Surface contamination by microbes is a major public health concern. A damp environment is one of potential sources for microbe proliferation. Smart photocatalytic coatings on building surfaces using semiconductors like titania (TiO₂) can effectively curb this growing threat. Metal-doped titania in anatase phase has been proven as a promising candidate for energy and environmental applications. In this present work, the antimicrobial efficacy of copper (Cu)-doped TiO₂ (Cu-TiO₂) was evaluated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) under visible light irradiation. Doping of a minute fraction of Cu (0.5 mol %) in TiO₂ was carried out via sol-gel technique. Cu-TiO₂ further calcined at various temperatures (in the range of 500–700 °C) to evaluate the thermal stability of TiO₂ anatase phase. The physico-chemical properties of the samples were characterized through X-ray diffraction (XRD), Raman spectroscopy, X-ray photo-electron spectroscopy (XPS) and UV–visible spectroscopy techniques. XRD results revealed that the anatase phase of TiO₂ was maintained well, up to 650 °C, by the Cu dopant. UV–vis results suggested that the visible light absorption property of Cu-TiO₂ was enhanced and the band gap is reduced to 2.8 eV. Density functional theory (DFT) studies emphasize the introduction of Cu⁺ and Cu²⁺ ions by replacing Ti⁴⁺ ions in the TiO₂ lattice, creating oxygen vacancies. These further promoted the photocatalytic efficiency. A significantly high bacterial inactivation (99.9999%) was attained in 30 min of visible light irradiation by Cu-TiO₂.

In pure synthetic titanium dioxide, the anatase to rutile phase transition usually occurs between the temperatures of 600 °C and 700 °C. The phase transition temperature can be altered by various methods, including modifying the precursor or by adding dopant or modifier to the TiO₂ sample. In an attempt to investigate the phase transition using aromatic carboxylic acids, the current study examines the impact of increasing concentrations of benzoic acid (1 : 0, 1 : 1, 1 : 4 and 1 : 8 molar ratio TiO₂ : benzoic acid) on anatase to rutile transition. The samples were characterised using Raman spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) studies. At 500 °C, all samples contained only anatase. At 600 °C, the 1 : 1, 1 : 4 and 1 : 8 samples contain only anatase and the control (which contains no modifier) was a mixture of 27% anatase and 73% rutile. At 700 °C, the 1 : 1 molar ratio sample contained 50% anatase/rutile, 1 : 4 and 1 : 8 molar ratio samples were observed to have a majority of anatase, 76% and 71% respectively. When the temperature was increased to 800 °C, the sample with the 1 : 4 molar ratio contained 10% anatase and at the same temperature the 1 : 8 ratio sample contained 7% anatase; the remaining samples (1 : 0 and 1 : 1) at this temperature contained only rutile. These results show that there is a significant % anatase still present when the doped samples were calcined to 700 °C when compared with the control (100% rutile). There are small amounts of the anatase phase in the 1 : 4 and 1 : 8 samples at 800 °C. Therefore, benzoic acid has induced a delay in the rutile formation.