Shik Chi Tsang

Shape and Size Effects of ZnO Nanocrystals on Photocatalytic Activity

A wet-chemical method was employed to prepare zinc oxide nanocrystals having controlled morphology through thermal decomposition of a zinc precursor in self-assembled supramolecular structures in solvent under mild conditions. This solution method offers finer tailoring of the size and shape of the nanocrystals and is complementary to most reported physical methods. Understanding the morphological effects of pure or modified zinc oxide nanocrystals on photocatalytic activity is important in regard to enhanced solar energy capture and utilization but has been scarcely addressed in the past. The photocatalytic rate was found to have no dependence on ZnO particle size, but the shape factor seems to be of overriding importance. Hexagonal platelike nanocrystals were found to display at least 5 times higher activity than rod-shaped crystals, which clearly suggests that the polar (001) and (001) faces are more active surfaces than the nonpolar surfaces perpendicular to them.

Hydrogen production from formic acid decomposition at room temperature using a Ag–Pd core–shell nanocatalyst

Formic acid (HCOOH) has great potential as an in situ source of hydrogen for fuel cells, because it offers high energy density, is non-toxic and can be safely handled in aqueous solution. So far, there has been a lack of solid catalysts that are sufficiently active and/or selective for hydrogen production from formic acid at room temperature. Here, we report that Ag nanoparticles coated with a thin layer of Pd atoms can significantly enhance the production of H₂ from formic acid at ambient temperature. Atom probe tomography confirmed that the nanoparticles have a core-shell configuration, with the shell containing between 1 and 10 layers of Pd atoms. The Pd shell contains terrace sites and is electronically promoted by the Ag core, leading to significantly enhanced catalytic properties. Our nanocatalysts could be used in the development of micro polymer electrolyte membrane fuel cells for portable devices and could also be applied in the promotion of other catalytic reactions under mild conditions.

Recent Advances in CO2 Capture and Utilization

Energy and the environment are two of the most important issues this century. More than 80 % of our energy comes from the combustion of fossil fuels, which will still remain the dominant energy source for years to come. It is agreed that carbon dioxide produced from the combustion process to be the most important anthropogenic greenhouse gas leading to global warming. Atmospheric CO(2) concentrations have indeed increased by almost 100 ppm since their pre-industrial level, reaching 384 ppm in 2007 with a total annual emission of over 35 Gt. Prompt global action to resolve the CO(2) crisis is therefore needed. To pursue such an action, we are urged to save energy without the unnecessary production of carbon emissions and to use energy in more efficient ways, but alternative methods to mitigate the greenhouse gas have to be considered. This Minireview highlights some recent promising research activities and their prospects in the areas of carbon capture and storage and chemical fixation of CO(2) in constructing a future low-carbon global economy with reference to energy source, thermodynamic considerations, net carbon emissions and availability of reagents.

Recent advances in the conversion of methane to synthesis gas

Abstract A brief review on the recent developments of alternative routes for synthesis gas production, namely catalytic methane partial oxidation and methane reforming with carbon dioxide, is presented. Particular attention is given to reaction thermodynamics, catalyst formulation, reaction mechanism and problems of carbon deposition.

A study of carbon deposition on catalysts during the partial oxidation of methane to synthesis gas

The deposition of carbon on catalysts during the partial oxidation of methane to synthesis gas has been investigated and it has been found that the relative rate of carbon deposition follows the order Ni>Pd>Rh>Ir. Methane decomposition was found to be the principal route for carbon formation over a supported nickel catalyst, and electron micrographs showed that both “whisker” and “encapsulate” forms of carbon are present on the catalyst. Negligible carbon deposition occurred on iridium catalysts, even after 200 h.

The immobilisation of proteins in carbon nanotubes

Carbon nanotubes, fullerene-related structures, have been used for the immobilisation of proteins and enzymes. We have been able to demonstrate, for the first time, direct imaging by high resolution transmission electron microscopy of Zn2Cd5-metallothionein, cytochromes c, c, and β-lactamase 1. This was achieved, without modification, because the biomolecules encapsulated within nanotubes appear to be shielded from the consequences of exposure to the intense electron beam. The results indicate that the internal surface of the nanotubes interacts strongly with the enzymes resulting in their immobilisation. In some cases, the proteines are seen to be distorted giving a concave meniscus inside the tubes. Single protein molecules, their dimers, tetramers and higher oligomers are observed inside the central cavity. Comparison of the catalytic activities of immobilised β-lactamase 1 on or in nanotubes with the free enzyme in the hydrolysis of penicillin, however, showed a significant amount of the immobilised enzyme remained catalytically active, implying that no drastic conformational change had taken place. The carbon nanotube appears to act as a benign host in its ability to encapsulate protein molecules within an environment which offers some protection.

High-resolution electron microscopy studies of non-graphitizing carbons

Abstract High-resolution electron microscopy is used to study the structure of two typical non-graphitizing carbons before and after heat treatment at temperatures in the range 2100–2600°C. It is found that these heat treatments can result in the formation of closed carbon nanoparticles, which are apparently fullerene-like in structure. This suggests that fullerene-like elements were present in the original carbons and leads us to propose a new model for the structure of non-graphitizing carbons.

Shape‐Dependent Acidity and Photocatalytic Activity of Nb2O5 Nanocrystals with an Active TT (001) Surface

Nb(2)O(5) nanorods and nanospheres were synthesized, and their photocatalytic activity for methylene blue decomposition in water compared. Nb(2)O(5) nanorods clearly displayed higher activity, despite their comparable surface area. With a shape-dependent surface acidity, hydrothermal stability, and high photoactivity, these Nb(2)O(5) nanorods are a unique and exciting nanomaterial for non-classical photocatalytic mineralization of organic compounds in water.

Size dependent oxygen buffering capacity of ceria nanocrystals

The structural, chemical and electronic changes of ceria as a function of decreasing particle size have been studied: at sizes below 5 nm the total amount of reducible oxygen dramatically increases due to superoxide formation on the ceria surface, a result indicative of a size dependent oxygen buffering capacity.

Significant enhancement in photocatalytic reduction of water to hydrogen by Au/Cu2ZnSnS4 nanostructure

Enhanced photocatalytic activities by Au core Novel Au/Cu2 ZnSnS4 core/shell nanoparticles (NPs) are synthesized for the first time via wet chemistry approach. The insertion of Au core into CZTS NPs dramatically enhances light absorption due to surface plasmon resonance effect, especially in the Vis-NIR region. Au/CZTS core/shell NPs show much higher photocatalytic activities for hydrogen evolution compared with other CZTS nanostructures.