Home – Home – Jornals – Chemistry for Sustainable Development 2017 number 4

The paper studies low-temperature (77 K) radiolysis of various modifications of silica, such as macroporous glass (MPG) with a pore diameter of 2000 and 1500 Å, regular sodium glass, and fused quartz by the electron paramagnetic resonance (EPR) method. Paramagnetic centres in various modifications of SiO₂ may vary significantly, depending on origin, the presence of impurities, treatment conditions, and radiation activation of samples, as demonstrated. Hole centres in oxygen and silicon atoms and electron centres in silicon atoms and alkaline metal ions are the main paramagnetic centres in γ-irradiated SiO₂; their contribution in glasses and quartz is 90–95 and ~70 %, respectively. The number of radical centres in all silicas (H^•, Si^•, >Si^•–H) does not exceed 3–4 %. The radiation yield of atomic hydrogen G_H = 0.02–0.4 per 100 eV. Spectra of НО₂^• radicals and SiO₂^• macroradicals are recorded during heating of irradiated samples in the oxygen atmosphere. According to the data of quantum chemical calculations, the doublet with the splitting α^H = 12.5 mT registered during heating of irradiated MPG and quartz belongs to formyl radicals that are formed from the self-hydrogenation reaction of natural impurities of CO in silicas. The doublet with α^H ≈ 1.0 mT, g = 2.002 is referred to hole centres –Si⁺(OH)H in the surface silicon atoms containing hydroxyl groups and the H atom.