Optimizing the influential variables for enhanced photocatalytic performance of synergistic Ag–TiO2/FLG heterojunctions towards rapid mineralization of emerging polystyrene microplastics in water

Abstract

The existence of microplastics (MPs) in marine and terrestrial environments is increasing tremendously. Due to their size (<5 mm), MPs could easily pass through the filtration processes of typical water treatment plants and ultimately reach surface water. Separation of MPs from aqueous media is expensive, and the treatment methods generally used for macro-plastic waste are unsuitable for MPs. Therefore, photocatalysis is an alternative technique to tackle environmental MP pollution. Though the photocatalytic degradation of various MPs has been reported, the effect of process parameters on photocatalytic degradation has not been investigated extensively. To fill this gap, the influence of various operating variables such as irradiation time, initial concentration of MPs, photocatalyst loading, initial pH, and reaction temperature on the photocatalytic degradation process of polystyrene (PS) MPs was investigated using a novel photocatalyst, i.e., Ag⁺ doped TiO₂, heterojunctioned with few-layered graphene (ATG) under visible light irradiation. Further, photodegraded samples were analyzed using a nephelometer, FESEM, FTIR, XPS, TOC, GC-MS, and ¹H-NMR analyses to determine the effectiveness of the proposed photocatalyst. The results have revealed that visible-light-driven photocatalysis enhances PS polymeric chain scissions and reduces the concentration of PS MPs up to 63.28% within 120 h of irradiation. With a fixed amount of ATG, the increase in MP concentration decreased the degradation percentage. Similarly, the optimum ATG loading value with a pre-fixed MP concentration value improved the percentage mass loss. Further, ATG has exhibited a better performance at the pH value of 6.2 and ambient temperature.