Tunable aryl alkyl pyrazolium tetrafluoroborate ionic liquids/salts: synthesis, characterization, and applications for removal of methyl orange from aqueous solution.

ABSTRACT

In this work, new tunable aryl alkyl pyrazolium tetrafluoroborate ionic liquids/salts, 2-ethyl-1-(p-X-phenyl)-3,5-dimethylpyrazolium tetrafluoroborate [X -Br (4a), -OCH3 (4b), -NO2 (4c)] and 2-butyl-1-(p-X-phenyl)-3,5-dimethylpyrazolium tetrafluoroborate [X -Br (5a), -OCH3 (5b), -NO2 (5c)], were synthesized by following halide-free synthetic route. Their chemical structures were identified through NMR (1H, 13C, 19F), IR, elemental analysis, and HRMS data. The synthesized 4a-4c and 5a-5c salts were used for the removal studies of methyl orange dye from aqueous solutions. The effects of specific parameters such as nature of the solvent, pH, contact time, amount and structure of the salts, and concentration of potassium chloride on the removal efficiencies were investigated. Experimental results revealed that methyl orange could be removed from the aqueous solution up to 99.7% under the optimized conditions. The composition of the ion pairs between the cation of the 4b and anion of methyl orange was determined. The reuse of the 4b was achieved up to five cycles, with high extraction efficiencies of over 90 %. Accordingly, a time-efficient, simple, and highly effective method has been presented to remove methyl orange dye from aqueous solutions.