Approaches to Mitigate Metal Catalyst Deactivation in Solid Oxide Fuel Cell (SofC) Fuel Electrodes

While Ni/YSZ cermets have been used successfully in SOFCs, they also have several limitations, thus motivating the use of highly conductive ceramics to replace the Ni components in SOFC anodes. Ceramic electrodes are promising for use in SOFC anodes because they are expected to be less susceptible to sintering and coking, be redox stable, and be more tolerant of impurities like sulfur. In this thesis, for catalytic studies, the infiltration procedure has been used to form composites which have greatly simplified the search for the best ceramics for anode applications. In the development of ceramic fuel electrodes for SOFC, high performance can only be achieved when a transition metal catalyst is added. Because of the high operating temperatures, deactivation of the metal catalyst by sintering and/or coking is a severe problem. In this thesis, two approaches aimed at mitigating metal catalyst deactivation which was achieved by: 1) designing a catalyst that is resistant to coking and sintering and 2) developing a new method for catalyst deposition, will be presented. The first approach involved synthesizing a self-regenerating, smart catalyst, in which Co, Cu, or Ni were inserted into the B-site of a perovskite oxide under oxidizing conditions and then brought back to the surface under reducing conditions. This restores lost surface area of sintered metal particles through an oxidation/reduction cycle. Results will be shown for each of the metals, as well as for Cu-Co mixed metal systems, which are found to exhibit good tolerance to carbon deposition and interesting catalytic properties. The second strategy involves depositing novel Pd@CeO2 core-shell nanostructure catalysts onto a substrate surface which had been chemically modified to anchor the nanoparticles. The catalyst deposited onto the chemically modified, hydrophobic surface is shown to be uniform and well dispersed, and exhibit excellent thermal stability to temperatures as high as 1373 K. Similar metal catalyst deposition method was also employed to access their suitability for use in SOFC anodes

Synthesis and characterization of surface engineered nanomaterials via catechol derivatives

Department of Chemical EngineeringAll nanomaterials exhibit large surface to volume ratio in common and their surfaces have great influence with physicochemical properties of them. Therefore, surface engineering of nanomaterials is key to the utilization of unique nanomaterials properties and flexible strategies for deign of advanced materials. In this respect, catechol based nanocoating have been significantly attracted for application of nanocrystals and functionalization of substrates because of its adaptability to universal surface and high affinity in harsh condition. This dissertation demonstrates fabrication and characterization of nanocoating through amine mediated redox modulation of catechol. Synthetic mechanism of the nanocoating was suggested and surface engineering of metal oxide nanoparticles by the coating method have been studied. In addition, compact, biocompatible, and charge modulated iron oxide nanoparticles were synthesized and its bio-application was reported. First, conformal nanocoatings to nanostructured materials was achieved through amine-mediated redox control of a catechol system by separating catechol and amine, which effectively suppress cohesion and enhance a adhesion to yield an optimized nanocoating. The amine-assisted catechol nanocoating exhibits roughness of <0.358 nm and thickness of 1.69 nm on flat substratesthe hydrodynamic diameter of coated iron oxide nanoparticles is less than 20 nm. Surface characterization, density functional theory calculations, and effect of separated amine were investigated to elucidate the coating mechanism. Three key roles of separated amine in the catechol-based nanocoating were suggested as follows, adhesion promotion, suppression of polymerization, and additional stabilization through an in-situ generated, newly designed catechol-amine adduct. Second, multidentate catechol based polyethylene glycol random copolymer ligands was synthesized by reverse addition and fragmentation transfer polymerization. Compact, biocompatible and colloidal stable iron oxide nanoparticles have been synthesized by the ligands via the amine assisted catechol nanocoating method and applied into in vivo magnetic resonance contrast agents. High resolution magnetic resonance angiography with long circulation time was reported. Finally, charge modulated metal oxide nanoparticles were synthesized by surface engineering with multidentate catechol based polymeric ligands. The charged iron oxide nanoparticles exhibit different behavior in vitro cell experiments and gene delivery into cell by positive charged nanoparticles was demonstrated.clos

