The effect of N-methyl Morpholine N-Oxide (NMMO), 1-ethyl-3-methyl-imidazolium acetate ([Emim]Ac) and 1-ethyl-3-methyl-imidazolium diethyl phosphate ([Emim]DEP) on pretreatment and enzymatic hydrolysis of dissolving pulp was studied. X-ray diffraction measurements of regenerated cellulose from these solvents showed that solvent pretreatment reduces the crystallinity of cellulose. However, crystallinity might not be a major factor affecting the in-situ enzymatic hydrolysis of cellulose in these solvents. Although regenerated cellulose from [Emim]DEP showed the lowest crystallinity index (~15%), in-situ enzymatic hydrolysis of cellulose dissolved in NMMO showed the highest cellulose conversion (68% compared to 65% for [Emim]Ac and 37% for [Emim]DEP at enzyme loading of 122 FPU/g). Moreover, results showed that enzymes could tolerate up to NMMO concentration of 100 g/L and still yield full conversion of cellulose. Since it is not necessary to remove all the NMMO, less amount of water will be required for the washing step and thus the process will be more economical. The HCH-1 model was used in an attempt to model the enzymatic hydrolysis of cellulose in NMMO. With the incorporation of NMMO inhibition and a factor to account for unreacted cellulose, the model was able to correlate the experimental data of the enzymatic hydrolysis of cellulose (6.68 g/L) at various NMMO concentrations (0, 50, 100, 150 and 250 g/L). However, the experimental results also suggest that NMMO might be deactivating the enzymes rather than inhibiting them. More studies need to be done at varying cellulose, NMMO and enzyme concentrations to find the exact nature of this deactivation of NMMO. / A Thesis submitted to the Graduate School in partial fulfillment of the requirements for the degree of Master in Science. / Summer Semester, 2012. / April 23, 2012. / Includes bibliographical references. / Subramanian Ramakrishnan, Professor Directing Thesis; John Collier, Committee Member; John Telotte, Committee Member; Eric Hellstrom, Committee Member.

In order to obtain an increased through-thickness thermal conductivity in carbon fiber reinforced composites, a novel method using heterogeneously structured resin with conductive filler was studied. Samples were produced using an alternating line pattern deposition of a highly concentrated silver-resin mixture and the neat resin. Microstructures and properties of the resulting composites were compared to those of a homogeneously dispersed filler matrix composite of similar loadings. Two different sets of pattern sample composites were produced using similar methods, but one used a manually deposited pattern method of depositing the resin, and the other used a dispenser. Both produced repeatable results which were comparable to each other, but the dispenser allowed for more uniform line deposition. The thermal diffusivity and conductivity of the resultant composites were measured by use of the LFA 457 Microflash device, and tensile and flexural tests were also conducted to obtain their mechanical properties. The results show that using a heterogeneously structured resin matrix with conductive filler on the composite leads to a significant increase in thermal conductivity over the homogeneous counterpart of the same loading, and an even greater increase over the neat carbon fiber/epon 862 composite. Through-thickness thermal conductivity in excess of 5 W/m K was obtained by using a 9 wt% silver loading heterogeneous composite. Also the mechanical properties of higher filler loading composites were comparable between the heterogeneously structured matrix and the homogeneously structured matrix composites. / A Thesis submitted to the Program in Materials Science in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester, 2012. / April 20, 2012. / Carbon Fiber, Composites, Heterogeneous, Silver, Thermal Conductivity, Through-Thickness / Includes bibliographical references. / Zhiyong Liang, Professor Directing Thesis; Tao Liu, Committee Member; James Brooks, Committee Member.

