Hierarchical TiO2 superstructures with desired architectures and intriguing physico-chemical properties are considered to be one of the most promising candidates for solving the serious issues related to global energy exhaustion as well as environmental deterioration via the well-known photocatalytic process. In particular, TiO2 mesocrystals, which are built from TiO2 nanocrystal building blocks in the same crystallographical orientation, have attracted intensive research interest in the area of photocatalysis owing to their distinctive structural properties such as high crystallinity, high specific surface area, and single-crystal-like nature. The deeper understanding of TiO2 mesocrystals-based photocatalysis is beneficial for developing new types of photocatalytic materials with multiple functionalities. In this paper, a comprehensive review of the recent advances toward fabricating and modifying TiO2 mesocrystals is provided, with special focus on the underlying mesocrystallization mechanism and controlling rules. The potential applications of as-synthesized TiO2 mesocrystals in photocatalysis are then discussed to shed light on the structure–performance relationships, thus guiding the development of highly efficient TiO2 mesocrystal-based photocatalysts for certain applications. Finally, the prospects of future research on TiO2 mesocrystals in photocatalysis are briefly highlighted.

Nanostructured TiO2-based Z-scheme heterojunctions have been widely accepted to be among the most effective photocatalysts for environmental remediation owing to their broadened light absorbance, high efficiency of photogenerated charge carrier separation, and well-preserved strong oxidation and reduction capability. In this review, we will first introduce the photogenerated charge carrier transportation mechanism of three different types of Z-scheme heterojunction systems, namely, liquid-phase Z-scheme photocatalytic system, all-solid-state indirect Z-scheme photocatalytic system, and all-solid-state direct Z-scheme photocatalytic system. Subsequently, we will describe the recent advances toward the rational design and fabrication of all-solid-state nanostructured TiO2-based Z-scheme heterojunctions. The applications of the thus-constructed all-solid-state nanostructured TiO2-based Z-scheme heterojunctions in the degradation of volatile organic compounds, removal of waste water organic pollutants, and upgradation of greenhouse gas CO2 will then be presented one by one. Finally, the advantages and disadvantages of all-solid-state nanostructured TiO2-based Z-scheme heterojunction for photocatalytic environmental remediation will be briefly discussed, and the direction of future development will be prospected as well.

Nonaqueous sol−gel routes are considered to be effective alternatives to aqueous approaches for producing nanostructured metal oxides with desired morphologies and intriguing photo-electronic properties for harvesting and converting solar energy to alleviate serious problems of water pollution. Despite significant progress, the exploration of green and recyclable organic solvents for producing functional nanostructures of metal oxides remains a great challenge. Herein, we demonstrate that by utilizing ethyl formate, which is generally recognized as safe by the U.S. Food and Drug Administration and widely employed in the food industry, as the sole solvent, nanosized carbonate-doped TiO 2−x mesocrystals could be controllably fabricated via nonaqueous solvothermal reactions and subsequent calcination in air at moderate temperatures. Such a green solvent of ethyl formate could be recycled and further used at least three more times, with the mesocrystalline architecture of the precipitated anatase crystals well retained, illustrating its high effectiveness in mesocrystal production with a minimized impact on the environment. Owing to their carbonate-doped, oxygen-deficient, and mesocrystalline nature, the as-synthesized nanosized carbonated-doped TiO 2−x mesocrystals exhibited strengthened light harvesting and bolstered photogenerated electron−hole separation and thus displayed a noticeable enhancement on photocatalytic activity toward the removal of the water pollutants sulfathiazole and Cr VI under visiblelight irradiation.