Standardization of research methods employed in assessing the interaction metallic-based nanoparticles and the blood-brain barrier: present and future perspectives

peer-reviewedThe full text of this article will not be available until the embargo expires on the 18/01/2020.Treating diseases of the central nervous system (CNS) is complicated by the presence of the blood-brain barrier (BBB), a semipermeable boundary layer protecting the CNS from toxins and homeostatic disruptions. However, this layer also excludes almost 100% of therapeutics, impeding the treatment of CNS diseases. The advent of nanoparticles, in particular metallic-based nanoparticles, presents the potential to overcome this barrier and transport drugs into the CNS. Recent interest in metallic-based nanoparticles has generated an immense array of information pertaining to nanoparticles of different materials, sizes, morphologies, and surface properties. Nanoparticles with different physico-chemical properties lead to distinct nanoparticle-host interactions; yet, comprehensive characterization is often not completed. Similarly, in vivo testing has involved a mixed evaluation of parameters, including: BBB permeability, integrity, biodistribution, and toxicity. The methods applied to assess these parameters are inconsistent; this complicates the comparison of different nanoparticle-host system responses. A systematic review was conducted to investigate the methods by which metallic-based nanoparticles are characterized and assessed in vivo. The introduction of a standardized approach to nanoparticle characterization and in vivo testing is crucial if research is to transition to a clinical setting. The approach suggested, herein, is based on equipment and techniques that are accessible and informative to facilitate the routine incorporation of this standardized, informative approach into different research settings. Thorough characterization could lead to improved interpretation of in vivo responses, which could clarify nanoparticle properties that result in favorable in vivo outcomes whilst exposing nanoparticle-specific weaknesses. Only then will researchers successfully identify nanoparticles capable of delivering life-saving therapeutics across the blood-brain barrier

Nanofluids as Novel Alternative Smart Fluids for Reservoir Wettability Alteration

This chapter presents an account of two metal oxide nanoparticles (zirconium and nickel oxide) on basis of their structure, morphology, crystallinity phases, and their wetting effect on solid-liquid interface. As a preliminary step to sound understanding of process mechanisms; wettability, nanoparticles, and their relations thereof were scrutinized. To investigate the nanofluids wetting inclinations, complex mixtures of the nanoparticles and NaCl brine (ZrO2/NaCl; NiO/NaCl) were formulated and their technical feasibility as wetting agents tested via contact angle measurement. The result shows that the nanoparticles exhibit different structural and morphological features and capable of addressing reservoir wettability challenges owing to favorable adsorption behavior on the surface of the calcite which facilitated the wetting changes quantified by contact angle. We believe this study will significantly impact the understanding of wetting at solid-liquid interface which is crucial for recovery process optimization

Synthetic Amorphous Silicon Dioxide (NM-200, NM-201, NM-202, NM-203, NM-204): Characterisation and Physico-Chemical Properties

The European Commission's Joint Research Centre (JRC) provides scientific support to European Union policy including nanotechnology. Within this context, the JRC launched, in February 2011, a repository for Representative Test Materials (RTMs), based on preparatory work started in 2008. It supports both EU and international research projects, and especially the OECD Working Party on Manufactured Nanomaterials (WPMN). The WPMN leads an exploratory testing programme "Testing a Representative set of Manufactured Nanomaterials" for the development and collection of data on characterisation, toxicological and ecotoxicological properties, as well as risk assessment and safety evaluation of nanomaterials. The purpose is to understand the applicability of the OECD Test Guidelines for the testing of nanomaterials as well as end-points relevant for such materials. The Repository responds to a need for nanosafety research purposes: availability of nanomaterial from a single production batch to enhance the comparability of results between different research laboratories and projects. The availability of representative nanomaterials to the international scientific community furthermore enhances and enables development of safe materials and products. The present report presents the physico-chemical characterisation of the synthetic amorphous silicon dioxide (SiO2, SAS) from the JRC repository: NM-200, NM-201, NM-202, NM-203 and NM-204. NM-200 was selected as principal material for the OECD test programme "Testing a representative set of manufactured nanomaterials". NM-200, NM-201 and NM-204 (precipitated SAS) are produced via the precipitation process, whereas NM-202 and NM-203 (fumed or pyrogenic SAS) are produced via a high temperature process. Each of these NMs originates from one respective batch of commercially manufactured SAS. They are nanostructured, i.e. they consist of aggregated primary particles. The SAS NMs may be used as a representative material in the measurement and testing with regard to hazard identification, risk and exposure assessment studies. The results for more than 15 endpoints are addressed in the present report, including physical-chemical properties, such as size and size distribution, crystallite size and electron microscopy images. Sample and test item preparation procedures are addressed. The results are based on studies by several European laboratories participating to the NANOGENOTOX Joint Action, as well as the JRC.JRC.I.4-Nanobioscience