After nearly seven years of research effort since the discovery of iron-based superconductors, wires and tapes of K-doped BaFe2As2 have finally been developed by the inexpensive and scalable powder-in-tube technique with critical current densities reaching over 0.1 MAcm-2 at 4.2 K. Such progress relies heavily on the development of synthesis techniques that eliminate cracks and secondary phases. High energy ball milling, during which mechanochemical reactions take place, proves to be effective in producing high quality bulk material. The consolidation of high quality powders under high pressure produces bulk material with a fine grain microstructure and surprising high intergranular current density. We explore the dependence of doped Ba2Fe2As2 superconducting properties on sintering temperature in bulks, wires, and tapes to further optimize these materials and find that grain boundaries continue to act as weak-links, effectively blocking current, and limiting the intergranular critical current density in these materials. However, evidence for composition variation and impurity segregation across grain-boundaries suggests that the weak-linked behavior may still be of an extrinsic nature. Despite the current limiting effects of these weak-links, transport current is high enough in our fine grain material to demonstrate the first > 1 T magnet made out of an iron-based superconductor. These results provide a positive outlook for the potential future use of these materials to produce high field magnets. / A Dissertation submitted to the Department of Materials Science and Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2015. / April 9, 2015. / Ba122, ferropnictide, mechanochemical, superconductivity, superconductor / Includes bibliographical references. / Eric Hellstrom, Professor Directing Dissertation; Gregory Boebinger, University Representative; David Larbalestier, Committee Member; Theo Siegrist, Committee Member; Per Arne Rikvold, Committee Member.

As research progresses towards nanoscale materials, there has become a need for a more efficient and effective way to obtain ultra-thin samples for imaging under transmission electron microscope (TEM) for atomic resolution analysis. There are various methods used to obtain thin samples (<50 nm in thickness). However, most of the resultant TEM images of soft materials, such as CNT/epoxy composites, are of poor quality due to the sample cutting difficulties. Such poor quality samples are characterized by uneven sample thicknesses, objective overlapping, overall darkness due to large thickness, and defects such as cutting scratches. This research is a continuous effort to study and improve the ultra-microtome cutting technique to provide an effective and reliable approach of obtaining an ultra-thin (25-50 nm) cross section of a CNT/polymer composite for high resolution TEM analysis. Improvements were achieved by studying the relationships between the chosen cutting parameters, sample characteristics and TEM image quality. From this information, a cutting protocol was established so that ultra-thin sample slices can be achieved by different microtome operators for high resolution TEM analysis. In addition, a custom tool was created to aid in the sample collection process. In this research, three composite samples were studied for both microtome cutting and TEM analysis: 1) Unidirectional (UD) IM7/BMI composite; 2) Single-layer CNT buckypaper (BP)/ epoxy nanocomposite; 3) 3-layer CNT BP/BMI nanocomposite. The resultant TEM images revealed a clear microstructure consisting of amorphous resin and graphite crystalline packing. UD IM7/BMI composite TEM results did not reveal an interfacial region resulting in a need for even thinner sliced cross sections. TEM results for the single-layer CNT BP/epoxy nanocomposite revealed the alignment direction of the nanotubes and numerous stacks of CNT bundles. In addition, there was visible flattening of CNT packing into dumbbell shapes similar to results obtain by Alan Windle. TEM results for the 3-layer CNT BP/BMI nanocomposite revealed uniformly cut resin. However, when the diamond knife reached graphite crystalline regions, the nanotube either became deformed into a cone-like structure, was cut at a thicker thickness than the resin, or folded over onto itself. This is most likely a result of the nanotubes high mechanical properties in response to the stress of cutting. / A Thesis submitted to the Material Science and Engineering Program in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester, 2014. / April 11, 2014. / Carbon Nanotube, Nanocomposites, TEM, Ultra Microtome / Includes bibliographical references. / Richard Liang, Professor Directing Thesis; Okenwa Okoli, Committee Member; Mei Zhang, Committee Member.

The BaLn(sub)2(/sub)O(sub)4(/sub) family has been synthesized successfully as single crystals by the flux-growth method. The phases crystallize in the CaV(sub)2(/sub)O(sub)4(/sub) structure prototype in space group Pnma (# 62). The structure has been studied using single-crystal x-ray diffraction, and stoichiometry confirmed with EDS, and the unit cell parameters and atomic positions have been determined for the whole lanthanide series (with the exception of the Lu compound). The effects of the lanthanide ionic radius on the atomic positions in the unit cell has been studied in terms of fractional atomic coordinates, bond lengths and angles, and bond valence sums. Magnetic measurements have been performed on the series with the exception of the La, Eu, and Lu members in the form of susceptibility versus temperature. The crystals all show signs of geometric antiferromagnetic frustration with the Néel temperatures significantly below the temperature predicted by the Weiss constant. Additionally some members of the family, namely BaCe(sub)2(/sub)O(sub)4(/sub), BaNd(sub)2(/sub)O(sub)4(/sub), BaPr(sub)2(/sub)O(sub)4(/sub), BaSm(sub)2(/sub)O(sub)4(/sub), BaTb(sub)2(/sub)O(sub)4(/sub), and BaYb(sub)2(/sub)O(sub)4(/sub) show significant crystal field splitting, that causes deviation from Currie-Weiss behavior / A Thesis submitted to the Interdisciplinary Program in Materials Science in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester, 2014. / July 21, 2014. / Includes bibliographical references. / Theo Siegrist, Professor Directing Thesis; Susan Latturner, Committee Member; Sachin Shanbhag, Committee Member.

