Jozef Hodyl PhD Thesis - Theses - Flinders University

materials in mmol of the attached species per gram of material. Thermal studies alsorevealed that the materials contained 4% physisorbed water, which was also takeninto account when processing the data from thermal combustion experiments.4.2.5 Loading level: Linker materialsComparison of the loading level of the two linker species Si-GPS, 33, and, Si-GPDMS, 83, illustrates the correlation between the loading capacity and thedifference in the mode of attachment of each of the parent linker compounds, GPTS,32, and GPDMES, 82. It is assumed that the number of silanol centres available toeach of these species is similar; therefore, if the potential for polymerisation isexcluded, it could be argued that as the GPTS, 32, species has three groups able toreact with the silica surface, its coverage would be one third that of GPDMES, 83,which has only one group able to link with the silica surface. However, this outcome,is not evident from the microanalytical data. In fact Si-GPS, 33, exhibits a surfacecoverage approximately three times more than Si-GPDMS, 83, Table 4.1. This resultmust be due to the tendency of GPTS, 32, to form a polymeric layer on the silica asshown in Figure 4.4.Surface loading of GPS decreases slightly on the smaller mesh 230 - 400 silicagel, Si 230-400 -GPS, 80, due to inconsistency with respect to the distribution andcharacter of the surface silanol groups. Most of the increase in surface area of the230 - 400 mesh compared to 70 - 230 mesh silica gel is accommodated within thepores. The surface coverage of linker molecules polymerised across the surfacecannot access the silanol groups in the pores. Thus, the GPTS, 32, molecule may betoo large to take advantage of the higher surface area of the 230 - 400 mesh becauseit cannot react with the internal surface silanol groups. However, the coverage ofGPS linker groups on the MCM-41 material, MCM-41-GPS, 81, shows a marked83