Selective removal of Cr(VI) using polyvinylpyrrolidone and polyacrylamide co-modified MoS2 composites by adsorption combined with reduction

Cr(VI), one of the most hazardous metal pollutants, poses significant threats to the environment and human health. Herein, a novel MoS2 composite (MoS2/PVP/PAM) modified by polyvinylpyrrolidone (PVP) and polyacrylamide (PAM) was synthesized to enhance the removal of Cr(VI). Characterization analysis including SEM, XRD, FTIR, and XPS indicated that PVP and PAM could increase the interlayer spacing and the dispersibility of MoS2, and introduce pyrrolic N and amino functional groups. The batch experiments showed that MoS2/PVP/PAM represented excellent Cr(VI) removal performance over a wide pH range, and exhibited a significantly higher maximum Cr(VI) adsorption capacity (274.73 mg/g, at pH 3.0, and 298 K) than pure MoS2. The adsorption of Cr(VI) followed Langmuir and pseudo-second-order kinetic model, which was a homogeneous monolayer chemisorption process. MoS2/PVP/PAM showed stable removal of Cr(VI) in the presence of humic acid (HA), interfering cations and anions at different concentrations. Moreover, it had excellent selectivity for Cr(VI) (Kd value of 1.69 × 107 mL/g) when coexisting with a variety of competing ions. Multiple characterization revealed that Cr(VI) was reduced to low toxicity Cr(III) by Mo4+ and S2−, and then chelated on the surface of the adsorbent by pyrrolic N. This research expanded the design concept for MoS2 composites by demonstrating the potential of MoS2/PVP/PAM as a promising material for selective elimination of Cr(VI) in water.