Development of activated carbons derived from wastes: coffee grounds and olive stones as potential porous materials for air depollution

Agro-industrial byproducts and food waste necessitate an environmentally friendly way of reducing issues related to their disposal; it is also necessary to recover as much new raw material from these resources as possible, especially when we consider their potential usage as a precursor for preparing depolluting materials, such as activated carbon. In this work, coffee grounds and olive stones were chosen as precursors and the adsorption capacity of the obtained porous carbons for volatile organic compounds (VOCs) was studied. Microporous activated carbons (ACs) were prepared using chemical (K2CO3) and physical (CO2) activation. The influence of the activation process, type, and time of activation was also investigated. Measurements of VOCs adsorption were performed, and methyl-ethyl-ketone (MEK) and toluene were chosen as the model pollutants. The surface areas and total pore volumes of 1487 m2/g and 0.53 cm3/g and 870 m2/g and 0.22 cm3/g for coffee ground carbons and olive stone carbons, respectively, were obtained via chemical activation, whereas physical activation yielded values of 716 m2/g and 0.184 cm3/g and 778 cm2 g-1 and 0.205 cm3/g, respectively. As expected, carbons without activation (biochars) showed the smallest surface area, equal to 331 m2/g and 251 m2/g, and, hence, the lowest adsorption capacity. The highest adsorption capacity of MEK (3210 mg/g) and toluene (2618 mg/g) was recorded for chemically activated coffee grounds. Additionally, from the CO2 isotherms recorded at a low pressure (0.03 bar) and 0 °C, the maximum CO2 adsorption capacity was equal to 253 mg/g.