Ppm Formaldehyde Gas Research Articles

MIL-68 derived In2O3 microtubes and Co3O4/In2O3 heterostructures for high sensitive formaldehyde gas sensors

The gas sensors with high response and selectivity are important for detecting and monitoring formaldehyde gas in real-time. In this paper, In2O3 microtubes are derived from metal organic framework named MIL-68 and Co3O4 nanoparticles are successfully loaded on the surface of In2O3 microtubes to form Co3O4/In2O3 heterostructures via one-step hydrothermal and calcination methods. The crystal structure, surface morphology and components of all samples are characterized and the formaldehyde gas-sensing performance is investigated in detail. All results indicates that Co3O4 nanoparticles greatly improve the formaldehyde gas-sensing performance of Co3O4/In2O3 heterostructures. Specifically, Co3O4/In2O3 (9 wt%) sensor exhibits a higher response (1215.47) to 10 ppm formaldehyde gas, which is about 10.16 times than that of pristine In2O3 sensor. Furthermore, Co3O4/In2O3 (9 wt%) sensor possesses a shorter recovery time (81 s), lower working temperature (190 °C), excellent selectivity, superior linear properties. As a result, Co3O4/In2O3 sensors exhibit excellent gas-sensing properties because of the synergistic effect of the catalytic activity of Co3O4 nanoparticles, the formation of p-n heterojunction and the increasing surface oxygen.

Template preparation of porous Pt-modified SnO2 microflowers for high-response detection of VOCs

Porous SnO2 microflowers consisting of uniform nanosheets modified by Pt nanoparticles were synthesized using a self-sacrificing template followed by a reduction strategy. The Pt@SnO2, SnO2–Se, and SnO2–S samples were characterized using a series of techniques. The gas-sensing behaviors of the samples toward volatile organic compounds (VOCs) were studied. The Pt@SnO2 sensors exhibited superior gas-sensing performance for formaldehyde gas. The Pt@SnO2 sensors presented a stronger response (100.2), shorter response–recovery times (14 s/23 s), and lower working temperature (200 °C) for 100 ppm formaldehyde gas. The Pt@SnO2 sensors also showed excellent responses toward other VOCs, such as 100 ppm ethanol (82.5), acetone (73.9), and isopropanol (62.1). The gas-sensing mechanism of the Pt@SnO2 sensors was examined. The larger available surface area, favorable hierarchical flower-like nanostructure assembled by nanosheets, larger pore size, and larger proportion of oxygen vacancies and adsorption-state oxygen species, smaller crystallite size, and spillover effect of Pt catalysts contributed to the enhanced gas-sensing behaviors of Pt@SnO2 sensors. Overall, the synthetic strategy for flower-like SnO2 nanostructures can be applied widely.

Platinum Nanoclusters-Modified Porous In2O3 Nanocubes for Highly Sensitive and Selective Formaldehyde Gas Sensing at Room Temperature

The detection of formaldehyde gas generally requires a relatively high temperature. It is still challenging to simultaneously possess high sensitivity and strong selectivity for the detection of low-concentration formaldehyde at room temperature. The activation energy of the reaction can be reduced by introducing oxygen vacancies or loading the metal clusters on the surface of metal oxide-based semiconductors, leading to an improvement in the performance and detection limit of the sensor. However, this approach may lead to an increased cross-sensitivity to other gases and a reduction in the selectivity of the sensors. In this study, In2O3 can capture a significant amount of adsorbed oxygen by increasing the oxygen vacancies and introducing platinum nanoclusters on the surface of In2O3 synthesized with a specific morphology, leading to high sensitivity and selectivity for the detection of formaldehyde gas at room temperature. The Pt-In2O3 sensor exhibits a response value of approximately 38 to a concentration of 1 ppm formaldehyde gas at 20 °C. Moreover, the developed sensor demonstrates excellent performance in a complex atmosphere and exhibits good long-term stability. The achieved high sensitivity and selectivity for the detection of formaldehyde gas at low temperatures hold significant implications for research and practical applications in the field of sensors.

