Polymer-Nanoparticle Hybrid Materials for Plasmonic Hydrogen Detection

Plasmonic metal nanoparticles and polymer materials have independently undergone rapid development during the last two decades. More recently, it has been realized that combining these two systems in a hybrid or nanocomposite material comprised of plasmonically active metal nanoparticles dispersed in a polymer matrix leads to systems that exhibit fascinating properties, and some first attempts had been made to exploit them for optical spectroscopy, solar cells or even pure art. In my thesis, I have applied this concept to tackle the urgent problem of hydrogen safety by developing Pd nanoparticle-based “plasmonic plastic” hybrid materials, and by using them as the active element in optical hydrogen sensors. This is motivated by the fact that hydrogen gas, which constitutes a clean and sustainable energy vector, poses a risk for severe accidents due to its high flammability when mixed with air. Therefore, hydrogen leak detection systems are compulsory in the imminent large-scale dissemination of hydrogen energy technologies. To date, however, there a several unresolved challenges in terms of hydrogen sensor performance, whereof too slow sensor response/recovery times and insufficient resistance towards deactivation by poisoning species are two of the most severe ones. In this thesis, I have therefore applied the plasmonic plastic hybrid material concept to tackle these challenges. In summary, I have (i) developed hysteresis-free plasmonic hydrogen sensors based on PdAu, PdCu and PdAuCu alloy nanoparticles; (ii) demonstrated ultrafast sensor response and stable sensor operation in chemically challenging environments using polymer coatings; (iii) introduced bulk-processed and 3D printed plasmonic plastic hydrogen sensors with fast response and high resistance against poisoning and deactivation

Palladium-based Nanoplasmonics for Ultrafast and Deactivation-Resistant Hydrogen Detection

In the hydrogen economy scenario, hHydrogen gas is ispotential to be the main energy carrier in the hydrogen economy scenario in the upcoming future. It receives much attention since the reaction with oxygen generates electricity and produces only clean waterhydrogen is attractive as energy carrier since the energy produced by its reaction with oxygen only producesleaves water as by-product. However, \ua0hHydrogen , however, is flammable when mixed within ambient air even at low concentration, i.e. above 4 vol.%. Therefore, safety systems areis mandatory to monitor and prevent any leaks. The However, existing hydrogen sensor technology today, unfortunately, has not been able to passdoes not meet the stringent future safetyperformance targets for safety sensors standard.Motivated by thise safety issuefactat, in this thesis we I exploit the localized surface plasmon resonance (LSPR) of palladium (Pd)Pd and Pd-alloy nanoparticles to buildin the quest to develop next generation optical based hydrogen sensors. The uUnique features of an optical sensor among with respect to the other types are the inherent free-of-spark-free operation (thus safer), the possibility to perform a remote readout by light and the possibility forof a multiplexing. Specifically, I PalladiumPd, however, has limitations which hinders the hydrogen sensor to meet the requirement.My thesis reportsIn this thesis I focus onreport two key aspects related to the hydrogen sensor challenge: (i) the \ua0development of the palladiumPd-alloy based nanoplasmonic sensors that are both deactivation resistant and meet the stringent response time target, and (ii) the fundamental studies onunderstanding of nanoparticle-hydrogen interactions in the presence of different coatings. the hydrogen-palladiumPd nanoparticleAs the key results, I have developed two different types of plasmonic hydrogen sensor platforms either based on a PdAuCu ternary alloy or utilizing thin polymer film coatings. They exhibit exceptional deactivation resistance towards poisoning gases like carbon monoxide or nitrogen dioxide, and they meet the most stringent sensor response time target defined by the US Department of Energy. Furthermore, I have devised generic design rules for the optimization of plasmonic hydrogen sensor detection limits based on fundamental understanding, and systematically characterized the impact of surfactant molecules widely used in colloidal synthesis of Pd nanocrystals on their interaction with hydrogen gas. All in all, . The former implementation aspect includes two different strategies to optimize the sensor: (i) Au and Cu alloying and (ii) polymer (PMMA, PTFE) coating. The later fundamental aspect covers two studies on: (i) the correlation between the absorbed hydrogen and the optical response correlation and (ii) the (de)hydrogenation of surfactant/stabilizer-coated nanoparticle.Finally, weWe \ua0managed to achieve excellent hydrogen sensor performance that meets the strict demand and we acquired deeper insight on the hydrogen sensing mechanism which is important for the sensor design. tThese findings hopefully contribute to the safety aspect ofa safer hydrogen economy safety aspect and enable wider applicationsin the future

