Preparation Of Rice Husk-based Nano-microstructure Materials And Their Application

With the rapid development of economy and technology,human society required more energy for the use of production and their daily life,but they need to resolve the coming energy crisis and a series of environmental issues.Exploiting and utilizing renewable resources has attracted the global interests of researchers.Biomass that primarily comes from the photosynthesis of plants,is renewable and natural abundant in the earth.Rice husk is one of the most abundant biomass,with an annual production of above 40 million tons in China.Previously,farmers burnt out the useless rice husks resulting in heavy environmental pollution,while an appropriate utilization will lead to a large amount of economic,environmental and energy benefits.Rice husks contain a unique lignocellulose-silica network,so they are potential to prepare various nano-microstructures including silicon-based material,carbon-based material and silicon/carbon composites,which can be applied in many different fields.In this study,according to the characteristic lignocelluloses-silica microstructure,we used facile methods to design and prepare rice husk-based nano-microstructure materials.These sustainable materials were applied as rubber reinforcing fillers and supercapcitor electrodes.The obtained results were shown as follows:1.The composite?pyrolitic rice husks,PRH?contained biochar and SiO₂ can be prepared by a low-temperature pyrolysis of rice husks.Biochar and SiO₂ in PRH were connected by a covalent bond to overcome the surface difference,so they could develop the synergistic effect for a better reinforcing performance than the single component.Furthermore,the influence of ball milling on the characterizations of PRH was investigated.The optimal milling product EM-400 had the decreased particle sizeIIIfrom 15.03?m to 5.24?m,leading to much enhancement in tensile strength and tear strength of vulcanizates.The tensile strength of EM-400/NR?20.7 MPa?was even higher than that of Carbon black?N550?/NR?19.9 MPa?,implying a promising future to replace the renewable carbon black fillers.2.A nanoscale lignin/SiO₂?LS?hybrid material was prepared from the bulky rice husks using a facile sol-gel method.The lignin and SiO₂ were self-assembled together via hydrogen bonds,which significantly avoided the lignin-lignin or SiO₂-SiO₂ aggregation,leading to a small particle size of 320 nm and a spherical shape.The obtained LS was used as a partial substitute filler of commercial carbon black?N550?.The resultant 10LS/40CB/NR vulcanizates showed improved tensile strength,tear strength and wear resistance than the 50CB/NR vulcanizates filled with single carbon black.The addition of LS would not only reduce the use of nonrenewable carbon black,but also improve the machenical properties of rubber composites.3.Using a selective SiO₂ removal pretreatment,following with KOH activation to prepare high surface area porous carbon as supercapacitor electrode material.Herein,we investigated the SiO₂ distribution in the pyrolytic rice husks and its influence on KOH activation.By a controlled NaOH pretreatment,the SiO₂ particles without template effect were leached out,resulting in the enhanced activation efficiency.The obtained porous carbon product exhibited high surface area 2756 m²g^-1,hierarchical porosities containing micropores,mesopores and macropores,and high gravimetric capacitance 402 F g^-1 at 0.5 A g^-1 in 1 M H₂SO₄ electrolyte.4.N-doped porous carbon?NPC?was prepared by the pyrolysis of urea immersed rice husks,following with the removal of SiO₂ template.Dispensing with chemical activation to ensure high carbon density,the porosity was created by the thermal degradation of lignocelluloses and the template effect of SiO₂.N-containing functional groups which could generate pesudocapacitance without sacrificing carbon density were introduced into porous carbon via Maillard reaction from the decomposed urea.The optimal NPC product exhibited both high gravimetric capacitance 242 F g^-1 and high volumetric capacitance 306 F cm^-3 at 0.5 A g^-1,which was suitable for the fabrication of potable energy storage device.5.Using the rice husk residue after the synthesis of LS material to prepare porous carbon sheets?PCS?.The none-toxic and recycled NaCl/KCl salts were used as activation agents and the synthesis procedure was achieved in air.The optimal product showed a sheet-like structure,with the surface area of 977 m² g^-1.As the supercapacitor electrode,the PCS exhibited high capacitance of 288 F g^-1 and excellent cycling stability.6.We proposed a new route for comprehensive utilization of rice husks:consecutively converting hemicelluloses into xylose,lignin and SiO₂ into LS as rubber fillers,and cellulose into PCS as electrodes.Every component has been converted into valuable product and no waste discharged in this method.