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The trade-off between efficiency and stability has limited the application of TiO2 as a catalyst due to its poor surface reactivity. Here, we present a modification of a TiO2 layer with highly stable Sub-5 nm Fe2O3 nanoparticles (NP) by modulating its structure-surface reactivity relationship to attain efficiency-stability balance via a voltage-assisted oxidation approach. In situ simultaneous oxidation of the Ti substrate and Fe precursor using high-energy plasma driven by high voltage resulted in uniform distribution of Fe2O3 NP embedded within porous TiO2 layer. Comprehensive surface characterizations with density functional theory demonstrated an improved electronic transition in TiO2 due to the presence of surface defects from reactive oxygen species and possible charge transfer from Ti to Fe; it also unexpectedly increased the active site in the TiO2 layer due to uncoordinated electrons in Sub-5 nm Fe2O3 NP/TiO2 catalyst, thereby enhancing the adsorption of chemical functional groups on the catalyst. This unique embedded structure exhibited remarkable improvement in reducing 4-nitrophenol to 4-aminophenol, achieving approximately 99% efficiency in 20 ​min without stability decay after 20 consecutive cycles, outperforming previously reported TiO2-based catalysts. This finding proposes a modified-electrochemical strategy enabling facile construction of TiO2 with nanoscale oxides extandable to other metal oxide systems.

Rate maps quantify the variability of surface rates during the dissolution of crystalline matter. Recently, highly spatially resolved rate maps revealed the existence of rhythmic pulses of the material flux from the crystal surface. The mechanism underpinning this behavior is not yet understood but the two potential influencing factors are surface-controlled or transport-controlled conditions that may govern the resulting pulsating reaction kinetics in the system. In this study, we apply two numerical methods to identify the dominating mechanism of pulsating dissolution. First, the influence of solute transport is simulated using a reactive transport model, which yields dissolution rates and concentration distribution due to the flow field, i.e., extrinsic reactivity. Second, the influence of intrinsic surface reactivity inherent to the material is simulated using kinetic Monte Carlo (KMC) simulations, where the distribution of reactive sites over time is observed on an atomic scale. Local dissolution rates can be reproduced with the reactive transport model, but no kinetically effective periodic changes of the concentration gradients can be observed and no new dissolution pulses are generated. Control via periodic changes in extrinsic reactivity is thus ruled out as a governing mechanism. In contrast, pulsating dissolution is clearly observed in the KMC simulation, leading to the conclusion that the self-assembly of varying reactive surface building blocks causes the pulsating dissolution. The simulation results suggest that etch pits generate regions with a high number of steps of single crystal layers and, consequently, with sites of increased reactivity at periodic intervals. These steps move over the crystal surface outward from the pit center and are followed by a region with a low number of surface steps. Only when the steps reach a certain spacing to the center new steps are generated at the transition between the hollow core and the etch pit. This self-assembly is observed as a fundamental behavior of crystalline dissolution in KMC models, without any additional parametrization. It thus represents a fundamental mechanism in crystal dissolution and should be considered for an accurate atomic understanding of crystal dissolution. [ABSTRACT FROM AUTHOR]

Accurate soot modeling in flames is one important tool contributing to an understanding of soot behavior in combustion. Soot models reflect the four principal processes that govern soot dynamics: nucleation, coagulation, surface growth, and oxidation. Existing oxidation models reflect both the temperature-dependent surface oxidation chemical kinetics and also the fact that the surfaces become less reactive as they age. This surface deactivation process has been modeled primarily by using in-flame soot measurements as a basis for developing functional forms and parameters to describe the decay of α, the ratio of active oxidation sites divided by total surface sites. These existing models, in general, overpredict oxidation rates in turbulent diffusion flames. This study presents an alternative soot aging factor model that is based on the analogous process of coal char oxidation deactivation, a well-studied problem. The proposed framework provides a basis for application to a wide range of turbulent diffusion flames. This new model is configured to provide the same parameter α that appears in existing approaches. As such it can be easily applied to the existing published models. The approach is implemented in the fixed-pivot sectional soot model, with the performance compared against literature data for ethylene/air turbulent diffusion flames. With only very minor adjustment from the baseline parameters developed for coal char, the model shows good agreement with the literature flame data. [ABSTRACT FROM AUTHOR]

The paper provides a detailed overview of heterogeneous chemical reactions leading to the electrode surface modification and further reactivity of various functionalized surfaces. Notably, the present paper is different from other typical reviews and books about chemically modified electrodes—it is not aimed at highlighting the recent achievements in the research area, but provides a detailed analysis of the area background produced about 30–50 years ago. While there are many reviews on the present state-of-the-art (mostly describing specific applications), the background of the research area is not well remembered, particularly by young researchers and students. Therefore, the paper is mainly aimed at educational aspects, rather than highlighting the modern applications, which are only briefly mentioned in the concluding section. The chemical structures exemplified in the paper represent a comprehensive collection of the systems produced by various modification reactions. [ABSTRACT FROM AUTHOR]

Adsorption and desorption of ethylene on BaO-terminated (001) barium titanate are investigated by X-ray photoelectron spectroscopy. Carbon is found in an oxidized state, at a binding energy similar to that resulting from CO adsorption on BaTiO3(001). The amount of carbon adsorbed on the surface is also similar to the case of CO/BaTiO3(001). Upon heating the substrate up to the loss of its ferroelectric polarization, the C 1s signal from the oxidized spectral region vanishes. At the same time, there was no noticeable oxygen depletion of the surface after repeated C2H4 adsorption and desorption. The substrate remains stable after repeated oxidative adsorption and desorption of ethylene. Desorption occurs at different temperatures, depending on the adsorption temperature, which suggests different adsorption geometries: non-dissociated adsorption at high temperature with ethylene bond on two surface oxygen atoms, and locally dissociated adsorption at lower temperatures, in “formaldehyde-like” local configurations.

