The urgent need of clean and renewable energy drives the exploration of effective strategies to produce molecular hydrogen. With the assistance of highly active non-noble metal electrocatalysts, electrolysis of water is becoming a promising candidate to generate pure hydrogen with low cost and high efficiency. Very recently, transition metal phosphides (TMPs) have been proven to be high performance catalysts with high activity, high stability, and nearly ∼100% Faradic efficiency in not only strong acidic solutions, but also in strong alkaline and neutral media for electrochemical hydrogen evolution. In this tutorial review, an overview of recent development of TMP nanomaterials as catalysts for hydrogen generation with high activity and stability is presented. The effects of phosphorus (P) on HER activity, and their synthetic methods of TMPs are briefly discussed. Then we will demonstrate the specific strategies to further improve the catalytic efficiency and stability of TMPs by structural engineering. Making use of TMPs as cocatalysts and catalysts in photochemical and photoelectrochemical water splitting is also discussed. Finally, some key challenges and issues which should not be ignored during the rapid development of TMPs are pointed out. These strategies and challenges of TMPs are instructive for designing other high-performance non-noble metal catalysts.

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Recent advances in transition metal phosphide nanomaterials: synthesis and applications in hydrogen evolution reaction

Surface-enhanced Raman scattering (SERS) has become a mature vibrational spectroscopic technique during the last decades and the number of applications in the chemical, material, and in particular life sciences is rapidly increasing. This Review explains the basic theory of SERS in a brief tutorial and-based on original results from recent research-summarizes fundamental aspects necessary for understanding SERS and provides examples for the preparation of plasmonic nanostructures for SERS. Chemical applications of SERS are the centerpiece of this Review. They cover a broad range of topics such as catalysis and spectroelectrochemistry, single-molecule detection, and (bio)analytical chemistry.

Surface-enhanced Raman spectroscopy: concepts and chemical applications.

SERS: Materials, applications, and the future

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

/pdf/present-and-future-of-surface-enhanced-raman-scattering-34aqgcm385.pdf

Present and Future of Surface-Enhanced Raman Scattering

When light interacts with a metal nanoparticle (NP), its conduction electrons can be driven by the incident electric field in collective oscillations known as localized surface plasmon resonances (LSPRs). These give rise to a drastic alteration of the incident radiation pattern and to striking effects such as the subwavelength localization of electromagnetic (EM) energy, the formation of high intensity hot spots at the NP surface, or the directional scattering of light out of the structure. LSPRs can also couple to the EM fields emitted by molecules, atoms, or quantum dots placed in the vicinity of the NP, leading in turn to a strong modification of the radiative and nonradiative properties of the emitter. Since LSPRs enable an efficient transfer of EM energy from the near to the far-field of metal NPs and vice versa, we can consider plasmonic nanostructures as nanoantennas, because they operate in a similar way to radio antennas but at higher frequencies. Typically, plasmonic nanoantennas at optical frequencies are made of gold and silver due to their goodmetallic properties and low absorption. Controlling and guiding light has been one of science’s most influential achievements. It affects everyday life in many ways, such as the development of telescopes, microscopes, spectrometers, and optical fibers, to name but a few. These examples exploit the wave nature of light and are based on the reflection, refraction and diffraction of light by optical elements such as mirrors, lenses or gratings. However, the wave nature of light limits the resolution to which an object can be imaged, as well as the size of the transverse cross section of efficient guiding structures to the wavelength dimension. Plasmonic resonances in nanoantennas overcome these constraints, allowing unprecedented control of light-matter interactions within subwavelength volumes (i.e., within the nanoscale at optical frequencies). Such properties have attracted much interest lately, due to the implications they have both in fundamental research and in technological applications. Metal NPs have been used since antiquity. Due to their strong scattering properties in the visible range, they show attractive colors. One of their first applications, dating back to the Roman Empire more than 2000 years ago, was as a colorant for clothing. In art, they were used to stain window glass and ceramics. Obviously, it was not known then that the colorants being used contained metal NPs or that the spectacular colors were due to the excitation of LSPRs. The first reported intentional production of metal NPs dates from 1857, when Faraday synthesized gold colloids. However, at the time there was not much interest in understanding the physics behind the optical properties of colloids due to the impossibility of synthesizing NPs with well-controlled shapes and sizes, as well as the lack of accurate detection techniques. The first theoretical work on the scattering of light by particles smaller than the incident wavelength was carried out by Lord Rayleigh at the end of the 19th century. He analyzed the diffusion of light by diluted gases, and his theory explained physical phenomena such as the blueness of the sky, the redness of the sunset, or the yellow color of the sun. Mie took the next step forward by deriving an analytical solution to Maxwell’s equations to describe the interaction of light with spheres of arbitrary radius and composition. Subsequently, based on the results of Rayleigh and Mie, Gans considered elliptical geometries. He demonstrated that the optical response of metal NPs is

Plasmonic nanoantennas: fundamentals and their use in controlling the radiative properties of nanoemitters.

