English

• 0.   Introduction

  In recent years, environmental pollution has become an urgent problem for all countries because it has restricted sustainable development and endangered the health of humans^[1]. Among them, water pollution including organic dye^[2], heavy metals^[3], and antibiotics^[4-7] has become one of the main factors threatening human race survival. Hence, several common techniques for removing dyes from water have been reported, including adsorption^[8-9], biological degradation^[10-11], electrochemical methods^[12-13], advanced oxidation processes, etc^[14-15]. Photocatalysis is one of the most promising green approaches to degrade organic dyes because of its simplicity, high efficiency, and good reproducibility^[16-18]. Choosing a suitable semiconductor photocatalyst can not only absorb ultraviolet light but also absorb visible light, which will improve the light utilization efficiency and photocatalysis effect^[19-21].

  Up to now, among many semiconductor photocatalysts, CdS has become one of the most attractive photocatalytic materials due to its relatively narrow band gap, suitable conduction and valence band edges, and excellent reactivity^[22]. However, pure CdS nanoparticles have some drawbacks. For example, pure CdS nanoparticles are prone to aggregate during synthesis and catalysis, resulting in a decrease in specific surface area^[23]. In addition, the rapid recombination of photogenerated electron-hole pairs and strong photo-corrosion greatly reduce the photocatalytic activity of CdS and limit its application^[24]. Studies have found that combining cocatalysts such as Pt^[25-26], MoS₂^[27], TiO₂^[28], CdSe^[29] with CdS can effectively improve photocatalytic activity.

  On the other hand, the introduction of magnetic nanoparticles can realize material recovery and reuse through convenient magnetic separation, which not only reduces catalyst loss but also avoids the generation of new waste^[30]. Among many magnetic materials, Fe₃O₄ has attracted broad attention owing to its superior magnetism, low cost, good biocompatibility, and excellent photochemical stability^[31]. Fe₃O₄ has high conductivity and proper band structure, which can effectively hinder the recombination of photogenerated charge carriers^[32]. In addition, Fe₃O₄ acts as a photo-induced electron-trapping site and can generate active species after a series of reactions further improving the photocatalytic activity^[33].

  Motivated by the above concerns, we report a simple approach to prepare CdS/Fe₃O₄ nanocomposites. Compared with pure CdS, the CdS/Fe₃O₄ nanocomposites exhibited a significantly increased photocatalytic activity.

  1.   Experimental

  1.1   Materials

  Tetrahydrate cadmium (Cd(NO)₃·4H₂O), thiourea (CH₄N₂S), ferric chloride hexahydrate (FeCl₃·6H₂O), polyvinyl alcohol (PVA), rhodamine B (RhB), sodium sulfate (Na₂SO₄), ethylene glycol, and absolute ethyl alcohol (C₂H₅OH) were obtained from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). All chemicals were used as received.

  1.2   Preparation of CdS

  3.16 g CH₄N₂S and 4.27 g of Cd(NO)₃·4H₂O were dissolved in 30 mL of ethanol and continuously stirred for complete dissolution. Then, the mixed solution was poured into a 100 mL Teflon reactor and the reaction was carried out at 120 ℃ for 24 h. By centrifugal washing and drying, the obtained yellow solid was denoted as CdS.

  1.3   Synthesis of CdS/Fe₃O₄

  0.25 g CdS, 4.38 g FeCl₃·6H₂O, and 3.24 g polyethylene glycol were poured into 60 mL ethylene glycol solution, which was poured into 100 mL of Teflon reactor and kept at 200 ℃ for 12 h. After centrifugal washing and drying, the black sample was tagged as CdS/Fe₃O₄ (1∶5) according to the mass ratio of 1∶5 of CdS to Fe₃O₄. Using the same method, three sets of samples with different mass ratios (1.2∶5, 2∶5, 3∶5) of CdS to Fe₃O₄ were prepared and marked sequentially as CdS/Fe₃O₄ (1.2∶5), CdS/Fe₃O₄ (2∶5), and CdS/Fe₃O₄ (3∶5).

  1.4   Characterization

  The composition and morphology of the prepared samples were observed by X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250), Raman spectrum (Invia, Renishaw) with a laser of the wavelength of 514 nm), transmission electron microscopy (TEM, JEM-2100, JEOL, 20 kV), field emission-scanning electron microscopy (FE-SEM, Merlin Compact, Zeiss) and energy-dispersive spectrometer (EDS, Aztec X-max 50, Oxford). The phase composition was tested by X-ray diffraction (XRD, Ultima-Ⅳ, Rigaku), using a Cu Kα source (λ=0.151 4 nm) at 40 kV with a working current of 40 mA and a scan rate of 10 (°)·min^-1. The absorption spectrum of the samples was recorded by Hitachi UV-3010 UV-visible spectrophotometer. Photochemical experiment results were recorded by the electrochemical system (CHI600E, China).

