Study on triphase of polymorphs TiO₂ (anatase/rutile/brookite) for boosting photocatalytic activity of metformin...

The elution of pharmaceutical products such as metformin at higher concentrations than the safe level in aquatic systems is a serious threat to human health and the ecosystem. Photocatalytic technology using TiO₂ semiconductors potentially fixes this problem. This study aims to synthesize triphasic anatase-rutile-brookite TiO₂ using ultrasound assisted sol-gel technique in the presence of acid and its application to photodegradation of metformin under UV light irradiation. Based on X-ray diffraction analysis, a TiO₂ sample consisted of anatase (76%), rutile (7%), and brookite (17%) polymorph (A₇₆R₇B₁₇) that was fully crystallized. Scanning electron microscopy (EM)-energy dispersive X-ray spectra results showed agglomerated triphasic A₇₆R₇B₁₇ with irregular spherical clusters. Transmission EM results revealed that the crystal size of A₇₆R₇B₁₇ was 4-14 nm. The Brunauer-Emmett-Teller analysis showed the sample's specific surface area of 149 m² g^-1. The degradation test of metformin demonstrated that the A₇₆R₇B₁₇ exhibited a 75.4% degradation efficiency after 120 min under UV light irradiation, significantly higher than using biphasic and single-phase TiO₂ photocatalysts. This difference could be attributed to the heterojunction effect of triphasic materials that effectively reduced electron-hole recombination rate as well as the combination of effective electron transfer from conduction band of brookite and anatase and the utilization of wider range of UV-visible light using rutile.