Green Synthesis of 3D Chemically Functionalized Graphene Hydrogel for High-Performance NH3 and NO2 Detection at Room Temperature

Hierarchical Porous Aggregate-Enabled Chromatography-Inspired Single-Sensor E-Nose for Volatile Monitoring

Monitoring volatile organic compounds (VOCs) is crucial for ensuring safety and health. In this study, we introduce a strategy to engineer a chromatography-inspired single-sensor (CISS) e-nose tailored for VOC monitoring. This approach overcomes the limitations of traditional methodologies and conventional e-noses. A hierarchical porous multicomponent aggregate, named CuP@G, was initially developed as the sole sensor material. This aggregate integrates a Cu2+-polydopamine (CuP) network with reduced graphene oxide, enhancing its chemoresistive properties. Using laser processing, we fabricated a grooved laser-induced graphene interdigitated electrode that is loaded with CuP@G ink and subsequently integrated into a compact laser-engraved microchamber. This process results in the production of the CISS e-nose. Notably, this e-nose enables swift, reversible, and precise detection of various VOCs using a time-space-resolved methodology. The developed module, known for its affordability and portability, is especially suitable for the point-of-care testing (POCT) of VOCs. Consequently, our research advances the development of streamlined cost-effective e-noses that are essential for proficient VOC monitoring.

Enhanced room temperature ammonia gas sensing based on a multichannel PSS-functionalized graphene/PANI network

Disordered polymerization of polymers widens the polymerization degree distribution, which leads to uncontrollable thickness and significantly weakens their sensing performance. Herein, poly(sodium p-styrenesulfonate)-functionalized reduced graphene oxide (PSS-rGO) with multichannel chain structures coated with thin polyaniline layer (PSS-rGO/PANI) nanocomposites was synthesized via a facile interfacial polymerization route. The morphology and microstructure of the PSS-rGO/PANI nanocomposites were characterized using Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The flexible PSS-rGO/PANI-2 sensor exhibits excellent room temperature NH3 sensing performance, including a higher sensitivity of 362% and a faster response/recovery time of 23/158 s towards 100 ppm NH3 than other PSS-rGO/PANI nanocomposites. In addition, the flexible PSS-rGO/PANI-2 sensor has a low detection limit of 10 ppb, superior selectivity, repeatability, and long-term stability over 75 days. Remarkably, the flexible PSS-rGO/PANI-2 sensor shows excellent humidity resistance (196 ± 3%, 50 ppm) even at a high relative humidity of 80%. The gas sensing mechanism was systematically investigated through high protonation states and strong π-π conjugation of PSS-rGO/PANI. This work provides a convenient method to construct multichannel thin polyaniline layer-coated graphene nanocomposites and promotes their application in flexible wearable electronics.

Insights into Translational and Biomedical Applications of Hydrogels as Versatile Drug Delivery Systems

Hydrogels are a network of crosslinked polymers which can hold a huge amount of water in their matrix. These might be soft, flexible, and porous resembling living tissues. The incorporation of different biocompatible materials and nanostructures into the hydrogels has led to emergence of multifunctional hydrogels with advanced properties. There are broad applications of hydrogels such as tissue culture, drug delivery, tissue engineering, implantation, water purification, and dressings. Besides these, it can be utilized in the field of medical surgery, in biosensors, targeted drug delivery, and drug release. Similarly, hyaluronic acid hydrogels have vast applications in biomedicines such as cell delivery, drug delivery, molecule delivery, micropatterning in cellular biology for tissue engineering, diagnosis and screening of diseases, tissue repair and stem cell microencapsulation in case of inflammation, angiogenesis, and other biological developmental processes. The properties like swellability, de-swellability, biodegradability, biocompatibility, and inert nature of the hydrogels in contact with body fluids, blood, and tissues make its tremendous application in the field of modern biomedicines nowadays. Various modifications in hydrogel formulations have widened their therapeutic applicability. These include 3D printing, conjugation, thiolation, multiple anchoring, and reduction. Various hydrogel formulations are also capable of dual drug delivery, dental surgery, medicinal implants, bone diseases, and gene and stem cells delivery. The presented review summarizes the unique properties of hydrogels along with their methods of preparation and significant biomedical applications as well as different types of commercial products available in the market and the regulatory guidance.

Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors

Breathing is an inherent human activity; however, the composition of the air we inhale and gas exhale remains unknown to us. To address this, wearable vapor sensors can help people monitor air composition in real time to avoid underlying risks, and for the early detection and treatment of diseases for home healthcare. Hydrogels with three-dimensional polymer networks and large amounts of water molecules are naturally flexible and stretchable. Functionalized hydrogels are intrinsically conductive, self-healing, self-adhesive, biocompatible, and room-temperature sensitive. Compared with traditional rigid vapor sensors, hydrogel-based gas and humidity sensors can directly fit human skin or clothing, and are more suitable for real-time monitoring of personal health and safety. In this review, current studies on hydrogel-based vapor sensors are investigated. The required properties and optimization methods of wearable hydrogel-based sensors are introduced. Subsequently, existing reports on the response mechanisms of hydrogel-based gas and humidity sensors are summarized. Related works on hydrogel-based vapor sensors for their application in personal health and safety monitoring are presented. Moreover, the potential of hydrogels in the field of vapor sensing is elucidated. Finally, the current research status, challenges, and future trends of hydrogel gas/humidity sensing are discussed.

Microgels based on 0D-3D carbon materials: Synthetic techniques, properties, applications, and challenges

Microgels are three-dimensional (3D) colloidal hydrogel particles with outstanding features such as biocompatibility, good mechanical properties, tunable sizes from submicrometer to tens of nanometers, and large surface areas. Because of these unique qualities, microgels have been widely used in various applications. Carbon-based materials (CMs) with various dimensions (0-3D) have recently been investigated as promising candidates for the design and fabrication of microgels because of their large surface area, excellent conductivity, unique chemical stability, and low cost. Here, we provide a critical review of the specific characteristics of CMs that are being incorporated into microgels, as well as the state-of-the art applications of CM-microgels in pollutant adsorption and photodegradation, H₂ evoluation, CO₂ capture, soil conditioners, water retention, drug delivery, cell encapsulation, and tissue engineering. Advanced preparation techniques for CM-microgel systems are also summarized and discussed. Finally, challenges related to the low colloidal stability of CM-microgels and development strategies are examined. This review shows that CM-microgels have the potential to be widely used in various practical applications.

Modular Assembly of MXene Frameworks for Noninvasive Disease Diagnosis via Urinary Volatiles

Volatile organic compounds (VOCs) in urine are valuable biomarkers for noninvasive disease diagnosis. Herein, a facile coordination-driven modular assembly strategy is used for developing a library of gas-sensing materials based on porous MXene frameworks (MFs). Taking advantage of modules with diverse composition and tunable structure, our MFs-based library can provide more choices to satisfy gas-sensing demands. Meanwhile, the laser-induced graphene interdigital electrodes array and microchamber are laser-engraved for the assembly of a microchamber-hosted MF (MHMF) e-nose. Our MHMF e-nose possesses high-discriminative pattern recognition for simultaneous sensing and distinguishing of complex VOCs. Furthermore, with the MHMF e-nose being a plug-and-play module, a point-of-care testing (POCT) platform is modularly assembled for wireless and real-time monitoring of urinary volatiles from clinical samples. By virtue of machine learning, our POCT platform achieves noninvasive diagnosis of multiple diseases with a high accuracy of 91.7%, providing a favorable opportunity for early disease diagnosis, disease course monitoring, and relevant research.

Gas-Sensitive Cellulosic Triboelectric Materials for Self-Powered Ammonia Sensing

