Construction And Application Of Room Temperature Electro-assisted Wet Air Oxidation Process On Co@CoO/GF Electrode

As a typical kind of advanced oxidation technology?AOP?,wet air oxidation?WAO?is an effective technology for the treatment of organic pollutants in wastewaters.Such a technology makes use of molecular oxygen?O₂?in air for oxidative removal of aqueous pollutants at high air pressures and temperatures.This process can transform dissolved organic pollutants into highly oxidized intermediates and eventually produce carbon dioxide and water.The efficiency of WAO is strongly dependent upon the temperature because it requires a large amount of energy to trigger the reaction between oxygen and organic compounds.In order to reduce the energy consumption of the wet air oxidation reaction,it is necessary to find alternative oxygen activation methods under milder conditions.In this work,we report the synthesis of partially oxidized cobalt?Co-CoO?nanoparticles on a porous graphite felt?GF?support and its catalytic activity in an electrocatalytic wet air oxidation?ECWAO?process for the degradation of biorefractory organic pollutants under normal temperature and pressure.The system efficiency,reaction mechanism,and reaction kinetics were studied in detail.The main research work of the article is as follows:Co-CoO nanoparticles were fabricated on a GF support and an ECWAO process was constructed on the Co@CoO/GF electrode.The ECWAO process showed extensive effectiveness in mineralizing a variety of biorefractory organic pollutants.A probe pollutant,bisphenol A?BPA?,could be rapidly degraded within 180 min and the mineralization efficiency reached 89%.The dyes of congo red,crystal violet,rhodamine B,and methylene blue were completely mineralized in 180 min,and the PPCPs including ciprofloxacin,sulfamethoxazole and triclosan were mineralized at efficiencies higher than 70%in 300 min.The MCEs of the ECWAO process in treating different pollutants were all higher than 100%,which meant that the organic pollutants are mineralized by air oxidation rather than electrochemical oxidation.Such higher MCE values reflected the energy advantage of ECWAO process,as compared to conventional electro-chemical oxidation processes,which presented MCE values significantly lower than 100%due to inevitable charge losses in the electrode reaction.The Co@CoO/GF electrode showed good stability and p H adapatability during the ECWAO process.The oxidation of organic pollutants by air in the ECWAO process took place through the adsorption of oxygen and consumption of chemisorbed oxygen species on CoO surface.Oxygen molecules were first adsorbed onto the CoO and underwent dissociation to form chemisorbed oxygen species O^-/O^2-,which were then activated in the anode electric field via electro-oxidation reaction.The activated O^-/O^2-species would oxidize organic pollutants at room temperature.The oxidation of BPA was chosen as a model reaction to gain kinetic data about the ECWAO process.The oxidation of BPA showsed a pseudo-first order kinetic behavior.The intermediate products for removing oxidative degradation of BPA in this process were p-isopropenylphenol,benzoquinone,propanedioic acid,etc.A kinetic model,taken into account of initial concentration of BPA and intensity of electric field,was constructed to describe the removal of BPA in the ECWAO process.Under the optimized conditions of the kinetic model,the toxicity and biodegradability of the degradation solution of BPA,triclosan and sulfamethoxazole were evaluated.The results showed that the ECWAO process could completely eliminate the toxicity of PPCP pollutants,and the treated samples showed good aerobic biodegradability,making this process a pretreatment method combined with biological treatment technology.Compared with the traditional oxidation technology,the ECWAO process using Co@CoO/GF as the electrode has the advantages of high efficiency,low energy consumption,and environmental friendliness,and has great potential for application in actual wastewater treatment.The ECWAO system is anticipated to provide new research ideas and practical experience for the realization of low energy consumption and efficient treatment of refractory organic pollutants in wastewater.This is of great significance for improving the efficiency of water resources recycling in China and improving the quality of the water environment.