Nanoparticle synthesis: Joined at the hip
Hybrid 'Janus' nanoparticles made from gold and titania have high catalytic activity and extraordinary durability
As recently as twenty-five years ago, chemists considered gold to be one of the most inert metallic elements, until the discovery that nanoscale-sized dispersions of gold had high catalytic activity forced a re-think of old principles.
The exposed nature of the gold surface in Janus nanoparticle gold-titania hybrids (left) leads to greater catalytic activity than eccentric (center) and concentric (right) structure. The protective titania coating confers durability on the catalyst.
Copyright : © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Researchers soon found that gold nanoparticles could promote many industrially important reactions, such as the removal of harmful carbon monoxide gas from emission streams. Whilst the benefits of nanoscale gold are well-attested, preparing the material in a durable and reusable form remains a significant challenge that limits its uptake by manufacturers.
Work by the teams of Ming-Yong Han of the Institute of Materials Research and Engineering and Yong-Wei Zhang from the Institute of High Performance Computing both at A*STAR has revealed that the stability of gold nanoparticle catalysts can be enhanced by coating them with protective titania (TiO2) layers. Conceived by co-author Zhi Wei Seh, an A*STAR National Science Scholar, this new technique produces so-called Janus nanostructures that retain nearly all the catalytic activity of bare gold nanoparticles without suffering from irreversible aggregation that diminishes the reactivity of the latter.
Named after the twin-faced Roman god of beginnings and transitions, Janus nanostructures join two or more equal-sized components together through very small junctions — an arrangement that maximizes the active surface area of each substance. The beneficial effects of pairing gold nanoparticles with titania is well known, but until the work by A*STAR researchers, a detailed understanding of the mechanism by which these two species fuse together had proved elusive.
Han and co-workers used an unconventional chelating compound called titanium diisopropoxide bis(acetylacetonate) to nucleate the growth of TiO2 onto gold at extremely slow rates. By carefully controlling the addition of this reagent to rod- and spherical-shaped gold nanoparticles, the researchers observed three distinct nanostructures (see image): a Janus geometry; a partially encapsulating ‘eccentric’ geometry; and a ‘concentric’ core-shell arrangement.
Catalytic experiments revealed that the reactivity and durability of gold-titania Janus structures have unique advantages over other nanoparticles. Due to the exposed nature of their gold surfaces, the former catalyze the reduction of the molecule 4-nitro phenol at much faster rates than eccentric and concentric nanoparticles whose gold surfaces are more confined. Furthermore, the protective TiO2 coating of the hybrid catalysts allowed them to be reused repeatedly with little loss of activity. In contrast, bare gold nanoparticles agglomerated into un-reactive clumps after just five usage cycles.
Futher theoretical investigations by the team revealed that the formation of Janus nanostructures as the energetically stable species is promoted by the addition of smaller volumes of the titania precursor — a finding that may help the researchers generate other metal–oxide hybrids for catalytic applications in the near future.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering and the Institute of High Performance Computing.
Seh, Z. W. et al. Anisotropic growth of titania onto various gold nanostructures: Synthesis, theoretical understanding, and optimization for catalysis. Angewandte Chemie International Edition 50, 10140–10143 (2011).
Eugene Low | Research asia research news
The most recent press releases about innovation >>>
Die letzten 5 Focus-News des innovations-reports im Überblick:
Researchers from Göttingen University discover additional function of opsins
Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...
Researchers embark on aerial campaign over Northeast Greenland
On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...
Data collected on ocean-ice interactions in the little-researched regions of the far south
The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...
At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.
When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...
At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.
Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...