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Prof Vincent O. Nyamori is a Professor (Inorganic & Material Science) and Academic Leader in the School of Chemistry and Physics, University of KwaZulu-Natal (UKZN). Also, he is the former President of the South African Chemical Institute (SACI). He is a Fellow of the Royal Society of Chemistry, FRSC, and an active member of the American Chemical Society (ACS). He is the Chair of the UKZN Nanotechnology Platform and the leader of the NanoChemistry Research Group. Prof Vincent O. Nyamori received his Ph.D. from Nelson Mandela Metropolitan University (NMMU) and, thereafter, carried his post-doctorate studies at the University of the Witwatersrand (Wits). His research interests include Green and Sustainable Chemistry, Nanotechnology and Materials Science. Also, Prof Nyamori research group has interests in advanced nanomaterials for various applications, in particular catalysis and energy devices. These nanomaterials include carbon nanotubes, graphene, graphitic carbon nitride, organo-inorganic hybrid materials and perovskites. Prof Nyamori is widely published and has a good citation record. He is a recipient of the UKZN top 30 published researchers and UKZN Vice-Chancellor Award. He has been the Chair of key national and international conferences and has also been an Invited Speaker at a number of them.
The low fabrication cost, solution processability and easy scalability of perovskite solar cells (PSCs), coupled with the rapid increase in their power conversion efficiency (PCE) from an initial value of 3.8% to a recently certified value of ∽25.5%, have enabled PSCs to compete with silicon‐based solar cells that currently exhibit PCEs of above 26.0%. However, unlike silicon‐based devices that have been commercialized, the commercialization of PSCs is being hindered by factors such as their poor long‐term operational stability, the high toxicity of lead (Pb) and the use of expensive materials, e.g., gold (Au) or silver (Ag). Hence, to address the aforementioned issues, significant research effort has been exerted on novel graphene‐based materials, with their merits, which include low‐cost, excellent stability, non‐toxicity and remarkable optoelectronic properties. Nevertheless, graphene‐based PSCs have been relatively less studied, and are still in their infancy. This study presents recent developments in applying graphene‐based materials in electrodes, perovskite active layers, charge transport layers and encapsulation layers of PSCs, focusing particularly on breakthroughs achieved over the last three years (2018‐2020). The merits, shortcomings and outlook of this field are discussed to propose future research directions for the low‐cost fabrication and commercialization of highly efficient and sustainable PSCs.
Edigar Muchuweni; Bice S. Martincigh; Vincent O. Nyamori. Perovskite Solar Cells: Current Trends in Graphene‐Based Materials for Transparent Conductive Electrodes, Active Layers, Charge Transport Layers, and Encapsulation Layers. Advanced Energy and Sustainability Research 2021, 2100050 .
AMA StyleEdigar Muchuweni, Bice S. Martincigh, Vincent O. Nyamori. Perovskite Solar Cells: Current Trends in Graphene‐Based Materials for Transparent Conductive Electrodes, Active Layers, Charge Transport Layers, and Encapsulation Layers. Advanced Energy and Sustainability Research. 2021; ():2100050.
Chicago/Turabian StyleEdigar Muchuweni; Bice S. Martincigh; Vincent O. Nyamori. 2021. "Perovskite Solar Cells: Current Trends in Graphene‐Based Materials for Transparent Conductive Electrodes, Active Layers, Charge Transport Layers, and Encapsulation Layers." Advanced Energy and Sustainability Research , no. : 2100050.
The ongoing research toward meeting global energy demands requires novel materials from abundant renewable resources. This work involves an investigation on nitrogen-doped carbon nanotubes (N-CNTs) synthesized from relatively low-cost and readily available biomass as carbon precursors and their use as electrodes for supercapacitors. The influence of the ionic liquid 1-butyl-3-methylimidazolium chloride, or its combination with either sugarcane bagasse or cellulose (IL-CNTs, ILBag-CNTs, and ILCel-CNTs, respectively), in the synthesis of N-CNTs and the resultant effect on their physical and electrochemical properties was studied. Systematic characterizations of the N-CNTs employing transmission electron microscopy (TEM), thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), elemental analysis, nitrogen sorption analysis, cyclic voltammetry, and electrochemical impedance spectroscopy were performed. TEM data analysis showed that the mean outer diameters decreased, in the order of IL-CNTs > ILBag-CNTs > ILCel-CNTs. The N-CNTs possess only pyridinic and pyrrolic nitrogen-doping moieties. The pyridinic nitrogen-doping content is lowest in IL-CNTs and highest in ILCel-CNTs. The N-CNTs are mesoporous with surface areas in the range of 21–52 m2 g−1. The ILCel-CNTs had the highest specific capacitance of 30 F g−1, while IL-CNTs has the least, 10 F g−1. The source of biomass is beneficial for tuning physicochemical properties such as the size and surface areas of N-CNTs, the pyridinic nitrogen-doping content, and ultimately capacitance, leading to materials with excellent properties for electrochemical applications.
Kudzai Mugadza; Annegret Stark; Patrick Ndungu; Vincent Nyamori. Effects of Ionic Liquid and Biomass Sources on Carbon Nanotube Physical and Electrochemical Properties. Sustainability 2021, 13, 2977 .
AMA StyleKudzai Mugadza, Annegret Stark, Patrick Ndungu, Vincent Nyamori. Effects of Ionic Liquid and Biomass Sources on Carbon Nanotube Physical and Electrochemical Properties. Sustainability. 2021; 13 (5):2977.
