Ppb Level Research Articles

Conductometric sensor for ppb-level lithium-ion battery electrolyte leakage based on Co/Pd-doped SnO2

Safety problem caused by the leakage of electrolyte in lithium-ion batteries (LIB) have become a critical hot issue. However, since the main components of LIB electrolyte, such as dimethyl carbonate (DMC), are volatile or redox, trace electrolyte leakage is difficult to detect. Therefore, in order to realize early detection of electrolyte leakage and real-time monitoring of LIB health, here we report a success of DMC gas detection by MOS sensor based on Co/Pd-doped SnO2 nanomaterial for LIB health monitoring. In detail, the sensor showed high response to DMC when compared to interfering gases. Especially, the sensor could detect DMC down to the ppb level (the response value of the 500 ppb DMC is about 1.6). The response and recovery time for 1 ppm DMC were about 66 s and 240 s, respectively. The response of the sensor was obvious even when the leakage levels were as low as only 0.1 μL electrolyte. Furthermore, in the simulated electrolyte leakage via LIB penetration experiment, the sensor successfully exhibited an instant response, which proved that this work effectively provides a new approach for LIB real-time health and safety monitoring.

One-step synthesis of thiol-functionalized metal coordination polymers: effective and superfast removal of Hg (II) in the different matrices to ppb level

The mercury in water bodies has posed a great threat to the environment and humans, and removing mercury and purifying wastewater has become a global environmental issue. Adopting Zn(II) coordination polymers (Zn-CPs) emerged as a new approach, however, the kind of Zn-CPs, which solely consisted of amino groups, exhibited unsatisfactory performance in capturing Hg(II) at a low level and causing the subsequent leaching of Zn(II) after adsorption. In this study, we fabricated the thiol-modified Zn-based coordination polymers (Zn-CPs-SH) through a one-step solvothermal reaction to efficiently capture Hg(II) from wastewater. Its preeminent adsorption performance could be maintained across a broad range of pH (2–7), ion strength (Cl−, SO42−, and NO3− at 0–10,000 mg/L), and dissolved organic matter (0–100 mg/L). The impressive properties, including fast kinetics (k2∼1.01 × 10−4 L/min), outstanding adsorption capacity (1278.72 mg/g, 298 K), superior selectivity (Kd∼2.3 × 104 mL/g), and excellent regeneration capability (Re = 93.54% after 5 cycles), were attributed to the ultra-abundance of adsorption sites donating from thiol groups, which was revealed by XPS analysis, DFT calculations, and molecular orbital theory. Noteworthy, the high practical application potential of Zn-CPs-SH was demonstrated by its outstanding Hg(II) removal efficiency (Re ≥ 99.10%) in various Hg(II)-spiked water matrices, e.g., tap water, river water, and industrial wastewater. Importantly, the residual Hg(II) in the treated water declined to the ppb level without any Zn(II) leaching. Overall, it is highly anticipated that the incorporation of Zn-CPs-SH would facilitate the practical implementation of highly efficient Hg(II) removal in wastewater treatment owing to its exhibiting high selective affinity, superior adsorption capacity, and enhanced efficiency.

Room temperature operated flexible La-ZnO/MWCNTs sensor for ppb level carbon monoxide detection

The advancement of gas sensors with ppb level concentration experiences profound challenges. In this research, Lanthanum (La)-Zinc Oxide (ZnO)/multi-walled carbon nanotubes (MWCNTs) composites were successfully fabricated and loaded on a flexible polyimide substrate where interdigitated electrodes (thickness: 300 µm and spacing: 300 µm) were prepared using a laser carbonation technique for room temperature (RT) carbon monoxide (CO) gas detection. The synthesized composites were characterized using scanning electron microscopy, energy dispersive x-ray spectroscopy, UV–visible spectrophotometry, x-ray diffraction, and Fourier transform infrared spectroscopy. When compared to the La-ZnO composite, the addition of MWCNTs on the synthesized composite-based sensor exhibited ∼8 times higher response than La-ZnO to 100 ppm CO at 27 °C. The response of the La-ZnO/MWCNTs composite sensors to 20 ppm CO was tested at six different relative humidity (RH) levels ranging from 0% to 90% in the increments of 20% RH. These sensors exhibited humidity tolerant properties, as evidenced by their responses to different humidity levels. Even when exposed to 90% RH, the sensor only showed ∼13% reduction in response compared to 0% RH, indicating that it is a humidity tolerant sensor. Furthermore, the La-ZnO/MWCNTs sensor has excellent selectivity and can detect low CO concentrations of 100 ppb. As a result, the proposed high-performance flexible sensor has a lot of potential for use in wearable devices to sense CO gas at RT for trace level detection.

