Search

In this work, we synthesized water-soluble L-cysteine-capped alloyed CdSeTe core quantum dots (QDs) and investigated the structural and optical properties of deposition of each of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shell layers. Photophysical results showed that the overcoating of a CdS shell around the alloyed CdSeTe core [quantum yield (QY) = 8.4%] resulted in effective confinement of the radiative exciton with an improved QY value of 93.5%. Subsequent deposition of a ZnSe shell around the CdSeTe/CdS surface decreased the QY value to 24.7%, but an increase in the QY value of up to 49.5% was observed when a ZnS shell was overcoated around the CdSeTe/CdS/ZnSe surface. QDs with shell layers showed improved stability relative to the core. Data obtained from time-resolved fluorescence measurements provided useful insight into variations in the photophysical properties of the QDs upon the formation of each shell layer. Our study suggests that the formation of CdSeTe/CdS core/shell QDs meets the requirements of quality QDs in terms of high photoluminescence QY and stability, hence further deposition of additional shells are not necessary in improving the optical properties of the core/shell QDs. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Despite extensive electrification of low-income residential areas on the South African Highveld, extensive use is still made of wood and coal as domestic fuels, particularly for winter space heating. In informal settlements characterised by poverty and lacking electrification, coal is combusted in non-standardised, inefficient and polluting metal braziers, colloquially known as imbaulas. Copious emissions from domestic coal fires result in elevated household and ambient air pollution levels well above national air quality limits. Despite the severity of this pollution as a public health issue, emissions data from residential coal-burning braziers are still scarce. Consequently, there is a need to evaluate the emission characteristics of these devices. In this paper, we report on controlled combustion experiments carried out to investigate systematically influences of fire-ignition methods and stove ventilation rates on gaseous and condensed matter (smoke) emissions from informal residential coal combustion braziers. Two methods of stove ignition--conventional bottom-lit updraft (BLUD) and the top-lit updraft (TLUD) (colloquially known as the Basa njengo Magogo) were investigated. Emission factors (EFs) were found to be dependent on fire ignition method and stove ventilation rates. The top-lit ignition method reduces PM10/PM2.5 by 76% to 80% compared to the BLUD method. Carbon monoxide emissions do not change significantly with the ignition method. Pollutant emissions from normal combustion in high ventilation conditions were low compared to pollutants emitted when an oxygen deficient atmosphere was created under low ventilation conditions. High stove ventilation rates resulted in a 50% reduction in PM10/PM2.5 emissions compared to the low ventilation rates. Emissions of gaseous and particulate matter from incomplete combustion can be minimised by design optimisation of the braziers. Ideally, the emissions of condensed matter particles (which form the bulk of emitted particles in residential coal fires) can be reduced through good mixing of emitted gases and air, and by ensuring a long residence time in the high temperature oxygen rich post combustion zone, to allow for complete oxidation. This study is significant in that it presents the first systematic and comprehensive study of factors affecting emissions from coal braziers. [ABSTRACT FROM AUTHOR]

Semi-continuous emissions monitors (SCEM) are widely used for the determination of atmospheric mercury. These sophisticated instruments perform nearly real-time measurements of atmospheric mercury. However, their high cost and limited mobility do not make them suitable tools for field measurements. On the other hand actively pumped Hopcalite-type sorbent tubes, connected to a vacuum pump, can be deployed to sample air even at remote locations without the need for an instrument shelter. This is particularly important for developing countries where the cost of a dedicated mercury analyser may be prohibitive to its wide-spread use. Analysis of the mercury content of exposed sorbent tubes may be performed by cold vapour atomic absorption spectroscopy (CVAAS). The necessary instrumentation is versatile, not limited to the determination of mercury and is used in many laboratories. During a five month monitoring campaign in Pretoria, South Africa, weekly average atmospheric mercury concentration data were generated using an Opsis HG 200 SCEM. They were compared to results obtained by exposing Carulite C300 sorbent tubes to ambient air, followed by CVAAS analysis of the absorbed mercury. The mean mercury concentration during four months of measurements with the Opsis analyser was 1.7 ± 1.9 ng m-3 mercury, while 1.6 ± 0.4 ng m-3 were determined by sorbent tube I CVAAS analysis. [ABSTRACT FROM AUTHOR]

