Edman Tsang

Bio: Edman Tsang is an academic researcher from University of Oxford. The author has contributed to research in topics: Catalysis & Chemistry. The author has an hindex of 6, co-authored 8 publications receiving 107 citations.

Chapter 5 Chemical Methods for Preparation of Nanoparticles in Solution

Abstract: The technology for synthesis of nanomaterials with defined dimensions, structure and composition is one of the most important pre-requisite criteria before new applications such as bio-separation, drug delivery, imaging, catalysis, sensing and data storage can be systematically studied. Chemical synthesis represents a key approach for the production of materials, which generally involves a number of steps taking place in liquid or gas phase. The formation of atoms can be accomplished by using chemical reaction(s) under controlled but mild reaction conditions. Thus, freshly formed atoms can then undergo elementary nucleation followed by growth processes leading to the formation of defined nanoparticles. This chapter will highlight some common chemical methodologies for the synthesis of metal and metal core-shell nanoparticles with particular emphasis on the important roles of solvent, capping agent, additive and stabilizer for kinetic controls of tailored nanomaterials.

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl-KCl Eutectics.

Abstract: Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3- with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl-KCl-Li3 N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3- to NH3 is grossly over-simplified. We find that Li3 N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H- (H oxidation state -1) and H+ in the form of NH2- /NH2 - /NH3 (H oxidation state +1) in the absence of applied current, resulting in non-Faradaic release of NH3 . It is further observed that NH2- and NH2 - possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3 N, N2 can be reduced to N3- while stoichiometric amounts of H- are oxidised to H2 . The H2 can then react spontaneously with N3- to form NH3 , regenerating H- and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10-8 mol cm-2 s-1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15 N2 confirms the resulting NH3 is from catalytic N2 reduction.

2D MOF with Compact Catalytic Sites for the One‐pot Synthesis of 2,5‐Dimethylfuran from Saccharides via Tandem Catalysis

Abstract: Abstract One pot synthesis of 2,5‐dimethylfuran (2,5‐DMF) from saccharides under mild conditions is of importance for the production of biofuel and fine chemicals. However, the synthesis requires a multitude of active sites and suffers from slow kinetics due to poor diffusion in most composite catalysts. Herein, a metal‐acid functionalized 2D metal‐organic framework (MOF; Pd/NUS‐SO3H), as an ultrathin nanosheet of 3–4 nm with Lewis acid, Brønsted acid, and metal active sites, was prepared based on the diazo method for acid modification and subsequent metal loading. This new composite catalyst gives substantially higher yields of DMF than all reported catalysts for different saccharides (fructose, glucose, cellobiose, sucrose, and inulins). Characterization suggests that a cascade of reactions including polysaccharide hydrolysis, isomerization, dehydration, and hydrodeoxygenation takes place with rapid molecular interactions.

The Applications of Nano-Hetero-Junction in Optical and Thermal ­Catalysis

Abstract: Semiconductors, metal oxides in particular, are usually regarded as key components in most industrial catalysts. It has been reported that the band structures of semiconductors can significantly influence their catalytic properties. As one of the most effective methods for tuning the band structure of semiconductors, the establishment of nano-hetero-junctions in catalysts is attracting increasing attention due to the use of rational design and the facile synthesis procedure. This Microreview covers the applications of nano-hetero-junctions in both photocatalytic and traditional thermal catalytic reactions. The applications of these reactions range from removal of pollutants to renewable energy production to new chemical synthesis routes, all of which are closely knitted into our daily lives. In photocatalysis, improvement is mainly attributed to the separation of photogenerated electrons and holes, which prolongs their lifetimes and eventually allows the occurrence of chemical reactions with adsorbed substrate molecules. Our research group were amongst the first to apply this concept in the design of metal/metal oxide catalysts in traditional thermal catalysis. It has been found that the establishment of electronic nano-hetero-junctions in support materials with use of two semiconducting metal oxides of different energy levels influences the catalytic properties of the dispersed metal particles from two perspectives: (i) the potential energy upon excitation, created by the charge separation on semiconducting oxide support in proximity to the overlying metal particles, and (ii) under H2, the accumulated electrons on one semiconducting oxide support can facilitate direct reduction of metal cations in this support to metal atoms, while the accumulated holes (activated oxygen) on the other semiconducting oxide are relaxed by water formation through hydrogen oxidation. The metallic atoms from the support surface thus act as modifiers to the primary metal particles through the formation of a bimetallic phase. As a result, the electronic configuration of the supported metal particles can be modified in a subtle manner that consequently influences the catalytic performance. It is believed that this concept of designing nano-hetero-junctions should empower scientists to approach new catalytic reactions in a systematic manner, allowing fine-tuning of catalysts with superior performance.