Gas-sensitive materials are capable of dynamic identification and content monitoring of specific gases in the environment, and their applications in the field of gas sensing are promising. However, weak adsorption properties are the main challenge limiting the application of gas-sensitive materials. A highly adsorbent gas-sensitive cellulose nanofibril (CNF)-based triboelectric material with a layered structure is prepared here and it is applied to self-powered gas sensing. The layered structure of the triethoxy-1H,1H,2H,2H-tridecafluoro-n-octylsilane cellulose nanofiber (PFOTES-CNF)-based gas-sensitive material further enhances the adsorption of the material due to electrostatic adsorption in the electrostatic field induced by triboelectricity. It is found that the ammonia-sensitive material obtained by loading Ti3 C2 Tx in PFOTES-CNF has a fast response/recovery (12/14 s), high sensitivity response (Vair /Vgas  = 2.1), high selectivity response (37.6%), and low detection limit (10 ppm) for 100 ppm of ammonia gas. In addition, the ammonia-sensitive CNF-based triboelectric material can accurately identify NH3 concentration changes in the range of 10-120 ppm and transmit the signal wirelessly to the user interface, facilitating real-time online monitoring of NH3 in the environment. A novel strategy is provided here for designing and preparing high-performance gas-sensitive composites and the analysis of self-powered gas sensing is guided.

Hydrogel- and organohydrogel-based stretchable, ultrasensitive, transparent, room-temperature and real-time NO2 sensors and the mechanism

Highly stretchable, sensitive and room-temperature nitrogen dioxide (NO₂) sensors are fabricated by exploiting intrinsically stretchable, transparent and ion-conducting hydrogels and active metals as the novel transducing materials and electrodes, respectively. The NO₂ sensor exhibits high sensitivity (60.02% ppm^-1), ultralow theoretical limit of detection (6.8 ppb), excellent selectivity, linearity and reversibility at room temperature. Notably, the sensitivity can be maintained even under 50% tensile strain. For the first time, it's found that the metal electrodes significantly impact the sensing performance. Specifically, the sensitivity is boosted from 31.18 to 60.02% ppm^-1 by replacing the anodic silver with copper-tin alloy. Importantly, by applying specially designed sensing tests, and microscopic and composition analyses, we have obtained the inherent NO₂ sensing mechanism: the anodic metal tends to be oxidized and the NO₂ molecules tend to react in the cathode-gel interface. The introduction of glycerol converts the hydrogel into the organohydrogel with remarkably enhanced anti-drying and anti-freezing capacities and toughness, which effectively improved the long-time stability of the sensors. Importantly, we execute sound/light alarms and a wireless smartphone alarm by utilizing a designed circuit board and applet. This work gives an incisive investigation for the preparation, performance improvement, mechanism and application of hydrogel-based NO₂ sensors, promoting the evolution of hydrogel ionotronics.

Self-Healing, Self-Adhesive and Stable Organohydrogel-Based Stretchable Oxygen Sensor with High Performance at Room Temperature

With the advent of the 5G era and the rise of the Internet of Things, various sensors have received unprecedented attention, especially wearable and stretchable sensors in the healthcare field. Here, a stretchable, self-healable, self-adhesive, and room-temperature oxygen sensor with excellent repeatability, a full concentration detection range (0-100%), low theoretical limit of detection (5.7 ppm), high sensitivity (0.2%/ppm), good linearity, excellent temperature, and humidity tolerances is fabricated by using polyacrylamide-chitosan (PAM-CS) double network (DN) organohydrogel as a novel transducing material. The PAM-CS DN organohydrogel is transformed from the PAM-CS composite hydrogel using a facile soaking and solvent replacement strategy. Compared with the pristine hydrogel, the DN organohydrogel displays greatly enhanced mechanical strength, moisture retention, freezing resistance, and sensitivity to oxygen. Notably, applying the tensile strain improves both the sensitivity and response speed of the organohydrogel-based oxygen sensor. Furthermore, the response to the same concentration of oxygen before and after self-healing is basically the same. Importantly, we propose an electrochemical reaction mechanism to explain the positive current shift of the oxygen sensor and corroborate this sensing mechanism through rationally designed experiments. The organohydrogel oxygen sensor is used to monitor human respiration in real-time, verifying the feasibility of its practical application. This work provides ideas for fabricating more stretchable, self-healable, self-adhesive, and high-performance gas sensors using ion-conducting organohydrogels.

