Jozef Hodyl PhD Thesis - Theses - Flinders University

GPTSGPDMESFigure 4.4Schematic depiction of the difference in surface coverage by: GPTS, 32, oligomeric andmultidirectional (black) or monolithic (red); and, GPDMES, 82, monolithic (blue).4.1.3 Endcapping residual surface silanol groupsThe process of functionalising the surface of silica gel does not necessarily consumeall of the available surface silanol groups. 153 A proportion of these are unattainabledue to accessibility restrictions originating from steric hindrances, for example, thosethat reside within pores in the silica gel. These residual silanol groups tend to beweakly acidic with a pK a ~5, so there is the potential for them to undergo somecation exchange in solutions containing metal ions, Equation 4.1.M + (SiOH) M(OSi−) + H Equation 4.1Because of this it was considered desirable to chemically inactivate these residualsilanol groups to prevent their complexation with metal ions when conducting metal153, 208uptake studies (Chapter 5) This is commonly known as endcapping.The general procedure for endcapping is to silanise the silica gel surface, afterderivatisation with the desired moiety, using trimethylchlorosilane (TMCS), 84.74