The effects of a microwave heating method on the production of activated carbon from agricultural waste: A review

A review of the effect of a microwave treatment on the production of activated carbon (AC) from agricultural waste is presented in this study. Although the thermal heating method is one of the most usual and applicable methods for the production of AC, this method has some disadvantages such as a thermal gradient from the surface to the interior of a particle, high cost of heating, long preparation time and fast firing. A microwave radiation method has been used recently by many researchers as an alternative method for heating. In this review, these two different methods of producing AC were compared. Previous studies on the preparation of AC using a microwave radiation method showed that the more significant parameters are the microwave radiation time, the microwave power level, the impregnation ratio and the agent flow rate. Accordingly, in this review, the effects of these parameters on the physical and chemical properties of AC, such as the pore structure, the adsorption capacity, the carbon yield and the surface functional groups, were discussed. In general, the physical properties of AC (adsorption capacity, pore volume and carbon yield) improved when these parameters were enhanced up to their optimum points, and then these properties decreased when these parameters were increased beyond their optimum values. The carbon/oxygen ratio was increased by the microwave method due to the elimination of acidic oxygen-containing functional groups on the surfaces of the ACs.