Enhanced photocatalytic degradation of anionic azo dyes using copper-doped lanthanum oxide nanoparticles
摘要
Lanthanum oxide (La2O3) is a p-type semiconductor with a typical direct band gap of > 5 eV and hence is generally considered as not suitable for photocatalysis in the pure state. To make it a suitable photocatalyst, the effects of 1–9% copper-doped La2O3 for the degradation of acid red 88 (AR 88) and eriochrome black T (EBT) anionic azo dyes have been studied. The nanoparticles are synthesised via the facile solution combustion method using banana peel powder extract as a green fuel. The X-ray diffraction, analysed by various models, reveals a considerable decrease in particle size and an increase in microstrain with doping. The direct band gap decreases from 5.72 eV for the host to 4.94 eV at an optimum doping level of 5%, thereafter increasing slightly. All doped catalysts show better efficiency for the degradation of both AR 88 and EBT dyes compared to the undoped La2O3 (labelled LC0). The optimised 5% copper-doped catalyst (LC5) achieved near complete degradation of AR 88 in 45 min with more than double the rate constant compared to LC0. The scavenger studies for the degradation of AR88 by LC5 indicate the oxidation of dye by the hydroxyl radical (OH.) as the main mechanistic pathway followed. The results revealed an ameliorating effect of copper doping on the degradation efficiency of lanthanum oxide nanoparticles, with an optimum doping achieved at 5–7% copper.