In this study, a novel magnetic nanocomposite was prepared using waste toner (WT) through high temperature decomposition, and calcination was conducted in different atmospheres (air, ammonia, and vacuum). WT calcined in ammonia (WT(NH3)), and it was then utilized as an efficient absorbent for the reduction of Cr(VI) in aqueous solutions; a batch experiment with different conditions was performed to investigate its Cr(VI) removal ability. The effects of two pH-regulating acid (HCl and H2SO4) treatments were also studied. It was found that WT(NH3) could remove about 99% Cr(VI) at pH 2 under H2SO4 treatment. The XRD and TEM results coupled with VSM results confirmed that WT(NH3) is an Fe3O4/Fe2N nanohybrid, which possesses excellent water-dispersibility and remarkable magnetic properties. XPS analysis showed the presence of Cr(VI) and Cr(III) on the surface of WT(NH3), which indicated that Cr(VI) was reduced to Cr(III). Furthermore, H2SO4 regulation also promoted the reduction of Cr(VI) by WT(NH3), and this reduction was higher than that obtained by HCl regulation.
