Explore the vast range of titles available.

Creating specific noble metal/metal‐organic framework (MOF) heterojunction nanostructures represents an effective strategy to promote water electrolysis but remains rather challenging. Herein, a heterojunction electrocatalyst is developed by growing Ir nanoparticles on ultrathin NiFe‐MOF nanosheets supported by nickel foam (NF) via a readily accessible solvothermal approach and subsequent redox strategy. Because of the electronic interactions between Ir nanoparticles and NiFe‐MOF nanosheets, the optimized Ir@NiFe‐MOF/NF catalyst exhibits exceptional bifunctional performance for the hydrogen evolution reaction (HER) (η10 = 15 mV, η denotes the overpotential) and oxygen evolution reaction (OER) (η10 = 213 mV) in 1.0 m KOH solution, superior to commercial and recently reported electrocatalysts. Density functional theory calculations are used to further investigate the electronic interactions between Ir nanoparticles and NiFe‐MOF nanosheets, shedding light on the mechanisms behind the enhanced HER and OER performance. This work details a promising approach for the design and development of efficient electrocatalysts for overall water splitting. A meticulously designed heterojunction bifunctional catalyst Ir@NiFe‐MOF/NF, derived from anchoring Ir nanoparticles in NiFe‐MOF/NF nanosheet arrays, exhibits a robust Ir─O─Ni/Fe interface interaction confirmed by XPS, Raman, and XAFS analyses. Such interaction augments H2O and intermediate adsorption, resulting in the superior HER and OER activities of the catalyst, which can serve as a promising bifunctional candidate for efficient electrocatalytic water splitting.

Photo‐thermal catalytic CO2 hydrogenation is currently extensively studied as one of the most promising approaches for the conversion of CO2 into value‐added chemicals under mild conditions; however, achieving desirable conversion efficiency and target product selectivity remains challenging. Herein, the fabrication of Ir‐CoO/Al2O3 catalysts derived from Ir/CoAl LDH composites is reported for photo‐thermal CO2 methanation, which consist of Ir‐CoO ensembles as active centers that are evenly anchored on amorphous Al2O3 nanosheets. A CH4 production rate of 128.9 mmol gcat⁻1 h⁻1  is achieved at 250 °C under ambient pressure and visible light irradiation, outperforming most reported metal‐based catalysts. Mechanism studies based on density functional theory (DFT) calculations and numerical simulations reveal that the CoO nanoparticles function as photocatalysts to donate electrons for Ir nanoparticles and meanwhile act as “nanoheaters” to effectively elevate the local temperature around Ir active sites, thus promoting the adsorption, activation, and conversion of reactant molecules. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) demonstrates that illumination also efficiently boosts the conversion of formate intermediates. The mechanism of dual functions of photothermal semiconductors as photocatalysts for electron donation and as nano‐heaters for local temperature enhancement provides new insight in the exploration for efficient photo‐thermal catalysts. This work prepares Ir‐CoO/Al2O3 catalysts to realize the highly efficient photo‐thermal catalytic CO2 methanation under mild conditions. The CoO nanoparticles function as photocatalysts to donate electrons for Ir nanoparticles and meanwhile act as “nanoheaters” to effectively elevate the local temperature around Ir active sites, thus promoting the adsorption, activation, and conversion of reactant molecules.

Engineering surface structure of catalysts is an efficient way towards high catalytic performance. Here, we report on the synthesis of regular iridium nanospheres (Ir NSs), with abundant atomic steps prepared by a laser ablation technique. Atomic steps, consisting of one-atom level covering the surface of such Ir NSs, were observed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The prepared Ir NSs exhibited remarkably enhanced activity both for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acidic medium. As a bifunctional catalyst for overall water splitting, they achieved a cell voltage of 1.535 V @ 10 mA/cm2, which is much lower than that of Pt/C-Ir/C couple (1.630 V @ 10 mA/cm2).

The reduction of nitroarenes to aromatic amines is one of the potential pathways to remediate the hazardous impact of toxic nitroarenes on the aquatic environment. Aromatic amines obtained from the reduction of nitroaromatics are not only less toxic than nitroaromatics but also act as important intermediates in the synthesis of dyes, drugs, pigments, herbicides, and polymers. There is a huge demand for the development of cost-effective, and eco-friendly catalysts for the efficient reduction of nitroarenes. In the present study, Fe 3 O 4 @trp@Ir nanoparticles were explored as efficient catalysts for the reduction of nitroarenes. Fe 3 O 4 @trp@Ir magnetic nanoparticles were fabricated by surface coating of Fe 3 O 4 with tryptophan and iridium by co-precipitation method. As-prepared Fe 3 O 4 @trp@Ir nanoparticles are environmentally benign efficient catalysts for reducing organic pollutants such as 4-nitrophenol (4-NP), 4-nitroaniline (4-NA), and 1-bromo-4-nitrobenzene (1-B-4-NB). The key parameters that affect the catalytic activity like temperature, catalyst loading, and the concentration of reducing agent NaBH 4 were optimized. The obtained results proved that Fe 3 O 4 @trp@Ir is an efficient catalyst for reducing nitroaromatics at ambient temperature with a minimal catalyst loading of 0.0025%. The complete conversion of 4-nitrophenol to 4-aminophenol took only 20 s with a minimal catalyst loading of 0.0025% and a rate constant of 0.0522 s −1 . The high catalytic activity factor (1.040 s −1  mg −1 ) and high turnover frequency (9 min −1 ) obtained for Fe 3 O 4 @trp@Ir nanocatalyst highlight the possible synergistic effect of the two metals (Fe and Ir). The visible-light photocatalytic degradation of 4-NP was also investigated in the presence of Fe 3 O 4 @trp@Ir. The photocatalytic degradation of 4-NP by Fe 3 O 4 @trp@Ir is completed in 20 min with 95.15% efficiency, and the rate of photodegradation of 4-NP (0.1507 min −1 ) is about twice the degradation rate of 4-NP in the dark (0.0755 min −1 ). The catalyst was recycled and reused for five cycles without significant reduction in the conversion efficiency of the catalyst.

Surface segregation of components is a key factor in determining the physicochemical properties and catalytic activity of bimetallic nanoparticles. In this study, computer simulations are used to analyze the metal distribution of Ir-Pd nanoparticles synthesized via microemulsions. Based on the high difference between the reduction potentials, an Ir-core/Pd-shell structure is expected. However, experimental results have shown a higher Ir fraction at the surface (15–23%). The hypothesis is that this unexpected results may be due to differences in nucleation rates. To investigate this, we performed a systematic study on the influence of critical nucleus size on the final nanostructure when the two metals have very different reduction rates. Our aim was to determine the conditions under which Ir can reach the nanoparticle surface. The results confirm that the large difference in reduction rates mainly governs metal segregation, leading to core-shell structures. However, when the concentration is close to the critical nucleus value, a slower nucleation rate results in higher Ir enrichment at the surface. It can be attributed to both a slow homoatomic nucleation rate and to a slow heteroatomic nucleation rate of Ir-Pd. At higher concentrations, this effect disappears as the higher reactant availability facilitates nucleation, resulting in similar metal segregation regardless of the critical nucleus size. Good agreement between experimental and simulation results supports the conclusions of this study.

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.

Nanocatalysis using metal nanoparticles constitutes one of the emerging technologies for destructive oxidation of organics such as dyes. This paper deals with the degradation of acid red-26 (AR-26), an azo dye by hexacyanoferrate (abbreviated as HCF) (III) using iridium nanoparticles. UV-vis spectroscopy has been employed to obtain the details of the oxidative degradation of the selected dye. The effect of various operational parameters such as HCF(III) concentration, pH, initial dye concentration, catalyst and temperature was investigated systematically at the λmax, 507 nm, of the reaction mixture. Degradation kinetics follows the first order kinetic model with respect to AR-26 and Ir nano concentrations, while with respect to the HCF(III) concentration reaction it follows first order kinetics at lower concentrations, tending towards zero order at higher concentrations. Thermodynamic parameters have been calculated by studying the reaction rate at four different temperatures. The UV-vis, high performance liquid chromatography (HPLC), liquid chromatography–mass spectrometry (LC-MS) analysis of degradation products showed the formation of carboxylic acid and substituted carboxylic acids as major degradation products, which are simple and less hazardous compounds. The big advantage of the present method is the recovery and reuse of iridium nanoparticles. Moreover, turnover frequencies for each catalytic cycle have been determined, indicating the long life span of Ir nanoparticles. Thus, the finding is a novel and highly economical alternative for environmental safety against pollution by dyes, and extendable for other contaminants as well.

Aim. To develop an amperometric biosensor based on glucose oxidase (1.1.3.4) from Aspergillus niger immobilized in the IrNPs/Ludox/GOx matrix for glucose detection. Methods. To achieve a highly selective and sensitive glucose detection, the enzymatic membrane was functionalized with Ir nanoparticles (IrNPs) and silica composite Ludox. The enzymatic selective layer was formed on the surface of a platinum disk electrode using immobilization in glutaraldehyde vapor. Results. The voltamperometric characteristics of the transducers with modified IrNPs/Ludox/GOx matrix were studied. Enzyme immobilization on the surface of amperometric transducers was optimized to perform sample analysis. Modified transducers improved biosensor sensitivity. The analytical characteristics of amperometric transducer were determined: detection limit is 0.1 µM (s/n = 3), linear working range is 0.05–3.2 mM, sensitivity is 106 mA×M–1×cm–2. Conclusions. Application of the matrix modified with Ir nanoparticles and silica composite Ludox was investigated for the amperometric glucose biosensor as the most studied model of biosensors. A significant increase in the biosensor sensitivity was obtained using the new approach of glucose oxidase immobilization; therefore application of the matrix modified with mesoporous silica composite and nanometals opens new possibilities to obtain a bioselective membrane of high sensitivity and stability at the development of new electrochemical biosensors.

The formation mechanism of Pd–Ir nanoparticles during thermal decomposition of double complex salt [Pd(NH 3 ) 4 ][IrCl 6 ] has been studied by in situ X-ray absorption (XAFS) and photoelectron (XPS) spectroscopies. The changes in the structure of the Pd and Ir closest to the surroundings and chemical states of Pd, Ir, Cl, and N atoms were traced in the range from room temperature to 420 °C in inert atmosphere. It was established that the thermal decomposition process is carried out in 5 steps. The Pd–Ir nanoparticles are formed in pyramidal/rounded Pd-rich (10–200 nm) and dendrite Ir-rich (10–50 nm) solid solutions. A d charge depletion at Ir site and a gain at Pd, as well as the intra-atomic charge redistribution between the outer d and s and p electrons of both Ir and Pd in Pd–Ir nanoparticles, were found to occur. Graphical Abstract

In this article, we present the results of a solvent-free synthesis of iridium(0) nanoparticles, both water washed and unwashed. IrCl 3 and NaBH 4 , as starting materials, are mixed using an agate mortar and milled for 15 min until a black powder is obtained, which is heated in a nitrogen-controlled atmosphere oven at 200 °C for 2 h. If the product of the reaction is not washed before heating, NaBH 4 and IrO 2 impurities are observed. On the other hand, if the reaction product is washed before the heating, the obtained powder is free of impurities. We study the effect of the variation in reducing agent concentration and the annealing temperature used after the reaction. In all cases, the calculated particle size is less than 10 nm.