Study On Preparation Of Carbon Based Nanocomposite Materials And Their Application In Catalytic Degradation Of Organic Pollutants

Under the background of strained resources and the rapidly deterioration of water pollution, how to rapidly and efficiently degrade wastewater has gradually become a pressing problem. Therefore, to develop novel heterogeneous catalysts with higher efficiency and stability has attracted great attention of many scientists. In this paper, based on resource utilization of coconut shell, sewage sludge and algae as catalyst support, the new heterogeneous catalysts were prepared by hydrothermal method and pyrolysis process. The catalytic degradation of the organic pollutants was investigated and the primary conclusion was as followed.(1) A highly active nano-MnOx on coconut shell activated carbon (CSAC) prepared via hydrothermal process was explored and the prepared nano-MnOx@CSAC as an oxidant for the degradation of organic pollutants was investigated. It was found nano-MnOx@CSAC prepared by hydrothermal method exhibited much higher activity towards degradation of azo dyes in comparison with MnOx@CSAC prepared by calcination under nitrogen or air atmosphere. The hydrothermal treatment led to the in situ synthesis of nano-MnOx onto CSAC surfaces with the incorporation of the multi-valence oxidation states of manganese. The MnOx@CSAC also could effectively degrade other anionic dyes with a removal rate of over 90%. Additionally, the oxidation activity of the MnOx@CSAC was relatively stable and efficient. Due to the acid condition, there was a few of manganese leaching. Through GC-MS analyses, the most detectable degradation products were mainly low-molecular-weight organic acids, which are known to be biologically degradable.(2) For dewatering and resource utilization of sewage sludge, a MnOx heterogeneous catalyst from wet sludge via hydrothermal process was developed and the prepared MnOx/HCAS as heterogenous catalyst of peroxymonosulfate (Oxone) for the degradation of organic pollutions under neutral pH condition were investigated. MnOx/HCAS showed stronger catalytic activity for the heterogeneous activation of Oxone. With the addition of 1.0 g/L catalyst and 1.0 g/L Oxone, the dye degradation efficiency can be at 98% and COD removal rate was 45% by MnOx/HCAS-Oxone system. Radical quenching tests proved that SO4-· radicals were the main reactive species. XPS characterization result of the fresh and used MnOx/VHCAS indicated the highly catalytic activity could be attributed to the multi-valence oxidation states of manganese. The contents of the heavy metals in MnOx/VHCAS catalyst before and after reaction did not dramatically change and the concentration of heavy metals from the supernatant solution after reaction was very low, which posed no harmful impact on the environment. Different kinds of wet sludge based on MnOx catalysts exhibited excellent catalytic performance to azo dyes, which also decided the possibility of practical applications for fabrication of MnOx heterogeneous catalyst from wet sludge.(3) Due to the occurrences of algal blooming and difficult algae removal, the rational utilization of biological resources strategy was proposed. FeNi-N/Al2O3/C mixed-phase on hollow carbon spheres were synthesized and characterized as a Fenton-like catalyst for the degradation of several organic pollutions near neutral pH condition. It was found FeNi-N/Al2O3/C exhibited excellent catalytic activity towards the degradation of azo dye and phenol near neutral pH condition. The addition of FeNi-N/Al2O3/C (0.4 g/L) induced azo dye (50 mg/L) and phenol (30 mg/L) degradation removal of 95% in 30 min in the presence of 40 mM H2O2, respectively. TOC removal rates were 69.9% and 76.0%, respectively. The utilization efficiencies of H2O2 were 65.7% and 67.6%, respectively. Moreover, FeNi-N/Al2O3/C also exhibited excellent catalytic stability and easy recyclability. There was no significant change in the morphology of FeNi-N/Al2O3/C during the reaction. XPS characterization result of the fresh and used FeNi-N/Al2O3/C indicated the highly catalytic activity could be attributed to the redox pair of Fe3+/Fe2+ species. Based on in situ Raman and ESR analysis of the catalytic degradation process in the FeNi-N/Al2O3/C/H2O2 system, a detail mechanism for FeNi-N/Al2O3/C induced organic pollutants degradation was proposed. The cycle of Fe2+/Fe3+ increased the formation of HO·, causing higher degradation and mineralization of organic pollutants.