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- ItemMultidimensional analytical protocols for the fractionation and analysis of complex polyolefins(Wiley Online Library, 2021-05-03) Pasch, H.; Ndiripo, A.; Bungu, P.S.EAlthough produced from simple monomers that contain just carbon and hydrogen, polyolefin have complex molecular structures that are characterized by distributions in molar mass, chemical composition, and branching. Accordingly, a variety of advanced analytical techniques are needed for the comprehensive characterization of the molecular heterogeneity of polyolefins. These include different fractionation, spectroscopic, and thermal analysis methods. Very frequently, method couplings such as two‐dimensional liquid chromatography or the coupling of crystallization‐ and column‐based techniques are required. This review presents the current state of the art in multidimensional analysis of complex polyolefins. It discusses methods for bulk analysis as well as different analytical and preparative fractionation protocols. For different types of polyolefins it is shown that a preparative fractionation according to chemical composition/branching or molar mass helps to reduce the molecular complexity of the sample. Sample libraries can be obtained that may have narrow distributions regarding one molecular parameter. A detailed investigation of such library samples regarding other (broadly distributed) molecular parameters helps to fully explore the molecular heterogeneity of a complex sample.
- ItemApplication of Unmodifed Brachystegia spiciformis Leaf Biomass in the Adsorption of Nitrate Ions(Springer, 2021-09-18) Ruwaya, K.; Mokone, J.G.; Chiririwa, H.; Majoni, SThe application of Brachystegia spiciformis leaf powder in the adsorption of nitrate ions was conducted on both synthetic and real water samples. Optimum adsorption conditions for nitrate adsorption were pH of 4, equilibration time of 45 min, and biosorbent dose of 1.5 g. Batch adsorption was used in this study and nitrate ions were analyzed using the salicylic acid method. Non-linear adsorption isotherm fitting indicated that the experimental data was described well by the Langmuir model with a monolayer adsorption capacity of 5.97 mg/g. The Langmuir`s separation factor, , values were in the range, 0 < < 1, indicating favorable interactions between nitrate ions and Brachystegia spiciformis leaf powder adsorbent. The pseudo first order model provided the best fit to the experimental kinetics data with an R2 value of 0.9880 and a rate constant of min−1. The Brachystegia spiciformis leaf powder adsorbent achieved 100% and 78% nitrate ions removal from dam water and industrial effluent water respectively. We have shown that a cheap biomass adsorbent that has high activity towards nitrate ions adsorption can be produced and applied in the adsorption of nitrates from water.
- ItemImproving temperature gradient interaction chromatography of polyolefins by simultaneous use of different stationary phases(Elsevier, 2021-07-14) Ndiripo, A.; Ndlovu, P.Z.; Albrecht, A.; Pasch, H.,Temperature gradient interaction chromatography (TGIC) at high temperatures is a powerful method for the chemical composition separation of polyolefins. TGIC is a two-step process where the sample is crystallized on the stationary phase at low temperature followed by the elution of the sample components using a temperature gradient towards high temperatures. For TGIC typically a porous graphitic carbon (PGC) stationary phase is used. The separation mechanism is based on crystallization and adsorption/desorption phenomena and it has been shown that co-crystallization and co-adsorption may affect the separation. The present study reports on the simultaneous use of a non-adsorptive and an adsorptive stationary phase (column) in series to utilize both crystallization and adsorption for improved separation in TGIC. A silica column is used as the non-adsorptive support to allow for the crystallization of the polyolefin sample in the absence of an adsorptive force followed by the typical PGC column for adsorption/desorption. Accordingly, the loci of crystallization and adsorption/desorption are well separated from each other and can be adjusted independently. This novel column setup allows the sample to be introduced slowly onto the second (adsorptive) column eliminating possible co-adsorption and poor selectivity. Low molar mass polyethylene comprising of oligomers with approximately C30single bondC130 was used to illustrate the importance of a non-adsorptive column for improved separation. Utilizing a non-adsorptive silica column allows for higher dynamic flow rates during crystallization, which improves separation. Shorter adsorptive columns are found to be more efficient in this experimental protocol as compared to standard TGIC experiments. Smaller PGC column sizes result in reduced longitudinal and Eddy diffusion and, hence, higher resolution of low and high molar mass polyolefins.