A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements

Abstract: The electrochemical synthesis of ammonia from nitrogen under mild conditions using renewable electricity is an attractive alternative1–4 to the energy-intensive Haber–Bosch process, which dominates industrial ammonia production. However, there are considerable scientific and technical challenges5,6 facing the electrochemical alternative, and most experimental studies reported so far have achieved only low selectivities and conversions. The amount of ammonia produced is usually so small that it cannot be firmly attributed to electrochemical nitrogen fixation7–9 rather than contamination from ammonia that is either present in air, human breath or ion-conducting membranes9, or generated from labile nitrogen-containing compounds (for example, nitrates, amines, nitrites and nitrogen oxides) that are typically present in the nitrogen gas stream10, in the atmosphere or even in the catalyst itself. Although these sources of experimental artefacts are beginning to be recognized and managed11,12, concerted efforts to develop effective electrochemical nitrogen reduction processes would benefit from benchmarking protocols for the reaction and from a standardized set of control experiments designed to identify and then eliminate or quantify the sources of contamination. Here we propose a rigorous procedure using 15N2 that enables us to reliably detect and quantify the electrochemical reduction of nitrogen to ammonia. We demonstrate experimentally the importance of various sources of contamination, and show how to remove labile nitrogen-containing compounds from the nitrogen gas as well as how to perform quantitative isotope measurements with cycling of 15N2 gas to reduce both contamination and the cost of isotope measurements. Following this protocol, we find that no ammonia is produced when using the most promising pure-metal catalysts for this reaction in aqueous media, and we successfully confirm and quantify ammonia synthesis using lithium electrodeposition in tetrahydrofuran13. The use of this rigorous protocol should help to prevent false positives from appearing in the literature, thus enabling the field to focus on viable pathways towards the practical electrochemical reduction of nitrogen to ammonia. A protocol for the electrochemical reduction of nitrogen to ammonia enables isotope-sensitive quantification of the ammonia produced and the identification and removal of contaminants.

Magnetite-containing spherical silica nanoparticles for biocatalysis and bioseparations （vol 76, pg 1316, 2004）

Abstract: The simultaneous entrapment of biological macromolecules and nanostructured silica-coated magnetite in sol-gel materials using a reverse-micelle technique leads to a bioactive, mechanically stable, nanometer-sized, and magnetically separable particles. These spherical particles have a typical diameter of 53 +/- 4 nm, a large surface area of 330 m(2)/g, an average pore diameter of 1.5 nm, a total pore volume of 1.427 cm(3)/g and a saturated magnetization (M(S)) of 3.2 emu/g. Peroxidase entrapped in these particles shows Michaelis-Mentan kinetics and high activity. The catalytic reaction will take place immediately after adding these particles to the reaction solution. These enzyme entrapping particles catalysts can be easily separated from the reaction mixture by simply using an external magnetic field. Experiments have proved that these catalysts have a long-term stability toward temperature and pH change, as compared to free enzyme molecules. To further prove the application of this novel magnetic biomaterial in analytical chemistry, a magnetic-separation immunoassay system was also developed for the quantitative determination of gentamicin. The calibration for gentamicin has a working range of 200-4000 ng/mL, with a detection limit of 160 ng/mL, which is close to that of the fluorescent polarization immunoassay (FPIA) using the same reactants.

Synthesis of silver nanoparticles using reducing agents obtained from natural sources ( Rumex hymenosepalus extracts)

Abstract: We have synthesized silver nanoparticles from silver nitrate solutions using extracts of Rumex hymenosepalus, a plant widely found in a large region in North America, as reducing agent. This plant is known to be rich in antioxidant molecules which we use as reducing agents. Silver nanoparticles grow in a single-step method, at room temperature, and with no addition of external energy. The nanoparticles have been characterized by ultraviolet-visible spectroscopy and transmission electron microscopy, as a function of the ratio of silver ions to reducing agent molecules. The nanoparticle diameters are in the range of 2 to 40 nm. High-resolution transmission electron microscopy and fast Fourier transform analysis show that two kinds of crystal structures are obtained: face-centered cubic and hexagonal.

Colloidal nanocrystal synthesis and the organic-inorganic interface

Abstract: Colloidal nanocrystals are nanometer-sized, solution-grown inorganic particles stabilized by a layer of surfactants attached to their surface. The inorganic cores exhibit useful properties controlled by composition as well as size and shape, while the surfactant coating ensures that these structures are easy to fabricate and process. It is this combination of features that makes colloidal nanocrystals attractive and promising building blocks for advanced materials and devices. But their full potential can only be exploited if we achieve exquisite control over their composition, size, shape, crystal structure and surface properties. Here we review what is known about nanocrystal growth and outline strategies for controlling it.

Electrochemical Nitrogen Reduction: Identification and Elimination of Contamination in Electrolyte

Abstract: The new agreement specifically addresses what authors can do with different versions of their manuscript – e.g. use in theses and collections, teaching and training, conference presentations, sharing with colleagues, and posting on websites and repositories. The terms under which these uses can occur are clearly identified to prevent misunderstandings that could jeopardize final publication of a manuscript (Section II, Permitted Uses by Authors).