Photocatalytic and degradation mechanisms of anatase TiO2: a HRTEM study

Abstract

The photocatalytic process for degradation of methylene blue with P25 TiO 2 was directly observed using a high-resolution transmission electron microscopy (HRTEM). It was found that:(1) the pristine anatase TiO 2 nanoparticles exhibited a perfect crystal lattice with a clear HRTEM image; (2) after adsorption and degradation, there were many methylene blue crystals as 1 nm molecular adsorbed at the surface of TiO 2 nanoparticles, which therefore resulted in a fuzzy HRTEM image; (3) when the TiO 2 was exposed in air for a period of time, the methylene blue molecules disappeared and the TiO 2 lattice image again became integrated as the pristine one; (4) however, if the TiO 2 nanoparticles became deactivated after degradation of methylene blue for more than 20 cycles, the HRTEM lattice image was fuzzy fully and could not recover even it was exposed in air for a long time. The results reveal that the lattice distortion on the anatase TiO 2 (101) surface induced by chemical adsorption of methylene blue molecules is a crucial intermediate step during photocatalyzing. The distorted lattice atoms absorb photons under illumination of light and tend to recover and cut the molecule bond which causes the degradation of methylene blue. Furthermore, we propose that there exists a surface lattice driving force forming on the surface distortion leads to the TiO 2 lattice HRTEM image from fuzzy to integrate, and it decides the photocatalytic ability.

Preparation and Characterization of Mg/TiO2 for Visible Light Photooxidative-Extractive Deep Desulfurization

“…Two different length of lattice fringes were also identified from which were tabulated in Table 2. The shorter and more consistent d-spacing of 0.332-0.361 nm was assigned to anatase TiO 2 (101) (Lu et al 2008;Parra et al 2008;Zhang et al 2011). No surface lattice distortion on TiO 2 was observed even when incorporated with higher Mg loading ).…”

Lattice distortion mechanism study of TiO2 nanoparticles during photocatalysis degradation and reactivation

“…23 This adsorption would form a few S + -O -bonds. 25 Due to the mismatch of MB molecular and TiO 2 lattice, the bonding would make the distortion of the surface lattice up to 5%, 16 which finally resulted in increase of small-size defects in TiO 2 nanoparticles. Compared to the longer τ 1 , the τ 2 value of sample S A had only a small changes, because it was related to larger defects, such as vacancy clusters, grain boundaries and voids, etc.…”

“…The average light intensity at the position of the solution surface was about 23 mW cm −2 . 16 The photocatalytic reaction was aerobic, so the solution was exposed to the air and stirred continuously during photocatalysis. The temperature was 22 o C in the lab room.…”

“…[13][14][15] The urgency for the mechanism drives cutting-edge researches to the relationship between the lattice changes and photocatalytic activity of TiO 2 . In our previous work, 16 we studied the photocatalytic process in an atomic scale by using HRTEM. It was found that the surface lattice distortion induced a kind of "surface lattice driving force", which provided energy to disconnect the molecule bonds and degrade methylene blue substance.…”

Effectiveness of photodecomposition of rhodamine B and malachite green upon coupled tricomponent TiO2(Anatase-Rutile)/ZnO nanocomposite

“…In response to this, materials which can remove the harmful pollutants irreversibly and eliminate them completely have been developed [1][2][3][4][5][6][7][8][9][10]. Heterogeneous photocatalysis is an emerging technique for environmental remediation, where semiconductor materials are used as photocatalysts [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. When organic pollutants are decomposed by heterogeneous catalytic reactions, the pollutant molecules are adsorbed on the surface of the catalysts, where chemical bonds are broken and formed, and eventually small organic molecules or carbonate are released as decomposed products.…”