Pt-Anchored CuCrO2 for Low-Temperature-Operating High-Performance H2S Chemiresistors

Finding Natural, Dense, and Stable Frustrated Lewis Pairs on Wurtzite Crystal Surfaces for Small-Molecule Activation

The surface frustrated Lewis pairs (SFLPs) open up new opportunities for substituting noble metals in the activation and conversion of stable molecules. However, the applications of SFLPs on a larger scale are impeded by the complex construction process, low surface density, and sensitivity to the reaction environment. Herein, wurtzite-structured crystals such as GaN, ZnO, and AlP are found for developing natural, dense, and stable SFLPs. It is revealed that the SFLPs can naturally exist on the (100) and (110) surfaces of wurtzite-structured crystals. All the surface cations and anions serve as the Lewis acid and Lewis base in SFLPs, respectively, contributing to the surface density of SFLPs as high as 7.26×1014 cm-2. Ab initio molecular dynamics simulations indicate that the SFLPs can keep stable under high temperatures and the reaction atmospheres of CO and H2O. Moreover, outstanding performance for activating the given small molecules is achieved on these natural SFLPs, which originates from the optimal orbital overlap between SFLPs and small molecules. Overall, these findings not only provide a simple method to obtain dense and stable SFLPs but also unfold the nature of SFLPs toward the facile activation of small molecules.

Chameleon-like Response Mechanism of Gold-Silver Bimetallic Nanoclusters Stimulated by Sulfur Ions and Their Application in Visual Fluorescence Sensing

Herein, 2-mercapto-5-benzimidazolesulfonate acid sodium salt dihydrate (MBZS)-protected gold-silver bimetallic nanoclusters, named MBZS-AuAg NCs, were synthesized. Interestingly, we found that MBZS-AuAg NCs solutions can exhibit different fluorescence color changes under sulfide stimulation. A series of modern analytical testing techniques were used to explore the interaction mechanism between MBZS-AuAg NCs and sulfide. Sulfide ions can not only cause MBZS-AuAg NCs to exhibit rich fluorescence color changes similar to those of a chameleon but also have four linear relationships between the response intensity and sulfide concentration. A wide-range sulfide fluorescence sensing platform was constructed based on four linear segments with different fluorescence color responses. This sensing platform can be directly used for the determination of S2- with a detection limit as low as 11 nM. The portable test paper based on MBZS-AuAg NCs can realize the visual and rapid detection of gaseous hydrogen sulfide with a detection limit of 100 ppb (v/v). The wide detection range of the proposed method not only allows it to be used as an alternative method for sulfide detection in environmental samples but also has potential applications in the rapid detection and early warning of hydrogen sulfide gas in industrial and mining scenarios.

Delafossite CuGaO2-Based Chemiresistive Sensor for Sensitive and Selective Detection of Dimethyl Disulfide

Dimethyl disulfide (DMDS) is a common odor pollutant with an extremely low olfactory threshold. Highly sensitive and selective detection of DMDS in ambient humid air background, by metal oxide semiconductor (MOS) sensors, is highly desirable to address the increased public concern for health risk. However, it has still been a critical challenge up to now. Herein, p-type delafossite CuGaO2 has been proposed as a promising DMDS sensing material owing to its striking hydrophobicity (revealed by water contact angle measurement) and excellent partial catalytic oxidation properties (indicated by mass spectroscopy). The present CuGaO2 sensor shows a selective DMDS response, with satisfied humidity resistance performance and long-term stability at a relatively low operation temperature of 140 °C. An ultrahigh response of 100 to 10 ppm DMDS and a low limit of detection of 3.3 ppb could be achieved via a pulsed temperature modulation strategy. A smart sensing system based on a CuGaO2 sensor has been developed, which could precisely monitor DMDS vapor in ambient humid air, even with the presence of multiple interfering gases, demonstrating the practical application capability of MOS sensors for environmental odor monitoring.

Bifunctional role of PDMS membrane in designing humidity-tolerant H2S chemiresistors with high selectivity

A thermally evaporated hydrophobic PDMS membrane could significantly mitigate humidity interference/poisoning (without a decline in response at 50% RH for nearly 3 months) and enhance the selectivity of a CuCrO₂ chemiresistor toward erosive H₂S, offering an avenue for the practical applications of (H₂S) chemiresistors in an ambient humid air atmosphere.

Voltage driven chemiresistor with ultralow power consumption based on self-heating bridged WO3 nanowires

Metal oxide semiconductor (MOS)-based chemiresistors have been widely used for detecting harmful gases in many industrial and indoor/outdoor applications, which possess the advantages of small size, low cost, integratability, and ease of use. However, power consumption has become a critical parameter for practical applications. Several methods have been explored to reduce power consumption including reducing the operation temperature, use of micro-electro-mechanical systems (MEMS), and self-heating working mode. Among them, the self-heating working mode has attracted significant attention. Herein, a facile approach of modulating bridged NW chemiresistor by Joule heating effect is proposed to combine both the superiority of single crystal nanowire (NW) carrier channels and power consumption optimization of the self-heating mode. The WO₃-bridged NW chemiresistors and WO₃ film NW chemiresistors are both constructed to investigate gas responses and power consumption. Substantially magnified electrical responses (R_g/R_a) of WO₃ NW chemiresistor toward NO₂ is demonstrated by constructing a bridged structure. Under the optimal external heating condition, the responses of chemiresistors toward 5 ppm NO₂ can be boosted from 369.7 (film NW) to 1089.7 (bridged NW). The responses to 5 ppm NO₂ under the self-heating mode also can be boosted from 13.6 (film NW) to 24.6 (bridged NW) with a drastically declined power consumption. Self-heating bridged NWs allows for localizing the Joule heat within the nanojunction, and thus substantially lowers the power consumption to 0.13 μW (300 °C). This provides an additional opportunity for reducing power consumption of oxide chemiresistors for air quality monitoring in future.

Enhancement of H2S sensing performance of rGO decorated CuO thin films: experimental and DFT studies

We demonstrate a highly selective and sensitive Cupric oxide (CuO) thin film-based low concentration Hydrogen sulfide (H₂S) sensor. The sensitivity was improved around three times by decorating with reduced graphene oxide (rGO) nanosheets. CuO thin films were deposited by Chemical Vapor Deposition followed by inter-digital electrode fabrication by a thermal evaporations system. The crystal structure of CuO was confirmed by x-ray diffraction. The sensing response of pristine CuO was found around 54% at 100 °C to 100 ppm of H₂S. In contrast, the sensing response was enhanced to 167% by decorating with rGO of 1.5 mg ml^-1concentration solution. The sensing was improved due to the formation of heterojunctions between the rGO and CuO. The developed sensor was examined under various gas environments and found to be highly selective towards H₂S gas. The improvement in sensing response has been attributed to increased hole concentration in CuO in the presence of rGO due to the Fermi level alignment and increased absorption of H₂S molecules at the rGO/CuO heterojunction. Further, electronic structure calculations show the physisorption behavior of H₂S molecules on the different adsorption sites. Detailed insight into the gas sensing mechanism is discussed based on experimental results and electronic structure calculations.