Novel p−n heterojunction nanocomposite: TiO₂ Qds/ZnBi₂O₄ photocatalyst with considerably enhanced photocatalytic activity under visible-light irradiation

The practical and widespread application of photocatalysts is limited by the problem of visible-light absorption, the immediate recombination of photogenerated electron−hole pairs, and the low number of active sites on their surface. We synthesized a series of novel TiO₂ QDs/ZnBi₂O₄ nanocomposites through the hydrothermal method to overcome these problems. The formation of nanocomposites and their features were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, photocurrent, field-emission scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy, photoluminescence, Brunauer−Emmett−Teller, ultraviolet−visible diffuse reflection spectroscopy, and total organic carbon techniques. Among the different ratios of nanocomposites, the TiO₂ QDs/ZnBi₂O₄ (10%) displayed the highest photocatalytic activity under visible-light irradiation, and the corresponding rhodamine B (RhB) degradation rate constant was 1022 × 10⁻⁴ min⁻¹, which was nearly 77 and 5.9 times that of the TiO₂ and TiO₂ QD samples, respectively. In light of the mechanism study, the photocatalytic activity improvement can be ascribed to the p−n heterojunction formation, which led to an increase in the visible-light absorption, suppression of electron−hole recombination, and promotion of charge-carrier transfer. h^+•O₂⁻, and ^•OH were also identified as active species responsible for RhB photodegradation through the scavenging test. Phenol, Congo red, malachite green, and methyl orange were also degraded as various pollutants to ensure the prepared nanocomposites’ potential for practical applications. The nanocomposite stability was assessed during reuse evaluation experiments and showed good stability after four consecutive cycles. This work proposes a novel nanocomposite and provides an overview of its features for future applications.