Spotlights pubs.acs.org/JPCL
Spotlights: Volume 8, Issue 5
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PHOTOISOMERIZATION KINETICS AND MECHANICAL STRESS IN AZOBENZENE-CONTAINING MATERIALS
UNDERSTANDING AND CONTROLLING THE AGGREGATIVE GROWTH OF PLATINUM NANOPARTICLES IN ATOMIC LAYER DEPOSITION: AN AVENUE TO SIZE SELECTION Supported nanoparticles play a major role in a wide range of applications from catalysis to electronic, optical, and energy storage devices. Scaling materials down to the nanoscale not only maximizes the number of active surface sites but also brings about unique size-dependent functionalities. The latter, however, can be understood and harnessed only through the advent of synthesis routes that enable the deposition of nanoparticles with narrow particle size distributions (PSDs). Despite its potential, the scalable synthesis of size-selected NPs on high-surface-area supports, which are relevant to most practical applications, has so far proved elusive. Using a joint experimental and modeling approach, Grillo et al. (10.1021/ acs.jpclett.6b02978) studied the evolution of the PSDs of platinum nanoparticles in oxygen-based platinum atomic layer deposition on bulk quantities of graphene nanoplatelets. They found that, while different deposition temperatures resulted in virtually the same amount of deposited metal, the temperature had a dramatic effect on the PSD shape and its evolution with the number of cycles. Low temperatures resulted in narrow PSDs and a mode that gradually shifts toward the large-size side with increasing numbers of cycles, whereas high temperatures resulted in PSDs presenting a persistent peak in the small-size side and a gradual broadening with increasing numbers of cycles. Their findings depart from the current atomistic understanding of the formation and growth of platinum nanoparticles in atomic layer deposition, where layer-by-layer growth and Ostwald ripening are thought to be the dominant mechanisms. Instead, the growth of the nanoparticles is best described in terms of Smoluchowski aggregation, i.e., nanoparticle diffusion and coalescence. Their report may inform the study of the diffusion, assembly, and stability of supported nanoparticles.
Can your car repair its own dents? Can your clothing detect a health emergency? The answer may be no now, but that could change. Research is ongoing to develop smart materials that could transform the way we live. One area of study is lightinduced molecular motion, where the smart material can transform light energy into directional mechanical stress. It has been shown that light-induced stress can reach 2 GPa, break the metallic layer on the surface of a glassy azo-polymer, and deform covalent bonds, but a theoretical explanation for lightinduced stress of such a large magnitude has not been found. Toward that end, Toshchevikov et al. (10.1021/acs.jpclett.7b00173) studied the kinetics of photoisomerization and the time evolution of ordering in azobenzene-containing materials theoretically and through computer simulations, and they show that the influence of light is equivalent to the action of the effective potential, which reorients chromophores perpendicularly to polarization direction. The strength of the potential is defined by the optical and viscous characteristics of the material. The potential generates photomechanical stress on the order of ∼GPa, in accordance with recent experimental findings for azobenzene materials deep in a glassy state. The proposed approach may provide a deeper understanding of photocontrollable smart compounds, which have the potential for micro- and nanoapplications including nanotemplates, sensors, microrobots, micropumps, and artificial muscles.
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SURFACE LIGAND-MEDIATED PLASMON-DRIVEN PHOTOCHEMICAL REACTIONS
Research has shown that localized surface electromagnetic fields can drive photochemical reactions at low photon flux at room temperature. This finding is significant in two increasingly important areas: harvesting solar energy and decontaminating chemical waste. Although plasmon-driven surface photochemical reactions have been the subject of recent study, less work has been done to determine the effect of surface ligands, which has been thought to be limited to poisoning catalytic activity of nanocrystals by blocking the active sites. In their Letter, Kafle et al. (10.1021/acs.jpclett.7b00106) provide experimental evidence that surface ligands can enhance the reactivity of surfaces and induce important reaction pathways in plasmon-driven photochemical reactions. They used the plasmon-driven photochemistry of p-aminothiophenol on resonant plasmonic gold nanorods as a model reaction to study the effect of surface ligands on reaction selectivity by comparing the results obtained in the presence of citrate, hexadecyltrimethylammonium bromide, and no surface ligands. The authors found that the same plasmonic nanocrystals can lead to different photochemical reaction pathways depending on the surface ligands. © 2017 American Chemical Society
Published: March 2, 2017 1093
DOI: 10.1021/acs.jpclett.7b00429 J. Phys. Chem. Lett. 2017, 8, 1093−1093
