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Properties of traveling ionospheric disturbances (TIDs) over the Western Cape, South Africa
No full textTravelling Ionospheric Disturbances (TIDs) are said to be produced by atmospheric gravitational
waves propagating through the neutral ionosphere. These are smaller in amplitude and period when
compared to most ionospheric disturbances and hence more difficult to measure. Very little is known
about the properties of the travelling ionospheric disturbances (TIDs) over the Southern Hemisphere
regions since studies have been conducted mostly over the Northern Hemisphere regions. This study
presents a framework, using a High Frequency (HF) Doppler radar to investigate the physical properties
and the possible driving mechanisms of TIDs. This research focuses on studying the characteristics
of the TIDs, such as period, velocity and temporal variations, using HF Doppler measurements
taken in South Africa. By making use of a Wavelet Analysis technique, the TIDs’ characteristics
were determined. A statistical summary on speed and direction of propagation of the observed
TIDs was performed. The winter medium scale travelling ionospheric disturbances (MSTIDs) observed
are generally faster than the summer MSTIDs. For all seasons, the MSTIDs had a preferred
south-southwest direction of propagation. Most of the large scale travelling ionospheric disturbances
(LSTIDs) were observed during the night and of these, the spring LSTIDs were fastest when compared
to autumn and summer LSTIDs. The general direction of travel of the observed LSTIDs is
south-southeast. Total Electron Content (TEC), derived from Global Positioning System (GPS) measurements,
were used to validate some of the TID results obtained from the HF Doppler data. The
Horizontal Wind Model (HWM07), magnetic K index, and solar terminators were used to determine
the possible sources of the observed TIDs. Only 41% of the observed TIDs were successfully
linked to their possible sources of excitation. The information gathered from this study will be
valuable in future radio communications and will serve as means to improve the existing ionospheric
models over the South African region
Organosilicon compounds as fluorescent chemosensors for fluoride anion recognition
No full textRecent developments in organosilicon-based chemosensors for F− recognition are reviewed. The design strategies for improving the photophysical properties of organosilicon-based chemosensors are elaborated, with an emphasis placed on their utility for biological applications. The photophysical properties and electronic structures are analyzed in depth with reference made to the results of molecular modeling calculation and possible future research directions are assessed.Original publication is available at http://dx.doi.org/10.1016/j.ccr.2014.10.00
Synthesis and characterization of Na(Y,Gd)F4 upconversion nanoparticles and an investigation of their effects on the photophysical properties of an unsubstituted tetrathiophenoxy phthalocyanine
No full textSphere- and star-shaped Na(Y,Gd)F4:Yb/Er(Tm)upconversion nanoparticles (UCNP) were successfully synthesized utilizing a methanol-assisted thermal decomposition approach and their spectroscopic (absorption, emission and luminescence lifetime) properties fully characterized. The factors affecting the size and shape of the UCNPs were studied and discussed in detail. The size of the nanoparticles was determined using TEM primarily and found to be approximately 19 and 30 nm for the Er and Tm spheres, respectively, while the Er and Tm “stars” were found to be much larger with sizes ranging from 110 to 240 nm, respectively (as determined along the width of the nanoparticle). In addition, their influence on the spectroscopic properties of an unsubstituted tetrathiophenoxy phthalocyanine (H2Pc) was investigated. The UCNP were found to produce characteristic upconversion luminescence emissions in the blue, green, red and NIR regions. Simple mixing with an H2Pc in toluene was found to exert no obvious changes in the spectroscopic properties of the Pc, although a considerable increase in the radiative lifetimes is observed for the Pc in the presence of the UCNPs. The singlet oxygen generation mediated by the red light excitation of the H2Pc mixed with UCNP was found to decrease in the presence of the NPs.Original publication is available at http://dx.doi.org/10.1007/s11051-015-2889-
Enhanced optical limiting behaviour of indium phthalocyanine derivatives when in solution or embedded in poly(acrylic acid) or poly(methyl methacrylate) polymers
No full textThe optical limiting performance of indium phthalocyanine-based polymer thin-films with large nonlinear absorption coefficients (βeff) and low limiting threshold intensity (Ilim) are described. The absorption cross-sections and the population dynamics of the excited states are also reported. The excited state absorption cross-sections (σexc) are shown to depend on the transition moment between the T1 and T2 states. βeff values have been shown to be related to the population density of the molecules in the T1 state. The improved optical limiting performance recorded for the investigated phthalocyanine complexes in the presence of polymer matrices has been attributed to the aggregation effects of the complexes in the polymer thin-films. The optical properties of the indium phthalocyanine moieties were found to possess robust sensitivity to a change of the polymer materials.Original publication available at http://dx.doi.org/10.1016/j.jphotochem.2015.02.00
Enhanced triplet state parameters for zinc carboxy phenoxy phthalocyanine following conjugation to ascorbic acid: effects of adsorption on single walled carbon nanotubes
