Fabrication and characterisation of self-assembled monolayers of N-[3-(trimethoxysilyl)propyl]diethylenetriamine on silica particles

This study focuses on a facile approach to create N-[3-trimethoxysilyl)propyl]diethylenetriamine (C10H27N3O3Si, TRIS in short) self-assembled monolayers (SAMs) on silica particles for water treatment without the use of any organic solvents. A range of TRIS concentration has been examined to establish the window of SAM formation. In order to determine the coverage and characterise the stability of the TRIS-monolayer, the active amine functional groups of the monolayer are quantitatively characterised by titration method. Its thermal stability and TRIS uptake are characterised by thermogravimetric analysis (TGA) and the analysis is correlated with a model calculation of the maximum TRIS-coverage considering the surface area of hydroxyl (OH) concentration on the surface of the silica particles. X-ray photoelectron spectroscopy (XPS) analyses clearly reveal the existence of the TRIS-monolayer on the particles. The TGA results show TRIS-layers are stable up to 225 °C and fully degraded at 650 °C. The determined weight loss (%) correlates within the analytical error with the values determined by titration. Monolayer formation is observed only up to low concentration of TRIS (0.32 mmol/g) and above which it is predominated by the formation of multilayer. The correlation of the experimental results with model calculations of the maximum TRIS-coverage confirms this effect to be due to TRIS-multilayer formation.