Uses of electrochemical systems in environmental control technology are described for the removal and separation of metals from solution and the destruction of dye molecules in effluents. A novel concentrator cell system for the removal of lead and cadmium from solution is developed. The operation of this system permits the pH-independent recovery of metals from solution by electrodeposition. The formation of complexes with suitable ligands is exploited to achieve the separation of metals by electrochemical methods. The separations of tin, lead and indium from each other, the separation of nickel from cobalt and the separation of copper and palladium from cobalt are used to illustrate the benefits of complex formation. A three-compartment electrodialysis cell for removal of nickel from cobalt exploiting the greater stability of the nickel-EDTA complex compared with the Co-EDTA complex is described. Efficient removal of nickel from cobalt can be achieved but there is a compromise between cobalt purity and the percentage of cobalt transferred to the catholyte chamber for recovery. The anodic oxidation of a number of dye molecules including methylene blue, acid blue 25, reactive blue 2 and reactive blue 15 in chloride solution has been studied. The anodic oxidation of methylene blue results in the formation of seven neutral and two charged intermediates. The main intermediate is identified by X-ray diffraction crystal structure determination and accurate mass spectrometry as the novel compound 4,6-dichloro-7-dimethylamino-3H-phenothiazin-3 -one, (C14HjoCI2N20S) formed by replacement of one of the diirnethylamino groups of methylene blue with oxygen accompanied by regiospecific chlorination of the carbocylic system. The mass spectra of other intermediates formed are interpreted in terms of this structure. An electroadsorption system combining adsorption and electrolytic processes to achieve the elimination of the chlorinated compounds that are formed during the electro-oxidation of methylene blue is also reported.

Copper vapour laser (CVL) pumped dye lasers offer a source of high power, kilohertz repetition rate, tunable narrow-bandwidth radiation suitable for many spectroscopic applications in the visible and infra-red. Furthermore, the nonlinear frequency conversion of CVL-pumped dye laser radiation extends the wavelength range of these laser sources into the blue and ultra-violet. A series of experimental investigations have been undertaken to gain a physical understanding of the fundamental parameters necessary for the optimization of the CVL-pumping of dye lasers. Issues addressed include the influence of the CVL cavity design, the pump beam polarization and geometry, the dye oscillator cavity design, the choice of grating materials, and the dye flow rate. A model based on the rate equation analysis of the kinetic processes relevant to optical amplification in dye lasers has been developed, and the results have been used to design amplifiers with extraction efficiencies in excess of 45 %. As a result of the aforementioned investigations, three commercially available pulsed dye lasers have been successfully optimized for CVL-pumping for the first time. Once modified, these dye lasers have typically shown conversion efficiencies in excess of 20%, with frequency bandwidths as narrow as 800MHz, and beam qualities approaching the diffraction limit. The theory of second harmonic generation is reviewed, and a suite of corresponding computer models have been developed to form the basis for a coherent experimental investigation of UV generation using the CVL and CVL-pumped dye lasers. CVL SHG has been demonstrated in jS-barium borate (BBO) and lithium triborate (LBO), with SHG efficiencies in excess of 18% realized for the CVL 511nm line in BBO. For the first time, an experimental comparison of spherically and elliptically focused second harmonic generation has been undertaken. Optimized elliptical focusing is found to be up to 30% more efficient than using conventional spherical focusing in agreement with theoretical predictions. The superior divergence and transverse coherence of CVL-pumped dye lasers, in comparison to those of the CVL, is reflected in the SHG efficiencies achieved in BBO, LBO and lithium iodate. Conversion efficiencies approaching 40% have been demonstrated in lithium iodate, with harmonic conversion coefficients approaching 2400mW/W2 realized at low input powers. The Boyd and Kleinman theory of SHG with focused Gaussian beams is found to provide an excellent description of SHG with CVL-pumped dye laser radiation, and accurately predicts the optimum strength of focusing and harmonic conversion coefficient. For the first time, sum frequency mixing (SFM) of the CVL with a dye laser has been demonstrated, and found to provide a potentially efficient source for tunable UV radiation. Finally, the application of CVL-pumped dye lasers to resonant ionization mass spectrometry and tropospheric hydroxyl (OH) radical detection is discussed, and the spectroscopic potential of a frequency doubled CVL-pumped dye is demonstrated by recording the absorption spectrum of OH at 308nm.

No description available.

Thesis (MVisArts)--University of South Australia, 2001

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 76-78). Also available via the Internet.