Metal flux synthes is a useful alternative method to high temperature solid state synthesis; it allows easy diffusion of reactants at lower temperatures, and presents favorable conditions for crystal growth. A mixed flux of calcium and lithium in a 1:1 ratio was explored in this work; this mixture melts at 300°C and is an excellent solvent for main group elements and CaH₂. Reactions of p-block elements in a 1:1 Ca/Li flux have produced several new intermetallic and Zintl phases. Electronegative elements from groups 14 and 15 are reduced to anions in this flux, yielding charge-balanced products. More electropositive metals from group 13 are not fully reduced; the resulting products are complex intermetallics. The reactions of tin or lead and carbon in Ca/Li flux produced the analogous phases Ca₁₁Tt₃C8 (Tt = Sn, Pb) in the monoclinic C21/c space group (a = 13.2117(8) Å, b =10.7029(7) Å, c = 14.2493(9) Å, β = 105.650(1)° for the Sn analog). These compounds are carbide Zintl phases that includes the rare combination of C₃⁴ and C₂² units as well as Sn⁴ or Pb⁴ anions. Ca/Li flux reactions of CaH2 and arsenic have produced the Zintl phases LiCa₃As₂H in orthorhombic Pnma (a = 11.4064(7), b = 4.2702(3), c = 11.8762(8) Å), and Ca13As6C0.46N1.155H6.045in tetragonal P4/mbm (a = 15.7493(15), c = 9.1062(9) Å). The complex stoichiometry of the latter phase was caused by incorporation of light element contaminants and was studied by neutron diffraction, showing mixing of anionic sites to achieve charge balance. Ca/Li flux reactions with group 13 metals have resulted in several new intermetallic phases. Reactions of indium and CaH₂ in the Ca/Li flux (with or without boron) formed Ca₅₃In₁₃B₄₋ₓH₂₃(2.4 < x < 4.0) in cubic space group Im-3 (a = 16.3608(6) Å) which features metallic indium atoms and ionic hydride sites. The electronic properties of this "subhydride" were confirmed by ¹H and ¹¹⁵In NMR spectroscopy. Attempts to replace boron with carbon yielded Ca₁₂InC₁₃₋ₓ, (Im-3, a = 9.6055(8)Å) which contains C34- units. A very similar phase, Ba12InC18H4 (Im-3,a = 11.1415(8) Å), was grown from the reaction of indium, carbon, and LiH in Ba/Li flux. This compound also includes C₃⁴ units. Preliminary Ca/Li flux reactions of aluminum with other main group elements have produced several new phases: a hydride clathrate Ca₃₁Al₂H₂₅ in cubic Fd-3m (a=18.0835(15) Å), Ca24Al2(C1-xHx)N2H16 in tetragonal P42/nmc (a=15.9069(12) Å, c=13.7323(10) Å, and Ca4Al2N5 in orthorhombic Pna2₁ (a = 11.2331(1) Å, b=9.0768(8) Å, c=6.0093(5) Å. / A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester, 2014. / September 25, 2014. / Acetylide, Allenylide, Boride, Carbide, Hydride / Includes bibliographical references. / Susan Latturner, Professor Directing Dissertation; Albert Stiegman, Committee Member; Igor Alabugin, Committee Member.

