Room Temperature Formaldehyde Research Articles

Ultrahigh humidity-resistance ppb-level formaldehyde sensing at room temperature induced by fluorinated dipole based "umbrella" and "bridge"

Formaldehyde (HCHO) is a major indoor pollutant that is extremely harmful to human health even at ppb-level. Meanwhile, ppb-level HCHO is also a potential disease marker in the exhalation of patients with respiratory diseases. Higher humidity resistance and lower practical limit of detection (pLOD) both have to be pursued for practical HCHO sensors. In this work, by assembling indium oxide (In2O3) and fluorinated dipole modified reduced graphene oxide (rGO), we prepared a high-performance room temperature HCHO sensor (In2O3 @ATQ-rGO). Excellent sensing properties toward HCHO under visible illumination have been achieved, including ultra-low pLOD of 3 ppb and high humidity-resistance. By control experiments and density functional theory calculation, it is indicated that the introduced fluorinated dipoles act as not only an "umbrella" to improve the humidity resistance of the composite, but also a "bridge" to accelerate the electron transport, improving the sensitivity of the material. The significant practicality and reliability of the obtained sensors were verified by in-situ simulation experiments using a 3 m3 test chamber with a humidity control system and by detection of the simulated lung disease patient’s exhalation. This work provides an effective strategy of simultaneously achieving high humidity-resistance and low pLOD of room temperature formaldehyde sensing materials.

Development of SnO2 functionalized In2O3 porous microrods for trace level detection of formaldehyde at room temperature

Room temperature detection is a crucial objective in semiconductor sensor research, given its inherent benefits including reduced energy consumption, extended sensor lifespan, and significant reduction of safety hazards. Herein, novel room temperature sensing materials, SnO2-modified In2O3 porous microrods were synthesized, which exhibited exceptional sensing capability towards formaldehyde at room temperature. Specifically, the 5%-SnO2/In2O3 porous microrods demonstrate an impressive sensing response across varying formaldehyde concentrations, even at sub-ppm levels (0.1 ppm, 5.22), with a theoretical detection limit of 5.47 ppb, thereby enabling the detection of trace amounts of formaldehyde. Moreover, the sensors exhibit superior formaldehyde selectivity, rapid response characteristic, as well as good stability and reproducibility. The exceptional formaldehyde sensing ability of the SnO2/In2O3 sensor primarily arises from the creation of n-n heterojunctions at the SnO2/In2O3 interface, effectively modulating the interfacial potential. Additionally, the presence of SnO2 enhances the amount of surface-adsorbed oxygen species and active sites, thereby boosting sensing response. The porous rod-like structures further facilitate gas adsorption and diffusion, enhancing gas sensing capabilities. This work presents a novel strategy for constructing SnO2-In2O3 heterojunctions to achieve room-temperature formaldehyde detection.

Deactivation of layered MnO2 catalyst during room temperature formaldehyde degradation and its thermal regeneration mechanism

Layered δ-MnO2 prepared by a one-step redox method was shown to be deactivated during oxidation of formaldehyde at room temperature. Recovery of the formaldehyde degradation activity was investigated after thermal regeneration at different temperatures. XRD, SEM, TEM, H2-TPR, XPS, TGA and DRIFTS characterization were used to analyze the physical properties of fresh, deactivated and thermally regenerated catalysts. The results showed that deactivation of catalyst was caused by less oxygen vacancies due to increased Mn4+ content during formaldehyde degradation and formation of formate blocking active sites. Thermal regeneration helped to decompose formate at the catalyst surface, restoring some of the active sites. Interplanar spacing of MnO2 became wider and the number of Mn3+ on exposed crystal faces increased. More oxygen vacancies were formed. The activity of deactivated catalyst was restored. Formaldehyde degradation rate of catalyst regenerated at 200 °C remained above 80 % after 6 h, demonstrating the possibility of waste layered catalyst recycling.

