http://repository.unn.edu.ng/handle/123456789/391 2026-09-02T20:26:58Z 2026-09-02T20:26:58Z Obiekwe, Clara Amalachi http://repository.unn.edu.ng/handle/123456789/5762 2018-03-16T14:59:25Z

Catalyst Development from Locally Available Resources - (A Case Study of Nickel-Silica Catalyst) Obiekwe, Clara Amalachi The efficacy of silica obtained from our local sand as a carrier in synthesis of Nickel-Silica catalyst was investigated. Six samples of soil were collected from two different sites (comprising five white coloured samples collected from Iva valley, lower part of Milliken hill, namely: pottery 2 (P2), down iva (DI), run-off iva (ROI), pottery rock (POR), white chalk (WTC) and one brown coloured sample (UdS) collected from Udi Siding) in Enugu, Nigeria. Prior to treatment by flotation method, some properties that could affect their catalytic use like organic matter content, texture, porosity and pH were assayed. (i) P2 (pH, 4.7; fine sand, 74.29 %; organic matter, 0.26 %), (ii) DI (pH, 4.7; fine sand, 72.72 %; organic matter, 0.26 %), (iii) ROI (pH, 7.4; fine sand, 87.42 %; organic matter, 0.19 %), (iv) POR (pH, 6.4; fine sand, 85.65 %; organic matter, 0.0%), (v) WTC (pH, 4.7; fine sand, 83.59 %; organic matter, 0.07 %) and (vi) UdS (pH, 4.4; fine sand, 32.79 %; organic matter, 0.19 %). Three of the samples with the best results ROI, POR, and WTC as can be seen above were selected. The pre-treated sand was purified by leaching process using 20 % HF, 20 % H2SO4, 10 % NaOH and distilled water. Comparison of the XRD results of the raw sand sample and silica extract showed complete removal of Al, Ca, and other oxide impurities from the raw sand. The silica was coupled with nickel employing two catalyst preparation methods. The Deposition method was used to couple silica with Ni(NO3)2 to prepare the catalyst named DPNN and NiCl2 to prepare the catalyst named DPNC. In the Co-precipitation method, silica was coupled with NiCl2 to prepare the catalyst named CPNC. The surface area, pore volume and particle size distributions of the catalyst samples were determined by N2 adsorption at 77 K using Trister II Plus BET analyzer. The elemental composition was obtained by XRF spectroscopy. Effect of using two different nickel precursors for coupling was investigated; the result showed that NiNO3 gave a higher degree of Ni dispersion and incorporation compared to NiCl2. Effect of using two different catalyst preparation methods was also investigated; Co-precipitation method allowed the highest degree of Ni incorporation and improved surface properties. The results showed that Ni-silica catalysts prepared using silica from the local soil has catalytic properties that are similar to the standard Ni-Silica catalyst, Euro Ni-1, and better catalytic properties than some previously synthesized ones reported by Unichema, C. B. V. (1990), Wang, W. et al (2006), and Hermida, L. et al (2012).

Balogun, Bashiru Bolaji http://repository.unn.edu.ng/handle/123456789/5260 2017-06-11T23:52:16Z 2017-06-02T00:00:00Z

