Amount Of OH Groups Research Articles

Study on hydrophilic property of hydro-oxygenated amorphous TiO x:OH thin films

This paper is on hydrophilicity of amorphous TiO x thin films, which were prepared by plasma enhanced chemical vapor deposition, including a large amount of OH groups. The as-deposited film showed a good hydrophilicity (water contact angle below 5°) that deteriorated after long time storage in a dark ambient air (water contact angle of 59°). By UV light irradiation, the film surface recovered its initial hydrophilicity. Atomic force microscopic measurements of tip–sample adhesion force showed homogeneous distribution on the film surface before and after UV light irradiation. We suppose that the OH groups have a strong effect on the film hydrophilicity. Measurements of dark and photo-excited currents suggested that the deposited films have high photo-efficiency and very long lifetime of photo-excited carriers. Hence, we refer to them as hydro-oxygenated amorphous TiO x (a-TiO x :OH) films in analogy with a-Si:H. Furthermore, it was observed that the conductivity of a-TiO x :OH films was sensitive to the surrounding gases, especially to electron-withdrawing oxygen. In ambient air, it is deduced that the photo-excited electrons diffuse toward the film surface and react with oxygen to generate O 2 − . Considering the good hydrophilicity of the as-deposited a-TiO x :OH film and the strong oxidation power of O 2 − , it is concluded that the hydrophilicity of the a-TiO x :OH film was recovered by the photo-catalytic decomposition of hydrophobic adsorbates on the film surface.

Determination of the hydroxyl group content in silica by thermogravimetry and a comparison with [formula omitted] MAS NMR results

The hydroxyl group content in nine different types of silicas was determined by thermogravimetry (TG). The TG measurements were performed by heating the silica samples (15–30 mg) at a rate of 5°C min −1 from room temperature to 1250°C in an argon flow. The dehydration and dehydroxylation phenomena (two mass loss steps) were distinguished with the help of the differential TG curve (DTG). The temperature where physisorbed water was assumed to be totally released was dependent on the silica and was found to range from 100 to 130°C. The OH group content was calculated from the second mass loss step by assuming that there were only siloxane bridges left in silica at 1250°C. The total hydroxyl group content was calculated from the entire mass loss of the second step. The remaining amount of OH groups at any temperature below 1250°C could also be calculated and was done in this study at 550 and 1000°C. When comparing the total OH group content and the OH group content at 550°C determined by the TG method with the results of calcined samples measured by 1 H MAS NMR, they were found to be in a good agreement with each other. However, a significant difference was observed between the methods regarding the remaining OH group content at 1000°C.

Characterization of alkali‐treated jute fibers for physical and mechanical properties

AbstractChanges occurring in jute fibers when treated with a 5% concentration of a NaOH solution for 0, 2, 4, 6, and 8 h were characterized by weight loss, linear density, tenacity, modulus, FTIR, and X‐ray measurements. A 9.63% weight loss was measured during 2 h of treatment with a drop of hemicellulose content from 22 to 12.90%. The linear density value showed no change until 2 h of treatment followed by a decrease from 33.0 to 14.5 denier by 56% after 6 h of treatment. The tenacity and modulus of the fibers improved by 45 and 79%, respectively, and the percent breaking strain was reduced by 23% after 8 h of treatment. X‐ray diffractograms showed increase in crystallinity of the fibers only after 6 h of treatment, while FTIR measurements showed much of the changes occurring by 2 h of treatment with an increased amount of OH groups. By measuring the rate of change of the modulus, tenacity, and percent breaking strain with the time of treatment, a clear transition was apparent at 4 h of treatment with the dissolution of hemicellulose, causing a weight loss and drop in the linear density before and development of crystallinity with an improvement in the properties after the transition time. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1013–1020, 2001

Comparison of hydrophilic properties of amorphous TiOx films obtained by radio frequency sputtering and plasma-enhanced chemical vapor deposition

The hydrophilic properties of amorphous TiOx films prepared by different methods, e.g., radio frequency (rf) sputtering and plasma-enhanced chemical vapor deposition (PECVD), were studied. It was found that the hydrophilicity strongly depends on the film structure. The best hydrophilicity was realized with the PECVD amorphous film having distorted Ti–O bonds due to a large amount of OH groups. These characteristics of the PECVD amorphous film suggest that such a low-density film including distorted Ti–O bonds could increase the photoenhancement efficiency by ultraviolet radiation. This reason is also supported from the results that a low-density rf sputtered film presented a higher hydrophilicity compared to a high-density radio frequency sputtered film. Furthermore, both electrical and chemical effects of OH groups will also contribute to the good hydrophilicity of the PECVD film.