Chicago/Turabian StyleKudzai Mugadza; Annegret Stark; Patrick Ndungu; Vincent Nyamori. 2021. "Effects of Ionic Liquid and Biomass Sources on Carbon Nanotube Physical and Electrochemical Properties." Sustainability 13, no. 5: 2977.
Introduction The aggressive search for renewable energy resources and essential pyrosynthetic compounds has marked an exponential rise in the thermal degradation of biomass materials. Consequently, clean and sustainable transport fuels are increasingly desirable in a highly industrialized economy, for energy security and environmental protection. For this reason, biomass materials have been identified as promising alternatives to fossil fuels despite the challenges resulting from the possible formation of toxic nitrogen-based molecules during biomass degradation. In order to understand the free radical characteristic challenges facing the use of bio-oil, a brief review of the effects of free radicals in bio-oil is presented. Methodology Pyrolysis was conducted in a tubular flow quartz reactor at a residence time of 2 s at 1 atm. pressure, for a total pyrolysis time of 5 min. The thermal degradation of biomass components was investigated over the temperature range of 200 to 700 °C typically in 50 °C increments under two reaction conditions; pyrolysis in N2 and oxidative pyrolysis in 5% O2 in N2. The pyrolysate effluent was analysed using a Gas chromatograph hyphenated to a mass selective detector (MSD). Results The yield of levoglucosan in the pyrolysis of cellulose in the entire pyrolysis temperature range was 68.2 wt % under inert conditions and 28.8 wt % under oxidative conditions. On the other hand, formaldehyde from pyrolysis of cellulose yielded 4 wt % while that from oxidative pyrolysis was 7 wt % translating to ⁓ 1.8 times higher than the yield from pyrolysis. Accordingly, we present for the first time dioxin-like and dibenzofuran-like nitrogenated analogues from an equimassic pyrolysis of cellulose and tyrosine. Levoglucosan and formaldehyde were completely inhibited during the equimassic pyrolysis of cellulose and tyrosine. Conclusion Clearly, any small amounts of N-biomass components such as amino acids in cellulosic biomass materials can inhibit the formation of levoglucosan–a major constituent of bio-oil. Overall, a judicious balance between the production of bio-oil and side products resulting from amino acids present in plant matter should be taken into account to minimize economic losses and mitigate against negative public health concerns.
Samuel K. Kirkok; Joshua K. Kibet; Thomas Kinyanjui; Francis I. Okanga; Vincent O. Nyamori. Dioxin and dibenzofuran like molecular analogues from the pyrolysis of biomass materials—the emerging challenge in bio-oil production. BMC Chemistry 2021, 15, 1 -10.
AMA StyleSamuel K. Kirkok, Joshua K. Kibet, Thomas Kinyanjui, Francis I. Okanga, Vincent O. Nyamori. Dioxin and dibenzofuran like molecular analogues from the pyrolysis of biomass materials—the emerging challenge in bio-oil production. BMC Chemistry. 2021; 15 (1):1-10.
Chicago/Turabian StyleSamuel K. Kirkok; Joshua K. Kibet; Thomas Kinyanjui; Francis I. Okanga; Vincent O. Nyamori. 2021. "Dioxin and dibenzofuran like molecular analogues from the pyrolysis of biomass materials—the emerging challenge in bio-oil production." BMC Chemistry 15, no. 1: 1-10.
Lately, there has been increased interest in the design of graphene‐based hybrid nanomaterials and their application to modify properties of organic solar cells (OSCs). Herein, we demonstrate an efficient route for the successful hydrothermal synthesis of reduced graphene oxide‐anatase titania (RGOT) nanocomposites. Five nanocomposites with different titania concentrations, that is, RGOT‐50, RGOT‐75, RGOT‐86, RGOT‐90, and RGOT‐92, were prepared. The nanocomposite RGOT‐92 with the overall best properties was used to modify both the photoactive layer (P3HT:PCBM:RGOT) and hole transport layer (PEDOT:PSS:RGOT) of an OSC so as to assist in solar energy absorption by way of enhancing optical absorption and creating an efficient charge transport channel. The nanocomposites prepared consist of highly crystalline, spherical, and uniformly shaped TiO2 nanoparticles, with an average particle size of approximately 3.0 nm, deposited on the basal plane of reduced graphene oxide. Also, the nanocomposites show much reduced bandgap energies and low rates of electron‐hole recombination. The incorporation of RGOT in the active layer effectively improved photon absorption, leading to high photoexciton generation. In addition, effective exciton dissociation was energetically favoured in the RGOT‐modified hole transport layer (HTL), which concurs with the observed enhanced conductivity of the medium. Thus, the integration of RGOT in the active layer and HTL remarkably resulted in a high short‐circuit current density (Jsc), low sheet resistance (Rs), and, consequently, improved photovoltaic performance. An enhanced photocurrent was noted, as high as 13 mA cm−2, from the OSCs by inlaying RGOT in the photoactive layer. An increased power conversion efficiency of up to 64% was achieved by the incorporation of RGOT in the photoactive layer. Thus, the utilized hydrothermal synthesis route provided nanocomposites with enhanced photoelectronic properties, with promising applications in nanoelectronic devices.
Hassan O. Shoyiga; Bice S. Martincigh; Vincent O. Nyamori. Hydrothermal synthesis of reduced graphene oxide‐anatase titania nanocomposites for dual application in organic solar cells. International Journal of Energy Research 2020, 45, 7293 -7314.
AMA StyleHassan O. Shoyiga, Bice S. Martincigh, Vincent O. Nyamori. Hydrothermal synthesis of reduced graphene oxide‐anatase titania nanocomposites for dual application in organic solar cells. International Journal of Energy Research. 2020; 45 (5):7293-7314.
