Faculty of Science Engineering and Technology

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Formation of trimetallic complexes containing redox-active nitrosyl molybdenum tris(3,5-dimethylpyrazolyl)-borato groups. Schiff base compounds containing two Mo and one Cu centre
(Elsevier, 1994) Kagwanja, Stanley M.; Jones, Christopher J.; Maher, John P.; McCleverty, Jon A.
The reaction of [Mo(NO)Tp*Cl2] [Tp* = tris(3,5-dimethylpyrazolyl)borate] with copper(II) Schiff base complexes derived by condensation of two mole equivalents of 2,5-dihydroxybenzaldehyde with α,ω-diamines [1,2-C6H4(NH2)2, NH2(CH2)nNH2, n = 2–5] affords trimetallic species containing three potential redox centres. The IR, UV-vis and EPR spectroscopic properties of these compounds are described and it is shown that, with increasing chain length in the diimino bridges of the Schiff base complexes, there are small distortions from planarity, probably towards tetrahedral structures. From cyclic and differential pulse voltammetry it is shown that the trimetallic species primarily undergo two accessible sequential one-electron reductions associated with the {Mo(NO)Tp*Cl} centres, and by determination of conproportionation constants for the mono-reduced species, it is established that there is weak interaction between these two centres. Attempts to obtain reduced trimetallic species are described.
Reaction of molybdenum mononitrosyl halides with Schiff bases: Hydrolysis of azomethine links,formation of monometallic tris
(Elsevier, 1996-06) Kagwanja, Stanley M.; Jeffery, John C.; Johns, Christopher J.; McCleverty, John A.
The reaction of 2 mol equiv. of [Mo(NO){HB(dmpz)3}X2] ((HBdmpz)3 = tris(3,5-dimethylpyrazolyl)borate; X = Cl or I) with Schiff base ligands derived by condensation of 2 mol equiv. of para- and meta-hydroxybenzaldehyde with 1,4-C6H4(NH2)2 and 1,6-NH2(CH2)6NH2 afforded monometallic complexes [Mo(NO) {H(dmpz3)} X(OC6H4 CHO)]. Sodium borohydride reduction of the Schiff bases obtained from the hydroxybenzaldehydes and 1,4-C6H4(NH2)2 followed by reaction with [Mo(NO){HB(dmpz)3 Cl2}] afforded the bimetallic species [{Mo(NO)HB(dmpz)3}Cl{(OC6H4CH2NH)2C6H4}]. These compounds were characterized spectroscopically and the structure of a closely related compound, [Mo(NO){HB(dmpz)3}Cl{OC6H3(3-CHO)(4-OH)}], has been determined crystallographically.
Trimetallic complexes containing Nickel or Palladium and two Molybdenum nitrosyl groups
(1997) Kagwanja, Stanley M.; Johns, Christopher J.; McCleverty, Jon A.
The reaction of [Mo(NO){HB(dmpz)3}Cl2] [HB(dmpz)3 = tris(3,5-dimethylpyrazolyborate] with nickel(II) and palladium(II) Schiff-base complexes derived by condensation of two mole equivalents of 2,5-dihydroxybenzaldehyde with α,ω-diamines [1,2-C6H4(NH)2),(CH2)nNH2, n = 2–4 for Ni, n = 2 for Pd) affords trimetallic species. From cyclic, square wave and differential pulse voltammetric data it is shown that the species may be reduced to a dianion and that the sites of reduction are probably the two molybdenum nitrosyl fragments. From the electrochemical and limited EPR spectral data obtained from reduced species, it is clear that there is very weak electronic and minimal magnetic interaction between the redox centres.
Synthesis and electrochemical studies of heterobinuclear complexes containing copper and molybdenum nitrosyl groups linked by Schiff base ligands
(Springer, 2000-08) Lutta, Samwel T.; Kagwanja, Stanley M.
