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- ItemThermal Solid-State Isomerization Reactions in Re and Mo 'Piano Stool' Organometallic Complexes(2002) Adeyemi, Olalere
- ItemThe Solid-state Isomerization of cis and trans-(η5 -C5H4Me)Mo(CO)2(P(Oi Pr)3)I(2002-06-16) Adeyemi, OlalereThe cis- and trans-(η5 -C5H4Me)Mo(CO)2(P(Oi Pr)3)I complexes undergo a bi-directional thermal ligand isomerization reaction to yield an equilibrium mixture of isomers (30/70 cis/trans ratio, 90 °C, < 80 min) in the solid state. The activation energy barrier for the cis-trans isomerization reaction (80–100 °C) was found to be 68 ± 10 kJ mol–1. In benzene (reflux, 2 h) this isomer ratio was found to be 70:30 cis/trans. DSC and powder XRD studies have revealed reactions that occur in the solid state entailing decomposition and isomerization. DSC experiments did not reveal the presence of the cis–trans isomerization reaction.
- ItemSolvent-Free Organometallic Migratory Insertion Reactions(2003-03-10) Adeyemi, OlalereMigratory insertion reactions of organometallic complexes have been shown to occur in the absence of solvent and, more significantly, between solid reagents. Reaction between (η5-C5H5)M(CO)3Me (M ) Mo, W) or (η5-C5H5)Fe(CO)2Me and PPh3 (no solvent) took place at temperatures between 40 and 90 °C and gave the products (η5-C5H5)M(CO)2(PPh3)COMe and (η5-C5H5)Fe(CO)(PPh3)COMe in moderate to good yield (60-99%). The Mo and W complexes reacted in the solid state when T < 80 °C. The decarbonylation of (η5-C5H5)- Mo(CO)2(PPh3)COMe to yield (η5-C5H5)Mo(CO)2(PPh3)Me also occurred in the solid state (120 °C). Reaction of (η5-C5H5)Mo(CO)3Me with a range of ligands, L (L ) PPh3, P(p MeOC6H4)3, PCy3, PEt3, AsPh3, POPh3, P(OEt)3; 1:1 reagent ratio, 90 °C, 15 min), in the absence of solvent gave (η5-C5H5)Mo(CO)2(L)COMe (7-100% yield) and, on extended reaction, (η5-C5H5)Mo(CO)2(L)Me in varying yields. A kinetic study of the solid-state reaction between (η5-C5H5)Mo(CO)3Me and PPh3 yielded rate constants, e.g. k ) 5.18 × 10-5 s-1 (Mo:P ) 1:10; 50 °C), which compares with the literature solution data in toluene (k ) (0.8-2.5) × 10-5 s-1, 50 °C) using similar metal to ligand ratios. The data are consistent with a pseudo-first order reaction in the presence of PPh3. Diffusional effects on the reaction rate are detected at low temperature and low PPh3 ratios
- ItemAdsorption of some heavy metal ions on sulfate- and phosphate-modified Kaolin(Elsevier, 2004) Unuabonah, EmmanuelKaolin (bright white lumps) from Ubulu-Ukwu in Delta State of Nigeria was modified with 200 µg mL-1 of phosphate and sulphate anions to give phosphate- and sulfate-modified adsorbents, respectively. The adsorption of four metal ions (Pb2+, Cd2+, Zn2+, and Cu2+) was studied as a function of metal ions concentration. The metal ions showed stronger affinity for the phosphate-modified adsorbent with Pb2+, Cu2+, Zn2+, and Cd2+ giving an average of 93.28%, 80.94%, 68.99%, and 61.44% uptake capacity. The order of preference for the various adsorbents shown by the metal ions was as follows: Pb2+>Cu2+>Zn2+>Cd2+. Desorption studies showed that the phosphate-modified adsorbent had the highest affinity for the metal ions, followed by the sulfate-modified clay while the unmodified clay had the least affinity. The experimental data were fitted by both the Langmuir and Freundlich models
