Research Articles (Chemical Engineering)

Permanent URI for this collectionhttp://hdl.handle.net/2263/1691

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Enhanced parameter estimation for liquid-liquid equilibrium using homotopy continuation as stability constraints
(Elsevier, 2025-08) Bamikole, John O.; Narasigadu, Caleb; Seedat, Naadhira
Parameter estimation for the activity models such as NRTL and UNIQUAC for liquid-liquid equilibrium (LLE) is a nontrivial task, and this is due to the complex nature of these models and the need to uniquely fit the binary interaction parameters that predict phase behaviour and compositions similar to the experimental ones while ensuring satisfaction of the stability criterion and other conditions. To achieve this task, there is a need for a robust formulation that will capture all the necessary constraints and a good algorithm that will proffer the right solution. This study formulated an LLE problem by introducing the homotopy continuation to create discretised points for tracking the tie-lines to ensure phase stability. Other constraints were also included in this formulation to avoid fictitious phase prediction. The algorithm was applied to several LLE problems, including binary, ternary, and quaternary, for isothermal and non-isothermal LLE systems. The algorithm tackled all the problems, and the estimated parameters predicted stable phases with existent behaviour and compositions with very small discrepancies from the measured compositions. Though the constraint may increase the computational effort, it was beneficial, and the formulation also avoids the back and forth of a posteriori check.
Facile recovery of polycationic metals from acid mine drainage and their subsequent valorisation for the treatment of municipal wastewater
(MDPI, 2025-03) Muedi, Khathutshelo Lilith; Tendenedzai, Job Tatenda; Masindi, Vhahangwele; Haneklaus, Nils Hendrik; Brink, Hendrik Gideon; deon.brink@up.ac.za
Please read abstract in the article.
Crystallinity engineering of FexO through doping and ligand design for improved oxygen catalysis in zinc-air batteries
(Elsevier, 2025-05) Peng, Jiao; Liu, Fangfang; Huang, Xinjie; Feng, Lijuan; Wang, Hui; Wang, Xuyun; Ren, Jianwei; Wang, Rongfang; jianwei.ren@up.ac.za
Please read abstract in the article.
ZnO–polyaniline nanocomposite functionalised with Laccase enzymes for electrochemical detection of Cetyltrimethylammonuium Bromide (CTAB)
(MDPI, 2024-12) Kyomuhimbo, Hilda Dinah; Feleni, Usisipho; Haneklaus, Nils H.; Brink, Hendrik Gideon; deon.brink@up.ac.za
Please read abstract in article.
Eco-organic system and silicon-based biostimulant as a strategy for vegetable production under multistress conditions in South Africa : a review
(Society for Advancement of Horticulture, 2024) Moyo, K.; Khetsa, Z.P.; Masowa, M.M.; Van Der Watt, E.; Moloantoa, K.M.; Unuofin, John Onolame
Plants get exposed to multiple stresses throughout their phenological growth stages. At most, these stresses are attributed to single or combined stresses like salinity, water deficits, wounding, mineral deficiencies, potting bag size, soil/root media density and type, soil pH, and the type of production system employed. Multistress factors have been widely reported to reduce the plant growth and development, strength, yield, and quality of horticultural crops globally. In the literature, reports extensively recommended the use of silicon-based biostimulants to improve the growth and development of commercial horticultural plants; however, little has been reported in South Africa on the recovery response mechanisms of beetroot (Beta vulgaris L.), lettuce (Lactuca sativa L.), tomato (Solanum lycopersicum L.), and kale (Brassica oleracea L.) grown under multi-stress conditions treated with silicon-based biostimulants, and using the cheaper eco-friendly production systems. In South Africa, most silicon-based biostimulant production companies reserve their novel concoctions as their company secrets; thus, many of the products are never tested in public to ascertain and monitor compliance with the Fertilizers, Farm Feeds, Agricultural Remedies, and Stock Remedies Act 36 of 1947 in South Africa. On the other hand, emerging farmers and smallholder growers are failing to afford existing agricultural insurance options, thereby affecting their yields against the commercially developed farmers. Although the government aids farmers, the assistance does not cover all costs associated with the multistress losses. Some farmers and growers adopted advanced production systems; however, at most, these systems are costly and rely primarily on electricity as a source of power, which is a challenge in South Africa. This paper explains various production systems used by commercial and emerging farmers, and the smallholder growers in South Africa to reduce costs related to multistress losses. Moreover, an alternative eco-organic production system that applies silicon-based biostimulant as a novel idea for commercial vegetables grown under extreme multi-stress conditions is recommended for emerging farmers and smallholder growers in South Africa. Future studies should be based on eco-friendly production systems in vegetable production in line with Sustainable Development Goals, to combat poverty and improve the livelihood of the African countries.
