Chemically deposited palladium nanoparticles on graphene for hydrogen sensor applications

Nanoribbon Yarn with Versatile Inorganic Materials

Nanomaterial-based yarns have been actively developed owing to their advantageous features, namely, high surface-area-to-volume ratios, flexibility, and unusual material characteristics such as anisotropy in electrical/thermal conductivity. The superior properties of the nanomaterials can be directly imparted and scaled-up to macro-sized structures. However, most nanomaterial-based yarns have thus far, been fabricated with only organic materials such as polymers, graphene, and carbon nanotubes. This paper presents a novel fabrication method for fully inorganic nanoribbon yarn, expanding its applicability by bundling highly aligned and suspended nanoribbons made from various inorganic materials (e.g., Au, Pd, Ni, Al, Pt, WO3, SnO2, NiO, In2O3, and CuO). The process involves depositing the target inorganic material on a nanoline mold, followed by suspension through plasma etching of the nanoline mold, and twisting using a custom-built yarning machine. Nanoribbon yarn structures of various functional inorganic materials are utilized for chemical sensors (Pd-based H2 and metal oxides (MOx)-based green gas sensors) and green energy transducers (water splitting electrodes/triboelectric nanogenerators). This method is expected to provide a comprehensive fabrication strategy for versatile inorganic nanomaterials-based yarns.

Hydrogen Sensing with Palladium-Based Materials: Mechanisms, Challenges, and Opportunities

Palladium morphologies are prominently used in Hydrogen gas sensing applications owing to their unique characteristics and properties. In this review article, Palladium nanoparticles, thin films, and alloys were designated as the scope of Palladium morphologies. The aim of this review article is to explore Hydrogen sensing using Palladium, focusing on the recent advancements in the field.. The principles underlying Hydrogen sensing mechanisms with Palladium are discussed initially, highlighting the unique properties of Palladium that make it a promising material for this purpose. Special attention is given to the surface interactions and structural modifications that influence the sensitivity and selectivity of Palladium-based sensors The study also addresses key challenges and recent innovations in the field which contribute to the enhancement of Palladium-based Hydrogen sensing capabilities. The current state of research is critically examined to identify gaps in knowledge and future research directions are highlighted. The prospects and challenges associated with the use of Palladium for Hydrogen sensing, emphasizing its pivotal role in advancing sensor technologies for Hydrogen detection are also discussed.

New palladium(II) β-ketoesterates for focused electron beam induced deposition: synthesis, structures, and characterization

We report the synthesis and characterization of new palladium(II) β-ketoesterate complexes [Pd(CH3COCHCO2R)2] with alkyl substituents R = tBu, iPr, Et. These compounds can have potential use in focused electron beam induced deposition (FEBID), which is a direct write method for the growth of structures at the nanoscale. However, it is still a major challenge to obtain deposits with a high metal content, and new precursor molecules are needed to overcome this. Single crystal X-ray diffraction, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and density-functional theory calculations were used to confirm the compounds' composition and structure. Using thermal analysis and sublimation experiments, we investigate their thermal stability and volatility. These studies show that the palladium complexes sublimate over the range 348-353 K under 10-2 mbar pressure. The electron-induced decomposition of the complex molecules in the gas phase and their thin layers on silicon substrates were analysed using electron impact mass spectrometry (EI MS) and microscopy studies (SEM/EDX). They confirm that the precursor electron-induced fragmentation depends on the molecular structure. The obtained results reveal that [Pd(CH3COCHCO2tBu)2] with cis-positioned tert-butyl groups may be a promising FEBID precursor, and we carried out preliminary deposition experiments using this compound.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Lignosulfonate-Assisted In Situ Deposition of Palladium Nanoparticles on Carbon Nanotubes for the Electrocatalytic Sensing of Hydrazine

This paper presents a novel modified electrode for an amperometric hydrazine sensor based on multi-walled carbon nanotubes (MWCNTs) modified with lignosulfonate (LS) and decorated with palladium nanoparticles (NPds). The MWCNT/LS/NPd hybrid was characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The electrochemical properties of the electrode material were evaluated using cyclic voltammetry and chronoamperometry. The results showed that GC/MWCNT/LS/NPd possesses potent electrocatalytic properties towards the electro-oxidation of hydrazine. The electrode demonstrated exceptional electrocatalytic activity coupled with a considerable sensitivity of 0.166 μA μM-1 cm-2. The response was linear from 3.0 to 100 µM L-1 and 100 to 10,000 µM L-1, and the LOD was quantified to 0.80 µM L-1. The efficacy of the modified electrode as an electrochemical sensor was corroborated in a study of hydrazine determination in water samples.

