Polypyrrole/waste molasses composites as a superior adsorbent for highly efficient and selective removal of Cr(VI) from aqueous environments

Abstract

Reduction of Cr(VI) to Cr(III) or elimination of Cr(VI) from aqueous environments is the most commonly used method to address Cr(VI) contamination. Waste molasses (WM) is a by-product from the sugar industry, if discharged arbitrarily without treatment can lead to waste of resources and cause serious environmental pollution. In this study, the modification of polypyrrole (PPy) with WM (PPy/WM) not only provided PPy with good dispersibility and higher specific surface area, but it can also enrich the functional groups on the surface of PPy. The findings indicated that PPy/WM composites can serve as superior adsorbent materials for highly efficient and selective removal of Cr(VI) when different interfering ions are present. e.g., 150 mg/L of Cr(VI) can be eliminated completely within 6 h under the condition of PPy/WM amount of 0.8 g/L, temperature of 303 K, and pH of 2.0. PPy/WM showed excellent performance for removal of Cr(VI) in a wide pH range (2.0 - 10.0). PPy/WM exhibited excellent reusability for five cycles without obvious loss of its adsorption capacity. The maximum Cr(VI) adsorption capacity of PPy/WM was 662.25 mg/g at 323 K, evidently higher than that of unmodified PPy (194.17 mg/g). Cr(VI) removal by PPy/WM was chiefly accomplished by electrostatic adsorption, ion exchange and in-site reduction. This study not only provides a new technology for efficient adsorption and in-situ reduction of Cr(VI), but also realizes the resource utilization of WM and solves the WM pollution problems.