Tuning of defect levels is the major concern for the application of ZnO nanoparticles. These nanoparticles with different defect concentration were prepared by simple combustion method at 700 degrees C and subsequent quenching in air. The catalyst was characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electroh Microscope (FESEM), UV-vis spectroscopy measurements. XRD reveals that the cell volume increased with large temperature difference between 700 degrees C and quenched media. FTIR confirmed that the vibrational frequencies shifted from 519 cm(-1) to 535 cm(-1) point out the role of quenching defects. FESEM shows the size is of the order of 20-45 nm and found irregular distribution of grain boundaries in the quenched induced defects. Different morphology plays a major role in the enhancement of photocatalytic efficiency of synthesized nanoparticles. PL intensity indicates more oxygen vacancies for air quenched ZnO whereas; DTA study demonstrates that the synthesized ZnO is thermally stable. Kinetics study confirmed the photodegradation of methyl orange (MO) dye using this photocatalyst follows first order rate constant. It exhibits the complete degradation of dye only in 150 min under UV irradiation. Kinetic study revealed the rate constant of nanoparticles is 0.0165 min(-1). Air quenched sample showed the higher intensity of defect band as compared to pristine ZnO. (C) 2017 Elsevier Ltd. All rights reserved.