BiVO4/WO3 nano-composite: characterization and designing the experiments in photodegradation of sulfasalazine.

A BiVO4-WO3 nano-composite (NC) was hydrothermally prepared and characterized by different techniques including X-ray diffraction (XRD), scanning electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer, X-ray mapping, UV-Vis reflectance spectroscopy (DRS), and photoluminescence spectroscopy (PL). The average crystallite size of 8.5 nm was estimated for the composite by the Williamson-Hall equation. The band gap energies of 2.46, 3.02, and 2.95 eV were obtained for the direct electronic transitions of BiVO4, WO3, and the composite, respectively. The point of zero charges (pHpzc) of the composite was also estimated at 5. The composite was then used in the photodegradation of sulfasalazine (SSZ). When the moles of WO3 was four times greater than BiVO4, the best photocatalytic activity and the lowest PL intensity were obtained. The simultaneous effects of the experimental variables on the boosted photocatalytic activity of the composite (to the single semiconductors) were studied by the response surface methodology (RSM). A significant quadratic model was confirmed for processing the data based on the F value of a model F value of 63.55 > F0.05, 14, 13 = 2.55. This was also confirmed by LOF F value of 2.56 < F0.05, 10, 3 = 8.79. Besides, the multiple correlation coefficients R2 (R2 = 0.9856), adjusted R2 (adj-R2 = 0.9701), and predicted R2 (pred-R2 = 0.9098) confirm the goodness of the model. The optimal run included CSSZ 9 mg/L, pH 4, 40 min irradiation time, and 0.8 g/L of the composite under the visible light irradiation.