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Pure and copper-modified photocatalytic TiO 2 nanopowders were prepared via a green sol−gel route and heated to 450°C. Copper does not enter the TiO 2 lattice but forms as smaller ∼2 nm Cu-based nanocrystals, decorating the surface of ∼10 nm TiO 2 nanoparticles. The surface of the larger TiO 2 nanoparticles (NPs) is partially covered by much smaller Cu NPs, attached to the surface of the larger NPs but not completely covering them due to the small quantity present (1−10 mol % Cu). This retards the anatase-to-rutile phase transition and titania domain growth through a grain-boundary pinning mechanism. These hybrid nanoparticles show tunable photochromic behavior under both UVA and visible light. Under UVA, Cu 2+ nanoparticles reduce to Cu + , and then to Cu 0. Under visible-light, Cu 2+ reduces to Cu + , although to a lesser extent. The induced photochromism can be tuned by varying the light source or exposure time. One mol % Cu causes a reduction of Cu 2+ , and lowers the d−d absorption band, to 50% after only 12 s, and 95% after 10 min, under UVA-light, and has a reduction of 25% in 1 min, 50% in 4 min, and 80% in 1 h under visible-light. This is the first report of inorganic compounds, in this case Cu-TiO 2 hybrid nanoparticles, to exhibit tunable photochromism under both UVA and visible-light exposure. This rapid and sensitive effect can potentially be used to modify, tune, or monitor the progress of photoactivated behavior in a new generation of smart/active multifunctional materials and photoactive devices or sensors.

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With the increasing demand for nanomaterials, it is essential that they are produced, where possible, by sustainable or “green” synthesis methods, avoiding environmentally harmful processes and solvents, with the aim of reducing the production of hazardous byproducts and wastes and minimizing environmental impact. In this work, Ag-modified titania nanoparticles (NPs) were synthesized via a green aqueous sol–gel method. The products of the synthesis were thermally treated at 450 and 600 °C, and their photocatalytic (in liquid–solid and gas–solid phases) and antibacterial properties were assessed using both UV- and visible-light exposure. The microstructure and phase composition of the prepared samples were also characterized using advanced X-ray powder diffraction methods (whole powder pattern modeling). Results showed that both the amount of Ag and the thermal treatment greatly influenced not only the phase composition and microstructure but also the functional properties of the TiO2. The increasing levels of Ag retarded the anatase-to-rutile phase transition to a greater extent, and 2 mol % was the optimum amount of Ag for methylene blue photodegradation with both UV- and visible-light irradiation. When using a UV-light source, samples showed a much greater antibacterial activity toward Escherichia coli (E. coli; Gram-negative) than methicillin-resistant Staphylococcus aureous (Gram-positive). It was observed that UV light caused a change in the oxidation state of silver, from ionic silver to metallic (Ag+ → Ag0 NPs), this being detrimental for the antibacterial activity. However, under artificial white light irradiation this did not occur and the material kept its excellent antibacterial properties (higher activity than commercial P25); because of this, it could be suitable for use in health care, helping to greatly reduce the spread of Gram-negative type bacteria such as E. coli

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Perovskite-structured solid solutions intended for use as microwave dielectric resonators were studied by Raman spectroscopy. Two distinct categories were investigated: (i) simple perovskite–simple perovskite solid solutions, that is, CaTiO3–SrTiO3 (CTST), CaTiO3–CaZrO3 (CTCZ), CaTiO3–NdAlO3 (CTNA), and CaTiO3–LaGaO3 (CTLG); and (ii) simple perovskite–complex perovskite solid solutions, such as CaTiO3–SrMg1/3Nb2/3O3 (CTSMN). In the latter category, the influence of A-site ion radius was also addressed by examining 0.5CaTiO3– 0.5LaMg1/2Ti1/2O3 (0.5CT–0.5LMT), 0.5SrTiO3 (ST)–0.5LMT, and 0.5BaTiO3 (BT)–0.5LMT. Raman data from the end members and solid solutions are compared, paying particular attention to F2g and A1g mode bands, often associated with ordering of B-site species.