Preparation of defected SWCNTs decorated with en-APTAS for application in high-performance nitric oxide gas detection

Room-Temperature Nitric Oxide Gas Sensors Based on NiO/SnO2 Heterostructures

Nitric oxide (NO) is a very well-known indoor pollutant, and high concentrations of it in the atmosphere lead to acid rain. Thus, there is great demand for NO sensors that have the ability to work at room temperature. In this work, NiO/SnO2 heterostructures have been prepared via the polyol process and were tested against different concentrations of NO gas at room temperature. The structural and morphological characteristics of the heterostructures were examined using X-ray diffraction and scanning electron microscopy, respectively, while the ratio of NiO to SnO2 was determined through the use of energy-dispersive spectrometry. The effects of both pH and thermal annealing on the morphological, structural and gas-sensing properties of the heterostructure were investigated. It was found that the morphology of the heterostructures consisted of rod-like particles with different sizes, depending on the temperature of thermal annealing. Moreover, NiO/SnO2 heterostructures synthesized with pH = 8 and annealed at 900 °C showed a response of 1.8% towards 2.5 ppm NO at room temperature. The effects of humidity as well as of stability on the gas sensing performance were also investigated.

Assembly of Core/Shell Nanospheres of Amorphous Hemin/Acetone-Derived Carbonized Polymer with Graphene Nanosheets for Room-Temperature NO Sensing

Implementing parts per billion-level nitric oxide (NO) sensing at room temperature (RT) is still in extreme demand for monitoring inflammatory respiratory diseases. Herein, we have prepared a kind of core-shell structural Hemin-based nanospheres (Abbr.: Hemin-nanospheres, defined as HNSs) with the core of amorphous Hemin and the shell of acetone-derived carbonized polymer, whose core-shell structure was verified by XPS with argon-ion etching. Then, the HNS-assembled reduced graphene oxide composite (defined as HNS-rGO) was prepared for RT NO sensing. The acetone-derived carbonized polymer shell not only assists the formation of amorphous Hemin core by disrupting their crystallization to release more Fe-N₄ active sites, but provides protection to the core. Owing to the unique core-shell structure, the obtained HNS-rGO based sensor exhibited superior RT gas sensing properties toward NO, including a relatively higher response (R_a/R_g = 5.8, 20 ppm), a lower practical limit of detection (100 ppb), relatively reliable repeatability (over 6 cycles), excellent selectivity, and much higher long-term stability (less than a 5% decrease over 120 days). The sensing mechanism has also been proposed based on charge transfer theory. The superior gas sensing properties of HNS-rGO are ascribed to the more Fe-N₄ active sites available under the amorphous state of the Hemin core and to the physical protection by the shell of acetone-derived carbonized polymer. This work presents a facile strategy of constructing a high-performance carbon-based core-shell nanostructure for gas sensing.

Gas Sensors Based on Single-Wall Carbon Nanotubes

Single-wall carbon nanotubes (SWCNTs) have a high aspect ratio, large surface area, good stability and unique metallic or semiconducting electrical conductivity, they are therefore considered a promising candidate for the fabrication of flexible gas sensors that are expected to be used in the Internet of Things and various portable and wearable electronics. In this review, we first introduce the sensing mechanism of SWCNTs and the typical structure and key parameters of SWCNT-based gas sensors. We then summarize research progress on the design, fabrication, and performance of SWCNT-based gas sensors. Finally, the principles and possible approaches to further improving the performance of SWCNT-based gas sensors are discussed.

Effective Air Purification via Pt-Decorated N3-CNT Adsorbent

Effectively removal of air pollutants using adsorbents is one of the most important methods to purify the air. In this work, we proposed for the first time that PtN3-CNT is an effective adsorbent for air purification. Its air purification performance was studied by calculating the adsorption behaviors and electronic structures of 12 gas molecules, including the main components of air (N2, O2, H2O, CO2) and the most common air pollutants (NO, NO2, SO3, SO2, CO, O3, NH3, H2S), on the surface of PtN3-CNT using first-principles calculations. The results showed that these gases were adsorbed stably via the coordination between Pt and the coordinated atoms (C, N, O, and S atoms) in the gas molecules, and the adsorption energies vary in the range of −0.81∼−4.28 eV. The obvious chemical interactions between PtN3-CNT and the adsorbed gas molecules are mainly determined by the apparent overlaps between the Pt 5d orbitals and the outmost p orbitals of the coordination atoms. PtN3-CNT has strong adsorption capacity for the toxic gas molecules, while relatively weaker adsorption performance for the main components of the air except oxygen. The recovery time of each adsorbed molecule calculated at different temperatures showed that, CO2, H2O, and N2 can be desorbed gradually at 298∼498 K, while the toxic gases are always adsorbed stably on the surface of PtN3-CNT. Considering the excellent thermal stability of PtN3-CNT at up to 1000 K proved by AIMD, PtN3-CNT is very suitable to act as an adsorbent to remove toxic gases to achieve the purpose of air purification. Our findings in this report would be beneficial for exploiting possible carbon-based air purification adsorbents with excellent adsorbing ability and good recovery performance.

Enhanced NO2 Sensing Performance of Graphene with Thermally Induced Defects

This paper demonstrates the enhanced NO2 sensing performance of graphene with defects generated by rapid thermal annealing (RTA). A high temperature of RTA (300-700 °C) was applied to graphene under an argon atmosphere to form defects on sp2 carbon lattices. The density of defects proportionally increased with increasing the RTA temperature. Raman scattering results confirmed significant changes in sp2 bonding. After 700 °C RTA, ID/IG, I2D/IG, and FWHM (full width at half maximum)(G) values, which are used to indirectly investigate carbon-carbon bonds' chemical and physical properties, were markedly changed compared to the pristine graphene. Further evidence of the thermally-induced defects on graphene was found via electrical resistance measurements. The electrical resistance of the RTA-treated graphene linearly increased with increasing RTA temperature. Meanwhile, the NO2 response of graphene sensors increased from 0 to 500 °C and reached maximum (R = ~24%) at 500 °C. Then, the response rather decreased at 700 °C (R = ~14%). The results imply that rich defects formed at above a critical temperature (~500 °C) may damage electrical paths of sp2 chains and thus deteriorate NO2 response. Compared to the existing functionalization process, the RTA treatment is very facile and allows precise control of the NO2 sensing characteristics, contributing to manufacturing commercial low-cost, high-performance, integrated sensors.