In the preparation of composite, 0.5 mg/mL of g-C3N4 was dispersed in the distilled water and 0.1 mol of Zn(NO3)2.6H2O and 0.2 mol of Co(NO3)2.6H2O was dissolved in solution. 6 mmol of urea was added as the reducing agent in the reaction and solution is stirred for 30 mins. Then the solution is transferred into Teflon lined autoclave and maintained at 160 oC for 12 hours. After the completion of reaction, the autoclave is automatically cooled and precipitate is obtained from it by cleaning it with distilled water and ethanol for three times. Finally, the precipitate is dried and annealed at 450 oC for 2 hours and named as ZCO/Z-CN-35. Similarly, comparison material was prepared without addition of g-C3N4 and named it as ZCO-Z.