Chemistry of Nanoscale Solids and Organic Matter in Sustainable Water Management Systems

To alleviate global water scarcity and improve public health, engineered water treatment and management systems have been developed for purifying contaminated water and desalinating brackish or ocean water. These engineered systems provide substantial amounts of potable water and lessen environmental concerns about the release of contaminated water. Wastewater treatment plants (WWTPs), water desalination plants (WDPs), and managed aquifer recharge systems (MARs) are three representative sustainable water management (SWM) systems. But the operation of all three poses two fundamental questions: (1) What is the fate of nanoscale solids (e.g., engineered nanomaterials, naturally occurring nanoparticles) in SWM systems and how will their physicochemical properties be changed when they encounter other water constituents, including cations and anions, reactive radical species, and organic matter? (2) How can our current knowledge enable more stable, scalable, and sustainable nanomaterial-based technologies for next-generation water treatment? To seek answers to these two questions, this dissertation focuses on the interface of chemistry and environmental engineering in 3 Systems: advanced oxidation processes (AOPs), managed aquifer recharge (MAR), and membrane distillation (MD), to (i) pursue in-depth and systematic investigations on solid-liquid interfacial interactions between nanoparticles and different water constituents (e.g., organic matter) in both water treatment and subsurface systems, and (ii) to utilize the knowledge obtained from fundamental mechanistic studies to develop nature-inspired nanomaterial-based membranes for sustainable water treatment.First, System 1 focused on investigating the surface chemistry of engineered nanomaterials (ENMs) in advanced oxidation processes (AOPs). The widespread industrial applications of ENMs, such as titanium oxide, cerium oxide, and graphene-based carbon materials, have increased the likelihood of their release into aquatic systems, including engineered water treatment systems, where they can undergo surface chemistry changes induced by water components. Using cerium oxide nanoparticles (CeO2 NPs) as representative ENMs, I examined on the effects of both reactive oxygen species (ROS) generated during UV/H2O2 treatment and dissolved organic matter (DOM) on the NPsՠcolloidal stability and surface chemistry. During UV/H2O2 treatment, superoxide radicals (O2_) dominated in neutralizing the surface charge of CeO2 NPs, leading to decreased electrostatic repulsive forces between nanoparticles and a higher extent of sedimentation. DOM was found to complex with the CeO2 NPsՠsurface and to act as a protective layer, making direct reactions between ROS and CeO2 and their impacts on colloidal stability insignificant in a short reaction period. These new findings have important implications for understanding the colloidal stability, sedimentation, and surface chemical properties of CeO2 NPs in aqueous systems where DOM and ROS are present.Second, System 2 aimed at investigating sustainable water management by managed aquifer recharge (MAR). To alleviate groundwater over-drafting, MAR has widely applied the engineered injection of secondary water sources into aquifers. However, groundwater chemistry changes induced by recharged water can significantly affect arsenic mobility in subsurface reservoir systems. Elevated arsenic mobility can result from increased oxidative dissolution of arsenic-bearing sulfide minerals, including arsenopyrite (FeAsS). In System 2, the effects of different water components, such as abundant oxyanions (i.e., phosphate, silicate, and bicarbonate) and DOM (natural and effluent organic matter), on the arsenic mobility from FeAsS were studied. Suwannee River DOM (SRDOM) was found to decrease arsenic mobility in the short term (\u3c 6 hours) by inhibiting arsenopyrite oxidative dissolution, but it increased arsenic mobility over a longer experimental time (7 days) by inhibiting secondary iron(III) (hydr)oxide precipitation and decreasing arsenic adsorption onto iron(III) (hydr)oxide. In situ grazing incidence small-angle X-ray scattering (GISAXS) measurements suggested that SRDOM decreased iron(III) (hydr)oxide nucleus sizes and growth rates. A combined analysis of SRDOM and other proteinaceous or labile DOM (alginate, polyaspartate, and glutamate) revealed that DOM with higher molecular weights caused more increased arsenic mobility. In addition to DOM, phosphate showed a time-dependent reversed effect on arsenic mobility. In the short term (6 hours), phosphate promoted the dissolution of FeAsS through monodentate mononuclear surface complexation, while over a longer experimental time (7 days), the enhanced formation of secondary minerals, such as iron(III) (hydr)oxide (maghemite, _-Fe2O3) and iron(III) phosphate (phosphosiderite, FePO4塲H2O), helped to decrease arsenic mobility through re-adsorption. Over the entire 7-day reaction, silicate increased arsenic mobility, and bicarbonate decreased arsenic mobility in our batch experiments. The phosphate system showed the highest amount and largest sizes of secondary precipitates among the three oxyanions (phosphate, silicate, and bicarbonate). These new observations advance our understanding of the impacts of DOM and oxyanions in injected water on arsenic mobility and on secondary precipitate formation during the geochemical transformation of arsenic-containing sulfide minerals in MAR.In many natural and engineered aquatic