South African Journal of Chemistry - Volume 68, Issue 1, 2015
Volumes & issues
Volume 68, Issue 1, 2015
Solid state NMR characterization and adsorption properties of lignocellulose-clinoptilolite composites prepared with siloxanes coupling agents : research articleSource: South African Journal of Chemistry 68, pp 143 –152 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a21More Less
This study reports the preparation of lignocellulose-clinoptilolite composites by means of N-terminated siloxanes as coupling agents, after acid hydrolysis. Reactions were carried out in the presence of dibutyltin dilaurate as catalyst by reacting lignocellulose modified with the coupling agents and clinoptilolite at 140 °C in DMF under nitrogen atmosphere. The light in weight and fluffy composites obtained were characterized by FT-IR, XRD, TGA, SEM and Solid State NMR. Results depicted possible chemical interactions between the two materials (lignocellulose and clinoptilolite). Used as adsorbents, the composites showed to be good candidates for the removal of used motor oil from aqueous solution, with up to 92mg g-1 of chemical oxygen demand removed.
Multiwalled carbon nanotube-titania nanocomposites : understanding nano-structural parameters and functionality in dye-sensitized solar cells : research articleSource: South African Journal of Chemistry 68, pp 153 –164 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a22More Less
Nanocomposites consisting of multiwalled carbon nanotubes and titania were synthesized by two methods, namely, sol-gel and chemical vapour deposition (CVD) methods. The work takes advantage of the bridging ability of nanotechnology between macromolecules and the solid state process in engineering alternative nanomaterials for various applications including solar cell fabrication. Physical and chemical characterization of the mesoporous nanocomposites from the two synthetic methods were investigated using Raman spectroscopy, thermogravimetric analysis, Fourier transformation infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, surface characterization and X-ray diffraction analysis. Physicochemical properties in the nanocomposites such as thermal stability, pore volume, crystallinity and surface area were observed to be a subject of MWCNT: titania ratios and synthetic methods. From the CVD synthetic method, observed attributes include more uniform and smoother coating; better crystallinity and larger pore width than sol-gel method. On the other hand, nanocomposites from sol-gel synthetic method had larger surface areas, were more defective and less thermally stable than those from CVD. Nanocomposites by the CVD method performed 39.2% more efficient than those from sol-gel in light-harvesting experiments. The study shows that the nanocomposites synthesized were more effective than titania alone when the cheaper natural dye, Eosin B, was used. This highlights the great potential of typical nanomaterials in improving the performances of titania in DSSCs as well as lowering the cost of the ultimate devices.
Source: South African Journal of Chemistry 68, pp 163 –171 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a23More Less
Batch experiments were conducted to study the effects of contact time, pH (3 to 8), initial concentration, presence of carbonate, sulphate, and competing ions (Fe3+, Ca2+, Sr2+, Mg2+) on the adsorption of U(VI) on ammonium-modified zeolite (AMZ). The structural features of the modified zeolite were assessed by Fourier Transform Infra Red Spectroscopy (FTIR) while the metal content was determined by Inductively Coupled Plasma Optical Emission Specroscopy (ICP-OES). The removal of uranium was effective and maximal under acidic conditions (pH 3 to 5). The kinetics of adsorption of U-nitrate and U-sulphate on AMZ were described by the pseudo-second-order model (R2 ≥ 0.9820). In the presence of SO42- and CO32-, a significant reduction of 67.88 % and 71.63 %, respectively, in uranium uptake was observed. The distribution coefficient, KD (L g-1), was in the order of: U-nitrate (1.116) > U-sulphate (0.029) > U-carbonate (0.019), suggesting that AMZ had a high affinity for U-nitrate. The presence of Fe3+ enhanced the removal of U(VI) from U-nitrate, U-sulphate and U-carbonate by 20.18 %, 72.48%and 82.43 %, respectively, while the presence of Ca2+, Mg2+ and Sr2+ reduced the removal to 19.57 %, 31.60 % and 23.65 %, respectively. AMZ is an effective adsorbent for uranium removal from aqueous solutions dominated by nitrate, carbonate and sulphate.
