Research Articles (Chemistry)

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Open Access
Comparison of the spectroscopically measure catalyst transformation and electrochemical properties of Grubbs' first- and second-generation catalysts
(American Chemical Society, 2021) Swart, Marthinus R.; Marais, Charlene; Erasmus, Elizabeth
According to UV–vis spectroscopy (0.10 mM, CH2Cl2 at 25 °C), the catalyst transformation (which could possibly include ligand dissociation with active catalyst formation, dimer formation, and decomposition) rate constants (kobs) of Grubbs’ first (1) and second (2) generation catalysts are 7.48 × 10–5 and 1.52 × 10–4 s–1, respectively. From 31P NMR (0.1 M, CD2Cl2, at 25 °C), the catalyst transformation was 5.1% for 1 and 16.5% for 2 after 72 h. However, due to the larger concentrations of the NMR samples compared to the UV–vis samples, the extent of transformation did not correspond. The oxidation potential of the RuII/RuIII couple of 2 (E°’ = 27.5 mV at v = 200 mV s–1) was considerably lower than that of 1 (E°’ = 167 mV at v = 200 mV s–1). In the case of 1, a second reduction peak appeared at slow scan rates. This may probably be ascribed to an electrochemically active compound that was formed from the intermediate cation 1•+ and the subsequent reduction of the latter. The oxidation/reduction of 1 proceeds according to an ErCi electrochemical mechanism (Er = electrochemically reversible step, Ci = chemically irreversible step), whereas 2 proceeds according to an ErCr electrochemical mechanism (Er = electrochemically reversible step, Ci = chemically reversible step).
Open Access
Data to understand the nature of non-covalent interactions in the thiophene clusters
(Elsevier, 2021) Malloum, Alhadji; Conradie, Jeanet
We have reported herein the data to understand the nature and number of non-covalent interactions that stabilize the structures of the thiophene clusters. In addition, we have also provided the optimized Cartesian coordinates of all the structures of the investigated thiophene clusters. Initially, the geometries have been generated using the ABCluster code which performs a global optimization to locate local and global minima structures of molecular clusters. The located geometries have been optimized at the MP2/aug-cc-pVDZ level of theory using Gaussian 16 suite of programs. To understand the nature of non-covalent interactions, we have performed a quantum theory of atoms in molecules (QTAIM) analysis on all the structures of the thiophene dimer. Furthermore, the QTAIM analysis has been performed also on the most stable structure of the thiophene trimer and tetramer. We have used the AIMAll program to perform the QTAIM analysis. The data reported in this paper contains the critical points, the bonds paths and their related properties, for each investigated structures. Besides, the data contains the optimized Cartesian coordinates of all the investigated structures of the thiophene clusters. This can be use for any further investigations involving thiophene clusters. For further information and analysis, the reader is referred to the original related research article (Malloum and Conradie, 2022).
Open Access
Density functional theory calculated data of the iodomethane oxidative addition to oligothiophene-containing rhodium complexes – importance of dispersion correction
(Elsevier, 2021) Mateyise, Nandisiwe Ghandi Sibongile; Conradie, Jeanet; Conradie, Marrigje M.
Electronic and free energy data of density functional theory calculated optimized geometries of the reactants, transition state of the oxidative addition reaction and different reaction products of the [Rh(RCOCHCOCF 3 )(CO)(PPh 3 )] + CH 3 I reactions (R = C 4 H 3 S, C 4 H 3 S-C 4 H 2 S and C 4 H 3 S-C 4 H 2 S-C 4 H 2 S) are presented to illustrate the influence of the amount of thiophene groups, the implicit solvent and dispersion correction on the calculated energies. All calculations were done with the B3LYP functional, in gas as well as in solvent phase, with and without dispersion correction. The data can save computational chemists time when choosing an appropriate method to calculate reaction energies of oxidative addition reactions. Detailed knowledge of energies involved in the oxidative addition reaction of methyl iodide to rhodium complexes have an important implication in catalysis, for example the Monsanto process where methanol is converted to acetic acid catalysed by a rhodium complex. For more insight in the reported data, see the related research article “Synthesis, characterization, electrochemistry, DFT and kinetic study of the oligothiophene-containing complex [Rh((C 4 H 3 S- C 4 H 2 S)COCHCOCF 3 )(CO)(PPh 3 )]”, published in Polyhedron.
