Search

CoMo sulfides are typical catalysts for selective hydrodeoxygenation (HDO) of phenolics to aromatics which is important in bio-oil upgrading. However, it is still a challenge to promote the intrinsic activity of Co-MoS2 catalysts. Defect chemistry provides a good option to improve surface reactivity in catalysis. In this work, we report a facile H2O2 etching method to tailor the concentration of surface acidic sites. The molar ratio of H2O2/MoS2 can be altered to tune sulfur defects on the MoS2 surface for stabilizing Co species to form CoMoS active sites. The optimized Co-MoS2-2 catalyst, with the highest concentration of acidic sites, exhibits 3.4 times higher activity than the Co-MoS2-0 sample in the HDO of p-cresol to toluene. It is also found the HDO activity shows a linear relationship with the amount of surface acid (both Lewis and Bronsted acid) over the Co-MoS2-x catalysts. We believe that the understanding of the role of surface acidity would provide new opportunities for the rational design of efficient Co-MoS2 catalysts.

Covalent functionalization has been demonstrated to be an effective strategy to improve the stability of monolayer black phosphorus (BP); however, the effect of chemical functionalization on the ca...

Poly(hydroxybutyrate) (PHB) has been considered as a promising biopolymer produced in certain microbes under specific fermentative and physiological conditions. Being less functional, hydrophobic and brittle, the processability of PHB is difficult which limits its widespread applications. However, its blends with suitable biopolymers, for instance biopolyesters, may impart in them desirable structural functionalities and properties, such as surface reactivity, amphiphilicity, controlled degradation and mechanical strength; thus making them inevitable candidates for biomedical applications. Herein, various chemical modification approaches have been discussed and analyzed including hydroxylation, aminolysis, block copolymerization (via either grafting or blending) with suitable biopolymers. The mentioned approaches may tune the mechanical and other desirable properties of resultant blends for value added biomedical applications particularly in drug delivery, tissue engineering and so on. Furthermore, some key areas have been highlighted where the future research may be focused.

Material changes in yttrium-doped barium zirconate, BaZr0.8Y0.2O3–x, were studied using in situ Raman spectroscopy and ex situ x-ray photoelectron spectroscopy analysis. During in situ Raman analysis, samples were heated to temperatures of 300–600 °C and exposed to both dry and humidified H2 atmospheres. At the lower temperatures (300–450 °C), a new vibrational peak appears in the Raman spectra during exposure to humidified H2. The appearance of this feature is reversible, dependent on previous sample history, and possibly results from new, secondary phase formation or lattice distortion.

The surface ligands of semiconductor nanocrystals (NCs) are central for determining their properties and for their flexible implementation in diverse applications. Thus far, the thermodynamic characteristics of ligand exchange reactions were attained by indirect methods. Isothermal titration calorimetry is utilized to directly and independently measure both the equilibrium constant and the reaction enthalpy of a model ligand exchange reaction from oleate-capped CdSe NCs to a series of alkylthiols. Increased reaction exothermicity for longer chains, accompanied by a decrease in reaction entropy with an overall enthalpy-entropy compensation behavior is observed, explained by the length-dependent interchain interactions and the organization of the bound ligands on the NCs' surface. An increase in the spontaneity of the reaction with decreasing NC size is also revealed, due to their enhanced surface reactivity. This work provides a fundamental understanding of the physicochemical properties of the NC surface with implications for NC surface ligand design.

Hybrid materials based on Mesoporous Silica Nanoparticles (MSN) have attracted plentiful attention due to the versatility of their chemistry, and the field of Drug Delivery Systems (DDS) is not an exception. MSN present desirable biocompatibility, high surface area values, and a well-studied surface reactivity for tailoring a vast diversity of chemical moieties. Particularly important for DDS applications is the use of external stimuli for drug release. In this context, light is an exceptional alternative due to its high degree of spatiotemporal precision and non-invasive character, and a large number of promising DDS based on photoswitchable properties of azobenzenes have been recently reported. This review covers the recent advances in design of DDS using light as an external stimulus mostly based on literature published within last years with an emphasis on usually overlooked underlying chemistry, photophysical properties, and supramolecular complexation of azobenzenes.

In this study, we synthesized high-performance Carbon Fiber/ Gold/ Copper (CF/Au/Cu) composite wires by using a 2-step deposition method via sputtering and electrodeposition. After Au was sputtered on PAN-based CFs as a pre-treatment, the wettability and surface reactivity of the CFs were improved, resulting in a homogeneous deposition of Cu on their surface. At different Cu electrodeposition time, the resulting CF/Au/Cu composite wires could possess a high strength of up to 3.27 GPa ( ∼ 10 times stronger than copper wires) while their electrical conductivity could be as high as 4.4 × 10 5 S/cm ( ∼ 75 % of that for copper). More importantly, since the composite wires were lightweight (up to 70 % lower than Cu mass density), they are a promising candidate to substitute conventional heavy metal wires in the future electrical applications.

Micro/nanorobots have been extensively explored as a tetherless small-scale robotic biodevice to perform minimally invasive interventions in hard-to-reach regions. Despite the emergence of versatile micro/nanorobots in recent years, matched in vivo development remains challenging, limited by unsatisfactory integration of core functions. Herein, we report a polydopamine (PDA)-coated magnetic microswimmer consisting of a magnetized Spirulina (MSP) matrix and PDA surface. Apart from the properties of the existing MSP (e.g., robust propulsion, natural fluorescence, tailored biodegradation, and selective cytotoxicity), the introduced PDA coating enhances the photoacoustic (PA) signal and photothermal effect of the MSP, thus making PA image tracking and photothermal therapy possible. Meanwhile, the PDA's innate fluorescence quenching and diverse surface reactivity allows an off-on fluorescence diagnosis with fluorescence probes (e.g., coumarin 7). As a proof of concept, real-time image tracking (by PA imaging) and desired theranostic capabilities of PDA-MSP microswimmer swarms are demonstrated for the treatment of pathogenic bacterial infection. Our study suggests a feasible antibacterial microrobot for in vivo development and a facile yet versatile functionalization strategy of micro/nanorobots.

