Graphene-Based Fiber Materials for Gas Sensing Applications: State of the Art Review

The importance of gas sensors is apparent as the detection of gases and pollutants is crucial for environmental monitoring and human safety. Gas sensing devices also hold the potential for medical applications as health monitoring and disease diagnostic tools. Gas sensors fabricated from graphene-based fibers present a promising advancement in the field of sensing technology due to their enhanced sensitivity and selectivity. The diverse chemical and mechanical properties of graphene-based fibers-such as high surface area, flexibility, and structural stability-establish them as ideal gas-sensing materials. Most significantly, graphene fibers can be readily tuned to detect a wide range of gases, making them highly versatile in gas-sensing technologies. This review focuses on graphene-based composite fibers for gas sensors, with an emphasis on the preparation processes used to achieve these fibers and the gas sensing mechanisms involved in their sensors. Graphene fiber gas sensors are presented based on the chemical composition of their target gases, with detailed discussions on their sensitivity and performance. This review reveals that graphene-based fibers can be prepared through various methods and can be effectively integrated into gas-sensing devices for a diverse range of applications. By presenting an overview of developments in this field over the past decade, this review highlights the potential of graphene-based fiber sensors and their prospective integration into future technologies.

Ag modified ZnO nanoflower gas sensitive sensor for selective detection of n-butanol

Ag modified ZnO nanoflowers were successfully prepared by sunlight induced solvent reduction method. The samples were characterized by x-ray diffractometer, field emission scanning electron microscope, transmission electron microscope and energy dispersive x-ray spectrum, and the results confirmed the presence of Ag nanoparticles on the ZnO nanoflower. The gas sensing performance of the materials was studied at different operating temperatures and different n-butanol concentrations. The results showed that the Ag modified ZnO nanoflower sensor responded to 50 ppm n-butanol up to 147.17 at 280 °C, and the Ag modified ZnO nanoflower sensor exhibited excellent repeatability, stability and response recovery time. In addition, different target gases were employed for the selectivity study of the Ag modified ZnO nanoflower. It can be found that the Ag modified ZnO nanoflower had good selectivity for n-butanol. The improved response of the Ag modified ZnO nanoflower sensor was attributed to the catalytic effect of Ag nanoparticles. The results indicate that the Ag modified ZnO nanoflower will become a very promising sensing material for n-butanol gas detection.

Impact of Ligand Substitution and Metal Node Exchange in the Electronic Properties of Scandium Terephthalate Frameworks

The search for sustainable alternatives to established materials is a sensitive topic in materials science. Due to their unique structural and physical characteristics, the composition of metal-organic frameworks (MOFs) can be tuned by the exchange of metal nodes and the functionalization of organic ligands, giving rise to a large configurational space. Considering the case of scandium terephthalate MOFs and adopting an automatized computational framework based on density-functional theory, we explore the impact of metal substitution with the earth-abundant isoelectronic elements Al and Y, and ligand functionalization of varying electronegativity. We find that structural properties are strongly impacted by metal ion substitution and only moderately by ligand functionalization. In contrast, the energetic stability, the charge density distribution, and the electronic properties, including the size of the band gap, are primarily affected by the termination of the linker molecules. Functional groups such as OH and NH2 lead to particularly stable structures thanks to the formation of hydrogen bonds and affect the electronic structure of the MOFs by introducing midgap states.

Effective removal of humic acid by mesoporous Zr-MOF adjusted through SDBS

Humic acid (HA) in makeup water is one of the important safety issues of high-parameter power plants. Herein, the Zr-based metal-organic frameworks (NH₂-UiO-66) was applied to remove humic acid in water. The mesoporous of NH₂-UiO-66 was controlled by surfactants sodium dodecyl benzene sulfonate (SDBS) to increase the adsorption of HA. The adsorption of HA at 25°C and pH 7 increased fast at the first 0.5 h and then gradually reached equilibrium after 10 h. The maximum adsorption capacity was 108.93 mg g^-1, which removal efficiency was high as 95.0%. The morphology and adsorption properties of NH₂-UiO-66 were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), surface charge, Fourier transform infrared (FT-IR), N₂ adsorption-desorption, and adsorption test. The adsorption process of HA accorded with the pseudo-second-order kinetics, while the adsorption isotherm conformed to be the Langmuir model and the adsorption was proved to be monolayer adsorption. Adsorption was the spontaneous and endothermic process (ΔG°<0, ΔH°>0). The accessible surface area provided by mesopores on the 5 different Zr-MOFs was the reason for the enhanced HA adsorption capacity. These results provided useful information for effective HA removing and enhanced our understanding of the adsorption mechanism of HA on NH₂-UiO-66.

