Geoffrey N. Kamau

Electrochemistry of bipyridyl derivatives of cobalt in solutions of anionic and cationic micelles

Abstract Electroreductions of tris(2,2′-bipyridyl) and 4,4′-dimethyl-2,2′-bipyridyl complexes of Co(II) in 0.1 M solutions of sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) were investigated. Electrochemical, UV and NMR results showed that all complexes studied were bound to micellar aggregates. Co(II) complexes were bound close to the Stern layer of SDS micelles, and to hydrophobic regions of CTAB micelles. Differences in the distribution of the complexes are explained in terms of coulombic and hydrophobic interactions of solutes with the micellar aggregates. Rates of electron transfer were slower in surfactant solutions than in acetonitrile (MeCN), following the order MeCN > CTAB > SDS. Dimethylbipyridyl and long chain bpyC 16 complexes gave slower electron transfer than Co(bpy) 2+ 3 . Also, equilibria and/or kinetics of dissociation of Co(bpy) − 3 , Co(dmbpy) + 3 , and Co(dmbpy) − 3 were altered in CTAB as compared to acetonitrile. Co(−I) complexes reduced water in SDS, but not in CTAB. Adsorption of some Co(I) and Co(−I) complexes at the glassy carbon electrode occurred in CTAB.

Adsorption and detection of some phenolic compounds by rice husk ash of Kenyan origin

Rice husk ash (RHA) obtained from a rice mill in Kenya has been used as an inexpensive and effective adsorbent (and reagent) for the removal (and detection) of some phenolic compounds in water. The abundantly available rice mill waste was used in dual laboratory-scale batch experiments to evaluate its potential in: (i) the removal of phenol, 1,3-dihydroxybenzene (resorcinol) and 2-chlorophenol from water; and (ii) the detection of 1,2-dihydroxybenzene (pyrocatechol) and 1,2,3-trihydroxybenzene (pyrogallol) present in an aqueous medium. The studies were conducted using synthetic water with different initial concentrations of the phenolic compounds. The effects of different operating conditions (such as contact time, concentration of the phenolic compounds, adsorbent quantity, temperature, and pH) were assessed by evaluating the phenolic compound removal efficiency as well as the extent of their color formation reactions (where applicable). RHA exhibits reasonable adsorption capacity for the phenolic compounds and follows both Langmuir and Freundlich isotherm models. Adsorption capacities of 1.53 x 10(-4), 8.07 x 10(-5), and 1.63 x 10(-6) mol g(-1) were determined for phenol, resorcinol and 2-chlorophenol, respectively. Nearly 100% adsorption of the phenolic compounds was possible and this depended on the weight of RHA employed. For the detection experiments, pyrocatechol and pyrogallol present in water formed coloured complexes with RHA, with the rate of colour formation increasing with temperature, weight of RHA, concentration of the phenolic compounds and sonication. This study has proven that RHA is a useful agricultural waste product for the removal and detection of some phenolic compounds.

Influence of surfactant-based microheterogeneous fluids on aggregation of copper phthalocyanine tetrasulfonate

Electronic absorption spectroscopy was used to measure the molecular association of copper phthalocyanine tetrasulfonate in micellar solutions, a microemulsion made with cationic surfactant, and homogeneous solvents. Analysis of absorbance versus concentration data using a multiple-aggregation model and non-linear regression analysis gave values of association constants, molar absorptivities and estimates of average aggregation number. Microemulsions and aqueous micellar solutions made with alkylammonium surfactants inhibited aggregation, probably because of interactions between the phthalocyanine sulfonate groups and the cationic surfactant head groups at interfacial surfaces. Similar aggregation behavior was observed previously in multiple-bilayer films of cationic surfactants. Water and aqueous solutions containing tetraethylammonium bromide or anionic SDS micelles provide environments facilitating extensive aggregation of CuIIPcTS4−. The major species are dimers in water and acetonitrile/water, but the formation of higher aggregates is promoted by addition of SDS or TEAB. Aprotic organic solvents provide environments intermediate between these two extremes, giving relatively large aggregation numbers (i.e. five to seven) but smaller association constants than aqueous media not containing cationic surfactants.

Microelectrode voltammetry of TCNQ in aprotic solvent at low concentrations of non-reducing and reducing salts

Abstract In aprotic solvent containing electrolyte, tetracyanoquinonedimethane (TCNQ) and its radical anion (TCNQXXX) give well separated reversible reductions by cyclic voltammetry at conventional sized electrodes. However, without purposely added electrolyte in solvents such as tetrahydrofuran/acetonitrile (2:1) the reduction wave of TCNQ at microelectrodes was accompanied by only a barely detectable second wave. Addition of non-reducing salts such as tetrabutylammonium tetrafluoroborate (TBABF4) increased the limiting current of the second wave. Results suggest an ECE pathway in which TCNQ is reduced to TCNQXXX. Results are interpreted by assuming formation of an ion pair with the salt cation, e.g. (TGNQXXX)(TBA+), which is reduced in the second wave. TBAI reduced TCNQ to TCNQ− in aprotic solvents in an equilibrium chemical redox step. Steady state voltammograms in these systems feature an anodic wave at −0.1 V for the catalytic oxidation of iodide, and a cathodic wave at about −0.8 V probably involving reduction of TCNQXXX and I2. Results showed that reduction of TCNQ to its anion radical by iodide, as well as ion pair formation involving TCNQXXX, proceeds at rapid rates at room temperature and below.

