Department of Chemistry - Research Articles

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An approach to dealing with the difficulties undergraduate chemistry students experience with stoichiometry.
(South African Chemical Institute (SACI), 2004-03-04) Marais, Fiona; Combrinck, Sandra
Chemistry for first year students has been identified by Tshwane University of Technology as one of the subjects with a low pass rate. It is apparent that students often memorize formulae and definitions, without understanding the underlying concepts required to work with abstract units of measure. We have found that the majority of students at this university are unable to balance reaction equations satisfactorily. They are also unable to predict the reaction yield or identify limiting reagents. It is imperative that these and other related problems are overcome before any meaningful change to the high failure rate at first year level will be realized. All conventional forms of lecture presentation failed to make any significant impact on the success rate. Structured worksheets were developed and used, together with tactile models, to address the problems and the initial findings showed a marked improvement. It was discovered that the students’ problems originated from their inability to understand the meaning of subscripts and coefficients in chemical equations. The worksheets and the impact they have made on the students ’understanding of stoichiometry are shared in this paper.
True nickel-catalyzed oligomerization versus hetero-oligomerization: development of indicators for determining the mode of oligomerization as a function of reaction temperature.
(Springer, 2004-03-16) Heveling, Josef; Nicolaides, Christakis P.; Scurrell, Michael S.
Ni (II)-exchanged amorphous silica–aluminas are effective catalysts for the oligomerization of lower alkenes. The mode of the reaction and the product spectrum obtained depends largely on the reaction temperature employed. At low temperatures (~120), mainly selective nickel-catalyzed oligomerization is observed (true oligomerization). As the reaction temperature is raised, the formation of hydrocarbons composed of non-integral multiples of the monomer increases (hetero-oligomerization). Plots of the ratio of integral multiples to non-integral multiples of the monomer versus reaction temperature are powerful indicators of the mode of oligomerization taking place. These plots are described by exponential relationships, and on a logarithmic scale, straight lines are obtained. The catalysts studied by us were grouped into two classes, those of (i) low to medium catalytic activity, and (ii) high catalytic activity. For group (i) catalysts (of relatively low nickel loading), the temperature of 180 C marks the changeover from predominantly true oligomerization to predominantly hetero-oligomerization. For group (ii) catalysts (high nickel loadings), the contributions of true nickel-catalyzed oligomerization extends further into the high-temperature region (up to ~300 C). The Y-intercepts of the plots can be taken as a measurement of the intrinsic selectivity of the catalysts (true versus heterooligomerization), while the value of the slopes quantifies the sensitivity of the selectivity to increasing reaction temperature (changeover from selective true to unselective hetero-oligomerization).
Symbiotic performance of selected cyclopia vent. (honeybush) rhizobia under nursery and field conditions.
(Symbiosis Group, 2008-10-22) Spriggs, Amy c.; Dakora, Felix D.
Three newly selected strains of Cyclopia rhizobia together with an inoculant strain, which has never been tested in the field with adequate experimental design, was assessed under both nursery and field conditions for symbiotic performance. The three new test strains were initially selected for their superior Nz-fixing abilities under glasshouse conditions, and then evaluated in this study for field performance. Cyclopia subternata Vogel and Cyclopia genistoides (L.) R. Br., which have the potential for producing high quality honeybush tea, were used as host plants in both the nursery and field studies. The effect of seedling inoculation at the nursery level was also examined for the four test strains under nursery conditions. The inoculation of cuttings under nursery conditions produced. Significant increases in shoot biomass, shoot %N and shoot N content. More specifically, inoculating C. subternata with strains UCT44b and UCT61a significantly increased shoot biomass and N content relative to strain PPRICI3. Strains UCT44b and UCT61a also showed better nodulation with C. subternata cuttings compared to strains UCHOa and PPRICI3. Field inoculation of Cyclopia increased all growth parameters relative to the uninoculated control, except for leaf %N. Cyclopia subternata inoculated with strains UCT44b, UCT40a and UCT61a produced significantly lower b15N values than the uninoculated. subternata reference plant. Using the 15N natural abundance method, C. subternata was estimated to be gaining about half of its N from Nz fixation, while C. genistoides obtained less than half of its N from symbiotic nutrition.
Effect of legume plant density and mixed culture on symbiotic N2 fixation in five cowpea (Vigna unguiculata L. Walp.) genotypes in South Africa.
