Chemical Speciation of Chromium in Various Matrices in South African Terrestrial Water Using an Optimised Adsorptive Stripping Voltammetric Procedure

Optimization of analytical procedure for the determination of chromium (III)/(VI) speciation is described. A very sensitive adsorptive-catalytic stripping voltammetry method in the presence of diethylenetriaminepentaacetic acid (DTPA) is used for chromium speciation study in surface and ground water with in very different matrices. The effects of various parameters (pH, ligand concentration, potential, collection time, equilibration time,) on the response are optimized. Concentration ratio of chromium (III)/(VI), and interferences from other metals and anions, typical for South African waters, are considered. Results for total chromium determination are compared with atomic absorption spectrometry (AAS) measurements. South African Journal of Chemistry Vol.54 2001: 264-28

Synthesis of bulk ion-imprinted polymers (IIPs) embedded with oleic acid coated Fe3O4 for selective extraction of hexavalent uranium

A selective and reliable method for the extraction of trace quantities of U(VI) by the use of a magnetic U(VI) ion-imprinted polymer (IIP) was developed. In this study, oleic acid (OA) coated magnetite nano-particles were incorporated into the cross-linked polymeric matrix of the selective sorbent, in order to gain the physical advantages of separating the polymers. Many physico-chemical factors influence the adsorption process; uranyl ion uptake ability based on these parameters was investigated. The optimum parameters obtained were sample pH 4,50 mg of the magnetic polymer, a contact time of 45 min and an initial U(VI) concentration of 2 mg·ℓ-1. The adsorption capacities for the magnetic NIP and IIP were found to be 0.95 mg·g1 and 1.21 mg·g-1, respectively. The adsorption behaviour of U(VI) in the presence of other competing metal ions onto the cross-linked magnetic polymers was also examined in binary mixtures and the order of selectivity was found to be U(VI) > Pb(VI) > Ni(II). The resulting magnetic nano-composite polymers were found to be stable up to the sixth cycle of use and reuse. The Freundlich adsorption model was used for the mathematical description of the adsorption equilibrium and the adsorption kinetic data fitted the pseudo-first-order model with R2 > 0.92.Keywords: Bulk, magnetic imprinted polymers, oleic acid, uraniu

Determination of naproxen, ibuprofen and triclosan in wastewater using the polar organic chemical integrative sampler (POCIS): A laboratory calibration and field application

In this study, the occurrence in wastewater of two non-steroidal  anti-inflammatory drugs (NSAIDs), naproxen and ibuprofen, and one  personal care product, triclosan, was assessed using the polar organic  chemical integrative sampler (POCIS). The samplers were initially  calibrated in the laboratory to obtain sampling rates (Rs) for each target compound followed by deployment in the influent and effluent of  Goudkoppies and Northern Wastewater Treatment Plants (WWTPs), South Africa. Exposure was done for 14 days in 2012. High performance liquid chromatography (HPLC) system with ultraviolet (UV) and fluorescence (FLD) detectors was used to analyse POCIS extracts. Laboratory calibration of POCIS yielded Rs values for the three compounds that were between 0.087 and 0.383l.d-1 in quiescent conditions, and 0.125 and 0.936 l.d-1 in  stirred conditions. From the accumulated amounts in field-deployed  samplers, estimated freely dissolved concentrations of the studied compounds in wastewater influent ranged from 55.0 to 78.4 µg.l-1 and 52.3 to 127.7 µgl.-1 in Goudkoppies and Northern WWTPs, respectively. Average concentrations of these compounds in the treated effluent ranged from 10.7 to 13.5 µgl.-1 in Goudkoppies WWTP, and 20.4 to 24.6 µgl.-1 in Northern WWTP. Analyte removal efficiencies varied between 68 and 86% in Goudkoppies WWTP and 61 and 82% in Northern WWTP. Grab samples processed by SPE method yielded higher analyte concentrations (up to three-fold) as compared to POCIS-derived estimates. This  discrepancy was attributed to SPE's ability to extract both the free  dissolved, and particle sorbed fractions of the contaminants.Keywords: Polar organic chemical integrative sampler, pharmaceuticals and personal care products, wastewater, wastewater treatment plant

Column adsorption studies for the removal of U by phosphonated cross-linked polyethylenimine: modelling and optimization.

