Density Of Surface Hydroxyl Groups Research Articles

Redox-Inactive CO2 Determines Atmospheric Stability of Electrical Properties of ZnO Nanowire Devices through a Room-Temperature Surface Reaction.

Emerging interactive electronics for the Internet of Things era inherently require the long-term stability of semiconductor devices exposed to air. Nanostructured metal oxides are promising options for such atmospherically stable semiconductor devices owing to their inherent stability in air. Among various oxide nanostructures, ZnO nanowires have been the most intensively studied for electrical and optical device applications. Here, we demonstrate a strategy for achieving the atmospheric electrical stability of ZnO nanowire devices. Although the chemically active oxygen and water in air are strong candidates for affecting the electrical stability of nanoscale metal oxides, we found that the ppm-level redox-inactive CO2 in air critically determines the atmospheric electrical stability of hydrothermally grown single-crystalline ZnO nanowires. A series of analyses using atmosphere-controlled electrical characterization of single nanowire devices, Fourier transform infrared spectroscopy, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy consistently revealed that atmospheric CO2 reacts substantially with the ZnO nanowire surfaces, even at room temperature, to form an electrically insulative zinc carbonate thin layer. The formation of this layer essentially limits the atmospheric electrical stability of the ZnO nanowire devices. Based on this surface carbonation mechanism, we propose a strategy to suppress the detrimental surface reaction, which is based on (1) reducing the density of surface hydroxyl groups and (2) improving the nanowire crystallinity by thermal pretreatment. This approach improves the atmospheric electrical stability to at least 40 days in air.

The Crystallinity and Aspect Ratio of Cellulose Nanomaterials Determine Their Pro-Inflammatory and Immune Adjuvant Effects In Vitro and In Vivo.

Nanocellulose is increasingly considered for applications; however, the fibrillar nature, crystalline phase, and surface reactivity of these high aspect ratio nanomaterials need to be considered for safe biomedical use. Here a comprehensive analysis of the impact of cellulose nanofibrils (CNF) and nanocrystals (CNC) is performed using materials provided by the Nanomaterial Health Implications Research Consortium of the National Institute of Environmental Health Sciences. An intermediary length of nanocrystals is also derived by acid hydrolysis. While all CNFs and CNCs are devoid of cytotoxicity, 210 and 280 nm fluorescein isothiocyanate (FITC)-labeled CNCs show higher cellular uptake than longer and shorter CNCs or CNFs. Moreover, CNCs in the 200-300 nm length scale are more likely to induce lysosomal damage, NLRP3 inflammasome activation, and IL-1β production than CNFs. The pro-inflammatory effects of CNCs are correlated with higher crystallinity index, surface hydroxyl density, and reactive oxygen species generation. In addition, CNFs and CNCs can induce maturation of bone marrow-derived dendritic cells and CNCs (and to a lesser extent CNFs) are found to exert adjuvant effects in ovalbumin (OVA)-injected mice, particularly for 210 and 280 nm CNCs. All considered, the data demonstrate the importance of length scale, crystallinity, and surface reactivity in shaping the innate immune response to nanocellulose.

Understanding the synergetic effect from foreign metals in bimetallic oxides for PMS activation: A common strategy to increase the stoichiometric efficiency of oxidants

