Hofmann-Type Cyanide Bridged Coordination Polymers for Advanced Functional Nanomaterials

Since the discovery of Hofmann clathrates of inorganic cyanide bridged coordination polymers (Hofmann-type CN-CPs), extensive research is done to understand their behavior during spin transitions caused by guest molecules or external stimuli. Lately, research on their nanoscale architectures for sensors and switching devices is of interest. Their potential is reported for producing advanced functional inorganic materials in two-dimensional (2D) morphology using a scalable solid-state thermal treatment method. For instance, but not restricted to, alloys, carbides, chalcogenides, oxides, etc. Simultaneously, their in situ crystallization at graphene oxide (GO) nanosheet surfaces, followed by a subsequent self-assembly to build layered lamellar structures, is reported providing hybrid materials with a variety of uses. Hence, an overview of the most recent developments is presented here in the synthesis of nanoscale structures, including thin films and powders, using Hofmann-type CN-CPs. Also thoroughly demonstrated are the most recent synthetic ideas with the modest control over the size and shape of nanoscale particles. Additionally, in order to create new functional hybrid materials for electrical and energy applications, their thermal decomposition in various environments and hybridization with GO and other guest molecules is examined. This review article also conveyed their spin transition, astounding innovative versatile adhesives, and structure features.

In situ growth of Prussian blue analogue-derived Fe-doped NiS on Ni(OH)2 for efficient hydrogen evolution reaction

The energy industry is placing more and more emphasis on the need for effective and affordable electrocatalysts for hydrogen evolution reactions (HER). In this work, an iron-doped NiS/Ni(OH)₂/CC composite material was synthesized by simple hydrothermal sulfurization processes of bimetallic Prussian blue analogue (PBAs) precursors grown in situ on three-dimensional (3D) Ni(OH)₂ nanosheets. The overpotential can be 103 mV to attain current densities of 10 mA cm^-2. The excellent catalytic activity of Fe-NiS/Ni(OH)₂/CC is because of the unique 3D structure and the uniform doping of iron caused by the in situ growth of PBA, as well as the high conductivity of the self-supported electrode carbon cloth.

New Concept for the Facile Fabrication of Core-Shell CuO@CuFe2O4 Photocathodes for PEC Application

The CuO@CuFe₂O₄ core–shell structure represents a new family of photocatalysts that can be used as photoelectrodes that are able to produce hydrogen under a broad spectrum of visible light. Herein, we report a novel approach for the production of this active film by the thermal conversion of CuFe Prussian Blue Analogues. The outstanding photoelectrochemical properties of the photocathodes of CuO@CuFe₂O₄ were studied with the use of combinatory photo-electrochemical instrumental techniques which proved that the electrodes were stable over the whole water photolysis run under relatively positive potentials. Their outstanding performance was explained by the coupling of two charge transfer mechanisms occurring in core–shell architectures.

Ligand-induced synthesis of two Cu-based coordination polymers and derivation of carbon-coated metal oxide heterojunctions for enhanced photocatalytic degradation

In this study two new Cu-CPs have been constructed as precursors for the preparation of carbon-coated metal oxide heterojunctions. Moreover, we have used Mo metal as a doping agent to boost the photodegradation activity of the CP-derived carbon nanostructures.

Thermal Decomposition Behavior of Prussian Blue in Various Conditions

Prussian blue analogs (PBA) are widely studied for radioactive cesium decontamination. However, there are fewer works related to their post use storage. Considering the oxidative stabilization of the material after the selective uptake of Cs, the thermogravimetric properties in powder and bead form, with various Cs and other alkali metal ions adsorbed, and various heating rates were studied. TG-DTA taken in dry air condition shows an exothermic decomposition at ~270 °C. This temperature varied with the heating rate, mass, and the proportion of adsorbed ions. The best condition for complete oxidation of Prussian blue (PB) is found to be a gradual oxidative decomposition by heating in the temperature range of 200–220 °C until the total mass is decreased by >35%. After this, the temperature could be safely increased to >300 °C for the complete oxidative decomposition of PB that formed iron oxide and salt of the adsorbed Cs. A pilot scale test conducted using the radioactive Cs adsorbed Prussian blue microbeads (PB-b) confirmed that no Cs was released in the effluent air during the process.

Mechanistic insight in site-selective and anisotropic etching of prussian blue analogues toward designable complex architectures for efficient energy storage

Engineering coordination compounds, e.g., prussian blue (PB) and its analogues (PBAs), with designable complex nanostructures via chemical etching holds great opportunities for improving energy storage performances by adjusting topological geometry, selectively exposing active sites, tuning electronic properties and enhancing accessible surface area. Unfortunately, it remains ambiguous particularly on site-selective and anisotropic etching behaviors. Herein, for the first time, we propose that two distinct regions are formed inside NiCo PBA (NCP) cubes due to the competition between classical ion-by-ion crystallization and non-classical crystallization based on aggregation. Such a unique structure ultimately determines not only the etching position but also the anisotropic pathway by selectively exposing unprotected Ni sites. According to this principle, complex PBA architectures, including nanocages, open nanocubes (constructed by six cones sharing the same apex), nanocones, and chamfer nanocubes can be intentionally obtained. After thermal annealing, NCP nanocones are converted to morning glory-like porous architectures composed of NiO/NiCo2O4 heterostructures with a mean particle size of 5 nm, which show improved rate performance and cycling stability.