Parmotrema austrosinense (Zahlbr.) Hale lichens were collected from the Pretoria central business district (CBD), as well as three sites to the east of Pretoria; the National Botanical Gardens, the CSIR campus and the suburb of Lynnwood, with the aim of utilising these lichens as biomonitors of air quality to determine the effects of the phasing out of leaded petrol and the simultaneous introduction of manganese anti-knock additives to fuel in South Africa. In addition to lichens, roadside dust and soil samples were collected from the CBD and CSIR campus, and all samples were analysed by flame atomic absorption spectrometry after acid digestion. There was no significant difference (95 % confidence) between the Mn content of lichens from all sampling sites (overall average of 97.1 ± 39.1 μg·g-1, n= 28), which was most likely due to an even suspension of Mn-containing particles arising from soil dust. Additional contributions to Mn loading as a result of vehicle emissions were currently not evident. For all non-CBD sites, higher Pb levels were found in lichens which were nearer to busy roads, suggesting an historical impact by vehicular emissions of Pb arising from leaded petrol usage. The Pb concentrations in lichens found in the CBD (average of 181.1 ± 98.0 μg·g-1, n=10) were significantly higher (95 % confidence limits) than those of lichens growing outside of the CBD area (average of 41.5 ± 36.4 μg·g-1, n=118), and the Pb levels were higher than those of Mn, which was contrary to that found in sites outside the CBD. [ABSTRACT FROM AUTHOR]

In this study, we show for the first time the removal of Pb(II) from aqueous solutions by tassel powder. Batch experiments were conducted on tassel powder, and the effects of contact time, pH, temperature and concentration on the extent of Pb(II) removal studied. The highest adsorption (about 80 %) was at pH 7, and equilibrium was established between contact times 4-24 h. Adsorption of 5 mg/L Pb(II) standard concentration was rapid suggesting that ad- sorption may have been controlled by external diffusion. When increasing the concentration from 10-20 mg/L, the controlling step of adsorption was suggested to be that of internal diffusion. [ABSTRACT FROM AUTHOR]

A novel graphene wool material was synthesised by non-catalytic chemical vapour deposition using a high-purity quartz wool substrate. The in situ synthesis method avoids post-growth transfer and isolation steps and allows the graphene to be directly synthesised into graphene wool. In the absence of a catalyst during graphene growth, the cracking of methane and nucleation is not as efficient, resulting in graphene defects which can be minimised by optimising the growth conditions. The roles of the methane and hydrogen flow rates in the synthesis of the graphene wool were investigated, as was the effect of growth temperature, growth time and cooling rates. The precursor flow rates and growth temperature were found to be the most vital parameters. The best quality graphene wool showed a minimum ratio of the disordered carbon relative to the graphitic carbon (ID/IG ≈ 0.8) with a calculated crystallite grain size of 24 nm. The morphology of the optimised graphene wool was flake-like, and the X-ray photoelectron spectroscopy analysis revealed a surface composition of 94.05 at.% C 1s and 5.95 at.% O 1s. With this new material, the integrity of the synthesised graphene surface is preserved in use and it has the added advantage of structural support from the quartz substrate. Unlike many other forms of graphene, this fibrous graphene wool is flexible, malleable and compressible, allowing for a wealth of potential applications including in electronics, energy storage, catalysis, and gas sorption, storage, separation and sensing applications. [ABSTRACT FROM AUTHOR]