Abstract The reaction of [MoCl(NO)Tp * = tris(3,5-dimethylpyrazolylborate] with copper Schiff base complexes derived by condensation of one mole each of 2,5-dihydroxybenzaldehyde and salicylaldehyde with α,ω diamines [NH2(CH2) n NH2, n = 2–4] yields heterobinuclear complexes with two potential redox centres. I.r., electronic and e.s.r. spectroscopic properties of these complexes are described. Cyclic voltammetric data of the base complexes in DMSO reveal that the copper redox centres undergo irreversible one electron reduction at potentials which vary slightly with the polymethylene carbon chain backbone of the Schiff base ligands. Incorporation of [MoCl(NO)Tp *]+ groups in the copper Schiff base complexes, results to a slight anodic shift (100 mV) in the reduction potential of the copper centre which remains invariant as the polymethylene carbon chain lengthens. Electrochemical data of the heterobinuclear complexes using CH2Cl2 and DMSO as solvents indicate the solvent dependence of the reduction potentials of these complexes. In CH2Cl2, the reduction potential of the copper centre shifts cathodically by 100 mV, while that of the molybdenum centre shifts anodically by 200 mV. However, accumulated electrochemical data of the heterobinuclear complexes indicate minimal electronic interactions between the copper and molybdenum redox centres.
On The Convexity of A Generalized q-Numerical Range’’
(2005-01) Musundi, Sammy Wabomba
For a given $q in kom$ with $|q| le 1$, we study the $C$-numerical range of a Hilbert space operator where $C$ is an operator of the form [ left( begin{array}{ccc} qI_n & sqrt{1-|q|^2}I_n \ 0_n & 0_n end{array} right) oplus 0. ] Some known results on the $q$-numerical range are extended to this set.
A botanical inventory and diversity assessment of Mt. Marsabit forest, a sub-humid montane forest in the arid lands of northern Kenya
(Blackwell Publishing Ltd, 2007) Githae, Eunice W. 1,2; Chuah-Petiot, Mins 2; Mworia, John K. 2; Odee, David W. 1*
A botanical inventory and diversity of trees, shrubs (‡5 cm diameter at breast height [dbh]), herbs, climbers and lianas was assessed in plots (154) of 20 · 5 m in Mt. Marsabit forest, northern Kenya. We recorded 52 species of trees and shrubs, twelve species of herbs and six species of climbers and lianas. They belonged to 35 families and 64 genera. Rubiaceae was the richest family with nine species followed by Euphorbiaceae (six), Oleaceae (five), Rutaceae (four), Capparaceae, Labiatae and Leguminosae (three each). The rest of the families were represented by one or two species. Rinorea convallarioides (Bak.f.) Eyles ssp. Marsabitensis Grey-Wilson (Violaceae), an endemic species, and Drypetes gerrardii Hutch. (Euphorbiaceae), were the two most important species, accounting for more than third of the combined importance value. Species diversity indices were 2.735 (Shannon–Wiener), 0.88 (Simpson’s) and 0.296 (Evenness). There was a strong evidence of disturbance arising from anthropogenic and wildlife foraging activities. This inventory has affirmed Mt. Marsabit forest as a unique habitat for several endemic, rare, threatened or vulnerable plant species, which should be conserved.
The effect of organic binders on the fracture properties of kaolin refractories, Journal of Material Science
(Springer, 2008-06) Njogu, M. S.; Nyongesa, W.; Aduda, B. O.
The fracture properties of kaolin-based refrac-tories prepared using plant-derived binders from okra and‘‘mrenda’’ have been investigated and compared. It wasobserved that the MOR of fired samples improved from37.5±0.1 MPa (for binder-free samples) to 69.6±0.1 MPa, and to 120.0±0.1 MPa for okra- and ‘mrenda’-plasticized samples, respectively, while the fracturetoughness increased from 3.9±0.1 MPa (for binder-freesamples) to 5.6±0.1 and 5.7±0.1 MPa for okra and‘mrenda’-plasticized samples, respectively. It is concludedthat the use of organic binders enhances the reliability andservice life of kaolin refractories used in thermally fluctu-ating environments
Synthesis, characterization and electrochemistry of heterobimetallic complexes containing molybdenum(II) nitrosyl and manganese(II)-schiff base centers
(Chemical Society of Ethiopia, 2010) Odhiambo, Ruth; Muthakia, Gerald K.; Kagwanja, S. M.
New complexes derived from the reaction of Mo (NO)Tp *Cl2; Tp * = tris(3,5-dimethylpyrazolyl) borate with a series of manganese(II) Schiff bases have been synthesized. Characterization by UV, IR, MS and elemental analysis support their formulations. Cyclic and differential pulse voltammograms of manganese (II) Schiff base monometallic complexes exhibit one reduction peak which may be associated with the reduction of the manganese (II) center. In CH3CN solutions, the molybdenum (II)-manganese (II) bimetallic complexes showed two reversible reduction peaks which are associated with the reduction of the molybdenum and manganese centers. In CH2Cl2, only the reduction of molybdenum (II) center exhibited reversibility while the reduction of manganese (II) center was irreversible. These observations demonstrate that reduction potentials for bimetallic complexes are solvent dependent.
