Dye rejection membranes prepared from oxidized graphite particles

This article reports the comparison of different chemical methods to produce graphite-based particles with varying degrees of oxidation as well as graphene oxide (GO) and pristine graphite (PG). Detailed physico-chemical characterization of the resulting materials was carried out, highlighting structural differences and variable oxygen content. The particles were then used to produce supported membranes, which were tested for the rejection of three different organic dyes (Rhodamine B, Methyl Blue and Congo Red), and their performance was rationalized in terms of a combination of properties of the membranes and dyes. In particular, membranes produced using edge-oxidized graphite (EOG) showed comparable performance to those derived from GO in the removal of Congo Red, providing a promising alternative to the aforementioned

Ultrasmooth gold surfaces prepared by chemical mechanical polishing for applications in nanoscience

For over 20 years, template stripping has been the best method for preparing ultrasmooth metal surfaces for studies of nanostructures. However, the organic adhesives used in the template stripping method are incompatible with many solvents, limiting the conditions that may subsequently be used to prepare samples; in addition, the film areas that can be reliably prepared are typically limited to ∼1 cm2. In this article, we present chemical-mechanical polishing (CMP) as an adhesive-free, scalable method of preparing ultrasmooth gold surfaces. In this process, a gold film is first deposited by e-beam evaporation onto a 76-mm-diameter silicon wafer. The CMP process removes ∼4 nm of gold from the tops of the grains comprising the gold film to produce an ultrasmooth gold surface supported on the silicon wafer. We measured root-mean-square (RMS) roughness values using atomic force microscopy of 12 randomly sampled 1 μm × 1 μm areas on the surface of the wafer and repeated the process on 5 different CMP wafers. The average RMS roughness was 3.8 ± 0.5 Å, which is comparable to measured values for template-stripped gold (3.7 ± 0.5 Å). We also compared the use of CMP and template-stripped gold as bottom electrical contacts in molecular electronic junctions formed from n-alkanethiolate self-assembled monolayers as a sensitive test bed to detect differences in the topography of the gold surfaces. We demonstrate that these substrates produce statistically indistinguishable values for the tunneling decay coefficient β, which is highly sensitive to the gold surface topography

Location of cobalt impurities in the surface oxide of stainless steel 316L and metal release in synthetic biological fluids

Since 2021, cobalt (Co) is in Europe classified as carcinogen in quantities exceeding 0.1 wt-%. This affects nickel-rich stainless steels, which contain about 0.2 wt-% Co impurities. Previous findings show the bioaccessibility of Co in stainless steel to be primarily determined by the corrosion resistance. It has been unclear whether Co is distributed heterogeneously in the alloy and the outermost surface and whether a specific location would pose a risk for Co release under specific exposure conditions. This study aimed at locating Co in stainless steel 316L (0.2 wt-% Co) surfaces prior to and after exposure to different synthetic body fluids for 24 h at 37 °C. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICPMS) investigated the location of Co in the surface oxide and extent of release along with other metals (iron, chromium, nickel, and manganese) into synthetic biological fluids (gastric fluid, pH 1.5; lysosomal fluid, pH 4.5; phosphate buffered saline-PBS, pH 7.4). Co was homogeneously distributed along with metallic nickel beneath the surface oxide and co-released with other metals upon surface reformation and passivation. Exposure in PBS resulted in the incorporation of both Co and phosphate in the oxide

Imaging Lipid Distributions in Model Monolayers by ToF-SIMS with Selectively Deuterated Components and Principal Components Analysis

Abstract Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) provides the capability to image the distribution of molecular ions and their associated fragments that are emitted from monolayer films. ToF-SIMS can be applied to the analysis of monolayers of complex lipid mixtures that act as a model to understand the organization of cell membranes into solid-like domains called lipid rafts. The ability to determine the molecular distribution of lipids using ToF-SIMS in monolayer films is also important in studies of the function of pulmonary surfactant. One of the limitations of the use of ToF-SIMS to studies of complex lipid mixtures found in biological systems, arises from the similarity of the mass fragments that are emitted from the components of the lipid mixture. The use of selectively deuterated components in a mixture overcomes this limitation and results in an unambiguous assignment of specific lipids to particular surface domains. The use of deuterium labeling to identify specific lipids in a multi-component mixture can be done by the deuteration of a single lipid or by the addition of more than one lipid with selectively deuterated components. The incorporation of deuterium into the lipid chains does not alter the miscibility or phase behavior of these systems. The use of deuterium labeling to identify lipids and determine their distribution in monolayer films will be demonstrated using two biological systems. Principal components analysis (PCA) is used to further analyze these deuterated systems checking for the origin of the various mass fragments present

