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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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- 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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- Infection, trauma, and autoimmunity trigger tissue inflammation, often leading to pain and loss of function. Therefore, approaches to control inflammation based on nanotechnology principles are being developed in addition to available methods. The metal-based nanoparticles are particularly attractive due to the ease of synthesis, control over physicochemical properties, and facile surface modification with different types of molecules. Here, we report curcumin conjugated silver (Cur-Ag) nanoparticles synthesis, followed by their surface functionalization with isoniazid, tyrosine, and quercetin, leading to Cur-Ag.sup.INH, Cur-Ag.sup.Tyr, and Cur-Ag.sup.Qrc nanoparticles, respectively. These nanoparticles possess radical scavenging capacity, haemocompatibility, and minimal cytotoxicity to macrophages. Furthermore, the nanoparticles inhibited the secretion of pro-inflammatory cytokines such as interleukin-6, tumor necrosis factor-[alpha], and interleukin-1[beta] from macrophages stimulated by lipopolysaccharide (LPS). The findings reveal that the careful design of surface corona of nanoparticles could be critical to increasing their efficacy in biomedical applications.
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- Heterocyclic dithiocarbamate complex of manganese and the adducts of the complex with 1,10-phenanthroline and 2,2-bipyridyl respectively were synthesized and characterized. The complexes were used as single-source precursors for the preparation of MnS nanoparticles via thermolysis in oleylamine (OLA) and dodecanethiol (DT). The optimized reaction parameters have resulted in the formation of α-MnS and γ-MnS nanoparticles depending on the dispersion medium and the nature of the precursor. The same precursors were also used for the deposition of MnS thin films by the aerosol-assisted chemical vapour deposition (AACVD) method in varying solvents and temperatures. The morphology and phase of the synthesized nanoparticles were shown to be affected by the precursor type and the nature of the surfactants. TEM images show the formation of nanoparticles of various morphologies ranging from spherical monodispersed to large elongated pointed rods, depending on the precursor type. SEM images showed that the morphology of the deposited thin films is affected by precursor type and the deposition temperature. Worm-like to rod-like films were observed on TEM images at 350 ◦C, which changes to spherical or cubic films at 450 ◦C. Magnetic measurements at room temperature showed the α-MnS and γ-MnS nanoparticles in paramagnetic states due to Mn2+moments. The susceptibility for the γ-phase is at least double that of the α-phase. Finite and small hysteretic effects in low fields are indicative of small ordered antiferromagnetic phases due to negative exchange interaction between Mn2+ions.
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- Nickel phosphide exists in various compositions, and the synthesis of pure-phase nickel phosphides is of immense interest due to their wide scale applications in different electrocatalytic reactions. We report the facile synthesis of nickel phosphides and rare transition metal-induced phase transformations within this system. Phase selective synthesis of pure Ni2PorNi5P4 was achieved by decomposition of nickel acetate tetrahydrate Ni(AC)2$4H2O in optimized mixed solvent systems, i.e., in tri-octylphosphine oxide (TOPO)/tri-n-octylphosphine (TOP) or hexadecylamine (HDA)/TOP, respectively, by hot injection route. The doping of 5% Cu or Mn in either of the nickel phosphide phases yielded a mixture of phases (Ni2P/ Ni5P4). However, increasing the Cu or Mn content to 10% resulted in the complete transformation of phase, i.e., from Ni2P to pure Ni5P4 and vice versa. Lattice stress and size of incorporated dopants, as well as the nature of surfactants employed, were discussed as probable causes of these rare phase transformations. Moreover, in order to establish structure–activity relationship, we studied the comparative effect of transition metal dopants in both nickel rich and nickel deficient phases. Therefore, initially formed and transformed phosphides were investigated as electrocatalysts for overall water splitting and supercapacitance. NiP-5 (Ni2P formed on 10% Cu doping of Ni5P4) delivered a current density of 10 mA cm2 with the lowest overpotential of 146 mV among all samples for HER while NiP-3 (Ni5P4 formed from Ni2P on 10% Cu doping) similarly required the least overpotential of 276 mV for the OER at the same current density. NiP-2 (pristine Ni5P4) had the highest calculated specific capacitance of 1325 F g 1 at 2 A g 1. These phase transformations resulted in better catalytic activity and stability as well as reaction kinetics indicating suitability in practical water splitting technologies.
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- 2023| ElsevierThe synthesis of photocatalysts with a suitable bandgap that could speed up the rate of oxidation of chemical effluent is of utmost importance to material chemists. It has been observed that chalcogenide nanostructures research continues to dominate scientific work over the last few years based on their exciting bandgap within the semiconductor bandgap range. In this research work, novel class I2-II-IV-VI4 quaternary chalcogenides nanoparticles were synthesised using co-precipitation by varying the reaction conditions of temperature (200 °C and 250 °C) and, essentially, capping agents (citric acid and glycerol) and the mole ratio of precursors. The resulting nanoparticles were purified and vacuum dried to give a black crystalline solid. The Powder-X-ray Diffraction analysis of the as-synthesised heterostructure chalcogenides showed novel pure phase materials that exhibited the orthorhombic and cubic Ag2FeSnS4 crystal systems reminiscent of the parent compounds Ag8SnS6 and AgSnS2 under different experimented reaction conditions. The morphological characterisation of the HC chalcogenides by Transmission Electron Microscope revealed that the nanomaterials formed were predominantly nanocubes, with particle diameters ranging from 22.98 ± 1.67 to 57.26 ± 12.93 nm. Further elucidation of the optical property of the HC nanoparticles by Tauc's plot based on the data derived from UV-Vis spectrophotometry measurement revealed that the bandgap ranged from 1.58 to 1.99 eV. The FTIR absorption character of the as-synthesised HC nanoparticles provided evidence for the surface functionalisation, confirming the presence of moieties like the hydroxyl (O-H) at 3396.16 cm−1 and carbonyl group (C=O) at 1712.31 cm−1. At the same time, the UV-Visible spectrophotometry, measured over a range of 250 to 1000 nm, showed broad absorbance between 420 and 800 nm, confirming the optical property of the nanoparticles. The result showed that heterostructure chalcogenide nanoparticles would have an excellent photocatalytic application.
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- Canfieldite Ag8SnS6 (STS) nanocubes were prepared by the solution decomposition of precursors using heat-up and hot injection protocols employing coordinating solvents (oleylamine - OLA and dodecanethiol - DT) to afford monodispersed silver tin sulfide (STS) nanoparticles. The phase and shape of nanoparticles were tuned by varying reactants' temperature and mole ratios. The powder X-ray diffraction (p-XRD) and transmission electron microscopy (TEM) analysis indicate phase pure orthorhombic Ag8SnS6 nanocrystals with nearly monodispersed particles ranging between 12 and 50 nm. The p-XRD patterns for the STS nanoparticles obtained by the heat-up method exhibited enhanced peak broadening than the hot injection route, accounting for the corresponding quantum confinement effects. Likewise, the (124), (227) and (266) planes of the reflections in OLA/DT capped STS crystals appeared well resolved, indicating that seed growth of a transitional Ag2S might be involved in the formation of the ternary chalcogenides. The values of the energy bandgap (Eg) were found in the range of 1.16–2.60 eV. At the same time, the STS nanoparticles exhibited high photon absorption and low quantum yield potentials, making them a possible candidate for photovoltaic cells and enhanced photoelectrochemical performance.
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