ENHANCEMENT OF 4-NITROPHENOL OZONATION IN WATER BY NANO ZnO CATALYST

The removal of 4-nitrophenol (4NP) from aqueous solution by ozone combined with nano-ZnO was investigated in a laboratory-scale reactor in which pH of solution, ZnO dosage and initial 4-nitrophenol concentration were considered as variables. The degradation of 4-nitrophenol was determined using UV-Vis and HPLC methods. Interestingly, the degradation of 4-nitrophenol was high under acidic condition where the degradation was about 93% at initial phenol solution pH=3. It was due to aggregation of nano-ZnO particles above pH=6.5. This result was different from the case of ozonation alone, in which higher pH had positive effect on the degradation of 4-nitrophenol due to the formation of hydroxyl radical. As expected, degradation efficiency increased by increasing the nano ZnO dosage and initial 4-nitrophenol concentration. It was found that the nanosized ZnO enhanced the degradation of ozone and the catalytic ozonation enhanced the degradation of 4-nitrophenol on the surface of the nanosized ZnO. In addition, the degree of degradation was also determined indirectly through Total Organic Carbon (TOC) of the samples. Carbon mineralization of 4-nitrophenol was obtained as 13.68% and 60.34% during ozonation and nano-ZnO catalytic ozonation, respectively, after 30 min reaction, proving that combined ozonator and nano-ZnO for reduction of TOC is more efficient. Also a high degree of nitrogen mineralization during catalytic ozonation was achieved at pH= 3 (7.61mg/L).