Effect of liquid viscosity and surface tension on the spray droplet size and the measurement thereof
(Isfahan University of Technology, 2024-12) Chideme, Nyasha; De Vaal, Philip L.; nyasha.chideme@tuks.co.za
This investigation focuses on the impact of liquid properties—viscosity, surface tension—and air pressure on the Sauter Mean Diameter (SMD) of atomization sprays. Utilizing a twin-fluid atomizer, the study resulted in derived equations that quantify these effects across a spectrum of liquid behaviours, with an emphasis on both viscous and non-viscous liquids. The derivation process for viscous liquids yielded equations showcasing an average deviation of 1.32% from experimentally observed SMD values, validated across a dataset of 250 experimental trials. These trials involved a total of 18,000 droplets analysed, with a standard error of 0.02%, spanning a liquid viscosity range of 3x10-3 to 20x10-3 kg/(m.s), and air pressures from 50 to 300 kPag. For non-viscous liquids, defined by a liquid viscosity threshold of < 3x10-3 kg/(m.s), the equations revealed a higher average deviation of 1.51% from the experimental SMD. These runs included the analysis of 19,600 droplets across liquid surface tensions from 20x10-3 N/m to 72.8x10-3 N/m, with a standard error of 0.03%. This distinction highlights the significant influence of surface tension in shaping the atomization outcomes for these liquids. A quantitative discovery of this research is how a 10% increase in viscosity for viscous liquids correlates to a substantial 33% increase in SMD, impacting around 10,500 droplets per viscosity level, with an observed standard deviation of 0.15% across viscosity measurements. This emphasizes the dominance of viscosity in influencing atomization dynamics for viscous liquids. Conversely, for non-viscous liquids, a 10% increase in surface tension translates to a 45% increase in SMD, affecting approximately 11,200 droplets per surface tension category, with a standard deviation of 0.18% in surface tension measurements. Moreover, this study pioneers the introduction of a particle tracking code, designed for high-speed camera frames, enabling the analysis of over 10,000 droplets per experimental run, summing up to more than 280,000 droplets analysed across all trials, with an overall precision rate of 99.5%. This novel technique enhances system performance by providing highly accurate and real-time droplet size distribution data, which is critical for optimizing atomization processes in industrial applications. In comparison with state-of-the-art studies, this research offers a comprehensive analysis of the combined effects of viscosity, surface tension, and air pressure on SMD, providing new insights and validated predictive models. The contributions of this work lie in its detailed quantitative results and the introduction of advanced measurement techniques, which together represent a significant advancement in the field of atomization.
