| Colloidal iron oxides are an important component in soil system and in water treatment processes. Humic-based organic compounds, containing both phenol and benzoate functional groups, are often present in these systems and compete strongly with phosphate species for binding sites on the iron oxide surface. As benzoic acid is one of the main functional groups present within humic acid, tannic, or gallic acid, we have chosen to investigate how benzoic acid groups interact with various iron oxides using chemical force microscopy (CFM) force titration experiments. Alkanethiol self-assembled monolayer (SAM) methods were used to prepare chemically modified AFM tips and control surfaces using 4-(12-mercaptododecyloxy)benzoic acid, 4-(12-mercaptododecyloxy)phenol and bis(11-thioundecyl)phosphate.;The surface pK1/2 of 4-(12-mercaptododecyloxy)benzoic acid was determined by force titration on control surfaces and was found to be about 4.0. The benzoate probe was observed to have the maximum peak in its force titration on unmodified FeO(OH) at a pH of 8.5. (Abstract shortened by UMI.). |