No full textZinc phthalocyanine bearing four ascorbic acid units (formed via ester bond between zinc carboxy phenoxy phthalocyanines and ascorbic acid) was synthesized and characterized using different spectroscopic methods. The complex (with or without ascorbic acid) was further adsorbed onto single walled carbon nanotubes (SWCNTs) and further characterized using Raman spectroscopy, X-ray diffractometry, transmission electron microscopy and thermogravimetric analysis. The photophysical properties of the complexes were studied. The synthesized complex showed better photophysical properties when compared to the carboxy phenoxy phthalocyanines alone, this is evident in the increase of the triplet quantum yields (ΦT), triplet life-times (τT) and singlet oxygen quantum yields (ΦΔ). The zinc phthalocyanines bearing ascorbic acid showed improved triplet life-times even in the presence of SWCNTs.Original publication is available at http://dx.doi.org/10.1016/j.poly.2015.01.03
Nanosecond nonlinear optical limiting properties of new trinuclear lanthanide phthalocyanines in solution and as thin films
No full text2,4,6-Tris[3-thio-9,10,16,17,23,24-hexa(4-tertbutylphenoxy) phthalocyaninato ytterbium (III) chloride]-s-triazin (3) and its lutetium counterpart (4) were synthesized. The nonlinear optical behavior of 3 and 4 were characterized in solution and when embedded in polymer as thin films. Thin films of complexes 3 and 4 in poly(bisphenol A carbonate) showed improved nonlinear optical properties when compared to solution. Complex 3 showed a lower threshold for optical limiting intensity (Ilim) than complex 4, and for phthalocyanines in general. Ilim values were even lower in films compared to solutions.Original publication is available at http://dx.doi.org/10.1016/j.poly.2014.08.04
The Development of Palladium(II)-Specific Amine-Functionalized Silica-Based Microparticles: Adsorption and Column Separation Studies
No full textThe adsorption and separation of platinum(IV) and palladium(II) chlorido species ([PtCl6]2− and [PdCl4]2−) on silica-based microparticles functionalized with ammonium centers based on ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetriamine (TETA) and tris-(2-aminoethyl)amine (TAEA) were investigated. The functionalized sorbent materials were characterized using SEM, XPS, BET, and FTIR. The sorbents were used in the batch and column study for adsorption and selective separation of [PtCl62− and PdCl4]2−. The adsorption model for both [PtCl6]2− and [PdCl4]2− on the different sorbent materials fitted the Freundlich isotherm with R2 values > 0.99. The S-TETA sorbent material was palladium(II) specific. Pd(II) loaded on the silica column was recovered using 3% m/v thiourea solution as the eluting agent. Separation of platinum and palladium was achieved by selective stripping of [PtCl6]2− with 0.5 M of NaClO4 in 1.0 M HCl while Pd(II) was eluted with 0.5 M thiourea in 1.0 M HCl. The separation of palladium (Pd) from a mixture containing platinum (Pt), iridium (Ir), and rhodium (Rh) was successful on silica functionalized with triethylenetriamine (TETA) showing specificity for palladium(II) and a loading capacity of 0.27 mg/g. S-TETA showed potential for use in the recovery of palladium from platinum group metals such as from solutions of worn out automobile emission control catalytic convertors and other secondary sources.Original publication is available at http://dx.doi.org/10.1080/01496395.2014.97801
Synthesis and photophysical properties of nanocomposites of aluminum tetrasulfonated phthalocyanine covalently linked to glutathione capped CdTe/CdS/ZnS quantum dots
No full textAluminum tetrasulfonated phthalocyanine (ClAlTSPc) was covalently linked with different sizes of glutathione capped CdTe/CdS/ZnS quantum dots (QDs). The photophysical and Förster resonance energy transfer (FRET) properties of the nanoconjugates were investigated. The CdTe/CdS/ZnS(6.3) nanocomposite showed the highest enhancement in its photophysical properties while (CdTe/CdS/ZnS(3.2) nanocomposite showed the least. Highest FRET efficiency was observed in the linked CdTe/CdS/ZnS(6.3) nanocomposites at 93%. Hence, the combination of CdTe/CdS/ZnS with ClAlTSPc exhibited excellent photophysical properties.Original publication is available at http://dx.doi.org/10.1016/j.synthmet.2015.04.01
Photodynamic therapy effect of zinc monoamino phthalocyanine–folic acid conjugate adsorbed on single walled carbon nanotubes on melanoma cells
No full textThis work reports on the photodynamic therapy effect of zinc monoamino phthalocyanine linked to folic acid represented as ZnMAPc-FA, which was further immobilized onto single walled carbon nanotube represented as ZnMAPc-FA-SWCNT on melanoma A375 cell line, the effect of SWCNT-FA (without ZnMAPc) was also examined. All the compounds were non-toxic to the melanoma A375 cell line in the absence of light. Upon irradiation of the melanoma A375 cell line with a 676 nm diode laser at a power density of 98 mW/cm2 at 5 J/cm2 about 60% and 63% cell death was observed in the presence of ZnMAPc-FA and ZnMAPc-FA-SWCNT respectively. SWCNT-FA had no significant photodynamic therapy or photothermal effect to the cell, only 23% of cell death was observed after irradiation.Original publication is available at http://dx.doi.org/10.1016/j.saa.2014.09.03
Lipophilic M(α,α′-OC5H11)8phthalocyanines (M = H2 and Ni(II)): synthesis, electronic structure, and their utility for highly efficient carbonyl reductions
No full textA lipophilic and electron-rich phthalocyanine (α,α′-n-OC5H11)8-H2Pc and its nickel(II) complex (α,α′-n-OC5H11)8-Ni(II)Pc have been synthesized and characterized. Detailed analyses of the electronic structure were carried out by spectroscopy, electrochemistry, spectroelectrochemistry, and TD-DFT calculations. A series of experiments demonstrate that the (α,α′-n-OC5H11)8-Ni(II)Pc complex can be used as a catalyst for highly efficient carbonyl reductions.Original publication is available at http://dx.doi.org/10.1039/C5DT03256