Advances in Nanotechnology-Based Biosensing of Immunoregulatory Cytokines.

Catalytic decomposition of N2O over monolithic supported noble metal-transition metal oxides

Two-dimensional (2D) materials such as graphene and graphene oxide are desirable for sensing applications owing to their high surface-to-volume ratio. Recently another class of 2D materials namely transition metal dichalcogenides (TMDs) with semiconducting properties have gained extensive attention for gas sensing studies due to their high surface area and excellent electronic and catalytic properties. TMDs form layered structures, where adjacent layers are held together by weak van der Waals forces. Accordingly, they can be easily exfoliated into individual 2D layers with high surface area which is a merit for sensing applications.WS2 is a promising 2D TMD for sensing applications thanks to high surface area and excellent electrical properties. However, for sufficient sensing applications its sensitivity needs to be improved more. A good strategy for that purpose is to functionalize with noble metal and metal oxide nanoparticles (NPs). NPs can make additional charge depletion zone in WS2 nanosheets, thereby amplifying their resistance modulation during interaction with gas molecules. Furthermore, NPs can provide a spillover effect; facilitating adsorption, dissociation, and transfer of target gases to WS2 nanosheets surface. This can lead to improved sensitivity towards a specific gas.In this study, WS2 nanosheets that are bare or decorated with Au, SnO2, or a combination of Au and SnO2 were realized on flexible polyamide substrates. The fabricated sensors were operated for CO gas sensing in applied-voltage-induced self-heating mode at room temperature (24 ºC). Not only optimal applied voltage was varied for the sensing of different gases, but also that the sensors behaved uniquely in response to CO gas. Therefore, the optimized applied voltage for the fabricated sensors and their room temperature sensing characteristics were investigated. Furthermore, we investigated that tilting, bending and stretching conditions to the optimized gas sensor. Also, we suggested that the enhanced response was related to the formation of Au-WS2 and Au-SnO2 Schottky junctions, n-SnO2-n-WS2 heterojunctions, and the catalytic performance of Au NPs towards CO gas. The results obtained in this study provide new avenues towards fabrication of flexible, low power gas sensors using metal chalcogenides.

Hydrogen possesses the potential to provide clean, reliable, and affordable energy supply to meet the growing global demand. A promising way to produce hydrogen is by splitting water using electricity. Large capital costs of current electrolyzer technologies are a major barrier to attaining the targeted hydrogen production cost. High capital costs arise due to the use of expensive catalyst materials, relatively small systems, relatively low efficiencies of the system, customized power electronics, and labor intensive fabrication. In the case of proton exchange membrane (PEM) electrolysis cells in particular, use of non-precious metal electro-catalysts for electrodes exhibiting high electrochemical activity and durability would considerably decrease the overall capital costs. Decreasing the noble metal loading as well as improving the electro-catalytic activity and durability could be achieved using novel synthesis techniques to generate high specific surface area (HSA) nanostructured electro-catalysts, or improved low cost support structure (diluents) for electro-catalysts.The present work is carried out to identify a novel support for electro-catalysts which can decrease the precious metal loading without compromising the electrochemical activity of the noble metal oxide electro-catalyst. F-doped SnO2 with different F concentration has already been extensively studied in order to improve the electrical conductivity of SnO2. Accordingly, we have shown in a recent publication that (Ir,Sn,Nb)O2 is a promising anode electro-catalyst resulting in ~60 mol.% reduction in IrO2 content without compromising the electrochemical activity1. Also, F has been shown as a novel dopant for IrO2 leading to improvement in the electro-catalytic activity of the oxygen evolution reaction in PEM electrolysis2. We also showed that F doped SnO2 as a support with IrO2 and/or RuO2 gives similar electrochemical activity with ~80 mol.% reduction in the noble metal oxide content3,4. In this study, F doped (Sn,Nb)O2 has been used as a support to be combined with IrO2as the catalyst for anode oxidation in PEM based water electrolysis.The present investigation is thus directed at the synthesis and characterization of F doped ternary Ir-Sn-Nb oxide solid solution systems. Consequently, solid solutions of F along with IrO2, SnO2 and NbO2, denoted as (Ir,Sn,Nb)O2:F, corresponding to composition (Ir0.30Sn0.35Nb0.35)O2:x wt. % F, where x ranges from 0 to 20% has been synthesized and studied. The catalyst containing 10 wt. % F exhibits electrochemical activity and stability matching that of pure IrO2. Results of the synthesis, structural, microstructural, and electrochemical activity of these novel catalysts will be presented and discussed. Figure 1 shows the polarization curve of (Ir,Sn,Nb)O2:F electro-catalysts in 1 N sulfuric acid conducted at a scan rate of 1mV/sec. In addition, to obtain a better understanding of the fundamental electrochemical activity and long term stability of the (Ir,Sn,Nb)O2:F electro-catalyst, first-principles calculations of the total energies and electronic structures of the model systems with chemical compositions similar to those of the experimentally synthesized materials have been carried out to complement the present experimental study.As a result, (Ir0.30Sn0.35Nb0.35)O2:F doped with ~10 wt.% of F is potentially a preferred oxygen evolution reaction (OER) electro-catalyst composition for water electrolysis resulting in almost ~70% reduction in noble metal content. Thus, the composition identified combined with its excellent performance can be considered viable for contributing to significant reduction in the overall capital cost of PEM based water electrolyzers.

