Highly active nanoscale zero-valent iron (nZVI)-Fe _3O _4 nanocomposites for the removal of chromium(VI) from aqueous solutions

摘要

For the first time, nanoscale zero-valent iron (nZVI)-Fe _3O _4 nanocomposites, prepared by an in situ reduction method, are employed for chromium(VI) removal in aqueous environment. 96.4% Cr(VI) could be removed by these novel materials within 2h under pH of 8.0 and initial Cr concentration of 20mgL ~(-1), compared with 48.8% by bare nFe _3O _4 and 18.8% by bare nZVI. Effects of several factors, including mass composition of nZVI-Fe _3O _4 nanocomposites, initial pH and Cr(VI) concentration, were evaluated. The optimal ratio of nFe _3O _4 to nZVI mass lies at 12:1 with a fixed nZVI concentration of 0.05gL ~(-1). Low pH and initial Cr(VI) concentration could increase both the Cr(VI) removal efficiency and reaction rate. Corresponding reaction kinetics fitted well with the pseudo second-order adsorption model. Free energy change (ΔG) of this reaction was calculated to be -4.6kJmol ~(-1) by thermodynamic study, which confirmed its spontaneous and endothermic characteristic. The experimental data could be well described by the Langmuir and Freundlich model, and the maximum capacity (q _(max)) obtained from the Langmuir model was 100 and 29.43mgg ~(-1) at pH 3.0 and 8.0, respectively. The reaction mechanism was discussed in terms of the mutual benefit brought by the electron transfer from Fe ~0 to Fe _3O _4.