Nanoscale & Nanoscale Advances Blog

TEM images and size distribution (inset) of various Au25 (1 wt%)/support samples before and after 300 °C calcination.

The use of nanogold (Au NP) catalysts has been widely established for various applications including pharmaceuticals and perfumes.  However, their usage has been limited due to the conventional protocols employed for Au NP synthesis producing polydisperse size ranges, which have proven problematic for identifying catalytic active sites. Recently, this issue has been circumvented through instead using Au nanoclusters (Au NCs), which produce defined cluster sizes with well-defined physiochemical properties. As a direct consequence of being able to exert such control, there have been a number of applications established using such catalysts for processes including CO oxidation, and the oxidation of styrene and cyclohexane. However, whilst the role of the solid support is well established for Au NP catalysis, there currently exists a lack of knowledge on what effect/role the support plays in Au NCs catalysis.

In this study, Fang and co-workers report a systematic assessment of thiolated Au NCs on five different solid supports through examination of the size and electronic structure evolution of the Au NCs during heat treatment, and their catalytic performance when applied to the hydrogenation of nitrobenzene and oxidation of styrene.  The solid supports investigated include hydroxy-apatite (HAP), TiO₂ (P25), activated carbon (AC), pyrolyzed grapheme oxide (PGO) and fumed SiO₂.

The key findings of these studies establish that AuNCs on HAP and P25 supports presented enhanced activities over the other considered supports. This was found to be due to a number of factors, including reduced NC growth during calcination (heat treatment) following the removal of the thiolated ligands from the nanocluster surface. Further to this, the catalytic activity established during the hydrogenation of nitrobenzene and oxidation of styrene overwhelmingly showed that AuNC-HAP had a greater activity than any of the other supported catalysts. This was found to be due to both the reduced NC growth following heat treatment, and a change in the electronic structure of bound Au, resulting in strengthened metal support interactions.

Although this study has shown HAP to be a superior support in comparison to the others investigated, it should be noted that during heat treatment, an increase in the size of the nanoclusters was still observed.  As a consequence of this, the authors have objectively established improvements which should be made for future studies, including pursuing different support methods and improving the conditions under which the thiolated ligands can be removed from the Au NCs.

The support effect on the size and catalytic activity of thiolated Au₂₅ nanoclusters as precatalysts
Jun Fang, Jingguo Li, Bin Zhang, Xun Yuan, Hiroyuki Asakura, Tsunehiro Tanaka, Kentaro Teramura, Jianping Xie and Ning Yan
Nanoscale, 2015, 7, 6325-6333. DOI: 10.1039/C5NR00549C

Dr Derek Craig is a guest web writer for the Nanoscale blog. He is a Post Doctoral Research Fellow at the University of St. Andrews based in the fields of Biophotonics and Materials Science. With a background in chemistry, his work mainly focuses on the synthesis of nano to meso materials and the use of imaging techniques to study biological samples.

Radiolabelling of core–shell and dumbbell-like nanoparticles

Bi-modal imaging agents are becoming more popular as they can be used to overcome limitations of single imaging modalities. In this work, radiolabelling of gold containing magnetic nanoparticles (Fe₃O_4-Au) with a nuclear isomer of technetium (^99mTc), a commonly used radionuclide for clinical photon emission computed tomography (SPECT), was assessed using two different methods.  In the first approach, Fe₃O_4-Au core-shell nanoparticles were coated with ligands containing thiol groups to bind to gold and chelator groups for [^99mTc(CO)₃]⁺. In the second approach, ^99mTc containing ligands were first synthesised, then attached to gold on Fe₃O_4-Au dumbbell-like nanoparticles. Both synthetic routes were successful in providing a sufficient radiochemical yield on the surface of magnetic nanoparticles, and are ideal candidates as dual magnetic resonance imaging MRI/SPECT imaging agents. In future studies, the authors plan to use the radiolabelled magnetic particles for bimodal imaging of tumours, through attachment of cancer-specific targeting vectors.

^99mTc radiolabelling of Fe₃O₄–Au core–shell and Au–Fe₃O₄ dumbbell-like nanoparticles
M. Felber and R. Alberto
Nanoscale, 2015, 7, 6653-6660. DOI: 10.1039/C5NR00269A

Dr Mike Barrow is a guest web writer for the Nanoscale blog. He currently works as a Postdoctoral Researcher at the University of Liverpool.

Visual image after EBL treatment, corresponding Raman spectroscopy map of a graphene flake and Raman spectra recorded at different spots on the sample.

Research articles on graphene have been numerously been presented throughout the last decade, indicating the promising future of this material. However, bridging the gap between laboratory research and industrial application remains difficult due to missing specialized large-scale production equipment.

A new article recently published by A. Caglinani et al. introduces an electron beam-based patterning technique using solely widely available clean-room equipment. Based on the findings of the paper, graphene structuring could become a more widespread processing technique.

The researchers developed a patterning process utilizing an industry-standard electron beam lithography system and a standard oven to achieve a resolution of 40 nm.

In the first step, a graphene layer is irradiated by the electron beam which locally generates defects within the crystal lattice. The damage was found by the researchers to be spatially confined to the exposed areas, thus allowing for arbitrary patterns.

The second step comprised etching the irradiated areas by means of hot air at atmospheric pressure. The high defect density (e.g. dangling bonds) induced by the electron beam lead to a large difference in the etch rate compared to the unmodified areas. By exposing the samples for 16 min at 435°C to air, the previously irradiated areas were selectively etched.

In conclusion, the presented process can be used to easily structure graphene layers for future application without the need for specialized equipment. According to the authors, future improvements could reduce the minimum feature size further.

Sebastian Axmann is a guest web-writer for the Nanoscale blog. His interests comprise manufacturing and metrology of nanostructures as well as their usage in current semiconductor devices. He also posts links to interesting research articles on Twitter: @SebastianAxmann.