Effect Of Surface Hydroxylation Research Articles

Insights into the structural and thermodynamic properties of fullerols [C60(OH)n, n = 12, 14, 16, 18, 20, 22, 24] in aqueous media

In recent years, fullerenes and their amphiphilic derivatives fullerols [C60(OH)n] have received considerable attention of researchers worldwide because of their unique structural and electronic properties that enables numerous industrial and medicinal applications. Because of surface hydroxylation in fullerols [C60(OH)n], one might expect a different behaviour of these hydrophobic-hydrophilic solutes in water. In the present study, we have performed classical molecular dynamics simulations of three different isomers of fullerols [C60(OH)n, where n = 12–24]. Hydration shells of water around these nanoparticles are characterized with the help of radial distribution functions (RDFs) and hydrogen bonding. RDFs indicate the presence of two hydration shells around the central solute molecule for all the isomers. Hydrogen bonding studies reveal that with uniform distribution of hydroxyl groups on fullerene cage, the average number of solute-solvent hydrogen bond increases with an increasing number of hydroxyl groups. The hydration free energy for the isomer with uniform distribution of hydroxyl group is found to be highly negative compared to all other isomers for all the fullerols, which suggests that the effect of surface hydroxylation is more dominant where the hydroxyl groups are uniformly distributed on the fullerene cage.

The Effect of Surface Hydroxylation on MOF Formation on ALD Metal Oxides: MOF-525 on TiO2/Polypropylene for Catalytic Hydrolysis of Chemical Warfare Agent Simulants.

Metal-organic framework (MOF) fibrous composites were synthesized in a variety of methods in attempt to incorporate the highly effective reactivity of MOFs into a more facile and applicable format. Recent advances have demonstrated incorporating a metal oxide nucleation surface or reactive layer promotes conformal, well-adhered MOF growth on substrates. These materials have demonstrated promising reactivity in capturing or degrading chemical warfare agents and simulants. Here, we examine the mechanisms for MOF nucleation from metal oxide thin films to explore why some metal oxide sources are better suited for one synthesis mechanism over another. We isolate metal oxide extent of hydroxylation as an indicative factor as to whether the film serves as a nucleation promoter or may be converted directly to the MOF thin films. MOF-525 growth on Al2O3, TiO2, and ZnO coated fibers is demonstrated to corroborate these findings and used to degrade chemical warfare agent simulant dimethyl-4-nitrophenyl phosphate.

Effect of surface hydroxylation on ultra-precision machining of quartz glass

Chemical mechanical polishing is a main technology to flatten the surface of quartz glass. However, the role of water in polishing slurry and the removal mechanism in the CMP process of quartz glass are still unclear. The simulation based on ReaxFF-MD method was utilized to explore the microphenomenon and the removal mechanism in the CMP process of quartz glass. The simulation results indicated that the H atoms dissociating from H2O in polishing slurry present a weakening effect on SiO bonds in quartz glass. Besides, the hydroxylation process when the pristine surface of quartz glass reacts with OH groups dissociating from H2O was elucidated explicitly in this simulation. To verify the correctness of this ReaxFF-MD simulation, a set of experiments including nanoindentation and nanoindentation were implemented on quartz glass modified in solutions with different concentrations of aqueous H2O2 and KOH. According to the results of experiments, surface modification of quartz glass contributes to the removal of surface materials and processability of quartz glass modified by 5% aqueous H2O2 is the best. This work combining simulations and experiments contribute to understand the chemical behavior of nanoparticles at the atomic scale and provide an effective method to choose the CMP slurry.

Computational Study of Methane Activation on γ-Al2O3.

The C–H activation of methane remains a longstanding challenge in the chemical industry. Metal oxides are attractive catalysts for the C–H activation of methane due to their surface Lewis acid–base properties. In this work, we applied density functional theory calculations to investigate the C–H activation mechanism of methane on various sites of low-index facets of γ-Al2O3. The feasibility of C–H activation on different metal–oxygen (acid–base) site pairs was assessed through two potential mechanisms, namely, the radical and polar. The effect of surface hydroxylation on C–H activation was also investigated to examine the activity of γ-Al2O3 under realistic catalytic surface conditions (hydration). On the basis of our calculations, it was demonstrated that the C–H activation barriers for polar pathways are significantly lower than those of the radical pathways on γ-Al2O3. We showed that the electronic structure (s- and p-band center) for unoccupied and occupied bands can be used to probe site-dependent Lewis acidity and basicity and the associated catalytic behavior. We identified the dissociated H2 binding and final state energy as C–H activation energy descriptors for the preferred polar pathway. Finally, we developed structure–activity relationships for the C–H activation of methane on γ-Al2O3 that account for surface Lewis acid–base properties and can be utilized to accelerate the discovery of catalysts for methane (and shale gas) upgrade.

