Pyridinic Dominance N-Doped Graphene: A Potential Material for SO2 Gas Detection

The sensors based on graphene have shown great promise in the detection of toxic air pollutants that are detrimental to nature and create risks to human health. Many recent experimental and computational efforts have been dedicated to sensor concepts incorporating pure graphene, graphene oxide, and doped graphene. Herein, a combination of spin-polarized density functional theory (DFT) with van der Waals correction and ab initio molecular dynamics (AIMD) approaches are utilized to assess the gas sensing potential of pyridinic dominance N-doped graphene (PNG) toward SO₂ detection. The potential of PNG systems as SO₂ sensing can be explored through an in-depth analysis of adsorption energies, electronic parameters, charge transfer, selectivity, and thermal stability. It is further demonstrated that external strains and the modulation of external electric fields are two effective ways to modify the adsorption strength. In light of these findings, our studies suggest that PNG monolayers have the potential to be an essential substrate for the detection of SO₂.

Exploring optical and electrical gas detection based on zinc-tetra-phenyl-porphyrin sensitizer

We developed optical waveguide (OWG), ultraviolet-visible spectrophotometry (UV-vis), and electrically operated gas sensors utilizing zinc-tetra-phenyl-porphyrin (ZnTPP) as sensitizer. Strikingly, ZnTPP thin-film/K⁺-exchanged glass OWG sensing element exhibits a superior signal-to-noise ratio of 109.6 upon 1 ppm NO₂ gas injection, which is 29.5 and 3.8 times larger than that of UV-vis (absorbance at wavelength of 438 nm) and ZnTPP electrical sensing elements prepared on an alumina ceramic tube, respectively. Further results on Fourier infrared spectra and UV-vis spectra, confirm a strong chemical adsorption of NO₂ gas on ZnTPP. Therefore, our studies highlight the selection of suitable detection technique for analyte sensing with ZnTPP.

Ultrasensitive Boron-Nitrogen-Codoped CVD Graphene-Derived NO2 Gas Sensor

Recent trends in 2D materials like graphene are focused on heteroatom doping in a hexagonal honeycomb lattice to tailor the desired properties for various lightweight atomic thin-layer derived portable devices, particularly in the field of gas sensors. To design such gas sensors, it is important to either discover new materials with enhanced properties or tailor the properties of existing materials via doping. Herein, we exploit the concept of codoping of heteroatoms in graphene for more improvements in gas sensing properties and demonstrate a boron- and nitrogen-codoped bilayer graphene-derived gas sensor for enhanced nitrogen dioxide (NO₂) gas sensing applications, which may possibly be another alternative for an efficient sensing device. A well-known method of low-pressure chemical vapor deposition (LPCVD) is employed for synthesizing the boron- and nitrogen-codoped bilayer graphene (BNGr). To validate the successful synthesis of BNGr, the Raman, XPS, and FESEM characterization techniques were performed. The Raman spectroscopy results validate the synthesis of graphene nanosheets, and moreover, the FESEM and XPS characterization confirms the codoping of nitrogen and boron in the graphene matrix. The gas sensing device was fabricated on a Si/SiO₂ substrate with prepatterned gold electrodes. The proposed BNGr sensor unveils an ultrasensitive nature for NO₂ at room temperature. A plausible NO₂ gas sensing mechanism is explored via a comparative study of the experimental results through the density functional theory (DFT) calculations of the adsorbed gas molecules on doped heteroatom sites. Henceforth, the obtained results of NO₂ sensing with the BNGr gas sensor offer new prospects for designing next-generation lightweight and ultrasensitive gas sensing devices.

Recent Developments in Graphene-Based Toxic Gas Sensors: A Theoretical Overview

Detecting and monitoring air-polluting gases such as carbon monoxide (CO), nitrogen oxides (NOx), and sulfur oxides (SOx) are critical, as these gases are toxic and harm the ecosystem and the human health. Therefore, it is necessary to design high-performance gas sensors for toxic gas detection. In this sense, graphene-based materials are promising for use as toxic gas sensors. In addition to experimental investigations, first-principle methods have enabled graphene-based sensor design to progress by leaps and bounds. This review presents a detailed analysis of graphene-based toxic gas sensors by using first-principle methods. The modifications made to graphene, such as decorated, defective, and doped to improve the detection of NOx, SOx, and CO toxic gases are revised and analyzed. In general, graphene decorated with transition metals, defective graphene, and doped graphene have a higher sensibility toward the toxic gases than pristine graphene. This review shows the relevance of using first-principle studies for the design of novel and efficient toxic gas sensors. The theoretical results obtained to date can greatly help experimental groups to design novel and efficient graphene-based toxic gas sensors.

Boron-doped few-layer graphene nanosheet gas sensor for enhanced ammonia sensing at room temperature

Heteroatom doping in graphene is now a practiced way to alter its electronic and chemical properties to design a highly-efficient gas sensor for practical applications. In this series, here we propose boron-doped few-layer graphene for enhanced ammonia gas sensing, which could be a potential candidate for designing a sensing device. A facile approach has been used for synthesizing boron-doped few-layer graphene (BFLGr) by using a low-pressure chemical vapor deposition (LPCVD) method. Further, Raman spectroscopy has been performed to confirm the formation of graphene and XPS and FESEM characterization were carried out to validate the boron doping in the graphene lattice. To fabricate the gas sensing device, an Si/SiO₂ substrate with gold patterned electrodes was used. More remarkably, the BFLGr-based sensor exhibits an extremely quick response for ammonia gas sensing with fast recovery at ambient conditions. Hence, the obtained results for the BFLGr-based gas sensor provide a new platform to design next-generation lightweight and fast gas sensing devices.

A boron-doped few-layer LPCVD graphene sensor is successfully designed and demonstrated for enhanced NH₃ gas sensing applications.

Controllable synthesis of an intercalated SnS2/aEG structure for enhanced NO2 gas sensing performance at room temperature

An intercalated SnS₂/aEG structure with abundant heterojunctions for enhanced NO₂ gas sensing performance at room temperature.

Complementary Dual-Channel Gas Sensor Devices Based on a Role-Allocated ZnO/Graphene Hybrid Heterostructure

Here, we present a new approach to dual-channel gas sensors on the basis of a role-allocated graphene/ZnO heterostructure, formed by the complementary hybridization of graphene and a ZnO thin film. The method enables cyclic and reproducible gas response as well as high gas response. The role allocation of graphene and ZnO was verified by studying the electrical transport properties of the heterostructure. The results indicated that the ZnO top layer and graphene bottom layer act as a gas adsorption layer and a carrier conducting layer, respectively. The charge interactions of the heterostructures were systematically explored by monitoring changes in transfer characteristics at room temperature and elevated temperature ( T = 250 °C) after introducing 20 ppm NO₂. These results can be understood in terms of the dual-channel effect of the graphene/ZnO heterostructures. Remarkably, an abrupt and reliable gas response under periodic NO₂ gas injection was unambiguously achieved by the heterostructure-based gas sensors and as ∼30 times higher than those of a graphene-based gas sensor. These proposed heterostructures represent a fundamental building block of a complementary hybrid gas sensor with highly sensitive and reproducible gas response.

Regioselectivity in hexagonal boron nitride co-doped graphene

The active electron transfer (ET) sites on the graphene surface can be controlled by hexagonal boron nitride (h-BN) doping.