A fundamental understanding of the interplay between ligand-removal kinetics and metal aggregation during the formation of platinum nanoparticles (NPs) in atomic layer deposition of Pt on TiO2 nanopowder using trimethyl(methylcyclo-pentadienyl)platinum(IV) as the precursor and O2 as the coreactant is presented. The growth follows a pathway from single atoms to NPs as a function of the oxygen exposure (PO2 × time). The growth kinetics is modeled by accounting for the autocatalytic combustion of the precursor ligands via a variant of the Finke–Watzky two-step model. Even at relatively high oxygen exposures (<120 mbar s) little to no Pt is deposited after the first cycle and most of the Pt is atomically dispersed. Increasing the oxygen exposure above 120 mbar s results in a rapid increase in the Pt loading, which saturates at exposures >> 120 mbar s. The deposition of more Pt leads to the formation of NPs that can be as large as 6 nm. Crucially, high PO2 (≥5 mbar) hinders metal aggregation, thus leading to narrow particle size distributions. The results show that ALD of Pt NPs is reproducible across small and large surface areas if the precursor ligands are removed at high PO2.@en

The effect of exposure to ambient air of MoS2-based, γ-Al2O3-supported, hydrodesulfurization (HDS) catalysts has been studied using high-resolution transmission electron microscopy (HRTEM). Analysis of unpromoted as well as Ni- and Co-promoted MoS2 samples showed that the number of MoS2 slabs and the average slab length decreased as a function of air exposure time. A parallel X-ray photoelectron spectroscopy (XPS) study showed this effect to be due to oxidation. During the first 24 h of exposure to air, all 1 bar sulfided (Ni/Co)MoS2 samples showed an initial slab length decrease of approximately 20%. After an additional month in air, the slabs had deteriorated significantly further. A sample of CoMoS2 sulfided at 30 bar showed a slightly enhanced effect of oxidation, particularly after the first 5 min in air. The combined HRTEM and XPS results lead to the proposal of the formation of a protective oxide ring around the remaining sulfidic species inside the MoS2 slabs to explain the mechanism of this oxidation process. The data obtained in this study emphasize the general necessity of shielding vulnerable catalyst samples from air during preparation and characterization, a message relevant in all fields of research related to catalysis.@en

Titanium white (TiO2) has been widely used as a pigment in the 20th century. However, its most photocatalytic form (anatase) can cause severe degradation of the oil paint in which it is contained. UV light initiates TiO2-photocatalyzed processes in the paint film, degrading the oil binder into volatile components resulting in chalking of the paint. This will eventually lead to severe changes in the appearance of a painting. To date, limited examples of degraded works of art containing titanium white are known due to the relatively short existence of the paintings in question and the slow progress of the degradation process. However, UV light will inevitably cause degradation of paint in works of art containing photocatalytic titanium white.In this work, a method to detect early warning signs of photocatalytic degradation of unvarnished oil paint is proposed, using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Consequently, a four-stage degradation model was developed through in-depth study of TiO2-containing paint films in various stages of degradation. The XPS surface analysis proved very valuable for detecting early warning signs of paint degradation, whereas the AFM results provide additional confirmation and are in good agreement with bulk gloss reduction.@en

To prevent sintering, ozone treatment at mild temperature is used to remove the capping agent from supported Au nanoparticles. The Au nanoparticles are first synthesized as a colloidal solution and then supported on alumina. Fourier Transform Infra Red (FTIR) shows the capping agent is removed completely. Transmission Electron Microscopy (TEM) and catalytic test reactions show the Au does not sinter significantly upon low temperature ozone treatment.@en

Background: Clinical studies investigating medicinal products need to comply with laws concerning good clinical practice (GCP) and good manufacturing practice (GMP) to guarantee the quality and safety of the product, to protect the health of the participating individual and to assure proper performance of the study. However, there are no specific regulations or guidelines for non-Medicinal Investigational Products (non-MIPs) such as allergens, enriched food supplements, and air pollution components. As a consequence, investigators will avoid clinical research and prefer preclinical models or in vitro testing for e.g. toxicology studies. The aim of this article is to: 1) briefly review the current guidelines and regulations for Investigational Medicinal Products; 2) present a standardised approach to ensure the quality and safety of non-MIPs in human in vivo research; and 3) discuss some lessons we have learned. Methods and results: We propose a practical line of approach to compose a clarifying product dossier (PD), comprising the description of the production process, the analysis of the raw and final product, toxicological studies, and a thorough risk-benefit-analysis. This is illustrated by an example from a human in vivo research model to study exposure to air pollutants, by challenging volunteers with a suspension of carbon nanoparticles (the component of ink cartridges for laser printers). Conclusion: With this novel risk-based approach, the members of competent authorities are provided with standardised information on the quality of the product in relation to the safety of the participants, and the scientific goal of the study.@en

