Modulating High‐Index Facets on Anatase TiO₂

Abstract

The atomic arrangement of titanium and oxygen on crystalline anatase TiO 2 formulates various facets, dominating the TiO 2 surface chemistry. Due to its unique surface atomic structure, TiO 2 with high-index facets has received great interest from a wide spectrum of science. Insights gained from the intricate link between the morphological modulation of anatase TiO 2 with distinct high-index facets and the properties of these modifications can expedite the rational fabrication of functional Fundamental BackgroundTitanium dioxide (TiO 2 ) has attracted considerable attention ever since the pioneer study by Fujishima and Honda in the 1970s.[1] TiO 2 materials have wide-ranged applications in photocatalysis, photoelectrochemical cells, rechargeable lithium ion batteries, sensors, and dye-sensitized solar cells. [2][3][4][5][6][7][8][9] All these applications are rooted in the distinctive physicochemical properties of these materials, [10][11][12] which are mainly influenced by the specific facets of the TiO 2 crystals. [13][14][15][16][17][18][19][20] Recently, high-index TiO 2 has been reported to exhibit unique properties with an advantage over low-index TiO 2 . The high-index facets are defined as a series of Miller indices {hkl} with at least one index being greater than one. [21] Nano-or microcrystals with exposed high-index facets are of paramount significance to both fundamental research and technical applications by virtue of their copious atomic steps, kinks, ledges, dangling bonds, and abundant unsaturated coordination sites. [5,14,[22][23][24][25][26][27][28] For instance, we observed that high-index {201} TiO 2 exhibited better adsorption and photooxidation performance than that of three low-index {001}, {100}, and {101} TiO 2 materials. [13] This observation is ascribed to the surface energy, which follows the order {201} (1.72 J/m 2 ) > {001} (0.90 J/m 2 ) > {010} (0.53 J/m 2 ) > {101} (0.44 J/m 2 ). [13,[29][30][31] {201} facets have more uncoordinated Ti atoms, facilitating the photogeneration of hydroxyl radicals. The surface energy and atomic structure of [a] 688 comprised spindles with stepped terraces at 1 h. The TEM images at 6 h (Figure 7c, d) reveal that the particle size increased with extending reaction time. It is noteworthy that the SAED and HRTEM images (Figure 7e, f ) further confirm that the TiO 2 nanorods were composed of {010}, {001}, {101}, and {103} facets. An extraordinary power conversion efficiency was observed for DSSCs assembled of these unique microstructures.

Recent Advancements in the Understanding of the Surface Chemistry in TiO2 Photocatalysis

“…An interesting application of anatase TiO 2 films is in the fabrication of resistive gas sensors. Liang et al [67] prepared two anatase samples: one containing predominantly (010) facets and a second containing predominantly (101) facets. It turned out (see Figure 7) that the drop in resistance upon exposure to acetone vapors was approximately twice as large for the sample containing (010) facets, an indication of more efficient charge injection into the (010) TiO 2 surface upon oxidation at the sensor working temperature (320 • C).…”

High-Index-Facet- and High-Surface-Energy Nanocrystals of Metals and Metal Oxides as Highly Efficient Catalysts

“…23 As for metal oxides, some low-index facets, e.g., anatase TiO 2 {110} facets, have rich dangling bonds, and thus possess higher surface energy. 44,45 There are four types of high-index facets: {hk0}, {hkk}, {hhl}, and {hkl}, which can form tetrahexahedral (THH), trapezohedral (TPH), trisoctahedral (TOH), and hexoctahedral (HOH) NCs, respectively. Besides polyhedra, some nanowires also have plenty of low-coordinated surface sites, which are also included in this review.…”

Fluorination of Defective Titanium Dioxide with an Efficient Photocatalytic Activity

“…Overcoming electron-hole pairs through unbalanced photogenerated recombination on the surface of crystallites has become an important prerequisite for the commercial application of TiO 2 [14,15]. Special facet exposure on TiO 2 samples is an effective way to improve the separation of photogenerated electrons and holes, electrons are enriched in the (101) plane, whereas holes are enriched in the (001) plane, which ultimately contributes to the photocatalysis [16][17][18]. For TiO 2 , the exposed crystal plane is generally the (101) crystal plane, the crystal plane energy (0.44 J/cm 2 ) of this crystal plane is low, and it has good reducing ability; therefore, it has good performance in photocatalytic hydrogen production, but its activity in degrading pollutants is lower than (001) [19].…”