Search

In the accident at the Fukushima Daiichi Nuclear Power Station, reaction of water vapor with hot zirconium led to the generation of hydrogen and a subsequent explosion in the reactor building. From the perspective of defense-in-depth, multiple hydrogen explosion prevention measures are desirable to improve the safety of nuclear power generation. In this research, we focus on a hydrogen treatment system that re-oxidizes hydrogen into water vapor using a fixed, packed bed of copper oxide pellets. The advantages of this method are that the hydrogen oxidation rate is rapid and no external source of oxygen is necessary. In this study, we conducted experiments and complementary numerical calculations for the hydrogen oxidation reaction using copper oxide pellets. The oxidation reaction of hydrogen by copper oxide is decomposed into five elementary reactions, the rate of each was determined experimentally. The resultant numerical calculation accurately modeled experimentally observed hydrogen oxidation rates and provides insights into the phenomena controlling the reaction progression. The results suggest that the commonly observed induction period is due to the presence of poorly adsorbing sites on the copper oxide surface. Moreover, when water vapor is present, competition between water vapor and hydrogen for adsorption sites further suppresses the hydrogen oxidation reactions.

Nitrous acid (HONO) is a household pollutant exhibiting adverse health effects and a major source of indoor OH radicals under a variety of lighting conditions. The present study focuses on gas-phase HONO and condensed-phase nitrite and nitrate formation on indoor surface thin films following heterogeneous hydrolysis of NO2, in the presence and absence of light, and nitrate (NO3-) photochemistry. These thin films are composed of common building materials including zeolite, kaolinite, painted walls, and cement. Gas-phase HONO is measured using an incoherent broadband cavity-enhanced ultraviolet absorption spectrometer (IBBCEAS), whereby condensed-phase products, adsorbed nitrite and nitrate, are quantified using ion chromatography. All of the surface materials used in this study can store nitrogen oxides as nitrate, but only thin films of zeolite and cement can act as condensed-phase nitrite reservoirs. For both the photo-enhanced heterogeneous hydrolysis of NO2 and nitrate photochemistry, the amount of HONO produced depends on the material surface. For zeolite and cement, little HONO is produced, whereas HONO is the major product from kaolinite and painted wall surfaces. An important result of this study is that surface interactions of adsorbed nitrite are key to HONO formation, and the stronger the interaction of nitrite with the surface, the less gas-phase HONO produced.

Molecular solar thermal (MOST) systems are a promising approach for the introduction of sustainable energy storage solutions. We investigated the feasibility of the dicyano‐substituted norbornadiene/quadricyclane molecule pair on Ni(111) for catalytic model studies. This derivatization is known to lead to a desired bathochromic shift of the absorption maximum of the parent compound. In our experiments further favorable properties were found: At low temperatures, both molecules adsorb intact without any dissociation. In situ temperature‐programmed HR‐XPS experiments reveal the conversion of (CN)2‐quadricyclane to (CN)2‐norbornadiene under energy release between 175 and 260 K. The absence of other surface species due to side reactions indicates full isomerization. Further heating leads to the decomposition of the molecular framework into smaller carbonaceous fragments above 290 K and finally to amorphous structures, carbide and nitride above 400 K. DFT calculations gave insights into the adsorption geometries. (CN)2‐norbornadiene is expected to interact stronger with the surface, with flat configurations being favorable. (CN)2‐quadricyclane exhibits smaller adsorption energies with negligible differences for flat and side‐on geometries. Simulated XP spectra are in good agreement with experimental findings further supporting the specific spectroscopic fingerprints for both valence isomers.

The study of chemical processes on solid surfaces is a powerful tool to discover novel physicochemical concepts with direct implications for processes based on chemical reactions at surfaces, largely exploited by industry. Recent upgrades of experimental tools and computational capabilities, as well as the advent of two-dimensional materials, have opened new opportunities and challenges for surface science. In this Perspective, we highlight recent advances in application fields strictly connected to novel concepts emerging in surface science. Specifically, we show for selected case-study examples that surface oxidation can be unexpectedly beneficial for improving the efficiency in electrocatalysis (the hydrogen evolution reaction and oxygen evolution reaction) and photocatalysis, as well as in gas sensing. Moreover, we discuss the adsorption-assisted mechanism in membrane distillation for seawater desalination, as well as the use of surface-science tools in the study of Li-ion batteries. In all these applications, surface-science methodologies (both experimental and theoretical) have unveiled new physicochemical processes, whose efficiency can be further tuned by controlling surface phenomena, thus paving the way for a new era for the investigation of surfaces and interfaces of nanomaterials. In addition, we discuss the role of surface scientists in contemporary condensed matter physics, taking as case-study examples specific controversial debates concerning unexpected phenomena emerging in nanosheets of layered materials, solved by adopting a surface-science approach. © the Owner Societies 2020.

In this work, the reaction mechanism in the atomic layer deposition (ALD) process of AlF3 thin films is studied with in situ quartz crystal microbalance and quadrupole mass spectrometer. The depositions are done with AlCl3 and TiF4 as precursors. Similar to many metal fluoride films deposited by ALD, the growth rate of the AlF3 is strongly temperature dependent. In addition, at low temperatures, the growth rate is exceptionally high for a traditional ALD process. In this study, the reasons behind these characteristics are studied and a detailed step-by-step mechanism for the AlF3 film growth process is presented.

usc Refereed/Peer-reviewed Electric fields can induce bond breaking and bond forming, catalyze chemical reactions on surfaces, and change the structure of self-assembled monolayers on electrode surfaces. Here, we study the effect of electric fields supplied either by an electrochemical potential or by conducting atomic force microscopy (C-AFM) on Si-based monolayers. We report that typical monolayers on silicon undergo partial desorption followed by the oxidation of the underneath silicon at +1.5 V vs Ag/AgCl. The monolayer loses 28% of its surface coverage and 55% of its electron transfer rate constant (ket) when +1.5 V electrochemical potential is applied on the Si surface for 10 min. Similarly, a bias voltage of +5 V applied by C-AFM induces complete desorption of the monolayer at specific sites accompanied by an average oxide growth of 2.6 nm when the duration of the bias applied is 8 min. Current-voltage plots progressively change from rectifying, typical of metal-semiconductor junctions, to insulating as the oxide grows. These results define the stability of Si-based organic monolayers toward electric fields and have implication in the design of silicon-based monolayers, molecular electronics devices, and on the interpretation of charge-transfer kinetics across them.

