Controllable Synthesis And Characterization Of TiO₂Nanocrystals And Their Composites Induced By Nanocrystalline Cellulose

With the development of science and industry, the environment is getting worse andworse. So how to develop useful and efficient functional materials to solve the problems ofenvironmental pollution has been of great importance for all the human beings. As animportant semiconductor with wide forbidden band, TiO₂nanocrystals has attracted greatattention during the past decades, due to its superior performances, such as chemical stability,low-cost, nontoxic, high photoreactivity and causing no secondary pollutions. In the presentdissertation, TiO₂nanocrystals with different morphologies and crystal structure wereprepared by hydrolysis of TiCl4in aqueous solution at a low temperature of30-80°C, usingnanocrystalline cellulose as inducing agent. Nanocrystalline cellulose （NCC） whose surfacepossesses of abundant hydroxyl groups acted as as hydrophilic substrate and morphologyinducing agent to promote the heterogeneous nucleation and crystal growth of TiO₂nanocrystals at low temperatures through strong hydrogen bonding with growth unit of TiO₂.Well-defined TiO₂nanocrystals can be obtained under the mild condition without calcinationsin the presence of NCC.The major research contents of this present work were as follows:Firstly, nanocrystalline cellulose with different microstructure and crystalline phase wasprepared by degrading natural cotton fiber in strong acid or alkaline environment. Highcrystallinity NCC （HNCC） was prepared by acid degradation process. Low crystallinity NCC（LNCC） was produced via alkali regeneration followed by being homogenized with a highpressure homogenizer. Regenerated nanocrystalline cellulose （RNCC） was obtained by alkaliregeneration of HNCC. The obtained HNCC, LNCC and RNCC were used as inducing agentseparately to make out the influence of crystal phase and microstructure of cellulose on thenucleation and crystal growth of TiO₂crystals. The growth mechanism was discussed on thebasis of the results of comparative experiments.Secondly, plenty of experiments were carried out to investigate the effect of temperature,reaction time, the concentration of TiCl4and additive on the morphology and structure ofTiO₂crystals in the presence of high crystallinity NCC. Cubic, flower-like, needle-like,spherical, thorny ball, chestnut-like TiO₂nanocrystals were obtained, and they were characterized by TEM, HRTEM, SEM, XRD and BET surface area analyzer. Thephotocatalytic activity of all the samples was detected by the decolourization of methylorange.Thirdly, metallic Ag nanoparticles were deposited on the flower-like TiO₂nanocrystalsby photoreduction and chemical reduction methods, obtaining Ag/TiO₂nanocomposites. Theinfluence of preparation technology, additive and concentration of AgNO3solution on thediameter and decentrality and of Ag particles was discussed. The photodegradationexperiment of MO solution indicated that the photocatalytic activity of Ag/TiO₂nanocomposites prepared by photoreaction method in the presence of NH3H2O and NaOHincreased obviously when the concentration of AgNO3solution was0.2%and0.5%. Theantibacterial performance of Ag/TiO₂samples were tested by inhibition zone method, S.cereus （ATCC29213） and E. coli （ATCC8739） were chosen as the experimental strains.Lastly, flower-like and cubic TiO₂nanocrystals were in situ grown on polyethyleneterephthalate （PET） non-woven fabric and glass fiber （GF） by hydrolysis of TiCl4in aqueoussolution in the presence of nanocrystal cellulose grafted PET fabric （HNCC-g-PET） and GF（HNCC-g-GF） at a low temperature of70°C. Characteristic results showed that strongchemical bondings were established between substrates and TiO₂nanocrystals. Thephotocatalytic activity of the obtained TiO₂/PET and TiO₂/GF composites was examined bydegradation of orange methyl under natural solar light and high-pressure mercury lamp. Theresults indicated that the TiO₂/PET composites exhibited good photocatalytic activity, and theTiO₂/GF showed even higher photoactivity. Loading TiO₂nanoparticles on supportingmaterials with large surface area where pollutants can be condensed can solve the difficulty infiltration and separation of fine particles in aqueous solution.