Synthesis, properties and applications of noble metal iridium nanomaterials

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

Iridium-Based Nanohybrids: Synthesis, Characterization, Optical Limiting, and Nonlinear Optical Properties

The present work reports on the synthesis and characterization of iridium (Ir)-based nanohybrids with variable chemical compositions. More specifically, highly stable polyvinylpyrrolidone (PVP) nanohybrids of the PVP-IrO₂ and PVP-Ir/IrO₂ types, as well as non-coated Ir/IrO₂ nanoparticles, are synthesized using different synthetic protocols and characterized in terms of their chemical composition and morphology via X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM), respectively. Furthermore, their nonlinear optical (NLO) response and optical limiting (OL) efficiency are studied by means of the Z-scan technique, employing 4 ns laser pulses at 532 and 1064 nm. The results demonstrate that the PVP-Ir/IrO₂ and Ir/IrO₂ systems exhibit exceptional OL performance, while PVP-IrO₂ presents very strong saturable absorption (SA) behavior, indicating that the present Ir-based nanohybrids could be strong competitors to other nanostructured materials for photonic and optoelectronic applications. In addition, the findings denote that the variation in the content of IrO₂ nanoparticles by using different synthetic pathways significantly affects the NLO response of the studied Ir-based nanohybrids, suggesting that the choice of the appropriate synthetic method could lead to tailor-made NLO properties for specific applications in photonics and optoelectronics.

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.

Rapid electrochemical biosensor composed of DNA probe/iridium nanoparticle bilayer for Aphanizomenon flos-aquae detection in fresh water

Toxic cyanobacteria pose a serious threat to aquatic ecosystems and require adequate detection and control systems. Aphanizomenon flos-aquae is a harmful cyanobacterium that produces the toxicant saxitoxin. Therefore, it is necessary to detect the presence of A. flos-aquae in lakes and rivers. We proposed a rapid electrochemical biosensor composed of DNA primer/iridium nanoparticles (IrNP) bilyer for the detection of A. flos-aquae in freshwater. The extracted A. flos-aquae gene (rbcL-rbcX) is used as a target, and it was fixed to the electrode using a 5'-thiolated DNA primer (capture probe). Then, Avidin@IrNPs complex for amplification of electrical signals was bound to the target through a 3'-biotinylated DNA primer (detection probe). To rapidly detect the target, an alternating current electrothermal flow technique was introduced in the detection step, which could reduce the detection time to within 20 min. To confirm the biosensor fabrication, atomic force microscopy was used to investigate the surface morphology. To evaluate the biosensor performance, cyclic voltammetry and electrochemical impedance spectroscopy were used. The target gene was detected at a concentration of 9.99 pg/mL in tap water, and the detection range was 0.1 ng/mL to 10³ ng/mL with high selectivity. Based on the combined system, we employed A. flos-aquae in tap water. This rapid cyanobacteria detection system is a powerful tool for CyanoHABs in the field.

Chemical Insights into the Formation of Colloidal Iridium Nanoparticles from In Situ X-ray Total Scattering: Influence of Precursors and Cations on the Reaction Pathway

Iridium nanoparticles are important catalysts for several chemical and energy conversion reactions. Studies of iridium nanoparticles have also been a key for the development of kinetic models of nanomaterial formation. However, compared to other metals such as gold or platinum, knowledge on the nature of prenucleation species and structural insights into the resultant nanoparticles are missing, especially for nanoparticles obtained from Ir_xCl_y precursors investigated here. We use in situ X-ray total scattering (TS) experiments with pair distribution function (PDF) analysis to study a simple, surfactant-free synthesis of colloidal iridium nanoparticles. The reaction is performed in methanol at 50 °C with only a base and an iridium salt as precursor. From different precursor salts─IrCl₃, IrCl₄, H₂IrCl₆, or Na₂IrCl₆─colloidal nanoparticles as small as Ir_∼55 are obtained as the final product. The nanoparticles do not show the bulk iridium face-centered cubic (fcc) structure but show decahedral and icosahedral structures. The formation route is highly dependent on the precursor salt used. Using IrCl₃ or IrCl₄, metallic iridium nanoparticles form rapidly from Ir_xCl_y^n- complexes, whereas using H₂IrCl₆ or Na₂IrCl₆, the iridium nanoparticle formation follows a sudden growth after an induction period and the brief appearance of a crystalline phase. With H₂IrCl₆, the formation of different Ir_n (n = 55, 55, 85, and 116) nanoparticles depends on the nature of the cation in the base (LiOH, NaOH, KOH, or CsOH, respectively) and larger particles are obtained with larger cations. As the particles grow, the nanoparticle structure changes from partly icosahedral to decahedral. The results show that the synthesis of iridium nanoparticles from Ir_xCl_y is a valuable iridium nanoparticle model system, which can provide new compositional and structural insights into iridium nanoparticle formation and growth.

