Steric and Electronic Influence of Aryl Isocyanides on the Properties of Iridium(III) Cyclometalates

Cyclometalated iridium complexes with efficient phosphorescence and good electrochemical stability are important candidates for optoelectronic devices. Isocyanide ligands are strong-field ligands: when attached to transition metals, they impart larger HOMO–LUMO energy gaps, engender higher oxidative stability at the metal center, and support rugged organometallic complexes. Aryl isocyanides offer more versatile steric and electronic control by selective substitution at the aryl ring periphery. Despite a few reports of alkyl isocyanide of cyclometalated iridium­(III), detailed studies on analogous aryl isocyanide complexes are scant. We report the synthesis, photophysical properties, and electrochemical properties of 11 new luminescent cationic biscyclometalated bis­(aryl isocyanide)­iridium­(III) complexes. Three different aryl isocyanides2,6-dimethylphenyl isocyanide (CNAr^dmp), 2,6-diisopropylphenyl isocyanide (CNAr^dipp), and 2-naphthyl isocyanide (CNAr^nap)were combined with four cyclometalating ligands with differential π–π* energies2-phenylpyridine (ppy), 2,4-difluorophenylpyridine (F₂ppy), 2-benzothienylpyridine (btp), and 2-phenylbenzothiazole (bt). Five of them were crystallographically characterized. All new complexes show wide redox windows, with reduction potentials falling in a narrow range of −2.02 to −2.37 V and oxidation potentials spanning a wider range of 0.97–1.48 V. Efficient structured emission spans from the blue region for [(F₂ppy)₂Ir­(CNAr)₂]­PF₆ to the orange region for [(btp)₂Ir­(CNAr)₂]­PF₆, demonstrating that isocyanide ligands can support redox-stable luminescent complexes with a range of emission colors. Emission quantum yields were generally high, reaching a maximum of 0.37 for two complexes, whereas btp-ligated complexes had quantum yields below 1%. The structure of the CNAr ligand has a minimal effect on the photophysical properties, which are shown to arise from ligand-centered excited states with very little contribution from metal-to-ligand charge transfer in most cases

Three-Dimensional Nanoporous Iron Nitride Film as an Efficient Electrocatalyst for Water Oxidation

Exploring efficient and durable catalysts from earth-abundant and cost-effective materials is highly desirable for the sluggish anodic oxygen evolution reaction (OER), which plays a key role in water splitting, fuel cells, and rechargeable metal–air batteries. First-row transition-metal (Ni, Co, and Fe)-based compounds are promising candidates as OER catalysts to substitute the benchmark of noble-metal-based catalysts, such as IrO₂ and RuO₂. Although Fe is the cheapest and one of the most abundant transition-metal elements, there are seldom papers reported on Fe-only compounds with outstanding catalytic OER activities. Here we propose an interesting strategy by growing iron nitride (Fe₃N/Fe₄N) based nanoporous film on three-dimensional (3D) highly conductive graphene/Ni foam, which is demonstrated to be a robust and durable self-supported 3D electrode for the OER featuring a very low overpotential of 238 mV to achieve a current density of 10 mA/cm², a small Tafel slope of 44.5 mV/dec, good stability, and 96.7% Faradaic yield. The high OER efficiency is by far one of the best for single-metal (Fe, Co, and Ni)-based catalysts, and even better than that of the benchmark IrO₂, which is attributed to the fast electron transfer, high surface area, and abundant active sites of the catalyst. This development introduces another member to the family of cost-effective and efficient OER catalysts

Secondary Oil Recovery Using Graphene-Based Amphiphilic Janus Nanosheet Fluid at an Ultralow Concentration

