Montmorillonite modified with hexadecylpyridinium chloride as highly efficient anion exchanger for perchlorate ion

Details of the anion-exchange properties of Na-montmorillonite modified with hexadecylpyridinium chloride (HDPyCl-montmorillonite) for perchlorate ions are reported herein. The perchlorate uptake on HDPyCl-montmorillonite from 0.01 mmol/dm3 or 0.10 mmol/dm3 solution rapidly attained equilibrium within 4 h. The perchlorate uptake on HDPyCl-montmorillonite followed the Langmuir isotherm model with capacity of 1.02 mmol/g. The perchlorate uptake of 0.70–0.80 mmol/g on HDPyCl-montmorillonite persisted in a wide pH range of 4–10. High selectivity of HDPyCl-montmorillonite for perchlorate ion was reflected in the high distribution coefficient values (>104 cm3/g) with selectivity sequence of HPO42− < SO42− < NO3− < ClO4− from multi-anion solution of 0.10, 1.0, or 2.0 mmol/dm3. This selectivity sequence corresponded to the sequence of increasing hydration energy of anions. These data revealed that the anion uptake on HDPyCl-montmorillonite accompanied with release of chloride ion into solution through anion-exchange processes.

Graphical abstractNa-montmorillonite modified with hexadecylpyridinium chloride showed high selectivity for ClO4− from multi-anion solution: HPO42− < SO42− < NO3− < ClO4−, similar to the Hofmeister series of anions based on free energy of hydration.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The montmorillonite modified with hexadecylpyridinium chloride was investigated. ► The material was highly selective for ClO4− at low concentration (0.10 mmol/dm3). ► The selectivity sequence was HPO42− < SO42− < NO3− < ClO4−. ► The material exhibited high ClO4− uptake (0.70–0.82 mmol/g) at pH 4–10. ► Langmuir isotherm type for ClO4− uptake with capacity of 1.0 mmol/g was reported.