Curious Behavior of Fe3+-As3+ Chemical Interactions and Nucleation of Clusters in Aqueous Medium.

The simultaneous presence of Fe3+ and As3+ ions in groundwater (higher ppb or lower ppm level concentrations at circumneutral pH) as well as in acid mine drainages (AMDs)/industrial wastewater (up to few thousand ppm concentration at strongly acidic pH) are quite common. Therefore, understanding the chemical interactions prevalent between Fe3+ and As3+ ions in aqueous medium leading to nucleation of ionic clusters/solids, followed by aggregation and growth, is of great environmental significance. In the present work, we attempt to probe the nucleation process of Fe3+-As3+ clusters in solutions of various concentrations and pHs (from AMD to groundwater-like) using a combination of experimental and theoretical techniques. Interestingly, our study reveals nucleation of primary FeAs clusters in nearly all of them independent of concentration or pH. Theoretical studies employed density functional theory (DFT) to predict the primary clusters as stable Fe4As4 units. The surprising resemblance of these clusters with known Fe3+-As3+ minerals at the local level was observed experimentally, which provides an important clue about solid-phase growth from a range of Fe3+-As3+ solutions. Our experimental findings are further supported by a stepwise reaction mechanism established from detailed DFT studies.

Gold Sensitized In2O3 nanocubes for ppb level NO2 gas sensing

Hydrothermally synthesized In2O3 nanocubes were sensitized with Au and gas sensing performance is analyzed. The Au sensitization was done using sputtering and gas sensing performance is studied as function of different sputtering time. The catalytic activity of Au particles on In2O3 films increases with the sputtering time but acquires saturation at high sputtering time. The Au sensitization with sputtering time of 5 s was found to show improved sensor response (Rg/Ra) of 8435 than the sensor response of 6876 for pure In2O3 film. The improved sensor response was attributed to the catalytic activity of Au particles on the In2O3 film surface. In addition, Au sensitized In2O3 also demonstrates the sensor response at 60 ppb.

Jointly augmented photocatalytic NO removal by S-scheme Bi12SiO20/Ag2MoO4 heterojunctions with surface oxygen vacancies

The deep oxidation of NO molecules to NO3– species with the avoidance of toxic NO2 generation is a big and challengeable concern, which can be solved by the rational design and construction of catalytic systems with satisfactory structural and optical features. For such, in this investigation binary composites Bi12SiO20/Ag2MoO4 (BSO-XAM) were fabricated through a facile mechanical ball-milling route. From microstructural and morphological analyses, heterojunction structures with surface oxygen vacancies (OVs) were simultaneously created, contributing to the enhanced visible-light absorption, reinforced migration and separation of charge carries, and further boosted generation of reactive species such as superoxide radicals and singlet oxygen. Based on the density-functional theory (DFT) calculations, surface OVs induced the strengthened adsorption and activation of O2, H2O, and NO molecules and oxidation of NO to NO2, while heterojunction structures were beneficial for the continuous oxidation of NO2 to NO3– species. Thus, the heterojunction structures with surface OVs synergistically guaranteed the augmented photocatalytic NO removal and constrained NO2 generation of BSO-XAM through a typical S-scheme model. This study may provide scientific guidances for the photocatalytic control and removal of NO at ppb level by Bi12SiO20-based composites through the mechanical ball-milling protocol.

Fast In-Field Determination of Trace Fe Ion in Steam-Water for Safety Management of Thermal Electric Power Plants

A fast in-field tool was proposed to detect ppb level Fe ion in the steam-water to monitor the corrosion of the pipeline in time in electric power plants. The detection method was based on fluorescent quenching of graphene oxide quantum dots (GOQDs) at the existence of Fe ion. A piece of glass wool was used as the test strip and embedded in a microfluidic chip, while the easily removable microfluidic chip ensures a continuous rapid in-field detection and the architecture of glass wool acted as a three-dimensional porous support for well dispersive loading of GOQDs. Application specific integrated circuit was developed to enhance the sensitivity, robustness and power-efficiency of this detector and reduce its size and cost. In result, the potable fluorescence detector exhibited approximately a linear detection range from approximately 0.5 ppb to 30 ppm, a rapid response in 4 minutes and an acceptable error compared to the standard laboratory method.