Abstract Denuder sampling devices consisting of two multi-channel silicone rubber traps separated by a quartz fibre filter, have been effectively employed for the simultaneous sampling of gas and particle associated semi-volatile organic compounds. Here controlled laboratory experiments were conducted to further elucidate the fundamental operating mechanisms of this portable denuder with respect to particle transmissions. Particle collection efficiency of the quartz fibre filters as well as particle transmission efficiency through the silicone rubber traps using ambient aerosol and aqueous suspensions of monodisperse polystyrene latex (PSL) as test particles (0.3, 0.5 and 0.8 µm), were evaluated for various scenarios. Particle size and number concentration were measured with a scanning mobility particle sizer. Transmission efficiency of the denuder was determined from the ratio of particle concentration transmitted by the denuder to that of a bypass line. All sizes of PSL particles were collected with high efficiency and reproducibility by the quartz fibre filter (>98% with variation coefficients <16%). Overall transmission efficiencies for all particles >100 nm ranged from 91% to 100% (variation coefficients of 2–14%). Transmission efficiencies decreased when PDMS tubes were twisted but were not significantly different for traps made by different individuals. Ambient particles, which were studied for the first time, were collected with 88–95% collection efficiency. Losses of smaller particle size fractions in the trap portion of the denuder were likely due to diffusion and electrostatic effects. The high particle collection and transmission efficiencies of all tested particle sizes indicated that these denuders are very effective tools for aerosol measurements. Highlights • The filter of the denuder sampler effectively collects various sized particles. • Hand-made silicone rubber traps show high, reproducible transmission efficiencies. • The denuder was tested with smaller ambient particles for the first time. • Twisting of PDMS tubing reduced particle transmission efficiencies. • No difference in transmission efficiencies of traps made by different individuals. [ABSTRACT FROM AUTHOR]

Multi-channel polydimethylsiloxane rubber traps were used to sample the headspace of rosemary samples (two essential oils from different sources, one oleoresin and one dried herb) followed by comprehensive two-dimensional gas chromatography - time of flight mass spectrometry (GCxGC-TOFMS) orGC-MS analyses.The aroma of different headspace samples was characterized using a custom-built olfactory apparatus. The differences between the aroma profileswere evident from bubble plots of the perceived aroma at different temperatures. The samples were heat-treated to simulate cooking of food products, and were then reassessed to determine any changes in the aroma profile. It was found that the intense menthol and cooling aromas subsided in all the samples with heating. GCxGC-TOFMS allowed for separation of the numerous components in the headspace samples. Many terpenes and aliphatics were thus tentatively identified and the relative peak areas were compared to better understand the mixture that contributes to the rosemary aroma. [ABSTRACT FROM AUTHOR]

We report on the surface passivation of a new alloyed ternary AgZnS shell layer on luminescent CdSe quantum dots (QDs) via the organometallic hot-injection pyrolysis of metal precursors, surfactant precursors and organic ligands in a non-coordinating solvent. Transmission electron microscopy, X-ray diffraction, Raman spectroscopy and UV/vis absorption and fluorescence emission spectrophotometry were used to characterize the QD nanocrystals. Fixed AgZnS shell alloying was used as the main fabrication strategy to engineer the band gap of CdSe/AgZnS core/alloyed shell QDs which in turn led to a blended mixture of homogenous and heterogenous particle size growth with spherical, quasi-spherical and trigonal-shaped particles. The crystal structure of CdSe/AgZnS QDs was mainly zinc blende but as the QDs size increased with time, a superimposition of zinc blende and wurtzite hexagonal structure was observed with the former being predominant in the diffraction pattern. The photoluminescence (PL) emission spectra of CdSe/AgZnS QDs were tuned across the visible region while the full width at half maximum was as low as 33 nm, representing an 8 nm decrease compared to 41 nm FWHM exhibited by CdSe QDs. As CdSe/AgZnS core/alloyed shell QDs grew with time, the PL quantum yield (QY) increased from 67% for CdSe to a maximum of ~100% for CdSe/AgZnS QDs and thereafter decreased steadily to a minimum of 36% upon further growth. By achieving ~100% PL QY, it appears that interfacial surface defect states in the core/alloyed shell QDs were completely eliminated via the AgZnS shell alloying process on the CdSe core. The unique optical properties exhibited by CdSe/AgZnS core/alloyed shell QDs as reported in this work shows great promise for light emitting QD applications. • New alloyed AgZnS shell layer was overcoated on CdSe quantum dots (QDs) surface. • Fixed AgZnS shell alloying was used as the fabrication strategy to engineer the QDs band gap. • The fluorescence emission of the CdSe/AgZnS QDs was tuned across the visible region. • The fluorescence quantum yield increased from 67% for CdSe to a maximum of ~100% for CdSe/AgZnS QDs. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are a group of emerging chemical pollutants that pose severe health challenges and toxicity to people and aquatic organisms exposed to these pollutants. This study sought to assess the types and levels of PAHs and their eco-toxicity indices in surface waters of Narok and Bomet counties of Kenya, which have witnessed an increase in charcoal-burning activities and vehicular emissions near water bodies. Sampling was done in eight regions of the two counties based on their proximity to PAH sources. Extraction of the water samples was done via a solid-phase mmethod. Seven US Environmental Protection Agency (US EPA) priority PAHs were detected. The concentrations of these PAHs varied from below the limits of detection up to 31.42 µg l -1 for dibenzo[ a,h ]anthracene. The majority of the PAHs from Narok County were pyrogenic, while those from Bomet were petrogenic based on PAH diagnostic ratios. The surface waters were significantly polluted with dibenzo[ a,h ]anthracene, with risk quotients above 1.0 in the surface waters, and were found to be hazardous, with hazard quotients above 10.0, thus indicating potential environmental risks. The findings indicate the need for stringent measures to be put in place to mitigate the risks posed by these PAHs., Competing Interests: We declare we have no competing interests., (© 2024 The Author(s).)

