Effect of nanoparticle size on the near-surface pH-distribution in aqueous and carbonate buffered solutions

An analytical solution for the effect of particle size on the current density and near-surface ion distribution around spherical nanoparticles is presented in this work. With the long-term aim to support predictions on corrosion reactions in the human body, the spherical diffusion equation was solved for a set of differential equations and algebraic relations for pure unbuffered and carbonate buffered solutions. It was shown that current densities increase significantly with a decrease in particle size, suggesting this will lead to an increased dissolution rate. Near-surface ion distributions show the formation of a steep pH-gradient near the nanoparticle surface (\u3c6 μm) which is further enhanced in the presence of a carbonate buffer (\u3c2 μm). Results suggest that nanoparticles in pure electrolytes not only dissolve faster than bigger particles but that local pH-gradients may influence interactions with the biological environment, which should be considered in future studies

Effect of nanoparticle size on the near-surface pH-distribution in aqueous and carbonate buffered solutions

An analytical solution for the effect of particle size on the current density and near-surface ion distribution around spherical nanoparticles is presented in this work. With the long-term aim to support predictions on corrosion reactions in the human body, the spherical diffusion equation was solved for a set of differential equations and algebraic relations for pure unbuffered and carbonate buffered solutions. It was shown that current densities increase significantly with a decrease in particle size, suggesting this will lead to an increased dissolution rate. Near-surface ion distributions show the formation of a steep pH-gradient near the nanoparticle surface (<6 m) which is further enhanced in the presence of a carbonate buffer (<2 m). Results suggest that nanoparticles in pure electrolytes not only dissolve faster than bigger particles but that local pH-gradients may influence interactions with the biological environment, which should be considered in future studies

The hydrogen evolution reaction: from material to interfacial descriptors

International audienceThe production of sustainable hydrogen with water electrolyzers is envisaged as one of the most promising ways to match the continuously growing demand for renewable electricity storage. While so far regarded as fast when compared to the oxygen evolution reaction (OER), the hydrogen evolution reaction (HER) regained interest in the last few years owing to its poor kinetics in alkaline electrolytes. Indeed, this slow kinetics not only may hinder the foreseen development of the anionic exchange membrane water electrolyzer (AEMWE), but also raises fundamental questions regarding the parameters governing the reaction. In this perspective, we first briefly review the fundamentals of the HER, emphasizing how studies performed on model electrodes allowed for achieving a good understanding of its mechanism under acidic conditions. Then, we discuss how the use of physical descriptors capturing the sole properties of the catalyst is not sufficient to describe the HER kinetics under alkaline conditions, thus forcing the catalysis community to adopt a more complex picture taking into account the electrolyte structure at the electrochemical interface. This work also outlines new techniques, such as spectroscopies, molecular simulations, or chemical approaches that could be employed to tackle these new fundamental challenges, and potentially guide the future design of practical and cheap catalysts while also being useful to a wider community dealing with electrochemical energy storage devices using aqueous electrolytes

The mineral/water interface probed with nonlinear optical spectroscopy

The interaction between minerals and water is manifold and complex: the mineral surface can be (de)protonated by water, thereby changing its charge; mineral ions dissolved into the aqueous phase screen the surface charges. Both factors affect the interaction with water. Intrinsically molecular-level processes and interactions govern macroscopic phenomena, such as flow-induced dissolution, wetting, and charging. This realization is increasingly prompting molecular-level studies of mineral–water interfaces. Here, we provide an overview of recent developments in surface-specific nonlinear spectroscopy techniques such as sum frequency and second harmonic generation (SFG/SHG), which can provide information about the molecular arrangement of the first few layers of water molecules at the mineral surface. The results illustrate the subtleties of both chemical and physical interactions between water and the mineral as well as the critical role of mineral dissolution and other ions in solution for determining those interactions

