A novel green synthesis of Bi2WO6-based photocatalysts for efficient pollutants degradation using low-power UV-A LEDs

Bismuth (Bi)-based photocatalysts were successfully prepared by the metathesis-assisted molten salts process by a straightforward, efficient, high-yield, and environmentally friendly novel methodology. The catalysts preparation in an in-situ generated molten LiNO3/NaNO3 reaction media has no precedent. Different loads of graphene (G), and silver nanoparticles (Ag-NPs) added to the catalysts affected phases composition, physicochemical characteristics, and photocatalytic performance. The as-prepared catalysts showed plate-like shapes with heterogeneous lateral length and nanometric thickness. Methylene blue (MB), Rhodamine (RhB) dyes and binary solutions (MB + RhB) were used to estimate the photocatalytic activity of the as-prepared Bi-based catalysts. Pristine Bi2WO6 (BWO) catalyst enhanced the degradation of RhB (%XRhB) achieving 100% within 60 min using a low-power (19 W) UV-A LED source. This %XRhB is superior to those reported in the literature, considering the rated power consumption-to-degradation efficiency. MB and RhB degradation over BWO and Ag/Bi2WO6 (Ag/BWO) were substantially influenced by the catalyst dosage, dyes initial concentration, and solution pH. Trapping tests revealed that h+ is the main oxidative species causing MB, and RhB photodegradation, and the degradation mechanism was postulated based on these findings. After the fourth reuse cycle, BWO showed high chemical stability (%XRhB = 100%). In binary solutions (RhB + MB), the RhB photodegradation was significantly diminished (%XRhB = 19%) over BWO and entirely hindered (%XRhB = 0%) using Ag/BWO since the active sites on the catalysts’ surface showed greater affinity towards the MB molecule.