Surface Chemistry Induced by High Energy Radiation in Silica of Small Particle Structures

Abstract

Spectroscopic techniques are used to investigate energy transfer and radiation-induced reactions on the surfaces of particulate silicas. Upon subjection to high energy radiation, hydrogen atoms are produced with significant yields in all silica samples pretreated at 150 °C, for an example, G(H) = 4.2 in silica gel Davisil 60. Subsequent hydrogen addition to aromatic adsorbates such as pyrene, N,N-dimethylaniline, and methyl viologen (MV2+) proceeds on the surface in competition with the hydrogen dimerization, leading to the formation of their H adducts. Hydrogen scavenging studies revealed that such addition reactions are heterogeneous in porous silica gel with contributions from a fast intrapore reaction within several nanoseconds and a much slower diffusion influenced interpore process over many microseconds. The efficient capture of H atoms by pyrene at a small percentage of surface coverage suggests that hydrogen is produced at the specific sites where pyrene adsorbs. Electron scavenging by CHCl3, Cd2...