Nanocomposites with polymer matrix offer excellent opportunities to explore new functionalities beyond those of conventional materials. TiO₂, as a reinforcement agent in polymeric nanocomposites, is a viable strategy that significantly enhanced their mechanical properties. The size of the filler plays an essential role in determining the mechanical properties of the nanocomposite. A defining feature of polymer nanocomposites is that the small size of the fillers leads to an increase in the interfacial area compared to traditional composites. The interfacial area generates a significant volume fraction of interfacial polymer, with properties different from the bulk polymer even at low loadings of the nanofiller. This review aims to provide specific guidelines on the correlations between the structures of TiO₂ nanocomposites with polymeric matrix and their mechanical properties. The correlations will be established and explained based on interfaces realized between the polymer matrix and inorganic filler. The paper focuses on the influence of the composition parameters (type of polymeric matrix, TiO₂ filler with surface modified/unmodified, additives) and technological parameters (processing methods, temperature, time, pressure) on the mechanical strength of TiO₂ nanocomposites with the polymeric matrix.

Applications of TiO₂ nanomaterials in photocatalysis, batteries, supercapacitors and solar cells, have seen widespread development in recent decades. Nowadays, black TiO₂ have won attention due to enhancing the solar light absorption by the formation of oxygen vacancies and Ti³⁺ defects, to promote the separation of photo-generated charge carriers leading to the improvement of the photocatalytic performance in H₂ production and pollutants degradation. The enhanced photocatalytic activity of black TiO₂ is also due to a lattice disorder on the surface and the presence of oxygen vacancies, Ti³⁺ ions, Ti-OH and Ti-H groups. Enhancing the optical absorption characteristics of TiO₂ and change of energy level and band-gap of materials have been successfully demonstrated to improve their photocatalytic activities, especially for black TiO₂ nanoparticles, which promote visible light absorption. The current review focuses on the investigation of the chemical reduction synthetic route for black TiO₂ nanomaterials, and their proposed association with green applications such as photodegradation of organic pollutants and photocatalytic water splitting. The synthesis methods of black TiO₂ involves the changes from Ti⁴⁺ to Ti³⁺ state, into different strategies: (1) The use of highly active hydrogen species such as H₂, H₂/Ar or H₂/N₂ gases, and metal hydrides (NaBH₄, CaH₂), (2) the reduction by active metals such as aluminum, magnesium and zinc, and (3) organic molecules such as imidazole and ascorbic acid.

The presence of toxic, non-biodegradable and harmful organic pollutants in soils, wastewater, and atmosphere has become an indisputable, and global fact as a significant environmental problem. The heterogeneous photocatalysis, an advanced oxidation process (AOP) using semiconductor materials as catalysts, is a topic of great interest considering the possibility of the pollutants removal from water. The photocatalytic degradation of organic contaminants (i.e., dyes, pesticides, phenolic compounds) present in water using semiconductor materials depends on a number of parameters such as: the bandgap energy, phase composition, crystallinity, morphology and surface area of catalyst, electron-hole recombination rate, intensity of light, and adsorption capacity of the dye on the photocatalyst surface. One of the important constraints related to the catalyst photocatalytic efficiency is the fast recombination of the photogenerated electrons and holes. Therefore, various strategies have been involved in promoting the charge separation, including the development of heterojunction between two semiconductor materials, by tailoring the photocatalysts properties. This mini-review deals with the recent developments on dyes photodegradation using as catalysts various heterojunctions based on copper sulfide nanostructures, such as copper sulfide/metal oxide, copper sulfide/metal sulfide, copper sulfide/graphene, copper sulfide/organic semiconductors etc. The effects of different parameters, such as synthesis parameters, particle size, bandgap energy, surface area, and morphology on the photocatalytic activity of copper sulfide heterojunctions for dyes degradation is also highlighted.