Graphene Loading with Polypyrrole Nanoparticles for Trace-Level Detection of Ammonia at Room Temperature

Scalable WS2-Graphene Hybrids for Ultralow NO2 Concentration Detection

This work presents a facile approach for fabricating hybrid heterostructures of tungsten disulfide (WS2), synthesized via atmospheric pressure chemical vapor deposition (APCVD) and commercial graphene. A simple airbrushing technique, with nitrogen (N2) as the carrier gas, was employed to fabricate the sensors. The morphological and structural characterizations of the hybrid material revealed a sheet-like synthesis of edge-enriched 2D WS2 decorated with multilayer graphene nanomaterial. The gas-sensing properties of the pristine and hybrid materials were evaluated for nitrogen dioxide (NO2) at various operating temperatures. The hybrid sensor with a WS2 to graphene ratio of 3:1 demonstrated exceptional sensitivity to ultralow NO2 concentrations (10 ppb) at a remarkably low operating temperature of 100 °C, outperforming both the graphene and WS2 counterparts. Additionally, the sensor's responses to CO, H2, C6H6, and NH3 were examined to assess its selectivity. The sensor was tested under different relative humidity conditions (RH at 25 °C; 25%, 50%, and 75%). The sensor response nearly doubled at RH = 50%, highlighting its potential for practical applications in selective NO2 detection. The sensor responses eventually reached saturation at 75% RH. In addition, the manuscript provides a detailed discussion of the NO2 gas sensing mechanism.

Ferrocene-decorated graphene nanosheets built by edge-to-face π-π interaction for room temperature ppb-level NO sensing

The development of materials toward ppb-level nitric oxide (NO) sensing at room temperature remains in high demand for the monitoring of respiratory inflammatory diseases. In order to find an iron-containing molecule without steric hindrance to combine with graphene for room temperature NO gas sensing, here a supramolecular assembly of ferrocene (Fc) and reduced graphene oxide (rGO) was designed and prepared for NO sensing. The assembly of Fc/rGO was characterized using FT-IR, TEM, and XPS measurements. The Fc/rGO-based sensors exhibited superior NO sensing properties at room temperature including high response (Ra/Rg = 1.73, 1 ppm), high selectivity against other exhaled gases, reliable repeatability and stability (less than 4 % decrease after 40 days). A practical limit of detection (LOD) of 200 ppb was achieved. The theoretical simulation demonstrates that ferrocene is assembled via π-π interaction with rGO in edge-to-face configuration which provides relatively lower energy than face-to-face configuration does for the whole assembly. It was first verified that the enhanced adsorption capacity and the charge transfer between NO and Fc/rGO would result in improvement of the assembly's sensitivity toward NO after ferrocene was assembled with graphene. This work provides a fresh approach of anchoring iron on graphene for gas sensing via supramolecular methods.

Regulation of PPy Growth States by Employing Porous Organic Polymers to Obtain Excellent Microwave Absorption Performance

Regulating the different growth states of polypyrrole (PPy) is a key strategy for obtaining PPy composites with high electromagnetic wave (EMW) absorption properties. This work finds that the growth states of PPy is regulated by controlling the amount of pyrrole added during the preparation of composites, so as to regulate the development of conductive networks to obtain excellent EMW absorption performance. The POP/PPy-200 composite achieves an effective absorption bandwidth (EAB) of 6.24 GHz (11.76-18.00 GHz) at a thickness of only 2.34 mm, covering 100% of the Ku band. The minimum reflection loss of -73.05 dB can be demonstrated at a thickness of only 2.29 mm, while at the same time showing an EAB of 5.96 GHz to meet the requirements of "thin", "light", "wide", and "strong". Such excellent EMW absorption performance is attributed to the conductive loss caused by the regulation of the growth states of PPy and the polarization loss caused by the heterostructure. This work also addresses the key challenge that porous organic polymers (POPs) cannot be applied to EMW absorption due to poor conductivity and providing new insights into the candidates for EMW absorbing materials.

