Scielo RSS <![CDATA[South African Journal of Chemistry]]> http://www.scielo.org.za/rss.php?pid=0379-435020220001&lang=pt vol. 76 num. lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Evaluating the influence of interactive simulations on learners' academic performance in stoichiometry</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100001&lng=pt&nrm=iso&tlng=pt Traditional teaching strategies dominate science classrooms in Lesotho, resulting in poor academic performance at each level. Information and Communication Technology tools such as simulations offer potential benefits for improving science teaching. The purpose of this quasi-experimental study was to evaluate the effect of simulations on learners' performance and retention of stoichiometry concepts using Solomon's four-group design. Purposive sampling of two existing Form E (Grade 12) classes, with 81 learners, led to the creation of four groups. The study responds to the research question: How does using simulations as part of an intervention affect learners' academic performance in stoichiometry? Data were collected as learners' scores for pre-tests and post-tests, designed to assess their understanding of stoichiometry, and analysed through ANOVA and t-tests. After the intervention, the experimental group's mean score (M = 44.2, a = 18) was higher than that of control group (M = 32.6, a = 15.8), and the difference between the two mean scores was statistically significant, namely t(81) = 3.14, p = 0.002. The experimental group had a higher mean score for retention in post-test (M = 47.4, a =16.1) than the control group (M = 37.2, a = 13.7) which was statistically significant, namely t(81) = 3.10, p = 0.003. Therefore, it was concluded that simulations enhanced learners' performance and could improve the retention of stoichiometry concepts. This study recommends that simulations be used to supplement the teaching and learning of science, in particular chemistry. <![CDATA[<b>Synthesis and characterization of amine-functionalized supported phosphine catalysts and their application in ethylene oligomerization</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100002&lng=pt&nrm=iso&tlng=pt A series of phosphorus and nitrogen-based ethylene oligomerization ligands of the type Ph2PN(X)PPh2 where X = i-propyl, n-butyl, ethylbenzene and cyclohexyl substituents are reported. These ligands were functionalized to enable tethering on amino-silica. The free ligands, amino-silica and the tethered ligands were characterized by BET, XRD, IR, TGA and NMR. The catalysts were tested for ethylene oligomerization using Cr(acac)3 (acac = acetylacetonate) as the precursor and MMAO (modified methylaluminoxane) as the activator. The activity and selectivity of these catalysts to 1-octene was monitored at 45 bar ethylene in the temperature range of45-100 °C. The activity of the supported catalysts was comparable to their homogeneous counterparts, surpassing them in some cases and selectivities to 1-octene in the C8 products were as high as 99 wt%. The steric effect of the substituent on the ligand as well as that of the support was found to influence the activity and product distribution. <![CDATA[<b>The analysis of alcohol content in hand sanitisers (in the Durban region) using gas chromatography-mass spectrometry during the COVID-19 pandemic</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100003&lng=pt&nrm=iso&tlng=pt The COVID-19 pandemic has resulted in an unprecedented surge in the demand for alcohol-based hand sanitisers (ABHS). The Centre for Disease Control (CDC) and World Health Organisation (WHO) recommend alcohol, i.e., isopropanol or ethanol, at a 60-95% concentration in ABHS for sufficient antiviral protection. Consumers need to be vigilant of substandard hand sanitisers being marketed to the public. The frequent exposure of microorganisms to alcohol concentrations below the recommended range for infection prevention may lead to resistant mutations, and above the range may be ineffective. Therefore, this study aimed to verify the stated alcohol content in hand sanitisers from their respective labels. We analysed 50 hand sanitiser samples available to our region in Durban, KwaZulu-Natal, South Africa, using a Shimadzu GC-MS-QP2010 Ultra equipped with a Zebron ZB-wax capillary column. The hand sanitisers analysed had a range of 44-93% alcohol content. The data from our study also revealed that 32% (16) of hand sanitisers did not adhere to the stated alcohol indicated on their labels. 