ZIF-X (8, 67) based nanostructures for gas-sensing applications

ZIF-8 and ZIF-67 are the most investigated zeolitic imidazolate frameworks (ZIFs) materials that have aroused enormous scientific interests in numerous areas of application including electrochemistry, gas storage, separation, and sensors by reason of their fascinating structural properties. Recently, there is a rapidly growing demand for chemical gas sensors for the detection of various analytes in widespread applications including environmental pollution monitoring, clinical analysis, wastewater analysis, industrial applications, food quality, consumer products, and automobiles. In general, the key to the development of superior gas sensors is exploring innovative sensing materials. ZIF-X (8, 67) based nanostructures have demonstrated great potential as ideal sensing materials for high-performance sensing applications. In this review, the general properties and applications of ZIF-X (8, 67) including gas storage and gas adsorption are first summarized, and then the recent progress of ZIF-X (8, 67) based nanostructures for gas-sensing applications and the structure-property correlations are summarized and analyzed.

Effective Removal of Humic Acid by Zr−MOFs with Surface Modification

Humic acid (HA) in makeup water is one of the important safety issues of high−parameter power plants. Herein, the Zr−based metal organic frameworks (Zr−MOFs) were applied to remove humic acid in water. The mesoporous and active sites of Zr−MOFs were controlled by different ratios of ligands to increase the adsorption of HA. The maximum adsorption capacity was 150.15 mg g−1. The morphology and adsorption properties of the Zr−MOFs were characterized using scanning electron microscopy (SEM), X−ray diffraction (XRD), surface charge, Fourier Transform infrared (FT−IR), N2 adsorption−desorption and adsorption test. The adsorption process of HA accorded with the pseudo−second−order kinetics, while the adsorption isotherm conformed to the Langmuir model and the adsorption was proved to be a spontaneous and endothermic process. Physical adsorption by the mesoporous materials and the hydrogen bonding interactions between the Zr−MOFs and HA were the driving forces of HA adsorption. These results provided useful information for the effective removal of HA and enhanced our understanding of the adsorption mechanism of HA on Zr−MOFs.

Enhancing triethylamine sensing of ZIF-derived ZnO microspheres arising from cobalt doping and defect engineering

Reasonable doping is beneficial to the generation of defects, which is a feasibility strategy to improve the ZnO sensing performance. Herein, we presented an in situ self-sacrificing template strategy for fabricating Co doped h-ZnO core-shell structures (h-ZnO/ZnCo_x) with different defect contents, pyrolyzing hierarchical porous ZnO (h-ZnO) sub-microspheres coated by zeolite imidazolate frameworks (h-ZnO/ZIF-ZnCo_x). The investigations of X-ray photoelectron (XPS), photoluminescence (PL) and Raman spectra indicate that donor defects include zinc interstitial (Zn_i) and oxygen vacancy (V_O) in h-ZnO/ZnCo_x can be tuned by Co dopant (x = 0-30%). Resultantly, the h-ZnO/ZnCo_x exhibits a significantly enhanced response and selectivity towards triethylamine (TEA), beyond the undoped h-ZnO, and 15% Co-doped h-ZnO (h-ZnO/ZnCo_15%) conducts the maximum responses of 1020 to 50 ppm TEA at 573 K, in the top set for the similar type of sensors. Further, the sensing mechanism of h-ZnO/ZnCo_x is elaborated, possibly resulting from abundant active oxygen species conversed from more oxygen adsorbed which corresponds to cobalt doping generating rich donor-related defects and additional electrons in h-ZnO/ZnCo_15%.