ESR study of the active oxygen species on hydroxyapatite activated by heat treatment

Abstract The paper deals with the ESR study of the active oxygen radical (O 2 − ) formed on the hydroxyapatite (HAP). The O 2 − species were generated by heating HAP in vacuo at 973 K followed by treating with oxygen at room temperature. They smoothly reacted with propylene, methane, hydrogen and benzene at room temperature where the reactivity decreased in that order. When the O 2 − species were reacted with propylene followed by heating in vacuo at 873 K for 1 h and treating with oxygen at room temperature, a quartet signal ( g  = 2.002, a  = 2.15 mT, 1:3:3:1) was formed. It decayed by heating at 573 K for 10 min and restored again the original O 2 − species with treatment of oxygen. The quartet lines were derived from the interaction of an unpaired electron with three equivalent phosphorus atoms. ESR spectra changed depending upon the temperature at which heating was applied on HAP after O 2 − had been reacted with propylene. The behavior was attributed to the different active species for O 2 produced by the series of treatments: formation of O 2 − on thermally activated HAP, reaction of the O 2 − species with propylene, heating at 673–973 K and treatment with O 2 .