Surface-enhanced Raman scattering (SERS) is a powerful spectroscopy technique that can provide non-destructive and ultra-sensitive characterization down to single molecular level, comparable to single-molecule fluorescence spectroscopy. However, generally substrates based on metals such as Ag, Au and Cu, either with roughened surfaces or in the form of nanoparticles, are required to realise a substantial SERS effect, and this has severely limited the breadth of practical applications of SERS. A number of approaches have extended the technique to non-traditional substrates, most notably tip-enhanced Raman spectroscopy (TERS) where the probed substance (molecule or material surface) can be on a generic substrate and where a nanoscale gold tip above the substrate acts as the Raman signal amplifier. The drawback is that the total Raman scattering signal from the tip area is rather weak, thus limiting TERS studies to molecules with large Raman cross-sections. Here, we report an approach, which we name shell-isolated nanoparticle-enhanced Raman spectroscopy, in which the Raman signal amplification is provided by gold nanoparticles with an ultrathin silica or alumina shell. A monolayer of such nanoparticles is spread as 'smart dust' over the surface that is to be probed. The ultrathin coating keeps the nanoparticles from agglomerating, separates them from direct contact with the probed material and allows the nanoparticles to conform to different contours of substrates. High-quality Raman spectra were obtained on various molecules adsorbed at Pt and Au single-crystal surfaces and from Si surfaces with hydrogen monolayers. These measurements and our studies on yeast cells and citrus fruits with pesticide residues illustrate that our method significantly expands the flexibility of SERS for useful applications in the materials and life sciences, as well as for the inspection of food safety, drugs, explosives and environment pollutants.

http://www.dstuns.iitm.ac.in/grouppresentations/2010/Shell-isolated%20nanoparticle%20-%20enhanced%20Raman%20spectroscopy.pdf

Shell-isolated nanoparticle-enhanced Raman spectroscopy

Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) as a new member of Raman technique garnered great attention among scientific community. In this work, we used an improved experimental setup to float the bare silver nanoparticles in air with the help of extraneous airflow, and used atomic layer deposition (ALD) method to coat ultra-thin inert shell without pinholes. Under optimal conditions, we successfully prepared three kinds of SHINERS NPs (Ag@Al2O3, Ag@SiO2 and Ag@TiO2) in large quantity without pinholes. The ultra-thin inert shell maintains the SERS activity of silver nanoparticles for long period of time. Transmission electron microscopy (TEM) images confirm the uniform coating of shell material on silver nanoparticles. Finally, the as-prepared SHINs have been applied to detect various samples to demonstrate the applications. The presented ALD method offers a unique way to coat ultrathin shell (1–10 nm) on metal nanoparticles in large quantity (1–10 g) for practical applications. Copyright © 2015 John Wiley & Sons, Ltd.

Large scale synthesis of pinhole‐free shell‐isolated nanoparticles (SHINs) using improved atomic layer deposition (ALD) method for practical applications

S1. Supplementary Methods S1.1. Preparation of Au@SiO2 core-shell NPs We first synthesized Au NPs with a diameter of about 55 nm as cores by a standard sodium citrate reduction method. A freshly prepared aqueous solution of 1 mM (3-Aminopropyl) trimethoxysilane (APS) was added to the gold sol under vigorous magnetic stirring in 15 min, ensuring complete complexation of the amine groups with the gold surface. Then a 0.54 wt% sodium silicate solution was added to the sol, again under vigorous magnetic stirring. To accelerate the synthesis procedure and make the ultra-thin silica shell, we elevated the reaction temperature from room temperature to 90 C, so that the original coating time of 2-3 days for coating silica shells of 4-5 nm can be shortened to ca. one hour. More importantly, this method ensures to form the ultra-thin shell thickness of only 2-4 nm that is free of pinholes (see S8) by carefully controlling parameters such as reaction time, temperature, pH, and the concentration.

http://www.nanoscience.gatech.edu/paper/2010/10_Nature_01_SI.pdf

Wei Zhang

Papers

Shell-isolated nanoparticle-enhanced Raman spectroscopy

Large scale synthesis of pinhole‐free shell‐isolated nanoparticles (SHINs) using improved atomic layer deposition (ALD) method for practical applications

Shelled-isolated nanoparticle-enhanced Raman spectroscopy