Rapid and Wide-Range Detection of NOx Gas by N-Hyperdoped Silicon with the Assistance of a Photovoltaic Self-Powered Sensing Mode

Portable analytical system integrating purge and trap and microplasma optical emission spectrometry for online discriminative detection of NOx

Pollution caused by nitrogen oxides (NOx, mainly NO and NO2) has attracted considerable attention due to its negative implications on the environment and human health. Herein, a novel, portable, and battery-operated system integrating a purge and trap (P&T) system with a miniaturized point discharge optical emission spectrometer (μPD-OES) was developed for monitoring atmospheric NOx. Among NOx, NO2 can be selectively and directly absorbed by sodium hydroxide (NaOH) solution and converted to nitrite (NO2-). In contrast to NO2, NO cannot be absorbed by NaOH and must be oxidized to NO2 by KMnO4 prior to its absorption. When NO2 and NOx samplers were exposed simultaneously, NO can be calculated as the difference. The concentration of NOx in the air was determined by analyzing the NO2-. The obtained NO2- solution was purged with an argon carrier gas at a rate of 400 mL min-1 for 5 min to remove all the volatile organic compounds contained in the solution before reacting with cyclamate to generate volatile cyclohexene, which was efficiently isolated and preconcentrated by P&T. Subsequently, the cyclohexene was desorbed from the P&T unit and swept into the μPD-OES for its detection under optimized conditions. The system demonstrated a detection limit of 0.02 ppbv (0.04 μg/m3) for NO2, surpassing conventional methods. Precision expressed as the relative standard deviation (RSD, n = 11) was better than 3.5 %. The system was validated by analyzing two NO2 standard gases and fourteen ambient air samples, and the obtained analytical results demonstrated its promising potential for rapid, sensitive, and precise NOx evaluation and monitoring.

Transparent TiO2/MoO3 Heterojunction-Based Photovoltaic Self-Powered Triethylamine Gas Sensor with IoT-Enabled Smartphone Interface

Conventional gas sensors encounter a significant obstacle in terms of power consumption, making them unsuitable for integration with the next generation of smartphones, wireless platforms, and the Internet of Things (IoT). Energy-efficient gas sensors, particularly self-powered gas sensors, can effectively tackle this problem. The researchers are making significant strides in advancing photovoltaic self-powered gas sensors by employing diverse materials and their compositions. Unfortunately, several of these sensors seem complex in fabrication and mainly target oxidizing species detection. To address these issues, we have successfully employed a transparent, cost-efficient solution processed bilayer TiO2/MoO3 heterojunction-based photovoltaic self-powered gas sensor with superior VOC sensing capabilities, marking a significant milestone in this field. The scanning Kelvin probe (SKP) measurement reveals the remarkable change in contact potential difference (-23 mV/kPa) of the TiO2/MoO3 bilayered film after UV light exposure in a triethylamine (TEA) atmosphere, indicating the highest reactivity between TEA molecules and TiO2/MoO3. Under photovoltaic mode, the sensor further demonstrates exceptional sensitivity (∼2.35 × 10-3 ppm-1) to TEA compared to other studied VOCs, with an admirable limit of detection (22 ppm) and signal-to-noise ratio (1540). Additionally, the sensor shows the ability to recognize TEA and estimate its composition in a binary mixture of VOCs from a similar class. The strongest affinity of TiO2/MoO3 toward the TEA molecule, the lowest covalent bond energy, and the highest electron-donating nature of TEA may be mainly attributed to the highest adsorption between TiO2/MoO3 and TEA. We further demonstrate the practical applicability of the TEA sensor with a prototype device connected to a smartphone via the IoT, enabling continuous surveillance of TEA.

Hierarchically porous ZnO derived from zeolitic imidazolate frameworks for high-sensitive MEMS NO2 sensor

Three-dimensional (3D) porous metal oxide nanomaterials with controllable morphology and well-defined pore size have attracted extensive attention in the field of gas sensing. Herein, hierarchically porous ZnO-450 was obtained simply by annealing Zeolitic Imidazolate Frameworks (ZIF-90) microcrystals at an optimal temperature of 450 °C, and the effect of annealing temperature on the formation of porous nanostructure was discussed. Then the as-obtained ZnO-450 was employed as sensing materials to construct a Micro-Electro-Mechanical System (MEMS) gas sensor for detecting NO2. The MEMS sensor based on ZnO-450 displays the excellent gas-sensing performances at a lower working temperature (190 °C), such as high response value (242.18% @ 10 ppm), fast response/recovery time (9/26 s) and ultralow limit of detection (35 ppb). The ZnO-450 sensor shows better sensing performance for NO2 detection than ZnO-based composites materials or commercial ZnO nanoparticles (NPs), which are attributed to its unique hierarchically structures with high porosity and larger surface area. This ZIFs driven strategy can be expected to pave a new pathway for the design of high-performance NO2 sensors.

Composite nanoparticle-metal-organic frameworks for SERS sensing

In recent years, metal-organic frameworks, in general, and zeolitic imidazolate frameworks, in special, had become popular due to their large surface area, pore homogeneity, and easy preparation and integration with plasmonic nanoparticles to produce optical sensors. Herein, we summarize the late advances in the use of these hybrid composites in the field of surface-enhanced Raman scattering and their future perspectives.