Humidity-enhanced NH3 sensor based on carbon quantum dots-modified SnS

Recently, SnS is been extensively investigated in the field of gas sensors due to its unique wrinkled honeycomb structure and high specific surface. However, the weak response to NH3 at room temperature and especially poor moisture resistance limit the application of SnS in high humidity environments. To overcome these challenges, carbon quantum dots (CQDs) with hydroxyl and carboxyl groups on the surface were employed to modify SnS in this work, and the nanocomposite of SnS/CQDs was prepared by hydrothermal and stirring methods, respectively. It is revealed that the hydrothermally prepared nanocomposite SnS/CQDs shows much higher density of CQDs attached to the SnS nanosheets compared to the stirred samples. Resultantly, the hydrothermally prepared SnS/CQDs sensor can sense NH3 in ppb level and has a 4.78-fold higher response to 10 ppm NH3 than pure SnS, which are attributed to the heterogeneous structure of SnS/CQDs. Notably, its response value to 2.5 ppm NH3 at 97 % RH (3.67) is 1.44 times higher than that at 25 % RH, showing a unique humidity-enhanced effect. It was further explained by combining first-principles calculations and humidity-boosted NH3 adsorption-ionization model. This study provides a feasible way to explore the application potential of SnS-based nanocomposites in high humidity environments.

Electronic Nose Development and Preliminary Human Breath Testing for Rapid, Non-Invasive COVID-19 Detection.

We adapted an existing, spaceflight-proven, robust "electronic nose" (E-Nose) that uses an array of electrical resistivity-based nanosensors mimicking aspects of mammalian olfaction to conduct on-site, rapid screening for COVID-19 infection by measuring the pattern of sensor responses to volatile organic compounds (VOCs) in exhaled human breath. We built and tested multiple copies of a hand-held prototype E-Nose sensor system, composed of 64 chemically sensitive nanomaterial sensing elements tailored to COVID-19 VOC detection; data acquisition electronics; a smart tablet with software (App) for sensor control, data acquisition and display; and a sampling fixture to capture exhaled breath samples and deliver them to the sensor array inside the E-Nose. The sensing elements detect the combination of VOCs typical in breath at parts-per-billion (ppb) levels, with repeatability of 0.02% and reproducibility of 1.2%; the measurement electronics in the E-Nose provide measurement accuracy and signal-to-noise ratios comparable to benchtop instrumentation. Preliminary clinical testing at Stanford Medicine with 63 participants, their COVID-19-positive or COVID-19-negative status determined by concomitant RT-PCR, discriminated between these two categories of human breath with a 79% correct identification rate using "leave-one-out" training-and-analysis methods. Analyzing the E-Nose response in conjunction with body temperature and other non-invasive symptom screening using advanced machine learning methods, with a much larger database of responses from a wider swath of the population, is expected to provide more accurate on-the-spot answers. Additional clinical testing, design refinement, and a mass manufacturing approach are the main steps toward deploying this technology to rapidly screen for active infection in clinics and hospitals, public and commercial venues, or at home.

Determination of polychlorinated biphenyls in marine fish samples by gas chromatography tandem mass spectrometry (GC-MS/MS)

Polychlorinated biphenyls (PCBs) are a typical group of persistent organic pollutants (POPs), which have been listed under Annex A (Elimination) and Annex C (Unintentional production) of the Stockholm Convention. In this study, a gas chromatography tandem mass spectrometry method was developed and applied to analyze concentrations of 28 PCB congeners in some Vietnamese marine fish samples. PCBs in fish samples were ultrasonically extracted with an acetone/n-hexane (1/1, v/v) mixture. The extracts were cleaned up by using multilayer silica gel columns with dichloromethane/n-hexane (1/1, v/v) as elution solvent. PCBs were separated on a DB-5MS column and quantified by using a triple quadrupole mass spectrometer. The MS detector was operated in positive electron impact ionization (EI) mode and selected reaction monitoring (SRM) mode. Calibration curves of 28 PCBs exhibited good linearity (R2 ≥ 0.9998). Instrument detection limits (IDLs) and method detection limits (MDLs) ranged from 0.08 to 0.023 ng/mL and from 0.07 to 1.84 ng/g, respectively. Recoveries of 28 PCBs native and 7 labeled standards in matrix-spike samples ranged from 62.3 to 88.1% and from 75.5 to 91.9%, satisfying criteria proposed by AOAC (recovery 60-115% for 10-100 ppb levels). The validated method was applied to analyze 10 marine fish samples, showing levels of ∑28PCBs from 17 to 851 (mean 230) ng/g lipid. The sum of 6in-PCBs (PCB-28; -52; -101; -138; -153; -180) based on wet weight (w/w) ranged from 1.24 to 3.15 ng/g, which is lower than the maximum level recommended by The European Union (75 ng/g (w/w). Congeners PCB-126 and PCB-169 were not detected in marine fish samples.