Nanofluid of graphene-based amphiphilic Janus nanosheets produced high-efficiency tertiary oil recovery at a very low concentration (0.01 wt %). The more attractive way is to use nanofluid during the secondary oil recovery stage, which can eliminate the tertiary stage and save huge amounts of water, especially at times when the price of oil is low. Here, we continue to report our findings on the application of the same nanosheets in secondary oil recovery, which increased oil recovery efficiency by ≤7.5% at an ultralow concentration (0.005 wt %). Compared with nanofluids of homogeneous nanoparticles, our nanofluid achieved a higher efficiency at a much lower concentration. The nanosize dimension of this two-dimensional carbon material improves transport in rock pores. After single-side surface hydrophobization of oxidized graphene with alkylamine, the partial restoration of the graphitic sp² network was detected by Raman, ultraviolet–visible, etc. The amphiphilic Janus nature of nanosheets led to their unique behavior at toluene–brine interface. Oil immersion testing clearly showed the change in the shape of the droplet. The three-phase contact angle decreased from 150° to 79°, indicating the change in the wettability of the solid surface from oleophilic to oleophobic. On the basis of the measured three-phase contact angles, the interfacial tension in the presence of the nanosheets was further calculated and was lower than the interfacial tension without the nanosheets. These interfacial phenomena can help residual oil detach from the solid surface, which contributes to the improved oil recovery performance

Controlled Growth of MoS₂ Flakes from in-Plane to Edge-Enriched 3D Network and Their Surface-Energy Studies

Controlled and tunable growth of chemically active edge sites over inert in-plane MoS₂ flakes is the key requirement to realize their vast number of applications in catalytic activities. Thermodynamically, growth of inert in-plane MoS₂ is preferred due to fewer active sites on its surface over the edge sites. Here, we demonstrate controlled and tunable growth from in-plane MoS₂ flakes to dense and electrically connected edge-enriched three-dimensional (3D) network of MoS₂ flakes by varying the gas flow rate using <i>tube-in-tube</i> chemical vapor deposition technique. Field emission scanning electron microscope results demonstrated that the density of edge-enriched MoS₂ flakes increase with increase in the gas flow rate. Raman and transmission electron microscopy analyses clearly revealed that the as-synthesized in-plane and edge-enriched MoS₂ flakes are few layers in nature. Atomic force microscopy measurement revealed that the growth of the edge-enriched MoS₂ takes place from the in-plane MoS₂ flakes. On the basis of the structural, morphological, and spectroscopic analysis, a detailed growth mechanism is proposed, where <i>in-plane</i> MoS₂ was found to work as a seed layer for the initial growth of edge-enriched vertically aligned MoS₂ flakes that finally leads to the growth of interconnected 3D network of edge-enriched MoS₂ flakes. The surface energy of MoS₂ flakes with different densities was evaluated by sessile contact angle measurement with deionized water (polar liquid) and diiodomethane (dispersive liquid). Both liquids show different nature with the increment in the density of the edge-enriched MoS₂ flakes. The total surface free energy was observed to increase with increase in the density of edge-enriched MoS₂ flakes. This work demonstrates the controlled growth of edge-enriched vertically aligned MoS₂ flakes and their surface-energy studies, which may be used to enhance their catalytic activities for next-generation green fuel production

Interaction of Organic Cation with Water Molecule in Perovskite MAPbI₃: From Dynamic Orientational Disorder to Hydrogen Bonding

Microscopic understanding of interaction between H₂O and MAPbI₃ (CH₃NH₃PbI₃) is essential to further improve efficiency and stability of perovskite solar cells. A complete picture of perovskite from initial physical uptake of water molecules to final chemical transition to its monohydrate MAPbI₃·H₂O is obtained with in situ infrared spectroscopy, mass monitoring, and X-ray diffraction. Despite strong affinity of MA to water, MAPbI₃ absorbs almost no water from ambient air. Water molecules penetrate the perovskite lattice and share the space with MA up to one H₂O per MA at high-humidity levels. However, the interaction between MA and H₂O through hydrogen bonding is not established until the phase transition to monohydrate where H₂O and MA are locked to each other. This lack of interaction in water-infiltrated perovskite is a result of dynamic orientational disorder imposed by tetragonal lattice symmetry. The apparent inertness of H₂O along with high stability of perovskite in an ambient environment provides a solid foundation for its long-term application in solar cells and optoelectronic devices