The development of nano-sized silicas as analytical tools

Abstract

Even at low concentrations the presence of toxic materials, such as metals or organic pesticides, in water can be harmful to humans. Extraction and preconcentration of these materials is an important part of many analytical procedures. In this work functionalised solid phase extractants, 250 nm in size (nanoscavenger), have been used to collect and concentrate metals and organic species from water using a nanoscavenger dispersion extraction (NSDE) approach.
Stöber-type silica with a mean diameter of ca. 250 nm and a surface area of ca. 20 m2 g-1 has been synthesized by hydrolysis and condensation of tetraethoxysilane in a methanol and ammonium hydroxide medium. Increasing the surface area to increase the loading of functional groups on the surface was achieved by adopting mesoporous silica as the nanoscavenger core. This was successfully synthesized from tetramethoxysilane in the presence of a dodecyltrimethylammonium bromide template: 250 nm particles prepared in this manner had a surface area of ca. 1325 m2 g-1. The properties of synthesized sub-micron silicas have been investigated using various techniques.
One of the main aims of this work was to use the nanoscavengers for the analytical recovery of trace analytes from water. Nanoscavengers were prepared by chemically modifying mesoporous silicas with groups such as mono- and diamines, dithiocarbamates, hydroxyquinoline, mercaptobenzamide and, for organic extractions, a mixed functionality diol and C18 modification. The nanoscavengers were characterized by Fourier transform infrared spectroscopy, scanning electron microscope, transmission electron microscope and thermogravimetric analysis. Copper capacity measurements for complexant nanoscavengers ranged between 0.1 and 2 mmol g-1 depending on the type of silica and the loading group.
The nanoscavengers were evaluated for the preconcentration of trace analytes from water. The dithiocarbamate, hydroxyquinoline and mercaptobenzamide nano- scavengers were used to preconcentrate eight metal ions (Cu2+, Cd2+, Ni2+, Pb2+, Co2+, Cr3+, Mn2+ and Zn2+) from water. A dual functionality diol/C18-nanoscavenger was used to collect four estrogenic compounds, polynuclear aromatic hydrocarbons and tributyltin from water. The recovery of extracted analytes by nanoscavengers exhibited good results

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