Chen Ling: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing 210023, P. R. China.
Xiaoyun Li: Stockbridge School of Agriculture, University of Massachusetts , Amherst, Massachusetts 01003, United States.
Zhiyun Zhang: Department of Food Science, University of Massachusetts , Amherst, Massachusetts 01003, United States.
Fuqiang Liu: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing 210023, P. R. China.
Yingqing Deng: Stockbridge School of Agriculture, University of Massachusetts , Amherst, Massachusetts 01003, United States.
Xiaopeng Zhang: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing 210023, P. R. China.
Aimin Li: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing 210023, P. R. China.
Lili He: Department of Food Science, University of Massachusetts , Amherst, Massachusetts 01003, United States.
Baoshan Xing: Stockbridge School of Agriculture, University of Massachusetts , Amherst, Massachusetts 01003, United States.
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 (-NH2) rather than secondary amines (-NH-). Mechanisms of SMZ adsorption by PSA (highest -NH2 content) were discussed as an example. Due to comparable pKa, H-bonding interactions of -NH2(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, -NH2(0) was partially protonated and electrostatic attraction between -NH3(+) 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 -NH2(0) prevailed, adsorption was accompanied by the stoichiometric (∼1.0) proton exchange with water, leading to OH(-) release and the formation of (-)CAHB [SO2N(-)···H···NH2]. 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.