Despite offering relatively high conversion efficiencies, dye-sensitised solar cells using liquid electrolytes containing either I-/I3 - redox couple or Co2+/Co3+ redox couple suffer from durability problems, such as electrode corrosion and electrolyte leakage. Replacements for liquid electrolytes have been extensively studied, but the efficiencies of the resulting devices remain low. One of the factors that limit the efficiency is the sensitising dye. Large sized hole-transport material results in poor pore-filling and thus leads to a fast back electron recombination that reduces the effective electron diffusion length to few micrometeres. The optimal TiO2 layer thickness (2 μm) for maximal power conversion in solid-state dye-sensitised solar cell is much smaller than the 6-10 μm layer thickness required for quantitative light absorption by many dye molecules. Thus, dyes that can absorb in both visible and near-IR region with high extinction coefficient are needed. In order to achieve this, novel oligomers and ruthenium (II) complexes are designed, synthesized and studied as sensitisers for both liquid state and solid state dye-sensitised solar cells in this thesis. Series of ‘donor-free’ dyes including oligo(3-hexylthiophene) (oligo-3HT) (Chapter 3) and oligo(4,4-dihexyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene) (oligo-CPDTs) (Chapter 4) functionalized with cyanoacrylic end groups are easily synthesized using cross-coupling. They were fully characterised through electrochemical, spectroscopic and computational techniques, showing versatile colour-tuning, as well as outstanding absorption coefficients up to 75000 M-1cm-1. Liquid and solid-state DSSCs device performances are studied and discussed in terms of the dye structures. These dyes are effective sensitisers for liquid-state and solid-state dye-sensitised solar cells, although they do not contain a typical donor group, thus open a new strategy of designing dyes in the future. New dyes containing different azo ligands as an additional chromophore moiety to enhance light harvesting of Ru complexes (Chapter 5) have been prepared using a protection/deprotection strategy that allows for convenient purification. The absorption spectrum of the dyes showed an enhanced light harvesting compared to the N719 dye that lacks the azo ligand and electrochemical study also showed properties suitable for application as sensitisers in DSSCs. Following hydrolysis, the complexes were investigated in DSSCs, with performance investigated using I-V measurements. Poor performance was observed and we attribute this as mostly likely due to poor charge injection due to short excited-state lifetime. Although the application of these current dyes in DSSCs is not feasible due to their poor performance, this study allowed us to determine the positions of the HOMO and LUMO orbitals and correlate it to the π-acidity of the dyes.

Previous studies of distributed feedback dye lasers (DFDL's) have identified that the linewidth of the device scales, to a first approximation, with the level of pumping employed. A more recent development is that the DFDL can be used to produce single ultrashort pulses. To produce such pulses the main requirement is that the laser is operated close to its threshold. An apparent contradiction exists here since, by lowering the pump power to achieve narrow linewidth operation, the near threshold region must be avoided since pulsing operation acts to increase the linewidth (to at least the Fourier transform of the pulse duration). This thesis further investigates the mechanisms which contribute to the temporal and linewidth properties of the laser. It is identified that by judicious choice of operating conditions a regime exists where the DFDL may be operated with a linewidth approaching that of the transform limit for the nanosecond pulse durations involved. After introducing the different types of distributed feedback lasers the thesis first reviews previously understood DFDL behaviour. Different DFDL geometries are considered with a view to their particular temporal and linewidth properties. A strategy for the development of a narrow linewidth DFDL is presented. The experimental laser system is described detailing the operation and characteristics of the frequency doubled Q switched Nd:YAG pump laser and the two different DFDL geometries. A high resolution computer aided interferometry (CAIN) system is described which provided single shot linewidth measurements. This system was used extensively in the experiments reported. DFDL linewidth is seen to depend on the thermo-optical properties of the dye's host solvent and as such a full characterization of commonly used solvents is presented. The temporal behaviour of the laser is considered theoretically with the aid of a coupled rate equation model which describes the interplay between the population inversion and the cavity photon flux. The model is used to predict short (picosecond) and smooth (nanosecond) pulse operation of the laser. Finally, a description of and the results obtained from various experimental investigations into the DFDL are presented. Temporal analysis, using a streak camera, revealed that, as expected, under certain circumstances multiple pulsing of picosecond duration could occur. Different conditions however, lead to narrow linewidth (~100 MHz) operation. A description of the two operating regimes is presented and these are related to the particular parameters involved e.g. the grating length or the level of pumping employed.