A novel catalyst preparation procedure is proposed in order to enhance the noble metal distribution at low loadings, while controlling the hierarchical porosity of the support material. Thus, a silica-supported platinum catalyst with hierarchical porosity was prepared using a combination of three processes performed in aqueous medium: emulsion polymerisation, sonochemistry and sol-gel synthesis. First, a polystyrene latex template of ca. 130 nm was synthesised by emulsion polymerisation and subsequently decorated with Pt nanoparticles of ca. 2.1 nm by sonochemical reduction of sodium tetrachloroplatinate. Then, the mesoporous silica support was prepared by a two-step acid-base catalysed sol-gel synthesis around the Pt-loaded latex spheres. Materials with specific surface areas and total pore volumes as high as 615 m2 g−1 and 0.74 cm3 g−1, respectively, were obtained.@en

Titanium dioxide is the most abundantly used white pigment of the 20th century. The pigment is still in use, both in the production of contemporary art and for the conservation of older artwork as a retouching pigment. Unfortunately, next to its positive characteristics, the pigment has one major potential drawback: its photocatalytic activity that can cause degradation of artworks in which it is used. In this paper, we report on a new method to test the photocatalytic activity of different quality grades of titanium dioxide white pigments. This can be done quantitatively in a chemical lab or qualitatively in a quick and easy way, in a museum or artists' studio, with limited use of lab equipment. The photocatalytic degradation of an organic dye, acid blue 9, in an aqueous solution containing titanium dioxide, is followed over time by means of UV–Vis spectrophotometry. Dye solutions containing pigments with high photocatalytic activity lose their color within several hours of UVA exposure. On the other hand, dye solutions containing UV-stable titanium dioxide do not degrade within 24 h of UVA exposure. Insight in the photocatalytic activity of titanium white pigments, which can be obtained with this novel test, is of great importance for preventive conservation of modern art.@en

We report the preparation of a novel type of mesoporous silica of the MSU-type family. This material was prepared with Pluronic P123 copolymer in mild acidity according to a two-step process. Its structure was explored by X-ray diffraction, N2 isotherms, SEM and TEM. The TEM study was completed by a 3D tomography analysis that allowed us to obtain information on the morphology of the pore-and-void system. The powder is homogeneous and made of nanoparticles (200 nm in size) built by the folding of ribbons with hexagonally-packed pores (pore diameter of 8.6 nm). This folding creates microvoids in the particles that give rise to an additional porosity. The properties of adsorption/separation of this new type of silica were tested for HPLC. Although the powder was not optimized for this application, the first results on ungrafted silica appear equivalent to those obtained with a commercial HPLC silica powder.@en

In order to elucidate the activation mechanism of iron based Fischer¿Tropsch catalysts, we performed in situ nanoscale structural and compositional analysis during carburization in CO atmosphere. We found that inside an ETEM at 20 Torr CO, hematite reduces while severe sintering occurs. This sintering is enhanced by low pressure conditions in combination with CO gas. The reduction inside the ETEM is so effective that metallic iron can be formed. During the process, about 50 nm sized iron carbide crystallites grow out of the iron (oxide) particles. Upon prolonged reaction, these newly formed crystallites reduce in size to about 5¿30 nm. In contrast to what has been described in the literature until now, no carbon deposits were found on the outer rim of these iron carbides at high temperature conditions. Note however that, in contrast to our measurements, previous studies involved catalysts that were cooled or passivated prior to (TEM) analysis.@en

The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2.@en

Understanding the atomistic details of how platinum surfaces are oxidized under electrochemical conditions is of importance for many electrochemical devices such as fuel cells and electrolysers. Here we use in situ shell-isolated nanoparticle-enhanced Raman spectroscopy to identify the intermediate stages of the electrochemical oxidation of Pt(111) and Pt(100) single crystals in perchloric acid. Density functional theory calculations were carried out to assist in assigning the experimental Raman bands by simulating the vibrational frequencies of possible intermediates and products. The perchlorate anion is suggested to interact with hydroxyl phase formed on the surface. Peroxo-like and superoxo-like two-dimensional (2D) surface oxides and amorphous 3D α-PtO2 are sequentially formed during the anodic polarization. Our measurements elucidate the process of the electrochemical oxidation of platinum single crystals by providing evidence for the structure-sensitive formation of a 2D platinum-(su)peroxide phase. These results may contribute towards a fundamental understanding of the mechanism of degradation of platinum electrocatalysts.@en

In situ surface X-ray diffraction and transmission electron microscopy at 1 bar show massive material transport of platinum during high-temperature NO reduction with H2. A Pt(110) single-crystal surface shows a wide variety of surface reconstructions and extensive faceting of the surface. Pt nanoparticles change their morphology depending on the gas composition: They are faceted in hydrogen-rich environments, but are more spherical in NO-rich environments, indicating the formation of vicinal surfaces. We conclude that high coverage of NO combined with sufficient mobility of platinum surface atoms is the driving force for the formation of steps on both flat surfaces and nanoparticles. Since the steps that are introduced provide strongly coordinating adsorption sites with potential catalytic benefits, this may be of direct practical relevance for the performance of catalytic nanoparticles under high-pressure conditions.@en