Surface oxygen radicals originating via redox reactions during the mechanical activation of crystalline SiO2 in hydrogen peroxide

Two surface dinuclear oxygen species simultaneously form when quartz is ground in a solution of hydrogen peroxide. They are the superoxide O−2 radical (gzz=2.044, gyy=2.010, gxx=2.002) and the peroxy SiOO· radical (gzz= 2.064, gyy= 2.007, gxx= 2.002). They are formed by contact of the freshly created surface, bearing reactive centres originated by cleavage of the SiOSi bonds, with H2O2. In parallel, OH· radicals are detected in the solution. A scheme involving the catalytic decomposition of hydrogen peroxide is proposed accounting for the radical species observed at the surface and in solution.