Fluorescent sensing and determination of mercury (II) ions in water

The presence of heavy metals released from industrial activities into water streams is an ever-growing challenge to ensuring a safe and clean aquatic environment. Detection and determination of the levels of these heavy metals in wastewater is an important step before any measures can be taken. In this study we report on a fluorescent sensing probe based on a naphthyl azo dye modified dibenzo-18-crown-6-ether (DB18C6) for the detection and determination of mercury (II) ions in water. The probe showed high sensitivity and selectivity towards the mercury (II) ion among various alkali, alkaline earth, and transition metal ions. The mercury (II) ion quenched the fluorescence of the probe. Stern-Volmer quenching constants (Ksv) were found to be highest for Hg2+ ion at 1.18 x 105 M-1 compared to 3.85 x 104 M-1 for copper (II) ion. The stoichiometry of the sensor–metal ion interaction was found to be 1:1 for both metal ions using Job plots. The detection limit for Hg2+ was 1.25 x 10-8 M. The dye modified crown ether was then used to detect mercury in a water sample from a coal-fired power plant and to determine the amount of mercury in the water sample.Keywords: azo dye, crown ether, fluorescence, mercury (II), sensor, wate

Characterisation of natural organic matter (NOM) and its removal using cyclodextrin polyurethanes

Natural organic matter (NOM) occurs in all natural water sources when animal and plant material breaks down. NOM in water may react with chlorine and other disinfectants to produce disinfection by-products (DBPs), many of which are either carcinogenic or mutagenic. In this study the NOM content of the raw water from the Vaalkop Water Treatment Plant (which uses both chlorination and ozonation as treatment protocols) was characterised after fractionation on ion-exchange resins. Fractionation at different pH values resulted in the isolation of a neutral, a basic and an acidic component of either predominantly hydrophobic or hydrophilic NOM. In addition, NOM results from 3 open water bodies in Johannesburg were evaluated in the same manner. As expected, NOM from all water sources was predominantly hydrophobic (~60%). Each of the 6 isolated NOM fractions was percolated through synthetic cyclodextrin (CD) polyurethanes to determine the extent to which the CD polymers can remove NOM from water. The hydrophobic basic fraction and the hydrophilic acid fraction were most efficiently removed (24% and 10%, respectively). The remaining fractions were not much affected by the polymer treatment

Natural organic matter (NOM) in South African waters: NOM characterisation using combined assessment techniques

In order to remove natural organic matter (NOM) from water in a water treatment train, the composition of the NOM in the source water must be taken into account, especially as it may not necessarily be uniform since the composition is dependent on the local environment. The main thrust of this study was to ascertain whether a cocktail of characterisation protocols could help to determine the nature, composition and character of NOM in South African waters. The characterisation of South African water sources was done by sampling 8 different water treatment plants located within the 5 major source water types in South Africa. The NOM composition of all of the samples was first studied by applying conventional techniques (UV, DOC, SUVA and bulk water parameters). NOM characterisation was then further conducted using advanced techniques (BDOC, PRAM and FEEM), which were aimed at developing rapid assessment protocols. The FEEM and UV results revealed that the samples consisted mainly of humic substances with a high UV-254 absorbance, while some samples had marine humic substances and non-humic substances. The samplefs DOC results were within the range of 3.5 to 22.6 mgE..1 C, which was indicative of the extent of variation of NOM quantities in the regions where samples were obtained. The BDOC fraction of the NOM ranged between 12 and 66%, depending on the geographical location of the sampling site. A modified PRAM was utilised to characterise the changes in NOM polarity in the water treatment process. PRAM results also indicated that the NOM samples were mostly hydrophobic. The composition and character of the NOM was found to vary from one water treatment plant to another. Combining conventional and advanced techniques could be a powerful tool for NOM characterisation and for extracting detailed information on NOM character, which should inform its treatability

The Synthesis of Nitrogen-Doped Multiwalled Carbon Nanotubes Using an Fe-Co/CaCO3 Catalyst

ACVDmethod was used to prepare high-quality nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) using acetonitrile as the nitrogen and carbon source and acetylene as a carbon source over an Fe-Co/CaCO3 catalyst in the temperature range 700–850 °C. This represents a continuation of earlier work in which Fe-Co on CaCO3 was used to make undoped carbon nanotubes. The effect of synthesis parameters (growth temperature and CH3CN vaporization temperature) on the yield, size, quality, morphology and thermal stability of the N-MWCNTs was studied. The resulting materials were characterized by TEM,SEM, TGA, BET, XPS, CN elemental analysis and Raman spectroscopy. TEM analysis revealed that the nanotubes exhibit bamboo-like structures with rough surfaces and a relatively uniform diameter. The bamboo compartment distance decreased with increase in synthesis temperature due to the increased nitrogen content inN-MWCNTs. The SEM examination showed that at high synthesis temperatures carbon spheres (CSs) with chain-like morphology and large sizes were also formed along with the N-MWCNTs. The XPS and CN elemental analysis revealed that nitrogen atoms were successfully doped into the carbon walls. The amount of nitrogen incorporated in the N-MWCNTs varied with increasing growth time and CH3CN vaporization temperature.Keywords: Carbon nanotubes, CVD synthesis, nitrogen doping, acetonitrile, Fe-Co/CaCO3 catalyst PDF and supplemetary file attached

Polyurethane composite adsorbent using solid phase extraction method for preconcentration of metal ion from aqueous solution

Polyurethane composite adsorbent polymeric material was prepared and investigated for selected solid-phase extraction for metal ions, prior to its determination by inductively coupled plasma optical emission spectrometry. The surface characterisation was done using Fourier transform infrared spectroscopy. The separation and preconcentration conditions of the analytes investigated includes influence of pH, sample loading flow rate, elution flow rate, type and concentration of eluents. The optimum pH for the highest efficient recoveries for all metal ions, which ranged from 70 to 85 %, is pH 7. The metal ions were quantitatively eluted with 5 mL of 2 mol/L HNO3. Common coexisting ions did not interfere with the separation. The percentage recovery of the metal ions ranged between 70 and 89 %, while the results for the limit of detection and limit of quantification ranged from 0.249 to 0.256 and 0.831 to 0.855, respectively. The experimental tests showed good preconcentration results of trace levels of metal ions using synthesised polyurethane polymer adsorbent composite

Cyclodextrin-dendrimer functionalized polysulfone membrane for the removal of humic acid in water

Please help populate SUNScholar with the full text of SU research output. Also - should you need this item urgently, please send us the details and we will try to get hold of the full text as quick possible. E-mail to [email protected]. Thank you.Journal Articles (subsidised)NatuurwetenskappeChemie & Polimeerwetenska