Synergistic effect was commonly observed in bimetallic oxide catalysts in sulfate radical-based advanced oxidation processes by forming spinel structures. In this paper, we found the incorporation of Cu demonstrated the most remarkable promotional effect to Co oxides comparing with Fe and Mn in PMS activation, and no spinel structure of mixed metals was found. Moreover, the synergism between oxides of Cu and Co was observed on various supports including MgAl layered double hydroxides, mesoporous MnO2 and ZnO. Under conditions of 0.2 g L−1 catalysts, 2 mM PMS, and 40 ppm 4-chlorophenol (4-CP), CuCo@ZnO/PMS system demonstrated excellent performance that 96.0% 4-CP could be removed, while the removal efficiency of 4-CP in Cu@ZnO/PMS and Co@ZnO/PMS systems was only 12.1% and 45.4%, respectively. The simultaneous incorporation of Co and Cu bimetallic oxides in CuCo@ZnO led to a higher surface hydroxyl density, and this surface hydroxyl density showed a linear relationship to their first order kinetic constant in 4-CP degradation. Moreover, the results of peroxymonosulfate (PMS) decomposition, quantification of sulfate radical (SO4−), EPR, XPS, H2-TPR, and CV indicated that the synergism of Cu/Co also arose from the electron transfer between Cu(I) and Co(III), which altered the redox circle of Co(II)/Co(III) and increased the steady concentration of oxidative radicals. Due to this synergism, the degradation percentage of organic contaminants, stability of heterogeneous catalysts and the stoichiometric efficiency of PMS were all improved. These findings were highly suggestive to the further development of bimetallic heterogeneous catalysts in persulfate based advanced oxidation processes.

Synergetic activation of peroxymonosulfate by MnO2-loaded β-FeOOH catalyst for enhanced degradation of organic pollutant in water

In this paper, manganese dioxide (MnO2) loaded iron oxyhydroxide (β-FeOOH) was synthesized aiming to improve the catalytic performance of β-FeOOH as peroxymonosulfate activator. The β-FeOOH@MnO2/PMS system exhibited excellent performance and its reaction rate constant of Acid Orange 7 (AO7) degradation (0.0533 min−1) was approximately 2.3 times as that in β-FeOOH/PMS system (0.0232 min−1). β-FeOOH@MnO2 possessed superior properties as catalyst than β-FeOOH, owing to the higher surface hydroxyl density with higher specific surface area, redox ability and electronic transmission rate. Moreover, on the basis of the analysis from FTIR and XPS, it was found that the redox reaction of Fe3+/Fe2+ and Mn4+/Mn3+ synergistically activated PMS as well as the generation of FeOH+ and MnOH2+ accelerated activating PMS in the β-FeOOH@MnO2/PMS system. Thus, MnO2 and FeOOH synergistically activated PMS to reactive oxygen species (ROS). And 1O2, O2− and OH were identified as predominant ROS in the β-FeOOH@MnO2/PMS system on the basis of the result from quenching experiments and ESR. As a result, TOC removal rate was increased up to 22.62%. Additionally, β-FeOOH@MnO2 exhibited good stability with low iron dissolution and manganese dissolution. Generally, this study proposed that β-FeOOH@MnO2 was an efficient and environmental catalyst as PMS activator for organic pollutant degradation in water.

Scalable Synthesis of Mesoporous TiO2 for Environmental Photocatalytic Applications.

Increasing environmental concern, related to pollution and clean energy demand, have urged the development of new smart solutions profiting from nanotechnology, including the renowned nanomaterial-assisted photocatalytic degradation of pollutants. In this framework, increasing efforts are devoted to the development of TiO2-based nanomaterials with improved photocatalytic activity. A plethora of synthesis routes to obtain high quality TiO2-based nanomaterials is currently available. Nonetheless, large-scale production and the application of nanosized TiO2 is still hampered by technological issues and the high cost related to the capability to obtain TiO2 nanoparticles with high reaction yield and adequate morphological and structural control. The present review aims at providing a selection of synthetic approaches suitable for large-scale production of mesoporous TiO2-based photocatalysts due to its unique features including high specific surface area, improved ultraviolet (UV) radiation absorption, high density of surface hydroxyl groups, and significant ability for further surface functionalization The overviewed synthetic strategies have been selected and classified according to the following criteria (i) high reaction yield, (ii) reliable synthesis scale-up and (iii) adequate control over morphological, structural and textural features. Potential environmental applications of such nanostructures including water remediation and air purification are also discussed.

Application of the CLAYFF and the DREIDING Force Fields for Modeling of Alkylated Quartz Surfaces.

