Innovative Green Strategy for the Regeneration of Spent Activated Carbon via Ionic Liquid-Based Systems

The widespread use of activated carbon (AC) as an adsorbent in diverse applications generates substantial amounts of AC waste, posing environmental and disposal challenges. Therefore, effective AC regeneration is essential to enhance the sustainability of adsorption-based technologies. However, conventional regeneration methods often involve harsh chemicals or energy-intensive processes, limiting environmental and economic feasibility. In this study, the regeneration of commercial AC saturated with synthetic dyes Acid Blue 9 (AB9) and Acid Yellow 23 (AY23) is investigated using aqueous solutions of ionic liquids (ILs) as a green alternative. A set of ILs with varying cation–anion structures was synthesized and screened for regeneration performance, where [TBP][Sal] was identified as the most effective. Process parameters such as IL concentration, temperature, time, and solid-to-liquid ratio were optimized using response surface methodology, achieving regeneration efficiencies of up to 99% for AB9-AC and 80% for AY23. These efficiencies persisted over three cycles, while adsorption capacity remained unchanged for AY23 and decreased by ~40% for AB9. To improve sustainability, a preliminary study was conducted by implementing an aqueous biphasic system for IL and dye concentration from the post-regeneration solution. This integrated strategy presents a promising step toward the development of near-zero waste adsorption–regeneration cycles for AC adsorption applications.