Nonlinear optical properties of Sn(IV) phthalocyanines: experimental and theoretical approach
- Authors: Louzada, Marcel Severiano
- Date: 2017
- Subjects: Phthalocyanines , Nonlinear optics
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/57852 , vital:26996
- Description: This work presents the nonlinear properties of six Sn(IV) Phthalocyanines. Three of the phthalocyanines are linked by an alkylthiol substituent and the rest are linked with a phenoxy substituent. For all six compounds non-linear optic analysis was carried out in four solvents: chloroform, toluene, dichloromethane, and tetrahydrofuran, and their differences were recorded. Calculation of the linear, singlet excited, triplet excited and two photon absorption cross-sections were also carried out and the results compared. To form a comparison the first order hyperpolarizabilities, DFT calculations were also performed and the results compared to see if the behaviour between the two properties can be predicted using DFT.
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- Date Issued: 2017
Template-assisted sol-gel synthesis of carbon doped titanium dioxide nanotubes and their characterization
- Authors: Takata, Nwabisa
- Date: 2017
- Subjects: Nanotechnology Titanium dioxide Nanostructures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/13194 , vital:39473
- Description: This study reveals the effects of doping on the morphological, structural and optical properties of titanium dioxide (TiO2) nanotubes (TNTs), synthesized by sol-gel template-assisted sol-gel technique. The nanotubes (TNTs) were prepared in anodic alumina membranes (AAM) with a pore diameter range of 110-210 nm by using titanium tetra butoxide as a sol-gel precursor and oxalic acid dihydrate as a dopant source. The synthesized nanotubes were evaluated using scanning electron microscope (SEM), energy dispersive spectroscopy (EDX), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), confocal Raman spectroscopy (CRS) and photoluminescence spectroscopy (PL). SEM analysis has revealed the presence of closely-packed TNTs, with a modal external tube diameters of 150, 170, 210,190 and 210 nm for the un-doped TNTs, 9 mM carbon doped-TNTs (C-TNTs), 27 mM C-TNTs, 45 mM C-TNTs and 75 mM C-TNTs respectively. The diameters are consistent with the AAM diameter range. EDX spectra revealed the presence of Ti peaks at 0.45 and 4.9 keV corresponding to Kα1 and Kβ1 emission lines respectively. Oxygen exhibits a signal at 0.5 keV corresponding to Kα1 emission line. The occurrence of these peaks in the EDX spectra endorses the existence of Ti and O atoms in the prepared titanium dioxide nanotubes. FTIR spectroscopy has revealed the presence of vibration modes at 580-660 cm-1 indicating the presence of Ti-O bonds and additional vibration modes at 2324 cm-1 resulting from C-O stretching in the C-TNTs. The XRD analysis has revealed the presence of a mixed anatase-brookite phase with diffraction peaks at 2θ angles of 25.49⁰, 38.11⁰, 40.60º, 48.14⁰, 54.58⁰, 63.00⁰, 70.11⁰ and 75.66⁰. Additionally, XRD analysis has revealed elongation of lattice parameter “c” from 9.143 to 9.830 Å with carbon concentration increase. Lattice expansion indicates the possibility of carbon substituting oxygen sites. Raman large area scan has revealed the presence of rutile, brookite and anatase for the undoped samples. On doping the rutile phase of TiO2 has shown to be suppressed by the presence of carbon atoms such that the doped samples consist of brookite and anatase phases only. The Eg1 mode of anatase of the undoped TNTs at 153. 78 cm-1 was red shifted by Δ9.78 cm-1 relative to the bulk anatase TiO2. This was attributed to decrease in particle size, presence of brookite and phonon confinement. Upon doping, the 9 mM C-TNTs, 27 mM TNTs and 75 mM TNTs have shown a red shift of Δ0. 09 cm-1, Δ1. 39 cm-1 and 1.81 cm-1 respectively, suggesting the incorporation of carbon in the TiO2 matrix. CRS depth profiling in the XZ direction has also validated the presence of a mixed anatase-brookite phase at Raman active modes 153.19 cm-1, 208.87 cm-1, 404.55 cm-1, 523.26 cm-1 and 648.55 cm-1. Photoluminescence spectra of carbon doped TiO2 showed two emission peaks at 398 nm attributed to annihilation of excitons while the broad peak at 400-460 nm was attributed to the presence of oxygen vacancies. The peak intensity of the 45 mM C-TNTs has shown a lower PL intensity suggesting that efficiency of charge separation was higher and recombination rate was lower than other carbon containing samples.
