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Publications


2020

Rop, K, Mbui D, Karuku GN, Michira I, Njomo N.  2020.  Characterization of water hyacinth cellulose-g-poly (ammonium acrylate-co-acrylic acid)/nano-hydroxyapatite polymer hydrogel composite for potential agricultural application. Results in Chemistry. 2:100020. AbstractResults in Chemistry

Description
Polymer nano-composite was prepared by grafting partially neutralized acrylic acid onto swollen cellulose isolated from water hyacinth in the presence of nano-hydroxyapatite (nano-HA) using N,N-methylene-bis-acrylamide (MBA) as the cross-linker and ammonium persulphate (APS) as the free radical initiator. Water absorption tests showed an increase in swelling ratio of the copolymer with increased nano-HA content to value of 120 g/g at 2.5% w/v above which it declined. FTIR spectrum of nano-composite revealed grafting of the monomer (acrylic acid/ammonium acrylate) onto cellulose and nano-HA. Transmission electron microscopy (TEM) images of nano-HA synthesized in the presence of Triton X-100 (non-ionic surfactant) displayed rod-shaped agglomerates and nano-particle dispersion within the copolymer matrix. Energy dispersive X-ray (EDX) spectra revealed the constituents of nano-composite to be …

2019

Rop, K, Karuku GN, Mbui D, Njomo N, Michira I.  2019.  Evaluating the effects of formulated nano-NPK slow release fertilizer composite on the performance and yield of maize, kale and capsicum. Annals of Agricultural Sciences. 64(1):9-19. AbstractAnnals of Agricultural Sciences

Description
Effect of formulated slow release NPK fertilizer [cellulose-graft-poly(acrylamide)/nanohydroxyapatite/soluble fertilizer] composite (SRF) on the performance and yield of maize, kale and capsicum was evaluated in a greenhouse experiment. No significant difference in growth parameters was observed between SRF and commercial fertilizer (CF) treatments. SRF recorded higher dry matter and yields relative to CF with similar application rates, though statistically insignificant. P deficiency was observed in maize at lowest SRF application rate of 45-57-17. N deficiency in CF was observed at the 8th week, but not in SRF with similar application rates during the same period. Kale showed both N and P deficiencies in the 7th week, while capsicum alone showed N deficiency in the 14th week in SRF at low application rates. NPK content in both maize and kale tissues, was significant between the amendments and control …

Rop, K, Mbui D, Njomo N, Karuku GN, Michira I, Ajayi RF.  2019.  Biodegradable water hyacinth cellulose-graft-poly (ammonium acrylate-co-acrylic acid) polymer hydrogel for potential agricultural application. Heliyon. 5(3):e01416. AbstractHeliyon

Description
Swollen cellulose fibres isolated from water hyacinth were utilized in the synthesis of water hyacinth cellulose-graft-poly(ammonium acrylate-co-acrylic acid) polymer hydrogel (PHG). Acrylic acid (AA) partially neutralized with NH3 was heterogeneously grafted onto swollen cellulose by radical polymerization reaction using N,N-methylene-bis-acrylamide (MBA) as the cross-linker and ammonium persulphate (APS) as the initiator. The reaction conditions were optimized through assessment of grafting parameters such as grafting cross-linking percentage (GCP), percentage grafting cross-linking efficiency (%GCE) and water absorption tests. Characterization of the copolymer by Fourier Transform Infra-red (FTIR) spectroscopy revealed successful grafting of the monomer onto cellulose. Transmission electron microscopy (TEM) image of acetone-extracted PHG displayed micro-porous structure. The optimized product …

2018

Rop, K, Karuku GN, Mbui D, Michira I, Njomo N.  2018.  Formulation of slow release NPK fertilizer (cellulose-graft-poly (acrylamide)/nano-hydroxyapatite/soluble fertilizer) composite and evaluating its N mineralization potential. Annals of Agricultural Sciences. 63(2):163-172. AbstractAnnals of Agricultural Sciences