  1.5   Photocatalytic activity measurements

  To evaluate the efficiency of degrading RhB (0.02 g·L^-1), photocatalytic measurements were carried out. The whole measurement was carried out under simulated visible irradiation by a 300 W xenon lamp equipped with an optical filter (λ≥400 nm). During visible-light photocatalytic experiments, 100 mg of catalyst was dispersed in a 100 mL aqueous solution of degrading RhB (0.02 g·L^-1). The resulting solution was further stirred for 30 min under dark conditions to ensure adsorption-desorption equilibrium between the organic dye and the catalyst. Aliquots (5 mL) of the suspension were taken out at an interval of 10 min and centrifuged. To ensure that the degradation of the dye was solely driven by a photocatalytic process, control experiments were carried out in the absence of catalyst conditions. The photodegradation efficiency was optimized by the decrease in intensity of the characteristic absorbance of RhB (552 nm) using a UV3900-Vis spectrophotometer. After the above test was completed, the catalyst will be recovered and reused in a new RhB solution for a second cycle test. Five cycles of photocatalysis were performed using the same operation, each cycle lasting 90 min.

  1.6   Photoelectrochemical measurement

  The photocurrent measurements were conducted on a CHI600E electrochemical workstation using a three-electrode cell with a saturated calomel electrode (SCE) as the reference electrode, and a Pt wire as the auxiliary electrode. The working electrode was made as follows: 1 mg of photocatalyst and 10 μL (C₂F₄)_n adhesive were dispersed into 0.5 mL of absolute ethanol by ultrasound. The electrodes were made by coating the resulting solution onto the fluorine-doped tin oxide (FTO) glass (1 cm×1 cm). A 300 W xenon lamp equipped with a 400 nm bandpass filter was used as the visible-light lamp. 0.5 mol·L^-1 Na₂SO₄ aqueous solution served as the electrolyte.

  2.   Results and discussion

  2.1   Phase composition analysis

  2.1.1   XRD and Raman analysis

  To investigate the phase and structure of the synthesized materials, XRD was performed. Fig. 1 displays the XRD patterns for pristine Fe₃O₄ and CdS/Fe₃O₄ nanocomposites with different mass ratios. As for the XRD pattern of Fe₃O₄, we can observe the typical diffraction peaks locating at 30.094°, 35.422°, 37.052°, 43.052°, 53.390°, 56.942°, and 62.541°, which can be well indexed to (220), (311), (222), (400), (422), (511), and (440) planes of face-centered cubic structure of Fe₃O₄ (PDF No.26-1136). With the increase of the addition of CdS, all these diffraction peaks were still observed and the intensity of the peaks for Fe₃O₄ was increasingly weak, which indicates that CdS does not change the crystal structure of Fe₃O₄ and the surface of Fe₃O₄ is surrounded by CdS and the growth is inhibited. It can be certified by the Scherrer equation:

  $ L=0.89 \lambda /(\beta \cos \theta) $

  (1)

  Figure 1

  

  Figure 1.  XRD patterns (a) and Raman spectra (b) of the prepared samples

  下载: 全尺寸图片 幻灯片

  where L is the crystallite size, λ is the wavelength of the X-ray radiation (0.154 18 nm), θ is the angle of Bragg diffraction, and β is the full-width at half-maximum (FWHM) of the (311) plane peak. Furthermore, the crystal lattice distortion (Δd/d) can be evaluated from the equation to evaluate the active sites^[34]:

  $ \Delta d / d=\beta /(4 \tan \theta) $

  (2)

  As shown in Table 1, CdS/Fe₃O₄ (2∶5) had the smallest grain size and the largest lattice distortion. Usually, the small crystallite size is favorable for the improvement in surface area, and the higher the specific surface area, the better the photocatalytic reaction. CdS/Fe₃O₄ (2∶5) possessed the best catalytic effect and this conjecture can be proved by the following conclusion^[35]. On the other hand, with increasing CdS content, the diffraction peaks located at 24.870°, 26.506°, 28.182°, 43.681°, 47.839°, and 51.823° indicate the existence of the wurtzite phase CdS (PDF No.47-1179) coated by Fe₃O₄. Based on the above results, showed that CdS and Fe₃O₄ were not simply mechanically mixed but formed into CdS/Fe₃O₄ nanocomposite.

