Two-dimensional metal-organic framework-graphene oxide hybrid nanocomposite proton exchange membranes with enhanced proton conduction

Self-supplying of hydrogen peroxide nanozyme-based colorimetric sensing array as electronic tongue for biothiol detection and disease discrimination

Developing a highly reliably and sensitive nanozyme-based colorimetric sensor array for biothiols analysis is critical owing to they play an essential role in diagnosing disease. The required procedure of introducing hydrogen peroxide (H2O2) directly into the colorimetric reaction systems in traditional biothiols array analysis limits its applicability due to its poor stability and inhibition in biomolecular activity by using the high-concentration H2O2. Herein, we carried out a "green" and convenient approach to propose for the biothiol detection and disease discrimination through nanozymes-based colorimetric sensor technique without adding the high-concentration H2O2 for the first time. The copper peroxide nanodots (CPNs) and graphene oxide (GO) modified CPNs (GO@CPNs) are as sensing units to release H2O2 and Cu2+ under acidic conditions, which triggered a Fenton-like reaction, generating hydroxyl radical (•OH) to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) accompanied by a change in TMB color from colorless to blue. Due to the synergistic effect of Cu2+ and GO, GO@CPNs showed increased the activity of peroxidase-like compared to CPNs. Therefore, the catalytic abilities of nanozymes-based colorimetric sensing array were inhibited to different degrees by different biothiols (i.e., glutathione (GSH), cysteine (Cys) and homocysteine (Hcy)) with a detection limit of 50 nM, which could be precisely distinguished by using pattern recognition method. Besides, the detection of a single biothiol at different concentrations and mixtures of biothiols has also been achieved. Moreover, the real biological samples (cells and human serum) can be accurately discriminated through array method, which demonstrated its potential application of medical diagnosis.

Fabricating MOF-GO Composites by Modulating Graphene Oxide Content to Achieve Superprotonic Conductivity

Metal-organic frameworks (MOFs) have emerged as crucial materials for proton conductivity, especially in the context of the growing need for alternative energy sources. Enhancing the proton conductivity of MOFs has been a major focus with one effective approach involving the integration of MOFs with graphene oxide (GO) to form composite materials. In this study, Cr-MIL-101 MOF is selected, and its growth on GO sheets has been achieved through in situ crystallization, leading to the formation of MOF-GO composites with varying GO content, MIL-101/GO(x%), (x = 1%, 2%, and 5%). The oxygen functional groups on the 2D-GO layer e.g., carboxyl, hydroxyl, and epoxy groups improve both the acidity and hydrophilicity of the composite, which directly contributes to improved proton conductivity. All the composites, fabricated in this work, exhibit higher conductivity than that of the parent MOF due to the additional acidic functional groups introduced by GO. Among the different composites, the MIL-101/GO(2%) composite exhibits the highest proton conductivity, achieving superprotonic conductivity value of 0.105 S cm-1 at 80 °C and 98% relative humidity (RH). These results highlight the potential of MOF-GO composites for their application as nanofillers in proton exchange membranes for proton exchange membrane fuel cells (PEMFCs) and other energy-related technologies.

Graphene oxide-based materials as proton-conducting membranes for electrochemical applications

The rapid advancements of graphene oxide (GO)-based membranes necessitate the understanding of their properties and application potential. Generally, proton (H+)-conducting membranes, including GO-based ones, are crucial components in various energy-relevant devices, significantly determining the transport process, selectivity, and overall efficiency of these devices. Particularly, GO-based membranes exhibit great potential in electrochemical applications owing to their remarkable conductivity and ease of undergoing further modifications. This review is aimed at highlighting recent functionalization strategies for GO with diverse substrates. It is also aimed at emphasizing how these modifications can enhance the electrochemical performances of GO-based membranes. Notably, key aspects, such as the enhanced H+-transfer kinetics, improved conductivity, functionalities, and optimization, of these membranes for specific applications are discussed. Additionally, the existing challenges and future directions for the field of functionalized GO are addressed to achieve precise control of the functionalities of these membranes as well as advance next-generation electrochemical devices.

Enhancing electrochemical properties of a two-dimensional zeolitic imidazole framework by incorporating a conductive polymer for dopamine detection

The zeolitic imidazole framework with a leaf-shaped morphology (ZIF-L) has a wide range of promising applications in gas storage, battery materials, catalytic reactions, and optoelectronic devices due to its planar leaf-like structure and large surface area. However, the low conductivity, weak catalytic activity, and poor stability in the water dielectric medium of ZIF-L limit its further practical application. To solve these problems, we added the conductive polymer heterocyclic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to ZIF-L for the sensitive detection of dopamine (DA). The synthesized composite ZIF-L/PEDOT:PSS (ZIF-L/PEDOT) not only retained the surface morphology of ZIF-L but also exhibited excellent electrochemical properties. The higher electrical conductivity of ZIF-L/PEDOT than that of ZIF-L was due to the enhanced electron transfer at the interface between ZIF-L and PEDOT:PSS. As a result, we developed an electrochemical biosensor based on the ZIF-L/PEDOT composite, which has a limit of detection of 7 nM for DA and a wide linear range from 25 nM to 500 μM. Furthermore, the current drop was negligible after 28 days, proving that the biosensor has excellent stability. Based on the above-mentioned outstanding performance, the ZIF-L/PEDOT-based biosensor was successfully used to detect DA in human serum samples. These results demonstrated that ZIF-L/PEDOT is expected to play an essential role in disease detection.

Rationalizing Structural Hierarchy in the Design of Fuel Cell Electrode and Electrolyte Materials Derived from Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are arguably a class of highly tuneable polymer-based materials with wide applicability. The arrangement of chemical components and the bonds they form through specific chemical bond associations are critical determining factors in their functionality. In particular, crystalline porous materials continue to inspire their development and advancement towards sustainable and renewable materials for clean energy conversion and storage. An important area of development is the application of MOFs in proton-exchange membrane fuel cells (PEMFCs) and are attractive for efficient low-temperature energy conversion. The practical implementation of fuel cells, however, is faced by performance challenges. To address some of the technical issues, a more critical consideration of key problems is now driving a conceptualised approach to advance the application of PEMFCs. Central to this idea is the emerging field MOF-based systems, which are currently being adopted and proving to be a more efficient and durable means of creating electrodes and electrolytes for proton−exchange membrane fuel cells. This review proposes to discuss some of the key advancements in the modification of PEMs and electrodes, which primarily use functionally important MOFs. Further, we propose to correlate MOF-based PEMFC design and the deeper correlation with performance by comparing proton conductivities and catalytic activities for selected works.

Label-Free Fluorescent Nanofilm Sensor Based on Surface Plasmon Coupled Emission: In Situ Monitoring the Growth of Metal-Organic Frameworks

We have proposed a universal label-free fluorescent nanofilm sensor based on surface plasmon coupled emission (SPCE). A metal-dye-dielectric (MDD) structure was fabricated to mediate the label-free monitoring based on SPCE. The nonfluorescent dielectric film smartly borrowed the fluorescence signal from the bottom dye layer and led to a new SPCE response through the adjacent metal film. The fluorescence emission angle and polarization strongly depended on the thickness of the nonfluorescent dielectric film on the MDD structure. As a demonstration, the growth of a two-dimensional zeolitic imidazolate framework film (ZIF-L) was in situ monitored in the liquid phase by MDD-SPCE for the first time. The label-free fluorescent sensors are facilely prepared by a spin coating technique, with the potential to be widely spread for in situ studies, especially toward nanomaterial growth processes.