(Symbiosis Group, 2008-08-22) Makoi, Joachim H.J.R.; Chimphango, Samson B.M.; Dakora, Felix D.
N2 fixation in cowpea plants grown in farmers' fields in the Upper West Region of Ghana, measured using 15N natural abundance.
(Symbiosis Group, 2008-08-27) Naab, Jesse B.; Chimphango, Samson M.B.; Dakora, Felix D.
Few studies have assessed the levels of symbiotic N nutrition in legumes grown by fanners in Africa. In this study, the shoots of cowpea plants were sampled from 63 farms in 12 villages within 5 districts of the Upper West Region of Ghana and assessed for growth and symbiotic N nutrition. The data revealed considerable differences in cowpea plant density per m2 , plant growth, 15N natural abundance (OI5N), %Ndfa, and N-fixed among different farms under one village, and between villages under the same district, and between districts in the Upper West Region. In farms where there were fewer cowpea plants per m2, plant growth was better and dry matter yield per plant significantly greater, leading to strong variations in O!5N values. Except for four farms at Bamahu which had cowpea shoot Ndfa values of 12.1%,30.0%,36.5% and 46.6%, one farm at Babile with Ndfa value of 58.1%, and three farms at Silbelle with Ndfa values of56.8%, 57.9% and 68.7%, the remaining 55 out of the 63 farms studied showed high shoot Ndfa values, ranging from 70.6% to 99.7%, which clearly indicates that cowpea cultivated by farmers in the Upper West Region of Ghana meet a large proportion of their N requirements from symbiotic fixation. At the district level, isotopic analysis showed that, on average, the 15N natural abundance values (%0) of cowpea shoots were -0.496±0.04 for Jirapa, -O.083±0.06 for Nadowli, 0.368±O.08 for Lawra, l.333±0.29 for Wa and 0.365±0.09 for Sissala district. Estimates of the legume's N derived from fixation were 66.3% for Wa district, 89.9% for Nadowli, 79.4% for Lawra, 78.9% for Sissala and 80.9% for Jirapa district. The amount of-fixed ranged from 402.3 mg. Plant' for Nadowli, 176.5 mg.plant" for Wa, 235.4 mg.plant' for Sissala, 179.0 rng.plant' for Lawra to 249.2 mg.plane! for the Jirapa district. Expressed on per-hectare basis using cowpea density per m2, the total amount of N-fixed was around 16.6 kg ha-! in the Nadowli district, 19.1 kg ha-! in Wa, 23.0 kg ha' in Sissala, 21.1 kg ha-I in Lawra and 17.6 kg ha-1in the Jirapa district. Averaged across all 5 districts, N-fixed by cowpea was about 19.5 kg ha-! in the Upper West Region of Ghana. These data suggest that, increasing N2 fixation in fanners' fields in Ghana would require optimization of cowpea plant density rather than biological manipulation of the symbiotic process (as %Ndfa values were generally very high.
Palladinized graphene oxide‑mof induced coupling of volmer and Heyrovsky mechanisms, for the amplification of the electrocatalytic efficiency of hydrogen evolution reaction.
(Nature Research, 2021-08-26) Makhafola, Mogwasha D.; Modibane, Kwena D.; Ramohlola, Kabelo E.; Maponya, Thabiso C.; Hato, Mpitloane J.; Makgopa, Katlego; Iwuoha, Emmanuel I.
In this study, a nanocomposite of palladium supported graphene oxide (GO)/metal–organic framework (MOF) was prepared using electroless deposition of Pd on GO followed by impregnation method of Pd@GO and MOF. The prepared materials were characterized with various analytical techniques and their applications as HER electrocatalysts were evaluated using cyclic voltammetry (CV), Tafel plots, and turn over frequencies (TOFs). The HER results showed a radical increment of H2 production in the nanocomposite through the Volmer reaction together with Heyrovsky or Tafel mechanism. This disclosed that the addition of Pd@GO/MOF in the electrolytic system possessed better catalytic characteristics with enhanced current density which may open a new way for hydrogen production and storage via HER.
Highlighting the importance of characterization techniques employed in adsorption using metal–organic frameworks for water treatment.
(MDPI, 2022-09-01) Maponya, Thabiso C.; Makgopa, Katlego; Somo, Thabang R.; Modibane, Kwena D.
