A Triptycene-Based Layered/Flower-Like 2D Conductive Metal-Organic Framework with 3D Extension as an Electrode for Efficient Li Storage

2D metal-organic frameworks (2D MOFs) with π conjugation have attracted widespread attention in the field of lithium storage due to their unique electron transfer units and structural characteristics. However, the periodic 2D planar extension structure hides some active sites, which is not conducive to the utilization of its structural advantages. In this work, a series of triptycene-based 2D conductive MOFs (M-DBH, M = Ni, Mn, and Co) with 3D extension structures are constructed by coordinating 9,10-dihydro-9,10-[1,2]benzenoanthracene-2,3,6,7,14,15-hexaol with metal ions to explore their potential applications in lithium-ion and lithium-sulfur batteries. This is the first study in which 2D conductive MOFs with the 3D extended molecule are used as electrode materials for lithium storage. The designed material generates rich active sites through staggered stacking layers and shows excellent performance in lithium-ion and lithium-sulfur batteries. The capacity retention rate of Ni-DBH can reach over 70% after 500 cycles at 0.2 C in lithium-ion batteries, while the capacity of S@Mn-DBH exceeds 305 mAh g-1 after 480 cycles at 0.5 C in lithium-sulfur batteries. Compared with the materials with 2D planar extended structures, the M-DBH electrodes with 3D extended structures in this work exhibit better performance in terms of cycle time and lithium storage capacity.

Metalloporphyrin-Based Metal-Organic Frameworks for the Ultrasensitive Chemiresistive Detection of NO2: Effect of the Central Metal on Tuning the Sensing Performance

The highly sensitive and selective detection of trace hazardous gases at room temperature is very promising for health protection and environmental safety. Herein, chemiresistive sensors for NO2 were fabricated based on self-assembled films of the four metalloporphyrin (MPor)-based metal-organic frameworks PCN-222-M (M = Cu, Ni, Co, Fe) by the quasi-Langmuir-Shäfer method. It is found that the relative responses of the four PCN-222-M films are linearly related to the NO2 concentration, and the PCN-222-Cu possessed an unprecedented high response to NO2 with a sensitivity of 2209% ppm-1 in the 4-20 ppb range and a low limit of detection (LOD) of 0.93 ppb, achieving the best performance reported so far for NO2 detection at room temperature. Meanwhile, PCN-222-Ni showed the fastest recovery among the four PCN-222-M films, which can be used for the rapid detection of NO2. Excellent reproducibility, stability, selectivity, and moisture resistance are shown for both PCN-222-Cu and PCN-222-Ni. Combining the experimental study and density functional theory (DFT) calculation, the essential roles of MPor units and the MPor/Zr6 cluster hybrid material in tuning the Fermi level and the electron transfer between PCN-222-M and NO2 were further proved. These were less considered topics in previous studies on MOFs. This work explores the application of MPor-based MOFs in gas sensing by selecting appropriate MPor units, thus providing guidance for the development of MOF-based chemiresistive sensors.

Au-Decorated 1D SnO2 Nanowire/2D WS2 Nanosheet Composite for CO Gas Sensing at Room Temperature in Self-Heating Mode

We have designed a new ternary structure to enhance the sensing properties of WS2 nanosheet (NS)-based gas sensors at room temperature (RT) in self-heating mode. SnO2 nanowires (NWs, 10–30 wt%) were added to WS2 NSs and then Au nanoparticles (NPs) were deposited on the surface of the resulting composites by UV irradiation. The Au-decorated 10 wt% SnO2–WS2 composition showed the highest gas sensing properties. The presence of SnO2 NWs on the WS2 NSs effectively enhanced the diffusion and adsorption of gas species into deeper parts of the gas sensor. Furthermore, the chemical sensitization of Au (increase in oxygen ionosorption; spillover effect and catalytic effect towards CO) contributed to an enhanced response to CO gas. Gas sensing tests performed in the self-heating mode demonstrated the possibility of realizing a low-voltage, low-power-consumption CO gas sensor based on the Au-decorated 10 wt% SnO2–WS2. The sensor response under 60% relative humidity (RH) conditions was 84% of that under dry conditions, which shows that CO sensing is possible in wet environments at room temperature operation.