Heterostructures of TiO₂@Fe₂O₃ with a specific electronic structure and morphology enable us to control the interfacial charge transport necessary for their efficient photocatalytic performance. In spite of the extensive research, there still remains a profound ambiguity as far as the band alignment at the interface of TiO₂@Fe₂O₃ is concerned. In this work, the extended type I heterojunction between anatase TiO₂ nanocrystals and α-Fe₂O₃ hematite nanograins is proposed. Experimental evidence supporting this conclusion is based on direct measurements such as optical spectroscopy, X-ray photoemission spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), and the results of indirect studies of photocatalytic decomposition of rhodamine B (RhB) with selected scavengers of various active species of OH^•, h^•, e^-, and ^•O₂^-. The presence of small 6-8 nm Fe₂O₃ crystallites at the surface of TiO₂ has been confirmed in HRTEM images. Irregular 15-50 nm needle-like hematite grains could be observed in scanning electron micrographs. Substitutional incorporation of Fe³⁺ ions into the TiO₂ crystal lattice is predicted by a 0.16% decrease in lattice parameter a and a 0.08% change of c, as well as by a shift of the Raman E_g(1) peak from 143 cm^-1 in pure TiO₂ to 149 cm^-1 in Fe₂O₃-modified TiO₂. Analysis of O 1s XPS spectra corroborates this conclusion, indicating the formation of oxygen vacancies at the surface of titanium(IV) oxide. The presence of the Fe³⁺ impurity level in the forbidden band gap of TiO₂ is revealed by the 2.80 eV optical transition. The size effect is responsible for the absorption feature appearing at 2.48 eV. Increased photocatalytic activity within the visible range suggests that the electron transfer involves high energy levels of Fe₂O₃. Well-programed experiments with scavengers allow us to eliminate the less probable mechanisms of RhB photodecomposition and propose a band diagram of the TiO₂@Fe₂O₃ heterojunction.

2D TiO₂ thin films and 3D flower-like TiO₂-based nanostructures, also decorated with SnO₂, were prepared by chemical and thermal oxidation of Ti substrates, respectively. The crystal structure, morphology and gas sensing properties of the TiO₂-based sensing materials were investigated. 2D TiO₂ thin films crystallized mainly in the form of rutile, while the flower-like 3D nanostructures as anatase. The sensor based on the 2D TiO₂ showed the best performance for H₂ detection, while the flower-like 3D nanostructures exhibited enhanced selectivity to CO(CH₃)₂ after sensitization by SnO₂ nanoparticles. The sensor response time was of the order of several seconds. Their fast response, high sensitivity to selected gas species, improved selectivity and stability suggest that the SnO₂-decorated flower-like 3D nanostructures are a promising material for application as an acetone sensor.