| Inspired by the miscellaneous forms of biologic species in nature, a surface sol-gel and its derived methods has been developed as a novel process of biotemplating to synthesize metal oxides with sophisticated morphological and structural ordering analogous to biologic species. Although the surface sol-gel process is characterized in the aspects of high efficiency, simple procedure and multi-scale replication, the commonly use of the highly reactive precursor of metal alkoxides still makes it challengeable for facile and precise replication of the biotemplates with metal oxides. To overcome the shortcomings of the surface sol-gel and its derivative methods, a facile, versatile and easily controlled two-step surface precipitation approach using an inorganic metal salt as a precursor has been developed in our lab to faithfully replicate micro-fibrous oxides from biologic fibers composed of chicken feather and cotton. The new method is demonstrated by nano-precision replication of alumina fiber with biologic fibers of chicken feather.In recent years, photocatalytic degradation of dyes in industrial wastewaters has received increasingly attention as an effective and environmentally benign technology, and the development of high-performance catalyst is the key factor for its large-scale application. Results indicate that the surface morphology and structural defects of the photocatalyst such as CuO are main factors in determining its catalytic performance.Based on the thus mentioned understandings, in this thesis, the following works have been carried out for the photocatalytic degradation of dyes in wastewaters by synthesizing special morphological oxides. Firstly, to further prove the validity of the two-step surface precipitation approach developed in our lab, metal oxides of CuO, NiO, CeO2, and SnO2are synthesized by using silk, wool, and micro crystalline cellulose as biotemplates, respectively. The ultraviolet (UV) photocatalytic degradation of dyes of the synthesized oxides are investigated by using methyl orange as a model compound, and the morphology, structure, and catalytic performance are correlated. Secondly, CuO/cotton composites are prepared via a low-temperature hydrothermal method by using cotton as a biotemplate and Cu(NO3)2as a precursor of CuO. The composites are evaluated for the UV photocatalytic degradation of methyl orange, and the synthesis parameters such as temperature, duration, and precursor concentration are optimized. Under optimal hydrothermal conditions, the composites of NiO/cotton, CeO2/cotton, and SnO2/cotton are prepared with the low-temperature hydrothermal method. Finally, the kinetics of the UV photocatalytic degradation of methyl orange are compared for these composite catalysts. The main works and conclusions are as follows.1. By using silk, wool, and micro crystalline cellulose as biotemplates, metal oxides of CuO, NiO, CeO2, and SnO2are synthesized with the precursors of Cu(NO3)2, Ni(NiO3)2, Ce(NiO3)3, and SnCL4, respectively, via the two-step surface precipitation method. The structure and morphology of the oxides are characterized by XRD and SEM. Morphology observation results indicate that all the microstructure of all the oxides is a nano-precision replication of the biotemplates, which confirms the versatile validity of the new approach. As revealed from XRD results, irrespective of the types of biotemplates and their presence or not, all the NiO or CeO2show the same crystal structure. However, in comparison with those synthesized without any biotemplates, the crystallinity and crystalline size of NiO and CeO2prepared with biotemplates are much smaller.2. By using a500W UV lamp and initial concentration of aqueous methyl orange Co=20mg/L, the photocatalytic performance of the biotemplated CeO2and NiO are evaluated. Results indicate that the photocatalytic activity of CeO2is much higher than that of NiO. Moreover, the templates used for the synthesis of the oxides have a significant impact on the catalytic activity of the oxide. Among all the oxides investigated, the CeO2templated by microcrystalline cellulose show the highest catalytic activity.3. Under largely varied hydrothermal conditions, i.e., temperatures of40-120℃, hydrothermal time of12-48h, a series of CuO/cotton composites are hydrothermally synthesized by using Cu(NO3)2as a precursor. All the composites are dried at80℃for12h. The UV photocatalytic degradation of methyl orange of the composites is investigated, and correlated with the preparation parameters of the composites. From XRD characterizations, the following phenomena can be observed:(1) There is no crystalline CuO formed on the cotton surface when the hydrothermal temperature is lower than90℃;(2) The crystalline CuO is formed on the cotton surface and its crystallinity is increased when the hydrothermal temperature is increased from95to120 ℃;(3) Even under the severest hydrothermal conditions applied, i.e.,120℃for24h, the crystal structure of cellulose is still well preserved, but its crystallinity is slightly decreased. For all the CuO/cotton composites, SEM results indicate that small particulates of CuO are evenly distributed on the cotton surface. From the results of the photocatalytic degradation of methyl orange, the composite synthesized at120℃for24h give the highest activity. Moreover, the catalytic activity per mass CuO in the CuO/cotton composite is much higher than that of the pure CuO synthesized without template, and the UV photocatalytic degradation of methyl orange over CuO/cotton follows the pseudo first-order kinetics.4. For comparison, NiO/cotton, Ce02/cotton, and SnO2/cotton composites are synthesized under optimized hydrothermal conditions, i.e.,120℃for24h, by using Ni(NO3)2, Ce(NO3)3, and SnCl4as a precursor, respectively. Interestingly, NiO/cotton and CeO2/cotton composites show very similar performance for the UV photocatalytic degradation of methyl orange, which is much higher than that of SnO2/cotton composite. However, all the composites show the zero-order kinetic behavior. |
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