Ionothermal synthesis of aluminophosphates used for ion exchange: Influence of choline chloride/urea ratio

Abstract

A wide variety of industrial processes produce aqueous effluents that contain heavy metals. Considering the toxicity of metal polluted wastewaters, ion exchange appears as an easy and inexpensive option to remove metal ions from these effluents. There is currently much investigation on synthetic and natural materials to be used as cation exchangers. Among these materials, using microporous molecular sieves have been proposed due to their high surface area, porous diameter and ion exchange capacity. In this work, aluminophosphates (AlPOs) were prepared by the ionothermal method using the eutectic mixture urea/choline chloride (CCh) as solvent and template. Different CCh ratios in the eutectic mixture used in gel synthesis resulted in different structures with very distinguished ion exchange capacities. The main structures obtained were SIZ-2 and AlPO-CJ2. Varying the percentage of CCh in the gel synthesis mixture, it was observed that the AlPO-CJ2 structure is obtained using CCh percentages greater than 50%, while SIZ-2 is obtained using 25% and 33.3% CCh. The structure-directing the interrupted structure are the ammonium cations coming from the partial decomposition of urea. The SIZ-2 prepared using 25% CCh has a somewhat higher ion exchange capacity than that observed using 33.3% CCh. This result is very interesting since CCh is the most expensive component in the eutectic mixture.