With the increasing interest in dry etching of silicon nitride, utilization of hydrogen-contained fluorocarbon plasma has become one of the most important processes in manufacturing advanced semiconductor devices. The correlation between hydrogen-contained molecules from the plasmas and hydrogen atoms inside the SiN plays a crucial role in etching behavior. In this work, the influences of plasmas (CF4/D2 and CF4/H2) and substrate temperature (Ts, from −20 to 50 °C) on etch rates (ERs) of the PECVD SiN films were investigated. The etch rate performed by CF4/D2 plasma was higher than one obtained by CF4/H2 plasma at substrate temperature of 20 °C and higher. The optical emission spectra showed that the intensities of the fluorocarbon (FC), F, and Balmer emissions were stronger in the CF4/D2 plasma in comparison with CF4/H2. From X-ray photoelectron spectra, a thinner FC layer with a lower F/C ratio was found in the surface of the sample etched by the CF4/H2 plasma. The plasma density, gas phase concentration and FC thickness were not responsible for the higher etch rate in the CF4/D2 plasma. The abstraction of H inside the SiN films by deuterium and, in turn, hydrogen dissociation from Si or N molecules, supported by the results of in situ monitoring of surface structure using attenuated total reflectance-Fourier transform infrared spectroscopy, resulted in the enhanced ER in the CF4/D2 plasma case. The findings imply that the hydrogen dissociation plays an important role in the etching of PECVD-prepared SiN films when the hydrogen concentration of SiN is higher. For the films etched with the CF4/H2 at −20 °C, the increase in ER was attributed to a thinner FC layer and surface reactions. On the contrary, in the CF4/D2 case the dependence of ER on substrate temperature was the consequence of the factors which include the FC layer thickness (diffusion length) and the atomic mobility of the etchants (thermal activation reaction).

The most promising source of alumina in the 21st century is the coal fly ash (CFA) waste of coal-fired thermal plants. The methods of alumina extraction from CFA are often based on the pressure alkaline or acid leaching or preliminary roasting with different additives followed by water leaching. The efficiency of the alumina extraction from CFA under atmospheric pressure leaching is low due to the high content of acid-insoluble alumina phase mullite (3Al2O3·2SiO2). This research for the first time shows the possibility of mullite leaching under atmospheric pressure after preliminary desilication using high liquid to solid ratios (L:S ratio) and Na2O concentration. The analysis of the desilicated CFA (DCFA) chemical and phase composition before and after leaching has been carried out by inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray diffraction (XRD). The morphology and elemental composition of solid product particles has been carried out by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). An auto-mated neural network and a shrinking core model (SCM) were used to evaluate experimental data. The Al extraction efficiency from DCFA has been more than 84% at T = 120◦C, leaching time 60 min, the L/S ratio > 20, and concentration of Na2O-400 g L−1. The kinetics analysis by SCM has shown that the surface chemical reaction controls the leaching process rate at T < 110◦C, and, at T > 110◦C after 15 min of leaching, the process is limited by diffusion through the product layer, which can be represented by titanium compounds. According to the SEM-EDX analysis of the solid residue, the magnetite spheres and mullite acicular particles were the main phases that remained after NaOH leaching. The spheric agglomerates of mullite particles with non-porous surface have also been found. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Funding: This work was funded by State Assignment, grant № 075-03-2021-051/5. The method of Al content analysis in CFA by ICP-OES was funded by a Ministry of Science and Higher Education of the Russian Federation scientific topic № 0137-2019-0023.

The synthesis of γ-valerolactone (GVL), a platform molecule that can be produced from lignocellulosic biomass, was performed in this work by hydrogenation of an alkyl levulinate over Ru/C. Kinetic models reported in the literature are typically not compared with rival alternatives, even if a discrimination study is needed to find the optimum operating conditions. Different surface reaction kinetic models were thus considered in this work, specifically addressing hydrogenation of butyl levulinate to GVL, where the latter was used as a solvent to minimize potential solvent interference with the reaction, including its evaporation. The Bayesian approach was applied to evaluate the probability of each model. It was found that non-competitive Langmuir-Hinshelwood with no dissociation of the hydrogen model has the highest posterior probability.

The surface reactivity of carbonaceous nanoparticles is revealed from the barrier height and reaction enthalpy of hydrogen abstraction reaction by H radicals computed at the M06-2X/6–311g(d,p)//B3LYP/6-311G(d,p) level of theory. Small polycyclic aromatic hydrocarbon (PAH) clusters are selected as the model system of carbonaceous nanoparticles. The PAHs considered are naphthalene, pyrene, coronene, ovalene and circumcoronene. Cluster sizes range from dimer to tetramer with a parallel or crossed configuration. All results show similar values as that of monomers, but naphthalene dimers with a crossed configuration yield a lower barrier height and reaction enthalpy by ∼2 kcal/mol. A minor size dependence is noticed in the series of naphthalene clusters where a larger cluster exhibits a smaller barrier height. Larger homogeneous PAH clusters in a size range of 1.1–1.9 nm are later generated to mimic nascent soot surface. It is found that the barrier height decreases with the increase in particle size, and the averaged values are ∼2 kcal/mol lower than that of monomers. More importantly, a larger particle shows a wider spread in barrier heights, and low barrier heights are seen in the surface shallow regions (e.g., surface pockets). The lowest barrier height of ∼8.5 kcal/mol is observed at a C-H site locating in a surface pocket. A set of model systems are built to reveal the underlying mechanism of reduction in barrier height. It is shown that the reduction is caused by local interactions between the neighboring atoms and the local curvature. Further analysis on the average localized ionization potential shows that larger particles have higher reactivity, further supporting our findings from the barrier height of hydrogen abstraction reactions. Therefore, it is concluded that the surface reactivity depends on the particle size and the most reactive sites always locate at the surface pockets.

