Microwave-Assisted Preparation of Coffee-Based Activated Carbons: Characteristics, Properties, and Potential Application as Adsorbents for Water Purification

Activated carbons were synthesized from coffee grounds using phosphoric acid as a chemical activator and microwave-assisted carbonization as a rapid and energy-efficient method. Then the prepared carbons were surface-treated with cold plasma to improve their chemical properties and adsorption efficiency. The structural properties and chemical structure of the carbons were determined using nitrogen adsorption-desorption analysis, X-ray photoelectron spectroscopy, as well as X-ray microanalysis by means of scanning electron microscopy. The effect of cold plasma treatment on surface functionality and porosity was investigated. The resulting activated carbons were tested for their potential use as sorbents for the removal of ciprofloxacin, a commonly used antibiotic, from aqueous solutions. The effects of solution pH, sorption kinetics, and initial concentration were investigated. Adsorption kinetics followed a pseudo-second-order model, and the equilibrium data were well described by both the Langmuir and Freundlich isotherms, indicating a combination of monolayer adsorption on homogeneous sites and multilayer adsorption on heterogeneous surfaces. Plasma-treated carbon demonstrated significantly increased adsorption capacity (42.6-120.6 mg g^-1) compared to the unactivated samples (20.2-92.4 mg g^-1). Desorption experiments revealed that the plasma-treated carbon retained over 90% efficiency after seven cycles, confirming its excellent reusability and regeneration potential for practical water treatment applications.