Three-dimensional Ni foam supported Pt/NiFe LDH catalyst with enhanced oxygen activation for room-temperature formaldehyde oxidation

Room-temperature catalytic oxidation of formaldehyde (HCHO) has been extensively investigated due to its high efficiency, convenience, and environmental friendliness. Herein, nickel-iron layered double hydroxide (NiFe LDH) nanosheets were synthesized in-situ on a nickel foil (NF) using a facile one-step hydrothermal method, followed by the deposition of ultra-low content (0.069 wt%) of Pt nanoparticles through NaBH4 reduction. The resulting three-dimensional (3D) hierarchical Pt/NiFe-NF catalyst exhibited exceptional activity for the complete decomposition of formaldehyde to carbon dioxide (CO2) at room temperature (∼95 % conversion within 1 h), as well as remarkable cycling stability. The 3D porous structure of Pt/NiFe-NF provides fast transport channels for the diffusion of gas molecules, making the active catalyst surfaces more accessible. Moreover, abundant hydroxyl groups in NiFe LDH serve as adsorption centers for HCHO molecules to form dioxymethylene (DOM) and formate intermediates. Furthermore, electronic interactions between NiFe LDH and Pt enhance the adsorption and activation of O2 on Pt surfaces, leading to the complete decomposition of intermediates into non-toxic products. This work presents new insights into the design and preparation of Pt-based 3D hierarchical catalysts with surface-rich hydroxyl groups for the efficient removal of indoor HCHO.

Enhancing Structural Integrity, Optical Properties, and Room Temperature Formaldehyde Sensing Through Optimized Spray Deposition Rates

This study explores the impact of deposition rate on the properties of TiO2 thin films produced via spray pyrolysis, focusing on their application in gas sensors. The analysis covers structural, morphological, optical, and gas sensing characteristics of TiO2 films deposited at rates between 1 and 2.5 ml min−1. Studies show optimizing TiO2 film deposition rates at 2 ml min−1 significantly enhances formaldehyde detection, improving selectivity and achieving a rapid response of 7.52 at 20 ppm concentration. This study underscores the pivotal role of deposition rate optimization in augmenting the gas-sensing efficacy of TiO2 films, particularly for formaldehyde detection at ambient conditions. Optimal deposition rates are instrumental in enhancing sensor performance. The synergistic application of XRD and Raman spectroscopy unequivocally confirmed the presence of the TiO2 anatase phase, which is of paramount significance in gas sensing applications. FESEM furnished high-resolution insights into the surface morphology, revealing a spherical architecture. Furthermore, UV–vis spectroscopy was employed to assess the optical band gap of the films, which exhibited a decrement correlating with the rate of deposition. Notably, a deposition rate of 2 ml min−1 markedly improved the TiO2 films’ sensing performance. These insights are critical for developing cost-effective, high-performance gas sensors for cutting-edge applications.

Gd3+ and Sm3+ doped CeO2 for IT-SOFC and room temperature formaldehyde gas sensing applications

An alternative solid electrolyte is imperative to replace YSZ for better IT-SOFC. Gd3+/Sm3+ doped ceria (Ce0.9Gd0.1O2-δ-GDC1, Ce0.8Gd0.2O2-δ-GDC2, Ce0.8Sm0.2O2-δ-SDC) were synthesized via sol–gel method. These compounds were investigated by using X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), Energy dispersive X-ray (EDX) spectra, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman and impedance spectroscopy. FESEM micrographs manifested that GDC1 has larger grain sizes than GDC2 and SDC. Interestingly, SDC exhibited more grain boundaries than GDC1 and GDC2. These high dense sol–gel derived compounds have exhibited better ionic conductivity than some of the previously reported Gd3+/Sm3+ doped ceria. Furthermore, the selectivity of calcinated GDC1, GDC2 and SDC sensors at room temperature (RT) for ammonia, methanol, ethanol and formaldehyde gases at 100 ppm was examined and found that GDC1 has displayed an applausive selectivity with superior response for formaldehyde gas sensing at RT as an operating temperature. The Raman analysis avowed the presence of oxygen vacancies which were identified as instrumental in both applications. The multiple gases detected by GDC1 at RT might provide various strategies to design novel gas sensors.

Fabrication of cobalt (II, III) oxide @nitrogen doped carbon/honeycomb ceramics with porous structure for room-temperature formaldehyde oxidation

The content of surface cobalt active sites and oxygen vacancy (VO) is vital to the catalytic performance of Co3O4 catalysts. Herein, a robust Co3O4@N doped C supported on honeycomb ceramics (Co3O4@NC-HC) catalyst with porous structure was prepared by an impregnation-calcination method using ZIF-67 as the precursor. The N2 calcining atmosphere and relatively closed environment are beneficial for the formation of more pyridine N, Co3+ surface active sites, and VO, which favors formaldehyde (HCHO) or O2 adsorption and activation. The higher content of NC in Co3O4@NC-HC than in Co3O4@NC-HC-open and Co3O4@NC-HC-air can disperse Co-containing catalysts better and promote electron transfer. The Co3O4@NC-HC catalysts exhibited excellent activity and stability for HCHO oxidation at room temperature. The 1.0 Co3O4@NC-HC sample with theoretical 7.7 wt% showed the maximum efficiency (96.5 %) for HCHO removal. The related catalytic mechanisms over Co3O4@NC/HC for HCHO oxidation were posed.