International audience; Since SrVO3 (SVO) can be used as a highly conductive material for perovskite heterostructures, the control of surface morphology and chemistry of such thin-films are essential. Using pulsed laser deposition, two distinct topographies can be produced. Thus, by tuning oxygen pressure in the growth chamber during cooling, smooth or partially covered by self-oriented Sr3V2O8 nanorods surfaces can be grown. This study manages to correlate the two typical topographies, revealed by atomic force microscopy (AFM), with their chemical compositions obtained by X-ray photoelectron spectroscopy (XPS). At first, a model describes their initial surface chemistry through the Sr/V cationic ratio and the (Sr+V)/Oox ratio. Furthermore, using sputter-depth profiling, post-thermal treatments and wet chemical etching, SVO thin-film chemical compositions are extensively studied. We demonstrate that they are composed of stoichiometric SVO phase covered by Sr-rich layer on top. Finally, treatment in water for 180 seconds helps to remove Sr-rich phases. Sr3V2O8 nanorods are found selectively dissolved leaving a surface nano-imprint. Moreover, on smooth SVO surfaces, a balanced Sr/V cationic ratio of 1.0±0.1 is obtained. These results appear very promising for SVO thin-films surface preparation and further development as electrodes for electronic devices.

Curved single crystals provide variable, but well-defined surface structures. These curved surfaces have enormous potential for applications in surface chemistry, e.g. to unravel the role of specific sites in the reaction mechanism. Measurements can be repeated on the same crystal with incremental changes of the surface structure. Because effectsof sample heterogeneity are avoided, curved crystals make it possible to detect even subtle differences in surface reactivities and assign them to specific surface sites. They were used throughout this thesis to study the effects of surface structure onelemental chemical reaction steps, such as hydrogen dissociation and recombination, or water desorption.

a bstract In this study, different types of waste aluminum produced in daily life and their pure equivalents were evaluated and compared in terms of their hydrogen generation performance through the water-splitting reaction. An experimental system was designed for the production process that consisted of electrodes, DC power supply, alkaline solution, and various waste aluminum products. The hydrogen generation rate of the aluminum source was then measured to determine the optimum conditions for hydrogen production with different types of pure and waste aluminum, normality of the aqueous solution, and applied DC voltage. The best results for micro-hydrogen generation were obtained using pure powder Aluminum, which was attributed to the increased active surface area for the reaction. For beverage can waste (and its powder form), the maximum hydrogen generation rate (cm3/g.min) was achieved using the powder form of the waste aluminum at 2 N alkaline solution. However, the total amount of hydrogen generation (cm3/g) yielded different results compared to the maximum hydrogen generation rate where, when the amount of hydrogen generation volume per mass was considered, the beverage can pieces achieved the best result under constant voltage. This result was attributed to a longer total reaction time.

Herein, the catalytic activities of Cu-and Pt-embedded graphene surfaces on the sequential decomposition reaction of NH3 molecule were investigated by density functional theory (DFT). Partial charge changes on the surfaces by embedding Cu and Pt atoms on the bare graphene surface were analyzed by the Bader charge analysis and depicted by the electron density difference maps. Grimme-D2 dispersion correction was employed for weak interactions between adsorbates and both graphene surfaces. The most stable geometries of the adsorption of NHx (x = 0 -> 3) and H species and their fragmented co-adsorption structures on both graphene surfaces were obtained. The internal energy barrier calculations required for the sequential decomposition of NH3 on both graphene surfaces were calculated by the CINEB method and the results obtained for complete decomposition of NH3 were illustrated by relative energy diagram. The findings revealed that the decomposition of NH3 to NH2, NH, and N on the Cu-embedded graphene surface had relatively lower activation barriers of 1.52 eV, 0.72 eV, and 0.64 eV, respectively, compared to the Pt-embedded graphene surface. The Cu-embedded graphene surface was of high selectivity over the NH3 sequential decomposition reaction. This information may paw the way for different strategies for the development of Cu-based catalysts for NH3 decomposition. (C) 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

A model to explain the hydrogen desorption kinetics in SiGe alloys is presented. This is an extension of a previous desorption model of hydrogen from Si, that considers the presence of three dimer types in the surface in which hydrogen atoms tend to pair before the desorption reaction. Surface diffusion is included in the model. The comparison with experimental results shows that desorption is a diffusion limited process.

Uranium hydride (UH3) is the direct product of the reaction between uranium metal and gaseous hydrogen. In the context of uranium storage, this corrosion reaction is considered deleterious, not just because the structure of the metal may become significantly degraded but also because the resulting hydride is pyrophoric and therefore potentially flammable in air if present in significant quantity. The current review draws from the literature surrounding the uranium-hydrogen system accrued over a 70-year period, providing a comprehensive assessment of what is known about hydride formation, decomposition and oxidation in the context of uranium storage applications

Boron-containing materials are increasingly drawing interest for the use in electronics, optics, laser targets, neutron absorbers, and high-temperature and chemically resistant ceramics. In this article, the first investigation into the deposition of boron-based material via electron beam-induced deposition (EBID) is reported. Thin films were deposited using a novel, large-area EBID system that is shown to deposit material at rates comparable to conventional techniques such as laser-induced chemical vapor deposition. The deposition rate and stoichiometry of boron oxide fabricated by EBID using trimethyl borate (TMB) as precursor is found to be critically dependent on the substrate temperature. By comparing the deposition mechanisms of TMB to the conventional, alkoxide-based precursor tetraethyl orthosilicate it is revealed that ligand chemistry does not precisely predict the pathways leading to deposition of material via EBID. The results demonstrate the first boron-containing material deposited by the EBID process and the potential for EBID as a scalable fabrication technique that could have a transformative effect on the athermal deposition of materials.