Stable In(III)-Based Metal–Organic Frameworks for Selective Detection of 4-Nitroaniline and Antibiotics in Water

Detection of harmful chemical reagents and pollutants is of great significance for protecting human health and environmental sustainability. In this work, a 3D metal–organic framework, named In-BTDI, has been synthesized, featuring a two-fold interpenetrated framework. In-BTDI shows intense luminescence with the emission peak at 502 nm and exhibits high structural and photo-stability in water and common organic solvents, which provides a good foundation to be unitized as a chemical sensor. In-BTDI can selectively and sensitively sense 4-nitroaniline (4-NA) and antibiotics by the fluorescence quenching effect not only in the organic solvent but also in water. It is noteworthy that the limits of detection (LOD) of 4-NA and antibiotics in water are 240 and 202 ppb, respectively, both reaching a ppb level, suggesting the good detection ability of trace analytes in water. The sensing mechanism was then discussed in detail.

Tuning the Microstructures of ZnO To Enhance Photocatalytic NO Removal Performances

Effective removal of kinetically inert dilute nitrogen oxide (NO, ppb) without NO2 emission is still a challenging topic in environmental pollution control. One effective approach to reducing the harm of NO is the construction of photocatalysts with diversified microstructures and atomic arrangements that could promote adsorption, activation, and complete removal of NO without yielding secondary pollution. Herein, microstructure regulations of ZnO photocatalysts were attempted by altering the reaction temperature and alkalinity in a unique ionic liquid-based solid-state synthesis and further investigated for the removal of dilute NO upon light irradiation. Microstructure observations indicated that as-tuned photocatalysts displayed unique nucleation, diverse morphologies (spherical nanoparticles, short and long nanorods), defect-related optical characteristics, and enhanced carrier separations. Such defect-related surface-interface aspects, especially Vo″-related defects of ZnO devoted them to the 4.16-fold enhanced NO removal and 2.76 magnitude order decreased NO2 yields, respectively. Improved NO removal and toxic product inhabitation in as-tuned ZnO was disclosed by mechanistic exploitations. It was revealed that regulated microstructures, defect-related charge carrier separation, and strengthened surface interactions were beneficial to active species production and molecular oxygen activation in ZnO, subsequently contributing to the improved NO removal and simultaneous avoidance of NO2 formation. This investigation shed light on the facile regulation of microstructures and the roles of surface chemistry in the oxidation of low concentration NO in the ppb level upon light illumination.

Investigation of CuAl IMCs Corrosion in Chloride Environment and its Prevention Strategy

Abstract In most current wire-bonding applications, electrical interconnection is accomplished by fine Cu wires bonded to Al bonding pads microfabricated on an IC chip and external contact pins of the PCB board. Corrosion-related failure defects between the Cu wire and Al bond pad have been an ongoing un-trackable reliability issue plaguing the IC packaging industry for the past ten years, despite approaching ppb levels. Most prior studies hypothesized that intermetallic compounds (IMCs) like Cu9Al4, and CuAl2 were responsible for the observed acute wire-bond lift-off corrosion defects. Further studies sought to quantify the rates of corrosion of these IMCs and explore the effects of mitigation efforts of adding Pd, relevant to Pd-coated Cu wire-bonding. However, utilizing a novel real-time corrosion screening approach, we previously established that peripheral bimetallic contact between Cu ball-bonds and Al bond pads also plays a substantial role in the aggressive Al pad corrosion, induced by chloride ion penetration, which often leads to device failure. In this work, we further explored the role of IMCs corrosion in wire-bond lift-off failure utilizing fundamental electrochemical studies to quantify rates of galvanic-induced corrosion of IMCs within the broader context of an interconnected stack of Al bond pad, Cu-Al IMCs and Cu bonding wire. We also explored the use of a corrosion inhibitor to suppress the galvanic corrosion currents of Al bond pad, and Al-rich IMCs when electrically connected to Cu wire or Cu-rich IMCs.

