Poly (ionic liquid) anchored granular activated carbon for efficient and selective removal of perchlorate: performance, DFT calculations and mechanism

The study developed a novel adsorbent for improving perchlorate removal efficiency by anchoring Poly (ionic liquid) (PIL) onto granular activated carbons (GACs) via radical polymerization. The authors characterized the physical–chemical properties of GAC modified by PIL (PIL-GAC), and investigated its performance and mechanism for perchlorate adsorption. The results show that the introduction of dicationic ionic liquids dramatically increases the positively charged nitrogen (12.59 %) and point of zero charge (pH pzc  = 9.79) of GAC, resulting in a higher attraction for perchlorate. Density Functional Theory (DFT) calculations reveal a better adsorption energy (−162.58 kJ/mol) of perchlorate on imidazole N, highlighting its potential selectivity over other N and O functional groups. PIL-GAC exhibits a maximum adsorption capacity (Q m ) of 300.05 mg/g at 25 °C, which is 12 times higher than that of pristine GAC and better than previously reported adsorbents. Additionally, this Q m is pH independent within pH 4 to 10. The perchlorate adsorption on PIL-GAC fits the Langmuir (R 2  ≥ 0.98) and pseudo second order kinetic (R 2  > 0.99) models, indicating a spontaneous process primarily driven by chemisorption. Remarkably, PIL-GAC also exhibits sustainable regeneration and greater selectivity for perchlorate with a lower hydration energy (−214 kJ/mol), over nitrate, chloride, and sulfate with higher hydration energy (−306, −347, and −1090 kJ/mol). After adsorption, PIL-GAC demonstrates a decrease of N + and an increase in Cl - , indicating that perchlorate adsorption of PIL-GAC mainly involves electrostatic interaction and ion exchange. Therefore, this study offers a promising method for efficient and selective removal of perchlorate from water.