Cellulose/titanium dioxide nanocomposites and silicon diimide gel as a stationery phase for chromatography

Sajedin, Seyed Mani

February 2015

Thesis or dissertation

© 2015 Seyed Mani Sajedin. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

There were two main aims of this thesis, both of which involved the synthesis, often using environmentally friendly (green) methods involving water as the solvent and reagent, and the analysis and determination of the physical properties of novel inorganic nanomaterials and nano-composites. The first part of this project was the study of the general methods for the preparation of titanium dioxide nanoparticles and the investigation of the most efficient ways of coating CP with these nanoparticles in order to improve UV-stability and also to increase the whiteness and reflectivity of the paper. The second part of this research involved investigation silicon diimide mesoporous gel as a basic stationary phase for thin film and column chromatography for acid-sensitive organic compounds.

A number of different methods have been investigated in order to improve the UV-stability and also to increase the whiteness and reflectivity of paper by using titanium dioxide nanoparticles to modify the optical properties of the surface of cellulose products and especially writing paper. The bleaching and yellowing of paper in visible light has been a common problem in the paper industry for very many years. A thin, but very efficient surface coating would allow a lighter paper with less standard stabilisers and whitening agents to be manufactured with enormous savings in terms of the processing and manufacture of paper. A higher brightness and whiteness of paper would also increase the optical contrast of writing paper, for example. The methods investigated in this project to attain these objectives include: preparation of bigger titanium dioxide nanoparticle powder for coating solutions with and without the formation of seeds, in-situ coating of titanium dioxide nanoparticles on CP, preparation of titanium dioxide nanoparticles as stable colloidal solutions, coating CP with core/shell TiO₂/SiO₂ nanoparticles and coating CP with TiO₂/APTES nanoparticles.

Two reaction approaches have been investigated to prepare titanium dioxide nanoparticles with a size of about 200 nm, i.e., preparation of titanium dioxide nanoparticles without seed formation and preparation of titanium dioxide nanoparticles with seed formation. In the preparation of the titanium dioxide nanoparticles without seed formation, different starting materials were used. The size of the secondary nanoparticles is about 120 nm for TiOSO₄.xH₂SO₄.xH₂O, about 50 nm for TiOSO₄.xH₂O and about 100-300 nm when using TiOCl₂ as the source of titania. Titanium dioxide nanoparticles with a size of about 200 nm were obtained using the method involving the formation of seeds.

In in-situ coating about 200 nm of titanium dioxide were coated on CP surface in just 20 min by heating of the CPs in the TiOSO₄ solution at 110 oC. The results also show that the titanium dioxide particle size increase with increasing of reaction time. Stable titanium dioxide nanoparticle colloidal solutions have been prepared with TiOCl₂ as a starting material. Because of high photocatalyst activity of small titanium dioxide nanoparticle, the surface of TiO₂-RP and TiO₂-P25 nanoparticles were protected by APTES and silica to reduce the photocatalytic degradation of organic material support.

In order to inhibit the photocatalytic degradation of organic material supports induced by small titania (TiO₂) nanoparticles, four kinds of titanium dioxide nanoparticles, that is, commercial P25-TiO₂, commercial rutile phase titanium dioxide (RA), rutile titanium dioxide nanorods (RP) and rutile titanium dioxide spheres (RP500), prepared from TiCl₄. Small titanium dioxide nanoparticles were coated with a thin, but dense, coating of silica (SiO₂) using a conventional sol-gel technique to form TiO₂/SiO₂ core/shell nanoparticles. These core/shell nanoparticles were deposited and fixed as a very thin coating onto the surface of CP samples via a wet-chemistry polyelectrolyte layer-by-layer approach. The TiO₂/SiO₂ nano-coated paper samples exhibit higher whiteness and brightness and greater stability to UV-bleaching than comparable samples of blank paper. Comparison of the physical property of TiO₂/SiO₂ core/shell with the result presented in literature for bulk titanium dioxide evidenced UV-stability, whiteness and reflectivity were improved in these core/shell coatings.

Titanium dioxide nanoparticles have also successfully modified with (3-aminopropyl)triethoxysilane (APTES). Commercially available-P25-titanium dioxide nanoparticles and rutile titanium dioxide nanorods, prepared from TiCl4, were first modified with a thin layer of APTES. These APTES-modified-P25 titanium dioxide nanoparticles and rutile titanium dioxide nanorods were then deposited and fixed onto the surface of paper samples via a simple, dip-coating process in water at room temperature. The resultant APTES-modified-P25 titanium dioxide nanoparticle-coated paper samples exhibit much greater stability to UV-illumination than uncoated blank reference paper and very little, or no, photo-degradation in terms of brightness and whiteness, respectively, of the-P25-TiO₂-nanoparticle-treated paper is observed. There are many other potential applications for this Green Chemistry approach to protect cellulosic fibres from UV-bleaching in sunlight and to improve their whiteness and brightness.

In the second part of this thesis mesoporous silicon diimide gel was prepared and used for the first time as a basic stationary phase in thin layer and column chromatography. Silicon diimide gel, Si(NH)₂, is the basic equivalent of silica gel, SiO₂, whereby the oxygen atoms of silica have effectively been replaced by nitrogen. Silica gel is the most commonly used stationary phase for thin film and column chromatography. However, it is lightly acidic and this acidity can lead to the chemical decomposition of acid-sensitive compounds during chromatography. The mesoporous silicon diimide gel used here was prepared and optimised using a sol-gel process developed previously at the University of Hull. It exhibits a large specific surface area, a weakly basic surface and it is ideal for the characterisation, separation and purification of acid-sensitive compounds.

The nanoparticles and nanocomposite materials prepared in this thesis were characterized by appropriate combinations of analytical techniques, such as SEM, TEM, EDX, XPS, ICP, UV-Vis, ζ-potential, FT-IR, XRD, CHN and NTA. The BET surface area, whiteness, brightness and some of the nanocomposite materials were also determined and the values compared with standard materials.

Department of Chemistry, The University of Hull
Kelly, S. M. (Stephen Malcolm); Wadhawan, Jay
Qualification level
Qualification name
9 MB
QR Code