The surface reactivity and chemical instability of de-lithiated Li-rich layered oxide at high voltages often leads to huge irreversible capacity (IC) loss in the first cycle leading to low initial coulombic efficiency (ICE). Herein we demonstrate that simple physical mixing of electrochemically active β-MnO2 with Li-rich layered Li1.2Mn0.54Ni0.13Co0.13O2 compound at different weight ratios effectively controls the initial IC loss and thereby enhances the ICE. It was observed that addition of β-MnO2 increased the ICE from 80.0% for the pristine material to 97.0% for composite containing 20 wt% β-MnO2. The dQ/dV plots of the composites showed that β-MnO2 becomes electrochemically active at lower potentials (

In this research the proficiency of a novel magnetic calcium ferrite and manganese ferrite nanocomposite (CF-MF-NC) was evaluated for adsorptive sequestration of Eriochrome black T (EBT) dye coupled with the ultrasonic irradiation. CF-MF-NC exhibits saturation magnetization of 38.17 emu/g, BET surface area of 47.67m2/g, and average pore diameter of 10.17 nm, which makes it a potential magnetic nano-scale adsorbent. The CF-MF-NC has shown superior adsorptive performance (~88%) towards EBT dye as compared to pure CaFe2O4 (~64%) and MnFe2O4 (~52%) and this may be due to the higher surface reactivity, and enhanced physicochemical properties of the composite. The pseudo-second order kinetic model could explain the sono-assisted adsorption of EBT dye onto CF-MF-NC and the involvement of ultrasound enhanced the diffusion rate. Performance evaluation study reveals that sono-assisted EBT dye adsorption onto CF-MF-NC was superior (~98% of EBT dye removal) to conventional adsorption process with batch stirring (78.33%) and shaker (84.34%).

Application of “bioactive materials”, as a modified version of biomaterials, can optimize the response of the biological system due to their surface reactivity and formation of strong interactions with the adjacent tissue upon implantation. However, choosing an appropriate bioactive material that suits to the application and provides the desired mechanical, physical, chemical and biological functionality, as well as understanding the aspects of biological reaction to the biomaterial, in particular immune response, it plays a key role in successful integration of the implant. In this review, we will discuss different bioactive materials including bioactive ceramics, polymers and composites and their applications in drug delivery and scaffold preparation in order to provide an adequate introduction to the recent studies. Considering the necessity of regulation of implant fate for higher biocompatibility, the comprehensive overview to the immune response will be reviewed with the focus on representing the cell-biomaterial interactions and more importantly, the inflammatory responses. Ultimately, we will also discuss about different approaches namely as immunomodulation to elicit the desired physiochemical properties and mimicking native cellular response using bioactive compounds, functionalizing the implant surface with active molecules and alteration of the surface morphology. With better understanding of bioactive materials and their interactions with body, more novel biomaterials representing desired properties can be designed.

The presence of leachable ions in multicomponent silicate glasses complicates the understanding of their surface structure and chemistry under a humid or aqueous environment, in particular when com...

A macromolecular concept of the structure of solids and induction constants are used to quantitatively assess the reactivity of hydroxyl groups on the surface of single-crystal matrices, as exemplified by silicon. The oxide layer on the surface of such matrices is shown to influence the reactivity of silanol groups in atomic layer deposition processes.

Multidrug-resistant (MDR) bacteria constitute a global health issue. Over the past ten years, interest in nanoparticles, particularly metallic ones, has grown as potential antibacterial candidates. However, as there is no consensus about the procedure to characterize the metallic nanoparticles (MNPs, i.e., metallic aggregates) and evaluate their antibacterial activity, it is impossible to conclude about their real effectiveness as a new antibacterial agent. To give part of the answer to this question, 12 nm gold and silver nanoparticles have been prepared by a chemical approach. After their characterization by transmission electronic microscopy (TEM), Dynamic Light Scattering (DLS), and UltraViolet-visible (UV-vis) spectroscopy, their surface accessibility was tested through the catalytic reduction of the 4-nitrophenol, and their stability in bacterial culture medium was studied. Finally, the antibacterial activities of 12 nm gold and silver nanoparticles facing Staphylococcus aureus and Escherichia coli have been evaluated using the broth microdilution method. The results show that gold nanoparticles have a weak antibacterial activity (i.e., slight inhibition of bacterial growth) against the two bacteria tested. In contrast, silver nanoparticles have no activity on S. aureus but demonstrate a high antibacterial activity against Escherichia coli, with a minimum inhibitory concentration of 128 µmol/L. This high antibacterial activity is also maintained against two MDR-E. coli strains.

International audience; In this article, we focused on the comprehension of the surface reactivity of layered β(III)-cobalt oxyhydroxide, β(III)-CoOOH, by implementing a multiscale study associating both experimental, surface characterization by X-ray photoemission spectroscopy (XPS) and scanning electron microscopy and first-principles calculations. The surface reactivity and the chemical properties of the surface are key factors in the charge-storage mechanism, and β(III)-CoOOH presents interesting characteristics to be used as pseudo-capacitive electrode materials in supercapacitors thanks to its large surface specific area (∼100 m2/gs) and its high electronic conductivity (10–3 to 1 S cm–1). The surface reactivity (basic and redox character) of the synthesized compounds, which consists in aggregates of particles with 60–100 nm length, has been explored from the adsorption of SO2 molecules followed by XPS analyses. A kinetic study of the reactivity allowed us to identify three steps in the adsorption mechanism of our β(III)-CoOOH samples. The coupling of XPS and computational results allows us to establish a link between the surface reactivity in the identified domains, the formation of sulfate and sulfite species, and the cobalt Co3+ and Co4+ species of the active sites along with the underlying electronic processes.

