Tareque Odoom-Wubah

Adsorption of anionic and cationic dyes on ferromagnetic ordered mesoporous carbon from aqueous solution: Equilibrium, thermodynamic and kinetics

Ordered mesoporous carbon (Fe-CMK-3) with iron magnetic nanoparticles was prepared by a casting process via SBA-15 silica as template and anthracene as carbon source, was used as a magnetic adsorbent for the removal of anionic dye Orange II (O II) and cationic dye methylene blue (MB) from aqueous solution. TEM and magnetometer images showed that the iron magnetic nanoparticles were successfully embedded in the interior of the mesoporous carbon. The effect of various process parameters such as temperature (25-45°C), initial concentration (100-500 mg L(-1)) and pH (2-12) were performed. Equilibrium adsorption isotherms and kinetics were also studied. The equilibrium experimental data were analyzed by the Langmuir, Freundlich, Temkin and Redlich-Peterson model. The equilibrium data for two dyes adsorption was fitted to the Langmuir, and the maximum monolayer adsorption capacity for O II and MB dyes were 269 and 316 mg g(-1), respectively. Pseudo-first-order and pseudo-second-order kinetic and intraparticle diffusion model were used to evaluate the adsorption kinetic data. The kinetic data of two dyes could be better described by the pseudo second-order model. Thermodynamic data of the adsorption process were also obtained. It was found that the adsorption process of the two dyes were spontaneous and exothermic.

Plant-mediated synthesis of platinum nanoparticles and its bioreductive mechanism.

Pt nanoparticles (PtNPs) were biologically synthesized by reducing Na2PtCl4 with Cacumen Platycladi Extract (CPE). The effects of reaction temperature, initial Pt(II) concentration, and CPE percentage on Pt(II) conversion and the size distribution of the PtNPs were studied. The results showed that the Pt(II) conversion rate reached 95.9% and that PtNPs measuring 2.4±0.8nm were obtained under the following conditions: reaction temperature, 90°C; CPE percentage, 70%; initial Pt(II) concentration, 0.5mM; reaction time, 25h. In addition, the bioreduction of Pt(II) was attributed to reducing sugars and flavonoids rather than proteins. The elucidation of bioreductive mechanism of Pt(II) ions was achieved by investigating the changes that occurred in the reducing sugar, flavonoid and protein concentrations in the plant extract, leading to a good insight into the formation mechanism of such biosynthesized PtNPs.

Fabrication of Au/Pd alloy nanoparticle/Pichia pastoris composites: a microorganism-mediated approach

Synthesis of metal nanoparticles (NPs) is in the limelight in modern nanotechnology. In this present study, bimetallic Au/Pd NP/Pichia pastoris composites were successfully fabricated through a one-pot microbial reduction of aqueous HAuCl4 and PdCl2 in the presence of H2 as an electron donor. Interestingly, flower-like alloy Au/Pd NP/Pichia pastoris composites were obtained under the following conditions, NaCl concentration 0.9% (w/v), molar ratio of Au/Pd (1:2) and the time for pre-adsorption of Au(III) and Pd(II) ions 15 min, through fresh yeast reduction. The mapping results from scanning transmission electron microscopy (STEM) with a high-angle annular dark field detector confirmed that the Au/Pd NPs on the surface of the yeast were indeed alloy. Furthermore, the energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements showed that the composition of the bimetallic NPs were consistent with the initial molar ratio of the precursors.

Facile fabrication of Pd nanoparticle/Pichia pastoris catalysts through adsorption-reduction method: A study into effect of chemical pretreatment

Based on rapid adsorption and incomplete reduction in Pd (II) ions by yeast, Pichia pastoris (P. pastoris) GS115, the effects of pretreatment on adsorption and reduction of Pd (II) ions and the catalytic properties of Pd NP/P. pastoris catalysts were studied. Interestingly, the results showed that the adsorption ability of the cells for Pd (II) ions was greatly enhanced after they were pretreated with aqueous HCl, aqueous NaOH and methylation of amino group. For the reduction in the adsorbed Pd (II) ions, more slow reduction rates by pretreated P. pastoris cells were displayed compared with the cells without pretreatment. Using the reduction of 4-nitrophenol as a model reaction, the Pd NP/P. pastoris catalysts based on the cells after pretreatment with aqueous HCl, aqueous NaOH and methylation of amino group exhibited higher stability than the unpretreated cells. The enhanced stability of the Pd catalysts can be attributed to smaller Pd NPs, better dispersion of the Pd NPs, and stronger binding forces of the pretreated P. pastoris for preparing the Pd NPs. This work exemplifies enhancing the stability of Pd catalysts through pretreatments.

Catalytic Application of Biogenic Platinum Nanoparticles for the Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol

Pt catalysts and Co doped Pt catalysts with TiO2 as the support were prepared by the sol immobilization method based on biological synthesis process, whereby Pt nanoparticles (PtNPs) were reduced from Na2PtCl4 using Cacumen Platycladi extract (CPE). The catalytic performance of the catalysts was studied using hydrogenation of cinnamaldehyde as the model reaction. For comparison, Co doped Pt/catalysts were also prepared by traditional impregnation method, TEM observation, and XRD measurement were carried out to characterize the catalysts. The effects of different Pt loadings and Co doping amounts were investigated. The results showed that the PtNPs could be well dispersed onto the TiO2 support with narrow size distribution between 4 and 6 nm. 1.0% was observed as the optimal Pt loading amount in our experiments showing a cinnamaldehyde conversion of 73.3% with 68.8% selectivity to cinnamyl alcohol. A proper Co doping amount was also essential to the catalytic performance of the prepared Pt/catalysts as well as a favorable for the reaction process, 1.0% doping amount showed the best activity in which a 70.4% conversion and 88.3% selectivity was achieved. Recyclability tests carried out revealed that the 1.0 Co–1.0 Pt/TiO2 catalysts possessed possessing good durability. In this work, Co-Pt/TiO2 catalysts prepared by the sol immobilization method based on biological reduction process, showed better selectivity than that from traditional impregnation method.