To extend applicability and to overcome limitations of combining rules for nonbond potential parameters, in this study, CLAYFF and DREIDING force fields are coupled at the level of atomic site charges to model quartz surfaces with chemisorpt hydrocarbons. Density functional theory and Bader charge analysis are applied to calculate charges of atoms of the OC bond connecting a quartz crystal and an alkyl group. The study demonstrates that the hydrogen atom of the quartz surface hydroxyl group can be removed and its charge can be redistributed among the oxygen and carbon atoms of the OC bond in a manner consistent with the results calculated at the density functional level of theory. Augmented with modified charges of the OC bond, force fields can then be applied to a practical problem of evaluation of the contact angle of a water droplet on alkylated quartz surfaces in a carbon dioxide environment, which is relevant for carbon geo-sequestration and in a broader context of oil and gas recovery. Alkylated quartz surfaces have been shown to be extremely hydrophobic even when the surface density of hydroxyl groups is close to the highest naturally observed density of 6.2 OH groups per square nanometer.

The Function of Surface Hydroxyl Groups of Incorporated Alumina on Catalytic Ozonation of Heavy Oil Produced Water

ABSTRACTγ-Al2O3 was incorporated with SiO2 and used as carrier to support Ni and Cu oxides for catalytic ozonation of heavy oil produced water. The change of catalytic activity was in accordance with that of surface hydroxyl density after incorporation or reuse of catalysts. Nitrogen adsorption and X-ray power diffraction analysis indicated that the specific surface area decreased and the mineral phase and crystal structure of metal oxides unchanged after incorporation. The results confirmed that the neutral surface hydroxyl groups of the carrier were the active sites during catalytic ozonation. Increasing of surface hydroxyl could be another way of improving the catalytic efficiency of catalytic ozonation.

Charge separation and ROS generation on tubular sodium titanates exposed to simulated solar light

The research focuses on a few key points concerning the light-driven processes taking place on TiO2 anatase and sodium titanates with tubular morphology, such as the relationship between the morphology and activity for H2 and CO2 production, density of surface hydroxyl groups, ROS (OH and O2−) production and photocatalytic activity, and charge separation at the interface of semiconducting domains and enhancement of activity. One key point discussed is whether the materials with peculiar morphologies (i.e. tubular) are superior to the conventional ones. The experimental evidences show that the main advantage of the tubular morphology of sodium titanate is given by its significantly higher surface area compared to parental anatase. FTIR and XPS progressive analyses evidence that the density of surface hydroxyl groups decreases with the development of the tubular morphology. The radical trapping experiments show that the variation of surface hydroxyl density is, generally, followed by activities for OH and O2− generation, as well as by the photocatalytic production of H2 and CO2 from water/methanol mixture. Consequently, the ROS, formed by action of photogenerated electrons and holes on adsorbed O2 and hydroxyl groups, respectively, play an important role in determining the photocatalytic activity of titania-based materials. The other major aspect revealed by this research is that the charge separation at the interfaces formed between anatase and sodium titanate crystalline phases has remarkable effect on the activity formation rates of H2 and CO2.

Particularities of trichloroethylene photocatalytic degradation over crystalline RbLaTa2O7 nanowire bundles grown by solid-state synthesis route

This is the first report on synthesis and photocatalytic activity for trichloroethylene (TCE) degradation under simulated solar light over RbLaTa2O7 layered perovskites with predominant nanowire or platelet morphologies. SEM images witnessed that the one step thermal treatment at 1200 °C lead to formation of RbLaTa2O7 nanowires with diameter of 80–320 nm and several microns in length associated in bundles and sharp-edged, merged platelets (minor phase). The two-step annealing at 950 °C and 1200 °C resulted in decrease of wires bundle population and increase in that of platelets merged in facetted particles. The RbLaTa2O7 nanowires are made of by well-aligned atomic rows with preferred orientation toward the c-axis, relatively free of defect. High density of hydroxyl groups on the sample calcined in mild conditions (RbLaTa_01) favors the photo mineralization of TCE. In contrast, the activity of RbLaTa_02 annealed in harsh conditions (950 and 1200 °C), poor in surface hydroxyl groups, remained modest. The weak surface basicity directed the reaction mainly to generation of intermediate chlorinated compounds. Pd and Au were supported on RbLaTa2O7 perovskites as an alternative strategy to boost the removal of chlorinated pollutants by combining photocatalytic (mineralization) and catalytic (hydrodechlorination, HDC) processes. The mineralization of TCE to Cl− was drastically hindered in presence of methanol due to quenching of ⋅OH radicals by alcohol. The results suggested that the density of RbLaTa2O7 surface hydroxyl groups is essential for photo mineralization of TCE whereas the surface carbonate is beneficial for the formation of intermediate chlorinated product.

