Ag decoration-enabled sensitization enhancement of black phosphorus nanosheets for trace NO2 detection at room temperature

High performance Pt-anchored MoS2based chemiresistive ascorbic acid sensor

Ascorbic acid (AA), known as vitamin C, is a vital bioactive compound that plays a crucial role in several metabolic processes, including the synthesis of collagen and neurotransmitters, the removal of harmful free radicals, and the uptake of iron by cells in the human intestines. As a result, there is an absolute need for a highly selective, sensitive, and economically viable sensing platform for AA detection. Herein, we demonstrate a Pt-decorated MoS2for efficient detection of an AA biosensor. MoS2hollow rectangular structures were synthesized using an easy and inexpensive chemical vapor deposition approach to meet the increasing need for a reliable detection platform. The synthesized MoS2hollow rectangular structures are characterized through field effect scanning electron microscopy (FESEM), energy-dispersive spectroscopy elemental mapping, Raman spectroscopy, and x-ray photoelectron spectroscopy. We fabricate a chemiresistive biosensor based on Pt-decorated MoS2that measures AA with great precision and high sensitivity. The experiments were designed to evaluate the response of the Pt-decorated MoS2biosensor in the presence and absence of AA, and selectivity was evaluated for a variety of biomolecules, and it was observed to be very selective towards AA. The Pt-MoS2device had a higher response of 125% against 1 mM concentration of AA biomolecules, when compared to that of all other devices and 2.2 times higher than that of the pristine MoS2device. The outcomes of this study demonstrate the efficacy of Pt-decorated MoS2as a promising material for AA detection. This research contributes to the ongoing efforts to enhance our capabilities in monitoring and detecting AA, fostering advancements in environmental, biomedical, and industrial applications.

Dual-Photosensitizer Synergy Empowers Ambient Light Photoactivation of Indium Oxide for High-Performance NO2 Sensing

Light-activated chemiresistors offer a powerful approach to achieving lower-temperature gas sensing with unprecedented sensitivities. However, an incomplete understanding of how photoexcited charge carriers enhance sensitivity obstructs the rational design of high-performance sensors, impeding the practical utilization under commonly accessible light sources instead of ultraviolet or higher-energy sources. Here, a rational approach is presented to modulate the electronic properties of the parent metal oxide phase, exemplified by this model system of Bi-doped In2O3 nanofibers decorated with Au nanoparticles (NPs) that exhibit superior NO2 sensing performance. Bi doping introduces mid-gap energy levels into In2O3, promoting photoactivation even under visible blue light. Additionally, green-absorbing plasmonic Au NPs facilitate electron transfer across the heterojunction, extending the photoactive region toward the green light. It is revealed that the direct involvement of photogenerated charge carriers in gas adsorption and desorption processes is pivotal for enhancing gas sensing performance. Owing to the synergistic interplay between the Bi dopants and the Au NPs, the Au-BixIn2-xO3 (x = 0.04) sensing layers attain impressive response values (Rg/Ra = 104 at 0.6 ppm NO2) under green light illumination and demonstrate practical viability through evaluation under simulated mixed-light conditions, all of which significantly outperforms previously reported visible light-activated NO2 sensors.

Black Phosphorus-Tungsten Oxide Sandwich-like Nanostructures for Highly Selective NO2 Detection

Modern chemical production processes often emit complex mixtures of gases, including hazardous pollutants such as NO2. Although widely used, gas sensors based on metal oxide semiconductors such as WO3 respond to a wide range of interfering gases other than NO2. Consequently, developing WO3 gas sensors with high NO2 selectivity is challenging. In this study, a simple one-step hydrothermal method was used to prepare WO3 nanorods modified with black phosphorus (BP) flakes as sensitive materials for NO2 sensing, and BP-WO3-based micro-electromechanical system gas sensors were fabricated. The characterization of the as-prepared BP-WO3 composite through X-ray diffraction scanning electron microscopy and X-ray photoelectron spectroscopy confirmed the successful formation of the sandwich-like nanostructures. The result of gas-sensing tests with 2-14 ppm NO2 indicated that the sensor response was 1.25-2.21 with response-recovery times of 36 and 36 s, respectively, at 190 °C. In contrast to pure WO3, which exhibited a response of 1.07-2.2 to 0.3-5 ppm H2S at 160 °C, BP-WO3 showed almost no response to H2S. Thus, compared with pure WO3, BP-WO3 exhibited significantly improved NO2 selectivity. Overall, the BP-WO3 composite with sandwich-like nanostructures is a promising material for developing highly selective NO2 sensors for practical applications.

