Fabrication of porous carbon sheet via organic acid salt activation for effective thallium(I) removal: Multiscale adsorption and DFT calculation

The novel ultra-micro porous carbon sheet (PCs) with exceptionally high surface area (3034 m 2 /g) were synthesized through green potassium citrate (K 3 C 6 H 5 O 7 ) activation for efficient thallium(I) [Tl(I)] removal from wastewater. The static adsorption results revealed that PCs achieved exceptional removal efficiencies above 95 % across pH 6–12, maintained high selectivity against competing ions (K + , Na + , Cl − , F − ) and organic interferents, and retained above 80 % capacity after five regeneration cycles. Adsorption followed Pseudo-second order kinetics and Freundlich isotherm models, indicating multilayer adsorption on heterogeneous surfaces, with thermodynamics confirming spontaneous exothermic processes. The density functional theory (DFT) calculation results demonstrated that lone pair electrons involved in complexation and π-electrons participating in coordination were supplied by oxygen-containing functional groups and aromatic rings, respectively. The sorption mechanisms included surface complexation, ion exchange, electrostatic attraction, and cation-π interaction. The column sorption results demonstrated the influent flow rate, bed height, and initial Tl(I) concentration-dependent removal performance. The Tl(I)-containing wastewater at ppm level could meet the discharge standard by optimizing influent flow rate and bed height in column adsorption. The dynamic sorption process was described properly by Thomas and Yoon-Nelson models. This study provides a systematic theoretical foundation for designing porous carbons in Tl-contaminated water remediation.