The quantitative analysis of the chemistry at the surface of functional plasma polymers is highly important for the optimization of their deposition conditions and, therefore, for their subsequent applications. The chemical derivatization of amine and carboxyl-anhydride layers is a well-known technique already applied by many researchers, notwithstanding the known drawback of the derivatization procedures like side or uncomplete reactions that could lead to “unreliable” results. In this work, X-ray photoelectron spectroscopy (XPS) combined with depth profiling with argon clusters is applied for the first time to study derivatized amine and carboxyl-anhydride plasma polymer layers. It revealed an additional important parameter affecting the derivatization reliability, namely the permeation of the derivatizing molecule through the target analysed layer, i.e. the composite effect of the probe molecule size and the layer porosity. Amine-rich films prepared by RF low pressure plasma polymerization of cyclopropylamine were derivatized with trifluoromethyl benzaldehide (TFBA) and it was observed by that the XPS-determined NH2 concentration depth profile is rapidly decreasing over top ten nanometers of the layer. The anhydride-rich films prepared by atmospheric plasma co-polymerization of maleic anhydride and C2H2 have been reacted with, parafluoroaniline and trifluoroethyl amine. The decrease of the F signal in top surface layer of the anhydride films derivatized by the “large” parafluoroaniline was observed similarly as for the amine films but the derivatization with the smaller trifluoroethylamine (TFEA) led to a more homogenous depth profile. The data analysis suggests that the size of the derivatizing molecule is the main factor, showing that the very limited permeation of the TFBA molecule can lead to underestimated densities of primary amines if the XPS analysis is solely carried out at a low take-off angle. In contrast, TFEA is found to be an efficient derivatization agent of anhydride groups with high permeability through the carboxyl-anhydride layer.

Oxygen vacancy formation and migration are vital properties for reducible oxides such as TiO2, CeO2 and Cr2O3 as the oxygen storage capacity (OSC) of these materials are important for a wide range of applications in photovoltaics, oxidative catalysis and solid oxide fuel cells. Substitutional doping these transition metal oxides enhances their OSC potential, in particular for oxygenation and surface reaction chemistry. This study uses density functional theory with on-site Coulomb interactions (PBE+U) for Cr 3d states (+U = 5 eV) and O 2p states (+U = 5.5 eV) to calculate the oxygen vacancy formation energy and oxygen diffusion pathways for alkali metal (Li, K, Na, Rb) doping of bulk chromium(III) oxide (α-Cr2O3). Substitutional doping of the lattice Cr3+ cations with alkali metals that have a +1 oxidation state, creates two hole states on the neighbouring lattice O atoms, and removal of a lattice oxygen charge compensates the dopants by filling the holes. The removal of the next oxygen describes the reducibility of doped Cr2O3. The oxygen vacancy formation energy is greatly promoted by the alkali dopants with a correlation between the ionic radius of the dopant cation and vacancy formation energy; larger dopants (K, Rb) improve the reducibility more than the smaller dopants (Li, Na). The activation barriers for oxygen migration along different directions in the alkali metal doped Cr2O3 bulk were also calculated to examine the effect of doping on the oxygen migration. The calculated activation energies for the undoped chromia are symmetric in three dimensions (isotropic) and the presence of the dopants break this isotropy. Alkali dopants promote oxygen migration in the oxygen intra-layers while suppressing oxygen migration across the Cr cation layers. The smaller dopants (Li, Na) facilitate easier migration in the oxygen intra-layers to a greater extent than the larger dopants (K, Rb). The Na–Cr2O3 bulk promotes both oxygen vacancy formation and migration which makes it a novel candidate for anode materials in medium temperature SOFCs and battery applications.

We report a facile, one-step, aqueous surface bioconjugation approach for producing an antifungal surface coating that prevents the formation of fungal biofilms. By direct reaction between surface epoxide groups and amine groups on caspofungin, it avoids the use of secondary chemicals. The coating withstands washing with detergent and reduces the growth of the fungal pathogens Candida albicans by log 6 and Candida glabrata by log 3. Importantly, we show that surface adsorption of albumin does not inhibit the activity of this antifungal coating. Refereed/Peer-reviewed

Svojstva međupovršine čvrsto/tekuće ovise o stanjima i električnim svojstvima površine raspršenog materijala. Ta stanja povezana su s površinskim potencijalom. U ovoj disertaciji obrađen je nastanak zajedničkog potencijala izloženih različitih ploha čestice kristala u otopini elektrolita. Mjerena su električna svojstava (električni otpor, dielektričnost) odabranih monokristala metalnih oksida. Čistoća pojedinih kristala (CeO2, TiO2, Fe2O3) provjerena je elektronskom mikroskopijom (SEM i XPS). Površinski potencijal mjeren je korištenjem modificiranih monokristalnih elektroda. Nakon utvrđivanja stabilnosti i ponovljivosti mjerenja, metodom potenciometrijske titracije proučavan je utjecaj pH, ionske jakosti, sastava otopine i protoka otopine uz površinu monokristala na potencijal elektroda izrađenih od monokristala CeO2, TiO2, Fe2O3 i SiO2. Potenciometrijska mjerenja napravljena su i na parovima pojedinih monokristala različitih orijentacija, kako bi se odredio utjecaj pojedinih ploha na zajednički potencijal. Rezultati mjerenja površinskih potencijala na monokristalima obrađeni su numeričkim simulacijama upotrebom modela površinskog kompleksiranja. Utvrđen je doprinos pojedinih ploha zajedničkom površinskom potencijalu, a rezultati su uspoređeni s površinskim potencijalima nanočestica istog kemijskog sastava. Uveden je i opisan ekvivalentni električni krug temeljen na kapacitetima te pripadajući računalni model koji povezuju različite tehnike istraživanja površina i omogućavaju bolje razumijevanje i predviđanje svojstava čestica u ovisnosti o morfologiji. Properties of solid/liquid interfaces are relevant to many physicochemical phenomena in nature and technology. Interfacial properties are related to the state of the surface of dispersed material, which is extremely large in the case of colloidal and nano- dispersions. Surface properties such as reactivity and ability of adsorption depends on the surface electrical properties. One of important such properties is the surface potential, which occurs as a result of charged surface groups formation, surface reactions, and distribution of ions between the interface and bulk. As contrary to particles, surface potentials of crystals can be measured directly by single crystal electrodes. Measured surface potentials contribute to the understanding of thermodynamic and kinetic of surface reactions. The measurements of individual, and common potentials of different crystallographic planes of the same mineral were used to determine their contribution to common potential. Individual surface potentials and common surface potentials of the same crystal were calculated using surface complexation models, and compared to the measured values. An equivalent electrical circuit based on capacities has been introduced and described, as well as its associated computing model which links different techniques of surface investigation, thus enabling better understanding and prediction of particles’ properties in dependence on morphology.