Synthesis, characterization and electrochemistry of heterobimetallic complexes containing molybdenum(II) nitrosyl and manganese(II)-Schiff base Bull.
(Chemical Society of Ethiopia, 2010) Odhiambo, R.; Muthakia, G. K.; Kagwanja, S. M.
ABSTRACT. ABSTRACT New complexes derived from the reaction of Mo(NO)Tp *Cl2; Tp * = tris(3,5-dimethylpyrazolyl) borate with a series of manganese(II) Schiff bases have been synthesized. Characterization by UV, IR, MS and elemental analysis support their formulations. Cyclic and differential pulse voltammograms of manganese(II) Schiff base monometallic complexes exhibit one reduction peak which may be associated with the reduction of the manganese(II) center. In CH3CN solutions, the molybdenum(II)-manganese(II) bimetallic complexes showed two reversible reduction peaks which are associated with the reduction of the molybdenum and manganese centers. In CH2Cl2, only the reduction of molybdenum(II) center exhibited reversibility while the reduction of manganese(II) center was irreversible. These observations demonstrate that reduction potentials for bimetallic complexes are solvent dependent.
Crystal structure of chlorido-(η6-p-cymene)-(N- (2-fluorophenyl)-1-(pyridin-2-yl) methanimine-κ2N, N′) ruthenium (II)–acetone (1/1), C22H23ClN2F7OPRu.
(2010-01) Gichumbi, Joel M.; Omondi, Bernard *; Friedrich, Holger B.
C 22 H 23 ClN 2 F 7 OPRu, monoclinic, P 2 1 / c (no. 14), a = 7.30480(10) Å, b = 12.9540(3) Å, c = 28.7076(6) Å, β = 96.6990(10)°, V = 2697.95(9) Å ³ , Z = 4, Rgt ( F ) = 0.0196, wRref ( F² ) = 0.0479, T = 100(2) K.
Hydrophobic polymer-coated metal oxide catalysts for effective low-temperature oxidation of CO under moisture-rich conditions
(American Chemical Society, 2010-05-04) Chen, Chun-Hu †; Njagi, Eric C. †,; Sun, Shih-Po ‡,; Genuino, Homer †; Hu, Boxun §; Suib, Steven L. *†§
The first example of a highly water-tolerant, hydrophobic polymer coated metal oxide catalyst systems is reported for CO oxidation. Studies show that protected catalysts have 5.3 times longer lifetimes than unprotected catalysts under highly humid conditions. This idea is simple and general for many different metal oxide catalyst systems.
Facile one-step template-free synthesis of uniform hollow microstructures of cryptomelane-type manganese oxide K-OMS-2
(2010-08) Galindo, Hugo M.; Carvajal, Yadira; Njagi, Eric
Hollow microstructures of cryptomelane-type manganese oxide were produced in a template-free one-step process based on the fine-tuning of the oxidation rate of manganese species during the synthesis. The tuning of the reaction rate brought about by a mixture of the oxidants oxone and potassium nitrate becomes apparent from the gradual physical changes taking place in the reaction medium at early times of the synthesis. The successful synthesis of the hollow uniform structures could be performed in the ranges 120-160 degrees C and 8.2-10.7 for temperature and mass ratio oxone/potassium nitrate, respectively. Independent of the conditions of the synthesis, all of the complex microstructures showed the same pattern for the array of very long nanofibers in which some of these elongated around the surface confining the cavity and the other fibers grew normal to the surface created by the previous arrangement. A mechanism based on the heterogeneous nucleation of the cryptomelane phase on the surface of an amorphous precursor and the growth of the nanoscale fibers by processes such as dissolution-crystallization and lateral attachment of primary nanocrystalline fibers is proposed to explain the formation of the hollow structures.
