Chemistry

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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.
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.
Synthesis and insecticidal activities of some selected hydroxytriazenes
(2011-10) Ombaka, O*; Gichumbi, J.M.
Eight hydroxytriazenes were synthesized and then subjected to spot tests. The composition of these hydroxytriazenes was analyzed using elemental analysis and their physical characteristics like melting point, crystal shape and colour were studied into details. The synthesized compounds were screened for their insecticidal activities against one day old male Drosophila melanogaster Meig (vinegar flies or fruit flies). Out of all the eight compounds screened, 3-hydroxy-3-m-tolyl-1-m-nitrophenyltriazene, 3- hydroxy-3-m-tolyl-1-p-methoxyphenyltriazene, 3-hydroxy-3-n-propyl-1-o-chlorophenyltriazene were the most active having LC50 values of 2.898, 3.898 and 1.812 ppm respectively. The least active compound is 3-hydroxy-3-m-tolyl-1-phenyltriazene having the value of 16.850 ppm. Heptachlor, a commercial product, had LC50 value of 1.570 ppm.
Synthesis and insecticidal activities of some selected hydroxytriazenes. Journal of Environmental Chemistry and Ecotoxicology
(2011-10) Ombaka, O.; Gichumbi, J. M.
Eight hydroxytriazenes were synthesized and then subjected to spot tests. The composition of these hydroxytriazenes was analyzed using elemental analysis and their physical characteristics like melting point, crystal shape and colour were studied into details. The synthesized compounds were screened for their insecticidal activities against one day old male Drosophila melanogaster Meig (vinegar flies or fruit flies). Out of all the eight compounds screened, 3-hydroxy-3-m-tolyl-1-m-nitrophenyltriazene, 3- hydroxy-3-m-tolyl-1-p-methoxyphenyltriazene, 3-hydroxy-3-n-propyl-1-o-chlorophenyltriazene were the most active having LC50 values of 2.898, 3.898 and 1.812 ppm respectively. The least active compound is 3-hydroxy-3-m-tolyl-1-phenyltriazene having the value of 16.850 ppm. Heptachlor, a commercial product, had LC50 value of 1.570 ppm.
Nonthermal synthesis of three-dimensional metal oxide structures under continuous-flow conditions and their catalytic applications
(American Chemical Society, 2011-10-25) King’ondu, Cecil K. †; Opembe, Naftali N. †; Genuino, Homer C. †; Garces, Hector F. ‡; Njagi, Eric C. †; Iyer, Aparna †; Huang, Hui †; Dharmarathna, Saminda †; Suib, Steven L. *†‡
Continuous-flow synthesis of one-dimensional (1D) metal oxide nanostructures and/or their integration into hierarchical structures under nonthermal conditions is still a challenge. In this work, a nonthermal, continuous-flow approach for the preparation of γ-manganese oxide (γ-MnO2) and cerium oxide (CeO2) microspheres has been developed. By this technique, γ-MnO2 materials with surface areas of 240, 98, and 87 m2/g and CeO2 microspheres with a surface area of 1 m2/g have been fabricated successfully. Characterization of the materials was carried out using powder X-ray diffraction, infrared and inductively coupled plasma optical emission spectrometer (ICP/OES), nitrogen sorption, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. The synthesized materials showed good catalytic activity in the oxidation of α-methyl styrene.
Spectrophotometric Determination of cobalt (II) in low concentrations using hydroxytriazene as selective chelating agents
(2011-12) Ombaka, Ochieng; Gichumbi, J. M.
The present work describes a selective, rapid and simple spectrophotometric method for the determination of cobalt (II) at trace levels using some selected hydroxytriazene. The method is based on the reaction of hydroxytriazene at pH 5.5 to 6.2, 6.0 to 6.8, 7.1 to 7.35, 7.3 to 7.9, 6.75 to 7.25 and 7.2 to 7.75 for hydroxytriazenes no (i), (ii), (iii), (iv), (v) and (vi) respectively and ethanol media with cobalt (II) to produce a highly absorbent yellow coloured chelate product with an absorption maximum at 393,397,417,406,410 and 412 nm for hydroxytriazenes no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The reaction is instantaneous and the absorption remains stable for 24 Hrs. The average molar absorption coefficient were 1.1 x 104, 1.2 x 104,1.8 x 104, 2.5 x 104, 2.1 x 104, 1.9 x 104 mol-1 dm3 cm-1 for hydroxytriazene no (i), (ii), (iii), (iv), (v), (vi) respectively and Sandell’s sensitivity in ng/cm2 were 5.4, 4.9, 3.3, 2.4, 2.9 and 3.1 for hydroxytriazene no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The stoichiometric composition of the chelate is 1:3 for hydroxytriazene no (i), (iv), (v), (vi), 1:2 for (ii) and 1:1 for (iii). A large excess of over 30 cations, anions and complexing agent do not interfere in the determination at equivalent amounts. The method was successfully used in Mussaenda arcu. The method has high precision and accuracy.
