A Preliminary Study on Photochemical Degradation of Phenol in Wastewater by the MnO_2-UV Combination

This paper has studied the degradation characteristics of phenol in wastewater by different combination of synthetic manganese oxides and UV.The results show that there are significant differences in the degradation ability of phenol among the various Mn oxides under no UV condition.The magnitude orders of the degrading rate and COD removing rate of phenol in wastewater under the condition of 1 g/L Mn oxides and 4 hours are decreased from cryptomelane(97.51%),to acidic birnessite(89.07%),to alkaline birnessite((11.36%),) to todorokite(9.67%) and from cryptomelane(87.79%),to acidic birnessite(53.11%),to alkaline birnessite(6.42%),and to todorokite(1.43%),subsequently.Under UV condition,the degrading rates of phenol in wastewater under the condition of various corresponding Mn oxides are increased in different degrees.The obvious surface photocatalytic property of the Mn oxides has increased the degrading rate of phenol and improved the COD removing rate remarkably.However,the degrading rate of phenol by direct UV photolysis is largely decreased due to the addition of Mn oxide minerals.The degrading rates of phenol by the Mn oxides under UV radiation are subsequently decreased from cryptomelane(99.48%),to acidic birnessite(91.86%),to alkaline birnessite((40.15%),) and to todorokite((35.95%).) The COD removing rates are decreased from cryptomelane(98.11%),to acidic birnessite(68.45%),to todorokite(27.57%),and to alkaline birnessite(24.27%).It is suggested that two mechanisms may be existed in the degrading of phenol by the MnO_2-UV combination.One is the direct chemical oxidization of phenol by MnO_2 oxides.Another is the photocatalytic degrading of phenol on the surface of MnO_2 oxides.