A versatile nanocomposite Fe0@SiO2@CaO2 for reductive, oxidative, and coagulation removal of organic and inorganic contaminants from water

Water scarcity is one of the most pressing global challenges and limits economic and social development. Multiple processes of current technologies for water purification are needed to meet water quality objectives due to their contaminant-specific removal capability. Here, we developed Fe0@SiO2@CaO2 nanocomposite with three layers of core–shell structure that could achieve an array of water contaminants removal by oxidation, reduction, and flocculation. >99 % of 50 mg/L tetracycline, 20 mg/L pentachlorophenol, 450 mg/L Cd(Ⅱ), 20 mg/L Cr(Ⅵ), or 80 mg/L P (in form of PO43−) was removed by 2 g/L Fe0@SiO2@CaO2 in 24 h. Moreover, Fe0@SiO2@CaO2 (2 g/L) showed an excellent performance in turbidity removal (239 mg/L kaolinite suspension, removal rate > 99 %) and water decolorization (50 mg/L humic acid, removal rate > 93 %). Cd(II) and Cr(VI) could be reduced to Cd(0) and Cr(III), respectively, through electronic reduction reactions using Fe0 and •H, which is formed during the reaction Fe0 + 2H+→2•H + Fe2+; Cd(Ⅱ) and the formed Cr(III) could coprecipitate with the formed orthosilicic acid and OH−. The removal of P was mainly resulted from the coordination with released Ca2+ and iron compounds. Charge neutralization by nanocomposite and coagulation with the products from nanocomposite transformation were responsible for the kaolinite removal. Reduction by •H and Fe0, oxidation by •OH derived from the Fenton reaction, and/or coagulation accounted for the organic contaminant removal. This work provides a novel material that can be used to simultaneously remove a range of contaminants in wastewater treatment.