ESR and HRTEM Study of Carbon-Coated Nanocrystalline MgO

Abstract

Carbon-coated nanocrystalline MgO samples were prepared by butadiene pyrolysis at 500 °C over aerogelprepared MgO samples. Samples with carbon loadings of 1.2, 3.2, 5.0, 10.0, and 15.9 wt % were prepared. Initial carbon formation rate was about 2 wt % per hour. According to HRTEM, the structure of the mineral component in the carbon-mineral materials was not altered by the carbon deposition. At low loading of carbon, it was found to deposit only inside the MgO aggregates 5-10 nm from their outside surface, forming thin individual bands 1.5-2 nm long. At the highest loading, carbon deposits form three-dimensional graphitelike multilayer structures filling the pore volume of the MgO aggregates and cover the outside surface of the aggregates with a thin monolayer coating. A single symmetric Lorentzian line with g ) 2.0029 attributable to carbon deposits has been observed in the ESR spectra of the carbon-mineral materials. It gradually narrows from 5.0 to 1.9 G as the carbon loading increases from 1.2 to 15.9 wt %. Nitroxyl radicals formed after dinitrobenzene adsorption on MgO nanocrystals have been used as a spin probe for estimation of the concentration of strong basic sites present on the surface of the carbon-mineral materials and degree of their coverage with carbon. The sample with the carbon loading of 15.9 wt % has practically all such sites blocked with carbon, while samples with carbon concentration between 5 and 10 wt % seem to be the most promising candidates for practical application as destructive adsorbents.

Nanocrystalline carbon coated alumina with enhanced phase stability at high temperatures

“…19,23 Earlier we have reported that the carbon coating deposited on the surface of the oxide nanoparticles can act as a nanoreactor shell. On the one hand, such coating can be penetrable for the reactant molecules from the gas 7,10,24,25 or liquid 26 phases making it possible to initiate various catalytic or solid-state reactions inside the nanoreactor. Moreover, the carbon coating prevents sintering of nanoparticles inside the shell during the temperature increase and stabilizes their sizes.…”

Adsorption of dimethyl methylphosphonate and trimethyl phosphate on calcium oxide: an ab initio study

“…MgO, CaO, and Al 2 O 3 [12][13][14][15]; MgO [16][17][18][19]; MgO, CaO, and Fe 2 O 3 [20]; Al 2 O 3 /MgO physical mixture [21], other oxides coated [22,23] or doped on CaO and MgO [24] were studied as destructive adsorbents for DMMP, other organophosphorus, fluoro-, chloro-, bromocarbons, and sulfur compounds. Nanocrystalline MgO, CaO, and Al 2 O 3 have shown remarkably high capacities to chemically adsorb organophosphorus compounds [12].…”

“…For organophosphorus compounds the heats of adsorption were found high and shown a small dependence on the substituent effects [16]. In the most cases, destructive adsorption, taking place on the surface of the MgO nanocrystals, proceeds so that the adsorbate is chemically dismantled and thereby made nont-oxic [18,19]. Decomposition of organophosphorus compounds on MgO surface proceeds due to yielded formic acid [20].…”

Study of MgO transformation into MgF2 in the presence of CF2Cl2•

“…These are conventional basic sites and low-coordinated surface ions, as well as highly active oxygen radical anions, electron-donor sites and acid sites identified using adsorption of nitroxyl radicals. 16,17,19,20 Oxygen radicals were observed on the MgO surface only after illumination in a vacuum installation and were not detected during reactions with halocarbons. Therefore, our main attention was attracted to highly active electron-donor and electron-acceptor sites.…”