Research On The Preparation And Performance Of New Carbon Materials For The Catalytic Wet Air Oxidation

Catalytic wet air oxidation (CWAO) is one of effective technologies treating highly concentrated, toxic and hazardous organic compounds in the wastewater, and the efficient heterogenous catalysts are one of the key roles in applying the technology in the wastewater treatment. Compared with metal catalysts, carbon materials used as catalysts avoid the use and leaching of metal active phases in the preparation and reaction processes, and have good chemical stability in the acidic and basic operating conditions. Therefore, carbon materials have attracted considerable research attention in the catalyst field. In this study, graphene oxide (GO) with high concentration of oxygen-containing functional groups, prepared by Hummers method, the different GO reduced by VC and ammonia, and the fullerene (C60) functionalized by different oxidants were used as catalysts in the absence of any metals in the CWAO reaction. The catalytic performance of carbon materials was investigated in the CWAO of phenol under the milder operating conditions in the batch reactor. Moreover, the free radicals produced were studied in the CWAO of phenol over GO as catalysts.GO, RGO and GO-N were used as catalysts in the CWAO of phenol at the reaction temperature of155℃, the oxygen pressure of1.8MPa, the catalyst dosage of0.2g/L and the initial phenol concentration of1000mg/L. The different GO catalysts displayed good activity, and the order was GO>RGO>GO-N. Moreover, the GO showed the best catalytic activity,100%phenol was removed after45min, and84%TOC was achieved after120min in the CWAO reaction. For the RGO, the efficiency of catalytic activity depends on the reduction time, and the phenol conversion decreased with increasing VC reduction time. On the other hand, it is noticed that the GO-N was inactive in the CWAO of phenol. In the CWAO cyclic reactions, the used GO obviously showed the lower catalytic activity. It is found that oxygened functional groups and specific surface area of the used GO catalysts decreased. The structural change could lead to the decrease of the catalytic activity for the GO sample during the cyclic reactions.C60, was functionalized with the different oxidants, such as HNO3-H2SO4, KMnO4/HNO3, and Ozone. The functionalized C60displayed good activity in the CWAO of phenol under the reaction temperature of175℃, the oxygen pressure of1.8MPa and the initial phenol concentration of1000mg/L. The order was C6o-2>C6o-1>C6o-3>C60-4≈WAO.100%phenol and74%TOC removals were obtained after120min reaction in CWAO of phenol over C60-2.According to the results of the carbon material structure, characterized by BET, SEM, TEM, Raman, FT-IR and XPS, and of the catalytic activity of carbon materials, the oxygened functional groups (especialy-COOH) on the surface of the carbon materials were the main active sites forming the strong free radicals in the CWAO of phenol. Moreover, it is found that the concentration of oxygen-containing functional groups has close relationship with the catalytic activity of carbon materials.The nitrobenzene was selected as an indicator to investigate the formed radicals in the CWAO of phenol over GO. The results showed that:(1) nitrobenzene (NB) was not removed in the CWAO of single NB with GO;(2) good NB removal (ca.38%) was attributed to the catalytic activity of the GO in the CWAO of NB in the presence of phenol. According to our results for the CWAO of NB with and without phenol, the radicals (OH-) are produced in the CWAO of phenol over the GO, and lead to the NB removal. In addition, the mechanism producing the radicals was suggested in the CWAO of phenol over carbon materials as catalysts.