Chicago/Turabian StyleHassan O. Shoyiga; Bice S. Martincigh; Vincent O. Nyamori. 2020. "Hydrothermal synthesis of reduced graphene oxide‐anatase titania nanocomposites for dual application in organic solar cells." International Journal of Energy Research 45, no. 5: 7293-7314.
Graphene-based materials can produce high performance and sustainable DSSCs, through tuning of their excellent optoelectronic, mechanical, thermal and chemical properties for use as photoanodes, photosensitizers, electrolytes and counter electrodes.
Edigar Muchuweni; Bice S. Martincigh; Vincent O. Nyamori. Recent advances in graphene-based materials for dye-sensitized solar cell fabrication. RSC Advances 2020, 10, 44453 -44469.
AMA StyleEdigar Muchuweni, Bice S. Martincigh, Vincent O. Nyamori. Recent advances in graphene-based materials for dye-sensitized solar cell fabrication. RSC Advances. 2020; 10 (72):44453-44469.
Chicago/Turabian StyleEdigar Muchuweni; Bice S. Martincigh; Vincent O. Nyamori. 2020. "Recent advances in graphene-based materials for dye-sensitized solar cell fabrication." RSC Advances 10, no. 72: 44453-44469.
An assortment of carbon‐based materials, such as nanotubes, nanorods, nanoribbons, nanofibers and graphene, is fast gaining significant research interest in developing various components of organic solar cells (OSCs) due to their unique optoelectronic properties. Among these, graphene‐based materials are more appealing owing to their remarkable optical, electrical, chemical, mechanical and thermal properties, coupled with their specific large surface area and flexibility, which are compatible with large‐scale roll‐to‐roll synthesis. Their low‐cost, abundance, non‐toxicity, high optical transparency and competitive electrical conductivity makes them potential replacement materials for the commonly used indium tin oxide (ITO) anodes in bulk heterojunction (BHJ)‐OSCs owing to the scarcity, high cost and toxicity of indium, which is the principal constituent element of ITO. Furthermore, the synergy between graphene‐based electron‐acceptor materials and donor polymers in the photoactive layer of BHJ‐OSCs results in enhanced photon harvesting, improved exciton generation, effective exciton dissociation and efficient charge transport. However, graphene‐based materials have been applied not only as anodes and electron acceptors but also as cathodes, electron‐transport layers and hole transport layers. Recently, the incorporation of graphene‐based materials into OSCs has led to a significant increase in power conversion efficiency (PCE) from ~0.63% to above 16.00%. The PCE can be further enhanced by employing recent breakthroughs to optimize the optoelectronic properties of the various OSC components; hence making graphene‐based state‐of‐the‐art OSCs approach PCEs of ~25%, which approach the favourable PCE values of above 26% exhibited by silicon‐based solar cells. Thus, graphene‐based OSCs can conceivably close the gap between OSCs and silicon‐based devices. Herein, we present an in‐depth review of the recent progress on applying graphene‐based materials in BHJ‐OSCs as electrodes, electron acceptors and interfacial layers, for the advancement and realization of high‐efficiency and sustainable devices, as a link‐bridge towards commercialization. The crucial photovoltaic parameters, such as short‐circuit current density, open‐circuit voltage, fill factor and PCE, are discussed to reveal the merits, drawbacks and future prospects of graphene‐based BHJ‐OSCs.
Edigar Muchuweni; Bice S. Martincigh; Vincent O. Nyamori. Organic solar cells: Current perspectives on graphene‐based materials for electrodes, electron acceptors and interfacial layers. International Journal of Energy Research 2020, 45, 6518 -6549.
AMA StyleEdigar Muchuweni, Bice S. Martincigh, Vincent O. Nyamori. Organic solar cells: Current perspectives on graphene‐based materials for electrodes, electron acceptors and interfacial layers. International Journal of Energy Research. 2020; 45 (5):6518-6549.
Chicago/Turabian StyleEdigar Muchuweni; Bice S. Martincigh; Vincent O. Nyamori. 2020. "Organic solar cells: Current perspectives on graphene‐based materials for electrodes, electron acceptors and interfacial layers." International Journal of Energy Research 45, no. 5: 6518-6549.
Graphitic carbon nitride (g-C3N4) is a metal-free photoactive material which has gained significant interest in the advancement of electronic and optical devices because of its attractive optoelectronic properties, such as tuneable band gap, and suitable chemical and thermal stability. This material has been utilized in a range of applications including photocatalysis, biosensing and photovoltaics. Bulk g-C3N4 (B-g-C3N4) has been shown to exhibit low photo-efficiency due to its low specific surface area and high rate of recombination of photo-generated charges; thus, there is a need for its exfoliation. Also, the type of exfoliation method utilized is crucial. In this work, two exfoliation methods of g-C3N4, namely, liquid and thermal etching exfoliation, were investigated. Both methods successfully produced g-C3N4 nanosheets, but those synthesized by liquid exfoliation (CNNS-LE) had a much larger specific surface area of 41.68 m2 g−1 than those prepared by thermal exfoliation (CNNS-TE) (14.76 m2 g−1) or the parent B-g-C3N4 (3.22 m2 g−1). The band gap energies of B-g-C3N4, CNNS-LE and CNNS-TE were found to be 2.71, 2.59 and 1.89 eV, respectively. Graphitic carbon nitride nanosheets prepared by thermal exfoliation (CNNS-TE) were found to be 2.5 times more effective in the photo-degradation of Rhodamine B than B-g-C3N4 and CNNS-LE. This is attributed to the positive effect of their porous structure, which gives rise to effective separation of charges, and their extended light absorption properties. Thus, thermal treatment introduces structural defects and electronic modifications that result in an enhanced photocatalytic performance. Consequently, thermal etching is effective in exfoliation of B-g-C3N4 to form a material suitable for photo-driven applications.
