Humidity-Mediated Anisotropic Proton Conductivity through the 1D Channels of Co-MOF-74

Graphitized Carbon-Supported Co@Co3O4 for Ozone Decomposition over the Entire Humidity Range

Ground-level ozone (O3) pollution has emerged as a significant concern due to its detrimental effects on human health and the ecosystem. Catalytic removal of O3 has proven to be the most efficient and cost-effective method. However, its practical application faces substantial challenges, particularly in relation to its effectiveness across the entire humidity range. Herein, we proposed a novel strategy termed "dual active sites" by employing graphitized carbon-loaded core-shell cobalt catalysts (Co@Co3O4-C). Co@Co3O4-C was synthesized via the pyrolysis of a Co-organic ligand as the precursor. By utilizing this approach, we achieved a nearly constant 100% working efficiency of the Co@Co3O4-C catalyst for catalyzing O3 decomposition across the entire humidity range. Physicochemical characterization coupled with density functional theory calculations elucidates that the presence of encapsulated metallic Co nanoparticles enhances the reactivity of the cobalt oxide capping layer. Additionally, the interface carbon atom, strongly influenced by adjacent metallic Co nuclei, functions as a secondary active site for the decomposition of O3 decomposition. The utilization of dual active sites effectively mitigates the competitive adsorption of H2O molecules, thus isolating them for adsorption in the cobalt oxide capping layer. This optimized configuration allows for the decomposition of O3 without interference from moisture. Furthermore, O3 decomposition monolithic catalysts were synthesized using a material extrusion-based three-dimensional (3D) printing technology, which demonstrated a low pressure drop and exceptional mechanical strength. This work provides a "dual active site" strategy for the O3 decomposition reaction, realizing O3 catalytic decomposition over the entire humidity range.

The role of sulfonate groups and hydrogen bonding in the proton conductivity of two coordination networks

The proton conductivity of two coordination networks, [Mg(H₂O)₂(H₃L)]·H₂O and [Pb₂(HL)]·H₂O (H₅L = (H₂O₃PCH₂)₂-NCH₂-C₆H₄-SO₃H), is investigated by AC impedance spectroscopy. Both materials contain the same phosphonato-sulfonate linker molecule, but have clearly different crystal structures, which has a strong effect on proton conductivity. In the Mg-based coordination network, dangling sulfonate groups are part of an extended hydrogen bonding network, facilitating a "proton hopping" with low activation energy; the material shows a moderate proton conductivity. In the Pb-based metal-organic framework, in contrast, no extended hydrogen bonding occurs, as the sulfonate groups coordinate to Pb²⁺, without forming hydrogen bonds; the proton conductivity is much lower in this material.

Flexible, non-contact and multifunctional humidity sensors based on two-dimensional phytic acid doped co-metal organic frameworks nanosheets

The development of high-performance humidity sensors is of great significance to explore their practical applications in the fields of environment, energy saving and safety monitoring. Herein, a flexible, non-contact and multifunctional humidity sensor based on two-dimensional Co-metal organic frameworks (Co-MOF) nanosheets is proposed, which is fabricated by simple bottom-up synthesis method. Furthermore, environmentally friendly, renewable and abundant biomass phytic acid (PA) is modified on the surface of Co-MOF nanosheets, which releases free protons being capable of etching the framework of MOF to improve the hydrophilicity and conductivity of MOF. Compared with Co-MOF-based sensor, the Co-MOF@PA-based sensor exhibits significantly enhanced sensitivity and broadened response range within 23-95% relative humidity (RH). The humidity sensor has an excellent humidity sensing response over 2 × 10³. The Co-MOF@PA-based sensor shows good flexibility and humidity sensing properties, endowing it with multifunctional applications in real-time facial respiration monitoring, skin humidity perception, cosmetic moisturizing evaluation and fruit freshness testing. Four respiration patterns, including slow breath, deep breath, normal breath and fast breath are wirelessly monitored in real time by Co-MOF@PA-based sensor and recorded by mobile phone software. The research work presents potential applications in human-machine interactions (HMI) devices in future.

