ABSTRACT
We synthesized high-heat-resistant adhesives based on metal - organic frameworks owing to their high decomposition temperature and the absence of a glass transition. Heat-resistance tests were performed on adhesive joints consisting of zeolitic imidazolate framework (ZIF)-67-based adhesives and a copper substrate. The as-synthesized ZIF-67-based adhesive exhibited heat resistances at 600 and 700°C in air and nitrogen atmospheres, respectively, comparable to those of conventional high-heat-resistant polymer-based adhesives. The degradation mechanism of the ZIF-67 adhesives was investigated, and their high heat resistance was attributed to the stable existence of the ZIF-67 qtz phase in the adhesive layer at high temperatures without the formation of voids. Thus, adhesives based on ZIF-67 and other metal - organic frameworks can be applied in high-temperature industrial systems.
By focusing on its high thermal stability and absence of glass transition, the ZIF-67 gel was found to have high potential that is comparable to existing heat-resistant adhesives.
ABSTRACT
To safely recycle spent lithium-ion batteries (LIBs), their deactivation as a pretreatment is essential. However, the conventional deactivation methods, mainly inducing an external short circuit, cannot be applied to LIBs with disconnected electrical circuits or Li deposited, despite their safety risk. Here, we propose a deactivation method using redox shuttles (RSs). The addition of an RS with redox potentials located between the two electrode potentials into a LIB electrochemically induces an internal short circuit with or without disconnected electrical circuits. A fully charged LIB discharges to approximately 0 V when a deactivation agent containing ferrocene or phenothiazine as an RS is added. Moreover, we demonstrate that RSs introduced into LIB can simultaneously dissolve Li deposited on the negative electrode surface and return it to the positive electrode as mobile ions. These characteristics of our method contribute to the improvement in safety and collection rate of Li in the recycling processes, promoting the sustainability of LIBs.
ABSTRACT
Metal-organic frameworks (MOFs)/coordination polymers are promising materials for gas separation, fuel storage, catalysis, and biopharmaceuticals. However, most applied research on MOFs is limited to these functional materials thus far. This study focuses on the potential of MOFs as structural adhesives. A sintering technique is applied to a zeolitic imidazolate framework-67 (ZIF-67) gel that enables the joining of Cu substrates, resulting in a shear strength of over 30 MPa, which is comparable to that of conventional structural adhesives. Additionally, systematic experiments are performed to evaluate the effects of temperature and pressure on adhesion, indicating that the removal of excess 2-methylimidazole and the by-product (acetic acid) from the sintered material by vaporization results in a microstructure composed of large spherical ZIF-67 crystals that are densely aggregated, which is essential for achieving a high shear strength.
ABSTRACT
In this study, we investigate the sintering behavior and mechanisms of metal-organic frameworks/coordination polymers (CPs) through physical and microstructural characterization of [Zn(HPO4)(H2PO4)2]·2H2Im (ZPI; a melting CP, Im = imidazole) and ZIF-8 (a non-melting CP). By performing simple compaction and subsequent sintering, a bulk body of CPs was obtained without losing the macroscopic crystallinity. The sintering behavior was found to be dependent on the temperature, heating rate, and physical properties of the CPs and, in particular, their meltability. During sintering, shrinkage occurred in both the CPs, but the observed shrinkage rate of the ZPI was in the 10-20% range, whereas that of the ZIF-8 was less than 1%. Additionally, the sintering mechanisms of the ZPI and ZIF-8 varied between low and high temperatures, and in the case of ZPI, localized melting between the primary particles was the dominant mechanism on the high-temperature side. However, substantial shrinkage did not correspond to an increase in density; on the contrary, a decrease in the apparent density of ZPI was observed as the sintering temperature was increased. The sintering technique is well established and commercially available; thus, the results obtained in this study can be utilized for optimizing the manufacturing conditions of melting CPs.
ABSTRACT
EuKGe2O6-, Ca3Fe2Ge3O12-, and BaCu2Ge2O7-type germanates are synthesized by a conventional solid-state method and characterized to reveal their oxide-ion-conducting properties. Materials of the EuKGe2O6 group exhibit oxide-ion conductivity (e.g., 4.6 × 10-3 S/cm at 973 K for Eu0.8Ca0.2KGe2O6-δ) and transport numbers above 96%, whereas materials of the Ca3Fe2Ge3O12 and BaCu2Ge2O7 groups exhibit mixed electron-/oxide-ion conduction. Conduction involves oxide-ion vacancies in the EuKGe2O6 group, interstitial oxide ions in the Ca3Fe2Ge3O12 group, and both oxide-ion vacancies and interstitial oxide ions in the BaCu2Ge2O7 group. The doping-induced formation of impurity phases decreases the amount of oxide-ion carriers relative to the expected values.
ABSTRACT
To accelerate material discovery, we develop a screening method for oxide-ion conductors that comprises combinatorial synthesis using chemical-solution deposition and high-throughput measurements using X-ray diffraction and conductivity. The present method allows us to form an arbitrary and uniform composition within an evaluation area at an arbitrary position in the library on a substrate. This screening method is applied to ABi2Zr x(Nb1- yTa y)1- xO9 bismuth-layered compounds, which are known to have relatively high oxide-ion conductivities but are yet to be examined thoroughly. By making systematic thin-film libraries for A = Sr or Ca, we aim to find the optimized composition. The total time required for synthesis, phase identification, and conductivity measurements is found to be significantly shorter than that with the conventional method, and the maximum oxide-ion conductivity of this compound in the libraries reaches 10-3 S/cm at 800 °C.
Subject(s)
Bismuth/chemistry , High-Throughput Screening Assays/methods , Oxides/chemistry , Combinatorial Chemistry Techniques , Electric Conductivity , Small Molecule Libraries , X-Ray DiffractionABSTRACT
A biased mutation-assembling method-that is, a directed evolution strategy to facilitate an optimal accumulation of multiple mutations on the basis of additivity principles, was applied to the directed evolution of water-soluble PQQ glucose dehydrogenase (PQQGDH-B) to reduce its maltose oxidation activity, which can lead to errors in blood glucose determination. Mutations appropriate for the reduction without fatal deterioration of its glucose oxidation activity were developed by an error-prone PCR method coupled with a saturation mutagenesis method. Moreover, two types of incorporation frequency based on their contribution were assigned to the mutations: high (80%) and evens (50%), in constructing a multiple mutant library. The best mutant created showed a marked reduction in maltose oxidation activity, corresponding to 4% of that of the wild-type enzyme, with 35% retention of glucose oxidation activity. In addition, this mutant showed a reduction in galactose oxidation activity corresponding to 5% of that of the wild-type enzyme. In conclusion, we succeeded in developing the PQQGDH-B mutants with improved substrate specificity and validated our method coupled with optimized mutations and their contribution-based incorporation frequencies by applying it to the development.