Efficient removal of antibiotics from water resources is a public health priority: a critical assessment of the efficacy of some remediation strategies for antibiotics in water

This review discusses the fundamental principles and mechanism of antibiotic removal from water of some commonly applied treatment techniques including chlorination, ozonation, UV-irradiation, Fenton processes, photocatalysis, electrochemical-oxidation, plasma, biochar, anaerobicdigestion, activated carbon and nanomaterials. Some experimental shortfalls identified by researchers such as certain characteristics of degradation agent applied and the strategies explored to override the identified limitations are briefly discussed. Depending on interactions of a range of factors including the type of antibiotic compound, operational parameters applied such as pH, temperature and treatment time, among other factors, all reviewed techniques can eliminate or reduce the levels of antibiotic compounds in water to varying extents. Some of the reviewed techniques such as anaerobic digestion generally require longer treatment times (up to 360, 193 and 170 days, according to some studies), while others such as photocatalysis achieved degradation within short contact time (within a minimum of 30, but up to 60, 240, 300 and 1880 minutes, in some cases). For some treatment techniques such as ozonation and Fenton, it is apparent that subjecting compounds to longer treatment times may improve elimination efficiency, whereas for some other techniques such as nanotechnology, application of longer treatment time generally meant comparatively minimal elimination efficiency. Based on the findings of experimental studies summarized, it is apparent that operational parameters such as pH and treatment time, while critical, do not exert sole or primary influence on the elimination percentage(s) achieved. Elimination efficiency achieved rather seems to be due more to the force of a combination of several factors.

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.

Surface-Dependent Intermediate Adsorption Modulation on Iridium-Modified Black Phosphorus Electrocatalysts for Efficient pH-Universal Water Splitting

2D black phosphorus (BP) is one promising electrocatalyst toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysis. The too strong adsorption of oxygen intermediates during OER, while the too weak adsorption of hydrogen intermediate during HER, however, greatly compromise its practical water splitting applications with overpotentials as high as 450 mV for OER and 420 mV for HER to achieve 10 mA cm^-2 under alkaline conditions. Herein, by rationally introducing the nanosized iridium (Ir) modifier together with optimized exposing surface toward electrolytes, an efficient Ir-modified BP electrocatalyst with much favorable adsorption energies toward catalytic intermediates possesses an outstanding pH-universal water splitting performance, surpassing the nearly all reported BP-based catalysts and the commercial noble-metal catalysts. The Ir-modified BP catalyst with the optimized exposed surfaces only requires an overall cell voltage of 1.54 and 1.57 V to achieve 10 mA cm^-2 in acidic and alkaline electrolysers, respectively. This design uncovers the potential applications of 2D BP in practical electrocatalysis fields via decreasing reaction intermediate adsorption energy barriers and promoting the interfacial electron coupling for heterostructured catalysts, and offers new insights into the surface-dependent activity enhancement mechanism.

The electro-oxidation of tetracycline hydrochloride in commercial DSA® modified by electrodeposited platinum

Tetracycline hydrochloride (TCH) electro-oxidation by commercial DSA® and commercial DSA® modified by platinum electrodeposition was evaluated. The electrodeposition was carried out at constant potential (E = - 0.73 V vs RHE) in different times (1200, 2400, and 4800 s). Scanning electron microscopy (SEM) images show that Pt electrodeposits have elongated shape particle forming a uniform surface, and energy dispersive spectroscopy (EDS) data confirms the presence of Pt on the surface. The electrochemical characterization by cyclic voltammetry showed an increase of the electrochemically active area (E_AA) in function of the Pt electrodeposition time. The electro-oxidation of the TCH 0.45 mmol L^-1 in H₂SO₄ 0.1 mol L^-1 solution was evaluated according to the applied current densities (j = 25, 50, 100 mA cm^-2). Both the amount of platinum deposited and j showed a slight improvement in the efficiency of TCH removal, reaching 97.2% of TCH removal to DSA®/Pt₄₈₀₀ and 100 mA cm^-2. The TCH mineralization (TOC removal), the percentage of mineralization current efficiency (MCE%), and energy consumption were 15.8%, 0.2649%, and 7.4138 kWh (g TOC)^-1, respectively. The DSA®/Pt electrodes showed higher stability to TCH electro-oxidation, indicating to be a promising material for the electro-oxidation of organic pollutants.

