Showing papers by "Tewodros Asefa published in 2016"
TL;DR: A critical appraisal of different synthetic approaches to Cu and Cu-based nanoparticles and copper nanoparticles immobilized into or supported on various support materials (SiO2, magnetic support materials, etc.), along with their applications in catalysis.
Abstract: The applications of copper (Cu) and Cu-based nanoparticles, which are based on the earth-abundant and inexpensive copper metal, have generated a great deal of interest in recent years, especially in the field of catalysis. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. In addition, the design and development of novel support and/or multimetallic systems (e.g., alloys, etc.) has also made significant contributions to the field. In this comprehensive review, we report different synthetic approaches to Cu and Cu-based nanoparticles (metallic copper, copper oxides, and hybrid copper nanostructures) and copper nanoparticles immobilized into or supported on various support materials (SiO2, magnetic support materials, etc.), along with their applications i...
1,823 citations
TL;DR: It is shown that efficient charge injection and the presence of naturally occurring sulfur vacancies are responsible for the observed increase in catalytic activity of the 2H basal planes of monolayer MoS2 nanosheets.
Abstract: The excellent catalytic activity of metallic MoS2 edges for the hydrogen evolution reaction (HER) has led to substantial efforts towards increasing the edge concentration. The 2H basal plane is less active for the HER because it is less conducting and therefore possesses less efficient charge transfer kinetics. Here we show that the activity of the 2H basal planes of monolayer MoS2 nanosheets can be made comparable to state-of-the-art catalytic properties of metallic edges and the 1T phase by improving the electrical coupling between the substrate and the catalyst so that electron injection from the electrode and transport to the catalyst active site is facilitated. Phase-engineered low-resistance contacts on monolayer 2H-phase MoS2 basal plane lead to higher efficiency of charge injection in the nanosheets so that its intrinsic activity towards the HER can be measured. We demonstrate that onset potentials and Tafel slopes of ∼-0.1 V and ∼50 mV per decade can be achieved from 2H-phase catalysts where only the basal plane is exposed. We show that efficient charge injection and the presence of naturally occurring sulfur vacancies are responsible for the observed increase in catalytic activity of the 2H basal plane. Our results provide new insights into the role of contact resistance and charge transport on the performance of two-dimensional MoS2 nanosheet catalysts for the HER.
639 citations
TL;DR: In this article, the synthesis of ultrathin nanosheet-based, hollow MoOx/Ni3S2 composite microsphere catalysts on nickel foam, using ammonium molybdate as a precursor and the triblock copolymer pluronic P123 as a structure-directing agent is reported.
Abstract: Making highly efficient catalysts for an overall water splitting reaction is vitally important to bring solar/electrical-to-hydrogen energy conversion processes into reality. Herein, the synthesis of ultrathin nanosheet-based, hollow MoOx/Ni3S2 composite microsphere catalysts on nickel foam, using ammonium molybdate as a precursor and the triblock copolymer pluronic P123 as a structure-directing agent is reported. It is also shown that the resulting materials can serve as bifunctional, non-noble metal electrocatalysts with high activity and stability for the hydrogen evolution reaction (HER) as well as the oxygen evolution reaction (OER). Thanks to their unique structural features, the materials give an impressive water-splitting current density of 10 mA cm−2 at ≈1.45 V with remarkable durability for >100 h when used as catalysts both at the cathode and the anode sides of an alkaline electrolyzer. This performance for an overall water splitting reaction is better than even those obtained with an electrolyzer consisting of noble metal-based Pt/C and IrOx/C catalytic couple—the benchmark catalysts for HER and OER, respectively.
426 citations
TL;DR: In this article, the synthesis of magnetic activated carbons via simultaneous activation and magnetization processes using carbonized biomass waste from coconut shells (Cb's) and FeCl3·6H2O as precursor is reported.
Abstract: The development of advanced carbon nanomaterials that can efficiently extract pollutants from solutions is of great interest for environmental remediation and human safety. Herein we report the synthesis of magnetic activated carbons via simultaneous activation and magnetization processes using carbonized biomass waste from coconut shells (Cb’s) and FeCl3·6H2O as precursor. We also show the ability of the materials to efficiently extract toxic organic dyes from solutions and their ease of separation and recovery from the solutions using a simple bar magnet. Textural characterization shows that the materials are microporous. Further analyses of the deconvoluted XPS spectra and X-ray diffraction patterns reveal that the materials possess magnetite, maghemite and hematite. SEM and TEM images show that an increase in the ratio of FeCl3·6H2O:Cb leads to an increase in the material’s magnetic properties. The point of zero charge (pHpzc) indicates that the materials have acidic characteristics. Adsorption kineti...