Solvated electron-induced synthesis of cyclodextrin-coated Pd nanoparticles: mechanistic, catalytic, and anticancer studies

Herein, using in situ generated solvated electrons in the reaction media, a highly time-efficient, one-pot green approach has been employed to synthesize palladium (Pd) nanoparticles (NPs) coated with a molecular assembly of α-cyclodextrin (α-CD). The appearance of a shoulder peak at 280 nm in the UV-Vis absorption spectra indicated the formation of Pd NPs, which was further confirmed from their cubic phase XRD pattern. The nanomorphology varied considerably as a function of the dose rate, wherein sphere-shaped NPs (average size ∼ 7.6 nm) were formed in the case of high dose rate electron-beam assisted synthesis, while nanoflakes self-assembled to form nanoflower-shaped morphologies in a γ-ray mediated approach involving a low dose rate. The formation kinetics of NPs was investigated by pulse radiolysis which revealed the formation of Pd-based transients by the solvated electron-induced reaction. Importantly, no interference of α-CD was observed in the kinetics of the transient species, rather it played the role of a morphology directing agent in addition to a biocompatible stabilizing agent. The catalytic studies revealed that the morphology of the NPs has a significant effect on the reduction efficiency of 4-nitrophenol to 4-aminophenol. Another important highlight of this work is the demonstration of the morphology-dependent anticancer efficacy of Pd NPs against lung and brain cancer cells. Notably, flower-shaped Pd NPs exhibited significantly higher cancer cell killing as compared to spherical NPs, while being less toxic towards normal lung fibroblasts. Nonetheless, these findings show the promising potential of Pd NPs in anticancer treatment.

Palladium nanoparticles as emerging pollutants from motor vehicles: An in-depth review on distribution, uptake and toxicological effects in occupational and living environment

Palladium nanoparticles (PdNPs) play an integral role in motor vehicles as the primary vehicle exhaust catalyst (VEC) for tackling environmental pollution. Automobiles equipped with Pd-based catalytic converters were introduced in the mid-1970s and ever since the demand for Pd has steadily increased due to stringent emission standards imposed in many developed and developing countries. However, at the same time, the increasing usage of Pd in VECs has led to the release of nano-sized Pd particles in the environment, thus, emerging as a new source of environmental pollution. The present reports in the literature have shown gradual increasing levels of Pd particles in different urban environmental compartments and internalization of Pd particles in living organisms such as plants, aquatic species and animals. Occupational workers and the general population living in urban areas and near major highways are the most vulnerable as they may be chronically exposed to PdNPs. Risk assessment studies have shown acute and chronic toxicity exerted by PdNPs in both in-vitro and in-vivo models but the underlying mechanism of PdNPs toxicity is still not fully understood. The review intends to provide readers with an in-depth account on the demand and supply of Pd, global distribution of PdNPs in various environmental matrices, their migration and uptake by living species and lastly, their health risks, so as to serve as a useful reference to facilitate further research and development for safe and sustainable technology.

Green syntheses of graphene and its applications in internet of things (IoT)-a status review

Internet of Things (IoT) is a trending technological field that converts any physical object into a communicable smarter one by converging the physical world with the digital world. This innovative technology connects the device to the internet and provides a platform to collect real-time data, cloud storage, and analyze the collected data to trigger smart actions from a remote location via remote notifications, etc. Because of its wide-ranging applications, this technology can be integrated into almost all the industries. Another trending field with tremendous opportunities is Nanotechnology, which provides many benefits in several areas of life, and helps to improve many technological and industrial sectors. So, integration of IoT and Nanotechnology can bring about the very important field of Internet of Nanothings (IoNT), which can re-shape the communication industry. For that, data (collected from trillions of nanosensors, connected to billions of devices) would be the 'ultimate truth', which could be generated from highly efficient nanosensors, fabricated from various novel nanomaterials, one of which is graphene, the so-called 'wonder material' of the 21st century. Therefore, graphene-assisted IoT/IoNT platforms may revolutionize the communication technologies around the globe. In this article, a status review of the smart applications of graphene in the IoT sector is presented. Firstly, various green synthesis of graphene for sustainable development is elucidated, followed by its applications in various nanosensors, detectors, actuators, memory, and nano-communication devices. Also, the future market prospects are discussed to converge various emerging concepts like machine learning, fog/edge computing, artificial intelligence, big data, and blockchain, with the graphene-assisted IoT field to bring about the concept of 'all-round connectivity in every sphere possible'.