The oxidation of dibenzothiophene using oxidovanadium(IV)-containing nanofibres as catalyst : research articleSource: South African Journal of Chemistry 68, pp 172 –180 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a24More Less
Polyvinylbenzylchloride nanofibres were fabricated by the electrospinning technique and subsequently functionalized with a tetradentate ligand, 2,2'-(1E,1'E)-(1,2-phenylenebis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)bis(4-aminophenol). VO2+ was then incorporated into the nanofibres to produce the catalyst VO-fibres. Microanalysis, TG and FT-IR were used for the characterization of VO-fibre, and EPR also confirmed the presence of oxidovanadium(IV) within the nanofibres. Oxidation of dibenzothiophene (DBT) was investigated by varying the catalyst amount, substrate amount, oxidant and temperature, and the progress of oxidation was followed with a gas chromatograph fitted with a flame ionization detector. An increase in the amount of oxidant caused an increase in the amount of dibenzothiophene sulfone (DBTO2), while a decrease in the quantity of dibenzothiophene resulted in an increase in the overall yield of dibenzothiophene sulfone under a constant temperature and oxidant (H2O2) concentration. Dibenzothiophene sulfone was confirmed as the oxidation product through 1H-NMR spectroscopy and single crystal X-ray diffraction.
Source: South African Journal of Chemistry 68, pp 181 –194 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a25More Less
To braai is part of the South African heritage that transcends ethnic barriers and socio-economic groups. In this paper, a comprehensive analysis of atmospheric gaseous and aerosol species within a plume originating from a typical South African braai is presented. Braai experiments were conducted at Welgegund - a comprehensively equipped regional background atmospheric air quality and climate change monitoring station. Five distinct phases were identified during the braai. Sulphur dioxide (SO2), nitrogen oxides (NOx) and carbon monoxide (CO) increased significantly, while ozone (O3) did not increase notably. Aromatic and alkane volatile organic compounds were determined, with benzene exceeding the 2015 South African one-year ambient air quality limit. A comparison of atmospheric PM10 (particulate matter of an aerodynamic diameter ≤10 µm) concentrations with the 24-hour ambient limit indicated that PM10 is problematic during the meat grilling phase. From a climatic point of view, relatively high single scattering albedo (ωo) indicated a cooling aerosol direct effect, while periods with lower ωo coincided with peak black carbon (BC) emissions. The highest trace metal concentrations were associated with species typically present in ash. The lead (Pb) concentration was higher than the annual ambient air quality limit. Sulphate (SO42-), calcium (Ca2+) and magnesium (Mg2+) were the dominant water-soluble species present in the aerosols. The largest number of organic aerosol compounds was in the PM2.5-1 fraction, which also had the highest semi-quantified concentration. The results indicated that a recreational braai does not pose significant health risks. However, the longer exposure periods that are experienced by occupational vendors, will significantly increase health risks.
A kinetic insight into the activation of n-octane with alkaline-earth metal hydroxyapatites : research articleSource: South African Journal of Chemistry 68, pp 195 –200 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a26More Less
Alkaline-earth metal hydroxyapatites are prepared by the co-precipitation method and characterized using XRD, ICP,NH3-TPD, SEM-EDX, TEM and N2 physisorption analysis. The metal present in the hydroxyapatite influences the acidity of the catalyst. Oxidative dehydrogenation reactions carried out in a continuous flow fixed bed reactor showed that the selectivity towards desired products was dependent on the alkaline-earth metal in the hydroxyapatite. All hydroxyapatite catalysts showed high selectivity towards carbon oxides, followed by cracked products, octenes and aromatics. The highest selectivity and turnover numbers towards C8 products and a high specific rate was shown by Sr-HAp. The activation of n-octane over these catalysts followed the Eley-Rideal mechanism.