A Self-Powered Portable Nanowire Array Gas Sensor for Dynamic NO2 Monitoring at Room Temperature

The fast development of the Internet of Things (IoT) has driven an increasing consumer demand for self-powered gas sensors for real-time data collection and autonomous responses in industries such as environmental monitoring, workplace safety, smart cities, and personal healthcare. Despite intensive research and rapid progress in the field, most reported self-powered devices, specifically NO₂ sensors for air pollution monitoring, have limited sensitivity, selectivity, and scalability. Here, a novel photovoltaic self-powered NO₂ sensor is demonstrated based on axial p-i-n homojunction InP nanowire (NW) arrays, that overcome these limitations. The optimized innovative InP NW array device is designed by numerical simulation for insights into sensing mechanisms and performance enhancement. Without a power source, this InP NW sensor achieves an 84% sensing response to 1 ppm NO₂ and records a limit of detection down to the sub-ppb level, with little dependence on the incident light intensity, even under <5% of 1 sun illumination. Based on this great environmental fidelity, the sensor is integrated into a commercial microchip interface to evaluate its performance in the context of dynamic environmental monitoring of motor vehicle exhaust. The results show that compound semiconductor nanowires can form promising self-powered sensing platforms suitable for future mega-scale IoT systems.

Mid-long wavelength infrared absorptance of hyperdoped silicon via femtosecond laser microstructuring

Hyperdoped silicon (hSi) fabricated via femtosecond laser irradiation has emerged as a promising photoelectric material with strong broadband infrared (IR) absorption. In this work, we measured the optical absorptance of the hSi in the wavelength of 0.3-16.7 µm. Unlike the near to mid wavelength IR absorption, the mid-long wavelength IR (M-LWIR) absorption is heavily dependent on the surface morphology and the dopants. Furthermore, calculations based on coherent potential approximation (CPA) reveal the origin of free carrier absorption, which plays an important role in the M-LWIR absorption. As a result, a more comprehensive picture of the IR absorption mechanism is drawn for the optoelectronic applications of the hSi.

Effect of Working Atmospheres on the Detection of Diacetyl by Resistive SnO2 Sensor

Nanostructured metal oxide semiconductors (MOS) are considered proper candidates to develop low cost and real-time resistive sensors able to detect volatile organic compounds (VOCs), e.g., diacetyl. Small quantities of diacetyl are generally produced during the fermentation and storage of many foods and beverages, conferring a typically butter-like aroma. Since high diacetyl concentrations are undesired, its monitoring is fundamental to identify and characterize the quality of products. In this work, a tin oxide sensor (SnO2) is used to detect gaseous diacetyl. The effect of different working atmospheres (air, N2 and CO2), as well as the contemporary presence of ethanol vapors, used to reproduce the typical alcoholic fermentation environment, are evaluated. SnO2 sensor is able to detect diacetyl in all the analyzed conditions, even when an anaerobic environment is considered, showing a detection limit lower than 0.01 mg/L and response/recovery times constantly less than 50 s.

Principles of odor coding in vertebrates and artificial chemosensory systems

The biological olfactory system is the sensory system responsible for the detection of the chemical composition of the environment. Several attempts to mimic biological olfactory systems have led to various artificial olfactory systems using different technical approaches. Here we provide a parallel description of biological olfactory systems and their technical counterparts. We start with a presentation of the input to the systems, the stimuli, and treat the interface between the external world and the environment where receptor neurons or artificial chemosensors reside. We then delineate the functions of receptor neurons and chemosensors as well as their overall I-O relationships. Up to this point, our account of the systems goes along similar lines. The next processing steps differ considerably: while in biology the processing step following the receptor neurons is the "integration" and "processing" of receptor neuron outputs in the olfactory bulb, this step has various realizations in electronic noses. For a long period of time, the signal processing stages beyond the olfactory bulb, i.e., the higher olfactory centers were little studied. Only recently there has been a marked growth of studies tackling the information processing in these centers. In electronic noses, a third stage of processing has virtually never been considered. In this review, we provide an up-to-date overview of the current knowledge of both fields and, for the first time, attempt to tie them together. We hope it will be a breeding ground for better information, communication, and data exchange between very related but so far little connected fields.

Preparation of PbS NPs/RGO/NiO nanosheet arrays heterostructure: Function-switchable self-powered photoelectrochemical biosensor for H2O2 and glucose monitoring

On the basis of synthesized PbS nanoparticles (PbS NPs)/reduced graphene oxide (RGO)/NiO nanosheet arrays (NiO NSAs) heterostructure, we constructed a function-switchable self-powered PEC sensing platform for the analysis of H2O2 and glucose. Ordered NiO NSAs have high electron mobility, modifying RGO onto the surfaces of NiO NSAs can connect the NiO NSAs with the PbS NPs and promoted the electron transfer rate between them, as well as enhance their photocurrent response. The PbS NPs/RGO/NiO NSAs heterostructure own excellent catalase-like activity can achieve H2O2 detection, only with one more step, after introducing glucose oxidase (GOD) onto the surface of PbS NPs/RGO/NiO NSAs heterostructure, we realized the detection conversion between H2O2 and glucose. Under optimal conditions, the proposed biosensor exhibited superior analytical performance toward H2O2 and glucose, a limit of detection (LOD) of 0.018 mM (S/N = 3) and 5.3 × 10-8 M (S/N = 3) were obtained, respectively. Moreover, good accuracy was obtained in the real samples analysis of H2O2 disinfectant and human serum samples.