Open Access
Dimethylsulfoxide (DMSO) clusters dataset: DFT relative energies, non-covalent interactions, and cartesian coordinates
(Elsevier, 2022) Malloum, Alhadji; Conradie, Jeanet
Theoretical understanding of dimethylsulfoxide (DMSO) liquid depends on the understanding of the DMSO clusters. In this work, we provide the structures and the energetics of the DMSO clusters. The structures have been generated using ABCluster and further optimized at the MP2/aug-cc-pVDZ level of theory. The final structures have been optimized at two different levels of theory: PW6B95D3/aug-cc-pVDZ and ωB97XD/aug-cc-pVDZ. The Cartesian coordinates of the structures optimized at the MP2/aug-cc-pVDZ level of theory are also reported. The relative energies of the structures can be used to locate the most favorable structures of the DMSO clusters. The Cartesian coordinates of the structures can be used for further investigations on DMSO clusters. In addition, we report the data related to the quantum theory of atoms in molecule (QTAIM) analysis of the investigated clusters. The QTAIM data reported in this work can be used to understand and determine the nature of non-covalent interactions in DMSO clusters. For further reading and discussion on the data reported here, please report to the original manuscript Malloum and Conradie (2022).
Open Access
Free energy and enthalpy data of neutral and protonated clusters in the solvent phase
(Elsevier, 2021) Malloum, Alhadji; Conradie, Jeanet
Structures of neutral and protonated acetonitrile in the sol- vent phase are important to describe proton behavior and to calculate thermodynamic quantities related to the solva- tion of ions or molecules in acetonitrile. In this work, we provide data related to the calculation of the solvation free energy and enthalpy of the proton in acetonitrile. We have thoroughly explored the potential energy surfaces (PESs) of neutral and protonated acetonitrile clusters from dimer to heptamer in the solvent phase at both MN15/6–31 ++ G (d,p) and MP2/aug-cc-pVDZ levels of theory. We report the struc- tures and relative stability of neutral and protonated acetoni- trile clusters in the solvent phase at the MN15/6–31 ++ G (d,p) level of theory. In addition, enthalpies and free energies of neutral and protonated acetonitrile are also reported at the MP2/aug-cc-pVDZ and MP2/CBS levels of theory. Further- more, Cartesian coordinates of the clusters in the solvent phase as optimized at the MP2/aug-cc-pVDZ level of theory are provided as supplementary file. The data provided in this work will be useful for further investigations that would in- volve neutral and protonated acetonitrile clusters. The free energies and enthalpies of the investigated clusters in the solvent phase have been used to compute the solvation free energy and enthalpy of the proton in acetonitrile. For more insights on the solvation free energy and enthalpy of the pro- ton in acetonitrile, see the related main research paper.
Open Access
Isotherm, kinetic, thermodynamics and reusability data on the adsorption of antidepressant onto silver nanoparticle-loaded biowaste
(Elsevier Inc., 2021) Akpomie, Kovo G.; Conradie, Jeanet
There has been an increase in the use of antidepressant drugs owing to significant economic challenges across the globe. Consequently, the increase in production of such drugs has impacted pharmaceutical pollution of industrial wastew- aters discharged into the environment. Hence, there is a need to develop efficient adsorbents for antidepressant wastewa- ter treatment. The impregnation of silver nanoparticles on biowaste was found to be highly effective in the treatment of oil-polluted water but has not been utilized in the adsorp- tion of drugs. Herein, the dataset associated with the adsorp- tion of antidepressants onto Ananas Comosus Peel (AP) and Silver nanoparticle-loaded Ananas Comosus peel (AgAP) was reported. Batch adsorption methodology was used to study the effect of antidepressant concentration (10–50 mg/L), son- ication time (10–120 min), temperature (300–320 K) and adsorbent dosage (0.10–0.18 g). The concentration of an- tidepressant (Nortriptyline) in solution before and after ad- sorption was determined by the UV-Spectrophotometer at a maximum wavelength of 239 nm. The isotherm dataset was obtained from the Langmuir, Freundlich, Temkin and Dubinin-Raduskevich models, while kinetic data was eval- uated by the pseudo-first order-pseudo-second-order, film diffusion and intraparticle diffusion rate equations. The data on the thermodynamics and adsorbent reusability were also provided. The dataset showed an adsorption capacity of 3.27 mg/g and 4.74 mg/g for AP and AgAP, respectively. The dataset is important to material and environmental scientists and revealed the efficiency of AP and AgAP in the treatment of antidepressant wastewater.
