Concentration Of OH Groups Research Articles

Exploring PEGylated and immobilized laccases for catechol polymerization

Laccases have been reported for their ability to eliminate hazardous phenolic compounds by oxidative polymerization. The exploitation of the oxidative behavior of different laccase forms, namely free/native, free/PEGylated, immobilized/native and immobilized/PEGylated, was assessed in this study. We found that PEGylated and immobilized laccase forms have differentiated catalytic behavior revealing distinct conversion rates and differentiated poly(catechol) chains, as confirmed by UV–Visible spectroscopy, by the total content of OH groups and by MALDI-TOF spectroscopy. The synergy underlying on the immobilized/PEGylated enzyme forms reveal to be responsible for the highest conversion rates and for the longer polymers produced.

Characterization of Two Novel Bio-based Materials from Pulping Process Side Streams: Ecohelix and CleanFlow Black Lignin

The characteristics of two novel types of technical lignin, namely Ecohelix (EH) and CleanFlow black lignin (CFBL), isolated from two different pulping process side streams, were analyzed. EH and CFBL were analyzed in terms of general composition, chemical functionalities, molar mass distribution, and thermal stability. For comparison, two relevant types of commercially available lignosulfonate and kraft lignin were used. The results showed that EH contains a large amount of sulfonated lignin, together with carbohydrates and ash. As such, it can be considered a lignin-carbohydrate hybrid molecule. CFBL was found to contain 91.5% Klason lignin and the lowest amount of carbohydrates (0.3%). EH showed the highest content of aliphatic OH groups (5.44 mmol/g) and CFBL a high content of phenols (4.73 mmol/g). EH had a molecular weight of 31.4 kDa and a sufficient thermal stability. CFBL had the lowest molecular weight (Mw = 2.0 kDa) and thermal stability of all kraft lignins analyzed in this study. These properties highlighted that EH is a suitable building block for material development and that CFBL is a promising material for the production of biofuel and biochemicals.

Anti-ageing skin effects of Korean bamboo salt on SKH1 hairless mice.

Bamboo salt is generated by baking bamboo and sea salt and is used as a traditional food or medicine. The aim of this study was to investigate the anti-ageing skin effects of Korean bamboo salt and to compare the antioxidant, anti-ageing and anti-inflammatory effects of various salts, including purified salt, solar salt, bath solar salt, Masada solar salt, 1-time baked bamboo salt (1× bamboo salt), and 9-times baked bamboo salt (9× bamboo salt). Based on the content of mineral elements, pH, OH groups and redox potential amperometric analysis, the 9× bamboo salt showed the most antioxidant components and characteristics compared to the other salts. The in vitro results showed that the 9× bamboo salt could inhibit oxidative damage by hydrogen peroxide (H2O2) treatment in HaCaT keratinocytes, and its effect was better than that of the other salts. In an in vivo experiment, SHK-1 hairless mice were treated with UV (ultraviolet) radiation to induce ageing. The epidermal thickness and epidermal structures were then assessed by phenotypic and histological analyses. The 0.2% 9× bamboo salt- and 1× bamboo salt-treated mice had a thinner epidermis than the control mice, and the sebaceous glands were almost intact with a regular arrangement that was similar to those in the normal group. Compared with the UV-treated group (control group) and other salt-treated groups, the 9× bamboo salt- and 1× bamboo salt-treated groups had higher dermal collagen and elastic fibre content. Fewer mast cells were observed in the 9× bamboo salt- and 1× bamboo salt-treated groups than in the control group. The activities of the skin antioxidant-related enzymes superoxide dismutase (SOD) and catalase (CAT) in the 9× bamboo salt- and 1× bamboo salt-treated groups were higher than those in other groups and similar to those in the normal group, but lipid peroxide (LPO) activity and carbonylated protein levels showed the opposite trends. Furthermore, the 9× bamboo salt- and 1× bamboo salt-treated groups had protein contents similar to those of the normal group. In addition, the 9× bamboo salt and 1× bamboo salt effectively down-regulated the expression of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) and up-regulated the expression of tissue inhibitor expression of matrix metalloproteinase-1 (TIMP-1), matrix metalloproteinase-2 (TIMP-2), SOD and CAT compared to the other salts at a concentration of 0.2% (p < 0.05). These results suggest that at appropriate concentrations, bamboo salt could prevent skin ageing induced by ultraviolet radiation b (UVB) photodamage.

