Mesoporous activated carbon prepared from macadamia nut shell waste by carbon dioxide activation: Comparative characterisation and study of methylene blue removal from aqueous solution

Activated carbons are the most widely used adsorbents; however, producing high-performance mesoporous activated carbons with simple technology still remains a challenge. In this research, waste macadamia nut shell (MNS) was explored as precursor for preparing mesoporous activated carbons by carbon dioxide activation. The material characteristics of MNS-based activated carbon (MAC) were thoroughly examined in comparison with a premium-grade commercial activated carbon (CAC). MAC and CAC had specific surface areas of 830 and 1,299m, respectively. Although CAC had a predominantly microporous structure, about 74% of the pore volume of MAC is composed of mesopores. Adsorption performances were evaluated in batch experiments using methylene blue model pollutant and demonstrated 135 and 181mgg saturation capacities for MAC and CAC, respectively. Non-linear regression found that the fractal-like pseudo first-order model accurately described sorption kinetics, and intraparticle diffusion was the rate-limiting step. Among 6 established isotherm models, the Liu equilibrium model showed the best statistics. Thermodynamic analysis verified that the process was favourable and involved physisorption. These results show that valuable mesoporous activated carbons can be prepared from the biowaste MNS with simple production technology to suit environmental and industrial applications.