Preparation and adsorptive application of novel superparamagnetic zirconia material

A novel superparamagnetic zirconia (ZrO2/SiO2/Fe3O4, SPMZ) material has been successfully synthesized via three sequential steps: chemical precipitation of magnetite, sol–gel coating of silica and sol–gel covering of zriconia. The physicochemical properties were characterized with N2 adsorption at 77 K, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), superconducing quantum interference device (SQUID), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA) and electrophoresis. SEM/EDX showed that zirconium is abundant on the surface with high atomic percent and the size of the aggregate is approximately smaller than 100 nm. Powder XRD illustrated the coexistence of tetragonal and monoclinic crystals. TGA indicated that conversion rate of pre-SPMZ before final calcination is affected by pyrolysis temperature. The adsorption behavior of sulfate on SPMZ from aqueous solution was examined as an index of adsorptive application. The removal efficiency of sulfate via adsorption is rather sensitive to the pH value of the solution in the range of 4–5.8. The further adsorption of sulfate on SPMZ is restrained as the pH value of solution reaches the point of zero charge pHPZC of SPMZ. The adsorption capacity of sulfate on SPMZ under a fixed pH value of 4 can be comparable to that of commercially nanopowder of zirconia. Furthermore, the adsorption rate of sulfate on SPMZ is rather fast in 1 min and then gradually slows down reaching the adsorption equilibrium. The liquid–solid separation can be easily carried out via the magnetic separation.