Synthetic magnetite, maghemite, and haematite activation of persulphate for orange G degradation

Due to the widespread application of persulphate (PS) for in-situ chemical oxidation (ISCO), the PS activating role of naturally occurring minerals, such as iron oxides, has been the subject of a number of studies. However, major discrepancies remain as to the effectiveness, mode, and factors that influence iron oxides activation of PS. In this study, an attempt has been made to bridge this important knowledge gaps by a systematic study of PS activation, measured by orange G degradation, using commercial and self-synthesised magnetite, maghemite, and haematite particles. The results showed that the activation of PS by iron oxides does not depend on mineralogy, surface area or concentration of surface OH groups, but on crystalline inhomogeneities or structural irregularities. Significant dissolution of iron oxides accompanied PS activation, in a mainly homogeneous process, requiring a low pH environment to be effective. The activation of PS by iron oxides at neutral pH was found to be no better than dissolved iron activation contrary to some earlier publications. The results also suggest that under alkaline conditions, PS alone was more effective in degrading orange G than with iron oxides or dissolved iron activation. Phosphate buffer significantly retarded orange G degradation by iron-activated or unactivated PS with negative implication for ISCO in non-acidic, buffering environments. The results of this study contribute to enhancing the fundamental understanding of ISCO processes.

Sorption of cationic organic substances onto synthetic oxides: Evaluation of sorbent parameters as possible predictors

Knowledge on the sorption behavior of cationic organic substances in aquatic systems is vital for their risk assessment due to the increasing detection of such chemicals in the hydrosphere. Their sorption behavior is strongly influenced by sorption processes onto mineral surfaces (e.g., oxides, clays). To contribute to the development of prediction tools, the impact of sorbent characteristics on the sorption strength was studied in a highly-idealized model system. In addition to the properties of the solid phase, the concentration of other ions in direct competition for sorption sites and the molecular structure of the sorbate were changed to separate ion exchange and non-ion exchange processes. The study includes in total 120 systematic column experiments using five extensively characterized synthetic oxides (three silica gels, two aluminum oxides), three probe molecules (two structurally related cationic substances, one neutral compound), and four distinctively different NaCl concentrations. The results show that the concentration of OH groups on the sorbent surface is a meaningful descriptor for the observed variations in sorption capacity onto different oxides. Compound-specific linear correlations were obtained, enabling the prediction of sorption coefficients. In addition, a more complex sorption behavior of organic cations compared to uncharged molecules were observed as demonstrated by the sorption results at different electrolyte concentrations. Thus, the study provides an important step towards a better principal mechanistic understanding of organic cation sorption. However, further work using other sorbents including natural ones and other probe molecules is needed to verify the identified relationships within the scope of developing reliable prediction models for cation sorption.

The effect of plasma treatment on the osseointegration of rough titanium implant: A histo-morphometric study in rabbits

Background/purposeThe surface properties, such as hydrophilicity and functional OH groups, play an important role in bone fixation in vivo. In our previous study, the plasma treatments of large grit and acid etching (SLA) method produce functional OH groups on the rough surface. There is no report in discussing the integration between basic Ti—OH groups and bone-to-implant contact (BIC). The aim of this study was to evaluate the effect of the functional OH groups on the rough surface both in vitro and in vivo.Materials and methodsFunctional hydroxyl groups were produced on a SLA-treated surface. The surface topography, roughness, wettability, and chemical composition were examined using various techniques. Twenty-four implants were inserted into the proximal tibia of four New Zealand white rabbits. The biological responses were measured in terms of histomorphometric analysis 4 and 8 weeks post-implantation.ResultsThe surface morphology and roughness were similar among all groups. However, the concentration of OH groups and hydrophilicity were found increased in the plasma treatment. The cell morphology in RF-plasma treated groups had more polygonal type and higher expression of actin and vinculin. The bone-to-implant contact (BIC) ratios of RF-200W were significantly higher than other groups (P < 0.05). The relationship between basic OH groups and BIC showed linear correspondence.ConclusionThe Ti—OH groups introduced on the rough surface by plasma treatments can trigger cell adhesion which further initiate new bone apposition. We propose that RF-plasma treatment can help to enhance bone healing at 4 and 8 weeks.

