Search

Amino-modified metal oxide materials are essential ina wide rangeof applications, including chromatography, ion adsorption, and asbiomaterials. The aim of this study is to compare different functionalizationtechniques on a selection of metal oxides (SiO2, TiO2, ZrO2, and SnO2) in order to determinewhich combination has the optimal properties for a certain application.We have used the nanocasting approach to synthesize micrometer-sizedTiO2, ZrO2, and SnO2particles, whichhave similar morphologies and porosities as the starting mesoporousSiO2microparticles (Lichroprep Si 60). These metal oxideswere subsequently functionalized by four different approaches, (a)covalent bonding of 3-aminopropyltriethoxysilane (APTES), (b) adsorptionof 2-aminoethyl dihydrogen phosphate (AEDP), (c) surface polymerizationof aziridine (AZ), and (d) electrostatic interaction of poly(ethylenimine)(PEI), to produce a high surface coverage of amino groups on theirsurfaces. Scanning electron microscopy, nitrogen physisorption, andX-ray diffraction were used to characterize the unmodified metal oxideparticles, while thermogravimetric analysis, ninhydrin adsorption,and ζ potential titrations were applied to gain insight intothe successfulness of the various surface modifications. Finally,the hydrolytic stability at pH 2 and 10 was investigated by ζpotential measurements. Unfortunately, the AEDP approach was not ableto produce efficient amino-modification on any of the tested metaloxide surfaces. On the other hand, modifications with APTES, aziridine,and PEI appeared to give fairly stable amino-functionalizations athigh pH values for all metal oxides, while these modifications wereeasily detached at pH 2, with the exception of SnO2, wherethe AZ and PEI samples were stable up to 40 h. The results are expectedto give valuable insights into the possibility of replacing amino-modifiedsilica with more hydrolytically stable metal oxides in various applicationfields, for example, chromatography and drug delivery. [ABSTRACT FROM AUTHOR]

Abstract: The need for novel packing materials in both capillary electrochromatography (CEC) and capillary liquid chromatography (CLC) is apparent and the development towards more selective, application-oriented chromatographic phases is under progress world-wide. In this study we have synthesized new polyethyleneimine (PEI) functionalized Mn2O3, SiO2, SnO2, and ZrO2 particles for the fabrication of packed capillary columns for CEC and CLC. The nanocasting approach was successful for the preparation of functionalized metal oxide materials with a controlled porosity and morphology. PEI functionalization was done using ethyleneimine monomers to create particles which are positively charged in aqueous solution below pH 9. This functionalization allowed the possibility to have both hydrophobic (due to its alkyl chain) and ionic interactions (due to positively charged amino groups) with selected compounds. For comparison aminopropyl-functionalized silica was also synthesized and tested. Both slurry pressure and electrokinetic packing procedures used gave similar results, but fast sedimentation of the material caused some problems during the packing. The high stability and wide pH range of PEI-functionalized SiO2 material, with potential for hydrophobic and electrostatic interactions, proved to be useful for the CEC and CLC separation of some model acidic and neutral compounds. [Copyright &y& Elsevier]