- ItemApplication of polymer‑coated Macadamia integrifolia nutshell biomass impregnated with palladium for chromium(VI) remediation(Scientific Reports, 2021) Moyo, M.; Modise, S. J.; Pakade, V. E.Freely suspended and porous basket restrained granules of palladium nanoparticles supported on polymer-grafted Macadamia nutshell biomass (Pd@Polym-MNS) composite were used for the treatment chromium(VI)-containing water. In the presence of formic acid, the Pd@Polym-MNS demonstrated its activity in the adsorption-reduction-based conversion of noxious chromium(VI) to less toxic chromium(III) with a low activation energy of 13.4 kJ mol–1, ΔH0 (+ 10.8 kJ mol–1), ΔS0 (−270.0 J mol–1 K–1), and ΔG0 (+ 91.3 to + 98.0 kJ mol–1) indicated the exothermic, endergonic and non-spontaneous nature of the catalytic redox reaction. In addition to facilitating easy recovery, rinsing, and reuse, restraining the Pd@Polym-MNS in the basket reactor helped maintain the integrity of the catalysts by preventing violent collisions of suspended granules with the mixing apparatus and the walls of the reaction vessel. Whereas the pseudo-first-order rate constant was recorded as 0.157 min–1 upon initial use, values of the mean and relative standard deviation for the second, third and fourth consecutive uses were found to be 0.219 min–1 and 1.3%, respectively. According to a response surface methodological approach to batch experimentation, the initial concentration of chromium(VI) and catalyst dosage had the greatest impact on the redox reaction rate, accounting for 85.7% and 11.6% of the variability in the value of the pseudo-first-order rate constant, respectively. Mutually beneficial effects of the combinations of high formic acid and low chromium(VI) concentration, high temperature and catalyst dosage as well as high formic acid and catalyst dosage were recorded.
- ItemMajor challenges for commercialization of perovskite solar cells: A critical review(ELSEVIER, 2025-01-09) Seyisi, T.; Fouda-Mbanga, B.G.; Mnyango, J.I.; Nthwane, Y. B.; Nyoni, B.; Mhlanga, S.; Hlangothi, S. P.; Tywabi-Ngeva, Z.Global electricity consumption increases rapidly creating strain on the grid. In contrast, the primary sources of electricity are fossil fuels such as gas, coal, and oil which are non-renewable and limited, resulting in energy crises. Therefore, the global energy crisis remains a big challenge that requires renewable and sustainable solutions. Perovskite solar cell is a type of solar cell that uses a perovskite-structured compound, usually a hybrid organic-inorganic lead or tin halide-based material as the light-harvesting active layer. In the development of perovskite solar cells spanning 2009–2024, exceptional power conversion efficiencies ranging from 3.8 % to 26.1 % have been reported. As such, perovskite solar cells hold significant promise as the next generation of affordable and effective photovoltaic solar cell technology. Moreover, perovskite solar cells have recently gained popularity and presented an excellent commercial opportunity because they are made from readily available and inexpensive raw materials. However, the commercial production and utilization of perovskite solar cells remains immature. It has been shown that perovskite solar cells containing titanium dioxide as the electron transport layer exhibit poor stability, degrading quickly under prolonged exposure to sunlight and humid conditions. These instability concerns are the major drawbacks that threaten efforts that are directed at the commercialization of perovskite solar cells. As such, there are significant efforts to improve the development of scalable fabrication of perovskite solar cells and the establishment of industrial production lines. The main objective of this review is to outline the primary obstacles that hinder the commercialization of perovskite solar cells. Firstly, a brief discussion on the principles of perovskite solar cells is done. Secondly, challenges associated with the commercialization of erovskite solar cells and counterstrategies are discussed. The review concludes by looking at perspectives and prospects highlighting the importance of continued research and collaboration in overcoming challenges to commercialization. We hope that this review will provide useful insights for future research on improving the stability of cutting-edge perovskite devices as they approach commercialization.