Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “FLUORINATION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Fluorinated High-Voltage Electrolytes To Stabilize Nickel-Rich Lithium Batteries

As state-of-the-art (SOA) lithium-ion (Li-ion) batteries approach their specific energy limit (~250 Wh kg -1 ), layer-structured, nickel-rich (Ni-rich) lithium transition metal oxide-based cathode materials, e. g., LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811), have attracted great interest owing to their practical high specific capacities (>200 mAhg -1 ). Coupled with their high average discharge voltages (~4 V vs Li/Li + ), Ni-rich cathode-based lithium batteries possess a great potential to achieve much higher specific energies (>350 Wh kg -1 at the cell level) than the SOA Li-ion counterparts. In addition, Ni-rich oxides are low-cost battery cathode materials due to their low cobalt contents. However, Ni-rich cathode-based lithium batteries suffer quick capacity degradations upon cycling, particularly at high upper cutoff voltages (e.g., ≥= 4.5 V vs Li/Li + ), due to crystal structure changes of the active cathode materials and parasitic side reactions at the electrolyte/electrode interfaces. In this study, a fluorinated-solvent-based, high-voltage stable electrolyte (HVE), i.e., 1 M Li bis(trifluoromethanesulfonyl)imide (LiTFSI) in fluoroethylene carbonate (FEC), bis(2,2,2-trifluoroethyl) carbonate (FDEC), and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) with Li difluoro(oxalate)borate (LiDFOB) additive, was formulated and evaluated in Li/NMC811 battery cells. Further, to the best of our knowledge, this class of electrolyte has not been investigated for Ni-rich cathode-based lithium batteries. Li/NMC811 cells with HVE exhibited a superior long-term cycle performance stability, maintaining ~80% capacity after ~500 cycles at a high cutoff voltage of 4.5 V (vs Li/Li + ) than a baseline carbonate-solvent-based electrolyte (BE). The superior cycle stability of the Li/NMC811 cells is attributed to the inherently high-voltage stability of HVE, supported by the physical and electrochemical analyses. This conclusion is supported by our density functional theory (DFT) modeling where HVE shows a less tendency of deprotonation/oxidation than BE, leading to the observed cycle stability. The findings in this study are important to help tackle the technical challenges facing Ni-rich cathode-based lithium batteries to realize their high energy density potentials with a long cycle life.

25 ENERGY STORAGE↗
DOE OSTI2012

Positron annihilation studies of fluorine-vacancy complexes in Si and SiGe

The formation of fluorine-vacancy (FV) complexes in strained Si-SiGe-Si multilayer structures and relaxed SiGe layers of varying Ge content has been investigated using variable-energy positron annihilation spectroscopy, including Doppler-broadened spectra ratio curves. It has been found that in all sample types there are two distinct regions defined only by the damage created by the implanted F ions. The first, shallower region (from the surface to a depth of {approx}200 nm) was found to contain a mixture of undecorated vacancies and FV complexes; there is no correlation between the vacancy or F concentration in this region and the Ge content. The multi-layer samples may also have O contamination that is not present in the relaxed samples. The second region (at depths {approx}200-440 nm) contains primarily FV complexes in all samples. In the multi-layer samples secondary ion mass spectrometry (SIMS) results show peaks of F accumulating in, or at the interfaces of, each SiGe multi-layer; the FV complexes, however, are distributed over depths similar to those in the relaxed samples, with some localization at the SiGe layer located within the second region. The positron response is primarily to FV complexes formed by the F implant in all samples. The F: FV ratios are approximately 3-7: 1 in the relaxed samples. Positrons appear to be relatively insensitive to the largest of the F SIMS peaks which lies beyond the second region. This is probably because the F has filled all the open volume at the SiGe layer, leaving no positron trapping sites.

