Almond and Walnut Shell Activated Carbon for Methylene Blue Adsorption

Activated carbon (AC) from nutshells has the potential to be an economically attractive product. This study developed ACs from almond and walnut shells and compared their performance against two commercial ACs (Calgon Carbon Filtersorb 400 and Kuraray YP50) in adsorbing methylene blue (MB) at various concentrations. Activated carbons were generated from nutshell biochar using 2 levels of activation to investigate the effect of activation residence time on material properties including pore development and MB adsorption. Raw nutshells, nutshell biochars, and nutshell ACs were characterized using elemental (CHNSO) analysis, proximate analysis, thermogravimetric analysis, activation kinetics, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), MB adsorption testing, Brunauer-Emmett-Teller (BET) surface area and pore size distribution, and linear regression analysis on incremental pore volume and methylene blue adsorption capacity. Results demonstrated that almond and walnut shells can be used to make activated carbon that has a similar or better methylene blue adsorption performance than the tested commercial carbons. Almond shell, walnut shell, and YP50 and Filtersorb 400 activated carbons showed MB adsorption capacities of 440, 358, 487, and 310 mg g^–1, respectively. Physical activation using carbon dioxide led to enhanced micropore development, and specifically, greater volume of pores with widths between 8-18 Å led to higher MB adsorption capacity. Activated carbon manufactured from nutshells shows significant potential for wastewater applications as well as other applications requiring microporous carbon.