Open Access
Kinetic study of the oxidative addition reaction between methyl iodide and [Rh(imino-β-diketonato)(CO)(PPh)3] complexes, utilizing UV–vis, IR spectrophotometry, NMR spectroscopy and DFT calculations
(MDPI, 2022) Ferreira, Hendrik; Conradie, Marrigje Marianne; Conradie, Jeanet
The oxidative addition of methyl iodide to [Rh(β-diketonato)(CO)(PPh)3] complexes, as modal catalysts of the first step during the Monsanto process, are well-studied. The β-diketonato ligand is a bidentate (BID) ligand that bonds, through two O donor atoms (O,O-BID ligand), to rhodium. Imino-β-diketones are similar to β-diketones, though the donor atoms are N and O, referred to as an N,O-BID ligand. In this study, the oxidative addition of methyl iodide to [Rh(imino-β-diketonato)(CO)(PPh)3] complexes, as observed on UV–Vis spectrophotometry, IR spectrophotometry and NMR spectrometry, are presented. Experimentally, one isomer of [Rh(CH3COCHCNPhCH3)(CO)(PPh3)] and two isomers of [Rh(CH3COCHCNHCH3)(CO)(PPh3)] are observed—in agreement with density functional theory (DFT) calculations. Experimentally the [Rh(CH3COCHCNPhCH3)(CO)(PPh3)] + CH3I reaction proceeds through one reaction step, with a rhodium(III)-alkyl as the final reaction product. However, the [Rh(CH3COCHCNHCH3)(CO)(PPh3)] + CH3I reaction proceeds through two reaction steps, with a rhodium(III)-acyl as the final reaction product. DFT calculations of all the possible reaction products and transition states agree with experimental findings. Due to the smaller electronegativity of N, compared to O, the oxidative addition reaction rate of CH3I to the two [Rh(imino-β-diketonato)(CO)(PPh)3] complexes of this study was 7–11 times faster than the oxidative addition reaction rate of CH3I to [Rh(CH3COCHCOCH3)(CO)(PPh3)].
Open Access
Metal exchange of ZIF-8 and ZIF-67 nanoparticles with Fe(II) for enhanced photocatalytic performance
(American Chemical Society, 2021) Mphuthi, Lehlonoholo E.; Erasmus, Elizabeth; Langner, Ernst H. G.
Zeolitic imidazolate frameworks (ZIFs), such as ZIF-8 and ZIF-67, were found to be efficient catalysts. However, ZIFs are not used much in photocatalysis due to their low photocatalytic activity for most reactions. The photocatalytic activity can be improved by modifying the framework by exchanging the Zn(II) ions (ZIF-8) and Co(II) ions (ZIF-67) with a more photocatalytically active metal(II) ion to form an efficient bimetallic ZIF photocatalyst. Redox-active iron (Fe)-based materials are known to be highly potent photocatalysts. Thus, incorporating iron into ZIFs could significantly enhance their photocatalytic performance. In this study, we modified nanosized ZIF-8(Zn) and ZIF-67(Co) via metal (Fe2+) exchange to produce bimetallic frameworks that are photocatalytically more active than their parent ZIFs. Nanosized ZIF-8 and ZIF-67 were synthesized isothermally in either water or methanol under ambient conditions. From these, Fe-containing bimetallic ZIF-8 and ZIF-67 nanoparticles were synthesized via the metal exchange, and their performance on the photocatalytic degradation of dye was evaluated. The morphology and crystal structures of the pristine ZIF-8 and ZIF-67 nanoparticles were retained to a large extent during the iron exchange. Their Brunauer−Emmett−Teller (BET) surface areas decreased by less than 15% for nZIF-8 and less than 12% for nZIF-67. The binding energy values on X-ray photoelectron spectroscopy (XPS) confirmed the preservation of the oxidation state of Fe(II) during the exchange process. A remarkably higher catalytic activity was observed for the photocatalytic degradation of dye by the Fe-exchanged nZIF-8 and nZIF-67 compared to their parent ZIFs. This proved that the incorporation of Fe(II) centers into the ZIF framework enhanced the photocatalytic activity of the framework dramatically. In addition, these catalysts can be regenerated and reused without an appreciable loss in activity.
