NANOSCALE METAL-OXIDE PARTICLES AS CHEMICAL REAGENTS - HEATS OF ADSORPTION OF HETEROATOM-CONTAINING ORGANICS ON HEAT-TREATED MAGNESIUM-OXIDE SAMPLES OF VARYING SURFACE-AREAS

Heats of adsorption (immersion) were measured via a solution calorimeter for a series of heteroatom (oxygen, sulfur, phosphorus) containing organic compounds on thermally activated magnesium oxide (heat treated at 700-degrees-C overnight in vacuo followed by cooling to room temperature). For phosphates, phosphites, and phosphines the heats of adsorption were high and showed a small dependence on substituent effects. For sulfur compounds, -S-H-containing compounds yielded the highest values. For oxygen systems very high heats of adsorption were found for carbonyl compounds. In addition, the strongly basic nature of the MgO surface was demonstrated by the extremely high heats of adsorption/reaction with carboxylic acids. Heats observed for 1-butanol adsorption varied linearly with MgO surface area. Surprisingly, cyclohexane dilution of 1-butanol caused a dramatic lowering of adsorption heats, demonstrating the competitive nature of even such unreactive solvents. The observed heats of adsorption/reaction combined with spectroscopic data allowed some conclusions about the type of surface bonding that took place. The strong interactions of several of these organics demonstrate the nature of heat-treated MgO as a destructive adsorbent for many toxic chemicals. Since MgO is nontoxic and inexpensive and can be prepared in highly surface activated forms, it shows promise for use in air-purification schemes.