Palladium Nanosheet-Based Dual Gas Sensors for Sensitive Room-Temperature Hydrogen and Carbon Monoxide Detection

Palladium has long been explored for use in gas sensors because of its excellent catalytic properties and its unique property of forming hydrides in the presence of H₂. However, pure Pd-based sensors usually suffer from low response and a relatively high limit of detection. Palladium nanosheets (PdNS) are of particular interest for gas sensing applications due to their high surface area and excellent electrical conductivity. Here, we demonstrate the design and fabrication of low-cost PdNS-based dual gas sensors for room-temperature detection of H₂ and CO over a wide concentration range. We fabricated sensors using multiwalled carbon nanotube@PdNS (MWCNT@PdNS) composites and compared their performance against pure PdNS devices for hydrogen sensing based on electrical resistive response. Devices using PdNS alone had a response and response time of 0.4% and 50 s, respectively, to 1% H₂ in air. MWCNT@PdNS (1:5 mass ratio) showed enhanced performance at a lower hydrogen concentration with a limit of detection (LOD_H2) of 5 ppm. Nearly an order of magnitude increase in response was observed on increasing the amount of MWCNT to 50 mass % in the nanocomposite, but the response fell off at low H₂ concentration. Overall, these PdNS-based sensors were found to show good repeatability, stability, and performance under humid conditions. Their response was selective for H₂ versus CH₄, CO₂, and NH₃; the response to CO was comparable in magnitude but opposite in sign to the response to H₂. Upon simultaneous exposure to equal concentrations (10 ppm each) of H₂ and CO, the response to CO was dominant. The PdNS showed high sensitivity to CO, detecting as little as 1 ppm CO in air at room temperature. The sensitivity to CO could be used either in a stand-alone room-temperature CO detector, where H₂ is known not to be present, or in combination with CO and combustible gas detectors to distinguish H₂ from other combustible gases.

Recent trends in gas sensing via carbon nanomaterials: outlook and challenges

The presence of harmful and poisonous gases in the environment can have dangerous effects on human health, and therefore portable, flexible, and highly sensitive gas sensors are in high demand for environmental monitoring, pollution control, and medical diagnosis. Currently, the commercialized sensors are based on metal oxides, which generally operate at high temperatures. Additionally, the desorption of chemisorbed gas molecules is also challenging. Hence, due to the large surface area, high flexibility, and good electrical properties of carbon nanomaterials (CNMs) such as carbon nanotubes, graphene and their derivatives (graphene oxide, reduced graphene oxide, and graphene quantum dots), they are considered to be the most promising chemiresistive sensing materials, where their electrical resistance is affected by their interaction with the analyte. Further, to increase their selectivity, nanocomposites of CNMs with metal oxides, metallic nanoparticles, chalcogenides, and polymers have been studied, which exhibit better sensing capabilities even at room temperature. This review summarizes the state-of-the-art progress in research related to CNMs-based sensors. Moreover, to better understand the analyte adsorption on the surface of CNMs, various sensing mechanisms and dependent sensing parameters are discussed. Further, several existing challenges related to CNMs-based gas sensors are elucidated herein, which can pave the way for future research in this area.

Recent Advances and Challenges of Nanomaterials-Based Hydrogen Sensors

Safety is a crucial issue in hydrogen energy applications due to the unique properties of hydrogen. Accordingly, a suitable hydrogen sensor for leakage detection must have at least high sensitivity and selectivity, rapid response/recovery, low power consumption and stable functionality, which requires further improvements on the available hydrogen sensors. In recent years, the mature development of nanomaterials engineering technologies, which facilitate the synthesis and modification of various materials, has opened up many possibilities for improving hydrogen sensing performance. Current research of hydrogen detection sensors based on both conservational and innovative materials are introduced in this review. This work mainly focuses on three material categories, i.e., transition metals, metal oxide semiconductors, and graphene and its derivatives. Different hydrogen sensing mechanisms, such as resistive, capacitive, optical and surface acoustic wave-based sensors, are also presented, and their sensing performances and influence based on different nanostructures and material combinations are compared and discussed, respectively. This review is concluded with a brief outlook and future development trends.

