Study On The Preparation Of FR-CNTs-PbO₂/SnO₂-Sb/Ti Electrode And Its Applications In Electro-catalytic Degradation Of Rhodamine B And17α-ethinylestradiol

Persistent Organic Pollutants (POPs) are a class of pollutants widely present in the environment, many of which are inherent toxicity, bioaccumulation potential, persistence, and susceptibility to long-range transport. As one effective approach to the treatment of POPs, electrocatalytic oxidation has attracted ever-increasing interests for the degradation of wastewater containing toxic or biorefractory organic compounds due to its merits of simple structure, easy applicability to automation, high efficiency, no secondary pollution, and environmental compatibility, etc. Furthermore, it is the key deciding degradation efficiency to choose an anode with effective electrocatalysis, high oxygen evolution potential, high chemical stability, and low cost in POPs degradation by electrocatalytic oxidation technology.This paper was aimed at preparing FR-CNTs-PbO2/SnO2-Sb/Ti electrode, and using it for the removal of typical POPs, such as Rhodamine B (RhB) and17a-ethinyloestradiol (EE2). And the influence of fators, such as time, current density, pH, initial concentration, on the degradation efficiency, and the electrocatalytic oxidation property, kinetic modeling, and possible reaction pathways were also studied.Firstly, the doped FR-CNTs-PbO2/SnO2-Sb/Ti electrode was prepared by an electrolytic deposition technique based on the excellent performance of carbon nanotubes (CNTs) and the hydrophobicity of fluorine resin (FR). The surface morphologies and composition of this electrode were examined by scanning electron microscopy (SEM) and X-Ray Diffraction (XRD). The electrochemical performances of FR-CNTs-PbO2/SnO2-Sb/Ti electrode were investigated using the contact angle meter and anode polarization curve. The results showed that the FR-CNTs-PbO2/SnO2-Sb/Ti anode exhibits higher hydrophobia and oxygen evolution potential than those of FR-PbO2/SnO2-Sb/Ti and PbO2/SnO2-Sb/Ti electrodes, which would be beneficial to the enhancement of electro-catalytic performance and current efficiency. Under the current density of30mA cm-2, the removal efficiency of10μmol L-1RhB can be90.21%in15min using the FR-CNTs-PbO2/SnO2-Sb/Ti electrode for RhB degradation. However, the removal efficiency of RhB on FR-PbO2/SnO2-Sb/Ti electrode was69.08%under the same conditions. Moreover, the reaction rate constant of FR-CNTs-PbO2/SnO2-Sb/Ti electrode can be0.2215min-1, which is nearly twice as high as FR-PbO2/SnO2-Sb/Ti electrode(k=0.1191min-1). Thus, the electrochemical properties and the electro-catalytic effect of FR-CNTs-PbO2/SnO2-Sb/Ti electrode were significantly improved due to the enhancement of hydrophobia and oxygen evolution potential.Secondly, on the basis of above study, this paper investigated the electrocatalytic degradation of RhB in aqueous solution by the FR-CNTs-PbO2/SnO2-Sb/Ti anode. The electrocatalytic property of this electrode was examined by cyclic voltammogram (CV) test, showing that the RhB degradation must be achieved via indirect electrocatalytic oxidation, mediated by OH radicals. The influence of fators, such as pH and initial concentration of RhB, on the degradation efficiency was also studied, no significant effect of initial pH on RhB degradation. And the efficiency of RhB degradation increased with decreased initial concentration20、15、10、5、2.5μmol L-1, however, when RhB low to10,5,2.5μmol L-1, the increase of degradation efficiency was not significant. The intermediates formed during the degradation were detected by gas chromatography-mass spectrometry (GC-MS), and13products were identified. On the basis of the data, the possible reaction pathway of RhB degradation has been elucidated:the·OH radicals generated on FR-CNTs-PbO2/SnO2-Sb/Ti anode surface could directly attack the central carbon of RhB to degrade it into smaller compounds, such as phthalic acid, salicylic acid, which then degrade into small molecule acids, and eventually to CO2and H2O.Thirdly, this paper further investigated the electrocatalytic removal of17a-ethinyloestradiol (EE2), the most potent synthetic estrogen, in aqueous solution by the FR-CNTs-PbO2/SnO2-Sb/Ti anode. Under the current density of13.33mA cm-2, the removal efficiency of10umol L-1EE2can be92.00%in25min during EE2degradation process, which follows a first-order reaction of LnC=0.1052t-0.2036and the apparent rate constants of0.1052min-1with correlation coefficient higher than0.966. Moreover, after20min of degradation, the new absorption peak occurred in the range of230-270nm, which might be caused by the intermediate products in degradation process, of which the main products might be some meterials containing benzene ring. The influence of fators, such as current density, pH and initial concentration of EE2, on the degradation efficiency was also studied. The current density could be a major role during the removal process with most suitable value of13.33mA cm-2, and there was no significant effect of initial pH on EE? degradation. And the efficiency of EE2degradation increased with decreased initial concentration, but, when EE2low to8,6μmol L-1, the increase of degradation efficiency was not significant. The intennediates formed during the degradation were detected by GC-MS, and15products were identified. On the basis of the data, the possible reaction pathway of EE2degradation has been elucidated:the OH radicals generated on FR-CNTs-PbO2/SnO2-Sb/Ti anode surface could directly attack the carbon atoms of EE2molecular structure to degrade it into two kinds of main byproducts, which containing or not containing benzene ring, all of these substance attacked by-OH radicals would then open the ring or fracture into small molecule acids, and eventually to CO, and H2O.