Recent advances on preparation and environmental applications of MOF-derived carbons in catalysis

Chemi-resistive sensors based on hybrid functional materials are promising candidates for gas sensing with high responsivity, good selectivity, fast response/recovery, great stability/repeatability, room-working temperature, low cost, and easy-to-fabricate, for versatile applications. This progress report reviews the advantages and advances of these sensing structures compared with the single constituent, according to five main sensing forms: manipulating/constructing heterojunctions, catalytic reaction, charge transfer, charge carrier transport, molecular binding/sieving, and their combinations. Promises and challenges of the advances of each form are presented and discussed. Critical thinking and ideas regarding the orientation of the development of hybrid material-based gas sensor in the future are discussed.

/pdf/gas-sensors-based-on-chemi-resistive-hybrid-functional-i76a6c6prl.pdf

Gas Sensors Based on Chemi-Resistive Hybrid Functional Nanomaterials

Review of ZnO-based nanomaterials in gas sensors

Membrane filtration and absorption strategies based on superwetting surfaces for oil–water separation have regained tremendous attention due to their being low cost, highly efficient and environmentally friendly. Besides the usual superhydrophobic, superhydrophilic/underwater superoleophobic and dual superlyophobic surfaces, very novel and unprecedented surfaces with special extreme wetting behavior have been widely used in oil–water separation. In this review, novel surfaces with extreme wetting behavior for oil-water separation reported over the past three years including superhydrophilic–superoleophobic, superamphiphobic, superhydrophilic-underoil superhydrophilic, underoil superhydrophobic-underwater superoleophobic and liquid-infused surfaces, as well as oil–water separation mechanisms, separation approaches and design principles for obtaining novel superwetting membranes, are systematically summarized. The most common problems in the process of oil–water separation-membrane pollution and solutions are discussed. In addition, the selection of substrates, the swelling of hydrophilic membranes and the wettability conversion of intelligent response membranes are analyzed. The current trends, challenges and future research opportunities are also proposed, providing a road map for the future development of high-efficiency oil–water separation technology.

Designing novel superwetting surfaces for high-efficiency oil–water separation: design principles, opportunities, trends and challenges

Transition metal compositions (Fe, Co and Ni) have always been promising candidates for electromagnetic wave (EMW) absorbers. In this study, the FeCo layered double hydroxide (LDH) supported on raspberry-like carbon spheres (RCs) was synthesized by a simple hydrothermal method and the spontaneous electrostatic self-assembly process. The surface FeCo-LDH is then transformed into FeCo layered double oxide (LDO) with different compositions after calcination treatment (650 °C and 700 °C), forming a typical hierarchical structure. The sample calcined at 700 °C exhibited an ultra-wide effective absorption bandwidth (fe) (RL

Facile synthesis of FeCo layered double oxide/raspberry-like carbon microspheres with hierarchical structure for electromagnetic wave absorption.

It is challenging for current metal oxides based acetone sensors to realize excellent ppb-level acetone sensing properties at low working temperature. Herein, the hollow ZnO/MoS2 nanosheets (HZnO/MoS2) core/shell heterogeneous structures are originally produced. Fast gas transport channels and n–p heterojunctions are produced by the decoration of MoS2 nanosheets on HZnO surface, resulting in high acetone response and fast response/recovery speed. Ultraviolet (UV) light is introduced to further improve acetone response and drastically reduce working temperature. The light diffraction and reflection caused by the decoration of hierarchical MoS2 nanosheets could significantly enhance light harvesting. Hence, the excellent acetone sensing properties are obtained by the synergistic effect of UV light and HZnO/MoS2 core/shell heterogeneous structures. Exactly, at 100 °C, the HZnO/MoS2 possesses a stable response (1.52) to 100 ppb acetone with UV irradiation while it exhibits no response to 100 ppb acetone without UV. Even at room temperature (30 ℃), UV activated HZnO/MoS2 still exhibits a stable response (∼1.33) and fast recovery/recovery time (19 s/97 s) to 50 ppm acetone. Furthermore, the DFT calculations are performed to demonstrate the underlying acetone sensing mechanism. The results demonstrate that UV activated HZnO/MoS2 heterostructure could achieve trace-acetone detection at low temperature.