Catalytic decomposition of nitrous oxide (N2O) is one of the most efficient methods for the removal of N2O which is of high greenhouse potential and ozone-depleting property. Recent progress in the decomposition of N2O has been reviewed with the focus on noble meal and metal oxide catalysts. The influence factors, such as catalyst support, preparation method, alkali metal additives and the reaction conditions (including O2, H2O, SO2, NO and CO2), on the performance of deN2O catalysts have been discussed. Finally, future research direction for the catalytic decomposition of N2O is proposed.

Noble metal oxides are highly valuable and act as a key component of metal-oxide interfaces in oxide-supported noble metal catalysts, which play a crucial role in modern industrial society. Here, we investigate the structure of four common and stable noble metal oxides using 17O solid-state NMR. The optimal isotopic labeling temperature ensures the highest labeling efficiency while preserving the structure of the oxides. The variation in characteristic signals for each noble metal oxide reveals oxygen species in different chemical environments, while the NMR parameters related to chemical shift anisotropy and quadrupolar interaction obtained from spectral fitting indicate more structural information. DFT calculations are used to assist spectral assignments for various oxygen species. This work serves as a prerequisite for studying solid-state NMR of oxide-supported noble metal catalysts.

Vascular dysfunction in response to reactive oxygen species (ROS) plays an important role in the development and progression of atherosclerotic lesions. In most cells, mitochondria are the major source of cellular ROS during aerobic respiration. Under most conditions the rates of ROS formation and elimination are balanced through mechanisms that sense relative ROS levels. However, a chronic imbalance in redox homeostasis is believed to contribute to various chronic diseases, including atherosclerosis. Uncoupling protein-2 (UCP2) is a mitochondrial inner membrane protein shown to be a negative regulator of macrophage ROS production. In response to a cholesterol-containing atherogenic diet, C57BL/6J mice significantly increased expression of UCP2 in the aorta, while mice lacking UCP2, in the absence of any other genetic modification, displayed significant endothelial dysfunction following the atherogenic diet. Compared with wild-type mice, Ucp2(-/-) mice had decreased endothelial nitric oxide synthase, an increase in vascular cell adhesion molecule-1 expression, increased ROS production, and an impaired ability to increase total antioxidant capacity. These changes in Ucp2(-/-) mice were associated with increased aortic macrophage infiltration and more numerous and larger atherosclerotic lesions. These data establish that in the vasculature UCP2 functions as an adaptive antioxidant defense to protect against the development of atherosclerosis in response to a fat and cholesterol diet.

Effect of polymer-coating on carbon blacks for Pt utilization efficiency of polymer electrolyte membrane fuel cells

Pt-decorated ZnFe2O4 sensors prepared via a facile impregnation method free of reductants and surfactants for conductometric acetone sensing