An Overview on Recent Progress of the Hydrogels: From Material Resources, Properties to Functional Applications

Hydrogels, as the most typical elastomer materials with three-dimensional network structures, have attracted wide attention owing to their outstanding features in fields of sensitive stimulus response, low surface friction coefficient, good flexibility and bio-compatibility. Because of numerous fresh polymer materials (or polymerization monomers), hydrogels with various structure diversities and excellent properties are emerging, and the development of hydrogels is very vigorous over the past decade. This review focuses on state-of-the-art advances, systematically reviews the recent progress on construction of novel hydrogels utilized several kinds of typical polymerization monomers, and explores the main chemical and physical cross-linking methods to develop the diversity of hydrogels. Following the aspects mentioned above, the classification and emerging applications of hydrogels, such as pH response, ionic response, electrical response, thermal response, biomolecular response, and gas response, are extensively summarized. Finally, we have done this review with the promises and challenges for the future evolution of hydrogels and their biological applications. cross-linking methods; functional applications; hydrogels; material resources This article is protected by copyright. All rights reserved.

Effect of GNWs/NiO-WO3/GNWs Heterostructure for NO2 Gas Sensing at Room Temperature

Recently, as air pollution and particulate matter worsen, the importance of a platform that can monitor the air environment is emerging. Especially, among air pollutants, nitrogen dioxide (NO₂) is a toxic gas that can not only generate secondary particulate matter, but can also derive numerous toxic gases. To detect such NO₂ gas at low concentration, we fabricated a GNWs/NiO-WO₃/GNWs heterostructure-based gas sensor using microwave plasma-enhanced chemical vapor deposition (MPECVD) and sputter, and we confirmed the NO₂ detection characteristics between 10 and 50 ppm at room temperature. The morphology and carbon lattice characteristics of the sensing layer were investigated using field emission scanning electron microscopy (FESEM) and Raman spectroscopy. In the gas detection measurement, the resistance negative change according to the NO₂ gas concentration was recorded. Moreover, it reacted even at low concentrations such as 5–7 ppm, and showed excellent recovery characteristics of more than 98%. Furthermore, it also showed a change in which the reactivity decreased with respect to humidity of 33% and 66%.

Ion-Conductive Hydrogel-Based Stretchable, Self-Healing, and Transparent NO2 Sensor with High Sensitivity and Selectivity at Room Temperature

Here stretchable, self-healable, and transparent gas sensors based on salt-infiltrated hydrogels for high-performance NO₂ sensing in both anaerobic environment and air at room temperature, are reported. The salt-infiltrated hydrogel displays high sensitivity to NO₂ (119.9%/ppm), short response and recovery time (29.8 and 41.0 s, respectively), good linearity, low theoretical limit of detection (LOD) of 86 ppt, high selectivity, stability, and conductivity. A new gas sensing mechanism based on redox reactions occurring at the electrode-hydrogel interface is proposed to understand the sensing behaviors. The gas sensing performance of hydrogel is greatly improved by incorporating calcium chloride (CaCl₂ ) in the hydrogel via a facile salt-infiltration strategy, leading to a higher sensitivity (2.32 times) and much lower LOD (0.06 times). Notably, both the gas sensing ability, conductivity, and mechanical deformability of hydrogels are readily self-healable after cutting off and reconnection. Such large deformations as 100% strain do not deprive the gas sensing capability, but rather shorten the response and recovery time significantly. The CaCl₂ -infiltrated hydrogel shows excellent selectivity of NO₂ , with good immunity to the interference gases. These results indicate that the salt-infiltrated hydrogel has great potential for wearable electronics equipped with gas sensing capability in both anaerobic and aerobic environments.

Highly sensitive and chemically stable NH3 sensors based on an organic acid-sensitized cross-linked hydrogel for exhaled breath analysis

