Single nanoparticle catalysis
Nanoparticles are the most important industrial catalysts and heterogeneity is a general feature among them. Recently, owing to the fascinating advances of shape-selected nanocrystal synthesis, particles with well-controlled size, shape and chemical composition have become available. Yet, even with shape-selection, structural and compositional heterogeneity prevails at the individual particle level. Therefore, even in ensembles of shape-selected nanoparticles, the sample heterogeneity problem cannot be completely avoided. This is hampering significantly the generation of deeper understanding of how catalyst particle size, shape and composition affect its activity and selectivity, as these parameters directly control the catalytic performance by determining which surface sites that are exposed to the reactants. Assessing the state, activity and selectivity of individual nanoparticles with high resolution is therefore vital to the development of efficient catalysts. Moreover, operating experimentally at the level of a single nanoparticle facilitates a unique and direct link between experiment and electronic structure-based theory. Therefore, in the ERC StG project SINCAT and the Knut and Alice Wallenberg Foundation project Single Particle Catalysis in Nanoreactors, we will develop an experimental platform to study individual catalyst nanoparticle in operando by combining plasmonic nanospectroscopy, mass spectrometry and fluorescence microscopy with nanofluidics. The KAW project is a team effort coordinated by us and carried out in collaboration with the groups of Fredrik Westerlund, Kasper Moth-Poulsen, Paul Erhart, Hanna Härelind, Henrik Sundén and Anders Hellman at the Biology, Chemistry and Physics Departments at Chalmers.
Hydrogen metal interactions at the nanoscale and hydrogen sensors
In a hydrogen economy fossil fuels are replaced by hydrogen as the clean and sustainable energy vector. For this scenario to become reality the development of safe, cost-effective, and practical means of producing, storing but also detecting hydrogen for safety reasons is crucial. The latter is of high urgency due to the market introduction of hydrogen powered fuel cell cars by, for example, Toyota and Hyundai, as well as the progress made in installing a hydorgen fuel station infrastructure in the World, in Europe and Sweden. Specifically, cheap, reliable hydrogen sensors are important because hydrogen in air, at concentrations above 4% is highly flammable, and above 18.3 % highly explosive. We exploit the optical changes in metal hydrides upon hydrogen sorption in combination with plasmonic antennas to develop efficient hydrogen sensing schemes. The optical detection of hydrogen is attractive because it does not involve any current leads, which makes it intrinsically safe as no sparks can be generated. In response to this challenge, we explore nanoplasmoinc sensing based solutions for next generation hydrogen sensors within the SSF RMA11-0037 project Functional Electromagnetic Metamaterials and Optical Sensing.
Nanoplasmonic gas sensors
Ensuring a healthy and livable urban environment is a priority all over the world due to rapidly progressing urbanization. In cities, high concentrations of ground level emissions, mainly from combustion processes and transportation, cause alarming damage to both flora and fauna and human health. Consequently, a technological breakthrough enabling equally accurate but mobile, simple and spatially highly resolved air quality monitoring devices is urgently needed. Together with our industry partner Insplorion AB, we are developing a miniaturized and portable air pollutant sensor device based on optical plasmonic nanosensor technology. These efforts are funded by the Swedish Foundation for Strategic Environmental Research via their Mistra Innovation Programme.
Nanoantenna-enhanced photocatalysis by optical absorption engineering
We explore combinations of different metals in heterometallic plasmonic nanoantenna arrangements for optical absorption engineering. Since we are interested in the hot electrons generated by light absorption in these systems as mediators for catalytic reactions, we combine the strong surface plasmon excitations in Gold and Silver with the intrinsic catalytic activity of other metals. The latter are typically also characterized by large optical losses (=large absorption) at UV and visible frequencies due to their intrinsic electronic structure. By tailoring the mutual coupling between antenna elements consisting of different metals with different function we can engineer and significantly enhance light absorption in an element of choice and, consequently, boost hot electron formation to drive a catalytic reaction. This research is funded by my Swedish Research Council project 2014-4956.
