Fluorescence probing of the interfaces of solid calcium carbonate, calcium hydroxide, and calcium oxide with benzene and heptane
Abstract IR and fluorescence probing studies have been used to investigate the solid surfaces of CaO, Ca(OH) 2 , and CaCO 3 in contact with benzene. IR studies show that organic acids interact with CaO and Ca(OH) 2 to form adsorbed anions, while free acids are adsorbed to CaCO 3 . Pyrene butyric acid, PBA, binds to the surfaces and the fluorescence of the pyrene chromophore reports back on events at the surface. At least two surface sites exist for PBA on all surfaces, one at the solid-benzene interface and one away from the surface in a cleft or pore. Reactions of excited surface-adsorbed PBA with nitromethane, nitroethanol, and nitropropionic acid, which are also bound to the surfaces, fall into two classes. The first class, exhibited by CaCO 3 indicates dynamic quenching where both reactants move on the surface. The second, illustrated by Ca(OH) 2 , shows static quenching where both reactants are bound on the surface in very close proximity. The studies show marked differences between the various surfaces, which has also been observed in a more limited extent on colloids of these materials in oil.