Photochemical Sensing of NO2 with SnO2 Nanoribbon Nanosensors at Room Temperature This work was supported by the Camille and Henry Dreyfus Foundation, 3M Corporation, the National Science Foundation, and the University of California, Berkeley. P.Y. is an Alfred P. Sloan Research Fellow. Work at the Lawrence Berkeley National Laboratory was supported by the Office of Science, Basic Energy Sciences, Division of Materials Science of the US Department of Energy. We thank the National Center for Electron Microscopy for the use of their facilities.

Jebakumar D.S., Rikka V.R.

Shahid M.A., Rahman M.M., Hossain M.T., Hossain I., Sheikh M.S., Rahman M.S., Uddin N., Donne S.W., Hoque M.I.

The rapid developments in conductive polymers with flexible electronics over the past years have generated noteworthy attention among researchers and entrepreneurs. Conductive polymers have the distinctive capacity to conduct electricity while still maintaining the lightweight, flexible, and versatile characteristics of polymers. They are crucial for the creation of flexible electronics or gadgets that can stretch, bend, and adapt to different surfaces have sparked momentous interest in electronics, energy storage, sensors, smart textiles, and biomedical applications. This review article offers a comprehensive overview of recent advancements in conductive polymers over the last 15 years, including a bibliometric analysis. The properties of conductive polymers are summarized. Additionally, the fabrication processes of conductive polymer-based materials are discussed, including vacuum filtering, hydrothermal synthesis, spray coating, electrospinning, in situ polymerization, and electrochemical polymerization. The techniques have been presented along with their advantages and limitations. The multifunctional applications of conductive polymers are also discussed, including their roles in energy storage and conversion (e.g., supercapacitors, lithium-ion batteries (LIBs), and sodium-ion batteries (SIBs)), as well as in organic light-emitting diodes (OLEDs), organic solar cells (OSCs), conductive textiles, healthcare monitoring, and sensors. Future scope and associated challenges have also been mentioned for further development in this field.

Sayago I., Sánchez-Vicente C., Santos J.P.

Chemical nanosensors based on nanoparticles of tin dioxide and graphene-decorated tin dioxide were developed and characterized to detect low NO2 concentrations. Sensitive layers were prepared by the drop casting method. SEM/EDX analyses have been used to investigate the surface morphology and the elemental composition of the sensors. Photoactivation of the sensors allowed for detecting ultra-low NO2 concentrations (100 ppb) at room temperature. The sensors showed very good sensitivity and selectivity to NO2 with low cross-responses to the other pollutant gases tested (CO and CH4). The effect of humidity and the presence of graphene on sensor response were studied. Comparative studies revealed that graphene incorporation improved sensor performance. Detections in complex atmosphere (CO + NO2 or CH4 + NO2, in humid air) confirmed the high selectivity of the graphene sensor in near-real conditions. Thus, the responses were of 600%, 657% and 540% to NO2 (0.5 ppm), NO2 (0.5 ppm) + CO (5 ppm) and NO2 (0.5 ppm) + CH4 (10 ppm), respectively. In addition, the detection mechanisms were discussed and the possible redox equations that can change the sensor conductance were also considered.

Mohamed M.Y., Ferjani H., Oyewo O.A., Ogunjinmi O.E., Hamed S.M., Amairia C., Makgato S., Onwudiwe D.C.

Nanotechnology has emerged as a new route for addressing most environmental and medical challenges, hence this field of research continues to generate research interest. Herein, Bi2O3 was synthesized by a microwave-assisted thermal process. X-ray diffraction (XRD) result confirmed that a nanocrystalline monoclinic crystal structure of the α-phase was formed, and both the Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis confirmed that the synthesized α-Bi2O3 were rod-like in shape. The length of the nanorods was in the range of 60–160 nm, with an average dimension of 101.5 nm, while the width has an average value of 23 nm. A band gap energy value of 2.75 eV was obtained from the absorption spectroscopy, and they absorbed light in the UV to visible range, with an absorption maximum of around 345 nm. Photocatalytic activity of the nanorods under UV irradiation was investigated by assessing the degradation of Bromocresol green (BG) as a model pollutant. The degradation process of the dye molecules was studied at different concentrations (20 to 80 mg/L), varied photocatalyst dosage (0.025, 0.05, 0.075, and 1.0 g), and a range of solution pH (3, 6, 9, and 12). About 75 % optimum photocatalytic efficiency was achieved at pH 6 after 3 h. In addition, the results showed that an increase in catalyst dosage and concentration of dye molecules contributed to promoting the degradation effect. Moreover, the photocatalyst was found to be stable after 4 consecutive cycles, with negligible loss of efficiency. The antioxidant potency of the nanorods was assessed by evaluating their free radical scavenging capabilities across 4 different assays: 1,1-diphenyl-2-picrylhydrazyle (DPPH), Nitric oxide (NO), Hydrogen peroxide (HP) radical inhibition, and Reducing power (RP). The results from the IC50 values indicated the sample exhibited better inhibition of HP (25.22 µg/mL), followed by RP (28.22 µg/mL), NO (29.37 µg/mL), and DPPH (32.72 µg/mL) respectively. However, the standard Ascorbic acid exhibited IC50 values of 16.25, 24.50, 25.07, and 28.40 µg/mL for DPPH, RP, HP, and NO, respectively. These unique properties of the nanorods showed that they have good antioxidant potential that is comparable with that of Ascorbic acid used as the standard.

