Effect Of Surface Fluorination Research Articles

Enhanced dispersion stability and fluidity of rutile TiO2 particles using surface fluorination

Abstract To investigate the effect of surface fluorination on dispersion stability and powder fluidity of rutile TiO2 particles, they were fluorinated using F2 gas under various conditions. Reaction temperature, fluorine pressure and reaction time were set at 25∼200 ℃, 1∼50 kPa, and 1h, respectively. Even at 200℃ of fluorination temperature, the crystal structure did not change in XRD results. Some fluorenes were found on the surface of TiO2 particles in XPS results, and their contents increased with increasing the F2 pressure. From a result of sedimentation test with water, the dispersion stability of TiO2 particles was improved using the surface fluorination. The average size and zeta potentials of fluorinated TiO2 particles were almost 2 times smaller and 2 times larger, respectively, than those (1x103 mm and -20 mV) of untreated TiO2 particles. And in the results of FT4 powder rheometer and repose angle, the powder fluidity of rutile TiO2 particles was improved using surface fluorination. Consequently, the fluorine existed on the surface of TiO2 particles made to improve a dispersion stability and fluidity of TiO2 particles

Effect of surface fluorination on the hydrophilicity of the anodised films for dental implant applications

ABSTRACT Hydrophilicity is an important factor for dental implant applications. It can improve the implant surface-blood interaction resulting in improved implant osseointegration. The aim of this research was to investigate the effect of fluoride on the hydrophilicity of the anodised films. The anodised films were performed by two-step anodisation at low current density in mixing solution of 1M H3PO4 (20 ml) + 80% v/v C2H5OH (20 ml) with different NaF concentrations of 0.25, 0.5, 1, 2, 4 wt % (20 ml). The two-step anodisation using 2 mA/cm2 in 1M H3PO4 + 80% v/v C2H5OH + 4 wt % NaF could enhance hydrophilicity to the anodised films due to hydroxyl groups, surface roughness and the F−ions incorporated into the anodised films. Therefore, a high content of F−ions (4 wt % NaF) was shown to promote hydrophilicity of the anodised films.

The Effect of Surface Fluorination of Thermoplastic Elastomers on their Abrasion Resistance

The Effect of Surface Fluorination of Thermoplastic Elastomers on their Abrasion Resistance

Effect of surface fluorination on space charge behavior in multilayered polyimide films

In recent years, the multilayered polyimide films have been widely used in flexible Print-Circuit Board in order to reduce the thickness of the combination of the flexible Print-Circuit Board. The existence of space charge as a main reason for dielectric breakdown, has a great effect on breakdown characteristic. So it is important to study the space charge characteristics of the multilayered polyimide films. Fluorination can change the chemical component in surface layer of polymers and therefore can influence the charge injection from electrodes and affect the electrical properties of the surface layer. This paper presents a study aimed at clarifying the effect of fluorination on space charge behavior in multilayered polyimide films. Samples were fluorinated in a laboratory vessel at 328 K (55 °C) using a F 2 /N 2 mixture with 20% F 2 by volume and 0.05 MPa (500 mbar) for respectively 15, 30, 45 and 60 minutes. The surface chemical compositions of the films were characterized by attenuated total reflection infrared analysis. The space charge distributions in multilayered polyimide films were measured by using the pulsed electroacoustic (PEA) method. Obtained results showed that the space charge distribution of multilayered film stacking with five fluorinated samples was quite different from that of multilayered film stacking with five untreated samples. It is also suggested that the fluorination can significantly suppress the injection of space charge.

Effect of Surface Fluorination on Photocatalytic Activity of Titania Nano-Powder

This work, surface fluorination process was used for improvement photocatalytic activity of TiO2. Photocatalytic activity was observed by degradation of methylene blue (MB). TiO2 nanopowders were prepared by sol-gel technique from titanium-tetraisopropoxide (TTIP): 2-propanal (2-PP) with the ratios of 1:5, 1:15, and 1:30 (V/V) then adjusted pH by nitric acid at 2. The result showed that grain size of TiO2 powder decreased as 2-PP ratio increase. The grain sizes of TiO2 were in the range of 14-25 nm. Photocatalytic activity was considered by characteristic time constant. The results showed that F-TiO2 presented higher photo-degradation than naked TiO2. At 1:30 for TTIP: 2-PP ratio with improvement by surface fluorination (F-TiO2) could degrade MB faster than other samples under weak-UV at irradiation time of 1 hr. The 1:30 sample degraded MB reach to 96%. The results led to conclude that surface fluorination is the good process to improve photocatalytic activity for TiO2.

