Three-dimensional hierarchical Prussian blue composed of ultrathin nanosheets: enhanced hetero-catalytic and adsorption properties

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.

Removal of cesium and strontium for radioactive wastewater by Prussian blue nanorods

In this work, novel Prussian blue tetragonal nanorods were prepared by template-free solvothermal methods to remove radionuclide Cs and Sr. The as-prepared Prussian blue nanorods were identified and characterized by scanning electron microscopy, transmission electron microscope, Fourier transform infrared spectroscopic, thermogravimetric analysis, zeta potential, and surface analysis, and its sorption performance was tested by batch experiments. Our results suggest that Prussian blue nanorods exhibited better adsorption performance than co-precipitation PB or Prussian blue analogue composites. Thermodynamic analysis implied that the adsorption process was spontaneous and endothermic which was described well with the Langmuir isotherm and pseudo-second-order equation. The maximum adsorption capacity of PB nanorod was estimated to be 194.26 mg g^-1 and 256.62 mg g^-1 for Cs⁺ and Sr²⁺(adsorbate concentration at 500 mg L^-1, the temperature at 298 k, pH at 7.0). Moreover, the experimental results showed that the Prussian blue nanorods have high crystallinity, few crystal defects, and good stability under alkaline conditions. The adsorption mechanism of Cs⁺ and Sr²⁺ was studied by X-ray photoelectron spectroscopy, X-ray diffraction, and ⁵⁷Fe Mössbauer spectroscopy. The results revealed that Cs⁺ entered the PB crystal to generate a new phase, and most of Sr²⁺ was trapped in the internal crystal and the other exchanged Fe²⁺. Furthermore, the effect of co-existing ions and pH on PB adsorption process was also investigated. The results suggest that PB nanorods were an outstanding candidate for removing Cs⁺ and Sr²⁺ from radioactive wastewater.

Novel One-Pot Solvothermal Synthesis of High-Performance Copper Hexacyanoferrate for Cs+ Removal from Wastewater

Efficient removal of radioactive cesium from complex wastewater is a challenge. Unlike traditional precipitation and hydrothermal synthesis, a novel vast specific surface area adsorbent of copper hexacyanoferrates named EA-CuHCF was synthesized using a one-pot solvothermal method under the moderate ethanol media characterized by XRD, SEM, EDS, BET, and FTIR. It was found that the maximum adsorption capacity towards Cs+ was 452.5 mg/g, which is far higher than most of the reported Prussian blue analogues so far. Moreover, EA-CuHCF could effectively adsorb Cs+ at a wide pH range and low concentration of Cs+ in geothermal water within 30 minutes, and the removal rate of Cs+ was 92.1%. Finally, the separation factors between Cs+ and other competitive ions were higher than 553, and the distribution coefficient of Cs+ reached up to 2.343 × 104 mL/g. These properties suggest that EA-CuHCF synthesized by the solvothermal method has high capacity and selectivity and can be used as a candidate for Cs+ removal from wastewater.

Prussian Blue: A Nanozyme with Versatile Catalytic Properties

Nanozymes, nanomaterials with enzyme-like activities, are becoming powerful competitors and potential substitutes for natural enzymes because of their excellent performance. Nanozymes offer better structural stability over their respective natural enzymes. In consequence, nanozymes exhibit promising applications in different fields such as the biomedical sector (in vivo diagnostics/and therapeutics) and the environmental sector (detection and remediation of inorganic and organic pollutants). Prussian blue nanoparticles and their analogues are metal–organic frameworks (MOF) composed of alternating ferric and ferrous irons coordinated with cyanides. Such nanoparticles benefit from excellent biocompatibility and biosafety. Besides other important properties, such as a highly porous structure, Prussian blue nanoparticles show catalytic activities due to the iron atom that acts as metal sites for the catalysis. The different states of oxidation are responsible for the multicatalytic activities of such nanoparticles, namely peroxidase-like, catalase-like, and superoxide dismutase-like activities. Depending on the catalytic performance, these nanoparticles can generate or scavenge reactive oxygen species (ROS).

Prussian Blue Analogs and Their Derived Nanomaterials for Electrochemical Energy Storage and Electrocatalysis

Prussian blue analogs (PBAs), the oldest artificial cyanide-based coordination polymers, possess open framework structures, large specific surface areas, uniform metal active sites, and tunable composition, showing significant perspective in electrochemical energy storage. These electrochemically active materials have also been converted to various functional metal containing nanomaterials, including carbon encapsulated metals/metal alloys, metal oxides, metal sulfides, metal phosphides, etc. originating from the multi-element compositions as well as elaborate structure design. In this paper, a comprehensive review will be presented on the recent progresses in the development of PBA frameworks and their derivatives based electrode materials and electrocatalysts for electrochemical energy storage and conversion. In particular, it will focus on the synthesis of representative nanostructures, the structure design, and figure out the correlation between nanomaterials structure and electrochemical performance. Lastly, critical scientific challenges in this research area are also discussed and perspective directions for the future research in this field are provided, in order to provide a brand new vision into the further development of novel active materials for the next-generation advanced electrochemical devices.

