Photocatalytic degradation of Congo red using doped zinc oxide nanoparticles

Abstract

The photocatalytic degradation of Congo Red (CR) was studied using zinc oxide (ZnO) nanoparticles as catalyst (ZC, NZ, AZ and ANZ) under UV light, solar and dark. ZnO nanoparticles were synthesized by one-step liquid impregnation and each nanoparticles was calcined at 60 ^oC for 4 hours. The UV-vis spectra study assured that the band gap decreased as N and Ag doped to ZnO and hence the absorption band shifts toward the longer wavelength region (red shift). The morphological structures of as-synthesized nanomaterials were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The parameters studied were catalyst dosage and the pH of the reaction mixture. The degradation of the dye was found to be effective in the range; catalyst dose of 0.10, 0.20, 0.30 and 0.4 g ZnO catalyst/100 mL of dye solution, initial concentration 10 mg/L, and pH 8.11. Experimentation on different catalyst dosage of ZnO nanoparticles showed that 0.2 g ZnO catalyst/100 mL with the percentage degradation (ZC 70%, ANZ 99.7%, AZ 92.5%, NZ 85.8%) is the most suitable catalyst dosage for degrading CR under UV irradiation at 120 min of irradiation time. Photocatalytic processes were found to work better in basic condition and the best pH value was 8.0. The results showed that a percentage Congo Red degradation of 99.7% could be obtained when treating an effluent with 10 mg/L of Congo Red for 120 mins at 0.2 g ZnO catalyst/100 mL of effluent and pH 8 under UV irradiation using nitrogen doped silver co-doped zinc oxide, ANZ) both under solar and UV than (NZ) and silver- nitrogen doped zinc oxide (A), this was attributed to the lower rate of recombination of the photo-generated electrons and holes as well as its lower gap energy.