New isoreticular phosphonate MOFs based on a tetratopic linker

The tetratopic linker 1,1,2,2-tetrakis(4-phosphonophenyl)ethylene (H₈TPPE) was used to synthesize the three new porous metal-organic frameworks of composition [M₂(H₂O)₂(H₂TPPE)]·xH₂O (M = Al³⁺, Ga³⁺, Fe³⁺), denoted as M-CAU-53 under hydrothermal reaction conditions, using the corresponding metal nitrates as starting materials. The crystal structures of the compounds were determined ab initio from powder X-ray diffraction data, revealing small structural differences. Proton conductivity measurements were carried out, indicating different conductivity mechanisms. The differences in proton conductivity could be linked to the individual structures. In addition, a thorough characterization via thermogravimetry, elemental analysis, IR-spectroscopy as well as N₂- and H₂O-sorption is given.

Trojan Horse Thiocyanate: Induction and Control of High Proton Conductivity in CPO-27/MOF-74 Metal-Organic Frameworks by Metal Selection and Solvent-Free Mechanochemical Dosing

Proton-conducting metal-organic frameworks (MOFs) have been gaining attention for their role as solid-state electrolytes in various devices for energy conversion and storage. Here, we present a convenient strategy for inducing and tuning of superprotonic conductivity in MOFs with open metal sites via postsynthetic incorporation of charge carriers enabled by solvent-free mechanochemistry and anion coordination. This scalable approach is demonstrated using a series of CPO-27/MOF-74 [M₂(dobdc); M = Mg²⁺, Zn²⁺, Ni²⁺; dobdc = 2,5-dioxido-1,4-benzenedicarboxylate] materials loaded with various stoichiometric amounts of NH₄SCN. The modified materials are not achievable by conventional immersion in solutions. Periodic density functional theory (DFT) calculations, supported by infrared (IR) spectroscopy and powder X-ray diffraction, provide structures of the modified MOFs including positions of inserted ions inside the [001] channels. Despite the same type and concentration of proton carriers, the MOFs can be arranged in the increasing order of conductivity (Ni < Zn < Mg), which strongly correlates with amounts of water vapor adsorbed. We conclude that the proton conductivity of CPO-27 materials can be controlled over a few orders of magnitude by metal selection and mechanochemical dosing of ammonium thiocyanate. The dosing of a solid is shown for the first time as a useful, simple, and ecological method for the control of material conductivity.

Pyridine Detection Using Supramolecular Organic Frameworks Incorporating Cucurbit[10]uril

A physical impregnation method is presented in this study, providing a facile approach to encapsulating functional guest molecules (GMs) into robust crystalline supramolecular organic frameworks incorporating cucurbit[10]uril (Q[10]-SOF). As Q[10]-SOF has high evaporated pyridine affinity under normal atmospheric pressure, pyridine molecules in this method were successfully encapsulated into the nanospace formed by GMs and Q[10]-SOF while retaining their crystal framework, morphology, and high stability. GMs@Q[10]-SOF solid materials were found to respond to pyridine, being suitable to be used as solid sensors. Notably, Q[10]-SOF loading with pyrene exhibited a unique response to pyridine along with dramatic fluorescence quenching; loading with dansyl chloride exhibited a unique response to pyridine along with significant fluorescence enhancement, having a quick response within 60 s. Our findings represent a critical advancement in the design of pyridine detection and adsorption for commercial gas identification and sensing.

Single-crystal-to-single-crystal transformation and proton conductivity of three hydrogen-bonded organic frameworks

In this communication, we report the SCSC transformation and proton conductivity of three H-bonded organic frameworks. The results show that H-bonded systems can improve their proton conductivity by uptaking water molecules based on the adaptability.