systems, including MAR, acid mine drainage, and hydraulic fracturing systems, poorly crystalline iron(III) (hydr)oxide nanoparticles with sizes on the order of 1б0 nm form ubiquitously. In particular, newly formed iron(III) (hydr)oxide nanoparticles can precipitate heterogeneously on substrates, altering the substrateճ surface reactivity and serving as powerful sorbents for heavy metals (Cu, Zn, Pb, or Cd), anionic contaminants (As, Cr), and organic pollutants. Yet the thermodynamic and kinetic parameters, i.e., the effective interfacial (_\u27) and apparent activation (Ea) energies of iron(III) (hydr)oxide nucleation on earth-abundant mineral surfaces, have not been determined, which hinders accurate prediction and control of iron(III) (hydr)oxide formation and its interactions with other water constituents. Using a flow-through, time-resolved, and in situ grazing incidence small-angle X-ray scattering (GISAXS) method, the work experimentally obtained the interfacial and activation energies of iron(III) (hydr)oxide heterogeneous nucleation on quartz. GISAXS measurements successfully enabled the detection of the nucleation rates of iron(III) (hydr)oxides under different supersaturations (_, by varying pH between 3.3_3.6) and temperatures (12 弃_35 弃). Quantifying these rates led to the quantification of _\u27 and Ea, respectively, which were not previously available. The thermodynamic and kinetic parameters obtained benefit predictions using reactive transport models and controlling iron(III) (hydr)oxideճ formation, as well as understanding its effects on pollutantճ fate and transport in natural and engineered water systems.Third, System 3 was developed to apply mechanistic knowledge gained from studies of solidзater interfaces to the development of nature-inspired nanomaterial-based membranes for sustainable desalination. In remote or underdeveloped areas, it is challenging to produce clean water because centralized water treatment techniques require high energy input and management cost. To support resilient community development, water treatment techniques for these areas should be sustainable in terms of material design and energy consumption. To address these needs, a new water treatment system based on membrane distillation (MD) has been developed. In this novel MD system, called photothermal membrane distillation (PMD), the membrane is embedded with light-absorbing photothermal materials that harvest solar energy and generate localized heat at the water-membrane interface to drive the MD process. To develop several PMD membranes with high solar conversion efficiency, polydopamine (PDA), which possesses the advantages of easy synthesis, good biocompatibility, and excellent light-to-heat conversion, was used as the photothermal material. First, a simple, stable, and scalable PDA-coated polyvinylidene fluoride (PVDF) membrane was synthesized for PMD. In a direct contact membrane distillation (DCMD) system under 0.75 kW/m2 solar irradiation, the membrane showed a high solar energy conversion efficiency (45%) and a high water flux (0.49 kg/m2塨) This performance was facilitated by the PDA coating, whose broad light absorption and outstanding photothermal conversion properties enabled a higher transmembrane temperature difference and increased the driving force for vapor transport. In addition, the excellent hydrophobicity achieved by fluoro-silanization gave the membrane great wetting resistance and high salt rejection. More importantly, the robustness of the membrane, stemming from the excellent underwater adhesion of the PDA, made it an outstanding candidate for real-world applications. Further, to increase the solar energy conversion efficiency, bacterial nanocellulose (BNC) was utilized to replace commercial PVDF membranes to decrease heat conductive loss from the photothermal layer to the cold distillate. A new photothermal membrane was thermally-engineered to incorporate a bilayered structure composed of two environmentally sustainable materials, PDA particles and BNC. The size-optimized PDA particles on the top layer maximized sunlight absorption and sunlight-to-heat conversion, and the bottom BNC aerogel insulating layer achieved high vapor permeability and low conductive heat loss. This thermally engineered design enabled a permeate flux of 1.0 kg/m2塨 under 1 sun irradiation, and a record high solar energy-to-collected water efficiency of 68%, without ancillary heat or heat recovery systems. Moreover, the membrane showed effective bactericidal activity and was easily cleaned, increasing its lifespan. This study provides a new paradigm for using photothermal material incorporated in an aerogel to sustainably purify water. Using renewable solar energy, the PMD system can also provide decentralized desalination for remote or underdeveloped areas and can support resilient community development.In summary, the work described in this dissertation offers an in-depth and mechanistic understanding of the fate of nanoscale solids (e.g., engineered nanomaterials and naturally occurring nanoparticles) in SWM systems in the presence of different water constituents (e.g., anions, reactive radical species, and organic matter). It also provides insights for designing more stable, scalable, and sustainable nanomaterial-based membranes for water treatment and desalination. Ultimately, this research will better define the chemistry of nanoscale solids and organic matter in water management systems, benefiting the design of next-generation water treatment systems that are environmentally safer and more sustainable

