Carbons Prepared From Naoh-pretreated Rice Husks By Low-temperature Solution-processed Carbonization

In China, a large of population consumes rice; China and India account for more thanhalf of world rice production. Therefore, the production of a greater quantity of paddiesresults in the production of a larger of amount of rice husk. Rice husks are commonly used asa low-value energy resource, burned in the field or discarded, which are detrimental to theenvironment. Considering that rice husks, mainly composed of organic hemicellulose,cellulose, lignin and inorganic silicon dioxide, have great potentiality to be utilized to preparetask-specific products, such as silica-based and carbonaceous materials.The main research work is as follow:1. A coupling of low-temperature sulfuric acid-assisted carbonization and H3PO4activation was employed to convert NaOH-pretreated rice husks into activated carbons withextremely high surface area (2028m2g1) and integrated characteristics. The influences ofthe activation temperature and impregnation ratio on the surface area, pore volume ofactivated carbons were thoroughly investigated. The morphology and surface chemistry ofactivated carbons was characterized using N2sorption, FTIR, XPS, SEM, TEM, etc.2. The adsorption capacity of resulting carbons obtained under optimum preparationconditions was systematically evaluated using methylene blue as model dye under varioussimulated conditions. The adsorption process can be well described by both Langmuirisotherm model and the pseudo-second order kinetics models; and the maximum monolayercapacity of methylene blue was ca.578mg/g.3. By comparing various physicochemical properties of activated carbons prepared withpotassium carbonate, zinc chloride pellets and potassium hydroxide and phosphoric acid, therelationship between preparation procedures and textural and adsorption characters has beenestablished. Activation treatment not only developed various porous structures, but alsointroduced different types of oxygen or phosphorus-containing functional groups on thesurface of four types of samples. Comparatively, the process of methylene blue adsorptiononto ASPC showed faster adsorption rate and larger adsorption capacity than the other three samples. Moreover, the adsorption isotherms, kinetics, and thermodynamics of the modelcompound over resulting carbons were also discussed. Possibly, results of this work are ofinterest for environmental applications of activated carbons prepared from biomass waste,especially on the choice of suitable activation process.