WS2/MoS2/graphene composite for the fast photocatalytic degradation of recalcitrant dyes and pharmaceuticals under solar light

The performance of WS 2 -MoS 2 /graphene (WS 2 -MoS 2 /G) and WS 2 -MoS 2 photocatalysts was evaluated for the degradation of recalcitrant methylene blue (MB, 40 ppm) and rhodamine B (RhB, 20 ppm) dyes as well as for the degradation of Fedrimin drug (composed by a mixture of ambroxol (AMB) + theophylline (THP), 20 ppm). The WS 2 -MoS 2 /G and WS 2 -MoS 2 composites quickly degraded MB and RhB dyes with efficiencies >99% under solar light (after 10-15 minutes). If UV light is utilized for the photocatalytic degradation of RhB, efficiencies above 99% are obtained, but longer time is needed (45 minutes). Furthermore, photocatalytic experiments were carried out for the degradation of Fedrimin and found that a higher degradation percentage is produced using the WS 2 -MoS 2 /G composite and sunlight (92%) instead of UV light (78%). In addition, hydroxyl radicals (•OH) were identified through scavenger tests as the main oxidizing species for the MB, RhB and Fedrimin degradation. Additionally, WS 2 -MoS 2 /G composite produced the maximum removal of total organic carbon (92% for RhB and 96% for MB) under solar light, indicating the efficient mineralization of the organic pollutants without the generation of byproducts. In general, WS 2 -MoS 2 /G composite had the highest absorbance in the visible region, which enhances electron transfer and delays the electron-hole recombination, improving the photocatalytic efficiency. Overall, the WS 2 -MoS 2 /G composite is a viable alternative for eliminating organic contaminants from water and could replace the conventional oxide based photocatalysts for the degradation of contaminants. Particularly, we demonstrated the degradation of a mixture of pharmaceuticals, which has been scarcely reported in the literature. • WS 2 -MoS 2 /G produced fast degradation of dyes and pharmaceuticals under solar light • WS 2 -MoS 2 /G under sunlight achieved over 99% degradation of RhB and MB within 10 min • The maximum degradation for Fedrimin was 92% after 150 min under sunlight • The main oxidizing agents for the degradation of pollutants were (•OH) >(h + ) >( • O 2 − ) • The highest TOC removal of 90% was reached using the WS 2 -MoS 2 /G composite