Biomimetic route to hybrid nano-Composite scaffold for tissue engineering

Hydroxyapatite-poly(vinyl) alcohol-protein composites have been prepared by a biomimetic route at ambient conditions, aged for a fortnight at 30±2°C and given a shape in the form of blocks by thermal cycling. The structural characterizations reveal a good control over the morphology mainly the size and shape of the particles. Initial mechanical studies are very encouraging. Three biocompatibility tests, i.e., hemocompatibility, cell adhesion, and toxicity have been done from Shree Chitra Tirunal, Trivandrum and the results qualify their standards. Samples are being sent for more biocompatibility tests. Optimization of the blocks in terms of hydroxyapatite and polymer composition w.r.t the applications and its affect on the mechanical strength have been initiated. Rapid prototyping and a β-tricalcium – hydroxyapatite combination in composites are in the offing

NANOSTRUCTURED MATERIALS FOR SOLAR HYDROGEN GENERATION

Hydrogen can be considered a nonpolluting and inexhaustible energy carrier for the future. However, hydrogen is not readily available for use as a fuel. It exists in bound form with other elements (e.g. water, hydrocarbons) and as such energy is required to abstract molecular hydrogen from various feedstocks. Solar energy due to its abundance and low cost is being considered as the energy source for environmentally safe hydrogen generation. This dissertation focuses on the development and characterization of nano-structured materials for solar thermochemical hydrogen generation, on the principle that concentrated solar radiation can be employed as the high-temperature energy source for driving an endothermic hydrogen generation process. The reaction mechanism and kinetics of different solar thermochemical processes using those nano-structured materials as reactants or catalysts were investigated. The experimental works in this dissertation can be divided into two main areas. The first area is to study the properties and reactivity of in-situ generated Zn nanocrystals (NCs) for solar thermochemical Zn/ZnO water splitting cycle for hydrogen production. The particle size-resolved kinetics of Zn NCs oxidation, evaporation, and hydrolysis were studied using a tandem ion-mobility method in which the first mobility characterization size selects the NCs, whereas the second mobility characterization measures changes in mass resulting from a chemical reaction of the NCs. The second part of the dissertation is concentrated on the investigation of in-situ generated nano-sized metal particles as catalysts in liquid hydrocarbon decomposition process for hydrogen generation. Catalytic decomposition of liquid fuels (n-octane, iso-octane, 1-octene, toluene and methylcyclohexane) was achieved in a continuous tubular aerosol reactor as a model for the solar initiated production of hydrogen, and easily separable CO free carbonaceous aerosol product. The effects of fuel molecular structure and catalyst concentration on the overall hydrogen yield were studied. Using the similar aerosol catalysis idea, ignition of liquid fuels catalyzed by in-situ generated metal nanoparticles was investigated. The morphological change of catalyst particles during fuel ignition process and the catalytic ignition mechanism are discussed

Nanoplasmonic Alloy Hydrogen Sensors

The hydrogen economy proposes hydrogen gas as the main energy carrier thanks to its high energy density and the possibility to produce it in a sustainable way without CO2 emission. However, the wide flammability range of hydrogen-air mixtures dictates that hydrogen sensors will be a mandatory accessory to any appliance or vehicle fueled by hydrogen. Exploiting a phenomenon occurring at the nanoscale, a new type of hydrogen sensor based on the strong interaction of light with metal nanoparticles has rapidly developed in the past years. These so-called nanoplasmonic hydrogen sensors rely on hydride-forming metal nanoparticles that sustain localized surface plasmon resonance (LSPR); a collective oscillation of electrons in the nanoparticles induced by irradiated light. The energy at which the resonance occurs depends on the permittivity, as well as size and shape of the nanoparticles. Since both size and permittivity change significantly when a metal transforms into a metal hydride upon absorption of hydrogen, this effect can be used to detect it. To this date, palladium (Pd) has been the prototype material for both fundamental studies related to hydrogen sorption mechanisms in metals and in next-generation hydrogen detection devices across all sensing platforms. Specifically for the hydrogen detection, however, pure Pd does not satisfy the required sensing performance standard due to its inherent hysteresis during hydrogen absorption and desorption and slow kinetics. Furthermore it is also prone to deactivation by species like carbon monoxide and nitric oxides.To address these limitations, in this thesis a new class of plasmonic hydrogen sensors based on noble metal alloy nanoparticles comprised of Pd, Gold (Au) and Copper (Cu) is explored. To enable such sensors, we first developed a nanofabrication method to produce alloy nanoparticles with precise control of their composition, size and shape. Investigating the fundamental properties of these alloy systems upon interaction with hydrogen, we found a universal correlation between the amount of hydrogen absorbed and the optical response, independent of alloy composition. Moreover, we demonstrated how segregation of Au atoms to surface of PdAu nanoparticles can be measured as a distinct change in the plasmonic response. Focusing on the optical hydrogen sensor application, we then studied in detail the performance of various PdAu, PdCu and PdAuCu alloys, as well as the use of thin polymer selective membrane coatings to prevent sensor deactivation by poisoning gases. As the main result, we created sensors with hysteresis-free sub-second response with sub-5 ppm sensitivity that meet or exceed stringent performance targets. To push the concept closer to application, we also demonstrated the integration of alloy nanoparticles with optical fibers for hydrogen sensing

