Preparation of activated carbons from coffee residue for the adsorption of formaldehyde

Six types of activated carbons were prepared from coffee residues by varying activating agents of zinc chloride, nitrogen, carbon dioxide and steam. Characterization of these samples was performed by using nitrogen adsorption isotherms, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) in order to understand the coffee residue activated carbon and its adsorptive capacity. All of activated carbons and one commercial activated carbon (CH-I1000) were subjected to the adsorption of formaldehyde vapor. The coffee activated carbon prepared with ZnCl2 impregnation and nitrogen activation (CZnN2) demonstrates its highest capacity of formaldehyde adsorption owing to the hydrophilic functional groups of OH, CO, CO on the surface. The coffee activated carbon prepared with ZnCl2 impregnation coupled with carbon dioxide activation (CZnN2CO2) yields the highest total surface area (914 ± 21 m2/g) and total pore volume (1.010 ± 0.003 cc/g) with the hydrophobic groups on the surface adsorbed formaldehyde less than CZnN2. Therefore, we conclude that the formaldehyde adsorption by activated carbons in this work is affected by surface chemistry more than texture characteristics of surface area and pore volume.