Semiconductor photocatalysis has caused enormous attention in recent year and has been demonstrated to be one of the "green" and effective methods for water and air purification, water disinfection, hazardous waste remediation, antibacterial, and self-cleaning. However, owing to low photocatalytic efficiency, the environmental applications of various photocatalytic materials and technologies are still very limited. Thus, more improvement and investigations are highly required from the viewpoint

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... of practical use. This special issue contains 20 papers, which are mainly related to pollutant degradation and environmental purification. Among them, 10 papers are related to composite of two semiconductors including TiO 2 and other semiconductors, 4 papers deal with fabrication of new photocatalytic materials, 2 papers are about doping of TiO 2 , and 4 papers are devoted to immobilization of TiO 2 . Furthermore, there are 13 papers devoting degradation of pollutant in water, 4 papers on air purification including decomposition of formaldehyde, NO and benzene, 2 papers related to hydrogen production, and 1 paper dealing with bactericidal activity of TiO 2 . We would like to express our sincere thanks to all the authors for submitting their interesting works to this special issue. A brief summary of all 20 accepted papers is provided as follows. In "A cost-effective solid-state approach to synthesize g-C 3 N 4 coated TiO 2 nanocomposites with enhanced visible light photocatalytic activity, " the authors describe the fabrication and photocatalytic performance of g-C 3 N 4 /TiO 2 nanocomposites by a facile solid-state method using urea and commercial TiO 2 as precursors. The prepared nanocomposites exhibited enhanced absorption and photocatalytic performance for degradation of aqueous MB in visible light region. The paper "Synthesis and characterization of pyrochlore Bi 2 Sn 2 O 7 doping with praseodymium by hydrothermal method and its photocatalytic activity study" reports preparation of Pr-doped Bi 2 Sn 2 O 7 (BSO) by a hydrothermal method. The photocatalytic activity of the prepared samples was evaluated by the degradation of rhodamine Bextra (RhB) and 2,4-dichlorophenol (2,4-DCP) in aqueous solution under visible light. Pr-doped BSO samples exhibited enhanced visible-light photocatalytic activity and the optimal dopant amount of Pr was determined to be 1.0 mol%. The paper "Single step formation of C-TiO 2 nanotubes: influence of applied voltage and their photocatalytic activity under solar illumination" presents fabrication of self-aligned and high-uniformity carbon (C)-titania (TiO 2 ) nanotube arrays by single step anodization of titanium (Ti) foil at 30 V for 1 h. The photocatalytic activity evaluation of C-TiO 2 samples was performed by degradation of methyl orange (MO) solution. The results revealed that controlled nanoarchitecture C-TiO 2 photocatalyst led to a significant enhancement in photocatalytic activity.