Hypercrosslinked microporous polymer networks for effective removal of toxic metal ions from water Buyi Li a , Fabing Su b , He-Kuan Luo c , Liyun Liang a,⇑ , Bien Tan a,⇑⇑ a School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China b State Key Laboratory of Multi-phase Complex System, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China c Institute of Chemical and Engineering Sciences, A * STAR (Agency for Science, Technology and Research), 1 Pesek Road, Jurong Island, Singapore 627833, Singapore article info Article history: Received 22 June 2010 Received in revised form 28 August 2010 Accepted 31 August 2010 Available online 7 September 2010 Keywords: Hypercrosslink Microporous polymer Sulfonation Metal ions Adsorption abstract Sulfonic acid-modified microporous hypercrosslinked polymers (SAM-HCPs) synthesized by sulfonation of microporous hypercrosslinked polymers (HCPs, also known as ‘‘Davankov Resins”) have been investi- gated as a high-capacity adsorbent for toxic metal ions. The materials were characterized using proton magnetic resonance ( 1 H NMR), Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), thermogravimetric analysis (TGA), transmission electron microscope (TEM), X-ray photoelectron spec- troscopy (XPS) and nitrogen adsorption method. The results show that the modified resins retained their original microporous structure and spherical morphology, and possess sulfonic acid groups as hydrophilic groups and active sites. Sulfonic acids-modified hypercrosslinked ‘‘Davankov Resins” (SAM-HCP-DR) have been found to attain very good adsorption capacity for metal ions (e.g., Cu 2+ 51.45 mg g 1 at 303 K, 54.82 mg g 1 at 313 K, and 57.68 mg g 1 at 323 K), which is due to the synergic effect of microporous structure and active sites. The kinetic data obtained from adsorption experiments supports a pseudo-sec- ond order model and adsorption isotherms obtained at different temperatures (303 K, 313 K and 323 K) are all fitted with the Langmuir isotherms. In addition, the thermodynamic parameters, i.e., Gibbs free energy change (DG 0 ), enthalpy change (DH 0 ), entropy change (DS 0 ) of the adsorption process were cal- culated, and the results confirmed the adsorption to be spontaneous and endothermic. Moreover, these modified resins can be recycled several times with minimal loss of adsorption capacity and thus may have potential industrial applications. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Some metals are toxic to human beings and other living organ- isms if their concentrations exceed the tolerance limit [1,2]. Phys- ical and chemical processes such as adsorption, coagulation floatation, chemical precipitation, ultra filtration, and electrochem- ical methods have been extensively studied for removal of these toxic metal pollutants from water [3]. Adsorption has been widely regarded as one of the most efficient and economic methods at the low ion concentrations [3]. In general, porous materials such as clay [4], activated carbon [5], zeolite [6], and biomass [7] are usu- ally used as toxic metal ions adsorbents because of their high sur- face area, large pore volume, and the presence of exchangeable ions. For better adsorption performance, the pore size of a porous adsorbent should match the adsorbate atomic/molecular size [8], and the optimum ratio of the pore diameter to the adsorbate atom- ic/molecular diameter falls in the range from two to six times [9]. The ionic radius (both Van der Waals radii and hydrated radii) of toxic metal ions are usually several angstrom (Cu 2+ 0.73 Å, 2.40 Å; Pb 2+ 1.19 Å, 2.65 Å; Cr 3+ 0.62 Å, 1.96 Å; Cd 2+ 0.95 Å, 2.30 Å; Hg 2+ 1.02 Å, 2.42 Å; Ni 2+ 0.69 Å, 2.06 Å; the first value is Van der Waals radii and the second value is hydrated radii) [10– 12], and theoretically micropores (pore size < 2 nm) are the most suitable for adsorbing such toxic metal ions. Compared to traditional ‘‘hard” microporous adsorbents such as activated carbons and zeolites, ‘‘soft” organic microporous poly- mers possess various advantages. Firstly, their pore structure can be finely tuned by the rigid node-strut topology, in particular by the average strut length [13,14]. Secondly, the surface functional- ities can be introduced by a wide variety of synthetic strategies, for example, moieties that could enhance binding affinities or monomers in molecular level [15]. Thirdly, it is well known that most organic polymers are highly stable to air and water moisture. More importantly, some organic polymers can be synthesized reproducibly from well-defined monomers, although this is often a challenge with activated carbons. They can also be easily woven into desired soft patterns, which is almost impossible for the ‘‘hard” adsorbents [16]. These advantages render microporous 1387-1811/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2010.08.023 ⇑ Corresponding author. Tel.: +86 27 87558172; fax: +86 27 87543632. ⇑⇑ Corresponding author. Tel.: +86 27 87558172; fax: +86 27 87543632. E-mail addresses: lly720@gmail.com (L. Liang), bien.tan@mail.hust.edu.cn (B. Tan). Microporous and Mesoporous Materials 138 (2011) 207–214 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso