Nanostructures For Catalysis Research Articles

Metallic Heterostructures for Plasmon-Enhanced Electrocatalysis.

Metallic heterogeneous nanostructures with plasmonic functionality have attracted great attention in the field of plasmon-enhanced electrocatalysis, where surface plasmons produced under light excitation could facilitate the overall electrocatalytic performances. Owing to their controllability, multifunctionality, and complexity, heterogeneous metallic nanostructures take advantages of the properties from individual components and synergistic effects from adjacent components, thus may achieve remarkable electrocatalytic performances. This review highlights the state-of-the-art progress of the application of metallic heterostructures for plasmon-enhanced electrocatalysis. First, a brief introduction to plasmonic heterogeneous nanostructures is demonstrated. Then, fundamental principles of localized surface plasmon resonance and the underlying mechanisms of plasmonic heterogeneous nanostructures in catalysis are discussed. This is followed by a discussion of recent advances of plasmonic heterogeneous nanostructures in plasmon-enhanced electrocatalysis, in which the enhanced activity, selectivity, and stability are particularly emphasized. Finally, an outlook of remaining challenges and future opportunities for plasmonic heterogeneous nanomaterials and plasmon-related electrocatalysis is presented.

Supercritical CO2 Directional-Assisted Synthesis of Low-Dimensional Materials for Functional Applications.

Supercritical CO2 (SC CO2 ), as one of the unique fluids that possess fascinating properties of gas and liquid, holds great promise in chemical reactions and fabrication of materials. Building special nanostructures via SC CO2 for functional applications has been the focus of intense research for the past two decades, with facile regulated reaction conditions and a particular reaction field to operate compared to the more widely used solvent systems. In this review, the significance of SC CO2 on fabricating various functional materials including modification of 1D carbon nanotubes, 2D materials, and 2D heterostructures is stated. The fundamental aspects involving building special nanostructures via SC CO2 are explored: how their structure, morphology, and chemical composition be affected by the SC CO2 . Various optimization strategies are outlined to improve their performances, and recent advances are combined to present a coherent understanding of the mechanism of SC CO2 acting on these functional nanostructures. The wide applications of these special nanostructures in catalysis, biosensing, optoelectronics, microelectronics, and energy transformation are discussed. Moreover, the current status of SC CO2 research, the existing scientific issues, and application challenges, as well as the possible future directions to advance this fertile field are proposed in this review.

Space-confined pyrolysis for fabrication of peacods-like Fe3O4@C-Ni nanostructures for catalysis and protein adsorption

A unique nanostructure of Fe3O4 nanoparticles (NPs)-in/carbon layer/out-Ni NPs was developed and proved to be an efficient catalyst and protein adsorbent. This kind of nanostructure was formed through a space-confined pyrolysis procedure using polydopamine-Ni2+ coated Fe-NTA nanowires as the precursor. A N-doped carbon interlayer derived from polydopamine (PDA) supported a large amount of Ni NPs and entrapped well-defined Fe3O4 NPs, which were obtained through reduction of Ni2+, Fe3+ by carbonized NTA groups and a PDA layer. The contributions of the unique configuration along with the high density of Ni NPs in Fe3O4@C-Ni are significant for improving catalysis and protein adsorption performance, which is expected to be a promising alternative to other conventional catalysts and protein adsorbents. Due to the unique novel nanostructure, this nanocomposite possesses a wide range of applications, not only for catalytic reactions but also for other inhomogeneous reactions.

Comparative study between homo-metallic & hetero-metallic nanostructures based agar in catalytic degradation of dyes

Herein, comparison between eco-friendly homo-metallic (Ag) and hetero-metallic (AgAu and Ag-Au-Pd) nanostructures in catalysis was studied. The homo-metallic and hetero-metallic nanostructures were greenly synthesized using Agar as nano-generator. The sequential reduction of metal ions to give homo- and hetero-metallic nanostructures was initially confirmed via UV–Visible spectra. Tracking of transmission electron microscope and zetasizer data showed that, all the produced nanostructures were well-dispersed and spherical in shape. Small-sized AgNPs with mean size of 9.1 nm were enlarged to 23.7 nm for AgAu bimetallic nanostructure. While, trimetallic nanoshells of Ag-Au-Pd was diminished to be 13.6 nm. The FT-IR and 13CNMR spectral analyses were detected to investigate the reaction mechanism for synthesis of nanostructures. The catalytic performance of the synthesized nanostructures in degradation of methylene blue and methyl orange dyes was a strongly correlated to the composition of nanostructures. Half time of methylene blue and methyl orange degradation was diminished from 45.90 and 47.15 to 0.97 and 0.69 min by using trimetallic nanostructures as a catalyst, respectively. The current strategy can present an environmentally benign and valuable methodology for fabrication of hetero-metallic nanostructures with desirable size and have efficient catalytic activity.

Manifestation of Concealed Defects in MoS2Nanospheres for Efficient and Durable Electrocatalytic Hydrogen Evolution Reaction

MoS2 nanospheres were formed using a template free hydrothermal process, which exhibit high catalytic activity towards hydrogen evolution reaction (HER). The extend of defect sites are probed by extended X-ray absorption fine structure which found decrease in co-ordination number at Mo site rather than at S site. DFT calculations identified an uneven strain and defect distribution between two S planes of curved MoS2. Based on hydrogen adsorption on various sites, we identify a new pathway called “extended activity @ shielded defects”, for Volmer-Tafel and Volmer-Heyrovsky mechanisms, where H adsorption occurs at exposed S layer driven by defects in underneath S layer of nanosphere. Having higher defect concentration it exhibited excellent HER activity with overpotential of −0.12 V, Tafel slope of 90 mV/decade, and higher turnover frequency. Our findings provide an avenue to design and engineer advanced nanostructures for catalysis, electronic devices, and other potential applications.

