Ammonia Capture within Isoreticular Metal-Organic Frameworks with Rod Secondary Building Units

The efficient removal, capture, and recycling of ammonia (NH3) constitutes a demanding process, thus the development of competent adsorbent materials is highly desirable. The implementation of metal-organic frameworks (MOFs), known for their tunability and high porosity, has attracted much attention for NH3 adsorption studies. Here, we report three isoreticular porphyrin-based MOFs containing aluminum (Al-PMOF), gallium (Ga-PMOF), and indium (In-PMOF) rod secondary building units with Brønsted acidic bridging hydroxyl groups. NH3 sorption isotherms in Al-PMOF demonstrated reversibility in isotherms. In contrast, the slopes of the adsorption isotherms in Ga-PMOF and In-PMOF were much steeper than Al-PMOF in lower pressure regions, with a decrease of NH3 adsorbed amounts observed between first cycle and second cycle measurements. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) suggested that the strength of the Brønsted acidic -OH sites was controlled by the identity of the metal, which resulted in stronger interactions between ammonia and the framework in Ga-PMOF and In-PMOF compared to Al-PMOF

Direct Sintering Behavior of Metal Organic Frameworks/Coordination Polymers

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

Metal–organic framework adhesives with exceptionally high heat resistance

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.</p