Degradation Of Diclofenac In Reclaimed Water By Titanium Oxide Membrane Electrode

In recent years,China has vigorously advocated sewage resource utilization,but in the process of reclaimed water utilization,a large number of drugs and personal care products（PPCPs）will enter the corresponding scene with reclaimed water.Therefore,an efficient technology is needed for the advanced treatment of reclaimed water.However,the traditional treatment technology is not suitable for the treatment of reclaimed water.Electrocatalytic oxidation technology is a kind of advanced oxidation technology with development prospect,in which the efficient mass transfer in the electrochemical degradation process is the key to improve the removal efficiency of pollutants.In this paper,with the core of titanium oxide membrane electrode,the electro-catalytic oxidation system was constructed to strengthen the electrochemical mass transfer process,and the degradation of diclofenac（DCF）in water was studied,in order to provide technical theoretical support for the application of titanium oxide membrane electrode to degrade PPCPs organic pollutants in reclaimed water.Scanning electron microscopy（SEM）and X-ray diffraction（XRD）were used to characterize the titanium oxide films with different pore sizes.The results show that the electrode with an average pore size of 5μm has more abundant pore structure and the crystal phase composition is mainly Ti₄O₇.Electrochemical tests showed that the titanium oxide surface was mainly an indirect electrochemical oxidation reaction,and the pore size had no effect on the reaction type of the titanium oxide film.The electrode with an average pore size of 5μm had larger electrochemical active surface area and more active sites.Through the analysis of mass transfer performance,both pore size and permeation flux affect the mass transfer performance of electrocatalytic oxidation system,small pore size improves the mass transfer effect;In a certain range of permeable flux,the increase of permeable flux also increases the mass transfer rate constant by enhancing convective diffusion of solute.The degradation efficiency of simulated wastewater by diclofenac was compared with three kinds of electrodes with different pore sizes.The results showed that under the same conditions,the degradation rate of diclofenac within 120 min was in the following order:5μm（88.83%）>30μm（82.98%）>100μm（75.99%）,the degradation process conforms to the pseudo first-order reaction kinetics model,and the order of reaction rate constant is:The degradation rate and reaction rate constant of k_5μm(1.91×10^-2min-1)>k_30μm(1.48×10^-2min^-1)>k_100μm(1.00×10^-2min^-1)decreased with the increase of pore size.When the film flux increased by 25.17 m L·cm^-2·min^-1,the effect of mass transfer on the degradation of diclofenac decreased,and the difference of degradation rate and reaction rate constant of the titanium oxide film electrode with different average pore size decreased.Different experimental conditions can affect the degradation of diclofenac.The response surface optimization method was used to analyze the single factor experiment,and the optimal experimental conditions were as follows:current density 18.4 m A·cm^-2,p H 6.25 and electrolyte concentration 0.06 mol·L^-1.Under the best experimental conditions,the removal rate can reach 99.47%after 120 min when k value is 5.86×10^-2min^-1.The degradation effect of Na Cl>Na₂SO₄>Na NO₃was different in different electrolyte systems.The main active free radicals were different in different electrolyte systems.The average formation rate of hydroxyl radical was 6.983μmol·L^-1·min^-1.The intermediates and degradation paths in the degradation process of titanium oxide film electrode were analyzed.The results showed that there were 8 intermediates.Based on the intermediates,three degradation paths were proposed,which were hydroxylation of benzene ring on diclofenac molecule,and then oxidative dechlorination.Decarboxylation of alkyl chain on benzene ring,followed by ring opening dechlorination oxidation;diclofenac molecule dechlorination and further intramolecular reaction,benzene ring reaction with SO₄·^-,thus further oxidative degradation.The intermediate products were further converted into small organic acids and small alcohols to achieve the harmless treatment of diclofenac.