A continuous fixed-bed adsorption study was carried out by using phosphonated cross-linked polyethylenimine as an adsorbent for the removal of uranium (U) from aqueous solutions. The effect of inlet metal ion concentration (40, 70, and 100 mg L-1), feed flow rate (1, 2, and 3 mL min(-1)), and polymer bed height (2.5, 3.2 and 4.5 cm) on the breakthrough characteristics of the fixed-bed adsorption system at pH 2 were studied. The results showed that the breakthrough time appeared to increase with increase of bed height but decreased with increase of both influent U concentration and flow rate. Modelling of the dynamics of the fixed-bed adsorption process was studied and the application of different models to describe the breakthrough curves showed that the Thomas and Yoon-Nelson model gave better results for the operating conditions.SP201

Selective adsorption of uranium (VI) on NaHCO3 leached composite γ-methacryloxypropyltrimethoxysilane coated magnetic ion-imprinted polymers prepared by precipitation polymerization

Ion imprinted nano-magnetic composite polymers for selective removal of hexavalent uranium were prepared by a precipitation polymerization technique in the presence of γ-methacryloxypropyltrimethoxysilane (γ-MPS) coated magnetite and other pre-polymerization reagents. The synthesized magnetic polymers were then leached with NaHCO3 to produce magnetic ion imprinted polymers (IIPs) with fabricated adsorption sites complementary to the uranyl ions in terms of size and shape. Several parameters were investigated to obtain conditions which gave the optimum adsorption of the uranyl onto the magnetic IIPs and their corresponding controls, magnetic ion non-imprinted polymers (NIPs). The optimum amount of magnetic sorbent, initial concentration and contact time were 50 mg, 2.5 mg L-1 and 45 min, respectively. The adsorption capacity of the magnetic IIP (1.15 ± 0.01 mg g-1) was higher than that of the magnetic NIP (0.93 ± 0.02 mg g-1). This indicated that the former had a somewhat higher affinity for U(VI) than the later. The magnetic polymers also displayed good selectivity of the order: U(VI) > Ni(II) > Mg(II). After six cycles of use, the magnetic polymers illustrated good stability and reusability.SP201

Development and Application of Solid Phase Extraction Method for Polycyclic Aromatic Hydrocarbons in Water Samples in Johannesburg Area, South Africa

A solid phase extraction (SPE) technique has been developed for the quantitative determination of polyaromatic hydrocarbons (PAHs) in aqueous samples. The SPE technique involved extraction of PAHs froma 100 mL sample containing 10 % methanol as a modifier onto C18 cartridges. 40 % methanol in water was used as conditioning solvent, and 3 mL acetone:THF (1:1) as eluting solvent. After eluting, the extract was reduced to 1 mL under nitrogen and then analyzed by GC-MS. The extraction was optimized for the addition of organic modifier, sample load volume, conditioning solvent, washing solvent and eluting solvent. In order to evaluate the practical applicability of SPE technique, water samples were spiked with the PAHs to give final sample concentrationsbetween 3 and 7 μg L–1. Enrichment factors of 81–135 were achieved with relative standard deviations (RSDs) of less than 6 %. Recoveries obtained ranged from 81 to 135 %. Detection limits ranged from 20.0–52.0 ng L–1. The optimized method was validated by analyzing certified reference materials. The optimized method was then applied to spiked real river samples in and around the Johannesburg area, South Africa. The concentrations obtained varied from 22.0 to 1040.0 ng L–1. The RSDs were between 2.3 and 13 %. The overall order of PAHs levels was: phenanthrene > acenaphthene > naphthalene > fluoranthene > pyrene.Keywords: Solid phase extraction, polycyclic aromatic hydrocarbons, water samples, Johannesburg, South Afric

Selective removal of chromium (VI) from sulphates and other metal anions using an ion-imprinted polymer

A linear copolymer was prepared from 4-vinylpyridine and styrene. An ion-imprinted polymer (IIP) specific for Cr (VI) adsorption was prepared by copolymerisation of the quaternised linear copolymer (quaternised with 1,4-chlorobutane), 2-vinylpyridine functional monomer and ethylene glycol dimethacrylate (EGDMA), as the cross-linking monomer, in the presence of 1,1’-azobis(cyclohexanecarbonitrile) as initiator. Ammonium dichromate and aqueous methanol were used as a template and porogenic solvent, respectively. Leaching of the chromate template from the polymer particles was achieved with successive stirring of the ion-imprinted polymer (IIP) particles in 4 M HNO3 solutions to obtain leached materials, which were then used for selective rebinding of Cr (VI) ions from aqueous solutions. Similarly, the non-imprinted polymer/ control polymer (NIP/CP) material was also prepared under exactly the same conditions as the IIP but without the chromate anion template. Various parameters, such as solution pH, initial concentration, aqueous phase volume, sorbent dosage, contact time and leaching solution volumes, were investigated. Scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, BET surface area and pore size analysis were used for the characterisation of IIP (both unleached and leached) and CP materials. Optimal parameters were as follows: solution pH, 3; contact time, 120 min; eluent, 20 mℓ of 0.1 M NaOH; and sorbent amount, 125 mg. Maximum retention capacity of IIP and CP was 37.58 and 25.44 mg∙g-1, respectively. The extraction efficiencies of the IIP and CP were compared using a batch and SPE mode of extraction. In the absence of high concentrations of ions, especially sulphate ions, both CP and IIP demonstrated no differences in binding of Cr (VI), which was almost 100%. However, in the presence of high concentrations of sulphate ions, the selectivity on the CP completely collapsed. The study clearly demonstrates the suitably of the developed IIP for selective extraction of Cr (VI) in complex samples such as those from acid mine drainage. The selectivity was also compared by direct injection of the real-world sample, both spiked and non-spiked, into that obtained after IIP selective extraction. Despite the method’s very low detection limits for direct injection (below 1 μg∙ℓ-1), no Cr (VI) was obtained. However, after IIP selective extraction, spiked Cr (VI) was detected in the spiked sample