  Table 1

  

  Table 1.  Structural parameters extracted from XRD patterns and photocatalytic results of different nanocomposites

  下载: 导出CSV

  Sample	β / (°)	2θ / (°)	Crystallite size / nm	Δd / d	Degradation rate / %
  Fe3O4	0.166	35.35	49.25	0.146	—
  CdS/Fe3O4 (1∶5)	0.208	35.34	39.30	0.183	86.7
  CdS/Fe3O4 (1.2∶5)	0.250	35.29	37.70	0.190	80.4
  CdS/Fe3O4 (2∶5)	0.225	35.30	36.33	0.228	98.8
  CdS/Fe3O4 (3∶5)	0.172	35.34	47.53	0.151	70.1

  It can be seen from Fig. 1b that CdS had a strong phonon absorption peak of longitudinal optical waves at 276 and 470 cm^-1. However, with the gradual increase of the doping amount of CdS, the phonon absorption peak tended to shift to the direction of high frequency. This may be due to the gradual decrease of Fe₃O₄ on CdS per unit area, which weakens the interaction between the two and leads to the offset of the phonon absorption peak^[36]. In addition, Fe₃O₄ had characteristic peaks of A_1g at 231 cm^-1 and E_1g at 406 and 595 cm^-1, and an obvious longitudinal optical phonon (LO) peak near 1 280 cm^-1. This result is similar to that obtained by Chourpa et al.^[37], and the characteristic absorption peak still tends to shift to a larger frequency direction. In summary, it indicates that CdS/Fe₃O₄ nanocomposites have been successfully prepared, which is consistent with the XRD conclusion.

  2.1.2   XPS analysis

  To further investigate the chemical composition and surface electronic states of the CdS/Fe₃O₄ binary composites, XPS analysis has been carried out. Fig. 2a shows the comparative analysis of XPS data of Cd in CdS and CdS/Fe₃O₄ (2∶5). The peak of Cd3d_3/2 in pure CdS in Fig. 2a was about 411.1 eV and the peak of Cd3d_5/2 was about 404.3 eV, while the peak of Cd3d_3/2 in CdS/Fe₃O₄ composites was about 411.5 eV and the peak of Cd3d_5/2 was about 404.8 eV^[38-39]. Fig. 2b presents the Fe2p XPS spectrum with peaks of Fe2p_1/2 at about 723.7 eV and Fe2p_3/2 at about 710.2 eV in pure Fe₃O₄, whereas the peak of Fe2p_1/2 in CdS/Fe₃O₄ composites was about 723.4 eV and the peak of Fe2p_3/2 was about 709.6 eV^[40-41]. Obviously, for CdS/Fe₃O₄ (2∶5), the peaks of Cd were shifted to the direction of high binding energy, and the peaks of Fe were shifted to the direction of low binding energy, which indicates that the binding energy of the existence of an extremely strong interaction between CdS and Fe₃O₄. Above all, the successful formation of the CdS/Fe₃O₄ binary composites is confirmed.

  Figure 2

  

  Figure 2.  (a) Cd3d and (b) Fe2p XPS spectra of CdS, Fe₃O₄, and CdS/Fe₃O₄ (2∶5)

  下载: 全尺寸图片 幻灯片

  2.2   Morphological analysis

  Fig. 3a-3d correspond to the SEM images of CdS/Fe₃O₄ (1∶5), CdS/Fe₃O₄ (1.2∶5), CdS/Fe₃O₄ (2∶5), and CdS/Fe₃O₄ (3∶5). In the binary composite, Fe₃O₄ was spherical, and CdS covered its surface, forming a binary heterojunction. The change in CdS content does not affect the overall morphology of the composite. Fig. 3e-3h is the element distribution diagram of CdS/Fe₃O₄ (2∶5). Cd, S, Fe, and O were evenly distributed in CdS/Fe₃O₄ (2∶5), indicating that CdS and Fe₃O₄ were well dispersed and well combined. Fig. 3i-3k are the TEM images of CdS/Fe₃O₄ (2∶5). It can be seen that CdS and Fe₃O₄ were closely combined to form heterojunction, which is conducive to the transmission of photogenerated electrons.

  Figure 3

  

  Figure 3.  SEM images of (a) CdS/Fe₃O₄ (1∶5), (b) CdS/Fe₃O₄ (1.2∶5), (c) CdS/Fe₃O₄ (2∶5), and (d) CdS/Fe₃O₄ (3∶5); (e-h) Mapping images and (i-k) TEM images of CdS/Fe₃O₄ (2∶5)

  下载: 全尺寸图片 幻灯片

  2.3   Performance analysis

  According to the analysis of solid UV reflectance spectra of the prepared samples (Fig. 4a), the light absorption capacity of CdS is significantly enhanced in the visible region after the composite with Fe₃O₄, which is conducive to improving its photocatalytic performance. Photocurrent densities of four kinds of CdS/Fe₃O₄ composites are compared in Fig. 4b. Transient photocurrents of four kinds of catalysts showed the following orders: CdS/Fe₃O₄ (2∶5) > CdS/Fe₃O₄ (3∶5) > CdS/Fe₃O₄ (1.2∶5) > CdS/Fe₃O₄ (1∶5).