Titanium Dioxide, NM-100, NM-101, NM-102, NM-103, NM-104, NM-105: Characterisation and Physico-Chemical Properties

The European Commission's Joint Research Centre (JRC) provides scientific support to European Union policy including nanotechnology. Within this context, the JRC launched, in February 2011, a repository for Representative Test Materials (RTMs), based on preparatory work started in 2008. It supports both EU and international research projects, and especially the OECD Working Party on Manufactured Nanomaterials (WPMN). The WPMN leads an exploratory testing programme "Testing a Representative set of Manufactured Nanomaterials" for the development and collection of data on characterisation, toxicological and ecotoxicological properties, as well as risk assessment and safety evaluation of nanomaterials. The purpose is to understand the applicability of the OECD Test Guidelines for the testing of nanomaterials as well as end-points relevant for such materials. The Repository responds to a need for nanosafety research purposes: availability of nanomaterial from a single production batch to enhance the comparability of results between different research laboratories and projects. The availability of representative nanomaterials to the international scientific community furthermore enhances and enables development of safe materials and products. The present report presents the physico-chemical characterisation of the Titanium dioxide series from the JRC repository: NM-100, NM-101, NM-102, NM-103, NM-104 and NM-105. NM-105 was selected as principal material for the OECD test programme "Testing a representative set of manufactured nanomaterials". NM-100 is included in the series as a bulk comparator. Each of these NMs originates from one batch of commercially manufactured TiO2. The TiO2 NMs may be used as representative material in the measurement and testing with regard to hazard identification, risk and exposure assessment studies. The results for more than 15 endpoints are addressed in the present report, including physico-chemical properties, such as size and size distribution, crystallite size and electron microscopy images. Sample and test item preparation procedures are addressed. The results are based on studies by several European laboratories participating to the NANOGENOTOX Joint Action, as well as by the JRC.JRC.I.4-Nanobioscience

Versatile Ultrathin Films of Conducting Polymers by Vapor Phase Polymerization at Atmospheric Pressure: Synthesis, Process Optimization, and Characterization

