Fluorine Modification Research Articles

Influence of the Chemical Modification of the Nanodiamond Surface on Electron Paramagnetic Resonance/Electron-Nuclear Double Resonance Spectra of Intrinsic Nitrogen Defects

A high-frequency/high-magnetic field (94 GHz/3.3 T) electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) study of monocrystalline nanodiamonds (ND) is carried out. Influence of the hydrogen and fluorine modification of the ND surface on EPR and ENDOR signals from the superficial and bulk paramagnetic centers is observed. The effect shows that the ND bulk paramagnetic centers could serve as the intrinsic probe of ND surface modification despite deep localization, shielding from the environment and two-layered surface of the diamond nanoparticle.

Fluorinated 2D Lead Iodide Perovskite Ferroelectrics

Hybrid perovskite materials are famous for their great application potential in photovoltaics and optoelectronics. Among them, lead-iodide-based perovskites receive great attention because of their good optical absorption ability and excellent electrical transport properties. Although many believe the ferroelectric photovoltaic effect (FEPV) plays a crucial role for the high conversion efficiency, the ferroelectricity in CH3 NH3 PbI3 is still under debate, and obtaining ferroelectric lead iodide perovskites is still challenging. In order to avoid the randomness and blindness in the conventional method of searching for perovskite ferroelectrics, a design strategy of fluorine modification is developed. As a demonstration, a nonpolar lead iodide perovskite is modified and a new 2D fluorinated layered hybrid perovskite material of (4,4-difluorocyclohexylammonium)2 PbI4 , 1, is obtained, which possesses clear ferroelectricity with controllable spontaneous polarization. The direct bandgap of 2.38 eV with strong photoluminescence also guarantees the direct observation of polarization-induced FEPV. More importantly, the 2D structure and fluorination are also expected to achieve both good stability and charge transport properties. 1 is not only a 2D fluorinated lead iodide perovskite with confirmed ferroelectricity, but also a great platform for studying the effect of ferroelectricity and FEPV in the context of lead halide perovskite solar cells and other optoelectronic applications.

Enhanced Photoelectrochemical Water Oxidation Performance by Fluorine Incorporation in BiVO4 and Mo:BiVO4 Thin Film Photoanodes.

Anion substitution is an emerging strategy to enhance the photoelectrochemical performance of metal oxide photoelectrodes. In the present work, we investigate the effect of fluorine incorporation on the photoelectrochemical water oxidation performance of BiVO4 and Mo:BiVO4 thin film photoanodes. The BiVO4 and Mo:BiVO4 thin film photoanodes were prepared by a straightforward organometallic solution route involving dip coating and subsequent calcination in air. Fluorine modification was realized by applying a soft and low-cost solid-vapor reaction route involving fluorine-containing polymers and an inert gas atmosphere leading to novel F:BiVO4 and F/Mo:BiVO4 thin film photoanodes with substantially increased photoelectrochemical water oxidation properties. Deposition of the cobalt phosphate (CoPi) water oxidation catalyst allowed further enhancement of the photoelectrochemical performance. While Mo doping mainly improves light-harvesting, charge transport, and charge separation efficiencies, F modification was demonstrated to primarily affect the charge transfer efficiency at the semiconductor-electrolyte interface, thereby leading to a photocurrent increase of 40 and 21% upon fluorination of the BiVO4 and Mo:BiVO4 photoanodes, respectively, and an applied bias photon-to-current efficiency increase of 35 and 5%, respectively. We thereby could demonstrate that cation and anion co-doping in BiVO4 as demonstrated for Mo and F allows combining the photoelectrochemically relevant benefits associated with each type of dopant.

Insights into the improved photocatalytic performance of fluorine surface modified mpg-C3N4 at room temperature under aqueous conditions

A novel fluorine surface modified mesoporous carbon nitride (mpg-C3N4) photocatalysts were synthesized by etching SiO2 with NH4HF2. The mechanism of formation and the factors that affect its photocatalytic activity were investigated. Interestingly, the introduction of F atoms improves the performance of surface state and widens the energy band gap of surface-modified mpg-C3N4 due to the higher separation and efficient mobility of the photoinduced carriers. Consequently, the fluorine-modified mpg-C3N4 exhibits higher carrier lifetime (8.64 ns) than mpg-C3N4 (7.14 ns), which improves the photocatalytic efficiency under ultraviolet light. The enhanced photocatalytic activity was evaluated by studying the degradation experiments of Rhodamine B. It is expected that the present fluorine modification at the surface of mpg-C3N4 may provide new insights in basic research and energy conversion.