- ItemSolid-state Isomerisation Reactions of (g5 -C5H4R)M(CO)2(PR3 0 )I (M ¼ W, Mo; R ¼ t Bu, Me; R0 ¼ Ph, Oi Pr3(2004-04-06) Adeyemi, OlalereThe cis and trans monosubstituted cyclopentadienyl tungsten and molybdenum complexes (g5-C5H4R)M(CO)2(L)I (1) (M¼ W, R ¼ Me, t Bu, L ¼ P(Oi Pr)3, PPh3; M ¼ Mo, R ¼ Me, L ¼ PPh3) have been synthesised and fully characterised by elemental analysis and IR and NMR spectroscopy. It was found that 1 underwent a thermal solid-state ligand isomerisation reaction and that the favoured direction of the isomerisation reaction is related to the melting points of the cis and trans isomers, i.e., with intermolecular forces in the solid state. No obvious relationship between the melting point and the metal, the ring-substituent or the ligand was observed. Crystal structure determinations of the cis and trans isomers of (g5-C5H4Me)W(CO)2(PPh3)I reveal that a limited amount of isomer conversion can be accommodated in the unit cell of the trans isomer, prior to crystal fragmentation. The rearrangement of the molecules within the unit cell, during isomerisation, also leads to disorder in the crystal
- ItemThe solid-state isomerization of cis and trans-(η5 -C5H4Me)Mo(CO)2(P(Oi Pr)3)I(2004-04-06) Adeyemi, OlalereThe cis and trans monosubstituted cyclopentadienyl tungsten and molybdenum complexes (g5-C5H4R)M(CO)2(L)I (1) (M¼ W, R ¼ Me, t Bu, L ¼ P(Oi Pr)3, PPh3; M ¼ Mo, R ¼ Me, L ¼ PPh3) have been synthesised and fully characterised by elemental analysis and IR and NMR spectroscopy. It was found that 1 underwent a thermal solid-state ligand isomerisation reaction and that the favoured direction of the isomerisation reaction is related to the melting points of the cis and trans isomers, i.e., with intermolecular forces in the solid state. No obvious relationship between the melting point and the metal, the ring-substituent or the ligand was observed. Crystal structure determinations of the cis and trans isomers of (g5-C5H4Me)W(CO)2(PPh3)I reveal that a limited amount of isomer conversion can be accommodated in the unit cell of the trans isomer, prior to crystal fragmentation. The rearrangement of the molecules within the unit cell, during isomerisation, also leads to disorder in the crystal.
- ItemRemoval of Lead from Aqueous Solution by Palm Kernel Fibre(SABINET, 2005) Unuabonah, EmmanuelThe sorption of lead on palm kernel fibre, an agricultural waste product, has been studied. The sorption process was studied as a function of initial lead concentration and initial solution pH. The percentage lead removal was found to increase with increasing initial solution pH up to pH 5 and then to decrease as pH was increased to 6. The pseudo-second order kinetic rate model was employed in the analysis of the kinetics of lead uptake onto the palm kernel fibre. The results show that the pseudo-second order model fits the experimental data with high coefficients of determination (r2). The equilibrium sorption capacity was found to be 33.33 mg g–1 when 1.0 g of fibre was contacted with 90 mg dm–3 of lead solution at pH 5. Mathematical expressions were derived to relate the pseudo-second order rate constant, k, and the change in solution pH with initial lead concentration.