Effect of in doping on the formaldehyde sensing performance of ZnSnO3 cubes ceramics

In this paper, Zn1-xInxSnO3 cubes were synthesized by a simple co-precipitation method, and the morphology and structure of the samples were characterized by various techniques. The results show that Zn1-xInxSnO3 has a regular cube structure with a size range of 900–1000 nm. It is obtained by N2 absorption and BET calculation that doping In element improves the specific surface area of the material, promotes the reaction between the measured gas and the gas-sensing material, and thus improves the gas-sensing property of the material. The gas-sensing test results indicate that contrasted with the pure ZnSnO3 sample, the optimal operating temperature of the Zn1-xInxSnO3 (ZISO) sample is reduced (200 °C), and the response value is improved. Especially, Zn0·95In0·05SnO3 (ZISO-5) showed a significantly improved response to 100 ppm formaldehyde gas at the optimum operating temperature of 200 °C, which provided rapid, real-time and efficient technical support for formaldehyde detection. In addition, we also discuss the gas-sensing mechanism of the Zn1-xInxSnO3 cube obtained by In doping to formaldehyde. This study provides technical support and theoretical basis for the optimization of gas-sensing property of ZnSnO3 gas-sensing materials.

Fe-doped ZnSnO3 cubes for high-performance detection of formaldehyde

ZnSnO3 is a typical metal semiconductor oxide (MOS), which has wide-band gap, n-type transport characteristics and excellent gas sensing performance. Fe doping plays a pivotal role in enhancing the formaldehyde sensing performance of ZnSnO3. In this paper, Fe-doped ZnSnO3 cubes were prepared successfully by a simple co-precipitation method. A series of characterization results show that Fe-doped ZnSnO3 is a cubic structure with uniform size of about 1.1 μm, and Fe doping increases the specific surface area and oxygen vacancy, which is responsible for the enhanced sensing performance. The gas-sensing tests show that Fe-doped ZnSnO3 cubes have a significant selectivity for formaldehyde gas, and the response value of Fe-doped ZnSnO3 cubes (3 mol%) to 100 ppm formaldehyde gas is about 5 times that of pure ZnSnO3 at 200 °C. In addition, the sensor has a fast response/recovery time (12/12 s), good recovery and reproducibility. Its excellent sensing performance is attributed to Fe doping, which leads to more defects and active sites in Fe-doped ZnSnO3 gas sensor. This work confirms that Fe-doped ZnSnO3 is a promising preparation scheme for formaldehyde sensors.

A highly efficient room-temperature formaldehyde gas sensor based on a Ni-doped ZnO hierarchical porous structure decorated with NiS illuminated by UV light

Developing room-temperature formaldehyde gas sensors with superior response-ability is crucial for many applications including the detection of indoor air pollutants. Herein, we synthesized a series of Ni-doped ZnO (Ni-ZnO) hierarchical porous structures decorated with NiS (NiS/Ni-ZnO) composite materials by the simple hydrothermal method, and the room-temperature (25 ± 1 ℃) UV light-activated photoelectronic formaldehyde sensors based on the ZnO, Ni-ZnO and NiS/Ni-ZnO composites were presented and compared. The response value of 0.2% NiS/0.4% Ni-ZnO material reached 330% toward 10 ppm formaldehyde gas, which was nearly 2.5 times higher than that of pure ZnO, and the faster response/recovery time (39.4 s/40.7 s) was obtained using UV light at room temperature. XPS, SPV, TPV spectrum analysis, and density functional theory (DFT) calculation showed that 0.2% NiS/0.4% Ni-ZnO sensor's excellent sensing performance was due to the synergistic effect of Ni doping and NiS modification which improved the separation efficiency and accelerated the migration of charge carriers. Here, the relationship between the response time of photoelectric gas sensors and the behavior of photogenerated carriers is firstly discussed in detail, which provides new insight into the development of room-temperature photoelectric gas sensors with superior response-ability. • NiS/Ni-ZnO hierarchical porous structure has been fabricated using hydrothermal method. • NiS/Ni-ZnO sensor exhibits fast response and high responsivity to formaldehyde at room temperature. • Excellent gas sensing performance of NiS/Ni-ZnO sensor is explained from the dynamic behavior of photogenerated carriers. • The relationship between the response time of gas sensor and the behavior of carriers is firstly discussed in detail.