Synthesis of Graphene-Polyaniline Nanostructured Composite for High-Performance Supercapacitors Balogun, Bashiru Bolaji Presently, there are deep concerns over the environmental consequences and the consumption of non-renewable energy sources, with the accelerated greenhouse effect which triggered enormous interest in the use of renewable energy sources e.g. solar, hydropower, wind and geothermal. However, the intermittent nature of harvesting renewable energy sources has recently gained considerable attention in the alternative, reliable, cost effective and environmentally friendly energy storage devices. The supercapacitors are considered more efficient electrical energy storage devices than the conventional energy storage systems. This is due to the fact that they are usable in plethoric wide range of devices owing to their high power and high energy density. This is particularly true as they have found usability in portable electronic devices and Electrical Vehicles (EVs) or Hybrid Electrical Vehicles (HEVs) in recent times. In order to make the efficient usage of these stationary energy storage devices, state of the art research on new and advanced electrode material is highly needed. The aim of this research is to investigate the scope of graphene-polyaniline nanocomposite electrodes for light weight, high power density and wider voltage-window supercapacitor devices. Graphene-polyaniline nanostructured composite films fabricated on both non-conducting quartz and FTO substrates at ambient temperature is reported. The top-quality and well-reproducible nanostructured composites have been derived through the oxidative polymerization of anilinium ion by ammonium persulphate, APS [(NH4)2S2O8] in an acidic aqueous medium using chemical bath deposition (CBD) on pre-deposited graphene films synthesized through vacuum filtration of ultrasonicated turbostratic graphite flakes. These films were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), x-ray diffraction (XRD), UV-vis spectrophotometry, cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD). The AFM images, depending on the annealing temperature, show that the films are composed of both nearly cone-shaped and irregular spherical-shaped grains/clusters uniformly distributed with lots of pores on the surface area. Also, the thicknesses, ranging from ~50 – 96 nm of the films were found to be dependent on the annealing temperatures of synthesized thin films. An average root-mean-square (RMS) value of roughness of ~ 103 nm was estimated for polyaniline, graphene and composite films. The SEM analysis corroborates the AFM results as they depict homogenous, nanofibrous and highly porous surface which also increases with annealing temperatures of the films. The XRD analysis confirmed that polyaniline films are structurally amorphous even when annealed in nitrogen atmosphere at high temperature while the graphene and graphene-polyaniline nanocomposite shows sharp and well defined peaks at ~260 corresponding to [0 0 2] plane with differing intensities. Particularly for the composite films, we observe that graphene retained its highly ordered structure when dispersed in polyaniline matrix during polymerization. The optical absorption analysis of polyaniline, graphene and graphene-polyaniline hybrid films revealed that direct optical transition exists in the photon energy range 1.27 – 6.05 eV, 1.13 – 6.30 eV and 1.13 – 4.50 eV with bandgaps 2.30, 1.24 and 2.60 eV respectively. The refractive index has peak at 405 nm, 474 nm and 430 nm in the dispersion region 300 – 1100 nm respectively. The films exhibit high transmittance of about 80% in the visible region of the e-m spectrum. For the electrochemical studies, polyaniline, graphene and graphene-polyaniline hybrid electrodes were tested using CV and GCD techniques in 1 M H2SO4 electrolyte within the potential range -0.1 to +0.8 V vs at 0.5 mA.cm2 current density. We observed through CV, the adverse effects of annealing temperature on the supercapacitive properties of the polyaniline electrodes. This is adequately confirmed by the decrease in the specific capacitances of polyaniline electrodes as annealing temperature increases. Graphene-polyaniline composite electrode revealed reasonably good specific capacitance of 983 F/g than individual electrodes of polyaniline and graphene having 872 and 433 F/g respectively. The specific power, specific energy and columbic efficiency of the composite film is also seen to be enhanced than the pristine materials with values of 5.28 kW/kg, 997 Wh/kg and 64%. The GCD analysis corroborates the CV results. As well, the stability and charge-discharging ability of the electrodes revealed a better profile for the composite film which is as a result of the introduction of graphene preventing polyaniline from mechanical deformation (i.e. shrinkage and breakage). Hence, we found that our system could withstand about 2000 cycles without a significant decrease in the specific capacitance, which adequately clarify highly stable (90%) nature of graphene-PANI composite electrode in energy storage applications

2017-06-02T00:00:00Z Offie, Ogochukwu Ethel http://repository.unn.edu.ng/handle/123456789/4298 2017-06-11T23:48:40Z 2017-03-31T00:00:00Z