Description
Polymer nano-composite fertilizer formulation has the potential to enhance nutrient use efficiency. Slow release fertilizer (SRF) composite was formulated by incorporating nano-hydroxyapatite (nano-HA) and water soluble fertilizers (urea, (NH4)2HPO4 and K2SO4) into water hyacinth cellulose-graft-poly(acrylamide) polymer hydrogel. Fourier Transform Infra-red spectra revealed existence of chemical interaction between the monomer, cellulose, urea and nano-HA. The release of nutrients was assessed using laboratory incubation experiment. Significantly higher content of mineral nitrogen (MN) was observed in the first 4 weeks in conventional fertilizer (CF) compared to SRF treatments and the control. MN content in SRF treatments increased considerably between the 8th and 12th week, and declined in the 16th week. The values of potentially mineralizable N estimated using first order kinetics model related well …

2016

Dywili, N, Njomo N, Ikpo CO, Yonkeu ALD, John SV, Hlongwa NW, Raleie N, Iwuoha EI.  2016.  Anilino-Functionalized Graphene Oxide Intercalated with Pt Metal Nanoparticles for Application as Supercapacitor Electrode Material. Journal of Nano Research. 44:79-89. AbstractJournal of Nano Research

Description
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Nanostructured anilino-functionalized reduced graphene oxide intercalated with Pt metal nanoparticles was successfully synthesized. Graphene oxide nanosheets were synthesized using a modified Hummers method with simultaneous in-situ functionalization with aniline and ionic Pt reduction and dispersion through sonication. The nanomaterial was characterised with FTIR, UV-visible, SEM, TEM, EDX, XRD and Raman spectroscopy to ascertain surface, chemical, elemental and crystalline properties, composite structures, size, morphology and successful entrapment of metal nanoparticles while the electro-conductivity of the nanomaterial was interrogated using CV. The graphene oxide was successfully functionalized with aniline with new peaks belonging to the NH and CN group being present and calculated band gaps of 5.35 eV and 4.39 eV which are attributed to …

2015

Matinise, N, Ajay FR, Ikpo CO, Njomo N, Ross N, Baker P, Iwuoha EI.  2015.  Investigation of the electrocatalytic properties of spherical palladium nanoparticles and palladium (100) iridium bimetallic nanocomposites towards ammonia electrooxidation on …. Int. J. Electrochem. Sci. 10:8531-8548. Abstract

Description
The electrocatalytic properties of cubic palladium-iridium {Pd (100) Ir} bimetallic nanocomposite and spherical nanoparticles {Pd NPs} towards the electrochemical oxidation of ammonia were investigated in sodium hydroxide on platinum electrode. Interrogation of their electrocatalytic properties through cyclic and square wave voltammetric techniques (CV and SWV)) revealed that the bimetallic nanocomposite {Pd (100) Ir} has better conductivity and higher catalytic activity as evidenced by the maximum current density reached for NH3 oxidation at 1.9838 x 10-4 A with a decreased onset potential. The Pd NPs gave a maximum catalytic current value of 1.45 x 10-4 A. This was further validated by the results from electrochemical impedance spectroscopy (EIS) where the bimetallic nanocomposite gave charge transfer and solution resistance values of 96.35 Ω and 137.9 Ω, respectively with the nanoparticles exhibiting higher resistances at 670.6 and 189.5 Ω. These results confirm that facile interfacial electron transfer processes occur on the Pt/Pd (100) Ir electrode during the electrocatalytic ammonia oxidation and were made possible by the synergistic effect of the bimetallic palladium and iridium in the nanocomposite which causes a weakening of the adsorption strength of poisonous adsorbed nitrogen (Nads) during the electrooxidation process.

Masikini, M, Mailu SN, Tsegaye A, Njomo N, Molapo KM, Ikpo CO, Sunday CE, Rassie C, Wilson L, Baker PGL, Iwuoha EI.  2015.  A fumonisins immunosensor based on polyanilino-carbon nanotubes doped with palladium telluride quantum dots. Sensors. 15(1):529-546. AbstractSensors