Hao Y., Xiao Y., Liu X., Ma J., Lu Y., Chang Z., Luo D., Li L., Feng Q., Xu L., Huang Y.

In this study, we prepared the SnO2/ZnFe2O4 (SZ) composite magnetic photocatalyst via a two-step hydrothermal method. Structural and performance analyses revealed that SZ-5 with a ZnFe2O4 mass ratio of 5% (SZ-5) exhibited optimal photocatalytic activity, achieving a 72.6% degradation rate of Rhodamine B (RhB) solution within 120 min. SZ-5 consisted of irregular nano blocks of SnO2 combined with spherical nanoparticles of ZnFe2O4, with a saturated magnetization intensity of 1.27 emu/g. Moreover, the specific surface area of SnO2 loaded with ZnFe2O4 increased, resulting in a decreased forbidden bandwidth and expanded light absorption range. The construction of a Z-type heterojunction structure between SnO2 and ZnFe2O4 facilitated the migration of photogenerated charges, reduced the recombination rate of electron-hole pairs, and enhanced electrical conductivity. During the photocatalytic reaction, RhB was degraded by·OH, O2−, and h+, in which O2− played a major role.

Xie Y., Zhang Z., Meng F., Shida H., Hu X., Niu P., Wu E.

Abstract Selective and sensitive detection of volatile organic compounds (VOCs) holds paramount importance in real-world applications. This study proposes an innovative approach utilizing a single ReS2 field-effect transistor (FET) characterized by distinct in-plane anisotropy, specifically tailored for VOC recognition. The unique responses of ReS2, endowed with robust in-plane anisotropic properties, demonstrate significant difference along the a-axis and b-axis directions when exposed to four kinds of VOCs: acetone, methanol, ethanol, and IPA. Remarkably, the responses of ReS2 were significantly magnified under ultraviolet (UV) illumination, particularly in the case of acetone, where the response amplified by 10–15 times and the detection limit decreasing from 70 to 4 ppm compared to the dark conditions. Exploiting the discernible variances in responses along the a-axis and b-axis under both UV and dark conditions, the data points of acetone, ethanol, methanol and IPA gases were clearly separated in the principal component space without any overlap through principal component analysis, indicating that the single ReS2 FET has a high ability to distinguish various gas species. The exploration of anisotropic sensing materials and light excitation strategies can be applied to a broad range of sensing platforms based on two-dimensional materials for practical applications.

Lu Z., Pei X., Wang T., Gu K., Yu N., Wang M., Wang J.

Thermal oxidation of 2D SnS flakes at ≥800 °C leads to 2D porous SnO2 flakes, which exhibit superior sensitivity, response/recovery speed, selectivity, and a low limit of detection for NO2 gas sensing.

Rangel-Cortes E., Garcia-Islas J.P., Gutierrez-Rodriguez J., Montes de Oca S., Garcia-Gonzalez J.A., Nieto-Jalil J.M., Miralrio A.

