Kinetics of hexavalent chromium removal from water by chitosan-Fe0 nanoparticles

Chitosan-Fe0 nanoparticles (chitosan-Fe0) were prepared using nontoxic and biodegradable chitosan as a stabilizer. Batch experiments were conducted to evaluate the influences of initial Cr(VI) concentration and other factors on Cr(VI) reduction on the surface of the chitosan-Fe0. The overall disappearance of Cr(VI) may include both physical adsorption of Cr(VI) onto the chitosan-Fe0 surface and subsequent reduction of Cr(VI) to Cr(III). The rate of reduction of Cr(VI) to Cr(III) can be expressed by a pseudo-first-order reaction kinetics. The rate constants increase with the increase in temperature and iron loading but decrease with the increase in initial Cr(VI) concentration and pH. The apparent activation energy is found to be 33 kJ mol−1, which is characteristic of a chemically controlled reaction. Characterization with high-resolution X-ray photoelectron spectroscopy reveals that after the reaction, relative to Cr(VI) and Fe(0), Cr(III) and Fe(III) are the predominant species on the surface of chitosan-Fe0. Chitosan has also been found to inhibit the formation of Fe(III)–Cr(III) precipitation due to its high efficiency in chelating the Fe(III) ions. This study demonstrates that chitosan-Fe0 has the potential to become an effective agent for in situ subsurface environment remediation.