Amorphous TiO2 nanostructures: synthesis, fundamental properties and photocatalytic applications

Titanium dioxide (TiO2) nanostructures have been extensively investigated in the field of photocatalysis, and many previous review articles have summarized the progress made in the design and synthesis of crystalline TiO2 with tailored nanostructures. However, the physical and chemical properties of TiO2, including light absorption, surface adsorption, and charge carrier separation, are related to the disordered arrangement of intrinsic atoms. Therefore, amorphous TiO2 (am-TiO2) with long-range atomic disorder plays an important role in the photocatalytic performances. Unfortunately, at present we still know less about amorphous TiO2-based materials than crystalline ones from a scientific viewpoint, and a comprehensive review on am-TiO2 is lacking and highly desirable to further advance the development of novel function-oriented TiO2-based nanostructures. In this review, we comprehensively summarize the structural characteristics, optical properties, synthesis principles and current morphologies of am-TiO2 nanostructures. In particular, photocatalytic applications with regard to am-TiO2-based nanostructures are highlighted. Additionally, we briefly propose several perspectives on the challenges and new direction for future investigation. This review will act as a useful guideline for researchers who are currently concentrating on TiO2 materials to fabricate novel amorphous-based nanomaterials for photochemical applications.