High Gas Response Performance Based on Reduced Graphene Oxide/SnO2 Nanowires Heterostructure for Triethylamine Detection

SnO2 nanowires are locally synthesized by a simple thermal evaporation method and its growth mechanism is confirmed. Here, we present a simple strategy for realizing reduced graphene oxide (RGO)/SnO2 nanowires heterostructure. As expected, the heterostructure gas-sensing response is up to 63.3 when the gas concentration of trimethylamine (TEA) is 50 ppm, and it exhibits an excellent dynamic response with high stability at 180 °C. A low detection limit of 50 ppb level is fully realized. Compared to SnO2 nanowires, the sensing performance of the RGO/SnO2 heterostructure-based sensor is greatly enhanced, which can be ascribed to the RGO and the heterostructure. The RGO/SnO2 composite engineering poses an easy way to make full use of the advantages originating from RGO and heterostructure.

Au Nanocage/In2O3 Nanoparticle-Based Hybrid Structures for Formaldehyde Sensors

Detecting the trace ppb level of formaldehyde (HCHO) in indoor ambient and human exhaled breath using a metal oxide semiconductor gas sensor has attracted increasing attention. A hybrid nanostructure consisting of In2O3 nanoparticles grown on a Au nanocage (NC) surface was synthesized using a one-step solvothermal method, which was then used to be fabricated as HCHO sensors. The 0.5 wt % Au NC/In2O3 sensor featured an ultrahigh response of 8.8 for 1 ppm of HCHO at a low operating temperature (145 °C), which was nearly 2.5 times higher than that of the pure In2O3 sensor. Furthermore, it possessed outstanding selectivity and a low detection limit (25 ppb) toward HCHO. This excellent sensing property was possibly due to the increase in chemisorbed oxygens on its surface due to the Au NC spillover mechanism, an enhanced adsorption capability for HCHO because of the phase transition from cubic to rhombohedral In2O3, good gas diffusion, and a large surface area with a Au NC/In2O3 3D hierarchical structure, as well as the widened electron depletion layer derived from the Schottky barriers and homojunctions between the components of Au NC/In2O3.

Investigating the Electrochemically Driven Capture and Release of Long-Chain PFAS by Redox Metallopolymer Sorbents.

The remediation of perfluoroalkyl substances (PFAS) is an urgent challenge due to their prevalence and persistence in the environment. Electrosorption is a promising approach for wastewater treatment and water purification, especially through the use of redox polymers to control the binding and release of target contaminants without additional external chemical inputs. However, the design of efficient redox electrosorbents for PFAS faces the significant challenge of balancing a high adsorption capacity while maintaining significant electrochemical regeneration. To overcome this challenge, we investigate redox-active metallopolymers as a versatile synthetic platform to enhance both electrochemical reversibility and electrosorption uptake capacity for PFAS removal. We selected and synthesized a series of metallopolymers bearing ferrocene and cobaltocenium units spanning a range of redox potentials to evaluate their performance for the capture and release of perfluorooctanoic acid (PFOA). Our results demonstrate that PFOA uptake and regeneration efficiency increased with more negative formal potential of the redox polymers, indicating possible structural correlations with the electron density of the metallocenes. Poly(2-(methacryloyloxy)ethyl cobaltoceniumcarboxylate hexafluorophosphate) (PMAECoPF6) showed the highest affinity toward PFOA, with an uptake capacity of more than 90 mg PFOA/g adsorbent at 0.0 V vs Ag/AgCl and a regeneration efficiency of more than 85% at -0.4 V vs Ag/AgCl. Kinetics of PFOA release showed that electrochemical bias greatly enhanced the regeneration efficiency when compared to open-circuit desorption. In addition, electrosorption of PFAS from different wastewater matrices and a range of salt concentrations demonstrated the capability of PFAS remediation in complex water sources, even at ppb levels of contaminants. Our work showcases the synthetic tunability of redox metallopolymers for enhanced electrosorption capacity and regeneration of PFAS.

Facile Synthesis of Quinolinecarboxylic Acid-Linked Covalent Organic Framework via One-Pot Reaction for Highly Efficient Removal of Water-Soluble Pollutants.

