An ion-imprinted polymer based on palygorskite as a sacrificial support for selective removal of strontium(II)
Graphical Abstract
► Attapulgite is a hydrated octahedral layered magnesium aluminum silicate mineral which have siloxane groups in the bulk and silanol groups on its surface. It is available to be a support in surface-imprinting technique because of its particular intensity, special structure, stable chemical property and abundant raw materials. ► Then a new approach was used to synthesize a novel ion-imprinted polymer (IIP) based on surface ion-imprinting technique with attapulgite as a sacrificial-support material and chitosan incorporated sol–gel process. During this process, attapulgite as a support material was coated with a pre-polymerization ion-imprinting mixture. In a following step, the attapulgite was dissolved and removed, resulting in hollow spherical beads (S-IIP) with greater surface area and pore volume. Subsequently, the adsorption behaviors of S-IIP and non-imprinted polymer (NIP) for Sr2+ (containing adsorption parameters, isotherms, kinetics, thermodynamics, and selective recognition) were investigated, the structural characteristics and imprinting mechanism of S-IIP were discussed in detail. ► A model for selective removal of target radioelements could be set up according to the results.
Introduction
In the latest decades, the ion-imprinting technique was recognized as a convenient and powerful method for synthesizing an artificial receptor-like recognition polymer by co-polymerizing suitable monomers in the presence of desired template ions. After removing the template ions, imprinted cavities providing tailor-made binding sites for these ions are left on the ion-imprinted polymer (IIP) (Zhang et al., 2007). However, most of these traditional IIP exhibit high selective recognition but poor site accessibility to the target ions, as the template ions and functional groups are totally embedded inside the polymer network and the mass transfer is low (Janiak et al., 2009).
Surface-imprinting technique first proposed by Takagi's group in 1992 utilized an amphiphilic functional monomer forming a stationary complex with the template at the interface of emulsion droplets (Tsukagoshi et al., 1993). Subsequently, various surface-imprinting systems with faster mass transfer kinetics were established, such as emulsion (suspension) polymerization and surface-imprinting process based on support materials like SiO2 (Kodakari et al., 1997), TiO2 (Wu, et al., 2007), α-Al2O3 (Pérez et al., 2001), CdS (Diltemiz et al., 2008), ZnS (Wang et al., 2009a, Wang et al., 2009b), carbon nanotubes (Suzuki et al., 2002), silica gel (Li et al., 2006), and magnetic Fe3O4 (Wang et al., 2009a, Wang et al., 2009b). Palygorskite can be used as a support in the surface-imprinting technique because of its chemical, mechanical and thermal stability, and low cost.
Recently, the design and synthesis of hollow functional materials with surface-imprinting technique and sacrificial-support concept arose intense interest because of their novel applications in advanced separation technologies. Yilmaz et al. (2002) prepared spherical molecular imprinted polymer (MIP) by using common C4-silica particles as a sacrificial support. He et al. (2008) prepared imprinted silica with testosterone as template molecule. The surface-imprinting technique in combination with the sacrificial-support process is a versatile method to prepare the uniformly sized adsorbents, and to improve the kinetics of the adsorption and desorption by increasing the specific surface area, pore volume and active binding sites of the adsorbents.
Strontium-90 (90Sr) usually accumulates in human liver, lung and kidney along with the increase of the food chain and is difficult to remove from body in metabolism. 90Sr has a long half-life time (28 years) and could substitute calcium in the body, increasing the probability of leukemia and other diseases. The main purpose of this work was to present a new approach to synthesize a novel IIP (S-IIP) based on surface ion-imprinting technique in the presence of palygorskite as a sacrificial support (Fig. 1). Palygorskite was coated with a pre-polymerization ion-imprinting mixture. In a following step, palygorskite was dissolved and removed, resulting in hollow spherical beads (S-IIP). Subsequently, the adsorption behaviors of S-IIP for Sr2+ were studied.
