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.