Estimation of oxyhydroxide specific surface area using the amounts of OH groups adsorbed

A procedure for pH-metric determination of the limiting adsorption of OH groups (AOH) by FeIII, ZrIV, CrIII, and InIII oxyhydroxide hydrogels from 0.1 and 1.0 M solutions of NaCl is described. Data on the molecular area occupied by a single OH group on the hydrogel surface (SOH) and the Sspec values, which were calculated from AOH and SOH, are presented. The Sspec value does not depend on the pH of hydrogel precipitation; the true Sspec value can be determined only from sorption of the OH groups at the actual point of zero charge of the hydrogel. The AOH values for hydrogels were found to change only slightly during aging of hydrogels in electrolyte solutions.

Catalysts based on fiberglass supports: I. Physicochemical properties of silica fiberglass supports

The physicochemical properties and structure of supports prepared by leaching soda–silica fiberglass materials were studied using a set of physicochemical techniques (BET; IR spectroscopy; transmission electron microscopy; and 29Si, 23Na, 27Al, 133Cs, and 129Xe (of adsorbed molecules) NMR spectroscopy). A matrix that corresponded in chemical composition to SiO2was formed at high degrees of leaching; however, it was considerably different from ordinary silica gels in properties. The structure and properties of this matrix are most adequately described by the model of a pseudolayer intercalation structure, which includes alternating layers of several silicon–oxygen tetrahedrons separated by narrow (<4 A) cavities. Considerable amounts of OH groups (∼5000 μmol/g) are contained in these cavities, and these OH groups are different from the surface hydroxyl groups of ordinary globular silica. Although the interlayer spaces are small, comparatively bulky cations can be intercalated into them.

Crystallinity of boehmite and its effect on the phase transition temperature of alumina

The effect of the crystallinity of boehmite powders on the temperatures of γ-Al 2 O 3 formation and the θ- to α-Al 2 O 3 transformation was investigated using boehmite powders of varying crystallite size prepared under various hydrothermal conditions. With increasing crystallite size of the boehmite powders, the specific surface area decreased and the expanded (020) d-spacing approached the reported value. Thermogravimetric (TG) profiles of more poorly crystalline boehmite indicated the presence of excess water molecules of different binding energy located on the surface or in the interlayer. The crystallite size of boehmite also showed a strong correlation with the formation temperature of γ-Al 2 O 3 and the phase transition temperature of θ- to α-Al 2 O 3 . Since both these temperatures are increased with increasing the crystallite size of boehmite, this is an important factor in determining the conditions for obtaining γ-, θ- and α-Al 2 O 3 from boehmite. By relating the TG weight loss to the water and OH contents in boehmite and γ-Al 2 O 3 , respectively, the crystallite size of boehmite can be related to the water content. This indicates that the γ-Al 2 O 3 transformed from boehmite of smaller crystallite size contains larger amounts of OH groups, implying more poorly crystalline γ-Al 2 O 3 . The reported topotactic transformation of boehmite via γ- to θ-Al 2 O 3 indicates a relationship between the crystallite size of the boehmite and that of the resulting transition alumina, which could explain the change of the phase transition temperature from θ- to α-Al 2 O 3 .

Silicon nitride and oxide powder surface characterization by TPD

Surfaces of silicon nitride powders produced by three different production processes were analyzed by temperature programmed desorption (TPD) technique. The main desorbed species detected in the temperature range 40–1300 °C are H 2, H 2O, NH 3 and N 2 from Si 3N 4 and Si 2N 2O powders, and H 2 and H 2O with small amounts of N 2 from SiO, SiO 2(am and c). Powders SiO and SiO 2(am) show much larger desorption quantities than the other powders investigated. The distributions of desorbed species fractions reflect the production process and nitridation media. Powders produced using N 2 are strongly affected by the final treatment. Heating in air produces a powder with large amount of OH groups (B1), meanwhile acid and water washings reduce the -OH groups and increase -NH 2 and -NH groups (C5, C6). For a powder using NH 3(g) + CH 4 as nitridation media, the heat treatment in air does not seem to increase -OH (B2), however shows similar desorption distribution to the powder using NH 3(g) as nitridation media, but produced by a different method (A2). The use of NH 3(l) appears to enhance the formation of surface groups which evolve as NH 3 and N 2, with respect to the use of NH 3(g) (A1).