Due to interference by the high moisture content and complicated compositions of human exhaled breath, the trace-level detection of ammonia (NH₃) with desirable selectivity and stability is a large challenge for exhaled breath analysis. Carboxyl-sensitized hydrogels can be activated by moisture to exhibit a significant response and excellent selectivity to NH₃. However, the high activity of carboxyl groups in hydrogels is a double-edged sword, resulting in poor chemical stability during NH₃ detection. Herein, organic acids were embedded into a cross-linked poly(ethylene glycol) diacrylate (PEGDA) hydrogel via thiol-ene photochemistry to form stable hydrogels for NH₃ detection in a humid atmosphere. As a result, under high humidity conditions (80% RH), the optimal sensors exhibited superior selectivity to NH₃ among various interfering gas species, a remarkably high NH₃ response (Z_a/Z_g=6.20) towards 20 ppm NH₃, and an extremely low actual detection limit (50 ppb) at room temperature. Moreover, the sensors exhibited excellent chemical stability due to the moderate equilibrium water content of the hydrogel composites and acid dissociation constant of the acid groups. The moisture-activated NH₃ sensing mechanism was thoroughly investigated by complex impedance spectroscopy (CIS), quartz crystal microbalance (QCM) measurements, Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). To explore the application prospects of cross-linked hydrogel sensors for detecting NH₃ in exhaled breath, a simulated exhaled breath test was also performed.

High Performance Acoustic Wave Nitrogen Dioxide Sensor with Ultraviolet Activated 3D Porous Architecture of Ag-Decorated Reduced Graphene Oxide and Polypyrrole Aerogel

Surface acoustic wave (SAW) devices have been widely explored for real-time monitoring of toxic and irritant chemical gases such as nitrogen oxide (NO₂), but they often have issues such as a complicated process of the sensing layer, low sensitivity, long response time, irreversibility, and/or requirement of high temperatures to enhance sensitivity. Herein, we report a sensing material design for room-temperature NO₂ detection based on a 3D porous architecture of Ag-decorated reduced graphene oxide-polypyrrole hybrid aerogels (rGO-PPy/Ag) and apply UV activation as an effective strategy to further enhance the NO₂ sensing performance. The rGO-PPy/Ag-based SAW sensor with the UV activation exhibits high sensitivity (127.68 Hz/ppm), fast response/recovery time (36.7 s/58.5 s), excellent reproducibility and selectivity, and fast recoverability. Its enhancement mechanisms for highly sensitive and selective detection of NO₂ are based on a 3D porous architecture, Ag-decorated rGO-PPy, p-p heterojunction in rGO-PPy/Ag, and UV photogenerated carriers generated in the sensing layer. The scientific findings of this work will provide the guidance for future exploration of next-generation acoustic-wave-based gas sensors.

Nitrogen Dioxide Gas Sensor Based on Ag-Doped Graphene: A First-Principle Study

High-performance tracking trace amounts of NO2 with gas sensors could be helpful in protecting human health since high levels of NO2 may increase the risk of developing acute exacerbation of chronic obstructive pulmonary disease. Among various gas sensors, Graphene-based sensors have attracted broad attention due to their sensitivity, particularly with the addition of noble metals (e.g., Ag). Nevertheless, the internal mechanism of improving the gas sensing behavior through doping Ag is still unclear. Herein, the impact of Ag doping on the sensing properties of Graphene-based sensors is systematically analyzed via first principles. Based on the density-functional theory (DFT), the adsorption behavior of specific gases (NO2, NH3, H2O, CO2, CH4, and C2H6) on Ag-doped Graphene (Ag–Gr) is calculated and compared. It is found that NO2 shows the strongest interaction and largest Mulliken charge transfer to Ag–Gr among these studied gases, which may directly result in the highest sensitivity toward NO2 for the Ag–Gr-based gas sensor.

Recent Progress of Toxic Gas Sensors Based on 3D Graphene Frameworks

Air pollution is becoming an increasingly important global issue. Toxic gases such as ammonia, nitrogen dioxide, and volatile organic compounds (VOCs) like phenol are very common air pollutants. To date, various sensing methods have been proposed to detect these toxic gases. Researchers are trying their best to build sensors with the lowest detection limit, the highest sensitivity, and the best selectivity. As a 2D material, graphene is very sensitive to many gases and so can be used for gas sensors. Recent studies have shown that graphene with a 3D structure can increase the gas sensitivity of the sensors. The limit of detection (LOD) of the sensors can be upgraded from ppm level to several ppb level. In this review, the recent progress of the gas sensors based on 3D graphene frameworks in the detection of harmful gases is summarized and discussed.