How silanization influences aggregation and moisture sorption behaviours of silanized silica: analysis of porosity and multilayer moisture adsorption.

Based on the results of nitrogen adsorption and dynamic vapour sorption as well as analysis by the Hailwood–Horrobin (H-H) model, the effects of γ-methacryloxypropyltrimethoxysilane (MPTS) on the agglomeration and moisture sorption properties of fumed silica particles were investigated. After adding various concentrations (2%, 4%, 6% and 8%) of MPTS, different degrees of silanization were obtained by showing various ─OH group contents on the silica surface, which resulted in silica agglomerates with different porous structures. The bigger mesopores in the unmodified silica agglomerates became smaller and finally disappeared after MPTS modification and the Bruanuer–Emmett–Teller surface area decreased more gradually with an increase in MPTS concentration. The H-H model fitted the sorption isotherms very well, and both hydrated water and dissolved water showed decreasing trends with the increase in MPTS concentration, showing reduced hygroscopicity. Up to 6% MPTS, the ─OH groups decreased with increasing MPTS concentration, as indicated by reduced Kh and W parameters, while at 8% MPTS an extensive self-condensation of MPTS occurred. Adsorption hysteresis appeared for moisture sorption on silanized silica, especially at low relative humidity values and at low MPTS concentrations, which could be explained by a synergistic effect of the surface ─OH group content and pore characteristics. These results could aid our understanding of the applications of silane-modified silica particles.

One-step process based on the order of hydrothermal and alkaline treatment for producing lignin with high yield and antioxidant activity

Three one-step processes based on the order of hydrothermal (170 °C, 30 min) and alkaline treatment (2% NaOH, 90 °C, 120 min) have been proposed for the production of lignin from wheat straw. The yield, purity, dissociation mechanism, structural transformation, and antioxidant activity of the lignins obtained from the various processes were systematically investigated. It was found that the order of hydrothermal and alkaline treatments had significant effects on the structural features and antioxidant activities of lignins. Hydrothermal process facilitated the subsequent alkaline delignification, releasing lignins with the highest yield (90.3%) and purity (97.4%). The β-O-4 linkages were obviously cleaved during the hydrothermal treatment, which resulted in an increase content of phenolic OH groups. The types and content of phenolic OH groups in lignins were closely related to its antioxidant properties. The lignins released during the one-step process based on successive hydrothermal and alkaline treatment had a high yield and antioxidant activity and the process would be very beneficial to the industrial production of potential antioxidant for food oils and fats, as well as food preservative that prevent the loss of food flavour.

Controlling the growth of activated carbon supported nickel phosphide catalysts via adjustment of surface group distribution for hydrodeoxygenation of palmitic acid

Nickel phosphides were known to be promising substitute for noble metal used in various catalysts. The traditional method of controlling the growth of nickel phosphide species, including Ni2P, Ni3P, and Ni12P5, was either modulating Ni/P molar ratio or changing support. Here, we report a new method to control the growth of nickel phosphide species by tuning the types of surface oxygenated group types on activated carbon. The pretreatment of activated carbon with HNO3 remarkably increased the content of OCO groups. In the preparation process of activated carbon supported nickel phosphide catalyst, the OCO groups might interact with P to form POCO groups. The formed POCO inhibited the reduction of P species at low temperature, and thus inhibited the formation of the nickel phosphides; whereas at 873 K reduction, the formation of pure Ni2P on activated carbon was enhanced. However, the content of -OH groups content increased on activated carbon treated by NH3∙H2O, which might be favorable for the simultaneous formation of Ni2P and Ni12P5 with 1/1 ratio, and the thus formed catalyst displayed excellent catalytic hydrodeoxygenation activity for palmitic acid. Our results demonstrated how simple base and acid pretreatment could be used to tune the interfacial group distribution, hereby providing a strategy to rationally design transition metal phosphide supported catalysts.