Robust Above‐Room‐Temperature Ferromagnetism in Few‐Layer Antimonene Triggered by Nonmagnetic Adatoms

Abstract2D ferromagnets have attracted considerable attention due to their strong potential in the post‐Moore Law era. However, intrinsic 2D ferromagnetic materials typically suffer from suppressed Curie temperature due to thermal fluctuation, magnetic order instability in the 2D limit, and others. Herein, a nonmagnetic fluorine modification strategy is proposed to control the ferromagnetism of air‐stable antimonene. It is demonstrated that fluorinated antimonene (F‐antimonene), synthesized via an electrochemical exfoliation and synchronous fluorination method, exhibits robust ferromagnetism with a Curie temperature of up to 717 K (compared with a Curie temperature of 220 K for pristine antimonene) and a saturation magnetization of ≈0.1 emu g−1 (determined by the fluorination degree). First‐principles simulations confirm that the robust long‐range ferromagnetic order in the half‐metallic F‐antimonene is induced by the low‐density sp‐electron‐polarized impurity subbands. The study constitutes a nonmagnetic control of robust above‐room‐temperature ferromagnetism in monoelemental 2D semiconductors and paves a new route toward 2D atomic layer‐based spin devices.

Fluorine modification on titanium dioxide particles: Improving the anti-icing performance through a very hydrophobic surface

In this study, fluorine modification was successfully conducted on titanium dioxide (TiO2) to enhance the anti-icing property through fabricating a very hydrophobic surface. TiO2 was firstly modified with 3-methacryloxypropyl-trimethoxysilane (MPS) to introduce CC bonds. Then, dodecafluoroheptyl methacrylate (DFHMA) monomers were successfully grafted on the TiO2 particles via CC bonds introduced by MPS. Herein, azobisisobutyronitrile (AIBN) was used as initiator to initiate the reaction. The chemical components of the TiO2 particles were investigated by X-ray photoelectron spectroscopy (XPS). XPS analysis of fluorine-modified TiO2 revealed that the fluorine content reached a peak value of 7.3%, while the water contact angle enhanced to a maximum value of 146°. This water contact angle value of 146° was dramatically increased by 131° in comparison with unmodified TiO2, indicating a very hydrophobic surface. The crystallization temperature of a water droplet on the corresponding fluorine-modified TiO2 decreased to −19.4 °C (10.3 °C decrease in comparison with that of a water droplet on unmodified TiO2). Also, the freezing delay time on the fluorine-modified TiO2 is more than 25 min under the testing temperature of −10 °C, exhibiting excellent anti-icing property.

Fluorine Modified TAPO-5: Synthesis and Catalytic Performance in Cyclohexanone Ammoximation

A series of fluorine modified TAPO-5 molecular sieves was synthesized by one-pot method using ammo-nium hexafluorotitanate as titanium and fluorine sources. The XPS and DRS UV-Vis results indicated that the exis-tence of F could promote the formation of tetrahedrally coordinated framework Ti and Al, meanwhile, inhibit the formation of anatase TiO2 in TAPO-5 sieves due to the unique role of F in the sol-gel process of metal ions. Further-more, TG, contact angle test, Py-FTIR and 27Al MAS NMR results revealed that fluorine modification increased the surface hydrophobicity and the Lewis acidity of Ti active sites through forming Al x F y units in the neighborhood. All these factors make these fluorine modified TAPO-5 sieves exhibit good catalytic performance in the ammoximation of cyclohexanone.

Enhanced rate performance and high potential as well as decreased strain of LiNi0.6Co0.2Mn0.2O2 by facile fluorine modification