Nicholas Rono; Joshua K. Kibet; Bice S. Martincigh; Vincent O. Nyamori. A comparative study between thermal etching and liquid exfoliation of bulk graphitic carbon nitride to nanosheets for the photocatalytic degradation of a model environmental pollutant, Rhodamine B. Journal of Materials Science: Materials in Electronics 2020, 32, 687 -706.
AMA StyleNicholas Rono, Joshua K. Kibet, Bice S. Martincigh, Vincent O. Nyamori. A comparative study between thermal etching and liquid exfoliation of bulk graphitic carbon nitride to nanosheets for the photocatalytic degradation of a model environmental pollutant, Rhodamine B. Journal of Materials Science: Materials in Electronics. 2020; 32 (1):687-706.
Chicago/Turabian StyleNicholas Rono; Joshua K. Kibet; Bice S. Martincigh; Vincent O. Nyamori. 2020. "A comparative study between thermal etching and liquid exfoliation of bulk graphitic carbon nitride to nanosheets for the photocatalytic degradation of a model environmental pollutant, Rhodamine B." Journal of Materials Science: Materials in Electronics 32, no. 1: 687-706.
Boron-doping enhanced the occurrence of the energy bandgap, the pore structure and interfacial charge transfer characteristics.
Nonjabulo P. D. Ngidi; Moses A. Ollengo; Vincent O. Nyamori. Tuning the properties of boron-doped reduced graphene oxide by altering the boron content. New Journal of Chemistry 2020, 44, 16864 -16876.
AMA StyleNonjabulo P. D. Ngidi, Moses A. Ollengo, Vincent O. Nyamori. Tuning the properties of boron-doped reduced graphene oxide by altering the boron content. New Journal of Chemistry. 2020; 44 (39):16864-16876.
Chicago/Turabian StyleNonjabulo P. D. Ngidi; Moses A. Ollengo; Vincent O. Nyamori. 2020. "Tuning the properties of boron-doped reduced graphene oxide by altering the boron content." New Journal of Chemistry 44, no. 39: 16864-16876.
Considering its availability, renewable character and abundance in nature, this review assesses the opportunity of the application of biomass as a precursor for the production of carbon-based nanostructured materials (CNMs). CNMs are exceptionally shaped nanomaterials that possess distinctive properties, with far-reaching applicability in a number of areas, including the fabrication of sustainable and efficient energy harnessing, conversion and storage devices. This review describes CNM synthesis, properties and modification, focusing on reports using biomass as starting material. Since biomass comprises 60–90% cellulose, the current review takes into account the properties of cellulose. Noting that highly crystalline cellulose poses a difficulty in dissolution, ionic liquids (ILs) are proposed as the solvent system to dissolve the cellulose-containing biomass in generating precursors for the synthesis of CNMs. Preliminary results with cellulose and sugarcane bagasse indicate that ILs can not only be used to make the biomass available in a liquefied form as required for the floating catalyst CVD technique but also to control the heteroatom content and composition in situ for the heteroatom doping of the materials.
Kudzai Mugadza; Annegret Stark; Patrick G. Ndungu; Vincent O. Nyamori. Synthesis of Carbon Nanomaterials from Biomass Utilizing Ionic Liquids for Potential Application in Solar Energy Conversion and Storage. Materials 2020, 13, 3945 .
AMA StyleKudzai Mugadza, Annegret Stark, Patrick G. Ndungu, Vincent O. Nyamori. Synthesis of Carbon Nanomaterials from Biomass Utilizing Ionic Liquids for Potential Application in Solar Energy Conversion and Storage. Materials. 2020; 13 (18):3945.
Chicago/Turabian StyleKudzai Mugadza; Annegret Stark; Patrick G. Ndungu; Vincent O. Nyamori. 2020. "Synthesis of Carbon Nanomaterials from Biomass Utilizing Ionic Liquids for Potential Application in Solar Energy Conversion and Storage." Materials 13, no. 18: 3945.
Eric M. Njogu; Bernard Omondi; Vincent O. Nyamori. Corrigendum to “Silver(I)-pyridinyl Schiff base complexes: Synthesis, structural characterization and reactivity in ring-opening polymerisation of ε-caprolactone” [Inorg. Chim. Acta 457 (2017) 160–170]. Inorganica Chimica Acta 2020, 512, 119905 .
AMA StyleEric M. Njogu, Bernard Omondi, Vincent O. Nyamori. Corrigendum to “Silver(I)-pyridinyl Schiff base complexes: Synthesis, structural characterization and reactivity in ring-opening polymerisation of ε-caprolactone” [Inorg. Chim. Acta 457 (2017) 160–170]. Inorganica Chimica Acta. 2020; 512 ():119905.
Chicago/Turabian StyleEric M. Njogu; Bernard Omondi; Vincent O. Nyamori. 2020. "Corrigendum to “Silver(I)-pyridinyl Schiff base complexes: Synthesis, structural characterization and reactivity in ring-opening polymerisation of ε-caprolactone” [Inorg. Chim. Acta 457 (2017) 160–170]." Inorganica Chimica Acta 512, no. : 119905.
