Preparation Of Chiral Titania Nanomaterials Through Sol-gel Transcription And Investigation Of Their Optical Activity

As one of the most important photo catalyst, titania possesses strong oxidability,chemical stability, corrosion-resistance and non-toxicity to humans. Therefore, theresearch on titania became a hot topic in recent years. Lots of research work onimproving the photo catalytic efficiency of titania has been carried out, includingincreasing the reaction active sites, developing ordered pore structure and surfacemodification. However, the reports on chiral titania nanomaterials are rare. In this thesis,titania nanomaterials with optical activity were prepared through a sol-gel transcriptionapproach using the self-assemblies of the low-molecule-weight amphiphilies (LMWAs)as the templates. Moreover, the research on the origin of the optical activity was carriedout, which lay a foundation for the application of titania in asymmetric catalysis.Firstly, a series of trans-1,2-diaminocyclohexane derivatives were synthesized,including chiral mono-and bola-type cationic and carboxylic ones. They werecharacterized using FT-IR,1H-NMR and elemental analysis. Thereafter, theirself-assembly behaviors were studied using scanning electron microscopy and circulardichroism spectrophotometer.Secondly, various of single-handed helical titania nanostructures, includingnanotubes, double helical nanofibers and nanoribbons, were prepared through a sol-geltranscription using the self-assemblies of the chiral LMWAs as the templates. Themorphologies of the titanias were controlled by tuning templates, solvent, concentration,catalyst and temperature. Moreover, the formation mechanism of these chiralnanostructures was studied. Other chiral metal oxides might be also prepared based onthis approach.Finally, diffuse reflectance circular dichroism was used to characterize the opticalactivity of the titania nanomaterials. The results indicated that:(i) the titania prepared by sol-gel transcription exhibited optical activity. The chirality of the organicself-assemblies has been successfully transferred to titania. The hydrogen bondingbetween Ti-OH of titania and the N-H group of the LMWA was proposed to drive thischiral transfer. Other metal oxides with optical activity were also proposed to be formedthrough non-covalent bondings.(ii) The chirality is in ngstrom scale and do not relatesto the helicity in nano scale.(iii) The acid and thermo treatment experiments indicatedthat the chirality existed at the surfaces of the nanotubes. The chirality was proposed tobe formed due to supramolecular imprinting or chiral defects.(iv) When the chiraltitanias were used as asymmetric catalysts, the ee value of product is relatively high,indicating that the titanias exhibit chirality at ngstrom level. The results shown heregive us a better understanding of the formation of titania with optical activity and laythe foundation for the applications of chiral titania.In summary, titania with optical and molecular chirality is prepared through asol-gel transcription approach. The chirality was transferred from organicsupramolecular self-assembly to the inner surface of titania. It is expected that thisapproach would be applicable for the preparation of chiral materials with nointrinsically chirality. The obtained chiral nanomaterials are potentially applied forasymmetric catalysis, nonlinear optics and chirality detection.