Enhanced catalytic ozonation treatment of dibutyl phthalate enabled by porous magnetic Ag-doped ferrospinel MnFe2O4 materials: Performance and mechanism

Enhanced catalytic ozonation of di-n-butyl phthalate (DBP), a recalcitrant waterborne pollutant, was enabled by a family of novel Ag-doped spinel ferrites (MnFe2O4) materials. A sol-gel approach was used to synthesize the Ag-doped MnFe2O4 catalysts, resulting in a highly porous structure with good magnetic property. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the incorporation of Ag into the MnFe2O4 structure. The Ag-doped MnFe2O4 significantly accelerated ozonation of DBP, and a Ag doping of 0.5% (relative to Mn) enhanced the apparent rate constants by a factor of three and two under circumneutral conditions, compared to the ozone-alone and undoped MnFe2O4 systems, respectively. Catalyst surface hydroxyl groups were identified as a critical factor for ozone decomposition and the subsequent hydroxyl radical production. Spectroscopic and electrochemical measurements showed that Ag doping enhanced DBP degradation by increasing the density of surface hydroxyl groups and promoting the electron transfer and cycling between the catalyst and ozone. The Ag-doped MnFe2O4 catalysts exhibited high stability and can be used for multiple cycles.

Influencing investigation of metal ions on heterogeneous catalytic ozonation by ceramic honeycomb for the degradation of nitrobenzene in aqueous solution with neutral pH

Abstract Influence of metal ions on heterogeneous catalytic ozonation by ceramic honeycomb for degradation of nitrobenzene in aqueous solution was investigated through the semi-continuous batch experiments to compare apparent reaction rate constant (kapp) and hydroxyl radical ( OH) formation rate ( k · OH ) in the presence of different metal ions including monovalent (Na+, K+ and Ag+), divalent (Zn2+, Ni2+, Co2+, Mn2+, Ca2+, Fe2+, Cu2+ and Mg2+) and trivalent ions (Fe3+, Al3+ and Cr3+). Each metal ion can increase kapp and k · OH in the process of ozonation alone under the present experimental conditions. Except for the positive influence of Mn2+, the others all show the early enhancement effect and the latter inhibition effect on kapp and k · OH , namely existing a critical maximum concentration of metal ion for catalytic ozonation. The ratio of OH initiation from heterogeneous and homogeneous systems decreases with the increasing concentration of metal ion, indicating that the contribution of OH initiation derived from heterogeneous catalytic system decreases. Results confirm that the increasing concentration of metal ion causes the decrease in density of surface hydroxyl groups on ceramic honeycomb, and a novel correlation is established between the density decrease rates of surface hydroxyl group and the standard reduction potentials of metal ions.

A high-performance TiO2 nanotube supercapacitor by tuning heating rate during H2 thermal annealing

TiO2 nanotube is a promising material for supercapacitor electrodes. Thermal annealing has been proved as an effective way enhancing the performance of TiO2 nanotube supercapacitors. However, heating rate, as an important parameter in the thermal annealing, has been overlooked as a factor that can influence the electrochemical performance of TiO2 nanotube supercapacitors. In this paper, we demonstrate that the electrochemical performance of TiO2 nanotube supercapacitors fabricated by anodization process can be significantly improved by tuning heating rate during hydrogen thermal annealing. At the optimal condition, the areal capacitance of TiO2 nanotube supercapacitors increased from 27.36 to 52.40 mF cm−2 with a scan rate of 100 mV s−1, while maintaining a high capacitance retention of 65.9% when the scan rate increased from 10 to 1000 mV s−1. Moreover, outstanding long-term cycling stability with only 4.8% capacitance reduction after 5000 charge–discharge cycles is observed. It is found that the electronic carrier densities, surface hydroxyl group density, as well as crystallite size in TiO2 are maximized at the optimal annealing condition, all of which are accounted for the enhancement of the electrochemical performance.

