Synthesis of Mesoporous Single Crystal Co(OH)2 Nanoplate and Its Topotactic Conversion to Dual-Pore Mesoporous Single Crystal Co3O4

Designing Sphere-like FeSe2-Carbon Composites with Rational Construction of Interfacial Traits towards Considerable Sodium-storage Capabilities

Due to their low cost and high stability, sodium-ion batteries have been increasingly studied. However, their further development is limited by the relative energy density, resulting in the search for high-capacity anodes. FeSe₂ displays high conductivity and capacity but still suffers from sluggish kinetics and serious volume expansion. Herein, through sacrificial template methods, a series of sphere-like FeSe₂-carbon composites are successfully prepared, displaying uniform carbon coatings and interfacial chemical FeOC bonds. Moreover, benefiting from the unique traits of precursor and acid treatment, rich structural voids are prepared, effectively alleviating volume expansion. Utilized as anodes of sodium-ion batteries, the optimized sample displays considerable capacity, achieving 462.9 mAh g^-1, with 88.75% coulombic efficiency at 1.0 A g^-1. Even at 5.0 A g^-1, their capacity can be kept at approximately 318.8 mAh g^-1, while the stable cycling can be prolonged to 200 cycles above. Supported by the detailed kinetic analysis, it can be noted that the existing chemical bonds facilitate the fast shuttling of ions at the interface, and the enhanced surface/near-surface properties are further vitrified. Given this, the work is expected to offer valuable insights for the rational design of metal-based samples toward advanced sodium-storage materials.

Sonochemically synthesized mesoporous cobalt oxide nanoparticles for luminol-enhanced chemiluminescence sensing

In recent years, mesoporous cobalt oxides have attracted more attention due to their exceptional physical and chemical properties and their important applications in various fields. The synthesis of cobalt oxides of various sizes, morphologies, and porosity is still a challenging process. In this report, mesoporous Co₃O₄NPs with different porosity were synthesized through facile, one-step, and cost-effective routes, without using any complicated materials or instruments, via the sonochemical process. X-ray powder diffraction (XRD), BET, and transmission electron microscopy (TEM) were used to characterize the as-synthesized NPs. XRD technique was used to determine the crystal structure and phase of the NPs, BET to describe the porous nature of the NPs, and TEM to investigate the structure and morphology of the NPs. Next, the effect of as-synthesized Co₃O₄NPs as a catalyst for the luminol-H₂O₂chemiluminescence system was studied. Co₃O₄NPs were chosen since they have nanoscale size, high specific surface area, and mesoporous nature. Therefore, these NPs can form more active sites and thus show unique catalytic activity than common ionic catalysts such as Co²⁺, Fe³⁺, Cu²⁺used in the luminol-H₂O₂CL system. Finally, this system was used to detect and measure H₂O₂and glucose under optimal conditions. A good linear relationship was observed between the chemiluminescence intensity of the designed system and the concentration of H₂O₂and glucose. A linear range like 0.25-10 pM for H₂O₂and 1-30 nM for glucose was obtained. The excellent LOD of the proposed method for measuring H₂O₂was about 0.07 pM, and for measuring glucose was about 0.14 nM.

General Microwave Route to Single-Crystal Porous Transition Metal Nitrides for Highly Sensitive and Stable Raman Scattering Substrates

The synthesis of metallic transition metal nitrides (TMNs) has traditionally been performed under harsh conditions, which makes it difficult to prepare TMNs with high surface area and porosity due to the grain sintering. Herein, we report a general and rapid (30 s) microwave synthesis method for preparing TMNs with high specific surface area (122.6-141.7 m² g^-1) and porosity (0.29-0.34 cm³ g^-1). Novel single-crystal porous WN, Mo₂N, and V₂N are first prepared by this method, which exhibits strong surface plasmon resonance, photothermal conversion, and surface-enhanced Raman scattering effects. Different from the conventional low-temperature microwave absorbing media such as water and polymers, as new concept absorbing media, hydrated metal oxides and metallic metal oxides are found to have a remarkable high-temperature microwave heating effect and play key roles in the formation of TMNs. The current research results provide a new-concept microwave method for preparing high lattice energy compounds with high specific surface.