Applications of nano-materials in diverse dentistry regimes

Research and development in the applied sciences at the atomic or molecular level is the order of the day under the domain of nanotechnology or nano-science with enormous influence on nearly all areas of human health and activities comprising diverse medical fields such as pharmacological studies, clinical diagnoses, and supplementary immune system. The field of nano-dentistry has emerged due to the assorted dental applications of nano-technology. This review provides a brief introduction to the general nanotechnology field and a comprehensive overview of the synthesis features and dental uses of nano-materials including current innovations and future expectations with general comments on the latest advancements in the mechanisms and the most significant toxicological dimensions.

Electrochromic behaviour of Ir(iii) bis-cyclometalated 1,2-dioxolene tetra-halo complexes: fully reversible catecholate/semiquinone redox switches

Neutral cyclometalated Ir(iii) complexes of general formula [Ir(ppy)2(O^O)squi], where ppy = 2-phenylpyridine and (O^O)squi = TBC (tetrabromocatechol) or TCC (tetrachlorocatechol) in their semiquinone (squi) monoanionic redox state, were synthesized by chemically oxidizing the anionic parent complexes NBu4[Ir(ppy)2(O^O)cat], in which (O^O)cat represents the corresponding ancillary dioxolene ligand in its dianionic catecholate (cat) redox state. This chemical oxidation leads to the modification of both the photophysical and the magnetic properties of the complexes. While the NBu4[Ir(ppy)2(O^O)cat] complexes are diamagnetic (D) and yellow-orange solids, the corresponding oxidized complexes [Ir(ppy)2(O^O)squi] display paramagnetic (P) properties and are characterized by a dark-green color. The conversion between the two forms (squi vs. cat) is electrochemically and chemically fully reversible. Indeed, the anionic NBu4[Ir(ppy)2(O^O)cat] complexes are quantitatively restored by chemical reduction of the neutral [Ir(ppy)2(O^O)squi] parents. These complexes therefore represent interesting redox based switches between multi-parameter states since they allow switching from a neutral paramagnetic to an anionic diamagnetic form together with a significant change in chromicity. Taking advantage of the significant color difference between the oxidized and the reduced form, an electrochromic cell was prepared with [Ir(ppy)2(TBC)squi] and its spectroelectrochemical properties are reported.

Ultra-small iridium nanoparticles as active catalysts for the selective and efficient reduction of nitroarenes

The ultra-small noble metal iridium nanoparticles (IrNPs) possessing super catalytic activity can be applied in the efficient and selective catalytic reduction of nitroarenes under mild reaction conditions for the first time.

Facile Synthesis of IrCu Microspheres Based on Polyol Method and Study on Their Electro-Catalytic Performances to Oxygen Evolution Reaction

The development of Ir-based catalyst with high efficiency for oxygen evolution reaction (OER) in acidic conditions is of great significance to the development of clean energy, but it still remains a significant challenge for shape controlled synthesis of Ir-based catalysts. This article presented a facile one-pot synthesis method that is based on polyol method for preparing IrCu microspheres. In the process of synthesis, formaldehyde solution and ethylene glycol were used as reducing agent and solvent, respectively, while poly(vinylpyrrolidone) was used as surfactant and dispersant, and all of them played important roles in the successful synthesis of Ir-Cu microspheres. The Ir-Cu microspheres, as synthesized, showed well sphere shape and smooth surface, while their alloy features were quite clear and the composition could be adjusted. Benefitting from the synergistic electronic effect between the Iridium and Cupric atoms from the alloy, the IrCu_0.77 microspheres exhibited excellent electrocatalytic activity towards OER in 0.1 M HClO₄ electrolyte, and to achieve 10 mA cm⁻², IrCu_0.77 microspheres only required the overpotential of 282 mV, which was much lower than that of commercial Ir/C catalysts.