Effect of Surface Fluorination on the Electrochemical Behavior and Surface State of Li4Ti5O12 for Lithium Ion Battery

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Effect of Surface Fluorination on the Electrochemical and Photoelectrocatalytic Properties of Nanoporous Titanium Dioxide Electrodes

Titanium dioxide is a widely used photocatalyst whose properties can be modified by fluoride adsorption. This work is focused on the effect of surface fluorination on the electrochemical and photoelectrocatalytic properties of TiO(2) nanoporous thin films. Surface fluorination was achieved by simple addition of HF to the working solution (pH 3.5). Open circuit potential as well as ex situ XPS measurements verify that surface modification takes place. Fluorination triggers a significant capacitance increase in the accumulation potential region, as revealed by dark voltammetric measurements for all the TiO(2) samples studied. The photoelectrocatalytic properties (measured as photocurrents under white light illumination) depend on the substrate being oxidized and, in some cases, on the nature of the TiO(2) sample. In particular, the results obtained for electrodes prepared with a mixed phase (rutile + anatase) commercial nanopowder (PI-KEM) indicate that the processes mediated by surface trapped holes, such as the photooxidation of water or methanol, are accelerated while those occurring by direct hole capture from the adsorbed state (formic acid) are retarded. The photooxidation of catechol and phenol is also enhanced upon fluorination. In such a case, the effect can be rationalized on the basis of a diminished recombination and a surface displacement of both the oxidizable organic substrates and the poisoning species formed as a result of the organics oxidation. Photoelectrochemical and in situ infrared spectroscopic measurements support these ideas. In a more general vein, the results pave the way toward a better understanding of the photocatalysis phenomena, unravelling the importance of the reactant adsorption processes.

Fluorination effect of activated carbon electrodes on the electrochemical performance of electric double layer capacitors

The surface of phenol-based activated carbon (AC) was fluorinated at room temperature with different F 2:N 2 gas mixtures for use as an electrode material in an electric double-layer capacitor (EDLC). The effect of surface fluorination on EDLC electrochemical performance was investigated. The specific capacitance of the fluorinated AC-based EDLC was measured in a 1 M H 2SO 4 electrolyte, in which it was observed that the specific capacitances increased from 375 and 145 F g −1 to 491 and 212 F g −1 with the scan rates of 2 and 50 mV s −1, respectively, in comparison to those of an unfluorinated AC-based EDLC when the fluorination process was optimized via 0.2 bar partial F 2 gas pressure. This enhancement in capacitance can be attributed to the synergistic effect of increased polarization on the AC surface, specific surface area, and micro and mesopore volumes, all of which were induced by the fluorination process. The observed increase in polarization was derived from a highly electronegative fluorine functional group that emerged due to the fluorination process. The increased surface area and pore volume of the AC was derived from the physical function of the fluorine functional group.

Selective Aerobic Oxidation of Aromatic Alcohols Catalyzed by TiO<sub>2</sub>: An Insight on the Effect of Surface Fluorination

To achieve better activity, TiO2 was modified through surface fluorination using hydrofluoric acid (denoted as HF-TiO2). The photocatalytic activities of the as-prepared HF-TiO2 and pure TiO2 photocatalysts were evaluated for selective aerobic oxidation of benzyl alcohol. Experimental results indicated that without any loss of selectivity (>98%), distinct rate enhancement can be observed on HF-TiO2 comparing to pure TiO2. To optimize the condition of pretreatment, different concentrations of hydrofluoric acid were also used and the optimal concentration was determined to be 2%. Moreover, the dynamics of benzyl alcohol oxidation followed pseudo-first-order kinetic. By ESR technique and experiments adding different captures, the active specie is determined to be O2 while O2.- and H2O2 were byproducts of the reaction. In a word, this study opens a new path to obtain both high selectivity and conversion yield by TiO2 photocatalysis.

