Low-Temperature Sol–Gel Synthesis and Photoactivity of Nanocrystalline TiO2 with the Anatase/Brookite Structure and an Amorphous Component

Visible light photoluminescence in TiO2/CdS nanopowders synthesized by sol-gel route: effect of gel aging time

“…In samples with short aging time (1 h) and containing the maximum amount of CdS nanoparticles up to 9%, visible emission is maximum, and is significantly higher than in the original pure components. As shown above and discussed in detail in our previous work [26], there are no significant differences between the structural properties of the components of the TiO 2 /CdS composite and the original bare sol-gel TiO 2 nano-powder and CdS nanoparticles. However, the increased defect concentrations in the TiO 2 /CdS interface region, detected by MD simulations of CdS @ TiO 2 composite particles, will affect surface defect states and lead to an increased visible PL emission, especially in the early stages of aging.…”

“…The drop in the concentration of CdS nanoparticles is associated with the decreases in the content of the amorphous phase in the TiO 2 matrix and the calculated thermodynamic stability of the composite CdS @ TiO 2 nanoparticles depending on the structure of the titanium shell: amorphous titania > polycrystalline titania (anatase or brookite). HRTEM images confirmed that colloidal CdS nanoparticles are incorporated into all anatase/brookite matrices [26]. A typical HRTEM image of the incorporated CdS nanoparticle with zone axis [001] is given in the Fig.…”

“…Estimations made by Peakfit decomposition of XRD spectra showed that CdS nanoparticles concentration decreases with increasing gel aging time and is 9, 2 -3 and about 1% CdS for TiO 2 /CdS samples with 1, 3 and 4 h aging, respectively. This effect was discussed in detail using the Molecular Dynamic simulations in our previous work [26]. The drop in the concentration of CdS nanoparticles is associated with the decreases in the content of the amorphous phase in the TiO 2 matrix and the calculated thermodynamic stability of the composite CdS @ TiO 2 nanoparticles depending on the structure of the titanium shell: amorphous titania > polycrystalline titania (anatase or brookite).…”

“…Gel aging time, as has been shown, can affect the crystallinity degree of titania (amorphous/nanocrystalline ratio), and content of the incorporated CdS nanoparticles [25]. In addition, it must be taken into account that the stage of low-temperature gel aging promotes polycondensation of hydrolysis products to form titania and decrease of the oxygen vacancy and the hydroxyl group in synthesized titania [26].…”

Low Temperature Synthesis of Photocatalytic Mesoporous TiO2 Nanomaterials

“…Indeed, the anatase phase has been generally regarded as the most photoactive crystalline phase of TiO 2 [12,13]; however, several examples of increased photoactivity due to a mix of different crystalline phases have been reported [14,15]. The concomitant presence of different crystalline phases can be seen as being beneficial to improve the photocatalytic efficiency of the TiO 2 , as a suitable combination of crystalline phases, with an appropriate alignment of the conduction and valence band edge positions, enable a charge transfer between the different phase domains, thus limiting the detrimental recombination phenomena of electrons and holes [16][17][18]. Most of the reported synthetic approaches needs high reaction temperatures and/or single or multiple post-synthesis calcination steps at a temperature higher than 300 • C to promote crystallization in anatase phase [19][20][21].…”