Stepwise no chemisorption processes on synthetic chrysotile asbestos : tubular crystals with acidic and basic surfaces

Abstract

Nitric oxide adsorption on synthetic chrysotile asbestos has been studied by a gravimetric method and F.t.i.r. spectroscopy at 303 K. The NO adsorptio isotherm on chrysotile had tow steps : the first step at low NO pressure arises from NO adsorption on the outer, basis Mg(OH)₂ surfaces of tubular chrysotile crystals, and the second step at high NO pressure from that on the inner, acidic SiO₂ surfaces. NO is adsorbed as an NO^–₂ species on Mg(OH)₂ surfaces which gives rise to the pair of absorptions at 1140 and 1280 cm^–1, and as an NO^–₃ species on SiO₂ surfaces, which gives rise to the doublet peat at 1380 cm^–1. The i.r. band at 1600–1720 cm^–1 may be assigned to NO^{– or physisorbed H₂}O, produced by the surface reaction of NO with surface hydroxyls. Aslo the effect of surface modification a chrysotile on the NO adsorption supported the stepwise NO adsorption process.