Wide-range and high-accuracy wireless sensor with self-humidity compensation for real-time ammonia monitoring

Real-time and accurate biomarker detection is highly desired in point-of-care diagnosis, food freshness monitoring, and hazardous leakage warning. However, achieving such an objective with existing technologies is still challenging. Herein, we demonstrate a wireless inductor-capacitor (LC) chemical sensor based on platinum-doped partially deprotonated-polypyrrole (Pt-PPy+ and PPy0) for real-time and accurate ammonia (NH3) detection. With the chemically wide-range tunability of PPy in conductivity to modulate the impedance, the LC sensor exhibits an up-to-180% improvement in return loss (S11). The Pt-PPy+ and PPy0 shows the p-type semiconductor nature with greatly-manifested adsorption-charge transfer dynamics toward NH3, leading to an unprecedented NH3 sensing range. The S11 and frequency of the Pt-PPy+ and PPy0-based sensor exhibit discriminative response behaviors to humidity and NH3, enabling the without-external-calibration compensation and accurate NH3 detection. A portable system combining the proposed wireless chemical sensor and a handheld instrument is validated, which aids in rationalizing strategies for individuals toward various scenarios.

A highly stable full-polymer electrochemical deionization system: dopant engineering & mechanism study

Electrochemical deionization (ECDI) has emerged as a promising technology for water treatment, with faradaic ECDI systems garnering significant attention due to their enhanced performance potential. This study focuses on the development of a highly stable and efficient, full-polymer (polypyrrole, PPy) ECDI system based on two key strategies. Firstly, dopant engineering, involving the design of dopants with a high charge/molecular weight (MW) ratio and structural complexity, facilitating their effective integration into the polymer backbone. This ensures sustained contribution of strong negative charges, enhancing system performance, while the bulky dopant structure promotes stability during extended operation cycles. Secondly, operating the system with well-balanced charges between deionization and concentration processes significantly reduces irreversible reactions on the polymer, thereby mitigating dopant leakage. Implementing these strategies, the PPy(PSS)//PPy(ClO4) (PSS: polystyrene sulfonate) system achieves a high salt removal capacity (SRC) of 48 mg g-1, an ultra-low energy consumption (EC) of 0.167 kW h kgNaCl-1, and remarkable stability, with 96% SRC retention after 104 cycles of operation. Additionally, this study provides a detailed degradation mechanism based on pre- and post-cycling analyses, offering valuable insights for the construction of highly stable ECDI systems with superior performance in water treatment applications.

Electroactive polylactic acid nanofiber multilayer membranes as "Green" flexible electrode for supercapacitor

Against the backdrop of the post-COVID-19 era, the demand for masks has become increasingly steady, discarded masks have brought about new environmental problems due to the lack of effective means of disposal as well as recycling mechanisms. To solve this problem, we make secondary use of discarded polylactic acid (PLA) masks. The nanofiber multilayer membranes PLA/PDA/GO/PPy were synthesized by layer-by-layer self-assembly for flexible supercapacitors (SCs). The multiple coating on PLA significantly increases the capacitive performance. Optimization of the PLA/PDA/GO/PPy demonstrates capacitance up to 1331 mF cm-2. Symmetric aqueous SCs using PLA/PDA/GO/PPy electrodes show higher energy density than other literature-reported SCs based on nanofiber multilayer membranes. In addition, we also explored the effects of discarded PLA/PDA/GO/PPy on the growth of ryegrass and canola in the soil. The exceptional combination of remarkable electrochemical properties and excellent environmental friendliness makes the PLA membrane promising for supercapacitors.