The recent discovery that anaerobic methanogens can reductively dissolve pyrite and utilize dissolution products as a source of iron and sulfur to meet their biosynthetic demands for these elements prompted the development of atomic‐scale nanoparticle models, as maquettes of reactive surface sites, for describing the fundamental redox steps that take place at the mineral surface during reduction. The given report describes our computational approach for modeling n(FeS2) nanoparticles originated from mineral bulk structure. These maquettes contain a comprehensive set of coordinatively unsaturated Fe(II) sites that are connected via a range of persulfide (S22−) ligation. In addition to the specific maquettes with n = 8, 18, and 32 FeS2 units, we established guidelines for obtaining low‐energy structures by considering the pattern of ionic, covalent, and magnetic interactions among the metal and ligand sites. The developed models serve as computational nano‐reactors that can be used to describe the reductive dissolution mechanism of pyrite to better understand the reactive sites on the mineral, where microbial extracellular electron‐transfer reactions can occur. [ABSTRACT FROM AUTHOR]

Although the significance of open metal sites for controlling metal nanoparticle catalysis have been well-documented, the direct identification of authentic active sites remains a grand challenge. In this work, we report a new couple of “isostructural” copper nanoclusters, namely, [Cu41Cl2(2-F-C6H4S)12(CF3COO)6(PPh3)6H19]2- (1H) and [Cu41(2,5-di-Methyl-C6H3S)12(BO3)3Cl3(PPh3)6H19] (2H), from which heavy dependence of catalytic activity on coordinatively unsaturated metal sites is directly visualized. Both clusters have been characterized by various advanced techniques including high resolution mass spectroscopy (MS), ultra-violet visible spectroscopy (UV-Vis), nuclear magnetic resonance (NMR), density functional theory (DFT) calculations and X-ray single crystal diffraction. The clusters adopt a core-shell arrangement, in which the Cu29 core is grown via the face-fusion of three Cu13 units. Notably, such Cu13-based growth mode is observed for the first time for copper nanoclusters. The main difference of the two Cu41 clusters lies in the presence or absence of two additional chlorides on the surface, which in turn heavily control the exposure of metal sites. 2H with more open metal sites exhibits, as envisioned, much higher activity than 1H in catalytic hydrogenation reaction (6-fold increase in rate constant). This work thus not only represent a mode system to directly visualize the true active sites of metal nanoclusters, but also provides the atomistic evidence on highlighting the importance of exposed metal sites for controlling performance of metal nanocatalysts.

Clay minerals and cyanobacteria occur ubiquitously in nature, and both independently influence trace metal cycling due to their high specific surface areas and reactivity. Although the surface reactivity of each is well-studied, the reactivity of clay-cyanobacterial aggregates has received less attention. Here, we performed potentiometric acid-base titrations and Cd adsorption experiments on various concentrations of clay-cyanobacterial aggregates using three clay minerals (kaolinite, illite, and montmorillonite) and two model planktonic cyanobacteria, the freshwater species Synechocystis sp. PCC 6803 and marine species Synechococcus sp. PCC 7002. A component additivity surface complexation modeling (CA-SCM) approach was applied to study the impacts of the aggregation processes on the total surface reactivity. Results demonstrate that the CA-SCM approach effectively predicted the acid-base titration and Cd adsorption behaviors of aggregates at low aggregate concentrations (up to 2.5 g of clay/L for acid-base titration and 0.1 g of clay/L for Cd adsorption), indicating the additivity of the reactivity for the two components. However, at higher aggregate concentrations (25 g of clay/L for acid-base titration and 10 g of clay/L for Cd adsorption), the CA-SCM approach overestimates the acid-base titration and Cd adsorption behaviors for the aggregates, indicating significant surface site blockage during aggregation. Our SEM images show that both cyanobacterial species were covered by layered clay minerals at the surfaces and formed relatively larger aggregates at high aggregate concentrations than at low aggregate concentrations. Based on the combined results, we propose that the interaction between clays and cyanobacteria is relatively weak at low aggregate concentrations (e.g., <10 g of aggregate/L), but that significant obstruction of surface adsorption sites occurs at high aggregate concentrations (e.g., >10 g of aggregate/L), possibly due to the encrustation of bacteria by clay minerals. The implication of this work is that where turbid rivers discharge into estuaries or deltas with high primary phytoplankton productivity, aggregation (or flocculation) processes will cause the depression of surface reactivity of the aggregates and lead to a decrease in metal-binding capacity. Therefore, depending on whether the trace elements are nutrients (e.g., phosphorous) or potentially toxic (e.g., cadmium), this process has the potential to impact the marine biosphere. To ground truth this hypothesis, we further analyzed the correlation between total organic carbon (TOC) content and trace metal compositions in a compiled shale database and the results show clear negative correlation between Cd concentration and the concentration of TOC, Al and Si. Although this offers only an indirect assessment of the role of clay-plankton aggregation, as a first-order test it does indeed show that the aggregation between clay minerals and phytoplanktonic bacteria in estuaries is an essential factor that influences trace-elemental cycling. [ABSTRACT FROM AUTHOR]

In the field of healthcare and dentistry, 316L stainless steel is widely used for its corrosion resistance. However, the presence of lactic acid in salivary solutions can affect its surface reactivity. This study employed electrochemical methods to investigate the influence of lactic acid on 316L stainless steel's corrosion resistance in Fusayama Meyer saliva and saliva doped with varying lactic acid concentrations. The results revealed a significant decrease in polarization resistance as the lactic acid concentration increased, despite a shift toward more positive corrosion potentials. Consequently, the study suggests that the lactic acid presence in salivary solutions should be considered when evaluating the corrosion susceptibility of 316L stainless steel devices. [ABSTRACT FROM AUTHOR]

The oxidation of the (100) surface of Au‐Si‐Ho quasicrystalline approximant was studied using low‐energy electron diffraction and X‐ray photoelectron spectroscopy. The combination of these two techniques provides evidence for a Ho and Si surface segregation induced by O2 adsorption, resulting in the loss of surface long‐range order. [ABSTRACT FROM AUTHOR]

