High Adsorption of Sulfamethoxazole by an Amine-Modified Polystyrene-Divinylbenzene Resin and Its Mechanistic Insight

摘要

Sulfamethoxazole (SMZ) adsorption by a series of amine-modified polystyrene-divinylbenzene resins (PSA/B/ C/D) was investigated. All resins showed a similar pH dependent adsorption of SMZ but their capacities were linearly related with the contents of primary amines (-NH_2) rather than secondary amines (-NH-). Mechanisms of SMZ adsorption by PSA (highest -NH_2 content) were discussed as an example. Due to comparable pK_1, H-bonding interactions of -NH_2~0 with SMZ~0 (regular H-bond) and SMZ~- (negative charge-assisted H-bond, (-)CAHB) successively contributed most adsorption (pH 4-9). At weakly acidic pH, -NH_2~0 was partially protonated and electrostatic attraction between -NH_3~+ and SMZ~- occurred concurrently, but could be hindered by increased loading of SMZ~0. Hydrophobic/ π-π interactions were not major mechanisms as phenanthrene and nitrobenzenes had little effect on SMZ adsorption. At alkaline pH, where SMZ~- and -NH_2~0 prevailed, adsorption was accompanied by the stoichiometric (～1.0) proton exchange with water, leading to OH~- release and the formation of (-)CAHB [SO_2N~-…H…NH_2]. The interaction and SMZ spatial distribution in the resin-phase were further confirmed by FTIR and Raman spectra. SMZ was uniformly adsorbed on external and interior surfaces. SMZ adsorption by PSA had low-interference from other coexistent matter, but high stability after multiple regenerations. The findings will guide new adsorbent designs for selectively removing target organics.