36 MATERIALS SCIENCE↗
DOE OSTI2012

The fluorine destruction in stars: First experimental study of the {sup 19}F(p,{alpha}){sup 16}O reaction at astrophysical energies

The {sup 19}F(p,{alpha}){sup 16}O reaction is an important fluorine destruction channel in the proton-rich outer layers of asymptotic giant branch (AGB) stars and it might also play a role in hydrogendeficient post-AGB star nucleosynthesis. So far, available direct measurements do not reach the energy region of astrophysical interest (E{sub cm}{approx} 300 keV), because of the hindrance effect of the Coulomb barrier. The Trojan Horse (TH) method was thus used to access this energy region, by extracting the quasi-free contribution to the {sup 2}H({sup 19}F,{alpha}{sup 16}O)n reaction. The TH measurement of the {alpha}{sub 0} channel, which is the dominant one at such energies, shows the presence of resonant structures not observed before that cause an increase of the reaction rate at astrophysical temperatures up to a factor of 1.7, with potential important consequences for stellar nucleosynthesis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

THE FLUORINE DESTRUCTION IN STARS: FIRST EXPERIMENTAL STUDY OF THE {sup 19}F(p, {alpha}{sub 0}){sup 16}O REACTION AT ASTROPHYSICAL ENERGIES

The {sup 19}F(p, {alpha}){sup 16}O reaction is an important fluorine destruction channel in the proton-rich outer layers of asymptotic giant branch (AGB) stars and it might also play a role in hydrogen-deficient post-AGB star nucleosynthesis. So far, available direct measurements do not reach the energy region of astrophysical interest (E {sub cm} {approx}< 300 keV), because of the hindrance effect of the Coulomb barrier. The Trojan Horse (TH) method was thus used to access this energy region, by extracting the quasi-free contribution to the {sup 2}H({sup 19}F, {alpha}{sup 16}O)n and the {sup 19}F({sup 3}He, {alpha}{sup 16}O)d reactions. The TH measurement of the {alpha}{sub 0} channel shows the presence of resonant structures not observed before, which cause an increase of the reaction rate at astrophysical temperatures up to a factor of 1.7, with potential consequences for stellar nucleosynthesis.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Energy loss of keV fluorine ions scattered off a missing-row reconstructed Au(110) surface under grazing incidence

A joint experimental and theoretical study of energy loss is presented for 1-to-4-keV fluorine negative ions in grazing scattering on a missing-row reconstructed Au(110) surface. Measurements of energy losses for various azimuthal orientations of the crystal have been performed by means of a time-of-flight method with a pulsed beam. The dependence of the fraction of surviving negative ions on azimuthal angles, was determined. Our energy-loss data are discussed in light of trajectory and stopping-power calculations, where the explicit inclusion of the nonuniform electron density at the surface provides good agreement with the experimental data. The simulation allows us to delineate various trajectory classes that correspond to different contributions in the energy-loss spectra for various azimuthal orientations of the surface.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Conformal LiF Stabilized Interfaces via Electrochemical Fluorination on High Voltage Spinel Cathodes (≈4.9 V) for Lithium-Ion Batteries

The high voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) spinel is one of the promising cathodes for the lithium-ion batteries due to its high energy densities, good rate performance. However, its high operating potential (≈4.75 V) causes extensive oxidation of conventional carbonate electrolytes, resulting an unstable and thick cathode electrolyte interphase (CEI) layer with a large irreversible capacity and low coulombic efficiency. In this work, we report the formation of thin LiF stabilized interfaces on LNMO via electrochemical fluorination that significantly improves the cycling stability and enhanced the capacity. An electrochemically induced conformal LiF layer acts as a part of a robust CEI by reducing the leakage of electrons and allowing the conduction of Li ions through it. Because of the robust LiF stabilized CEI, LNMO delivers a discharge capacity of ≈148.5 and ≈117.1 mAh g -1 at 0.1 and 1 C rate, respectively. It exhibits excellent cyclability with 80% capacity retention (CR) after 600 cycles in lithium-half cell and ≈90% CR after 200 cycles in full cell with only 0.03% and 0.05% capacity decay per cycle in conventional carbonate electrolytes without additives. Such an excellent electrochemical performance could lead to the potential development of high energy density batteries with high voltage cathodes for grid-based applications.