- ItemQuantification of steric interactions in phosphine ligands from single crystal X-ray diffraction data. Crystal structures of (g5 -C5H4Me)Mo(CO)2(PR3)I (R3 = PhMe2, PhEt2, Et3)(2005-12-05) Adeyemi, OlalereDistorted square pyramidal complexes of molybdenum (g5 -C5H4Me)Mo(CO)2(PR3)I (R3 = PhMe2 (2a); PhEt2 (3a) and Et3 (4a)) have been synthesized and the structures of the lateral (cis) isomers have been determined by X-ray diffraction. The cone (H) and solid (X) angles as well as the angular profiles of the phosphine ligands in the complexes have been computed using the program STERIC. Values for the crystallographic cone and solid angles calculated for 2a, 3a and 4a are H (129 , 135 and 139 ) and X (2.73, 2.99 and 2.93 sr), respectively. A search of the Cambridge Structural Database (CSD) was made for piano stool, 5- and 6-coordinate complexes containing the title phosphine ligands. Results from this study show a wide range of sizes for each of the ligands and even the seemingly simple PPhMe2 ligand exhibited a wide range of values for the cone (113–137 ) and solid (2.49–3.07 sr) angles. These observations have been rationalized and related to the possible group conformations from the crystallographic data
- ItemThe Effect of some Operating Variables in the Adsorption of Lead and Cadmium ions unto Modified Kaolin Clay(Elsevier: Journal of Hazardous Materials, 2005-12-15) Unuabonah, EmmanuelModification of kaolinite clay mineral with orthophosphate (p-modified sample) enhanced adsorption of Pb and Cd ions from aqueous solutions of the metal ions. Increasing pH of solutions of metal ions, increasing adsorbent dose and increasing concentration of metal ion, increased the adsorption of metal ions. Adsorption of both metal ions simultaneously on both unmodified and p-modified samples indicates that adsorption of one metal ion is suppressed to some degree by the other. The presence of electrolyte and their increasing concentration reduced the adsorption capacities of both unmodified and p-modified samples for the metal ions. Ca-electrolytes had more negative effect on the adsorption capacities of the adsorbents than Na-electrolytes. Ca-electrolytes reduced adsorption capacities of the adsorbents for Pb and Cd ions. From Langmuir plots it was observed that these electrolytes increased the binding energy constant of the metal ions unto the adsorbents especially on the p-modified samples. The rate of adsorption of Pb and Cd ions on p-modified adsorbent were increased and equilibrium of metal ion solution were more quickly reached (8 min for Pb ions and 12 min for Cd ions) with p-modified adsorbent as against 20 min for adsorption of both metal ions on unmodified adsorbent when 200 mg/L of metal ion solutions were used during the kinetic studies. When adsorption data were fitted against Langmuir, Freundlich, Toth and Langmuir–Freundlich isotherms, satisfactory fits were found with the Freundlich isotherm. However, at low concentration of metal ions, data also showed satisfactory fits to Langmuir isotherm.
- ItemAdsorption of Lead and Cadmium Ions from Aqueous Solutions by Tripolyphosphate-Impregnated Kaolinite Clay(Elsevier, 2006-06) Unuabonah, EmmanuelThe pretreatment of Kaolinite clay with tripolyphosphate (TPP) increased the cation exchange capacity (CEC) of Kaolinite clay from 13.45 meq/100 g to 128.7 meq/100 g. The equilibrium adsorption capacity of TPP–Kaolinite clay for Pb2+ and Cd2+ was 126.58 mg/g and 113.64 mg/g, respectively. The presence of Na- and Ca-electrolytes and with increase in their concentrations reduced the selectivity of TPP–Kaolinite clay for Pb2+ than Cd2+. TPP–Kaolinite clay showed higher selectivity for Pb2+ in the presence of these electrolytes and at all concentrations of these electrolytes used for the study. Binary mixtures of Pb2+ and Cd2+ in various concentrations caused a decrease in the adsorption capacity of TPP–Kaolinite for either metal ion. However, this may have caused the adsorption of Cd2+ onto high energy sites on the surface of the TPP–Kaolinite clay. Non-linear Chi-square model analysis of adsorption data using Langmuir, Langmuir–Freudlich, Freudlich, Toth and Temkin isotherms reveals that the adsorption of Pb2+ and Cd2+ by TPP–Kaolinite clay were best described by the Toth and Freudlich isotherms, respectively. At low concentrations (≤500 mg/L) the adsorption of these metal ions showed better fits to the five models with Langmuir–Freudlich and Freudlich isotherms giving the best fits for Pb2+ and Cd2+, respectively.
