Facile Synthesis of Manganese Dioxide Nanoparticles for Efficient Removal of Aqueous As(III)

The development of highly efficient adsorbents for arsenic removal remains a challenge. In this paper, we propose the facile synthesis of hydrous manganese dioxide (HMO) and investigate its application in removal of As(III). By controlling the ratio of precursors, HMOs with different vertical bar ZP vertical bar values were successfully synthesized. It is found that HMO with a smaller value of vertical bar ZP vertical bar achieves a higher arsenic removal rate. Adsorption efficiency is confirmed to be pH-dependent and directly related to the adsorbent dosage. In addition, thermodynamics analysis shows that the adsorption reaction appears to be spontaneous and is accompanied by exothermic phenomena. Furthermore, the removal process of As(III) has the best fitting effect by the Freundlich adsorption model and pseudo-secondary dynamics model, which reveal that the adsorption sites are evenly distributed in the adsorption process. The FT-IR and XPS analysis further proves that the arsenite ions and HMO adsorbents have first formed a complex through electrostatic interaction, which is further converted into a more stable internal structure by a redox reaction. This work not only offers a relatively low cost and highly efficient candidate on the treatment of heavy As(III)-contaminated water but also provides a deep understanding of the relationship between the vertical bar ZP vertical bar value and adsorption behavior.