Effect of phase structures on the photocatalytic activity of surface fluorinated TiO2

Nanocrystalline TiO2 with different contents of anatase were tailored by hydrothermal treatment of the mixed solution of Ti(SO4)2 and TiCl4 at 250°C for 24h, and then calcined at 500°C for 3h. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, nitrogen sorption, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectra. The as-prepared TiO2 samples with different contents of anatase have similar BET specific surface areas (30–40m2/g) and crystalline sizes (30–40nm). The effect of surface fluorination on the adsorption and photocatalytic activity of TiO2 samples was evaluated using Brilliant Red X3B, an anionic azo dye, as the target organic molecule at pH 3.0. Both on anatase and rutile TiO2, the dark adsorption of X3B was greatly decreased in the presence of fluoride, ascribed to competitive adsorption of fluoride that reduces the positive charges on the catalyst surface. After surface fluorinated by 1.0mmol/L NaF, the photocatalytic activity of anatase was enhanced by a factor of 2.63. However, 81.3% of the photocatalytic activity was reduced for rutile TiO2 after surface fluorinated under the same condition. Only when the content of anatase is higher than 40%, can fluoride shows positive effect on the photocatalytic activity of TiO2. Two reaction models were put forward, based on the photocurrent response, degradation kinetics, hydroxyl radicals quenching and detecting, to illustrate the different effects of fluoride on the photocatalytic degradation of X3B in anatase and rutile TiO2 suspensions.

Effect of surface fluorination and conductive additives on the electrochemical behavior of lithium titanate (Li 4/3Ti 5/3O 4) for lithium ion battery

Effect of surface fluorination and conductive additives on the charge/discharge behavior of lithium titanate (Li 4/3Ti 5/3O 4) has been investigated using F 2 gas and vapor grown carbon fiber (VGCF). Surface fluorination of Li 4/3Ti 5/3O 4 was made using F 2 gas (3 × 10 4 Pa) at 25–150 °C for 2 min. Charge capacities of Li 4/3Ti 5/3O 4 samples fluorinated at 70 °C and 100 °C were larger than those for original sample at high current densities of 300 and 600 mA/g. Optimum fluorination temperatures of Li 4/3Ti 5/3O 4 were 70 °C and 100 °C. Fibrous VGCF with a large surface area (17.7 m 2/g) increased the utilization of available capacity of Li 4/3Ti 5/3O 4 probably because it provided the better electrical contact than acetylene black (AB) between Li 4/3Ti 5/3O 4 particles and nickel current collector.

Effect of surface fluorination on the photocatalytic and photo-induced hydrophilic properties of porous TiO 2 films

Porous surface-fluorinated TiO 2 (F-TiO 2) films were prepared through PEG modified sol–gel method and surface fluorination. The as-prepared films were characterized with XRD, FTIR, AFM, XPS and UV–vis DRS. The effects of surface fluorination on the photocatalytic activity and hydrophilicity of porous TiO 2 film were studied by photocatalytic degradation of rhodamine B (RhB) as well as water contact angle (CA) on porous TiO 2 film. The results showed that the surface fluorination increased the adsorption of RhB on the porous TiO 2 film and enhanced the photocatalytic degradation of RhB. The concentration and pH of NaF solutions affected much the photocatalytic activity of porous TiO 2 film. Porous F-TiO 2 film prepared in 40 mM NaF solution at pH 4.0 showed the highest photocatalytic activity. Because of its porous structure, the porous F-TiO 2 film had original water CA of 22.7°, which is much smaller than that of normal F-TiO 2 film. Under UV light irradiation, the water CA of porous F-TiO 2 film decreased to 5.1° in 90 min.

Effect of Surface Fluorination and Sulphonation on the Adhesion and Tribological Properties of Polymers

Effect of Surface Fluorination and Sulphonation on the Adhesion and Tribological Properties of Polymers

Effect of Surface Fluorination on Diffusion through a High Density Polyethylene Geomembrane

The relative improvement of the diffusive barrier function of high density polyethylene ~HDPE! geomembranes to volatile organic compounds ~VOCs! when subjected to surface fluorination is experimentally examined. The surface fluorination consisted of applying elemental fluorine, which exchanged with hydrogen along polymer chains at the surface of a polyolefin substrate. Sorption and diffusion tests were performed on both traditional untreated and 1.5 mm HDPE geomembranes using dilute aqueous organic contaminants commonly found in municipal solid waste leachate. The partitioning coefficient is shown to remain essential the same after the surface fluorination; however, the surface fluorination resulted in a reduction in both the diffusion and the permeation coefficients by factors ranging between 1.5 and 4.5, depending on the hydrocarbon examined. Modeling of VOC diffusion through a geomembrane/compacted clay composite liner indicated that contaminant impacts were about 1.7-2.9 times lower when a fluorinated geomembrane is used. To achieve the same level of protection as provided by the fluorinated geomembrane underlain by 0.60 m of compacted clay, one would need an additional 0.4- 0.9 m of compacted clay in conjunction with a conventional ~untreated! geomembrane. The importance of the thickness of the treated layer is highlighted.