Engineering SnO2 nanorods/ethylenediamine-modified graphene heterojunctions with selective adsorption and electronic structure modulation for ultrasensitive room-temperature NO2 detection

Ever-increasing concerns over air quality and the newly emerged internet of things (IoT) for future environmental monitoring are stimulating the development of ultrasensitive room-temperature gas sensors, especially for nitrogen dioxide (NO₂), one of the most harmful air pollution species released round-the-clock from power plants and vehicle exhausts. Herein, tin dioxide nanorods/ethylenediamine-modified reduced graphene oxide (SnO₂/EDA-rGO) heterojunctions with selective adsorption and electronic structure modulation were engineered for highly sensitive and selective detection of NO₂ at room temperature. The modified EDA groups not only enable selective adsorption to significantly enrich NO₂ molecules around the interface but also realize a favorable modulation of SnO₂/EDA-rGO electronic structure by increasing the Fermi level of rGO, through which the sensing performance of NO₂ is synergistically enhanced. The response of the SnO₂/EDA-rGO sensor toward 1 ppm NO₂ reaches 282%, which exceeds the corresponding SnO₂/rGO sensor by a factor of 2.8. It also exhibits a low detection limit down to 100 ppb, enhanced selectivity, and rapid response/recovery kinetics. This approach to designing a novel heterojunction with significantly enhanced chemical and electric effects may shed light on the future engineering of gas-sensing materials.

Novel Graphene Oxide Nanohybrid Doped Methacrylic Acid Hydrogels for Enhanced Swelling Capability and Cationic Adsorbability

Novel versatile hydrogels were designed and composited based on covalent bond and noncovalent bond self-assembly of poly(methacrylic acid) (PMAA) networks and nanohybrids doped with graphene oxide (GO). The structures and properties of the neat PMAA and the prepared PMAA/GO hydrogels were characterized and analyzed in detail, using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, swelling and cationic absorption, etc. The swelling results showed that the water penetration follows the non-Fick transport mechanism based on swelling kinetics and diffusion theory. The swelling capacity of PMAA and composited PMAA/GO hydrogels toward pH, Na+, Ga2+, and Fe3+ was investigated; the swelling ratio was tunable between 4.44 and 36.44. Taking methylene blue as an example, the adsorption capacity of PMAA/GO hydrogels was studied. Nanohybrid doped GO not only self-associated with PMAA via noncovalent bonding interactions and had a tunable swelling ratio, but also interacted with water molecules via electrostatic repulsion, offering a pH response of both the network and dye absorption. Increases in pH caused a rise in equilibrium swelling ratios and reduced the cumulative cationic dye removal.

CsPbI3NC-Sensitized SnO2/Multiple-Walled Carbon Nanotube Self-Assembled Nanomaterials with Highly Selective and Sensitive NH3 Sensing Performance at Room Temperature

It is an effective strategy to enhance the sensitivity of semiconductor metal oxides (SMOs) being sensitized with CsPbI₃ nanocrystals (NCs) by adjusting the heterostructure between CsPbI₃NC and SMO nanomaterials. In this work, for the first time, a porous 3D multiple-walled carbon nanotube (MWCNT) network uniformly coated with SnO₂ quantum nanoparticles (QNPs) and CsPbI₃ nanocrystals were prepared via a simple solvent vapor-induced self-assembly method. The fabricated CsPbI₃NC-SnO₂QNP/MWCNT nanocomposite with vapor-induced self-assembly exhibits superior stability against the moisture as well as an excellent sensing response. The results imply that the rational design of the metal halide perovskite NC/SMO heterostructure can not only improve the stability but also meet the requirements of sensing application. The self-assembled SnO₂QNP/MWCNT can facilitate the dispersion of small-sized nanoparticles and efficaciously prevent the detachment of CsPbI₃NC. Compared with pristine SnO₂QNP and SnO₂/MWCNT sensors, the CsPbI₃NC-modified SnO₂QNP/MWCNT nanostructure exhibited a remarkable sensitivity of 39.2 for 0.2 ppm NH₃, rapid response/recovery time of 17/18 s, and excellent selectivity towards NH₃. In particular, we applied machine learning methods, including principal component analysis (PCA) and support vector machines (SVMs), to analyze the sensing performance of the CsPbI₃NC-SnO₂QNP/MWCNT sensor and found that the combined effects of CsPbI₃NC-SnO₂QNP/MWCNT heterointerfaces contributed to the improvement of selectivity of sensors. The excellent NH₃ for sub-ppm level concentration is ascribed to the high sensing activity of the CsPbI₃ NC-based heterojunction. This work may not only enrich the family of high-performance breath detection materials but also provide a good example for designing reasonable composite materials with specific properties in the field of metal halide perovskite/SMO heterojunctions.