The adsorption of CO, NO, and O2 molecules onto Cu, Ag, and Au atoms placed in the S vacancies of a WS2 monolayer was elucidated within dispersion-corrected density functional theory. The binding energies computed for embedded defects into S vacancies were 2.99 (AuS), 2.44 (AgS), 3.32 eV (CuS), 3.23 (Au2S2), 2.55 (Ag2S2), and 3.48 eV/atom (Cu2S2), respectively. The calculated diffusion energy barriers from an S vacancy to a nearby site for Cu, Ag, and Au were 2.29, 2.18, and 2.16 eV, respectively. Thus, the substitutional atoms remained firmly fixed at temperatures above 700 K. Similarly, the adsorption energies showed that nitric oxide and carbon oxide molecules exhibited stronger chemisorption than O2 molecules on any of the metal atoms (Au, Cu, or Ag) placed in the S vacancies of the WS2 monolayer. Therefore, the adsorption of O2 did not compete with NO or CO adsorption and did not displace them. The density of states showed that a WS2 monolayer modified with a Cu, Au, or Ag atom could be used to design sensing devices, based on electronic or magnetic properties, for atmospheric pollutants. More interestingly, the adsorption of CO changed only the electronic properties of the MoS2-AuS monolayer, which could be used for sensing applications. In contrast, the O2 molecule was chemisorbed more strongly than CO or NO on Au2S2, Cu2S2, or Ag2S2 placed into di-S vacancies. Thus, if the experimental system is exposed to air, the low quantities of O2 molecules present should result in the oxidation of the metallic atoms. Furthermore, the O2 molecules adsorbed on WS2-Au2S2 and WS2-CuS introduced a half-metallic behavior, making the system suitable for applications in spintronics.

Mehta M., Deepti, Sinha A.K., Wadhwa S., Kumar A., Avasthi D.K.

In this study, we synthesized Pd-graphene oxide (Pd-GO) nanocomposite layers on SiO2/Si substrates using chemical method. Pd-GO layers were treated with swift heavy ion irradiation (100 MeV Ag ions, 1013 ions/cm2). The structural properties of the pristine as well as the ion irradiated samples were investigated using synchrotron grazing incidence x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. XRD shows peaks corresponding to Pd (FCC, space group-Fd-3m), GO and synthetic graphite. The relative graphite peak intensities increased after ion irradiation, indicating reduction of GO. The sensor responses of nanocomposite layers towards exposure of 35 ppm H2 at 100 °C, were measured for several cycles. Ion-irradiated Pd-GO samples show enhancement in the sensing response of H2 gas by about 24% and with lower recovery times (25%), as compared to pristine Pd-GO nanocomposite samples. The change in type of conductivity from p-type gas sensing layer in pristine nanocomposite to n-type conductivity, along with an increase in conductivity (about 500 times) in ion irradiated samples were observed. The change in type of conductivity on ion-irradiation is attributed to the reduction of GO layer and the changes in conductivity on hydrogen exposure is explained due to hydrogen spill-over effect in the two-component system. The improvement in sensitivity upon ion-irradiation was due to the increase in concentration of structural defects due to electronic energy loss, as studied by SRIM simulation. This study points towards using ion induced electronic energy loss as a new tool for varying the gas sensing properties of GO based sensors.

Kim J., John A.T., Li H., Huang C., Chi Y., Anandan P.R., Murugappan K., Tang J., Lin C., Hu L., Kalantar‐Zadeh K., Tricoli A., Chu D., Wu T.

AbstractGas sensors are of great interest to portable and miniaturized sensing technologies with applications ranging from air quality monitoring to explosive detection and medical diagnostics, but the existing chemiresistive NO2 sensors still suffer from issues such as poor sensitivity, high operating temperature, and slow recovery. Herein, a high‐performance NO2 sensors based on all‐inorganic perovskite nanocrystals (PNCs) is reported, achieving room temperature operation with ultra‐fast response and recovery time. After tailoring the halide composition, superior sensitivity of ≈67 at 8 ppm NO2 is obtained in CsPbI2Br PNC sensors with a detection level down to 2 ppb, which outperforms other nanomaterial‐based NO2 sensors. Furthermore, the remarkable optoelectronic properties of such PNCs enable dual‐mode operation, i.e., chemiresistive and chemioptical sensing, presenting a new and versatile platform for advancing high‐performance, point‐of‐care NO2 detection technologies.

Sharma A., Gupta G.

The discovery of harmful gases has grown increasingly significant regarding environmental protection, safety, and industrial applications. Traditional gas sensors based on semiconducting oxide material have exceptional sensitivity; however, they suffer from poor recovery and high-temperature operation. The high-temperature process leads to significant power consumption and other safety concerns. Recently, metal-selenide materials such as WSe2, MoSe2, PtSe2, etc., have received considerable interest in low-power sensing applications due to their unique electrical, mechanical, and chemical characteristics, which distinguish them apart from the other layered materials. The metal selenides with layered structures, high surface-to-volume ratio, and the reactive surface will be an ideal candidate for gas sensing applications. The metal mono- and di-selenide-based materials utilized in gas sensing applications are summarized as their prospects for future applications. In addition, the flexible and wearable gas sensors based on metal selenide for innovative sensing applications have also been discussed.

