Preparation And Electrocatalytic Properties Of Fe～(3+), In～(3+), Sb～(5+), Co-doped SnO₂ Electrode

With their broad application in the fields like coking, pesticide, wood manufacture, and petrochemical processing, more and more phenols and sulfur-containing organic compounds, are discharged in a form of industrial waste water. This has resulted in a serious pollution to water resources, because both phenols and sulfur-containing organic compounds are difficult to be degraded. In recent years, as to the treatment of phenols and sulfur-containing organic compounds, the technique of electrocatalytic oxidation, being more advantageous than others, has been attracting considerable attention all over the world. As electrode materials play a key role in electrochemical technique, this work would address the preparation and characterization of novel high-performanced electrodes and their application in the electrocatalytic oxidation of phenols and sulfur-containing organic compounds.Doped Ti/SnO₂ DSA electrodes have been reported to possess many merits over others and to be used in the degradation of organic pollutant in waste water. In this work, three groups of doped Ti/SnO₂ electrodes, SnO₂:Sb5+, SnO₂:Sb5+-Fe3+and SnO₂:Sb5+-In3+, were prepared over Ti substrate via thermal decomposition method from precursor sols containing chlorides of Sn4+, Sb5+, Fe3+or In3+. Influencing factors, such as, the batch composition, the annealing temperatures, and the annealing time, were studied systematically, and the electrodes prepared were characterized by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and liner voltage sweep (LVS). It is found that the electrocatalytic performance of Ti/SnO₂ electrode was improved largely after doping. By optimizing preparation conditions, the doped Ti/SnO₂ electrodes with composition of , SnO₂:Sb⁵⁺(5%), SnO₂:Sb⁵⁺(5%)-Fe³⁺(0.5%) and SnO₂:Sb⁵⁺(5%)-In³⁺(0.3%) prepared at an annealing temperature of 400 oC and an annealing time of 3 h, were identified to be the best performanced ones.The as-prepared electrodes had been utilized in the electrocatalytic oxidations of a series of phenols and sulfur-containing organic compounds. It is found that activity of electrocatalytic oxidation is dependent largely on the characteristics of electrodes, i.e., the nature and content of the dopes, and the structural properties of phenols and sulfur-containing organic compounds, i.e., the type of substituent or functional groups and their position in skeleton. The doping of Sb⁵⁺ improved the electrocatalytic performance of Ti/SnO₂ electrode, so did not the doping of Fe3+ or In3+. However, when the Ti/SnO2 electrode was co-doped with (Fe3+, Sb5+) or (In3+, Sb5+), a cooperative promoting effect occurred, with the electrocatalytic performances of the SnO2:Sb5+(5%)-Fe3+(0.5%) and SnO2:Sb5+(5%)-In3+(0.3%) electrodes being much more better than that of the SnO2:Sb5+(5%) one. The EDX examination to the elemental compositions of the prepared electrodes shows that the concentrations of Sb5+ increased obviously for the SnO2:Sb5+(5%)-Fe3+(0.5%) and SnO2:Sb5+(5%)-In3+(0.3%) electrodes than for the SnO2:Sb5+(5%) one. Thus, it is concluded reasonably that, the trivalent ions, Fe3+ and In3+, did not participate directly the electrocatalytic oxidation of the organics. However, the presence of the trivalent ions was very helpful for the substitution of Sb5+ to Sn4+ in SnO2 lattice, increasing the amounts of active species, Sb5+, and thus, improving the electrocatalytic activity of the electrode. As to the effect of the structure of phenols, it is found that nature of substituent or functional groups and their position in skeleton affected obviously the reactivities of the compounds. The more is of attractive to electron for substituent or functional groups, the lower reactivity the phenol possesses.