International audience; Graphene-based materials (GBMs) are extremely promising and their increasing number urges scientists to conduct more and more toxicity studies. However, case-by-case approaches are rarely the best options in the earliest phases of industrial processes. Grouping can show great assets in this context: it is defined as the process of gathering substances into a common group. Oxidative stress being a major mechanism of nanotoxicity, an important grouping criterion is the surface reactivity, for which a relevant assessment is the FRAS (ferric reducing ability of the serum) assay. However, the application of the FRAS to GBMs is questioned due to their hydrophobicity. In this study, we explored the relevance and feasibility of the FRAS for grouping, working on 22 GBMs and 2 carbon blacks. We concluded that with few adjustments, the FRAS method appeared perfectly adapted to these materials and allowed a classification as "reactive" or "non-reactive" in agreement with results of ROS production for 84% of our GBMs. While not self-sufficient for toxicity assessment, the FRAS presents interesting qualities: it is fast, cheap, and simple. Therefore, we recommend studying GBMs using the FRAS as a step of a grouping process, a complement to other assays or as an early screening tool.

International audience; This paper investigates the role of the stacking fault (5%, 20% and 50%) and the morphology of Li2MnO3 lamellar materials, issued from coprecipitation method with three annealing temperatures, on the surface reactivity. The structure and the morphology have been characterized by XRD, SEM and TEM. We studied the surface reactivity of these materials by combining X-ray photoemission spectroscopy (XPS), gaseous adsorption and first-principle calculations. An evolution of the reactivity toward the SO2 acid gaseous probe has been observed for the three materials, from pure redox mechanism toward mixed acid-base/redox mechanisms, respectively for 5% and 50% of stacking faults. We demonstrated that the electronic structure of Li2MnO3 being not modified by stacking faulted. Thus, the surface reactivity of faulted Li2MnO3 is not linked to the SF rate but only governed by the accessible crystalline surfaces and the manganese environments at the surface atomic layer. The formation of (0 0 1)-Li surface according to the Li-overstoichiometry on the extreme surface and the random particles shape of the more faulted materials are responsible of the reactivity tuning.

Chemical reactions on indoor surfaces play an important role in air quality in indoor environments, where humans spend 90% of their time. We focus on the challenges of understanding the complex chemistry that takes place on indoor surfaces and identify crucial steps necessary to gain a molecular-level understanding of environmental indoor surface chemistry: (1) elucidate key surface reaction mechanisms and kinetics important to indoor air chemistry, (2) define a range of relevant and representative surfaces to probe, and (3) define the drivers of surface reactivity, particularly with respect to the surface composition, light, and temperature. Within the drivers of surface composition are the roles of adsorbed/absorbed water associated with indoor surfaces and the prevalence, inhomogeneity, and properties of secondary organic films that can impact surface reactivity. By combining laboratory studies, field measurements, and modeling we can gain insights into the molecular processes necessary to further our understanding of the indoor environment., Graphical Abstract, The Bigger Picture Humans spend ∼90% of their time indoors. However, understanding the chemistry that occurs on indoor surfaces and its impact on air quality is still in its nascent stages due to the complexity of indoor surfaces. High surface-to-volume ratios indoors increase gas-surface collisions, but molecular mechanisms for surface reactions are often poorly understood, despite their importance becoming increasingly clear. Equilibrium thermodynamics poorly explain indoor surface chemistry, with key kinetic effects observed. Drivers of surface reactivity include relative humidity, temperature, light, and surface pH. Highlighted findings are the ubiquitous presence of aqueous and secondary organic films, their ability to act as reservoirs of contaminants, and impacts on gas and particle lifetimes. Indoor surface chemistry impacts multiple U.N. Sustainable Global Goals that point to the importance of further integration of laboratory, modeling, and real-world measurements to understand the air we breathe indoors.

To improve the performance of metallic catalysts, alloying provides an efficient methodology to design state-of-the-art materials. As emerging functional materials, rare-earth metal compounds can integrate the unique orbital structure and catalytic behavior of rare earth elements into metallic materials. Such rare-earth containing alloy catalysts proffer an opportunity to tailor electronic properties, tune charged carrier transport, and synergize surface reactivity, which are expected to significantly improve the performance and stability of catalysis. Despite its significance, there are only few reviews on rare earth containing alloys or related topics. This review summarizes the composition, synthesis, and applications of rare earth containing alloys in the field of catalysis. Subsequent to comprehensively summarizing and constructively discussing the existing work, the challenges and possibilities of future research on rare-earth metal compound materials are evaluated.

In tribocorrosion, the mechanic dominates the total wear. However, the corrosion wear should not be neglected for passive materials. As the film reactivity depends on pH, tribocorrosion experiments were performed on a ferritic stainless steel in sulphate solution (pH 1.5, 6.5 or 12.5). The passive film formation and degradation was evaluated through galvanic coupling tests while the degradation is quantified by image analysis. Wear results follows the Archard's law however, a non-linear dependence of the Archard's coefficient to the pH is found. The study of the worn surface reactivity highlights the role of the pH in the wear behaviour of the material as its influence on the film rebuilt kinetics and its contribution in the total wear.

The synthesis of blue phosphorene by molecular beam epitaxy (MBE) has recently come under the spotlight due to its potential applications in electronic and optoelectronic devices. However, this synthesis remains a significant challenge. The surface reactivity between the P atoms and the Au atoms should be considered for the P/Au(111) system. In the MBE process, the temperature of the substrate is a key parameter for the growth of blue phosphorene. During the initial growth stage, irregularly shaped Phosphorus clusters grow on top of Au(111) surface at room temperature. When the substrate temperature is increased, these clusters transform into a phosphorene-like structure with a honeycomb lattice. An atom exchange reaction is observed between the P and first layer Au atoms under thermal activation at higher temperature, where the P atoms replace Au atoms to form a blue phosphorene structure within the top Au layer and at the step edges.

In this study, a comprehensive investigation of the role of sulfur vacancies on the electronic structure and surface reactivity of molybdenum disulfide is presented. A 2H-MoS2 single crystal was annealed at two different temperatures, namely, 300 and 500 degrees C in vacuum, in order to generate sulfur vacancies in a controlled manner. The detailed characterization of the electronic structure by means of X-ray and ultraviolet photoelectron spectroscopy clearly evidences the formation of a strong surface dipole as well as surface band bending due to the excess of negative charge on the Mo centers, as a consequence of the generated sulfur vacancies. After thermal treatment, a mercaptoundecylphosphonic acid molecule, which consists of a thiol (S-H) tail group and a phosphonic acid group on the other end, was covalently attached on the surface through wet chemical functionalization in order to refill the sulfur vacancies. As a consequence of the vacancy refilling, the surface band bending is reversed and the surface dipole is remarkably decreased, being close to the initial value of the pristine surface.

The interaction of oxygen with Ni-Cr(100) alloy surfaces is studied using scanning tunneling microscopy (STM) and spectroscopy (STS) to observe the initial steps of oxidation and formation of the alloy-oxide interface. The progression of oxidation was observed for Ni(100) and Ni-Cr(100) thin films including Ni-8 wt % Cr(100) and Ni-12 wt % Cr(100), which were grown on MgO(100) in situ. These surfaces were exposed to between 1 and 150 L O

A comprehensive understanding of chemical bonding and reactions at the surface of nanomaterials is of great importance in the rational design of their functional properties and applications. With the rapid development in cluster science, it has become clear that atomically precise metal clusters represent ideal models for resolving various important and/or unsolved issues related to surface science. This Account highlights our recent efforts on the fabrication of ligand-stabilized coinage nanoclusters with atomic precision from the viewpoint of surface coordination chemistry in particular. The successful synthesis of a large variety of metal clusters in our group has greatly benefitted from the development of an effective amine-assisted NaBH

Increasing concerns over the possible risks of nanotechnology necessitates breakthroughs in structure–activity relationship (SAR) analyses of engineered nanomaterials (ENMs) at nano-bio interfaces. However, current nano-SARs are often based on univariate assessments and fail to provide tiered views on ENM-induced bio-effects. Here we report a multi-hierarchical nano-SAR assessment for a representative ENM, Fe2O3, by metabolomics and proteomics analyses. The established nano-SAR profile allows the visualizing of the contributions of seven basic properties of Fe2O3 to its diverse bio-effects. For instance, although surface reactivity is responsible for Fe2O3-induced cell migration, the inflammatory effects of Fe2O3 are determined by aspect ratio (nanorods) or surface reactivity (nanoplates). These nano-SARs are examined in THP-1 cells and animal lungs, which allow us to decipher the detailed mechanisms including NLRP3 inflammasome pathway and monocyte chemoattractant protein-1-dependent signaling. This study provides more insights for nano-SARs, and may facilitate the tailored design of ENMs to render them desired bio-effects., Understanding nano-bio interactions is key to optimizing the biocompatible design of nanomaterials. Here, the authors combine proteomic and metabolomics studies to evaluate the effect of varying physicochemical properties of iron oxide nanoparticles in macrophage-like cells and mouse lungs.

Graphene oxide (GO) is an oxidised form of graphene that has attractedcommercial interest in multiple applications, including inks, printedelectronics and spray coatings, which all raise health concerns due topotential creation of inhalable aerosols. Although a number of studies havediscussed the toxicity of GO sheets, the invivo impact of their lateral dimensions is still not clear. Here, we compared the effects of large GO sheets (l-GO, 1 µm– 20 µm) with those of small GO sheets (s-GO, < 1 µm) in terms of mesothelialdamage and peritoneal inflammation, after intraperitoneal (i.p.) injection inmice. To benchmark the outcomes, long and rigid multi-walled carbon nanotubes(MWCNTs) that were shown to be associated with asbestos-like pathogenicity onthe mesothelium were also tested. Our aim was to assess whether lateraldimensions can be a predictor of inflammogenicity for GO sheets as good aslength is for MWCNTs. While long MWCNTs dispersed in 0.5% BSA induced a granulomatous responseon the diaphragmatic mesothelium and immune cell recruitment to the peritonealcavity, GO sheets dispersed under similar conditions did not cause anyresponse, regardless of their lateral dimensions. We further interrogatedwhether tuning the surface reactivity of GO by testing different dispersions(5% dextrose instead of 0.5%BSA) may change the biological outcome. Although the change of dispersion didnot alter the impact of GO on the mesothelium (i.e. no granuloma), weobserved that, when dispersed in protein-free 5% dextrose solution, s-GOelicited a greater recruitment of monocytic cells to the peritoneal cavity thanl-GO, or when dispersed in protein containing solution. Such recruitmentcoincided with the greater ability of s-GO to interact in vivo withperitoneal macrophages and was associated with a greater surface reactivity incomparison to l-GO.In conclusion, large dimension was not a determining factor of the immunological impact of GO sheets afteri.p. administration. For an equal dose, GO sheets with lateral dimensionssimilar to the length of long MWCNTs were less pathogenic than the MWCNTs. Onthe other hand, surface reactivity and the ability of some smaller GO sheets tointeract more readily with immune cells seem to be key parameters that can be tunedto improve the safety profile of GO. In particular, the choice of dispersionmodality, which affected these two parameters, was found to be of crucialimportance in the assessment of GO impact in this model. Overall, thesefindings are essential for a better understanding of the parameters governingGO toxicity and inflammation, and the rational design of safe GO-basedformulations for various applications, including biomedicine.

Nano-ecotoxicology is extensively debated and nanomaterial surface reactivity is an emerging topic. Iron oxide nanoparticles are widely applied, with organic or inorganic coatings for stabilizing their suspensions. Surface active maghemite nanoparticles (SAMNs) are the unique example of naked iron oxide displaying high colloidal and structural stability in water and chemical reactivity. The colloidal behavior of SAMNs was studied as a function of the medium salinity and protocols of acute and chronic toxicity on Daphnia magna were consequently adapted. SAMN distribution into the crustacean, intake/depletion rates and swimming performances were evaluated. No sign of toxicity was detected in two model organisms from the first trophic level (P. subcapitata and L. minor). In D. magna, acute EC50 values of SAMN was assessed, while no sub-lethal effects were observed and the accumulation of SAMNs in the gut appeared as the sole cause of mortality. Fast depuration and absence of delayed effects indicated no retention of SAMNs within the organism. In spite of negligible toxicity on D. magna adults, SAMN surface reactivity was responsible of membrane bursting and lethality on embryos. The present study offers a contribution to the nascent knowledge concerning the impact of nanoparticle surface reactivity on biological interfaces.

The aim of this paper is to quantify the effect of low-salinity (LS) water on oil recovery from sandstone cores at different temperatures and at various permeabilities, oil viscosities, and Ca2+ concentrations in the formation water. Six sandstone cores were waterflooded with high-salinity (HS) and LS water at various temperatures ranging from 25 to 90 °C. Four cores were allocated to oil recovery experiments, and the other two were dedicated to surface reactivity tests. The S wi and S or of the cores were established, and then the cores were pre-aged for 3 days at 70 °C with oil in a closed container. We examined the effect of different ionic solutions (HS water, LS water, and double Ca2+ HS water) at different temperatures. The surface reactivity test cores were flooded with the same HS and LS brines that were used in oil recovery forced-imbibition experiments. During flooding, samples of the effluent were analyzed for pH and Ca2+. The absence of an oil phase enabled us to isolate and quantify the important water–rock reactions. Ca2+ desorption from the core that was aged in the double Ca2+ concentration was larger than that desorbed from the other core, but pH and pressure was less than the other core during surface reactivity tests. Due to dehydration at high temperatures, the desorption of Ca2+ decreased as the temperature increased. Also, as the temperature increased, the pH gradient between the HS and LS water effluents decreased. Oil recovery forced-imbibition experiments with a double Ca2+ concentration showed a small LS water effect at all temperatures, meaning that the cores became more water-wet; however, the LS water effect was much greater when the amount of Ca2+ in the HS water was decreased by half. Furthermore, as the core permeability and oil viscosity increased, our tests showed a greater positive effect from the LS water. This work attempts to isolate the separate effects and thus examines the oil recovery achieved with the most important LS waterflood factors, which are temperature, ion exchange, and pH.

Inhalation is the prevailing route of inadvertent exposure for manufactured nanomaterials (MNs). For assessing potential adverse effects, indepth knowledge about Exposure-Dose-Response relationships is required to define a risk as a function of hazard and relevant exposure. Intrinsic (physico-chemical) and extrinsic (functional) MN properties determine the biological/toxicological properties (effects) of MNs. Predictive testing strategies are useful for comparative hazard and risk characterization against toxicologically well-defined positive and negative benchmark materials involving studies in rodents, cells, and cell-free (abiotic) assays. Inhalation studies can be used for hazard identification as well as for hazard and risk characterization of inhaled MNs. A design to provide dose-response data is ideal, but less so if only exposure-response data are available. Information should also be provided for biokinetics and for identifying secondary targets. Bolus-type dosing (intratracheal instillation; oropharyngeal aspiration) can be useful for hazard identification and characterization, but not for risk characterization. Combining results from bolus dosing or in vitro tests with results of a subchronic inhalation study of the same group of MNs can be a suitable predictive bridging approach. In vitro cellular assays designed to determine in vivo effects and underlying mechanisms present additional challenges. Cellular dose equivalency to in vivo is difficult to achieve because of static, mostly acute in vitro systems with no MN clearance. The dose dependency of mechanisms has to be considered as well. Still, in vitro tests are suitable for toxicity ranking against well-characterized benchmarks (Hazard ID). Regarding abiotic assays, predictive toxicity ranking using the metric of specific MN surface reactivity (ROS assays) is a promising screening tool, but requires further validation and standardization. Dynamic abiotic dissolution assays are also a promising tool for predicting in vivo dissolution rates but require standardization. Information about MN dissolution using static (equilibrium solubility, μg/L) and dynamic (dissolution rate, ng/cm2/day) abiotic in vitro assays provide different information about the solubilization of MNs reflecting either static in vitro or dynamic in vivo conditions. Results of both assays may be useful for categorization if performed in physiologically relevant fluids. Because the in vivo dissolution rates of MNs can differ widely, it is too simplistic to group MNs just into soluble and poorly soluble materials. Static (equilibrium solubility) and dynamic (dissolution rate) abiotic assays are based on different concepts. Results from dynamic dissolution in relevant physiological fluids - rather than just water - add valuable information about the extrinsic functional characteristics of MNs, which may be considered as a grouping tool into high, moderate, low and insoluble MNs. Systemic biodistribution of MNs depends on the point-of-entry. For example, MNs deposited by inhalation or instillation in the respiratory tract distribute differently than intravenously administered MNs; thus, biokinetic models based on data from intravenous MN administration should not be used to model biodistribution following inhalation. The significance of biodissolution for biokinetics, effects and underlying mechanisms has to be assessed in separate in vivo studies, involving biopersistence/biodurability and ultra-high resolution imaging for analysing bioprocessing and biotransformations at a sub-cellular level. With respect to grouping, several strategies are necessary to cover all classes of MNs of different compositions and for different exposure routes, all of which are to be considered in regulatory decision-making. The suggested grouping and extrapolation framework presented in this paper could be pivotal in leveraging subchronic inhalation data with data from alternative test methods, thus leading to more efficient, cost-effective, and – in the long run – animal and cost saving methods to obtain needed input data for regulatory use.