Synthesis of multishelled SnOx/Co3O4 amorphous/crystalline heterophase with galvanic replacement reaction for superior HCHO sensing

Amorphous/crystalline heterophase composites possess expansive reaction interfaces and abundant oxygen vacancy defects, providing novel electron-hole transmittal mode and significantly facilitating the surface adsorptions and redox reactions. Herein, galvanic replacement reaction (GRR) was used to construct amorphous SnOx/ crystalline Co3O4 multishell heterostructures. Characterizations indicated the continuous transition from Co3O4 to amorphous SnOx on each shell, generating abundant amorphous/crystalline interfaces. Moreover, the oxygen vacancy defects concentration also increased with the GRR proceeding. Benefitting from theses, the surface oxygen adsorption was facilitated due to more surface active sites and enhanced carrier densities. However, with further increasing the reaction time, decreased adsorbed oxygen concentrations were detected, owning to the unexpected high potential barriers induced by excessive heterojunctions. Gas sensing results showed that the sensors with 1 h GRR exhibited the best sensing performance with an exceptional response (1268) to 100 ppm formaldehyde gas and low detection limit (21 ppb) at low working temperatures (100 °C). The synergistic effects between oxygen vacancy defects and amorphous/crystalline heterophase interfaces on the superior gas sensing behaviors were also investigated. Most importantly, results presented will shed lights on the rational design of highly sensitive gas sensors through amorphous/crystalline interfaces constructions.

Hydrophobic metal organic framework for enhancing performance of acoustic wave formaldehyde sensor based on polyethyleneimine and bacterial cellulose nanofilms

A surface acoustic wave (SAW) formaldehyde gas sensor was fabricated on a 42° 75′ ST-cut quartz substrate, with a composite sensing layer of zeolitic imidazolate framework (ZIF)-8 on polyethyleneimine (PEI)/bacterial cellulose (BC) nanofilms. The addition of snowflake-like ZIF-8 structure on the PEI/BC sensitive film significantly improves the hydrophobicity of the SAW sensor and increases its sensitivity to formaldehyde gas. It also significantly increases surface roughness of the sensitive film. The hydrophobic nature of ZIF-8 prevents water molecules from entering into the internal pores of the BC film, thereby avoiding a significant mass loading caused by humidity when the sensor is used to detect low-concentration formaldehyde gas. The Zn2+ sites at the surface of ZIF-8 improves the sensor's response to formaldehyde gas through enhanced physical adsorptions of gas molecules. Experimental results show that the ZIF-8@PEI/BC SAW sensor has a response (e.g., frequency shift) of 40.3 kHz to 10 ppm formaldehyde gas at 25 °C and 30% relative humidity (RH). When the relative humidity is increased from 30 to 93%, the response of the sensor only varies ~ 5%, and the change in response is negligible at medium humidity levels (~ 50 to 60% RH).

CdO–ZnO nanorices for enhanced and selective formaldehyde gas sensing applications

This paper reports synthesis, properties and gas sensing applications of ZnO nanoflowers and CdO–ZnO nanorices prepared by hydrothermal process. The morphological characterizations confirmed the formation of well-defined nanoflowers and nanorices structures for ZnO and CdO–ZnO nanomaterials, respectively. The structural properties revealed the wurtzite hexagonal phase of the synthesized materials. The sensor devices based on ZnO nanoflowers and CdO–ZnO nanorices were fabricated and tested towards various gases including ethanol, methanol, ammonia, carbon monoxide, methane and formaldehyde. The fabricated gas sensor based on CdO–ZnO nanorices exhibited a high response (34.5) towards 300 ppm formaldehyde gas at 350 °C compared to ZnO nanoflowers (14.5) under the same experimental conditions. The response and recovery times for ZnO nanoflowers-based sensor were~9.8 s and ~6 s while for CdO–ZnO based sensor, these were ~10s and ~6s, respectively. A rapid response (34.5) for CdO–ZnO nanorices based formaldehyde gas sensor was observed as compared to other gases such as ammonia (12.3), methanol (16.5), ethanol (20), carbon monoxide (16.3) and methane (12.4), which confirm the high-selectivity towards formaldehyde gas. Finally, a plausible formaldehyde gas sensing mechanism is proposed.