Rational Integration of SnMOF/SnO2 Hybrid on TiO2 Nanotube Arrays: An Effective Strategy for Accelerating Formaldehyde Sensing Performance at Room Temperature.

Formaldehyde is ubiquitously found in the environment, meaning that real-time monitoring of formaldehyde, particularly indoors, can have a significant impact on human health. However, the performance of commercially available interdigital electrode-based sensors is a compromise between active material loading and steric hindrance. In this work, a spaced TiO2 nanotube array (NTA) was exploited as a scaffold and electron collector in a formaldehyde sensor for the first time. A Sn-based metal-organic framework was successfully decorated on the inside and outside of TiO2 nanotube walls by a facile solvothermal decoration strategy. This was followed by regulated calcination, which successfully integrated the preconcentration effect of a porous Sn-based metal-organic framework (SnMOF) structure and highly active SnO2 nanocrystals into the spaced TiO2 NTA to form a Schottky heterojunction-type gas sensor. This SnMOF/SnO2@TiO2 NTA sensor achieved a high room-temperature formaldehyde response (1.7 at 6 ppm) with a fast response (4.0 s) and recovery (2.5 s) times. This work provides a new platform for preparing alternatives to interdigital electrode-based sensors and offers an effective strategy for achieving target preconcentrations for gas sensing processes. The as-prepared SnMOF/SnO2@TiO2 NTA sensor demonstrated excellent sensitivity, stability, reproducibility, flexibility, and convenience, showing excellent potential as a miniaturized device for medical diagnosis, environmental monitoring, and other intelligent sensing systems.

Low cost ternary metal oxide based nanocomposites as a room temperature formaldehyde sensor

To protect human health from hazardous gases, it is necessary to rapid detection of toxic gases utilizing gas sensors. Though there are various gas sensors, despite that, they endure inaccuracy in selectivity and sensitivity in the real-time monitoring of the low concentration of gases. In this context, the practical design for developing a cost-effective formaldehyde (HCHO) sensor using a hetero-type ternary nanocomposite ZnO/CdO/CuO (ZCCO) metal oxide (MOX) materials with porous structure is an ideal choice. In this study, ZCCO heterostructures demonstrated rapid selectivity towards HCHO compared with other volatile organic compounds and exhibited excellent long-term stability for up to 80 d. The sensor capability has been further improved with the heterostructures’ porous morphology, greater specific surface area, huge reaction sites, and electron sensitization effects of highly dispersed nanocomposite material. This work reports the Lowest Detection Limit (LDL) towards HCHO at room temperature as 250 ppb. These heterostructures enable the charge transport mechanism between the interparticle ZnO/CdO (n–n junctions) and the ZnO/CuO (n–p junctions) that can simultaneously enhance the sensitivity of the gas molecule’s reactions.

A platinum ensemble catalyst for room-temperature removal of formaldehyde in the air

Minimal use of noble metals is ideal in developing catalytic systems against carcinogenic formaldehyde (FA) in air. Although single-atom catalysts (SACs) have been proposed to maximize atomic utilization, metals dispersed to the single-atom limit are less durable in redox environments. A highly dispersed platinum (Pt) ensemble (Ptn) on titanium dioxide (TiO2) was synthesized and validated to achieve 100% conversion of 100 ppm FA in dry air at room temperature (RT) at a gas hourly space velocity of 47,771 h−1. In contrast, Pt SAC (Pt1/TiO2) and a reference Pt nanoparticle catalyst (PtNP/TiO2) exhibited much lower performances. The turnover frequencies (TOFs) of Ptn/TiO2, Pt1/TiO2, and PtNP/TiO2 for the RT FA oxidation reaction were 0.03, 0.01, and 0.005 s−1, respectively. The critical role of the surface lattice oxygen (Olatt) in the overall reaction was supported by the prominence of the Mars van Krevelen kinetics in FA oxidation by the Ptn catalyst. The performance of the PtNP catalyst matched with Ptn only when the Pt loading in the former was raised to 2 wt%. Hence, the Pt dose can be reduced by one-fourth through the ensemble form dispersed at the sub-nanometer scale. The density functional theory simulation also distinguished the roles of different Pt catalysts. The Ptn sites could serve as an oxygen reservoir (effective dissociation of molecular oxygen) to promote proximate reactions (between the adsorbed –CHO and surface Olatt species). Conversely, Pt1 is a single site that restricts proximate reactions with vulnerability to surface poisoning.