25 ENERGY STORAGE↗
DOE OSTI2023

High‐Performance Lithium Metal Batteries Enabled by a Fluorinated Cyclic Ether with a Low Reduction Potential

Abstract Electrolyte engineering is crucial for developing high‐performance lithium metal batteries (LMB). Here, we synthesized two cosolvents methyl bis(fluorosulfonyl)imide (MFSI) and 3,3,4,4‐tetrafluorotetrahydrofuran (TFF) with significantly different reduction potentials and add them into LiFSI‐DME electrolytes. The LiFSI/TFF‐DME electrolyte gave an average Li Coulombic efficiency (CE) of 99.41 % over 200 cycles, while the average Li CEs for MFSI‐based electrolyte is only 98.62 %. Additionally, the TFF‐based electrolytes exhibited a more reversible performance than the state‐of‐the‐art fluorinated 1,4‐dimethoxylbutane electrolyte in both Li||Cu half‐cell and anode‐free Cu||LiNi 0.8 Mn 0.1 Co 0.1 O 2 full cell. More importantly, the decomposition product from bis(fluorosulfonyl)imide anion could react with ether solvent, which destroyed the SEI, thus decreasing cell performance. These key discoveries provide new insights into the rational design of electrolyte solvents and cosolvents for LMB.

25 ENERGY STORAGE↗
DOE OSTI2025

Constructing Water‐Stable Porous Organic Salts via Suppressed Proton Integration Using Fluorinated Tetrazole Tectons

Porous organic salts (POSs) are an emerging class of materials with ordered ionic architectures, offering excellent proton transfer and water uptake properties. However, conventional POS synthesis via strong acid–base neutralization (e.g., ─SO₃H and ─NH₂) leads to extensive hydrogen bonding with water, compromising stability in aqueous and water-lean environments. Here, we address this challenge by designing POSs with hydrophobic porous channels and minimal hydrogen bonding formation. Our key innovation is the use of fluorinated tetrazole as a weak acid tecton and a tetra-substituted imidazole precursor devoid of active protons as the base. Single-crystal analysis and computational modeling reveal that the structural integrity of the synthesized POSs arises primarily from cation–anion interactions, with water confined as clusters in the pores, independent of hydrogen bonding with the scaffold. Robustness of the POS structure under aqueous and water-lean conditions is confirmed by X-ray and neutron scattering, as well as computational modeling, confirming preserved packing and crystal structures. The stability of POS is further demonstrated in aqueous iodine capture, with imidazolium cations and C–F functionalizations serving as strong adsorption sites. As a result, the approach developed herein further pushes the boundary of POS materials to withstand both aqueous and water-lean conditions.

Fluorinated tecton↗
DOE OSTI2019

Novel fluorinated quaternary ammonium salts and their in vitro activity as trypanocidal agents

As the impact of aromatic rings and fluorine substituents in commercial drugs is attributed to their electronic distribution and structure rigidity that determine metabolic stability and toxicity, 30 quaternary ammonium salts (QAS) of the form [X-CH{sub 2}N(CH{sub 3}){sub 2}(CH{sub 2}){sub n}CH = C(Ar{sub 2})]{sup +}I{sup −} (where X=H, Cl or I, n = 2 or 3, and Ar = m-C{sub 6}H{sub 4}CF{sub 3}, p-C{sub 6}H{sub 4}CF{sub 3}, m-C{sub 6}H{sub 4}F, p-C{sub 6}H{sub 4}F or C{sub 6}H{sub 5}) were tested as potential trypanocidal agents and assessed their cytotoxicity on U-937 cells. CF{sub 3}-substituted QASs exhibited LC{sub 50} values in the range of 0.5 to 6.4 μg/mL and trypanocidal EC{sub 50} values between 0.6 and 7.0 μg/mL, while the LC{sub 50} values for F-substituted analogs are between 7.0 and 207 μg/mL and EC{sub 50} values range from 3.8 to 40.9 μg/mL. As a general trend, the more effective are those bearing an N-iodomethyl moiety or having a longer tether, and para-substituted ones. Few drugs therapies are in use for Chagas disease, so this study becomes a promising contribution.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2011

Formation of an SEI on a LiMn(2)O(4) Cathode during Room Temperature Charge-Discharge Cycling Studied by Soft X-Ray Absorption Spectroscopy at the Fluorine K-edge