Nitrogen-doped carbon nano-onions/polypyrrole nanocomposite based low-cost flexible sensor for room temperature ammonia detection

One of the frontier research areas in the field of gas sensing is high-performance room temperature-based novel sensing materials, and new family of low-cost and eco-friendly carbon nanomaterials with a unique structure has attracted significant attention. In this work, we propose a novel low-cost flexible room temperature ammonia gas sensor based on nitrogen-doped carbon nano-onions/polypyrrole (NCNO-PPy) composite material mounted low-cost membrane substrate was synthesized by combining hydrothermal and in-situ chemical polymerization methods. The proposed flexible sensor revealed high sensing performance when employed as the sensing material for ammonia detection at room temperature. The NCNO-PPy ammonia sensor exhibited 17.32% response for 100 ppm ammonia concentration with a low response time of 26 s. The NCNO-PPy based flexible sensor displays high selectivity, good repeatability, and long-term durability with 1 ppm as the lower detection limit. The proposed flexible sensor also demonstrated remarkable mechanical robustness under extreme bending conditions, i.e., up to 90° bending angle and 500 bending cycles. This enhanced sensing performance can be related to the potential bonding and synergistic interaction between nitrogen-doped CNOs and PPy, the formation of defects from nitrogen doping, and the presence of high reactive sites on the surface of NCNO-PPy composites. Additionally, the computational study was performed on optimized NCNO-PPy nanocomposite for both with and without NH3 interaction. A deeper understanding of the sensing phenomena was proposed by the computation of several electronic characteristics, such as band gap, electron affinity, and ionization potential, for the optimized composite.

Designing State-of-the-Art Gas Sensors: From Fundamentals to Applications

Gas sensors are crucial in environmental monitoring, industrial safety, and medical diagnostics. Due to the rising demand for precise and reliable gas detection, there is a rising demand for cutting-edge gas sensors that possess exceptional sensitivity, selectivity, and stability. Due to their tunable electrical properties, high-density surface-active sites, and significant surface-to-volume ratio, nanomaterials have been extensively investigated in this regard. The traditional gas sensors utilize homogeneous material for sensing where the adsorbed surface oxygen species play a vital role in their sensing activity. However, their performance for selective gas sensing is still unsatisfactory because the employed high temperature leads to the poor stability. The heterostructures nanomaterials can easily tune sensing performance and their different energy band structures, work functions, charge carrier concentration and polarity, and interfacial band alignments can be precisely designed for high-performance selective gas sensing at low temperature. In this review article, we discuss in detail the fundamentals of semiconductor gas sensing along with their mechanisms. Further, we highlight the existed challenges in semiconductor gas sensing. In addition, we review the recent advancements in semiconductor gas sensor design for applications from different perspective. Finally, the conclusion and future perspectives for improvement of the gas sensing performance are discussed.

3D Temperature-Controlled Interchangeable Pattern for Size-Selective Nanoparticle Capture

Patterned surfaces with distinct regularity and structured arrangements have attracted great interest due to their extensive promising applications. Although colloidal patterning has conventionally been used to create such surfaces, herein, we introduce a novel 3D patterned poly(N-isopropylacrylamide) (PNIPAM) surface, synthesized by using a combination of colloidal templating and surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) polymerization. In order to investigate the temperature-driven 3D morphological variations at a lower critical solution temperature (LCST) of ∼32 °C, multifaceted characterization techniques were employed. Atomic force microscopy confirmed the morphological transformations at 20 and 40 °C, while water contact angle measurements, upon heating, revealed distinct trends, offering insights into the correlation between surface wettability and topography adaptations. Moreover, quartz crystal microbalance with dissipation monitoring and electrochemical measurements were employed to detect the topographical adjustments of the unique hollow capsule structure within the LCST. Tests using different sizes of PSNPs shed light on the size-selective capture-release potential of the patterned PNIPAM, accentuating its biomimetic open-close behavior. Notably, our approach negates the necessity for expensive proteins, harnessing temperature adjustments to facilitate the noninvasive and efficient reversible capture and release of nanostructures. This advancement hopes to pave the way for future innovative cellular analysis platforms.

