Versatilities of Multifunctional Nanomaterials for Energy Applications From Renewable to Conventional
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CitationLei, Yu. 2015. Versatilities of Multifunctional Nanomaterials for Energy Applications From Renewable to Conventional. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractThe biological materials are the versatile scaffolds to fabricate functional nanomaterials. There is an increasing trend of applying the functional nanomaterials in energy applications ranged from conventional sources to renewables. In my early attempts of research, the M13 bacteriophage is used as a versatile bio-scaffold for the fabrication of nanomaterials. In this study, photocatalytically active perovskite strontium titanate (SrTiO3) nanowires are fabricated for the first time using genetically engineered AEEE–M13 phage and metal alkoxide precursors. One newly developed doping approach with an ammonia gas treatment efficiently produced strontium titanate nanowires, which split water and produce hydrogen under visible-light irradiation. The optical absorption of nitrogen doped strontium titanate can be tuned by varying the processing conditions, and lies in the visible spectrum range when treated at 625oC – 650oC. XPS results show that nanowires treated under ammonia flow between 625°C and 650°C have high nitrogen content. The excellent hydrogen evolution rate of these nanomaterials is correlated with both optical absorption and nitrogen doping level. This doping approach is expected to provide a new pathway for the fabrication of other visible-light active photocatalysts including tantalates. Beside to the anodic material, bismuth vanadium oxide (BVO4) nanowires as a cathode is synthesized in a similar method. This material is characterized by XPS, XRD, and TEM to confirm the formation of preferred crystallinity and size. The full reaction of water splitting has been tested by applying both materials and the initial results prove both nanowire materials can sustain for long time without any degradation while maintaining high performances.
The electrocatalytic reduction of carbon dioxide by using SrTiO3 and TaON phage template nanowires is unique and innovative approach. Meanwhile, in the research, they have been proven to be more effective than any other bulk catalysts. Controlling the morphology and crystallinity of the electrocatalysts provides the new opportunities to produce various kinds of products including carbon monoxide, formic acid, methanol, ethanol, and methane. In research, we are capable to generate selective products by choosing the catalysts and varying the experimental conditions.
Expended from the M13 bacteriophage bio-scaffold, a new biological functional nanomaterial is studied in my second project. DNA is biological ready-made sensor, and it is also small, customizable, and adaptive. The second project aims to develop new tools to improve the process of conventional energy extraction. More specifically, the research focuses to use functional nanomaterials to protect and delivery surfactants during the enhanced oil recovery (EOR). In order to recover hard-to-access oil, surfactants are pumped underground to help release the oil. The delivery area is large and it can take several weeks for the surfactant to reach the oil, which leads to dilution of and loss of the surfactant when it sticks to rocks. In order to improve the oil-to-surfactant yield, a controlled delivery method is of interest. In this project we are developing methods based on biological approaches for delivering surfactants to underground oil fields using nanoparticles that are stable for several weeks under high temperature and high salt conditions. We are using both biomimetic approaches mimicking structures such as diatoms and calcium based algae as well as genetic engineering to build high surfaces area biological sponges to act as surfactants.
Motivated from previous project, the same microparticle system encapsulates various kinds of DNA is designed and fabricated for the underground detection to further improve the process of petroleum extraction. Inorganic microparticles containing various DNA segments were designed to be tracers that are used to identify the oilfield’s underground tunnel formations. CaCO3 is designed to encapsulate DNA nanoparticles. In order to prove the existence of DNA inside of particles after the synthesis, confocal imaging is taken on the fluorescence-label DNA particles, and the positive evidences of DNA that is inside of the particles is observed. After releasing the particle by dissolving the shell, the method of PCR is taken to amplify the DNA population and the gel electrophoresis is used to identify the size of DNAs. The same DNA strand that is initially encapsulated into the particle is confirmed as a result. Hence, it proves that the system of nanoparticle encapsulating the DNA is a successful application in the purpose as proposed.
Many useful applications derived from the same encapsulation platform are studied and developed. More specifically, various DNA nanostructures are explored and encapsulated in the microparticles. The size control of microparticles is revisited to fulfill specific needs of the different applications. In addition, the particle buoyancy or density is engineered in order to improving the recyclability of the sensors from the aqueous media. The ability of encapsulation is also extended beyond various structures of nucleotide strands. In a few experiments, encapsulations of the gold nanoparticles and upconverting nanoparticles have been proven successfully. These extend the range of applications based on the functional materials inside that enable optical, biological, and environmental functions. Imaging techniques are improved to direct visualize the existence of specific structures. The adoption of typhoon provides a sensitive detection of low concentration of DNA. PAGE gel, compared to agarose gel that is introduced in previous chapter, is used to ensure a better separation among various structured macromolecules and hence a better resolution. DNA nanostructures act as the fundamental sensors responding to pH, ionization, and temperature changes. Learned many valuable insights from previous researches, with proper modifications, we propose new methods of fabricating sensors that allows people to detect the environments that currently no technology can do so.
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