Study On NMR Spectroscopy Of Water Between Graphite Oxide Layers

As a hydrophilic material,graphite oxide(GO)can be bound water molecules in the interlayer for studying two-dimensional bound water.NMR spectroscopy are used to study the character of bond water and the motion pattern.The GO sample preparing by Hummers method with the interlayer spacing of 9.1 A contains two layers water after placing in heavy water vapor.The method that sample is exchanged by deuterium is called spin dilution.1H MAS NMR spectra has two peaks at 6.6ppm and 1.7ppm,corresponding to water and hydroxyl.The dynamics of bond water between graphite oxide(GO)layers was investigated by H NMR,D NMR and cross-polarization(cp)NMR.Cross-polarization experiment shows the strong coupling of water molecules and group on GO Sheet.Variable contact time experiments give the arrangement of bond water between GO layers.The Difference of chemical shift of several samples shows that the strength of hydrogen bond in GO is much stronger than that in liquid water.Variable temperature experiments give the information of rotational motion and translational motion of water molecules.FWHM of 1H NMR spectrum always decreases with increasing temperature in 240K-330K because of the motional narrowing effect of bond water.The water resonance peak width at half maximum is about 4 kHz at room temperature,that is wider than liquid water and narrower than ice.Therefore the rotation frequency of bound water in constrained state is much slower than liquid water according to the relationship of line width and motion frequency.FWHM of 2H NMR spectrum decreases with increasing temperature first,and be invariable above 280K.Considering the form of dipole-dipole and quadrupole interaction,the invariable line width reflects the broadening effect of electric field gradient(EFG)between GO layers.Besides,a small and sharp peak appears in 2H NMR spectrum above 300K,that reveals the breaking of hydrogen bond and the rotation of heavy water molecules.