ESR STUDIES OF 5 COALS BEFORE AND AFTER REACTION WITH SPIN TRAPS (MICROWAVE-DRIVEN) - ESR AND XPS OF THE COALS FOLLOWING REACTION WITH DIIODINE

Microwave-driven reactions of the spin trap phenyl-N-t-butylnitrone wi th five coals of different rank are reported. Comparison is made betwe en the e.s.r. data for the raw coals and the spin-trap-treated materia ls. It is concluded that the major effect of the spin trap is to alter relaxation times and that the concentration of reactive radicals in t he coals is low. When reacted with silylated bituminous coal, the spin trap causes replacement of the trimethylsilyl groups with t-butyl gro ups. A new microwave method of char generation is introduced and e.s.r . data for the new chars are presented. The reactions of the coals wit h diiodine are re-examined. Results are compared with those of other r ecent investigations of diiodine 'complexes' and it is suggested that the increase in spin density observed may result from a favourable cha nge in relaxation time, as a result of intercalation of the halogen, f or one suite of radicals, rendering them detectable in the e.s.r. expe riment. The materials were also examined using X-ray photoelectron spe ctroscopy (XPS), and it is suggested that the common assumption that d iiodine is present as I-2 molecules in these coals may need revision. Copyright (C) 1996 Elsevier Science Ltd.