Potential antitermite compounds from Juniperus procera extracts

Thin layer chromatography (TLC) analysis revealed that destructive distillation of Juniperus procera tree gave ten major components, whereas Croton megalocarpus tree yielded five components. This was confirmed by gas chromatography (GC). The components were isolated by column chromatography and analysed using infrared, ultra-violet, visible and mass spectroscopy (MS) techniques. The whole extract was about 30.3% of the starting material (sawdust) and consisted of 77.5% water and 22.5% oily reddish-brown layer. The extracts had alcoholic and phenolic compounds together with acids. Cedrol, a tertiary tricyclic alcohol, was found to be in the greatest proportion in the oily layer. IR spectra with a peak beyond 3000 cm(-1), UV-VIS absorption maxima at 230 nm and mass spectra with m/e 204 suggested the presence of cedrene in the extract.

Air and Blood Lead Levels in Lead Acid Battery Recycling and Manufacturing Plants in Kenya

The concentration of airborne and blood lead (Pb) was assessed in a Pb acid battery recycling plant and in a Pb acid battery manufacturing plant in Kenya. In the recycling plant, full-shift area samples taken across 5 days in several production sections showed a mean value ± standard deviation (SD) of 427 ± 124 μg/m3, while area samples in the office area had a mean ± SD of 59.2 ± 22.7 μg/m3. In the battery manufacturing plant, full-shift area samples taken across 5 days in several production areas showed a mean value ± SD of 349 ± 107 μg/m3, while area samples in the office area had a mean ± SD of 55.2 ± 33.2 μg/m3. All these mean values exceed the U.S. Occupational Safety and Health Administrations permissible exposure limit of 50 μg/m3 as an 8-hr time-weighted average. In the battery recycling plant, production workers had a mean blood Pb level ± SD of 62.2 ± 12.7 μg/dL, and office workers had a mean blood Pb level ± SD of 43.4 ± 6.6 μg/dL. In the battery manufacturing plant, production workers had a mean blood Pb level ± SD of 59.5 ± 10.1 μg/dL, and office workers had a mean blood Pb level ± SD of 41.6 ± 7.4 μg/dL. All the measured blood Pb levels exceeded 30 μg/dL, which is the maximum blood Pb level recommended by the ACGIH®. Observations made in these facilities revealed numerous sources of Pb exposure due to inadequacies in engineering controls, work practices, respirator use, and personal hygiene.

Variation of plant p,p′-DDT uptake with age and soil type and dependence of dissipation on temperature

Abstract The extent to which DDT may be absorbed and translocated from 14 C-p,p′-DDT contaminated soils into cowpeas plant tissues, and the variation of uptake of p,p′-DDT by the plants in relation to the dissipation of p,p′-DDT in the soils was studied using a radioisotope technique for three months (90 d). Substantial absorption and accumulation of residues was observed for the cowpeas grown in two different sites, namely, in the coastal province Mombasa and highland region, Nairobi. The degree of uptake varied with soil type and growing conditions. Total residue levels ranging from 0.945±0.040 mg/kg to 7.765±0.211 mg/kg were obtained for 2 to 12 week old Mombasa plants. However, Nairobi plant values fell in the range of 1.136±0.038 mg/kg to 3.239±0.007 mg/kg. The Mombasa plants gave a range of residue levels from 0.800±0.065 mg/kg to 6.110±0.038 mg/kg and 0.084±0.001 mg/kg to 1.390±0.003 mg/kg for extractable and non-extractable (bound) residue, respectively. The corresponding values for Nairobi samples were 1.034±0.011 mg/kg to 2.241±0.014 mg/kg and 0.080±0.002 mg/kg to 0.411±0.007 mg/kg, respectively. Further, results suggest that the higher the water retention by the soil, the higher the rate of evaporation of DDT. Extractable DDT in soils decreased with temperature while soil-bound DDT increased with temperature. Coastal region soil-p,p′-DDT samples indicated p,p′-DDE to be the major metabolite over a period of 292 d. The levels of DDT decreased with time. The reverse was true for DDE, as expected. First order rate constant for DDT dissipation in soils was confirmed by half-life measurements. The rate constants (k), calculated from the data, for Mombasa and Nairobi, were 5.6 × 10−6 min −1 and 5.1 × 10 −6 min −1 , respectively. Within a period of 90 d, DDT residue in the plants ranged from 0.94 to 7.73 mg/kg, while that in soils ranged from 88.9 to 32.0 mg/kg.

