Plate-Like Colloidal Metal Nanoparticles

The pseudo-two-dimensional (2D) morphology of plate-like metal nanoparticles makes them one of the most anisotropic, mechanistically understood, and tunable structures available. Although well-known for their superior plasmonic properties, recent progress in the 2D growth of various other materials has led to an increasingly diverse family of plate-like metal nanoparticles, giving rise to numerous appealing properties and applications. In this review, we summarize recent progress on the solution-phase growth of colloidal plate-like metal nanoparticles, including plasmonic and other metals, with an emphasis on mechanistic insights for different synthetic strategies, the crystallographic habits of different metals, and the use of nanoplates as scaffolds for the synthesis of other derivative structures. We additionally highlight representative self-assembly techniques and provide a brief overview on the attractive properties and unique versatility benefiting from the 2D morphology. Finally, we share our opinions on the existing challenges and future perspectives for plate-like metal nanomaterials.

Green Synthesis of Iridium Nanoparticles from Winery Waste and Their Catalytic Effectiveness in Water Decontamination

An environmentally friendly procedure was adopted for the first time to prepare green iridium nanoparticles starting from grape marc extracts. Grape marcs, waste of Negramaro winery production, were subjected to aqueous thermal extraction at different temperatures (45, 65, 80, and 100 °C) and characterized in terms of total phenolic contents, reducing sugars, and antioxidant activity. The results obtained showed an important effect of temperature with higher amounts of polyphenols and reducing sugars and antioxidant activity in the extracts with the increase of temperature. All four extracts were used as starting materials to synthesize different iridium nanoparticles (Ir-NP1, Ir-NP2, Ir-NP3, and Ir-NP4) that were characterized by Uv-Vis spectroscopy, transmission electron microscopy, and dynamic light scattering. TEM analysis revealed the presence of very small particles in all samples with sizes in the range of 3.0-4.5 nm with the presence of a second fraction of larger nanoparticles (7.5-17.0 nm) for Ir-NPs prepared with extracts obtained at higher temperatures (Ir-NP3 and Ir-NP4). Since the wastewater remediation of toxic organic contaminants on catalytic reduction has gained much attention, the application of the prepared Ir-NPs as catalysts towards the reduction of methylene blue (MB), chosen as the organic dye model, was evaluated. The efficient catalytic activity of Ir-NPs in the reduction of MB by NaBH₄ was demonstrated and Ir-NP2 was prepared using the extract obtained at 65 °C, showing the best catalytic performance, with a rate constant of 0.527 ± 0.012 min^-1 and MB reduction of 96.1% in just six min, with stability for over 10 months.

Iridium and IrOx nanoparticles: an overview and review of syntheses and applications

Precious metals are key in various fields of research and precious metal nanomaterials are directly relevant for optics, catalysis, pollution management, sensing, medicine, and many other applications. Iridium based nanomaterials are less studied than metals like gold, silver or platinum. A specific feature of iridium nanomaterials is the relatively small size nanoparticles and clusters easily obtained, e.g. by colloidal syntheses. Progress over the years overcomes the related challenging characterization and it is expected that the knowledge on iridium chemistry and nanomaterials will be growing. Although Ir nanoparticles have been preferred systems for the development of kinetic-based models of nanomaterial formation, there is surprisingly little knowledge on the actual formation mechanism(s) of iridium nanoparticles. Following the impulse from the high expectations on Ir nanoparticles as catalysts for the oxygen evolution reaction in electrolyzers, new areas of applications of iridium materials have been reported while more established applications are being revisited. This review covers different synthetic strategies of iridium nanoparticles and provides an in breadth overview of applications reported. Comprehensive Tables and more detailed topic-oriented overviews are proposed in Supplementary Material, covering synthesis protocols, the historical role or iridium nanoparticles in the development of nanoscience and applications in catalysis.

Preserving the shape of silver nanocubes under corrosive environment by covering their edges and corners with iridium

Silver nanocubes have found use in an array of applications but their performance has been plagued by the shape instability arising from the oxidation and dissolution of Ag atoms from the edges and corners. Here we demonstrate that the shape of Ag nanocubes can be well preserved by covering their edges and corners with a corrosion-resistant metal such as Ir. In a typical process, we titrate a Na3IrCl6 solution in ethylene glycol (EG) into a suspension of Ag nanocubes in an EG solution in the presence of poly(vinylpyrrolidone) (PVP) held at 110 °C. The Ir atoms derived from the reduction of Na3IrCl6 by EG and Ag are deposited onto the edges and then corners for the generation of Ag-Ir core-frame nanocubes. Remarkably, our results indicate that a small amount of Ir atoms on the edges and corners is adequate to prevent the Ag nanocubes from transforming into nanospheres when heated in a PVP/EG solution up to 110 °C. We further demonstrate that these Ag-Ir nanocubes embrace plasmonic properties comparable to those of the original Ag nanocubes, making them immediately useful in a variety of applications. This strategy for stabilizing the shape of Ag nanocubes should be extendible to Ag nanocrystals with other shapes or nanocrystals comprised of other metals.

Advancing Applications of Black Phosphorus and BP-Analog Materials in Photo/Electrocatalysis through Structure Engineering and Surface Modulation

Black phosphorus (BP), an emerging 2D material semiconductor material, exhibits unique properties and promising application prospects for photo/electrocatalysis. However, the applications of BP in photo/electrocatalysis are hampered by the instability as well as low catalysis efficiency. Recently, tremendous efforts have been dedicated toward modulating its intrinsic structure, electronic property, and charge separation for enhanced photo/electrocatalytic performance through structure engineering. Simultaneously, the search for new substitute materials that are BP-analogous is ongoing. Herein, the latest theoretical and experimental progress made in the structural/surface engineering strategies and advanced applications of BP and BP-analog materials in relation to photo/electrocatalysis are extensively explored, and a presentation of the future opportunities and challenges of the materials is included at the end.

Ultrafine α-CoOOH Nanorods Activated with Iron for Exceptional Oxygen Evolution Reaction

Two-dimensional oxyhydroxide materials are proved to be a potential candidate for oxygen evolution reaction (OER). Robust, efficient, and cost-effective electrocatalysts are critical to overcome the sluggish kinetics and high overpotential of OERs. Herein, a simple co-precipitation method followed by solvothermal treatment is used to synthesize Fe-doped α-CoOOH at higher pH under optimum conditions for OER. The α-Fe_0.24Co_0.76OOH/NF illustrates superior OER electrocatalytic performance and requires an overpotential of only 280 mV to produce a current density of 50 mA cm^-2 with excellent stability. The detailed analysis reveals that the exceptional OER performance originates from thin nanorods and partially due to the replacement of Fe in α-CoOOH. This work illustrates the presence of interlayer chloride ions through energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.

Cost-Effective Plasmonic Platforms: Glass Capillaries Decorated with Ag@SiO2 Nanoparticles on Inner Walls as SERS Substrates

A cost-effective method for the fabrication of a glass capillary based plasmonic platform for the selective detection and identification of analytes of importance in health, environment, and safety is demonstrated. This was achieved by coating Ag@SiO₂ nanoparticles (Ag ∼ 60 nm) having silica shell of varying thickness (∼2 and ∼25 nm) on the inside walls of glass capillaries, over 2 cm in length, with uniform coverage. It was found that the particle density on the surface plays a decisive role on the enhancement of Raman signals. Multiple hot spots, which are essentially junctions of amplified electric field, were generated when ∼30 Ag@SiO₂ particles/μm² were bound onto the walls of glass capillaries. The pores of the silica shell allow the localization of analyte molecules to the vicinity of hot spots resulting in signal enhancements of the order of 10¹⁰ (using pyrene as analyte; excitation wavelength, 632.8 nm). The applicability of Ag@SiO₂ coated capillaries for the detection of a wide range of molecules has been explored, by taking representative examples of polyaromatic hydrocarbons (pyrene), amino acids (tryptophan), proteins (bovine serum albumin), and explosives (trinitrotoluene). By increasing the thickness of the silica shell of Ag@SiO₂ nanoparticles, an effective filtration cum detection method has been developed for the selective identification of small molecules such as amino acids, without the interference of large proteins.

Surfactant assisted formation of ruthenium nanochains under mild conditions and their catalytic CO oxidation activity

Spontaneous formation of ruthenium nanochains is accomplished in aqueous medium under mild conditions using a seed mediated protocol with cetyl trimethylammonium bromide (CTAB) as the capping agent. They are formed due to the random self-assembly of Ru seeds of ∼3.5 nm size. These 1D nanostructures exhibit better catalytic activity towards the oxidation of CO relative to the ∼3.5 nm seeds and 6 nm Ru nanospheres. The synthesis strategy adopted here is found to be simple, facile and environmentally friendly.

High Aspect-Ratio Iridium-Coated Nanopillars for Highly Reproducible Surface-Enhanced Raman Scattering (SERS)

A variety of different gold and silver nanostructures have been proposed over the years as high sensitivity surface-enhanced Raman scattering (SERS) sensors. However, efficient use of SERS has been hindered by the difficulty of realizing SERS substrates that provide reproducible SERS response over the whole active area. Here, we show that atomic layer deposition (ALD) grown iridium can be used to produce highly reliable SERS substrates. The substrates are based on a periodic array of high aspect-ratio iridium coated nanopillars that feature efficient and symmetrically distributed hot spots within the interpillar gaps (gap width<10 nm). We show that the enhancement with the iridium based nanostructures is of significant magnitude and it equals the enhancement of silver based reference substrates. Most notably, we demonstrate that the ordered and well-defined plasmonic nanopillars offer a measurement-to-measurement variability of 5%, which paves the way for truly quantitative SERS measurements.

The dual role of borohydride depending on reaction temperature: synthesis of iridium and iridium oxide

Temperature dependent reaction products are observed when borohydride is present in aqueous solutions containing Ir³⁺.

The morphology dependent electrocatalytic activity of Ir nanostructures towards oxygen reduction

Oxygen reduction on Ir nanoparticles and nanochains in acidic and alkaline media.