Tuning Metallic Co0.85Se Quantum Dots/Carbon Hollow Polyhedrons with Tertiary Hierarchical Structure for High-Performance Potassium Ion Batteries

Potassium-ion batteries (KIBs) are a potential candidate to lithium-ion batteries (LIBs) but possess unsatisfactory capacity and rate properties. Herein, the metallic cobalt selenide quantum dots (Co_0.85Se-QDs) encapsulated in mesoporous carbon matrix were designed via a direct hydrothermal method. Specifically, the cobalt selenide/carbon composite (Co_0.85Se-QDs/C) possesses tertiary hierarchical structure, which is the primary quantum dots, the secondary petals flake, and the tertiary hollow micropolyhedron framework. Co_0.85Se-QDs are homogenously embedded into the carbon petals flake, which constitute the hollow polyhedral framework. This unique structure can take the advantages of both nanoscale and microscale features: Co_0.85Se-QDs can expand in a multidimensional and ductile carbon matrix and reduce the K-intercalation stress in particle dimensions; the micropetals can restrain the agglomeration of active materials and promote the transportation of potassium ion and electron. In addition, the hollow carbon framework buffers volume expansion, maintains the structural integrity, and increases the electronic conductivity. Benefiting from this tertiary hierarchical structure, outstanding K-storage performance (402 mAh g^-1 after 100 cycles at 50 mA g^-1) is obtained when Co_0.85Se-QDs/C is used as KIBs anode. More importantly, the selenization process in this work is newly reported and can be generally extended to prepare other quantum dots encapsulated in edge-limited frameworks for excellent energy storage.

Low-temperature pseudomorphic transformation of polyhedral MIL-88A to lithium ferrite (LiFe3O5) in aqueous LiOH medium toward high Li storage

The ability to develop novel nanomaterials, and to precisely manufacture their functional structures at the nano- and microscales would benefit many emerging device applications. Herein, as a first example, we describe the exploration of feasibility for the morphological replacement of an iron-based MOF bearing trimeric FeIII-O clusters, MIL-88A preform, with a polyhedral architecture of around 0.4 × 1.2 μm by a lithium ferrite (LiFe3O5) phase via solid-liquid pseudomorphic transformation reactions in biologically and environmentally favourable aqueous lithium hydroxide (LiOH). The reaction proceeds at 170 °C, and the overall reaction can be described as Fe3O(H2O)2(FMA)3(OH)·nH2O (MIL-88A) + 7OH- + Li+ → LiFe3O5 + 3FMA2- + (n + 6) H2O (FMA = fumarate). It was proposed that through the coordination substitution of a MOF ligand by OH-, follow-up dehydration and dehydroxylation, and final H+/Li+ ionic exchange, the monolithiated iron oxides formed thermodynamically at comparatively low temperatures, which transcribe the global nanostructure morphologies of the polyhedral MOF preforms with the hexagonal symmetry, but were composed of interconnected LiFe3O5 particles (about 16 nm) that crystallize in a typical magnetite-type cubic (Fd3[combining macron]m) structure. Given the characteristic texture and structure of the Li-Fe oxide replica, cubic LiFe3O5 was preferentially employed as a new type of electrode material in rechargeable lithium cells. Notably, from the electrochemical evaluation, this metal oxide system exhibits decent anodic performances by undergoing a nine-electron conversion reaction, showing a substantially high specific capacity with an average potential of 0.8 V versus lithium metal, a long service life (700 cycles), and exceptional high-rate capability (up to 2.0 A g-1). The synthetic paradigms demonstrated that the MIL-88A to LiFe3O5 conversion may be transferable to other advanced inorganic-based electrodes from the parent metal compound such as LiFeO2, LiMn2O4 or LiCoO2 toward sustainable energy fields.