Surface reactivity and near-surface electronic properties of SrO-terminated SrTiO3 and iron doped SrTiO3 were studied with first principle methods. We have investigated the density of states (DOS) of bulk SrTiO3 and compared it to DOS of iron-doped SrTiO3 with different oxidation states of iron corresponding to varying oxygen vacancy content within the bulk material. The obtained bulk DOS was compared to near-surface DOS, i.e. surface states, for both SrO-terminated surface of SrTiO3 and iron-doped SrTiO3. Electron density plots and electron density distribution through the entire slab models were investigated in order to understand the origin of surface electrons that can participate in oxygen reduction reaction. Furthermore, we have compared oxygen reduction reactions at elevated temperatures for SrO surfaces with and without oxygen vacancies. Our calculations demonstrate that the conduction band, which is formed mainly by the d-states of Ti, and Fe-induced states within the band gap of SrTiO3, are accessible only on TiO2 terminated SrTiO3 surface while the SrO-terminated surface introduces a tunneling barrier for the electrons populating the conductance band. First principle molecular dynamics demonstrated that at elevated temperatures the surface oxygen vacancies are essential for the oxygen reduction reaction.

The cadmium yellow paints used in several paintings of the early 1900s are undergoing a process of deterioration the reasons of which are still unclear. Structural defects in CdS, among other possible causes like photo-oxidative reactions, may play a role in the degradation process. Their presence in the pigment surface enhances the reactivity of cadmium sulfide. We present a theoretical study of the interaction between the hexagonal defective (1010) surface of CdS and O-2 and H2O molecules to simulate the combined effects of exposure to air and humidity. The geometrical and electronic structures as well as the adsorption energies are determined with the use of a first principles method. All the calculations are performed within the framework of the Density Functional Theory (DFT) in the Generalized Gradient Approximation (GGA-PBE) with the use of ultrasoft pseudopotentials. The nudged elastic band method (NEB) is also considered to evaluate activation barriers and minimum reaction paths in two case studies, namely the dissociation of a water molecule in the presence of a cadmium vacancy and the uptake of one oxygen molecule by the CdS surface containing a sulfur vacancy. This paper highlights the key role that theoretical modelling can play in the application of materials science to art conservation. (C) 2017 Elsevier B.V. All rights reserved.

The adsorption and reaction of acetaldehyde on the clean and CO pre-covered Ru(0001) surfaces have been investigated using temperature programmed desorption method. On the clean Ru(0001) surface, the decomposition of acetaldehyde is the main reaction channel, with little polymerization occurring. However, on the CO pre-covered Ru(0001) surface, the decomposition of acetaldehyde is inhibited considerably with increasing CO coverage. Whereas, the polymerization occurs efficiently, especially at high CO coverage (θCO>0.5 ML), which is strongly CO coverage dependent. Combined with previous studies, the well-ordered hexagonal structure of CO layer formed on the Ru(0001) surface at high CO coverage that matches the configuration of paraldehyde is likely to be the origin of this remarkable phenomenon.

During the process of metal oxide semiconductors (MOS) gas sensing, the chemisorbed oxygen on the surface plays a significant important role, which determines the surface reactivity and controls the film conductivity. Therefore, it is necessary to improve the amount of chemisorbed oxygen on MOS surface. In this paper, the effect of doping on the accumulation of chemosorbed oxygen on SnO2 surface was studied. SnO2, Co-SnO2 and Nb-SnO2 were successfully synthesized via nonaqueous sol-gel method to study the effect of acceptor doping and donor doping on accumulation of chemosorbed oxygen and gas response. And dynamic program cooling (DPC) was also carried out in different concentrations of acetone and different gases respectively to obtain the R-T curve and gas response. The results showed that the Co doped SnO2 obviously improved the accumulation of chemosorbed oxygen and dynamic gas response, while the Nb doping has little improvement. The reason of these results was also analyzed by band theory in this paper.

In this work, the new calcium-magnesium-silicate Ca5MgSi3O12 ceramic was made via traditional solid-state reaction. The bioactivities were investigated by immerging the as-made ceramics in simulated body fluid (SBF) for different time at body temperature (37 °C). Then the samples were taken to measure X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), X-ray energy-dispersive spectra (EDS), and Fourier transform infrared spectroscopy (FT-IR) measurements. The bone-like hydroxyapatite nanoparticles formation was observed on the ceramic surfaces after the immersion in SBF solutions. Ca5MgSi3O12 ceramics possess the Young’s modulus and the bending strength and of 96.3 ± 1.2 GPa and 98.7 ± 2.3 MPa, respectively. The data suggest that Ca5MgSi3O12 ceramics can quickly induce HA new layers after soaking in SBF. Ca5MgSi3O12 ceramics are potential to be used as biomaterials for bone-tissue repair. The cell adherence and proliferation experiments are conducted confirming the reliability of the ceramics as a potential candidate.

We report on a high-performance room-temperature NO 2 sensor based on porous and multi-defective reduced porous graphene (rPG). The rPG sebsor exhibits much higher responsivity than that of sensor made from reduced graphene oxide (rGO) without artificial nanopores, especially under lower NO 2 concentration. The limit of detection of rPG sensor is as much as 28% towards 500 ppb NO 2 . The remarkable surface reactivity stemmed from abundant defective sites, especially edge-defective sites of nanopores, is highly responsible for the excellent responsivity and sensitivity of rPG sensor. Moreover, the unique porous structure of rPG also contributes to the outstanding gas-sensing performance by providing open gas diffusion path, and thus significantly improving the utilization of surface active sites.