  Figure 4

  

  Figure 4.  (a) Solid UV reflectance spectra of the prepared samples; (b) Photocurrents of CdS/Fe₃O₄ nanocomposites; (c) Photocatalytic degradation rates of RhB by the prepared samples under visible light irradiation; (d) Effects of cycle times on the degradation rate of RhB by CdS/Fe₃O₄ (2∶5) under visible-light irradiation

  下载: 全尺寸图片 幻灯片

  To compare the photocatalytic property of as-prepared CdS/Fe₃O₄ nanocomposites with different ratios, RhB was selected as a photodegradable substance under visible light irradiation. From Fig. 4c, it can be seen that in the photodegradation of RhB, pure CdS and pure Fe₃O₄ as catalysts were much weaker than CdS/Fe₃O₄ nanocomposites. Meanwhile, CdS/Fe₃O₄ nanocomposites showed excellent degradation rates of 86.7%, 80.4%, 98.8%, and 70.1% in the order of legend. When the loading mass ratio of CdS was 2∶5, the CdS/Fe₃O₄ performed the highest photocatalytic activity, and more CdS or less CdS will result in the descent of the activity. The reason may be that overfull CdS can also be the recombination centers of photoinduced charges rather than the electron acceptors^[42]. In addition, CdS/Fe₃O₄ nanocomposites had better photocatalytic performance than other sulfide composites and oxide composites for example, MoS₂/Fe₃O₄^[33], CdS/TiO₂^[43] and so on. It displays that CdS/Fe₃O₄ nanocomposites have superior photocatalytic activity.

  The stability of the as-prepared composite photocatalyst is an important consideration for their practical application. Five-cycle experiments were conducted to investigate the stability of CdS/Fe₃O₄ (2∶5) nanocomposite. The degradation rate of CdS/Fe₃O₄ (2∶5) for RhB decreased slightly from 98.8% to 96.2% (Fig. 4d) after being reused five times, indicating that the CdS/Fe₃O₄ (2∶5) possessed excellent recyclability and chemical stability under visible light irradiation.

  2.4   Photocatalytic mechanism analysis

  According to Mott-Schottky curves, it could be seen that the conduction band (CB) position of CdS and Fe₃O₄ were -0.75 and -2.59 eV (Fig. 5a, 5b). As shown in Fig. 5c, the band gap widths of CdS and Fe₃O₄ were 2.30 and 1.90 eV respectively. The valence band (VB) and CB positions of Fe₃O₄ were lower than CdS (Fig. 5d)^[44]. Therefore, during illumination, a built-in electric field (BEF) was formed ranging from Fe₃O₄ to CdS, the hole of Fe₃O₄ and the electrons of CdS would compound between the BEF, which changed the moving path of electrons and holes, reduced the recombination of electrons and holes, reduced the degree of photo corrosion of cadmium sulfide and improved the photocatalytic efficiency of the CdS/Fe₃O₄ composites. The electrons of Fe₃O₄ could react with O₂ adsorbed on CdS/Fe₃O₄ to generate superoxide radicals (·O₂^-), and the holes (h⁺) on CdS could also react with H₂O to form ·OH. Finally, both ·O₂^- and ·OH could react with RhB to become CO₂ and H₂O^[45].

  Figure 5

  

  Figure 5.  Mott-Schottky curves of (a) CdS and (b) Fe₃O₄; (c) (αhν)² vs hν plots of CdS and Fe₃O₄; (d) Schematic photocatalytic mechanism of CdS/Fe₃O₄

  下载: 全尺寸图片 幻灯片

  3.   Conclusions

  Four kinds of CdS/Fe₃O₄ core-shell nanocomposites were successfully synthesized by a simple hydrothermal method. When CdS/Fe₃O₄ nanocomposites were exposed to visible light, the electrons generated by CdS in CdS/Fe₃O₄ nanocomposites were transferred to the Fe₃O₄ surface, which reduced the recombination probability of photogenerated electrons and holes, improved the photocatalytic performance of CdS and increased the stability of CdS/Fe₃O₄ photocatalysts. Under visible light irradiation, after five cycles of testing, the degradation rate of RhB decreased from 98.8% to 96.2%, which proved that CdS/Fe₃O₄ photocatalysts had good photocatalytic stability. Fe₃O₄ nanoparticles in the composite were magnetic, which made CdS/Fe₃O₄ nanocomposites easy to recover and recycle. In conclusion, CdS/Fe₃O₄ photocatalysts have broad application prospects in sewage treatment, which also provides a new theoretical basis for the treatment of organic pollutants in wastewater.