16% (8) contained &gt;80% and 12% (6) contained <60%, while 6% (3) of the ABHS contained 1-propanol and ethyl acetate as contaminants, respectively. This study clearly emphasises manufacturers' exploitation of the pandemic and the need for stricter guidelines and regulations for consistency amongst ABHS manufacturers. The public should also be more alert to the % alcohol stated (ideal range 60-80%) on the sanitizer bottle and note one needs to rub their hands together until it feels dry. <![CDATA[<b>The simultaneous synthesis of carbon dots and carbon spheres with tunable sizes using a vertical chemical vapour deposition method</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100004&lng=pt&nrm=iso&tlng=pt Herein we report on the direct synthesis of solid hydrophobic carbon dots (CDs) and simultaneously carbon spheres (CSs), using a vertical chemical vapour deposition (CVD) reactor. The HRTEM data indicated that the CDs and CSs originated from different carbon building blocks indicated that the CDs and CSs originated from different carbon building blocks. The CDs were obtained by reacting acetylene (C2H2) and Ar mixtures at high flow rates (>500 sccm) and high temperatures (800-1000 °C). TEM studies indicated that the CDs produced were graphene-like quantum dots that increased in size from c. 3 nm to 8 nm as the Ar flow rate (constant C2H2 flow rate) was decreased, while small solid CSs (c. 100 nm) were also synthesised in the process. The CSs had a typical spherical layered structure with no graphitic core. A mechanism to rationalise the observation that the CDs and CSs grew simultaneously by different pathways with no formation of intermediate-sized particles is given. <![CDATA[<b>Comparison of laser nephelometric and HPLC techniques for efficient determination of solubility of ibuprofen and its 2-hydroxypropyl-β-cyclodextrin inclusion complex</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100005&lng=pt&nrm=iso&tlng=pt Poor drug solubility is a major problem that hinders the discovery and development of new drugs. There is a need for rapid and inexpensive techniques for acquiring reliable drug solubility data. In this study, the suitability of laser nephelometry for the determination of solubility was investigated using ibuprofen, as a model drug of low solubility, and its 2-hydroxypropyl-p-cyclodextrin inclusion complex (ic). This investigation involved the preparation of ibuprofen-ic-cyclodextrin (1:1) using coprecipitation and characterisation. Thermal analysis and assessment of molecular vibrations confirmed the existence of the inclusion complex. The shake flask testing method was employed and carried out in acidic and alkaline media, and solubility data were verified against high-performance liquid chromatography (HPLC). Results obtained via nephelometry showed relative enhanced solubility of ibuprofen in both acidic (0.565 mg ml-1) and basic (7.5 mg ml-1) media, respectively, which was enabled via inclusion complex formation. Relative to nephelometry data, HPLC results showed a similar trend with increased solubility values in acidic (0.454 mg ml-1) and basic (201.73 mg ml-1) media, respectively. The application of laser nephelometry proved to be a quick and relatively cost-effective technique for solubility measurements of the parent drug and its carrier system. <![CDATA[<b>A non-dispersive infrared sensor for real-time detection of cyanogen chloride</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100006&lng=pt&nrm=iso&tlng=pt Cyanogen chloride, as a systemic toxic agent, can cause death rapidly. In this paper, a non-dispersive infrared sensor was designed for the infrared absorption detection of cyanogen chloride at 800 cm-1. The roughness of the internal coating material was analyzed by experiments, and the gold-plated gas chamber was selected. The light path propagation of different cross-section gas chambers was simulated, and the circular section gas chamber was selected to increase the infrared detector signal. The effect of flow rate on voltage was studied. The standard curve between voltage and concentration was obtained under the optimal condition of 0.4 L min-1. The maximum response time was 19 s, and RSD was less than 2%. The interference experiment results showed that common gases entering the gas chamber do not cause interference. The non-dispersive infrared sensor for cyanogen chloride has good stability and detects cyanogen chloride in real-time. <![CDATA[<b>Catalytic hydrogen combustion using platinum supported on anodized aluminium oxide adhered to metallic aluminium</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100007&lng=pt&nrm=iso&tlng=pt The implementation of catalytic hydrogen combustion (CHC) can mitigate the dependence on solid fuel combustion typically used in Sub-Saharan Africa as a means of heating. However, low-cost and readily available materials for catalyst fabrication are relatively unexplored. Considering the economic constraints regarding platinum group metals generally used for CHC, the cost of support materials and its functionalization as catalyst support has to be minimized. Typically, materials such as silicon carbide foam, extruded aluminium oxide-based ceramics, and titanium oxide mesh/sintered plates are used to withstand the high temperatures associated with CHC. In this paper, nanostructured anodized aluminium oxide (AAO) was synthesized as the support material via the anodization of high purity (>99%) aluminium (Al). The AAO layer intimately adhered to a metallic Al core acted as a thermal conduit to disperse heat throughout the catalyst. Platinum (Pt), considered as the reactive metal, was deposited to the AAO as nanoparticles with a diameter of approximately 19.3 nm. The CHC reaction proceeded spontaneously on the surface of the Pt/AAO catalyst. A combustion temperature of408 ± 18 °C was maintained for 70 h at a 100 normal (N) mL min-1 