The goal of the research described in this thesis was to study the amount of noble metals required in bifunctional catalysts for hydroconversion by tuning the nanoparticle location, without compromising the catalytic performance. The catalysts that were studied each contained three main components: (noble) metal (oxide) nanoparticles, zeolite or zeotype material, and a binder. In Chapter 2 a new tool for controlling the metal nanoparticle location in Pd/zeolite and Pd/zeotype catalysts is described. We show that performing a direct reduction (DR) on ammonium palladate exchanged zeolites/zeotypes results in enrichment of Pd on the outer surface of the solid acid crystallites, whereas slow calcination followed by reduction (CR) resulted in more Pd nanoparticles being confined inside the zeotype crystallites. The focus in Chapter 3 is on the minimum amount of platinum required as function of Pt nanoparticle location. Two sets of catalysts were prepared: one set was based on mordenite and the other one on ZSM-22. In the set with mordenite the Pt nanoparticles were either inside the mordenite crystallites or on alumina binder. The ZSM-22 set had the Pt nanoparticles either on the ZSM-22 crystallites or on the alumina binder. Pt weight loadings of 0.005 to 0.5 wt% were used. At loadings of 0.01 wt% catalysts with Pt on alumina binder were much less active. Extensive characterization revealed that this was a result of strong metal-support interaction of the Pt clusters with alumina. Since the lower catalytic performance of Pt-on-alumina with ≤ 0.01 wt% Pt loadings in Chapter 3 was a result of γ-alumina lacking chemical inertness, we explored the replacement of this binder by silica in Chapter 4. Catalysts with 0.005 to 0.5 wt% Pt on ZSM-22 or on silica were prepared and characterized. These catalysts were then applied in the hydroconversion of n-heptane. Moreover, for the first time the effect of the low loadings on the catalytic performance during n-hexadecane was assessed. Diminishing noble metal utilization could also mean replacement with earth abundant metals. Chapter 5 is dedicated to an exploration of nickel based bifunctional catalysts for hydroconversion. We show that Ni based catalysts typically display high hydrogenolysis activity to produce mainly methane. However, the combination of the use of n-alkanes with higher molecular weight (e.g. n-hexadecane) and emplacing Ni (oxide) nanoparticles at the right place could reduce hydrogenolysis activity and improve i-hexadecane selectivity. Lastly, Chapter 6 provides a summary & outlook and ‘een Nederlandse samenvatting’ (Dutch summary).

With increasing commercialization of high volume, two-dimensional carbon nanomaterials comes a greater likelihood of environmental release. In aquatic environments, black carbon binds contaminants like aromatic hydrocarbons, leading to changes in their uptake, bioavailability, and toxicity. Engineered carbon nanomaterials can also adsorb pollutants onto their carbon surfaces, and nanomaterial physicochemical properties can influence this contaminant interaction. We used 2D graphene nanoplatelets and isometric carbon black nanoparticles to evaluate the influence of particle morphology and surface properties on adsorption and bioavailability of benzo(a)pyrene, a model aromatic hydrocarbon, to brine shrimp (Artemia franciscana) and a fish liver cell line (PLHC-1). Acellular adsorption studies show that while high surface area carbon black (P90) was most effective at a given concentration, 2D graphene nanoplatelets (G550) adsorbed more benzo(a)pyrene than carbon black with comparable surface area (M120). In both biological models, co-exposure to nanomaterials lead to reduced bioavailability, with G550 graphene nanoplatelets cause a greater reduction in bioavailability or response than the M120 carbon black nanoparticles. However, on a mass basis the high surface area P90 carbon black was most effective. The trends in bioavailability and adsorption were consistent across all biological and acellular studies, demonstrating the biological relevance of these results in different models of aquatic organisms. While adsorption is limited by surface area, 2D graphene nanoplatelets adsorb more benzo(a)pyrene than carbon black nanoparticles of similar surface area and charge, demonstrating that both surface area and shape play important roles in the adsorption and bioavailability of benzo(a)pyrene to carbon nanomaterials.

There is a growing demand for the synthesis of high surface area carbons, also known as carbon nanoparticles (CNPs). Existing synthesis methods for high surface area carbons have limited environmental benignity and economic viability due to the requirement of multistep and batch processes and harsh activating and/or templating chemicals. Herein, we demonstrate the synthesis of high surface area CNPs from lignin, a waste byproduct, through a single-step, continuous gas phase aerosol technique without the use of activating or templating chemicals. This continuous approach requires significantly less time for synthesis: on the order of seconds in comparison to hours for conventional methods. Properties of carbon materials synthesized from lignin are controlled by temperature and residence time, and the role of these parameters inside the aerosol reactor on carbon nanoparticle size, morphology, molecular structure, and surface area is systematically investigated. Furthermore, the as-obtained carbon nanoparticles are tested for specific capacitance, and the best-performing material (surface area 925 m2/g) exhibited a specific capacitance of 247 F/g at 0.5 A/g with excellent capacity retainment of over 98% after 10,000 cycles. This is a clear demonstration of their superior performance compared with supercapacitors synthesized earlier from lignin. Overall, the simple (single-step, continuous, and rapid) operation and the avoidance of the use of activating/templating chemicals make the aerosol technique a promising candidate for the scalable and sustainable synthesis of CNPs from lignin.

