As a widely used support, TiO2has often been combined with Pd to form highly sensitive gas-chromic materials. Herein, we prepared a series of Pd/TiO2catalysts with different Pd content (from 0.1 to 5 wt.%) by the impregnation method for their utilization in fast room-temperature CO detection. The detection was simply based on visible color change when the Pd/TiO2was exposed to CO. The sample with 1 wt.% Pd/TiO2presented an excellent CO gasochromic character, associated with a maximum chromatic aberration value of 90 before and after CO exposure. Systematic catalyst characterizations of XPS, FT-IR, CO-TPD, and N2adsorption–desorption and density functional theory calculations for the CO adsorption and charge transfer over the Pd and PdO surfaces were further carried out. It was found that the interaction between CO and the Pd surface was strong, associated with a large adsorption energy of −1.99 eV and charge transfer of 0.196e. The color change was caused by a reduction in Pd2+to metallic Pd0over the Pd/TiO2surface after CO exposure.
Dali Wu,Yile Shi,Xiang Liu,Chenggong Zhang,Min Hua,Xuhai Pan
In the study of WO 3 -based gasochromic materials, the color-change rate and contrast are key indicators for evaluating sensor performance, while long-term stability is equally critical, as it directly determines the service life and reliability of the material in practical applications. In this work, h-WO 3 /m-WO 3 gasochromic materials with a hexagonal–monoclinic mixed-phase structure were successfully synthesized by regulating the annealing temperature. Pd nanoparticles were introduced as essential catalysts to enable room-temperature hydrogen-induced coloration of WO 3 . The Pd–WO 3 –400 sample exhibits excellent response to 1 % hydrogen at room temperature, with a rapid response time of only 13 s and a maximum total color difference (ΔE) of 8.1. Moreover, after one year of cyclic testing, this sample shows the slowest performance degradation, demonstrating outstanding long-term stability. In the mixed-phase structure, the open ionic diffusion channels of the hexagonal phase synergize with the structural stability of the monoclinic phase, while phase interfaces further enhance electron and hydrogen-ion transport. These combined effects significantly improve the gasochromic response. This study provides a strategy for designing gasochromic materials that balance high sensitivity and long-term stability, supporting the practical application of visual hydrogen-leak detection.
Real-time monitoring of carbon dioxide (CO 2 ) is imperative for medical diagnosis and effective environmental preservation. Despite the formidable challenge posed by the inherent chemical inertness of CO₂ molecules, a pioneering CO 2 sensor based on MOF-804 cofunctionalized with ionic liquid (IL) and m-cresol purple (mCP) is successfully developed. By ingeniously integrating hydrogen bonding, electrostatic interactions, and hydrophobic properties within the sensitive layer, the sensor achieves a state-of-the-art sensitivity (Δf = 384 Hz), an exceptionally vast detection range spanning 400–80 000 ppm, and remarkable stability with minimal sensitivity drift even at relative humidity (RH) levels exceeding 80%. Furthermore, the inherent gasochromic property, stemming from the zwitterionic mechanism, paves the way for innovative self-sustaining CO 2 test strips and groundbreaking applications, including CO 2 tracking and CO 2 -encrypted security labeling technology. Collectively, the realization of this ultra-sensitive and robust CO 2 monitoring approach, coupled with its CO 2 -triggered visual and multifunctional capabilities, opens up novel avenues for dynamic CO 2 detection, advanced military encryption strategies, and enhanced health management systems.
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