RESUMEN
MXenes are 2D transition metal carbides, nitrides, and/or carbonitrides that can be intercalated with cations through chemical or electrochemical pathways. While the insertion of alkali and alkaline earth cations into Ti3C2Tx MXenes is well studied, understanding of the intercalation of redox-active transition metal ions into MXenes and its impact on their electronic and electrochemical properties is lacking. In this work, we investigate the intercalation of Cu ions into Ti3C2Tx MXene and its effect on its electronic and electrochemical properties. Using X-ray absorption spectroscopy (XAS) and ab initio molecular dynamics (AIMD), we observe an unusual phenomenon whereby Cu2+ ions undergo partial reduction upon intercalation from the solution into the MXene. Furthermore, using in situ XAS, we reveal changes in the oxidation states of intercalated Cu ions and Ti atoms during charging. We show that the pseudocapacitive response of Cu-MXene originates from the redox of both the Cu intercalant and Ti3C2Tx host. Despite highly reducing potentials, Cu ions inside the MXene show an excellent stability against full reduction upon charging. Our findings demonstrate how electronic coupling between Cu ions and Ti3C2Tx modifies electrochemical and electronic properties of the latter, providing the framework for the rational design and utilization of transition metal intercalants for tuning the properties of MXenes for various electrochemical systems.
RESUMEN
In this Perspective, we sketch out a vision of fast charging and self-healable energy systems that are primarily organic, feature only abundant elements, and operate with ions other than lithium. Using conductive oligomers as highly configurable building blocks, it is possible to create intrinsically adaptable conductive polymeric networks that can be rejuvenated and recycled using simple and safe chemical treatments. Using the versatile organic chemistry toolbox, these oligomers can be further functionalized, for example, with redox-active side chains for high charge storage capacity and ligands capable of complexing metal centers. Cross-linking with metal ions converts the soluble oligomers into insoluble supramolecular networks to yield high-performing electrode materials. The oligomer-based approach can thus provide an exceptional level of control to the design of organic-based battery materials.
RESUMEN
Controlling the structure sensitivity of catalyzed reactions over metals is central to developing atom-efficient chemical processes. Approaching the minimum ensemble size, the properties enter a non-scalable regime in which each atom counts. Almost all trends in this ultra-small frontier derive from surface science approaches using model systems, because of both synthetic and analytical challenges. Exploiting the unique coordination chemistry of carbon nitride, we discriminate through experiments and simulations the interplay between the geometry, electronic structure, and reactivity of palladium atoms, dimers, and trimers. Catalytic tests evidence application-dependent requirements of the active ensemble. In the semi-hydrogenation of alkynes, the nuclearity primarily impacts activity, whereas the selectivity and stability are affected in Suzuki coupling. This powerful approach will provide practical insights into the design of heterogeneous catalysts comprising well-defined numbers of atoms.
RESUMEN
Single-atom heterogeneous catalysts (SACs) attached to carefully chosen hosts are attracting considerable interest; principally because they offer maximum utilization per metal atom and are usually readily recyclable. However, diminution of the atomic population of nanoparticles or nanoclusters to single atoms can significantly alter reactivity because of the consequent changes in the active-site structure. By examining various diverse applications, we ascertain whether the performance of SACs is enhanced or suppressed. We also note that SACs generally display unique kinds of catalytic cycles. The choice of host is crucial since it influences both the electronic and steric environment of the metal center. Moreover, it may function as a cocatalyst. All these aspects impact upon the design of new SACs, which exhibit similarities to hetero- and homogeneous predecessors. Additionally, SACs offer a viable replacement of soluble metal complexes in processes that remain difficult to heterogenize.
RESUMEN
Palladium-catalysed cross-coupling reactions, central tools in fine-chemical synthesis, predominantly employ soluble metal complexes despite recognized challenges with product purification and catalyst reusability1-3. Attempts to tether these homogeneous catalysts on insoluble carriers have been thwarted by suboptimal stability, which leads to a progressively worsening performance due to metal leaching or clustering4. The alternative application of supported Pd nanoparticles has faced limitations because of insufficient activity under the mild conditions required to avoid thermal degradation of the substrates or products. Single-atom heterogeneous catalysts lie at the frontier5-18. Here, we show that the Pd atoms anchored on exfoliated graphitic carbon nitride (Pd-ECN) capture the advantages of both worlds, as they comprise a solid catalyst that matches the high chemoselectivity and broad functional group tolerance of state-of-the-art homogeneous catalysts for Suzuki couplings, and also demonstrate a robust stability in flow. The adaptive coordination environment within the macroheterocycles of ECN facilitates each catalytic step. The findings illustrate the exciting opportunities presented by nanostructuring single atoms in solid hosts for catalytic processes that remain difficult to heterogenize.
RESUMEN
The adsorption of the anticoagulant warfarin onto unmodified (UMS) and modified (phenyl (PhMS), methyl (MMS), mercaptopropyl (MPMS)) mesoporous silica materials was studied at pH 1.6 and 7.4 and in the temperature range of 293-325 K. The silica materials were prepared by sol-gel method for further characterization by FTIR spectroscopy, N2 adsorption/desorption method, transmission electron microscopy and zeta potential measurements. The effects of medium pH, temperature and surface modification of mesoporous silica material on their adsorption characteristics (adsorption capacity, thermodynamic parameters of adsorption) relative to anticoagulant warfarin were investigated. It was found that medium acid-base properties strongly affect the adsorption of warfarin due to the pH-dependent structural diversity of the drug and ionization state of the silica surfaces. The adsorption capacity of the silica materials at pH 1.6 decreases in the order: MMS > MPMS > UMS > PhMS. The influence of various non-covalent interactions on the adsorption capacity of the silica materials and energy of the drug-silica interactions is discussed. These results may be useful for the development of a novel delivery system of warfarin.