International audience; A kinetic theory describing chemical reactions on crystal surfaces is introduced. Kinetic equations are used to model physisorbed-gas particles and chemisorbed particles interacting with fixed potentials and colliding with phonons. The phonons are assumed to be at equilibrium and the physisorbed-gas and chemisorbed species equations are coupled to similar kinetic equations describing crystal atoms on the surface. An arbitrary number of surface species and heterogeneous chemical reactions are considered, covering Langmuir-Hinshelwood as well as Eley-Rideal mechanisms and the species may be polyatomic. A kinetic entropy is introduced for the coupled system and the H theorem is established. Using a fluid scaling and a Chapman-Enskog method, fluid boundary conditions are derived from the kinetic model and involve complex surface chemistry as well as surface tangential multicomponent diffusion.

Layered double hydroxides are increasingly studied as heavy metal scavengers but the effect of particle size in their removal behavior has not been explored yet. Here, these aspects were studied in three solids with similar structure and composition but different in size and morphology. Nano-sized LDHs were synthesized by a coprecipitation method with separate nucleation and aging steps and compared to a micro-sized LDH. Proton and Cu2+ uptake were studied using both kinetics and isotherms, which were fitted using different models. Decreasing particle size caused an increasing Mg2+ leaching in neutral and basic media and an increased dissolution speed in acid media, both of them due to the larger exposed surface of smaller particles. Depending on the Cu2+ concentration and LDH buffering capacity, Cu2+ removal was produced by Cu(OH)2 precipitation at the particle surface or by isomorphic substitution of Mg2+ ions at the octahedral sites of LDH layers (diadochy). The uptake rate of the latter was controlled by the intraparticle diffusion of Mg2+ ions and, consequently, it was quite independent of the particle size. On the other hand, the uptake capacity decreased with increasing particle size due to the site availability diminution with increasing diffusion path, which led to a decreasing volume of the layer available for Cu2+ uptake for increasing particle size values. Fil: Rojas Delgado, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

This work is a continuation of the article "Surface reactions with participation of oxides of molybdenum and tungsten", published in the previous issue of the journal. The influence of the electric field and the pressure of oxygen in the gas phase on the rate of surface reactions for the synthesis of molybdates of manganese and copper were investigated. It’s found that for the synthesis reaction of molybdate of copper the nature of the dependency of the rate of synthesis and rate of surface reactions from the external parameters are the same, indicating the crucial contribution of surface diffusion to the reactive mass transfer. For the synthesis reaction of molybdate of manganese the dependences of the rate of synthesis and of rate of surface reactions by external parameters differ, indicating that for this reaction, surface diffusion isn’t the main mechanism of mass transfer.

Intrinsically chiral metal surfaces provide enantiospecific reaction environments without the need of co-adsorbed modifiers. Amongst the intrinsically chiral copper surfaces, Cu{531} has the smallest unit cell and the highest density of chiral sites. XPS, NEXAFS and TPD were employed to investigate the adsorption and decomposition behaviour of the two chiral enantiomers of tartaric acid on this surface. The results obtained from XPS and NEXAFS show that at saturation coverage both enantiomers of tartaric acid adsorb in a ?4 configuration through the two carboxylic groups, which are rotated with respect to each other by 90° ± ? 15° within the surface plane. At intermediate coverage the R,R enantiomer adopts a similar configuration, but the S,S enantiomer is different and shows a high degree of dissociation. Growth of multilayers is observed at high exposures when the sample is kept at below 370 K. TPD experiments show that multilayers desorb between 390 K and 470 K and decomposition of the chemisorbed layer occurs between 470 K and 600 K. The desorption spectra support a two-step decomposition mechanism with a Odouble bondCdouble bondCdouble bondO or HO-HCdouble bondCH-OH intermediate that leads to production of CO2 and CO. Enantiomeric differences are observed in the desorption features related to the decomposition of the chemisorbed layer.

The grafting of biogenic monoamine can provide an effective route to modify the surface properties of apatite materials. This study presents the modification of the hydroxyapatite surface by Tyramine prepared by hydrothermal reaction. The nanoparticles of Tyramine grafted hydroxyapatite were characterized by x-ray diffraction, infrared spectroscopy, solid-state NMR spectroscopy, thermal analysis, TEM microscopy, and measurements of the specific surface area (SBET). In situ grafting of Tyramine onto the HAp surface reduces crystal growth through the formation of organic-inorganic hybrid nanoparticles, thereby developing a multifunctional surface, thus providing a good compatibility with surface interaction for cell-modified HAp. To better illustrate the surface properties of the prepared biomaterials, the interaction of methyl-orange with the modified HAp was studied using a modified method developed within the framework of this work. Effect of the grafting rate on the adsorption performance was examined. The adsorption kinetics were well described by a second order model, which is remarkably influenced by the Tyramine grafting rate.

Bismuth has been identified as a material of interest for electronic applications due to its extremely high electron mobility and quantum confinement effects observed at nanoscale dimensions. However, it is also the case that Bi nanostructures are readily oxidised in ambient air, necessitating additional capping steps to prevent surface re-oxidation, thus limiting the processing potential of this material. This article describes an oxide removal and surface stabilization method performed on molecular beam epitaxy (MBE) grown bismuth thin-films using ambient air wet-chemistry. Alkanethiol molecules were used to dissolve the readily formed bismuth oxides through a catalytic reaction; the bare surface was then reacted with the free thiols to form an organic layer which showed resistance to complete reoxidation for up to 10 days.

Layered halide perovskites have recently shown extraordinary potential for low-cost solution-processable optoelectronic applications because of their superior moisture stability over their 3D counterparts. However, few studies have investigated the effect of light on layered hybrid perovskites. Here, the mechanically exfoliated nanoflakes of the 2D perovskite (PEA) 2PbI 4 (PEA, 2-phenylethylammonium) are used as a model to investigate their intrinsic photostability. The light-induced degradation of the flakes is investigated by using in situ techniques including confocal laser scanning microscopy, wide-field fluorescence microscopy, and atomic force microscopy. Under resonant photoexcitation, (PEA) 2PbI 4 degrades to PbI 2. It is clearly shown that this process is initiated at the crystal edges and from the surface. As a consequence, the photoluminescence of (PEA) 2PbI 4 is progressively quenched by surface traps. Importantly, the light-induced degradation can be suppressed by encapsulation using hexagonal boron nitride (hBN) flakes and/or polycarbonates. This report sheds light on a specific mechanism of light-induced degradation in layered perovskites and proposes a new encapsulation method to improve their photostability.

