Bio-Inspired Synthesis And Optical Properties Of Biotemplate-Based Nanocomposites

Optical nanomaterials are widely used in biology, medical, computer science, and so on. Usually, optical nanoparticles are combined with matrix materials, like modification components and substrate structures, in order to obtain smart and multifunctional nanocomposites. However, there are some problems in dealing with these nanocomposites, for instance, the synthesis of nanoparticles requires harsh conditions, the hybridization process is complicated, and the pattern of nanostructures is limited. In this field, nature has some valuable solutions via millions of years'evolution. One is biocomponents: the active biocomponents in organisms could direct the synthesis and assembly of nanoparticles under mild environment, and form natural nanocomposites with excellent properties. The other is biostructures: nature has created all kinds of multifunctional biostructures, some of which are still hardly achieved artificially. Inspired by nature, people directly take biomasses as the templates to fabricate novel functional materials. Since biocomponents and biostructures have several advantages, the bio-inspired idea is supposed to accomplish simplified fabrication routes as well as novel functional materials with subtle nanostructures and attracting properties.Based on these investigations, we suggest that biomasses can serve as the templates to fabricate optical nanomaterials. Owing to the active biocomponents and subtle structures of biomasses, this process might give a solution to the above mentioned problems. In detail, active biocomponents can direct the synthesis and assembly of nanoparticles, which simplify the fabrication process. Then, they may modify the nanoparticles to improve the biocompatibilities. And the subtle biostructures could provide solid substrates and give additional optical properties to the final products. Therefore, the bio-inspired fabrication of optical nanocomposites would bring new opportunities to functional materials. The main contents and results are as follows:1. In situ synthesis of chalcogenide nanoparticles on silk fibroin fibers Reactive silk fibroin fibers (SFF) were chosen as the biotemplates to direct the in situ synthesis and assembly of the typical optical materials CdS nanoparticles (nano-CdS), in order to investigate whether the bio-inspired fabrication route is suitable for optical nanomaterials.We proposed a room-temperature facile process to synthesize and assemble nano-CdS on SFF, producing solid products nano-CdS/SFF and liquid products nano-CdS/silk fibroin (SF) dispersed in CaCl2 solution. During the process, SFF provided reactive sites, served as solid substrate, as well as assembled nanoparticles. As-prepared CdS were hexagonal phase nanocrystallites with diameters that proportional to the immersing time and inverse proportional to the S-precursor concentration (range: 3.8~7.9 nm). Nano-CdS could be assembled into nanoparticle strings and hexagons by SFF, which was also influenced by the immersing time and S-precursor concentration. The optical properties of the nanocomposites can be controlled by the nanoparticles'size and assembly patterns. The absorption edge and the band-edge fluorescence emission of the products were blue-shifted as nano-CdS became smaller. CdS nanoparticle strings performed fluorescence emission similar to that of separate nano-CdS, while CdS nanoparticle hexagons displayed red-shifted and broadened fluorescence emission compared with that of separate nano-CdS. This investigation demonstrated that it is possible to in situ synthesize and assemble nano-CdS on SFF under mild condition, which was the basis of the flowing works.2. Oxide nanoparticles/SFF(SF) biocompatible optical nanocomposites Based on the investigation of chalcogenide nanoparticles/SFF nanocomposites, the bio-inspired process was further introduced to fabricate optical nanocomposites with potential applications in biomedical fields. In this case, we used SFF to direct the fabrication of nano-ZnO, which were chosen for their nontoxicity and long wavelength visible photoluminescence. Then, as prepared nano-ZnO were directly modified by biocompatible SF. We proposed a facile route to obtain solid products nano-ZnO/SFF and liquid products nano-ZnO/SF. During the process, SFF provided reactive sites, served as solid substrate, as well as controlled the shape and defects of nanoparticles, while experimental conditions influenced the distribution of nano-ZnO. As-prepared ZnO were mainly hexagonal phase spherical nanoparticles with average diameter around 13 nm. The solid products appeared white under sunlight, and emitted orange-yellow phosphorescence centered around 600 nm with persisting time >0.1 ms under the UV excitation <370 nm. Their UV resistance was better than original SFF's. The liquid products combined the optical functionalities of nano-ZnO as well as the biocompatibilities of SF. They displayed orange under UV illumination, and didn't perform distinct cytotoxicity. Thus, nano-ZnO/SF might be used as bioimage labels. The above investigations have potential applications in biomedical fields.3. Semiconductor nanoparticles/natural photonic crystals novel nanocomposite photonic crystalsBased on the experience of using solid biomasses SFF to synthesize semiconductor nanoparticles, the bio-inspired process was further introduced to fabricate novel nanocomposite photonic crystals (PhCs) with potential applications in nanoscaled optical devices. In this case, unobtainable subtle natural PhC structures were taken as the solid biotemplates to direct the synthesis and ordered assembly of optical nanoparticles, which resulted in novel nanocomposite PhCs with superior abilities of controlling visible light.We proposed a relatively facile route to obtain nano-ZnO/feathers nanocomposites. During the process, the original active sites of feathers played important role to form homogeneously distributed hexagonal phase nano-ZnO. The particle size was proportional to the solvothermal reaction time (range: 8.5 to 13.5 nm). Due to the interaction between nanoparticle and feather keratin, nano-ZnO performed a visible defect emission. Also, we proposed the"activation-in situ synthesis-solvothermal"fabrication route to obtain nano-CdS/natural PhCs. During the process, natural PhCs gained additional active sites by the activation step, then directed the in situ synthesis of CdS seeds and ordered assembly of nano-CdS, finally provided solid substrate for the self-sustainable products. As-prepared nano-CdS were mainly cubic phase nanocrystallites with diameter around 6 nm. By taking diverse scales and adjusting procedure factors, the assembly patterns of nano-CdS/wings could be controlled at two levels: one was the PhC structures (>100 nm), the other was the nano-CdS small clusters (<100 nm). The obtained novel nanocomposite PhC had superior abilities of controlling visible light. Their reflection properties could be tuned by changing PhC styles and parameters, as well as detecting directions, which were inherited from natural PhCs. In addition, they were also influenced by nano-CdS loading amounts. The reflectance at longer wavelength decreased as nano-CdS loading amounts increased. Moreover, the reflection spectra of nano-CdS/feathers 2D nanocomposite PhCs revealed the optical interaction between nano-CdS and natural PhCs. The reflection properties of nano-CdS/Papilio Paris butterfly matched the features of typical 1D PhCs. Nano-CdS/Euploea mulciber butterfly displayed subtle structures and attractive"shining-dim"phenomenon. In addition, the primary simulations of the reflection spectra agreed with the experimental results. The above investigations provided novel composite systems"semiconductor nanoparticles/ natural PhCs"as well as design inspirations to the PhCs research fields.In this thesis, we systematically investigated the bio-inspired synthesis and optical properties of the novel optical nanocomposites constructed by natural biomasses and semiconductor nanoparticles. It is proven that the active and biocompatible components in natural biomasses could facilitate the fabrication of nanomaterials. And it is observed that the optical interaction between nano-CdS and natural PhCs exists in the nanocomposites. Moreover, it is achieved that as-prepared nanocomposites perform ordered nanostructures and specific optical properties that are hardly obtained by usual way. This work provides new ideas and new solutions to the design and fabrication of functional nanocomposites.