Lead Exposure and Blood Pressure among Workers in Diverse Industrial Plants in Kenya

The study evaluated airborne exposures and blood lead (BPb) levels in 233 production workers at six diverse industrial plants in Kenya. Blood and personal breathing zone air samples were collected and analyzed for lead (Pb) using atomic absorption spectroscopy. Blood pressure (BP) levels were measured using a standard mercury sphygmomanometer. The results indicated mean airborne Pb levels ± standard deviation (SD) as follows: 183.2 ± 53.6 μg/m3 in battery recycling, 133.5 ± 39.6 μg/m3 in battery manufacturing, 126.2 ± 39.9 μg/m3 in scrap metal welding, 76.3 ± 33.2 μg/m3 in paint manufacturing, 27.3 ± 12.1 μg/m3 in a leather manufacturing, and 5.5 ± 3.6 μg/m3 in a pharmaceutical plant. The mean airborne Pb levels exceeded the U.S. Occupational Safety and Health Administration (OSHA) 8-hr time-weighted average (TWA) permissible exposure limit (PEL) for Pb of 50 μg/m3 in the battery manufacturing, battery recycling, welding, and paint manufacturing plants. Similarly, mean BPb concentrations exceeded the American Conference of Governmental Industrial Hygienists (ACGIH®) biological exposure index (BEI) for Pb of 30 μg/dl. A significant positive association was observed between BPb and breathing zone air Pb (R2 = 0.73, P < 0.001). Approximately 30% of the production workers (N = 233) were in the hypertensive range with an average systolic and diastolic blood pressure (BP) of 134.7 ± 12.7 mmHg and 86.4 ± 8.9 mmHg, respectively. In the multivariate regression analysis, age, duration of work, airborne Pb and BPb levels were significantly associated (P < 0.05) with a change in BP. We recommend improved engineering controls, work practices, and personal hygiene to reduce Pb exposures. In addition, workers should undergo comprehensive medical surveillance to include BPb and BP testing, and airborne Pb assessments in all industries with significant lead exposures.

Status of organochlorine (DDT) pollutants and steps toward electrocatalytic reductions

The accumulation of DDT in the environment over the years is a major concern in the world today. The extent to which DDT may be absorbed and translocated from 14C-p,p¢-DDT contaminated soils into cowpea plant tissues, and the variation of uptake of p,p¢-DDT by the plants in relation to the dissipation of p,p¢-DDT in the soils was studied using a radioisotope technique. Significant absorption and accumulation of residues was observed for the cowpeas grown in two different sites, coastal and highland regions. The degree of uptake varied with soil type and growing conditions. Further results indicated that the higher the water retention by the soil the higher the rate of evaporation of p,p¢-DDT. Coastal region p,p¢-DDT soil samples showed DDE to be the major metabolite. DDT residue in the plants ranged from 0.94 to 7.73 mg/kg, while that in the soils ranged from 88.9 to 32.0 mg/kg. Preliminary electrode reactions indicated lowering of overpotential for reduction of p-chlorophenol by about 1 V, using copper phthalocyanine tetrasodium tetrasulfonate as the catalyst in microemulsion. Microemulsions and appropriate catalysts are a promising system for the decomposition of DDT.

Microemulsions as media for destruction of organohalide pollutants by electrolysis

Abstract This paper reviews recent work on the dehalogenation of organohalide pollutants by electrochemical catalysis in bicontinuous microemulsions of didodecyldimethylammonium bromide (DDAB)—water—dodecane. Compared with alternative toxic, expensive organic solvents, the catalytic efficiency for the dehalogenations was enhanced for non-polar organohalides in DDAB microemulsions. Using metal phthalocyanine tetrasulfonates as catalysts, the catalytic efficiencies for the reactions of 1,2-dibromobutane and 1,2-dibromocyclohexane were much larger in a microemulsion than in a homogeneous solvent. The reverse was found for trichloroacetic acid. Since DDAB and the catalysts adsorb on the carbon cathode, results suggest that a DDAB layer on the cathode preconcentrates non-polar dibromides but not the polar trichloroacetic acid. For complex mixtures of polychlorinated biphenyls, DDAB microemulsions performed better in bench-scale catalytic dechlorinations than aqueous DDAB dispersions, which performed better than aqueous CTAB micelles. Complete conversion of 100 mg of a 60% chlorine industrial PCB mixture in a 20 ml microemulsion could be carried out overnight using an activated lead cathode, zinc phthalocyanine as catalyst, and ultrasonic mass transport. Finally, the dechlorination of DDT (1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane), which has both aliphatic and aromatic chlorines, was also explored in the microemulsions. Preliminary results suggest that oxygen may be an effective catalyst for the dechlorination of DDT in DDAB microemulsions to 1,1-diphenylethane using a carbon cathode.