Highly Selective Adsorption of Antimonite by Novel Imprinted Polymer with Microdomain Confinement Effect

The design and synthesis of metalloid imprinted materials is a challenge due to lack of a feasible functional monomer. A novel cyclic functional monomer (CFM) was used to develop Sb­(III)-ion imprinted polymer (CFM-IIP) for efficient and selective removal Sb­(III). CFM possesses positively charged imidazolium moiety and specific cyclic size matching with Sb­(III). CFM-IIP has a maximum Sb­(III) adsorption capacity of 79.1 mg·g–1, while that of a noncyclic functional monomer imprinted polymer (NCFM-IIP) is only 30.9 mg Sb­(III)·g–1. The relative selectivity coefficients of CFM-IIP compared to NCFM-IIP for Sb­(III)/Cl–, Sb­(III)/NO3 –, Sb­(III)/PO4 3–, Sb­(III)/SO4 2–, and Sb­(III)/Cr2O7 2– were 6.6, 78.4, 5.9, 3.0, and 3.2, respectively. Kinetic data fitted well with pseudo-second-order model. The adsorption between Sb­(III) and CFM-IIP was identified to be feasible, spontaneous, and endothermic. ζ-Potential, X-ray photoelectron spectroscopic analysis, and density functional theory calculations revealed the mechanism of Sb­(III) adsorption on CFM-IIP is as follows: the microdomain confinement effect, derived from the nanoscale imprinted cavities of CFM-IIP, facilitates the hydrolysis of Sb­(OH)3 to SbO4 5–, which is subsequently sequestered within the imprinted cavities of CFM-IIP due to the strong electrostatic attraction and size matching of CFM-IIP to SbO4 5–. Therefore, CFM-IIP is very promising adsorbent for the efficient and selective removal of Sb­(III) from aqueous solutions.