UV to the visible region. In the first articles of this group, Asahi et al. present an overview on nitrogen-doped TiO2 nanomaterials, 22 which summarizes the design strategies for visible-light absorption, the synthesis and properties of nitrogen-doped TiO2 nanomaterials, and their applications in textile, interior, air, and water purification. 22 In the following article, Dahl, Liu, and Yin discuss another hot topic, notably property modification of TiO2 nanomaterials by formation of composites with other materials, eg metals, metal oxides, nonoxide semiconductors, and nanostructured carbon materials. 23 One of the advantages of these composites is the formation of heterojunctions between TiO2 and the other materials which favor separation of photoexcited carriers. 23 In the third article of this group, Liu and Chen summarize recent work on the property changes induced by so-called self-structural modifications, 2 which include effects due to the surface, lattice strain, defects, nanoscale size, synergistic effects between mixed phases, and lattice deformations in amorphous and hydrogenated phases. 24 They emphasize the dramatic property changes in the hydrogenated phases and the related physical and chemical characteristics. 24 The last six articles of this thematic issue are devoted to various applications of TiO2 nanomaterials, from the more established ones, such as photocatalysis, to the more recent ones, such as biosensing. First, Schneider et al. examine the environmental applications of TiO2 based photocatalysis. 25 They summarize time-resolved analysis of the photocatalytic process, the synthesis and properties of doped TiO2 nanoparticles, visible-light responsive thin films, and photoinduced surface wettability changes. 25 Next, Ma et al. focus on the application of TiO2 nanomaterials to photocatalytic fuel generation. 26 They describe the different aspects of photocatalytic hydrogen generation from water splitting and biomass reforming, summarize the progress in photocatalytic reduction of CO2 into fuels on various TiO2 nanomaterials, along with the impacts of reaction conditions and the reaction mechanisms. 26 In the following article, Liu et al. present an overview of bioinspired TiO2 nanomaterials with special wettability. 27 They start with fundamental theories and next describe superhydrophilic, superhydrophobic. and superoleophobic TiO2 surfaces and their applications as antibacterial, anticorrosion, antifogging, biomedical, self-cleaning, water condensation, etc., surfaces. 27 The photovoltaic applications of TiO2 nanomaterials are the subject of the following review, by Bai et al., 28 which includes discussions of the fundamental principles, organic− inorganic interactions, electron transport and recombination, and surface treatments in various types of solar cells. 28 In the following paper, Bai and Zhou review the use of TiO2 nanomaterials for sensor applications, notably gas sensors, chemical oxygen demand (COD) sensors, and biosensors. 29 Finally, in the last article of this thematic issue, Rajh et al. provide an overview of the relatively new area of biomedical applications of TiO2 nanomaterials. 30 Discussed topics include the importance of surface sites, nanoparticle redox active centers, reactive oxygen species, phototoxicity, sensitization of TiO2, TiO2− DNA hybrid, TiO 2− protein hybrid, drug delivery, and imaging guided therapy. 30

In summary, with 21 outstanding review articles from leading experts, this issue provides an exhaustive overview of the state-ofthe-art research on TiO2 nanomaterials that can be useful both as an introduction for newcomers and as a reference for experienced researchers in this field. We hope that this issue …