Fluorite-type Zr-based oxides with the composition Ga₂Zr_2−xW_xO₇(x= 0, 0.05, 0.1, 0.15 and 0.2) were prepared using the citrate technique. Appropriate characterizations of all prepared materials were carried out. X-ray diffraction clarified that the undoped and W-doped Ga₂Zr₂O₇samples were crystallized in the cubic fluorite phase structure. The average particle size of the samples was in the range of 3–8 nm. The lowest band gap (1.7 eV) and the highest surface area (124.3 m²g⁻¹) were recorded for Ga₂Zr_0.85W_0.15O_7.The photocatalytic impacts of the prepared systems were studied by removal of crystal violet (CV) dye employing visible light illumination and taking into consideration the initial dye concentrations, duration of visible irradiation treatment, catalysts dose and the dopant concentration. The obtained results showed higher dye removal with the boost of the catalyst dosage. W doping shifted the absorption to the visible light range by decreasing the band gap from 4.95 eV for parent Ga₂Zr₂O₇to 1.7 eV for 15 mol% tungsten-doped Ga₂Zr₂O₇enhancing the photocatalytic decolourization of CV from 4.2% to 83.6% for undoped and 15 mol% W-doped Ga₂Zr₂O₇, respectively, at optimum operating conditions (pH 9, 1 g l⁻¹catalyst dose and 300 min) while heavily doped W sample containing 20 mol% W showed lower removal than 15 mol% W-doped Ga₂Zr₂O₇. Complete CV degradation using 15 mol% W-doped Ga₂Zr₂O₇was attained with the assistance of 25 mmol l⁻¹hydrogen peroxide. The reaction is aligned to pseudo-first-order kinetics. Different scavengers were introduced to decide the significance of the reactive species in CV degradation.O2−∙and h⁺had the major role in the degradation of CV by Ga₂Zr_2−xW_xO₇system compared with HO^•.

Two sol–gel methods (the citric acid gel and the Pechini methods) were used for the preparation of nano-sized undoped, Bi-doped and Bi, Cu co-doped SrTiO ₃ samples to optimize their properties for the photocatalytic degradation of dibutyl phthalate. The perovskite-like phase was detected for the samples prepared by the citric acid gel method after calcination at 800 °C for 3 h, while in the case of the Pechini method; it was detected after calcination at 800 °C for 9 h. The particle size of the samples prepared by the citric acid gel method is greater than that of the samples prepared by the Pechini method. Cu doping in both methods increased the particle size. Cu doping, Bi doping and Bi, Cu co-doping in both methods shifted the absorption edge to the visible light range as well. The band gap of Bi, Cu co-doped SrTiO ₃ is smaller than that of Bi doped SrTiO ₃ , which in turn is smaller than that of undoped SrTiO ₃ . The highest removal of the total organic carbon (TOC) of DBP was obtained using a Bi, Cu co-doped SrTiO ₃ sample prepared by the citric acid gel method. TOC removal of DBP followed pseudo-first order kinetics.