Reusable and removable PmPD/PVA membrane for effective Cr(vi) adsorption and reduction

Abstract

Poly(m-phenylenediamine) (PmPD) is an efficient material for the adsorption of Cr(VI). However, it is facile to aggregate in water, which reduces its adsorption capacity, and it is not facile to be separated from water. Hence, magnetic or membrane structures by compositing PmPD with other functional materials are usually synthesized to solve the above problems. Here, we utilized polyvinyl alcohol (PVA) chains to obtain a dense network structure, which embedded and constrained PmPD into the network to form a membrane. PmPD constrained in the membrane existed stably and was facilely separated from water due to the large size of the membrane. Meanwhile, the PmPD/PVA membranes showed good mechanical properties and combined both the extraordinary adsorption capacity and reusability. In this study, the maximum Cr(VI) adsorption capacity of the composite membrane structures was 498.87 mg g⁻¹ at room temperature. The adsorption and removal mechanism can be explained by the fact that the protonated imine units adsorb Cr(VI) via electrostatic attraction; following this, Cr(VI) changed to Cr(III) by reduction and chelated on the imine units. This study demonstrated that the PmPD/PVA membrane has a great potential for the separation of Cr(VI) from wastewater due to its low-cost and high adsorption capacity.