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Adsorption of boric acid on pure and humic acid coated amorphous-aluminum hydroxide : a Raman and XANES spectroscopy studyXu, Dani 28 November 2006
The fate and mobility of boric acid in the environment is largely controlled by adsorption reactions with soil organic matter and soil minerals to form surface complexes (Marzadori et al., 1991; Su and Suarez, 1995; Yermiyahu et al., 1995; Peak et al., 2002). The effects of humic acid (HA) and dissolved CO2 on boric acid adsorption on amorphous (am)-Al(OH)3 were investigated as their influence on sorption is potentially important. Although a model system was used in the studies, the findings should be generally useful to better understand the mobility and bioavailability of boric acid in the soil ecosystems.<p>In this dissertation, boric acid adsorption on pure am-Al(OH)3 and 5% w/w HA coated am-Al(OH)3 were investigated both as a function of pH (4.5 11) and initial boric acid concentration (0 4.5 mmol L-1). Batch adsorption isotherm experiments were also conducted with samples exposed to atmospheric CO2 and anaerobic (N2) conditions to examine the effects of dissolved CO2 on boric acid adsorption. Both the pH envelope and the adsorption isotherm experiments showed that the HA coating on am-Al(OH)3 and the presence of dissolved CO2 decreased boric acid adsorption. <p>Raman spectroscopy and boron (B) K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy were used to investigate the coordination of boric acid adsorbed at mineral/water interfaces. The Raman spectroscopy was less successful than expected as there were difficulties in identifying B bands in the 5% w/w HA coated am-Al(OH)3 samples.<p>The B K-edge XANES spectroscopy yielded better results. The XANES spectra of boric acid adsorption samples showed that both trigonal BO3 and tetrahedral BO4 coordinated complexes are present on the pure and HA coated mineral surfaces. At pH 7.0 and 9.2, the adsorption of boric acid on am-Al(OH)3 is predominantly inner-sphere trigonal complexes; with minor amounts of inner-sphere tetrahedral complexes. Both macroscopic and spectroscopic experiments revealed that the combination of HA coating on am-Al(OH)3 and dissolved CO2 decreased boric acid adsorption compared to adsorption on pure am-Al(OH)3.<p>The discoveries in this dissertation contribute significantly in understanding the effects of HA and dissolved CO2 has on boric acid adsorption in the environment. Since B speciation and the stability of am-Al(OH)3 mineral and HA changes with pH, the bioavailability of B is expected to change as well with pH. The adsorption on boric acid on am-Al(OH)3 and/or HA coated am-Al(OH)3 is expected to decrease the amount of boric acid available to plants. Therefore the nutrient management regimen will have to be modified for soils that are high in natural organic matter, carbonate and/or aluminum hydroxyl species.
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Computational Study of Electronic and Transport Properties of Novel Boron and Carbon Nano-StructuresSadrzadeh, Arta 24 July 2013 (has links)
In the first part of this dissertation, we study mainly novel boron structures and their electronic and mechanical properties, using ab initio calculations. The electronic structure and construction of the boron buckyball B80, and boron nanotubes as the α-sheet wrapped around a cylinder are studied. The α-sheet is considered so far to be the most stable structure energetically out of the two dimensional boron assemblies. We will argue however that there are other sheets close in energy, using cluster expansion method. The boron buckyball is shown to have different possible isomers. Characterization of these isomers according to their geometry and electronic structure is studied in detail. Since the B80 structure is made of interwoven double-ring clusters, we also investigate double-rings with various diameters. We investigate the properties of nanotubes obtained from α-sheet. Computations confirm their high stability and identify mechanical stiffness parameters. Careful relaxation reveals the curvature-induced buckling of certain atoms off the original plane. This distortion opens up the gap in narrow tubes, rendering them semi-conducting. Wider tubes with the diameter d 1.7 nm retain original metallic character of the α-sheet. We conclude this part by investigation into hydrogen storage capacity of boron-rich compounds, namely the metallacarboranes. In the second part of dissertation, we switch our focus to electronic and transport properties of carbon nano-structures. We study the application of carbon nanotubes as electro-chemical gas sensors. The effect of physisorption of NO2 gas molecules on electron transport properties of semi-conducting carbon nanotubes is studied using ab initio calculations and Green’s function formalism. It is shown that upon exposure of nanotube to different concentrations of gas, the common feature is the shift in conductance towards lower energies. This suggests that physisorption of NO2 will result in a decrease (increase) in conductance of p-type (n-type) nanotubes with Fermi energies close to the edge of valence and conduction band. Finally we study the effect of torsion on electronic properties of carbon nano-ribbons, using helical symmetry of the structures.
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Development of a Kinetic Monte Carlo CodePedersen, Daniel January 2013 (has links)
A framework for constructing kinetic monte carlo (KMC) simulations of diffusive events on a lattice was developed. This code was then tested by running simulations of Fe adatom diffusion on graphene and graphene-boron nitride surfaces. The results from these simulations was then used to show that the modeled diffusion adheres to the laws of brownian motion and generates results similar to recent research findings.
