Activated Carbons Prepared Via Reflux-Microwave-Assisted Activation Approach With High Adsorption Capability For Methylene Blue

The paper reported a facile method to prepare activated carbons (ACs) with high methylene blue (MB) adsorption capabilities via reflux-microwave-assisted activation approach. The low-cost agricultural waste corncob precursor was first refluxed in the aqueous solution of activating agents (i.e., ZnCl2 or KOH) for pretreatment, followed by microwave-assisted activation. The reflux process significantly shortens the pretreatment time to 4 h, compared to usually 24 h soaking in the traditional practice; and meanwhile greatly facilitates the diffusion of the activating agents into the precursor; whereas the microwave-assisted activation endows the ACs with hierarchical pore structures and a high specific area (e.g, 1405 m2/g for KOH pretreated AC). The ACs are also featured with rich oxygen-containing functional groups such as hydroxyl groups on the surface, and exhibit high adsorption capacity using MB as a model adsorbate because of the electrostatic interactions. Under the optimum condition (the impregnation ratio of KOH to the corncob of 2:1 (wt. %), microwave power of 600 W, and microwave time of 7 min), the prepared KAC demonstrates an adsorption capacity of as high as 636.94 mg/g. Moreover, the ACs can be readily regenerated by alkaline solution and still show satisfying adsorption performance after three times of regeneration. These findings indicate the feasibility of preparing high adsorption performance ACs by reflux-microwave-assisted activation approach.