Enhanced Gas Sensing of Tin Dioxide Based Sensor for Indoor Formaldehyde Application

Indoor formaldehyde detection is of great important at present. Using efficient solvothermal method, nanosheet-constructed and nanorod-constructed hierarchical tin dioxide (SnO2) microspheres were successfully synthesized in this work and used for the gas sensing material for indoor formaldehyde application. The as-prepared two kinds of SnO2 gas sensing materials were applied to fabricate the gas sensors and formaldehyde gas sensing experiments were carried out. The HCHO gas sensing tests indicate that the gas response of the nanosheet-constructed SnO2 microspheres is about 1.7 times higher than that of the nanorod-constructed SnO2 microspheres. In addition, both of the two SnO2 based gas sensors show almost fast response and recovery time to HCHO gas. For the nanosheet-constructed microspheres, the response value is estimated to be 32.0 at 350 °C to 60 ppm formaldehyde gas, while the response and recovery times are 7 and 5 s, respectively. The simple and efficient preparation method and improved gas sensing properties show that the as-synthesized hierarchical SnO2 microsphere that is constructed by a large amount of nanosheets exhibits significant potential application for the indoor formaldehyde sensing.

Constructing 3D porous SnO2 nanomaterials for enhanced formaldehyde sensing performances

3D porous SnO2 nanomaterials enhanced gas sensitivity properties for formaldehyde has been successfully prepared by a simple template method. The morphology of the synthesized SnO2 was observed by a scanning electron microscope (SEM) as a 3D porous structure with a pore diameter of 120 nm. We systematically studied the gas sensing performance of 3D porous SnO2 and particulate SnO2. The result shows that the response value of 3D porous SnO2 to 100 ppm formaldehyde gas was 51.0 at low temperature 230 ℃, which was 6.4 times higher than that of particulate SnO2 (8.0), and the response/the recovery time of 3D porous SnO2 was 8 s/15 s. The minimum detection concentration of 3D porous SnO2 was 0.5 ppm formaldehyde with the response value of 2. However, particulate SnO2 can only be detected 10 ppm with the response value of 2. In addition, the selectivity coefficient of 3D porous SnO2 for formaldehyde was up to 7, which is better than particulate SnO2 (1). The reason for the enhanced sensitivity of 3D porous SnO2 formaldehyde gas is not only related to its porous structure and smaller grain size, but also to the increase in oxygen vacancies.

Formaldehyde Gas Sensor Based on Melamine Foam and Tin Dioxide Composites

Formaldehyde (HCHO) is a volatile organic compound (VOC). It can caused great harm to human and environment. Since the increasing concerns of this problem, to develop effective methods to detect this toxic and hazardous gas has become more and more important , which play an important role in personal safety and environment protection. In this study, melamine foam and tin oxide composites were prepared by in-situ growth and subsequent treatment by using a simple hydrothermal reaction. The morphology, structure and sensing properties of the composites were systematically studied. The results show that tin oxide nanoparticles can grow well on the melamine foam skeleton through a simple hydrothermal reaction and has a good stable morphology. It is found that the three-dimensional spherical/skeletal composite material has better gas sensitivity and selectivity to formaldehyde gas than the pristine tin dioxide under a suitable concentration. The response of the composite to 5 ppm formaldehyde gas can reach 30.0 at 120°C. The reactant of formaldehyde on the surface of the material was studied by in situ IR. At the same time, melamine foam has a certain flexibility, which will have a good development for flexible, miniaturized and wearable formaldehyde sensor. Keywords：melamine foam plastics；tin oxide；formaldehyde；gas sensor Figure 1

Integrated sensing layer of bacterial cellulose and polyethyleneimine to achieve high sensitivity of ST-cut quartz surface acoustic wave formaldehyde gas sensor

