Tuning the photocatalytic/electrocatalytic properties of MoS 2 /MoSe 2 heterostructures by varying the weight ratios for enhanced wastewater treatment and hydrogen production.

Two-dimensional (2D) heterojunctions with layered structures give high flexibility in varying their photocatalytic/electrocatalytic properties. Herein, 2D/2D heterostructures of MoS 2 /MoSe 2 with different weight-ratios (1 : 1, 1 : 3, and 3 : 1) have been prepared by a simple one-step microwave-assisted technique. The characterization studies confirm formation of crystalline MoS 2 /MoSe 2 nanoparticles with a high surface area (60 m 2 g -1 ) and porous structure. The high synergistic-effect (1.73) and narrow bandgap (∼1.89 eV) of the composites result in enhanced photo-degradation efficiency towards methylene blue dye (94%) and fipronil pesticide (80%) with high rate constants (0.33 min -1 and 0.016 min -1 respectively) under visible light. The effect of pH, catalyst dose, and illumination area on photodegradation has been optimized. Photodegradation of real-industrial wastewater shows 65% COD and 51.5% TOC removal. Trapping experiments confirm that holes are mainly responsible for degradation. The composites were highly reusable showing 75% degradation after 5-cycles. MoS 2 /MoSe 2 composites show excellent electrochemical water-splitting efficacy through hydrogen-evolution-reaction (HER) exhibiting a stable high current density of -19.4 mA cm -2 after 2500 cyclic-voltammetry (CV) cycles. The CV-plots reveal high capacitance activity ( C dl value ∼607 μF cm -2 ) with a great % capacitance retention (>90%). The as-prepared 2D/2D-catalysts are highly active in sunlight and beneficial for long-time physico-chemical wastewater treatment. Moreover, the electrochemical studies confirm that these composites are potential materials for HER activity and energy-storage applications.