Synthesis And Environmental Application Of New Carbon-based Catalysts

As a novel environmental friendly, renewable materials, the nano-scale carbon materialhas attracted more and more attentions in many fields. Owing to its excellent structuralcharacteristics, performance, thermal, magnetic, optical, mechanical and other properties,the research on its application has being a frontier technology especially in the field ofenvironment.This thesis focuses on the preparation of nano carbonaceous catalysts-carbonnanotubes and carbon nano onions and the activities in environmental catalytysis, includingdirect catalytic decomposition of nitrogen oxides and photocatalytic degaradation of organicwastewater under visible light. Especially, the nano carbon onions is investigated as a newenvironmental catalyst support. The main works are as follows.(1) Carbon nanotubes supported metal catalysts (Fe/CNTs, Mn/CNTs and Cu/CNTs)were successfully prepared and showed better catalytic activities of NO decomposition. TheNO conversion and N2selectivity by Fe/CNTs catalyst performed excellently. At thetemperature of500℃, NO conversion rate and N2selectivity over Fe/CNTs was76%and87%, respectively. Over the three catalysts, the activity and selectivity followed the order ofFe/CNTs> Mn/CNTs> Cu/CNTs. Chemical reactions between Fe, Mn and the CNTsoccurred and forming carbides. However, in the Cu/CNTs sample, copper carbonate wasfound. We proposed that the carbide phase for the direct decomposition of NO to N2and O2is more effective. At the temperature between300-500℃the catalysts showed betteracticities and avoiding being oxidized strongly. (2) CNOs (onion-like carbon) was studied as nitrogen oxide decomposition catalystsupport and doped with Cu, Mn and Cu-Mn, wherein the Cu-Mn/CNOs showed higher NOactivity and N2selectivity. At the temperature of500℃, NO conversion was77%, N2selectivity was90%. Cu-Mn alloy structure was more conducive than the copper carbonateand manganese carbide structure to the formation of oxygen species O2-2and O-2, makingrapid desorption of oxygen. Interaction between Mn2-δ-Cu2+δenabled rapid desorption ofoxygen species, resulting in high NO conversion rate and high selectivity of N2.(3) SDP (Spinning Disc Process)/sol-gel method was applied to synthesizeMWCNTs-TiO2photocatalyst, which was calcined at different temperatures. The resultsshowed that compared to the conventional sol-gel method, the SDP way was beneficial forthe formation of samller particles and more uniform dispersion of nanoparticles. Calcinationtemperature played an important role in the visible light response, MCT3calcined at thetemperature of450℃exhibitted strongest visible light adsorption and betterphotocatalytic degradation activity of quinoline, which was greater than80%.Photosensitizing mechanism of carbon was proposed.(4) By using MCT3, coking wastewater was degradated through central compositedesign response surface methodology (CCD). At the optimal parameters: pH of6.72,catalyst dosage of0.94g L-1, aeration rate of0.98L min-1and the initial concentration of50mg L-1, the highest degradation rate of coking wastewater was reached at86.57%.(5) By using SDP/sol-gel method, visible light responsible and magnetic separable,bifunctional CEMNs-TiO2nanocomposite was synthesized. The calcination temperature aswell as the magnetic properties were investigated to test the catalytic activity. It can notonly ensure the visible light photocatalytic activity, but also show good separation effect.The introduction of carbon effectively avoided the interaction between the inner metalmagnetic core and TiO2. The remanence was negligible with the Mr/Msvalue of0.016. Thehysteresis loop was like "S" curve, superparamagnetic property was discovered, which canbe magnetic separated and the catalysts showed better catalytic activity.(6) CEMNs-TiO2nanocomposite dispersed well in the aqueous phase, its large specific surface area contacted well with the organic pollutants. After the reaction, it can beseparated by means of an external magnetic field for recycling. After six cycles, themethylene blue degradation rate dropped to69.88%and the magnetic recovery rate was90.6%.(7) The role of carbon was not only the adsorption or dispersion of TiO2, but also theformation of Ti-O-C bond, which caused the visible light response, while high graphitizedCEMNs may also act as a photosensitizer, which affectted the visible light photocatalyticdegradation of methylene blue.