Photocatalytic degradation of methylene blue dye by molybdenum disulfide-doped polyacrylamide/polyvinylpyrrolidone hydrogel

Inorganic micro- and nanoparticles are promising photocatalysts for removing toxic dyes from aqueous media. However, their dispersion in water and subsequent separation after the photocatalytic process remain challenging. In this study, MoS₂, a transition metal disulfide, was successfully dispersed in a water–ethanol mixture with the help of polyvinylpyrrolidone (PVP) and immobilized in a polyacrylamide (PAM) hydrogel to be easily separated from the medium after photodegradation. The resulting composite material was characterized, and its photocatalytic performance against methylene blue dye was studied. Optimal photocatalytic degradation was achieved at pH 9.0, using 40 mg of MoS₂ and 1.0 g of the composite hydrogel, resulting in a dye degradation efficiency of approximately 88.6% within 120 min. Kinetic studies indicated that the photodegradation of methylene blue dye followed second-order kinetics (R² = 0.989). Radical scavenging experiments revealed that superoxide radicals ·O2-, hydroxyl radicals ·OH, and holes (h⁺) played predominant roles in the degradation process. Additionally, the composite hydrogel demonstrated promising reusability, retaining over 60% of its removal efficiency after four successive photocatalytic cycles.