The solid electrolyte interface (SEI) formation on the surface of LiMn{sub 2}O{sub 4} electrodes during room temperature charge-discharge cycling was studied using soft X-ray absorption spectroscopy at the Fluorine (F) K-edge. LiMn{sub 2}O{sub 4} electrodes without any binder were prepared by electrostatic spray deposition to eliminate the signal originating from the PVDF binder in the F K-edge X-ray absorption spectra. The F K-edge absorption spectra show that the SEI layer forms at a very early stage of cycling. SEI growth takes place during discharge. In addition, LiF formation is accelerated if the discharge step follows a charge step. The F K-edge absorption spectra suggest that the major component of the SEI is LiF.

25 ENERGY STORAGE↗
DOE OSTI2017

The high matrix acquisition technique for imaging of atherosclerotic plaque inflammation in fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography with time-of-flight: Phantom study

Background: Motion artifact and partial volume effect caused underestimation of coronary plaque inflammation. This study evaluated the high matrix acquisition technique using time-of-flight (TOF) positron emission tomography/computed tomography for imaging of atherosclerotic plaque inflammation with fluorine-18 fluorodeoxyglucose in small and moving phantoms. Methods and Results: All images were reconstructed using a conventional algorithm without TOF (4 × 4 × 4 mm{sup 3} voxel size) and a high matrix algorithm with TOF (2 × 2 × 2 mm{sup 3} voxel size). Microsphere phantoms of 10, 7.9, 6.2, 5.0, and 4.0 mm diameters were acquired in 3-dimensional list-mode for 30 minutes. A heart phantom mimicking cardiac motion consisted of a hot spot simulating a plaque (φ 4 mm, φ 2 mm) on the outside of the left ventricle. In the microsphere and heart phantom study, visual discrimination, maximum activity, and target-to-background ratio using the high matrix algorithm with TOF were better than those using the conventional algorithm without TOF. Conclusion: The high matrix algorithm with TOF improves detection of small targets in phantoms.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Calculations of energies, transition rates, and lifetimes for the fluorine-like isoelectronic sequence with Z=31−35

Employing two state-of-the-art methods, multiconfiguration Dirac–Hartree–Fock and second-order many-body perturbation theory, highly accurate calculations are performed for the lowest 200 fine-structure levels arising from the 2l{sup 7},2l{sup 6}3l{sup ′} and 2l{sup 6}4l{sup ′} configurations of the fluorine-like isoelectronic sequence with Z=31−35. Complete and consistent atomic data, including excitation energies, lifetimes, wavelengths, and E1, E2, M1, M2 line strengths, oscillator strengths, and transition rates among these 200 levels are provided. Comparisons are made between the present two data sets, as well as with other available experimental and theoretical values. The present data are accurate enough for identification and deblending of emission lines involving the n=3,4 levels, and are also useful for modeling and diagnosing fusion plasmas.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Mechanistic understanding of aging behaviors of critical-material-free Li 4 Ti 5 O 12 //LiNi 0.9 Mn 0.1 O 2 cells with fluorinated carbonate-based electrolytes for safe energy storage with ultra-long life span

Behind-the-meter storage (BTMS) systems - a viable method to minimize potential risk of blackout events and stabilize the grid - require a different type of cost-effective energy storage with excellent safety, ultra-long (>20 years) cycle life and reasonable energy density compared that of electric vehicles. To increase the energy density and reduce the cost of a long-term cyclable lithium-titanate-based cell, it is required to employ a critical-material-free high voltage cathode and an electrolyte with good electrochemical and transport properties. In this report the long-term electrochemical performance and behaviors of selected critical-material-free Li 4 Ti 5 O 12 (LTO)//LiNi 0.9 Mn 0.1 O 2 (LNMO) full cells for BTMS applications are evaluated and analyzed in the optimized voltage range of 1.4-2.7 V at 45 degrees C with different fluorinated carbonate-based electrolytes. The fluoroethylene carbonate (FEC)-based electrolyte cell shows the highest capacity retention of 57.9% and Coulombic efficiency (CE) of 99.96% after 1000 cycles, potentially attributed to a dense, homogenous and less resistive LiF-rich solid-electrolyte interphase (SEI) layer formed on the surface of LTO that may mitigate electrolyte decomposition and maintain relatively low cell impedance during cycling. The 3,3,3-fluoroethylmethyl carbonate (F-EMC)-based electrolyte cell, however, presents the worst performance with lower capacity and a sharp decrease of CE, due to unstable and non-uniform SEI formation and continuous oxidative electrolyte decomposition. This mechanistic understanding of cell aging behaviors and failure mechanisms with detailed analysis of surface chemistry and electrode morphology can guide design of new electrode chemistries and electrolyte formulations for the development of BTMS batteries.

