Effect of gadollunium doping on visible light photocatalytic performance of Ag3PO4: Evaluation of activity in degradation of an anthraquinone dye and mechanism study

Abstract

Gadolinium (Gd)-doped silver orthophosphate (Ag₃PO₄) nanoparticles, with spherical morphology, were synthesized by a co-precipitation method and their photocatalytic activities were evaluated in degradation of Reactive Blue 19 (RB19), as a model organic pollutant. The synthesized Ag₃PO₄ and Gd-doped Ag₃PO₄ were characterized using X-ray diffraction pattern analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, diffuse reflectance UV–vis spectroscopy and photoluminescence spectroscopy. In comparison with Ag₃PO₄, the experimental results revealed a considerable enhancement in photocatalytic activity of Gd-doped Ag₃PO₄. The optimum mole fraction of Gd loading in Ag₃PO₄ was 3%. Lower photocatalytic degradation efficiency of RB19 in the presence of oxalate anion and p-benzoquinone indicated the crucial role of photogenerated holes and superoxide anion-radicals in photocatalysis on Gd-doped Ag₃PO₄. The enhancement of photocatalytic activity was attributed to scavenge the photoexcited electrons, and to suppress their recombination with holes and generation of active oxygen species. A nonlinear empirical kinetic model was introduced to predict the apparent first order rate constant (k_app) as a function of operational parameters, including initial RB19 concentration, Gd-doped Ag₃PO₄ dosage and light intensity. Degradation byproducts were identified using gas chromatography-mass spectrometry and a probable pathway was proposed. Moreover, Gd-doped Ag₃PO₄ samples displayed adequate reusability after three successive experiments.