Band-Structure Engineering of TiO₂ Photocatalyst by AuSe Quantum Dots for Efficient Degradation of Malachite Green and Phenol

Abstract

In this work, 0.5, 2.5, 5.0, and 7.5 wt% AuSe QDs/TiO₂ nanocomposites (x-AST NCs) were successfully fabricated and characterized. According to the XRD and TEM results, the crystal sizes of the tetragonal anatase TiO₂ NPs ranged from 40 to 50 nm, whereas those of the spherical AuSe quantum dots (AuSe QDs) ranged from 3.71 to 9.58 nm. The AST NCs showed higher surface areas in the range of 26.51–42.14 m²/g depending on the AuSe QDs content (0.5–7.5 wt%) compared to the neat TiO₂ itself (18.61. m²/g). According to the TGA curves, adding AuSe QDs onto the TiO₂ NPs resulted in higher thermal stability reached 530 °C at 7.5-AST NC. The UV/vis-diffuse reflectance spectra of x-AST NCs showed a visible light absorption band, a red shift in the absorption to visible light, and a narrow double energy gap. The AuSe QDs, when decorated onto TiO₂, enable precise engineering of the band structure of TiO₂ NPs with suitable narrow-band energy, which can be controlled to achieve enhanced charge separation and generation of extra oxidizing species, peroxy radicals, both beneficial for enhancing the photocatalytic performance. As expected, the fabricated x-AST NC NCs displayed excellent photocatalytic performance. The 5.0-AST NC exhibited the highest photocatalytic performance reached complete elimination (100%), which is almost 3-folds in comparison to that of neat TiO₂ NPs (33.62% and 33.10%) within 45 and 60 min for MG and phenol, respectively. The 5.0-AST NC was recycled five times and is of high stability.