Enhanced CO2 Sensing by Oxygen Plasma-Treated Perovskite-Graphene Nanocomposites

Carbon dioxide (CO2) is a major greenhouse gas responsible for global warming and climate change. The development of sensitive CO2 sensors is crucial for environmental and industrial applications. This paper presents a novel CO2 sensor based on perovskite nanocrystals immobilized on graphene and functionalized with oxygen plasma treatment. The impact of this post-treatment method was thoroughly investigated using various characterization techniques, including Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The detection of CO2 at parts per million (ppm) levels demonstrated that the hybrids subjected to 5 min of oxygen plasma treatment exhibited a 3-fold improvement in sensing performance compared to untreated layers. Consequently, the CO2 sensing capability of the oxygen-treated samples showed a limit of detection and limit of quantification of 6.9 and 22.9 ppm, respectively. Furthermore, the influence of ambient moisture on the CO2 sensing performance was also evaluated, revealing a significant effect of oxygen plasma treatment.

Enhancement of NO2 Gas Sensing Properties of Polypyrrole by Polarization Doping with DBS: Experimental and DFT Studies

A new technique of polarization doping was adopted to improve NO2 gas sensing properties of the polypyrrole (PPy) sensor. PPy nanosheets polarization doped with sodium dodecyl benzenesulfonate (SDBS) were synthesized by low-temperature polymerization. The semiagglomerated PPy nanosheets were well-dispersed and a large specific surface areas due to the introduction of dodecyl benzenesulfonate (DBS). The DBS doped PPy sensor shows excellent NO2 sensing performance. Polarization of sulfonate ions to PPy enhanced the adsorption ability of NO2 with the synergistic effect of NO2. The adsorption energy (-0.676 eV) and electron transfer (0.521 |e|) of PPy to NO2 increased greatly after doping. An unoccupied electron state is observed in the valence band electron structure of PPy/DBS after the adsorption of NO2 by calculations of Density Functional Theory (DFT). The intermolecular synergy between NO2 and PPy/DBS causes a strong polarization, resulting in a high polarization potential, which enhances the NO2 sensing performance of PPy sensor. It is of great significance to develop NO2 detection device based on PPy that works at room temperature.

Silver Decorated and Graphene Wrapped Polypyrrole@Ni(OH)2 Quaternary Nanocomposite for High Performance Energy Storage Devices

In this work, silver (Ag) anchored over graphene (GN) wrapped polypyrrole (PPy)@ nickel hydroxide (Ni(OH)₂) nanocomposites were synthesized through a combination of oxidative polymerization and hydrothermal processes. The synthesized Ag/GN@PPy-Ni(OH)₂ nanocomposites were characterized for their morphological characteristics by field emission scanning electron microscopy (FESEM), while the structural investigations were done by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The FESEM studies showed Ni(OH)₂ flakes and silver particles attached over the surface of PPy globules, along with the presence of GN sheets and spherical silver particles. The structural analysis also showed the presence of constituents, i.e., Ag, Ni(OH)₂, PPy, GN, and their interaction, therefore vouching that the synthesis protocol is efficacious. The electrochemical (EC) investigations were done in potassium hydroxide (1 M KOH) using a three electrode setup. The quaternary Ag/GN@PPy-Ni(OH)₂ nanocomposite electrode showed the highest specific capacity of 237.25 C g^-1. The highest electrochemical performance of the quaternary nanocomposite is associated with the synergistic/additional effect of PPy, Ni(OH)₂, GN, and Ag. The assembled supercapattery with Ag/GN@PPy-Ni(OH)₂ as a positive and activated carbon (AC) as a negative electrode displayed eminent energy density of 43.26 Wh kg^-1 with the associated power density of 750.00 W kg^-1 at a current density of 1.0 A g^-1. The cyclic stability of the supercapattery (Ag/GN@PPy-Ni(OH)₂//AC), comprising a battery-type electrode, displayed a high cyclic stability of 108.37% after 5500 cycles.

