Target-Driven Z-Scheme Heterojunction Formation for ppb H₂S Detection from Exhaled Breath at Room Temperature

Abstract

As a biomarker of periodontitis, sensitive and timely monitoring of hydrogen sulfide (H2S) in exhaled breath at room temperature (RT) is important for the early intervention of oral diseases. However, the required high operation temperature to achieve high sensitivity is still a technical challenge for directly monitoring exhaled breath. In this study, by integrating metal–organic frameworks (MOFs) into self-aligned TiO2 nanotube arrays (NTs), a chemiresistor gas sensor with outstanding sensitivity and selectivity was constructed for the detection of H2S at RT. The precise regulation of a Co­(III)-based MOF CoBDC-NH2 (BDC-NH2 = 2-aminoterephthalic acid) not only induced more active surface for the preconcentration of the target gas but also caused a buildup of Z-scheme heterojunctions in the H2S atmosphere that induced an ultrahigh sensitivity at RT via 365 nm light-emitting diode irradiation. The response and recovery times decreased to ∼50 and ∼28%, respectively, when this system was exposed to UV light. The sensing chips based on the as-prepared TiO2/CoBDC-NH2 NTs exhibited the highest-ranking H2S sensing performance, i.e., a limit of detection of 1.3 ppb and excellent selectivity even to 100 times high concentration of interference gases, owing to the synergistic chemical environment provided by NH2-functionalized Co-MOFs and abundant photogenerated electrons provided by Z-scheme heterojunctions. This sensing chip was also used in a practical application for the timely monitoring of halitosis from direct exhaled breath. This study provides a reliable and sensitive design for clinically aiding the timely detection of H2S in a complex oral environment.

Customizing Wettability of Defect-Rich CeO2/TiO2 Nanotube Arrays for Humidity-Resistant, Ultrafast, and Sensitive Ammonia Response

“…However, despite having achieved a strong and fast sensing response, the poor humidity resistance remains a major challenge for MOS-based gas sensors. 35 Compared to the response at 25% RH, the NH 3 response was found to significantly decrease with increasing humidity (Figure S8). As shown in Figure 3d, a response of only ∼20% was retained upon exposure to high humidity conditions (75% RH), which greatly limited the application of the present sensor.…”

“…This could be attributed to the defective CeO 2 nanowires and perpendicular TiO 2 nanotube arrays, enabling effective exchange and transport of electrons. However, despite having achieved a strong and fast sensing response, the poor humidity resistance remains a major challenge for MOS-based gas sensors . Compared to the response at 25% RH, the NH 3 response was found to significantly decrease with increasing humidity (Figure S8).…”

A bio-inspired and switchable H+/OH− ion-channel for room temperature exhaled CO2 chemiresistive sensing

“…The concentration of the interfering gas that we detected was higher than that of human exhaled breath (approximately 15 ppb–1.75 ppm), which clearly demonstrates the selectivity of this CSPH ion channel sensor. 51–59 The high selectivity of the CSPH ion channel-based sensor is mainly attributed to the material having two CO 2 binding sites, including the hydroxide ion and the tertiary amines on RhB, which greatly increases the ability to interact with CO 2 . In order to explore the effect of humidity, the CSPH ion channel-based sensor was placed at a relative humidity of 5–70% (RH), and then the response of 1000 ppm CO 2 was measured.…”

Achieving One Part Per Billion Hydrogen Sulfide (H2S) Level Detection through Optimizing Composition and Crystallinity of Gold-Decorated Tungsten Trioxide (Au-WO3) Nanofibers

“…Although conventional gas detection methods, such as gas chromatography–mass spectrometry, quantum cascade lasers, infrared laser spectroscopy, and fluorescence spectrometry, provide high accuracy, these instruments are bulky, lack portability, and are expensive. – Chemiresistive gas sensors, which are the most ubiquitous type of gas sensors, have garnered increased interest due to their rapid response, good accuracy, cost effectiveness, easy fabrication processes, and flexible configuration capabilities . Metal oxide semiconductors (MOS) have been widely used as gas sensing materials in chemiresistive gas sensors due to excellent sensing performance such as high sensitivity and fast response and recovery time. – Among the diverse range of metal oxides, WO 3 is one of the most attractive MOS sensing materials in which the robust empirical evidence demonstrates its impressive sensitivity toward NO 2 , NH 3 , and volatile organic compounds (VOCs). ,– Its band gap energy of around 2.4 to 2.8 eV, and abundant oxygen vacancies suggest a significant promise for its application in H 2 S detection. , Unfortunately, pristine WO 3 does not respond well to H 2 S. For example, Urasinska-Wojcik et al reported a WO 3 -based sensor only exhibited a response ( R air / R gas ) of 1.4 toward 100 ppb H 2 S . Herein, several strategies from morphology to composition modulation have been proposed to modulate the material properties, which could contribute to the enhancement of gas sensing performance. ,, 1-Dimensional (1-D) nanostructures are highly considered as the top choice for gas sensing material morphology due to their large surface area to volume ratio that enhances their reactive and interactive potential .…”