Open Access
Octakis(dodecyl)phthalocyanines: influence of peripheral versus non-peripheral substitution on synthetic routes, spectroscopy and electrochemical behaviour
(MDPI, 2022) Swart, Glendin; Fourie, Eleanor; Swarts, Jannie C.
Non-peripherally octakis-substituted phthalocyanines (npPc’s), MPc(C12H25)8 with M = 2H (3) or Zn (4), as well as peripherally octakis-substituted phthalocyanines (pPc’s) with M = Zn (6), Mg (7) and 2H (8), were synthesized by cyclotetramerization of 3,6- (2) or 4,5-bis(dodecyl)phthalonitrile (5), template cyclotetramerization of precursor phthalonitriles in the presence of Zn or Mg, metal insertion into metal-free phthalocyanines, and removal of Mg or Zn from the phthalocyaninato coordination cavity. The more effective synthetic route towards pPc 8 was demetalation of 7. npPc’s were more soluble than pPc’s. The Q-band λmax of npPc’s was red-shifted with ca. 18 nm, compared to that of pPc’s. X-ray photoelectron spectroscopy (XPS) differentiated between N–H, Nmeso and Ncore nitrogen atoms for metal-free phthalocyanines. Binding energies were ca. 399.6, 398.2 and 397.7 eV respectively. X-ray photoelectron spectroscopy (XPS) also showed zinc phthalocyanines 4 and 6 have four equivalent Nmeso and four equivalent N–Zn core nitrogens. In contrast, the Mg phthalocyanine 7 has two sets of core N atoms. One set involves two Ncore atoms strongly coordinated to Mg, while the other encompasses the two remaining Ncore atoms that are weakly associated with Mg. pPc’s 6, 7, and 8 have cyclic voltammetry features consistent with dimerization to form [Pc][Pc+] intermediates upon oxidation but npPc’s 3 and 4 do not. Metalation of metal-free pPc’s and npPc’s shifted all redox potentials to lower values.
Open Access
Optimized CO2 capture of the zeolitic imidazolate framework ZIF‑8 modified by solvent-assisted ligand exchange
(American Chemical Society, 2021) Abraha, Yuel W.; Tsai, Chih-Wei; Niemantsverdriet, J. W. Hans; Langner, Ernst H. G.
Zeolitic imidazolate frameworks, like ZIF-8 and related structures, have shown great potential for the capture of carbon dioxide. Modifying their structure by exchanging part of the constituent organic ligands is a proven method for enhancing the capacity to absorb CO2. In this work, we performed solvent-assisted ligand exchange (SALE) on nanosized ZIF-8 (nZIF-8) with a series of functionalized imidazole derivatives (exchange percentages, after 24 h): 2-bromoimidazole (19%), 2-chloroimidazole (29%), 2-trifluoromethylbenzimidazole (4%), 2-mercaptobenzimidazole (4%), and 2-nitroimidazole (54%). The sodalite topology and porosity of nZIF-8 were maintained with all SALE modifications. Low-pressure CO2 adsorption of nZIF-8 (38.5 cm3 g–1) at STP was appreciably enhanced with all mixed-linker SALE products. Using halogenated (−Cl, −Br, and −CF3) imidazole derivatives in a 24 h SALE treatment resulted in increases between 11 and 22% in CO2 adsorption, while the thiol (−SH)- and nitro (−NO2)-functionalized SALE products led to 32 and 100% increases in CO2 uptakes, respectively. These CO2 uptakes were further optimized by varying the SALE treatment time. The SHbIm- and NO2Im-exchanged SALE products of nZIF-8 show 87 and 98 cm3 g–1 of CO2 uptakes after 60 and 120 h of SALE, respectively. These are record high CO2 adsorptions for all reported ZIF derivatives at low-pressure conditions.