This thesis describes the design and development of a frequency doubled, continuous wave dye laser and its application to a study of the high Rydberg states of Rubidium. The laser uses the dye rhodamine 6G as the active medium and is optically pumped with an argon ion laser. Frequency doubling is by an ADA (ammonium dihydrogen arsenate) or ADP (ammonium dihydrogen phosphate) crystal located within the laser cavity. Continuous output powers in the ultra-violet in excess of 30 mW and tunable over the wavelength range 285-315 nm have been produced. The linewidth can be chosen to be 0.02 nm broadband system) or 0.002 nm (narrowband system) depending on the frequency selecting elements used. In order to keep insertion losses small the crystals have optical faces cut at Brewster's angle, and in order to increase generation efficiency the intracavity radiation field is focused into the crystal. Such an arrangement introduces the aberrations of coma and astigmatism which must be compensated by suitable cavity design. A variety of cavity and crystal configurations have been analysed for aberrations, and a novel arrangement for the simultaneous elimination of coma and astigmatism developed. Several practical frequency doubled dye lasers have been investigated. In particular the performances of ADA and ADP as the frequency doubling crystals are compared and contrasted. ADA has the advantage that it can be non-critically phase matched at these wavelengths and this results in a higher generation efficiency and a better UV beam quality than encountered with ADP. However, since it can only be temperature tuned, the tuning range (292-302 nm for temperature range 20-80°C) is more limited than that for ADP (285-315 nm) which can also be angled tuned. For both types of crystal, thermal phase mismatching is identified as the process limiting generation efficiency. Evidence is also presented that thermal focusing ultimately limits the UV output power by upsetting cavity stability. A computer model of intracavity frequency doubling has been developed. Thermal phase mismatching effects in the crystal as well as excited state absorption in the dye are included. This model is used to investigate the influence of cavity losses and crystal absorption on generation efficiency. Optimization of conversion efficiency by correct choice of crystal parameters is considered. Two systems have been developed to allow continuous scanning over an extended frequency range. One allows the broadband laser (0.02 nm) to be continuously tuned over 3 nm, the other allows the narrowband laser (0.002 nm) to be continuously tuned over 2 nm. The operation of a single frequency version of the laser and its stabilization on an external reference cavity is also described. The excitation of high Rydberg states in Rubidium using the frequency doubled laser is described. The states are detected by a space-charge limited ionization detector. The principal series of Rb up to a principal quantum number of n = 74 has been detected. A novel triode arrangement of electrodes in the space charge detector has enabled a small electric field to be applied to the rubidium vapour. The consequent Stark mixing of n2S, n2P and n2S states has allowed the n2S and n2D states to be excited from the 52S ground state. New term values of the n2S and n2D series are reported.

Doctor of Philosophy / Department of Chemistry / Ping Li / Dye-decolorizing peroxidases (DyPs) comprise a new family of heme peroxidases, which have received much attention due to their potential applications in degradation of lignin and anthraquinone dyes. In this research, studies of two types of DyPs are carried out and reported in the following three sections. The first section includes the identification and characterization of class-A TcDyP from Thermomonospora curvata, a thermophilic actinomycete found in composted manure. The TcDyP was found to be highly active toward a wide range of substrates including phenolic lignin model compounds. Transient- and steady state- kinetics involving wild-type (wt) and mutant TcDyPs revealed that Asp220 and Arg327 are essential for compound I formation and reduction of compound II to resting state is the rate-limiting step. Additionally, replacement of His312 and Arg327 shifted the redox potential (E°′) to a more negative value. In the second section, the residues involved in the radical generation and substrate oxidation were explored. TcDyP contains 7 tryptophans and 3 tyrosines, which are the likely candidates of protein radicals and substrate oxidation sites. Crystal structure of TcDyP solved at 1.75Å revealed Trp263, Trp376 and Tyr332 as surface-exposed protein radical sites. Further studies using site-directed mutagenesis, steady-state and stopped-flow kinetics determined that the Trp263 is also one of the surface-exposed substrate oxidation sites. The Trp376 was characterized as the residue essential for covalent crosslinking of the enzyme units and an off-pathway electron sink. The highly conserved Tyr332 was found to be unimportant for substrate oxidation due to its extremely narrow surface exposure. The final section involves mechanistic study of a class-B DyP from Enterobacter lignolyticus (ElDyP), a bacterium capable of growing on lignin anaerobically. The crystal structure of ElDyP revealed the presence of two heme access channels measuring at ~3.0 and 8.0 Å in diameter and a water molecule as the sixth ligand to the heme center. Bisubstrate Ping-Pong mechanism was found operational in the catalytic cycle of ElDyP, in which conformational change of the enzyme resting state was proposed as the final step and the rate limiting step in the presence of ABTS. Microscopic events leading to Compound I formation was analyzed using D₂O₂. A kinetic isotope effect (KIE) of 2.4 at pD 3.5 suggested that Compound 0 is formed initially with protonation/deprotonation as the rate-limiting step. Compound I was directly reduced to the enzyme resting state via a 2-electron process, for which the rate increases as the pH decreases. Based on viscosity effect and solvent KIE (sKIE) with the reducing substrate, aquo release was found to be mechanistically important. Distal aspartate was proposed as the key residue that modulates the acidic pH optimum in Compound I reduction. These findings will pave the way for engineering DyPs for their applications in the degradation of lignin and synthetic dyes.

The dynamics of ultrashort pulse generation and amplification in dye lasers is studied in this dissertation. In particular, we have developed general semiclassical models for ultrashort pulse dye laser amplifiers and oscillators. These models start from Maxwell’s equation for the electric field and density matrix equations for the active laser medium. A finite coherence time or phase memory time of the molecular wave functions, a finite vibrational relaxation time for the lower electronic state of the dye laser transition, an isotropic molecular orientational distribution, and an arbitrary pump polarization are all taken into account. Based on these models, specific topics that are discussed herein include pump polarization effects, timing and detuning studies in synchronously pumped mode-locked dye lasers, and amplification of ultrashort pulses in dye laser amplifiers. Properties such as pulse width, pulse shape, pulse intensity, pulse stability, pulse amplification efficiency, etc., are studied in detail.