H2 production through the water-gas shift reaction: An in situ time-resolved x-ray diffraction investigation of manganese OMS-2 catalyst
(Science Direct, 2010-10-25) Sithambarama, Shanthakumar a; Wen, Wen c; Njagi, Eric a; Shen, Xiong-Fei b; Hanson, Jonathan C. c; Suib, Steven L. a, b
Manganese oxide octahedral molecular sieve (OMS-2) catalyst prepared by the reflux method was investigated for hydrogen generation via the water-gas shift reaction. Catalysts were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), The Brunauer–Emmett–Teller (BET) surface area and determination of average oxidation state (AOS). The OMS-2 catalyst showed very good catalytic activity for the water-gas shift reaction to generate hydrogen under laboratory conditions. An in situ study was conducted to monitor the structural changes in the catalyst during the water-gas shift reaction using synchrotron radiation-based time-resolved X-ray diffraction (TR-XRD). During the water-gas shift reaction, the mixed valent OMS-2 catalyst undergoes a structural transformation to form Mn2O3 and finally to form MnO. The study showed that OMS-2 catalysts can be used as inexpensive catalysts for hydrogen generation.
Chemical And Mineralogical Analysis of Geophagic Materials Consumed By Pregnant Women In Eastern Nairobi And Nyanza Provinces In Kenya
(2011) Gichumbi, J.; Ombaka, O.
Geophagy is the purposeful or deliberate consumption of Earth and clay deposits by animals, including man. It is a special type of pica, which is defined as the craving and subsequent consumption of non-food substances. The geochemical and mineralogical composition of the geophagic materials consumed by pregnant women and sold in open air markets in Eastern, Nairobi and Nyanza provinces were studied. The mineralogical composition of selected soil samples was investigated using X-ray diffractometry (XRD).The XRD data showed that the soils in these areas consisted mainly quartz, and the clay mineral kaolinite. The preliminary elemental analysis was carried out using Energy dispersive x-ray fluorescence. The geophagic materials were subjected to standard digestion procedures and analyzed for Zn, Cu, Co, Pb and Cd by atomic absorption spectroscopy (AAS). Analysis results showed the geophagic materials contain elevated levels of Fe for a 2.5 g sample. The present study has shown that the geophagic materials from the three provinces open air markets consist mainly of silica and alumina. The levels of Pb exceeded the levels recommended by WHO/FAO limits of 0.01 ppm but the levels obtained for Cd in the samples from Nairobi exceed the WHO/FAO limits of 0.003 ppm
Analyses of geophagic materials consumed by pregnant women in Embu, Meru and Chuka towns in eastern province, Kenya
(2011) Mwangi, Gichumbi J.; Ochieng, Ombaka; Mwangi, Gichumbi, J.; Ombaka, Ochieng
Geophagy is the deliberate consumption of soil and clay deposits by animals, including man. During pregnancy all the nourishment needed by the developing fetus comes from the mother, either the food she eats or the supplement she may take. The geochemical and mineralogical composition of the materials which are consumed by pregnant women from Meru, Embu and Chuka open air markets were studied. The geophagic materials were subjected to standard digestion procedures and analyzed for full assay and elemental analysis for Co, Zn, Mg, Cu, Pb and Cd using Atomic absorption spectrometry and Energy-dispersive x-ray fluorescence spectrometry in 30 geophagic samples. The mineralogical composition was investigated using X-ray diffractometry (XRD). The geochemical analysis revealed that the geophagic materials contain high levels of silica from 48.59 to 60.27%. Geophagic materials from Embu showed the highest concentration of Pb at 0.96 ppm. The levels of Pb in all samples exceeded the levels recommended by WHO/FAO limits of 0.01 ppm. The levels obtained for Cd in all the samples did not exceed the WHO/FAO limits of 0.003 ppm. The XRD data showed that the geophagic materials of the area consisted mainly of silica.
Geophysical structure of Homa Hills Geothermal field based on Gravity and magnetic survey
(2011) Adero, B. Otieno; Odek, A.; Ambusso, W.; Gitonga, G. J.
Gravity and ground magnetic surveys were conducted over an area of 76 Km 2 in order to investigate thermal structures responsible for geothermal manifestations such as hot springs in the Homa Hills geothermal prospect. The two surveys show that the southern part of the prospect has a potential for geothermal resource and should be investigated further to establish presence of an exploitable hydrothermal system. The magnetic survey indicates higher demagnetization in this part of the field compared to other parts of the field. The gravity survey is relatively sharp with a classic dome shaped profile associated with a large shallow dike
Self-assembly of manganese oxide nanoparticles and hollow spheres. Catalytic activity in carbon monoxide oxidation†
(2011) Ching, Stanton *a; Kriz, David A. a; Luthy, Kurt M. a; Njagi, Eric C. b; Suibb, Steven L.
