| Being compared with the existing technologies on treating toxic bio-refactory organic in wastewater,electrochemical oxidation method has showed superiority with its environmental friendliness and application prospect.At present,the popular issue of this method is to prepare a high-performance anode.Among common applied materials lead dioxide electrode has been attached a close attention because of its cost-effective. However,there is still a gap between exprimental test and practical application.It has been reported that doping a bit of additives can change the microstructure ofβ-PbO2 and improve its elctro-catalytic properties.On the basis of special nature of rare earth elements,some modified PbO2 anodes were prepared and their electrochemical properties in the inorganic and organic aqueous solution were also investigated in detail.CeO2 and La2O3 particles were selected as dopants to modify F-β-PbO2 electrodes in this study.Weight loss of the anode under accelerating electrolysis was carried out to optimize the plating conditions.The physicalchemical property and electro-catalytic characteristic of the modified anode were investigated using different surface analysis technologies and electrochemical tests.The intrinsic relations between electrode surface structure,service life,electro-catalytic activity of oxygen evolution(OE) in inorganic aqueous solution and the efficiency of electro-oxidation in organic aqueous solution were investigated and discussed.The results of this work could supply a theoretical basis for the further preparation PbO2 electrode with an excellent performance,and then could effectively promote the electrochemical technology in practical application of wastewater treatment.The experiemtnal results indicated that dense and even electrode surface coating could be obtained and its weight loss slowed down under the following plating conditions:a suitable concentration of rare earth oxide,the plating solution agitated by magnetic bar with an 1300r/min, temperature at 80℃,current density under 160mA/cm2,electrodepostion for 1h.The main crystal of modified electrode was stillβ-PbO2.Oxide adulteration could increase active surface and oxygen vacancy defect of PbO2,and oxide particle evenly distributed and embedded in the electrode coating.The active surface area of F-PbO2,CeO2-F-PbO2,La2O3-F-PbO2 electrode were 3.0,4.88,5.12cm2(the apparent area of the matrix 1cm2), respectively.In comparision of behaviors of their OE reaction in H2SO4 aqueous solution,exchange current density and tafle slope of modified electrodes obviously decreased while apparent activation energy of OE reaction increased.The above results indicated that addition of rare earth oxide may disturb kinetic process of OE reaction and weaken formation of O2 as competitive reaction during electro-oxidative degradation of organics.The electro-catalytic properties,adsorption and deactivation behavior of modified electrodes in the 4-chlorophenol(4-CP) aqueous solution were investigated.The experimental results showed that rare earth oxide dopant could probably affect the existence of active intermediates on the electrode surface.The organic absorption capacity of CeO2-F-PbO2 electrode was almost twice than the undoped.The oxidative peak current(ip) of 4-CP on CeO2-F-PbO2 electrode remained high regardless of pH of solution after scanning for many times,showing high anti-deactivation.The adsorption capacity of La2O3-F-PbO2 electrode changed little in comparison with F-PbO2 electrode,and the ip of 4-CP decreased rapidly for four times,indicating its easy deactivation.4-CP degradation properties of different anodes were studied.The experimental results showed that doping of rare earth oxides could effectively improve the electro-oxidation characteristics of PbO2.The appearent kinetic parameter of 4-CP by different anodes increased because of an addition of rare oxide,thus leading to reduce energy consumption. For example,the COD removal rates of three electrodes under the same conditions were 34.2%,53.87%,71.61%after 8h electrolysis,respectively. The instantaneous current efficiency(ICE) declined rapidly during the first 2h of electrolysis.In general,CeO2-F-PbO2 and La2O3-β-PbO2 anode had one and three times ICE higher thanβ-PbO2 electrode had,respectively. From the present results,rare earth oxide may affect the existing life of the active intermediate species(·OH,etc.),which should be further confirmed by interrelated experimental evidences. |
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