In the quest to improve the optical absorption and electrical transport of poly-3-hexylthiophene (P3HT) and (6-6) phenyl-C61-butyric acid methyl ester (PCBM) blend film, reduced graphene oxide-germanium dioxide nanocomposite (rGO-GeO2) was employed in the photoactive layer of thin film organic solar cells. Bulk heterojunction solar cells (BHJ SCs) with rGO-GeO2 composite in the active layer exhibited an increase in power conversion efficiency (PCE) of up to 53%. Significant improvement in the measured photocurrent is achieved by the incorporation of rGO-GeO2 in the active layer. High short-circuit current density (Jsc) of up to 17 mA/cm2 is attained in the BHJ SCs. The high Jsc shows that the inlay of rGO-GeO2 in the active layer facilitates exciton separation and creates percolation pathways for charge transport to the electrodes. Charge separation is energetically favoured by a built-in potential difference between the donor and acceptor phases of the active layer. Hence, the incorporation of rGO-GeO2 composite in the active layer improves its charge photogeneration, separation and transport to yield high Jsc and enhanced PCE.
Tabitha A. Amollo; Genene T. Mola; Vincent O. Nyamori. Improved short-circuit current density in bulk heterojunction solar cells with reduced graphene oxide-germanium dioxide nanocomposite in the photoactive layer. Materials Chemistry and Physics 2020, 254, 123448 .
AMA StyleTabitha A. Amollo, Genene T. Mola, Vincent O. Nyamori. Improved short-circuit current density in bulk heterojunction solar cells with reduced graphene oxide-germanium dioxide nanocomposite in the photoactive layer. Materials Chemistry and Physics. 2020; 254 ():123448.
Chicago/Turabian StyleTabitha A. Amollo; Genene T. Mola; Vincent O. Nyamori. 2020. "Improved short-circuit current density in bulk heterojunction solar cells with reduced graphene oxide-germanium dioxide nanocomposite in the photoactive layer." Materials Chemistry and Physics 254, no. : 123448.
Graphitic carbon nitride (g-C3N4) has become an important material because of its attractive optoelectronic properties. It has been applied in various fields such as photovoltaics, biosensing, and photocatalysis. As an analog of graphene, it has layers which can be transformed into different morphologies including nanosheets, nanotubes, and quantum dots. Pristine g-C3N4 exhibits a low specific surface area and a high rate of recombination of photogenerated charges. Therefore, modification is required in order to improve its properties, for instance, by doping it with other atoms and transforming it into another morphology. In this review, the synthesis, modifications, and applications of g-C3N4 are evaluated. The use of theoretical strategies to understand various properties of g-C3N4 and its composites is highlighted. Moreover, the current status on the application of g-C3N4 is explored. Ultimately, this review will shed more light on the uses and modifications of g-C3N4 for future applications.
Nicholas Rono; Joshua K. Kibet; Bice S. Martincigh; Vincent O. Nyamori. A review of the current status of graphitic carbon nitride. Critical Reviews in Solid State and Materials Sciences 2020, 46, 189 -217.
AMA StyleNicholas Rono, Joshua K. Kibet, Bice S. Martincigh, Vincent O. Nyamori. A review of the current status of graphitic carbon nitride. Critical Reviews in Solid State and Materials Sciences. 2020; 46 (3):189-217.
Chicago/Turabian StyleNicholas Rono; Joshua K. Kibet; Bice S. Martincigh; Vincent O. Nyamori. 2020. "A review of the current status of graphitic carbon nitride." Critical Reviews in Solid State and Materials Sciences 46, no. 3: 189-217.
Background Research inventories on the co-pyrolysis of major biomass components such as cellulose with amino acid materials is scarce in literature despite the fact that such studies are critical in understanding toxic product relations from high temperature cooking, combustion of bio-fuels, cigarette smoking and forest fires. This paper explores, quantitatively, the yields of heterocyclic nitrogenated molecular reaction products of grave mutagenetic concern from the co-pyrolysis of model biomass materials; tyrosine and cellulose. Research has established that heterocyclic amines such as isocyanates are mutagens as well precursors for asthma, and other respiratory disorders. Methods An equimassic mixture of tyrosine and cellulose (50 ± 2 mg) by weight were pyrolyzed in a tubular quartz reactor in flowing nitrogen at 1 atm. Besides, varying combinations of tyrosine and cellulose in the ratios 3:1 and 1:3 were also explored for comparison. The reaction time was set at 2 s so as to simulate combustions events in nature. The pyrolysate was collected over 5 mL dichloromethane and characterized using a gas chromatograph coupled to a mass spectrometer detector. Results Evidently, it was noted that 1-methylindazole was released in high yields at 300 °C, constituting ~ 300 µg in the entire pyrolysis temperature range (200–700 °C). Nonetheless, isoindazole gave the highest yield ~ 730 µg while 1-naphthyl isocyanate gave a total yield of ~ 336 µg in the same temperature range. Remarkably, the change in char yield between 300 and 450 °C for the pyrolysis of 25% tyrosine in 75% cellulose was found to be ~ 48% whereas the change in char yield for the pyrolysis of 75% tyrosine in 25% cellulose was 49%. Conclusion The char and tar yields considered important residues of biomass burning have been reported in this study and found to be consistent with other research output in literature. The striking similarities of % yield of char across all temperatures for various combinations was the most significant observation in this investigation—char yield was independent of the mixing ratio during pyrolysis. From a mechanistic standpoint, it was noted that tyrosine inhibited cellulose based nitrogenated products. Thus N-products dominated the O-products.
Samuel K. Kirkok; Joshua K. Kibet; Francis Okanga; Thomas Kinyanjui; Vincent Nyamori. Mechanistic formation of hazardous molecular heterocyclic amines from high temperature pyrolysis of model biomass materials: cellulose and tyrosine. BMC Chemistry 2019, 13, 1 -9.