The aim of this study is to investigate the potential of Ti-doped graphene nanoflake (Ti-GNF) for the reduction of CO 2 to formic acid by H 2 . To get a deeper insight into the mechanism of this reaction, the reliable DFT calculations are performed. It is found that the large positive charge on the Ti atom can greatly regulate the surface reactivity of GNF. The formation of the formate group is the rate determining step for the reduction of CO 2 . The calculated activation energies demonstrate that Ti-GNF could be utilized as an efficient catalyst for the reduction of CO 2 to formic acid.

Surface reactivity of rutile TiO2 (110) surfaces has long been ascribed to bridging oxygen vacancies (VO), but recently, excess electrons introduced by donor defects are being considered as the main players. However, the spatial distribution of them is not yet clear due to difficulties in interpreting filled state images of scanning tunneling microscopy (STM). In this study, several different images available in the literature are consistently interpreted using density functional theory (DFT). The key factors are polarons in the second layer below Ti5c row (Ti5c-2nd polarons) and a temperature dependence of their concentration. Bright blobs in the experimental images are interpreted as Ti5c-2nd polarons. At 78 K, their concentration reaches 33.3% ML, where 1 ML is defined as the density of (1 × 1) unit cells, regardless of VO coverage. In contrast, at 5 K, it is twice the VO coverage. This discrepancy is understood by the ionization of donor defects other than VO, most probably subsurface Ti interstitials...

Extensive efforts have been made to regulate surface wettability using bivalent polymers composed of hydrophobic surface-reactive groups and hydrophilic groups. To further enhance the controllability, this study demonstrates that the balance between the surface reactivity and self-aggregation of bivalent poly(hydroxyethyl-co-methacryloxyethyl aspartamide) (PHMAA) is crucial in controlling the wettability of methacrylated glass and thus the adhesion of stem cells. In particular, the wettability of the glass and the subsequent cell spreading became maximal with PHMAA that led to the largest and most uniform coverage of hydroxyl groups. In summary, this study would be useful in advancing various molecules used for surface engineering.

Elastic strain provides a direct means to tune a material’s electronic structure from both computational and experimental vantage points and can thus provide insights into surface reactivity via changes induced by electronic structure shifts. Here we investigate the role of elastic strain on the catalytic activity of tungsten carbide (WC) in the hydrogen evolution reaction. WC makes an interesting material for such investigations as it is an inherently promising catalyst that can sustain larger elastic strains (e.g., −1.4 to 1.4%) than common transition-metal catalysts, such as Pt or Ni (e.g., −0.4 to 0.4%). On the basis of density functional theory calculations, a compressive uniaxial strain is expected to cause weakening of the surface–hydrogen interaction of 10–15 meV per percent strain, while a tensile strain is calculated to strengthen the surface–hydrogen interaction by a similar magnitude. Sabatier analysis suggests that weakening of the surface-hydrogen interaction would enhance catalysis. We prep...

Photocatalysis with modified titania is a promising approach to improve both air and health quality. Modified titania with novel photocatalytic properties under indoor light irradiation leads to smart coatings, which are benchmark materials suitable for their indoor applications. It is generally accepted that the photocatalytic activity is affected by the light absorption, charge creation/recombination rate and surface reactivity. In this contribution we focus on modified TiO2 as catalyst in heterogeneous photo-catalytic processes and address the efficiency of TiO2-based building and construction materials on the removal of environmental pollutants indoors and outdoors. We also present data on the presence of eventually formed, toxicologically relevant and harmful by-products as the result of the photo-induced degradation of pollutants in an effort for better evaluation of induced risks for human health from the application of TiO2 modified materials. Finally, we present recent results on the disinfection performance of these material and the inactivation of severe pathogens contained in water and indoor air environments.

The effects of HCl on the oxidation of CH4 at CeO2(111) have been studied by using density functional theory calculations corrected by on-site Coulomb interactions (DFT+U). The calculated results show that the presence of HCl barely affects the CH4 dissociation, but can provide new reaction channels to produce CH3Cl. The effects of surface defects and orientations on the surface reactivity were also considered. The total oxidation of CH4 can be partially prohibited by the high barriers for the further dissociation of CH3 at reduced surfaces due to the strong electronic repulsion of heavily accumulated localized electrons. CeO2(110) shows higher activity and selectivity for CH3Cl formation than CeO2(111), indicating that the morphologies of CeO2 nanocatalysts would be key to the catalytic activities toward CH4 activation.

We used temperature-programmed reaction spectroscopy (TPRS) and synchrotron-radiation-based photoelectron spectroscopy (PES) to investigate the adsorption and oxidation of methanol (CH3OH) on Tb2O3(111) and TbO2(111) thin films grown on Pt(111). We find that methanol mainly desorbs from the Tb2O3 surface through both molecular and recombinative processes and that a relatively small amount of adsorbed methanol (

We demonstrate the reproducible epitaxial growth of 100 nm thick Ir(001) films on a heteroepitaxial stack consisting of 5 nm Ir and 100 nm yttria-stabilized zirconia (YSZ) grown on Si(001) substrat...

