Search

Plasmonic nanostructures have been proved effective not only in catalyzing chemical reactions, but also in improving the activity of non-plasmonic photocatalysts. It is essential to reveal the synergy between the plasmonic structure and the non-plasmonic metal photocatalyst for expounding the underlying mechanism of plasmon-enhanced catalysis. Herein, the enhancement of resazurin reduction at the heterostructure of silver nanowire (AgNW) and palladium nanoparticles (PdNPs) is observed in situ by single-molecule fluorescence microscopy. The catalysis mapping results around single AgNW suggest that the catalytic activity of PdNPs is enhanced for ∼ 20 times due to the excitation of localized surface plasmon resonance (LSPR) in the vicinity of the AgNW. This catalysis enhancement is also highly related to the wavelength and polarization of the excitation light. In addition, the palladium catalysis is further enhanced by ∼ 10 times in the vicinity of a roughened AgNW or a AgNW-AgNW nanogap because of the improvement of catalytic hotspots. These findings clarify the contribution of plasmon excitation in palladium catalysis at microscopic scale, which will help to deepen the understanding of the plasmon-enhanced photocatalysis and provide a guideline for developing highly efficient plasmon-based photocatalysts. [ABSTRACT FROM AUTHOR]

Cuboid fine crystals of methylammonium lead tribromide (MAPbBr) perovskite have been synthesized by ligand-free reprecipitation method employing N,N-dimethylformamide (DMF) and 1,2,4-trichlorobenzene (TCB) as good and poor solvents, respectively. A small amount of DMF solution dissolving precursor chemicals of MAPbBr was rapidly injected to TCB under vigorous stirring to promote the reprecipitation. Mean crystal size could be varied between 70 and 600 nm by controlled addition of cyclohexane to TCB, since cyclohexane has been found to play a role to retard droplet diffusion. Cyclohexane was miscible with TCB but poorly miscible with DMF. Thus, addition of cyclohexane to TCB retarded diffusion of the injected droplets of DMF solution for reprecipitation of MAPbBr. As the mixing of good and poor solvents was retarded, the recrystallization process was also slowed down, resulted in a small number of nuclei and their growth to large size. Moreover, extreme addition of cyclohexane has resulted in a hollow core spherical particles of MAPbBr due to aggregation of the cuboid fine crystals at the boundary between the added droplet and the poor solvent, so that the spheres formed preserving the shape of the droplet. Due to the limited miscibility of cyclohexane to DMF, increasing the cyclohexane content resulted in reduced rate of diffusion of the injected MAPbBr solution, thus increasing the size of the crystals. [ABSTRACT FROM AUTHOR]

Even though polymer chains are well studied, the convolution and diffraction effect of microscopes may cause the quality of the images to be blurry and/or noisy. This paper aims to present an automatic method to extract the curve representing a polymer chain. This curve is useful for chemical studies; for instance, the length of a polymer chain and its curvature are related to its chemical properties. A movement of the polymer chain may lead to complex geometries with possible intersections. In response to this, we developed an approach computing a piecewise curve traversing the shape. This technique relies on computing several geodesics by browsing distinct parts of the shape. Fusing these elements together allows the entire shape to be represented. The curve orientation is already preserved by considering the fusion as a graph traversal problem. The method provides promising results, validated by experts and approved by simulation. [ABSTRACT FROM AUTHOR]

Developing molecular systems with functions analogous to those of macroscopic machine components, such as rotors, gyroscopes and valves, is a long-standing goal of nanotechnology. However, macroscopic analogies go only so far in predicting function in nanoscale environments, where friction dominates over inertia. In some instances, ratchet mechanisms have been used to bias the ever-present random, thermally driven (Brownian) motion and drive molecular diffusion in desired directions. Here, we visualize the motions of surface-bound molecular rotors using defocused fluorescence imaging, and observe the transition from hindered to free Brownian rotation by tuning medium viscosity. We show that the otherwise random rotations can be biased by the polarization of the excitation light field, even though the associated optical torque is insufficient to overcome thermal fluctuations. The biased rotation is attributed instead to a fluctuating-friction mechanism in which photoexcitation of the rotor strongly inhibits its diffusion rate. [ABSTRACT FROM AUTHOR]

Catalytic processes on surfaces have long been studied by probing model reactions on single-crystal metal surfaces under high vacuum conditions. Yet the vast majority of industrial heterogeneous catalysis occurs at ambient or elevated pressures using complex materials with crystal faces, edges and defects differing in their catalytic activity. Clearly, if new or improved catalysts are to be rationally designed, we require quantitative correlations between surface features and catalytic activity—ideally obtained under realistic reaction conditions. Transmission electron microscopy and scanning tunnelling microscopy have allowed in situ characterization of catalyst surfaces with atomic resolution, but are limited by the need for low-pressure conditions and conductive surfaces, respectively. Sum frequency generation spectroscopy can identify vibrations of adsorbed reactants and products in both gaseous and condensed phases, but so far lacks sensitivity down to the single molecule level. Here we adapt real-time monitoring of the chemical transformation of individual organic molecules by fluorescence microscopy to monitor reactions catalysed by crystals of a layered double hydroxide immersed in reagent solution. By using a wide field microscope, we are able to map the spatial distribution of catalytic activity over the entire crystal by counting single turnover events. We find that ester hydrolysis proceeds on the lateral {1010} crystal faces, while transesterification occurs on the entire outer crystal surface. Because the method operates at ambient temperature and pressure and in a condensed phase, it can be applied to the growing number of liquid-phase industrial organic transformations to localize catalytic activity on and in inorganic solids. An exciting opportunity is the use of probe molecules with different size and functionality, which should provide insight into shape-selective or structure-sensitive catalysis and thus help with the rational design of new or more productive heterogeneous catalysts. [ABSTRACT FROM AUTHOR]