Highly reactive {001} facets of TiO2-based composites: synthesis, formation mechanism and characterization

Abstract

Titanium dioxide (TiO2) is one of the most widely investigated metal oxides due to its extraordinary surface, electronic and catalytic properties. However, the large band gap of TiO2 and massive recombination of photogenerated electron-hole pairs limit its photocatalytic and photovoltaic efficiency. Therefore, increasing research attention is now being directed towards engineering the surface structure of TiO2 at the most fundamental and atomic level namely morphological control of {001} facets in the range of microscale and nanoscale to fine-tune its physicochemical properties, which could ultimately lead to the optimization of its selectivity and reactivity. The synthesis of {001}-faceted TiO2 is currently one of the most active interdisciplinary research areas and demonstrations of catalytic enhancement are abundant. Modifications such as metal and non-metal doping have also been extensively studied to extend its band gap to the visible light region. This steady progress has demonstrated that TiO2-based composites with {001} facets are playing and will continue to play an indispensable role in the environmental remediation and in the search for clean and renewable energy technologies. This review encompasses the state-of-the-art research activities and latest advancements in the design of highly reactive {001} facet-dominated TiO2via various strategies, including hydrothermal/solvothermal, high temperature gas phase reactions and non-hydrolytic alcoholysis methods. The stabilization of {001} facets using fluorine-containing species and fluorine-free capping agents is also critically discussed in this review. To overcome the large band gap of TiO2 and rapid recombination of photogenerated charge carriers, modifications are carried out to manipulate its electronic band structure, including transition metal doping, noble metal doping, non-metal doping and incorporating graphene as a two-dimensional (2D) catalyst support. The advancements made in these aspects are thoroughly examined, with additional insights related to the charge transfer events for each strategy of the modified-TiO2 composites. Finally, we offer a summary and some invigorating perspectives on the major challenges and new research directions for future exploitation in this emerging frontier, which we hope will advance us to rationally harness the outstanding structural and electronic properties of {001} facets for various environmental and energy-related applications.

2D/2D Graphitic Carbon Nitride (g-C3N4) Heterojunction Nanocomposites for Photocatalysis: Why Does Face-to-Face Interface Matter?

“…By harvesting solar energy as the source of renewable energy, photocatalysis will make significant impacts in the areas of (1) light-driven water splitting to hydrogen (H2) and oxygen (O2) (Chen et al, 2010;Bai et al, 2016;Wei et al, 2016;Putri et al, 2017;Yubin et al, 2017), (2) conversion of carbon dioxide (CO2) to energy bearing fuels (Ong et al, , 2014cTan et al, 2014Tan et al, , 2016Tan et al, , 2017Gui et al, 2015;Guo et al, 2016a;Zhang et al, 2016c), (3) mineralization of waste and pollutants (Ong et al, 2014d,e;Fang et al, 2016;Liu et al, 2016c;Topcu et al, 2016;Zhao et al, 2016b), (4) selective organic transformations (Liu et al, 2014;Zhao et al, 2016a), and (5) disinfection of bacteria (Keane et al, 2014;Bing et al, 2015) (Figure 1). Very recently, two-dimensional (2D) semiconductor photocatalysts have triggered a renaissance of interest in the field of energy, and environmental-related applications thank to the high ratio of surface-to-volume and unprecedented electronic and optical characteristics (Ong et al, 2014b;Bai et al, 2015;Liang et al, 2015d;Fang et al, 2016;Kalantar-zadeh et al, 2016;She et al, 2017;Xueting et al, 2017). Among a large array of photocatalysts, research targeting at graphitic carbon nitride (g-C3N4) has been flourishing in recent years.…”

Porous (001)-faceted anatase TiO2nanorice thin film for efficient dye-sensitized solar cell

“…Since many surface reaction favours to occur at the high-energy site, such as defect, twinning or kinks [18,19], to synthesize anatase TiO 2 nanostructures having such structural properties promises enhanced performance in applications. Moreover, anatase TiO 2 with high-energy plane, such as (001), and anisotropic-shape (such as nanorice) [20], containing high-surface area and high-defect further promotes active surface reaction and facile electron transfer in the device [5,21]. Thus, highperformance solar cell or photocatalysis can be obtained from the structure.…”

“…TiO 2 nanostructure with a larger surface area is ideal for solar cells [1][2][3], photolysis [4], sensors [5] and photocatalytic applications [4,6,7], as it improves the charge-transfer reaction, enhances the redox potential of photogenerated electrons and holes, and reduces the electron-hole recombination. For a solar cell application, TiO 2 with large surface area provides many active centers for reagent adsorption and reaction, improves dye molecules loading and facilitates facile electrolyte diffusion, leads to a facile electron transport in the device [8][9][10][11][12].…”

Photocatalytic Decolorization of Dye with Self-Dye-Sensitization under Fluorescent Light Irradiation

“…Titanium dioxide (TiO 2 ) and zinc oxide (ZnO) have drawn great attention, because they have become one of the most effective photocatalysts in the mineralization of toxic organic substances, owing their virtues of low cost, highly chemical stability, and nontoxicity [1,2]. However, these catalysts can only be excited by the irradiation of UV light, due to their wide band gaps.…”