Physicochemical Characterization and Antioxidant Activity of Humic Acids Isolated from Peat of Various Origins

Although humic acids (HAs) from peat exhibit various therapeutic properties, there is little information available concerning their physicochemical and antioxidant properties. To address this issue, nine different types of peat, including oligotrophic, mesotrophic, and minerotrophic peat samples, were used for isolation of HA fractions by basic (HAb) and pyrophosphate (HAp) extractions. Physical parameters of the HAs were analyzed by UV-Vis, fluorescent, infrared (IR), and electron paramagnetic resonance (EPR) spectroscopy. Average Mr of the fractions ranged from 17.2 to 39.7 kDa, while their humification index (HIX) varied from 0.49 to 1.21. HAp fractions had a higher content of aromatic structures compared to HAb fractions. Moreover, HAp fractions had a significantly higher content of phenolic OH groups (3.6 ± 0.5 mmol/g) versus HAb (3.1 ± 0.5 mmol/g). All HA fractions exhibited antioxidant activity in radical scavenging and electrochemical assays, and their EPR signal had a single line with g = 2.0035, which is consistent with semiquinone type radicals. Furthermore, the HIX was found to be important in determining the number of semiquinone-type free radicals in the HA structures. Overall, these data provide a molecular basis to explain at least part of the beneficial therapeutic properties of peat-derived HAs.

Changing the characteristics and properties of zeolite Y and nano-anatase in the formation of a nano-anatase/Y composite with improved photocatalytic and adsorption properties

Zeolite Y and the NTD/Y nanocomposite, which were synthesized in situ (the addition of zeolite Y to the reaction mixture in the course of the synthesis of NTD by the sulfate method), were studied by a variety of methods. The decrease in the particle size (scanning electron microscopy) and the water content in pores (X-ray powder diffraction study, the full-profile Rietveld method, IR spectroscopy, differential scanning calorimetry), the increase in OH groups content and the decrease in the water content on the surface of zeolite (X-ray photoelectron spectroscopy) in the composition of NTD/Y compared to the initial zeolite Y were all established. A larger specific surface area of NTD/Y (Brunauer–Emmet–Teller method) compared to the initial zeolite Y is due to the fact that zeolite Y in the nanocomposite contains a smaller amount of water because of the synthesis conditions and the presence of nanocrystalline NTD on the surface of zeolite particles. It was found that NTD/Y nanocomposite exhibits a higher photocatalytic activity in the model decomposition reaction of methyl orange under UV and adsorption capacity for the extraction of P(V) and As(V) ions from aqueous media compared to the initial zeolite and pure NTD obtained under the same conditions, which differs from NTD/Y by the larger particle size, the smaller specific surface and the smaller content of OH groups and water on the surface. The role of Bronsted and Lewis centers in the realization of properties is discussed.

Fenton Reaction-Oxidized Bamboo Lignin Surface and Structural Modification to Reduce Nonproductive Cellulase Binding and Improve Enzyme Digestion of Cellulose

Nonproductive adsorption of cellulase on lignin was a major inhibitory mechanism reducing the enzymatic saccharification efficiency of lignocellulosic material. The surface and structural properties of Fenton reaction-oxidized lignins (FRLs) and their effects on the nonproductive binding of enzymes to lignin and enzymatic saccharification of Avicel were examined. The Fenton chemistry pretreatment not only decreased the ratio of syringyl to guaiacyl units and the phenolic OH group content in lignin preparations but increased the carboxylic content and the negative zeta potential of lignin, all of which could be responsible for reducing the unproductive adsorption of cellulase on lignin. And Langmuir adsorption isotherms also proved that FRLs were provided with a lower binding ability to the cellulase enzyme when compared with untreated milled bamboo lignin (MBL). Finally, when the nonproductive binding of cellulase to FRLs was reduced significantly, the 72 h glucose yields of Avicel with 3-FRL and 5-FRL we...