The non‐radiative recombination at the interfaces of perovskite solar cells (PSCs) is a crucial issue that limits the efficiency and stability of the devices. State‐of‐the‐art surface passivation strategies usually utilize alkyl ammonium halides to suppress the non‐radiative recombination of PSCs, but their high surface reactivity leads to the transformation into 2D perovskites under working conditions, limiting the passivation effect and the charge transport of PSCs. Herein, a non‐halide ionic salt 1‐naphthylmethylammonium formate (NMACOOH) is synthesized for surface passivation of perovskite films. In contrast to the traditional 1‐naphthylmethylammonium iodide, NMACOOH treatment hinders the formation of 2D perovskite and forms a thermally stable PbI2‐NMACOOH adduct on the perovskite surface. Surface characterization reveals that NMA+ can passivate the cation vacancies of the 3D perovskite while HCOO− passivates the metallic Pb0 and halide‐vacancy defects. Therefore, the non‐radiative recombination of PSCs is dramatically suppressed and a high open‐circuit voltage of 1.19 V is obtained. Finally, PSCs with high efficiency of 24.75% and improved long‐term stability (98% of the initial efficiency after 1800‐h storage) are obtained. Moreover, the NMACOOH‐passivated devices also show robust operational stability, retaining 83% of the initial efficiency after working for 658 h under continuous one‐sun illumination. [ABSTRACT FROM AUTHOR]

Effect of zinc oxide (ZnO) nanoparticles on vulcanization mechanism of natural rubber and crosslinking structure of its vulcanizate was investigated by rubber‐state NMR spectroscopy. Natural rubber was compounded with various ZnO nanoparticles (c‐ZnO, NC105, NC205, NC23, NC234(STA), and AZ12N), stearic acid, N‐tert‐butyl‐2‐benzothiazole sulfonamide (TBBS), N‐(1,3‐dimethylbutyl)‐N′‐phenylenediamine (6PPD), and sulfur. Vulcanization of the compounded natural rubber was analyzed with a moving die rheometer. The resulting natural rubber vulcanizates were characterized by swelling method, rubber‐state NMR spectroscopy, and tensile test. The rubber‐state NMR measurements revealed that natural rubber was efficiently vulcanized with NC205 and AZ12N but not with c‐ZnO, NC234, and NC234(STA). A relationship between the structure of vulcanized natural rubber and surface activity, surface structure, and particle size of the ZnO nanoparticles was investigated in this study. The mechanical properties of vulcanized natural rubber were found to depend on not only strain‐induced crystallization but also amount of effective CS linkages. [ABSTRACT FROM AUTHOR]

MXene materials have found emerging applications as catalysts for chemical reactions due to their intriguing physical and chemical applications. In particular, their broad light response and strong photothermal conversion capabilities are likely to render MXenes promising candidates for photothermal catalysis, which is drawing increasing attention in both academic research and industrial applications. MXenes are likely to satisfy all three criteria of a desirable photothermal catalyst: strong light absorption, effective heat management, and versatile surface reactivity. However, their specific functionalities are largely dependent on their structure and composition, which makes understandings of the structure–function relationship of crucial significance. In this review, we mainly focus on the recent progress of MXene–based photothermal catalysts, emphasizing the functionalities and potential applications of MXene materials in fields of photothermal catalysis, and provide insights on design principles of highly efficient MXene–based photothermal catalysts from the atomic scale. This review provides a relatively thorough understanding of MXene–based materials for photothermal catalysis, as well as an in–depth investigation of emerging high-prospect applications in photothermal catalysis.

The Mars–van Krevelen mechanism is the foundation for oxide-catalyzed oxidation reactions and relies on spatiotemporally separated redox steps. Herein, we demonstrate the tunability of this separation with peroxide species formed by excessively adsorbed oxygen, thereby modifying the catalytic activity and selectivity of the oxide. Using CuO as an example, we show that a surface layer of peroxide species acts as a promotor to significantly enhance CuO reducibility in favor of H2 oxidation but conversely as an inhibitor to suppress CuO reduction against CO oxidation. Together with atomistic modeling, we identify that this opposite effect of the peroxide on the two oxidation reactions stems from its modification on coordinately unsaturated sites of the oxide surface. By differentiating the chemical functionality between lattice oxygen and peroxide, these results are closely relevant to a wide range of catalytic oxidation reactions using excessively adsorbed oxygen to activate lattice oxygen and tune the activity and selectivity of redox sites. [ABSTRACT FROM AUTHOR]

MXene materials have found emerging applications as catalysts for chemical reactions due to their intriguing physical and chemical applications. In particular, their broad light response and strong photothermal conversion capabilities are likely to render MXenes promising candidates for photothermal catalysis, which is drawing increasing attention in both academic research and industrial applications. MXenes are likely to satisfy all three criteria of a desirable photothermal catalyst: strong light absorption, effective heat management, and versatile surface reactivity. However, their specific functionalities are largely dependent on their structure and composition, which makes understandings of the structure–function relationship of crucial significance. In this review, we mainly focus on the recent progress of MXene–based photothermal catalysts, emphasizing the functionalities and potential applications of MXene materials in fields of photothermal catalysis, and provide insights on design principles of highly efficient MXene–based photothermal catalysts from the atomic scale. This review provides a relatively thorough understanding of MXene–based materials for photothermal catalysis, as well as an in–depth investigation of emerging high-prospect applications in photothermal catalysis. [ABSTRACT FROM AUTHOR]

Mitigating the release of dihydrogen resulting from metal corrosion or water radiolysis is an important issue for the disposal of certain types of cemented radwaste packages. The approach investigated in this work consists in adding an oxide getter (γ-MnO 2 /Ag 2 CO 3) to the cement matrix. Since the efficiency of the getter decreases under wet environment, two self-desiccating binders (calcium sulfo-aluminate and magnesium potassium phosphate cements), are used to obtain significant desaturation of the pore network by the sole hydration reactions. The getter slightly influences the rate of cement hydration at early age, but has no effect afterwards. Sorption of ions released by dissolution of cement phases onto γ-MnO 2 is evidenced, as well as partial or total destabilization of silver carbonate. Nevertheless, the getter still enables to reduce strongly the outgassing of dihydrogen from mortars encapsulating Al-metal, which opens new perspectives to improve the conditioning of waste producing H 2 in a cement matrix. • Design of cement-based materials for hydrogen sequestration • Dispersion of an oxide getter (87 % γ-MnO 2 – 13 % Ag 2 CO 3) in the cement matrix • Limited influence on calcium sulfoaluminate and magnesium phosphate cements hydration • Sorption of ions onto γ-MnO 2 and destabilization of Ag 2 CO 3 in cement environment • Strong decrease of H 2 outgassing from mortars encapsulating Al metal [ABSTRACT FROM AUTHOR]

