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 monoclinic basic aluminum sulfate Na-0.1[AlO4Al12(OH)(24)(H2O)(12)](SO4)(3.55). The dehydroxylation of the basic aluminum sulfate has been studied by Fourier transform in-situ infrared emission spectroscopy over a temperature range of 200 degrees to 750 degrees C at 50 degrees C intervals. 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 observed. Upon heating from approximate to 350 degrees to 400 degrees C major changes are observed, especially in the bandwidth and band intensities. The bands in the hydroxyl stretching region due to the Al-13 group disappear, whereas the bands around 1050 cm(-1) display various changes in bandwidths, intensities and positions associated with the dehydration and dehydroxylation of the basic sulfate and the changing of the structure into an aluminum oxosulfate. The nitrate bands diminish upon heating. (C) 1998 Elsevier Science B.V.