227 citations
TL;DR: In this Account, notable heteroatom-doped carbon catalysts that have been developed for reactions in fuel cells and water electrolyzers, the various synthetic procedures employed to make them, and the challenges involved in their synthesis as well as their characterizations are discussed.
Abstract: ConspectusThe large-scale deployment of many types of fuel cells and electrolyzers is currently constrained by the lack of sustainable and efficient catalysts that can replace the less earth-abundant, noble metal-based catalysts, which are commonly used in these renewable energy systems. This burgeoning issue has led to explosive research efforts worldwide to find alternative, metal-free and noble metal-free catalysts that are composed of inexpensive and earth-abundant elements. Hence, the recent discoveries that doping carbon nanomaterials with heteroatoms (such as N, S, B, etc.) can give sustainable materials with good electrocatalytic activity for reactions carried out in fuel cells and electrolyzers have been not only quite exciting but also very promising to address these challenging issues. Interestingly, even though they contain no metals or involve only the inexpensive, more earth-abundant ones, the catalytic activity of some of these materials fares well with those of the commercially used noble ...
178 citations
TL;DR: In this paper, a comprehensive review of different synthetic approaches to copper and copper-based nanoparticles (metallic copper, copper oxides, and hybrid copper nanostructures) and their applications is presented.
Abstract: The applications of copper (Cu) and Cu-based nanoparticles, which are based on the earth-abundant and inexpensive copper metal, have generated a great deal of interest in recent years, especially in the field of catalysis. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. In addition, the design and development of novel support and/or multimetallic systems (e.g., alloys, etc.) has also made significant contributions to the field. In this comprehensive review, we report different synthetic approaches to Cu and Cu-based nanoparticles (metallic copper, copper oxides, and hybrid copper nanostructures) and copper nanoparticles immobilized into or supported on various support materials (SiO2, magnetic support materials, etc.), along with their applications i...
151 citations
TL;DR: In this paper, the synthesis of N-S-doped mesoporous carbon (NSMC) using bone char (BC) as template and heteroatoms precursor was evaluated through a synthesis of a material without the use of BC.
54 citations
TL;DR: A template-free solid-state synthesis of a morphologically controlled and highly organized iron(III)oxide micro-mesoporous Fenton catalyst has been engineered through a simple two-step synthetic procedure.
Abstract: A template-free solid-state synthesis of a morphologically controlled and highly organized iron(III)oxide micro–mesoporous Fenton catalyst has been engineered through a simple two-step synthetic procedure. The 3D nanoassembly of hematite nanoparticles (5–7 nm) organized into a rod/flower-like morphology shows the highest rate constant reported to date for the decomposition of H2O2 (1.43 × 10−1 min−1) with superior efficiency for the degradation of aromatic (phenol, benzene, ethylbenzene) and chlorinated (trichloroethylene) pollutants in contaminated water. The morphological arrangement of nanoparticles is therefore considered one of the key variables that drive catalysis.
44 citations
TL;DR: Nitrogen and oxygen co-doped mesoporous carbons that can serve as metal-free electrocatalysts are synthesized via a novel synthetic route using milled rice as a precursor and colloidal silica as a template to electrocatalyst the hydrazine oxidation reaction with only a small onset potential.
40 citations
TL;DR: The synthesis of monodisperse, polyaniline (PANI)-derived mesoporous carbon nanoparticles (PAMCs) that can serve as efficient metal-free electrocatalysts for the hydrogen peroxide reduction reaction (HPRR) as well as the oxygen reduction Reaction (ORR) in fuel cells.
Abstract: In our quest to make various chemical processes sustainable, the development of facile synthetic routes and inexpensive catalysts can play a central role. Herein we report the synthesis of monodisperse, polyaniline (PANI)-derived mesoporous carbon nanoparticles (PAMCs) that can serve as efficient metal-free electrocatalysts for the hydrogen peroxide reduction reaction (HPRR) as well as the oxygen reduction reaction (ORR) in fuel cells. The materials are synthesized by polymerization of aniline with the aid of (NH4)2S2O8 as oxidant and colloidal silica nanoparticles as templates, then carbonization of the resulting PANI/silica composite material at different high temperatures, and finally removal of the silica templates from the carbonized products. The PAMC materials that are synthesized under optimized synthetic conditions possess monodisperse mesoporous carbon nanoparticles with an average size of 128 ± 12 nm and an average pore size of ca. 12 nm. Compared with Co3O4, a commonly used electrocatalyst for...