Surface acoustic wave (SAW)-based formaldehyde gas sensor using bi-layer nanofilms of bacterial cellulose (BC) and polyethyleneimine (PEI) was developed on an ST-cut quartz substrate using sol-gel and spin coating processes. BC nanofilms significantly improve the sensitivity of PEI films to formaldehyde gas, and reduces response and recovery times. The BC films have superfine filamentary and fibrous network structures, which provide a large number of attachment sites for the PEI particles. Measurement results obtained using in situ diffuse reflectance Fourier transform infrared spectroscopy showed that the primary amino groups of PEI strongly adsorb formaldehyde molecules through nucleophilic reactions, thus resulting in a negative frequency shift of the SAW sensor due to the mass loading effect. In addition, experimental results showed that the frequency shifts of the SAW devices are determined by thickness of PEI film, concentration of formaldehyde and relative humidity. The PEI/BC sensor coated with three layers of PEI as the sensing layer showed the optimal sensing performance, which had a frequency shift of 35.6 kHz for 10 ppm formaldehyde gas, measured at room temperature and 30 % RH. The sensor also showed good selectivity and stability, with a low limit of detection down to 100 ppb.

A novel composite of CdS nanorods growing on a polyaniline-Cd2+ particles surface with excellent formaldehyde gas sensing properties at low temperature.

A novel composite, CdS nanorods growing on a polyaniline-Cd2+ particles surface (CdS/PANI) with a hexagonal wurtzite structure phase, was prepared using a hydrothermal synthesis method. Methods of XRD, SEM, and FTIR were used to analyze the structure and morphology of the compounds. SEM shows that CdS/PANI consists of sea urchin-like nanorods of about 200–500 nm in length and about 50 nm in diameter. Furthermore, the FTIR spectra show that some characteristic peaks of CdS/PANI are much weaker than those of PANI and the corresponding peaks shift to a higher wavenumber. In addition, the IR stretching frequency of the Cd–S bond for CdS/PANI moved from 630 cm−1 to 674 cm−1. In the gas sensing experiments, the CdS/PANI-based sensor showed an excellent response to low concentration formaldehyde gas in a wide temperature range of 80–140 °C. The highest response of CdS/PANI could reach about 4.8 to 5 ppm formaldehyde gas at 120 °C. The response and recovery times of the sensor based on CdS/PANI were about 25 s and 30 s to 10 ppm formaldehyde gas, respectively.

Detection of Trace Formaldehyde Gas Based on Quartz Crystal Microbalance Sensor in Living Environment

Using four types of calixarene derivatives (RCT, PCT, MRCT, TBCA) as coating materials, quartz crystal microbalance (QCM) sensors have been examined for detection of toxic formaldehyde gas indoors. The results showed that PCT was the most efficient adsorption coating material for host-guest recognition of formaldehyde molecule, when the coating mass was 43.93 μg. The PCT based QCM sensor possessed a linear response range of 109 ~ 2721 ppm formaldehyde gas. In comparison with gas chromatography method, the QCM sensor had a recovery of 97.98~104.59 % with a good reversibility, stability and reproducibility, showing that the PCT based QCM sensor can be well used for the determination of trace formaldehyde in the living environment.

Formaldehyde gas inactivation ofBacillus anthracis,Bacillus subtilis, andGeobacillus stearothermophilusspores on indoor surface materials

To evaluate the decontamination of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surface materials using formaldehyde gas. B. anthracis, B. subtilis, and G. stearothermophilus spores were dried on seven types of indoor surfaces and exposed to approx. 1100 ppm formaldehyde gas for 10 h. Formaldehyde exposure significantly decreased viable B. anthracis, B. subtilis, and G. stearothermophilus spores on all test materials. Significant differences were observed when comparing the reduction in viable spores of B. anthracis with B. subtilis (galvanized metal and painted wallboard paper) and G. stearothermophilus (industrial carpet and painted wallboard paper). Formaldehyde gas inactivated>or=50% of the biological indicators and spore strips (approx. 1x10(6) CFU) when analyzed after 1 and 7 days. Formaldehyde gas significantly reduced the number of viable spores on both porous and nonporous materials in which the two surrogates exhibited similar log reductions to that of B. anthracis on most test materials. These results provide new comparative information for the decontamination of B. anthracis spores with surrogates on indoor surfaces using formaldehyde gas.

