Sorption Enhancement of Aromatic Sulfonates onto an Aminated Hyper-Cross-Linked Polymer BINGCAI PAN,* QUANXING ZHANG, FANWEI MENG, XIAOTIAO LI, XIAO ZHANG, JIANZHONG ZHENG, WEIMING ZHANG, BINGJUN PAN, AND JINLONG CHEN School of the Environment, and State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing 210093, People’s Republic of China A macroreticular resin adsorbent CHA-101 was aminated by dimethylamine, and a novel sorbent named M-101 was obtained. Several industrially important aromatic sulfonates including sodium benzenesulfonate (BS), sodium p-tol- uenesulfonate (TS), and sodium 2-naphthalenesulfonate (NS) were selected as general solutes to evaluate the performance of the newly synthesized resin particles. X-ray photoelectron spectroscope (XPS) analyses was used to determine the protonation degree of amino group at different solution pH, and the effect of pH on the sorption of these solutes onto M-101 can be explained by the ion exchange mechanism. The experimentally observed sequence of the sorption capacity of the tested organic sulfonates onto M-101 indicates that the π-π interaction between the solute molecule and the polymer matrix plays an important role in uptake of organic sulfonates from aqueous solution. Sodium sulfate was selected as a typical competitive inorganic anion, and improved selectivity of BS sorption over sulfate on M-101 was observed by comparison with a common macroporous weak base anion exchanger D-301. In addition, both sorption and desorption kinetics of M-101 were also found to be faster than that of D-301. Analyses of sorption isotherms and thermodynamics proved that BS sorption on M-101 was an exothermic and more selective process than on D-301. Both column tests and field applications proved M-101 to be an effective sorbent that can be used to remove aromatic sulfonates from aqueous solution. Introduction HIOCs are hydrophobic ionizable organic compounds (1). One type of HIOC, the organic sulfonates that are widely used as industrial intermediates, is of particular interest due to its good solubility in water and negative environmental impacts once discharged into the receiving water system with industrial waste streams. Usually, these hydrophilic organic pollutants cannot be effectively removed by activated carbon and conventional synthetic polymeric adsorbents except for polymeric anion exchangers, which are able to remove effectively aromatic anions such as pentachlo- rophenate and benzenesulfonate from aqueous solution (2- 10). Though many inorganic anions coexist with aromatic anions in industrial waste streams at concentrations several orders of magnitude greater than target organic solutes (7), previous studies have shown very favorable sorption be- haviors of aromatic sulfonates and other organic anions in preference to many inorganic anions on strong or weak base anion exchanger (2-8). In general, such high sorption selectivities have been mainly attributed to the hydrophobic interactions resulting from the nonpolar moiety (NPM) of the aromatic anions, namely, the NPM-solvent and NPM- matrix interaction (3, 8). In many cases, strongly basic anion exchangers show a much higher selectivity for aromatic sulfonates sorption than weakly ones mainly due to their stronger electrostatic or Columbic interactions between the aromatic anion and the fixed positive charge on strong base anion exchangers. However, because of high sorption affinity of aromatic sulfonates on strong base anion exchangers, regeneration of the spent exchanger becomes a particularly challenging and costly task. A satisfactory regeneration process for these exchangers requires large volumes of concentrated brine or alkaline solution or even organic solvent (3). On the contrary, regeneration of a weak anion exchanger was much easier. For instance, in many cases, sodium hydroxide solution can achieve a complete regeneration process (7). The main problem with weak anion exchangers is their relatively low selectivity in removal of aromatic anions, such as sulfonates, in the existence of inorganic anions in aqueous solution (7). The objective of the current study is to synthesize a novel sorbent with higher capacity and selectivity and fast sorption and desorption kinetics for aromatic sulfonates. This was achieved by chemical modification of a commercial mac- roreticular adsorbent CHA-101 through amination with dimethylamine. Batch sorption experiments were conducted, and thermodynamic analyses were used to elucidate the sorption mechanism on the synthesized sorbent M-101. Sulfate ion was selected as a typical competitive anion in aqueous solution to evaluate the selectivity of M-101 for aromatic sulfonates in the existence of other inorganic anions. NaOH solution was used throughout the experiments to evaluate the regeneration efficiency of the spent sorbents. Materials and Methods Materials. Sodium benzenesulfonate (BS), sodium p-tolu- enesulfonate (TS), sodium 2-naphthalenesulfonate (NS), and sodium methylsulfonate (MS) were used in this study. All chemicals are of analytical grade and were purchased from Shanghai reagent station. CHA-101, a macroreticular poly- meric adsorbent, and D-301, a macroporous weakly basic anion exchanger, were provided kindly by Langfang Electrical Resin Co. Ltd. (Hebei Province, China). Both resins were obtained in spherical bead forms with sizes ranging from 0.4 to 1.0 mm. Physiochemical properties of the solutes and sorbents used in this study are presented in Tables 1 and 2. Resin Synthesis. Adsorbent CHA-101 is a macroreticular polystyrene resin adsorbent with some residual chlormethyl groups on its polymeric matrix during the synthetic process, and the chloro atom can have its place taken by other functional groups such as an amino group. To aminate CHA- 101 (10, 11), the resin particles were first soaked in benzene solution at 298 K for 12 h. The swollen resin particles were then filtered out of the suspension. Dimethylamine was then gradually introduced to a container containing the resin particles. After 12 h of amination at 318 K, extra dimeth- ylamine was removed by filtering the reaction mixture. To remove residual benzene left in the resin pore space, the * Corresponding author phone: +011 86 25 3326433; fax: +011 86 25 3707304; e-mail: bcpan@vip.sina.com. Environ. Sci. Technol. 2005, 39, 3308-3313 3308 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 9, 2005 10.1021/es048548j CCC: $30.25  2005 American Chemical Society Published on Web 03/10/2005