Hierarchical porous CoxFe3−xO4 nanocubes obtained by calcining Prussian blue analogues as anodes for lithium-ion batteries

Prussian blue analogue derived hierarchical porous Co_xFe_3−xO₄ nanocubes applied as LIBs anode material can provide large space to buffer volume expansion during the Li⁺ insertion/extraction processes and enhanced electrochemical performance.

Towards the synthesis of mixed oxides with controlled stoichiometry from Prussian blue analogues

The calcination of (nano) Prussian blue analogues is now a fully controlled and understood route to synthesize Co–Fe spinel oxides.

Cyano-Bridged Cu-Ni Coordination Polymer Nanoflakes and Their Thermal Conversion to Mixed Cu-Ni Oxides

Herein, we demonstrate the bottom-up synthesis of 2D cyano-bridged Cu-Ni coordination polymer (CP) nanoflakes through a controlled crystallization process and their conversion to Cu-Ni mixed oxides via a thermal treatment in air. The chelating effect of citrate anions effectively prevents the rapid coordination reaction between Cu²⁺ and K₂[Ni(CN)₄], resulting in the deceleration of the crystallization process of CPs. Specifically, with addition of trisodium citrate dehydrate, the number of nuclei formed at the early stage of the reaction is decreased. Less nuclei undergo a crystal growth by interacting with [Ni(CN)₄]^2-, leading to the formation of larger Cu-Ni CP nanoflakes. Following heat treatment in air, the -CN- groups present within the CP nanoflakes are removed and nanoporous Cu-Ni mixed oxide nanoflakes are generated. When tested as an electrode material for supercapacitors using a three-electrode system, the optimum Cu-Ni mixed oxide sample shows a maximum specific capacitance of 158 F g^-1 at a current density of 1 A g^-1. It is expected that the proposed method will be useful for the preparation of other types of 2D and 3D CPs as precursors for the creation of various nanoporous metal oxides.

Synthesis of Hollow Co-Fe Prussian Blue Analogue Cubes by using Silica Spheres as a Sacrificial Template

Herein, we report a novel method for the formation of hollow Prussian blue analogue (CoFe–PBA) nanocubes, using spherical silica particles as sacrificial templates. In the first step, silica cores are coated by a CoFe–PBA shell and then removed by etching with hydrofluoric acid (HF). The cubic shape of CoFe–PBA is well‐retained even after the removal of the silica cores, resulting in the formation of hollow CoFe–PBA cubes. The specific capacity of the hollow CoFe–PBA nanocubes electrodes is about two times higher than that of solid CoFe–PBA nanocubes as storage materials for sodium ions. Such an improvement in the electrochemical properties can be attributed to their hollow internal nanostructure. The hollow architecture can offer a larger interfacial area between the electrolyte and the electrode, leading to an improvement in the electrochemical activity. This strategy can be applied to develop PBAs with hollow interiors for a wide range of applications.

Ion exchange for synthesis of porous CuxO/SnO2/ZnSnO3 microboxes as a high-performance lithium-ion battery anode

Integrating other oxides and ZnSnO₃ with porous structures can accommodate volume expansion and enhance the electrochemical performance.

Carbon-Coated Fe3O4/VOx Hollow Microboxes Derived from Metal-Organic Frameworks as a High-Performance Anode Material for Lithium-Ion Batteries

As the ever-growing demand for high-performance power sources, lithium-ion batteries with high storage capacities and outstanding rate performance have been widely considered as a promising storage device. In this work, starting with metal-organic frameworks, we have developed a facile approach to the synthesis of hybrid Fe₃O₄/VO_x hollow microboxes via the process of hydrolysis and ion exchange and subsequent calcination. In the constructed architecture, the hollow structure provides an efficient lithium ion diffusion pathway and extra space to accommodate the volume expansion during the insertion and extraction of Li⁺. With the assistance of carbon coating, the obtained Fe₃O₄/VO_x@C microboxes exhibit excellent cyclability and enhanced rate performance when employed as an anode material for lithium-ion batteries. As a result, the obtained Fe₃O₄/VO_x@C delivers a high Coulombic efficiency (near 100%) and outstanding reversible specific capacity of 742 mAh g^-1 after 400 cycles at a current density of 0.5 A g^-1. Moreover, a remarkable reversible capacity of 556 mAh g^-1 could be retained even at a current density of 2 A g^-1. This study provides a fundamental understanding for the rational design of other composite oxides as high-performance electrode materials for lithium-ion batteries.

Synergetic nanoporous Mn–Ru oxides as efficient electrocatalysts for the oxygen reduction reaction

Nanoporous Mn–Ru mixed oxides were derived from Mn–Ru CP nanocubes with a similar morphology through annealing in air at 400 degree for effecient electrocatalytic reduction of oxygen.

Nanostructuring of nanoporous iron carbide spheres via thermal degradation of triple-shelled Prussian blue hollow spheres for oxygen reduction reaction

A controlled thermal treatment of the triple-shelled Prussian blue hollow spheres yielded well-retained nanoporous iron carbide for efficient electrocatalytic ORR.