25 ENERGY STORAGE↗
DOE OSTI2012

Usefulness of Positron Emission Tomography With Fluorine-18-Fluorodeoxyglucose in Predicting Treatment Response in Unresectable Hepatocellular Carcinoma Patients Treated With External Beam Radiotherapy

Purpose: To assess the significance of the ratio between standardized uptake values (SUV) of tumor and normal liver tissue obtained from positron emission tomography with fluorine-18-fluorodeoxyglucose (FDG-PET) in predicting the response of hepatocellular carcinoma (HCC) patients treated with external beam radiotherapy (EBRT). Methods and Materials: We retrospectively analyzed 35 HCC patients who were treated with EBRT between January 2004 and June 2007. All patients underwent FDG-PET in which SUV values were obtained from tumor and normal liver tissues and were used to calculate the ratios (SUV{sub Tumor}/SUV{sub Liver}). After FDG-PET, patients received liver treatment including concurrent chemoradiation, transarterial chemoembolization plus RT, or intraarterial chemotherapy plus RT. Using three-dimensional conformal RT, median dose of 45 Gy was delivered in conventional fractions. Patients underwent abdominal/pelvic CT 1 month after RT, and treatment responses were evaluated according to the Response Evaluation Criteria in Solid Tumors criteria. Results: Patients were divided into high-SUV ratio group (n = 20) and low-SUV ratio group (n = 15) according to SUV ratio at a cutoff value of 2.5. Objective responses consisting of either complete response (CR) or partial response (PR) were observed in 16 and 6 patients (46% vs. 17%, p = 0.015), respectively; median survivals after RT were 8 months and 5 months (p = 0.41) for the high-SUV ratio group and the low-SUV ratio group, respectively. Rates of intrahepatic metastases (9% vs. 11%, p = 0.39) and distant metastases (32% vs. 32%, p = 0.27) showed no significant difference between two groups. Conclusions: External beam RT for HCC patients with higher SUV ratios resulted in higher response rates than for patients with lower SUV ratios. Treatment of HCC with higher SUV ratios did not result in increased survival; high rates of intrahepatic and distant metastases in both SUV groups may have affected patient survival. SUV ratios from pre-RT FDG-PET may be beneficial for selecting patients who are likely to respond to EBRT for unresectable HCC.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Understanding fluorine-free electrolytes via small-angle X-ray scattering

Fluorine-free electrolytes have attracted great attention because of its low-cost and environmental friendliness. However, so far, little is known about the solution structures of these electrolytes. Here, we compare the solvation phenomenon of sodium tetraphenylborate (NaBPh 4 ) salt dissolved in organic solvents of propylene carbonate (PC), 1,2-dimethoxyethane (DME), acetonitrile (ACN) and tetrahydrofuran (THF). Small-angle X-ray scattering (SAXS) reveals a unique two-peak structural feature in this salt concentrated PC electrolyte, while solutions using other solvents only have one scattering peak. Molecular dynamics (MD) simulations further reveal that there are anion-based clusters in addition to the short-range charge ordering in the concentrated NaBPh4/PC electrolyte. Raman spectroscopy confirms the existence of considerable contact ion pairs (CIPs). Here, this work emphasizes the importance of global and local structural analysis, which will provide valuable clues for understanding the structure performance relationship of electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2022

High voltage stable cycling of all-solid-state lithium metal batteries enabled by top-down direct fluorinated poly (ethylene oxide)-based electrolytes