39 citations
TL;DR: A facile synthetic route is presented that produces a porous Ga-In bimetallic oxide nanophotocatalyst with atomically thin pore walls that exhibits superior photocatalytic activity toward the hydrogen evolution reaction (HER).
Abstract: A facile synthetic route is presented that produces a porous Ga-In bimetallic oxide nanophotocatalyst with atomically thin pore walls. The material has an unprecedented electronic structure arising from its ultrathin walls. The bottom of the conduction band and the top of the valence band of the material are distributed on two opposite surfaces separated with a small electrostatic potential difference. This not only shortens the distance by which the photogenerated charges travel from the sites where they are generated to the sites where they catalyze the reactions, but also facilitates charge separations in the material. The porous structure within the walls results in a large density of exposed surface reactive/catalytic sites. Because of these optimized electronic and surface structures, the material exhibits superior photocatalytic activity toward the hydrogen evolution reaction (HER).
TL;DR: In this paper, the authors used cellulose filter paper both as a precursor and a self-template for the synthesis of nanoporous carbon electrocatalysts for the hydrazine oxidation reaction (HOR).
TL;DR: The in situ synthesis of silver nanoparticles (AgNPs) within covalently-modified poly(ethylene terephthalate) (PET) films possessing ultra-thin layer of PVA and PAA is successfully demonstrated and can be used for producing plastic surfaces with versatile antimicrobial and antibacterial properties.
TL;DR: It was evaluated the influence of the graphitic organization on the general properties and nickel was found as the more appropriate metal since it leads to a more organized material and also to a high activity toward HER.
TL;DR: In this article, a new use for BCA is presented, where a highly sensitive method for detection of cyanide ions in solutions by using Cu 2+ -BCA complex as the chemosensing agent is demonstrated.
Abstract: Bicinchoninic acid (BCA) is reagent that is widely used to determine the concentration of proteins in solutions through the colored complex it forms with Cu(I) and the proteins In this report, we present a new use for BCA, where a highly sensitive method for detection of cyanide ions in solutions by using Cu 2+ –BCA complex as the chemosensing agent is demonstrated The detection of cyanide ions is achieved by taking advantage of the nucleophilic attack of the Cu 2+ –BCA complex by cyanide ions Upon the addition of cyanide ions, the Cu 2+ –BCA complex undergoes transformations to free BCA via a series of equilibriums and, as a result, forms different Cu(II)–(BCA) x (CN) y species depending on the concentrations of cyanide ions in the solution These different Cu(II)–(BCA) x (CN) y species, in turn, give different metal-to-ligand charge transfer electronic spectra and colors that are easily detectable both with naked eyes and UV–vis spectroscopy As the cyanide ion concentration increases, the color of the solution containing the complexes changes from green to purple, red, yellow, and finally colorless, giving a corresponding blue shift in the absorption maxima on their UV–vis spectra Through this process, the complexes enable detection of cyanide ions with a detection level of up to 006 ppm in solutions Thus, this colorimetric technique based on Cu 2+ –BCA can make low concentrations of cyanide detectable, well before the concentrations possibly reach lethal amounts Furthermore, the method is shown to give fast detection response with no interference from other anionic and cationic species and has the potential to be adopted for accurate and convenient analysis of cyanide ions in drinking water sources as well as industrial effluents
TL;DR: The high-resolution TEM, SEM/EDX, UV-vis and XRD studies confirmed the homogeneous distribution of crystalline nanoparticles of circa 4’nm and their aggregates of 10-20 nm and have a potential to be employed in sensing, optoelectronics and catalysis.
Abstract: This study describes a novel approach for the in situ synthesis of metal oxide–polyelectrolyte nanocomposites formed via impregnation of hydrated polyelectrolyte films with binary water/alcohol solutions of metal salts and consecutive reactions that convert metal cations into oxide nanoparticles embedded within the polymer matrix. The method is demonstrated drawing on the example of Nafion membranes and a variety of metal oxides with an emphasis placed on zinc oxide. The in situ formation of nanoparticles is controlled by changing the solvent composition and conditions of synthesis that for the first time allows one to tailor not only the size, but also the nanoparticle shape, giving a preference to growth of a particular crystal facet. The high-resolution TEM, SEM/EDX, UV-vis and XRD studies confirmed the homogeneous distribution of crystalline nanoparticles of circa 4 nm and their aggregates of 10–20 nm. The produced nanocomposite films are flexible, mechanically robust and have a potential to be employed in sensing, optoelectronics and catalysis.