Nanoscopic materials have demonstrated a versatile role in almost every emerging field of research. Nanomaterials have come to be one of the most important fields of advanced research today due to its controllable particle size in the nanoscale range, capacity to adopt diverse forms and morphologies, high surface area, and involvement of transition and non-transition metals. With the introduction of porosity, nanomaterials have become a more promising candidate than their bulk counterparts in catalysis, biomedicine, drug delivery, and other areas. This review intends to compile a self-contained set of papers related to new synthesis methods and versatile applications of porous nanomaterials that can give a realistic picture of current state-of-the-art research, especially for catalysis and sensor area. Especially, we cover various surface functionalization strategies by improving accessibility and mass transfer limitation of catalytic applications for wide variety of materials, including organic and inorganic materials (metals/metal oxides) with covalent porous organic (COFs) and inorganic (silica/carbon) frameworks, constituting solid backgrounds on porous materials.

Proton exchange membrane fuel cells (PEMFCs) which have high efficiency have attracted attention as one of the most promising energy conversion devices. Currently the catalysts in PEMFCs are mainly carbon supported noble metals where the support can afford the electron transport environment to improve catalyst efficiency and decrease catalyst loss by strengthening catalyst–support bonding [1]. Due to high electrical conductivity and surface area, carbon-based catalyst supports are widely used in PEMFCs. However, the high electric fields applied to the fuel cell can easily cause carbon corrosion and further accelerate catalyst loss.New alternative support materials are needed to reduce costs and increase the lifetime of PEMFC electrodes. Recently, silica-based supports such as silicon oxide [2, 3] and silicon carbide [4] have been considered feasible as catalyst supports due to efficient catalyst utilization and their resistance to carbon corrosion. As a silica-based material, hydrophilic silica nanosheets (SN) derived from cheap natural vermiculite [5] is for the first time to be combined with carbon black (CB) as a catalyst support in this work. SN-CB supported platinum (Pt) catalysts were prepared according to different weight ratios of SN and CB using a modified polyol reduction method [6]. After 18000-cycle accelerated stress test (AST), as shown in Fig. 1a and b, the electrochemical surface area (ECSA) of Pt/SN2-CB3 (the weight ratio of SN to CB is 2: 3) decays from 23.7 to 22.5 m2/g (only 4.8% degradation) compared to Pt/CB (25.8% degradation from 16.0 to 11.9 m2/g). Meanwhile, Pt/SN2-CB3 shows comparable initial onset potential (0.850 V) and high half-wave potential (0.654 V) compared to 0.881 V onset potential and 0.625 V half-wave potential for Pt/CB as shown in Fig. 1c and d. The half-wave potential of Pt/SN2-CB3 after AST test demonstrated the addition of SN into the support can result in a stable oxygen reduction reaction (ORR) durability. The possible reason why the ECSA, ORR activity and durability of SN-CB supported platinum catalysts are enhanced is that the synergic interactions among carbon, silica nanosheets and Pt nanoparticles may hinder carbon corrosion, Pt agglomeration and dissolution [2]. Different weight ratios between SN and CB and the functionalized SNs are currently being tested and the real fuel cell data will be presented. Reference [1] Y.-J. Wang, D.P. Wilkinson, J. Zhang, Noncarbon support materials for polymer electrolyte membrane fuel cell electrocatalysts, Chemical reviews, 111 (2011) 7625-7651.[2] P. Dhanasekaran, A. Shukla, S.V. Selvaganesh, S. Mohan, S. Bhat, Silica-decorated carbon-Pt electrocatalyst synthesis via single-step polyol method for superior polymer electrolyte fuel cell performance, durability and stack operation under low relative humidity, Journal of Power Sources, 438 (2019) 226999.[3] P. Dhanasekaran, S.V. Selvaganesh, A. Rathishkumar, S. Bhat, Designing self-humidified platinum anchored silica decorated carbon electrocatalyst for boosting the durability and performance of polymer electrolyte fuel cell stack, International Journal of Hydrogen Energy, 46 (2021) 8143-8155.[4] L. Dong, J. Zang, J. Su, Y. Jia, Y. Wang, J. Lu, X. Xu, Oxidized carbon/nano-SiC supported platinum nanoparticles as highly stable electrocatalyst for oxygen reduction reaction, International journal of hydrogen energy, 39 (2014) 16310-16317.[5] Z. Guo, J. Chen, J.J. Byun, R. Cai, M. Perez-Page, M. Sahoo, Z. Ji, S.J. Haigh, S.M. Holmes, High-performance polymer electrolyte membranes incorporated with 2D silica nanosheets in high-temperature proton exchange membrane fuel cells, Journal of Energy Chemistry, 64 (2022) 323-334.[6] Z. Ji, M. Perez-Page, J. Chen, R.G. Rodriguez, R. Cai, S.J. Haigh, S.M. Holmes, A structured catalyst support combining electrochemically exfoliated graphene oxide and carbon black for enhanced performance and durability in low-temperature hydrogen fuel cells, Energy, 226 (2021) 120318. Figure 1