Construction of Flower-like ZnO Nanoclusters on Functionalized Graphene Nanosheets for Room Temperature Formaldehyde Sensing

Background: Formaldehyde (HCHO) is one of the sources of indoor air pollution and a recognized carcinogenic gas, which sets a huge threat to human health. Therefore, it is urgent to develop a formaldehyde gas sensor with high efficiency, low consumption, and low limit of detection. Methods: With solvothermal and supramolecular assembly methods, we fabricate a nanocomposite of ZnO/5-aminonaphthalene-1-sulfonic acid (ANS)-reduced graphene oxide (rGO) through in situ assembling flower-like ZnO nanoclusters on ANS-modified graphene nanosheets for room temperature formaldehyde detection. Results: The flower-like ZnO/ANS-rGO based gas sensor exhibits high response (32%, 5 ppm), ultra-fast response/recovery times (18/23 s), high selectivity, long-term stability and a low practical limit of detection (pLOD) of 1 ppm toward HCHO at room temperature, offering significant advantages and competitiveness in chemiresistive room temperature HCHO sensors. Conclusion: The unique flower-like nanostructure of ZnO and the functionalization with ANS molecules jointly improved the HCHO sensing performance of the composite at room temperature. This work provides a new approach to designing and preparing high-performance room temperature gas sensing materials.

A highly selective room-temperature formaldehyde gas sensor based on vertically aligned 1D NiCo2O4 nanoneedles

The challenge to detect formaldehyde gas at room-temperature (RT) using metal oxide semiconductors is still unaddressed. High temperature requirement of metal oxide gas sensors restricts their usage in various hand-held devices. To address this unattended regime of metal oxide gas sensors,a novel RT-based formaldehyde sensor using the 1D nickel cobalt oxide (NiCo2O4) has been reported. It is synthesized via a single-step hydrothermal route. FESEM and TEM micrographs reveal micro-flower like morphology, consisting of huge numbers of interwoven, vertically aligned 1D nanoneedles while chemical characterization data confirm successful growth of this binary metal oxide. This sensor exhibits quick response/recovery time (22 s /57 s) at RT over the linear region of 10–100 ppm formaldehyde with excellent selectivity and stability. Thus, it paves an avenue for development of affordable, RT gas sensing devices for air quality monitoring applications.

Lead-free defective halide perovskites Cs2SnX6 (X = Cl, Br, I) for highly robust formaldehyde sensing at room temperature

In this contribution, all-inorganic lead-free halide perovskites Cs2SnX6 (X = Cl, Br, I) were synthesized by simple room-temperature precipitation. Material characterization demonstrated their feature in rich defects of halogen vacancies. As room-temperature formaldehyde (HCHO) sensing materials, Cs2SnX6 exhibited reliable sensitivity order of Cs2SnCl6 < Cs2SnBr6 < Cs2SnI6. Notably, the Cs2SnI6 sensor showed excellent selectivity for HCHO at room temperature with high response (Sr = 78, 100 ppm), short response/recovery time (3.6 s/7.2 s), good repeatability and long-term stability. Finally, the HCHO sensing mechanism was investigated via in-situ infrared analysis, conforming abundant intermediates of dioxymethylene, formate, and carbonate. The excellent sensing performance is attributed to rich iodine vacancies (VI) as active sites induced boosted stepwise oxidation of HCHO molecules on Cs2SnI6 surface. This work provides a fine candidate for practical HCHO detection at room temperature, and furthermore, gives new insights in designing halide perovskites for next-generation sensory devices.

Regulation of Oxygen Vacancies in Ceria-Zirconia Nanocatalysts by Pluronic P123-Templated for Room Temperature Formaldehyde Total Oxidation

Regulation of Oxygen Vacancies in Ceria-Zirconia Nanocatalysts by Pluronic P123-Templated for Room Temperature Formaldehyde Total Oxidation

Boosting the catalytic performance of Pt/TiO2 catalysts in room-temperature formaldehyde elimination by incorporating CeO2 promoters