The accumulation of toxic heavy metal ions continues to be a global concern due to their adverse effects on the health of human beings and animals. Adsorption technology has always been a preferred method for the removal of these pollutants from wastewater due to its cost-effectiveness and simplicity. Hence, the development of highly efficient adsorbents as a result of the advent of novel materials with interesting structural properties remains to be the ultimate objective to improve the adsorption efficiencies of this method. As such, advanced materials such as metal– organic frameworks (MOFs) that are highly porous crystalline materials have been explored as potential adsorbents for capturing metal ions. However, due to their diverse structures and tuneable surface functionalities, there is a need to find efficient characterization techniques to study their atomic arrangements for a better understanding of their adsorption capabilities on heavy metal ions. Moreover, the existence of various species of heavy metal ions and their ability to form complexes have triggered the need to qualitatively and quantitatively determine their concentrations in the environment. Hence, it is crucial to employ techniques that can provide insight into the structural arrangements in MOF composites as well as their possible interactions with heavy metal ions, to achieve high removal efficiency and adsorption capacities. Thus, this work provides an extensive review and discussion of various techniques such as X-ray diffraction, Brunauer–Emmett–Teller theory, scanning electron microscopy and transmission electron microscopy coupled with energy dispersive spectroscopy, and X-ray photoelectron spectroscopy employed for the characterization of MOF composites before and after their interaction with toxic metal ions. The review further looks into the analytical methods (i.e., inductively coupled plasma mass spectroscopy, ultraviolet-visible spectroscopy, and atomic absorption spectroscopy) used for the quantification of heavy metal ions present in wastewater treatment.
Great South African molecules: The case for mycothiol.
(South African Chemical Institute (SACI), 2017-03-17) Nkambule, Comfort M.
SouthAfrica has one of the oldest chemical societies in the world and has a long history of natural products, synthetic, and medicinal chemistry yet the visibility of molecules discovered or synthesized in South Africa is very low. Is this because South African scientists are incapable of discovering influential and celebrated molecules, or is there inadequate publicity of such discoveries? Perspective profiles on the discovery and scope of research on ‘Great South African Molecules’ should be a good start to redress this state of affairs. One such molecule deserving publicity is the antioxidant mycothiol which is produced by mycobacteria. This is a molecule of interest not only because of its medicinal potential in the fight against tuberculosis, but also from synthetic methodology and enzyme inhibition studies. This review aims to illuminate the scope of research in mycothiol chemistry for the purpose of promoting multidisciplinary investigations related to this South African molecule.
Palladium deposition on copper(II) phthalocyanine/metal organic framework composite and electrocatalytic activity of the modified electrode towards the hydrogen evolution reaction.
(Elsevier Ltd., 2017-11-29) Monama, Gobeng R.; Mdluli, Siyabonga B.; Mashao, Gloria; Makhafola, Mogwasha D.; Ramohlola , Kabelo E.; Molapo, Kerileng M.; Hato, Mpitloane J.; Makgopa, Katlego; Iwuoha , Emmanuel I; Modibane, Kwena D.
Pd-supported copper phthalocyanine/metal organic frameworks (Pd@CuPc/MOF) composite was synthesized by the reaction between CuPc and MOF followed by electroless Pd plating. The structural properties of MOF, Pd@MOF and Pd@CuPc/MOF composite were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), simultaneous thermal analysis (STA), ultraviolet visible spectroscopy (UVevis), scanning electron microscopy (SEM/EDS) and Brunauer-Emmett-Teller (BET). The XRD, UVevis and FTIR analyses showed that Pd was coated on CuPc/MOF composite. SEM and EDS results revealed that Pd nanoparticles were well-dispersed and anchored tightly on the composite. The thermal stability of MOF increased upon addition of Pd and CuPc. The electrochemical hydrogen evolution reaction (HER) performance of the synthesized materials was studied by cyclic voltammetry (CV) and Tafel analysis. The Tafel slope of the composite was 176.9 mV/dec and the transfer coefficient of 0.67 which is close to 0.5. The HER results revealed that the Pd@CuPc/MOF composite has better catalytic characteristic such as high catalytic activity and lowest onset potential compared to MOF. More importantly, the significant enhancement of HER performance at ambient temperature for the composite with Pd content can be ascribed to the hydrogen spillover mechanism in such system.
Extraction potential of lolium perenne L. (Perennial Rye Grass) for metals in landfill soil: Its tolerance and defense strategies.