MnO 2 phase of manganese oxide was identified as the final product of a multiple steps reaction in near ambient pressure-X-ray photoemission (NAP-XPS) chamber. At the first stage of the reaction, an intermediate stable manganese hydroxide film was obtained at ∼ 400 °C in presence of p(O 2) and p(H 2 O) and verified by the formation of sizeable hydroxide peak, OH, at binding energy 531.4 (1) eV. The Mn hydroxide film is kept unaltered even when is subsequently exposed to p(O 2)= 2 mbar at ∼ 450 °C, and it is modified into δ -MnO 2 phase at ∼ 480 °C when p(O 2) pressure is suddenly reduced to below 10−9 mbar. Thus, the OH spectral feature becomes the main signature in O 1s core level spectral regions and a Mn 4 + related feature is identified in Mn 2p energy range. The multiple step reaction follows the proposed mechanism for the MnO 2 formation in electrolytic cell and it is the first observation in a controlled way in NAP-XPS chamber. The findings open new roots for the birnessite manganese oxide phase formation and its manipulation. [Display omitted] • Reactivity of Mn 3 O 4 under near ambient pressure of H 2 O and O 2. • MnO 2 thin film formation. • Mn oxidation state modification in near ambient pressure reaction. [ABSTRACT FROM AUTHOR]

In the field of healthcare and dentistry, 316L stainless steel is widely used for its corrosion resistance. However, the presence of lactic acid in salivary solutions can affect its surface reactivity. This study employed electrochemical methods to investigate the influence of lactic acid on 316L stainless steel’s corrosion resistance in Fusayama Meyer saliva and saliva doped with varying lactic acid concentrations. The results revealed a significant decrease in polarization resistance as the lactic acid concentration increased, despite a shift toward more positive corrosion potentials. Consequently, the study suggests that the lactic acid presence in salivary solutions should be considered when evaluating the corrosion susceptibility of 316L stainless steel devices.

Considering the increasing production of engineered nanomaterials (ENMs), new approach methodologies (NAMs) are essential for safe-by-design approaches and risk assessment. Our aim was to enhance screening strategies with a focus on reactivity-triggered toxicities. We applied in vitro tests to 10 selected benchmark ENMs in two cell models, lung epithelial A549 and differentiated THP-1 macrophage-like cells. Previously, we categorized ENMs based on surface reactivity. Here we elucidated their reactivity-triggered cytotoxicity and mode of action using the WST-1 assay (metabolic activity), LDH assay (cell membrane integrity), autophagosome detection, and proteomics. Nonreactive SiO 2 NM-200 showed no significant impact on cell viability. Conversely, highly reactive CuO and ZnO (NM-110 and NM-111) disrupted cell homeostasis. Interestingly, moderately reactive TiO 2 (NM-101 and NM-105) and CeO 2 (NM-211 and NM-212), apparently without an adverse effect, induced autophagosome formation, evidencing autophagy as a defensive mechanism. Our improved in vitro testing strategy, combined with state-of-the-art reactivity information, screens ENMs for potential reactivity-triggered toxicity.

This work presents the results of comparative studies using complementary methods, such as scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), and thermal desorption spectroscopy (TDS) to investigate the local surface morphology and chemistry of flower-like ZnO nanostructures synthesized by the thermal oxidation technique on native Si/SiO2 substrates. SEM studies showed that our flower-like ZnO nanostructures contained mostly isolated and irregular morphological low-dimensional forms, seen as rolled-up floss flowers, together with local, elongated, complex stalks similar to Liatris flowers, which contained joined short flosses in the form of nanodendrites. Beyond this, XPS studies showed that these nanostructures exhibited a slight surface nonstoichiometry, mostly related to the existence of oxygen-deficient regions, combined with strong undesired C surface contamination. In addition, the TDS studies showed that these undesired surface contaminations (including mainly C species and hydroxyl groups) are only slightly removed from the surface of our flower-like ZnO nanostructures, causing an expected modification of their nonstoichiometry. All of these effects are of great importance when using our flower-like ZnO nanostructures in gas sensor devices for detecting oxidizing gases because surface contamination leads to an undesired barrier for toxic gas adsorption, and it can additionally be responsible for the uncontrolled sensor aging effect. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) have the potential to be a paradigm-shift for rational catalyst discovery but this new type of alloy requires a completely new approach to predict the surface reactivity. In addition to the ligand effect perturbing the surface-adsorbate bond, the random configuration of elements in the surface will also induce local strain effects due to the varying radii of neighboring atoms. Accurate modelling of HEA surface reactivity requires an estimate of this effect: To what degree is the adsorption of intermediates on these lattice distorted atomic environments affected by local strain? In this study, more than 3,500 density functional theory (DFT) calculated adsorption energies of *OH and *O adsorbed on the HEAs IrPdPtRhRu and AgAuCuPdPt are statistically analyzed with respect to the lattice constants of the alloys and the surfaces of each individual binding site. It is found that the inherent distortion of the lattice structure in HEAs releases the local strain effect on the adsorption energy as the atomic environment surrounding the binding atom(s) settles into a relaxed structure. This is even observed to be true for clusters of atoms of which the sizes deviate significantly from the atomic environment in which they are embedded. This elucidates an important aspect of binding site interaction with the neighboring atoms and thus constitutes a step towards a more accurate theoretical model of estimating the reactivity of HEA surfaces. [ABSTRACT FROM AUTHOR]

