Carbon paramagnetic defects in silica sol-gel prepared materials.

Antonio Barbon (1) , Silvia Gross (2) , Eugenio Tondello (1) , Marina Brustolon (1)

1 Dip. Scienze Chimiche
2 CNR–ISTM

Silica obtained by annealing in air of gels produced from the controlled hydrolysis and condensation of methacryloxypropyltrimethoxysilane (MAPTES) exhibit lorentzian and gaussian EPR signals centered at g=2.0037 similar to those found in coals. The number and widths of lorentzian lines depend on the annealing temperature, and are attributed to graphitic clusters of different sizes showing spin exchange. These results agree with the estimated average dimensions of the clusters at the different annealing temperatures, obtained by correlating the carbon content with the number of spins. Inhomogeneous components have been identified by using the echo-detected EPR method and are attributed to smaller isolated clusters. These latter analyzed by ESEEM and HYSCORE show strong signals at the free nuclear frequencies of 13C and 1H nuclei only, and hyperfine interactions of 5 MHz with a 13C nucleus.

Mots clés: Physical Sciences

Antonio Barbon, Silvia Gross, Eugenio Tondello, Marina Brustolon. Carbon paramagnetic defects in silica sol-gel prepared materials.. Molecular Physics, 2008, 105 (15-16), pp.2177-2183. ⟨10.1080/00268970701747207⟩. ⟨hal-00513157⟩