Spectrophotometric determination of cobalt (ii) in low concentrations using hydroxytriazene as selective chelating agents.
(2011-12) Ombaka, O. *; Gichumbi, J. M.
The present work describes a selective, rapid and simple spectrophotometric method for the determination of cobalt (II) at trace levels using some selected hydroxytriazene. The method is based on the reaction of hydroxytriazene at pH 5.5 to 6.2, 6.0 to 6.8, 7.1 to 7.35, 7.3 to 7.9, 6.75 to 7.25 and 7.2 to 7.75 for hydroxytriazenes no (i), (ii), (iii), (iv), (v) and (vi) respectively and ethanol media with cobalt (II) to produce a highly absorbent yellow coloured chelate product with an absorption maximum at 393,397,417,406,410 and 412 nm for hydroxytriazenes no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The reaction is instantaneous and the absorption remains stable for 24 Hrs. The average molar absorption coefficient were 1.1 x 104 , 1.2 x 104 ,1.8 x 104 , 2.5 x 104 , 2.1 x 104 , 1.9 x 104 mol-1 dm3 cm-1 for hydroxytriazene no (i), (ii), (iii), (iv), (v), (vi) respectively and Sandell’s sensitivity in ng/cm2 were 5.4, 4.9, 3.3, 2.4, 2.9 and 3.1 for hydroxytriazene no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The stoichiometric composition of the chelate is 1:3 for hydroxytriazene no (i), (iv), (v), (vi), 1:2 for (ii) and 1:1 for (iii). A large excess of over 30 cations, anions and complexing agent do not interfere in the determination at equivalent amounts. The method was successfully used in Mussaenda arcu. The method has high precision and accuracy.
Spectrophotometric Determination of Iron (III) by New Analytical Reagents Derived from Coupling Arylhydroxylamine and Aryldiazonium salt
(2012) Ombaka, O.; Gichumbi, J. M.
A highly sensitive and selective spectrophotometric method is developed for the determination of iron(III) in aqueous solution withhydroxytriazenes. In this work, the effect of pH variation, the composition of the complex of Fe3+ to hydroxytriazenes, precision, Sandell'ssensitivity and interference studies were investigated. This investigation was done under the optimum reaction conditions and otherimportant analytical parameters. Hydroxytriazenes reacts with the Fe3+ and forms coloured complexes. The Fe(III) complex is detected atλmax = 410 nm and pH range 3-4 for reagent no(i), 530 nm and 4-5 for reagent no (ii), 410 nm and 4.5 -5.5 for reagent (iii), 396 nm and 3.5-5.0 for reagent (iv), 467 nm and 2.5-3.5 for reagent no.(vi). Beer-Lambert's law is obeyed in the concentration range (1.0-5.0) × 10-5M,(1.5-9.0) × 10-5 M, (0.5-4.0) × 10-5 M, (0.3-1.8) × 10-5 M, (0.6-3.6) × 10-5 M, (2-12) × 10-5 M for nos. (i), (ii), (iii), (iv), (v), (vi)respectively. The molar ratio of Fe(III) to the hydroxytriazenes was found as 1:3. The limiting concentration for interference for 35diverse ions are reported. The standard deviation ranges between 0.019 to 0.088. The Sandell's sensitivity in ng/cm3 ranges between2.5.579 to 4.189. Reagent nos. (iii), (iv), (v), which were very sensitive were used to determine the level of iron in veg etable samples fromBaharini, Nakuru To wn and the results obtained were compared with those of atomic absorption spectrophotometer.
Status of Water Quality of Naka River in Meru South, Kenya.
(2012) Ombaka, O. 1*; Gichumbi, J. M. !; Kinyua, C. G. 2
The study was carried out for a period of two seasons (wet and dry) in a year. The physicochemical, bacteriological parameters of water and trace metals in sediment samples were evaluated at selected sites of river Naka. Result indicated that the levels of Fe, Mn, Cr, Pb, Al, MPN of coliform organisms/100 mL and E. coli /100 mL in water samples were above maximum permissible limits of WHO. The rest of the parameters measured fall within these limits. The results of sediments revealed that Fe2O3, Al2O3 and SiO2 are the major oxides in the sediments and the rest exist in trace amounts. The small values obtained from the loss on ignition indicate that sediments have lower carbonaceous matter and higher mineral contents. The levels of trace metals in sediments were higher than those in water samples
Physico-Chemical Analysis of Ground Water from Kihara Division, Kiambu County, Kenya
(2012) Gichuki, J. G.