Water disinfection inevitably leads to disinfection byproduct formation, such as haloacetic acids. Many disinfection byproducts reportedly have adverse health effects and, in many instances, including four haloacetic acids, are classified as potential carcinogens. As the global awareness of these compounds increases, more regulatory bodies include certain disinfection byproduct groups in their regulations. Rugged, fast, and cheap analytical quantification methods are therefore crucial. In this paper, a thin film extraction method for haloacetic acids is outlined. Thin films were synthesized in-house using a spin coating procedure, which allowed for easy adjustment of the sorbent choice and film geometry. PDMS, Carboxen®, and HLB were of interest and their extraction potential for HAAs from spiked water was tested in three film variations. PDMS films impregnated with HLB or Carboxen® improved the extraction drastically compared to PDMS films. Specifically, HLB impregnated films achieved excellent extraction efficiencies for tri-substituted analytes (51% for BDCAA, 77% for CDBAA, and 92% TBAA), which are often present at extremely low concentrations in water. In addition to the extraction experiment, a computational model was applied to compare PDMS and HLB. Trends observed in the computational data reflected in the experimental results, showing the validity of the model and confirming that physisorption through hydrogen bonding was mainly responsible for successful extraction.

Agricultural fires are a major source of biomass-burning organic aerosols (BBOAs) with impacts on health, the environment, and climate. In this study, globally relevant BBOA emissions from the combustion of sugar cane in both field and laboratory experiments were analyzed using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry. The derived chemical fingerprints of fresh emissions were evaluated using targeted and nontargeted evaluation approaches. The open-field sugar cane burning experiments revealed the high chemical complexity of combustion emissions, including compounds derived from the pyrolysis of (hemi)cellulose, lignin, and further biomass, such as pyridine and oxime derivatives, methoxyphenols, and methoxybenzenes, as well as triterpenoids. In comparison, laboratory experiments could only partially model the complexity of real combustion events. Our results showed high variability between the conducted field and laboratory experiments, which we, among others, discuss in terms of differences in combustion conditions, fuel composition, and atmospheric processing. We conclude that both field and laboratory studies have their merits and should be applied complementarily. While field studies under real-world conditions are essential to assess the general impact on air quality, climate, and environment, laboratory studies are better suited to investigate specific emissions of different biomass types under controlled conditions., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Narok and Bomet are agricultural counties in Kenya which depend on flowing surface waters for farming activities. Agrochemicals have frequently been used to increase agricultural produce in this region. Occasionally, appropriate pesticide utilization measures are not followed. These surface waters are also consumed domestically by humans, livestock, and wild animals thus posing safety concerns to them. The current study sought to evaluate the levels and nature of pesticide residues found in surface waters in the dry and wet seasons of these counties. Eight water samples were collected in July (dry season) and October (wet season) at four different river sites in each of the two counties predetermined by the agricultural activity of its proximate environs. Pesticides extracted by solid phase extraction were analyzed by gas chromatography-mass spectrometry. At least 38 different pesticides were detected in the two counties with the highest concentration being recorded for chlorpyrifos and piperidine in Narok and Bomet counties, respectively. The pesticides chlorpyrifos, cypermethrin, cyfluthrin, and cyhalothrin were more prevalent in Narok County while triazine, semicarbazone, and epinephrine were more prevalent in Bomet County. There were significantly more pesticides detected during the wet season (P ≤ 0.05). Out of the nine prevalent pesticides detected, four of them posed serious ecotoxicology concerns with risk quotients above 1.0 (high risk); thus, there is a need for more government policy interventions in deterring farming near riparian lands and in training of famers regarding best practice for pesticide applications., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Here we functionalized micro-scaled polymer beads with nano-scaled quantum dots and demonstrate optical trapping and tweezing, with in-situ fluorescence measurement, in an all-digital all-optical configuration. We outline the chemistry required to facilitate this, from deactivating the optical trapping environment to size, adhesion and agglomeration control. We introduce a novel holographic optical trapping set-up that leverages on vectorially structured light, allowing for the delivery of tuneable forms of light from purely scalar to purely vector, including propagation invariant flat-top beams for uniform illumination and tailored intensity gradient landscapes. Finally, we show how this has the potential to quench bleaching in a single wavelength trap by linear (spatial mode) rather than non-linear effects, advancing the nascent field of optics for chemistry., (© 2022. The Author(s).)

