Application Of Nanometer-sized Materials 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.However, due to the fine grain size of nanometer TiO2, when the suspension nanometer TiO2 is used for adsorption of metal ions, it is easy to coacervate and loss of activity, and difficult to recovered. These problems can be avoided by immobilizing nanometer TiO2 in different substrates. Nanometer TiO2 supported on silica gel has been applied widely in photocatalytic degradation, however, rarely in separation/preconcentration as adsorbents. Similarly, though mutiwalled carbonnanotubes(MWNTs) has been applied in many fields, it rarely is regarded as solid phase adsorbent to separate and preconcentrate the metal ions.The aim of this dissertation is to systematically study the adsorption characteristics of some metal ions on nanometer TiO2 supported on silica gel and multiwalled carbon nanotubes, 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 ICP-AES for simultaneous determination of trace elements in real samples was proposed.(2) The adsorption behaviors of nanometer TiO2 supported on silica gel towards the speciation of chromium were investigated by ICP-AES and a new method was proposed for the determination of Cr(III) and Cr(VI) using supported nanometer TiO2 as solid-phase extractant. The proposed method was applied to the determination of Cr(III) and Cr(VI) in natural water samples with good results.(3) The adsorption characteristics of heavy metal ions on multiwalled carbon nanotubes under dynamic conditions was studied, and the conditions for preconcentration of trace elements were optimized. A new method of multiwalled carbon nanotubes separation/preconcentration coupled with ICP-AES for simultaneous determination of heavy metal ions in real samples was proposed.