Fabrication and characterisation of neodymium-doped silica glass by sol-gel process

Neodymium-doped silica glass possesses many properties ideal for high-power laser applications. These include low thermal expansion coefficient, high temperature stability, and low nonlinear index of refraction. For the first time, the sol-gel process has been successfully employed to prepare highly doped neodymia silica glass, up to 5wt% Nd for homogeneous dopant distribution. The optical characteristics of the silica glass and its in-process gel, including the UV/VIS absorption spectra, infrared absorption spectra, fluorescence emission spectrum and the fluorescence lifetime, are measured and analyzed. The structure of the sample is also characterized by means of XRD and SEM. A porous gel is observed to have formed when the heat treatment temperature reaches 300oC. Wavelength shifts in the absorption peak corresponding to the 4I9/2 to 4F5/2 transition have been observed during the densification process and for different Nd weight contents. The FTIR spectra have shown that high temperature heat treatment can greatly reduce the amount of OH groups and organic residue in the silica. We have also shown that a high OH content contributes to weak fluorescence intensity and short fluorescence lifetimes.

Effect of SiO2 Surface Treatment on the Solid‐Phase Crystallization of Amorphous Silicon Films

The decrease in nucleation rate for solid‐phase crystallization was investigated. underlayers were treated with various wet chemicals before depositing amorphous Si (a‐Si) films in a low pressure chemical vapor deposition tube, using disilane at 480°C. These amorphous Si films were crystallized by subsequent annealing at 600°C for various times. The nucleation rate depended on the surface treatment by (DHF) or (APM). Consequently, poly‐Si films with a large grain size, two or three times as large as that without any treatment could be obtained. The steady‐state nucleation rate decreased as the degree of hydrophilicity of the underlayer was enhanced, whereas the incubation time for the nucleation remained almost constant for the degree of hydrophilicity. Moreover, attenuated total reflection measurements indicated that the amount of the OH groups on the surface was increased by the DHF treatment. These results indicate that nucleation occurred at the interface and that this depended on the amount of OH groups on the surface at room temperature.

Raman study of structural defects in SiO2 aerogels

The structure of the silica aerogels was studied by Raman spectroscopy. The spectra of the solid network resembles that of bulk silica with additional bands related to organic groups and a large amount of OH groups.

Determination of Components of Cassiterite Surface Free Energy from Contact Angle Measurements

Measurements of contact angle for water, glycerol, formamide, diiodomethane, and bromoform on cassiterite surface with different initial treatments were conducted. Using the values of contact angle, the total surface free energy of cassiterite, and its components resulting from different kinds of intermolecular interactions were calculated. For this purpose, various approaches to the solid-liquid interfacial free energy have been considered. Next, the usefulness of these approaches for the determination of the cassiterite-water interfacial free energy and of the work of adhesion of water to the cassiterite surface were tested. Thus, it was found that the surface free energy of cassiterite previously dried at 110°C and not treated with HNO 3 is mainly the result of dispersion intermolecular interactions and this energy strongly depends on the amount of OH groups and/or coordinated and physisorbed water molecules on its surface. The presence of OH groups and/or water molecules gives rise to the acid-base components of the cassiterite free energy. It was also found that all the approaches tested for a given sample gave, in many cases, near the same value of the total cassiterite surface free energy; however, their usefulness to predict the cassiterite-water interfacial free energy and the work of adhesion of water to the cassiterite surface was not the same. Using the values of the Lifshitz-van der Waals, electron-acceptor and electron-donor components of the surface free energy for both cassiterite and water, the free energy of interaction between two particles of cassiterite in water was calculated and related with observations of the aggregation process of cassiterite and it was stated that if the energy of interaction is negative the aggregation process of cassiterite particles takes place.

Two-dimensional properties of surfactant-like polymer monolayrs

A functional polymer monolayer at an air/water interface has been studied systematically by substituting a hydrophobic backbone with a hydrophilic moiety (OH) by measuring the surface pressure as a function of surface concentration for different molecular weight polymers. The characteristic scaling exponent (ν) estimated from the isotherms and the overlap surface concentration suggests that the air/water interface becomes a better solvent as the amount of hydrophilic functional groups is increased. Also, the isotherms show that the area per polymer molecule increases with increasing amounts of OH groups. However, the water surface tension is most effectively reduced at the 50% substitution level, not at 100%. This optimum amount of OH group on the hydrophobic polymer is equivalent to the hydrophic/lypophic balance of a surfactant in the formation of microemulsions. Furthermore, the surface occupied area per OH group ( σ o) is estimated with the ideal gas law at a dilute surface concentrations. The results show that the σ o is a minimum at the same substitution level at which the reduction of water surface tension is a maximum.

