| During the past few years, our major energy resources still originate from limited and non-renewable fossil fuels, such as coal, oil and natural gas. However, the combustion of these fossil fuels has caused a series of critical environmental problems, ranging from air and water contamination to global warming. Therefore, water splitting under sunlight has received much attention for production of renewable hydrogen from water on a large scale. Solar hydrogen will play an important role in prospective sustainable-energy societies because it is storable, transportable and can be converted into electricity efficiently using fuel cells whenever it is necessary.The advanced hierarchically nanoarchitectures of semiconductors TiO2, ZnO, CeO2and WO3can all act as photoactive materials for redox/charge-transfer processes due to their electronic structures which are characterized by a filled valence band and an empty conduction band.The exploration of synthetic techniques for the fabrication of hierarchically nanostructured materials having controllable morphologies has emerged as a fast-growing subfield of nanotechnology research. Advanced functional materials incorporating well defined nanoarchitectures have shown great potential for nanotechnological applications, such as miniaturized nanoelectronics, ultrafast quantum computing, high-density memory/data storage media, ultrasensitive chemical sensing/biosensing, and generation of high-efficiency catalytic substrates. However, the production of such materials remains a great challenge for materials scientists. In the meanwhile, nature exploits sustainable methods for creation of materials with sophistication, hierarchical organizations, function hybridization, miniaturization, environment-resistance and adaptability on the nanoscale for a variety of applications. Replicating these nature’s designs faithfully reproduced over millions of years presents perhaps the most straightforward route to success.Biomimicking including mimicking natural structures, functions, mechanisms, and/or the wholesystem rises as a bio-inspired strategy for the facile fabrication of materials with hierarchical biomorphic-structures. In this paper, we employed this low-cost and environmentally benign routed to prepare ceria with biomorphic structures for photocatalytic water splitting into hydrogen and oxygen, which has become a promising strategy for converting solar energy into clean and carbon-neutral H2fuel. A series of novel functional biological materials are designed to achieve some fantastic properties by introducing natural biomaterials with the certain components and special hierarchical structures into relevant bio-inspired synthesis. The main contents and conclusions are shown as follows:In this study, the petals of lotus, rose, and field poppy petals were used as templates to fabricate biomorphic cerium oxide. The products were characterized by XRD, HRTEM, FESEM, ESEM, AFM and Nitrogen adsorption-desorption measurement. The results reveal the biomorphic CeO2derived from petal was composed of ultrathin layers with the thickness less than5nm; The ceria microspheres was synthesized by using diatoms, lotus pollen, bacteria as templates. The characterizing results show the products were accumulated of cerium oxide nanocrystals, which formed hierarchical macro-meso porous structure; The CeO2microtubes were obtained by using lens cleaning paper, egg membrane, and fungal hypha as templates. From the characterization, we found that the morphology of biomorphic ceria faithfully replicated the original structure of the template. The ceria derived from fungal hypha contained considerable ultrathin films due to replication of cell wall. This study proposes a biomimetic synthetic mechanism of biomorphic ceria, both from the perspective of biology and chemistry.On the basis of the preparation of the material, the further investigation of XPS spectra of nine kinds of biomorphic ceria were analyzed. From the analysis results, the concentration of oxygen vacancies grows with the increase of Ce3+ratio and nitrogen-doped amount. Ultrathin CeO2films also improve the concentration of oxygen vacancies, especially the film with thickness of less than4nm. The H2-TPR analysis displays the CeO2nanoparticles are well dispersed. The shift of reduction peak temperature shows the enhancement of its catalytic activity. Similarly, UV visible diffuse spectra also show the red shift of absorption edge with the increase of the amount of doping nitrogen, oxygen vacancies and the structure of ultra-thin layers. Calculated from the UV curve, the bandgap of biomorphic CeO2derived from fungal hypha is2.85eV. The narrowing of the bandgap is attributed to the ultrathin film consisting of3.57nm, a high concentration oxygen vacancies and nitrogen doping amount. This new catalytic materials displays the best photocatalytic performance for degradation of methylene blue under visible light irradiation.Photolytic water splitting result of biomorphic CeO2ultrathin layers, microspheres, microtubes showed that the increase of oxygen vacancies and doping nitrogen would efficiently improve the performance of hydrogen production. This is attributable to multiple gradient energy levels which were introduced into CeO2band gap by oxygen vacancies and N2p. Consequently, the electron transition and generation of hydrogen become easy. Among obtained biomorphic CeO2, the ceria derived from fungal hypha achieve the best photolytic water performance, the hydrogen production reached378μmol/g after420min. It is not only because of its ultra-thin film structure with thickness of about3.57nm, but also a high concentration of oxygen defects and nitrogen doping. It’s consistent with the results of the analysis of UV, TPR and XPS. |
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