainable technology, has shown great potential in solving energy and environmental problems, and has therefore attracted increasing attention. A typical photocatalytic process begins with a semiconductor absorbing photons, which excites the generation of photogenerated electron-hole pairs. These photogenerated charges, possessing sufficient redox capabilities, then participate in the target redox reaction. However, research shows that most photogenerated electron-hole pairs recombine and are not fully utilized, a problem that severely limits the practical application of photocatalysis. Therefore, developing photocatalysts with strong visible light absorption and high carrier separation efficiency is crucial for achieving highly efficient photocatalytic reactions.

[0004] Among various semiconductor materials, metal sulfides have been extensively studied in the field of photocatalysis due to their narrow band gaps and high solar energy utilization. Cadmium sulfide (CdS), with its wide light absorption edge and suitable band gap position, is widely used in photocatalytic water splitting and pollutant removal. However, pure cadmium sulfide is easily oxidized by photogenerated holes and suffers from a high recombination rate of photogenerated carriers, leading to self-corrosion and poor photocatalytic performance. Currently, there are no reports on the preparation of heterojunction photocatalysts to significantly improve photocatalytic performance by in-situ growth of three-dimensional materials such as indium hydroxide cubes (In(OH)3NCs) on one-dimensional substrate semiconductor materials such as cadmium sulfide nanowires (CdSNWs) using a one-step hydrothermal method. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing S-type indium hydroxide / cadmium sulfide heterostructures based on a one-step hydrothermal method. This invention employs a one-step hydrothermal method to grow In(OH)3NCs in situ on the surface of CdSNWs, preparing a highly efficient composite photocatalyst with a 3D / 1D heterostructure.

[0006] The present invention further provides the application of the above-mentioned S-type indium hydroxide / cadmium sulfide heterostructure in the catalytic reduction of hexavalent chromium.

[0007] The technical solution adopted by the present invention to achieve the above objectives is as follows: This invention provides a method for preparing S-type indium hydroxide / cadmium sulfide heterostructures based on a one-step hydrothermal method, comprising the following steps: (1) Add cadmium nitrate tetrahydrate and thiourea to ethylenediamine and mix well to obtain a mixture; then react the mixture; after naturally cooling to room temperature, collect the precipitate, wash and dry to obtain CdS NWs; (2) Disperse CdS NWs and InCl3・4H2O in distilled water and stir until homogeneous; slowly pour in indium trichloride aqueous solution into cadmium sulfide nanowire suspension and adjust pH value; react the mixture; collect the precipitate, wash and dry to obtain composite material In(OH)3NCs / CdS NWs.

[0008] Preferably, in step (1), the molar ratio of cadmium nitrate tetrahydrate to thiourea is 1-1.5:2-3; and the ratio of cadmium nitrate tetrahydrate to ethylenediamine is 2-3 g:67.5 mL.

[0009] Preferably, in step (1), the reaction is carried out at 180°C for 24 hours.

[0010] Preferably, in step (2), the mass ratio of CdS NWs to InCl3·4H2O is 15:6; and the pH value is adjusted to 9~10.

[0011] Preferably, in step (2), the reaction is carried out at 120°C for 4 hours.

[0012] The present invention also provides an S-type indium hydroxide / cadmium sulfide heterostructure prepared by the above preparation method.

[0013] Another object of the present invention is to provide the application of the above-mentioned S-type indium hydroxide / cadmium sulfide heterostructure in the photocatalytic reduction of hexavalent chromium.

[0014] The In(OH)3NCs / CdS NWs composite material prepared by this invention exhibits a wide light absorption edge, significantly enhancing its photocatalytic reduction capability of Cr(VI) under visible light. Specifically, the nanowire structure of CdS NWs facilitates the rapid long-distance transport of photogenerated carriers, while the hollow nanocube structure of In(OH)3NCs contributes to improved light utilization through its strong light-trapping effect. In the composite material provided by this invention, after In(OH)3NCs are loaded onto the surface of CdS NWs, the excellent 3D / 1D interface coupling formed in the heterostructure further accelerates the separation of photogenerated carriers, allowing more strongly reducing electrons to transfer from In(OH)3NCs to CdS NWs and participate in the photocatalytic reaction. Thanks to its unique structure and good 3D / 1D interface coupling effect, the optimized In(OH)3NCs / CdS NWs composite material can achieve a photocatalytic reduction efficiency of 100% for Cr(VI) within 20 minutes, which is more than 2.6 times and more than 1.5 times that of pure In(OH)3NCs and pure CdS NWs, respectively. Moreover, the reaction mechanism of the photocatalytic reduction of Cr(VI) by this material conforms to the S-type interface charge transfer pathway.

