Photo-catalytic Degradation of Methylene Blue Dye in Water Over Mn-N co-doped ZnS Nanoparticles

Objective: The reported work was aimed to remove methylene blue dye, a toxic chemical, from its aqueous solution by photo-catalytic degradation technique and to observe the effect of doping Mn and N on photo-catalytic activity of ZnS. Method: Nanosize ZnS, Mn-doped-ZnS, N-doped-ZnS and Mn-N co-doped ZnS were prepared by chemical co-precipitation method and characterized these using XRD, TEM and UV - visible spectroscopic techniques. Activity of as-synthesized photo-catalysts under UV and visible radiations were compared using degradation of methylene blue dye, as a probe. Results: The average crystallite size of above photo-catalysts, from XRD analysis, were: 7.8,7.5, 6.6 and 6.6 nm, respectively. Doping of N in ZnS caused a red shift of photo-absorption resulting in the decrease of band gap of ZnS. Co-doping of Mn and N in ZnS showed synergistic effect in enhancing oxidative degradation of the dye. The observed maximum degradation of 10 mg L-1 methylene blue at 3 hrs over Mn-N co-doped ZnS, separately, under UV and Visible radiations were: 55.6 % and 70.8%, respectively. Conclusion: Doping of Mn and N into ZnS exhibit synergism in increasing photo-catalytic activity of ZnS. The photo-catalytic degradation of methylene blue follows a pseudo first order kinetic under UV as well as visible radiation.