Chitosan induced synthesis of few-layer MoS2/Fe-doped biochar and its dual applications in Cr(VI) removal

The removal of Cr(VI) from wastewater still faces many challenges. This study reports on chitosan-induced synthesis of few-layer MoS2/Fe-doped biochar (Mo-Fe0.5-CS) with dual applications in Cr(VI) removal. Using chitosan as a soft template, the MoS2 in the composite had only about 3 layers with an interlayer spacing greater than that of pure MoS2, while Fe was embedded in the carbon skeleton in the form of 6-coordination with O/N. The Mo-Fe0.5-CS composite showed high affinity for Cr(VI), with rapid adsorption reaching 100% removal within 15 min for a single solution of Cr(VI). It follows the Langmuir isotherm model with a maximum adsorption capacity of up to 180 mg/g. Furthermore, the Mo-Fe0.5-CS composite demonstrated catalytic activity for Fenton-like reactions, which allowed for the simultaneous removal of organic pollutants and Cr(VI). In a mixture solution of Cr(VI) and Acid Red 73 (AR73), the removal efficiencies using Mo-Fe0.5-CS and H2O2 in 30 min were 99.7% and 96.6%, respectively. The MoS2 acted as a cocatalyst to improve the reduction of Fe(III), and the catalysis of Cr(VI) also contributed to the removal of AR73 to a certain extent. Even at pH 10, the system was effective due to the 1O2 produced in the reaction and the acidic microenvironment constructed by unsaturated S atoms. These findings provide insights into the effective removal and utilization of Cr(VI) in wastewater treatment.