One-step synthesis and characterization of core–shell Fe@SiO2 nanocomposite for Cr (VI) reduction

Abstract A facile one-step method was developed to fabricate mono-dispersed Fe nanoparticles (Fe NPs) coated with SiO 2 shell by aqueous reduction method combined with modified Stober method. Borohydride was acted not only as a reductant for iron salt but also as a catalyst for hydrolysis and polycondensation reaction of tetraethylorthosilicate (TEOS), and more importantly, there was no need to use surface primer for the generation of Fe NPs and catalyst NH 4 OH for SiO 2 . Both the Fe NPs agglomeration and SiO 2 shell thickness can be controlled through the synthetic conditions. Lower potassium borohydride (KBH 4 ) injection speed was preferable to assemble Fe NPs. The SiO 2 shell thickness increased gradually with the increase of TEOS amount. Under the condition of TEOS amount of 0.1 mL and KBH 4 injection speed of 5 mL/min, 25 nm single Fe NP was coated with SiO 2 shell with thickness of about 9 nm. The resulting nanoporous SiO 2 shell was proved to allow reactant to reach the Fe NPs while at the same time protect them from aggregation. The reactivity characterization of the SiO 2 -coated Fe nanoparticles (Fe@SiO 2 ) showed that both TEOS concentration and KBH 4 injection speed had effect on Cr (VI) degradation ability. The highest removal capacity of Fe@SiO 2 can reach 467 mg Cr/g Fe at an initial Cr (VI) concentration of 70 mg/L under pH 6.0 ± 0.1. XPS and TEM results showed that Cr (VI) was converted to nontoxic Cr (III) and the reaction product was completely adsorbed to SiO 2 shell.