HCHO Sensor Research Articles

Ab initio characterization and experimental validation on the roles of oxygen-containing groups in graphene based formaldehyde sensors.

The development of formaldehyde (HCHO) sensors employing reduced graphene oxide (rGO) as sensing materials calls for a profound, atomic level understanding on the roles of oxygen-containing groups. In this work, the performances of rGO-based HCHO sensors were investigated using ab initio calculations and experimental validation. Density functional theory (DFT) simulations were performed to calculate the adsorption energy (Eads) and charge transfer (ΔQ) for the adsorption of HCHO on pristine graphene, rGO with epoxides, rGO with hydroxyl groups, and rGO with carboxyl groups. The results show that the incorporation of oxygen-containing groups leads to an obvious increase of Eads and ΔQ values, with an order of carboxyl group > hydroxyl group > epoxides > pristine graphene. The increase of Eads and ΔQ values could increase the variation in the concentration of charge carriers, the change of conductance of the sensing materials, and hence the sensor response. The experimental measurements indicate that with a decrease in the C/O atomic ratio from 16.2 to 6.6, the sensor response to 1 ppm HCHO increases from 0.10% to 0.73%, confirming the DFT calculation results. Moreover, even with a certain C/O atomic ratio of ∼6.6, rGO with 6.80% carboxyl groups exhibits a distinctly larger response to 0.2-3 ppm HCHO, compared with the counterpart with 3.09% carboxyl groups. The as-obtained insights into the effects of oxygen-containing groups on the response of rGO to HCHO could be instructive for preparing rGO-based HCHO sensors for advanced performances.

Synthesis and catalytic activity of Ag nanoparticles dispersed on nitrogen-doped GOPx toward direct electrooxidation of formaldehyde

Silver nanoparticles (Ag NPs) were synthesized and dispersed on the electronically conductive and electrochemically accessible surface of a GOPx composite, which was then employed as a probe for formaldehyde (HCHO) oxidation. The surface nanostructure, crystallographic properties, and oxidation state of the metal present in the GOPx-Ag nanocomposite were investigated using high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. HCHO electrooxidation was evidenced by the appearance of a very well defined anodic peak with an onset potential of −0.783V, which is unique in the literature. The effect of various electroanalytical parameters like concentration, scan rate, and upper potential limit was investigated toward HCHO electrooxidation on GOPx-Ag catalyst. Amperometric study showed remarkable HCHO electrooxidation response with a wide linear range of 1μM–70mM, limit of detection (LOD) 0.167μM, limit of quantification (LOQ) 0.556μM and sensitivity of 35.74μAmM−1cm−2. The experimental results further indicated the long-term stability and practical feasibility of the GOPx-Ag catalyst, with excellent recoveries for HCHO oxidation. The remarkable catalytic efficiency and anti-poisoning properties were far superior to those of many previously reported HCHO sensors. The astonishing analytical performance of GOPx-Ag opens up a new path for fabricating promising HCHO sensors.

High selectivity to ppb-level HCHO sensor based on mesoporous tubular SnO2 at low temperature

Distinctive mesoporous SnO2 microtubes were synthesized via a facile and environmentally friendly solvothermal method. The gas sensor based on such SnO2 microtubes exhibited not only the lower detection limit to detect formaldehyde and remarkable selectivity comparison with other various gases when operating within 92°C, but also good linear relationship under concentration ranges of ppm level (1–100ppm) and ppb level (10–100ppb). The sensing properties of such SnO2 microtubes have been greatly improved compared to previously reported hollow structures. This might be attributed to their large specific surface area and porous structure, which can promote the diffusion of gas molecules and their adsorption on the surface of the sensing material.

Development of a Novel Formaldehyde OTFT Sensor Based on P3HT/Fe2O3 Nanocomposite Thin Film

The formaldehyde (HCHO) is considered as a major cause of sick building syndrome (SBS). The majority of conventional HCHO sensors have some drawbacks such as sensitivity, long sampling time and high operating temperature. In this report, a novel organic thin film transistor (OTFT) HCHO sensor based on poly-3-hexylithiophene (P3HT)/ferric oxide (Fe2O3) nanocomposite thin films was developed by the spraying process. The results showed that the P3HT/Fe2O3 nanocomposite thin film OTFT sensor has the improved response and reproducibility compared with the single P3HT thin film OTFT, which may be ascribed to porous surface morphology of the nanocomposite thin film partially.

ZnO–SnO2 nanotubes surface engineered by Ag nanoparticles: synthesis, characterization, and highly enhanced HCHO gas sensing properties

Novel Ag nanoparticles (NPs) coated ZnO–SnO2 nanotubes (NTs, diameter ∼250 nm, wall thickness ∼20 nm) were fabricated using a facile electrospinning technique together with a seed-mediated growth procedure, and the amount of surface Ag NPs was systematically controlled. They were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis spectra and X-ray photoelectron spectroscopy (XPS) techniques, which showed that strong interactions occurred between the ZnO–SnO2 NTs and the Ag NPs. The sensing properties of the Ag coated ZnO–SnO2 NTs for HCHO gas were carefully studied and the results indicated that the sensing properties were significantly modified by the coating of Ag NPs, including a considerably decreased working temperature, a highly improved response and shortened response dynamics. The 10% Ag coated NTs gas sensor was the optimum sensor, demonstrating an enhanced response of ∼6 times that of the ZnO–SnO2 NTs, while the working temperature was decreased by about 140 °C. Additionally, it showed a very low detection limit (9 ppb) for HCHO. The main reason for the enhanced HCHO gas sensing properties was attributed to “spillover effects” between the Ag NPs and ZnO–SnO2 NTs. Overall, the Ag coated ZnO–SnO2 NTs synthesized through electrospinning make a promising ppb-level HCHO sensor and an effective indoor HCHO detector.

A novel formaldehyde sensor containing AgPd alloy nanoparticles electrodeposited on an ionic liquid–chitosan composite film

A novel formaldehyde (HCHO) sensor fabricated by electrodeposition of AgPd alloy nanoparticles (NPs) on chitosan (Ch)–ionic liquid (IL, i.e., 1-octyl-3-methylimidazolium hexafluorophosphate, OMIM·PF6) films is developed. A scanning electron micrograph of the AgPd/Ch–IL composite film shows a uniform distribution of spherical AgPd NPs with particle sizes of 30–60nm. Energy-dispersive X-ray measurements indicate that the mass ratio of Pd and Ag in the alloy is 21:5. Cyclic voltammetric studies show that an electrode coated with the AgPd/Ch–IL composite film exhibits high electrocatalytic activity and stability towards electrooxidation of HCHO. The HCHO sensor exhibits linear behavior in the concentration range from 0.060mM to 20mM, allowing quantitative analysis of HCHO with a detection limit of 0.022mM (S/N=3).

HCHO sensing properties of Ag-doped In 2O 3 nanofibers synthesized by electrospinning

Ag-doped In 2O 3 nanofibers with diameters ranging from 60 to 130 nm and lengths of several tens of micrometers were synthesized by an electrospinning method. The XRD results indicated that the dopant in the nanofibers was metal Ag. The sensor fabricated from these fibers exhibited excellent HCHO sensing properties at 115 °C. The sensitivity was up to 3 when the sensor was exposed to 5 ppm HCHO, and the response and recovery time were about 5 and 10 s, respectively. Good selectivity was also observed in our investigations. These results indicated that the Ag-doped In 2O 3 nanofibers could be used to fabricate high performance HCHO sensors in practice.