Polypyrrole coated molybdenum disulfide composites as adsorbent for enhanced removal of Cr(VI) in aqueous solutions by adsorption combined with reduction

Abstract In this study, polypyrrole coated molybdenum disulfide organic–inorganic composites (PPy/MoS2) were fabricated by a simple in-situ oxidative polymerization, and used as a novel adsorbent for removal Cr(VI). The sorption of Cr(VI) was consumingly pH-reliant behavior, which the optimal elimination efficiency was attained at pH 2. Meanwhile, the adsorption of Cr(VI) on PPy and PPy/MoS2 followed the pseudo-second-order kinetic model and Langmuir isotherm model. Compared with PPy, PPy/MoS2 exhibited better elimination ability for Cr(VI) because of its well-dispersion and massive surface active sites. The maximum sorption capacity of Cr(VI) by PPy/MoS2 reached 257.73 mg/g at 298 K, which was obviously higher than that of Cr(VI) by PPy (151.29 mg/g). The thermodynamic parameters demonstrated that the sorption process was endothermic and spontaneous. The coexisting ions like K+, Na+, Ca2+, Mg2+, NO3–, Cl- and SO42- had no significant influence for Cr(VI) elimination, whereas H2PO4- was main competitors. Mechanism investigation indicated that the ion exchange, electrostatic interactions, chemical reduction (Cr(VI) to Cr(III)) and surface chelation played a crucial role in the elimination of Cr(VI). In addition, the PPy/MoS2 composites could be employed for three continuous cycles without significantly reducing the sorption capacity of Cr(VI). This work demonstrated that PPy/MoS2 composites were a promising sorbent for efficient treatment Cr(VI) in polluted water.