Berlin Green Framework-Based Gas Sensor for Room-Temperature and High-Selectivity Detection of Ammonia

Ammonia detection possesses great potential in atmosphere environmental protection, agriculture, industry, and rapid medical diagnosis. However, it still remains a great challenge to balance the sensitivity, selectivity, working temperature, and response/recovery speed. In this work, Berlin green (BG) framework is demonstrated as a highly promising sensing material for ammonia detection by both density functional theory simulation and experimental gas sensing investigation. Vacancy in BG framework offers abundant active sites for ammonia absorption, and the absorbed ammonia transfers sufficient electron to BG, arousing remarkable enhancement of resistance. Pristine BG framework shows remarkable response to ammonia at 50-110 °C with the highest response at 80 °C, which is jointly influenced by ammonia's absorption onto BG surface and insertion into BG lattice. The sensing performance of BG can hardly be achieved at room temperature due to its high resistance. Introduction of conductive Ti₃CN MXene overcomes the high resistance of pure BG framework, and the simply prepared BG/Ti₃CN mixture shows high selectivity to ammonia at room temperature with satisfying response/recovery speed.

Prussian Blue: A Safe Pigment with Zeolitic-Like Activity

Prussian blue (PB) and PB analogues (PBA) are coordination network materials that present important similarities with zeolites concretely with their ability of adsorbing cations. Depending on the conditions of preparation, which is cheap and easy, PB can be classified into soluble PB and insoluble PB. The zeolitic-like properties are mainly inherent to insoluble form. This form presents some defects in its cubic lattice resulting in an open structure. The vacancies make PB capable of taking up and trapping ions or molecules into the lattice. Important adsorption characteristics of PB are a high specific area (370 m2 g-1 determined according the BET theory), uniform pore diameter, and large pore width. PB has numerous applications in many scientific and technological fields. PB are assembled into nanoparticles that, due to their biosafety and biocompatibility, can be used for biomedical applications. PB and PBA have been shown to be excellent sorbents of radioactive cesium and radioactive and nonradioactive thallium. Other cations adsorbed by PB are K+, Na+, NH4+, and some divalent cations. PB can also capture gaseous molecules, hydrocarbons, and even luminescent molecules such as 2-aminoanthracene. As the main adsorptive application of PB is the selective removal of cations from the environment, it is important to easily separate the sorbent of the purified solution. To facilitate this, PB is encapsulated into a polymer or coats a support, sometimes magnetic particles. Finally, is remarkable to point out that PB can be recycled and the adsorbed material can be recovered.

Solvent-assisted synthesis of dendritic cerium hexacyanocobaltate and derived porous dendritic Co3O4/CeO2 as supercapacitor electrode materials

Here, we report a solvent-mediated synthetic route for preparing cerium hexacyanocobaltate with a dendritic shape. The porous dendritic Co₃O₄/CeO₂ was prepared after annealing at 500 °C, served as a supercapacitor electrode.

Hierarchically porous metal-organic frameworks: synthesis strategies, structure(s), and emerging applications in decontamination

Metal-organic frameworks (MOFs) with high porosity have received much attention as promising materials for many applications owing to their unique properties. However, to date, most of the reported MOFs have microporous structures, which slow down diffusion/mass transfer and limit the accessibility of bulky molecules to its internal surface. Thus, it is crucial to develop an efficient way to create larger pores (mesoporous and/or macroporous) into microporous MOFs to form hierarchical porous metal-organic frameworks (HP-MOFs), which facilitate the diffusion and mass transfer of guest molecules. HP-MOFs are excellent and promising candidates for environmental applications under the background of environmental contaminations. In this review paper, we are primarily focusing on the latest progress in the preparation of HP-MOFs by employing template-assisted and template-free synthetic approaches for environmental cleaning applications. Particularly, the adsorptive purification of the most common toxic substances, including gases, dyes, heavy metal ions, and antibiotics from the environment using HP-MOFs as adsorbents is briefly discussed. The overall results clearly showed that the superiority of HP-MOFs compared with conventional microporous MOFs. Finally, we summarize the remaining challenges and provide personal perspectives on possible future development of HP-MOFs.