(MDPI, 2023-06-28) Masotla, Mmatsheko Kgaladi Leah; Melato, Funzani Asnath; Mokgalaka-Fleischmann, Ntebogeng Sharon
Landfill sites open and close frequently throughout the world, taking over a significant amount of land and leaving it contaminated and unavailable to the surrounding population for use. Different forms of remediation methods have been employed to rehabilitate contaminated land to a state that poses less of a threat to the environment. Phytoremediation is one of the remediation techniques that has proven to be effective, economical and easier to implement compared to other methods. The main aim of this study was to explore the potential use of Lolium perenne L. to remediate and restore metal-contaminated landfill soil and determine its stress tolerance mechanism(s). The metal uptake, determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and inductively coupled plasma-mass spectroscopy (ICP-MS), revealed that Lolium perenne accumulate a higher amount of metals in the roots than in leaves, which was further confirmed by the translocation factor (TF) values of all of the metals that were below 1, ranging between 0.2 and 0.8, while Cu, Cr and Pb had a bioaccumulation factor (BCF) > 1. This confirms that L. perenne is capable of absorbing metals into the root matrix but might restrict further movement into other parts of the plant as a defense mechanism against metal toxicity. In response to metal-induced stress, L. perenne displayed an increase in enzyme activity of superoxide dismutase, glutathione S-transferase, peroxidase and amylases in plants grown in landfill soil. Peroxidases displayed the highest level of enzyme activity, while total amylolytic activity had the most significant increase in activity over time. Although not a hyperaccumulator, L. perenne is a potential candidate for the phytoremediation of landfill soil and the phytostabilization of Cu, Cr and Pb.
Electrochemical performance of hybrid supercapacitor device based on birnessite-type manganese oxide decorated on uncapped carbon nanotubes and porous activated carbon nanostructures.
(Elsevier Ltd., 2018-09-04) Ochai-Ejeh, F.; Madito, M.J.; Makgopa, K.; Rantho, M.N.; Olaniyan, O.; Manyala, N.
Birnessite-type MnO2 synthesized on the surface of carbon nanotubes (CNTs) via facile hydrothermal reflux technique to produce MnO2-CNT nanocomposite and 3D microporous nanostructured activated carbon (AC) derived from cork (Quercus Suber) with good microstructural, morphological and electrochemical properties are herein reported. A hybrid supercapacitor device comprising of MnO2-CNT nanocomposite as positive electrode and AC as the negative electrode was successfully fabricated and tested for energy storage application. The device displayed a maximum working potential of up to 2 V due to the excellent synergistic contribution from the MnO2-CNT nanocomposite and AC material derived from cork (Quercus Suber). The fabricated device displayed good electrochemical performance having an energy density of ~25Wh Kg1 that corresponds to a power density of 500WKg1 at a current density of 0.5 A g1 in a 1M Li2SO4 aqueous neutral electrolyte. The device exhibited an excellent stability of ~100% coulombic efficiency after 10,000 charge-discharge cycles and excellent capacitance retention after potentiostatic floating test for 60 h.
Hierarchiral 4-tetranitro copper(II)phthalocyanine based metal organic framework hybrid composite with improved electrocatalytic efficiency towards hydrogen evolution reaction.
(Elsevier B.V., 2019-08-02) Monama, Gobeng Release; Hato, Mpitloane Joseph; Ramohlola, Kabelo Edmond; Thabiso Carol , Maponya; Mdluli, Siyabonga Beizel; Molapo, Kerileng Mildred; Modibane, Kwena Desmond; Iwuoha, Emmanuel I.; Makgopa, Katlego; Teffu, Malesela Daniel
A novel hybrid-hybrid nanocomposite based on 4-tetranitro copper (II)phthalocyanine (TNCuPc) grown on metal organic frameworks (MOF) as a noble metal-free catalyst for hydrogen evolution reaction (HER) was developed by a simple impregnation method. The structure, surface area and the morphology of the bare MOF, TNCuPc and the TNCuPc/MOF composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, Brunauer-Emmet-Teller, scanning electron microscopy, transmission electron microscopy and simultaneous thermal analysis. The electrocatalytic activity of the samples towards the HER was evaluated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry, exchange current density, i0, Tafel slope value, b, as well as charge transfer coefficient, α. The spectroscopic analyses indicated a successful synthesis of TNCuPc and its composite. The morphological results showed the development of rod-like structures of TNCuPc on the surface of the MOF. The composite exhibited an onset potential of about −0.713 V vs. Ag/AgCl in 0.1M TBAP/DMSO and 0.3M H2SO4 solutions, which is 44 mV and 9 mV more positive than that of MOF and TNCuPc respectively. The composite showed the rate determining step (RDS) to be the Volmer reaction in conjunction with either Heyrovsky or Tafel reaction as the RDS due to the Tafel slope value of 147 mV/dec and an α of 0.4. The i0 value of the TNCuPc/MOF composite was about 1.6 times that of the bare MOF. The EIS results showed the charge transfer resistance (Rct) of 12.6 kΩ for the TNCuPc/MOF composite as compared to MOF and TNCuPc values of 41 and 18.6 kΩ, respectively, demonstrating an excellent conductivity of the composite. In addition, Rct values of materials follow the sequence, blank < MOF < TNCuPc < TNCuPc/MOF. The fabricated composite displayed high activity towards the HER, high thermal stability, and excellent tolerance. Therefore, TNCuPc/MOF non-noble electrocatalyst can be a promising electrochemical catalyst to replace Pt-based catalysts for electrochemical hydrogen production.