  
  
• 1. [1]

     Escher B I, Stapleton H M, Schymanski E L. Tracking complex mixtures of chemicals in our changing environment[J]. Science, 2020, 367(6476):  388-392. doi: 10.1126/science.aay6636

  2. [2]

     Miao Q Y, Wang Y, Chen D R, Cao N, Pang J H. Development of novel ionic covalent organic frameworks composite nanofiltration membranes for dye/salt separation[J]. J. Hazard. Mater., 2023, 465:  133049.

  3. [3]

     Yin H F, Yuan C Y, Lv H J, Chen X, Zhang K Y, Zhang Y Z. Construction of 0D/2D CeO₂/CdS direct Z-scheme heterostructures for effective photocatalytic H₂ evolution and Cr(Ⅵ) reduction[J]. Sep. Purif. Technol., 2022, 295:  121294. doi: 10.1016/j.seppur.2022.121294

  4. [4]

     Yin H F, Yuan C Y, Lv H J, Zhang K Y, Chen X, Zhang Y Z. Hierarchical Ti₃C₂ MXene/Zn₃In₂S₆ Schottky junction for efficient visible-light-driven Cr(Ⅵ) photoreduction[J]. Ceram. Int., 2022, 48(8):  11320-11329. doi: 10.1016/j.ceramint.2021.12.355

  5. [5]

     Zhang M, Arif M, Dong Y Y, Chen X B, Liu X H. Z-scheme TiO_2-x@ZnIn₂S₄ architectures with oxygen vacancies-mediated electron transfer for enhanced catalytic activity towards degradation of persistent antibiotics[J]. Colloids Surf. A Physicochem. Eng. Asp., 2022, 649(222):  129530.

  6. [6]

     Yang H, Zhao Z C, Yang Y P, Zhang Z, Chen W, Yan R Q, Jin Y X, Zhang J. Defective WO₃ nanoplates controllably decorated with MIL-101(Fe) nanoparticles to efficiently remove tetracycline hydrochloride by S-scheme mechanism[J]. Sep. Purif. Technol., 2022, 300:  121846. doi: 10.1016/j.seppur.2022.121846

  7. [7]

     Zhang K J, Gu S W, Wu Y, Fan Q W, Zhu C. Preparation of pyramidal SnO/CeO₂ nano-heterojunctions with enhanced photocatalytic activity for degradation of tetracycline[J]. Nanotechnology, 2020, 31(21):  215702. doi: 10.1088/1361-6528/ab73b4

  8. [8]

     Dong Z, Wang Y, Wen D, Peng J, Zhao L, Zhai M L. Recent progress in environmental applications of functional adsorbent prepared by radiation techniques: A review[J]. J. Hazard. Mater., 2022, 424:  126887. doi: 10.1016/j.jhazmat.2021.126887

  9. [9]

     Fang M M, Shao J X, Huang X G, Wang J Y, Chen W. Direct Z-scheme CdFe₂O₄/g-C₃N₄ hybrid photocatalysts for highly efficient ceftiofur sodium photodegradation[J]. J. Mater. Sci. Technol., 2020, 56:  133-142. doi: 10.1016/j.jmst.2020.01.054

  10. [10]

      Mustafa G, Zahid M T, Kurade M B, Alvi A, Ullah F, Yadav N, Park H K, Khan M A, Jeon B H. Microalgal and activated sludge processing for biodegradation of textile dyes[J]. Environ. Pollut., 2024, 349:  123902. doi: 10.1016/j.envpol.2024.123902

  11. [11]

      Baldisserri C, Ortelli S, Blosi M, Costa A L. Pilot-plant study for the photocatalytic/electrochemical degradation of rhodamine B[J]. J. Environ. Chem. Eng., 2018, 6(2):  1794-1804. doi: 10.1016/j.jece.2018.02.008

  12. [12]

      Xu T, Fu L Y, Lu H Y, Zhang M Y, Wang W L, Hu B N, Zhou Y H, Yu G. Electrochemical oxidation degradation of rhodamine B dye on boron-doped diamond electrode: Input mode of power attenuation[J]. J. Clean. Prod., 2023, 401:  136794. doi: 10.1016/j.jclepro.2023.136794

  13. [13]

      Zhao X, Hu G Z, Tan F, Zhang S S, Wang X Z, Hu X, Kuklin A V, Baryshnikov G V, Ågren H, Zhou X H, Zhang H B. Copper confined in vesicle-like BCN cavities promotes electrochemical reduction of nitrate to ammonia in water[J]. J. Mater. Chem. A, 2021, 9(41):  23675-23686. doi: 10.1039/D1TA05718A

  14. [14]

      Hang Z S, Yu H L, Luo L P, Huai X. Nanoporous g-C₃N₄/MOF: High-performance photoinitiator for UV-curable coating[J]. J. Mater. Sci., 2019, 54(22):  13959-13972. doi: 10.1007/s10853-019-03896-9

  15. [15]

      Chen W, Chang L, Ren S B, He Z C, Huang G B, Liu X H. Direct Z-scheme 1D/2D WO_2.72/ZnIn₂S₄ hybrid photocatalysts with highly-efficient visible-light-driven photodegradation towards tetracycline hydrochloride removal[J]. J. Hazard. Mater., 2020, 384:  121308. doi: 10.1016/j.jhazmat.2019.121308

  16. [16]

      Li R, Qiu L P, Cao S Z, Li Z, Gao S L, Zhang J, Ramakrishna S, Long Y Z. Research advances in magnetic field-assisted photocatalysis[J]. Adv. Funct. Mater., 2024, 3:  2316725.