Fluorine is interesting for improving the electrochemical performance of current electrode materials, but the preparation process faces challenges because of the difficult homogeneous mixing of powders. A facile novel strategy of surface fluorine modification using polytetrafluoroethylene (PTFE) emulsion at low temperature, where the powders are easy to be homogeneously mixed and evenly covered by fluorine polymer, has been proposed to enhance the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 material. Though the initial discharge capacities of LiNi0.6Co0.2Mn0.2O2-yFy (y = 0.02, 0.05, 0.08) are slightly decreased at 0.1C, the capacity retention ratios at higher current densities, higher potential and elevated temperatures are improved compared to that of the pristine one. Among the samples with different fluorine contents, LiNi0.6Co0.2Mn0.2O1.95F0.05 exhibits the best performance, and the average discharge capacity fade rate in one cycle and the residual stress after 50 cycles at 1.0 C, as well as the discharge capacity after 10 cycles at 4.0 C are respectively about 0.03%, 10.3 MPa, 129.5 mAh g−1, while the corresponding values of the pristine samples are around 0.12%, 29.4 MPa, and 99.7 mAh g−1, respectively. After 50 cycles at 1.0 C between 2.8 and 4.7 V, LiNi0.6Co0.2Mn0.2O1.95F0.05 improves the capacity retention ratio and the discharge capacity of the pristine sample from 80.0% to 90.4%, and from 156.7 to 176.3 mAh g−1, respectively. The electrode reaction process and fluorine modification mechanisms have been discussed using various techniques. This method is easily achievable and may be used to modify other powder materials via a simple solid-solution mixing and an in-situ surface modification.

Deciphering the Fluorine Code-The Many Hats Fluorine Wears in a Protein Environment.

Deciphering the fluorine code is how we describe not only the focus of this Account, but also the systematic approach to studying the impact of fluorine's incorporation on the properties of peptides and proteins used by our groups and others. The introduction of fluorine has been shown to impart favorable, but seldom predictable, properties to peptides and proteins, but up until about two decades ago the outcomes of fluorine modification of peptides and proteins were largely left to chance. Driven by the motivation to extend the application of the unique properties of the element fluorine from medicinal and agro chemistry to peptide and protein engineering we have established extensive research programs that enable the systematic investigation of effects that accompany the introduction of fluorine into this class of biopolymers. The introduction of fluorine into amino acids offers a universe of options for modifications with regard to number and position of fluorine substituents in the amino acid side chain. Moreover, it is important to emphasize that the consequences of incorporating the C-F bond into a biopolymer can be attributed to two distinct yet related phenomena: (i) the fluorine substituent can directly engage in intermolecular interactions with its environment and/or (ii) the other functional groups present in the molecule can be influenced by the electron withdrawing nature of this element (intramolecular) and in turn interact differently with their immediate environment (intermolecular). Based on our studies, we have shown that a change in number and/or position of as subtle as one single fluorine substituent has the power to considerably modify key properties of amino acids such as hydrophobicity, polarity, and secondary structure propensity. These properties are crucial factors in peptide and protein engineering, and thus, fluorinated amino acids can be applied to fine-tune properties such as protein folding, proteolytic stability, and protein-protein interactions provided we understand and become able to predict the outcome of a fluorine substitution in this context. With this Account, we attempt to analyze information we gained from our recent projects on how the nature of the fluorine atom and C-F bond influence four key properties of peptides and proteins: peptide folding, protein-protein interactions, ribosomal translation, and protease stability. These results impressively show why the introduction of fluorine creates a new class of amino acids with a repertoire of functionalities that is unique to the world of proteins and in some cases orthogonal to the set of canonical and natural amino acids. Our concluding statements aim to offer a few conserved design principles that have emerged from systematic studies over the last two decades; in this way, we hope to advance the field of peptide and protein engineering based on the judicious introduction of fluorinated building blocks.

Selective conversion of bio-ethanol to propene over nano-HZSM-5 zeolite: Remarkably enhanced catalytic performance by fluorine modification

A series of fluorinated nano-HZSM-5 zeolite catalysts were prepared by impregnating with NH4F solutions of various concentrations and applied to the selective conversion of bio-ethanol to propene at 500°C, atmospheric pressure, and WHSV of 10h−1. The characterizations by XRD, TEM, N2 adsorption, ICP-OES, EDX, 27Al MAS NMR, NH3-TPD, Py-IR, and TG techniques revealed that fluoride treatment had a major effect on the channel structure together with the acidic properties. The newly formed mesopores increased the coke tolerance capacity and reduced the probability of coke formation by facilitating mass transfer, and the weakened acidity suppressed the formation of coke. Hence, fluorine modification with suitable content (20wt%) significantly enhanced the selectivity of propene as well as the catalytic stability. In addition to coke, elimination of aluminum in the zeolite framework was also an important reason for the deactivation of fluorinated nano-HZSM-5 zeolite catalyst.