Effect of surface fluorination on the electrochemical behavior of petroleum cokes for lithium ion battery

Surface structure change and electrochemical behavior of fluorinated petroleum coke samples (petroleum cokes: petroleum coke and those heat-treated at 1860 °C, 2300 °C and 2800 °C, abbreviated to PC, PC1860, PC2300 and PC2800, respectively) have been investigated. Surface oxygen of petroleum coke was decreased by the fluorination using elemental fluorine. Raman and EPR spectroscopies revealed that surface fluorination increased surface disorder and lattice defects. 19F NMR spectrum suggests that distribution of fluorine atoms in PC fluorinated 300 °C was similar to that in graphite fluoride with covalent C F bonds. Surface areas of fluorinated petroleum cokes were nearly the same as those of non-fluorinated ones or only slightly increased by fluorination, except PC fluorinated at 300 °C. It is noted that first coulombic efficiencies of PC2300 and PC2800 were highly increased to 80–84% by the fluorination at 300 °C. These values of 80–84% were 12–18% higher than those of non-fluorinated PC2300 and PC2800.

The Limiting Stage of Migration of a Modifier from an Elastomer and the Effect of Surface Fluorination

The Limiting Stage of Migration of a Modifier from an Elastomer and the Effect of Surface Fluorination

The effect of surface fluorination on the wettability of high density polyethylene

High-density polyethylene (HDPE) samples have been fluorinated and oxyfluorinated for different times. Dynamic contact angle analysis was used to determine the effect of fluorine gas mixtures on the surface of HDPE. The total surface tension of HDPE increased drastically with the length of oxyfluorination treatment, but levelled off after longer treatments. Fluorination resulted in a marked decrease in the total surface tension of HDPE. During fluorination, the dispersive component of the surface tension decreased progressively with fluorination time, while the polar component increased initially but decreased again with longer fluorination treatments. This indicates that short fluorination times lead to increased wettability by polar liquids, while longer fluorination times have the opposite effect. Fluorinated and oxyfluorinated surfaces were exposed to elevated temperatures. Whereas it was found that fluorinated surfaces changed measurably, oxyfluorinated surfaces changed dramatically upon heating at 100 °C. Photoacoustic FT-IR spectroscopy indicated that this was probably due to migration of surface polar groups into the bulk of the polymer, rather than chemical change.

Surface fluorination of poly (phenylene oxide) composite membranes Part I. Transport properties

The effect of surface fluorination on the gas transport properties of composite membranes, comprising an inert porous ceramic support and a selective layer consiting of poly (phenylene oxide), was examined. A small reactor volume permitted the treatment time and the fluorine feed concentration to be investigated independently. The gas transport properties of the treated membranes were evaluated for six gases (N 2, O 2, CH 4, H 2, He and CO 2), in terms of permeance ( P/ l or pressure-normalized flux) and the ideal selectivity for eight pairs of these gases. It was generally found that fluorination at different fluorine feed concentrations and reaction times reduced the permeance of all of the gases. The permeance of the lighter gases (He and H 2) was reduced by a smaller factor than that of the heavier gases (N 2 and CH 4). Fluorination increased the selectivity of He and H 2 relative to N 2 or CH 4 by a small factor, but reduced the selectivity of O 2 and CO 2 relative to N 2 or CH 4. When the membranes were coated with a layer of poly(dimethylsiloxane) (PDMS) subsequent to fluorination, the permeance decreased, considerably more for N 2 and CH 4 than for the other gases. Surface coating also substantially increased the selectivities of all the gas pairs. The largest gains in selectivity after fluorination and coating were found at the higher concentration (0.1 % F 2) and intermediate treatment times of 3 to 5 min. Based on these results, surface coating with PDMS is recommended as a post-treatment step in the fluorination process.

Effect of Surface Fluorination with CCIF3 on Catalytic Activity of SiO2–Al2O3 for Alkylation of Benzene with Propene

Abstract For surface modification, the vapor-phase fluorination of SiO2–Al2O3 with CCIF3 was carried out at various temperatures ranging from 350 to 550°C in a conventional flow reactor. It was found that surface fluorination at about 400°C was especially effective for the enhancement of both the catalytic activity and the maintenance of the catalytic activity for the vapor-phase alkylation of benzene with propene. Ammonia–TPD revealed that the surface acidity of SiO2–Al2O3 could be somewhat increased by surface fluorination at about 400°C. The vapor-phase adsorption of water, hexane, propene, benzene, and cumene showed that the SiO2–Al2O3 surface became hydro- and lipo-phobic after surface fluorination. Thus, an enhancement of catalytic activity maintenance was assignable to a decrease in the affinity of the catalyst surface to reaction products.