EPR study of paramagnetic centers in SiO2:C:Zn nanocomposites obtained by infiltration of fumed silica with luminescent Zn(acac)2 solution

Silica-carbon with zinc (SiO2:C:Zn) nanocomposites obtained via infiltration with aged luminescent zinc acetylacetonate (Zn(acac)(2)) ethanol solution of two concentrations (1 or 4%) into the fumed silica (SiO2) matrix have been studied using EPR within the temperature range 6...296 K before and after thermal annealing. The EPR spectrum of SiO2:C:Zn nanocomposites consists of three signals with the Lorentzian lineshape corresponding to paramagnetic centers with S = 1/2, which are related to carbon dangling bonds (CDB) (g = 2.0029(3)), silicon dangling bonds (g = 2.0062(3)) and oxygen-centered carbon-related radicals (CRR) (g = 2.0042(3)). A small EPR linewidth (<1 mT) observed for CDB and oxygen-centered CRR allows us to conclude that they are in the sp(3)-hybridized state. It was found that the temperature dependence of the EPR signal integrated intensity of the CDB and oxygen-centered CRR follows the Curie-Weiss law with a small positive value of the Curie-Weiss constant, which indicates that the weak ferromagnetic exchange interaction takes place in the spin system of CDB and oxygen-centered CRR. It was supposed that the carbon-related centers are clustered in SiO2:C:Zn nanocomposites. We assume that the oxygen-centered CRR in the sp(3)-hybridized state are associated with luminescent centers in previously reported aged Zn(acac)(2)/C2H5OH solution.

Automated summary

The study focused on the impact of aged luminescent zinc acetylacetonate ethanol solution on SiO2:C:Zn nanocomposites, revealing that carbon dangling bonds and oxygen-centered carbon-related radicals are in the sp(3)-hybridized state with weak ferromagnetic exchange interaction.