Chemical, thermogravimetric and elemental characterization of Nigerian groundnut and cowpea shells for sustainable valorization
(IOP Publishing, 2024) Onyelucheya, Chioma Mary; Nwabanne, Joseph Tagbo; Daramola, Michael Olawale; Iwarere, Samuel Ayodele
In this study, the chemical, thermogravimetric, and elemental composition of Nigerian groundnut (Arachis hypogaea L.) and cowpea shells (Vigna unguiculata) were investigated to understand their potential as valuable waste resources. Analysis of the carbohydrates and lignin content was performed using the National Renewable Energy Laboratory method. Fourier transform infrared (FTIR) spectroscopy was used to determine the chemical structure of the substrates. Elemental analysis was performed using X-ray fluorescence (XRF) and an elemental analyzer to determine the carbon, hydrogen, nitrogen, and sulphur. In addition, thermogravimetric analysis was used to assess the thermal stability of the substrates. The chemical composition analysis revealed that the cowpea shells contain 21.32% cellulose, 21.46% hemicellulose, and 28.37% lignin. On the other hand, groundnut shells comprise 26.31% cellulose, 19.5% hemicellulose, and 38.33% lignin. The XRF results indicated the presence of significant elemental compositions in both substrates, including Si, Al, Mg, Na, P, Fe, K, Ca, and S. The carbon content of both substrates was found to be 43%. Thermogravimetric analysis revealed that groundnut shells exhibit a higher cellulose decomposition temperature at 350 °C, whereas cowpea shells manifest this phenomenon at 322 °C. The results show that the cowpea shells had a higher heating value as they exceeded that of the groundnut shell by 0.89 per cent. These comprehensive findings show the substantial potential of Nigerian groundnut and cowpea shells as valuable waste materials, which can be effectively used to produce valuable products such as bioethanol, biochemicals, biochar, and bio-composite materials. This research contributes to understanding the composition and properties of these agricultural by-products, thus paving the way for their sustainable use in various industrial applications.
Enhancing hydrothermal durability of gas diffusion layer by elevated temperature treatment technique for proton exchange membrane fuel cell application
(Elsevier, 2025-03) Su, Huaneng; Wu, Tianen; Liu, Huiyuan; Zhang, Weiqi; Xu, Qian; Ren, Jianwei
Liquid water flooding is one of the major challenges in the high current density operation of proton exchange membrane fuel cells (PEMFCs). Optimizing microstructure and properties of gas diffusion layer (GDL), as an essential diffusion medium in PEMFCs, is considered as a promising approach to ensure the long-term stable operation of PEMFCs at high current densities. Herein, we report a simple elevated temperature treatment technique to enhance the hydrothermal durability and water removal capacity of GDLs. Although elevating the heat-treatment temperature from 330 °C (most commonly used) to 430 °C has no obvious impact on the GDLs’ surface hydrophobicity, the GDL treated at 430 °C exhibits excellent hydrothermal stability and water removal capacity due to the increased dispersion of polytetrafluoroethylene (PTFE). In PEMFC, the membrane electrode assembly (MEA) containing the elevated-temperature-treated GDL could maintain high performance at high current densities and high humidity conditions. 200 h steady state test at high current densities and high humidity conditions manifests that the MEA with elevated-temperature-treated GDL is more stable and has better water removal capacity than the MEA with normal-temperature-treated GDL.
Optimisation, synthesis, and characterisation of ZnO nanoparticles using Leonotis ocymifolia (L. ocymifolia) leaf extracts for antibacterial and photodegradation applications
(MDPI, 2024-11) Mutukwa, Dorcas; Taziwa, Raymond Tichaona; Tichapondwa, Shepherd Masimba; Khotseng, Lindiwe E.
