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Prof
Revaprasadu, Neerish
Department: Chemistry
Research Interest(s): Nanotechnology, Nanomaterials, Electrocatalysis.
Active Research Project(s): NRF/SASOL
NIMPO Incentive Grant
Active Community Engagement: ASSAF, RSC, and SACI
Biography: Neerish Revaprasadu is a Senior Professor of Chemistry and former SARChI Chair holder in Nanotechnology at the University of Zululand, South Africa. He obtained my B.Sc. (Hons.) from the University of Natal in 1993 and his PhD from Imperial College, London in 2000. He started as a Senior Lecturer at UNIZULLU in 2000 promoted to Associate Professor in 2004, and full Professor in 2009. In 2007, I was awarded the DST/NRF SARCHi research chair in Nanotechnology. He has taught undergraduate and postgraduate courses. These include General Chemistry (1st year), Analytical Chemistry (2nd, 3rd and Hons), Inorganic Chemistry (3rd year and Hons), and has supervised 15 postdocs, 20 PhD, and 16 MSc students. Professor Revaprasadu has published 240 articles in peer-reviewed journals, 25 book chapters, and attended 80 national and international conferences. He has been the editor of the SPR Nanoscience book series (Vol. 4-7) published by the Royal Society of Chemistry since 2016, and also the associate editor of the Nanoscience and Nanotechnology RSC book series. He was elected a Member of the South African Academy of Science (ASSAF) in 2014.
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- Exploitation of agricultural waste as green starting materials to produce various valuable products is attracting the attention of academic, industrial and other practitioners. Cashew nut shell (CNS) and its liquid extract (CNSL) in particular have been identified as agro-wastes rich in valuable and functional renewable products. The unique structural features of the CNSL constituents offer the possibility for different modifications to suit various applications. This review article provides recent developments in CNS and CNSL as green sources for use in the production of biorenewable chemicals, materials and energy. Extraction methods and applications of CNS, CNSL and isolates are discussed. Furthermore, a literature survey of the current status and efforts made on the utilization of these agricultural and food wastes for different applications is well outlined.
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- 2021| ElsevierFabrication of polymer-based nanocomposites for numerous biomedical applications represents a predominant form of therapeutics for combating microbial and bacterial infections. Herein, we firstly synthesized metal oxide nanoparticles (MONPs) by previously reported precipitation methods. Hydrogel nanocomposites were then prepared by free radical polymerization of a combination of the synthesized MONPs, polyvinylpyrrolidone (PVP) and acrylamide. The hydrogel nanocomposites were characterized by FTIR, XRD and investigated for potential antibacterial protection. FTIR spectra of the prepared hydrogel nanocomposites revealed significant characteristic peaks of the distinctive MONPs within the polymer matrix. XRD micrographs revealed slight shifting of peak positions in nanocomposites; the change in peak intensity, coupled with the observed slight shift in the diffraction peaks of both CuO and ZnO nanoparticles confirmed the successful incorporation of the MONPs into the polymer matrix. The presence of the MONPs, in combination with PVP, displayed a synergistic antibacterial activity, with increasing concentration of the MONPs. The treatment against S.pneumoniae, revealed a zone of inhibition phenomenon which showed zones of PVP-5 > PVP-8 > PVP-6 > PVP-9 > PVP-7. PVP-1, PVP-2, PVP-3, PVP-4 did not show any significant zone of inhibition on treatment due to the quantity of MONPs present. The findings show that the hydrogel nanocomposites are potential topical wound dressing materials for the management of bacterial infections.
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- Photoelectrochemical (PEC) water splitting has emerged as a promising technology for the storage of renewable energy sources, via the production of hydrogen, a clean and multi-purpose chemical energy vector. The key component in a PEC cell is the photoanode where light energy is absorbed and transformed into electron-hole pairs of appropriate energy for water photo-oxidation. We report on the synthesis of g-C3N4 materials, with an elongated nano-structure, fabricated by the direct pyrolysis of supramolecular melamine used as a chemical precursor. The as-prepared material was used to host specific amounts of bismuth, a doping element used to adjust the band gap of the hosting matrix. The presence of Bi in the photoanodes was confirmed by energy dispersive x-ray analysis (EDX) analysis. Powder X-ray (p-XRD) and Fourier transform infrared (FT-IR) measurements performed on the photoanodes confirmed the absence of Bi-based oxides, and showed that bismuth may bonded to nitrogen atoms inside the voids of the g-C3N4 skeleton. Differential reflective spectroscopy (DRS) measurements revealed that the band gap energy was reduced upon introduction of Bi into g-C3N4. From photoluminescence (PL) plots, it was observed that the 2.5% Bi doping induced a 6-fold electron-hole separation, compared to the pristine g-C3N4. PEC water splitting measurements showed that 2.5% Bi doping approximately doubled the activity of g-C3N4 towards water oxidation. Electrochemical impedance spectroscopy (EIS) measurements showed that Bi doping was an effective method for decreasing the charge transfer across the electrode/electrolyte interface; 2.5% Bi-g-C3N4 was reduced by around 2.4 times compared to that of pristine g-C3N4. Bode-phase plots accompanied EIS spectra revealed that the lifetime of the photo-generated electrons in neat g-C3N4 was improved as a result of Bi doping. The band gaps and the positions of the valence and conduction bands were determined from Mott–Schottky plots.