UV assisted ppb-level acetone detection based on hollow ZnO/MoS2 nanosheets core/shell heterostructures at low temperature

For the first time, Co-MOF-74 derived Co3O4/graphene heterojunction nanoscrolls (Co3O4/GNS) structure is synthesized by a simple one-step hydrothermal strategy and subsequent calcination process. Theoretically, the growth mechanism of Co3O4/GNS is revealed by molecular dynamic simulation, demonstrating that a high loading of Co-MOF-74 nanoparticles is needed for effective rolling of GO. The sensor based on Co3O4/GNS exhibits high response of 58.1 (34-fold enhancement compared with that of Co3O4), short response/recovery time of 12 s/66 s (157 s/200 s for Co3O4) toward 1 ppm acetone at 190 °C and superior selectivity, which are much better than those of most reported acetone sensors. Moreover, the Co3O4/GNS can even detect as low as 50 ppb acetone with a notable response (1.24). The appreciable response together with rapid response/recovery of Co3O4/GNS is attributed to the large heterojunction interface between Co3O4 and graphene nanoscroll and high-speed gas transfer pathways provided by nanoscroll. This unique structure design is believed to offer guidance for generalizable synthesis of metal oxide/GNS that can be effectively applied in the fields of ppb-level gas detection.

Co-MOF-74 derived Co3O4/graphene heterojunction nanoscrolls for ppb-level acetone detection

It is imperative to explore an accurate ppb-level acetone sensor for noninvasive detection of diabetes. In this work, two dimensional p-type MoS2 nanosheets are introduced on the surface of p-type ZnO derived from metal-organic frameworks (MOFs) to produce ZnO@MoS2 core/shell heterojunctions as a novel acetone sensor, showing a great enhancement of acetone response, about two orders of magnitude than that of pure ZnO derived from MOFs. For example, the ZnO@MoS2 exhibits about 80 times enhancement in response to 100 ppb acetone than that of pure ZnO. More importantly, this ZnO@MoS2 heterojunctions sensor exhibits an ultra-fast response/recovery to ultra-low concentration acetone (60 s/40 s @ 5 ppb), which is the best acetone sensing performance for the metal oxide-based materials reported to date. Moreover, the acetone sensing performances are negligibly affected by humidity and other gas, which is suitable for exhaled acetone detection. Finally, it is elucidated that the sharp increase of negative heterojunction interface resistance, ultra-fast gas diffusion rates in MoS2 nanosheets and strong interaction energy are key factors for the excellent acetone sensing properties of ZnO@MoS2. This work opens up a novel and efficient way for ultra-low concentration gas detection.

Metal-organic frameworks derived ZnO@MoS2nanosheets core/shell heterojunctions for ppb-level acetone detection: Ultra-fast response and recovery

Enhancing oil-in-water emulsion separation performance of polyvinyl alcohol hydrogel nanofibrous membrane by squeezing coalescence demulsification

The demand of acetone gas sensors with great response value and fast response/recovery time to low concentration acetone is increasing in practical diagnosis for diabetes. In this work, metal-organic frameworks (MOFs) derived flower-like ZnO/Co3O4 heterojunctions based sensor is prepared by a simple solution mixing method at room temperature. The sensor shows high acetone response value, short response/recovery time, excellent selectivity and good stability. For example, the response value of ZnO/Co3O4 heterojunctions based sensor is up to 120 % towards 500 ppb acetone at 300 ℃, which is about 30-fold enhancement than these of intrinsic ZnO and Co3O4. Moreover, its minimal detection limitation is 100 ppb acetone and it shows ultra-fast response/recovery time for ppb-level acetone (22 s/27 s@500 ppb). The excellent acetone sensing properties of flower-like ZnO/Co3O4 heterojunctions based sensor is attributed to the sharp resistance variation of heterojunction interface between ZnO and Co3O4 and the ultra-fast gas transport channel provided by ZnO nanosheets. This finding provides important insights and useful guidance for the detection of ppb-level acetone.

Xurong Qiao

Papers

UV assisted ppb-level acetone detection based on hollow ZnO/MoS2 nanosheets core/shell heterostructures at low temperature

Co-MOF-74 derived Co3O4/graphene heterojunction nanoscrolls for ppb-level acetone detection

Metal-organic frameworks derived ZnO@MoS2nanosheets core/shell heterojunctions for ppb-level acetone detection: Ultra-fast response and recovery

Enhancing oil-in-water emulsion separation performance of polyvinyl alcohol hydrogel nanofibrous membrane by squeezing coalescence demulsification

Metal-organic frameworks derived hierarchical flower-like ZnO/ Co3O4 heterojunctions for ppb-level acetone detection