Preparation of a novel polypyrrole/dolomite composite adsorbent for efficient removal of Cr(VI) from aqueous solution.

A novel adsorbent, deposited PPy on the DMI (PPy/DMI) composite, was successfully synthesized for Cr(VI) removal from aqueous solution. PPy/DMI composite was characterized by BET, SEM, TEM, XRD, and XPS. The SEM and TEM analyses revealed that DMI can greatly reduce the aggregation of PPy and significantly enhance its adsorption performance. The Cr(VI) removal was highly pH dependent. The high selectivity of PPy/DMI composite for Cr(VI) removal was found even in the presence of co-existing ions. The adsorption kinetic process followed the pseudo-second-order equation, demonstrating that the Cr(VI) adsorption behavior onto PPy/DMI is chemisorption. Furthermore, the intra-particle diffusion model implied that the adsorption was controlled by both liquid membrane diffusion and internal diffusion. The adsorption isotherm data fitted well with the Langmuir model with the maximum adsorption capacity (406.50 mg/g at 323 K) which was considerably higher than that of other PPy-based adsorbents. The Cr(VI) adsorption onto PPy/DMI composite was endothermic. The main mechanisms of Cr(VI) removal are involved in adsorption through electrostatic attractions, ion exchange, and in situ reduction. The results suggested that PPy/DMI composite could be a promising candidate for efficient Cr(VI) removal from aqueous solution.