AMA StyleSamuel K. Kirkok, Joshua K. Kibet, Francis Okanga, Thomas Kinyanjui, Vincent Nyamori. Mechanistic formation of hazardous molecular heterocyclic amines from high temperature pyrolysis of model biomass materials: cellulose and tyrosine. BMC Chemistry. 2019; 13 (1):1-9.
Chicago/Turabian StyleSamuel K. Kirkok; Joshua K. Kibet; Francis Okanga; Thomas Kinyanjui; Vincent Nyamori. 2019. "Mechanistic formation of hazardous molecular heterocyclic amines from high temperature pyrolysis of model biomass materials: cellulose and tyrosine." BMC Chemistry 13, no. 1: 1-9.
Six ferrocenyl imidazole derivatives substituted with -Cl, -NO2 and -CH3 on the 2-position of the 1H-imidazole ring have been synthesized. Of the six compounds, the di-substituted ferrocenes, i.e. compounds 4 (1,1'-ferrocenylmethyl(2-chloroimidazole)), 5 (1,1'-ferrocenyl(2-nitroimidazole)), and 6 (1,1'-ferrocenylmethyl(2-methylimidazole)) are reported for the first time. The structure-property relationships of compounds 4, 5 and 6 were investigated by means of UV-visible, FTIR, 1H-NMR, 13C-NMR spectroscopy and electrochemical studies. UV-visible analysis in acetonitrile showed that the π -π* band of compounds 2 (1-ferrocenylmethyl(2-nitroimidazole)) and 5 appeared at longer wavelength compared to 1 (1-ferrocenylmethyl(2-chloroimidazole)), 3 (1-ferrocenylmethyl(2-methylimidazole)), 4 and 6. This phenomenon is due to the different electronics around the imidazole moieties. In cyclic voltammetry analysis, all compounds exhibited a quasi-reversible redox wave for the ferrocenyl and imidazole moieties. Density functional theoretical (DFT) calculations with the B3LYP/6-311+G(d) basis set were performed on compounds 1-6, and the calculated HUMO-LUMO band gap energies correlated with those obtained from electrochemical and spectroscopic data. The X-ray crystallographic analysis highlighted the effect of electron-withdrawing and electron-donating substituents on the conformation of the cyclopentadienyl rings attached to the ferrocenyl moiety.
Ayomide H. Labulo; Bernard Omondi; Vincent O. Nyamori. Synthesis, crystal structures and electrochemical properties of ferrocenyl imidazole derivatives. Heliyon 2019, 5, e02580 .
AMA StyleAyomide H. Labulo, Bernard Omondi, Vincent O. Nyamori. Synthesis, crystal structures and electrochemical properties of ferrocenyl imidazole derivatives. Heliyon. 2019; 5 (10):e02580.
Chicago/Turabian StyleAyomide H. Labulo; Bernard Omondi; Vincent O. Nyamori. 2019. "Synthesis, crystal structures and electrochemical properties of ferrocenyl imidazole derivatives." Heliyon 5, no. 10: e02580.
The greatest challenge in graphene-based material synthesis is achieving large surface area of high conductivity. Thus, tuning physico-electrochemical properties of these materials is of paramount importance. An even greater problem is to obtain a desired dopant configuration which allows control over device sensitivity and enhanced reproducibility. In this work, substitutional doping of graphene oxide (GO) with nitrogen atoms to induce lattice–structural modification of GO resulted in nitrogen-doped reduced graphene oxide (N-rGO). The effect of doping temperatures and various nitrogen precursors on the physicochemical, optical, and conductivity properties of N-rGO is hereby reported. This was achieved by thermal treating GO with different nitrogen precursors at various doping temperatures. The lowest doping temperature (600 °C) resulted in less thermally stable N-rGO, yet with higher porosity, while the highest doping temperature (800 °C) produced the opposite results. The choice of nitrogen precursors had a significant impact on the atomic percentage of nitrogen in N-rGO. Nitrogen-rich precursor, 4-nitro-ο-phenylenediamine, provided N-rGO with favorable physicochemical properties (larger surface area of 154.02 m2 g−1) with an enhanced electrical conductivity (0.133 S cm−1) property, making it more useful in energy storage devices. Thus, by adjusting the doping temperatures and nitrogen precursors, one can tailor various properties of N-rGO.
Nonjabulo P. D. Ngidi; Moses A. Ollengo; Vincent O. Nyamori. Effect of Doping Temperatures and Nitrogen Precursors on the Physicochemical, Optical, and Electrical Conductivity Properties of Nitrogen-Doped Reduced Graphene Oxide. Materials 2019, 12, 3376 .
AMA StyleNonjabulo P. D. Ngidi, Moses A. Ollengo, Vincent O. Nyamori. Effect of Doping Temperatures and Nitrogen Precursors on the Physicochemical, Optical, and Electrical Conductivity Properties of Nitrogen-Doped Reduced Graphene Oxide. Materials. 2019; 12 (20):3376.
Chicago/Turabian StyleNonjabulo P. D. Ngidi; Moses A. Ollengo; Vincent O. Nyamori. 2019. "Effect of Doping Temperatures and Nitrogen Precursors on the Physicochemical, Optical, and Electrical Conductivity Properties of Nitrogen-Doped Reduced Graphene Oxide." Materials 12, no. 20: 3376.