Reactions between MnSO4 and KMnO4 in the presence of carboxylic acids provide a facile, one-pot route to nanostructured manganese oxides with high surface areas. Acetic and propionic acid induce formation of hierarchical nanosphere morphologies whereas butyric acid promotes assembly of hollow spheres. The materials are active catalysts for CO oxidation.
Enhancement of the photo degradation of N-nitrosodimethylamine in water using amorphous and platinum manganese oxide catalysts
(ELSEVIER, 2011-01-25) Genuino, Homer C. a; Njagi, Eric C. a; Benbow, Evan M. a; Hoag, George E. b; Collins, John B. b; Suib, Steven L. a
The enhancement of the photodegradation of toxic N-nitrosodimethylamine (NDMA) in water using amorphous manganese oxide (AMO) and platinum manganese oxide (Pt/Mn3O4) catalysts was investigated. Characterization of the catalysts was carried out using XRD, FESEM, TEM, EDXS, BET, XPS, and AOS. Pt/Mn3O4 and its precursor AMO, synthesized by a redox reaction of Mn2+ and Mn7+, showed similar morphologies. High surface area AMO was confirmed to be amorphous, whereas Pt/Mn3O4 was a mixture of two crystalline structures. The optimum catalyst loading was 25 mg per 100 mL NDMA solution for which the photocatalytic activity was maximized. The average hydrodynamic particle size of a given amount of catalyst increased due to aggregation as a result of an increase in temperature during UV illumination (λ = 254 nm). Photocatalytic studies showed that NDMA degraded according to zero-order kinetics under air saturation at pH 7.0. AMO and Pt/Mn3O4 showed photostability and comparable activities with pure TiO2 and platinized TiO2. Mixed valencies of Mn and the presence of O2 on the surface of the catalysts, which reacts with photogenerated electrons to form reactive oxygen species (hydroxyl and superoxide anion radicals), played significant roles in the enhancement of the photodegradation of NDMA in water.
Light-assisted synthesis of metal oxide heirarchical structures and their catalytic applications
(American Chemical Society, 2011-02-18) King’ondu, Cecil K.; Lyer, Alpana; Njagi, Eric C.; Opembe, Naftali; Genuino, Homer; Huang, Hui; Ristau, Roger; Suib, Stephen
Short reaction times and morphology control in the synthesis of inorganic materials under nonthermal conditions remain a challenge. Herein we report a rapid, self-templating, and nonthermal method based on ultraviolet light to prepare metal oxide hierarchical structures. With this method, the morphology of the metal oxides was controlled readily without using templates.
“Effect of AC Helmholt magnetic field on the mass of Rosecoco deans”
(Taylor and Francis Online, 2011-06-09) Kamweru, P. K.; Ndiritu, F. G.; Kinyanjui, T. K.; Muthui, Z. W.; Ngumbu, R. G.; Odhiambo, P. M.
Plastic bags mostly made of polyethylene (PE) cause pollution as solid waste due to their non-degradability nature. Initiation of a degradative process by enhanced photo-oxidation is a possible method for an accelerated degradation. This paper presents temperature treatment effects on PE films where photodegradation was initiated using ultraviolet (UV) irradiation in the ranges of 200–300 nm and 300–400 nm for 2 hr. Effects of temperature of 40°C and 55°C on non-UV-irradiated and UV-irradiated PE films processed by conventional methods were investigated and evaluated after 50 hr, 150 hr, and 350 hr of temperature exposure. The effects of UV wavelength range irradiation on the degradation were deduced. Measuring the dynamic moduli using a dynamic mechanical analyzer monitored the degradation. The decrease in average storage modulus was 62% with treatment at 55°C, higher than the 16% drop at 40°C for unirradiated samples after 350-hr exposure. Cross-linking in UV-exposed samples, characterized by an increase in dynamic modulus (stiffening), was observed followed by a reduction of storage modulus. Temperature treatment at 55°C together with 300–400-nm UV range irradiation resulted in the largest increase, i.e., 22% after 150 hr, followed by the largest reduction of storage modulus, i.e., 74.6% for a cumulative 350-hr exposure.

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