Green analytical study of zinc oxide nanoparticle photocatalysis for the removal of phenazopyridine from aqueous media using UV–Vis spectrophotometry

This study investigates the removal of Phenazopyridine (Pyridium, C₁₁H₁₁N₅, Php), an azo dye, from aqueous media using zinc oxide nanoparticles (ZnONPs). The surface properties of the prepared adsorbent were systematically characterized to determine its morphology, structure, and elemental composition using XRD, SEM, FTIR, TEM, and BET/BJH. The measurements confirmed the formation of well-formed nanoparticles with high chemical purity, porosity, and a large surface area. Catalytic photolysis experiments were conducted to evaluate the effect of parameters under optimal conditions, including catalyst dosage (0.05–0.3 g). Photolysis efficiency increased with increasing weight, and the highest photolysis efficiency (91.89%) was achieved at an intensity of 8 milliwatts per square centimetre (mWcm-²). The initial drug concentration of 25–100 mg L-1 affected photolysis efficiency, with higher concentrations reducing it; illumination intensities of 1.84-2.4 mWcm-2 were also observed. The results showed the highest photolysis performance at 50 mg L-1, attributed to increased light penetration and a greater number of surface-active sites. The amount of zinc oxide used also contributed to achieving an optimal photolysis value, whereas increasing the weight decreased photolysis efficiency due to particle aggregation and light scattering. Under optimized conditions (0.2 g ZnONPs, pH 7.0, and a flow rate of 4.0 L min⁻¹), a decolorization efficiency of 91.89% was achieved, as determined by UV–Vis spectrophotometry at λmax = 430 nm (π → π*, –N=N–). These results confirm that ZnO-based surface oxidation is an efficient, environmentally friendly, and practical method for removing toxic pollutants from wastewater.