Water quality is an index of health and is one of the areas of major concern to environmentalists, since industrialization, urbanization and modern agricultural practices have a direct impact on the water resources. Borehole water is the major source of water supply in Kihara division, Kiambu County. In this paper an attempt has been made to evaluate water quality parameters of selected boreholes. Chemical parameters which were analyzed are Total Alkalinity, Chlorides, Nitrates and heavy metals. Physical parameters like pH, Total Dissolved Solids (TDS), and Turbidity were also analyzed and the results were compared with standard permissible limits set by WHO. The results revealed that some of the parameters were above WHO standard for drinking water, so there is need for strict monitoring to ensure quality water supply for human health. The analysis data of heavy metal elements concentration Fe, Pb, Cu, Cd, Ni and Zn were within the permissible limits except for Pb in B4 and B8
Spectrophotometric Determination of Iron(III) by New Analytical Reagents Derived from Coupling Arylhydroxylamine and Aryldiazonium Salt
(2012) Ombaka, O.*; Gichumbi, J. M.
A highly sensitive and selective spectrophotometric method is developed for the determination of iron(III) in aqueous solution with hydroxytriazenes. In this work, the effect of pH variation, the composition of the complex of Fe3+ to hydroxytriazenes, precision, Sandell's sensitivity and interference studies were investigated. This investigation was done under the optimum reaction conditions and other important analytical parameters. Hydroxytriazenes reacts with the Fe3+ and forms coloured complexes. The Fe(III) complex is detected at lmax = 410 nm and pH range 3-4 for reagent no(i), 530 nm and 4-5 for reagent no (ii), 410 nm and 4.5 -5.5 for reagent (iii), 396 nm and 3.5-5.0 for reagent (iv), 467 nm and 2.5-3.5 for reagent no.(vi). Beer-Lambert's law is obeyed in the concentration range (1.0-5.0) × 10-5 M,(1.5-9.0) × 10-5 M, (0.5-4.0) × 10-5 M, (0.3- 1.8) × 10-5 M, (0.6-3.6) × 10-5 M, (2-12) × 10-5 M for nos. (i), (ii), (iii), (iv), (v), (vi) respectively. The molar ratio of Fe(III) to the hydroxytriazenes was found as 1:3. The limiting concentration for interference for 35 diverse ions are reported. The standard deviation ranges between 0.019 to 0.088. The Sandell's sensitivity in ng/cm3 ranges between 2.5.579 to 4.189. Reagent nos. (iii), (iv), (v), which were very sensitive were used to determine the level of iron in vegetable samples from Baharini, Nakuru Town and the results obtained were compared with those of atomic absorption spectrophotometer.
Geochemical and Mineralogical Characteristics of Geophagic Materials from Kiambu, Kenya
(2012) 22. Gichumbi, J.M.; Ombaka, O.; Gichuki, J.G.
Geophagia is the deliberate consumption of soil and clay. The practice of geophagia is due to reasons of culture, medicinal, religious and mineral deficiency. Geophagy is widespread among pregnant and breast feeding women in sub-Saharan Africa and this is evidenced by the sale of geophagic materials in markets across Africa. This study is aimed at studying the geochemistry and mineralogy of geophagic samples sold in Kiambu County, Kenya. The geophagic samples were analyzed by atomic absorption spectrometry, X-ray fluorescence spectrometry, X-ray diffractometry, Fourier transform infrared spectrometry. The results obtained showed that the materials consist mainly of silica (SiO2) and alumina (Al2O3). They also contain the elevated levels of iron oxides. The mineralogical analysis showed that quartz and kaolinite were the major phases. (2) (PDF) Geochemical and Mineralogical Characteristics of Geophagic Materials from Kiambu, Kenya. Available from: https://www.researchgate.net/publication/335635018_Geochemical_and_Mineralogical_Characteristics_of_Geophagic_Materials_from_Kiambu_Kenya [accessed Oct 29 2020].
Antibacterial and antifungal activities of novel hydro
(2012) Ombaka, A. O.*; Muguna, A. T.; Gichumbi, J. M.
In a search for new leads potent antimicrobial agents, an array of novel hydroxytriazenes i-xi were synthesized and characterized through their melting point, crystal shape, colour and elemental analysis. In vitro microbiological evaluations were carried out for all the synthesized compounds against both bacterial and fungi using the turbidimetric method. The reagent number x and xi showed significant antibacterial activities against two gram positive [Streptococcus feacalis, Staphylococcus aureus, penicillin resistance (2500 units)]. All synthesized hydroxytriazenes except reagent number viii showed antifungal activities against five fungi [Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mantagrophytes, Aspergillus fumigatus}. The minimum inhibitory concentration (mic) values against these bacteria and fungi ranged from <12.5 to 50 μg/ml. Some hydroxytriazenes (x, xi) showed an unusual combined antibacterial and antifungal action, which suggest that hydroxytriazenes revealed a wide range of antimicrobial activity.

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