Microwave modification of surface hydroxyl density for g-C3N4 with enhanced photocatalytic activity

Microwave modification was performed on graphitic carbon nitride (g-C3N4) photocatalysts to tail the surface hydroxyl content for enhanced photocatalytic activity in this work. The influence of microwave heating on the surface hydroxyl density was investigated by a suite of characterization methods. The microwave treated g-C3N4 (MT-g-C3N4) delivered a higher photocatalytic activity in degradation of Rhodamine B (RhB) under visible light irradiation than pristine g-C3N4 due to its improved separation efficiency of photogenerated charge carries and promoted absorption capacity of RhB reactants on surface, which resulted from the increased surface hydroxyl density induced by microwave treatment. This study provides a simple and convenient method to modify g-C3N4 materials with enhanced photocatalytic activity for the potential application in photocatalytic elimination of environmental pollutants.

Degradation of organic pollutants by Co3O4-mediated peroxymonosulfate oxidation: Roles of high-energy {0 0 1}-exposed TiO2 support

Co3O4-mediated heterogeneous activation of peroxymonosulfate (PMS) is an efficient strategy to generate sulfate radicals for environmental pollutants degradation. The rate-limiting step is CoOH− complex formation, and it highly depends on the thermodynamic capacity of water dissociation to generate surface hydroxyl groups. Herein, for efficient PMS activation and pollutants degradation, the water dissociation capacity of TiO2, a promising Co3O4 support, was facilely refined by its shape-tailored synthesis with dominant high-energy {0 0 1} facet. The polar {0 0 1} facet is characterized by a high density of atomic steps, edges and kinks of the low-coordinate surface atoms with a large number of dangling bonds, all of which can serve as reactive sites for water adsorption and dissociation and thus improve CoOH− complex formation dynamics in sulfate radical formation. Co3O4 deposited on TiO2-{0 0 1} exhibited a much higher PMS activation capacity and pollutants degradation efficiency, i.e. p-nitrophenol and rhodamine B, and a much lower Co2+ leaching. This superiority could be mainly attributed to the strong Ti5c-centered water adsorption and dissociation, the high density of surface hydroxyl groups, the robust CoOH− complex generation and the intimate catalyst-support interactions. Our findings might provide a new chance to refine Co-mediated sulfate radical generation and other Fenton-like systems for advanced water treatment with reduced secondary pollution.

The mineralization of oxalic acid and bio-treated coking wastewater by catalytic ozonation using nickel oxide.

Coking wastewater after biological treatment still possesses potential environmental risk and should be mineralized further. This work focused on the mineralization of bio-treated coking wastewater using catalytic ozonation by NiO. First, oxalic acid, the typical by-product of advanced oxidation process (AOPs), was used to test the catalytic performance of NiOs, prepared by modified hydrothermal methods upon addition of different surfactants. This demonstrated that NiO upon addition of hexadecyltrimethylammonium (CTAB) had the best catalytic activity, due to its high concentration surface hydroxyl density and strong stability. Moreover, the best NiO was applied for the catalytic ozonation of bio-treated coking wastewater. Under our experimental conditions, the total organic carbon (TOC) removal reached 100% after 420min. In addition, the spectroscopic analysis suggested that compounds with conjugated structures could be significantly removed by both ozonation and catalytic ozonation. Some of these substances were transformed into by-products with aliphatic C-C and O=C-O groups such as organic acids that can inhibit further mineralization.