Thin Film and Nanostructured Pd-Based Materials for Optical H2 Sensors: A Review

In this review paper, we provide an overview of state-of-the-art Pd-based materials for optical H2 sensors. The first part of the manuscript introduces the operating principles, providing background information on the thermodynamics and the primary mechanisms of optical detection. Optical H2 sensors using thin films (i.e., films without any nanostructuring) are discussed first, followed by those employing nanostructured materials based on aggregated or isolated nanoparticles (ANPs and INPs, respectively), as well as complex nanostructured (CN) architectures. The different material types are discussed on the basis of the properties they can attribute to the resulting sensors, including their limit of detection, sensitivity, and response time. Limitations induced by cracking and the hysteresis effect, which reduce the repeatability and reliability of the sensors, as well as by CO poisoning that deteriorates their performance in the long run, are also discussed together with an overview of manufacturing approaches (e.g., tailoring the composition and/or applying functionalizing coatings) for addressing these issues.

Photothermochemical Nanoassembly of 3D Porous Graphene and Palladium Nanoparticles for High-Performance Hydrogen Detection

Hybrid materials comprising graphene and palladium nanoparticles (PdNPs) are desirable for high-performance hydrogen detection because of the high specific surface area, electron mobility, and flexibility of graphene and the high electrochemical responsivity and reversibility of PdNPs. However, obtaining hybrid materials is energy-intensive and time-consuming. Here, a facile and rapid laser photothermochemical single-step processing method to synchronously produce a nanoassembly of three-dimensional porous graphene and PdNPs from polymer films is reported. Polymers with intrinsic microporosity show high solubility in volatile solvents and miscibility with inorganic materials, allowing the fabrication of homogeneous polymer films containing Pd ligands. The films are photothermally processed using a laser to generate a nanohybrid via photoinduced thermal and chemical processes. The nanohybrid exhibits four-times-enhanced electrical conductivity compared to plain porous graphene, high crystallinity, and coherent covalent metal bonds with a homogeneous size and distribution of PdNPs in hierarchical micro/meso/macroporous graphene structures, allowing high-performance hydrogen sensing (1 ppm) with outstanding mechanical reliability, flexibility, and durability upon bending and twisting. The nanoassembly is integrated with a wireless sensing platform, and hydrogen leakage (1 ppm) is detected using a smart phone. This laser-based nanomanufacturing of the nanoassembly can potentially be applied to wearable detector production platforms in the military and industry.

Flexible fiber-shaped hydrogen gas sensor via coupling palladium with conductive polymer gel fiber

Rational design of fiber-shaped gas sensors with both excellent mechanical properties and sensing performance is of great significance for boosting future portable and wearable sensing electronics, however, it is still a challenge. Herein, we develop a novel fiber-shaped hydrogen (H₂) sensor by directly electrochemically growing palladium (Pd) sensing layer on conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) fiber electrode. This approach produces free-standing functional fiber (PEDOT:PSS@Pd) with promising mechanical features of flexibility, light weight, knittability and high mechanical strength, and good H₂ sensing performance at room temperature. The PEDOT:PSS@Pd fiber sensor exhibits short response time of 34 (± 6) s@1% and 19 (± 4) s@4% H₂ and excellent cycling stability. In addition, the fiber sensor remains good sensing behavior under different mechanical bending states, showing potential for constructing wearable sensor devices for timely H₂ leak detection. Therefore, this work has provided a smart design strategy of fiber-based gas sensor, offering an effective sensing platform and is believed to stimulate the development of wearable electronics.

Deep neural network analysis of nanoparticle ordering to identify defects in layered carbon materials

Smoothness/defectiveness of the carbon material surface is a key issue for many applications, spanning from electronics to reinforced materials, adsorbents and catalysis. Several surface defects cannot be observed with conventional analytic techniques, thus requiring the development of a new imaging approach. Here, we evaluate a convenient method for mapping such "hidden" defects on the surface of carbon materials using 1-5 nm metal nanoparticles as markers. A direct relationship between the presence of defects and the ordering of nanoparticles was studied experimentally and modeled using quantum chemistry calculations and Monte Carlo simulations. An automated pipeline for analyzing microscopic images is described: the degree of smoothness of experimental images was determined by a classification neural network, and then the images were searched for specific types of defects using a segmentation neural network. An informative set of features was generated from both networks: high-dimensional embeddings of image patches and statics of defect distribution.

A Review on Functionalized Graphene Sensors for Detection of Ammonia

Since the first graphene gas sensor has been reported, functionalized graphene gas sensors have already attracted a lot of research interest due to their potential for high sensitivity, great selectivity, and fast detection of various gases. In this paper, we summarize the recent development and progression of functionalized graphene sensors for ammonia (NH3) detection at room temperature. We review graphene gas sensors functionalized by different materials, including metallic nanoparticles, metal oxides, organic molecules, and conducting polymers. The various sensing mechanism of functionalized graphene gas sensors are explained and compared. Meanwhile, some existing challenges that may hinder the sensor mass production are discussed and several related solutions are proposed. Possible opportunities and perspective applications of the graphene NH3 sensors are also presented.

