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Abstract
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.
Highlights
The formation of microbial colonies inside the wet or damp indoor environments is one of the major contributing elements to the deterioration of indoor air quality [1,2]
A reduction in the band gap was reported in all studies and this is attributed to a combination of Cu 3d and O 2p states above the valence band maximum (VBM)
The inclusion of a +U correction for Cu 3d states is important in correctly describing the Cu2+ oxidation state [48,49,61]. They reported greater band gap reduction with increases in dopant concentration due to the covalent character of the Cu-O interaction leading to new states at the valence band maxima (VBM)
Summary
The formation of microbial colonies inside the wet or damp indoor environments is one of the major contributing elements to the deterioration of indoor air quality [1,2]. These microorganisms have the potential to produce contaminants like spores, allergens and toxins affecting the health of the occupants [3,4]. This kind of continuous exposure can lead to various health concerns like respiratory or skin diseases [5,6].
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