Browsing by Author "Revaprasadu, Neerish"

Now showing 1 - 8 of 8
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    Alloying normal and inverse spinel (Zn–Co ferrite) nanostructures via direct precursor pyrolysis for enhanced supercapacitance and water splitting
    (Elsevier, 2023) Malima, Nyemaga Masanje; Khan, Malik Dilshad; Choi, Jonghyun; Gupta, Ram K.; Revaprasadu, Neerish
    The nanocrystals comprising of multiple redox-active cations are generally proficient electrocatalysts for renewable and sustainable energy applications. Ferrites have rich redox chemistry and crystallographically, they can be classified into normal spinel structures or inverse spinel structures, depending on the type of occupancy at tetrahedral and octahedral sites. Herein, taking advantage of the simplicity and environmental benignity of the solventless method, a series of mixed inverse and normal spinel nanocatalysts (Co1-xZnxFe2O4 (0 = x ≤ 1)) have been successfully synthesized and tested for supercapacitance and overall water splitting. The p-XRD and EDX analyses confirmed the successful nucleation of CoFe2O4 and ZnFe2O4 to form monophasic Co1-xZnxFe2O4 solid solutions over the entire composition range. The solid solutions with composition Co0·4Zn0·6Fe2O4 demonstrated higher discharge time, indicating higher specific capacitance of the material than other electrode compositions. The Co0·8Zn0·2Fe2O4 showed relatively low overpotentials of 317 mV to afford the current density of 10 mA/cm2 for oxygen evolution reaction (OER), while Co0·6Zn0·4Fe2O4 exhibited an overpotential of 169 mV for hydrogen evolution reaction (HER), outperforming most of the electrocatalysts reported in the literature. More impressively, such solid solutions demonstrated negligible deviation between the first and the 1 k cycles, suggesting high durability for the electrolysis of water.
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    Aquasomes: a novel nanocarrier system for drug delivery
    (Elsevier, 2023) Ayom, Gwaza Eric; Malima, Nyemaga Masanje; Owonubi, Shesan John; Revaprasadu, Neerish
    Aquasomes are three layered self-assembled nanoparticles that are emerging as drug carriers or systems for the delivery of drugs. They are composed of an inner core which is usually coated with a polyhydroxyl carbohydrate and a loaded drug. The solid nanocrystalline inner core provides the structural stability of the aquasomes while the carbohydrate coat shields the loaded drug against dehydration. These self-assembled particles maintain the conformational integrity of the loaded drugs and hence have been exploited as carriers of drugs including insulin, hemoglobin, oxygen, antigens, and antibodies. This system of drug delivery has also been shown to improve the solubility of poorly soluble drugs. This chapter presents aquasomes’ preparation, properties, applications, and potential as drug carriers.
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    Development of bacterial resistant acrylamide-polyvinylpyrrolidone-metal oxide hydrogel nanocomposites
    (Elsevier, 2021) Owonubi, Shesan John; Agwuncha, S.C.; Malima, Nyemaga Masanje; Sadiku, E.R.; Revaprasadu, Neerish
    Fabrication 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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    Eco-friendly mixed metal (Mg–Ni) ferrite nanosheets for efficient electrocatalytic water splitting
    (Springer Science and Business Media LLC, 2023) Malima, Nyemaga M.; Khan, Malik Dilshad; Masikane, Siphamandla C.; de Souza, Felipe M.; Choi, Jonghyun; Gupta, Ram K.; Revaprasadu, Neerish
    Eco-friendly and cost-effective catalysts with multiple active sites, large surface area, high stability and catalytic activity are highly desired for efficient water splitting as a sustainable green energy source. Within this line, a facile synthetic approach based on solventless thermolysis was employed for the simple and tunable synthesis of Ni1−xMgxFe2O4 (0 ≤ x ≤ 1) nanosheets. The characterization of nanosheets (via p-XRD, EDX, SEM, TEM, HRTEM, and SAED) revealed that the pristine ferrites (NiFe2O4 and MgFe2O4), and their solid solutions maintain the same cubic symmetry throughout the composition regulation. Elucidation of the electrochemical performance of the nanoferrite solid solutions showed that by tuning the local chemical environment of Ni in NiFe2O4 via Mg substitution, the intrinsic catalytic activity was enhanced. Evidently, the optimized Ni0.4Mg0.6Fe2O4 catalyst showed drastically enhanced HER activity with a much lower overpotential of 121 mV compared to the pristine NiFe2O4 catalyst. Moreover, Ni0.2Mg0.8Fe2O4 catalyst exhibited the best OER performance with a low overpotential of 284 mV at 10 mA/cm2 in 1 M KOH. This enhanced electrocatalytic activity could be due to improved electronic conductivity caused by the partial substitution of Ni2+ by Mg2+ in the NiFe2O4 matrix as well as the synergistic effect in the Mg-substituted NiFe2O4. Our results suggest a feasible route for developing earth-abundant metal oxide-based electrocatalysts for future water electrolysis applications.
