green synthesized tio₂–p25/wo₃ photocatalyst for methylene blue degradation under sunlight in a spherical reactor

Nanostructured semiconductors have emerged as promising photocatalysts for sustainable wastewater purification. among them, tio₂–p25 (commercial tio₂) is widely used; however, its wide band gap restricts visible light activity. a simple and eco friendly approach to overcome this limitation is the formation of heterostructures. in this work, tio₂–p25/wo₃ heterostructures were synthesized via a rapid, additive free aqueous sonochemical route (10 min ultrasonication). the structural characteristics of the composites were examined by xrd, ftir, raman spectroscopy and fesem, while their optical and interfacial properties were assessed by drs, ζ potential and eis analyses. these characterizations confirmed that the anatase–rutile tio₂–p25 and monoclinic wo₃ phases remained intact without the appearance of new interfacial bonds, while close physical contact between the two oxides improved visible light absorption and facilitated interfacial charge transfer. the photocatalytic performance was evaluated in a spherical quartz reactor under real sunlight using methylene blue (mb) as a model pollutant. response surface methodology with a central composite design was employed to investigate the effects of catalyst dose (0.5–1.5 mg/l), initial mb concentration (20–40 mg/l), and ph (5–9). under the optimized conditions (20 mg/l mb, 1.5 mg/l catalyst, ph 9), 69.5% of mb was removed by dark adsorption within 30 min, and subsequent sunlight irradiation resulted in 94.6% total removal after 70 min, with a reaction rate constant of 0.042 min⁻¹. taken together, these results demonstrate that this simple aqueous synthesis provides an efficient and eco friendly pathway to prepare tio₂–p25/wo₃ photocatalysts for large scale wastewater remediation under real sunlight.