Adsorption Properties Of Functional Silicas Towards Some Toxic Metal Ions In Water Solutions


Institute of Surface Chemistry of National Academy of Sciences of Ukraine, Gen. Naumov Street 17, 03164 Kyiv, Ukraine


Chemistry Department of Kyiv National Taras Shevchenko University, Ukraine


Franko State University, Zhitomir, Ukraine

Abstract. Processes of preconcentration of heavy toxic metal ions, such as Pb(II), Cd(II), Zn(II), Hg(II), and Mo(VI) on the silica with covalently bound complexing phenolic-type analytical reagents 8-hydroxyquinoline, 1-(2-pyridylazo)-2-naphthol, 4-(2-pyridylazo)resorcinol have been studied. Structures of the surface complexes of toxic metals with grafted analytical reagents were determined using IR, ESR and electronic diffuse reflectance spectroscopies. Possibility of simultaneous determination of micro amounts of heavy metals was demonstrated using the x-ray fluorescence analysis of modified adsorbents after absorption of metal ions from their multicom-ponent mixtures in natural and artificial water solutions. Silica gel with adsorbed polyionene (1,4-MePh) was shown to have high adsorption properties towards some metal-containing anions, in particular MoO42_, WO42_ and Cr2O72" in water solutions. Adsorption isotherms of these metal-containing anions on initial silica gel and silica-supported polyionene were investigated.

Keywords: modified silica; immobilized 8-hydroxyquinoline; 1-(2-pyridylazo)-2-naphthol; 4-(2-pyridylazo)resorcinol; polyionene; preconcentration; heavy metal ions; x-ray fluorescence analysis

Low concentrations of toxic metals in natural and waste waters can be efficiently determined after their extraction and concentrating using modified silica adsorbents functionalized with complexing ligands. As such complexing ligands it is possible to apply 8-hydroxyquinoline and some heterocyclic azo compounds 1-(2-pyridylazo)-2-naphthol (PAN), 4-(2-pyridylazo)resorcinol (PAR) forming stable complexes with heavy metal ions in solutions.1' 2

Silica carriers with supported oxine or physically adsorbed azo reagents are usually used for metal ions preconcentration.3-5 These adsorbents are characterized by a different level of washing out of the adsorbed complexing reagents under different conditions of application. On the contrary, adsorbents with covalently bound ligands, having hydrolytically stable chemical bonds with the carrier surface sites, are more stable to washing out and they have more reproducible properties. Method of the multi-step surface assembly reaction involving grafting of benzene rings, their nitration with following reduction, diazotization and azo coupling had been usually applied for synthesis of adsorbents with covalently bound oxine, PAR and PAN.6'7 Such synthetic pathway results in non-uniform chemical composition of the modifying surface layer and low content of the grafted complexing groups. Recently the single-stage aminomethylation reaction with simultaneous use of amino-containing alkoxysilane and paraformaldehyde was successfully realized for covalent anchorage of the phenolic-type analytical reagents on the silica surface.8

Chemical attachment of phenolic-type analytical reagents (8-hydroxy-quinoline, PAN, PAR) was carried out in accordance with the following scheme:



Introducing polymers with the quaternary nitrogen atom into the surface layer of silica carrierss permits one to obtain inorganic adsorbents with pronounced anion-exchange properties. In this respect the application of water-soluble polyionens with the quaternary nitrogen atoms in the main chain is of obvious interest.

0 0

Post a comment