Microwave-assisted preparation of almond shell-based activated carbon for methylene blue adsorption

This study reports the synthesis of a novel adsorbent, hereinafter named almond shell-based activated carbon (ASAC), from waste almond shells (AS) via exposure to microwave radiation and the use of ZnCl2 as a chemical activator. Synthetic conditions were further elaborated using the response surface methodology to optimize the adsorption capacity of ASAC for methylene blue (MB) dye. The optimized ASAC preparation conditions were found to be as follows: a mass (ZnCl2/AS) ratio of 3:1 (w/w) and microwave heating time period of 15 min at 900 W. A maximum ASAC yield of 39.67% and a MB adsorption capacity of 314.20 mg/g were obtained. ASAC was also characterized by N-2 adsorption-desorption measurement, scanning electron microscopy (SEM), Fourier-transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), and point of zero charge measurement. Optimized ASAC had a Brunauer-Emmett-Teller surface area of 839.60 m(2)/g and a total volume of 0.406 cm(3)/g. FTIR and XPS analysis exhibited a decline in oxygen-containing groups of ASAC as compared with AS. The adsorption behavior of ASAC for MB was fitted well to the pseudo-second-order model and the Langmuir isotherm model. These findings support the ease of preparation and cost effectiveness that make ASAC promising for use in environmental remediation.