Recent Advances in Optical Hydrogen Sensor including Use of Metal and Metal Alloys: A Review

Optical sensing technologies for hydrogen monitoring are of increasing importance in connection with the development and expanded use of hydrogen and for transition to the hydrogen economy. The past decades have witnessed a rapid development of optical sensors for hydrogen monitoring due to their excellent features of being immune to electromagnetic interference, highly sensitive, and widely applicable to a broad range of applications including gas sensing at the sub-ppm range. However, the selection of hydrogen selective metal and metal alloy plays an important role. Considering the major advancements in the field of optical sensing technologies, this review aims to provide an overview of the recent progress in hydrogen monitoring. Additionally, this review highlights the sensing principles, advantages, limitations, and future development

21st Century Nanostructured Materials

Nanostructured materials (NMs) are attracting interest as low-dimensional materials in the high-tech era of the 21st century. Recently, nanomaterials have experienced breakthroughs in synthesis and industrial and biomedical applications. This book presents recent achievements related to NMs such as graphene, carbon nanotubes, plasmonic materials, metal nanowires, metal oxides, nanoparticles, metamaterials, nanofibers, and nanocomposites, along with their physical and chemical aspects. Additionally, the book discusses the potential uses of these nanomaterials in photodetectors, transistors, quantum technology, chemical sensors, energy storage, silk fibroin, composites, drug delivery, tissue engineering, and sustainable agriculture and environmental applications

Morphological characterization and physio-chemical properties of nanoparticle - review

The discovery by researchers that the physio-chemical properties of a substance can be influenced by size led to a realization of the importance of Nano particles. Due to its excellent characteristics, these materials have been a source of interest for researchers in multidisciplinary fields. The morphological features of nanoparticles always garner prodigious attention because of the influence morphology has over most of the Nanoparticles’ properties. This review provides insight to the morphological characterization and physio-chemical of its properties

Nanoplasmonic Spectroscopy of Single Nanoparticles Tracking Size and Shape Effects in Pd Hydride Formation

Localized surface plasmon resonance (LSPR) is a phenomenon of collective oscillation of conduction electrons in metal nanoparticles smaller than the wavelength of light that is used for its excitation. Plasmonic metal nanoparticles are able to confine light to extremely small volumes around them, i.e. below the diffraction limit. This gives rise to strongly localized and enhanced electromagnetic fields in so-called “hot spots” of the plasmonic nanoparticle. These hot spots usually correspond to the edges, sharp corners or tips of monomer structures, and, in case of coupled multimer arrangements, to the antenna junctions. Plasmonic hot spots are highly advantageous for sensing, since any object that is inserted there will influence the optical resonance of the system via coupling to the local field. Placing a well-defined catalytic nanoobject in the hot spot of a plasmonic nanoantenna offers thus unique possibilities to obtain detailed information about the role of specific features (e.g. facets, size, shape or relative abundance of low-coordinated sites, etc.) of that particle for its functionality/activity at the single particle level. Consequently, there is an increasing interest to use plasmonic antennas as a tool to investigate catalytic processes in/on single functional nanomaterials in situ. Single particle measurements are possible with the use of dark-field scattering spectroscopy, since plasmonic nanoparticles efficiently scatter light and are easily observable in the dark-field microscope. In this context, this work was dedicated to: 1) Development of a fabrication method for making plasmonic nanoantenna structures with the possibility to place a nanoparticle of interest (catalyst) in the hot spot of the antenna. 2) Investigation of the role of size and shape in hydride formation thermodynamics of wet-chemically synthesized single palladium (Pd) nanocrystals. The latter was possible by attaching the Pd nanocrystal to a plasmonic nanoantenna (gold sphere) by means of electrostatic self-assembly. The role of size was investigated for Pd nanocubes ranging from 20 to 50 nm. The role of shape was considered by modulating the Pd nanocrystal shape from cube to rod to octahedron