Magnetic activated carbon from spent coffee grounds: iron-catalyzed CO 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 activation at 800 °C for 90 min, and magnetization and pore formation were simultaneously achieved during heat treatment. The sample was characterized by N 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 FeO derived from Fe species can be reduced to Fe by carbon at high temperatures, followed by subsequent reoxidation to FeO by CO, and the redox cycle between Fe and FeO favored the formation of pores. The promotion effects of Fe species on CO 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 g, 0.327 cm g, and 11.59 emu g, respectively. The Langmuir model was applicable for the adsorption isotherm data for LMO with the maximum adsorption capacity of 95 mg g, and thermodynamic analysis revealed that the adsorption process was endothermic and spontaneous. This study demonstrated that Fe-catalyzed CO activation was an effective method of converting SCG into magnetic separable adsorbent for LMO removal from aqueous medium.