Pt and black phosphorus co-modified flower-like WS2 composites for fast NO2 gas detection at low temperature

Incomplete recovery, baseline drift, and a long response time have been impeding the practical applications of transition metal dichalcogenide (TMD)-based gas sensors. Here, we report WS2 sensors with significantly improved gas recovery, rapid response, and negligible baseline drift by the incorporation of black phosphorus (BP) as well as the decoration of Pt to detect NO2 for the first time. Compared to bare WS2, the BP-WS2 sensors show higher sensitivity, better repeatability, and more excellent selectivity towards NO2 at the optimal operating temperature of 50 °C. Furthermore, the optimized 30%BP-WS2/Pt sensors exhibit a continuous enhancement in the recovery level and sensitivity with negligible baseline drift. The 30%BP-WS2/Pt sensor also exhibits a shorter response time of 28 s than 49.5 s for its counterpart WS2 sensor towards 32 ppm NO2. The enhanced sensing properties are primarily due to the combined effects of more adsorption sites provided by BP, the spill-over effect of Pt catalysis, and the WS2/BP heterostructure. Therefore, the Pt-decorated 30%BP-WS2 sensor exhibits prominent gas-sensing properties of high gas sensitivity, a low detection limit of 100 ppb, good selectivity, and fast response. Our strategy provides a new route for designing and optimizing TMD-based gas sensors with excellent gas-sensing performance.

Sodium titanate: A proton conduction material for ppb-level NO2 detection with near-zero power consumption

Constrained by the traditional charge transfer sensing mechanism, it is quite challenging to fabricate NO2 sensors that simultaneously exhibit high sensitivity, rapid response/recovery, and low power consumption. Herein, sodium titanate (NTO), a layered material with abundant surface-rooted OH groups (OHR), is demonstrated to be a promising NO2 sensing material. To understand the sensing behavior of NTO, the influences of operating temperature, applied voltage, and relative humidity are investigated, and a novel OHR-enabled proton conduction sensing mechanism is proposed. The sensing process mainly involves selective NO2 adsorption on OHR, thereby lowering the activation energy for proton transportation along the NTO surface. Meanwhile, the moderate intermolecular interaction makes NO2 both easily adsorbed and desorbed at room temperature. Hence, NTO exhibits a highly sensitive, rapid, and fully recoverable response (∼5.7-1 ppm NO2 within 3 s), wide detection range (1 ppb-20 ppm), good stability (>2 months), and near-zero power consumption (0.5 nW). Finally, we demonstrate that NTO has an excellent practical indoor/outdoor NO2 sensing ability. This work offers a new pathway to resolve the inherent conflicts in available NO2 sensors by using NTO via the OHR-enabled proton conduction sensing mechanism, which may also provide insight into designing high-performance sensors for other gases.

Fabrication of noble metal (Au, Ag, Pt)/polythiophene/reduced graphene oxide ternary nanocomposites for NH3 gas sensing at room temperature

Room temperature NH₃ gas sensors composed of noble metal (Au, Ag or Pt)/polythiophene/reduced graphene oxide (Au, Ag or Pt/PTh/rGO) ternary nanocomposite films were fabricated using a simple one-pot redox reaction. The surface morphology and composition of Au, Ag or Pt/PTh/rGO ternary nanocomposite films were analyzed using Fourier transform infrared spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films, obviously bright Au nanoparticles were observed on the surface of the massive lamination PTh film which wrapped the rGO, and encapsulated Au nanoparticles were observed in the Au/PTh/rGO film. Comparative gas sensing results showed that the Au/PTh/rGO ternary nanocomposite film had the highest response compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films at room temperature, especially when the testing concentration of NH₃ gas was below 5 ppm. The Au/PTh/rGO ternary nanocomposite film also had a fast response time and good reproducibility. The combination of the high catalytic activity of naked Au nanoparticles and the formation of effective carrier transfer channels by encapsulated Au nanoparticles was responsible for the improved response of the Au/PTh/rGO ternary nanocomposite film.

Amine-Functionalized Black Phosphorus Nanosheets toward Ultrafast and Room-Temperature Trace Carbon Dioxide Sensing

Carbon dioxide (CO₂) poses a significant effect on global climate, indoor activity, and crop yield, thus necessitating real-time and high-performance detection. Traditional CO₂-sensing materials always suffer from weak and sluggish reaction, elevated operation temperature, and poor detection limit. To surmount these obstacles, in this work a series of amine-rich polymer functionalized black phosphorus nanosheets (BP) were prepared for room-temperature CO₂ detection. Superior to TMMAP or 3-DEAPTES modified counterparts, the BP-10% APTES sensor delivered a response of 28.5% and ultrafast response/recovery time of 4.7 s/4.8 s toward 10 ppm of CO₂ under 36% RH at 22 °C, a lowest detection limit of 5 ppm, as well as excellent selectivity. Also, a nice repeatability and long-term operation stability were demonstrated. Thus, BP-APTES composites offer a promising strategy for high-performance CO₂ detection in terms of high sensitivity, low power-consumption, and convenient fabrication, and showcase brilliant prospects in portable optoelectronic detection systems and the Internet of Things.