Exploring the Environmental Photochemistry on the TiO2(110) Surface in Situ by Near Ambient Pressure X-ray Photoelectron Spectroscopy

Heterogeneous reactions of nitrogen oxides on metal oxide surfaces have been suggested to play a significant role in environmental chemistry, physics, and engineering. Many of the metal oxide compounds found among atmospheric mineral dust particles are inherently semiconducting substrates. Due to their low band gap, they are effective photoactive materials in the environmentally relevant ultraviolet (UVA) range of solar radiation. Here, we have studied nitrogen oxide species evolution and photochemistry on TiO2(110) surfaces in the context of atmospheric chemistry by means of near ambient pressure X-ray photoelectron spectroscopy (AP-XPS) coupled with a 375 nm UV-laser module. In the presence of molecular O2 only, changes in TiO2 surface potential under UV irradiation were observed, attributed to band flattening. Under humid conditions, a significant increase in the BE range attributed to surface hydroxyl groups was observed, which may be the basis for the light-induced superhydrophilicity observed elsewhere with titania-based nanomaterials. The formation of surface nitrite and nitrate was observed after exposure to NO2 in the dark. Core-level metal cation, O, and N XPS spectra were measured at elevated pressures of O2, NO2, and H2O. By selective UV irradiation of only the XPS measurement spot on the sample, we obtained differential information on the surface chemical state on the UV-irradiated compared to dark reference spots. Upon UV irradiation, increased oxidation of NO2 was observed, while in turn a substantial increase of a reduced nitrate species possibly from electron transfer to nitrate and of a further reduced nitrogen species was observed during exposure to UV-radiation. The effect of surface hydroxylation and the involvement of carbon-containing surface compounds in the formation of nitrogenated organic species are emphasized.

Effect of surface hydroxylation on the catalytic activity of a Cr(II)/SiO2 model system of Phillips catalyst

Cr/SiO2 systems (0.1wt% of Cr) in the form of high surface area glasses have been synthesized. After proper activation in the 823–1023K range, they transformed to Cr(VI)/SiO2 and then to Cr(II)/SiO2 due to CO reduction (performed at 623K). Subsequently, C2H4 polymerization activity on these samples has been followed. Surprisingly, ethylene polymerization proceeds faster on samples obtained at 823K, those ones coming from activation at 1023K resulting less performing. UV–Vis and FT-IR spectroscopies revealed that the progressive increase of activation temperature leads to even more defined and protruding Cr(II) species at highly de-hydroxylated silica surface: this opens new questions on features of active sites and on the role of silica in preparing such species. Finally, the obtained experimental data have been used as references to validate models and methods adopted to simulate the Cr(II)/SiO2 system, foreseeing to further investigation of the reactivity of Cr(II) toward ethylene.

Adsorption of Arginine–Glycine–Aspartate Tripeptide onto Negatively Charged Rutile (110) Mediated by Cations: The Effect of Surface Hydroxylation

Classical molecular dynamics (MD) simulations were employed to investigate the adsorption behaviors of arginine-glycine-aspartate (RGD) tripeptide onto the negatively charged hydroxylated/nonhydroxylated rutile (110) surfaces, mediated by biologically important cations (Na+ or Ca2+). The simulation results indicate that the inherent nature of the cation determines its binding strength, thereby regulating the adsorption geometry of the peptide. The sparse hydroxyl groups on the nonhydroxylated rutile diminish the probability of H-bond formation between RGD and the surface, resulting in an early desorption of the peptide even with a mediating Na+ ion. In contrast, the negatively charged aspartate (Asp) side chain is bridged to the negatively charged hydroxylated rutile by an inner-sphere Na+ ion, in coordination with the Asp-rutile hydrogen bonds at the anchoring sites. The inner- and outer-sphere Ca2+ ions are demonstrated to be capable of "trapping" RGD on both hydroxylated and nonhydroxylated rutile, in the absence of hydrogen bonds with the surface. The strongly bound inner-sphere mediating Ca2+ ion exerts a "gluing" effect on the Asp side chain, producing a tightly packed RGD-rutile complex, whereas a less localized distribution density of the outer-sphere mediating Ca2+ ion results in a higher mobility of the Asp side chain. The intramolecular interaction is suggested to facilitate the structural stability of RGD adsorbed on the negative rutile in a "horseshoe" configuration.

Non‐destructive investigation of fibronectin adsorption on titanium surfaces using PM‐RAIRS: effect of surface hydroxylation

AbstractPolarisation‐modulation reflection‐absorption infrared spectroscopy (PM‐RAIRS) is a useful non‐destructive technique to study semi‐quantitatively the adsorption of proteins on metal surfaces. In this work, we employed PM‐RAIRS to study the effect of the degree of hydroxylation of the surface of titanium metal sheets, obtained by specific acidic or basic treatments, on the adsorption of fibronectin, a model plasma adhesion protein. Our results seem to indicate that the degree of hydroxylation does not influence significantly the adhesion properties of fibronectin, which is one of the main steps in titanium osseointegration process. Copyright © 2010 John Wiley & Sons, Ltd.