Nanoporous Silicon Thin Film-Based Hydrogen Sensor Using Metal-Assisted Chemical Etching with Annealed Palladium Nanoparticles

This article reports a nanoporous silicon (Si) thin-film-based high-performance and low-power hydrogen (H₂) sensor fabricated by metal-assisted chemical etching (MaCE). The nanoporous Si thin film treated with Pd-based MaCE showed improvement over a flat Si thin film sensor in H₂ response (ΔI/I₀ = 4.36% → 12.4% for 0.1% H₂). Furthermore, it was verified that the combination of thermal annealing of Pd and subsequent MaCE on the Si thin film synergistically enhances the H₂ sensitivity of the sensor by 65 times as compared to the flat Si thin film sensor (ΔI/I₀ = 4.36% → 285% for 0.1% H₂). This sensor also showed a very low operating power of 1.62 μW. After the thermal treatment, densely packed Pd nanoparticles agglomerate due to dewetting, which results in a higher surface-to-volume ratio by well-defined etched holes, leading to an increase in sensor response.

Hydrogen Sensing at Room Temperature Using Flame-Synthesized Palladium-Decorated Crumpled Reduced Graphene Oxide Nanocomposites

We present a unique three-dimensional palladium (Pd)-decorated crumpled reduced graphene oxide ball (Pd-CGB) nanocomposite for hydrogen (H₂) detection in air at room temperature. Pd-CGB nanocomposites were synthesized using a rapid continuous flame aerosol technique. Graphene oxide reduction and metal decoration occurred simultaneously in a high-temperature reducing jet (HTRJ) process to produce Pd nanoparticles that were below 5 nm in average size and uniformly dispersed in the crumpled graphene structure. The sensors made from these nanocomposites were sensitive over a wide range of H₂ concentrations (0.0025-2%) with response value, response time, and recovery time of 14.8%, 73 s, and 126 s, respectively, at 2% H₂. Moreover, they were sensitive to H₂ in both dry and humid conditions. The sensors were stable and recoverable after 20 cycles at 2% H₂ with no degradation associated with volume expansion of Pd. Unlike two-step methods for fabricating Pd-decorated graphene sensors, the HTRJ process enables single-step formation of Pd- and other metal-decorated graphene nanocomposites with great potential for creating various gas sensors by simple drop-casting onto low-cost electrodes.

Graphene-Based Hydrogen Gas Sensors: A Review

Graphene is a material gaining attention as a candidate for new application fields such as chemical sensing. In this review, we discuss recent advancements in the field of hydrogen gas sensors based on graphene. Accordingly, the main part of the paper focuses on hydrogen gas sensors and examines the influence of different manufacturing scenarios on the applicability of graphene and its derivatives as key components of sensing layers. An overview of pristine graphene customization methods is presented such as heteroatom doping, insertion of metal/metal oxide nanosized domains, as well as creation of graphene-polymer blends. Volumetric structuring of graphene sheets (single layered and stacked forms) is also considered as an important modifier of its effective use. Finally, a discussion of the possible advantages and weaknesses of graphene as sensing material for hydrogen detection is provided.

Computational Analysis of the Silver Nanoparticle-Human Serum Albumin Complex

Drug delivery in excess concentrations and at not-specified sites inside the human body adversely affects the body and gives rise to other diseases. Several methods have been developed to deliver the drugs in required amounts and at specific targets. Nanoparticle-mediated drug delivery is one such approach and has gained success at primary levels. The effect of nanoparticles on the human body needs important apprehension, and it has been unraveled by assessing the protein-nanoparticle interactions. Here, we have measured the impact of silver nanoparticles (AgNPs) on the human serum albumin (HSA) structure and function with the help of all-atom molecular dynamics simulations (MDS). HSA is a transport protein, and any change in the structure may obstruct its function. The post MD analyses showed that the NP interacts with HSA and the conjugated system got stabilized with time evolution of trajectories. The present investigation confirms that the AgNP interacts with HSA without affecting its tertiary and secondary structures and in turn the protein function as well. AgNP application is recommended in transporting conjugated drug molecules as it has no adverse effect on serum proteins. Since HSA is present in the circulatory system, it may open various applications of AgNPs in the biomedical field.