Role of oxygen vacancy in the plasma-treated TiO2 photocatalyst with visible light activity for NO removal

Role of zinc interstitials and oxygen vacancies of ZnO in photocatalysis: a bottom-up approach to control defect density

“…In connection to lattice defects, depending on the type and energetic location of the defect, their character is determined to capture either an electron or a hole, thereby delaying the recombination process. [1][2][3][4]6,[8][9][10][11][12][13] As a consequence, the captured or free charge carrier participates in photocatalytic activity (PCA), in which the catalysis occurs at the conduction band (CB), valance band (VB) and the defect site, if available on the surface. 4,8 Note that the defects form intermediate bands within the band gap, which allow visible light harvest especially in the case of wide band gap semiconductors.…”

“…1,4,8,[15][16][17] The lattice defects connected to PCA are basically intrinsic (vacancies, interstitials, anti-site) or extrinsic (induced by impurities) in nature. 1,4,6,[8][9][10][11][12][13]15,18 However, it is rather hard, though intriguing, to determine which defect is more benecial for PCA, especially in the context of ZnO because controlling the defect density and maintaining a balance among various defect types is quite challenging. 15 On the other hand, dominant defect density can compromise optical quality; nevertheless, it increases PCA, as recently reported by us.…”

“…25,26 Note that the controllability of the defect density depends on the type of defect and the semiconductor itself. 1,6,[8][9][10][11][12][13] In the context of ZnO, numerous studies deal with V O s, 4,8,10,11,13,21 which is not the case with Zn i s. It is also notable that the balance between the relative densities of Zn i s and V O s is still challenging. 15 The presence of Zn i s and V O s in ZnO can be easily identied by simple photoluminescence (PL) experiments, [15][16][17]27 indicated by blue and green emissions, respectively.…”

“…16,17,[28][29][30][31][32] In contrast, typically synthesized ZnO is predominant with V O s. 4,8,16,17,27,31,32 Consequently, photocatalysis studies involving V O s dominate the literature. 1,4,6,[8][9][10]13,21 In this context, it is very useful and important to study the effect of Zn i s in PCA and their efficiency against V O s. In addition to the fundamental interest, the results of such a study enable an efficient and cost effective design of novel photocatalysts. As shown earlier, 33 Zn i s are very unstable when compared to V O s, which are found to be stable even at 400 C. Aer nearly two years, theoretical support for this instability was provided by Janotti et al, 34 where the authors suggest that Zn i s diffuse faster through a migration barrier as low as 0.57 eV, cf.…”

Controlling Surface Defects and Photophysics in TiO2 Nanoparticles

“…For example, in a 4 nm TiO 2 particle roughly 31% of the atoms are on the surface. 18 There are several methods used for creating surface defects in TiO 2 : UV radiation, 19 annealing in vacuum, 20 ion sputtering, 20 plasma-treating 21 and controlling the calcination atmosphere during synthesis. 15 Unfortunately, these methods affect not only surface properties, but also size, shape, and crystallinity of nanoparticles.…”