It is through the comparison of experimental results and theoretical calculations that the mechanistic details of several surface photoreactions initiated upon UV(A) illumination of adsorbed oxalic acid on rutile and anatase can be proposed. The absorption of light is found to be rather localized at surface Ti atoms and at the adsorbed species on both TiO2 polymorphs, respectively. Different surface complexes exhibit different photoreactivities, and consequently, each of them may follow a different reaction mechanism. Experimental data can be explained involving reactions such as the interconversion of monodentate into bidentate species which may further be oxidized to CO2 or may even produce OH radicals, while the reduction of monodentate species to the respective aldehyde results in combination with the oxidation of a neighbouring adsorbed OH group into the formation of an adsorbed OOH radical. On the basis of the results presented herein, it is concluded that the direct action of the photocatalytically produced electron-hole pairs on the adsorbed species is the primary step of the photocatalytic reaction, while the intermediate formation of free radical species followed by their reaction with an oxalate molecule can be regarded as a secondary process. Within the system described in this work, OH radicals only appear to be produced following the direct interaction of a hole with the adsorbed organic compound, but not with chemisorbed water molecules. Fil: Mendive, Cecilia Beatriz. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Química; Argentina. Leibniz Universitaet Hannover; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bredow, Thomas. Universitaet Bonn; Alemania Fil: Schneider, Jenny. Leibniz Universitaet Hannover; Alemania Fil: Blesa, Miguel Angel. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de General Sarmiento; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bahnemann, Detlef. Leibniz Universitaet Hannover; Alemania

An investigation of the nature of adsorption of H2O and CO2 on a nitrogen doped zinc oxide cluster surface and the resultant reaction between them has been performed using hybrid density functional theory (DFT) calculations at the B3LYP level of theory in a vacuum. The stable chemisorption modes of CO2 and H2O on metal, oxygen and nitrogen sites were examined. The calculated adsorption energies reveal that the formation of CO2- attached to N is the most favorable process for CO2 on the Zn18O17:N cluster surface, with a binding energy of -1.86 eV. The water molecule spontaneously dissociates on the same surface to produce chemisorbed H? and?OH with an interaction energy of -0.77 eV. The model calculations rationalize the hydrogenation of CO2 by H2 generated from H2O on the cluster surface. Thermodynamically favorable reaction pathways for the formation of methanol on the catalytic surface in a vacuum were proposed. Among the three pathways, methanol formation follows the carbamate route. The carbamate formed undergoes hydrogenation to generate COOH? units, followed by its exothermic decomposition to?CO attached to N and?OH. Further hydrogenation of CO ultimately yields methanol. All of the above steps were computationally evaluated. � The Royal Society of Chemistry 2015.

A novel procedure was developed to determine the direction of silica growth during the formation of a silica shell around aqueous microdroplets in water-in-oil Pickering emulsions. Two fluorescently labeled silica precursors were added consecutively and the resulting microcapsules were visualized via confocal fluorescence microscopy, allowing the conclusion that the locus of reaction moves in the positive radial direction, i.e. from the inside to the outside. A consequence of the growth direction is that water has to diffuse through the shell to participate in the reaction on the outer surface of the shell. This journal is cop. The Royal Society of Chemistry.

Mixtures of straight and defect-free multiwalled carbon nanotubes (MWCNTs), single walled carbon nanohorns (SWCNHs), and multiwalled carbon nanohorns (MWCNHs) were prepared by the arc discharge method. Functionalized Carbon Nanotubes (FCNTs) composed of MWCNTs, MWCNHS and SWCNHs were obtained using acid functionalization process. TiO2/FCNTs (CTP) nanohybrid photocatalysts were obtained with different amounts of FCNTs (2-20 wt%), by wet impregnation method. The photocatalytic activity of both pristine TiO2 as well as the nanohybrids were studied in aqueous glycerol solution under solar irradiation. Reaction parameters such as amount of catalyst and amount of FCNTs in nanohybrids were optimized to ensure high rates of H2 production. With a relatively low amount of pristine TiO2, a high rate of H2 production of 2134 ?mol h-1 gcat -1 has been obtained and is likely due to several factors such as well dispersed catalyst, reduced particle-particle agglomeration, resulting in enhanced light absorption (less light shielding), improved separation of charge carriers and utilization for red-ox reactions. Even better results were obtained with the use of nanohybrid catalysts. The enhanced photocatalytic activities of the nanohybrid catalysts are ascribed to the synergetic effects of FCNTs that minimize light reflection which promotes enhanced solar light sensitization, good dispersion of the catalysts in the reaction solution, and improved surface-interface reactions of photogenerated charge carriers. In the present study 10 wt% FCNTs in nanohybrid (CTP-10) exhibited superior photocatalytic activity for H2 generation, nearly 3 times higher than that of pristine TiO2 catalyst. The CTP-10 photocatalyst exhibited photostability under the experimental conditions studied. The nanohybrid photocatalysts were characterized in order to confirm the crystal structure, morphology, surface chemical composition and optical properties. The present work demonstrates the unique beneficial photocatalytic properties of carbon nanotubes and nanohorn mixtures in nanohybrid photocatalysts, for enhanced H2 production. � 2014 Hydrogen Energy Publications, LLC.

International audience; Oxidative dissolution of pyrite (FeS2) in air-equilibrated solutions was investigated with electrochemical techniques (polarization measurements and electrochemical impedance spectroscopy) at different solution pH (1 to 5) and temperatures (25 to 40 °C). We have found that, at a given temperature, the oxidation current density (jox) varies only slightly from initial pH 1 to 4, but was significantly lower at initial pH 5, while oxidation potential (Eox) decreases when pH increases. At the investigated temperatures, the reaction order with respect to hydrogen ions has been found to be zero, suggesting that H+ is not involved into the rate-determining step of the oxidation rate. The jox values increase with temperature, whereas Eox potentials are hardly affected by temperature from 25 to 40 °C. Activation energies (Ea) were estimated from polarization data and vary between 57 ± 28 kJ/mol (initial pH 5) and 19 ± 3 kJ/mol (initial pH 4). The obtained values indicate that the rate-determining step of the overall oxidative dissolution of FeS2 involves a surface reaction. The importance of surface reaction is also supported by the electrochemical impedance spectroscopy measurements which show that interfacial transfer of electrons is dominated by surface charge transfer and the elementary surface reaction which controls the mineral oxidative dissolution is the electron transfer from the conduction band of pyrite to adsorbed O2.