Presented herein is the nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) production from a residue, sugarcane bagasse, using 1-butyl-3-methylimidazolium chloride [C4MIM]Cl as the solvent and nitrogen source, and ferrocene as the catalyst source. N-MWCNTs were synthesised using the floating catalyst chemical vapour deposition method at 850 °C. The synthesised N-MWCNTs were characterised using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), X-ray diffraction (XRD) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. Hollow tubular structures of N-MWCNTs were observed using TEM. These observations correlated morphology from SEM which showed spaghetti-like structures, and also EDS detected the presence of nitrogen. Raman spectroscopy indicated MWCNT bands, around 1350 and 1580 cm−1 assigned to D-band and G-band due to defective and graphitic carbon vibrations, respectively. Also, XRD patterns showed typical N-MWCNT structures with a strong intensity peak at 2θ = 26.4° which was indexed as the C(002) reflection of graphite. TGA showed an N-CNTs thermogram curve, with the main decomposition temperature around 590 °C. The study showed that N-MWCNTs were successfully synthesised from sugarcane bagasse. The study significantly establishes a strategy for utilisation and value addition of a residue which is abundant from sugar production mills.
Kudzai Mugadza; Patrick G. Ndungu; Annegret Stark; Vincent O. Nyamori. Conversion of residue biomass into value added carbon materials: utilisation of sugarcane bagasse and ionic liquids. Journal of Materials Science 2019, 54, 12476 -12487.
AMA StyleKudzai Mugadza, Patrick G. Ndungu, Annegret Stark, Vincent O. Nyamori. Conversion of residue biomass into value added carbon materials: utilisation of sugarcane bagasse and ionic liquids. Journal of Materials Science. 2019; 54 (19):12476-12487.
Chicago/Turabian StyleKudzai Mugadza; Patrick G. Ndungu; Annegret Stark; Vincent O. Nyamori. 2019. "Conversion of residue biomass into value added carbon materials: utilisation of sugarcane bagasse and ionic liquids." Journal of Materials Science 54, no. 19: 12476-12487.
Photovoltaics is a portentous alternative to the nonrenewable energy resources. Organic solar cells (OSCs) offer several advantages over inorganic counterparts in terms of low-cost device production, simple solution-based processing, flexibility, light-weight and compatibility with roll-to-roll fabrication. This review comprehensively examines the latest research developments towards high-performance OSCs. Device processing conditions and engineering along with material developments for the active and interfacial layers are examined. Different device structures and their benefits and limitations are highlighted. The interfacial layer materials including the polymers and metal oxides together with their integration and performance in functional OSCs are examined. A salient aspect of this review is the design of donor and acceptor materials to address the optical and electronic properties requirement for optimized device efficacy of OSCs. In this regard, the prospects of tailoring the band gap of donor polymers alongside the adoption of non-fullerene acceptors with complementary optical absorption for improved solar energy harvesting is elucidated. Further, graphene’s feasibility as an active or interfacial layer material is reviewed. Hence, this article provides perspectives and strategies on further development of solution-processable donor, acceptor and interfacial materials for high efficiency devices, required in commercialization of OSCs.
Tabitha A. Amollo; Genene T. Mola; Vincent O. Nyamori. Organic solar cells: Materials and prospects of graphene for active and interfacial layers. Critical Reviews in Solid State and Materials Sciences 2019, 45, 261 -288.
AMA StyleTabitha A. Amollo, Genene T. Mola, Vincent O. Nyamori. Organic solar cells: Materials and prospects of graphene for active and interfacial layers. Critical Reviews in Solid State and Materials Sciences. 2019; 45 (4):261-288.
Chicago/Turabian StyleTabitha A. Amollo; Genene T. Mola; Vincent O. Nyamori. 2019. "Organic solar cells: Materials and prospects of graphene for active and interfacial layers." Critical Reviews in Solid State and Materials Sciences 45, no. 4: 261-288.
Carbon nanostructured materials (CNMs) have vast capability in the field of energy, for storage and conversion purposes. Consequently, extensive greener and environmentally benign synthesis techniques that employ natural and readily renewable, low-cost waste materials need to be established. Herein, cellulose is considered as an alternative precursor source for the synthesis of CNMs. In the past decade, ionic liquids (ILs) have exhibited a great potential in a diverse number of applications. However, insignificant attention has been paid to the structure of ILs in relation to their extended application as a media for the dissolution of cellulose to avail carbon for CNMs synthesis. As baseline, a number of ionic liquids were used as carbon sources for CNM production, and distinct differences were found, depending on the type of ionic liquid used and the temperature of synthesis. Furthermore. CNMs were fabricated using a combination of the ionic liquid, 1-butyl-3-methylimidazolium chloride, [C4MIM]Cl, and cellulose, in the presence of ferrocene as catalyst precursor, using the floating catalyst chemical vapour deposition technique. Typical spaghetti like, hollow tubular structures with bamboo compartments, resembling N-doped multiwalled tubular carbon nanomaterials were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) respectively. Thermal stability studies showed thermogram profiles with a stability of around 550 °C. The sample synthesised with cellulose was more stable than the sample synthesised from IL and ferrocene only. Characteristic D- and G-bands were observed around 1380 and 1560 cm−1, respectively, for Raman spectroscopy. X-ray diffraction (XRD) showed characteristic tubular carbon nanomaterials and or graphitic/N-graphitic diffraction patterns.
Kudzai Mugadza; Patrick G. Ndungu; Annegret Stark; Vincent O. Nyamori. Ionic liquids and cellulose: Innovative feedstock for synthesis of carbon nanostructured material. Materials Chemistry and Physics 2019, 234, 201 -209.
AMA StyleKudzai Mugadza, Patrick G. Ndungu, Annegret Stark, Vincent O. Nyamori. Ionic liquids and cellulose: Innovative feedstock for synthesis of carbon nanostructured material. Materials Chemistry and Physics. 2019; 234 ():201-209.