Composites of ion-in-conjugation polysquaraine and SWCNTs for the detection of H2S and NH3 at ppb concentrations

Several different methods are established for the analysis of gases, including optical spectroscopy, photoacoustic spectroscopy as well as colorimetric and resistive sensing, the measurements systems are either too complex or have limited sensitivity. In particular, when the goal is to apply a large number of sensors in networks, it is highly desirable to have devices that are simple, have low cost and energy consumption, yet sensitive and selective to monitor analytes even in traces. Herein, we propose a new type of resistive sensor device based on a composite of single-wall carbon nanotubes and an ion-in-conjugation polymer, poly(1,5-diaminonaphthalene-squaraine), capable of detecting H2S and NH3 in air even at room temperature with a theoretical concentration limit of ∼1 ppb and ∼7 ppb, respectively. Density functional theory calculations revealed that H atoms of the analytes and O atoms of the polymer chain interact and form hydrogen bonds, and the electron withdrawal from the gas molecules by the polymer chain results in the change of its electrical conductivity. To demonstrate the feasibility of the new nanocomposites in sensing, we show the devices for monitoring food safety with good sensor stability of operation for at least 3 months of period of time.

Exploring the Silent Aspect of Carbon Nanopores

Recently, owing to the discovery of graphene, porous carbons experienced a revitalization in their explorations. However, nowadays, the focus is more on search for suitable energy advancing catalysts sensing, energy storage or thermal/light absorbing features than on separations. In many of these processes, adsorption, although not emphasized sufficiently, can be a significant step. It can just provide a surface accumulation of molecules used in other application-driving chemical or physical phenomena or can be even an additional mechanism adding to the efficiency of the overall performance. However, that aspect of confined molecules in pores and their involvement in the overall performance is often underrated. In many applications, nanopores might silently advance the target processes or might very directly affect or change the outcomes. Therefore, the objective of this communication is to bring awareness to the role of nanopores in carbon materials, and also in other solids, to scientists working on cutting-edge application of nonporous carbons, not necessary involving the adsorption process directly. It is not our intention to provide a clear explanation of the small pore effects, but we rather tend to indicate that such effects exist and that their full explanation is complex, as complex is the surface of nanoporous carbons.

Graphene and Perovskite-Based Nanocomposite for Both Electrochemical and Gas Sensor Applications: An Overview

Perovskite and graphene-based nanocomposites have attracted much attention and been proven as promising candidates for both gas (H₂S and NH₃) and electrochemical (H₂O₂, CH₃OH and glucose) sensor applications. In this review, the development of portable sensor devices on the sensitivity, selectivity, cost effectiveness, and electrode stability of chemical and electrochemical applications is summarized. The authors are mainly focused on the common analytes in gas sensors such as hydrogen sulfide, ammonia, and electrochemical sensors including non-enzymatic glucose, hydrazine, dopamine, and hydrogen peroxide. Finally, the article also addressed the stability of composite performance and outlined recent strategies for future sensor perspectives.

Stretchable, Stable, and Room-Temperature Gas Sensors Based on Self-Healing and Transparent Organohydrogels

