Solid-State NMR Studies Of Surface Structure Of Tin Dioxide And Gamma Alumina Nanomaterials

Recently, nanosized oxides have showed great potential in fields of energy, catalysis, environmental management, biology applications. Since the properties of nanomaterials are closely associated with the surface structure, the detailed structure information on atomic/molecular scale has to be obtained. Solid-state NMR is a powerful tool with which to study short-range order and medium-range order of solid materials. In this thesis, solid-state NMR spectroscopy, in combination with X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transforminfrared spectroscopy (FT-IR), thermogravimetry analysis(TGA), atomic force microscopy (AFM), and density functional theory (DFT) calculations, is used to investigate the structure of SnO2 and Al2O3 nanostructures.1. Ultra thin SnO2 nanosheets have been prepared by using a hydrothermal method. The influences of the hydrothermal time on the products have been studied. On the basis of 119Sn MAS-NMR data and DFT calculation results, different Sn species can be distinguished, suggesting that solid-state NMR spectroscopy can be used to extract the ratio of surface atoms in nanomaterials.2. Single layer of Al2O3 is deposited on the surface of MgGa2O4 by atomic layer deposition (ALD).27Al & 1H MAS-NMR spectroscopy, as well as XRD, have been used to investigated the structure of surface Al species in Al2O3/MgGa2O4 system at different temperature. With the increase of the temperature, the 27Al MAS NMR signal becomes weaker for the the samples with the same weight. It can be ascribed to the strcuture change of Al species, which results to much larger quadrupole coupling constant (CQ) and thus wider spectral line width, making some signals undetected by NMR.