Presence Of NH4F Research Articles

Surface modification of hemimorphite via double-complexation by ammonium fluoride and copper ion to promote sulfidation

The effects of NH4F and Cu2+ ion on hemimorphite corrosion modification were studied. The recovery of hemimorphite in the presence of NH4F was 33.58% higher than that in the absence of NH4F. AFM and SEM-EDS imaging showed that the surface of hemimorphite after treatment in NH4F and Cu2+ solution than when treated with Cu2+ solution. This showed that the F− ions reacted with Si ions on the mineral surface and corroded the mineral surface. NH3 reacted with Cu2+ ions to form Cu(NH3)i2+ (i = 1, 2, 3, 4), which adsorbed onto the mineral surface. XPS analysis revealed that the −O−Si− bonds of the hemimorphite surface were damaged by NH4F, and Cu(NH3)i2+ (i = 1, 2, 3, 4) promoted CuS film formation via catalytic sulfidation to obtain hydrophobic hemimorphite. DFT calculations and ICP analysis showed that the dissociative adsorption of H2O molecule on hemimorphite surface were observed, which hindered the further adsorption of HS on the surface. The strength of the chemical bond between S−Cu−O− hemimorphite was the key to ensuring the stability of the sulfide layer after Cu(NH3)−HS adsorption. The double-complexation of NH4F and Cu2+ ensured the satisfactory sulfidation flotation separation of hemimorphite and quartz.

Modulation of the Band Bending of CdS by Fluorination to Facilitate Photoinduced Electron Transfer for Efficient H2 Evolution over Pt/CdS

The potential barrier (Schottky barrier), embodied in the upward band bending of an n-type semiconductor at the interface of a Pt-loaded semiconductor, often makes it difficult for the interfacial photoinduced electron transfer from the conduction band of the semiconductor to the loaded Pt, giving rise to the recombination probability of the photogenerated charges. In this work, we prepared fluorinated CdS by a facile hydrothermal process in the presence of NH4F. With the assistance of the noble metal Pt, the fluorinated CdS exhibits a superior photocatalytic H2 evolution to pristine CdS. Various characterization results revealed that the incorporation of the fluorine anions into the CdS lattice by fluorination apparently lowers the Fermi level to weaken the upward band bending of CdS at the Pt/CdS interface, favoring the interfacial photoinduced electron transfer from the conduction band of CdS to the loaded Pt for an efficient H2 evolution. This work highlights the role of weakening the potential barrier at the Pt/CdS interface in promoting the interfacial photoinduced electron transfer for efficient H2 evolution.

Enhancement of lipid signals with ammonium fluoride in negative mode Nano-DESI mass spectrometry imaging

Lipids play an important role in biology. Their structural diversity presents challenges for untargeted mass spectrometry imaging (MSI) and analysis techniques. Enhancing the lipid coverage of MSI experiments is an important step to understanding their role in biological processes. Herein, we use nanospray desorption electrospray ionization mass spectrometry imaging (nano-DESI MSI) to explore the effect of ammonium fluoride (NH4F) as a solvent additive for enhanced detection of lipids in biological tissues. Although fatty acids and phospholipids are readily observed in nano-DESI MSI, other lipid classes are difficult to detect due to their low abundance and low ionization efficiency. We have evaluated enhancement factors of lipids in negative ionization mode in the presence of NH4F in the nano-DESI solvent. We observed a 10–110-fold enhancement in lipid signals detected as [M − H]- ions using 500 μM NH4F in 9:1 methanol:water in comparison with 9:1 methanol:water, which is typically used in nano-DESI MSI experiments. The observed signal enhancement is attributed to the efficient proton abstraction from lipids by F−. The enhancement factors observed for fatty acids are correlated to their interfacial pKa values. The optimized solvent composition enables sensitive imaging of both high- and low-abundance lipids without any adverse effect on the noise level. Overall, our results demonstrate a substantial improvement in sensitivity of nano-DESI MSI of lipids in biological tissues when NH4F is added to the nano-DESI solvent.

