Preparation and characterization of bio-safe activated charcoal derived from coffee waste residue and its application for removal of lead and copper ions

Activated charcoal was prepared by the pyrolysis of coffee ground waste residues impregnated by phosphoric acid and potassium hydroxide at 600 °C. In our study, spent coffee was collected from the university canteen and the prepared activated charcoal impregnated with potassium hydroxide gave the highest surface area of 708.1 ± 0.1 m² g^-1, which was determined by using the methylene blue adsorption method. The activated charcoal was characterized by using scanning electron microscopy and Fourier transform infrared spectroscopy. In order to ensure that the activated charcoal produced is bio-safe, all samples were tested for possible toxic substances, including toxic heavy metals by using ICP-OES, and toxic organics such as acrylamide by using chromatography methods. In addition, all samples showed no ecotoxicity towards Escherichia coli and no cytotoxicity toward human HaCaT skin cells. The phosphoric acid activated charcoal demonstrated a high Q _max of 95.2 and 38.2 mg g^-1, respectively for lead and copper adsorption. For potassium hydroxide activated charcoal, the values of Q_max were found to be 45.4 and 21.2 mg g^-1, respectively for lead and copper adsorption.