Microwave-assisted production of activated carbon in an adapted domestic oven from lignocellulosic waste

Efficient and low-cost production of activated carbon (AC) is a challenge due to environmental and economic concerns. The combination of microwave pyrolysis and the use of lignocellulosic waste is a promising alternative to reduce the AC production costs in a sustainable way. In the present study, the adaptation performed in a domestic microwave oven is described, with no radiation leak, being a safe, simple, and fast method for AC production. Activated carbon samples from coffee grounds (CG), olive stones (OS), and Kraft lignin (KL) were produced by chemical activation (H3PO4 as activating agent), resulting in surface areas of 550, 1125, and 1170 m(2)g(-1) and yields of 19, 21, and 23%, respectively. Phosphoric acid favored the microwave absorption by the lignocellulosic material (CG, OS, and KL), making the AC production viable for all tested raw materials. This result was confirmed by FTIR and XRD analyses, showing, respectively, the reduction of functional groups and the presence of characteristic carbon bands at 24 degrees and 44 degrees in the treated samples. Scanning electron microscopy analyses confirmed that the morphology of ACs is strongly influenced by the nature of the precursors. The maximum adsorption capacity of methylene blue dye (MB) was of 80, 90, and 85 mgg(-1), i.e., 82, 95, and 92% for the ACCG, ACOS, and ACKL samples, respectively. The obtained results allow concluding that the microwave-assisted pyrolysis is a process with great potential for rapid and low-cost AC production.