Super-alkalis as building blocks of one-dimensional hierarchical electrides

Photoacid-macroion assemblies: how photo-excitation switches the size of nano-objects

Electrostatic self-assembly of photoacids with oppositely charged macroions yields supramolecular nano-objects in aqueous solutions, whose size is controlled through light irradiation. Nano-assemblies are formed due to electrostatic attractions and mutual hydrogen bonding of the photoacids. Irradiation with UV light leads to the deprotonation of the photoacid and, consequently, a change in particle size. Overall, the hydrodynamic radii of the well-defined photoacid-macroion nano-objects lie between 130 and 370 nm. For a set of photoacids, we determine the acidity constants in the ground and excited state, discuss the sizes of photoacid-macroion nano-objects (by dynamic and static light scattering), their composition and the particle shapes (by small-angle neutron scattering), and relate their charge characteristics to size, structure and shape. We investigate the association thermodynamics and relate nanoscale structures to thermodynamics and, in turn, thermodynamics to molecular features, particularly the ionization energy of the photoacid hydroxyl group proton. Structure-directing effects completely differ from those for previously investigated systems, with hydrogen bonding and entropic effects playing a major role herein. This combined approach allows developing a comprehensive understanding of assembly formation and photo-response, anchored in molecular parameters (pKa, ionization energy, substituent group location), charge characteristics, and the association enthalpy and entropy. This fundamental understanding again paves the way for tailoring application solutions with novel photoresponsive materials.

Anisotropic electrene T'-Ca2P with electron gas magnetic coupling as anode material for Na/K ion batteries

There is an urgent need for high-performance rechargeable electrical storage devices as a supplement or a substitution for lithium ion batteries (LIBs) due to the shortage of lithium in nature. Herein we propose a stable 2D electrene T'-Ca₂P as an anode material for Na/K ion batteries developed using first principles calculations. Our calculated results show that the T'-Ca₂P monolayer is an antiferromagnetic semiconducting electrene with a spin-polarized electron gas. It exhibits suitable adsorption for both Na and K atoms, and its anisotropic migration energy barriers are 0.050/0.101 eV and 0.037/0.091 eV in the b/a direction, respectively. The theoretical capacities for Na and K are both 482 MA h g^-1, whereas the average working voltage platforms are 0.171-0.226 V and 0.013-0.267 V, respectively. All the results reveal that the T'-Ca₂P monolayer has promising prospects for application as an anode material for Na/K ion batteries.

Role of Size and Composition on the Design of Superalkalis

Superalkalis and superhalogens are atomic clusters that mimic the chemistry of alkali and halogen atoms, respectively; the ionization energies of the superalkalis are less than those of alkali atoms, while the electron affinities of superhalogens are larger than those of the halogen atoms. These superions can serve as the building blocks of a new class of supersalts with applications in solar cells, metal-ion batteries, multiferroic materials, and so on. While considerable progress has been made in the design and synthesis of superhalogens, a similar understanding of superalkalis is lacking. Using density functional theory with hybrid exchange-correlation functional and Gaussian basis sets, we have systematically studied the role of size and composition on the properties of two different classes of clusters whose stabilities are governed by the Wade-Mingos polyhedral skeletal electron pair theory. One class belongs to the closo-borane family Li_mB_nX_n (m = 1, 2, 3; n = 6, 12; X = H, F, CN), while the other to the Zintl ions Li_m[Be@Ge₉]. We show that Li₃B_nX_n and Li₃[Be@Ge₉] clusters are superalkalis with ionization energies as low as 2.84 eV in Li₃B₆H₆. However, contrary to expectation, the ionization energies do not decrease with increasing cluster volume. Instead, ionization energies are linked to the X ligands' electron affinities; the larger the electron affinity, the higher is the ionization energy. The understanding gained here will help in the discovery of superalkalis and, hence, enrich the library of supersalts.

Two-dimensional Ca4N2 as a one-dimensional electride [Ca4N2]2+·2e- with ultrahigh conductance

Electrides possess high electrical conductance and reactivity and are promising for novel applications in electronics and catalysis. Here, we predict a new thermodynamically and kinetically stable two-dimensional (2D) Ca4N2 using first-principles density functional theory (DFT) calculations. 2D Ca4N2 can serve as a one-dimensional (1D) electride [Ca4N2]2+·2e- with anionic electrons confined in the surface channels. In particular, we demonstrate that 2D Ca4N2 possesses high Fermi velocity (0.42 × 106 m s-1), electron effective Fermi mass (∼1me), ultrahigh charge density (1.14 × 1015 cm-2), and high carrier mobility (215 and 5.29 × 106 cm2 V-1 s-1 at a room temperature of 300 K and a low temperature of 2 K), resulting in ultrahigh conductance up to 0.039 and 966 S respectively for 300 and 2 K, compared to existing 2D materials and the best conductors (Cu and Ag). Furthermore, the first finding of 1D anionic electron behaviour on the surface of 2D materials can be used to stimulate the design of new kinds of electrides for exploring the physics of 1D and quasi-1D systems.

