Magnetic Nickel Nanoparticles Supported on Oxidized Charcoal as a Recoverable Catalyst for <i>N</i>‑Alkylation of Amines with Alcohols

Herein, we present a hassle-free approach to synthesize Ni nanoparticles (NPs) and support them onto oxidized charcoal (OC) to produce Ni-oxidized charcoal nanomaterials (Ni-OC). Subsequently, Ni-NPs and Ni-OCs are characterized using powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron (XPS) spectroscopy, transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) techniques. The size distribution curve reveals that the diameter of the Ni-NPs embedded in OC falls in the range of 3–7 nm. Surface area studies show that Ni-NPs and Ni-OC have specific surface areas of 36.5 and 248.9 m2/g, respectively. Interestingly, Ni-OC exhibits the soft ferromagnetic nature of nickel. Ni-NPs and Ni-OC are used as catalysts for the N-alkylation reaction between aniline and benzyl alcohol. The Ni-OC nanomaterials show excellent yields (70–92%) of N-alkylated products. Notably, a catalyst loading of only 0.0482 mmol is sufficient to activate a broad substrate scope with a large functional group tolerance. In addition, the developed synthetic protocol can be further exploited for the catalytic synthesis of 1,2-disubstituted benzimidazole derivatives in excellent yields (65–89%) and effective functional group tolerance. It has been observed that the hydrogen-borrowing mechanism powers both catalytic processes. The Ni-OC exhibits outstanding catalytic reusability and magnetic recoverability for the N-alkylation reaction of aniline with benzyl alcohol for more than seven reaction cycles. In contrast to Ni-NPs, the Ni-OC catalyst exhibits higher catalytic activity for the N-alkylation reaction. This could be explained by the interactions between Ni-NPs and the functional groups available on the oxidized charcoal, which enhance the surface area of the Ni-OC

Oxide Heteroepitaxy for Flexible Optoelectronics

The emerging technological demands for flexible and transparent electronic devices have compelled researchers to look beyond the current silicon-based electronics. However, fabrication of devices on conventional flexible substrates with superior performance are constrained by the trade-off between processing temperature and device performance. Here, we propose an alternative strategy to circumvent this issue via the heteroepitaxial growth of transparent conducting oxides (TCO) on the flexible mica substrate with performance comparable to that of their rigid counterparts. With the examples of ITO and AZO as a case study, a strong emphasis is laid upon the growth of flexible yet epitaxial TCO relying muscovite’s superior properties compared to those of conventional flexible substrates and its compatibility with the present fabrication methods. Besides excellent optoelectro-mechanical properties, an additional functionality of high-temperature stability, normally lacking in the current state-of-the-art transparent flexitronics, is provided by these heterostructures. These epitaxial TCO electrodes with good chemical and thermal stabilities as well as mechanical durability can significantly contribute to the field of flexible, light-weight, and portable smart electronics

Flexible Multiferroic Bulk Heterojunction with Giant Magnetoelectric Coupling <i>via</i> van der Waals Epitaxy

Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate clamping effect still remains a major hurdle in realizing the ultimate magnetoelectric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric–ferrimagnetic bulk heterojunction on a flexible muscovite <i>via</i> van der Waals epitaxy is adopted. In this study, we investigated the magnetoelectric coupling in a self-assembled BiFeO₃ (BFO)–CoFe₂O₄ (CFO) bulk heterojunction epitaxially grown on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate clamping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO–CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm·Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance