Preparation Of Carbon Nanotube Modified Nickle Foam Gas Diffusion Electrode And Its Application For Electro-Fenton Degradation Of P-Nitrophenol

Electro-Fenton technology has attracted a wide attention in the field of biorefractory organic compounds recently due to the virtue of less secondary pollution and environmentally friendly. Electrocatalytic activity of electrode material and pH range are two key issues for research or industrial application. Gas diffusion electrode has channels for gas transfer, and provides favourable environment of gas, liquid and solid coexistence for oxygen reduction, which is not limited by the solubility and mass transfer of oxygen, so the yield of H2O2 and current efficiency would be improved greatly. Generally, some organic acid generates as the intermediate products in the process of electro-Fenton degradation, which leads to pH declination, so the pH range would broadened and iron sludge would be reduced if heterogeneous catalyst substitute for Fe2+. To solve the problems of the low yield of H2O2 and current efficiency, in the present study metal foam which has three-dimensional structure was selected as the basic cathode material, and a novel gas diffusion electrode was fabricated by modifying metal foam with CNT and NCNT; To solve the problem of narrow pH range, a cheap and readily available FCSW was prepared as heterogeneous catalyst; In addition, the degradation mechanisms of organic matter during Electro-Fenton process was analyzed using the p-nitrophenol as the model pollutant, and the obtained results provided the reliable theory basis for the application of highly efficient electro-Fenton technology in organic wastewater treatment. The detailed contents are as follows:(1) Two common metal foams, nickel foam and copper foam were prepared as the cathodes in electro-Fenton system. The morphology, structure, oxygen reduction performance and electro-Fenton oxidation of p-NP were compared. The results indicated that the NF and CF cathodes both could catalyze O2 to produce H2O2 via two electrons reduction in the solution pH 3.0 and 7.0. The yield of H2O2 and current efficiency were reached the maximum at the cathodic potential-0.9 V, and the yield of H2O2 was higher in acid condition than it's in neutral condition, but the current efficiency was just the opposite. The p-NP removal efficiency was both high using NF and CF cathodes in the solution pH 3.0 and 6.5, but the mineralization efficiency was both low. The p-NP removal rate at 180 min using CF cathode was 5.92% higher than using NF cathode under the cathodic potential-0.9 V in the solution pH 3.0, and the TOC removal rate was 1.49% higher under the same conditions; The p-NP removal rate was 7.82% higher using CF cathode than using NF cathode in the solution pH 6.5, but the TOC removal rate was 0.73% lower under the same conditions. The TOC removal rate improved 21.1% using NF cathode and 13.8% using CF cathode, respectively if 0.2 mmol/L FeSO4 was added into the solution of pH 3.0, and the energy consumption reduced 0.65 kWh/gTOC and 0.48 kWh/gTOC, respectively. The reusability of NF cathode was better than CF cathode because the removal efficiency of p-NP and the morphology of the cathode were not changed obviously after eight cycles.(2) A simple and efficient chemical method using strong oxidant and hydrazine hydrate was adopted to dope N into CNT. The changes of morphology, structure and oxygen reduction performance after N doped were investigated by SEM, TEM, Raman, XPS and RDE. Then a novel gas diffusion electrode was fabricated by modifying nickel foam with CNT and NCNT. The effect of operating parameters on H2O2 yield and p-NP degradation in the electro-Fenton system was studied. The results indicated that the morphology and structure of NCNT changed compared to CNT, including shorter length, bamboo-like structure and increased defects, the content of N was 2.96%, and mainly was the pyrrole N. The two-electron transfer path was confirmed by RDE using CNT or NCNT at the potential higher than-0.8 V, and the catalytic activity of NCNT was higher than CNT. The yield of H2O2 and current efficiency at 120 min were 394.4 mg/L and 81.8%, respectively using CNT-PTFE(1:3)/NF/NCNT-PTFE(1:1) gas diffusion electrode under the conditions that air was supplied with gas chamber, flow rate was 0.4 L/min, initial pH value was 5.0, Na2SO4 concentration was 0.1 mol/L and cathodic potential was-0.5 V. The repeatability test suggested that the stability of the gas diffusion electrode was very good. The apparent rate constant of p-NP using the gas diffusion electrode was 0.096 min-1, which was higher than it's with NF electrode or CNT-PTFE(1:3)/NF/NCNT-PTFE(1:1) gas diffusion electrode, and the TOC removal rate, mineralization current efficiency and energy consumption were 71.2%, 16.0% and 0.26 kWh/gTOC, respectively.(3) Cheap and readily available FCSW was prepared as heterogeneous catalyst to improve electro-Fenton degradation in near neutral pH condition using CNT-PTFE(1:3)/NF/ NCNT-PTFE(1:1) gas diffusion electrode. The main factors, such as cell voltage, FCSW concentration and pH value were studied and the possible reaction pathway was proposed. The results showed that the p-NP removal rate at 30 min was improved 77.8%,74.9% and 20.6%, respectively in AO-EF(FCSW) system than its in AO, AO-H2O2, AO-EF(Fe2+) systems under near neutral pH condition, and the TOC removal rate at 180 min was accordingly improved 56.0%,52.7% and 13.2%. The degradation process was a two-stage process, which both followed a pseudo-first-order kinetics, and the apparent rate constant in the first stage 0-15 min was lower than it in the second stage 15-30 min. Aromatic compounds and aliphatic acids were the intermediate products in AO-EF(FCSW) process.