  17. [17]

      Fang M M, Shao J X, Huang X G, Wang J Y, Chen W. Direct Z-scheme CdFe₂O₄/g-C₃N₄ hybrid photocatalysts for highly efficient ceftiofur sodium photodegradation[J]. J. Mater. Sci. Technol., 2020, 56:  133-142. doi: 10.1016/j.jmst.2020.01.054

  18. [18]

      Zhu Q H, Zhang K, Li D Q, Li N, Xu J K, Bahnemann D W, Wang C Y. Polarization-enhanced photocatalytic activity in non-centrosymmetric materials based photocatalysis: A review[J]. Chem. Eng. J., 2021, 426:  131681. doi: 10.1016/j.cej.2021.131681

  19. [19]

      Li Y X, Li S Q, Meng L H, Peng S Q. Synthesis of oriented J type ZnIn₂S₄@CdIn₂S₄ heterojunction by controllable cation exchange for enhancing photocatalytic hydrogen evolution[J]. J. Colloid Interface Sci., 2023, 650:  266-274. doi: 10.1016/j.jcis.2023.06.185

  20. [20]

      Li Y X, Han P, Hou Y L, Pleng S Q, Kuang X J. Oriented Zn_mIn₂S_m+3@In₂S₃ heterojunction with hierarchical structure for efficient photocatalytic hydrogen evolution[J]. Appl. Catal. B-Environ., 2018, 244:  604-611.

  21. [21]

      Li Y X, Hou Y L, Fu Q Y, Peng S Q, Hu Y H. Oriented growth of ZnIn₂S₄/In(OH)₃ heterojunction by a facile hydrothermal transformation for efficient photocatalytic H₂ production[J]. Appl. Catal. B-Environ., 2017, 206:  726-733. doi: 10.1016/j.apcatb.2017.01.062

  22. [22]

      Meng X Y, Wang S Y, Zhang C C, Dong C Z, Li R, Li B, Wang Q, Ding Y. Boosting hydrogen evolution performance of a CdS-based photocatalyst: In situ transition from type Ⅰ to type Ⅱ heterojunction during photocatalysis[J]. ACS Catal., 2022, 12(16):  10115-10126. doi: 10.1021/acscatal.2c01877

  23. [23]

      Lv J X, Zhang Z M, Wang J, Lu X L, Zhang W, Lu T B. In situ synthesis of CdS/graphdiyne heterojunction for enhanced photocatalytic activity of hydrogen production[J]. ACS Appl. Mater. Interfaces, 2018, 11(3):  2655-2661.

  24. [24]

      Li C H, Wang H M, Naghadeh S B, Zhang J Z, Fang P F. Visible light driven hydrogen evolution by photocatalytic reforming of lignin and lactic acid using one-dimensional NiS/CdS nanostructures[J]. Appl. Catal. B-Environ., 2018, 227:  229-239. doi: 10.1016/j.apcatb.2018.01.038

  25. [25]

      Li X H, Su Z Q, Jiang H Q, Liu J Q, Zheng L X, Zheng H J, Wu S T, Shi X W. Band structure tuning via Pt single atom induced rapid hydroxyl radical generation toward efficient photocatalytic reforming of lignocellulose into H₂[J]. Small, 2024, :  2400617.

  26. [26]

      Xiang X L, Zhang L Y, Luo C, Zhang J J, Cheng B, Liang G J, Zhang Z Y, Yu J G. Ultrafast electron transfer from CdS quantum dots to atomically-dispersed Pt for enhanced H₂ evolution and value-added chemical synthesis[J]. Appl. Catal. B-Environ., 2024, 340:  123196. doi: 10.1016/j.apcatb.2023.123196

  27. [27]

      Mou Z, Xu J L, Meng T T, Wang X P, Gao R X, Guo J J, Gu S W, Zhou Z P, Meng W, Zhang K J. Carbon nanotubes as electron mediators for CNTs/CdS/MoS₂ high efficient photodegradation of tetracycline under visible light[J]. J. Alloy. Compd., 2023, 967:  171699. doi: 10.1016/j.jallcom.2023.171699

  28. [28]