[0015] The beneficial effects of this invention are as follows: This invention reports for the first time that In(OH)3NCs can be grown in situ on CdS NWs via a one-step hydrothermal method, which can controllably prepare a highly efficient composite photocatalyst with a 3D / 1D heterostructure. This material achieves a synergistic improvement in Cr(VI) reduction performance and ultra-high structural stability under visible light through an S-type interface charge transfer path. Attached Figure Description

[0016] Figure 1 SEM images of the prepared photocatalysts; where (AB) CdS NWs, (C) In(OH)3NCs, and (D) In(OH)3NCs / CdS NWs; Figure 2 The elemental distribution diagram of the In(OH)3NCs / CdS NWs photocatalyst prepared in Example 1; Figure 3 XRD patterns of different catalysts; Figure 4 (A) Bar chart of the photocatalytic reduction performance of Cr(VI) by different materials after 20 minutes of visible light irradiation; (B) Cyclic experiment of photocatalytic reduction of Cr(VI) by In(OH)3 / CdS and CdS catalysts under visible light irradiation; Figure 5(A) Comparison of the photocatalytic reduction performance of In(OH)3 / CdS prepared by one-step hydrothermal method and physically mixed In(OH)3 / CdS after 20 minutes of visible light irradiation; (B) Effect of different scavengers on the photocatalytic reduction efficiency of In(OH)3 / CdS for Cr(VI) (wherein isopropanol IPA scavenges hydroxyl radicals, p-benzoquinone p-BQ scavenges superoxide radicals, and potassium bromate KBrO3 scavenges photogenerated electrons). Detailed Implementation

[0017] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0018] Experimental reagents: Cadmium nitrate tetrahydrate (Cd(NO3)2・4H2O), thiourea (CH4N2S), ethylenediamine (EDA), and anhydrous ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd. (Beijing, China); indium trichloride tetrahydrate (InCl3・4H2O), citric acid (C6H8O7), and potassium bromate (KBrO3) were purchased from Aladdin Reagent Co., Ltd. (Shanghai, China).

[0019] All reagents were of analytical grade and used directly without further purification. Deionized water was used throughout the experiment.

[0020] Example 1 (1) Synthesis of cadmium sulfide nanowires: 2.565 g of cadmium nitrate tetrahydrate and 1.89 g of thiourea were added to 67.5 mL of ethylenediamine and stirred for 30 minutes. The mixture was then transferred to a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and reacted at 180 °C for 24 hours. After the reactor cooled naturally to room temperature, the yellow precipitate was collected, washed with an ethanol-water mixture (volume ratio 1:1), and after multiple high-speed centrifugations, the CdS NWs sample was obtained by freeze drying.

[0021] (2) Preparation of indium hydroxide nanocubes / cadmium sulfide nanowire composites A composite material of indium hydroxide nanocubes / cadmium sulfide nanowires (In(OH)3NCs / CdS NWs) was synthesized by a one-step hydrothermal method.

[0022] The preparation process was as follows: 150 mg of the prepared CdS NWs and 60 mg of InCl3·4H2O were dispersed in 50 mL and 20 mL of distilled water, respectively, and stirred for 30 minutes each; an aqueous solution of indium trichloride was slowly poured into the suspension of cadmium sulfide nanowires, and stirring was continued for 15 minutes. The pH value was adjusted by sodium hydroxide to keep the mixed solution weakly alkaline (pH 9.5); then the mixture was transferred to a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and reacted at 120 °C for 4.0 hours; after the reactor cooled to room temperature, the precipitate was collected, washed with an ethanol-water mixture, and after multiple high-speed centrifugations, it was freeze-dried to obtain the target composite material.

[0023] Scanning electron microscope image of the composite material is shown below. Figure 1 As shown in the figure, CdS nanowires have a nanowire structure with a smooth surface and good diameter uniformity. In(OH)3NCs have a cubic structure with a relatively uniform size distribution. The composite material In(OH)3NCs / CdS nanowires has In(OH)3 cubics loaded on the surface of CdS nanowires.

[0024] The elemental distribution diagram of the prepared In(OH)3NCs / CdS NWs composite material is shown in the figure below. Figure 2 As shown. From Figure 2 It can be seen that the prepared material has a uniform elemental distribution, and the heterojunction can effectively promote the separation and migration of photogenerated carriers, thereby improving the photocatalytic efficiency.

[0025] Figure 3 The XRD spectra of different materials clearly show that CdS NWs, In(OH)3NCs, and In(OH)3NCs / CdS NWs composites have been successfully prepared and have good crystallinity.

[0026] Comparative Example 1 60 mg of InCl3·4H2O was dispersed in 20 mL of distilled water and stirred for 30 minutes. The pH of the indium trichloride aqueous solution was adjusted with sodium hydroxide to keep the mixed solution weakly alkaline (pH 9.5). The solution was then transferred to a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and reacted at 120 °C for 4.0 hours. After the reactor cooled to room temperature, the precipitate was collected, washed with an ethanol-water mixture, and after multiple high-speed centrifugations, it was freeze-dried to obtain In(OH)3NCs.

[0027] Comparative Example 2 Simply mix 150 mg of CdS NWs (prepared in the same way as in Example 1) and In(OH)3NCs (prepared in the same way as in Comparative Example 1, with the amount added being 60 mg of InCl3・4H2O) directly and physically until homogeneous.

[0028] Effect Example For comparison, pure In(OH)3NCs samples were prepared using the same method, without the addition of CdS NWs during the preparation process (comparative example 1).