This work presents a green synthesis route, which utilises extracts from an indigenous plant in South Africa, eastern and southern Africa that is understudied and underutilised, for preparing zinc oxide nanoparticles (ZnO NPs). This study involved optimisation of the green synthesis method using Leonotis ocymifolia (L.O.) extracts and performing comparative studies on the effects of using different zinc (Zn) salt precursors; zinc sulphate heptahydrate (Z001) and zinc acetate dihydrate (Z002) to synthesise the ZnO NPs. The comparative studies also compared the L.O-mediated ZnO NPs and chemical-mediated ZnO NPs (Z003). The as-prepared ZnO NPs were tested for their effectiveness in the photodegradation of methylene blue (MB) dye. Furthermore, antibacterial studies were conducted using the agar well diffusion method on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria. The structural, morphological, and optical characteristics of the synthesised ZnO NPs were analysed using XRD, FTIR, SEM, EDS, DRS, and BET techniques. The XRD results indicated that the L.O-mediated ZnO NPs had smaller crystallite sizes (18.24–19.32 nm) than their chemically synthesised counterparts (21.50 nm). FTIR confirmed the presence of biomolecules on the surface of the L.O-mediated NPs, and DRS analysis revealed bandgap energies between 3.07 and 3.18 eV. The EDS results confirmed the chemical composition of the synthesised ZnO NPs, which were made up of Zn and O atoms. Photocatalytic studies demonstrated that the L.O-mediated ZnO NPs (Z001) exhibited a superior degradation efficiency of the MB dye (89.81%) compared to chemically synthesised ZnO NPs (56.13%) under ultraviolet (UV) light for 240 min. Antibacterial tests showed that L.O-mediated ZnO NPs were more effective against S. aureus than E. coli. The enhanced photocatalytic and antibacterial properties of L.O-mediated ZnO NPs highlight their potential for environmental remediation and antimicrobial applications, thus supporting sustainable development goals.
Enhanced photodegradation of tetracycline by novel porous g-C3N4 nanosheets under visible light irradiation
(Elsevier, 2025-05) Phakathi, Nothando A.; Tichapondwa, Shepherd Masimba; Chirwa, Evans M.N.; u17381292@tuks.co.za
Please read abstract in the article.
Hydrogeochemical and hydrogeological baseline study following the mining of asbestos at the Havelock Mine, Bulembu, eSwatini
(Elsevier, 2025-04) Wolkersdorfer, Christian; More, Kagiso S.; Mugova, Elke; Nchabeleng, Nokuthula; Sotiralis, Anna Johanna
This study examined the hydrogeological and hydrochemical conditions around Bulembu, eSwatini, two decades post-closure of the Havelock asbestos mine. On-site parameters and water samples underwent chemical and stable isotope analysis, supplemented by flow measurements and tracer tests with NaCl and uranine. Multivariate statistical analysis and PHREEQC modelling identified three water groups: i) low mineralised surface water (32 mg/L TDS), ii) mining-influenced water from the Havelock mine pool (212 mg/L TDS), and iii) tailings seepage water (411 mg/L TDS). All are earth alkaline, hydrogen carbonate-dominant, dominated by Mg and hydrogen carbonate ions. Surface water complies with WHO standards, except for elevated As in the mine pool and Cr in waste rock seepage. Chemical and tracer test results indicate a well-mixed, low-residence-time mine pool. Both the Tutusi river catchment and the upper Nkomazana catchment as well as water courses downstream of the abandoned mine exhibit pristine water quality. The authors propose inclusion of the area in a trans-boundary national park with the Barbeton Makhonjwa Mountains UNESCO World Heritage Site. They recommend amelioration of tailings, not remining, to safeguard the environment and local population from asbestos exposure.
Highly efficient removal of Pb2+ from aqueous solution using polyaniline-cobalt composite nanorods : kinetics, isotherm and mechanistic investigation
(Elsevier, 2025-02) Bhaumik, Madhumita; Maity, Arjun; Brink, Hendrik Gideon
Please read abstract in the article.