This thesis examines the nanoscale morphology evolution during AlN and InN thin film growth. We used synchrotron-based real-time grazing-incidence small-angle X-ray scattering (GISAXS), in order to study the plasma-assisted atomic layer epitaxy (ALEp) process. The substrate for deposition was single-crystal GaN. We designed the load lock and other parts for the experiment, then performed experiments at the National Synchrotron Light Source-II of Brookhaven National Laboratory. Post-facto X-ray Diffraction (XRD), X-ray Reflection (XRR), Scanning Electron Microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDS), and Transmission Electron Microscopy (TEM) were performed at Boston University. In addition, Kinetic Monte Carlo (KMC) simulations were performed to compare with the synchrotron x-ray studies

To address the problem of low energy conversion efficiency in DSSC, a lot of ways have been applied to improve the light scattering and electrons transport abilities of photoanode. However, few have studied fabricating TiO2 nanowires on diatom frustules as photoanode material. To make better experimental design for the successful growth of TiO2 nanowires on diatom frustules with thermal evaporation method, a COMSOL Multiphysics model focused on the gas flow, heat transfer and mass transport based on momentum, energy, mass conservation equations was built to simulate the process of Ti vapor transport in a CVD furnace. The time required for a complete distribution of Ti vapor to reach steady state was estimated, Ti vapor concentration and flux variation with the change in experimental conditions, such as heating temperature, tube pressure and Ar flow rate were studied as well. The numerical simulation results indicated that higher heating temperature and higher tube pressure caused a higher Ti vapor concentration and flux along the tube, while higher Ar flow rate caused a higher Ti vapor flux but a lower concentration along the tube. With this model, growth characteristics of TiO2 nanowires on diatom frustules can be explained numerically. / 2021-05-07T00:00:00Z

Fluorinated alkoxide ligands, including perfluoropinacol (H2pinF), have been investigated for their ability to support high oxidation status for 3d transition metals. Molybdenum is a 4d transition metal used for its catalytic effect in nature as well as in industry. Three new Mo pinF -containing anions [MoO3(pinF)]2-, [Mo2O4(μ2-O)(pinF)2]2-, [Mo2O2(μ-O)2(pinF)2]2- have been synthesized and structurally characterized. The pinF ligands have been found to stabilize both monomeric and dimeric Mo(V) complexes and a dimeric Mo(VI) complex. These compounds can be further studied to look for catalytic redox reactions, and for potential understanding of the rates and mechanism of catalysis. Algal blooms are environmentally hazardous phenomena that cause major damage to aquatic ecosystems. One factor responsible for this effect is the overuse of nitrogen-based fertilizers that has led to accumulation of nitrate (NO3-) in open waters. Nitrate is a nutrient for algae, and when algae proliferate too quickly it causes hypoxia of water. Cu is a well-known catalyst for the electrocatalytic reduction of NO3- and Sn is known to promote selectivity for N2 as the final product of NO3- reduction. The catalytic effect of CuSn alloys for the reduction of nitrate and nitrite have been studied to find the optimum Cu to Sn ratio for this application. It was found that a ratio of 1:1 resulted in the highest peak catalytic current but still less than pure Cu. Additionally, deposition methods on a glassy carbon electrode (GCE) were optimized. It was found that Cu-Sn co-deposition on GCE by controlled potential electrolysis (CPE) was found to be most stable when surfactant K3citrate was added to the deposition solution. Analysis of the final products of NO3- reduction through a microcolorimetric assay was inconclusive and requires further optimization to obtain meaningful data.

Since the discover of graphene in 2004, two-dimensional (2D) materials have gained tremendous attention because of their distinctive properties relative to their bulk form. Particularly, transition metal dichalcogenides (TMDs) and 2D transition metal carbides and nitrides (MXenes) have shown promising applications in flexible electrical and optoelectronic devices. Due to the atomically thin nature, the electronic band structures of these materials are very sensitive to the small changes in the lattice and the surface functionalization, offering a dimension to tune the properties of the materials. In this thesis, approaches to functionalize monolayer WSe2 and MXene were explored. The as-grown chemical vapor deposition (CVD) monolayer WSe2 flakes were treated by plasma assisted doping method. Specifically, Methane plasma was used as carbon dopant source to introduce p-type lattice doping into monolayer WSe2. In addition, chemical reactions between perfluorophenylazides (PFPA) organic molecules and WSe2 flakes were conducted where the PFPA molecules may covalently bonded to the WSe2 surface. Similarly, the PFPA functionalization was applied to MXene, an emerging 2D material with high conductivity. Shifts and intensity change were observed in Raman spectra after the functionalization, indicating structural and electric structure changes might be introduced. Further characterizations of the structures and electric properties will be taken in the near future.