From Cellulose, Shrimp and Crab Shells to Energy Storage EDLC Cells: The Study of Structural and Electrochemical Properties of Proton Conducting Chitosan-Based Biopolymer Blend Electrolytes.

In this study, solid polymer blend electrolytes (SPBEs) based on chitosan (CS) and methylcellulose (MC) incorporated with different concentrations of ammonium fluoride (NH4F) salt were synthesized using a solution cast technique. Both Fourier transformation infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results confirmed a strong interaction and dispersion of the amorphous region within the CS:MC system in the presence of NH4F. To gain better insights into the electrical properties of the samples, the results of electrochemical impedance spectroscopy (EIS) were analyzed by electrical equivalent circuit (EEC) modeling. The highest conductivity of 2.96 × 10−3 S cm−1 was recorded for the sample incorporated with 40 wt.% of NH4F. Through transference number measurement (TNM) analysis, the fraction of ions was specified. The electrochemical stability of the electrolyte sample was found to be up to 2.3 V via the linear sweep voltammetry (LSV) study. The value of specific capacitance was determined to be around 58.3 F/g. The stability test showed that the electrical double layer capacitor (EDLC) system can be recharged and discharged for up to 100 cycles with an average specific capacitance of 64.1 F/g. The synthesized EDLC cell was found to exhibit high efficiency (90%). In the 1st cycle, the values of internal resistance, energy density and power density of the EDLC cell were determined to be 65 Ω, 9.3 Wh/kg and 1282 W/kg, respectively.

Hollow Square RodLike Microtubes Composed of Anatase Nanocuboids with Coexposed {100}, {010}, and {001} Facets for Improved Photocatalytic Performance.

In this study, hollow square rodlike microtubes composed of anatase nanocuboids with coexposed {100}, {010}, and {001} facets were successfully synthesized via a mild hydrothermal treatment method in the presence of NH4F by using layered H2Ti3O7 ribbons as the precursor. The precursor H2Ti3O7 ribbons were prepared from H+/Na+ ion-exchanged Na2Ti3O7. The suspension solution of protonated H2Ti3O7 ribbons was adjusted to desired pH values (0.5–13.0) prior to hydrothermal treatment. The elongated direction of the microtubes is along the b axis, according to the profile of the H2Ti3O7 ribbons. The transformation from staggered [Ti3O7]2– sheets to hollow square rodlike microtubes contained the formation and recombination of the dispersed octahedral [Ti(OH)2(OH2)4]2+ monomers, the formation and growth of the initial anatase nuclei, and the reassembly of the anatase nanocuboids along the b-axis direction during the continuous hydrothermal process. The degradation rate of pH 0.5-TiO2 was the highest at 1.66 × 10–2 min–1, which was 1.3, 1.5, 2.0, 2.3, and 18.4 folds higher than that of pH 3.0-TiO2 (1.27 × 10–2 min–1), pH 7.0-TiO2 (1.11 × 10–2 min–1), pH 5.0-TiO2 (0.83 × 10–2 min–1), P25–TiO2 (0.73 × 10–2 min–1), and the blank sample (0.09 × 10–2 min–1), respectively. Compared with P25–TiO2 and the other anatase TiO2 samples, pH 0.5-TiO2 exhibited the best photocatalytic activity, which was mainly attributed to its larger proportion of {010} (or {100}) facets, smaller crystalline size, higher band gap, and larger specific surface area.