Size reduction can generally enhance the surface reactivity of inorganic nanomaterials. The origin of this nano-effect has been ascribed to ultrasmall size, large specific surface area, or abundant defects, but the most intrinsic electronic-level principles are still not fully understood yet. By combining experimental explorations and mathematical modeling, herein we propose an electronic-level model to reveal the physicochemical nature of size-dependent nanomaterial surface reactivity. Experimentally, we reveal that competitive redistribution of surface atomic orbitals from extended energy band states into localized surface chemical bonds is the critical electronic process of surface chemical interactions, using H2O2-TiO2 chemisorption as a model reaction. Theoretically, we define a concept, orbital potential (G), to describe the electronic feature determining the tendency of orbital redistribution, and deduce a mathematical model to reveal how size modulates surface reactivity. We expose the dual roles of size reduction in enhancing nanomaterial surface reactivity—inversely correlating to orbital potential and amplifying the effects of other structural factors on surface reactivity. [ABSTRACT FROM AUTHOR]

A novel concept was successfully evaluated for the electrochemical quantitative analysis of zinc oxide nanoparticles originally in aqueous suspension. An aliquot of the suspension was first placed on the working area of a graphite screen-printed electrode and the water was evaporated to form a dry deposit of ZnO nanoparticles. Deposition of ZnO nanoparticles on the electrode was confirmed by energy-dispersive X-ray spectroscopy. A probe solution containing KCl and sodium metabisulfite was added on top of the deposit for electrochemical analysis by cyclic voltammetry. The anodic peak current (Ipa) for metabisulfite, measured at +1.2 V vs. Ag/AgCl, afforded a lower detection limit of 3 µg and exhibited a linear dependence on the mass of deposited ZnO nanoparticles up to 15 μg. Further, the current increased nonlinearly until it reached a saturation level beyond 60 μg of ZnO nanoparticles. The diffusion coefficient of metabisulfite anions through the electrical double layer was determined to be 4.16 × 10−5 cm2/s. Apparently the surface reactivity of ZnO originated from the oxide anion rather than the superoxide anion or the hydroxyl radical. Enhancement of the metabisulfite oxidation peak current can be developed into a sensitive method for the quantitation of ZnO nanoparticles. [ABSTRACT FROM AUTHOR]

We develop an encounter-based approach for describing restricted diffusion with a gradient drift toward a partially reactive boundary. For this purpose, we introduce an extension of the Dirichlet-to-Neumann operator and use its eigenbasis to derive a spectral decomposition for the full propagator, i.e. the joint probability density function for the particle position and its boundary local time. This is the central quantity that determines various characteristics of diffusion-influenced reactions such as conventional propagators, survival probability, first-passage time distribution, boundary local time distribution, and reaction rate. As an illustration, we investigate the impact of a constant drift onto the boundary local time for restricted diffusion on an interval. More generally, this approach accesses how external forces may influence the statistics of encounters of a diffusing particle with the reactive boundary. [ABSTRACT FROM AUTHOR]

Adsorption and desorption of ethylene on BaO-terminated (001) barium titanate are investigated by X-ray photoelectron spectroscopy. Carbon is found in an oxidized state, at a binding energy similar to that resulting from CO adsorption on BaTiO 3 (001). The amount of carbon adsorbed on the surface is also similar to the case of CO/BaTiO 3 (001). Upon heating the substrate up to the loss of its ferroelectric polarization, the C 1s signal from the oxidized spectral region vanishes. At the same time, there was no noticeable oxygen depletion of the surface after repeated C 2 H 4 adsorption and desorption. The substrate remains stable after repeated oxidative adsorption and desorption of ethylene. Desorption occurs at different temperatures, depending on the adsorption temperature, which suggests different adsorption geometries: non-dissociated adsorption at high temperature with ethylene bond on two surface oxygen atoms, and locally dissociated adsorption at lower temperatures, in "formaldehyde-like" local configurations., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Iron minerals are widespread in earth's surface water and soil. Recent studies have revealed that under sunlight irradiation, iron minerals are photoactive on producing reactive oxygen species (ROS), a group of key species in regulating elemental cycling, microbe inactivation, and pollutant degradation. In nature, iron minerals exhibit varying crystallinity under different hydrogeological conditions. While crystallinity is a known key parameter determining the overall activity of iron minerals, the impact of iron mineral crystallinity on photochemical ROS production remains unknown. Here, we assessed the photochemical ROS production from ferrihydrites with different degrees of crystallinity. All examined ferrihydrites demonstrated photoactivity under irradiation, resulting in the generation of hydrogen peroxide (H 2 O 2 ) and hydroxyl radical ( • OH). The photochemical ROS production from ferrihydrites increased with decreasing ferrihydrite crystallinity. The crystallinity-dependent photochemical • OH production was primarily attributed to conduction band reduction reactions, with the reduction of O 2 by conduction band electrons being the rate-limiting key process. Conversely, the crystallinity of iron minerals had a negligible influence on photon-to-electron conversion efficiency or surface Fenton-like activity. The difference in ROS productions led to a discrepant degradation efficiency of organic pollutants on iron mineral surfaces. Our study provides valuable insights into the crystallinity-dependent ROS productions from iron minerals in natural systems, emphasizing the significance of iron mineral photochemistry in natural sites with abundant lower-crystallinity iron minerals such as wetland water and surface soils.