hydrogen flow rate. The Pt-particles showed a relatively appreciable increase in particle size (from 19.3 nm to 25.0 nm), but the significance thereof was not evident during the 70 h CHC procedure. <![CDATA[<b>The use of ex-situ nitrogen-doped olive oil-derived carbon nano-onions for application in chemi-resistive gas sensors to detect acetone at room temperature</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100008&lng=pt&nrm=iso&tlng=pt This study reports on the synthesis of carbon nano-onions (CNOs; ca. d < 55 nm) and nitrogen-doped CNOs (N-CNOs) using a facile pyrolysis method and ex-situ doping of the CNOs. Elemental analysis of the N-CNOs revealed that their nitrogen content depended on the ammonia flow rate. Analysis of the N-CNOs revealed that they all exhibited structural defects. After the successful synthesis of CNOs and N-CNOs, polyvinylpyrrolidone (PVP):CNOs/N-CNOs:MnO2-nanorods (MONRs) composites were prepared and used as active sensing materials. In every case, the PVP polymer was used to stabilize the MONRs for acetone detection at 25 °C. The chemi-resistive gas sensors that showed the highest acetone sensitivity (pS = 2.0 x 10-4 ppm-1) was fabricated using a pristine CNOs (pCNOs) based composite. However, the N-CNOs based sensor (a15S) presented the lowest acetone limit of detection (LoD) at 1.2 ppm. The study implicated the effect of the nitrogen and oxygen content of the CNOs surfaces on the acetone detection. Thus, a higher sensitivity with lower LoD was observed at room temperature using the pCNOs based sensor, when compared to earlier literature reports. <![CDATA[<b>Synthesis, characterisation and optimisation of bulk molecularly imprinted polymers from nonsteroidal anti-inflammatory drugs</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100009&lng=pt&nrm=iso&tlng=pt The scope of this study was to synthesise and characterise the multi-template molecularly imprinted polymer (MIP) and to use target compounds, naproxen, ibuprofen, diclofenac, fenoprofen and gemfibrozil as templates so as to achieve all maximum extraction efficiency for all compounds. These compounds are a class of nonsteroidal anti-inflammatory drugs (NSAIDs) generally used by humans, as they have pain-relieving activities. MlPs are cross-linked polymeric materials that display high binding capacity and selectivity towards templates of interest. The synthesis consisted of a bulk polymerisation process at 60 °C by using NSAIDs as multi-templates, ethylene glycol dimethacrylate (EGDMA), 2-vinyl pyridine (2VP) and toluene as cross-linker, functional monomer and porogen, respectively. Nonimprinted polymer (NIP) was synthesised in a similar manner with the omission of the templates. Characteristics of the polymers were analysed using Scanning Electron Microscopy (SEM), Fourier Transformed Infrared Spectroscopy (FTIR), Solid State Nuclear Magnetic Resonance Spectroscopy (NMR) and Thermal Gravimetric Analysis (TGA). An adsorption method of NSAIDs using the bulk polymerised MIP was investigated under various pH, mass, concentration and time conditions. Other parameters included adsorption kinetics and adsorption isotherms. Uptake of NSAIDs from an aqueous medium was achieved with 40 mg of MIP at pH 4.0 within 10 min of contact time. The extraction efficiencies achieved for NSAIDs in aqueous solutions ranged from 90-98% for all compounds tested. The adsorption capacity obtained for MIP ranged from 1.230-1.249 mg g-1 and 0.90-1.136 mg g-1 for NIP, whereas the selectivity values ranged from 1.12-2.4. A kinetic study revealed that adsorption obeys a second-order rate, and the Langmuir model explains adsorption isotherm data. This work showed that the multi-template approach for all the target compounds has the potential to give maximum extraction efficiencies in MIP extraction systems from aqueous samples. <![CDATA[<b>Potentiometrie and spectroscopic study of isoniazid - an anti-tubercular drug</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502022000100010&lng=pt&nrm=iso&tlng=pt The copper, nickel and zinc complexes of isoniazid (ISO, isonicotinic acid hydrazide), an anti-tubercular drug, have been investigated to determine whether these metal-ions improve the permeability and bioavailability of the drug. Since such properties of isonazid depend on its solution speciation, the latter was investigated by determining the equilibrium constants for the reaction of H+, Cu(II), Ni(II) and Zn(II) with isonazid in aqueous solution at 25.00 ± 0.01 °C and 0.15 M (NaCl), using glass electrode potentiometry. The structure of the copper complex of isoniazid was investigated using ultraviolet-visible spectroscopy. The results support the structures postulated from the potentiometric data. This study also considered membrane permeability using a Franz cell and octanol/water distribution coefficients. Distribution coefficient studies showed that ISO and its metal complexes are hydrophilic. The incorporation of a metal-ion improves the hydrophilicity of the ligand. The presence of a metal ion greatly enhanced the permeation of ISO through an artificial membrane in the order Cu(II) > Ni(II) > Zn(II) > ISO at pH 2 and Zn(II) > Ni(II) > ISO > Cu(II) at pH 4.