Comprehensive study on enhanced photocatalytic activity of heterojunction ZnS-NiS/zeolite nanoparticles: Experimental design based on response surface methodology (RSM), impedance spectroscopy and GC-MASS studies

In the present work, coupled and supported NiS and ZnS onto the mechanically prepared clinoptilolite nanoparticles (NC) was prepared and characterized by XRD, FTIR, SEM-EDX, X-ray mapping, DRS, BET, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The obtained catalysts were used in photodegradation of metronidazole (MZ). The mole ratio of NiS/ZnS affects the degradation activity of the obtained catalysts so the best activity was obtained for the NZ4-NC (NiS1.0–ZnS5.2/NC, containing 1.0 and 5.2 W% of NiS and ZnS, respectively and mole ratio of ZnS/NiS about 4) catalyst. The simultaneous effects of the experimental parameters were studied using central composite design combined with response surface methodology (RSM). Results of CV and EIS have good agreement with photodegradation results, so the coupled NiS-ZnS-NC system with significant enhancement in charge transfer with respect to the monocomponent systems showed the best photodegradation activity. The best degradation extent of MZ was obtained at a run including pH 2, catalyst dose of 3 g L−1, 4 mg L−1 of MZ at irradiation time of 150 min. The high correlation coefficient (R2 = 0.9883) for the second-order polynomial model, showed that the data predicted using RSM were in good agreement with the experimental results. Change of initial pH of MZ solution from 5.5 to 4.1 during 150 min, confirms formation of acidic degradation intermediates.