Effect of Amino Acids on the Corrosion and Metal Release from Copper and Stainless Steel

Copper (Cu) and stainless steel 316 L are widely used for biomedical applications, such as intrauterine devices and orthopedic/dental implants. Amino acids are abundantly present in biological environments. We investigated the influence of select amino acids on the corrosion of Cu under naturally aerated and deaerated conditions using a phosphate-free buffer. Amino acids increased the corrosion of Cu under both aeration conditions at pH 7.4. Cu release was also significantly (up to 18-fold) increased in the presence of amino acids, investigated at pH 7.4 and 37 °C for 24 h under naturally aerated conditions. Speciation modelling predicted a generally increased solubility of Cu in the presence of amino acids at pH 7.4. 316 L, investigated for metal release under similar conditions for comparison, released about 1,000-fold lower amounts of metals than did Cu and remained passive with no change in surface oxide composition or thickness. However, amino acids also increased the chromium release (up to 52-fold), significantly for lysine, and the iron release for cysteine, while nickel and molybdenum release remained unaffected. This was not predicted by solution speciation modelling. The surface analysis confirmed the adsorption of amino acids on 316 L and, to a lower extent, Cu coupons

Chemical state determination of molecular gallium compounds using XPS

A series of molecular gallium compounds were analyzed using X-ray photoelectron spectroscopy (XPS). Specifically, the Ga 2p and Ga 3d photoelectron binding energies and the Ga L M M Auger electron kinetic energies of compounds with gallium in a range of assigned oxidation numbers and with different stabilizing ligands were measured. Auger parameters were calculated and used to generate multiple chemical speciation (or Wagner) plots that were subsequently used to characterize the novel gallium-cryptand[2.2.2] complexes 1-3 that possess ambiguous oxidation numbers for gallium. The results presented demonstrate the ability of widely accessible XPS instruments to experimentally determine the chemical state of gallium centers and, as a consequence, provide deeper insights into reactivity compared to assigned oxidation and valence numbers. 3/2 5/2 3 45 4

Versatile strained alkyne modified water-soluble AuNPs for interfacial strain promoted azide-alkyne cycloaddition (I-SPAAC)

Versatile water- and organic solvent-soluble AuNPs that incorporate an interfacial strained alkyne capable of efficient pour and mix strain promoted interfacial cycloadditions with azide partners have been synthesized and carefully characterized for the first time. The use of XPS to quantitate the loading of the strained alkyne on the AuNPs is noteworthy. The reactivity towards the interfacial strain promoted azide-alkyne cycloaddition reaction was demonstrated by using azide-decorated polymersomes as bioorthogonal reaction partners. © 2014 The Royal Society of Chemistry

Surface Mobility and Nucleation of a Molecular Switch: Tetraaniline on Hematite

Understanding the dynamics of organic thin film formation is crucial to quality control in organic electronics and smart coatings. We have studied the nucleation and growth of the reduced and the oxidized states of phenyl-capped aniline tetramer (PCAT) deposited on hematite(1000) surfaces by physical vapor deposition. The fully reduced PCAT molecules form 2D islands on the surface, whereas the fully oxidized molecules form 3D islands. Through scaled island size distribution, it was found that the critical island sizes, <i>i</i>, for the reduced and oxidized molecules are <i>i</i> = 4 and 5, respectively. From the dependence of the island density on substrate temperature, the activation energies for the diffusion of the molecules away from the critical cluster were calculated to be 1.30 and 0.55 eV, respectively. At low temperatures, the reduced and the oxidized PCAT molecules form compact islands on the surface. At higher temperatures, the reduced islands become dendritic, whereas the oxidized islands become slightly dendritic. The attempt frequencies for surface diffusion of the reduced and the oxidized islands were estimated to be about 5 × 10²⁵ and 8 × 10¹¹ s^–1, respectively. The former value is in line with the high degree of surface wetting by the reduced PCAT, whereas the latter value shows the higher degree of intermolecular interaction in the fully oxidized PCAT and the low degree of its interaction with the iron oxide surface. Interconversion between oxidized and reduced islands through exposure to a reducing environment, and its impact on island morphology was examined. We also found that the presence of Fe²⁺ defects on the hematite surface did not impact the nucleation and growth of the molecular islands, likely due to a discrepancy in time scale. This study elucidates the interactions between an oligoaniline-based molecular switch (PCAT) and hematite surfaces as a function of molecular oxidation state, with applications in molecular electronics, chemical sensors, and smart coatings