A novel "on-off-on" electrochemiluminescence aptasensor based on resonance energy transfer as signal amplification strategy for ultrasensitive detection of sulfadiazine in different samples

The misuse of antibiotics may contaminate the environment and cause harm to human health. Therefore, rapid and accurate detection of antibiotics is essential. In this study, a novel electrochemiluminescence resonance energy transfer (ECL-RET) pair was designed using a new ECL emitter (CPM, Ce-TBAPy) as the donor and Co-MOF@AuPt as the acceptor. Moreover, a highly sensitive and specific "on-off-on" ECL aptasensor was constructed for detecting sulfadiazine (SDZ). The aptasensor exhibited a broad linear range (from 10.0 fg mL-1 to 100 ng mL-1) for the SDZ concentration, with limit of detection and limit of quantification values of 1.14 fg mL-1and 3.75 fg mL-1, respectively. The aptasensor achieved good results in spiking experiments with milk and egg samples, and successfully quantified SDZ in fish meal quality control sample. The prepared aptasensor presents great potential for food and environmental safety by detecting antibiotics.

Enhancement of the Catalytic Activity of Double Metal Cyanides for the Oxidation of Styrene by the Presence of Included Alcohols

In recent years, people have focused on the development of simple and efficient heterogeneous catalysts for the styrene epoxidation reaction. In this work, a FeCo double metal cyanide (DMC) was modified with C1 to C6 linear alcohols, and the prepared materials were used to catalyze the reaction of styrene epoxidation in various solvents. It is noteworthy that the styrene conversion is mainly affected by modification with alcohols, while the selectivity in styrene oxide (SO) is obviously influenced by the solvent. FeCo DMC along with MeOH exhibits the best catalytic performance, with a conversion rate of 96% and a SO selectivity of 86%, in N,N-dimethylformamide (DMF) solvent. Various physical and chemical methods were used to analyze the structures and compositions of the materials. To clarify the mechanism of the improvement, we set up an original approach to investigate the kinetics of the adsorption process between the oxidant and the catalyst, using isothermal titration calorimetry (ITC). The obtained results illustrate that the adsorption process of the oxidant on the surface of FeCo DMC can be dramatically promoted by the presence of MeOH. Such a difference in adsorption thus explains the significant improvement of its catalytic activity by modification with MeOH. This study thus provides a new fundamental understanding of DMC catalysts for the styrene epoxidation reaction.

Construction of Co-Mn Prussian Blue Analog Hollow Spheres for Efficient Aqueous Zn-ion Batteries

Prussian blue analogs (PBAs) are considered as reliable and promising cathode materials for aqueous Zn-ion batteries (AZIBs), but they suffer from low capacity and poor cycling stability due to insufficient active sites and structural damage caused by the ion insertion/extraction processes. Herein, a template-engaged ion exchange approach has been developed for the synthesis of Co-substituted Mn-rich PBA hollow spheres (CoMn-PBA HSs) as cathode materials for AZIBs. Benefiting from the multiple advantageous features including hollow structure, abundant active sites, fast Zn2+ ion diffusion, and partial Co substitution, the CoMn-PBA HSs electrode shows efficient zinc ion storage properties in terms of high capacity, decent rate capability and prolonged cycle life.

Probing the Influence of Defects, Hydration, and Composition on Prussian Blue Analogues with Pressure

The vast compositional space of Prussian blue analogues (PBAs), formula A_xM[M′(CN)₆]_y·nH₂O, allows for a diverse range of functionality. Yet, the interplay between composition and physical properties—e.g., flexibility and propensity for phase transitions—is still largely unknown, despite its fundamental and industrial relevance. Here we use variable-pressure X-ray and neutron diffraction to explore how key structural features, i.e., defects, hydration, and composition, influence the compressibility and phase behavior of PBAs. Defects enhance the flexibility, manifesting as a remarkably low bulk modulus (B₀ ≈ 6 GPa) for defective PBAs. Interstitial water increases B₀ and enables a pressure-induced phase transition in defective systems. Conversely, hydration does not alter the compressibility of stoichiometric MnPt(CN)₆, but changes the high-pressure phase transitions, suggesting an interplay between low-energy distortions. AMnCo(CN)₆ (A^I = Rb, Cs) transition from F4̅3m to P4̅n2 upon compression due to octahedral tilting, and the critical pressure can be tuned by the A-site cation. At 1 GPa, the symmetry of Rb_0.87Mn[Co(CN)₆]_0.91 is further lowered to the polar space group Pn by an improper ferroelectric mechanism. These fundamental insights aim to facilitate the rational design of PBAs for applications within a wide range of fields.