Alkylation of [Pt2(µ-S)2(Pph3)4] With Boronic Acid Derivatives by Pressurized Sample Infusion Electrospray Ionization Mass Spectrometry (Psi-Esi-Ms) Technique Offie, Ogochukwu Ethel This project work present the alkylating reaction of [Pt2(μ-S)2(PPh3)4] with boronic acid alkylating agents.The reactivity of the metalloligand [Pt2(μ-S)2(PPh3)4] with the boron-functionalized alkylating agents BrCH2(C6H4)B(OR)2 (R = H or C(CH3)2) was investigated by electrospray ionization mass spectrometry (ESI-MS) in real time using the pressurized sample infusion (PSI). The macroscopic reaction of [Pt2(μ-S)2(PPh3)4] with one mole equivalent of alkylating agents BrCH2(C6H4)B{OC(CH3)2}2and BrCH2(C6H4)B(OH)2 gave the dinuclear monocationic µ-sulfide thiolate complexes [Pt2(µ-S){µ-SCH2(C6H4)B{OC(CH3)2}2}(PPh3)4]+ and [Pt2(µ S){µ-S+CH2 (C6H4)B(OH)(O–)}(PPh3)4]. The products were isolated as the [PF6]– salts and zwitterion respectively, and fully characterized by ESI-MS, IR, 1H and 31P NMR spectroscopy and single crystal X-ray structure determinations. The alkylation reaction of BrCH2(C6H4)B{OC(CH3)2}2 with [Pt2(µ-S)2(PPh3)4 + H]+was determined via kinetic analysis by PSI-ESI-MS to be second order consistent with the expected SN2 mechanism for an alkylation reaction. The PSI-ESI-MS microscale synthesis showed that[Pt2(µ-S)2(PPh3)4]disappeared rapidly with consequent formation of onlymonoalkylated cationic product, [Pt2(µ-S){µ-SCH2(C6H4)B{OC(CH3)2}2}(PPh3)4]+. This was indicated by the immediate appearance of the monoalkylated product peak at m/z 1720.6.The reaction came to completion within 6 minutes after injection and no trace of any other product or dialkylated species. The desk top synthesis observed after further stirring for six hours also show the formation of no other product. The reaction ofBrCH2(C6H4)B(OH)2, with({[Pt2(µ-S)2(PPh3)4] + H}+)within same time interval yielded three monocationic species that were detected by ESI-MS and assignable to the three alkylated products: [Pt2(µ-S){µ-SCH2C6H5)(PPh3)4]+, m/z 1593.4 from the loss of B(OH)2 moiety; a hemiketal-like species [Pt2(µ-S){µ-SCH2(C6H4)B(OH)(OCH3)}(PPh3)4]+, m/z 1651.5 and [Pt2(µ-S){µ-SCH2(C6H4)OH}(PPh3)4]+, m/z 1609.5. The laboratory scale synthesis indicated the same products.The masses were identified by comparing the experimental isotope patterns with calculated ones. No peak was observed in the mass spectrum that was attributable to the formation of the expected product [Pt2(µ-S){µ-SCH2(C6H4)B(OH)2}(PPh3)4]+. The structural determination by X-ray diffraction showed that the compound formed was a zwitter ion (neutral complex) [Pt2(µ-S){µ-S+CH2(C6H4)B(OH)(O-)}(PPh3)4]. [Pt2(µ-S){µ-S+CH2(C6H4)B(OH)(O-)}(PPh3)4] is a neutral species and not detectable in ESI-MS. 1H NMR spectra showed a complicated set of resonances in the aromatic region due to the terminal triphenylphosphine ligands and were broadly assigned as such. However, SCH2 hydrogen atoms were easily identified as broad peaks at δ 3.59 ppm and 3.60 ppm for [Pt2(µ-S){µ-SCH2(C6H4)B{OC(CH3)2}2}(PPh3)4]+PF6 and [Pt2(µ-S){µ-S+CH2(C6H4)B(OH)(O-)}(PPh3)4], respectively. The monoalkylated products shows IR and 31P{1H} NMR spectra expected of the complexes. The OH vibration (3336 cm-1) in 2.1 shifted to 3435 cm-1 in 2.1a. The absorption bands of the B-O bond in 2.2 (1355 cm-1) and 2.1 (1350 cm-1) shifted to 1360 cm-1 and 1367 cm-1 in 2.2a•(PF6) and 2.1a respectively. The 31P{1H} NMR spectra showed nearly superimposed central resonances and clearly separated satellite peaks due to 195Pt coupling. The 1J(PtP) coupling constants showed the differences due to the trans influences of the substituted and the unsubstituted sulfide centers. The trans influence of the unsubstituted sulfide is greater than the thiolate (substituted) species demonstrated by the coupling constants at (2628 and 3291 Hz) for 2.2a•(PF6) and (2632 and 3272 Hz) 2.1a,respectively.

