Nanoarchitectonics of Glass Coatings for Near-Infrared Shielding: From Solid-State Cluster-Based Niobium Chlorides to the Shaping of Nanocomposite Films

Engineering electronic structures of Nb6Ix superatomic clusters by metal atom incorporation: a first-principles study

Akin to the conventional building blocks of solids, the elements in the periodic table, the iodine capped Nb6Ix (x = 12-18) octahedron cluster is a well-known "superatomic building block" for designing not only cluster assemblies like Prussian blue analogues and hybrid perovskites but also for new catalysts. Recent achievements within the realm of atomic clusters using experimental and theoretical approaches have shown synthesis and precise tuning of magnetic and electronic properties of small octahedron clusters via atom-by-atom substitution. In this work, state-of-the-art density functional theory (DFT) calculations highlight the feasibility of tuning the valence electron concentration (VEC) by endohedral doping of 3d-block transition metals (M = Sc-Zn) inside the core of the homo-iodide Nb6 octahedron. The energetics of various structural isomers imply that all other M atoms can be doped within the Nb6Ix cluster with high I atom concentrations, except Sc and Ti. In-depth analysis shows the cohesive energy per atom and the formation energy (FE) of the clusters correlate with various structural and electronic parameters of these clusters exhibiting electronic shell closures with 18 and 24 VEC, with a substantial HOMO-LUMO gap within the range of 0.72 to 1.76 eV using HSE06 hybrid functionals. Interestingly, the FE calculations demonstrate that the MNb6I18 cluster can be formed even under M-rich conditions, having robust formation stability. We further explain how the Gibbs free energy (ΔGH) of adsorbed hydrogen correlates with different d-band centres of Nb and M atoms to highlight the impact of electronic structure on the catalytic activity towards the hydrogen evolution reaction (HER). Thus, it is possible to achieve potential HER catalysts with very small ΔGH for VNb6I18 to CoNb6I18 comparable to the Pt(111) surface. This work provides the atomic structure, stability, and electronic properties of endohedral doped Nb6Ix clusters that can pave the way for various potential applications in catalysis, molecular electronics and spintronics, and for further experimental research.

Topological Flat Bands in 2D Breathing-Kagome Lattice Nb3 TeCl7

Flat bands (FBs) can appear in two-dimensional (2D) geometrically frustrated systems caused by quantum destructive interference (QDI). However, the scarcity of pure 2D frustrated crystal structures in natural materials makes FBs hard to be identified, let alone modulate FBs relating to electronic properties. Here, the experimental evidence of the complete electronic QDI induced FB contributed by the 2D breathing-kagome layers of Nb atoms in Nb3 TeCl7 (NTC) is reported. An identical chemical state and 2D localization characteristics of the Nb breathing-kagome layers are experimentally confirmed, based on which NTC is demonstrated to be a superior concrete candidate for the breathing-kagome tight-binding model. Furthermore, it theoretically establishes the tunable roles of the on-site energy over Nb sites on bandwidth, energy position, and topology of FBs in NTC. This work opens an aveanue to manipulate FB characteristics in these 4d transition-metal-based breathing-kagome materials.

A review on functional nanoarchitectonics nanocomposites based on octahedral metal atom clusters (Nb6, Mo6, Ta6, W6, Re6): inorganic 0D and 2D powders and films

This review is dedicated to various functional nanoarchitectonic nanocomposites based on molecular octahedral metal atom clusters (Nb₆, Mo₆, Ta₆, W₆, Re₆). Powder and film nanocomposites with two-dimensional, one-dimensional and zero-dimensional morphologies are presented, as well as film matrices from organic polymers to inorganic layered oxides. The high potential and synergetic effects of these nanocomposites for biotechnology applications, photovoltaic, solar control, catalytic, photonic and sensor applications are demonstrated. This review also provides a basic level of understanding how nanocomposites are characterized and processed using different techniques and methods. The main objective of this review would be to provide guiding significance for the design of new high-performance nanocomposites based on transition metal atom clusters.

High performance {Nb5TaX12}@PVP (X = Cl, Br) cluster-based nanocomposites coatings for solar glazing applications

The development of highly ultraviolet (UV) and near-infrared (NIR) absorbent transparent coatings is an important enabling technology and area of research for environmental sustainability and energy conservation. Different amounts of K4[{Nb5TaXi 12}Xa 6] cluster compounds (X = Cl, Br) dispersed into polyvinylpyrrolidone matrices were prepared by a simple, nontoxic and low-cost wet chemical method. The resulting solutions were used to fabricate visibly transparent, highly UV and NIR absorbent coatings by drop casting. The properties of the solution and films were investigated by complementary techniques (optical absorption, electrospray ionization mass spectrometry and Raman spectroscopy). The UV and NIR absorption of such samples strongly depended on the concentration, dispersion and oxidation state of the [{Nb5TaXi 12}Xa 6] nanocluster-based units. By varying and controlling these parameters, a remarkable improvement of the figures of merit TL/TE and SNIR for solar-glazing applications was achieved compared to the previous results on nanocomposite coatings based on metal atom clusters.

Controlling the Deposition Process of Nanoarchitectonic Nanocomposites Based on {Nb6-xTaxXi12}n+ Octahedral Cluster-Based Building Blocks (Xi = Cl, Br; 0 ≤ x ≤ 6, n = 2, 3, 4) for UV-NIR Blockers Coating Applications

The antagonism between global energy needs and the obligation to slow global warming is a current challenge. In order to ensure sufficient thermal comfort, the automotive, housing and agricultural building sectors are major energy consumers. Solar control materials and more particularly, selective glazing are part of the solutions proposed to reduce global energy consumption and tackle global warming. In this context, these works are focused on developing new highly ultraviolet (UV) and near-infrared (NIR) absorbent nanocomposite coatings based on K4[{Nb6-xTaxXi12}Xa6]. (X = Cl, Br, 0 ≤ x ≤ 6) transition metal cluster compounds. These compounds contain cluster-based active species that are characterized by their strong absorption of UV and NIR radiations as well as their good transparency in the visible range, which makes them particularly attractive for window applications. Their integration, by solution processes, into a silica-polyethylene glycol or polyvinylpyrrolidone matrices is discussed. Of particular interest is the control and the tuning of their optical properties during the integration and shaping processes. The properties of the solutions and films were investigated by complementary techniques (UV-Vis-NIR spectrometry, ESI-MS, SEM, HRTEM, etc.). Results of these works have led to the development of versatile solar control coatings whose optical properties are competitive with commercialized material.