Membrane filtration of kraft lignin: Structural charactristics and antioxidant activity of the low-molecular-weight fraction

Lignin, which is the second most abundant biomass component and has carbon-rich phenolic content, is a promising renewable raw material for multiple applications, such as carbon fibers, adhesives, and emulsifiers. To use lignin efficiently, it is important to ensure its purity and homogeneity. As a result, the separation of lignin into fractions with high purity and narrow molecular-weight distributions is likely a prerequisite for several applications. Ultrafiltration using ceramic membranes has many advantages, including enabling direct lignin extraction from Kraft pulp cooking liquors without pH and temperature adjustment. One challenge with membrane filtration using such a system is the potential for reduced membrane performance over time, which is associated with fouling.In this study, LignoBoost Kraft lignin was fractionated using a ceramic membrane with a molecular weight cut-off of 1kDa. The separation behavior during ultrafiltration fractionation was investigated and the antioxidant properties of the recovered low-molecular-weight (low-MW) lignin samples were evaluated.Using this model system, the permeate fluxes were unstable during the 100h of membrane operation. However, a decrease in the average MW in the permeate over time was observed. The shift in MW was most pronounced for virgin membranes, while a more stable MW distribution was evident for membranes subjected to multiple cleaning cycles. According to 2D NMR analysis, low-MW lignin that was recovered after 100h of operation, consisted of smaller lignin fragments, such as dimers and oligomers, with a high content of methoxy-groups. This was confirmed using the size exclusion chromatography method, which indicated an weigh average molecular weight in the range of 450–500Da. 31P NMR spectroscopy showed that, despite the lower total content of phenolic OH groups, the low-MW sample had a higher proportion of non-condensed phenolic OH groups. The results of the antioxidant tests demonstrated the strong potential of lignin and its low-MW fraction as a natural antioxidant, particularly for lipid-containing systems. The low-MW lignin fraction showed better antioxidant activity than the non-fractionated LignoBoost lignin in the kinetic oxygen radical absorbance capacity (ORAC) test and demonstrated three-fold stronger inhibition of the substrate (fluorescein) than the reference antioxidant Trolox (a water-soluble derivative of vitamin E).

Investigations on the interactions between Li-TFSI and glass fibers in the ternary PP/GF/Li-TFSI composites

The polypropylene/glass fiber (PP/GF) composites with excellent antistatic performance and improved mechanical properties have been reported by incorporation of a very small amount of the organic salt, lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI), into the PP/GF composites. It was considered that GF could play the role as the pathways for the movements of ions in the ternary composites. In this work, the interactions between Li-TFSI and glass fiber and the effects of such interactions on the physical properties of the composites have been systematically investigated. Three types of glass fibers with different ―OH group concentrations have been prepared in order to compare the interactions between GF and Li-TFSI. It was found that the ―OH group concentrations on the surface of glass fiber have significant effects on interactions between glass fibers and Li-TFSI. Such interactions are crucial for both the antistatic and mechanical performances of the final PP/GF/Li-TFSI composites. The investigation indicated that the GF with high ―OH group concentrations confined the movement of TFSI−, which decreased the antistatic properties of PP/GF/Li-TFSI composites. On the other hand, the GF with low ―OH group concentrations inhibited the absorption of Li-TFSI onto the GF, which also hindered the formation of Li-TFSI conductive pathway. The best antistatic performance of the ternary composites can be achieved at the intermediate ―OH concentrations on the GF.

Surface Modification of Direct-Current and Radio-Frequency Oxygen Plasma Treatments Enhance Cell Biocompatibility.

The sand-blasting and acid etching (SLA) method can fabricate a rough topography for mechanical fixation and long-term stability of titanium implant, but can not achieve early bone healing. This study used two kinds of plasma treatments (Direct-Current and Radio-Frequency plasma) to modify the SLA-treated surface. The modification of plasma treatments creates respective power range and different content functional OH groups. The results show that the plasma treatments do not change the micron scale topography, and plasma-treated specimens presented super hydrophilicity. The X-ray photoelectron spectroscopy (XPS)-examined result showed that the functional OH content of the RF plasma-treated group was higher than the control (SLA) and DC treatment groups. The biological responses (protein adsorption, cell attachment, cell proliferation, and differentiation) promoted after plasma treatments, and the cell responses, have correlated to the total content of amphoteric OH groups. The experimental results indicated that plasma treatments can create functional OH groups on SLA-treated specimens, and the RF plasma-treated SLA implant thus has potential for achievement of bone healing in early stage of implantation.

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.