Unlocking the magnetic potential of Fe2O3 nanoparticles by single-step synthesis of cobalt-infused nanomaterials for chromium removal
(Springer, 2024-06) Balarabe, Bachir Yaou; Bomokayi, Primerose; Adjama, Iredon; Mahamane, Abdoulkadri Ayouba; Daramola, Michael Olawale; Iwarere, Samuel Ayodele; michael.daramola@up.ac.za
The study optimized the chromium removal capacity of Fe2O3 nanoparticles through the infusion of cobalt using a singlestep synthesis method. This approach not only enhanced their magnetic properties but also employs less-chemical synthesis techniques, ultimately yielding highly magnetic CoFe2O4 nanoparticles and less impurities. The prepared materials underwent comprehensive testing, encompassing examinations of their optical properties, structure, chemical composition, and surface characteristics using various analyticals methods. In a span of 90 min under visible light exposure, CoFe2O4 nanoparticles exhibit the ability to remove more that 90% of chromium. This was corroborated through analysis using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). Moreover, the study illustrates that increased temperatures amplify the endothermic process of chromium adsorption. Positive ΔH°, negative ΔS°, and heightened Cr(IV) adsorption are linked to the temperature effects on solubility, mobility, and dissolved oxygen. Both Langmuir ( R2 = 0.95, RL = 0.055) and Freundlich models ( R2 = 0.98, n = 0.69) suggest favorable adsorption. The efficient Cr(IV) adsorption by CoFe2O4 nanocomposite is attributed to a rapid reaction rate and substantial capacity, following pseudo-second order kinetics (rate constant 0.01 g mg− 1 min− 1, R2 = 0.99).
Uncovering thermally activated purple-to-blue luminescence in co-modified MgAl-layered double hydroxide
(Royal Society of Chemistry, 2024-04) Gevers, Bianca R.; Roduner, Emil; Leuteritz, Andreas; Labuschagne, F.J.W.J. (Frederick Johannes Willem Jacobus)
Thermally activated blue-to-purple luminescence of Co-modified nano-sandrose MgAl-layered double hydroxides (LDHs) is concentration dependent, occurring only for MgCoAl-LDH with a molar metal cation concentration of 15% Co. Temperature sweep luminescence spectroscopy between 83 K and 298 K shows that the luminescence is strongest at room temperature, increasing with an activation energy of 1 kJ mol−1 between these temperatures. The luminescence occurs in a broad, but fine-structured band below the conduction band (CB) edge at 3.0 eV after excitation at 5.0 eV.
Efficient aqueous copper removal by burnt tire-derived carbon-based nanostructures and their utilization as catalysts
(MDPI, 2024-03-13) Arunachellan, Iviwe Cwaita; Bhaumik, Madhumita; Brink, Hendrik Gideon; Kriveshini Pillay; Maity, Arjun; deon.brink@up.ac.za
This research focuses on valorising waste burnt tires (BTs) through a two-phase oxidation process, leading to the production of onion-like carbon-based nanostructures. The initial carbonization of BTs yielded activated carbon (AC), denoted as “BTSA”, followed by further oxidation using the modified Hummer’s method to produce onion-like carbon designated as “BTHM”. Brunauer– Emmett–Teller (BET) surface area measurements showed 5.49 m2/g, 19.88 m2/g, and 71.08 m2/g for raw BT, BTSA, and BTHM, respectively. Additional surface functionalization oxidations were observed through Fourier-Transform Infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) analyses. Raman spectroscopy indicated an increased graphitic nature during each oxidation stage. BTHM was assessed in batch adsorption studies for cupric wastewater remediation, revealing a two-phase pseudo-first-order behaviour dominated by mass transfer to BTHM. The maximum adsorption capacity for Cu2+ on BTHM was determined as 136.1 mg/g at 25 ◦C. Langmuir adsorption isotherm best described BTHM at a solution pH of 6, while kinetics studies suggested pseudo-second-order kinetics. Furthermore, BTHM, laden with Cu2+, served as a catalyst in a model coupling reaction of para-idoanisole and phenol, successfully yielding the desired product. This study highlights the promising potential of BTHM for both environmental remediation and catalytic reuse applications to avoid the generation of secondary environmental waste by the spent adsorbent.
Ruthenium thrifting – computation insights in NH3 decomposition onto Ru single atom catalyst CeO2
(Italian Association of Chemical Engineering, 2024) Motsa, Nomcebo P.; Oduma, Daniel A.; Ouma, C.N.M.; Oko, Eni; Daramola, Michael Olawale; nomcebo.motsa@up.ac.za
Please read abstract in article.