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Adsorption of boric acid on pure and humic acid coated amorphous-aluminum hydroxide : a Raman and XANES spectroscopy studyXu, Dani 28 November 2006 (has links)
The fate and mobility of boric acid in the environment is largely controlled by adsorption reactions with soil organic matter and soil minerals to form surface complexes (Marzadori et al., 1991; Su and Suarez, 1995; Yermiyahu et al., 1995; Peak et al., 2002). The effects of humic acid (HA) and dissolved CO2 on boric acid adsorption on amorphous (am)-Al(OH)3 were investigated as their influence on sorption is potentially important. Although a model system was used in the studies, the findings should be generally useful to better understand the mobility and bioavailability of boric acid in the soil ecosystems.<p>In this dissertation, boric acid adsorption on pure am-Al(OH)3 and 5% w/w HA coated am-Al(OH)3 were investigated both as a function of pH (4.5 11) and initial boric acid concentration (0 4.5 mmol L-1). Batch adsorption isotherm experiments were also conducted with samples exposed to atmospheric CO2 and anaerobic (N2) conditions to examine the effects of dissolved CO2 on boric acid adsorption. Both the pH envelope and the adsorption isotherm experiments showed that the HA coating on am-Al(OH)3 and the presence of dissolved CO2 decreased boric acid adsorption. <p>Raman spectroscopy and boron (B) K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy were used to investigate the coordination of boric acid adsorbed at mineral/water interfaces. The Raman spectroscopy was less successful than expected as there were difficulties in identifying B bands in the 5% w/w HA coated am-Al(OH)3 samples.<p>The B K-edge XANES spectroscopy yielded better results. The XANES spectra of boric acid adsorption samples showed that both trigonal BO3 and tetrahedral BO4 coordinated complexes are present on the pure and HA coated mineral surfaces. At pH 7.0 and 9.2, the adsorption of boric acid on am-Al(OH)3 is predominantly inner-sphere trigonal complexes; with minor amounts of inner-sphere tetrahedral complexes. Both macroscopic and spectroscopic experiments revealed that the combination of HA coating on am-Al(OH)3 and dissolved CO2 decreased boric acid adsorption compared to adsorption on pure am-Al(OH)3.<p>The discoveries in this dissertation contribute significantly in understanding the effects of HA and dissolved CO2 has on boric acid adsorption in the environment. Since B speciation and the stability of am-Al(OH)3 mineral and HA changes with pH, the bioavailability of B is expected to change as well with pH. The adsorption on boric acid on am-Al(OH)3 and/or HA coated am-Al(OH)3 is expected to decrease the amount of boric acid available to plants. Therefore the nutrient management regimen will have to be modified for soils that are high in natural organic matter, carbonate and/or aluminum hydroxyl species.
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Synthesis of Boron-Containing Carbon Nanotubes Catalyzed by Cu/£^- Al2O3Chen, Yun-chu 07 September 2011 (has links)
Boron-doped carbon nanotubes are predicted to behave as semiconductors over a large range of diameters and chiralities and might thus constitute a suitable class of material for nanoelectronics technology. Boron-doped CNTs were reported as by-products when BC2N nanotubes were prepared by an arc-discharge method. The potential doping of CNTs with different kinds of atoms might provide a mechanism for controlling their electronic properties. We have synthesized boron-doped carbon nanotubes (CNTs) directly on copper catalyst by decomposition of B(OCH3)3 in chemical vapor deposition method. The results were characterized and analyzed by scanning electron microscopy (SEM), Raman, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), solid-state NMR and TGA.
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Study on growth mechanism and characteristics of transparent conductive boron doped diamond thin filmsYeh, Kuan-Hung 28 November 2012 (has links)
This thesis presents the fabrication of transparent conductive Boron-Doped CVD diamond (BDD) thin film with the appropriate processing parameters. The BDD shows the transmittance in the visible wavelength and good electrical conductivity. The depositing rate of Diamond films yields 0.37 £gm per hour with Hydrogen, Argon, Methane and oxygen as gas sources, and B(OCH3)3 was used as the doping source. Microwave plasma chemical vapor deposition (MWCVD) was performed for the BDD deposition. Also, PECVD was applied to grow diamond-like Carbon (DLC) film on silicon as substrate. Through systematical experiments, the influence of carrier gas flow rates of B(OCH3)3, the variation of ratio of Argon, and growth pressure of BDD on the transmittance in the visible light and electrical conductivity has been studied. In addition, dc bias was applied to synthesize diamond films and extend long depositing time shows the stable growth rate of diamond films. The thickness of BDD films increases and acquired more than 60% optical transmittance. BDD samples were analyzed by Raman Spectroscopy for the diamond quality, N & K Analyzer for the film thickness and optical properties. Van Der Pauw I-V Measurement and Hall Measurement were analyzed p-type diamond films carrier mobility, carrier concentration, electrical resistivity.