Computational study on the structural and surface properties of amorphous hydroxylated TiO2 spherical nanoparticles

Monte Carlo simulations were carried out on amorphous titanium dioxide (TiO2) for both bulk and hydroxylated nanoparticles with particle sizes ranging from 1 to 10 nm. The potential developed by the Matsui and Akaogi (MA) was used to model the interatomic interactions of TiO2 in both cases (bulk and nanoparticles). Besides, Angular and Morse potentials proposed by the Tether, Cormack, Du et. al. (TCD) were introduced to model the interactions of hydroxyl groups on the TiO2 surfaces, i.e., the Ti-O-H groups with an experimental and theoretical angles of 125 o . The bulk system was developed using periodic boundary conditions. The TiO2 nanoparticles were extracted by applying a spherical cut section in the bulk TiO2 melt structure to obtain the required size. Free valences on the nanoparticle surfaces were saturated via additional hydroxyl groups and then quenched to 300 K under free boundary conditions. The bulk and surface properties of the nanoparticles were calculated at 300 K and zero pressure and characterized via radial distribution functions, bond angle distributions, bond distances, coordination numbers, OH group concentrations and radial density profiles. In addition, to understand the difference in properties of amorphous hydroxylated TiO2 nanoparticles and bulk amorphous TiO2, a comparative study was done at the same thermodynamic conditions. The study shows that the bulk properties of amorphous hydroxylated TiO2 nanoparticles are strongly size-dependent and different from those of the bulk TiO2. As expected, increasing the particle size leads to an approach of the particle’s bulk properties to the bulk properties of the (quasi) infinite system. The size effects show that decreasing the particle size results in increasing the surface effects and surface OH group concentrations. Accordingly, small-sized TiO2 nanoparticles have higher surface OH group concentrations and larger surface effects than large-sized TiO2 nanoparticles. Larger surface effects result significant changes in their bond angles, bond distances, and coordination numbers. The simulation results of the surface properties reveal that the surface titanium atoms in the TiO2 nanoparticles have the capability of accommodating up to 5 hydroxyl groups. The mean surface hydroxyl group density of the amorphous TiO2 spherical nanoparticles is estimated to be around 8.1/nm 2, which lies in the range of 8–16/nm 2, found by experimental and other simulation studies. Details of the modelling, simulations results and the study are presented in this paper.

Effect of heat treatment on the surface chemical structure of glass: Oxygen speciation from in situ XPS analysis

AbstractCompositional changes in unleached and acid‐leached soda‐lime silicate surfaces were tracked with in‐vacuo heating and X‐ray Photoelectron Spectroscopy. Surface oxygen speciation was determined using a stoichiometry‐based algorithm via elemental composition, instead of the typical O 1s peak‐fitting approach. Accurate surface hydroxyl quantification is shown to require dehydration at temperatures near 200°C. On the unleached surface, no change in surface hydroxyl density (~2.5 OH/nm2) is observed in the temperature range of 200°C‐500°C after the initial dehydration. However, repolymerization in the network (non‐bridging oxygen→bridging oxygen) is observed due to volatilization of sodium. The acid‐leached surface undergoes sodium out‐diffusion from the bulk at sub‐Tg temperatures with laterally resolved inhomogeneity and shows a reduction in the concentration of hydroxyls from 4.5 OH/nm2 (200°C) to 3.2 OH/nm2 (500°C) accompanied by an increase in bridging oxygen. These results suggest that when [OH] > 2.5~3/nm2, vicinal OH undergo dehydroxylation with evolution of water, whereas when [OH] < 2.5/nm2, most OHs are non‐interacting and isolated (at temperatures below Tg). Furthermore, at temperatures exceeding 300°C, sodium has enough thermal energy to desorb in vacuum and diffuse from the bulk (depending on the abundance & local structure).