Open Access
Photocatalytic decomposition of an ago dye using transition-metal-doped tungsten and molybdenum carbides
(American Chemical Society, 2022) Mabuea, Busiswe Petunia; Swart, Hendrik Christoffel; Erasmus, Elizabeth
The preparation, characterization, and photocatalytic application of tungsten or molybdenum carbides (Ni-WC, 1, Co-WC, 2, Ni-MoC, 3, Co-MoC, 4, NiCo-WC, 5, NiCo-MoC, 6, NiFe-WC, 7, and NiFe-MoC, 8) doped with transition metals (Fe, Co, and Ni) are reported. These transition-metal carbide (TMC) particles show that the submicrometer globular particles agglomerated to form larger particles, with smaller crystallites present on the surface of the large particles. These crystallite sizes range between 4 and 34 nm (as calculated from X-ray diffraction data) depending on the metal dopant and type of carbide. Oxidation of the metal carbides is evident from the two sets of photoelectron lines present in the X-ray photoelectron spectroscopy (XPS) of the W 4f area. The Mo 3d spectra reveal four sets of photoelectron lines associated with oxidized MoO2 and MoO3 as well as Mo2+ and Mo3+ associated with MoC1–x. The XPS of the dopant metals Ni, Co, and Fe also show partial oxidation. The photocatalytic decomposition of Congo red (an azo dye) is used as a model reaction to determine the photocatalytic activities of the transition-metal carbides, which is related to the TMCs’ optical band gap energies.
Open Access
Polypyridyl copper complexes as dye sensitizer and redox mediator for dye-sensitized solar cells
(Elsevier, 2021) Conradie, Jeanet
Developments on the application of polypyridyl-based copper complexes in dye-sensitized solar cells (DSSCs) are briefly discussed in this mini review. Copper complexes in solar cells are special in that they can be used either as dye sensitizer and/or as redox mediator (redox couple) in dye-sensitized solar cells (DSSCs). Both the abundance and low cost of copper motivates research on the use of copper complexes, as cheaper and non-toxic alternative to the mostly used iodide/triiodide (I- /I3- ) electrolyte redox couple, and the expensive and rare rutheniumbased dyes of good performance, which currently are best known.
Open Access
QTAIM analysis dataset for non-covalent interactions in furan clusters
(Elsevier, 2021) Malloum, Alhadji; Conradie, Jeanet
Furan clusters are very important to understand the dynam- ics and properties of the furan solvent. They can be used combined with quantum cluster equilibrium theory to theo- retically determine the thermodynamics properties of the fu- ran solvent. To understand the structures of the furan clus- ters, one needs to understand the non-covalent interactions that hold the furan molecules together. In this paper, we have provided the data necessary to understand the non-covalent interactions in furan clusters. Firstly, the structures of the furan clusters have been generated using classical molecu- lar dynamics as implemented in the ABCluster code. Sec- ondly, the generated structures have been fully optimized at the MP2/aug-cc-pVDZ level of theory. The optimized Carte- sian coordinates of all the investigated structures are re- ported in this work to enable further investigations of the furan clusters. These Cartesian coordinates will save compu- tational time for all further investigations involving the fu- ran clusters. Thirdly, to understand the nature of the non- covalent interactions in furan clusters, we have performed a quantum theory of atoms in molecule (QTAIM) analysis using AIMAll program. Using QTAIM, we have provided the critical points, bond paths and their related properties for all the in- vestigated structures. These data can be used to identify and classify the non-covalent interactions in furan clusters.