- ItemKinetic and Thermodynamic Aspects of the Adsorption of Pb2+ and Cd2+ Ions on Tripolyphosphate-Modified Kaolinite Clay.(Elsevier: Chemical Engineering Journal, 2007) Unuabonah, EmmanuelKaolinite clay obtained from Ubulu-Ukwu, Delta state in Nigeria was modified with tripolyphosphate reagent to obtain TPP-modified Kaolinite clay. The kinetics and thermodynamics of the adsorption of Pb2+ and Cd2+ by TPP-Kaolinite clay were studied. Increasing temperature and initial metal ion concentration increased the sorption capacity of the adsorbent. The rates of adsorption of both Pb2+ and Cd2+ increased with increasing temperature but decreased with increasing initial metal ion concentration and time. The pseudo-second-order initial sorption rates for the sorption of Pb2+ were found to be higher than those of Cd2+. Pseudo-first-order model was found to only describe well, the data obtained in the first 8 min of the adsorption process. The sorption of both metal ions was endothermic and spontaneous with H◦ values of +13.94 kJ mol−1 and +24.93 kJ mol−1 for Pb2+ and Cd2+, respectively. Activation energy values obtained were between +8 kJ mol−1 and +22 kJ mol−1. These values suggest that the rate-controlling step in the adsorption of Pb2+ and Cd2+ by TPP-Kaolinite clay was diffusion-controlled. The sorption of metal ions from binary solutions of both metal ions at different initial metal ion concentrations reduced the initial sorption rates of the adsorption of Pb2+ by TPP-Kaolinite clay and increased that for Cd2+. The adsorption capacity of TPP-Kaolinite clay for both metal ions was also decreased by simultaneous presence of both metal ions.
- ItemKinetic and Thermodynamic Studies of the Adsorption of Lead (II) ions onto Phosphate-modified Kaolinite Clay(Elsevier, 2007) Unuabonah, EmmanuelThis study is on the kinetics and thermodynamics of the adsorption of Pb2+ onto phosphate-modified and unmodified kaolinite clay obtained from Ubulu-Ukwu in Delta State of Nigeria. Increasing initial Pb2+ concentration increased the rate of Pb2+ adsorbed with increase in initial Pb2+ concentration from 300 to 1000 mg/L. Increasing Pb2+ concentration also increased the initial sorption rate h, from 1.404 to 13.11 mg g−1 min−1 for phosphate-modified kaolinite clay and 1.04–3.48 for unmodified kaolinite clay as Pb2+ concentration. Increase in temperature was found to increase the initial sorption rate of Pb2+ adsorption onto phosphate-modified adsorbent from 3.940 to 8.85 and 2.55 to 4.16 mg g−1 min−1 for the unmodified adsorbent. The overall sorption rate k, increased only slightly from 5.1 × 10−2 to 9.7 × 10−2 g mg−1 min−1 for phosphate-modified adsorbent, 3.8 × 10−2 to 5.4 × 10−2 g mg−1 min−1 for unmodified adsorbent. The adsorption reaction on both adsorbents was found to be chemically activated reaction and endothermic with energy of activation, E, at 500 mg/L of Pb2+ in solution as 19 and 10.68 kJ mol−1 for phosphate-modified and unmodified adsorbents, respectively. The positive values of both H◦ and S◦ obtained suggest an endothermic reaction and in increase in randomness at the solid–liquid interface during the adsorption of Pb2+ onto the adsorbents. G◦ values obtained were all negative indicating a spontaneous adsorption process. The presence of Cd2+ decreased both initial sorption rate and the amount of Pb2+ adsorbed on phosphate-modified and unmodified adsorbents at equilibrium. The adsorption process follows a pseudo-second-order reaction scheme.