To tackle the health threats caused by formaldehyde (HCHO) contamination, great efforts have been made to create high-performance and cost-efficiency catalysts that can completely remove HCHO at room temperature. Herein, we demonstrate an interface engineering strategy to improve the catalytic performance of Pt/TiO2 by introducing CeO2 promoters. When evaluated as catalysts in HCHO elimination reaction, the obtained 0.2Pt/5Ce-TiO2 catalysts possess remarkable catalytic activity and stability, which can completely convert 100 ppm HCHO into CO2 and H2O under a gas hourly space velocity of 120,000 mL gcat−1 h−1 at room temperature, and retain nearly 100% HCHO conversion after 28-h continuous test. Further structure-performance investigations reveal the crucial role of CeO2 that can significantly increase the contents of surface oxygen vacancies and Pt0 species, thereby the key intermediates including dioxymethylene, formate, and carbonate species can be easily converted. More importantly, the 0.2Pt/5Ce-TiO2 is readily sprayed onto the meltblown fabrics to construct an available face mask for protecting people against HCHO pollution, which can instantly remove 2.6 ∼ 4.0 ppm HCHO at room temperature, indicating the great potential in practical applications.

Tuning the p-type conductivity of NiO for the room temperature formaldehyde detection

The present research synthesizes pure Nickel Oxide (NiO) nanostructures via a coprecipitation route with exceptional surface modification by temperature treatment. The morphological, structural, elemental and gas sensing tests of the prepared NiO were done carefully. The study unveils the sensing performances of various volatile organic compounds (VOCs), specifically for HCHO. Furthermore, gas sensor testing of prepared samples was carried out at room temperature (RT) and at different concentrations of the target gas. For 100 ppm of target gases, NiO (300 ℃), NiO (500 ℃), and NiO (700 ℃) gas sensors exhibited 83.43, 5616, and 196 gas responses, respectively, at RT. Hence, NiO nanoparticles at 500℃ sintering temperature-based HCHO sensor showed a significant response than other NiO sensors.

Regulating the Pt-MnO2 Interaction and Interface for Room Temperature Formaldehyde Oxidation.

Formaldehyde (HCHO) is a hazardous pollutant in indoor space for humans because of its carcinogenicity. Removing the pollutant by MnO2-based catalysts is of great interest because of their high oxidation performance at room temperature. In this work, we regulate the Pt-MnO2 (MnO2 = manganese oxide) interaction and interface by embedding Pt in MnO2 (Pt-in-MnO2) and by dispersing Pt on MnO2 (Pt-on-MnO2) for HCHO oxidation over Pt-MnO2 catalysts with trace Pt loading of 0.01 wt %. In comparison to the Pt-in-MnO2 catalyst, the Pt-on-MnO2 catalyst has a higher Brunauer-Emmett-Teller surface area, a more active lattice oxygen, more oxygen vacancy activating more dioxygen molecules, more exposed Pt atoms, and noninternal diffusion of mass transfer, which contribute to the higher HCHO oxidation performance. The HCHO oxidation performance is stable over the Pt-MnO2 catalysts under high space velocity and high moisture humidity conditions, showing great potential for practical applications. This work demonstrates a more effective Pt-dispersed MnO2 catalyst than Pt-embedded MnO2 catalyst for HCHO oxidation, providing universally important guidance for metal-support interaction and interface regulation for oxidation reactions.

Aspect ratio control of TaS2nanosheets: a methodology for room temperature formaldehyde gas sensing performance optimization

This work presents a gas sensor optimization strategy based on aspect ratio control of transition metal dichalcogenide nanosheets.

Enhanced oxygen activation on an atomically dispersed Au catalyst with dual active sites for room-temperature formaldehyde oxidation

Formaldehyde (HCHO) is known to be a hazardous indoor air pollutant.

A room-temperature formaldehyde sensor based on hematite for breast cancer diagnosis.

Formaldehyde (HCHO) is regarded as one kind of indoor pollutant. Additionally, HCHO serves as a biomarker in the exhaled breath of breast cancer patients. Early warning and management are crucial for the environment and human health. Thus, we have elaborately synthesized hematite (α-Fe2O3) employing a facet-engineering hydrothermal strategy using the fine-tuned solvent composition, with special attention to the effect of different exposed surfaces on HCHO detection. The spindle-like α-Fe2O3 nanocrystals with the (012) facet exposed exhibited impressively higher response towards HCHO at room temperature than that of the disk-like α-Fe2O3 with mainly the (001) facet exposed, partly due to the abundant vacancy oxygen and adsorbed oxygen of high-index facets of α-Fe2O3. More importantly, our experimental results coincide with theoretical calculations. Overall, the surface engineering strategy could be extended to a versatile approach for HCHO detection.