| Environmental pollution and resource shortage have become two important issues blocking the economic and social sustainable development of the world, especially China. In the present thesis, from the perspective of environmental/resource sustainable development, in order to achieve the goal of environmental protection and high-value utilization of bioresources, based on coupling of bio-affinity adsorption, molecular imprinting, and nano photocatalysis, chitosan/TiO2/Ag NPs organic-inorganic bio-affinity composite was prepared and used for the removal of various trace environmental pollutants and photocatalytic conversion of bioresources. Furthermore, the visible-light photocatalytic mechanism was studied in depth. The main contents of this thesis are as follows.(I) Taking azo dyes to represent refractory organic pollutants, using surface molecular imprinting and surface adsorption, molecular imprinted chitosan/TiO2 bio-affinity composite was prepared employing a typical azo dye methyl orange as template. The photocatalytic degradation rate of the imprinted composite for methyl orange was 31% higher than that of the non-imprinted composite. And in methyl orange/rhodamine B and methyl orange/sunset yellow coexistence systems, the selectivity of the imprinted composite for methyl orange was 36% and 38% higher that of the non-imprinted composite, respectively. These results proved that molecular imprinting could improve the enrichment and degradation abilities of the composite towards trace target pollutants. During the photocatalytic process, TOC of the dye wastewater decreased proving that mineralization of organic pollutants could be achieved using this composite. Without further desorption and regeneration, the prepared composite could be reused for 10 cycles preserving over 60% of its photocatalytic degradation efficiency. Its reuse ability could reduce the operating cost obviously and is very important for the practical application in wastewater treatment.(Ⅱ) With coupling of chitosan bio-affinity adsorption and nano-Ti02 photocatalytic reduction, rapid reduction of Ag+ ions (less than 20 min) to generate well dispersed Ag nanoparticles at room temperature and light conditions (UV or visible) was achieved under etching effect of dissolved oxygen in a designed internally illuminated photocatalytic reactor. This preparation process was also feasible for Cu2+, Pb2+, Ni2+, and lead could form flake crystal with uniform morphology. The prepared Ag nanoparticles could catalyze 4-nitrophenol reduction and the conversion reached 100% in 120 min at room temperature. The catalytic activity of the prepared Ag NPs for 4-nitrophenol reduction could be maintained in 5 cycles. The Ag NPs also showed enhanced effect for Raman analysis of crystal violet, methylene blue, and E. coli cells and was expected to be an active SERS substrate for trace contaminants detection and biological analysis.(Ⅲ) Combining the advantages of chitosan and nano-TiO2, two kinds of low-cost, green, efficient antibacterial agents, two kinds of visible light responded bio-affinity photocatalytic antibacterial composites, namely chitosan/Fe-TiO2 antibacterial coating and chitosan/TiO2/Ag NPs bio-affinity composite, were prepared using Fe3+ or Ag NPs to modify nano-TiO2-Under visible light irradiation, chitosan/Fe-TiO2 antibacterial coating showed efficient antibacterial activity against bacteria, fungi, and molds with 100% sterilization rates in 4 h. Microbial cells could be completely killed by the visible light mediated photocatalytic reaction of antibacterial coating. Chitosan/TiO2/Ag NPs bio-affinity composite possessed highly effective bactericidal activity for various pathogenic microorganisms under visible light irradiation containing gram-positive bacteria, gram-negative bacteria, and fungi. The bactericidal rate of chitosan/TiO2/Ag NPs composite against E. coli increased by 20 times compared with that of chitosan/TiO2 composite. The composite could be recycled for 5 times maintaing its bactericidal rate over 99.99% and showed little toxicity towards mammalian cells, thus being potential for drinking water purification. Chitosan/TiO2/Ag NPs bio-affinity composite could not only destroy microbes’cell wall and membrane thereby altering its cellular structure, but also affect the metabolism processes significantly. The visible light photocatalytic antibacterial activity is due to the synergistic effects of the three components.(IV) Using Au nanoparticles as light absorption center, Ni nanoparticles as catalytic center, Au-Ni binary photocatalyst was prepared existing in two forms:independent Au, Ni NPs and Ni@Au core-shell nanostructure. At lower temperature, normal pressure, and visible light conditions, using green solvent 2-butanol as hydrogen donor, Au-Ni photocatalyst showed enhanced activity to cleave three kinds of aryl ethers in lignin by hydrogenolysis compared with dark condition with conversion over 98% and selectivity towards aromatic products higher than 60%. Au-Ni photocatalytic hydrogenolysis of aryl ethers could be regulated by controlling light intensity and wavelength. And the photocatalytic activity could be enhanced by increasing the reaction temperature, illustrating that Au-Ni binary photocatalyst could couple thermal and light energies to catalyze reactions. Au NPs could absorb visible light energy to active Ni NPs via exciting conduction band electrons to higher energy levels and enhancing local electromagnetic field. Then the activated Ni catalytic center could abstract hydrogen form 2-butanol and cleave three kinds of aryl ethers in lignin through transfer hydrogenolysis.The present thesis provides a useful reference for designing new bio-affinity organic-inorganic composite photocatalysts for trace environmental pollutants treatment and bioresources conversion and also new research ideas for studying visible light photocatalytic mechanism. |
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