Highly safe and ionothermal synthesis of Ti3C2 MXene with expanded interlayer spacing for enhanced lithium storage

Abstract MXene is a rising star of two-dimensional (2D) materials for energy relative applications, however, the traditional synthesis of MXene etched by hazard HF acid or LiF+HCl mixed solution is highly dangerous with the risk of splashing or pouring liquid solutions. In this work, we developed a water-free ionothermal synthesis of 2D Ti3C2 MXene via etching pristine Ti3AlC2 MAX in low-cost choline chloride and oxalic acid based deep eutectic solvents (DES) with the presence of NH4F, thus it was highly safe and convenient to operate solid precursor and product materials at room temperature. Benefited from the low vapor pressure and solvating properties of DES, the prepared Ti3C2 (denoted as DES-Ti3C2) possessed a high purity up to 98% compared with 95% for HF etched Ti3C2 (denoted as HF-Ti3C2). Notably, an expanded interlayer spacing of 1.35 nm could be achieved due to the intercalation of choline cations in DES-Ti3C2, larger than that of HF-Ti3C2 (0.98 nm). As a result, the DES-Ti3C2 anodes exhibited enhanced lithium storage performance, such as high reversible capacity of 208 mAh g−1 at 0.5 A g−1, and long cycle life over 400 times, outperforming most reported pure MXene anodes. The ionothermal synthesis of MXene developed here may pave a new way to safely prepare other MXene for various energy relating applications.

Bone marrow stromal cells interaction with titanium; Effects of composition and surface modification.

Inflammation and implant loosening are major concerns when using titanium implants for hard tissue engineering applications. Surface modification is one of the promising tools to enhance tissue-material integration in metallic implants. Here, we used anodization technique to modify the surface of commercially pure titanium (CP-Ti) and titanium alloy (Ti-6Al-4V) samples. Our results show that electrolyte composition, anodization time and voltage dictated the formation of well-organized nanotubes. Although electrolyte containing HF in water resulted in nanotube formation on Ti, the presence of NH4F and ethylene glycol was necessary for successful nanotube formation on Ti-6Al-4V. Upon examination of the interaction of bone marrow stromal cells (BMSCs) with the modified samples, we found that Ti-6Al-4V without nanotubes induced cell proliferation and cluster of differentiation 40 ligand (CD40L) expression which facilitates B-cell activation to promote early bone healing. However, the expression of glioma associated protein 2 (GLI2), which regulates CD40L, was reduced in Ti-6Al-4V and the presence of nanotubes further reduced its expression. The inflammatory cytokine interleukin-6 (IL-6) expression was reduced by nanotube presence on Ti. These results suggest that Ti-6Al-4V with nanotubes may be suitable implants because they have no effect on BMSC growth and inflammation.

Generalized ionothermal synthesis of silica-based zeolites

Abstract Ionothermal synthesis has been widely used for the preparation of aluminophosphate-based molecular sieves, coordination polymers, metal-organic frameworks, and covalent organic frameworks. However, this method is still challenging for synthesis of silica-based zeolites. Herein, we show a generalized ionothermal route to synthesize silica-based zeolites with MTT, TON, ITW, and MFI structures in the presence of NH4F as a mineralizing agent and ionic liquid as a solvent and/or structure directing agent. The presence of a suitable amount of NH4F plays a key role for the successful synthesis of these silica-based zeolites. This methodology might open a pathway to ionthermally synthesize silica-based zeolites.

Solvent-Free Secondary Growth of Highly b-Oriented MFI Zeolite Films from Anhydrous Synthetic Powder.

Up to date, zeolite films have been mainly fabricated by in situ crystallization, secondary growth in a solution/hydrogel, or occasionally by vapor phase transformation of dry gel. Here we demonstrate for the first time a solvent-free secondary growth method for b-oriented silica MFI zeolite films using the synthetic powder from ground anhydrous raw solids in the presence of NH4F. Typically, precisely b-oriented MFI zeolite films are synthesized from seed layers of highly b-oriented MFI zeolite crystals in the synthetic powder of 1SiO2:0.035TPABr:0.05NH4F at 175 °C for 6 h. If needed, b-oriented MFI zeolite multilayer films can be acquired by changing the synthesis time or the amount of NH4F in the synthetic powder. Compared with the traditional hydrothermal synthesis, the approach developed here may provide a new avenue for fabricating high quality zeolite films/membranes.

