Synthesis of Crumpled Graphene and Titanium Dioxide Based–Nanomaterials and the Application to Carbon Dioxide Photoreduction

With the rapid development of the economy, increasing combustion of fossils fuels has caused an increase in the atmospheric carbon dioxide (CO2) level, and has led to global climate change. As a mitigation approach, CO2 capture and conversion (CCC) can not only capture CO2, but also convert it to useable products, such as hydrocarbon fuels. Photocatalytic reduction is an attractive CCC option that directly harnesses inexpensive and abundant solar energy. Titanium dioxide (TiO2) is a widely used semiconductor for photocatalysis, and graphene nanosheets are a promising material for use in fabricating graphene-TiO2 hybridized photocatalysts. To realize the application of these materials for CO2 photoreduction, synthesis methods and pertinent material properties need to be investigated. In addition, a simple but practical kinetic model that can predict CO2 photoreduction performance is also needed, not only to save cost, but also to guide synthesis procedures. Research presented in this dissertation bridges scientific and engineering gaps in CO2 photoreduction technologies that incorporate TiO2 with or without graphene materials. The work was conducted in three broad steps: material synthesis, photocatalyst design and testing, and kinetic model development. (1) Synthesis of crumpled graphene-based materials and study of their chemical and physical properties A furnace aerosol reactor (FuAR) was used to synthesize crumpled graphene oxide (CGO) nanoparticles, and their mobility and charging characteristics were systematically investigated. The projected area equivalent diameter was found to be approximately equal to the electrical mobility diameter for the CGO particles, regardless of their morphology. A differential mobility analyzer (DMA) is a convenient and efficient tool to classify CGO particles according to their physical diameters. In the charging characteristics study, Fuch’s theory fits the experimental data better than Boltzmann’s theory for most of the measured charging fractions, indicating that the conductivity of CGO particles plays an important role in affecting their charging characteristics. In addition to studying FuAR synthesized material, we also characterized the carbon material formed as a side product in a NASA plasma reactor for methane post-processing. It was crumpled graphene with a low oxygen content, and was only a few layers in thickness. This crumpled graphene material was used to synthesize the anodes of lithium-ion batteries, which showed high electrochemical performance. (2) Design and performance testing of graphene-TiO2 based CO2 photocatalysts We used a single-step aerosol method to synthesize aminated, reduced graphene-based nanocomposites consisting of crumpled r-GO with encapsulated TiO2 nanoparticles, thus creating open core-shell nanostructures (referred to as CGOATI). Furthermore, we synthesized TiO2/nitrogen doped reduced graphene oxide (NrGO) composites by a one-step urea-assisted hydrothermal method. Both two types of N-modified graphene-TiO2 materials were used for simultaneous gas-phase CO2 adsorption and photoreduction. The mechanisms of graphene and N modification in enhancing the CO2 photoreduction performance were investigated systematically. Aerosol chemical vapor deposition (ACVD) was used to synthesize TiO2 thin films with columnar morphologies. To increase the CO yield of this columnar TiO2, oxygen vacancies and Ti-related defects (OTDs) were generated by applying electric potential to TiO2 under UV irradiation. We gained a mechanistic understanding of the formation and healing of these OTDs, and of enhanced CO2 photoreduction by defective TiO2 (TiO2-x) with electric potential. (3) Kinetic model development and CO2 photoreduction performance prediction We developed a kinetic model of gas-phase CO2 photoreduction over TiO2 thin films in a continuous flow reactor, considering three aspects: 1) light activation, 2) surface adsorption of reactants and products, and 3) reaction kinetics. The reaction rate constants were estimated by fitting the model with the experimental data, and used to further predict the CO yield for TiO2 thin films with different morphology parameters. This work identifies and addresses several key issues regarding the synthesis of (crumpled) graphene-TiO2 based materials for CO2 photoreduction. The findings and conclusion from this work, will impact such fields as the aerosol processing of materials, and the morphology design of photocatalysts

Distortional Buckling Experiment on Cold-Formed Steel Lipped Channel Columns with Circle Holes under Axial Compression

The objective of this paper is to research the distortional buckling mode and load-carrying capacity of cold-formed thin-walled steel columns with circle holes in web. Compression tests were conducted on 26 intermediate length columns with and without holes. The test members included four different kinds of circle holes. Test results show that the distortional buckling occurred for intermediate columns with holes and the strength of columns with holes was less than that of columns without circle hole. The ultimate strength of columns decreased with the increase of the total transverse width of hole in cross-section of members. For each specimen, a shell finite element Eigen-buckling analysis and nonlinear analysis was also conducted. Analysis results show that the holes can affect on the elastic buckling stress of columns. The shell finite element can be used to model the buckling modes of columns with holes and analyze the load-carrying capacities of members with holes. The comparison on ultimate strength between test results and calculated results using Chinese code GB50018-2002, North American specification AISI S100-2016 and nonlinear Finite Element method was made. The calculated ultimate strength show that results predicted with AISI S100-2016 and analyzed using finite element method are close to test results. The calculated results using Chinese code is higher than test results because Chinese code has no provision to calculate the ultimate strength of members with holes. So the calculated method for cold-formed steel columns with circle holes was proposed. The calculated results using this proposed method show good agreement with test results and can be used in engineering design of cold-formed steel columns with circle hole

Cell surface-specific N-glycan profiling in breast cancer

Aberrant changes in specific glycans have been shown to be associated with immunosurveillance, tumorigenesis, tumor progression and metastasis. In this study, the N-glycan profiling of membrane proteins from human breast cancer cell lines and tissues was detected using modified DNA sequencer-assisted fluorophore-assisted carbohydrate electrophoresis (DSA-FACE). The N-glycan profiles of membrane proteins were analyzed from 7 breast cancer cell lines and MCF 10A, as well as from 100 pairs of breast cancer and corresponding adjacent tissues. The results showed that, compared with the matched adjacent normal tissue samples, two biantennary N-glycans (NA2 and NA2FB) were significantly decreased (p <0.0001) in the breast cancer tissue samples, while the triantennary glycan (NA3FB) and a high-mannose glycan (M8) were dramatically increased (p = 0.001 and p <0.0001, respectively). Moreover, the alterations in these specific N-glycans occurred through the oncogenesis and progression of breast cancer. These results suggested that the modified method based on DSA-FACE is a high-throughput detection technology that is suited for analyzing cell surface N-glycans. These cell surface-specific N-glycans may be helpful in recognizing the mechanisms of tumor cell immunologic escape and could be potential targets for new breast cancer drugs