Exploring Reversible Thermochromic Behavior in a Rare Ni(II)-MOF System

Thermochromic metal-organic frameworks (MOFs) are promising functional materials for a wide range of applications due to their ability to exhibit color variation under external temperature stimuli, yet the development of them with high cyclability and efficient regeneration processes remains challenging. Here, presented is a rare example of an ultrastable Ni(II)-MOF exhibiting an unprecedented reversible four-step color change between two complementary colors in a wide temperature range, which could be repeated for at least 500 cycles without losing crystallinity and thermochromic performance. Notably, the regeneration can be achieved within 1 min by simply letting the crystals cool naturally in the air, facilitated by the unique nature of the channels' inner surface. The reversible thermochromic behavior is owing to a series of reversible crystal structure changes with temperature, including the stepwise dehydration/rehydration process, and structural changes. This work facilitates the future development of more MOF-based reversible thermochromic materials with excellent performance and improved practical applicability.

Density-functional-theory-predicted symmetry lowering from cubic to tetragonal in nickel hexacyanoferrate

Density-functional-theory (DFT) computations on a Prussian blue analogue (PBA), nickel hexacyanoferrate, Ni2+ 3[Fe3+(CN)6]2·nH2O, predict the existence of a tetragonal (P 4 m2) crystal structure that is energetically degenerate with the previously reported cubic (F 43m) structure for this PBA. The proposed tetragonal structure satisfies observations, such as X-ray diffraction and magnetic measurements, that have been reported previously. A van der Waals corrected exchange-correlation functional is used in the DFT+U computations for an improved description of hydrogen bonding. The results provide strong support for a revised and simplified crystallographic description of Ni2+ 3[Fe3+(CN)6]2·nH2O, and show how H2O molecules stabilize the crystal structure and affect its magnetic and electronic properties. The symmetry lowering in nickel hexacyanoferrate is attributed to the hydration shell of the interstitial nickel cation. Calculations strongly suggest a maximum of n = 7 interstitial H2O molecules per formula unit for nickel hexacyanoferrate at room temperature, and a higher water content at temperatures below T ≃ 200 K. Since the symmetry lowering relies on the presence of interstitial H2O molecules, this revised crystallographic description may be applicable more generally to the large class of F 43m-structured PBAs.

Metal-organic Framework-driven Porous Cobalt Disulfide Nanoparticles Fabricated by Gaseous Sulfurization as Bifunctional Electrocatalysts for Overall Water Splitting

Both high activity and mass production potential are important for bifunctional electrocatalysts for overall water splitting. Catalytic activity enhancement was demonstrated through the formation of CoS2 nanoparticles with mono-phase and extremely porous structures. To fabricate porous structures at the nanometer scale, Co-based metal-organic frameworks (MOFs), namely a cobalt Prussian blue analogue (Co-PBA, Co3[Co(CN)6]2), was used as a porous template for the CoS2. Then, controlled sulfurization annealing converted the Co-PBA to mono-phase CoS2 nanoparticles with ~ 4 nm pores, resulting in a large surface area of 915.6 m2 g-1. The electrocatalysts had high activity for overall water splitting, and the overpotentials of the oxygen evolution reaction and hydrogen evolution reaction under the operating conditions were 298 mV and -196 mV, respectively, at 10 mA cm-2.

Realization of Lithium-Ion Capacitors with Enhanced Energy Density via the Use of Gadolinium Hexacyanocobaltate as a Cathode Material

Li-ion storage devices having superior energy density are critical for one-time-charge long-term applications. Currently, much research endeavor is directed at enhancing the energy density of hybrid Li-ion capacitors, which incorporate the high energy of conventional Li-ion batteries with the elevated power density of Li-ion supercapacitors. Herein, we prepare orthorhombic GdCo(CN)₆ as a new Prussian blue analogue (PBA), showing that this compound offers excellent energy/power densities (605 W·h kg^-1 and 174 W kg^-1, respectively) and features Li-ion storage capacities (352 and 258 mA·h g_electrode^-1 at 100 and 1000 mA g^-1, respectively) that are almost twice higher than those of other cathode materials utilized in hybrid Li-ion capacitors. Thus, this study not only opens a new path for the exploration of new-type PBAs, but also provides insights on the use of lanthanides in energy storage applications.

High-pressure behaviour of Prussian blue analogues: interplay of hydration, Jahn-Teller distortions and vacancies

We report a high-pressure crystallographic study of four hydrated Prussian blue analogues: M[Pt(CN)₆] and M[Co(CN)₆]_0.67 (M = Mn²⁺, Cu²⁺) in the range 0-3 GPa. Mn[Co(CN)₆]_0.67 was studied by single-crystal X-ray diffraction, whereas the other systems were only available in polycrystalline form. The Mn-containing compounds undergo pressure-induced phase transitions from Fm3[combining macron]m to R3[combining macron] at ∼1.0-1.5 GPa driven by cooperative tilting of the octahedral units. No phase transition was found for the orbitally disordered Cu[Co(CN)₆]_0.67 up to 3 GPa. Mn[Co(CN)₆]_0.67 is significantly softer than the other samples, with a bulk modulus of ∼14 GPa compared to ∼35 GPa of the powdered samples. The discrepant pressure responses are discussed in terms of the presence of structural defects, Jahn-Teller distortions, and hydration. The implications for the development of polar systems are reviewed based upon our high-pressure study.