Investigation of photocatalytic behavior of modified ZnS:Mn/MWCNTs nanocomposite for organic pollutants effective photodegradation

Abstract In this research, zinc sulfide (ZnS) doped with manganese (Mn) is synthesized on functionalized multiwall carbon nanotubes (MWCNTs) nanocomposite by a facile co-precipitation method as the photocatalysis. Due to the excellent electrical and optical characteristics of ZnS:Mn/MWCNTs nanocomposite, it is worth to investigate its photodegradation activity. To investigate the photocatalytic degradation properties of organic pollutants, the synthesis conditions were optimized in the presence of four substances: COOH, ethylene glycol, sodium dodecyl sulfate, and polyvinyl-pyrrolidone. Surface studies of the photocatalyst, i.e., structural, morphological, optical and physical properties, were characterized by FTIR, PL, XRD, SEM, and TEM analyses. The results showed that Mn ions decreased the band gap energy of the nanocomposites and there was excellent adhesion between ZnS and MWCNTs in the synthesized composite. According to the results, MWCNTs effectively increased the photocatalytic activity of the ZnS nanoparticles by the electron-hole pair recombination of ZnS and MWCNTs, and the composites with the carboxylic functional group showed greater photocatalytic activity. In addition, the kinetic studies showed that the photocatalytic process obeyed the pseudo-first-order kinetic model. To determine the exact mathematical formula of the photocatalysis, response surface methodology was modeled by the central composite design method. Various parameters, such as the time of the treatment process and initial concentration of the pollutants were studied for a quadratic model that fit all the cases well and their mathematical models were obtained.