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- A series of Fe(III), Co(III), Ni(II), Cu(II), Zn(II) and In(III) N-morpholine-N'-benzoyl thiourea complexes have been synthesized and characterized by elemental analysis, thermal analysis, infrared spectroscopy, 1H nuclear magnetic resonance spectroscopy and single-crystal X-ray crystallography. Thermogravimetric analysis shows that all the complexes undergo a two-step decomposition process except for the iron(III) complex and the indium(III) complexes, which show three-step and one-step decompositions, respectively. The complexes are thermally stable up to approximately 300°C. The ligand coordinates the various metal ions in a bidentate (L-kO,S) chelating mode, facilitated by deprotonation of the acidic amide (–C(O) N'HC (S)) moiety. This mode of coordination allows for the facile formation of neutral bis/tris-6-membered chelates of type [M(L-kS,O)x] where x = 2 or 3 for divalent or trivalent metal ions, respectively.
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- 2021| Scientific and Techn...Cadmium dithiocarbamate and cadmium ethyl xanthate complexes were synthesized and characterized by microanalysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analyses. The complexes were employed as molecular precursors for the fabrication of CdS nanoparticles in hexadecylamine (HDA) and oleylamine (OLA) at a temperature of 250 C. Spherical and oval shaped particles with sizes ranging from 9.93±1.89 to 16.74±2.78 nm were obtained in OLA while spherical, oval and rod shaped particles with sizes ranging from 9.40±1.65 to 29.90±5.32 nm were obtained in HDA. Optical properties of the nanoparticles showed blue shifts as compared to the bulk CdS, with the OLA capped nanoparticles slightly more blue shifted than the corresponding HDA capped nanoparticles. Results of crystallinity patterns revealed hexagonal phase of CdS.
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- Metal oxide nanoparticles (MONPs) have been increasingly reported to possess diverse industrial and biomedical applications. Herein, we synthesized secondary (CuO, Fe2O3 (FeO), ZnO), ternary (ZnO/CuO-FeOx) and quaternary (ZnO-CuO-FeOx) co-assembled core-shelled MONPs by (co-) precipitation technique, characterized the synthesized MONPs and consequently investigated their antibacterial capacity. The UV-Vis absorption spectra of the prepared MONPs presented experimental band gaps; ZnO of 3.36 eV; ZnO-FeOx (x ¼ 0.1; x ¼ 0.5) with 3.38 eV and 3.37 eV; and ZnO-FeOx-CuOx (x ¼ 0.1; x ¼ 0.5) of 3.36 eV and 3.36 eV band gaps respectively. Thermogravimetric analysis revealed the stability of the prepared MONPs, by the presented total mass lost (%):ZnOFeO0.5 (1.34) > ZnOFeO0.1 (1.93) > ZnOFeO0.1CuO0.1 (2.12) > ZnOFeO0.5CuO0.5 (2.34) >CuOFeO0.1 (3.78) > CuOFeO0.5 (4.25) > Fe2O3 (4.44) > CuO (6.37) > ZnO (8.69). The XRD peak positions of the secondary MONPs prepared presented hexagonal structures for ZnO, monoclinic structures for CuO and rhombohedral structures for Fe2O3 without identified impurity peaks. Finally, the co-assembled MONPs prepared showed that they possessed varied efficiency for protection from different bacterial strains, with Staphylococcus.pneumonia growth being the most inhibited, with MONPs treatments CuO > ZnOFeO0.5CuO0.5 > CuOFeO0.5 > ZnOFeO0.1CuO0.1 >Fe2O3 > ZnOFeO0.5 > ZnO.
