Preparation Of Carbon Materials From Waste Biomass And Their Application For Sediments Remediation And Energy Storage

As a renewable resource, the application of agricultural and forestry biomass wastes has aroused great concern. Compared with open burning, biomass pyrolysis is a green, low-polluting treatment. The pyrolysis products mainly include biochar,bio-oil and waste gases. In this dissertation, we obtained biochar materials by biomass pyrolysis, and used them for environmental remediation and energy storage. In addition, the pyrolytic gases were served as carbon source to synthesize carbon nanomaterials. As a sediment repair agent, rice husk biochar protected the water from contamination by limiting the pollutants release from sediments. And N-doped porous biomass-based carbon materials were used for supercapacitor electrode materials with good electrochemical properties. The gas products derived from different biomass pyrolysis were used to synthesize 3D graphene foam, achieving the recycling of waste gases. The specific research and results of the dissertation are as follows:1. The release of pollutants in the sediment is a topic of concern. Rice husk biochar, a low-cost and non-toxic material, is a promising material in remediation of sediments. In the experiment, we used different thicknesses of biochar ?0.62,1.25,3.33 and 6.20 mm? to repair the sediments which were contaminated by Cu2+ and 4-chlorophenol ?4-CP?. The results showed that a certain amount of biochar could effectively limit the concentration of Cu2+ or 4-CP below the national standard at pH 5 or 7. For highly acidic water ?pH 3?, the 6.20 mm of biochar can reduce the concentration of Cu2+ by more than 10 times compared with the blank group. The kinetic simulation results revealed that the addition of biochar can increase the mass transfer resistance of pollutants, and the porous surface and rich functional groups inhibit the release of pollutants from sediment to water.2. We obtained N-doped porous biomass-based carbon materials by using straw biomass as carbon source, melamine as N source, and molten salts as the reaction solvent and pore-forming agent. The results of the capacitive tests showed that the material with a N content of 7.78% had a high capacitance ?447 F/g?, which was attributed to the increase of N-doping and surface area by the activation of salt templating. We found that the removal of silicon in the pyrolysis product contributed to the improvement of capacitance. But, there was a negative effect on capacitance if the silicon was removed from feedstocks before pyrolysis. The reason is that silicon can catalyze the formation of active nitrogen during N-doping and plays a hard template role in the post-treatment.3. There were a large amount of gases generated in preparation of biochar or bio-oil by biomass pyrolysis. The waste gases were usually discharged along with the carrier gas, causing air pollution. In the experiment, we used the thermogravimetric analysis and Fourier transform infrared ?TGA-FTIR? to analyze the gases of cellulose and lignin pyrolysis. The gas products mainly contained small molecular alkanes, CO₂,H2O and volatile organic compounds ?condensed into bio-oil?. Then we used the pyrolysis gases as carbon source and synthesized fewer-layer 3D graphene foam?3DGF? by using coupled rapid pyrolysis and atmospheric vapor deposition equipments. The same process was performed to prepare the 3DGF structures by using gases derived from wheat straw and sawdust pyrolysis, confirmed the feasibility of this method in the application of biomass pyrolysis gases.