In previous studies, TiO 2, which exhibits excellent chemical stability, photo-corrosion resistance, tunable light absorption, and is inexpensive (Wang et al., 2011 May Ix et al., 2020), has been widely explored in different reactions as an effective catalyst and support for loading different metal catalysts (Wang et al., 2019 Tian et al., 2020). However, Ag NPs are prone to aggregate and generally require dispersion on a support for exposure of the active site (Lo et al., 2021). These noble metals generally have a plasmon resonance that is responsive in the visible light region and extend the utilization of the photoexcited electron-hole pairs (Hariharan et al., 2020 Hu et al., 2021). Among different noble metals, silver nanoparticles (Ag NPs) have received considerable attention owing to their high catalytic activity for different reactions (Feng et al., 2020 Chishti et al., 2021a) and reasonable price. 4-NP can be effectively removed from aqueous media via catalytic conversion to the less toxic compound 4-AP, where the reaction is generally performed in an aqueous solution containing NaBH 4 as a reducing agent, with metal (such as Ag, Pt, Au, Pd) or other metal-supported materials as a catalyst (Rasaki et al., 2019 Liu et al., 2020 Alshammari et al., 2020). 4-NP is an organic pollutant that is commonly encountered in different effluents in the production of herbicides, pesticides, and synthetic dyes (Lv et al., 2019). The catalytic reduction of 4-nitrophenol (4-NP) to produce 4-aminophenol (4-AP) is a model reaction that is typically employed to evaluate the activity of newly prepared materials (Strachan et al., 2020 Lo et al., 2021). In summary, an Ag-loaded TiO 2–SiO 2–Fe 3O 4 sphere with high activity and recyclability for 4-NP reduction was prepared via a facile and simple stirring method, where the sample can be used as a promising material in environmental remediation. Moreover, due to the advantages of the core-shell structure, the magnetic properties of Fe 3O 4 were sufficient to enable facile recycling of the sample for further reaction SiO 2 could protect the Fe 3O 4 center from oxidation or reduction TiO 2 enabled Ag accommodation and absorbed light to generate electron-hole pairs. Under the optimized conditions, 5Ag-TSF (with 5 wt% of Ag) could promote the reduction of aqueous 4-NP solution (2 × 10 −4 M, 75 mL) in the presence of NaBH 4 (0.1 M, 5 mL) under irradiation by a metal halide lamp, affording over 98% reduction within 5 min and a rate constant of 0.185 min −1, demonstrating its promising activity. To improve the reduction activity of 4-NP, Ag was loaded onto TSF under stirring, with a variation of the temperature (2–130 ☌) and reaction time (1, 2, and 4 h). Fe 3O 4, SiO 2, and TiO 2 in the core-shell structure served as a magnetic center, protective layer, and light absorber, respectively. In this study, an Ag-loaded TiO 2–SiO 2–Fe 3O 4 (TSF) with a core-shell structure was employed for the photo-assisted reduction of 4-NP. Nitrogen-containing contaminants, such as 4-nitrophenol (4-NP), cause detrimental effects when discharged into the environment and thus should be reduced or removed from ecosystems.
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