Laccase enzyme embedded on Zinc oxide/silver doped zinc oxide nanoparticle-chitosan-PVPP composite beads
(Italian Association of Chemical Engineering, 2024) Kyomuhimbo, Hilda Dinah; Feleni, Usisipho; Brink, Hendrik Gideon; deon.brink@up.ac.za
Laccase enzyme has gained popularity due to its wide range of substrates, use of only molecular oxygen as a co-factor and release of water as a by-product. In this study, laccase enzyme was immobilized on zinc oxide-chitosan/polyvinylpolypyrrolidone (Lac-Zn-CS-PVPP) composite beads and the beads explored for the degradation of Bismarck brown dye. The beads showed significant dye removal in batch studies (with 89 % and 94 %) after 24 hours and continuous packed bed (with 72 % and 86 %) for Lac enzyme free and Lac enzyme loaded beads respectively. FTIR showed that adsorption of the dyes onto the beads was due electrostatic interaction between the hydroxyl, carbonyl and amine functional groups on the beads and the dye molecules.
Editorial for the special issue “Sustainable mining as the key for the ecological transition : current trends and future perspectives”
(MDPI, 2024-04-08) Brink, Hendrik Gideon; Dore, Elisabetta; Perlatti, Fabio; Lattanzi, Pierfranco
A crucial aspect in the pursuit of sustainable development is the necessary shift toward an “ecological transition”, a transformation in societal paradigms to align human activities with the global ecosystem. This change stems from the urgent need to tackle challenges such as climate change and growing social disparities.
Organic ligands and CeO2-induced generic valence modulation strategies to design Fe active sites for promoted oxygen involved reactions in rechargeable zinc-air batteries
(Royal Society of Chemistry, 2025-03) Peng, Jiao; Wang, Zining; Ren, Jianwei; He, Yudong; Li, Jiahao; Xin, Shichang; Wang, Xuyun; Wang, Hui; Wang, Rongfang; jianwei.ren@up.ac.za
Please read abstract in the article.
Enhancing polysulfide conversion in lithium–sulfur batteries through the synergistic effect of 2,6-Dihydroxyanthraquinone and Co atoms
(American Chemical Society, 2025-01) You, Huijuan; Liu, Fangfang; Wang, Hanxiao; Wang, Zining; Wang, Xuyun; Zhang, Boshen; Tang, Kuanshuo; Ren, Jianwei; Wang, Rongfang; jianwei.ren@up.ac.za
Currently, lithium–sulfur batteries for wider applications are challenged by both the shuttle effect in the cathodes as well as the slow kinetics of the sulfur redox reactions. Although metal compounds have been reported to suppress the shuttle effect of lithium polysulfides (LiPSs) by chemically adsorbing LiPSs and catalyzing their conversion, current methods for sulfur fixation on cathode materials remain insufficient. In this work, 2,6-dihydroxyanthraquinone (DHAQ) is tightly adsorbed on a Co-doped porous carbon (Co–C) substrate through π–π stacking. The abundant oxygen-containing functional groups in DHAQ form Li–O bonds with lithium in the LiPSs and enable in situ covalent fixation. Meanwhile, cobalt in Co–C forms Co–S bonds with sulfur in LiPSs, providing an efficient pathway for electron transfer and promoting LiPS conversion. Thus, the DHAQ/Co–C composite provides dual chemical adsorption capabilities that mitigate the “shuttle effect” of LiPSs. Additionally, the conductive merits of the DHAQ and Co–C networks accelerate electron transfer, enhance LiPS redox kinetics, and increase the battery’s specific capacity. In the end, the optimized S@DHAQ/Co–C composite demonstrates an initial discharge capacity (1385 mAh g–1) at 0.1C. After 600 cycles, the electrode displays a capacity decay rate of 0.062% at 1C. Compared with metal-based materials that rely solely on chemical sulfur fixation, the synergistic effect of organic oxygen atoms and metals in sulfur fixation offers significant improvements.

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