The limitations such as toxicity, brittleness, scarcity, and high cost of currently available materials for energy storage and transparent electrode applications in bendable electronics create a need for green, sustainable, and cost-effective alternatives. Organic conducting polymers (CPs) can transport charge across conjugated sp2 carbon network. Their low-tuneable band gap, flexibility, and transparency could make them viable alternatives. However, the challenges such as processability, stability, biocompatibility, and production cost remain milestones to achieve. Therefore, this thesis work is an effort toward a green and sustainable future. Poly(3, 4-ethylenedioxythiophene) (PEDOT), known for its conductivity, robustness, and biocompatibility and polyazulene (PAz), known for its high capacitance are selected for studies due to their unique abilities. Fabrication of highly electrically conducting ultra-thin films of PEDOT is done by developing and optimizing a cost-efficient vapor phase polymerization method at atmospheric pressure (AP-VPP) and combining a layer-by-layer (L-b-L) synthesis approach. As a result, AP-VPP PEDOT films showed comparative sheet resistance, transmittance, and conductivity with commercially available ITO-coated materials. In contrast, the flexible, green organic nature and high capacitance of PEDOT thin films overcome the competition with ITO-coated materials. Similarly, well-organized high-capacitance PAz films are L-b-L synthesized using an optimized AP-VPP process. The influence of factors such as substrate surface cleaning, oxidant solution, oxidant spin coating rate and time, cell and substrate temperature, polymerization time, drying and annealing temperature and time, air vs nitrogen atmosphere, and washingsolvents on film properties were studied during the optimization process for both the CPs. Properties like optical bandgap, sheet resistance, surface roughness, conductivity, capacitance, and % transmittance provided a route for process optimization. Furthermore, FTIR, Raman, and UV–Vis spectroscopy were utilized to analyse the extended conjugation along with the type and trend in the charge carriers generated upon doping the resulting films. Microscope imaging, AFM, and SEM were utilized to analyse surface morphologies and microstructures. The capacitance properties, transport of counterions across multiple layers, and charge transport resistance were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. In addition, the characterization techniques complement each other in data interpretation. PEDOT and PAz films produced in the present work and their properties are compared with available reports in the literature

GRAPHENE-BASED SEMICONDUCTOR AND METALLIC NANOSTRUCTURED MATERIALS

Exciting periods of scientific research are often associated with discoveries of novel materials. Such period was brought about by the successful preparation of graphene which is a 2D allotrope of carbon with remarkable electronic, optical and mechanical properties. Functional graphene-based nanocomposites have great promise for applications in various fields such as energy conversion, opteoelectronics, solar cells, sensing, catalysis and biomedicine. Herein, microwave and laser-assisted synthetic approaches were developed for decorating graphene with various semiconductor, metallic or magnetic nanostructures of controlled size and shape. We developed a scalable microwave irradiation method for the synthesis of graphene decorated with CdSe nanocrystals of controlled size, shape and crystalline structure. The efficient quenching of photoluminescence from the CdSe nanocrystals by graphene has been explored. The results provide a new approach for exploring the size-tunable optical properties of CdSe nanocrystals supported on graphene which could have important implications for energy conversion applications. We also extended this approach to the synthesis of Au-ceria-graphene nanocomposites. The synthesis is facilely conducted at mild conditions using ethylenediamine as a solvent. Results reveal significant CO conversion percentages between 60-70% at ambient temperatures. Au nanostructures have received significant attention because of the feasibility to tune their optical properties by changing size or shape. The coupling of the photothermal effects of these Au nanostructures of controlled size and shape with GO nanosheets dispersed in water is demonstrated. Our results indicate that the enhanced photothermal energy conversion of the Au-GO suspensions could to lead to a remarkable increase in the heating efficiency of the laser-induced melting and size reduction of Au nanostructures. The Au-graphene nanocomposites are potential materials for photothermolysis, thermochemical and thermomechanical applications. We developed a facile method for decorating graphene with magnetite nanocrystals of various shapes (namely, spheres, cubes and prisms) by the microwave-assisted-reduction of iron acetylacetonate in benzyl ether. The shape control was achieved by tuning the mole ratio between the oleic acid and the oleyamine. The structural, morphological and physical properties of graphene-based nanocomposites described herein were studied using standard characterization tools such as TEM, SEM, UV-Vis and PL spectroscopy, powder X-ray diffraction, XPS and Raman spectroscopy