Low-temperature CO oxidation over Ag/SiO2 catalysts: Effect of OH/Ag ratio

Combined application of TPx methods, H2‐O2 titration, UV–vis DRS, TGA‐DSC‐MS, TEM, XRD, N2 adsorption at −196 oC allowed proving the OH/Ag molar ratio as the key parameter defining the catalytic properties of silica-supported silver (Ag/SiO2) in low‐temperature CO oxidation. A new insight into the formation of active species on the catalyst surface is presented. In this study, Ag/SiO2 catalysts with Ag loading of 5 and 8 wt.% were prepared by incipient wetness impregnation method on the basis of commercial silicas preliminary calcined at 500, 700 and 900°C. Detailed characterization of catalysts by physicochemical methods revealed that molar ratio between the concentration of surface OH groups (normalized to support mass) and silver amount in the prepared catalysts (OH/Ag ratio) affects the silver dispersion, structure of silver nanoparticles (NPs) and their catalytic properties. Only at optimal value of OH/Ag ratio the silver NPs are stated to possess both high dispersion and defective multidomain structure (that consists of several nanodomains) providing the adsorption of weakly bound oxygen species responsible for high catalytic activity in CO oxidation at low‐temperature. Additionally, the co-existence of two types of active sites reacting with CO at room temperature with and without formation of adsorbed carbonate species is discussed. The first type of active sites was catalytically active in low-temperature CO oxidation with CO2 release at room temperature (RT). The second type may retain surface carbonate species up to ∼40–50°C. The balance between these species shifts towards the first type for the active catalyst.

Analysis of the change in the concentration of fluorine and hydrogen as a result of chemical dehydrofluorination of polyvinylidene fluoride

Chemical carbonization of polyvinylidene fluoride is necessary for the synthesis on its basis of quasi-one-dimensional carbon structures having a prospect of use in microelectronics. To determine the details of the carbonization process, the concentrations of 19F and 1H nuclei were measured and the changes in the concentration of CF2, CH2, and OH groups in partially dehydrofluorinated polyvinylidene fluoride samples were studied using nuclear magnetic resonance and infrared spectroscopy. The efficiency of substitution of fluorine and hydrogen atoms by OH groups in the process of dehydrofluorination of polymer chains is estimated.

Influence of surface hydroxylation on the Ru atom diffusion on the ZrO2(101) surface: A DFT study

The adsorption and diffusion of ruthenium adatoms on the (101) surface of tetragonal zirconia was studied by means of periodic Density Functional Theory (PBE+U) calculations. The surface termination has a decisive role in determining the diffusion capability of the adsorbed Ru atoms. On the defect-free and fully dehydroxylated surface, Ru adatoms have several stable adsorption sites with adsorption energies as large as 2.5–2.9eV However, the kinetic diffusion barriers between adjacent adsorption sites are around 0.5–0.6eV, indicating a rather fast diffusion process. Surface oxygen vacancies, if present, strongly bind ruthenium adatoms and act as nucleation sites. On hydroxylated surfaces, the adsorption energy of Ru atoms is comparable to the dehydroxylated case, but the kinetic barriers for diffusion are remarkably higher, thus indicating that adsorbed species are less mobile in presence of surface OH groups. The effect is more pronounced for high concentrations of OH groups, since this results in hydrogen bonded hydroxyl units that further limit the diffusion process. These results indicate a possible way to increase the life-time of RuZrO2 heterogeneous catalysts by tuning the level of surface hydroxylation, in order to slow down sintering of metal particles via Ostwald ripening process.

Influence of He+ long-time irradiation on silica luminescence spectrum

The paper deals with experimental investigation of 420keV He+ dose dependence of silica (medium OH-group contents) luminescence. It was founded that experimental spectra were good fitted by two Voigt peaks centered in 2.7 and 1.9eV. The absorption dose growth influenced on silica ionoluminescence spectra due to increase of radiation defects. We compared the obtained results with 420keV hydrogen ion irradiation data for the same samples. It was shown that relative intensity of red band correlated with specific energy losses and effective charge of ions in silica. The theoretical simulation of helium ion implantation and intrinsic defect dynamics was performed. The dependence of ionoluminescence intensity on observation angle was measured.