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This work reviews an eco-friendly process for producing TiO₂ via colloidal aqueous sol–gel synthesis, resulting in crystalline materials without a calcination step. Three types of colloidal aqueous TiO₂ are reviewed: the as-synthesized type obtained directly after synthesis, without any specific treatment; the calcined, obtained after a subsequent calcination step; and the hydrothermal, obtained after a specific autoclave treatment. This eco-friendly process is based on the hydrolysis of a Ti precursor in excess of water, followed by the peptization of the precipitated TiO₂. Compared to classical TiO₂ synthesis, this method results in crystalline TiO₂ nanoparticles without any thermal treatment and uses only small amounts of organic chemicals. Depending on the synthesis parameters, the three crystalline phases of TiO₂ (anatase, brookite, and rutile) can be obtained. The morphology of the nanoparticles can also be tailored by the synthesis parameters. The most important parameter is the peptizing agent. Indeed, depending on its acidic or basic character and also on its amount, it can modulate the crystallinity and morphology of TiO₂. Colloidal aqueous TiO₂ photocatalysts are mainly being used in various photocatalytic reactions for organic pollutant degradation. The as-synthesized materials seem to have equivalent photocatalytic efficiency to the photocatalysts post-treated with thermal treatments and the commercial Evonik Aeroxide P25, which is produced by a high-temperature process. Indeed, as-prepared, the TiO₂ photocatalysts present a high specific surface area and crystalline phases. Emerging applications are also referenced, such as elaborating catalysts for fuel cells, nanocomposite drug delivery systems, or the inkjet printing of microstructures. Only a few works have explored these new properties, giving a lot of potential avenues for studying this eco-friendly TiO₂ synthesis method for innovative implementations. Full article

The precursor for a lithium-ion sieve is prepared using an inorganic precipitation-peptization method with titanium sulfate as the titanium source and lithium acetate as the lithium source. The effects of Ni²⁺ (Nickel ions) doping on the stability of the sol, crystal morphology and interplanar spacing of Li₂TiO₃ are investigated. The results indicate that, after Ni²⁺ doping with varying fractions, the stability of the precursor sol first increases then decreases, and the maximum stabilization time of the precursor sol doped with 1% Ni²⁺ is 87 h. When doped with 1% Ni²⁺, the sol performance is most stable, the porous Li₂TiO₃ is obtained, and the specific surface area of Li₂TiO₃ increases by up to 1.349 m²/g from 0.911 m²/g. Accompanying the increase in calcination temperature, the inhibition of Ni²⁺ doping on the growth and crystallization of grains decreases. When the temperature is lower than 750 °C, Ni atoms replace the Ti atoms that are substituted for Li atoms in the original pure Li layer, forming lattice defects, resulting in the disappearance of (002) and (−131) diffraction peaks for Li₂TiO₃, the reduced ordering of crystal structure, a decrease in the interplanar spacing of the (002) plane, lattice expansion and an increase in the particle size to 100–200 nm. When the temperature exceeds 750 °C, with the increase of calcination temperature, the influence of Ni doping on the growth and crystallinity of grains decreases, and the (002) crystal surface starts to grow again. Full article