Application Of Immobilized Nanometer Titanium Dioxide In The Separation/Preconcentration And Speciation Of Trace Elements

Sensitive, rapid, reproducible, simple and accurate analytical methods are required for the determination of trace elements in geological, biological and environmental samples. The direct determination of extremely low concentrations of trace elements by modern atomic spectroscopic methods, such as atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) is often difficult. The limitations are associated not only with the insufficient sensitivity of these techniques but also with matrix interference. For this reason, the separation and preconcentration of trace elements is often required.Solid phase extraction(SPE) technique has become increasingly popular in trace elements separation/preconcentration with modern atomic spectroscopic methods. And the choice of solid-phase adsorbents is decisive factor that affects analytical sensitivity and selectivity. So, it has still been a heated research field to find new and effective adsorbents nowadays.Nanometer material is a new solid material that gained importance due to its special properties. The regime of nanoparticle is from 1 nm to almost 100 nm, falls between the classic fields of chemistry and solid-state physics. One of its properties is that most of the atoms of the nanoparticle are on the surface. The surface atoms are unsaturated and can therefore bind with other atoms, possess highly chemical activity. Consequently, nanometer material can adsorb selectively metal ions, and has a very high adsorption capacity.Nanometer TiO₂ supported on silica gel has been applied widely in photocatalytic degradation due to its many virtues, such as stabilization and uncoacervation, however, rarely in separation/preconcentration as adsorbents.The aim of this dissertation is to systematically study the adsorption characteristics of some metal ions on nanometer TiO₂ supported on silica gel and apply it to the separation/preconcentration and speciation analysis of trace elements. The major contents are described as follows:(1) Nanometer TiO₂ supported on silica gel was prepared and characterized with XRD and SEM. And the adsorption characteristics of heavy metal ions on nanometer TiO₂ supported on silica gel under static and dynamic conditions was studied, and the conditions for preconcentration of trace elements were optimized. A new method of nanometer TiO₂ supported on silica gel separation/preconcentration coupled with GFAAS and FAAS for determination of trace elements in standard refrence material was proposed.(2) The adsorption behaviors of nanometer TiO₂ supported on silica gel towards the speciation of arsenic were investigated by GFAAS and a new method was proposed for the determination of As(III) and As(V) using modified nanometer TiO₂ as solid-phase extractant. The proposed method was applied to the determination of As(III) and As(V) in natural water samples with good results.