Sonoelectrochemical oxidation of aged landfill leachate with high-efficiency Ti/PANI/PDMS-Ce-PbO2 anode

Abstract

In this work, a high-performance anode containing polyaniline (PANI) modified intermediate layer and polydimethylsiloxane (PDMS) and Ce co-doped surface layer was prepared. Scanning electron microscope (SEM) and X-ray diffraction (XRD) characterization exhibited that the Ti/PANI-α-PbO2/PDMS-Ce-β-PbO2 electrode (Ti/PANI/PDMS-Ce-PbO2) has denser surface morphology and smaller crystal size compared to the Ti/β-PbO2 electrode (Ti/PbO2). The BET test showed that the specific surface area of the modified PbO2 electrode increased from 0.2591 to 0.2783 m2 g−1, which also means an increase in active sites. The results of linear sweep voltammetry (LSV) indicated that the Ti/PANI/PDMS-Ce-PbO2 electrode has higher oxygen evolution potential of 1.91 V vs.SCE than the Ti/PbO2 electrode (1.74 V vs.SCE), which can effectively reduce the impact of oxygen evolution side reaction on organic pollutants degradation. The fitting results of electrochemical impedance spectroscopy (EIS) exhibited that the impedance of the Ti/PANI/PDMS-Ce-PbO2 electrode was greatly reduced to 39.5 Ω. The modified electrode showed higher current efficiency in the experiment of electrochemical oxidation of gallic acid, proving that the electrocatalytic performance of the modified PbO2 electrode was further improved. Therefore, the Ti/PANI/PDMS-Ce-PbO2 electrode was used for sonoelectrochemical oxidation of aged landfill leachate. The effects of three key parameters on the sonoelectrochemical system were investigated, including current density, initial pH, and ultrasonic power, and the results revealed that the current density played a dominant role. Under the optimal parameters: 42 mA cm−2 current density, initial pH of 6, 50 W ultrasonic power, 61.9% chemical oxygen demand (COD) removal was achieved. Both the ten repeated experiments and the accelerated life tests demonstrate that Ti/PANI/PDMS-Ce-PbO2 electrode has good stability and potential for long-term application. Furthermore, the results of inductively coupled plasma-mass spectrometry (ICP-MS) manifested that the sonoelectrochemical system with Ti/PANI/PDMS-Ce-PbO2 electrode will not cause secondary pollution to the effluent. The analysis results of ultraviolet–visible spectroscopy (UV-Vis) and gas chromatography-mass spectrometry (GC-MS) show that the organic components of the aged landfill leachate changed greatly after the treatment of sonoelectrochemical oxidation, and the refractory substances have been effectively removed.