Adsorption and Desorption Process of Chromium Ions Using Magnetic Iron Oxide Nanoparticles and Its Relevant Mechanism

In this study, adsorption of Cr(VI) from aqueous solution by Fe3O4 nanoparticles was investigated. Desorption process and recovery of nanoparticles using different solutions were then carried out, and it was observed that NaOH (0.5M) can remove 90 % of adsorbed chromium ions. Following the completion of adsorption/desorption cycles, it was determined that nanoparticles have still had a high ability of chromium ions adsorption after 4 cycles. In addition, it was found that when iron oxide nanoparticles are washed with NaOH solution, the adsorption efficiency increases in the next cycle. FTIR spectra and zeta potential analyses demonstrated the increase in the positively charged surface of nanoparticles leads to increased electrostatic attraction forces between the iron oxide nanoparticles and chromium ions, which finally resulted in the adsorption increase. Therefore, in this research, pretreatment of nanoparticles with NaOH solution modifies the surface of Fe3O4 nanoparticles by increasing positively-charged surface mechanism, and so the adsorption efficiency has improved in the next cycle.