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    Metal oxide nanoparticles: a welcome development for targeting bacteria
    (Elsevier, 2020) Fasiku, Victoria Oluwaseun; Owonubi, Shesan John; Malima, Nyemaga Masanje; Hassan, Daniel; Revaprasadu, Neerish
    Resistance to numerous antibiotics by a broad strain of microorganisms has become a global health concern. Conventional antibiotic agents and techniques have become inadequate to completely combat infectious diseases associated with this pathogen; thus, there is an increased rate of infectious disease mortality. In recent years, various scientific researchers have embarked on studies to explore alternate ways by which antibiotic resistance can be curbed. Nanotechnology has proven to be very promising, and a typical example of a nanotechnology strategy that has shown potential application in targeting different strains of resistant and nonresistant microbial strains is the treatment with metal oxide nanoparticles (MONPs). This chapter, therefore, focuses on different types of MONPs with antibacterial activities that have been studied, their method of synthesis, mechanisms of action, as well as the various fields that they can be potentially relevant in targeting pathogenic organisms.
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    Metal oxide–based nanocomposites as antimicrobial and biomedical agents
    (Elsevier, 2020) Owonubi, Shesan John; Malima, Nyemaga Masanje; Revaprasadu, Neerish
    Antibiotic and multidrug resistance are among the great challenges facing researchers in designing and developing effective antimicrobial and biomedical agents. Thus, various strategies are being explored for the design and development of novel and effective biomedical and antimicrobial agents, one of which involves the fabrication of metal oxide–based nanocomposites (MOBNCs). Inspired by remarkable advances in the synthesis and characterization techniques over the years, antimicrobial metal oxide nanocomposites have in recent times been explored as potential antibiotics to fight the rise of infectious diseases. In this chapter, we present a review of the synthesis and characterization techniques of MOBNCs. This is preceded by a brief account and classification of metal oxide nanocomposites. We also highlight key findings on the efficacy of various MOBNCs regarding their antimicrobial activities to the target organisms. Finally, we provide a brief account of the potential biomedical applications of MOBNCs.
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    Non-woody biomass as sources of nanocellulose particles: A review of extraction procedures
    (Springer Nature, 2021) Owonubi, Shesan J.; Agwuncha, Stephen C.; Malima, Nyemaga M.; Shombe, Ginena B.; Makhatha, Elizabeth M.; Revaprasadu, Neerish
    Nanocellulose has been reported to be a very useful biomaterial with applications in biomedical, pharmaceutical, built industry, automobile, aerospace and many more. Its advantages over synthetic fibers include renewability, energy efficiency, cost effectiveness, biodegradability and good mechanical and thermal properties. However, the production of cellulose nanoparticles (CNPs) has focused more on woody plant sources. Non-woody biomass constitutes a large group of plant sources that are yet to be given the proper attention for utilization as raw material for nanocellulose particle production. This group of lignocellulosic biomasses is generally obtained as waste from farming activities, home gardens or office wastes. They are majorly composed of cellulose, hemicellulose, and lignin. However, their composition varies widely from one plant source to another. The variation in their composition results in limitations in the procedures employed in extraction of CNPs and of processing of the extracted CNPs. This means that different biomasses may have different ways by which CNPs are extracted from them. Therefore, this review intends to x-ray these variations, its effect on the structural properties of extracted CNPs and possible ways such limitations can be mitigated.
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    Solventless synthesis of nanospinel Ni 1− x Co x Fe 2 O 4 (0≤ x≤ 1) solid solutions for efficient electrochemical water splitting and supercapacitance
    (The Royal Society of Chemistry, 2021) Malima, Nyemaga Masanje; Malik, Dilshad Khan; Choi, Jonghyun; Gupta, Ram K.; Mashazi, Philani; Nyokong, Tebello; Revaprasadu, Neerish
    The formation of solid solutions represents a robust strategy for modulating the electronic properties and improving the electrochemical performance of spinel ferrites. However, solid solutions have been predominantly prepared via wet chemical routes, which involve the use of harmful and/or expensive chemicals. In the present study, a facile, inexpensive and environmentally benign solventless route is employed for the composition-controlled synthesis of nanoscopic Ni1−xCoxFe2O4 (0 ≤ x ≤ 1) solid solutions. The physicochemical characterization of the samples was performed by p-XRD, SEM, EDX, XPS, TEM, HRTEM and UV-Vis techniques. A systematic investigation was also carried out to elucidate the electrochemical performance of the prepared nanospinels towards energy generation and storage. Based on the results of CV, GCD, and stability tests, the Ni0.4Co0.6Fe2O4 electrode showed the highest performance for the supercapacitor electrode exhibiting a specific capacitance of 237 F g−1, superior energy density of 10.3 W h kg−1 and a high power density with a peak value of 4208 W kg−1, and 100% of its charge storage capacity was retained after 4000 cycles with 97% coulombic efficiency. For HER, the Ni0.6Co0.4Fe2O4 and CoFe2O4 electrodes showed low overpotentials of 168 and 169 mV, respectively, indicating better catalytic activity. For OER, the Ni0.8Co0.2Fe2O4 electrode exhibited a lower overpotential of 320 mV at a current density of 10 mA cm−2, with a Tafel slope of 79 mV dec−1, demonstrating a fast and efficient process. These results indicated that nanospinel ferrite solid solutions could be employed as promising electrode materials for supercapacitor and water splitting applications.