Study On Preparation And Performance Of Rice Husk-based Silica And Silicates

Rice is the fourth largest agricultural product in the world,and a large amount of rice husk（RH）is produced during the rice hulling process.However,the main treatment methods of RH are landfill and incineration at present,which cause resource waste and environmental pollution.Therefore,the development and utilization of RH resources has become a research hotspot.Rice husk has a three-dimensional network structure composed of silica and organics,including about 20 wt.%silica and 80 wt.%lignocellulose.Compared with other biomass（corn cob,bamboo leaf,straw,etc.）,RH has the advantage of high silica content.With the continuous deepening of the research on RH,it is now possible to design and manufacture a variety of silicon-based materials with novel structures by using the siliceous components in RH.In view of existing literatures and practical problems encountered in the development of RH silica-based materials,relevant experiments and discussions were carried out in this paper.A variety of functional silica-based materials were designed and synthesized with the help of the unique chemical composition of rice husk,and the application of some samples in anti-friction and energy storage was preliminarily discussed.Firstly,two kinds of Rice Husk Ashes（RHAs）,water treated rice husk ash（WRHA）and acid treated rice husk ash（ARHA）,were prepared by different pretreatment of RH,and then pyrolysis under the same conditions.These were added into High Density Polyethylene（HDPE）as fillers respectively,and the effect of the variety and amount of fillers on the friction properties of HDPE composites were investigated;Secondly,the siliceous components of RH were transformed into cobalt silicate through hydrothermal reaction,and the feasibility and characteristics of cobalt silicate as capacitor electrode materials were explored;Thirdly,in order to further improve the capacitance performance of Transition Metal Silicates（TMSs）,TMSs were prepared by the method of double transition metal composite,and the effect of the molar ratio of the two metal elements on the performance of the electrode active material was investigated;Finally,calcium metasilicate nanorods were prepared by one-step molten salt method using RH as silicon source,and the effects of silicon source and synthesis conditions on the morphology of the products were investigated.The research results are as follows:1.Due to the different pre-treatment methods of rice husk,there were certain differences in the morphology of the two RHAs prepared.Through the scanning electron microscope（SEM）photos,it can be seen that the particle size of ARHA was significantly smaller than that of WRHA.According to Brunauer–Emmett–Teller（BET）method,ARHA has a specific surface area of up to 289.91 m²/g.2.Different amounts of RHAs obtained from different pretreatment were used as HDPE fillers by melt blending,and the friction properties were studied.The experimental results showed that the different amounts of fillers had a significant impact on the performance of the composites.The Coefficent of Friction（COF）of1.5ARHA/PE sample was the lowest when the filler content was 1.5wt.%,which reduced the COF by about 13%and 41%compared to pure HDPE and 1.5WRHA/PE,respectively.3.Cobalt silicate electrode active materials were prepared by hydrothermal method using commercial Si O₂,rice husk-based silica（RH-Si O₂）and rice husk-based carbon/silica composite（RH-C/Si O₂）as raw materials.Through a series of characterization and testing,the feasibility of cobalt silicate from rice husk siliceous composition in the application of capacitive electrode materials was verified.The experimental results showed that when the molar ratio of cobalt and silicon was 2:1,the mass specific capacitance of the active material prepared from rice husk reach264.80 F/g at the current density of 0.50 A/g.4.Various bimetallic composite silicate electrode active materials were systematically characterized and tested.The experimental results showed that the electrode active material prepared at the molar ratio of cobalt and nickel was 3:2 had the best capacitance performance.The mass specific capacitance of the electrode material was up to 548.20 F/g when the current density was 0.50 A/g,which was much higher than TMSs prepared by other molar ratio of cobalt and nickel under the same conditions.5.According to the test results,the change of the molar ratio of cobalt and nickel would change the binding energy of cobalt in the system.When the addition of nickel ion reaches its threshold,cobalt in silicate was in the best bonding environment,which was more conducive to the occurrence of redox reaction,thus making the material have better pseudo-capacitance properties.6.Calcium metasilicate nanorods were successfully prepared from RH by one-step molten salt method,and the effects of silicon source and synthesis conditions on the morphology of the products were investigated.The experimental results showed that under the nitrogen atmosphere of 800oC and the cooling rate of 5oC/min,with the help of the template provided by the RH matrix,the unique silica distribution in the RH and the coating and blocking effect of the RH-carbon,directly using the RH as the raw material can effectively avoid the melting and agglomeration of silica particles,so that wollastonite nanorods with a length-diameter ratio greater than 200could be prepared by one step.