Critical Review on Titania-Based Nanoparticles: Synthesis, Characterization, and Application as a Photocatalyst

TiO 2 nanoparticle is very important due to its non-toxicity, inexpensive, thermal, and chemical stability. TiO 2 exists in three crystalline forms: anatase, brookite, and, rutile. The crystal structure of anatase and rutile is tetragonal and brookite is orthogonal. TiO 2 is widely known for its photocatalytic behavior, which makes it a useful material in various applications. When exposed to light, TiO 2 generates electron–hole pairs, which can react with water and oxygen to produce reactive oxygen species (ROS) such as hydroxyl radicals. TiO 2 as a photocatalyst is used to remove environmental pollutants and convert solar energy into H 2 and electricity and detach pharmaceuticals and toxicity of photo products. The smaller size of TiO 2 has better photocatalytic properties as compared to the larger size. TiO 2 nanoparticles are prepared by various methods: sol–gel synthesis, hydrothermal method, solvothermal method, electrochemical method, organometallic synthesis, green synthesis, etc. TiO 2 nanoparticles are the heterogeneous catalyst and the transfer of electrons from TiO 2 particles by absorption of light causes a redox reaction which is used for organic transformation. TiO 2 nanoparticles also have various other important applications including wastewater treatment, air purification, reducing the toxicity of dyes, gas sensors, food and personal care, lithium-ion batteries, water splitting, etc. Herein, we summarized the mode of synthesis, characterization, and various organic transformations using titania-based nanoparticles.