3D Self-Supported Porous NiO@NiMoO4 Core-Shell Nanosheets for Highly Efficient Oxygen Evolution Reaction

Novel 3D self-supported porous NiO@NiMoO₄ core-shell nanosheets are grown on nickel foam through a facile stepwise hydrothermal method. Ultrathin NiO nanosheets on the nickel foam cross-linked to each other are used as the core, and tiny NiMoO₄ nanosheets are further engineered to be immobilized uniformly on the NiO nanosheets to form the shell. This step-by-step construction of the architecture composed of ultrathin primary and secondary nanosheets efficiently avoids the agglomeration problems of individual ultrathin nanosheets. The ingenious architecture possesses the advantages of numerous diffusion channels for electrolyte ions, ideal pathways for electrons, and a large interfacial area for electrochemical reaction. The introduction of the NiMoO₄ secondary nanosheets on the NiO primary nanosheets not only endows the heterostructure with high electrical conductivity and a large active area but also promotes an increase in oxygen vacancy content, which favors the improvement of electrocatalytic properties for the oxygen evolution reaction. The Tafel plot for the NiO@NiMoO₄ core-shell architecture is as low as 32 mV dec^-1, and the overpotential needed to reach 10 mA·cm^-2 for NiO@NiMoO₄ nanosheets is only 0.28 V.

Hierarchically structured TiO2-based composites for Fenton-type oxidation processes

A novel hierarchically structured composite aimed as a stable catalyst for the heterogeneous Fenton-type (HFT) oxidation process was developed by using a cost-effective and versatile technique. Prussian Blue nanoparticles (PBNP) were dispersed onto aligned macroporous TiO₂ (rutile) monoliths prepared via directional freezing of aqueous dispersions of TiO₂ nanoparticles. The catalytic performance was evaluated in the HFT oxidation of an azo dye frequently used as a model contaminant, Orange G (OG). Experiments were carried out in a liquid batch-recycle reactor, in which the liquid flow rate was set to ensure negligible external mass transfer resistance. The catalyst exhibited good activity to form highly oxidative radicals from hydrogen peroxide decomposition, which readily discolored OG. Significant reduction of the time required to attain complete discoloration and improvement in TOC removal were achieved by adjusting operating conditions and oxidant dosage strategies. Almost complete OG conversion at around 90 min and 34.4% of TOC removal after 4 h were achieved by using the best evaluated strategy. The catalyst activity was tested under specific operating conditions and remained unaltered during 42 cycles of 4 h each (total 168 h). The fresh and used PBNP/TiO₂ catalysts and the support were thoroughly characterized by several techniques. Results supported the excellent stability exhibited by the catalyst in the OG HFT oxidation.

Prussian blue-encapsulated Fe3O4 nanoparticles for reusable photothermal sterilization of water

Waterborne health issues continue to grow despite the large number of available solutions. Current sterilization techniques to fight with waterborne diseases struggle to meet the demands on cost, efficiency and reach. Effective alternatives are pressingly required. Here we introduce Prussian blue coated ferroferric oxide (Fe₃O₄@PB) composites for water sterilization. The composites exhibit superior photothermal inactivation of bacteria under solar-light irradiation, with nearly complete inactivation of bacterial cells in only 15 min. Even for the mixed bacteria in authentic water matrices, the composites show excellent bacterial inactivation performance. Moreover, the highly magnetized iron core of the Fe₃O₄@PB enables magnetic separation and recycling. Multiple cycle runs reveal that Fe₃O₄@PB composites have exceptional stability and reusability. This work demonstrates a scalable, low-cost, high-efficiency and reusable sterilization method to improve water quality and safety.

The electronic structure of f-element Prussian blue analogs determined by soft X-ray absorption spectroscopy

In molecular solids derived from Prussian blue, intermetallic charge transfer is fostered through a cyano bridge two metal ions. In this study, isostructural trivalent lanthanide and tetravalent actinide Prussian blue analogs' valence orbitals are probed by soft X-ray absorption measurements.

Microwave-assisted CVD-like synthesis of dispersed monolayer/few-layer N-doped graphene encapsulated metal nanocrystals for efficient electrocatalytic oxygen evolution

Herein a novel and general microwave-assisted chemical vapor deposition (CVD)-like synthetic strategy was developed to realize the ultrafast synthesis of a series of well-dispersed monolayer/few-layer N-doped graphene shell encapsulated metal nanocrystals (M@NC) by using a metal-organic framework (MOF) on graphene as precursors for the first time. Unlike traditional programmed heat treatment, this microwave-assisted method decomposed the MOF into separated metal and carbon- and nitrogen-containing gases rather than aggregated metal and carbon composites during the initial thermal transformation stages. This change ensured the effective control of the subsequent formation process of carbon on the surface of metal and led to the formation of well-dispersed M@NC with monolayer/few-layer NC. Moreover, the graphene substrate promoted the full exposure of all active monolayer/few-layer NC, and thus the obtained FeNi@NC/graphene displays the best electrocatalytic properties for the oxygen evolution reaction of all of the previously reported M@NC based catalysts, including the lowest overpotential (261 mV) at 10 mA cm-2 in alkaline electrolyte (1 M KOH), the smallest Tafel slope (40 mV dec-1) and excellent durability for at least 120 h.