Description
An impedimetric immunosensor for fumonisins was developed based on poly (2, 5-dimethoxyaniline)-multi-wall carbon nanotubes doped with palladium telluride quantum dots onto a glassy carbon surface. The composite was assembled by a layer-by-layer method to form a multilayer film of quantum dots (QDs) and poly (2, 5-dimethoxyaniline)-multi-wall carbon nanotubes (PDMA-MWCNT). Preparation of the electrochemical immunosensor for fumonisins involved drop-coating of fumonisins antibody onto the composite modified glassy carbon electrode. The electrochemical impedance spectroscopy response of the FB 1 immunosensor (GCE/PT-PDMA-MWCNT/anti-Fms-BSA) gave a linear range of 7 to 49 ng L− 1 and the corresponding sensitivity and detection limits were 0.0162 kΩ L ng− 1 and 0.46 pg L− 1, respectively, hence the limit of detection of the GCE/PT-PDMA-MWCNT immunosensor for fumonisins in corn certified material was calculated to be 0.014 and 0.011 ppm for FB 1, and FB 2 and FB 3, respectively. These results are lower than those obtained by ELISA, a provisional maximum tolerable daily intake (PMTDI) for fumonisins (the sum of FB 1, FB 2, and FB 3) established by the Joint FAO/WHO expert committee on food additives and contaminants of 2 μg kg− 1 and the maximum level recommended by the US Food and Drug Administration (FDA) for protection of human consumption (2–4 mg L− 1). View Full-Text

2014

Njomo, N, Waryo T, Masikini M, Ikpo CO, Mailu S, Tovide O, Ross N, Williams A, Matinise N, Sunday CE, Mayedwa N, Baker PGL, Ozoemena KI, Iwuoha EI.  2014.  Graphenated tantalum (IV) oxide and poly (4-styrene sulphonic acid)-doped polyaniline nanocomposite as cathode material in an electrochemical capacitor. Electrochimica Acta. 128:226-237. AbstractElectrochimica Acta

Description
Nanostructured poly(4-styrene sulphonic acid) and tantalum (IV) oxide-doped polyaniline nanocomposite were synthesised and their electro-conductive properties were determined. The oxide was synthesized using a modified sol-gel method and then dispersed in acidic media through sonication and entrapped in-situ into the polymeric matrix during the oxidative chemical polymerization of aniline doped with poly(4-styrene sulphonic acid). The oxides and novel polymeric nanocomposite were characterised with TEM, SEM, EDX, XRD, FTIR, UV-visible to ascertain elemental and phase composition, successful polymerization, doping, morphology and entrapment of the metal oxide nanoparticles. The electro-conductivity of the nanomaterial was interrogated using scanning electrochemical microscopy (SECM) and cyclic voltammetry (CV). The material was then anchored on activated graphitic carbon and used in the …

Ross, N, Iwuoha EI, Ikpo CO, Baker P, Njomo N, Mailu SN, Masikini M, Matinise N, Tsegaye A, Mayedwa N, Waryo T, Ozoemena KI, Williams A.  2014.  Amplification of the discharge current density of lithium-ion batteries with spinel phase Li (PtAu) 0.02 Mn1. 98O4 nano-materials. Electrochimica Acta. 128:178-183. AbstractElectrochimica Acta

Description
In this study the synergistic and catalytic properties of a novel nano-composite cathode material of nominal composition Li(M)xMn2-xO4 (M = Pt-Au; x # 0.2) has been explored. Li(PtAu)xMn2-xO4 nanomaterial for use in lithium-ion batteries (LIB) was synthesized by incorporation of the Pt-Au (1:1) nanoparticles onto the spinel phase LiMn2O4. Ultra-low scan rate (0.01 mV s−1) cyclic voltammetry of the cathode material in 1 M LiPF6 (in 1:1 EC:DMC), showed four sets of redox peaks, which reflect the typical redox process of the active material in the spinel structure due to lithium intercalation and deintercalation. The Li/Li(PtAu)0.02Mn1.98O4 cell had less polarization as it effectively accommodates the structural transformation during Li+ ion charge and discharge. The Li(PtAu)0.02Mn1.98O4 cathode showed an increase in discharge currents densities with an exchange current density, i0, value of 2.8 × 10−4 A cm−2 …

Tovide, O, Jaheed N, Mohamed N, Nxusani E, Sunday CE, Tsegaye A, Ajayi RF, Njomo N, Makelane H, Bilibana M, Baker PG, Williams A, Vilakazi S, Tshikhudo R, Iwuoha EI.  2014.  Graphenated polyaniline-doped tungsten oxide nanocomposite sensor for real time determination of phenanthrene. Electrochimica Acta. 128:138-148. AbstractElectrochimica Acta

Description
A graphenated polyaniline/tungsten oxide (PANI/WO3/GR) nanocomposite sensor was prepared by electropolymerisation of a mixture of aniline monomer and tungsten oxide on a graphene-modified glassy carbon electrode (GCE). The PANI/WO3/GR/GCE nanocomposite electrode was tested as a sensor for the determination of phenanthrene. The direct electro-oxidation behaviour of phenanthrene on the PANI/WO3/GR modified GCE was carefully investigated by cyclic voltammetry. The results indicated that the PANI/WO3/GR/GCE sensor was more sensitive to phenanthrene (with a dynamic linear range of 1.0 - 6.0 pM and a detection limit of 0.123 pM.) than GCE, PANI/GCE or PANI/WO3/GCE. The sensor exhibited excellent reproducibility and long-term stability. The sensor exhibits lower detection sensitivity than the WHO permissible level of 1.12 nM phenanthrene in wastewater.

