THE DEHYDROXYLATION OF BASIC ALUMINUM SULFATE - AN INFRARED-EMISSION SPECTROSCOPIC STUDY

The tridecameric aluminum polymer [AlO4Al12(OH)(24)(H2O)(12)](7+) was prepared by forced hydrolysis of Al3+ up to an OH/Al molar ratio of 2. 2. Upon addition of sulfate, the tridecamer crystallized as the monocl inic basic aluminum sulfate Na-0.1[AlO4Al12(OH)(24)(H2O)(12)](SO4)(3.5 5). The dehydroxylation of the basic aluminum sulfate has been studied by Fourier transform in-situ infrared emission spectroscopy over a te mperature range of 200 degrees to 750 degrees C at 50 degrees C interv als. The spectrum is characterized by the sulfate nu(1) (1024 cm(-1)), nu(3) doublet (1117 and 1168 cm-l) and the nu(4) doublet (568 and 611 cm(-1)) modes. Furthermore, minor bands assigned to nitrate are obser ved. Upon heating from approximate to 350 degrees to 400 degrees C maj or changes are observed, especially in the bandwidth and band intensit ies. The bands in the hydroxyl stretching region due to the Al-13 grou p disappear, whereas the bands around 1050 cm(-1) display various chan ges in bandwidths, intensities and positions associated with the dehyd ration and dehydroxylation of the basic sulfate and the changing of th e structure into an aluminum oxosulfate. The nitrate bands diminish up on heating. (C) 1998 Elsevier Science B.V.