      Li N X, Huang H L, Bibi R, Shen Q H, Ngulube R, Zhou J C, Liu M C. Noble-metal-free MOF derived hollow CdS/TiO₂ decorated with NiS cocatalyst for efficient photocatalytic hydrogen evolution[J]. Appl. Surf. Sci., 2019, 476:  378-386. doi: 10.1016/j.apsusc.2019.01.105

  29. [29]

      Marder A A, Cassidy J, Harankahage D, Beavon J, Gutiérrez-Arzaluz L, Mohammed O F, Mishra A, Adams A C, Slinker J D, Hu Z J, Savoy S, Zamkov M, Malko A V. CdS/CdSe/CdS spherical quantum wells with near-unity biexciton quantum yield for light-emitting-device applications[J]. ACS Mater. Lett., 2023, 5(5):  1411-1419. doi: 10.1021/acsmaterialslett.3c00110

  30. [30]

      Lie J S, Luo F L, Liu Y F, Yang Y X, Nie Q L, Chen X C, You R Y, Liu Y Z, Xiao X F, Lu Y D. Recyclable magnetic nanoparticles combined with TiO₂ enrichment and "off" to "on" SERS assay for sensitive detection of alkaline phosphatase[J]. Chem. Eng. J., 2024, 479:  147241. doi: 10.1016/j.cej.2023.147241

  31. [31]

      徐艳, 杨宏国, 牛慧斌, 田海林, 朴红光, 黄应平, 方艳芬. 磁性纳米颗粒Fe₃O₄的醇改性制备机理及应用[J]. 高等学校化学学报, 2021,42,(8): 2564-2573. XU Y, YANG H G, NIU H B, TIAN H L, PIAO H G, HUANG Y P, FANG Y F. Preparation mechanism and application of alcohol-modified Fe₃O₄ magnetic nanoparticles[J]. Chem. J. Chinese Universities, 2021, 42(8):  2564-2573.

  32. [32]

      Peng Q, Ma M, Chen S, Shi Y Q, He H W, Wang X. Magnetic-conductive bi-gradient structure design of CP/PGFF/Fe₃O₄ composites for highly absorbed EMI shielding and balanced mechanical strength[J]. J. Mater. Sci. Technol., 2023, 133:  102-110. doi: 10.1016/j.jmst.2022.05.057

  33. [33]

      Alexpandi R, Abirami G, Murugesan B, Durgadevi R, Swasthikka R P, Cai Y R, Ragupathi T, Ravi A V. Tocopherol-assisted magnetic Ag-Fe₃O₄-TiO₂ nanocomposite for photocatalytic bacterial-inactivation with elucidation of mechanism and its hazardous level assessment with zebrafish model[J]. J. Hazard. Mater., 2023, 442:  130044. doi: 10.1016/j.jhazmat.2022.130044

  34. [34]

      Zhao Y Y, Tang Q W, He B L, Yang P Z. Mo incorporated W₁₈O₄₉ nanofibers as robust electrocatalysts for high-efficiency hydrogen evolution[J]. Int. J. Hydrog. Energy, 2017, 42(21):  14534-14546. doi: 10.1016/j.ijhydene.2017.04.115

  35. [35]

      Zhu B L, Lin B Z, Zhou Y, Sun P, Yao Q R, Chen Y L, Gao B F. Enhanced photocatalytic H₂ evolution on ZnS loaded with graphene and MoS₂ nanosheets as cocatalysts[J]. J. Mater. Chem. A, 2014, 2(11):  3819-3827. doi: 10.1039/C3TA14819J

  36. [36]

      Lebedev A I, Saidzhonov B M, Drozdov K A, Khomich A A, Vasiliev R B. Raman and infrared studies of CdSe/CdS core/shell nanoplatelets[J]. J. Phys. Chem. C, 2021, 125(12):  6758-6766. doi: 10.1021/acs.jpcc.0c10529

  37. [37]

      Chourpa I, Douziech-Eyrolles L, Ngaboni-Okassa L, Fouquenet J F, Cohen-Jonathan S, Souce M, Marchais H, Dubois P. Molecular composition of iron oxide nanoparticles, precursors for magnetic drug targeting, as characterized by confocal Raman microspectroscopy[J]. Analyst, 2005, 130(10):  1395. doi: 10.1039/b419004a

  38. [38]

      Feng L P, Wang J H, Zhang L X, Li J D, Zhang Y F, Xu M H, Tang P S, Wang H. Construction of direct Z-scheme Co₉S₈/CdS with tubular heterostructure through the simultaneous immobilization and in-situ reduction strategy for enhanced photocatalytic Cr(Ⅵ) reduction under visible light[J]. J. Colloid Interface Sci., 2024, 675:  535-548. doi: 10.1016/j.jcis.2024.07.030

  39. [39]