Open Access
Redox data of tris(polypyridine)manganese(II) complexes
(MDPI, 2022) Mtshali, Zinhle; Von Eschwege, Karel G.; Conradie, Jeanet
Very little cyclic voltammetry data for tris(polypyridine)manganese(II) complexes, [MnII(N^N)3]2+, where N^N is bipyridine (bpy), phenanthroline (phen) or substituted bpy or phen ligands, respectively; are available in the literature. Cyclic voltammograms were found for tris(4,7-diphenyl-1,10-phenanthroline)manganese(II) perchlorate only. In addition to our recently published related research article, the data presented here provides cyclic voltammograms and corresponding voltage-current data obtained during electrochemical oxidation and the reduction of four [MnII(N^N)3]2+ complexes, using different scan rates and analyte concentrations. The results show increased concentration and scan rates resulting in higher Mn(II/III) peak oxidation potentials and increased peak current-voltage separations of the irreversible Mn(II/III) redox event. The average peak oxidation and peak reduction potentials of the Mn(II/III) redox events stayed constant within 0.01 V. Similarly, the average of the peak oxidation and reduction potentials of the ligand-based reduction events of [MnII(N^N)3]2+ were constant within 0.01 V.
Open Access
Review of DFT-simulated and experimental electrochemistry properties of the polypyridyl Row-1 Mn, Fe & Co, and Group-8 Fe, Ru and Os MLCT complexes
(Elsevier, 2022) Von Eschwege, Karel G.; Conradie, Jeanet
Ruthenium had up to date been pivotal in electro- and photocatalytic applications involving reduction of CO2 and H2O, and dye-sensitized solar cells. Commercial applications would seek use of earth-abundant metals instead. Towards this goal, it is key to review the synthesis, electrochemical and spectroscopical properties of associated metal-to-ligand charge transfer complexes of row-4 (Mn, Fe & Co) and column-8 (Fe, Ru & Os). The present report is limited to data obtained under exactly similar conditions, providing scientifically valid correlations. Only tris-coordinated bipyridyl and phenanthroline complex derivatives are considered, being representative of catalysts and dyes traditionally used in the above-mentioned fields. The accuracy of theoretical DFT techniques to simulate complex properties is highlighted.
Open Access
A review on graphene (GN) and graphite oxide (GO) based biodegradable polymer composites and their usage as selective adsorbents for heavy metals in water
(MDPI, 2023) Mokoena, Lesia Sydney; Mofokeng, Julia Puseletso
Water pollution due to heavy metal ions has become a persistent and increasing problem globally. To combat this, carbonaceous materials have been explored as possible adsorbents of these metal ions from solution. The problem with using these materials on their own is that their lifespan and, therefore, usability is reduced. Hence the need to mask them and an interest in using polymers to do so is picked. This introduces an improvement into other properties as well and opens the way for more applications. This work gives a detailed review of the major carbonaceous materials, graphene and graphene oxide, outlining their origin as well as morphological studies. It also outlines the findings on their effectiveness in removing heavy metal ions from water, as well as their water absorption properties. The section further reports on graphene/polymer and graphene oxide/polymer composites previously studied and their morphological as well as thermal properties. Then the work done in the absorption and adsorption capabilities of these composites is explored, thereby contrasting the two materials. This enables us to choose the optimal material for the desired outcome of advancing further in the utilization of carbonaceous material-based polymer composites to remove heavy metal ions from water.
Open Access
Spectroscopic behaviour of copper(II) complexes containing 2-hydroxyphenones
(MDPI, 2022) Chiyindiko, Emmie; Langner, Ernst H. G.; Conradie, Jeannet
Theoretical investigations by density functional theory (DFT) and time-dependent DFT (TD-DFT) methods shed light on how the type of ligand or attached groups influence the electronic structure, absorption spectrum, electron excitation, and intramolecular and interfacial electron transfer of the Cu(II) complexes under study. The findings provide new insight into the designing and screening of high-performance dyes for dye-sensitized solar cells (DSSCs).