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- Castor oil (CSTO), an extract from castor bean was used as capping material for CdTe quantum dots (QDs), synthesized from cadmium chloride and tellurium powder using a modified hot injection method. The formation of CdTe QDs in the colloidal solution was monitored by UV–Vis spectrophotometry. The average particle sizes were deduced from the absorption data, transmission electron microscopy (TEM) images and powdered-X-ray diffraction (p-XRD). The average particle size of CdTe QDs deduced from the UV–Vis absorption measurements range from 4.94 nm to 10.04 nm for CdTe QDs synthesized at 230 °C, 250 °C and 280 °C. TEM images of the CdTe QDs synthesized at 250 °C and 280 °C, for 2 h showed close to spherical geometry with average diameter of 7.38 ± 0.43 nm and 9.88 ± 0.67 nm, respectively. The p-XRD patterns confirmed the presence of CdTe crystallites with a cubic phase. The average diameter of CdTe QDs as deduced from the p-XRD patterns was 7.54 ± 0.03 nm and 9.69 ± 0.13 nm, respectively, which is in good agreement with the results from TEM and UV–Vis absorption measurements. The photoluminescence spectroscopy showed the formation of nearly monodispersed particles with emission maxima at 673 nm, 714 nm and 743 nm for CdTe QDs prepared at 230 °C for 30 min, 60 min and 120 min, respectively. These results show that green biomasses are valuable eco-friendly materials which can be used to stabilize nanomaterials.
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- Nickel sulfide is regarded as a material with tremendous potential for energy storage and conversion applications. However, it exists in a variety of stable compositions and obtaining a pure phase is a challenge. This study demonstrates a potentially scalable, solvent free and phase selective synthesis of uncapped α-NiS, β-NiS and α-β-NiS composites using nickel alkyl (ethyl, octyl) xanthate precursors. Phase transformation and morphology were observed by powder-X-ray diffraction (p-XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The comparative efficiency of the synthesized samples was investigated for energy storage and generation applications, in which superior performance was observed for the NiS synthesized from the short chain xanthate complex. A high specific capacitance of 1,940F/g, 2,150F/g and 2,250F/g was observed at 2mV/s for bare α-NiS, β-NiS and α-β-NiS composite respectively. At high current density of 1A/g, α-NiS showed the highest capacitance of 1,287F/g, with 100% of Coulombic efficiency and 79% of capacitance retention. In the case of the oxygen evolution reaction (OER), β-NiS showed an overpotential of 139mV at a current density of 10mA/cm2, with a Tafel slope of only 32mV/dec, showing a fast and efficient process. It was observed that the increase in carbon chain of the synthesized self-capped nickel sulfide nanoparticles decreased the overall efficiency, both for energy storage and energy generation applications.
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- 2020| Springer NatureInorganic two-dimensional semiconductor indium sulfide (In2S3) has recently attracted considerable attention as a buffer material in the field of thin-film photovoltaics, photo electrochemical cells and other energy-related applications. Compared with this growing interest, however, detailed characterizations of the commercial material are not done. The present investigation deals with the systematic investigation of the physical properties of powdered β-indium sulfide (In2S3). The crystalline structure, the composition, and the morphological properties of the samples were characterized using a range of techniques such as X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). X-ray diffraction patterns revealed mixed peaks of In2S3 and In2O3 for the sample annealed at 400 °C. The In2O3 peaks were crystalline with a cubic phase with a (222) preferential orientation. These results were supported by the FTIR, and XPS studies. Thus, a significant correlation was established between the annealing tem perature and the TEM images. The main conclusion of the paper opens the possibility of using In2S3 layers for solar cells.
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- Transition metal sulfides have been investigated as promising bifunctional materials for catalytic energy generation and energy storage applications. Although various strategies such as tuning the size, phase or defects and composition engineering have led to catalytic enhancement, there still remains the requirement for better performance for practical applications. In this study, we have used a potentially scalable solventless route for phase selective synthesis of α-NiS or β-NiS. Both phases were doped with different transition metals (Cu, Co and Fe) for enhanced catalytic performance. Interestingly, besides commonly observed thermal assisted phase transition, dopant (Co, Cu, and Fe) induced α- to β-phase transition or vice versa was also observed which has rarely been reported for NiS. The effect of dopants on the crystal structure and electrocatalytic activity has been investigated. The best supercapacitive behavior was observed for Co-doped α-NiS which showed a specific capacitance of 1586 F g−1 at a current density of 0.5 A g−1 and a high rate capability. On the other hand, Fe-doped α-NiS displayed the best electrocatalytic activity for both the OER (266 mV at 10 mA cm−2) and the HER (146 mV at 10 mA cm−2), with Tafel slopes of 79 and 113 mV dec−1 respectively. The Fe-doped α-NiS catalyst was also used as both the anode and cathode in an electrolyzer, in which an overpotential of about 410 mV at 10 mA cm−2 was observed. The prepared electrodes demonstrate outstanding stability and flexibility.
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