Hua Guo,Zhicheng Xu,Dan Wang,Shiyu Chen,Dan Qiao,Dan Wan,Hao Xu,Wei Yan,Xiaoliang Jin
This work investigates the electrochemical oxidation (EO) of diclofenac (DCF) in water with Ti/Ti 4 O 7 , Ti/Ru–Ir, Ti/Sb–SnO 2 and Ti/PbO 2 electrodes. Scanning electron microscope and X-ray diffraction results suggest that Ti/Ti 4 O 7 has porous stacked surface morphology and Ti/Sb–SnO 2 possesses the smallest grain size. Linear sweep voltammetry test results indicate that PbO 2 has the highest oxygen evolution potential, while Ti/Ti 4 O 7 and Ti/Ru–Ir show better oxygen evolution activity. DCF degradation results reveal that PbO 2 possessed the highest DCF removal ( R DCF = 99.2%) and chemical oxygen demand (COD) removal ( R COD = 97.0%), the fastest COD degradation rate ( k = 0.0275 min −1 , R 2 = 0.964), the lowest specific energy consumption ( EC DCF = 1.81 kWh . g DCF −1 , EC TOC = 6.90 kWh . g TOC −1 ). The toxicity variation of DCF during EO process on PbO 2 is rise first and then to fall. Considering the differences of the four electrodes in residual, conversion and mineralization aspects, mineralization selectivity ( MS ) was proposed to estimate the mineralization inclination of electrodes during EO process, and PbO 2 displays the strongest mineralization inclination ( MS = 0.594). In addition, the possible degradation pathway of DCF on PbO 2 electrode indicates a composite behavior of conversion and mineralization. All of them above indicate the promising application potential of PbO 2 in lower concentration pharmaceuticals and personal care products wastewater treatment . Moreover, MS could be employed as a supplementary index to assess the different inclinations of this composite behavior on various electrodes used for electrochemical treatment of organics in later studies.
A novel PbO 2 electrode was fabricated by adding graphene nanoplatelets (GNP) inter-layer into β-PbO 2 active layer (called GNP-PbO 2 ) and utilized to degradation of antibiotic enoxacin (ENO). The GNP-PbO 2 electrode had a much rougher surface than the typical PbO 2 electrode, with smaller crystal size and lower charge-transfer resistance at the electrode/electrolyte interface. Notably, the GNP inter-layer increased the oxygen evolution potential of PbO 2 electrode (2.05 V vs. SCE), which was very beneficial to inhibit oxygen evolution and promote ·OH production. The relatively best operating parameters for ENO removal and energy efficiency were current density of 20 mA cm −2 , initial pH of 7, initial ENO concentration of 100 mg L −1 and electrode distance of 4 cm. Furthermore, indirect radical oxidation was found to be the main way during electrolysis process. Based on the observed analysis of intermediate products, the main reaction pathways of ENO included hydroxylation, defluorination and piperazine ring-opening. Finally, combinating with the electro-oxidation capability, stability and safety evaluation, we can conclude that GNP-PbO 2 is a promising anode for treatment of various organic pollutants in wastewater.
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