Optimization of defect distribution in photodegradation of air pollutants via SiO2-shell-enhanced fluorine modification

The distribution of bulk and surface defects significantly affects the separation and injection of photogenerated charge carriers. In this study, we provide a strategy of SiO2-shell-enhanced F modification to optimize the distribution of bulk and surface defects. The effects of SiO2 coating and F modification on the physical structure, the separation behavior of photogenerated charge carriers, and the photocatalytic activity of P25 were studied by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and toluene degradation experiments. Results showed that the removal rate of toluene over SiO2-F-modified P25 was significantly higher than those over P25 and F modified P25. The SiO2-shell-enhanced F modification simultaneously increased the content of surface Ti3+ and reduced the bulk defects, thereby enhancing the separation of charge carriers. Furthermore, F doped at surface exerted a strong catalytic effect on the removal of toluene, whereas F doped in lattice caused the recombination of photogenerated charge carriers. The SiO2 coating and calcination treatment significantly increased the amount of F ions doped at TiO2 surface and inhibited F doping in lattice.

Preparation and failure behavior of fluorine-containing acrylic polyurethane coating

Abstract A kind of fluorine-containing acrylic copolymer was synthesized via a two steps of fluorine modification route. A hydrophobic fluorine-containing acrylic polyurethane coating was prepared with the synthesized fluorine-containing acrylic copolymer and trimer of hexamethylene diisocyanate curing agent. The fluorine-containing acrylic polyurethane coating was employed as the topcoat, while a kind of epoxy coating was used as the primer. The failure behavior of the acrylic polyurethane and epoxy composite coatings in 3.5 wt.% NaCl aqueous solution and 5 wt.% salt spray environments were studied. Chemical structure of the copolymer was confirmed by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance ( 19 F NMR). Glass-transition temperature (Tg) of the copolymer was determined with differential scanning calorimetry (DSC). The surface and cross-section morphologies of the coatings before and after failure test were explored via digital microscopy and field emission scanning electron microscopy (FESEM). The electrochemical impedance spectroscopy (EIS) was employed to analyze the coating corrosion resistance during the failure process. X-ray photoelectron spectroscopy (XPS) was used to provide insights into the chemical compositions of the coating surface. The results showed that the fluorine-containing copolymer and the corresponding coating were prepared as expected. The fluorine-containing acrylic polyurethane and epoxy composite coatings failed much faster in the salt spray environment than that in the NaCl aqueous solution. The different environment resulted in different surface chemical compositions.

Preparation and hydrophobicity failure behavior of two kinds of fluorine-containing acrylic polyurethane coatings

Two kinds of fluorine-containing acrylic copolymers, prepared following an in situ radical polymerization fluorine modification method and a post-polymerization fluorine modification route, respectively, achieved different failure behaviors and hydrophobicities.

Fluorine-Modified Porous Graphene as Membrane for CO2/N2 Separation: Molecular Dynamic and First-Principles Simulations

It is demonstrated that the fluorine-modified porous graphene membrane has excellent selectivity for CO2/N2 separation by using molecular dynamic (MD) simulations. We also investigated in detail the mechanism of the fluorine-modified porous graphene membrane for CO2/N2 separation by using first-principles simulations. We find that the diffusion barriers for CO2 and N2 to pass through the pore-22 (with 22 carbon atoms drilled out) graphene membrane are relatively small, which indicates that the pore-22 has a low selectivity for CO2/N2 separation. After fluorine modification, the diffusion barrier for CO2 to pass through decreases to 0.029 eV, while the diffusion barrier for N2 greatly increases to 0.116 eV. Therefore, N2 gets more difficult, while CO2 gets easier to penetrate through the fluorine-modified pore-22. The fluorine-modified pore-22 porous graphene shows a great enhancement of selectivity for CO2/N2 separation, which is consistent with the MD results. Our studies show that first-principles simul...

Fluorine Modification of the Surface of Diamondoids: A Time-Dependent Density Functional Study

We systematically study the fluorination of nanometer-sized diamond cages, diamondoids, by time-dependent density functional theory. We find that fluorination affects both the highest occupied and lowest unoccupied molecular orbitals. Partial fluorination may decrease the energy of the excited state, and the lowest unoccupied molecular orbital becomes less exposed to the environment around the fluorinated surface. These new features of fluorinated diamondoids could be very useful in several potential applications of fluorescent nanodiamonds such as nitrogen-vacancy center based sensing at nanoscale.

