Confinement size effect on dielectric properties, antimicrobial activity, and recycling of TiO₂ quantum dots via photodegradation processes of Congo red dye and real industrial textile wastewater

Abstract This article reports on the synthesis, characterization, and application of titanium dioxide quantum dots (TDS) for wastewater treatment. Three TDS samples were synthesized via a low-temperature precipitation method with calcination at 280°C (TDS1), 290°C (TDS2), and 300°C (TDS3). Characterization techniques such as X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy confirmed the high crystallinity, purity, and quantum confinement of the TDS with sizes of 3.1, 5.5, and 8.5 nm, respectively. The photocatalytic activity of TDS was evaluated by degrading Congo red dye under xenon lamp irradiation. TDS1, with the smallest size of 3.1 nm and the largest bandgap of 3.09 eV, showed the highest photodegradation rate of 22.49 × 10−3 S−1. TDS1 also showed effective degradation of real industrial textile wastewater under sunlight over nine repeated cycles of use. The antibacterial activity of TDS against Bacillus subtilis and Candida albicans was demonstrated, with the highest inhibition by TDS1 attributed to its higher surface area. Overall, the study shows the high photocatalytic and antimicrobial potential of synthesized TDS, especially the smallest 3.1 nm TDS1 sample. The recycling results also showcase the reusability of TDS for wastewater treatment.