Facile preparation of poly(pyrrole methane) modified melamine sponge as 3D recyclable adsorbent for Cr(VI) removal

The insufficient adsorption activity and poor solid-liquid separation performance limit the practical application of powder polypyrrole (PPy)-based adsorbents. Thus, poly(pyrrole methane), a PPy derivative, was synthesized and loaded onto melamine sponge to construct a 3D polymer adsorbent (MS@PPm), which could simultaneously address the two defects of traditional PPy adsorbents. The obtained MS@PPm contained abundant N- and O-containing sites, which were beneficial for Cr(VI) removal. The results in static batch experiments demonstrated that the elimination of Cr(VI) by MS@PPm was beneficial with lower pH values. The adsorption process agreed with pseudo-second-order kinetic model, implying that Cr(VI) was adsorbed onto MS@PPm by chemisorption. The saturated adsorption capacity of MS@PPm achieved 320.56 mg g⁻¹, which was superior than that of most PPy-based and other adsorbents in literatures. MS@PPm also showed prominent specificity for Cr(VI) adsorption even with coexisting anions. The removal rate still exceeded 82.43 % after 5 cycles, exhibiting an excellent regeneration and utilization performance. Moreover, Cr(VI) can be continuously removed by MS@PPm, and the removal efficiency exceeded 90 % in the 100 h continuous dynamic column experiments. The adsorption mechanism study revealed that Cr(VI) can not only be adsorbed onto MS@PPm by electrostatic attraction and ion-exchanging interactions, but also can be transformed to harmfulless Cr(III) and complexed on adsorbent. This study implied that MS@PPm had great potential for Cr(VI) remediation in water.