Poly(3-aminobenzoic acid) decorated with cobalt zeolitic benzimidazolate framework for electrochemical production of clean hydrogen.
(MDPI, 2020-07-16) Modibane, Kwena Desmond; Waleng, Ngwako Joseas; Ramohlola, Kabelo Edmond; Maponya, Thabiso Carol; Monama, Gobeng Release; Makgopa, Katlego; Hato, Mpitloane Joseph
A novel composite of poly (3-aminobenzoic acid) (PABA) and a cobalt zeolitic benzimidazolate framework (CoZIF) has been studied for the production of hydrogen through the hydrogen evolution reaction (HER). The structural characteristics and successful synthesis of PABA, CoZIF and the PABA/CoZIF composite were confirmed and investigated using dierent techniques. Probing-ray diraction for phase analysis revealed that the composite showed a decrease and shift in peak intensities, confirming the incorporation of CoZIF on the PABA backbone via in situ polymerization, with an improvement in the crystalline phase of the polymer. The thermal stability of PABA was enhanced upon composite formation. Both scanning electron microscopy and transmission electron microscopy showed that the composite had a rough surface, owing to an interaction between the CoZIF and the external surface of the PABA. The electrochemical hydrogen evolution reaction (HER) performance of the synthesized samples was evaluated using cyclic voltammetry and Tafel analysis. The composite possessed a Tafel slope value of 156 mV/dec and an of 0.38, suggesting that the Volmer reaction coupled with either the Heyrovsky or Tafel reaction as the rate determining step. The fabricated composite showed high thermal stability and excellent tolerance as well as high electroactivity towards the HER, showing it to be a promising non-noble electrocatalyst to replace Pt-based catalysts for hydrogen generation.
Near-infrared spectroscopy and chemometrics for rapid profiling of plant secondary metabolites.
(De Gruyter, 2013-09-30) Mokgalaka, Ntebogeng S.; Lepule, Sello P.; Regnier, Thierry; Combrinck, Sandra
In this study, near-infrared (NIR) spectroscopy, in combination with chemometrics, was used as a rapid tool for determining if exposure to contamination from mine tailings influences the matrices of the specimens, compared to those from natural populations. Principal component analysis (PCA) plots were made from the chemometric models obtained to establish if season of harvest, geographical origin, and level of soil contamination play a determining role in the chemical profiles of the individual specimens harvested from mine sites or natural populations. The random distribution on PCA score plots corroborated the intraspecies variation of Lippia scaberrima previously observed by gas chromatography flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS) essential oil profiles. Clustering according to the season and origin of the individual plants confirmed that the geographic location and the season of harvest influence the chemical profiles of L. scaberrima. The NIR data could not be correlated with the level of soil contamination to which the specimens were exposed. The PCA scores and loadings plots obtained from NIR data of Searsia pendulina suggest that the species is tolerant to pollution from mine tailings. Although separation was obtained in a three-component PCA model between specimens sampled during different seasons, some clustering was observed by specimens from the same geographical origin.
The crystal structure of fac-tricarbonyl(6-bromo- 2,2-bipyridine-κ2N,N)-(nitrato-κO)rhenium(I), C13H7BrN3O6Re.
(De Gruyter, 2023-04-14) Mkhatshwa, Marcus; Malan, Frederick P.; Makgopa, Katlego; Manicum, Amanda-Lee E.