In this project, funded by the Swedish Foundation for Strategic Research (SSF RMA15-0052 project Plastic Plasmonics) we are developing a new class of materials – Plastic Plasmonic Hybrids. They consist of plasmonic nanoparticle arrangements with tailored structural, optical and chemical properties, which are dispersed at the nanoscale in a polymer matrix for ease of processing into real devices by 3D printing or melt processing. In this way this project strives to deliver a breakthrougs for commercially viable functional plasmonic nanomaterials and their large scale processing into cheap devices. This project, coordinated by us, is a collaboration with the groups of Christian Müller, Kasper Moth-Poulsen, Paul Erhart and Anders Hellman at the Chemistry and Physics Departments at Chalmers.
Heterogeneous catalyst sintering and deactivation
Metal nanoparticles dispersed on high-surface-area support materials are widely used as catalysts in chemical synthesis, energy conversion, and environmental cleanup applications. The excess surface energy due to the large surface area of the catalyst nanoparticles renders them metastable, which means that they tend to coalesce into fewer but larger particles upon thermal activation. This process is known as catalyst sintering and it is a major cause of catalyst deactivation due to the loss of active catalyst surface area. The consequence is billions of dollars of extra cost associated with catalyst regeneration and renewal. Catalyst sintering also has a severe impact on the environment by, for example, deteriorating exhaust-cleaning catalysts in vehicles and increasing the use of raw materials and energy. We apply the INPS and other experimental techniques such as transmission electron microscopy to understand sintering mechanisms of catalyst nanoparticles and how metal-support interactions influence the latter. These efforts are a collaboration with the Competence Center for Catalysis at Chalmers.
Nanoplasmonic sensing for materials science applications
We develop and exploit nanoplasmonic sensing or “plasmonic nanospectroscopy” to probe a specific chemical or physical process of interest in a functional nanomaterial . The key benefits of using plasmonic nanoantennas as in situ probes for this purpose are their flexibility in terms of applicability to very different material systems and to harsh environments, the relative simplicity of the necessary optical and general experimental “hardware”, and their high local sensitivity at the nanoscale. Moreover, nanoplasmonic sensing employs low-power optical readout, which basically makes it non-invasive with minimal impact on the studied processes. Our “workhorse” is the NanoPlasmonic Sensing (NPS) platform, which also constitutes the patented proprietary technology of our spin-off company Insplorion AB. For the time being we specifically apply NPS to investigate the glass transition in thin polymer films used for organic photovoltaic devices (collaboration with the Müller group at Chalmers) and to characterize CO2 adsorption in micro and mesoporous materials for CCS applications (collaboration with Akzo Nobel and with Prof. Niklas Hedin at Stockholm University and the Berzelii Center EXSELENT).
Fundamental nanoplasmonics of new materials
Localized Surface Plasmon Resonances (LSPRs) are collective electronic oscillations that can be resonantly excited by external electric fields in any metallic nanoparticle. Traditionally, the focus has been almost entirely on Gold and Silver due to their favorable electronic properties at near-visible frequencies. We are specifically interested in mapping and understanding, at the fundamental level, how the significantly different bulk dielectric properties of other metals (compared to the classics Silver and Gold) as well as metal alloys, are reflected in the plasmonic response of their nanoparticles. As one interesting application of the above efforts we utilize the LSPR in a variety of metals to probe physical and chemical processes in the bulk or directly on the surface of the particles by using the LSPR as readout in what we coined “direct nanoplasmonic sensing” experiments.
Size and shape dependence of nanoparticle – biomolecule interactions during biocorona formation
Biomolecules such as proteins immediately adsorb on the surface of nanoparticles upon their exposure to a biological environment. The formed adlayer is commonly referred to as a biomolecule corona (biocorona) and defines directly the biological activity and toxicity of the nanoparticle. Therefore, it is essential to understand in detail the biocorona formation process, and how it is governed by parameters like composition of the biological environment, and nanoparticle size, shape and faceting. We deploy tailored surface-associated nanostrcutures with integrated plasmonic sensing function to assess the role of nanoparticle size and shape on the biocorona formation process as part of our efforts in the Mistra Environmental Nanosafety project funded by the Swedish Foundation for Strategic Environmental Research.