Mesoporous copper–cerium–oxygen hybrid nanostructures for low temperature catalytic oxidation of carbon monoxide

Mesoporous copper–cerium–oxygen hybrid nanostructures were prepared by one-pot cetyltrimethylammonium bromide surfactant-assisted method, and were characterized by thermogravimetry, X-ray diffraction, transmission electron microscopy, nitrogen adsorption–desorption, X-ray photoelectron spectroscopy and temperature-programmed reduction techniques. Low temperature carbon monoxide oxidation was used as probe reaction to investigate the application of the prepared mesoporous copper–cerium–oxygen hybrid nanostructures in catalysis. The product calcined at 400 °C, with disordered wormlike mesoporous structure, high specific surface area (SSA) of 117.4 m2/g and small catalyst particle size of 8.3 nm, shows high catalytic activity with the 100 % CO conversion at 110 °C, indicating its potential application in catalysis. Catalytic activity results from the samples calcinied at different temperature suggested that high SSA, small catalyst particle size, finely dispersed CuO species and synergistic effect between CuO and CeO2 were responsible for the high catalytic activity of the catalysts.

Tuning plasmon transitions and their applications in organic photochemistry

The ketone-photoinduced formation of Au, Ag, and Cu nanoparticles from their corresponding ions in solution has been carried out using benzoin photoinitiators. Ketones are good photosensitizers for nanoparticle synthesis not because of the energy they can absorb or deliver, but rather because of the reducing free radicals they can generate. Efficient photochemical nanoparticle generation thus requires a careful selection of substrates and experimental conditions such that free radical generation occurs with high quantum efficiency, where metal ion precursors do not inhibit radical formation. A key consideration to achieve nanoparticle synthesis with short exposure times is to minimize excited-state quenching by metal ions. Applications of nanostructures in catalysis require control of the nanoparticle characteristics, such as dimension, morphology, and surface properties. Part of this article describes the strategies to modify photochemically prepared particles. Finally, we illustrate some of the nanoparticle applications that interest us, with some emphasis on plasmon-mediated processes.

Architecture of Metallic Nanostructures: Synthesis Strategy and Specific Applications

Metallic nanoparticles are emerging as key materials use in catalysis, plasmonics, sensing, and spectroscopy. To approach these applications, the control of nanostructures provides increasing selectivity and functionality. This feature article highlights our recent research progress in this emerging field. This article discusses control of the shape of metallic nanostructures and their physical/chemical nature. The numerous approaches for synthesizing multishaped nanostructures include (i) the use of hard templates such as anodic aluminum oxide, (ii) the use of soft templates such as cetyltrimethylammonium bromide (CTAB), and (iii) the use of sacrificial templates. Finally, the use of such nanostructures in catalysis, sensing, and photothermal therapy are demonstrated. General strategies for these methods are discussed and related recent research directions will also be addressed in this feature article.

Ordered Macroporous Bimetallic Nanostructures: Design, Characterization, and Applications

Ordered porous metal nanomaterials have current and future potential applications, for example, as catalysts, as photonic crystals, as sensors, as porous electrodes, as substrates for surface-enhanced Raman scattering (SERS), in separation technology, and in other emerging nanotechnologies. Methods for creating such materials are commonly characterized as "templating", a technique that involves first the creation of a sacrificial template with a specific porous structure, followed by the filling of these pores with desired metal materials and finally the removal of the starting template, leaving behind a metal replica of the original template. From the viewpoint of practical applications, ordered metal nanostructures with hierarchical porosity, namely, macropores in combination with micropores or mesopores, are of particular interest because macropores allow large guest molecules to access and an efficient mass transport through the porous structures is enabled while the micropores or mesopores enhance the selectivity and the surface area of the metal nanostructures. For this objective, colloidal crystals (or artificial opals) consisting of three-dimensional (3D) long-range ordered arrays of silica or polymer microspheres are ideal starting templates. However, with respect to the colloidal crystal templating strategies for production of ordered porous metal nanostructures, there are two challenging questions for materials scientists: (1) how to uniformly and controllably fill the interstitial space of the colloidal crystal templates and (2) how to generate ordered composite metal nanostructures with hierarchical porosity. This Account reports on recent work in the development and applications of ordered macroporous bimetallic nanostructures in our laboratories. A series of strategies have been explored to address the challenges in colloidal crystal template techniques. By rationally tailoring experimental parameters, we could readily and selectively design different types of ordered bimetallic nanostructures with hierarchical porosity by using a general template technique. The applications of the resulting nanostructures in catalysis and as substrates for SERS are described. Taking the ordered porous Au/Pt nanostructures as examples for applications as catalysts, the experimental results show that both the ordered hollow Au/Pt nanostructure and the ordered macroporous Au/Pt nanostructure exhibit high catalytic ability due to their special structural characteristics, and their catalytic activity is component-dependent. As for SERS applications, primary experimental results show that these ordered macroporous Au/Ag nanostructured films are highly desirable for detection of DNA bases by the SERS technique in terms of a high Raman intensity enhancement, good stability, and reproducibility, suggesting that these nanostructures may find applications in the rapid detection of DNA and DNA fragments.