A review of contamination-resistant antireflective sol–gel coatings

Sol–gel derived silica antireflective (AR) coatings have been widely used as the optical components for high peak power laser systems because of their excellent optical properties and high laser-induced damage thresholds. However, the sol–gel derived coatings have a high surface area that is more susceptible to be contaminated by absorption of trace amounts of water vapor and other volatile organic compounds from the environment. In this paper, the major approaches to fabricate contamination resistant sol–gel derived silica AR coatings have been extensively reviewed. Different approaches, including solution-phase and vapor-phase silanization, ammonia–water vapor treatment and fluorine modification have been discussed. The optical properties and laser-induced damage thresholds of modified coatings have also been evaluated. The improved sol–gel AR coatings have been shown to possess superior contamination resistance to work in vacuum systems compare to the traditional sol–gel AR coatings.

Visible light responsive TiO2 modification with nonmetal elements

Developing visible light responsive (VLR) TiO2 photocatalysts is essential and attractive for the consideration of solar energy utilization. A large amount of work have shown TiO2 modified with several nonmetal elements having VLR performance, although according to DFT calculation, Asahi denied the VLR properties of fluorine, carbon, etc. in doping TiO2. Therefore, the origins of VLR activity desire further delicate discussion. In this mini-review, several strategies for VLR TiO2 modification have been introduced, including N doping or B/N codoping, surface modification with sensitizing matter such as carbonaceous or other organic substances, surface alkoxyls modification via a ligand-to-metal charge transfer (LMCT) process, and enhanced dye sensitization by fluorine modification. Besides doping, there are much more approaches to fabricate VLR TiO2 modified with nonmetal elements. However, it is still in demand to explore new methods to obtain more stable and efficient VLR TiO2 for practical application.

Role of sol-gel networking and fluorine doping in the silica Urbach energy

We present the results of the analysis of the ultraviolet (UV) absorption edge of fluorine-modified sol-gel silica. UV transmission data, obtained by means of synchrotron radiation, have been analyzed in the spectral range 7.5–8.5 eV, with a spectral resolution of about 10 meV. Data on silica samples with different F content (from 0 to few 10 − 1 mol%) have been analyzed and compared with literature data on quartz and pure synthetic commercial silica. The analysis allows us to discriminate between the effects of the fluorine addition and those ascribable to structural peculiarities of the sol-gel networking. The estimated Urbach energy E U ( T = 0) ranges between 45 and 55 meV, higher that in crystalline quartz and lower than in commercial synthetic silica. The study of the temperature dependence of E U ( T) shows that the fluorine modification of the silica network causes the lowering of the static disorder and the widening of the energy gap. However, there is also a relevant effect of the production process, since sol-gel silica samples show lower E U values with respect to other types of silica, quite independently of the fluorine content. The analysis of the Raman spectra however shows that the starting amount of fluorine-modified molecular precursor influences the network condensation process, independently of the final fluorine content into the matrix.

Effects of porous carbon additives and induced fluorine on low dielectric constant polyimide synthesized with an e-beam

We report the synthesis of a polyimide matrix with a low dielectric constant for application as an intercalation material between metal interconnections in electronic devices. Porous activated carbon was embedded in the polyimide to reduce the dielectric constant, and a thin film of the complex was obtained using the spin-coating and e-beam irradiation methods. The surface of the thin film was modified with fluorine functional groups to impart water resistance and reduce the dielectric constant further. The water resistance was significantly improved by the modification with hydrophobic fluorine groups. The dielectric constant was effectively decreased by porous activated carbon. The fluorine modification also resulted in a low dielectric constant on the polyimide surface by reducing the polar surface free energy. The dielectric constant of polyimide film decreased from 2.98 to 1.9 by effects of porous activated carbon additive and fluorine surface modification.

Highly Effective F-Modified HZSM-5 Catalysts for the Cracking of Naphtha To Produce Light Olefins

A series of fluorinated HZSM-5 zeolites (F/HZSM-5) were prepared by immersing the zeolites with different concentrations of NH4F solution, and their performances for the catalytic cracking of naphtha to produce light olefins were investigated. The results indicated that F-modified HZSM-5 zeolites are effective catalysts for the cracking of naphtha to light olefins. At the temperature of 600 °C, the yields of propene and ethene were achieved at 36.4 and 20.2%, which were 7.3 and 4.3% higher than those over parent HZSM-5 zeolite, respectively. The physicochemical features of F/HZSM-5 catalysts were characterized by means of X-ray diffraction (XRD), Brunauer−Emmett−Teller (BET), temperature-programmed desorption of ammonia (NH3-TPD), Fourier transform infrared (FTIR) spectra of adsorbed pyridine, etc. The results indicated that fluorine (F) modification not only regulates the pore characteristics of the HZSM-5 zeolites but also modulates the amount of acid sites, especially the amount of Bronsted (B) acid. C...