Current reactive transport model (RTM) uses transport control as the sole arbiter of differences in reactivity. For the simulation of crystal dissolution, a constant reaction rate is assumed for the entire crystal surface as a function of chemical parameters. However, multiple dissolution experiments confirmed the existence of an intrinsic variability of reaction rates, spanning two to three orders of magnitude. Modeling this variance in the dissolution process is vital for predicting the dissolution of minerals in multiple systems. Novel approaches to solve this problem are currently under discussion. Critical applications include reactions in reservoir rocks, corrosion of materials, or contaminated soils. The goal of this study is to provide an algorithm for multi-rate dissolution of single crystals, to discuss its software implementation, and to present case studies illustrating the difference between the single rate and multi-rate dissolution models. This improved model approach is applied to a set of test cases in order to illustrate the difference between the new model and the standard approach. First, a Kossel crystal is utilized to illustrate the existence of critical rate modes of crystal faces, edges, and corners. A second system exemplifies the effect of multiple rate modes in a reservoir rock system during calcite cement dissolution in a sandstone. The results suggest that reported variations in average dissolution rates can be explained by the multi-rate model, depending on the geometric configurations of the crystal surfaces. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mo-doped Ni-rich cathode possess superior radially aligned microstructure. • W-doped Ni-rich cathode possess more stable grain surface. • Differences induced by varied microstructure and surface stability are investigated. • Consequence of surface reactivity on cycle life of cathode is more critical. Capacity fading of Ni-rich cathode is thought to originate from the formation of inactive rock-salt phase induced by surface reactivity and the isolation of active material caused by microcracks due to anisotropic volume contraction of grains. It is generally assumed that inhibiting the formation of microcracks within secondary particle by radially aligned microstructure is a vital aspect for suppressing capacity fading. However, the new researches about reduction of microcracks simply by certain electrolytes call a question on the origin of microcracks and the critical factor for the cycle life of cathodes. Herein, LiNi 0.92 Co 0.04 Mn 0.04 O 2 cathodes with different surface characteristic and radially aligned microstructure were synthesized by doping with high valence elements using some hydroxide precursor. The effects of W6+ and/or Mo6+ induced surface phase and microstructure on electrochemical performance were investigated. Despite the inferior radially aligned, size-refined primary grains and higher degree of microcracks, W6+ doped cathode still possesses alleviated parasitic reactions, higher crystal structural stability and capacity retention than Mo6+ doped materials, because of the enhanced cathode-electrolyte interfacial stability. The results contend that the consequence of surface reactivity on determining cycle life of Ni-rich cathodes is more critical than that of microcracks, and efforts relating to constructing intact and uniform stable surface phase will exhibit greater potential to promote the performance of Ni-rich cathodes than microstructural refinement. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synergistic activation with Cu2+ and Pb2+ can significantly increase the flotation recovery of sulfidized hemimorphite. • Multi-metal sulfide species were formed on sulfidized hemimorphite after synergistic activation with Cu2+ and Pb2+. • Surface hydrophobicity of sulfidized hemimorphite was enhanced after synergistic activation with Cu2+ and Pb2+. In this work, the synergistic effects of Cu2+ and Pb2+ on the flotation behavior, surface properties, and xanthate adsorption of sulfidized hemimorphite were investigated through flotation experiments, surface analysis, and solution determination. The results of the micro-flotation tests indicated that the flotation recovery of sulfidized hemimorphite increased after synergistic activation with Cu2+ and Pb2+, the flotation index can reach about 87%, and superior to that treated with single Cu2+ or Pb2+. Zeta potential, XPS, and ToF-SIMS measurements showed that Cu2+ and Pb2+ were adsorbed onto the sulfidized hemimorphite surface, and multi-metal sulfide species, such as zinc sulfide, copper sulfide, and lead sulfide, were formed. Compared to a single treatment with Cu2+ or Pb2+, the content and activity of sulfidization products became increased after sulfidized hemimorphite was simultaneously activated. The formation of a greater amount of highly active copper and lead species was beneficial for the adsorption of xanthate onto the sulfidized hemimorphite surface, improving surface hydrophobicity. FT − IR, contact angle, and adsorption capacity measurements showed that more xanthate species interacted with the sulfidized hemimorphite surface activated with Cu2+ and Pb2+, and the surface hydrophobicity of the sulfidized hemimorphite was significantly enhanced. [ABSTRACT FROM AUTHOR]

Abstract Background Amorphous silica nanoparticles (SiO2 NPs) have been regarded as relatively benign nanomaterials, however, this widely held opinion has been questioned in recent years by several reports on in vitro and in vivo toxicity. Surface chemistry, more specifically the surface silanol content, has been identified as an important toxicity modulator for SiO2 NPs. Here, quantitative relationships between the silanol content on SiO2 NPs, free radical generation and toxicity have been identified, with the purpose of synthesizing safer-by-design fumed silica nanoparticles. Results Consistent and statistically significant trends were seen between the total silanol content, cell membrane damage, and cell viability, but not with intracellular reactive oxygen species (ROS), in the macrophages RAW264.7. SiO2 NPs with lower total silanol content exhibited larger adverse cellular effects. The SAEC epithelial cell line did not show any sign of toxicity by any of the nanoparticles. Free radical generation and surface reactivity of these nanoparticles were also influenced by the temperature of combustion and total silanol content. Conclusion Surface silanol content plays an important role in cellular toxicity and surface reactivity, although it might not be the sole factor influencing fumed silica NP toxicity. It was demonstrated that synthesis conditions for SiO2 NPs influence the type and quantity of free radicals, oxidative stress, nanoparticle interaction with the biological milieu they come in contact with, and determine the specific mechanisms of toxicity. We demonstrate here that it is possible to produce much less toxic fumed silicas by modulating the synthesis conditions.

Abstract Background Silica continues to represent an intriguing topic of fundamental and applied research across various scientific fields, from geology to physics, chemistry, cell biology, and particle toxicology. The pathogenic activity of silica is variable, depending on the physico-chemical features of the particles. In the last 50 years, crystallinity and capacity to generate free radicals have been recognized as relevant features for silica toxicity. The ‘surface’ also plays an important role in silica toxicity, but this term has often been used in a very general way, without defining which properties of the surface are actually driving toxicity. How the chemical features (e.g., silanols and siloxanes) and configuration of the silica surface can trigger toxic responses remains incompletely understood. Main body Recent developments in surface chemistry, cell biology and toxicology provide new avenues to improve our understanding of the molecular mechanisms of the adverse responses to silica particles. New physico-chemical methods can finely characterize and quantify silanols at the surface of silica particles. Advanced computational modelling and atomic force microscopy offer unique opportunities to explore the intimate interactions between silica surface and membrane models or cells. In recent years, interdisciplinary research, using these tools, has built increasing evidence that surface silanols are critical determinants of the interaction between silica particles and biomolecules, membranes, cell systems, or animal models. It also has become clear that silanol configuration, and eventually biological responses, can be affected by impurities within the crystal structure, or coatings covering the particle surface. The discovery of new molecular targets of crystalline as well as amorphous silica particles in the immune system and in epithelial lung cells represents new possible toxicity pathways. Cellular recognition systems that detect specific features of the surface of silica particles have been identified. Conclusions Interdisciplinary research bridging surface chemistry to toxicology is progressively solving the puzzling issue of the variable toxicity of silica. Further interdisciplinary research is ongoing to elucidate the intimate mechanisms of silica pathogenicity, to possibly mitigate or reduce surface reactivity.