Modelling the effects of competing anions on fluoride removal by functionalized polyacrylonitrile coated with iron oxide nanoparticlesSource: South African Journal of Chemistry 68, pp 201 –207 (2015)More Less
Fe2O3 nano particles supported on functionalized poly-acrylonitrile was prepared. PAN-oxime-nano Fe2O3 was characterized by XRD, FTIR and TEM and used for fluoride adsorption. The adsorption capacity increased with increasing initial fluoride concentration and reaction time. Fluoride-removal performance of PAN-oxime-nano Fe2O3 was also tested in the presence of various competing anions usually found in drinking water. Competitive sorption between fluoride and competing anions showed a minimum preference for chloride counterions. Carbonate was the greatest competitor for fluoride removal followed by phosphate and sulphate. Counterion presence decreased fluoride adsorption capacity in order of CO24- > PO34- >SO24- Cl3-. The presence of anions at various concentrations decreased fluoride adsorption capacity on PAN-oxime-nano Fe2O3 by 1.22 to 6.51 mg g-1. Effects of each two anions exist simultaneously in aqueous solution on fluoride adsorption was investigated using Tukey's test (called also a pairwise comparison). Tukey's HSD results indicate that the differences between various pairs of anions are significant (P < 0.05), except for chloride-sulphate (P = 0.08). In the design of PAN-oxime-nano Fe2O3 for environmental applications, the strong influence of the counter ions must be considered.
Kinetic and thermodynamic studies of charge-transfer complex formation between imipramine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (ddq) in acetonitrile and dichloromethane solutions : research articleSource: South African Journal of Chemistry 68, pp 208 –214 (2015)More Less
Spectro-kinetic studies revealed the formation of charge-transfer (CT) complex of imipramine as an electron donor with ð acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in acetonitrile and dichloromethane solutions. The resulted CT complexes exhibit spectra that were remarkably different from those of the donor and acceptor. The stoichiometry of the resulting complex was found to be 1:1 by the method of Job's continuous variation. The formation constants and thermodynamic parameters of the resulting electron-donor-acceptor (DA) complexes were determined by Benesi-Hildebrand and Van't Hoff equations, respectively. The time-dependent spectra recorded after mixing donor and acceptor has been related to an immediate formation of DA complex, which is followed by two relatively slow consecutive reactions. The pseudo-first-order rate constants for the formation of the ionic intermediate and the final product have been evaluated at various temperatures by computer fitting of the absorbance-time data to appropriate equations. The activation parameters, i.e. activation energy, enthalpy, and entropy of activation were computed from temperature dependence of the rate constants. The observed results afford evidence concerning the critical role of solvent polarity on the kinetics and stability of the resulting charge transfer complexes. The ionization potential of the donor in the two solvents was estimated and compared with the theoretical values.
A simple polarimetry technique for predicting the absolute configuration of the preferred enantiomer in chiral host-guest inclusion complexes : research articleSource: South African Journal of Chemistry 68, pp 215 –218 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a29More Less
A method for predicting the configuration of the preferred guest enantiomer in an inclusion complex with an optically pure host compound was developed. The method involves simply measuring the optical rotation of the host-guest inclusion complex as a whole, by means of polarimetry, and using this value in a calculation in order to obtain information about the guest configuration. The availability of standard optically pure guest materials is not required, nor is the isolation of the guest species from the host crystal, resulting in an attractive, inexpensive, rapid and simple procedure for this purpose.
New pyridazinium-based ionic liquids : an eco-friendly ultrasound-assisted synthesis, characterization and biological activity : research articleSource: South African Journal of Chemistry 68, pp 219 –225 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a30More Less
An eco-friendly ultrasound-assisted procedure was developed for the preparation of a series of novel pyridazinium ionic liquids (ILs) 1-8. The structures of the novel ILs were established based on their FT-IR, 1H, 13C NMR and mass spectra. Furthermore, the antimicrobial and anticancer activities of ILs 1-8 have been also investigated. The results of these screening experiments revealed that the ILs exhibited good to moderate antibacterial activity, such as IL 7, compared with standard drugs. Some of the newly synthesized ILs were also tested in vitro against human hepatocellular carcinoma (HEPG2), human breast adenocarcinoma (MCF7) and human colon carcinoma (HCT116) cell lines. Among the synthesized ILs, IL 8 was found to exhibit promising antiproliferative effects and produced the lowest IC50 values among the tested ILs.