Baleg, AA, Jahed N, Ozoemena KI, Yonkeu ADL, Njomo N, Mbambisa G, Molapo KM, Fuku XG, Fomo G, Makelane H, Tsegaye A, Waryo TT, Baker P, Vilakazi S, Tshikhudo R, Iwuoha EI.  2014.  Impedimetry and microscopy of electrosynthetic poly (propylene imine)-co-polypyrrole conducting dendrimeric star copolymers. Electrochimica Acta. 128:448-457. AbstractElectrochimica Acta

Description
A novel generation 2 poly(propylene imine)-co-polypyrrole conducting dendrimeric star copolymer (G2PPI-co-PPy) was synthesised electrochemically by oxidative copolymerization of pyrrole and pyrrole-functionalised dendrimer (G2PPI-2Py) in LiClO4 NMR spectra of G2PPI-2Py gave a new chemical shift at 8.1 ppm for N = CH, which confirmed the incorporation of 2-pyrrole aldehyde into the PPI dendrimer structure. Strong FT-IR bands appeared at 1630 cm−1 for N = C in the dendrimer moiety and at 729 cm−1 for C-H at the α-position of the PPy ring. Electroanalysis of the polymer films deposited on Pt electrode indicated that G2PPI-co-PPy has a lower electrochemical charge transfer resistance (Rct) value compared to PPy. The decrease in Rct is due to the increase in the conjugation length of the polymer as a result of the linking of the highly conjugated PPy to the PPI dendrimer. Bode impedimetric analysis …

2012

Iwuoha', EI, Baker P, Masikini M, Njomo N, Mailu SM, Mbambisa G, Ajayi RF.  2012.  Electronics of Conjugated Polymers (I): Polyaniline. electronics_of_conjugated_polymers...0001.pdfWebsite

2011

Iwuoha', E, Baker P, Njomo N, Ikpo CO, Baleg AA, Ndangili PM, Olowu RA.  2011.  Spectroelectrochemical Dynamics of Dendritic Poly (Propylene imine)- Polythiophene Star Copolymer Aptameric 1713-Estradiol Biosensor. AbstractWebsite

Aptamers, which are in vitro-selected functional oligonucleotides, have been employed to design novel aptasensor due to their inherent high selectivity and affinity compared to traditional biorecognition elements. This report presents a novel aptamer biosensor for determining the endocrine disrupting compound (EDC), 17~-estradiol (E2), which was constructed from a SELEX-synthesized 76-mer biotinylated aptamer for 17~-estradiol incorporated in a dendritic generation 1 poly(propylene imine)- poly thiophene (G 1PPT-co-PEDOT) star copolymer-functionalised Au electrode via biotin-avidin interaction. The sensor platform and aptasensor were interrogated with scanning electron microscopy (SEM), FTIR, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave voltammetry (SWV). The kinetic parameters of the sensor platform were determined by modelling the [Fe(CN)6r3/ - 4 (redox probe) Nyquist and Bode impedimetric spectra to the appropriate equivalent electrical circuit. The EIS spectra shows that at low frequencies (100 mHz) when the electronics of the electrode systems are only minimally perturb.ed.. the AuIG1PPT-co-PEDOT nanoelectrode exhibited greater semi-conductor behaviour (higher phase angle value) than AulG IPPT due to the incorporation of charged functionalized dendrimer. However, the Bode plot also shows that the charge transfer dynamics of the nanoelectrode can be frequency modulated. The biosensor response to 17 B-estradiol was based on the decrease in the SWV current as the EDC binds to the ssDNA aptamer on the biosensor. The dynamic linear range of the sensor was 0.1 - 100 nM. These initial studies also showed that the aptamer used in this study was very selective to, and reproducible for, 17 B-estradiol.

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