The application of TiO₂ nanoparticles in the photocatalytic treatment of chemically or biologically contaminated water is an attractive, albeit unoptimized, method for environmental remediation. Here, TiO₂ nanoparticles with mixed brookite/rutile phases were synthesized and calcined at 300–1100 °C to investigate trends in photocatalytic performance. The crystallinity, crystallite size, and particle size of the calcined materials increased with calcination temperature, while the specific surface area declined significantly. The TiO₂ phase composition varied: at 300 °C, mixed brookite/rutile phases were observed, whereas a brookite-to-anatase phase transformation occurred above 500 °C, reaching complete conversion at 700 °C. Above 700 °C, the anatase-to-rutile phase transformation began, with pure rutile attained at 1100 °C. The optical band gaps of the calcined TiO₂ nanoparticles decreased with rising calcination temperature. The mixed anatase/rutile phase TiO₂ nanoparticles calcined at 700 °C performed best in the photocatalytic degradation of methylene blue owing to the synergistic effect of the crystallinity and phase structure. The photocatalytic virus inactivation test demonstrated excellent performance against the MS2 bacteriophage, murine norovirus, and influenza virus. Therefore, the mixed anatase/rutile phase TiO₂ nanoparticles calcined at 700 °C may be considered as potential candidates for environmental applications, such as water purification and virus inactivation.

A novel, three-dimensional, ternary CdS/ZnIn₂S₄/TiO₂ heterojunction has been fabricated via a three-step facile hydrothermal method.

Brookite–rutile bi-crystalline phase of TiO₂ were synthesized and applied for the degradation of methylene blue under UV and visible light irradiation by photocatalytic reaction.