Magnetic activated carbon from spent coffee grounds: iron-catalyzed CO2 activation mechanism and adsorption of antibiotic lomefloxacin from aqueous medium

The facile fabrication of low-cost adsorbents possessing high removal efficiency and convenient separation property is an urgent need for water treatment. Herein, magnetic activated carbon was synthesized from spent coffee grounds (SCG) by Fe-catalyzed CO 2 activation at 800 °C for 90 min, and magnetization and pore formation were simultaneously achieved during heat treatment. The sample was characterized by N 2 adsorption–desorption, XRD, VSM, SEM, and FTIR. Batch adsorption experiments were conducted using lomefloxacin (LMO) as the probing pollutant. Preparation mechanism was revealed by TG-FTIR and XRD. Experimental results showed that Fe 3 O 4 derived from Fe species can be reduced to Fe by carbon at high temperatures, followed by subsequent reoxidation to Fe 3 O 4 by CO 2 , and the redox cycle between Fe and Fe 3 O 4 favored the formation of pores. The promotion effects of Fe species on CO 2 activation can be quantitatively reflected by the yield of CO as the signature gaseous product, and the suitable activation temperate range was determined to be 675 to 985 °C. The BET surface area, total pore volume, and saturated magnetization value of the product were 586 m 2 g −1 , 0.327 cm 3 g −1 , and 11.59 emu g −1 , respectively. The Langmuir model was applicable for the adsorption isotherm data for LMO with the maximum adsorption capacity of 95 mg g −1 , and thermodynamic analysis revealed that the adsorption process was endothermic and spontaneous. This study demonstrated that Fe-catalyzed CO 2 activation was an effective method of converting SCG into magnetic separable adsorbent for LMO removal from aqueous medium.