Magnetically Separable Fe₃ O₄ @CdS Type-II Nanohybrids with Excellent Photocatalytic Activity and Antibacterial Properties

A magnetically separable Fe₃ O₄ @CdS type-II core-shell nanohybrid (NH) photocatalyst, with excellent antibacterial properties and photocatalytic activity, was synthesized and characterized by means of structural, elemental, and morphological analyses. Steady-state and time-resolved emission and absorption spectroscopy were also exploited to realize the location of charge-carrier wave functions in the NHs. The antibacterial activity of NHs was then evaluated against Escherichia coli (1.4×10⁸ CFU mL^-1 ; CFU=colony forming units) and Staphylococcus saprophyticus (1.2×10⁸ CFU mL^-1 ) as model strains of Gram-negative and -positive microbes. Compared with CdS and Fe₃ O₄ , the as-synthesized Fe₃ O₄ @CdS composite exhibited highly improved bactericidal activity and recyclability. Concentration values of 5.0 and 4.0 mg mL^-1 were required for Fe₃ O₄ @CdS NHs to inhibit the growth of E. coli and S. saprophyticus, respectively. The contribution of OH^. radicals to photocatalysis at the Fe₃ O₄ @CdS surface was also considered. Moreover, thiobarbituric acid reactive substances and protein carbonyl assay protocols have been exploited to monitor levels of oxidative damage to lipids and proteins in cells. Additionally, the photocatalytic activity of Fe₃ O₄ @CdS NHs was monitored for the degradation of xylenol orange dye. Compared with CdS and Fe₃ O₄ , as-synthesized Fe₃ O₄ @CdS displayed superior performances in the photodegradation of xylenol orange. Possible mechanisms involved in the degradation of xylenol orange are also discussed.