Preparation And Application Of Starch-based Carbon Spheres

Carbon spheres with the unique subtlety in morphology and structure have been given many features and functionalitie s as a new material. It has been reported used on environmental conservation, energy storage medium, catalyst supports, owing to its porous structure, high specific area, stable physical and chemical properties and high mechanical strength. However, the existing process to prepare spherical carbon is low-yield, energy intensive and probably polluting. In order to obtain carbon spheres with advanced capabilities, investigations on extended precursors are still needed. Biomass resources are desirable as carbo n precursor due to its low price, abundant sources, widely origins and renewable. Thus, biomass resources as alternative resources have become a new trend of development. Starch is one of the most abundant organic substances on the earth, which is green and renewable, in addition, starch granules have natural spherical morphologies. Accordingly the carbon spheres with the original shape of cassava starch have been prepared. This carbon materials have been applied for adsorption and supercapacitor.In this study, spherical carbon retains its original shape after carbonization by using pre-oxidation method. The effect of different stages were characterized and the preparation mechanism also were investigated. The prepared process include pretreatment at 220 ℃ and carbonization at 600 ℃, and the process of pre-oxidation is the key steps. In the pre-oxidation process, a serials of changes has been occured include the evaporation of water, thermal pyrolysis, molecular rearrangement and polycondensation results in the destruction of chain-chain crystallite structure, which prohibits starch from melting and foaming during the carbonization.Owing to the carbonize products with no pores and less specific surface area, series of high specific surface area and ad vanced electrochemical performance activated carbon spheres were prepared by using KOH activation. With these advantages, the starch-based products have an excellent properties in adsorption and supercapacitor. The effect of activation parameters(such as activation temperature and time, amount of KOH) were investigated. In order to evaluate the sorption capacity of the activated carbon spheres(ACSs), phenol was selected as the model contaminant. The sorption isotherm is well fitted with a langmuir model. The maximum sorption of phenol by the ACSs was 350.4 mg·g-1, which is almost about 35 % of adsorbent self- weight. Furthermore, although the ACSs have been proven to be a good adsorbent for removal contaminants, it is hard to separate and retrieve. Magnetic AC composites possess effective adsorptive performance and can be separated with an external magnetic field.The capacitance of supercapacitor assembled with above activated carbon spheres were investigated, and the effect of pore structure on the electric double- layer capacitance was studied. The result indicate that ACSs with the particle size range from 5-20 μm acquired by carbonization and KOH activation shows good power and cycle performance. The sample with high specific surface area of 2818.99 m2·g-1 have a good capacitance of 300.8 F/g.At last, in order to improve its properties and enlarge its application fields, a novel starch-based carbon material with hierarchical porous structure was developed by a three-step preparation. Firstly, we prepared porous spheres from corn starch by enzymatic hydrolysis. Then, with the pre-oxidation method, the morphology and structure can be preserved from the porous starch. Finally, a new starch-based carbon spheres with hierarchical porous structure(HPACSs) has been obtained by KOH activation. Compared with the ACSs, the HPACSs with surface area of 2855.27 m2·g-1 has the better specific capacitance of 369.5 F/g.