Influence of Molecular Structure of Imidazolium Based Ionic Liquids on the Electrochemical Oxidation Performances of Resulting PbO2 Deposits

The PbO2 coatings were electrodeposited on titanium sheet from aqueous solution containing lead nitrate and imidazolium based ionic liquids (ILs) additive. Effects of molecular structure of ILs on electro-catalytic activities of resulting PbO2 electrodes were investigated. Electrochemical treatment of simulated wastewater containing phenol was carried out to investigate the electro-catalytic activities of the PbO2 electrodes modified by ILs. High performance liquid chromatography (HPLC) was employed to determine the amount of hydroxyl radicals (center dot OH) generated on the electrodes by using salicylic acid (SA) as a probe. The electrochemical properties of the samples were investigated by polarization curves tests. The surface structure and wetting ability of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle test respectively. The results showed that the electro-catalytic activities of PbO2 electrodes modified by [Emim] BF4 were significantly higher than that of PbO2 electrodes modified by [ Emim] Br or [ Emim] PF6. With BF(4)(-)fixed, the improvement order for the activity of modified PbO2 electrodes was as follows: [Bmim] BF4>[ Emim] BF4>[Hmim] BF4. XRD patterns and SEM micrographs showed a highly textured structure and controlled morphology of the PbO2 coatings by ILs modification. Both the anions and cation chain lengths of imidazolium based ILs had a significant effect on the surface properties and electro-catalytic activities of resulting PbO2 electrodes, with the influence of the former being more prominent than that of the latter. The modification may be attributed to the adsorption of ILs molecule on the anode surface during the electrodeposition of PbO2 coating. Meanwhile, the higher COD removal efficiency on PbO2 electrodes modified by [Bmim] BF4 can be attributed to its preferential orientation along (110) plane as well as its larger specific surface area and more active sites for the generation of hydroxyl radical. Furthermore, [Bmim] BF4 had the most significant positive impact on the reusability and stability of PbO2 coatings.