Section snippets
Instruments and apparatus
Infrared spectra (4000–400 cm− 1) were recorded on a Nicolet NEXUS-470FT-IR apparatus (U.S.A.). Transmission electron microscope (TEM) analysis was performed by using JEM-2010HR at 200 kv. The mean diameter of the particles was measured by BIC-90 laser particle size instrument. The specific surface area and pore volume of adsorbents were measured by nitrogen adsorption based on the Brunauer–Emmett–Teller (BET) model using the single point analysis (Flowsorb II 2300, Micromeritics Instrument
Imprinted polymers
FT-IR spectra of raw materials and polymers were described in Fig. 2. A strong and overlapped band around 3450 cm−1, from stretching vibrations of N–H and O–H in CTS (Fig. 2b), was shifted to 3415 cm−1 and narrowed in S-IIP before palygorskite dissolution (Fig. 2e). Compared with CTS, the absorption band of C–OH decreased from 1090 cm−1 to 1070 cm−1 (Fig. 2e), and its shape became sharp. Moreover, the characteristic feature of δsN–H at 1650 cm−1 and νasC–N at 1380 cm−1 showed no obvious change. All
Conclusions
A new type of Sr(II)-imprinted polymer was prepared by a surface-imprinting technique combined with a sacrificial-support process. S-IIP formed hollow microspheres with enhanced specific surface area and pore volume. Adsorption and selective recognition of Sr2+ followed the order S-IIP > NIP. Sr2+ adsorption onto the S-IIP and NIP fitted to the Langmuir model, indicating monolayer adsorption. ΔHo, ΔGo, and ΔSo showed that the adsorption of Sr2+ ions on S-IIP was endothermic and spontaneous. The
Acknowledgments
We are thankful to the financial support by the National Natural Science Foundation of China (No. 20877036), National Natural Science Foundation of China (No.30970309), and the Ph.D. Programs Foundation of Ministry of Education of China (No. 20093227110015).
References (19)
- et al.
Adsorption of metal ions onto Moroccan stevensite: kinetic and isotherm studies
J. Colloid Interface Sci.
(2005) - et al.
Quantum dot nanocrystals having guanosine imprinted nanoshell for DNA recognition
Talanta
(2008) - et al.
Adsorption of Ni(II) on clays
J. Colloid Interface Sci.
(2006) - et al.
Molecularly imprinted silica prepared with immiscible ionic liquid as solvent and porogen for selective recognition of testosterone
Talanta
(2008) - et al.
Molecular sieving property of silica overlayer on tin oxide generated by organic template
Appl. Surf. Sci.
(1997) - et al.
One-pot preparation of silica-supported hybrid immobilized metal affinity adsorbent with macroporous surface based on surface imprinting coating technique combined with polysaccharide incorporated sol-gel process
J. Chromatogr. A
(2006) - et al.
An ion-imprinted silica-supported organic-inorganic hybrid sorbent prepared by a surface imprinting technique combined with a polysaccharide incorporated sol-gel process for selective separation of cadmium(II) from aqueous solution
Talanta
(2007) - et al.
Adsorption of aqueous alkylphenol ethoxylate surfactants by mesoporous carbon CMK-3
J. Colloid Interface Sci.
(2006) - et al.
Design of catalytic sites at oxide surfaces by metal-complex attaching and molecular imprinting techniques
J. Mol. Catal. A: Chem.
(2002)
Cited by (48)
Monitoring the benefits of varying the template/monomer proportion in the synthesis of an ion-imprinted polymer for Ra(II) extraction
2023, Advances in Sample PreparationScreening of synthesis conditions for the development of a radium ion-imprinted polymer using the dummy template imprinting approach
2022, Chemical Engineering JournalPalygorskite nanomaterials: Structure, properties, and functional applications
2019, Nanomaterials from Clay Minerals: A New Approach to Green Functional MaterialsExtractive separation of Profenofos as an organophosphorous insecticide from wastewater and plant samples using molecular imprinted cellulose
2017, Journal of Environmental Chemical EngineeringPreparation of magnetic clinoptilolite/CoFe<inf>2</inf>O<inf>4</inf> composites for removal of Sr<sup>2+</sup> from aqueous solutions: Kinetic, equilibrium, and thermodynamic studies
2017, Journal of Saudi Chemical SocietyCitation Excerpt :Among these methods, the adsorption technology has been most widely used because of its low cost and ease of operation as well as greater efficiency. Several organic and inorganic adsorbents, such as microorganism [30,40], polysaccharide derivates [39], oxidized multiwall carbon nanotubes [8], clay mineral [26,41,33], activated carbon [7] and zeolites [12,36,4] were researched and applied to adsorb Sr2+. Clinoptilolite has received much attention due to (1) widespread occurrence, (2) high selectivity for Sr2+, and effectiveness in removing radioisotopes from wastewater, (3) good compatibility with cement matrix to improve the mechanical characteristics of the solidified cement matrix toward the safety requirements and reduce considerably the radionuclides leach rates [1,5].