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- Date Issued: 2017
The potential of hydrellia egeriae rodrigues (diptera: ephydridae) as a biocontrol agent for egeria densa planch. (hydrocharitaceae) in South Africa
- Authors: Smith, Rosali
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/53733 , vital:26314
- Description: The integrity of South Africa’s valuable freshwater ecosystems has been threatened by aquatic invasive plants since the 1900s. Floating aquatic weeds, such as Eichhornia crassipes (C. Mart) Solms (Pondederiaceae), Pistia stratiotes L. (Araceae), Salvinia molesta D.S. Mitchell (Salviniaceae), Azolla filiculoides Lam. (Azollaceae), and the emergent weed, Myriophyllum aquaticum Verdc. (Haloragaceae) benefited from open, nutrient-rich water bodies. Due to the limitations of mechanical and chemical control in aquatic environments, classical biological control has been a huge asset in managing these weeds; consequently bringing them under complete or substantial control. However, submerged aquatic weeds are widely distributed through the aquarium trade in South Africa; facilitating their invasion into new habitats. The removal of surface mats following the successful management of floating weeds has enhanced the growth and competitive ability of submerged aquatic weeds, such as Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae), Myriophyllum spicatum L. (Haloragaceae) and Egeria densa Planch. (Hydrocharitaceae) in South Africa. Of these species, E. densa has become the most widely distributed, invading numerous systems across South Africa. Compared to other exotic submerged aquatic plants, E. densa is the only species capable of inhabiting freshwater systems in every province and therefore, it is vital to manage existing populations and prevent its further distribution and invasion. Hydrellia spp. (Diptera: Ephydridae) biological control agents have been used extensively in the management of submerged aquatic weeds elsewhere, particularly those in the Hydrocharitaceae (Balciunas and Burrows 1996; Wheeler and Center 2001. Hydrellia egeriae Rodrigues (Diptera: Ephydridae) has been identified as a promising candidate for E. densa and was imported into quarantine at Rhodes University, Grahamstown in 2014. The aims of this study were to conduct a pre-release assessment of the potential of H. egeriae as a biological control agent for E. densa in South Africa. The first objective of this study was to establish the life history of the agent under controlled conditions on E. densa found in South Africa, as well as its population growth parameters to predict its invasion success in the field. Secondly, laboratory host-specificity testing was conducted to validate the host range of the agent, in view of published native range host-specificity testing, and to establish potential risks to non-target species, should it be released. Finally, a biological control agent should also effectively reduce the fitness of its host plant, and therefore, impact studies were conducted. Laboratory impact studies have been limited in the past, in that they only investigate agent damage for short ecological periods, thus underestimating the damage capacity of the agent under investigation. Therefore, the damage capacity of H. egeriae was investigated over three consecutive generations in multi-generational impact trials. In a controlled environment of 22 ± 2°C, H. egeriae exhibited the ability to rapidly increase in population size within a short period of time, which will enhance agent establishment and build-up in the field. Host-specificity trials indicated that H. egeriae has a host range restricted to the Hydrocharitaceae, with exploratory feeding and development on Lagarosiphon major Ridley, L. muscoides Harvey and Vallisneria spiralis L. However, only L. major supported agent development during paired larval choice tests, and continuation trials showed that the test species was not physiologically capable of supporting viable agent populations. Risk analysis illustrated that the feeding and reproductive risks that H. egeriae pose to non-target species are very low and therefore, H. egeriae should be safe for release in South Africa. Additionally, significant damage to vital plant structures (shoot growth and side shoot length) was only recorded under high (five larvae) agent abundances. Encouragingly, the number of leaves mined at the end of the experiment was similar for both intermediate (three) and high (five) larval abundances, suggesting that cumulative leaf-mining under intermediate larval abundances has the potential to reduce the fitness of E. densa, given sufficient time. Results from pre-release assessments provide a robust understanding of the specialization of the potential biological control agent to its host plant. Nevertheless, the absolute success of a biological control programme depends on the many factors after prerelease assessments that determine agent establishment, persistence and target weed suppression, e.g. mass-rearing, release protocols and a/biotic factors within the recipient community. Considering these factors, the best mass-rearing and release protocols are proposed here and future research priorities are identified. Finally, the long term success for managing E. densa in South Africa will require a holistic approach to address the underlying factors, such as eutrophication and human-mediated distribution that drive submerged aquatic plant invasions.
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- Date Issued: 2017