2017-03-31T00:00:00Z Okoye, Nkeoma Nkasi http://repository.unn.edu.ng/handle/123456789/4297 2017-06-11T23:54:40Z 2017-03-31T00:00:00Z

Characterisation of the Compounds of The Ethylacetate Extract of the Leaves Of Alstonia Boonei De Wild and Their Antioxidant And Antimicrobial Potentials Okoye, Nkeoma Nkasi Dried and pulverised leaves of A. boonei De Wild (Apocynacea) were extracted using methanol for 48 h. The methanol extract obtained was defatted using n-hexane and fractionated using ethylacetate. The ethyl acetate fraction of the extract was subjected to vacuum liquid chromatography (VLC) in silica gel using gradients of hexane-ethyl acetate. The VLC fractions were further separated on Sephadex LH-20. A total of 10 compounds were successfully isolated and purified using the reverse phase semi preparative HPLC (L-7100, Merck/Hitachi). The structures of these compounds were determined using UV, HPLC-MS, one-dimensional: 1H, 13C and DEPT NMR, and two-dimensional: 1H1H COSY, HMQC, and HMBC NMR. The antioxidant properties were assessed using the 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging test. The isolated compounds were also subjected to anti-microbial studies using Agar well diffusion technique against the organisms: Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. Based on the spectral data, the isolated compounds were identified as: quercetin-3-O- [α-L-rhamnopyranosyl(1→6) β-Dglucopyranoside] (1); quercetin-3-O- [α-L-rhamnopyranosyl(1→6) β-D-galactopyranoside] (2); kaempferol-3-O-[α-L-rhamnopyranosyl(1→6) β-D-glucopyranoside] (3); kaempferol-3-O-[α -Lrhamnopyranosyl(1→6) β-D-galactopyranoside] (4); quercetin-3-O-[α -Lrhamnopyranosyl(1→4) β-D-glucoctopyranoside] (5); kaempferol-3-O-[α -Lrhamnopyranosyl(1→4) β-D-glucopyranoside] (6); quercetin-3-O-[α -L-rhamnopyranosyl(→2)β-D-glucopyranoside] (7); quercetin-3-O-[α -L-rhamnopyranosyl(1→2) β-D-galactopyranoside] (8); chlorogenic acid (9) and 4,5-dicaffeoylcinnamic acid (10). Compounds 1, 2, 5, 7,8 (derivatives of quercetin) and 9, a caffeic acid derivative, showed a dose dependent antioxidantactivity on DPPH free radical scavenging model with IC50 values of 52, 48, 36, 66, 56 and 22μg/mL respectively. The three kaempferol derivatives (3, 4 and 6) showed poor anti-oxidant activity (IC50 >100 μg/mL). This suggests that the presence of at least two ortho coupled OH groups in RING B of the flavonoid nucleus is necessary for a good antioxidant activity. Compounds 7 and 8 were active against Escherichia coli with MIC values of 1.77 μg/mL and 1.92 μg/mL respectively. The profound antioxidant activity of the isolated quercetin derivatives and chlorogenic acid may explain the ethnomedicinal use of the leaf extract in the management of inflammatory disorders. These groups of compounds isolated could be very useful for SAR studies as well as other studies on the effects of glycosyl substitution patterns on chemical shifts of the ring carbons of flavonoid nuclei.

2017-03-31T00:00:00Z