Octahedral Molybdenum Iodide Clusters Supported on Graphene for Resistive and Optical Gas Sensing

This paper reports for the first time a gas-sensitive nanohybrid based on octahedral molybdenum iodide clusters supported on graphene flakes (Mo₆@Graphene). The possibility of integrating this material into two different transducing schemes for gas sensing is proposed since the nanomaterial changes both its electrical resistivity and optical properties when exposed to gases and at room temperature. Particularly, when implemented in a chemoresistive device, the Mo₆@Graphene hybrid showed an outstanding sensing performance toward NO₂, revealing a limit of quantification of about 10 ppb and excellent response repeatability (0.9% of relative error). While the Mo₆@Graphene chemoresistor was almost insensitive to NH₃, the use of an optical transduction scheme (changes in photoluminescence) provided an outstanding detection of NH₃ even for a low loading of Mo₆. Nevertheless, the photoluminescence was not affected by the presence of NO₂. In addition, the hybrid material revealed high stability of its gas sensing properties over time and under ambient moisture. Computational chemistry calculations were performed to better understand these results, and plausible sensing mechanisms were presented accordingly. These results pave the way to develop a new generation of multi-parameter sensors in which electronic and optical interrogation techniques can be implemented simultaneously, advancing toward the realization of highly selective and orthogonal gas sensing.

Recent Advances in Graphene-Based Nanocomposites for Ammonia Detection

The increasing demand to mitigate the alarming effects of the emission of ammonia (NH3) on human health and the environment has highlighted the growing attention to the design of reliable and effective sensing technologies using novel materials and unique nanocomposites with tunable functionalities. Among the state-of-the-art ammonia detection materials, graphene-based polymeric nanocomposites have gained significant attention. Despite the ever-increasing number of publications on graphene-based polymeric nanocomposites for ammonia detection, various understandings and information regarding the process, mechanisms, and new material components have not been fully explored. Therefore, this review summarises the recent progress of graphene-based polymeric nanocomposites for ammonia detection. A comprehensive discussion is provided on the various gas sensor designs, including chemiresistive, Quartz Crystal Microbalance (QCM), and Field-Effect Transistor (FET), as well as gas sensors utilising the graphene-based polymer nanocomposites, in addition to highlighting the pros and cons of graphene to enhance the performance of gas sensors. Moreover, the various techniques used to fabricate graphene-based nanocomposites and the numerous polymer electrolytes (e.g., conductive polymeric electrolytes), the ion transport models, and the fabrication and detection mechanisms of ammonia are critically addressed. Finally, a brief outlook on the significant progress, future opportunities, and challenges of graphene-based polymer nanocomposites for the application of ammonia detection are presented.

Metal loaded nano-carbon gas sensor array for pollutant detection. NANOTECHNOLOGY 2022;33:195501. [PMID: 35073524 DOI: 10.1088/1361-6528/ac4e43]

Many research works report a sensitive detection of a wide variety of gas species. However, their in-lab detection is usually performed by using single gases and, therefore, selectivity often remains an unsolved issue. This paper reports a four-sensor array employing different nano-carbon sensitive layers (bare graphene, SnO₂@Graphene, WO₃@Graphene, and Au@CNTs). The different gas-sensitive films were characterised via several techniques such as FESEM, TEM, and Raman. First, an extensive study was performed to detect isolated NO₂, CO₂, and NH₃molecules, unravelling the sensing mechanism at the operating temperatures applied. Besides, the effect of the ambient moisture was also evaluated. Afterwards, a model for target gas identification and concentration prediction was developed. Indeed, the sensor array was used in mixtures of NO₂and CO₂for studying the cross-sensitivity and developing a calibration model. As a result, the NO₂detection with different background levels of CO₂was achieved with anR²of 0.987 and an RMSE of about 22 ppb.

Polypyrrole and a polypyrrole/nickel oxide composite – single-walled carbon nanotube enhanced photocatalytic activity under visible light

A novel NiO/PPy/SWCNT composite for removal of organic dyes with an emphasis on the effect of photocatalytic charge carrier transport and photoluminescence properties.