Measurement and characterisation of glycans on surfaces

Glycans are a diverse group of compounds, which include glycoproteins and glycolipids and are ubiquitously present on cell surfaces. As a result glycan interactions are responsible for a number of medical conditions such as autoimmune diseases like rheumatoid arthritis, viral infections and as a cause of inflammation. Fully understanding the structure and function of these compounds requires the use of innovative surface analytical methods for screening large numbers of different glycans against serums, for biomarkers attributed to these illnesses. The main objective of this work was to produce and characterise glycan surfaces with reliable, reproducible and quantitative readouts. However, the complex nature of glycans means that analysis of their interactions on microarray surfaces doesn’t always produce reliable readouts. The surfaces analysed also include commercially available amine coated slides for quality assurance and maleimide slides, which were produced by treating amine coated slides with 6-maleimidohexanoic acid N-hydroxysuccinimide ester (‘EMCS’ as denoted by Sigma Aldrich). Thiolated sugars can then react and covalently bond with the maleimide surfaces. Heterogeneous glycan immobilisation within spots is characterised using surface chemical analysis and compared to literature observation. The progress of the project titled “Measurement and Characterisation of Glycans on Surfaces” to date involved producing microarrays of β-D-thioglucose on a maleimide functionalised surface in order to see how phosphate buffered saline affected the surface chemistry and characterisation of the spots on the surface by using time of flight – secondary ion mass spectrometry

Recent Research Progress in Surface Ligand Exchange of PbS Quantum Dots for Solar Cell Application

Colloidal quantum dots (CQDs) are considered as next-generation semiconductors owing to their tunable optical and electrical properties depending on their particle size and shape. The characteristics of CQDs are mainly governed by their surface chemistry, and the ligand exchange process plays a crucial role in determining their surface states. Worldwide studies toward the realization of high-quality quantum dots have led to advances in ligand exchange methods, and these procedures are usually carried out in either solid-state or solution-phase. In this article, we review recent advances in solid-state and solution-phase ligand exchange processes that enhance the performance and stability of lead sulfide (PbS) CQD solar cells, including infrared (IR) CQD photovoltaics. © 2020 by the author.1

Measurement and characterisation of glycans on surfaces

Glycans are a diverse group of compounds, which include glycoproteins and glycolipids and are ubiquitously present on cell surfaces. As a result glycan interactions are responsible for a number of medical conditions such as autoimmune diseases like rheumatoid arthritis, viral infections and as a cause of inflammation. Fully understanding the structure and function of these compounds requires the use of innovative surface analytical methods for screening large numbers of different glycans against serums, for biomarkers attributed to these illnesses. The main objective of this work was to produce and characterise glycan surfaces with reliable, reproducible and quantitative readouts. However, the complex nature of glycans means that analysis of their interactions on microarray surfaces doesn’t always produce reliable readouts. The surfaces analysed also include commercially available amine coated slides for quality assurance and maleimide slides, which were produced by treating amine coated slides with 6-maleimidohexanoic acid N-hydroxysuccinimide ester (‘EMCS’ as denoted by Sigma Aldrich). Thiolated sugars can then react and covalently bond with the maleimide surfaces. Heterogeneous glycan immobilisation within spots is characterised using surface chemical analysis and compared to literature observation. The progress of the project titled “Measurement and Characterisation of Glycans on Surfaces” to date involved producing microarrays of β-D-thioglucose on a maleimide functionalised surface in order to see how phosphate buffered saline affected the surface chemistry and characterisation of the spots on the surface by using time of flight – secondary ion mass spectrometry

Investigation of warm fog properties and fog modification concepts

Coalescence of warm fog droplets with ionic surfactants, effects of monomolecular layers on droplet nuclei, and fog dynamics - mathematical mode

Distribution of shallow NV centers in diamond revealed by photoluminescence spectroscopy and nanomachining

We performed nanomachining combined with photoluminescence spectroscopy to understand the depth distribution of nitrogen-vacancy (NV) centers formed by low energy nitrogen ion irradiation of the diamond surface. NV− and NV0 fluorescence signals collected from the surface progressively machined by a diamond tip in an atomic force microscope (AFM) initially rise to a maximum at 5 nm depth before returning to background levels at 10 nm. This maximum corresponds to the defect depth distribution predicted by a SRIM simulation using a 2.5 keV implantation energy per nitrogen atom. Full extinguishing of implantation produced NV− and NV0 zero phonon line peaks occurred beyond 10 nm machining depth, coinciding with the end of easy surface material removal and onset of significant tip wear. The wear ratio of for NV active, ion irradiated diamond compared to the single-crystal diamond tip was surprisingly found to be 22:1. The reported results constitute the first integrated study of in-situ machining and wear characterization via optical properties of the diamond surface containing shallow formed NV centers. We discuss possible metrology applications for diamond tools used in precision manufacturing