15 Mar 2016
TL;DR: It is found that cell viability is related to pore size, where 2D nanoporous structure is more beneficial for cell culture than 2D microporous structures.
Abstract: A facile and reproducible route that can lead to two-dimensional arrays of nanopores in thin polymer films is demonstrated. The formation of the pores in the polymer films involves breath figure phenomenon and occurs during the film deposition by spin coating. The formation of nanoporous thin films takes only few seconds, and the method does not require complex equipment or expensive chemicals. This method also constitutes a straightforward approach to control the size of the pores formed in thin films. Besides allowing control over the average pore size of the porous films, the use of dynamic deposition with the breath figure phenomenon causes the reduction in the pore size to nanometer scale. The nanoporous arrays obtained by the breath figure are applied as substrates for cell growth, and the effect of their nanopore size on cell growth was evaluated. Notably, it is found that cell viability is related to pore size, where 2D nanoporous structure is more beneficial for cell culture than 2D microporous structures. The change in the average pore size of the polymer films from 1.22 μm to 346 nm results in a threefold increase in cell viability.
TL;DR: Novel, hierarchically nanostructured, star-shaped ZnO (SSZ) microparticles are synthesized by a hydrothermal synthetic route and serve as effective platforms for electrochemical detection of amines in solution.
Abstract: Novel, hierarchically nanostructured, star-shaped ZnO (SSZ) microparticles are synthesized by a hydrothermal synthetic route. The SSZ microparticles serve as effective platforms for electrochemical detection of amines in solution. The morphology and structure of the materials are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and UV/Vis spectroscopy. The as-synthesized SSZ microparticles comprise self-assembled hexagonal prisms that possess nanometer and micrometer pores in their structure and on their surfaces-structural features that are conducive to sensing applications. An electrode fabricated by using the hierarchically nanostructured SSZ materials serve as a sensitive electrochemical sensor for detection of low concentrations of ethylenediamine, with a sensitivity of 2.98×10(-2) mA cm(-2) mm(-1) , a detection limit of 2.36×10(-2) mm, and a short response time of 8 s.
TL;DR: Graphene-doped zinc oxide with column-like morphology was synthesized by an in-situ hydrothermal method and its gas-sensing properties were then studied as mentioned in this paper.
TL;DR: In this article, hollow core/shell carbon microparticles are synthesized from yeast cells by coating the cells with silica shells, and then pyrolyzing the silica-protected yeast cells at 600 °C, and finally etching the shells off of the carbonized products.
Abstract: Hollow core/shell carbon microparticles, denoted HCSC600, are synthesized from yeast cells by coating the cells with silica shells, and then pyrolyzing the silica-protected yeast cells at 600 °C, and finally etching the silica shells off of the carbonized products. The microparticles possess a yolk/shell structure with very large interior hollow spaces and interconnected porous structures—structural features that are generally useful for adsorption and release of drug molecules. The microparticles are characterized by various methods, including scanning electron microscopy, transmission electron microscopy, nitrogen gas adsorption/desorption and X-ray photoelectron spectroscopy. Their adsorption properties are evaluated by using rhodamine B (RhB) as a model drug and the poorly soluble drug fenofibrate (FFB), a prodrug of fenofibric acid, which is widely used to treat hypertriglyceridemia. Compared with the control material prepared from yeast cells without silica coating (named YCC600), the HCSC microparticles showed much higher adsorption capacity for both compounds, suggesting that the silica coating is important not only for controlling the morphology of the particles but also for giving them high surface area. Furthermore, it is found that the HCSC600 material loaded with FFB allows the drug molecules to be released faster and better than they are from the bulk drug. The results indicate that HCSC microparticles have great potential to serve as drug delivery vehicles, especially for poorly bioavailable drugs such as FFB, for biomedical applications.
Patent•
13 May 2016TL;DR: A multi-catalytic material that includes a polyelectrolyte membrane and methods of preparing the same are provided in this paper, where the authors also present a method for preparing the membrane.
Abstract: A multi-catalytic material that includes a polyelectrolyte membrane and methods of preparing the same are provided herein.