- ItemElectron-transfer Chain Catalysis in Phosphine Replacement Reaction: Determination of Relative Donor Capability of Arylpyridylphosphines(2007-01-20) Adeyemi, OlalereThe slight differences in the donor capabilities of PPhnPy3 n (n = 0–3) could be measured directly in the equilibrium of phosphine replacement reaction on (g5 -C5H5)Fe(CO)2-phosphine complexes, taking advantage of the radical pathway to establish equilibrium rap idly. The simultaneous determination of equilibrium constants is done in a single experiment. The donor capability increases in the order PPh3 < PPh2Py < PPhPy2 < PPy3 with quantified ðg5-C5H5ÞFeðCOÞ2 þ-affinity scales at 1, 4.90, 11.0, and 20.3, respectively. 2006 Elsevier B.V. All rights reserved
- ItemComparison of sorption of Pb2+ and Cd2+ on kaolinite clay and polyvinyl alcohol-modified kaolinite clay.(Elsevier, 2008) Unuabonah, EmmanuelKaolinite clay obtained from Ubulu-Ukwu, Delta state in Nigeria was modified with polyvinyl alcohol (PVA) reagent to obtain PVA-modified Kaolinite clay adsorbent. Scanning Electron Microscopy (SEM) of the PVA-modified adsorbent suggests that Kaolinite clay particles were made more compact in nature with no definite structure. Modification of Kaolinite clay with PVA increased its adsorption capacity for 300 mg/L Pb2+ and Cd2+ by a factor of at least 6, i.e., from 4.5 mg/g to 36.23 mg/g and from 4.38 mg/g to 29.85 mg/g, respectively, at 298 K. Binary mixtures of Pb2+ and Cd2+ decreased the adsorption capacity of Unmodified Kaolinite clay for Pb2+ by 26.3% and for Cd2+ by 0.07%, respectively. In contrast, for PVA-modified Kaolinite clay, the reductions were up to 50.9% and 58.5% for Pb2+ and Cd2+, respectively. The adsorption data of Pb2+ and Cd2+ onto both Unmodified and PVA-modified Kaolinite clay adsorbents were found to fit the Pseudo-Second Order Kinetic model (PSOM), indicating that adsorption on both surfaces was mainly by chemisorption and is concentration dependent. However, kinetic adsorption data from both adsorbent generally failed the Pseudo-First order Kinetic model (PFOM) test. Extents of desorption of 91% Pb2+ and 94% Cd2+ were obtained, using 0.1 M HCl, for the Unmodified Kaolinite clay adsorbent. It was found that 99% Pb2+ and 97% Cd2+, were desorbed, for PVA-modified Kaolinite clay adsorbents within 3 min for 60 mg/L of the metal ions adsorbed by the adsorbents.
- ItemAdsorption of Pb (II) and Cd (II) from Aqueous Solution onto Sodium Tetraborate-modified Kaolinite Clay: Equilibrium and Thermodynamic Studies(Elsevier, 2008) Unuabonah, EmmanuelKaolinite clay sample obtained from Ubulu-Ukwu in Delta State of Nigeria was modified with sodium tetraborate to obtain NTB-modified kaolinite clay. XRD measurements of NTB-modified kaolinite adsorbent showed no observable change in the d-spacing of its crystal lattice. Also, the data of XRD confirmed that this kaolinite clay sample is a mixture of kaolinite and Illite clay minerals. The SEM of modified and unmodified samples showed irregular crystal structures. FTIR results proved the surface modification of the kaolinite at –Al–O and –Si–O centers. The NTB-modified adsorbent presented with broader peaks of inner –OH. Modification of kaolinite clay sample with sodium tetraborate decreased its PZC from pH 4.40 to 3.70 while its Specific Surface Area (SSA) was increased from 10.56 m2 g−1 to 15.84 m2 g−1 . Modification with sodium tetraborate reagent increased the adsorption capacity of kaolinite clay from 16.16 mg/g to 42.92 mg/g for Pb (II) and 10.75 mg/g to 44.05 mg/g for Cd (II) at 298 K. Increasing temperature was found to increase the adsorption of both metals onto both adsorbents suggesting an endothermic adsorption reaction. The simultaneous presence of electrolyte in aqueous solution with Pb and Cd (II) was found to decrease the adsorption capacity of NTB-modified adsorbent for Pb and Cd (II). Using the Pearson's Hard and Soft Lewis Acid and Base (HSAB) theory the higher selectivity of unmodified kaolinite clay adsorbent for Pb and NTB-modified kaolinite clay for Cd (II) was justified. The thermodynamic calculations for the modified kaolinite clay sample indicated an endothermic nature of adsorption (ΔHmean + 4.35 kJ mol−1 for Pb(II) and +3.79 kJ mol−1 for Cd (II)) and an increase in entropy as a result of adsorption of Pb (II) and Cd (II) (ΔSmean −21.73 J mol−1 K for Pb (II) and −18.30J mol−1 K for Cd (II)). The small positive values of free energy change (ΔGmean) indicated that the adsorption of Pb (II) and Cd (II) onto the modified adsorbent may require some small amount of energy to make it more feasible. Modeling equilibrium adsorption data obtained suggested that NTB-modified adsorbent sample has homogeneous adsorption sites and fit very well with Langmuir adsorption model. Regeneration studies suggest that ≈85% of the metals were desorbed from both adsorbents. On reuse of the adsorbents only ≈80% of metals were adsorbed. NTB-modified kaolinite clay sample show some very good potentials as a low-cost adsorbent for the adsorption of Pb (II) and Cd (II) from aqueous solutions
- ItemRemoval of Lead and Cadmium from aqueous solution by Polyvinyl alcohol-modified Kaolinite clay: a novel nanoclay adsorbent.(Multi-Science Publishing Co. Ltd, 2008) Unuabonah, EmmanuelKaolinite clay was modified with polyvinyl alcohol (PVA) to obtain a PVA–nano-clay adsorbent. X-Ray diffraction measurements of the adsorbent showed no observable change in the d-spacing of its crystal lattice. Scanning electron microscopy of the PVA-modified nano-clay adsorbent indicated the presence of irregular crystal structures. Infrared spectroscopy suggested that the PVA–nano-clay adsorbent basically possessed outer –OH functional groups. This adsorbent was found to have an adsorption capacity of 56.18 mg/g for Pb2+ ions and 41.67 mg/g for Cd2+ ions. The adsorption data obtained was well explained by the Diffuse Layer Model (DLM), which implies that the adsorption of both metal ions onto the modified adsorbent was via an inner-sphere surface complexation mechanism. The ∆H0 values for the adsorption of both metal ions onto the PVA–nano-clay were –12.48 kJ/mol for Pb2+ ions and –13.49 kJ/mol for Cd2+ ions, with both ions exhibiting negative adsorption entropies. Data-fitting indicated that both the PVA–nano-clay and the unmodified adsorbent possessed homogeneous and heterogeneous adsorption sites. Virtually complete desorption (ca. 99%) of both metal ions occurred from PVA–nano-clay within 3 min.
- ItemEquilibrium, Kinetic and Sorber Design Studies on the Adsorption of Aniline Blue Dye by Sodium Tetraborate-modified Kaolinite Clay adsorbent.(Elsevier: Journal of Hazardous Materials, 2008-01) Unuabonah, EmmanuelRaw Kaolinite clay obtained Ubulu-Ukwu, Delta State of Nigeria and its sodium tetraborate (NTB)-modified analogue was used to adsorb Aniline blue dye. Fourier transformed infrared spectra of NTB-modified Kaolinite suggests that modification was effective on the surface of the Kaolinite clay with the strong presence of inner –OH functional group. The modification of Kaolinite clay raised its adsorption capacity from 1666 to 2000 mg/kg. Modeling adsorption data obtained from both unmodified and NTB-modified Kaolinite clay reveals that the adsorption of Aniline blue dye on unmodified Kaolinite clay is on heterogeneous adsorption sites because it followed strongly the Freundlich isotherm equation model while adsorption data from NTB-modified Kaolinite clay followed strongly the Langmuir isotherm equation model which suggest that Aniline blue dye was adsorb homogeneous adsorption sites on the NTB-modified adsorbent surface. There was an observed increase in the amount of Aniline blue adsorbed as initial dye concentration was increased from 10 to 30 mg/L. It was observed that kinetic data obtained generally gave better robust fit to the second-order kinetic model (SOM). The initial sorption rate was found to increased with increasing initial dye concentration (from 10 to 20 mg/L) for data obtained from 909 to 1111 mg kg−1 min−1 for unmodified and 3325–5000 mg kg−1 min−1 for NTB-modified adsorbents. Thereafter there was a decrease in initial sorption rate with further increase in dye concentration. The linearity of the plots of the pseudo-second-order model with very high-correlation coefficients indicates that chemisorption is involved in the adsorption process. From the design of a single-batch adsorber it is predicted that the NTB-modified Kaolinite clay adsorbent will require 50% less of the adsorbent to treat certain volumes of wastewater containing 30 mg/L of Aniline blue dye when it is compared with the unmodified adsorbent. This will be cost effective in the use of NTB-modified adsorbent for the adsorption of Aniline blue dye from water and wastewater.
