Microwave assisted preparation of activated carbon from biomass: A review

Activated carbon has been widely used as adsorbents, catalyst support and energy storage materials. Microwave heating is a promising technique for thermochemical treatment and activation of activated carbons due to its fast, selective, uniform and volumetric heating. Previous reviews mainly focused on specific feedstocks (e.g. agricultural biomass or oil palm wastes) or ignored important parameters for microwave activation (e.g. mass of activated carbon precursor). Characteristics of activated carbons prepared from conventional and microwave treatment were not compared and economics of microwave activation were not described in previous studies. This paper presentst a state of the art review of activation under microwave irradiation for various biomass sources (e.g. agricultural wastes, woody biomass and sewage sludge). Characteristics of microwave heating, main activation parameters, research progress and technology status of activated carbon preparation and regeneration under microwave irradiation are investigated with key challenges and economics being addressed. Characteristics of activated carbons made from microwave irradiation and conventional activation are compared and the advantages of microwave-assisted preparation are highlighted. It shows that the BET (Brunauer–Emmett–Teller) surface area, iodine number, methylene blue adsorption capacity and the yield of activated carbons under microwave irradiation are up to 2500–3000 m2/g, 1800–2200 mg/g, 500–700 mg/g and 13–96 wt%, respectively, competitive with conventional methods on the quality of activated carbons and process economics. Potential applications and future perspectives are described with pertinent information on activated carbon preparation under microwave irradiation.