C13H7BrN3O6Re, monoclinic, P21/n (no. 14), a = 7.2645(1) Å, b = 10.0607(1) Å, c = 20.7717(2)Å, β = 97.1800(10) °, V = 1506.22(3) Å3, Z = 4, Rgt (F) = 0.0359, wRref (F2) = 0.0810, T = 150K.
One-step hdrothermal synthesis of nitrogen-doped reduced graphene oxide/hausmannite manganese oxide for symmetric and asymmetric pseudocapacitors.
(American Chemical Society, 2021-11-15) Makgopa, Katlego; Ratsoma, Mpho S.; Raju, Kumar; Mabena, Letlhogonolo F.; Modibane, Kwena D.
In this paper, the pseudocapacitive performance of nitrogen-doped and undoped reduced graphene oxide/tetragonal hausmannite nanohybrids (N-rGO/Mn3O4 and rGO/Mn3O4) synthesized using a one-pot hydrothermal method is reported. The nanohybrid electrode materials displayed exceptional electrochemical performance relative to their respective individual precursors (i.e., reduced graphene oxide (rGO), nitrogen-doped reduced graphene oxide (N-rGO), and tetragonal hausmannite (Mn3O4)) for symmetric pseudocapacitors. Among the two nanohybrids, N-rGO/Mn3O4 displayed greater performance with a high specific capacitance of 345 F g−1 at a current density of 0.1 A g−1, excellent specific energy of 12.0 Wh kg−1 (0.1 A g−1), and a high power density of 22.5 kW kg−1 (10.0 A g−1), while rGO/Mn3O4 demonstrated a high specific capacitance of 264 F g−1 (0.1 A g−1) with specific energy and power densities of 9.2 Wh kg−1 (0.1 A g−1) and 23.6 kW kg−1 (10.0 A g−1), respectively. Furthermore, the NrGO/ Mn3O4 nanohybrid exhibited an impressive pseudocapacitive performance when fabricated in an asymmetric configuration, having a stable potential window of 2.0 V in 1.0 M Na2SO4 electrolyte. The nanohybrid showed excellent specific energy and power densities of 34.6 Wh kg−1 (0.1 A g−1) and 14.01 kW kg−1 (10.0 A g−1), respectively. These promising results provide a good substance for developing novel carbon-based metal oxide electrode materials in pseudocapacitor applications.
Fabrication, characterization, and photovoltaic performance of titanium dioxide/metal-organic framework composite.
(Elsevier B.V., 2022-08-30) Ramaripa, Phuti S; Modibane, Kwena D.; Makgopa, Katlego; Seerane, Ostar A; Maubane-Nkadimeng, Manoko S.; Makhado, Edwin; Hato, Mpitloane J.; Ramoroka, Morongwa E.; Molapo, Kerileng M.; Iwuoha, Emmanuel
Titanium dioxide/metal organic framework (TiO 2 /MOF) nanocomposite was prepared using the sol-gel method and was employed as photoanode material for photovoltaic applications. X-ray diffraction patterns (XRD), Fourier transform infrared (FTIR), thermal gravimetric analysis/ differential thermal analysis (TGA/DTA), and Raman analyses showed the presence of MOF clusters in the TiO 2 sol-gel network. The scanning electron microscopic (SEM) images revealed the smooth irregular shape of TiO 2, the octahedral shape of MOF, and the continuous arrangement of pore-solid network structure for nanocomposite. The resultant nanocomposite material showed a Brunauer, Emmett and Teller (BET) surface area of 111.10 m 2 g − 1 as compared to the surface area of TiO 2 (262.90 m 2 g −1 ) and MOF (464.76 m 2 g -1 ). It was seen that an increase in average pore size of 3.40 nm for nanocomposite analogous with the pore size of TiO 2 (2.66 nm) and MOF (2.56 nm). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) were used to determine the energy level and suggest a fast electron transfer as well as high ionic conductivity. The overall power conversion efficiency of 0.722% along with a photocurrent density of 0.46 mA cm − 2 was achieved for composite. The approach proposed in this work is facile and can be used for the large-scale fabrication of efficient flexible photoanode electrodes for photovoltaic applications.
Influence of phthalocyanine nanowire dye on the performance of titanium dioxide-metal organic framework nanocomposite for dye-sensitized solar cells.
