Preparation Of Cathodic Materials And Investigation Of Rotating Disk Reactor For Electro-Fenton System

Electro-Fenton technology (EF) is a new, efficient and clean electrochemical advanced oxidation technology, which has attracted a great deal of attention in recent years. Since the production of H2O2is significantly dependent on the cathodes used, which directly influence the degradation efficiencies of pollutants in EF system, developing new efficient cathodic materials becomes one of the research focuses in the area.In this study, the commercial graphite felts with three-dimensional structure were used as the pristine cathode materials, chemical and electrochemical modification methods were used to improve the catalytic activities of oxygen reduction reaction (ORR), and the effects of the modification on the production of H2O2and EF degradation efficiency were investigated on the basis of characterization. In addition, the other important aspect for the EF——the reactor was also discussed, and a new dual-cathode rotating disk EF reactor was developed, impacts of the operational parameters were also studied. The main conclusions can be drawn as follows:1. Low-cost chemical reagents ethanol and hydrazine hydrate were used to modify the graphite felts (soft felts). The XPS analysis showed that after modification, plenty of carbon particles appeared on the surface of graphite felt fibers, and the hydrophilicity of the materials was improved. Approximately0.56at.%nitrogen element was detected in the hydrazine hydrate-ethanol modified sample (CF-B) in the forms of "graphite nitrogen" structure, pyridine nitrogen groups and the type of nitrogen oxide groups (such as-NOx or NOC), and there were more hydrophilic groups. Compared with the unmodified cathode, the modified ones showed stronger current responses, more negative hydrogen evolution potentials, and the increased electron transfer kinetics for ORR process. The highest H2O2accumulation was achieved at CF-B, up to175.8mg/L. The modification could improve the performance of EF, and the highest mineralization ratio in modified cases was51.4%,29.2%higher than before. CF-B was detected above45%of the mineralization of p-Np after10cycles of use, indicating a good stability of the modified electrodes.2. The influencing factors during the production of H2O2were investigated at the chemically modified graphite felt electrodes. The optimal concentration of hydrazine hydrate in the chemical modification was determined as10%, when the yield of H2O2was approximately as2.6time as before. The influence of the cathode potentials, pH and O2flow rate on the H2O2production and current efficiency (CE) were also investigated. The highest H2O2accumulation was achieved at-0.75V, neutral pH and0.4L/min of O2flow rate, up to247.2mg/L. The CE tended to decrease with the increase of potentials and decrease of pH, and a suitable aeration amount of O2is not only to promote the production of H2O2, also could effectively reduce operating costs.3. A non-toxic, simple, rapid electrochemical modification, so call "anodisation", was used to modify the graphite felt materials (hard felts). The ratio between O and C (O/C) on the electrode surfaces was detected increasing with with the increase of the electrochemical oxidation treatment cycles. Compared with the pristine cathode, the hydrophilic groups increased on the modified surface, which was favorable to improve the hydrophilic properties of the materials. After anodisation, the cathodes had stronger current responses, which were significantly increased with the increase of the anodising cycle times, the hydrogen evolution potential was more negative, and the trigger potential of ORR at modified. cathodes was about0.1V more positive than pristine one. The optimum anodising cycle times was10, when the mineralization ratio of the/p-Np increased27.9%-35.3%.4. A new dual-cathode rotating disk EF reactor was used for H2O2production and electrocatalytic degradation of pollutants. The positive effects of the rotating conditions on the current responses toward ORR were determined by linear sweep voltammetry. The highest yields of H2O2was achieved at100mA, with rotating speed of10rpm, in0.05mM Na2SO4electrolyte, up to108.1mg/L, and the CE was40.9%, which was as3times as at static conditions. The operational parameters such as Fe3+concentration, pH, support electrolytes and initial concentration of pollutants on the catalytic performance of the rotating disk system were investigated using the Methyl Orange (MO) as a target pollutant. The different influences of Fe3+on the decoloration and mineralization was found, due to the complexation between Fe3+and azo dyes, the addition of Fe3+can make the chromophore more stable. However, the existence of Fe3+was conducive to the removal of TOC, and the optimum concentration of Fe3+was0.2mM, when the mineralization ratio was48.2%, which was26.6%higher than the system without Fe3+. The suitable pH in rotating disk reactor was similar with other EF systems, and the decoloration can be completed within30min at pH around3. The degradation efficiency of MO in different electrolytes followed the order NaNO3> NaCl> Na2SO4, and the mineralization ratio in NaNO3electrolyte was51.2%.