Radiation Effects on Pure Silica Core Optical Fibers by γ-Rays: Relation between 2 eV Band and Non-Bridging Oxygen Hole Centers

The defect center causing the 2 eV absorption band induced in pure silica core fibers by 60Co γ-rays is discussed. The 2 eV band and non-bridging oxygen hole center (NBOHC, SI–O·) show almost the same thermal annealing characteristics. The peak wavelength of the 2 eV band in low-OH (≦6 ppm) fibers is 630 nm, but shifts to shorter wavelengths according to the amount of OH group the sample contains, and appears at 600 nm in high-OH (≧700 ppm) fibers. The peak shape is broader in high-OH fibers than in low-OH fibers. This shift and broadening is attributable to a hydrogen bond between NBOHC and a hydrogen atom. Based on the above results, the defect center responsible for the 2 eV band is considered to be NBOHC.

PROPERTIES OF NONALLOPHANIC ANDOSOLS FROM JAPAN

We studied various properties of nonallophanic Andosols in Japan. Our results showed that, despite many similarities between nonallophanic and allophanic Andosols, significant dissimilarities also exist between the two groups of soils. The nonallophanic Andosols used for our study formed from rhyolitic, dacitic, or andesitic volcanic ash in a humid temperature climate. They had distinctive morphological properties common to allophanic Andosols in Japan: (1) very dark, thick humus horizons, (2) granular structure in the humus horizons, (3) friable to very friable consistence, and (4) abrupt or clear smooth boundaries between humus and nonhumus horizons. The clay mineralogy of the nonallophanic Andosols was very different from that of the allophanic Andosols. In nonallophanic Andosols the clay fractions are mostly dominated by chloritized 2:1 minerals and the active Al (acid-oxalate-ex-tractable Al) consists largely or wholly of Al complexed with humus (pyrophosphate-extractable Al). The nonallophanic Andosols had mostly medium to fine textures and considerable high water retention at 15 bars. We noted that these soils have characteristically low bulk density, which is closely correlated with the organic carbon content. A remarkable accumulation of humus took place in the nonallophanic Andosols and was closely correlated with the formation of Al-humus complex. The high CEC of these soils was ascribed to the high humus content. We noted that nonallophanic Andosols are strongly acid to very strongly acid, reflecting the abundance of chloritized 2:1 minerals and the very low base saturation. Therefore, they had high Al saturation and large amounts of KCl-exchangeable Al, which is a major deterrent to plant growth in the soils. The average values of Al saturation and KC1-ex-changeable Al were 74.4% and 5.51 meq/ 100 g for humus horizon soils and 59.8% and 3.50 meq/100 g for nonhumus horizon soils, respectively. Almost all the nonallophanic Andosol samples had pH (NaF) >10 and phosphate retention > 85%. These values were significantly correlated with the acid-oxalate-extractable Al (Alo). Soils containing > 1% Alo have pH (NaF) > 9.4 and phosphate retention >85%. Therefore, we noted that Al complexed with humus has a significant amount of OH groups and is highly reactive. The analysis of pyro-phosphate-soluble components indicated that the humus associating with Al and Fe consists largely or wholly of humic acid with the highest degree of humification.

The effect of carriers of MoO 3CoO and MoO 3 catalysts on the activity for the hydrocracking of thiophene

The catalytic activity for the hydrocracking of thiophene of molybdenum-cobalt catalysts mounted on SiO 2Al 2O 3 of different compositions and the surface property of the carriers were studied. A correlation was found between the activity and the amount of MoO 3 mounted on the carriers. The amount of MoO 3 increased with the increase of the amount of anionic OH group on the carriers, which can be exchanged with fluorine ion. For a series of molybdenum catalysts mounted on various aluminas, magnesia-alumina, active carbon, etc., it was also found that the amount of MoO 3 correlated well with the amount of OH group. A MgOAl 2O 3 carrier which has the largest amount of OH group supported the largest amount of MoO 3. The role of anionic OH group for the interaction between MoO 3 and carriers is discussed.