Emulsion-templated macroporous ammonium based polymers: Synthesis and dye adsorption study

Abstract

Emulsion templating was used to prepare new hydrophilic macroporous polymers via o/w high internal phase emulsion (known as polyHIPEs) to be studied as adsorbents for anionic dye removal. A water soluble monomer, 2-(Methacryloyloxy)ethyl]trimethylammonium chloride (METAC) and a cross-linker comonomer (N,N’-methylenebisacrylamide) were polymerized in the continuous aqueous phase yielding in ammonium based monoliths with 10 and 15 % cross-linking density by varying the cross linker content. The prepared monoliths were characterized in terms of their structure, morphology and their ability to adsorb water. Macroporous structures with high ion exchange capacities were obtained. PolyHIPE-METAC-90 with the lower cross-linker percentage (10 %) reached very fast, within 30 min, a higher water uptake (corresponding to 18 times its weight) compared to the sample with the higher cross-linking degree (15 %). Moreover, a detailed study regarding PolyHIPE-METAC-90 adsorption behavior towards two anionic dyes, OII and RB-19 has been performed. The Pseudo-second order model for OII and the Elovich and the Langmuir models for both dyes agreed very well with the experimental data suggesting that chemisorption is the dominant adsorption mechanism. However, the Weber–Morris model indicated that three regimes are involved in the diffusion of anionic dyes, including film diffusion and intra-particle diffusion which is mainly the rate-controlling step. Thus, the synergistic effect of chemisorption and diffusion for the dye adsorption on polyHIPE structures was confirmed. The maximum adsorption capacity of RB-19 (1675.22 mg g−1) is the highest among other adsorbents reported in the literature, while the corresponding one for OII (1632.03 mg g−1) is also one of the highest, suggesting that these materials due to their superior performance, simple synthesis and easy regeneration can be used as highly efficient adsorbents for dyes.