Effect of different electrolytes and deposition time on the supercapacitor properties of nanoflake-like Co(OH)2 electrodes

The effect of ultrasonic treatment and deposition time on nanoflake-like Co(OH)₂ thin films were prepared using the potentiostatic mode of electrodeposition method on stainless steel substrates by a nitrate reduction reaction. After ultrasonic treatment, we used stainless steel substrates for deposition of the nanoflakes like Co(OH)₂ thin films. The effect of deposition times and electrolytes on different physico-chemical properties of Co(OH)₂ was investigated in detail, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), and electrochemical testing. After ultrasonic treatment Co(OH)₂ thin films had devolvement of the uniform and interconnected formation of nanoflakes nanostructures. Supercapacitor performance of the Co(OH)₂ electrodes suggest that, specific capacitance are depends on the surface morphology, and Co(OH)₂ electrodes after ultrasonic treatment exhibited higher performance than without ultrasonication. The maximum specific capacitance of the 30 min. deposited Co(OH)₂ nanoflakes exceeded 276 Fg^-1 in 0.5M KOH electrolyte at 5 mVs^-1 scan rate.

Porous Co3O4 nanoplates with pH-switchable peroxidase- and catalase-like activity

Porous Co3O4 nanoplates were synthesized via a soft template method. By using amphiphilic block copolymer F127 colloids as the pore producer, porous Co(OH)2 nanoplates were prepared. After the annealing procedure, the obtained Co3O4 reserved the hexagonal shape and a similar size to the Co(OH)2 precursor. The as-prepared porous Co3O4 nanoplates named Co3O4-F simultaneously possessed peroxidase and catalase mimetic activities. Interestingly, these two kinds of mimetic enzyme activities could be switched by pH. Meanwhile, temperature and the concentrations of Co3O4-F had a significant effect on the switch pH and the dual-enzyme mimetic catalytic ability. Moreover, Co3O4-F exhibited good peroxidase-like catalytic activity even in the neutral pH system, providing a new strategy for one-step analysis of glucose. A novel one-step colorimetric glucose biosensor was fabricated based on the Co3O4-F nanozyme, making the operation of detection simpler and easier.

One-step hydrothermal synthesis of thioglycolic acid capped CdS quantum dots as fluorescence determination of cobalt ion

Highly luminescent CdS quantum dots capped with thioglycolic acid (TGA@CdS QDs) were synthesized from cadmium chloride and thiourea as cadmium and sulfur sources via simple hydrothermal method. The room temperature photoluminescence (RTPL) properties of TGA@CdS QDs were investigated. The results indicate that the polarity of the solvent and the surface trap state resulted in the broadness Stokes shift between the maximum absorption wavelength and the emission wavelength of TGA@CdS QDs. The Co²⁺ sensing properties of fluorescence determination were investigated using TGA@CdS QDs. The as-synthesized CdS QDs exhibits the excellent selectivity and sensitivity of fluorescence quenching for cobalt ion (Co²⁺). The limit of detection (LOD) is as low as 0.05 μM which is much lower than maximum limit of cobalt ions in drinking water. The linear response range of Co²⁺ was from 0.5 to 80 μM. The sensing system revealed the advantages of low detection limit, excellent selectivity, high sensitivity, convenience and low cost. The color change of CdS QDs shows potential applications in the detection of Co²⁺.

Phase and morphology evolution of ultrathin Co(OH)2nanosheets towards supercapacitor application

The morphology and phase evolution strongly depends on a hydrothermal process driven by kinetics and thermodynamics.

Hollow Porous VOx/C Nanoscrolls as High-Performance Anodes for Lithium-Ion Batteries

Novel hollow porous VO_x/C nanoscrolls are synthesized by an annealing process with the VO_x/octadecylamine (ODA) nanoscrolls as both vanadium and carbon sources. In the preparation, the VO_x/ODA nanoscrolls are first achieved by a two-phase solvothermal method using ammonium metavanadat as the precursor. Upon subsequent heating, the intercalated amines between the vanadate layers in the VO_x/ODA nanoscrolls decompose into gases, which escape from inside the nanoscrolls and leave sufficient pores in the walls. As the anodes of lithium-ion batteries (LIBs), such hollow porous VO_x/C nanoscrolls possess exceedingly high capacity and rate capability (904 mAh g^-1 at 1 A g^-1) and long cyclic stability (872 mAh g^-1 after 210 cycles at 1 A g^-1). The good performance is derived from the unique structural features of the hollow hierarchical porous nanoscrolls with low crystallinity, which could significantly suppress irreversible Li⁺ trapping as well as improve Li⁺ diffusion kinetics. This universal method of annealing amine-intercalated oxide could be widely applied to the fabrication of a variety of porous electrode materials for high-performance LIBs and supercapacitors.