Controlled synthesis of Cd0.9Zn0.1S and Cd0.89Zn0.1Ni0.01S nanostructures by chemical co-precipitation route was reported. The XRD analysis confirmed the cubic structure of CdS on Zn doping and Zn, Ni dual doping without any secondary/impurity phases and no alteration in cubic phase was noticed by Zn/Ni addition. The shrinkage of crystallite size from 69 Å to 43 Å and the variation in lattice constants and micro-strain were described by the addition of Ni and the defects associated with Ni2+ ions. The enhanced optical absorbance in the visible wavelength and the reduced energy gap by Ni substitution showed that Cd0.89Zn0.1Ni0.01S nanostructures are useful to improve the efficiency of opto-electronic devices. The functional groups of Cd-S / Zn-Cd-S /Zn/Ni-Cd-S and their chemical bonding were verified by Fourier transform infrared studies. The elevated visible PL emissions such as blue and green emissions by Ni addition was explained by worsening of crystallite size and generation of more defects. Zn, Ni dual doped CdS nanostructures are identified as the probable an efficient photo-catalyst for the degradation of methylene blue dye. The liberation of more charge carriers, better visible absorbance, improved surface to volume ratio and the creation of more defects are accountable for the current photo-catalytic activity in Zn/Ni doped CdS which exhibited better photo-catalytic activity after sex cycling process. The noticed higher bacterial killing ability at Ni doped Cd0.9Zn0.1S is due to the collective effect of lower particle/grain size and also higher ROS producing capacity.