Degradation Of P-Nitrophenol By The Persulfate Catalytic Oxidation

Persulfate (S2O82-) is a strong oxidant with advantages such as high stability andsolubility, broad pH application range. It makes the sulfate radical (SO4) based advancedoxidation processes one of the most promising technology applied for groundwater andsoil remediation in recent years. Heat and microwave can activate persulfate effectively todegrade recalcitrant organic compounds in wastewater, while the efficacy of the transitionmetal activation is relatively low. Therefore, in this work p-Nitrophenol (PNP) was chosenas the target contaminant to investigate the effectiveness of persulfate activation byconventional heat, combined heat-transition metal and combined microwave-transitionmetal respectively.Investigation on the conventional heat activation involved the influence of persulfateconcentration, temperature, and initial pH on PNP degradation. Mechanism of the heatactivation process was also discussed. The results revealed that broad pH range could beapplied and that a higher persulfate concentration and temperature would significantlyincrease the PNP degradation ratio and reaction kinetics. When the concentration ofsodium persulfate reached30mM,100%of PNP was degraded. The pseudo-first-orderreaction rates under25oC,50oC,70oC and90oC were0.00003,0.0015,0.0276and0.2942min-1respectively. The intermediate products during the degradation process weredetected as2,4-Dinitrophenol,4-hydroxy-2’,3,4’-trinitrobiphenyl, p-benzoquinone, phenol,maleic acid and etc.Research on the conventional combined heat/metal ion activation included theinfluence of temperature, different metal ions (Fe2+and Cu2+) and metal ion concentrationon PNP degradation. The results indicated that both Fe2+and Cu2+were able to activatepersulfate to produce sulfate radical and that Fe2+led to a larger degradation ratio. In thepresence of metal ion, the degraded PNP ratio and reaction rate were observed to improvesignificantly due to higher temperature. Under lower temperature of50oC, the synergyeffect of heat and metal ion was obvious, dramatically enhancing the PNP degradation.With elevated temperature (70and90oC), the synergy effect diminished. Quenching ofsulfate radical by ferrous ion and precipitation of metal ion with intermediate productsprobably caused the hindrance of PNP degradation under high temperature. Study on the combined microwave-metal ion activation explored the influence oftemperature, initial concentrations of different metal ions (Fe2+and Cu2+) on PNP degradation.The results showed that microwave was able to lower the reaction activation energy, facilitatethe reaction rate and shorten the reaction time. Under50oC,70oC, and90oC, the combinedmicrowave/metal ion activation increased the degradation rate by1.5,2.9and1.8timescompared with the conventional methods. The activation energy decreased by4kJ mol-1.Similar to the combined heat-metal ion activation, quenching of sulfate radical by ferrousion and precipitation remained as the main inhibitors of PNP degradation.