This work presents the results of comparative studies using complementary methods, such as scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), and thermal desorption spectroscopy (TDS) to investigate the local surface morphology and chemistry of flower-like ZnO nanostructures synthesized by the thermal oxidation technique on native Si/SiO2 substrates. SEM studies showed that our flower-like ZnO nanostructures contained mostly isolated and irregular morphological low-dimensional forms, seen as rolled-up floss flowers, together with local, elongated, complex stalks similar to Liatris flowers, which contained joined short flosses in the form of nanodendrites. Beyond this, XPS studies showed that these nanostructures exhibited a slight surface nonstoichiometry, mostly related to the existence of oxygen-deficient regions, combined with strong undesired C surface contamination. In addition, the TDS studies showed that these undesired surface contaminations (including mainly C species and hydroxyl groups) are only slightly removed from the surface of our flower-like ZnO nanostructures, causing an expected modification of their nonstoichiometry. All of these effects are of great importance when using our flower-like ZnO nanostructures in gas sensor devices for detecting oxidizing gases because surface contamination leads to an undesired barrier for toxic gas adsorption, and it can additionally be responsible for the uncontrolled sensor aging effect.

A novel concept was successfully evaluated for the electrochemical quantitative analysis of zinc oxide nanoparticles originally in aqueous suspension. An aliquot of the suspension was first placed on the working area of a graphite screen-printed electrode and the water was evaporated to form a dry deposit of ZnO nanoparticles. Deposition of ZnO nanoparticles on the electrode was confirmed by energy-dispersive X-ray spectroscopy. A probe solution containing KCl and sodium metabisulfite was added on top of the deposit for electrochemical analysis by cyclic voltammetry. The anodic peak current (Ipa) for metabisulfite, measured at +1.2 V vs. Ag/AgCl, afforded a lower detection limit of 3 µg and exhibited a linear dependence on the mass of deposited ZnO nanoparticles up to 15 μg. Further, the current increased nonlinearly until it reached a saturation level beyond 60 μg of ZnO nanoparticles. The diffusion coefficient of metabisulfite anions through the electrical double layer was determined to be 4.16 × 10−5 cm2/s. Apparently the surface reactivity of ZnO originated from the oxide anion rather than the superoxide anion or the hydroxyl radical. Enhancement of the metabisulfite oxidation peak current can be developed into a sensitive method for the quantitation of ZnO nanoparticles.

Large-scale ab initio Meta-Dynamics simulations were applied to elucidate the molecular mechanism and reaction free energies of pyrophyllite dissolution at the (1 1 0) edge surface in pure water at close to neutral pH under far from equilibrium conditions. The simulation setup allows realistic representation of the clay mineral surface and explicit consideration of solvent dynamics at finite temperature. The simulation reveals that dissolution of a single tetrahedral or an octahedral unit from the clay mineral edge is a complex multi-step process with several reaction intermediates. Typically, each reaction step changes denticity of the reacting site in a step-by-step manner and leads, eventually, to the leaching of ions forming octahedral and tetrahedral sheets of the phyllosilicate. The solvent rearrangement and the proton transfer reactions in the first and the second coordination shell of the dissolving unit play a critical role in the stabilization of reaction intermediates and the net progress of the dissolution reactions. The overall reaction mechanism can be rationalized as sequence of concurrent and reversible elementary reaction events, which are: (1) the nucleophilic attack of H 2 O molecules or OH groups on the dissolving surface site. (2) ligand exchange reactions in the first coordination shell of the reacting sites leading to changes of its conformation and denticity at the mineral surface. (3) collective proton transfer reactions between the acidic and basic oxygen sites mediated via a chain of the hydrogen bonded molecules in the first and second coordination shell of the reacting site. The results obtained in this study are general and applicable to the group of 2:1 phyllosilicates in a wide range of chemical and thermodynamic conditions. [ABSTRACT FROM AUTHOR]

The surface reactivity of metals is fundamentally dependent on the local electronic structure generally tailored by atomic compositions and configurations during the synthesis. Herein, we demonstrate that Cu, which is inert for oxygen reduction reaction (ORR) due to the fully occupied d-orbital, could be activated by applying a visible-light irradiation at ambient temperature. The ORR current is increased to 3.3 times higher in the potential range between −0.1 and 0.4 V under the light of 400 mW·cm−2, and the activity enhancement is proportional to the light intensity. Together with the help of the first-principle calculation, the remarkably enhanced electrocatalytic activity is expected to stem mainly from the decreased metal-adsorbate binding by photoexcitation. This finding provides an additional degree of freedom for controlling and manipulating the surface reactivity of metal catalysts besides materials strategy. [ABSTRACT FROM AUTHOR]

Iron can be produced by the direct electrochemical reduction of hematite particles suspended in hot, concentrated NaOH solutions. Because various other iron sources can be considered, the present work was aimed at investigating the electrolytic treatment of the “red mud” generated by the Bayer process for alumina preparation from bauxite. Such sources contain very high amounts of impurities, in particular silicon and aluminium oxide-based minerals, in addition to other mineral phases. Electrolytic reductive treatment of the industrial red mud sample was shown to be possible but with both lower current density and current efficiency than for pure hematite. After deposition tests at a fixed current density, further experiments in simulation tests have been carried out for better understanding. In particular, hematite particles were tested with and without impurities introduced in the solution. Presence of little soluble impurities at the particle surface appear to hinder the reactivity of the suspended particles at the cathode surface, whereas side-hydrogen reaction still occurs.

