Solid-State NMR Studies On Ta₂O₅ And Cu₂O Nanomaterials

Nano-oxides have a variety of applications in different fields,including catalysis,energy storage and pollution control.In order to further understand the relationship between the properties of these materials and their structures,advanced characterization techniques are necessary.Solid-state NMR spectroscopy can provide the information for medium and short range structure and dynamics of materials,and is elemental specific,non-destructive and quantitative,making it ideal for the studies of oxide nanomaterials.This thesis mainly uses solid-state NMR methods,combined with X-ray diffraction,high-resolution transmission electron microscopy,N2 adsorption/desorption curves,and thermogravimetric analysis,etc.to investigate the structure of Ta2O5 and Cu2 O nanomaterials:1.Hexagonal-phase tantalum pentoxide nanorods and orthogonal-phase tantalum pentoxide nanoparticles were synthesized by hydrothermal methods in two different ways.17 O MAS NMR,1H MAS NMR and 17O-1H REDOR NMR were used to study the bulk oxygen species,surface oxygen species,surface hydroxyl species and adsorbed water of tantalum oxide nanorods.By applying 17 O MAS NMR technique,it is proved that the surface of tantalum nanorods is dominated by OTa2 species,while there are more OTa3 species in the “bulk” part.Combining 17O-1H double resonance NMR technique and 1H MAS NMR spectroscopy,it was preliminarily determined that the low-frequency resonance in 17 O MAS NMR spectroscopy arises from oxygen with very short O-H distances,specifically,O directly bound to H.The resonance in the 1H MAS NMR spectrum was also assigned.Based on the 17 O MAS NMR spectroscopy under different magnetic fields,the tantalum oxide nanoparticles and tantalum oxide nanorods were compared.Compared to the synthesized tantalum oxide nanoparticles,the fraction of OTa3 species is higher in the bulk part in the as-prepared tantalum oxide nanorods.2.Cubic cuprous oxide nanocubes were synthesized by a simple solution-mixing method.The detection of surface oxygen species of as-obtained cuprous oxide samples was achieved with low temperature selective isotopic labeling with H217 O.17O MAS NMR spectra show a new resonance,which may be related to surface hydroxyl species.The 17 O NMR data for cuprous oxide nanocubes were also obtained with different temperature and time during selective labeling.