(Elsevier B.V., 2023-03-29) Ramaripa, Phuti S.; Modibane, Kwena D.; Makgopa, Katlego; Seerane, Ostar A.; Maubane-Nkadimeng, Manoko S.; Makhado , Edwin; Pandey, Sadanand
In clean energy, dye-sensitized solar cells (DSSCs) have become a key tool for the photovoltaic effect. Copper phthalocyanine nanowire (CuPcNW) dyes can be used in DSSCs to generate low-cost devices, light-harvesting, fast electron transfer materials, and prevent recombination processes, as well as improve conductivity. This study investigates the effect of CuPcNW dye on TiO2, MOF, and TiO2-MOF in photovoltaic performance. Electrochemical characterizations such as cyclic voltammetry and electrochemical impedance spectroscopy (EIS) have also revealed the half-wave peak potentials of the ternary nanocomposite with values of 0.44 and 0.35 V for the oxidation and reduction reversible reactions. The EIS behavior revealed the improved conductivity of the nanocomposite with a value of 244 μS/cm. It was seen that the TiO2-MOF/CuPcNW nanocomposite achieved a maximum power conversion efficiency of 6.467 % owing to the presence of CuPcNW, which improved the photocurrent density, faster electron transport, and reduced charge recombination in the nanocomposite.
African legumes: A vital but under-utilized resource.
(Oxford University Press, 2009-11-25) Sprent, Janet I.; Odee, David W.; Dakora, Felix D.
Although nodulated legumes have been used by indigenous peoples in Africa for centuries, their full potential has never been realized. With modern technology there is scope for rapid improvement of both plant and microbial germplasm. This review gives examples of some recent developments in the form of case studies; these range from multipurpose human food crops, such as cowpea (Vigna unguiculata (L.) Walp.), through to beverages (teas) that are also income-generating such as rooibos (Aspalathus linearis (Burm. f.) R. Dahlgren, honeybush (Cyclopia Vent. spp.), and the widely used food additive gum arabic (Acacia senegal (L.) Willd.). These and other potential crops are well adapted to the many different soil and climatic conditions of Africa, in particular, drought and low nutrients. All can nodulate and fix nitrogen, with varying degrees of effectiveness and using a range of bacterial symbionts. The further development of these and other species is essential, not only for African use, but also to retain the agricultural diversity that is essential for a changing world that is being increasingly dominated by a few crops such as soybean.
Field assessment of symbiotic N2 fixation in wild and cultivated cyclopia species in the South African fynbos by 15N natural abundance.
(Oxford University Press, 2008-08-24) Spriggs, Amy C.; Dakora, Felix D.
Nitrogen (N) derived from symbiotic fixation of atmospheric N2 in wild and cultivated populations of Cyclopia, a woody endemic genus used to make honeybush tea in the Western Cape of South Africa, was quantified by the 15N natural abundance method. Because Cyclopia species are naturally mycorrhizal, non-N2-fixing arbuscular mycorrhizal shrubs of similar phenology to Cyclopia were chosen as reference plants to provide the d15Nvalue of soil-derived N. Isotopic analysis showed that wild populations of Cyclopia were highly dependent on N2 fixation for their nutrition, ranging from 70 ± 4%to 100 ± 7% (mean ± SE) at all sites, except for one. Further evidence of the high dependency of wild Cyclopia populations on symbiotic N was provided by their significantly higher foliar N concentrations compared with the non-legume reference plants. However, cultivated Cyclopia exhibited variable amounts of N2 fixation, with Cyclopia genistoides (L.) R. Br., for example, showing low amounts of N2 fixation at Sites P2 and P3 (0 ± 51% and 8 ± 46%, respectively) as a result of low D values (D is defined as the difference between the mean d15N value of the reference plants and the B value of the test Cyclopia species, where B is the d15N of an inoculated test legume grown in an N-free growth medium), whereas at Sites P1, P2, P5 and P6, up to 89 ± 2%, 94 ± 13%, 85 ± 13% and 100 ± 18%, respectively, plant N was derived from atmospheric fixation. The high symbiotic N nutrition observed for wild populations of Cyclopia suggests that these populations are major contributors to the N economy of the nutrient poor soils of the South African fynbos. These data indicate that by breeding for high N2 fixation rates in Cyclopia cultivars and selecting more efficient rhizobial strains, this legume has the potential to achieve higher N2 fixation rates under cultivation. The low variability in Cyclopia d15N values within sites, however, suggests that genetic variability is not a major factor influencing N2 fixation rates in cultivated Cyclopia, and that more benefit may be gained from soil amelioration and the selection of improved rhizobial strains.

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