Plant-mediated synthesis of ZnO supported Ni-Pd alloy catalyst for the selective hydrogenation of 1, 3-butadiene

We report the green synthesis of ZnO‐supported Ni‐Pd alloy nanoparticles for the gas‐phase selective hydrogenation of 1,3‐butadiene. The supported catalysts were synthesized through a simple bioreduction route using Cinnamomum Camphora leaf extract. We used XRD, SEM, TEM, and energy‐dispersive X‐ray spectroscopy to characterize and verify the nature of the catalysts. The results showed that the size of the Ni‐Pd alloy particles was (3.2±0.7), (3.4±0.3), and (3.8±0.6) nm for Ni1Pd1, Ni1Pd3, and Ni3Pd1 respectively. FTIR spectroscopy revealed that the presence of stretching vibrations from C−H, −C=C−, O−H, and −C−O−O groups that remained on the surface and act as stabilizers. The influence of some reaction variables, such as the type of S‐Pd (S=Au, Ag, Ni) bimetallic catalyst, the type of metal oxide support, and the reaction temperature, on the hydrogenation activity and selectivity towards total butene (trans‐2‐butene, 1‐butene, and cis‐2‐butene) is investigated. The bioreduced, supported catalysts showed excellent catalytic activity and selectivity to butene in the selective hydrogenation of 1,3‐butadiene. The calculated total butene selectivity was above 80 % for all supported S1‐Pd1 catalysts compared to 46.92 % for a monometallic Pd/ZnO catalyst. In addition, the Ni1‐Pd1/ZnO catalyst presented the best butene yield of 88.90 %, which was 1.9 times that of the Pd/ZnO catalyst. Moreover, it remained stable over a 10 h durability experiment.

Biosynthesis of Ag–Pd bimetallic alloy nanoparticles through hydrolysis of cellulose triggered by silver sulfate

We report a simple but efficient biological route based on the hydrolysis of cellulose to synthesize Ag–Pd alloy nanoparticles (NPs) under hydrothermal conditions. X-ray powder diffraction, ultraviolet-visible spectroscopy and scanning transmission electron microscopy-energy dispersive X-ray analyses were used to study and demonstrate the alloy nature. The microscopy results showed that well-defined Ag–Pd alloy NPs of about 59.7 nm in size can be biosynthesized at 200 °C for 10 h. Fourier transform infrared spectroscopy indicated that, triggered by silver sulfate, cellulose was hydrolyzed into saccharides or aldehydes, which served as both reductants and stabilizers, and accounted for the formation of the well-defined Ag–Pd NPs. Moreover, the as-synthesized Ag–Pd nanoalloy showed high activity in the catalytic reduction of 4-nitrophenol by NaBH4.

One-Step Synthesis of Au-Ag Nanowires through Microorganism-Mediated, CTAB-Directed Approach

Synthesis and applications of one dimensional (1D) metal nanostructures have attracted much attention. However, one-step synthesis of bimetallic nanowires (NWs) has remained challenging. In this work, we developed a microorganism-mediated, hexadecyltrimethylammonium bromide (CTAB)-directed (MCD) approach to synthesize closely packed and long Au-Ag NWs with the assistance of a continuous injection pump. Characterization results confirmed that the branched Au-Ag alloy NWs was polycrystalline. And the Au-Ag NWs exhibited a strong absorbance at around 1950 nm in the near-infrared (NIR) region, which can find potential application in NIR absorption. In addition, the Au-Ag NWs showed excellent surface-enhanced Raman scattering (SERS) enhancement when 4-mercaptobenzoic acid (MBA) and rhodamine 6G (R6G) were used as probe molecules.

Synthesis, Characterization, and Sintering of Yttrium Aluminum Garnet Powder Through Double Hydrolysis Approach

A double hydrolysis approach is first adopted to prepare yttrium aluminum garnet (YAG) powders using Y(NO3)3 · 6H2O and NaAlO2 as raw materials. A variety of techniques, such as thermogravimetry/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to characterize the as-synthesized samples. The results show that pure-phase YAG powders are accurately available at 900 °C and above. Among these, the YAG powders, produced at 1100°C, are elliptic in shape, with an average particle size of ~44 nm. Pellets of pressed YAG powders are sintered in vacuum at 1700°C for 8 h, resulting in a dense and nearly pore-free microstructure with an average grain size of ~7 μm.

Simple method for synthesizing aluminum-yttrium garnet (Nd:YAG) nanopowders by flushing (bubbling) with ammonia

A simple method is developed for synthesizing nanopowder of neodymium-doped yttrium aluminum garnet (Nd:YAG) by coprecipitation with flushing (bubbling) by ammonia. Different methods are used to study the specimens obtained, such as thermogravimetry/differential scanning calorimetry, X-ray powder diffraction, infrared spectroscopy based on a Fourier transform, scanning electron microscopy. Results show that stoichiometric Nd:YAG powders may be prepared by calcination of a precursor at 900°C for 2 h. In addition, it is detected that a slow ammonia supply rate (5 – 10 ml/min) is favorable for forming Nd:YAG powders with a good structure and with an average particle size of ~70 nm. The technology developed by us does not use manual titration for synthesizing multibasic oxides, as a result of which this technology may be readily used on an industrial scale.