Preparation Of Inverse Opal-like RuO₂ Electrode And Research On The Mechanism Of Degradation Of Pharmaceutical Pollutants

Pharmaceutical wastewater generally contains a large amount of pharmaceutical ingredients,intermediates and products.Due to its stable chemical properties,complex components and high toxicity,it is difficult to be biodegraded and potentially harmful to humans and the ecological environment,so that the discharge of pharmaceutical wastewater is strictly limited.Treatments of Pharmaceutical wastewater using traditional electrochemical oxidation technologies still have shortcomings,such as low catalytic efficiency and current efficiency.In this study,we prepared an inverse opal-like ruthenium dioxide electrode to improve the catalytic efficiency and systematically investigated the mechanism of enhanced oxidation by its inverse opal-like structures.The optimal operating parameters in the degradation of pyrazole and 5-fluorouracil were investigated.The main idea could be interpreted as following:The inverse opal-like ruthenium dioxide electrode was prepared by templated electro-deposition method using the hard template（polystyrene microsphere）.Its characteristics of inverse opal-like structures were investigated by the nitrogen adsorption/desorption test and the results show that the inverse opal-like ruthenium dioxide electrode exhibits the BET surface area as twice as that of the conventional flat electrode.LSV,CV and EIS was carried out and the results show that comparing to the conventional flat electrode,oxygen evolution potential of the inverse opal-like ruthenium dioxide electrode increases by about 0.1 V and its energy consumption for chlorine evolution was reduced by one time.Additionally,the inverse opal-like structures also increase the number of electrochemical active sites and reduce the resistance of charge transfer on the electrode surface.Chronoamperometry tests show that the mass transfer coefficient of the pollutant on the inverse opal-like electrode surface is 7.2×10^-4 cm² s^-1,which is 11.8 times larger than that of the conventional flat electrode.The inverse opal-like electrode was used to treat the pyrazole wastewater.The oxidation efficiencies of pyrazole by direct electron transfer and active chlorine-mediated indirect oxidation were compared.The results show that the degradation efficiency of pyrazole by direct electron transfer oxide was 4.2 times higher than that by active chlorine-mediated indirect oxidation.Then,the mechanism of enhanced degradation of pyrazole by the direct electron transfer on the inverse opal-like electrode was investigated.The results show that the large specific surface area accompanied by the inverse opal-like structures could effectively enhance the mass transfer of pollutants on the electrode surface,improving the current efficiency of pyrazole degradation.At 5 mA cm^-2,the removal rate of pyrazole on the anti-opal ruthenium dioxide electrode reachs up to 96.3%at 180 min,which is much higher than on conventional flat electrode（75%）.The electrocatalytic oxidation mechanism of pyrazole on inverse opal-like electrode was investigated by adding cleaning agent to the water.In the case of low current density,the adsorption and direct electron transfer of the anti-opal ruthenium dioxide electrode played a dominant role in the electrochemical degradation of pyrazole.When the current density increased to 2 mA cm^-2,indirect oxidation of hydroxyl radical occurred.However,the oxidation of oxygen and hydrogen peroxide made little contribution to the whole degradation process.The inverse opal-like electrode was also used to treat the 5-fluorouracil wastewater.The oxidation efficiencies of 5-fluorouracil by direct electron transfer and active chlorine-mediated indirect oxidation were compared.The results show that the oxidation efficiency of 5-fluorouracil by active chlorine-mediated indirect oxidation is 18.7 times higher than that by the direct electron transfer.Then,the mechanism of enhanced degradation of 5-fluorouracil by the inverse opal-like electrode was investigated.The results show that the large number of active sites provided by the inverse opal-like electrode could increase the production of active chlorine,improving the current efficiency of 5-fluorouracil degradation.The effects of current density on the degradation of 5-fluorouracil was investigated.The result shows that at current density of 10 mA cm^-2,the degradation efficiency would reach 97.1%at 15 min,and the corresponding energy consumption was only 0.0494 k Wh g^-1 TOC(Energy consumption for ton water treatment:141.142 k Wh t^-1).Actual wastewater containing 5-fluorouracil was degraded on the inverse opal-like electrode.After 30 minutes of electrolysis,the degradation rate was 65%lower than that in the simulated wastewater and LC_50,48h values rising from 18%to 35%.