Modern engineering surfaces are cut, grind, and polished to create surfaces that are isotropic, uniform, and homogeneous to enable easy assembly and manufacture. Commonly used surface descriptors such as Ra are based on these characteristics. In the 1990s, the magnetic hard disk drive storage industry began to use multiscale directionally aligned roughness to achieve its lubrication requirements successfully, and this leads to the concept of designed surface topography and textures to enable additional functionalities. The design and fabrication of surface topography to impart directionality, uniform reactivity, and patterned geometric dimples or protrusions can enhance or expand the surface properties to meet specific desirable application needs. Adding thin films, coatings, multilayer nanocomposites on the surface can alter the surface physical and chemical characteristics and enhance durability. Properly designed surface textures (dimples, grooves, and discrete shapes) can reduce friction, create drag reduction, as well as control the real area of contact and heat transfer characteristics. In terms of designing friction reducing surfaces for an application, the dominant friction mechanisms need to be understood and proper surface designs applied to reduce the dominant friction generation. Generally, roughness perpendicular to the sliding direction will increase frictional resistance while increasing the interfacial temperatures. Multiscale roughness parallel to the sliding direction, depending on the speed and load of the contact, will reduce scuffing and reduce friction. In this paper, we use surface textures coupled with diamond-like-carbon thin films and bonded chemical layer to effect friction reduction of piston ring-cylinder liner friction.

Protein adsorption on 45S5 bioactive glass (BG, Bioglass) surfaces influences the biocompatibility of Bioglass and the cellular response to the material. The medium pH greatly affects protein adsorption behavior. However, the influence of pH variation on protein adsorption on Bioglass has not been investigated in detail before, although an acidifying pH has been observed in fractured or injured bone tissues. This study investigates how the medium pH (pH 7, 5, and 2) affects protein (serum albumin) adsorption on Bioglass with or without preconditioning in simulated body fluid (SBF). The results show that Bioglass can adsorb a larger amount of bovine serum albumin (BSA) than bioinert glasses at all tested pHs. The BSA adsorption on Bioglass surfaces is pH‐dependent and a larger amount of adsorbed BSA is observed at lower pH (5 and 2). After preconditioning, BSA adsorption is significantly enhanced. However, the trend of pH‐dependent adsorption is attenuated. No significant difference in BSA adsorption is observed at different pHs after preconditioning. The results reveal for the first time the influence of medium pH on protein adsorption on Bioglass with or without preconditioning treatment in SBF, which provides useful information for developing Bioglass based biomedical devices that will be in contact with protein‐containing physiological fluids during applications. [ABSTRACT FROM AUTHOR]

Aluminum (Al) substitution into the lepidocrocite structure commonly occurs in redoximorphic soils. However, little is known about its effects on the local structure, morphology, and surface properties of lepidocrocite due to its metastability in the environment. In this study, a series of Al-substituted lepidocrocite samples was synthesized and the local structure and surface properties were characterized by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy, high resolution transmission electron microscopy (HRTEM), zeta potential and phosphate (P) adsorption kinetics. With the substitution of Al into the lepidocrocite structure, the lepidocrocite unit cell volume decreased due to the smaller ionic radius of Al3+ (r = 0.535 Å) than Fe3+ (r = 0.645 Å), and both the corner-sharing (along c-axis) and edge-sharing (along a-axis) Me-Me (Me = Al, Fe) distances decreased, with a more significant decrease in corner-sharing Me-Me distances. In addition, hydrogen bonding in the interlayer regions of the mineral along the b- axis was weakened with Al substitution. These changes of the local structure led to a gradual evolution of the lepidocrocite morphology: the aspect ratio (length to width) decreased with increasing Al substitution, and the Al-substituted lepidocrocite crystals became thinner, resulting in a decrease in the final ratios of coherent scattering domain (CSD) sizes of face (020) to those of terminating face (200) and (002). Theorfore, with increasing Al substitution, the relative proportion of face (020) with doubly coordinated oxygens per specific surface area decreased, leading to an increase of active hydroxyls and P adsorption density at the surface. These results shed new insights on the evolution mechanism of local structure and morphology of Al-substituted lepidocrocite and provided important information for evaluating the surface reactivity and environmental behaviors of lepidocrocite in soils. [ABSTRACT FROM AUTHOR]

Recently, laser additive manufacturing (AM) techniques have emerged as a promising alternative for the synthesis of bulk metallic glasses (BMGs) with massively increased freedom in part size and geometry, thus extending their economic applicability of this material class. Nevertheless, porosity, compositional inhomogeneity, and crystallization display themselves to be the emerging challenges for this processing route. The impact of these “defects” on the surface reactivity and susceptibility to corrosion was seldom investigated but is critical for the further development of 3D-printed BMGs. This work compares the surface reactivity of cast and additively manufactured (via laser powder bed fusion—LPBF) Cu47Ti33Zr11Ni6Sn2Si1 metallic glass after 21 days of immersion in a corrosive HCl solution. The cast material presents lower oxygen content, homogeneous chemical distribution of the main elements, and the surface remains unaffected after the corrosion experimentation based on vertical scanning interferometry (VSI) investigation. On the contrary, the LPBF material presents a considerably higher reactivity seen through crack propagations on the surface. It exhibits higher oxygen content, heterogeneous chemical distribution, and presence of defects (porosity and cracks) generated during the manufacturing process.

Abstract Mount Etna is Europe’s largest and most active volcano. In recent years, it has displayed enhanced explosive activity, causing concern amongst local inhabitants who frequently have to live with, and clean up, substantial ashfall. Basaltic volcanic ash is generally considered unlikely to be a respiratory health hazard due to its often coarse nature (with few particles sub-10 μm diameter) and lack of crystalline silica. However, a previous study by the authors showed the capability of basaltic ash to generate the hydroxyl radical, a highly-reactive species which may cause cell damage. That study investigated a single sample of Etna ash, amongst others, with data giving an early indication that the Etnean ash may be uniquely reactive. In this study, we analyse a suite of Etnean samples from recent and historical eruptions. Deposits indicate that Etna’s past history was much more explosive than current activity, with frequent sub-plinian to plinian events. Given the recent increase in explosivity of Etna, the potential hazard of similarly, or more-explosive, eruptions should be assessed. A suite of physicochemical analyses were conducted which showed recent ash, from 2001 and 2002 explosive phases, to be of similar composition to the historical deposits (trachy-basaltic) but rather coarser (< 2.4 c.v.% sub-10 μm material and