Pore-scale modeling and simulation of reactive flow in porous media has a range of diverse applications, and poses a number of research challenges. It is known that the morphology of a porous medium has significant influence on the local flow rate, which can have a substantial impact on the rate of chemical reactions. While there are a large number of papers and software tools dedicated to simulating either fluid flow in 3D computerized tomography (CT) images or reactive flow using porenetwork models, little attention to date has been focused on the pore-scale simulation of sorptive transport in 3D CT images, which is the specific focus of this paper. Here we first present an algorithm for the simulation of such reactive flows directly on images, which is implemented in a sophisticated software package. We then use this software to present numerical results in two resolved geometries, illustrating the importance of pore-scale simulation and the flexibility of our software package.

The conformality of ALD growth in narrow trenches is studied by using a long narrow lateral channel fabricated on a silicon wafer. The propagation of ALD growth in the channel is modeled by a diffusion process. The surface reaction is described by dynamic Langmuir adsorption. The film growth is calculated by solving the diffusion equation with surface reactions. Measured thickness distribution gives the equilibrium constant of adsorption and the sticking coefficient. Also the effect of channel narrowing due to film deposition is included in the model.

High permittivity (high-k) materials have received considerable attention as alternatives to SiO2 for CMOS and low-power flexible electronics applications. In this study, we have grown high-quality ZrO2 by using atmospheric-pressure plasma-enhanced spatial ALD (PE-sALD), which, compared to temporal ALD, offers higher effective deposition rates and uses atmospheric-pressure plasma to activate surface reactions at lower temperatures. We used tetrakis(ethylmethylamino)zirconium (TEMAZ) as precursor and O2 plasma as co-reactant at temperatures between 150 and 250◦C. Deposition rates as high as 0.17 nm/cycle were achieved with N- and C- contents as low as 0.4% and 1.5%, respectively. Growth rate, film crystallinity and impurity contents in the films were found to improve with increasing deposition temperature. The measured relative permittivity lying between 18 and 28 with leakage currents in the order of 5 × 10−8 A/cm2 demonstrates that atmospheric PE-sALD is a powerful technique to deposit ultrathin, high-quality dielectrics for low-temperature, large-scale microelectronic applications. © The Author(s) 2017.

The conformality of ALD growth in narrow trenches is studied by using a long narrow lateral channel fabricated on a silicon wafer. The propagation of ALD growth in the channel is modeled by a diffusion process. The surface reaction is described by dynamic Langmuir adsorption. The film growth is calculated by solving the diffusion equation with surface reactions. Measured thickness distribution gives the equilibrium constant of adsorption and the sticking coefficient. Also the effect of channel narrowing due to film deposition is included in the model.

In this paper, we present the progress in the growth of nanoscale semiconductors grown via atomic layer deposition (ALD). After the adoption by semiconductor chip industry, ALD became a widespread tool to grow functional films and conformal ultra-thin coatings for various applications. Based on self-limiting and ligand-exchange-based surface reactions, ALD enabled the low-temperature growth of nanoscale dielectric, metal, and semiconductor materials. Being able to deposit wafer-scale uniform semiconductor films at relatively low-temperatures, with sub-monolayer thickness control and ultimate conformality, makes ALD attractive for semiconductor device applications. Towards this end, precursors and low-temperature growth recipes are developed to deposit crystalline thin films for compound and elemental semiconductors. Conventional thermal ALD as well as plasma-assisted and radical-enhanced techniques have been exploited to achieve device-compatible film quality. Metal-oxides, III-nitrides, sulfides, and selenides are among the most popular semiconductor material families studied via ALD technology. Besides thin films, ALD can grow nanostructured semiconductors as well using either template-assisted growth methods or bottom-up controlled nucleation mechanisms. Among the demonstrated semiconductor nanostructures are nanoparticles, nano/quantum-dots, nanowires, nanotubes, nanofibers, nanopillars, hollow and core-shell versions of the afore-mentioned nanostructures, and 2D materials including transition metal dichalcogenides and graphene. ALD-grown nanoscale semiconductor materials find applications in a vast amount of applications including functional coatings, catalysis and photocatalysis, renewable energy conversion and storage, chemical sensing, opto-electronics, and flexible electronics. In this review, we give an overview of the current state-of-the-art in ALD-based nanoscale semiconductor research including the already demonstrated and future applications.

High permittivity (high-k) materials have received considerable attention as alternatives to SiO2 for CMOS and low-power flexible electronics applications. In this study, we have grown high-quality ZrO2 by using atmospheric-pressure plasma-enhanced spatial ALD (PE-sALD), which, compared to temporal ALD, offers higher effective deposition rates and uses atmospheric-pressure plasma to activate surface reactions at lower temperatures. We used tetrakis(ethylmethylamino)zirconium (TEMAZ) as precursor and O2 plasma as co-reactant at temperatures between 150 and 250◦C. Deposition rates as high as 0.17 nm/cycle were achieved with N- and C- contents as low as 0.4% and 1.5%, respectively. Growth rate, film crystallinity and impurity contents in the films were found to improve with increasing deposition temperature. The measured relative permittivity lying between 18 and 28 with leakage currents in the order of 5 × 10−8 A/cm2 demonstrates that atmospheric PE-sALD is a powerful technique to deposit ultrathin, high-quality dielectrics for low-temperature, large-scale microelectronic applications.

The theoretical study of catalysis would substantialy benefit from the use of atomistic simulations that can provide information beyond mean-field approaches. To date, the nanoscale understanding of surface reactions has been only qualitatively achieved by means of kinetic Monte Carlo coupled to density functional theory, KMC-DFT. Here, we examine a widely employed model for oxygen interaction with the RuO2(110) surface, a highly anisotropic system. Our analysis reveals several covert problems that render as questionable the model’s predictions. We suggest an advanced approach that considers all the relevant elementary steps and configurations while smoothing the intrinsic errors in the DFT description of oxygen. Under these conditions, KMC provides quantitative agreement to temperature-programmed desorption experiments. These results illustrate how KMC-based simulations can be pushed forward so that they evolve toward being the standard methodology to study complex chemistry at the nanoscale.

