Synthesis And Adsorption,Catalytic Properties Of Coal-based Magnetic Carbon Materials

Coal is an abundant and cheap natural resource in Xinjiang, China. In order to promote the efficient utilization of coal, it is very important to prepare coal based carbon materials with high performance and quality. Activated carbons（AC） are widely used in environment, catalysis, super capacitor, lithium ion battery and CO2 capture and H₂ storage due to the stable chemical and thermodynamic properties, high specific surface area and abundant pores. When they are exhausted or the effluent reaches the maximum allowable discharge level, powder activated carbons need to be separated from the aquatic system and regenerated by filtration. However, the filters are usually blocked, and AC are also easily lost. Thus, magnetic activated carbons（MAC） have attracted increasing attention, which can be readily separated by applying a magnetic field. The magnetic separation technique has been regarded as an excellent alternative to traditional filtration, which can overcome the disadvantage of filtration.In this paper, in order to improve the added-value of coal, carbon materials with magnetism were prepared, their adsorption and catalytic properties were studied. The research results could provide a theoretical basis for the industrial application of coal-based carbon materials with high performance. The main contents and results are as follows:1. MAC was one-step synthesized by using the two-stage carbonization and activation of coal, in which Kuche coal in Xinjiang was used as carbon source, Fe₂O₃ acted as the magnetic resource and KOH as an active agent. The effects of calcination temperature, the alkali/carbon ratio and mass fraction of Fe₂O₃ on the structures and properties of MAC were studied. It is concluded that the optimized parameters for preparing MAC are the first-stage temperature of 800 oC, the second-stage temperature of 1000 oC, Fe₂O₃ of 12% and the alkali/carbon ration of 1.0. At these conditions, MAC had a BET surface area of 2075 m2 g^-1 and a high adsorption capacity of 871 mg g^-1 for methylene blue（MB）. The data of adsorption kinetics and isotherms could be well fitted by using the pseudo-second-order equation and the Freundlich model. Importantly, MAC can be separated and recovered easily by applying a magnetic field due to the high saturation magnetization(15.02 emu g^-1).2. We present a simple, one-step method to prepare Ni and Fe metals supported on AC derived from coal through immersion method and calcination, in which Kuche coal in Xinjiang was used as carbon source, Ni（NO₃）₂·6H₂O or Fe（NO₃）₃·9H₂O as the magnetic resource and KOH as an active agent. The Ni- and Fe-based catalysts were used in catalytic reduction of 4-nitrophenol（4-NP）. The effects of the initial amount of Ni（NO₃）₂·6H₂O, alkali/carbon ratio and calcination temperature on the properties of Ni based catalyst were studied. Under the conditions of 2 g coal, 2.5 mmol Ni（NO₃）₂·6H₂O, alkali/carbon ratio of 0.5, calcination temperature of 600 oC, the obtained catalyst can completely convert 4-NP into 4-aminophenol（4-AP） within 3 min. Meanwhile, the effect of Fe（NO₃）₃·9H₂O initial amount on the structure and catalytic performance of Fe based catalyst was studied. It is found that the sample has not only the magnetic and catalytic properties, but also the layer structure is different from the traditional morphology of the active carbon. In addition, thickness of layers increased and pores are more abundant with the increase amount of Fe（NO₃）₃·9H₂O.3. The bimetal loaded catalyst NiFe/AC was prepared on the basis of Ni/AC and Fe/AC, which exhibits the highest catalytic activity with the reduction of 4-NP to be completed within only 2.5 min at room temperature. Moreover, the saturation magnetization of the catalyst is as high as 27.2 emu g^-1 and it can be fast separated from the reaction system. After being reused for several cycles, the NiFe/AC still shows good catalytic stability.In addition, we present a novel, simple and one-step method to synthesize magnetic carbon materials by using the carbonization and activation of coal in the presence of Fe₂O₃, Ni（NO₃）₂·6H₂O or Fe（NO₃）₃·9H₂O. The synthesized materials have good adsorption or catalytic performance and can be separated and reused easily due to their strong magnetism. And this simple synthetic method can be used to produce high-performance, low-cost magnetic carbon materials from coal at large scale, thus having a great potential for industrial applications.