The coupled WO3-AgBr nanocatalyst, part I: Experimental design, kinetics and mechanism studies of the boosted photocatalytic activity towards metronidazole in an aqueous solution

Abstract

The boosted photocatalytic activity of the coupled AgBr-WO3 nanocatalyst was observed towards metronidazole (MNZ) in an aqueous solution, and to study the simultaneous interaction effects between the influencing variables, experimental design was performed via the response surface methodology approach (RSM). The optimized run included MNZ solution pH: 9, catalyst dosage: 1 g/L, irradiation time: 45 min, and CMNZ: 10 mg/L. The goodness of the model was proven by greater model F-value than F0.05, 14, 15 = 2.42, and smaller lake of fit F-value than F0.05, 10, 5 = 4.74 and also by regression coefficient values of R2: 0.9994, Adjusted R2: 0.9988, Predicted R2: 0.9977. Based on the results obtained in the scavenging agent study, the following trend was suggested for the relative importance of the main four reactive species in MNZ photodegradation: Photoinduced h+> Hydroxyl radicals > Photoinduced e-> Superoxide radicals. The Z-scheme pathway well illustrates the mechanism pathway. The photodegradation kinetics obeyed the pseudo-first-order Hinshelwood model with a rate constant of 0.014 min−1 (t1/2 = 49.5 min). The photodegraded solutions' chemical oxygen demand (COD) confirmed the MNZ mineralization. Based on the COD results, a rate constant of about 0.018 min−1 (t1/2 = 38.5 min) was obtained. Reusing experiments confirmed the excellent stability of the binary catalyst for at least four reusing runs.