Theoretical investigation of perfect fullerene-like borospherene Ih-B20 protected by alkaline earth metal: multi-layered spherical electride molecules as electric field manipulated second-order nonlinear optical switches

A perfect fullerene-like borospherene B₂₀ with 12 B₅ rings stabilized in the electride molecule (Mg²⁺)₁₂&B₂₀¹⁸⁻ + 6e⁻.

Record-high stability and compactness of multiply-charged clusters aided by selected terminal groups

Multiply-charged clusters with compact sizes that are stable in the gas phase are important due to their potential applications as weakly-coordinating ions and building blocks of bulk materials.

Nanotechnology and nanomaterial-based no-wash electrochemical biosensors: from design to application

Nanotechnology and nanomaterial based electrochemical biosensors (ECBs) have achieved great development in many fields, such as clinical diagnosis, food analysis, and environmental monitoring. Nowadays, the single-handed pursuit of sensitivity and accuracy cannot meet the demands of detection in many in situ and point-of-care (POC) circumstances. More and more attention has been focused on simplifying the operation procedure and reducing detection time, and thus no-wash assay has become one of the most effective ways for the continuous development of ECBs. However, there are many challenges to realize no-wash detection in the real analysis, such as redox interferences, multiple impurities, non-conducting protein macromolecules, etc. Furthermore, the complex detection circumstance in different application fields makes the realization of no-wash ECBs more complicated and difficult. Thanks to the updated nanotechnology and nanomaterials, in-depth analysis of the obstacles in the detection process and various methods for fabricating no-wash ECBs, most issues have been largely resolved. In this review, we have systematically analyzed the nanomaterial based design strategy of the state-of-the-art no-wash ECBs in the past few years. Following that, we summarized the challenges in the detection process of no-wash ECBs and their applications in different fields. Finally, based on the summary and analysis in this review, we also evaluated and discussed future prospects from the design to the application of ECBs.

Recent Progress on the Design, Characterization, and Application of Superalkalis

Superalkalis are clusters or molecules featuring lower ionization energies (IEs) than that of cesium atoms, and thus exhibit excellent reducing properties. Such special species have great potential to be used in the synthesis of unusual charge-transfer salts and cluster-assembled nanomaterials with tailored properties, in the reduction of carbon dioxide, or as hydrogen storage materials and noble-gas-trapping agents, etc. In this regard, ongoing efforts have been devoted to designing and characterizing superalkalis of new types. The recent progress on the study of superalkalis in terms of theoretical design, characterization, and potential application is summarized in this minireview. We hope this review will not only provide a broad overview of this research field, but also highlight the prospect of further extending the experimental synthesis and practical application of superalkalis.

Mechanistic Insight into Photocatalytic Pathways of MIL-100(Fe)/TiO2 Composites

The integration of metal-organic frameworks (MOFs) with semiconductors has attracted mounting attention for photocatalytic applications. However, more efforts are needed to unravel the interface structure in MOF/semiconductor composites and its role in charge transfer. Herein, a MIL-100(Fe)/TiO₂ composite was synthesized as a prototypical photocatalyst and studied systematically to explore the interface structure and unravel the charge transfer pathways during the photocatalytic processes. The composite was fabricated by growing MIL-100(Fe) crystals on TiO₂ using surface-coated FeOOH as the precursor. The as-prepared MIL-100(Fe)/TiO₂ exhibited significantly improved photocatalytic performance over pristine TiO₂, which was mainly because of the enhanced charge separation as confirmed by transient absorption spectroscopy analysis. This enhancement partially arose from the special chemical structure at the interface, where the Fe-O-Ti bond was formed. As verified by the density functional theory calculation, this distinct structure would create defect energy levels adjacent to the valence band maximum of TiO₂. During the photocatalytic processes, the defect energy levels serve as sinks to capture excited charge carriers and retard the recombination, which subsequently leads to the increased charge density and promoted photocatalytic efficiency. Meanwhile, the intimate interactions between MIL-100(Fe) and TiO₂ would also help to improve the charge separation by transferring photo-induced holes through the ligands to Fe-O clusters. These findings would advance the fundamental understanding of the interface structure and the charge transfer pathways in MOF/semiconductor composite photocatalysts.