Silica beds and silica monoliths for pollutants removal and HPLC

This PhD thesis investigates mesostructured porous silica as a system for removal of pollutants and high performance liquid chromatography (HPLC). In these fields typically the materials used consist of a silica substrate modified with a compound, which has a high selectivity towards the analyte of interest. In this thesis two silica modifiers are proposed: cetyltrimetylammonium bromide (CTABr) and glyphosate. The CTABr was actually the cationic surfactant used as template for the mesostructure, which was not removed from the silica framework as it usually is by calcination. This surfactant was used for the retention of haloacetic acids (HAACs) and nitrate ion. The glyphosate is an aminoacid present in many commercial herbicides and it has a high complexation capability towards metals. It was linked onto the silica surface using an appropriate reagent, the 3-glycidoxypropyltrimethoxysilane. The behavior of HAACs, NO3- and metals has been investigated because they are some of the most dangerous and monitored pollutants in water. The chosen surface modifiers have been combined with two different systems: silica particles and silica monoliths. The silica particles have been used until the late 1990s for HPLC columns packing, and they are nowadays mainly used as adsorbents of compounds due to their elevated capacity and strong retention capability. The silica monoliths have become the state of the art in HPLC, because of their better mass transfer, higher efficiency and lower analysis time compared to particle packed columns. Four materials have been prepared combining the two morphologies with each modifier. Physical-chemical characterization has been performed using several techniques (FTIR, N2 isotherms at 77 K, SEM-EDS, XPS and TGA) then the materials capabilities have been investigated in their respective fields of application. The interesting results obtained with these brand new adsorbents may have a high impact over the fields of waters purification and analysis, which is one of the recent most important topics due to the huge raise of contaminants during the last 150 years.