Study On Preparation Of Ti-Based SnO₂-Sb Electrode And Catalytic Oxidation Of Phenol

Modified Ti-Based SnO₂-Sb electrodes was prepared by thermal decompositionmethods, and electrochemical degradation of phenol was investigated in this paper.The effects of preparation condition, such as thermal oxidation temperature（400℃,500℃,600℃,700℃）, doped element（La, Ce, Gd, Zr, Sr）and dopedcontents （molar ratio was Sn:Sb:Zr=100:10:X, X=0.5,1,2,3.5,5）, on themicrostructure, the crystal structure, the oxygen-evolution potential, the Tafel Slopeand the phenol removal rate of Ti-Based SnO₂-Sb electrodes were studied with thehelp of SEM, XRD, polarization curve, anode materials on the electrochemicaldegradation process of phenol. The experimental results show that the optimalpreparation condition of Ti-Based SnO₂-Sb electrodes was that: the thermal oxidationtemperature and Zr doped content were500℃and100:10:2（molar ratio）,respective. And the electrode had a more compact texture，no stress cracking，distributing equably, crystallizing and growing fully, the highest oxygen evolutionpotential and the most catalysis for the oxidative degradation of phenol.Take the optimized Ti-Based SnO₂-Sb electrode as anode, titanium plate ascathode, the stimulant phenolic wastewater was degraded in a electrolytic cell withoutdiaphragm. The effects of influencing factors of degradation of phenol such asoriginal pH value of electrolyte, initial concentration of phenol, electrolyteconcentration and electrical current density on degradation of phenol weresystematically investigated. It has been found that, the best removal effect of phenolwas in the original pH value from5to7of electrolyte and the worst was under thecondition of high pH value; he removal efficiency of phenol decreased with theincrease of initial phenol concentration gradually, but the absolute wiping off valueincreased obviously; the greater the electrolyte concentration, the better the removalefficiency of phenol in the concentration range of0.05to0.45mol/L,but not obviouslyexceeding0.25mol/L; the removal efficiency of phenol increased as electrical currentdensity increased electrical current gradually, but not obviously exceeding20mA/cm².Response surface methodology（RSM）was used to investigate the effects of thethree independent variables on Ti-Based SnO₂-Sb electrode electrocatalytic degradation of phenol and to determine the optimal conditions. ThroughDesign-Expert7software, a second-order polynomial model was obtained. The bestpH, phenol concentration and current density is5.85,28.4mAcm2and50mg/Lat thistime, the percent phenol removal reached the maximize（73.51%）. The regressionanalysis showed that high correlation coefficients R²and R²adjof0.9892and0.9754respectively imply that regression model fits to the experimental value well.Optimization using desirability functions indicated Box–Behnken design in corporatewith desirability functions could be effectively used to optimize the design forexperiments on the electrochemical removal of phenol.Phenol degradation pathway of Ti-Based SnO₂-Sb electrode and Zr dopedTi-Based SnO₂-Sb electrode were analyzed by high performance liquidchromatography（HPLC）.It was found that phenol degradation pathway were roughlythe same between Ti-Based SnO₂-Sb electrode and Zr doped Ti-Based SnO₂-Sbelectrode. The phenol degradation pathway was inferred that para-position andortho-position of phenol were attacked by hydroxyl radicals （·OH） radicals first, thenformed hydroquinone and catechol, the ring was broken into maleic acids and succinicacids, which were further oxidized into m oxalic acid. These small organic acids werefinally oxidized into CO₂. The results of high TOC analysis of electrolyte withdifferent degradation time show that the mineralization of organic compounds and themineralization current efficiency（MCE）of Zr doped Ti-Based SnO₂-Sb electrodewere both higher than none boped Ti-Based SnO₂-Sb electrode. X-ray photoelectronspectroscopy（XPS）was employed to study the composition and chemical state ofdifferent elements on electrode surface. Based on electrochemical phenol degradationexperiments, TOC, XPS and XRD investigations, the electro-catalysis mechanismwas discussed as well as the relation between structure and activity of Ti-BasedSnO₂-Sb electrode. Based on experimental and theoretical analysis, it is argued that,addition of Zr could reduce oxygen vacancy of SnO₂crystal, reduce the averageelectron density around the Sn4+, increase the Oadscontents, which contributed toincrease the number of hydroxyl radicals on the surface of electrode. So there weremore electrochemical combustion reacting, and the electrode electro-catalytic activityof electrode had been improved. TiO₂which have been prepared by anodization as the intermediate layers ofTi-Based SnO₂-Sb electrode was explored, it was found that it had a more compacttexture and a higher oxygen evolution potential, and could increase servicelifetime and electro-catalytic activity of electrode.It has important significance on investigation in mechanism of electrocatalyticoxidation of organic pollutants and preparing high catalytic efficient electrode forelectrocatalytic oxidation of organic pollutants.