Study On The Synthesis And Performance Of Hierarchical Biomorphic Functional Materials

Nowadays, functional materials with multi-dimension, multi-component, and multi-function, have developed and attracted more attention because of their potential for excellent and fascinating properties. Those guide lines bring more challenges for the design and preparation of this category of novel functional materials. In the progressive stage, the investigations and developments of the hierarchical functional materials are proceeding slowly, ascribed to the complexities of materials design, construction, and fabrication. However, natural organisms or biological structures with highly complex and elegant mechanisms give materials and chemistry scientists a great inspiration for the construction of hierarchical biostructures. It is based on the premise that amphiphilic and bioorganic macromolecules could be exploited for tailoring elaborate structures through the self-assembly of nanoscaled units to engender new functional properties. Noteworthy, the bio-inspired approach in aqueous systems has been developed into a promising fabrication technique for functional nanomaterials.In this dissertation, a series of novel functional inorganic materials with the predetermined morphologies are designed to achieve some fantastic properties by introducing natural biomaterials with the certain components and special hierarchical structures at the multi-scale into relevant bio-inspired synthesis. The main contents and conclusions are shown as follows:The biomaterials silk fibroin fibers (SFF) and eggshell membrane fibers (ESM) were infused into silver nitrate and palladium chloride solution at room temperature, espectively, to actualize the extracellular nucleation of noble metal nanocrystallites and in situ assembly into hierarchical nanostructures on the biofibers. Silver nanoparticles with the size of 10 nm and floriated nanoclusters with the size of 30 nm were formed on the basis of different precursor concentrations. 3⁴ nm palladium nanocrystallites were assembled into about 30 nm nanoclusters arraying porous pearl-necklace chains along ESM by controlling the reaction time. The synthesis was mainly based on the in situ reduction of metal ions by SFF tyrosine or some amido groups of ESM biomacromolecules, the directing and templating action also play important roles. As concerning the formation of Ag nanoparticles on SFF substrate, the reductive capabilities of amino acid tyrosine of SFF were enhanced under the alkaline conditions. Thus, Ag (I) ions could be reduced to Ag (0) and form Ag nanoclusters. The morphologies of silver nanoclusters were mostly attributed to the concentration of silver nitrate solution as well as special configurations and structures of silk fibroin macromolecules.Based on the synthesis of functional nanoparticles by the biogenic technique, the effects of hierarchy to the fabrications are further investigated. Herein ESM chosen as the biotemplates were separated from the CaCO3 shell of commercial eggs, cut into small sheets with about 2 cm in length, 1 cm in width and 5-10μm in thickness. The target materials were synthesized by immersing ESM sheets into the precursors and attending by relevant heat treatment. Herein the synthesis of biomorphic SnO₂ or TiO₂ hierarchy can be separated into two steps: the formation of amorphous Sn-gel or Ti-gel precursors adhered to the template ESM during the dipping pretreatment, and the crystallization of oxide films by the appropriate calcination treatment during the removal of ESM templates. The short-chained amino acids of ESM ingredients, e.g. glycoprotein, also function as the capping agents for the control on the growth of oxides nuclei. The biotemplating synthesis was also detailedly investigated by altering precursor category, concentration, and medium pH value, calcination temperature, heating rate, etc., on the nucleation, the growth, the assembly, the BET surface, and relative pore distribution of mesoporous materials. Similar procedures can be extended to the synthesis of other hierarchical metallic oxide nanomaterials, such as, ZnO, Co₃O₄, and PdO. As-synthesized these hierarchical oxides at 550°C had all retained the conformations of the natural ESM to present 3D interwoven porous morphologies. In addition, these building unit nanocrystallites exhibited diverse morphologies and had a narrow size distribution with an average crystallite size of 5 nm for ZnO, 9 nm for Co₃O₄, 11 nm for PdO, and with the pore distribution of 20 nm, 30 nm, and 80 nm, respectively.Hierarchical nanocomposite films, containing Pd-PdO nanoclusters being anchored uniformly on the inner surface of titania nanotubes, were achieved through a stepwise bioredox/artifical sol-gel approach involving ESM as the template. The Pd content ratio of Pd-PdO loading could be arbitrarily varied from 0 to 53 wt %, and the size of the Pd-PdO clusters was about 30-40 nm. The thickness of single TiO₂ tube of Pd-PdO/TiO₂ nanocomposites could be adjusted from 400 nm to 30 nm by the control of concentration, reaction time, and soakage cycles of Ti-sol medium. Calculated from the multi-point BET method, the specific surface area of the target nanocomposites Pd-PdO/TiO₂ was about 151 m2/g with a narrow pore-size distribution ranging from 2 to 3 nm, and the ESM-morphic nanocomposites Pd-PdO/TiO₂ exhibit porous and multi-phasic features, which facilitate light transport and molecule accessibility to the active site during photocatalytic reactions.The properties of as-synthesized hierarchial nanomaterials were investigated extensively. It was found that ESM-morphic SnO₂ nanomaterials have the good selectivity for liquefied petroleum gas (LPG) with the working temperature above 300°C while for ethanol below 270°C. The gas sensitivities of the target SnO₂ were significantly about 3-6 times higher than that of the corresponding ones involving no ESM biotemplates. The photocatalytic activities of as-prepared TiO₂ and Pd-PdO/TiO₂ nanocomposites were determined by the degradation of rhodamine B under ultraviolet radiation. It was found that the photocatalysis depended more on reagent concentration, dosage, and preparation conditions of target nanomaterials. As-synthesized hierarchical TiO₂ with highest degradation efficiency of rhodamine B (20mg/L) could be obtained under the conditions, namely with the dosage of 140 mg/L, the medium pH range of 1-3, and the ultraviolet radiation time of 70 min. The photocatalytic properties of the target TiO₂ were twice as the usual materials. The Pd-PdO/TiO₂ composites with the ratio of 10 wt % TiO₂ (5 wt % Pd of Pd-PdO loading) presented high degradation efficiency of 99.3% and performed a good stability when measured at the second and third run (about 95.3% and 94.6%). Herein, the as-prepared hierarchical SnO₂ and TiO₂ nanomaterials were proved to have the perfect gas sensing and photocatalytic performance, respectively. The bio-inspired routes to hierarchical functional nanomaterials can provide the exploration and accumulation for the development and application of advanced functional materials, further put up the important theories and give directions for the relative research fields.