We propose a metal ion-imprinted microsphere as a new metal ion-selective adsorbent. Imprinted microspheres were prepared by seeded emulsion polymerization of divinylbenzene, styrene, butyl acrylate, and methacrylic acid. The imprinted structure was introduced on the carboxylated microsphere by surface-imprinting, in which the carboxyl groups were reorganized through complexation with metal ions on the surface and then fixed by crosslinking polymerization in their specific orientation. The Cu(II), Ni(II), and Co(II)-imprinted microspheres were obtained as submicron particles with average diameters of 0.55—0.60 μm. They were immediately used as a metal ion-selective adsorbent without any further treatment, such as grinding and sieving. The adsorption behaviors of metal ions (Cu(II), Ni(II), and Co(II)) were examined, and the imprinted effects were verified on Cu(II)- and Ni(II)-imprinted microspheres. The imprinted microspheres adsorbed the corresponding guest ion more effectively than did unimprinted ones.

the Editor Keywords Imprinting polymerization, carboxylated microspheres, seeded emulsion polymerization, metal ion, selective adsorption of copper(II) and nickel (II) adsorption ofThe development of new materials for separation and concentration is a key step for progress in analytical science. A molecular imprinting technique) is one promising way to prepare highly-selective host polymers, since it requires neitherr precise molecular design nor multi-step procedures for host preparation. The imprinting technique is thus a practical method, in contrast with "supramolecular design".2,3 However, it has some fundamental problems: for example, the inapplicability to use a water-soluble substance as a guest and the need to grind and sieve the formed polymer before use. These problems result from the fact that the host preparation was made from solution . or bulk polymerization using an organic solvent or organic monomer, respectively. On the other hand, polymer microsphere and its aqueous dispersion have become of interest as highly-functional materials.4 A microsphere of submicron diameter is characterized by a large surface area, comparable with porous glass beads, and show a high reactivity near the surface.We now propose a new technique in which molecular imprinting is conducted on the microsphere surface; the imprinted microsphere is synthesized by seeded emulsion polymerization in water. Complexation between guest molecule and functional groups on the microsphere surface takes place through the reorganization of the groups while adapting to the imprinted structure. The new technique is, in principle, applicable to water-soluble substances, such as biological components; the polymer beads are well defined and uniform. Grinding and sieving are not necessary. In addition, this technique would improve the complexation behavior (such as capacity, reaction rate, and selectivity) owing to the unique features of sub-micron spheres.In this study, a heavy metal ion was adopted as a guest and a metal ion-imprinted structure was constructed on the carboxylated microsphere surfaces with the aid of the interaction between the metal ion and the carboxyl groups.The adsorption of metal ions onto the microsphere was examined and the imprinting effect was characterized. ExperimentalThe metal ion-imprinted microsphere was prepared according to Scheme 1. Seed emulsion (2) was obtained by the polymerization of styrene (S) (20.55 g), butyl acrylate (BA) (2.71 g), and methacrylic acid (MAA) (1.64 g), in water (75 g) at pH 2.2 (125 mg of K2S208 as initiator, 70° C, 7 h). The polymerization mixture was then brought to room temperature. Divinylbenzene (DVB) (29.86 g), BA (2.9 g), and water (95 g) were added and the emulsion was left at 2° C for 24 h at pH 9.5. The pH of the mixture was then lowered to 5.0, and a portion (8 cm3) of the emulsion was combined with 40 ml of a metal ion solution (0.01 mol dm-3 Cu(II) or Ni(II)) to achieve complexation between the metal ion and the carboxyl group on the surface (4). The DVB-containing emul...

In accordance with the concept of Surface Imprinting, as proposed by the present authors, a Cu(II)-imprinted microsphere was studied in detail in order to obtain information about the origin of the imprinting effect. Unimprinted and Cu(II)-imprinted microspheres were prepared under several pH (4.0, 5.0, 5.6, or 6.0) conditions in second-step polymerization. The obtained microspheres were characterized regarding particle form, size-distribution pattern, average diameter, Cu(II) adsorption behavior, and so on. During preparation at pH 4.0—5.6 in the second-step polymerization, imprinted microspheres adsorbed Cu(II) more effectively than did unimprinted microspheres in this pH range, indicating a clear metal-imprinting effect. On the other hand, the imprinting effect was not observed during preparation at pH 6.0, because of the formation of copper(II) hydroxide precipitates. The maximum imprinting effect was provided by microspheres obtained at pH 5.6. Spectroscopic studies were made on Cu(II)-loaded microspheres. The FT-IR spectra suggested that carboxyl groups on the microsphere surface participated in the Cu(II) binding in their ionized carboxylate forms. An FE-SEM (ångstrom SEM) observation of the microsphere indicated a smooth surface structure at the 10 nm level. The collected data indicate that the origin of the imprinting effect on a Cu(II)-imprinted microsphere is the interaction between Cu(II) and the carboxylate group at the aqueous-organic interface, supporting the concept of Surface Imprinting.

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