This work explores the potential use of cadmium-based quantum dots (QDs) coupled to mycolic acids (MAs) as a fluorescent probe to detect anti-MA antibodies which are biomarkers for tuberculosis (TB). The use of free MAs as antigens for the serodiagnosis of TB is known but has not been developed into a point of care test. This study focuses on the synthesis, solubility, and lateral flow of QDs coupled to MAs. Water-soluble CdSe/ZnS QDs capped with l-cysteine were synthesised and covalently coupled to MAs via amide linkages to form a water-soluble fluorescent probe: MA-CdSe/ZnS QDs. The MA-CdSe/ZnS QDs showed broad absorption bands and coupling, confirmed by the presence of amide bonds in the Fourier-transform infrared (FTIR) spectrum, resulting in a blue shift in fluorescence. Powder X-ray diffraction (XRD) revealed a shift and increase in the number of peaks for MA-CdSe/ZnS QDs relative to the L-cys-CdSe/ZnS QDs, suggesting that coupling changed the crystal structure. The average particle size of MA-CdSe/ZnS QDs was ~3.0 nm. Visual paper-based lateral flow of MA-CdSe/ZnS QDs was achieved on strips of nitrocellulose membrane with both water and membrane blocking solution eluents. The highly fluorescent MA-CdSe/ZnS QDs showed good water solubility and lateral flow, which are important properties for fluorescence sensing applications., (© 2021 John Wiley & Sons Ltd.)

Procedures for the design of a fluorescence sensor based on molecularly imprinted polymer-capped quantum dots (MIP@QDs) together with the synthesis of quantum dots and MIP@QDS are described. Spherical and monodispersed nanoparticles are suitable for fluorescence sensing of an analyte such as pharmaceuticals and polycyclic aromatic hydrocarbons (PAHs). In addition, excellent optical properties, higher quantum yield, and photoluminescence efficiency as well as easy detection of emission spectra are distinctive advantages of quantum dots as fluorescence sensors. Optimization of different variables and analytical applications of the sensor are also presented, which are of value for fluorescence sensing., (© 2021. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

In this work, we synthesized water-soluble L-cysteine-capped alloyed CdSeTe core quantum dots (QDs) and investigated the structural and optical properties of deposition of each of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shell layers. Photophysical results showed that the overcoating of a CdS shell around the alloyed CdSeTe core [quantum yield (QY) = 8.4%] resulted in effective confinement of the radiative exciton with an improved QY value of 93.5%. Subsequent deposition of a ZnSe shell around the CdSeTe/CdS surface decreased the QY value to 24.7%, but an increase in the QY value of up to 49.5% was observed when a ZnS shell was overcoated around the CdSeTe/CdS/ZnSe surface. QDs with shell layers showed improved stability relative to the core. Data obtained from time-resolved fluorescence measurements provided useful insight into variations in the photophysical properties of the QDs upon the formation of each shell layer. Our study suggests that the formation of CdSeTe/CdS core/shell QDs meets the requirements of quality QDs in terms of high photoluminescence QY and stability, hence further deposition of additional shells are not necessary in improving the optical properties of the core/shell QDs., (Copyright © 2015 John Wiley & Sons, Ltd.)