Invited feature articleA comprehensive study on enhancement and optimization of photocatalytic activity of ZnS and SnS2: Response Surface Methodology (RSM), n-n heterojunction, supporting and nanoparticles study

•Increased photoactivity of hybridized/supported SnS2-ZnS whit respect to monocomponent one.•Dependence of photocatalytic activity to SnS2/ZnS ratio.•Higher charge transfer of SnS2-ZnS-NC in impedance spectra whit respect to monocomponent systems.•Higher photocatalytic activity of SnS2-ZnS-NC in impedance spectra whit respect to monocomponent systems.

SnS2-ZnS supported clinoptilolite nanoparticles (NC) were used in photodegradation of metronidazole (MZ). The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results agreed with the photodegradation results, so the coupled SnS2-ZnS-NC system with higher charge transfer ability than the monocomponent systems showed the best photodegradation activity. The simultaneous effects of the experimental parameters were optimized using response surface methodology (RSM), which suggests that the interaction of solution pH and irradiation time had the important role on the response. The best run includes pH 3, catalyst dose of 3 g L−1, 2 mg L−1 of MZ at irradiation time of 250 min. R2 of 0.9868 confirms that the data predicted by RSM well agree with the experimental results. Initial pH and CMZ have an antagonistic effect on the response, meaning that increasing their values decrease MZ photodegradation. During the photodegradation of MZ over the SnZS-NC catalyst, sharp decrease in the UV-vis absorption was happened for the peak at 321 nm, while the intensity of the absorption peak about 234 nm was increased, indicating that the nitro group and nitrogen existing in metronidazole was degraded and formed nitrite ion.

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