[0029] (a) Photocatalytic performance test The photocatalytic performance of In(OH)3NCs / CdS NWs composite materials, pure CdS NWs, and pure In(OH)3NCs was evaluated using the reduction reaction of Cr(VI) under visible light as a model.

[0030] The experiment used a 300 W xenon lamp (equipped with a 420 nm cutoff filter) as the visible light source. 10 mg of photocatalyst was accurately weighed and added to 50 mL of a 10 mg / L Cr(VI) aqueous solution (prepared by dissolving potassium dichromate in distilled water). Before illumination, the suspension was magnetically stirred in the dark for 30 minutes to allow the photocatalyst and Cr(VI) to reach adsorption-desorption equilibrium. During the photocatalytic reduction reaction, 600 μL of the suspension was taken from the reaction system at set time intervals, centrifuged at high speed, and the supernatant was collected. The concentration of Cr(VI) in the supernatant was determined using the diphenylcarbazide spectrophotometric method, employing an enzyme-linked immunosorbent assay (ELISA) reader and a UV-Vis spectrophotometer at the maximum absorption wavelength of 540 nm.

[0031] To verify the stability of the prepared catalyst, five cycles of photocatalytic experiments were conducted on the In(OH)3NCs / CdS NWs composite material. After each cycle, the used catalyst was acid-washed to remove chromium-containing precipitates from its surface, and then dried overnight under vacuum at 60°C for use in the next cycle test. Figure 4 As shown in (A): During the photocatalytic reduction of Cr(VI) by different materials after 20 minutes of visible light irradiation, the photocatalytic activity of In(OH)3 alone was low, achieving only about 38% Cr(VI) removal; CdS alone could remove 65% of Cr(VI); while the composite material In(OH)3NCs / CdS NWs prepared in Example 1 could achieve complete removal. Figure 4 As shown in (B), the composite material still maintains good catalytic performance after five cycles of reaction. Single cadmium sulfide exhibits poor photocatalytic stability due to its rapid photogenerated carrier recombination rate or inherent self-corrosion problem.

[0032] To investigate the effect of the heterostructure of the composite material on the photocatalytic reduction of Cr(VI), the catalytic activities of In(OH)3 / CdS prepared by a one-step hydrothermal method and physically mixed In(OH)3 / CdS were compared and investigated. The results are as follows: Figure 5As shown in (A), the In(OH)3 / CdS prepared by a one-step hydrothermal method after 20 minutes of visible light irradiation exhibits superior photocatalytic reduction performance of Cr(VI) compared to physically mixed In(OH)3 / CdS. This is mainly due to the Fermi level difference between cadmium sulfide and indium hydroxide, which generates an electrostatic field at the heterojunction interface after loading. This electric field effectively promotes the separation of photogenerated carriers through an S-type charge transfer path, enabling more strongly reducing electrons to participate in the reduction reaction, thereby significantly improving the photocatalytic activity and stability of the material.

[0033] To investigate the main active species of the composite material in the photocatalytic reduction of Cr(VI), corresponding free radical scavengers were added to the photocatalytic reaction system: isopropanol IPA (1.0 mmol / L) as a hydroxyl radical scavenger, p-benzoquinone p-BQ (1.0 mmol / L) as a superoxide radical scavenger, and potassium bromate KBrO3 (1.0 mmol / L) as a photogenerated electron scavenger. Figure 5 (B) shows the effect of different trapping agents on the photocatalytic reduction performance of the composite material for Cr(VI): after the addition of potassium bromate and p-benzoquinone, the activity of In(OH)3 / CdS in reducing Cr(VI) was significantly reduced, while isopropanol had a smaller effect, indicating that photogenerated electrons and superoxide radicals are the main active species in this photocatalytic reduction process.

Claims

1. A method for preparing S-type indium hydroxide / cadmium sulfide heterostructures based on a one-step hydrothermal synthesis, characterized in that, Includes the following steps: (1) Add cadmium nitrate tetrahydrate and thiourea to ethylenediamine and mix well to obtain a mixture; then react the mixture; after naturally cooling to room temperature, collect the precipitate, wash and dry to obtain CdS NWs; (2) Disperse CdS NWs and InCl3・4H2O in distilled water and stir until homogeneous; slowly pour in indium trichloride aqueous solution into cadmium sulfide nanowire suspension and adjust pH value; react the mixture; collect the precipitate, wash and dry to obtain composite material In(OH)3 NCs / CdS NWs.

2. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of cadmium nitrate tetrahydrate to thiourea is 1-1.5:2-3; the ratio of cadmium nitrate tetrahydrate to ethylenediamine is 2-3g:67.5mL.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the reaction is carried out at 180°C for 24 hours.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (2), the mass ratio of CdS NWs and InCl3·4H2O is 15:6; the pH value is adjusted to 9~10.

5. The preparation method according to claim 1 or 4, characterized in that, In step (2), the reaction is carried out at 120°C for 4 hours.

6. An S-type indium hydroxide / cadmium sulfide heterostructure prepared by the preparation method according to any one of claims 1-5.

7. The application of the S-type indium hydroxide / cadmium sulfide heterostructure as described in claim 6 in the photocatalytic reduction of hexavalent chromium.

Images