Adsorption of mercury(II) onto activated carbons derived from Theobroma cacao pod husk : research articleSource: South African Journal of Chemistry 68, pp 226 –235 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a31More Less
Activated carbon prepared from Theobroma cacao pod husk was used as a low-cost biosorbent for the removal of mercury(II) from aqueous solutions. The influence of pH and contact time on the adsorption was investigated by conducting a series of batch adsorption experiments. The equilibrium data were fitted to the Langmuir and Freundlich isotherm models. The Langmuir isotherm was found to best describe the experimental data. The amount adsorbed increased with increasing temperature. The maximum adsorption capacity of mercury was found to be 105 ng g-1 for an initial mercury concentration of 100 ppb. The kinetics of adsorption were modelled by means of the Lagergren-first-order and pseudo-second-order models. The pseudo-second-order model was found to explain the adsorption kinetics most effectively. It was also found that pore diffusion played an important role in the adsorption, and intra-particle diffusion was the rate-limiting step during the first 30 min. A FTIR study revealed that the carbonyl and sulfur functional groups present on the surface of the adsorbing material were involved in chemical interaction with mercury(II).
An inquiry-based practical curriculum for organic chemistry as preparation for industry and postgraduate research : research articleSource: South African Journal of Chemistry 68, pp 236 –244 (2015) http://dx.doi.org/10.17159/0379-4350/2015/v68a32More Less
This paper describes the development of a new practical curriculum for third-year organic chemistry to replace the recipe-based approach typically used in undergraduate teaching laboratories. The new curriculum consists of an inquiry-based project set in a simulated industrial context preceded by two scaffolding experiments to prepare students for the task. The industrial project requires students to evaluate experimentally three multi-step synthetic routes to a given target based on cost, technical challenge and environmental impact in order to make a recommendation as to which route the 'company' should use to synthesize the compound. The project equips students with technical skills suitable for both postgraduate research and industry, and develops metacognition and understanding through the use of the jig-saw cooperative learning strategy and reflection. The students were found to engage with the practical work at a deep intellectual level, demonstrating that contextualized inquiry-based laboratory teaching afforded an improved quality of learning. In addition, the reported practical curriculum made a difficult subject accessible and even popular, to some measure grew the students' ability in all desired graduate attributes and resulted in the establishment of a professional identity for individual students.
A comparison of adsorption equilibrium, kinetics and thermodynamics of aqueous phase clomazone between faujasite X and a natural Zeolite from Kenya : researchSource: South African Journal of Chemistry 68, pp 245 –252 (2015)More Less
In this study, a well-studied synthetic faujasite X (FAU-X) zeolite and a recently discovered natural zeolite material from Kenya (NZ-K) were compared for their efficiency in removal of clomazone, a herbicide and water contaminant, from aqueous solution. The adsorption kinetics, isotherms and thermodynamics parameters were investigated. Equilibrium sorption data were describable by both the Langmuir and Freundlich models. The adsorption kinetics obeyed the pseudo-second-order kinetic law while pore diffusion was not the sole operating rate determining step. The derived thermodynamic parameters, namely DG and DH, indicated the adsorption process was feasible, spontaneous and exothermic for the natural zeolite and non-spontaneous for the synthetic zeolite via a physical and chemical process, respectively. The natural zeolite proved to be a suitable low-cost adsorbent for clomazone removal with removal efficiency above 70 %, five-fold more efficient than faujasite X.
Ab initio Studies of the Lewis Acid-Base Complexes of Boron Trifluoride with Acetonitrile and Methyl Cyanoacetylene,and Some of their Derivatives : research articleSource: South African Journal of Chemistry 68, pp 253 –262 (2015)More Less
The properties of the 1:1 molecular complexes formed between the Lewis acid boron trifluoride and the Lewis base acetonitrile have been computed ab initio at the second-order level of Møller-Plesset perturbation theory and with Dunning's augmented correlation-consistent polarized valence triple-zeta basis set. The properties of interest are the structures, the interaction energies, the perturbations of the vibrational spectra of the interacting monomers and the orbital reorganizations. The effects of substituting fluorine for hydrogen atoms in the series CHnF3-nCN on the computed properties have been examined. In addition, the effect of introducing a -C°C- bond between the CHnF3-n and CN fragments in the related series of bases CHnF3-nC3N have been explored. The variations in the properties of the complexes as the number of fluorine atoms is varied, for both families of complexes, have been rationalized.