Modification of kaolinite by Grafting of siderophilic ligands to the external octahedral surface

• Selective modification of μ-hydroxy surfaces via 1,2-dihydroxyphenyl-ligands
• Adsorption capacities were proven to be related to both basal and edge surfaces.
• The edge surface area was determined utilizing the adsorption of fluoride ions.
• The modification enhanced the suspension stability in organic solvents.
• This is capable to fine-tune the Janus-character of kaolinite platelets.

The modification of the external octahedral surface of kaolinite (Kaol) was investigated using two siderophilic ligands (SL): 3,4-dihydroxybenzophenone (DBP) and quercetin (Qu). These SL have a 1,2-dihydroxyphenyl group that forms chelate-complexes with aluminum cations. Adsorption isotherms were obtained colorimetrically. PXRD patterns proved that the adsorption was attributed only to the external surfaces. Furthermore, adsorption of fluoride ions was applied to quantify the non-μ-hydroxy groups of the edges and derive the surface area of edges.Comparing maximum adsorption capacities with surface area of edges, it can be safely concluded that SL are indeed capable to coordinate to the aluminol basal surface of Kaol. This conclusion is corroborated by significant bathochromic shifts upon adsorption of the ligands that indicate the formation of a surface complex with exposed Al3 +. Thus even small amounts of adsorbed SL changed the surface tension of Kaol significantly. Consequently, forced sedimentation experiments showed that the modified Kaol is rendered hydrophobic enough to form stable dispersions in organic solvents fostering preparation of clay polymer nanocomposites (CPN).