Correlation of regional formaldehyde flux predictions with the distribution of formaldehyde-induced squamous metaplasia in F344 rat nasal passages

Squamous epithelium lines the nasal vestibule of the rat, rhesus monkey, and human. Respiratory, transitional, and olfactory epithelia line most areas posterior to the nasal vestibule. Inhaled formaldehyde gas induces squamous metaplasia posterior to the nasal vestibule and does not induce lesions in the nasal vestibule in rats and rhesus monkeys, indicating that squamous epithelium is resistant to irritant effects of formaldehyde and that squamous metaplasia may be an adaptive response. If squamous metaplasia is determined by formaldehyde dosimetry rather than by tissue-specific factors, squamous epithelium may be protective by absorbing less formaldehyde than other epithelial types. In a previous study, a three-dimensional, anatomically accurate computational fluid dynamics (CFD) model of the anterior F344 rat nasal passages was used to simulate inspiratory airflow and inhaled formaldehyde transport. The present study consisted of two related parts. First, the rat CFD model was used to test the hypothesis that the distribution of formaldehyde-induced squamous metaplasia is related to the location of high-flux regions posterior to squamous epithelium. Regional formaldehyde flux into nonsquamous epithelium predicted by the CFD model correlated with regional incidence of formaldehyde-induced squamous metaplasia on the airway perimeter of one cross-sectional level of the noses of F344 rats exposed to 10 and 15 ppm formaldehyde gas for 6 months. Formaldehyde flux into nonsquamous epithelium was estimated to vary by an order of magnitude depending on the degree of formaldehyde absorption by squamous epithelium. These results indicate that the degree to which squamous epithelium absorbs formaldehyde strongly affects the rate and extent of the progression of squamous metaplasia with continued exposure to formaldehyde. In the second part of this study, the CFD model was used to predict squamous metaplasia progression. Data needs for verification of this model prediction are considered. These results indicate that information on the permeability of squamous epithelium in rats, monkeys, and humans is important for accurate prediction of uptake in regions posterior to the nasal vestibule.

Distribution, progression, and recovery of acute formaldehyde-induced inhibition of nasal mucociliary function in F-344 rats

A previous report of inhalation exposure of F-344 rats to formaldehyde gas, using a whole-body exposure system, described the induction of regional inhibition of nasal mucociliary function, with a clear concentration-response relationship. A head-only exposure system was subsequently developed in order to facilitate the present study of reversibility of acute effects of formaldehyde on the nasal mucociliary apparatus. This study also included an examination of more extensive areas of the nose than those reported in the previous work. Male F-344 rats were exposed to 2 or 15 ppm formaldehyde gas for 10, 20, 45, or 90 min or 6 hr with recovery groups examined 1 hr after the end of the 90-min and 6-hr exposures. No effects were observed in rats exposed to 2 ppm formaldehyde. In rats exposed to 15 ppm, the extent of formaldehyde-induced inhibition of mucociliary function detected in specific regions of the nose was time dependent, with increasing areas of mucostasis and ciliastasis being induced during a 6-hr exposure period. A 1-hr room-air exposure, following exposure to 15 ppm formaldehyde, resulted in marked recovery of mucociliary function, indicating the value of a head-only exposure system for rapid examination of mucociliary function following exposure. Recovery of mucociliary function occurred especially in the more posterior areas of affected regions of the nose. However, in areas of recovery mucus flow rate was reduced compared to unexposed control rates, indicating incomplete recovery of function in these areas. Regions of formaldehyde-induced inhibition of mucociliary function correlated well with the previously reported distribution of formaldehyde-induced nasal squamous cell carcinomas, with the exception of effects on the medial aspect of the maxilloturbinate. These findings were considered to provide further support for the proposal that both regional exposure and local tissue susceptibility may be responsible for the distribution of formaldehyde-induced nasal squamous cell carcinomas. It was also postulated, on the basis of mucus flow patterns derived from control animals in this study, that flow relationships between nasal mucus and inspired air form a countercurrent system which may optimize clearance of inhaled air contaminants.