State of arts on the bio-synthesis of noble metal nanoparticles and their biological application

Polymer electrolyte membrane (PEM) electrolysis is widely considered a promising technology for energy storage and clean hydrogen production, due to the advantages it has over state-of-the-art alkaline water electrolysis.1 Typically, PEM electrolysers can operate at higher current densities than their alkaline counterparts, have a more robust design, and due to the zero-gap design, exhibit smaller Ohmic losses. Furthermore, PEM electrolysers can yield hydrogen at elevated pressures, eliminating the need for compression. Nevertheless, a series of challenges hinder the large-scale commercial implementation of PEM electrolysers. One of the most critical drawbacks is the need for noble metal electrocatalysts, especially at the anode of the cell, such as iridium or ruthenium, to catalyze the oxygen evolution reaction (OER) (1).2H2O → O2 + 4H+ + 4e- E° = 1.23 V vs NHE (1)These metals are used due to their high catalytic activity and long-term stability in the corrosive acidic environment of the PEM cells and their replacement by more available materials is difficult. Over the years, the main efforts of the scientific community towards solving this challenge were focused on increasing the noble metal dispersion, by using various high surface area catalyst supports, using core-shell catalysts, with the aim to minimize the amount of noble metal, modifying the morphology of the electrode, to improve mass transport limitations and electric contact between components and maximize noble metal utilization.2-4 Antimony-doped tin oxide has been reported as a stable OER catalyst support, offering sufficient electronic conductivity at the same, in order to minimize Ohmic losses.5 Furthermore, recent reports indicate that SnO2 does not only act as a catalyst support but takes part in catalysis.6 Building upon literature reports, we prepared a series of Sn/Ir OER catalysts by a two-step sodium borohydride reduction method, in which Sn nanoparticles were deposited over the surface of iridium black particles, decorating it. Catalysts with varying Sn content were incorporated in membrane electrode assemblies (MEAs) and their cell performance was evaluated in a single cell PEM electrolyser. We found that catalysts with up to 20 wt% tin content exhibited an improved cell performance compared to MEAs with similar iridium black loading. We modeled Ohmic, kinetic and mass transport overpotential contributions to experimentally acquired polarization curves and identified that the better cell performance arises mainly from the higher intrinsic catalytic activity, reflected by a higher apparent exchange current density of Sn/Ir OER catalysts compared to Ir black catalysts. The Sn/Ir MEAs also displayed lower mass transport overpotentials, which indicate improved transport in the catalyst layer. This can be due to a more porous structure and less agglomeration of iridium particles induced by the presence of tin over their surface.Interestingly, this performance improvement was only observed for iridium black catalysts. We prepared a series of IrO2-SnO2 catalysts by solution combustion synthesis method, which is known to yield high surface area disperse oxide materials. Comparing the performance of these catalysts to commercial iridium oxide catalysts in the PEM electrolysis cell, the MEAs with SnO2-containing catalysts displayed worse cell performance than MEAs with commercial iridium oxide. Modelling the overpotential contributions showed a lower apparent exchange current density, indicating a lower intrinsic catalytic activity of IrO2-SnO2 catalysts, as well as a higher Ohmic resistance, due to SnO2 addition. These observations indicate the importance of iridium oxidation state for harnessing the promotion effect of tin addition and give important insights into designing more efficient OER catalysts for PEM electrolysis cells.