Jiang Q., Chai Z., Zong Z., Hu Z., Zhang S., Wu Z.

Being abundant as natural intelligence, plants have attracted huge attention from researchers. Soft film sensors present a novel and promising approach to connect plants with artificial devices, helping us to investigate plants’ intelligence further. Here, recent developments for micro/nano soft film sensors that can be used for establishing intelligent plant systems are summarized, including essential materials, fabrications, and application scenarios. Conductive metals, nanomaterials, and polymers are discussed as basic materials for active layers and substrates of soft film sensors. The corresponding fabrication techniques, such as laser machining, printing, coating, and vapor deposition, have also been surveyed and discussed. Moreover, by combining soft film sensors with plants, applications for intelligent plant systems are also investigated, including plant physiology detection and plant-hybrid systems. Finally, the existing challenges and future opportunities are prospected.

Betty C.A., Choudhury S., Shah A.

Nanocrystalline metal oxide thin films offer toxic gas sensing with higher sensitivity at lower temperature compared to their bulk counter parts leading to miniaturization of the sensors, making them wearable and easily portable for field trials without compromising on the sensitivity, but aided with improved selectivity. Nanomaterial of different size, morphology, geometry, preparation methods and composition play an important role in sensitivity, selectivity, response time and stability of the sensor. Although there are many reports about nanostructured materials for toxic gas sensing, they lack commercialization due to reliability issues. While some reviews have focused on toxic gas sensors based on macro and nanostructured materials which work at elevated temperatures and/or for a specific gas species, this review presents the systematic advances of room temperature operating sensors and their toxic gas sensing mechanism based on design of nanostructured metal oxide semiconductors and heterostructures, with insights into their high sensitivity, selectivity and reliability. Recent studies on room temperature operating trace gas sensors (for NH3, H2S, H2, NO2 and SO2) based on nanostructured semiconducting materials and their composites in the chemiresistive mode are discussed. The roles of nanocrystallite size, morphology, surface adsorbed species, surface charge depletion layers and heterostructure interfaces of metal oxide semiconductors and their composite materials for reliable room temperature gas sensing are discussed. The article concludes with current status and future scope for optimizing the nanostructures and their heterostructure interfaces for specific gas sensing at room temperature with an understanding of the various physicochemical properties involved in enhancing the sensitivity, selectivity, stability and commercial viability.

Sun X., Lan Q., Geng J., Yu M., Li Y., Li X., Chen L.

It is an effective strategy for increasing the sensitivity and shortening the response/recovery time of semiconductor gas sensors used at room temperature with visible light illumination. However, the large band gap and the serious carrier recombination under light illumination of the semiconductor will hinder the improvement of room temperature sensing performance. Herein, we assembled the films of TiO2 nanoparticles decorated with polyoxometalate (POM) and organic dye molecules to enable accelerated room-temperature NO2 gas sensing (25 ℃) under visible light illumination. The POM molecule as electron acceptor in the dye/TiO2 films can enable the rapid separation and transport of photogenerated carriers. Combining with organic dyes, POM decorated dye/TiO2 films exhibited excellent sensing characteristics over a wide range of NO2 concentrations (50ppb-5 ppm), such as high sensitivity (233.1–1 ppm), relatively low detection concentration, and high selectivity. Moreover, the response/recovery time of NO2 from the surface of this sensitive films could be constantly controlled down to 48 s and 66 s, respectively, without any thermal energy.

Suman P.H., Jorgetto A.O., Romeiro F.C., Felix A.A., Morais P.V., Melquíades M.O., Orlandi M.O.

Tin oxide is one of the most relevant semiconducting metal oxides (SMOx) of modern industry. The particular properties of different tin oxide stoichiometries (SnO 2 , Sn 2 O 3 , Sn 3 O 4 , and SnO) make them exciting materials for a wide variety of technological applications. One-dimensional (1D) nanomaterials, including nanowires, nanotubes, nanobelts, and nanofibers, are fascinating structures for a new generation of sensing and optoelectronic devices, allowing miniaturization, system integration, and low power consumption. This chapter introduces state-of-the-art research on the synthesis and applications of pristine and hybrid 1D tin oxide nanostructures. Easy controlling methods used to produce such materials and their recent application in gas sensing, photocatalysis, and other relevant purposes will be reviewed. Lastly, future outlooks concerning the application of multiple tin oxide materials will be addressed.