Open Access
Substitution reactivity and structural variability induced by tryptamine on the biomimetic rhenium tricarbonyl complex
(Royal Society of Chemistry, 2021) Jacobs, Frederick J. F.; Venter, Gertruida J. S.; Fourie, Eleanor; Kroon, Robin E.; Brink, Alice
A series of seven fac-[Re(CO)3(5Me-Sal-Trypt)(L)] complexes containing tryptamine on the N,O 5-methylsalicylidene bidentate ligand backbone and where L is MeOH, Py, Imi, DMAP, PPh3 coordinated to the 6th position have been studied, including the formation of a dinuclear Re2 cluster. The crystallographic solid state structures show marked similarity in structural tendency, in particular the rigidity of the Re core and the hydrogen bond interactions similar to those found in protein structures. The rates of formation and stability of the complexes were evaluated by rapid time-resolved stopped-flow techniques and the methanol substitution reaction indicates the significant activation induced by the use of the N,O salicylidene bidentate ligand as manifested by the second-order rate constants for the entering nucleophiles. Both linear and limiting kinetics were observed and a systematic evaluation of the kinetics is reported clearly indicating an interchange type of intimate mechanism for the methanol substitution. The anticancer activity of compounds 1–7 was tested on HeLa cells and it was found that all compounds showed similar cytotoxicity where solubility allowed. IC50-values between ca. 11 and 22 mM indicate that some cytotoxicity resides most likely on the salicylidene–tryptamine ligand. The photoluminescence of the seven complexes is similar in maximum emission wavelength with little variation despite the broad range of ligands coordinated to the 6th position on the metal centre.
Open Access
Synthesis and characterization of graphene oxide (GO) for the removal of lead ions in water
(Elsevier, 2024) Mokoena, L. S.; Mofokeng, J. P.
The synthesis and characterization of graphene oxide (GO) for water related applications has become an increasing area of research. GO was prepared via Hummer's method, and analysed for structure, morphology, thermal stability, and the ability to remove heavy lead ions from solution. In FTIR analyses, hydroxyl, carboxyl and ester groups were found to be on the structure of GO. XRD showed the interlayer spacing to have increased from graphite to graphene oxide, whereby the average crystallite size of GO was 16.13. Then SEM confirmed the morphology of GO to be exfoliated and wrinkled, with stacked layers. In TGA, EG degraded in a single step, while GO degraded in three distinct steps. When using AAS to analyse the Pb (II) ion intake properties of GO, it showed a maximum adsorption of 98.1% for 600 ppm lead ion solution. The Freundlich isotherm model was consistent with this adsorption, meaning that adsorption took place on a heterogenous surface, on a multilayer basis. The value of n for this isotherm was 0.1474, implying a dominant chemical adsorption. A significant contribution was done to the structure of GO, with its metal adsorption properties clearly portrayed.
Open Access
Trans–cis kinetic study of azobenzene-4,4′-dicarboxylic acid and aluminium and zirconium based azobenzene-4,4′-dicarboxylate MOFs
(MDPI, 2022) Mogale, Refilwe; Conradie, Jeanet; Langner, Ernst H. G.
Metal organic frameworks (MOFs) are porous hybrid crystalline materials that consist of organic linkers coordinated to metal centres. The trans–cis isomerisation kinetics of the azobenzene-4,4′-dicarboxylic acid (AZB(COOH)2) precursor, as well as the Al3+ (Al-AZB)- and Zr4+ (Zr-AZB)-based MOFs with azobenzene-4,4′-dicarboxylate linkers, are presented. The photo-isomerization in the MOFs originates from singly bound azobenzene moieties on the surface of the MOF. The type of solvent used had a slight effect on the rate of isomerization and half-life, while the band gap energies were not significantly affected by the solvents. Photo-responsive MOFs can be classified as smart materials with possible applications in sensing, drug delivery, magnetism, and molecular recognition. In this study, the MOFs were applied in the dye adsorption of congo red (CR) in contaminated water. For both MOFs, the UV-irradiated cis isomer exhibited a slightly higher CR uptake than the ambient-light exposed trans isomer. Al-AZB displayed a dye adsorption capacity of over 95% for both the UV-irradiated and ambient light samples. The ambient light exposed Zr-AZB, and the UV irradiated Zr-AZB had 39.1% and 44.6% dye removal, respectively.