An Investigation of Electrostatic Interactions Between Organically Functionalized Silica Particles, Surfaces, and Metal Ions

Author

Sarah M. Stahl, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2012

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Dave, Bakul

Abstract

This research focuses on the electrostatic interactions between silica particles and either coated surfaces or metal ions. This work has two objectives: to begin a preliminary investigation into particle-surface systems that may be ideal for further investigation as a sensor and to investigate metal-ligand interactions for the potential use of metal ions to aid in the self assembly of silica particles. Silica particles with various organic functionalizations were synthesized from trialkoxysilane precursors using variations of the Stöber synthesis method, a well-known colloidal suspensions technique. The functional groups that were used in this work include mercaptopropyl (MPTMS), ethylenediamine (enTMOS), and aminopropyl groups (APTES). The aminopropyl functionalized particles were synthesized by varying the mol% of APTES in a tetraethoxyorthosilicate (TEOS) particle formulation. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) were used to analyze the particles for size, shape, and composition. Silica particles with all three functionalizations were used for the particle-surface study, whereas only MPTMS particles were used in the metal-ligand study. The coatings used for the particle-surface study were synthesized using standard sol gel chemistry with trialkoxysilane precursors as well. The functional groups used in this study include methyl (MTMOS) and aminopropyl groups (TEOS/APTES). Sol gel coatings incorporating carboxy and ammonium groups were also investigated but were not suitable for further study. FTIR was used to analyze the MTMOS and TEOS/APTES coatings. The adsorption of the MPTMS particles onto TEOS/APTES coatings and enTMOS or TEOS/APTES particles onto MTMOS coatings over time was monitored using fluorescence spectroscopy. Since silica particles are not fluorescent in the visible light range, a fluorescent dye was incorporated into the particles, either rhodamine (MPTMS particles) or pyranine dye (enTMOS, TEOS/APTES particles). The enTMOS and TEOS/APTES particles were protonated to increase the charge of the particles; the increased charge was verified with titration curves of the particles before and after protonation. Two types of MPTMS particles were used for the metal-ligand investigation. The first was the same MPTMS particles (without fluorescent dye) used in the first study. The second was 10 mol% MPTMS concentration in a TEOS particle formulation, similar to the APTES functionalized particles used in the first study. Lead(II) and zinc(II) solutions of varying concentrations was added to the particles, and the self assembly of the particles with no metal ions along with the various concentrations was analyzed using SEM. The nature of the metal-ligand binding was investigated using both mercaptopropyl functionalized particles by adding zinc(II), copper(II), silver(I), and lead(II) solutions to the particles in varying concentrations and analyzing the metal ion binding location using FTIR analyses.