Investigating the temporal trends in PAH, PCB and OCP concentrations in Hartbeespoort Dam, South Africa, using semipermeable membrane devices (SPMDs)

The seasonal variability of persistent organic pollutants in Hartbeespoort Dam, South Africa, was investigated using semipermeable membrane devices (SPMDs) as passive samplers. Freely dissolved waterborne  polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were sampled to investigate  seasonal changes in their concentrations. Exposure of the passive  samplers was done for 14 days at the same sampling site in each of the four seasons of the year, in 2011. The SPMD-derived analyte amounts  enabled the calculation of time-weighted averages of free dissolved  waterborne levels of the contaminants. Concentrations ranged from 30.0 ng·l-1 to 51.5 ng·l-1 for PAHs, 38 pg l-1 to 150 pg·l-1 for PCBs, 9.2 to 10.4 ng·l-1 for HCHs and 0.3 to 0.8 ng·l-1 for DDTs, respectively. It was also  noted that the winter season generally exhibited higher contaminant  concentrations for most compounds studied, which likely reflects the  seasonality of their atmospheric deposition. An attempt was also made to identify possible sources of PAH contaminants in the dam by examining PAH ratios. These diagnostic ratios were inclined towards pyrogenic sources of pollution, except for the winter season where both pyrogenic and  petrogenic sources likely contribute to the contamination pattern.Keywords: Hartbeespoort dam, persistent organic pollutants,  semipermeable membrane devices, water-dissolved concentrations, temporal trends

Kinetic, equilibrium and thermodynamic modelling of the sorption of metals from aqueous solution by a silica polyamine composite

Batch sorption studies were conducted to assess the potential of a phosphonated silica polyamine composite (BPAP) to remove metals (Co, Cu, Fe, Mg, Mn, Ni, U and Zn) from mine waters. The metal adsorption showed a good Langmuir isotherm fit. Ni and Mn fitted both the Freundlich and Langmuir isotherms. The activation energies (Ea) of Co, Mg and Ni ranged between 5 and 40 kJ∙moℓ-1, signifying physisorption while U showed a chemisorption type of adsorption (with Ea > 50 kJ∙moℓ-1). Cu and Fe on the other hand gave negative Ea values, indicating their preference to bind to low-energy sites. The pseudo-second-order kinetic model provided the best correlation of the experimental data, except for Mg and Ni for which the pseudo-first-order model and the Elovich model gave a better fit, respectively. Adsorption was almost constant over a wide pH regime and increased with time. Adsorption increased with concentration of the metals with the exception of Co, Fe and Ni which displayed about a 40% drop at a concentration of 200 mg∙ℓ-1. Desorption experimental data gave poor results except for U which showed 99.9% desorption.Keywords: silica polyamine composite, sorption, kinetics, isotherms, desorptio

General Chemistry Student Attitudes and Success with Use of Online Homework: Traditional- Responsive versus Adaptive-Responsive

We investigated whether use of an adaptive-responsive online homework system (OHS) that tailors homework to students’ prior knowledge and periodically reassesses students to promote learning through practice retrieval has inherent advantages over traditional-responsive online homework. A quasi-experimental cohort control post-test-only design with nonequivalent groups and propensity scores with nearest neighbor matching (n = 6,114 pairs) was used. The adaptive system was found to increase the odds of a higher final letter grade for average, below average, and failing students. However, despite the learning advantages, students self-reported less favorable attitudes toward adaptive-responsive (3.15 of 5) relative to traditional-responsive OHS (3.31). Specific to the adaptive OHS, the following were found: (i) student attitudes were moderately and positively correlated (r = 0.36, p \u3c 0.01) to final letter grade, (ii) most students (95%) reported engaging in remediation of incorrect responses, (iii) a majority of students (69%) reported changes in study habits, and (iv) students recognized the benefit of using adaptive OHS by ranking its assignments and explanations or review materials as two of the top three most useful course aspects contributing to perceived learning. Instructors can use our findings to inform their choice of online homework system for formative assessment of chemistry learning by weighing the benefits, disadvantages, and learning pedagogies of traditional-responsive versus adaptive-responsive systems