Poly (ethylene oxide) (PEO)-based solid-state polymer electrolytes (SPEs) show prospects in all-solid-state lithium metal batteries. However, they suffer from low ionic conductivity at room temperature and interfacial instability with high voltage cathodes for long-term cycling. In this work, top-down fluorinated PEOs (F-PEOs) for the all-solid-state electrolytes, which are scalable and cost-effective, are developed to improve the battery performance. We demonstrate, that by enhancing the disordering of the F-PEO matrix, the SPE achieves a maximum Li + conductivity of 1.1 x 10 -4 S cm -1 at 40 °C, which is 20 times higher than the baseline. By forming robust cathode/SPE and Li/SPE interfaces, the F-PEO-based SPEs demonstrate stable cycling in the LiFePO 4 /Li and LiNi 0·8 Mn 0·1 Co 0·1 O 2 /Li (3-4.4 V, 500 cycles, capacity retention of 91.6%) based all-solid-state batteries at 40 °C. Therefore, our work highlights the significance of "disordering engineering" for energy storage materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

High performance dye-sensitized solar cells using graphene modified fluorine-doped tin oxide glass by Langmuir–Blodgett technique

Since the introduction of dye-sensitized solar cells (DSSCs) with low fabrication cost and high power conversion efficiency, extensive studies have been carried out to improve the charge transfer rate and performance of DSSCs. In this paper, we present DSSCs that use surface modified fluorine-doped tin oxide (FTO) substrates with reduced graphene oxide (r-GO) sheets prepared using the Langmuir–Blodgett (LB) technique to decrease the charge recombination at the TiO{sub 2}/FTO interface. R-GO sheets were excellently attached on FTO surface without physical deformations such as wrinkles; effects of the surface coverage of r-GO on the DSSC performance were also investigated. By using graphene modified FTO substrates, the resistance at the interface of TiO{sub 2}/FTO was reduced and the power conversion efficiency was increased to 8.44%. - Graphical abstract: DSSCs with graphene modified FTO glass were fabricated with the Langmuir Blodgett technique. GO sheets were transferred to FTO at various surface pressures in order to change the surface density of graphene and the highest power conversion efficiency of the DSSC was 8.44%. - Highlights: • By LB technique, r-GO sheets were coated on FTO without physical deformation. • DSSCs were fabricated with, r-GO modified FTO substrates. • With surface modification by r-GO, the interface resistance of DSSC decreased. • Maximum PCE of the DSSC was increased up to 8.44%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Enhancing the photocatalytic activity of nanocrystalline TiO{sub 2} by co-doping with fluorine and yttrium

Highlights: • (F, Y)-codoped TiO{sub 2} nanoparticles were prepared by a simple sol–gel method. • The highest photocatalytic activity (15 times of that over the pure TiO{sub 2}) was exhibited in the codoped TiO{sub 2} with 0.05% Y doping level. • The Y doping induced oxygen vancancies played a duel role on the photocatalyic activity of the codoped TiO{sub 2}. • The photocatalytic reactive oxygen species are critical to the photocatalytic degradation processes. - Abstract: Fluorine and yttrium codoped TiO{sub 2} nanoparticles were prepared using a simple sol–gel method. The products were characterized with various spectroscopic and analytical techniques to determine their structural, morphological, optical absorption and photocatalytic properties. The results reveal that neither F nor Y doping causes obvious absorption edge shift in TiO{sub 2}. Photoluminescence (PL) emission spectra present that the PL signal is enhanced, suggesting a decrease of photo-generated charge carrier separation efficiency, after the F or Y doping. The synergistic action by the F and Y doping leads to the highest photocatalytic activity for the degradation of methylene blue solution in the 0.05% (F, Y)-codoped sample (15 times of that over the pure TiO{sub 2}). With the increase of Y doping level, the photocatalytic performance in the codoped samples increases firstly and then decreases. The photocatalytic activity variations after the F and Y doping were interpreted by the formation of photocatalytic reactive oxygen species induced by the dopings.

36 MATERIALS SCIENCE↗