Conductive hydrogels have emerged as promising candidate materials for fabricating wearable electronics because of their fascinating stimuli-responsive and mechanical properties. However, the inherent instability of hydrogels seriously limits their application scope. Herein, the stable, ultrastretchable (upon to 1330% strain), self-healing, and transparent organohydrogel was exploited as a novel gas-responsive material to fabricate NH₃ and NO₂ gas sensors for the first time with extraordinary performance. A facile solvent substitution method was employed to convert the unstable hydrogel into the organohydrogel with a remarkable moisture retention (avoid drying within a year), frost resistance (freezing point below -130 °C), and unimpaired mechanical and gas sensing properties. First-principles simulations were performed to uncover the mechanisms of antidrying and antifreezing effects of organohydrogels and the interactions between NH₃/NO₂ and organohydrogels, revealing the vital role of hydrogen bonds in enhancing the stability and the adsorption of NH₃/NO₂ on the organohydrogel. The organohydrogel gas sensor displayed high sensitivity, ultralow theoretical limit of detection (91.6 and 3.5 ppb for NH₃ and NO₂, respectively), reversibility, and fast recovery at room temperature. It exhibited the capabilities to work at a highly deformed state with nondegraded sensing performance and restore all the electrical, mechanical, and sensing properties after mechanical damage. The gas sensing mechanism was understood by considering the gas adsorption on functional groups, dissolution in the solvent, and the hindering effect on the transport of ions.

Microwave-Assisted Rapid Synthesis of Reduced Graphene Oxide-Based Gum Tragacanth Hydrogel Nanocomposite for Heavy Metal Ions Adsorption

Reduced graphene oxide (RGO) was synthesized in this research via Tour's method for the use of filler in the hydrogel matrix. The copolymerization of N,N-dimethylacrylamide (DMA) onto the gum tragacanth (GT) was carried out to develop gum tragacanth-cl-N,N-dimethylacrylamide (GT-cl-poly(DMA)) hydrogel using N,N'-methylenebisacrylamide (NMBA) and potassium persulfate (KPS) as cross-linker and initiator correspondingly. The various GT-cl-poly(DMA) hydrogel synthesis parameters were optimized to achieve maximum swelling of GT-cl-poly(DMA) hydrogel. The optimized GT-cl-poly(DMA) hydrogel was then filled with RGO to form reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide (GT-cl-poly(DMA)/RGO) hydrogel composite. The synthesized samples were used for competent adsorption of Hg²⁺ and Cr⁶⁺ ions. Fourier transform infrared, X-ray powder diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy were used to characterize the gum tragacanth-cl-N,N-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide hydrogel composite. The experiments of adsorption-desorption cycles for Hg²⁺ and Cr⁶⁺ ions were carried out to perform the reusability of gum tragacanth-cl-N,N-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide hydrogel composite. From these two samples, reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide exhibited high adsorption ability. The Hg²⁺ and Cr⁶⁺ ions adsorption by gum tragacanth-cl-N,N-dimethylacrylamide and reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide were best suited for pseudo-second-order kinetics and Langmuir isotherm. The reported maximum Hg²⁺ and Cr⁶⁺ ions adsorption capacities were 666.6 mg g^-1 and 473.9 mg g^-1 respectively.

Synthesis and characterization of reduced graphene oxide using the aqueous extract of Eclipta prostrata

In this study, biological deoxygenation of graphene oxide (GO) using an Eclipta prostrata phytoextract was performed via the infusion method. The presence of oxide groups on the surface of graphene and removal of oxides groups by reduction were characterized through morphological and structural analyses. Field emission scanning electron microscopy images revealed that the synthesized GO and rGO were smooth and morphologically sound. Transmission electron microscopy images showed rGO developing lattice fringes with smooth edges and transparent sheets. Atomic force microscopy images showed an increase in the surface roughness of graphite oxide (14.29 nm) compared with that of graphite (1.784 nm) due to the presence of oxide groups after oxidation, and the restoration of surface roughness to 2.051 nm upon reduction. Energy dispersive X-ray analysis indicated a difference in the carbon/oxygen ratio between GO (1.90) and rGO (2.70). Fourier-transform infrared spectroscopy spectrum revealed peak stretches at 1029, 1388, 1578, and 1630 cm^-1 for GO, and a decrease in the peak intensity after reduction that confirmed the removal of oxide groups. X-ray photoelectron microscopy also showed a decrease in the intensity of oxygen peak after reduction. In addition, thermogravimetric analysis suggested that rGO was less thermally stable than graphite, graphite oxide, and GO, with rGO decomposing after heating at temperatures ranging from room temperature to 600 °C.