Application of mixture experimental design for photocatalytic ammonia degradation by sunlight-driven WO3-Ag3PO4-ZnO ternary photocatalysts

Using statistical mixture design, the best composition of a heterojunction photocatalyst containing ZnO, Ag3PO4, and WO3 was determined to maximize the sunlight driven ammonia removal from aqueous solution via both photocatalysis and adsorption processes. All samples were prepared by coprecipitation and immobilized over perlite granules as floatable support. X-ray diffraction (XRD), Fourier-transform infrared (FTIR), field emission scanning electron microscope (FESEM), Brunauer, Emmett, and Teller (BET), ultraviolet-visible (UV-vis), and photoluminescence (PL) analyses were used to characterize the catalysts. Three responses of ammonia removal by photocatalysis, adsorption, and the total ammonia removal were modeled by special cubic models, and the ANOVA confirmed the significance of them. The maximum ammonia removal, approximately 88%, was obtained by photocatalyst composed of 32.93-wt% WO3, 41.82-wt% Ag3PO4, and 25.26-wt% ZnO. The contribution of photocatalysis and adsorption was estimated to be 72.74% and 14.44%, respectively, indicating the dominance of photocatalysis process. According to kinetic study, the optimum photocatalyst showed the highest apparent rate constant and lowest half-life time of ammonia removal. The maximum quantum yield of 1.7% was calculated from the best photocatalyst composite at the maximum intensity of visible light received from sunlight. The reuse ability test revealed that the optimum ternary photocatalyst is suitable for wastewater treatments in practical applications.