Self-Templating Synthesis of Cobalt Hexacyanoferrate Hollow Structures with Superior Performance for Na-Ion Hybrid Supercapacitors

Prussian blue (PB) and its analogues (PBA), especially with hollow structures, have attracted growing attention from the researchers of energy storage field. Herein, we have developed a facile self-templating method to synthesize hollow-structured cobalt hexacyanoferrate (CoHCF) with controllable morphologies by using water-soluble precursors as templates. The method is versatile and can be extended to synthesize various PB/PBA hollow structures with tunable composition and morphology. Profiting from the unique hollow structure, the CoHCF hollow prisms manifest exceptional electrochemical performance in the Na₂SO₄ aqueous electrolyte, including a high specific capacitance (284 F g^-1 at 1 A g^-1), a high rate capability, and an excellent cycling stability (92% retention after 5000 cycles). A hybrid supercapacitor device assembled with the CoHCF hollow prisms and activated carbon shows a high specific density of 47 W h kg^-1 at a specific power of 1000 W kg^-1 and stable cycling performance.

Batch and fixed-bed column studies for selective removal of cesium ions by compressible Prussian blue/polyurethane sponge

Compressible Prussian blue/polyurethane sponges for selective removal of cesium ions were prepared and detailedly studied via fixed-bed column/batch adsorption experiments.

Hierarchical α-Ni(OH)2 Composed of Ultrathin Nanosheets with Controlled Interlayer Distances and Their Enhanced Catalytic Performance

Hierarchical α-Ni(OH)₂ assembled of ultrathin nanosheets with the intercalation of diatomic alcohol molecules were synthesized via a facile one-step solvothermal process. The assembly structure avoided the agglomeration of ultrathin nanosheets while retaining their atomic-scale thickness and high surface area. The intercalation of the diatomic alcohol molecules into the transition-metal layers provided larger interlayer spacing and more exposed active sites, which guaranteed the high activity of the α-Ni(OH)₂. The as-obtained hierarchical α-Ni(OH)₂ exhibited excellent catalytic performance in the reduction of p-nitrophenol, with a maximum reaction rate constant (k) of 6.23 × 10^-3 s^-1 and a super high activity factor K (K = k/m) of 216.69 s^-1 g^-1. The layer spacing played the most important role in the reaction, and the catalytic efficiency increased greatly with the increase of the layer spacing of the α-Ni(OH)₂. This design concept and synthetic method can also be extended to the production of a wide variety of hierarchical catalysts for other reactions.

Porous Fe2O3 Nanoframeworks Encapsulated within Three-Dimensional Graphene as High-Performance Flexible Anode for Lithium-Ion Battery

Integrating nanoscale porous metal oxides into three-dimensional graphene (3DG) with encapsulated structure is a promising route but remains challenging to develop high-performance electrodes for lithium-ion battery. Herein, we design 3DG/metal organic framework composite by an excessive metal-ion-induced combination and spatially confined Ostwald ripening strategy, which can be transformed into 3DG/Fe₂O₃ aerogel with porous Fe₂O₃ nanoframeworks well encapsulated within graphene. The hierarchical structure offers highly interpenetrated porous conductive network and intimate contact between graphene and porous Fe₂O₃ as well as abundant stress buffer nanospace for effective charge transport and robust structural stability during electrochemical processes. The obtained free-standing 3DG/Fe₂O₃ aerogel was directly used as highly flexible anode upon mechanical pressing for lithium-ion battery and showed an ultrahigh capacity of 1129 mAh/g at 0.2 A/g after 130 cycles and outstanding cycling stability with a capacity retention of 98% after 1200 cycles at 5 A/g, which is the best results that have been reported so far. This study offers a promising route to greatly enhance the electrochemical properties of metal oxides and provides suggestive insights for developing high-performance electrode materials for electrochemical energy storage.

Facile one-pot synthesis of magnetic Prussian blue core/shell nanoparticles for radioactive cesium removal

Magnetic Prussian blue/Fe₃O₄ core/shell nanoparticles for radioactive cesium removal were successfully fabricated via a facile one-pot method.