Chicago/Turabian StyleKudzai Mugadza; Patrick G. Ndungu; Annegret Stark; Vincent O. Nyamori. 2019. "Ionic liquids and cellulose: Innovative feedstock for synthesis of carbon nanostructured material." Materials Chemistry and Physics 234, no. : 201-209.
This work focused on the synthesis of 3D Pd-based nanocomposites which were tested in Heck coupling reactions and for the hydrogenation of nitroarenes. This was achieved by fabrication of graphene oxide/nitrogen-doped carbon nanotubes (G/N-CNTs) by mechanical grinding of 2D graphene oxide (GO) and 1D oxygen-treated nitrogen-doped CNTs (N-CNTs-OT) in a 3:1 ratio, respectively. The fabrication of G/N-CNTs is to overcome the habitual aggregation and restacking of graphene sheets. Palladium nanoparticles (Pd NPs) were deposited on the 3D G/N-CNTs nanocomposites via metal organic chemical vapour deposition method. The 3D Pd-based nanocomposites were characterized by TEM, SEM, HRTEM, XRD, TGA, XPS, ICP-OES, elemental analysis, BET analysis and Raman spectroscopy. For the Heck coupling reactions, aryl halides, olefins and 3D Pd-based nanocomposites were mixed in a suitable solvent and the reaction carried under microwave irradiation. The chemoselective hydrogenation of nitroarenes was done with dry ethanol in a Paar reactor, purged with H2 gas. These catalysts demonstrate excellent activity and selectivity in both reactions. The remarkable activity of the 3D Pd-based nanocomposites in Heck reactions and hydrogenation of nitroarenes may be attributed to the small particle size (3–10 nm) and a high degree of dispersion of Pd NPs. A comparative experiment was conducted with Pd/AC, Pd/CNTs, Pd/G/CNTs and Pd/rGO. Pd/G/N-CNTs-OT showed higher activity and selectivity than Pd/G/CNTs, Pd/G/N-CNTs, Pd/rGO and Pd/N-CNTs counterpart.
Ayomide H. Labulo; Bernard Omondi; Vincent O. Nyamori. Graphene/pyrrolic-structured nitrogen-doped CNT nanocomposite supports for Pd-catalysed Heck coupling and chemoselective hydrogenation of nitroarenes. SN Applied Sciences 2019, 1, 1 -22.
AMA StyleAyomide H. Labulo, Bernard Omondi, Vincent O. Nyamori. Graphene/pyrrolic-structured nitrogen-doped CNT nanocomposite supports for Pd-catalysed Heck coupling and chemoselective hydrogenation of nitroarenes. SN Applied Sciences. 2019; 1 (2):1-22.
Chicago/Turabian StyleAyomide H. Labulo; Bernard Omondi; Vincent O. Nyamori. 2019. "Graphene/pyrrolic-structured nitrogen-doped CNT nanocomposite supports for Pd-catalysed Heck coupling and chemoselective hydrogenation of nitroarenes." SN Applied Sciences 1, no. 2: 1-22.
The most frequently used counter electrode (CE) in dye‐sensitized solar cells (DSSCs) is platinum on fluorine‐doped tin oxide glass. This electrode has excellent electrical conductivity, chemical stability, and high electrocatalytic affinity for the reduction of triiodide. However, the high cost of metallic platinum and the poor electrochemical stability pose a major drawback in the commercial production. This has necessitated a search for a non‐precious metal and metal‐free electrocatalyst that demonstrates better catalytic activity and longer electrochemical stability for practical use in DSSCs. Graphene has been at the centre of attention due to its excellent optoelectronic properties. However, a defect‐free graphene sheet is not suitable as a CE in DSSCs, because of its neutral polarity which often restricts efficient charge transfer at the graphene/liquid interface, irrespective of the high in‐plane charge mobility. Hence, heteroatom‐doped graphene‐based CEs are being developed with the aim to balance electrical conductivity for efficient charge transfer and charge polarization for enhanced reduction activity of redox couples simultaneously. The elements commonly used in chemical doping of graphene are nitrogen, oxygen, boron, sulfur, and phosphorus. Halogens have also recently shown great promise. It has been demonstrated that edge‐selective heteroatom‐doping of graphene imparts both efficient in‐plane charge transfers and polarity, thereby enhancing electrocatalytic activity. Thus, heteroatom‐doped graphene serves as a good material to replace conventional electrodes and enhance power conversion efficiency in DSSCs. The focus is to reduce the cost of DSSCs. This review explores the performance of DSSCs, factors that influence the power conversion efficiency, and various physicochemical properties of graphene. It further outlines current progress on the synthetic approaches for chemical doping (substitutional and surface transfer doping) of graphene and graphene oxide with different heteroatoms in order to fine‐tune the electronic properties. The use of heteroatom‐doped graphene as a CE in DSSCs and how it improves the photovoltaic performance of cells is discussed.
Nonjabulo P. D. Ngidi; Moses Ollengo; Vincent O. Nyamori. Heteroatom-doped graphene and its application as a counter electrode in dye-sensitized solar cells. International Journal of Energy Research 2018, 43, 1702 -1734.
AMA StyleNonjabulo P. D. Ngidi, Moses Ollengo, Vincent O. Nyamori. Heteroatom-doped graphene and its application as a counter electrode in dye-sensitized solar cells. International Journal of Energy Research. 2018; 43 (5):1702-1734.
Chicago/Turabian StyleNonjabulo P. D. Ngidi; Moses Ollengo; Vincent O. Nyamori. 2018. "Heteroatom-doped graphene and its application as a counter electrode in dye-sensitized solar cells." International Journal of Energy Research 43, no. 5: 1702-1734.