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RESEARCH PRODUCT

Impact of acidic/hydrothermal treatment on pore structural and chromatographic properties of porous silicas

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description

Abstract A series of commercial silicas and a laboratory made product were subjected to acidic/hydrothermal treatment with solutions of HCI, HNO3, H2SO4 and HF. The concentration of acid and the temperature and duration of treatment were varied. The specific surface area, content of metal impurities, types and concentration of surface hydroxyl and siloxane groups and crystallinity were determined for native and treated silicas. Only changes in the structural order of the surface could be assessed by means of 19Si cross-polarization magic angle spinning NMR spectrometry and electron diffraction. The native and acid-treated silicas were surface modified to n-octyl derivatives and tested under reversed-phase conditions. A notable improvement in the column plate number and the asymmetry of the peaks was observed, whereas the solute capacity factors remained nearly unchanged. The effect of the conditions of acidic treatment (concentration, temperature and duration) was established by factorial experiments. Acidic/hydrothermal treatment caused a more ordered surface structure with quasi-crystalline domains, which improved the chromatographic mass-transfer kinetics and hence the column performance of acid-treated silicas.