      Duan F, Sheng J L, Shi S H, Li Y J, Liu W H, Lu S L, Zhu H, Du M L, Chen X, Wang J. Protonated Z-scheme CdS-covalent organic framework heterojunction with highly efficient photocatalytic hydrogen evolution[J]. J. Colloid Interface Sci., 2024, 675:  620-629. doi: 10.1016/j.jcis.2024.07.051

  40. [40]

      Hu T, Liu N B, Bu H T, Hu J H, Zhu Q S, Tang S P, Li Y T, Wang J J, Jiang B G. Self-separating core-shell spheres with a carboxymethyl chitosan/acrylic acid/Fe₃O₄ composite core for soil Cd removal[J]. Carbohydr. Polym., 2024, 343:  122428. doi: 10.1016/j.carbpol.2024.122428

  41. [41]

      Cui T, Chi J Q, Liu K, Zhu J W, Guo L L, Mao H M, Liu X B, Lai J P, Guo H L, Wang L. Manipulating the electron redistribution of Fe₃O₄ for anion exchange membrane based alkaline seawater electrolysis[J]. Appl. Catal. B-Environ., 2024, 357:  124269. doi: 10.1016/j.apcatb.2024.124269

  42. [42]

      Li S Q, Peng S Q, Li Y X. Constructing an open-structured J-type ZnIn₂S₄/In(OH)₃ heterojunction for photocatalytical hydrogen generation[J]. J. Phys. Chem. Lett., 2024, 15(19):  5215-5222. doi: 10.1021/acs.jpclett.4c00835

  43. [43]

      Gao H Z, Wang H G, Jin Y L, Lv J, Xu G Q, Wang D M, Zhang X Y, Chen Z, Zheng Z X, Wu Y C. Controllable fabrication of immobilized ternary CdS/Pt-TiO₂ heteronanostructures toward high-performance visible-light driven photocatalysis[J]. Phys. Chem. Chem. Phys., 2015, 17(27):  17755-17761. doi: 10.1039/C5CP01128K

  44. [44]

      Zhu Z, Huo P W, Lu Z Y, Yan Y S, Liu Z, Shi W D, Li C X, Dong H J. Fabrication of magnetically recoverable photocatalysts using g-C₃N₄ for effective separation of charge carriers through like-Z-scheme mechanism with Fe₃O₄ mediator[J]. Chem. Eng. J., 2018, 331:  615-625. doi: 10.1016/j.cej.2017.08.131

  45. [45]

      Cheng L, Xiang Q J, Liao Y L, Zhang H W. CdS-based photocatalysts[J]. Energy Environ. Sci., 2018, 11(6):  1362-1391. doi: 10.1039/C7EE03640J

• 

  Figure 1  XRD patterns (a) and Raman spectra (b) of the prepared samples

  下载: 全尺寸图片 幻灯片
  

  Figure 2  (a) Cd3d and (b) Fe2p XPS spectra of CdS, Fe₃O₄, and CdS/Fe₃O₄ (2∶5)

  下载: 全尺寸图片 幻灯片
  

  Figure 3  SEM images of (a) CdS/Fe₃O₄ (1∶5), (b) CdS/Fe₃O₄ (1.2∶5), (c) CdS/Fe₃O₄ (2∶5), and (d) CdS/Fe₃O₄ (3∶5); (e-h) Mapping images and (i-k) TEM images of CdS/Fe₃O₄ (2∶5)

  下载: 全尺寸图片 幻灯片
  

  Figure 4  (a) Solid UV reflectance spectra of the prepared samples; (b) Photocurrents of CdS/Fe₃O₄ nanocomposites; (c) Photocatalytic degradation rates of RhB by the prepared samples under visible light irradiation; (d) Effects of cycle times on the degradation rate of RhB by CdS/Fe₃O₄ (2∶5) under visible-light irradiation

  下载: 全尺寸图片 幻灯片
  

  Figure 5  Mott-Schottky curves of (a) CdS and (b) Fe₃O₄; (c) (αhν)² vs hν plots of CdS and Fe₃O₄; (d) Schematic photocatalytic mechanism of CdS/Fe₃O₄

  下载: 全尺寸图片 幻灯片

  Table 1.  Structural parameters extracted from XRD patterns and photocatalytic results of different nanocomposites

  Sample	β / (°)	2θ / (°)	Crystallite size / nm	Δd / d	Degradation rate / %
  Fe3O4	0.166	35.35	49.25	0.146	—
  CdS/Fe3O4 (1∶5)	0.208	35.34	39.30	0.183	86.7
  CdS/Fe3O4 (1.2∶5)	0.250	35.29	37.70	0.190	80.4
  CdS/Fe3O4 (2∶5)	0.225	35.30	36.33	0.228	98.8
  CdS/Fe3O4 (3∶5)	0.172	35.34	47.53	0.151	70.1

  下载: 导出CSV
•