By increasing Argon and applying negative dc bias can improve the growth rate and transmittance of diamond films. And the quality of diamond films could be improved by the coating of DLC on Si substrates. This work has achieved fabricating a transparent conducting BDD successfully.
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Synthesis, characterization, anion complexation and electrochemistry of cationic Lewis acidsChiu, Ching-Wen 15 May 2009 (has links)
Owing to the favored Coulombic attraction between the ammonium group and
anion which stabilizes the B-F/B-CN bond against heterolysis, cationic borane [25]+ has
great affinity toward anions than its neutral analog, and is capable of capturing fluoride
or cyanide from water under bi-phasic conditions. By placing the fluorophilic silyl
group adjacent to an electrophilic carbocation, a novel fluoride sensor [45]+ was
obtained. Sensing occurs via a fluoride induced methyl migration from the silicon to
adjacent electrophilic methylium center which is unprecedented. As a result of its
strong fluoride affinity, [45]+ is able to react with KF in aqueous media at pH 7.0.
The electrochemistry study of these cationic Lewis boranes reveals that the
cationic character of these boranes serves to decrease their reduction potential and
increase the stability of the resulting radicals. In this part of the research, we have
prepared a cationic borane [27]+, which features two reversible reduction waves at -0.86
and -1.56 (vs. Fc/Fc+) corresponding to the formation of stable neutral and anionic
derivatives. The one-electron reduction of [27]+ leads to the formation of a boron
containing neutral radical featuring an unusual boron-carbon one-electron π bond. Further reduction of 27• results in the formation of the borataalkene derivative [27]-,
which features a formal B=C double bond. The structural changes accompanying the
stepwise population of the B-C π-bond are also determined, and this sequential
population of B-C π-bonding orbital is also supported by theoretical computations.
In order to understand the impact of the cationic nature of these boranes on their
oxidative power, three novel cationic boranes ([34]+, [35]2+, and [36]3+) have been
synthesized and their oxidative power were examined via cyclic voltammetry. The CV
data of these compounds shows that the reduction potential of these triarylboranes is
linearly proportional to the number of the pendant cationic substituents. Substitution of
a mesityl group by an ArN+ group leads to an increase of the reduction potential by 260
mV.
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Amperomotric detection of sulfur-containing amino acids by capillary electrophoresis using boron-doped diamond microelectrodeLiu, Jung-chung 02 August 2004 (has links)
The fabrication and characterization of boron-doped diamond
microelectrodes for use in electrochemical detection
coupled with capillary electrophoresis (CE-EC) is
discussed. They exhibited low and stable background
currents and sigmoidally shaped voltammetric
curves for cysteine, cystine and Fe(CN)63-/4- .
Evaluation of the CE-EC
system and the electrode performance were accomplished
using a 10 mM borate buffer, pH 8.8, run
buffer, and a 70-cm-long fused-silica capillary (10-mm
i.d.) with seven sulfur-containing amino acids
(methionine, cysteine, cystine, homocysyeine, homocystine,
glutathionine, glutathionine disulfide) as test analytes.
Reproducible separation (elution time) and detection (peak
current) of seven sulfur-containing amino acids were observed with response precisions of 5% or less.
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(1) Synthetic Application of 4-Hydroxypiperidine (2) Synthetic Application of 4-HydroxyprolinePai, Chun-Li 08 June 2006 (has links)
We present the synthetic studies of coerulescine, horsfiline, and
streptorubin B in this report. And we also present the new
synthesis of 3-arylpyrrolines and cis-3,4-diarylpyrrolidines via
an easy and straightforward pathway in this report. All of these
researches are using 4-hydroxypiperidine and 4-hydroxyproline
as the starting material.
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Growth of Boron-doped Diamond Films on Porous Silicon by Microwave Plasma Chemical Vapor DepositionChuang, Yao-Li 27 June 2003 (has links)
Synthetic diamond thin films have potential for fabricating high-temperature semiconducting and optical devices because of its extraordinary properties. In this work, a microwave plasma chemical vapor deposition system has been setup. A two-steps deposition process will be applied for the growth of boron-doped diamond on silicon and on porous silicon. The effects of temperature, microwave power and of doping concentration of B2O3 have been studied by varying the growth parameters. The doping source of B2O3 solved in C2H5OH is applied with carrying gas of Ar. To vary the concentration of boron with the flow of Ar is controlled mixing into a reaction gas of CH4 and H2 mixture. Polycrystalline diamond thin films are examined by Raman, XRD and FTIR. In the SEM photograph a nano-wires structure has been found for higher doping of B2O3. A higher temperature the growth rate of the boron-doped diamond films will increase and the shape of crystallites will tend to polycrystalline. The diamond growth is in multi steps and the mechanism of deposition will change when the boron-doped diamond film grows up to a critical thickness. In this work a smooth diamond film was successfully grown on porous silicon without the step of nucleation.
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