Electrochromic nickel oxide (Ni 1− x O) pigment powder which was made from nickel acetate reacting with H 2 O 2 /urea solution followed by heat treatment of xerogels at 400 °C (24 h) was milled with zirconia beads in pure water or water with added nickel oxyhydroxy precipitate acting simultaneously as the dispersant and the coating binder. The corresponding pigment particle suspensions were spin coated on FTO glass and flexible ITO-PET foils, respectively, and cured at 150 °C. The optical properties of the deposited pigment coatings on FTO glass substrates were determined with an UV VIS spectrometer, providing total direct transmittance (TT), total diffuse transmittance (DT) and haze (in %). Haze increased with the coating thickness but did not exceed 4%. SEM micrographs of the deposited pigment coatings revealed that they consisted of agglomerated Ni 1− x O pigment with voids. Potential cycling of Ni 1− x O pigment coatings and Ni 1− x O thin films was performed in 1 M LiClO 4 /PC and 0.1 M TBA + triflate/PC electrolytes, revealing that the pigment coatings exhibited electrochemical and electrochromic activity also in lithium free (aprotic) electrolyte, while variations of the oxidation and reduction reaction peaks at various scan rates confirmed the presence of surface electrochemical reactions. The near-grazing incidence angle reflection–absorption spectroscopic technique (IR RA) was employed for identifying surface and inner-grain Ni–O stretching modes, the former being responsible for observed electrochemical properties, which was also demonstrated from the ex situ IR RA measurements performed for coatings charged/discharged in 1 M LiClO 4 /PC and 0.1 M TBA + triflate/PC electrolytes. The results disclosed in this study suggest that the electrochromic effect was not in direct correlation with the de-insertion/insertion of small ions into the NiO (bunsenite) grains but rather the pigment coatings behave similarly to nickel oxide electrochemical capacitors. The electrochromic response of a flexible EC devices made either of PEDOT (self-standing foil) or WO 3 and Ni 1− x O pigment coatings glued with PMMA based electrolytes without and with lithium salt were recorded for the demonstration of the possible practical application of wet deposited Ni 1− x O pigment coatings made as “electrochromic” paints.

This paper presents a systematic study on the effects of angstrom-thick atomic layer deposited (ALD) ZnO sheaths on hydrothermally-grown TiO2 nanowires (NWs) used as photoanodes in dye-sensitized solar cells (DSSCs). We designed, synthesized and characterized the samples prepared using different numbers of ZnO cycles and compared their photovoltaic (PV) performances. The device consisting of TiO2 NWs coated with the optimum thickness (two cycles) of ZnO shell exhibits a three-fold increase in efficiency compared to a control reference device. This paper reports results and features that demonstrate the passivation of surface state traps upon deposition of ZnO shells. While this passivation of surface traps provides a reduction in the back-reactions of the surface state mediated electrons (KET trap), it is speculated that ZnO-induced surface band bending (SBB) substantially reduces the recombination rate of the device by reducing the recombination rate of the conduction band (CB) electrons (KET CB). Moreover, an enhancement in the amount of dye uptake for ZnO-coated TiO2 samples is observed and explained with the isoelectric point (IEP) concept. In spite of the excellent PV power conversion efficiencies achieved by the first ZnO cycles, thicker layers impede the electron injection rate, reducing the efficiency of the device by capturing the photogenerated dye electrons in ZnO quantum wells. Here, we investigate the mechanisms contributing to this unprecedented change and correlate them with the enhancement in device efficiency. © The Royal Society of Chemistry 2014.

The adsorption of NO on Pd atoms and homonuclear transition metal dimers, Pd 2 , deposited on O 2− and Fs sites of the CdO (0 0 1) surface was studied by density functional calculations and an embedded cluster model. Geometrical optimization of adsorption of the molecule NO on Pd/CdO and Pd 2 /CdO with different spin states at particular sites was conducted. Spin polarized calculations were performed, and the systems in the most stable spin states were determined. Spin quenching occurs for Pd 2 complexes at the terrace and defective surfaces. Supported Pd 2 stabilized the low spin states of the adsorbed metals in comparison with free Pd 2 . Although the interaction of Pd and Pd 2 particles with Fs sites is much stronger than with regular O 2− sites, the adsorption of NO is stronger on Pd 2 /CdO (O 2− ) than on Pd 2 /CdO (Fs) with low spin state. Nevertheless, the greater interaction of NOPd and NOPd 2 at O 2− sites increases the energy required to switch from high to low spin. The variations observed in the magnetic properties of the adsorbed species at the CdO (0 0 1) surface are correlated with the energy gaps of the frontier orbitals. The adsorption properties of NO were analyzed with reference to the natural bond orbital, charge transfer, band gaps, the total charge-density contours, and pairwise and non-pairwise additivity. The binding of NO precursor is dominated by the E ( i ) Pd x − NO pairwise additive components, and the role of the support was not restricted to the metal or the dimer.

Highly luminescent germanium nanocrystals (NCs) are synthesized at room temperature by hydride reduction of germanium tetrachloride (GeCl4) within inverse micelles. Regulation of the Ge NC size is achieved by varying the alkyl chain length of the cationic quaternary ammonium surfactants used to form the inverse micelles. The Ge NCs are chemically passivated with allylamine ligands using a Pt-catalyzed hydrogermylation reaction, minimizing surface oxidation while rendering the NCs dispersible in a range of polar solvents. Transmission electron microscopy shows that the NCs are highly crystalline with well-defined core diameters tuned from 3 to 5 nm. UV-Vis absorbance and photoluminescence (PL) spectroscopy show significant quantum confinement effects, with moderate absorption in the UV spectral range, and a strong, narrow luminescence in the visible with a marked dependency on excitation wavelength. A maximum quantum yield of 20% is shown for the nanocrystals, and a transition from primarily blue to green emission is observed as the NC diameter increases to 4.5 nm.