To efficiently eliminate highly polar organic pollutants from water has always been a difficult issue, especially in the case of ultralow concentrations. Herein, we present the facile synthesis of quinolinecarboxylic acid-linked COF (QCA-COF) via the Doebner multicomponent reaction, possessing multifunction, high specific surface area, robust physicochemical stability, and excellent crystallinity. The marked feature lies in the quinolinyl and carboxyl functions incorporated simultaneously to QCA-COF in one step. The major cis-orientation of carboxyl arms in QCA-COF was speculated by powder X-ray diffraction and total energy analysis. QCA-COF demonstrates excellent adsorption capacity for water-soluble organic pollutants such as rhodamine B (255.7 mg/g), methylene blue (306.1 mg/g), gentamycin (338.1 mg/g), and 2,4-dichlorophenoxyacetic acid (294.1 mg/g) in water. The kinetic adsorptions fit the pseudo-second order model and their adsorption isotherms are Langmuir model. Remarkably, QCA-COF can capture the above four water-soluble organic pollutants from real water samples at ppb level with higher than 95% removal efficiencies and excellent recycling performance.

Sn2+ doped NiO hollow nanofibers to improve triethylamine sensing characteristics through tuning oxygen defects

The triethylamine (TEA) sensors with high response and selective detection have been widely reported. However, sluggish kinetics of recovery process, high operating temperature, unsatisfied long-term stability and high detection limit still restrict their further application. In this work, NiO nanofibers with different contents of Sn2+ are prepared via electrospinning method. Gas sensing investigation indicates that the sensor based on 6 at% Sn2+ doped NiO nanofibers with an elevated baseline resistance exhibits the highest gas response and excellent recovery characteristic to TEA at 200 °C. The sensor shows a low detection limit at ppb level and good long-term stability within three months. In addition, the sensor only has a small variation on baseline resistance, gas response and response/recovery speed under different relative humidity. The promising gas sensing performance can be mainly attributed to the increase of the oxygen vacancies defects caused by the difference of Sn2+ and Ni2+, resistance changes and the hollow structure of as-prepared nanofibers.

Design and development of multi-functional graphitic carbon nitride heterostructures embedded with copper and iron oxide nanoparticles as versatile sensing platforms for environmental and agricultural applications

In the recent past, agrotechnology has witnessed a tremendous change due to the advent of technologies employed towards enhancing the yield and quality of the crops. The application of nanotechnology in agriculture is promoting sustainable practices and smart farming. Currently, nanomaterial-based sensors are gaining considerable attention in agrotechnology, such sensors can detect the environmental conditions and support for crop growth and enhances the agricultural yield. Graphiticcarbon nitride (g-C3N4), a soft polymer belongs to a class of 2-D semiconductors which are affordable, metal-free, indispensable for sensing applications due to significant changes in their conductivity upon exposure to analyte molecules in nano-regime. Further, this g-C3N4 can be combined with other nano metal oxides to form nanocomposites with remarkable properties and superior performance. In this work we report development of high-performance sensors based on graphitic carbon nitride embedded with copper and iron oxide nanoparticles. These heterostructures offers tremendous improvement in the physical and chemical properties due to the synergetic interactions between various phases. The chemiresistive sensor fabricated from these nanocomposites exhibit excellent sensitivity towards monitoring methane gas @ ppb level, relative humidity (% RH), and soil moisture content. Owing to their excellent sensitivity, stability and selectivity, this graphitic carbon nitride embedded with Cu and Fe oxide nanoparticles could be potentially used as multifunctional sensors towards environmental monitoring and greenhouse conditions in agricultural applications.

High performance bimetal decorated PtNix-WO3 sensors and the cross-sensitivity investigation

Gas sensors play an essential bridge in connecting humans and health by helping people monitor the gas quality in their living spaces. In this work, PtNi3-WO3 gas sensors were fabricated and demonstrated superior selectivity, sensitivity, and stability to formic acid, which was sufficient for indoor air gas monitoring. The response to 100 ppm formic acid was as high as 591, with a response time of only 3 s, and detection range down to the ppb level. The bimetal PtNi3 decorated sensors showed a 30 times improvement in formic acid response compared to pure WO3 sensors. The cross-sensitivity was investigated, and we observed that the response initially decreased and then increased in a mixed gas with a constant concentration of carboxylic acid and increasing gradually concentration of formaldehyde. The adsorption and desorption mechanisms were studied, which implied that the decomposition and adsorption behavior of the gas could change and produce different intermediate products under different mixing environments. The results of the energy surface testing and density functional theory supported the proposed sensing mechanism. A machine-learning framework was developed for gas identification and concentration prediction, which achieved ultra-high identification accuracy. In addition, Bluetooth-based portable gas sensors were demonstrated, showing promising practical applications.