Design of Sr-Doped Titanate Combined with g-C3N4 for Efficient Photocatalytic Degradation of the Model Pollutant Caffeine

Photocatalytic processes have been studied as promising solutions to mitigate the impact of pollutants on aquatic environments. Here, the enhancement of photocatalytic performance and stability of titanate nanostructures (TNS), a well-established photocatalyst, were investigated through Sr modification. Structural characterization confirmed Sr in-corporation in the crystalline structure, mainly in the interlayers. The sample Sr(5%)TNS, synthesized with 5% (wt.), exhibited fine lamellar morphology, different from the elongated nanowires of pristine TNS. The photocatalytic performance of the Sr-modified sample was studied for the removal of a model pollutant, caffeine, under UV-Vis and visible irradiation. A clear enhancement in the caffeine removal rate was observed using Sr(5%)TNS as a photocatalyst, when compared with the pristine material. Further improvement in the photocatalytic performance was obtained by combining Sr(5%)TNS with graphitic-like carbon nitride (g-C3N4) as a novel composite film. This proved to be a promising strategy for enhancing both the visible-light photocatalytic efficiency and the stability of the films, while also facilitating their reuse. Various configurations of the hybrid system were tested, and the best results for caffeine degradation and catalyst robustness were achieved with a 4:1 ratio of Sr(5%)TNS to g-C3N4. Mechanisms for charge transfer in irradiated Sr(5%)TNS particles, and in Sr(5%)TNS/g-C3N4 composite films are proposed and discussed.