A dual-strategy for the valorization and regeneration of spent activated carbon

To accomplish the objective of reusing spent activated carbon (AC), this study achieved the in-situ regeneration of spent AC through a chemical oxidation process that produced carbon quantum dots (CQDs). The primary focus was to investigate the physical and chemical structural transformations occurring during the conversion of AC into CQDs, elucidating the in-situ regeneration mechanism of the spent AC. The ultimate aim was to develop a durable, efficient, and cost-effective activated carbon adsorbent. The findings indicate that the in-situ regenerated AC recovered 68 % of its original adsorption capacity during CQDs (with a quantum yield of 8 %) preparation process. Notably, the regenerated AC displayed a distinctive hierarchical petal-like structure and an increase in surface oxygenated functional groups, which shifted its adsorption mechanism from predominantly physical to chemical adsorption. Furthermore, the incorporation of the TiO₂ modifier reduced the band gap of the AC/CQDs to 2.13 eV, thus broadening the composite system's response spectrum under visible light and decreasing the recombination of photogenerated electron-hole pairs. Consequently, the in-situ regeneration of spent AC was enhanced and superior to that reported in existing literature.