Surface reactivity on metal oxide surfaces and its enhancement play important roles in heterogeneous catalytic reactions. In this work, the interactions of O2 and H2O with reduced CeO2 (111) surface are studied by density-functional theory calculations. The corresponding adsorption geometries, adsorption energies, and reaction barriers are reported. It is found that the diffusion of subsurface oxygen vacancies toward surface can be promoted by the adsorption of O2 on the CeO2 (111) surface. Then those oxygen vacancies diffused onto surface sites will be healed by the adsorbed O2, leaving behind an O adatom on the surface. Interestingly, at moderate temperatures, the surface O adatom will swap positions with surface lattice O dynamically. The adsorption of H2O may also induce the diffusion of oxygen vacancies from subsurface to surface, leading to the formation of two hydroxyls on the CeO2 (111) surface. In addition, the interaction between the paired hydroxyl groups and O2 will result in the formation of ...

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.

Glass surfaces are of considerable interest due to their disproportionately large influence on the performance of glass articles in many applications. However, the behavior of glass surfaces has proven difficult to model and predict due to their complex structure and interactions with the environment. Here, the effects of glass network topology on the surface reactivity of glasses have been investigated using reactive and nonreactive force field-based molecular dynamics simulations as well as density functional theory. A topological constraint-based description for surface reactivity is developed, allowing for improved understanding of the physical and chemical origins of surface reactivity. Results show evidence for the existence of a chemically stable intermediate phase on the surface of the glass where the glass network is mechanically isostatic.

Design of materials for solid oxide fuel cells cathodes and oxygen separation membranes and studying their oxygen transport characteristics are important problems of modern hydrogen energy. In the current work, fundamentals of such materials design based on characterization of their oxygen mobility by oxygen isotope exchange with C18O2 and 18O2 in flow and closed reactors for samples of Ruddlesden - Popper-type oxides Ln2-xCaxNiO4+δ, perovskite-fluorite nanocomposites PrNi0.5Co0.5O3-δ - Ce0.9Y0.1O2-δ, etc. are presented. Fast oxygen transport was demonstrated for PNC - YDC (DO ~10-8 cm2/s at 700°C) nanocomposites due to domination of the fast diffusion channel involving oxygen of the fluorite phase with incorporated Pr cations and developed perovskite-fluorite interfaces. For LnCNO materials a high oxygen mobility (DO ~10-7 cm2/s at 700°C) provided by the cooperative mechanism of its migration was demonstrated. Depending on Ca dopant content and Ln cation nature, in some cases 1-2 additional channels of the slow diffusion appear due to decreasing the interstitial oxygen content and increasing the energy barrier for oxygen jumps due to cationic size effect. Optimized by the chemical composition and nanodomain structure materials of these types demonstrated a high performance as SOFC cathodes and functional layers in asymmetric supported oxygen separation membranes. © The Authors, published by EDP Sciences, 2019. Russian Science Foundation, RSF: 16-13-00112 Support by the Russian Science Foundation (Project 16-13-00112) is gratefully acknowledged. The authors from the Ural Federal University are grateful to the Government of the Russian Federation (Agreement 02.A03.21.0006, Act 211). Ce0.9Y0.1O2-δ|Ce0.9Gd0.1O2-δ|Ni/Zr0.84Y0.16O2-δ anodic half-cells and Ni/Al foam substrates were kindly provided by H.C. Starck, Germany and Powder Metallurgy Institute NAN Belarus, respectively.

The project nanoGRAVUR (BMBF, 2015–2018) developed a framework for grouping of nanomaterials. Different groups may result for each of the three distinct perspectives of occupational, consumer and environmental safety. The properties, methods and descriptors are harmonised between the three perspectives and are based on: Tier 1 intrinsic physico-chemical properties (what they are) or GHS classification of the non-nano-form (human tox, ecotox, physical hazards); Tier 2 extrinsic physico-chemical properties, release from nano-enabled products, in vitro assays with cells (where they go; what they do); Tier 3 case-specific tests, potentially in vivo studies to substantiate the similarity within groups or application-specific exposure testing. Amongst all properties, dissolution and transformation are least modulated by different nanoforms within one substance, whereas dustiness, dispersion stability, abiotic and especially in vitro surface reactivity vary more often between different nanoforms. The methods developed or selected by nanoGRAVUR fill several gaps highlighted in the ProSafe reviews, and are useful to implement (i) the concept of nanoforms of the European Chemicals Agency (ECHA) and (ii) the concept of discrete forms of the United States Environmental Protection Agency (EPA). One cannot assess the significance of a dissimilarity, if the dynamic range of that property is unknown. Benchmark materials span dynamic ranges that enable us to establish bands, often with order-of-magnitude ranges. In 34 case studies we observed high biological similarity within each substance when we compared different (nano)forms of SiO2, BaSO4, kaolin, CeO2, ZnO, organic pigments, especially when we compared forms that are all untreated on the surface. In contrast, different Fe2O3 or TiO2 (nano)forms differ more significantly. The same nanoforms were also integrated in nano-enabled products (NEPs) for automotive coatings, clinker-reduced cements, cosmetic sunscreen, and lightweight polymers.

The increasing use of silver nanomaterials (AgNMs) in consumer products will result in an increased amount entering the environment, where AgNMs were recently found to cause phytotoxicity in the model plant Lolium multiflorum. To better understand the causes of the phytotoxicity, we have designed a new set of experiments to study the effect of AgNM dissolution. Dissolution of AgNMs was measured over a 1-month period to determine if dissolution alone caused phytotoxicity. Very little dissolution was observed over the testing period, suggesting a different mechanism caused the majority of the toxicity. To further confirm this hypothesis, AgNMs were physically separated from the seeds and plants by a dialysis membrane. Toxicity was ameliorated in AgNM-exposed plants, showing that direct contact between AgNMs and plant seeds/roots is a required condition for the observed phytotoxicity in plant models. Probing further, a surface reactivity assay showed increased surface reactivity of silver nanoparticles (AgNPs) and silver nanocubes (AgNCs) corresponded to increased toxicity compared to silver nanowires (AgNWs). The work here can help build the knowledge base regarding shape control of nanomaterials and reducing unintended side effects.