Mechanistic evaluation of ferrite AFe2O4 (A = Co, Ni, Cu, and Zn) catalytic performance in oxalic acid ozonation

Spinel ferrites AFe2O4 (A=Co, Ni, Cu, and Zn) synthesized by citrate sol-gel method were tested for their catalytic performance in ozonation of aqueous oxalic acid. The objectives of this work include the evaluation of catalytic activity and ferrites stability in mineralization of oxalic acid together with exploring the activation mechanisms of ferrite catalysts in catalytic ozonation process. The results indicated that CoFe2O4 was the most active in catalyzing oxalic acid mineralization, removing 68.3% of TOC within 120min in the reaction conditions of initial pH 2.3, oxalic acid concentration 5mM, inlet ozone concentration 14±1mgL−1, catalyst dose 1.0gL−1. All catalysts exhibited satisfactory composition stability in a batch experiment, although losing up to 4.67% of the catalyst mass in Fe3+ leaching from ZnFe2O4. H2-Temperature programmed reduction and cyclic voltammetry scan analysis revealed that these spinel ferrites had the potential reducibility and the electron donating ability to ozone molecule, respectively. Additionally, X-ray photoelectron spectroscopy showed that the surface metal ions’ valence state and the surface oxygen species played important roles in catalytic ozonation process. The reaction rate constant of oxalic acid mineralization were well fitted to non-linearly depend on variable metal valence and linearly depend on surface hydroxyl group density. The radical-based mechanistic reaction pathways involving A2+-A3+-A2+ cycle and positively charged surface hydroxyl groups were proposed.

The silanol content and in vitro cytolytic activity of flame-made silica

HypothesisThe surface chemistry of synthetic amorphous silicas is essential for their applicational performance and for understanding their interactions with biological matter. Synthesis of silica by flame spray pyrolysis (FSP) allows to control the content and type of hydroxyl groups which also affects the cytolytic activity. ExperimentsBy controlling the FSP process variables, silica nanoparticles with the same specific surface area but different surface chemistry and content of internal silanols are prepared by combustion of hexamethyldisiloxane sprays, as characterized by Raman and infrared spectroscopy, thermogravimetric analysis, and titration with lithium alanate. Cytolytic activity is assessed in terms of membrane damage in human blood monocytes in vitro. FindingsUnlike commercial fumed silica, FSP-made silicas contain a significant amount of internal silanol groups and a high surface hydroxyl density, up to ∼8OH/nm2, similar to silicas made by wet-chemistry. Increasing the residence time of particles at high temperature during their synthesis reduces the internal and surface hydroxyl content and increases the relative amount of isolated silanols. This suggests incomplete oxidation of the silica matrix especially in short and “cold” flames and indicates that the silica particle formation pathway involves Si(OH)4. The surface chemistry differences translate into lower cytolytic activity for “cold-” than “hot-flame” silicas.

Zirconium-based conversion film formation on zinc, aluminium and magnesium oxides and their interactions with functionalized molecules

Zirconium-based conversion treatment of zinc, aluminium and magnesium oxides have been studied in-situ using ATR-FTIR in a Kretschmann geometry. This set-up was coupled to an electrochemical cell, which allowed to obtain chemical and electrochemical information simultaneously as a function of conversion time. This elucidated the strong relation between physico-chemical surface properties and zirconium-based conversion kinetics. Whereas the surface hydroxyl density of zinc and aluminium increased during conversion, magnesium (hydr)oxide was shown to dissolve in the acid solution. Due to this dissolution, strong surface alkalization can be expected, explaining the rapid conversion kinetics. AES depth profiling was used to determine the final oxide thickness and elemental composition. This confirmed that magnesium is most active and forms a zirconium oxide layer approximately 10 times thicker than zinc. On the other hand, the presence of zirconium oxide on aluminium is very low and can be considered as not fully covering the metal oxide. Additionally, the converted oxide chemistry was related to the bonding mechanisms of amide functionalized molecules using ATR-FTIR and XPS. It was shown that inclusion of zirconium altered the acid-base properties, increasing the substrate proton donating capabilities in case of magnesium oxide and increasing hydrogen bonding and Bronsted interactions due to increased surface hydroxide fractions on zinc and aluminium substrates.