- ItemFocus on Glucose: A World of Sugar(Green Chemistry Network, 2008-03-23) Oyetunde, TemidayoExploring the diverse possibilities from sugar as a biomolecular platform
- ItemNeighbouring Metal Induced Oxidative Addition at the Iron Centre amongst the Iron–arylpyridylphosphine Complexes(2008-05-06) Adeyemi, OlalereComplexes of the type (g4 -BuC5H5)Fe(CO)2(P) (P = PPh2Py 3, PPhPy2 4, PPy3 5; Py = 2-pyridyl) were sat isfactorily prepared. Upon treatment of 3 with M(CO)3(EtCN)3 (M = Mo, 6a; W, 6b), the pyridyl N-atom could be coordinated to the metal M, which then eliminates a CO ligand from the Fe-centre and induced an oxidative addition of the endo-C–H of (g4 -BuC5H5). This results in a bridged hydrido heterodimetallic complex [(g5 -BuC5H4)Fe(CO)(l-P,N-PPh2Py)(l-H)M(CO)4] (M = Mo, 7a, 81%; W, 7b, 76%). The reaction of 4 or 5 with 6a,b did not give the induced oxidative addition, although these complexes contain more than one pyridyl N-atom. The reaction of 4 with M(CO)4(EtCN)2 (M = Mo, 9a; W, 9b) produced heterodimetal lic complexes [(g4 -BuC5H5)Fe(CO)2(l-P:N,N0 -PPhPy2)M(CO)4] (M = Mo, 10a, 81%; W, 10b, 83%). Treat ment of 5 with 6a,b gave [(g4 -BuC5H5)Fe(CO)2(l-P:N,N0 ,N00-PPy3)M(CO)3] (M = Mo, 12a, 96%; W, 12b, 78%)
- ItemOptimization of Kinetic Data for Two-Stage Batch Adsorption of Pb(II) Ions onto Tripolyphosphate-Modified Kaolinite Clay.(Society of Chemical Industry, 2009) Unuabonah, EmmanuelMost adsorption studies consider only the adsorption of pollutants ontolow cost adsorbentswithout considering how equilibrium and kinetic data can be optimized for the proper design of adsorption systems. This study considers the optimization of kinetic data obtained for the removal of Pb(II) from aqueous solution by a tripolyphosphate modified kaolinite clay adsorbent. Modification of kaolinite clay with pentasodium tripolyphosphate increases its cation adsorption capacity (CEC) and specific surface area (SSA) from 7.81 to 78.9 meq (100 g)−1 and 10.56 to 13.2 m2 g−1 respectively. X-ray diffraction patterns for both unmodified and tripolyphosphate-modified kaolinite clay suggest the modification is effective on the surface of the clay mineral. Kinetic data from the batch adsorption of Pb(II) onto the tripolyphosphate-modified kaolinite clay adsorbent were optimized to a two-stage batch adsorption of Pb(II) using the pseudo-second-order kinetic model. Mathematical model equations were developed to predict the minimum operating time for the adsorption of Pb(II). Results obtained suggest that increasing temperature and decreasing percentage Pb(II) removal by the adsorbent enhanced operating time of the adsorption process. The use of two-stage batch adsorption reduces contact time to 6.7 min from 300 min in the single-stage batch adsorption process for the adsorption of 2.5 m3 of 500 mg L−1 Pb(II) under the same operating conditions. Results show the potential of a tripolyphosphate-modified kaolinite clay for the adsorption of Pb(II) from aqueous solution and the improved efficiency of a two-stage batch adsorption process for the adsorption of Pb(II) even at increased temperature.