Bi-MOF-mediated valorisation of a TiO2-rich industrial wastewater-treatment residual into a Bi4Ti3O12-A-TiO2 photocatalyst for pentachlorophenol removal

Valorisation of TiO 2 -bearing residues from titanium white production offers an opportunity for the functional upgrading of process-derived TiO 2 . Here, a process-specific TiO 2 -rich feedstock recovered from a titanium white plant wastewater-treatment stream was converted into anatase TiO 2 (A-TiO 2 ). Owing to its prior processing history, the recovered A-TiO 2 exhibited a limited specific surface area and weak intrinsic photocatalytic activity, motivating further interfacial upgrading through a bismuth-based metal-organic framework (Bi-MOF)-directed strategy. The Bi-MOF intermediate served as an in situ precursor-organization platform for Bi species on A- TiO 2 , enabling subsequent thermal conversion into nanoscale Bi 4 Ti 3 O 12 (BTO)-related domains and the formation of intimate Bi 4 Ti 3 O 12 -A-TiO 2 (BTO-ATO) heterointerfaces. Among the composites, 30BTO-ATO with a nominal BTO loading of 30 wt% achieved 96% pentachlorophenol (PCP) removal within 60 min, with a pseudo-first-order rate constant of 0.05256 min −1 , nearly 20 times that of A-TiO 2 . Reactive-species trapping and electron spin resonance analyses identified h + as the primary reactive species, with ·O₂ − also contributing. Combined band-structure and photoelectrochemical analyses were consistent with a possible Z -scheme charge-transfer pathway. The Cl − release ratio reached 57.5% after 60 min, while gas chromatography–mass spectrometry analysis suggested dechlorination and oxidative ring-opening routes. Post-reaction characterization indicated largely retained major phases and surface chemical states, and cycling tests showed maintained activity with gradual decline. This work demonstrates the value-added conversion of a process-specific TiO 2 -rich wastewater-treatment residual into a photocatalyst for recalcitrant chlorinated pollutant removal.