Ni-Ti Layered Double Hydroxide@Graphitic Carbon Nitride Nanosheet: A Novel Nanocomposite with High and Ultrafast Sonophotocatalytic Performance for Degradation of Antibiotics.

Pollution of water resources by antibiotics is a growing environmental concern. In this work, nanocomposites of g-C3N4@Ni-Ti layered double hydroxides (g-C3N4@Ni-Ti LDH NCs) with high surface areas were synthesized through an optimized hydrothermal method, in the presence of NH4F. Application of various characterization techniques unraveled that the prepared nanocomposites are composed of porous Ni-Ti LDH nanoparticles and hierarchical g-C3N4 nanosheets. Further, these NCs were employed for photocatalytic and sonophotocatalytic removal of amoxicillin (AMX), as a model antibiotic, from aqueous solutions. In addition, sonocatalysis was performed. It was found out that the g-C3N4@Ni-Ti LDH NCs outperform their pure g-C3N4 and Ni-Ti LDH components in photocatalytic degradation of AMX under visible light irradiation. Also, the following order was determined for efficiency of the three adopted processes: sonocatalysis < photocatalysis < sonophotocatalysis. Furthermore, variation of the sonophotocatalysis conditions specified 500 W light intensity, 9 s on/1 s off ultrasound pulse modem and 1.25 g/L g-C3N4-20@Ni-Ti LDH as the optimal conditions. In this way, optimization of the highly efficient sonophotocatalytic process resulted in 99.5% AMX degradation within 75 min. Moreover, a TOC analyzer was employed to estimate the rate of AMX degradation over the nanocomposites. In addition, formation of hydroxyl radicals (•OH) on the surface of the g-C3N4-20@Ni-Ti LDH particles was approved using the terephthalic acid probe in photoluminescence (PL) spectroscopy. No significant loss was observed in the sonophotocatalytic activity of the nanocomposites even after five consecutive runs. Also, a plausible mechanism was proposed for the sonophotocatalysis reaction. In general, our findings can be considered as a starting point for synthesis of other g-C3N4-based NCs and application of the resultant nanocomposites to environmental remediation.

Hydrothermal synthesis of mixed phase blue titanium dioxide from oxalate stabilised sols

Blue coloured titanium dioxide nanoparticles were synthesised by the hydrothermal treatment of oxalic acid stabilised titania sols in the presence of NH4F as a modifying agent. The NH4F concentration determined the phase of titania produced and influenced the shape of the rutile crystallites produced. The blue colour originated from the F-stabilised Ti3+ centres formed under the reaction conditions. Organic residues in the sol decomposed to generate a hydrogen-rich atmosphere. Photocatalytic activity studies revealed the rutile phase titania produced was extremely active for a given surface area when compared to P-25.

Highly enhanced photoelectrocatalytic properties by α-Fe2O3 modified NF-TiO2 pyramids with dominant (101) facets

Visible-light-active Fe2O3/NF-TiO2 film was prepared by depositing α-Fe2O3 nanoparticles onto the surface of pyramid-shaped NF-TiO2 via sequential electro-deposition and electro-anodization processes. NF-TiO2 with dominant (101) facets was obtained via calcining TiO2 nanotubes (TiO2-NTs) in the presence of NH4F. The structural and optical properties were carefully studied by XRD, SEM, HRTEM, XPS and UV-Vis-DRS. Photoelectrochemical measurements, such as linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) plots, were also carried out to investigate the generation, separation and transfer of photogenerated charges. It was found that Fe2O3/NF-TiO2 exhibited the best photoelectrocatalytic (PEC) activity relative to Fe2O3/TiO2-NTs or Fe2O3/N-TiO2. The formation of anatase-rutile heterojunction, wider spectral response, increased photocurrent response and greatly reduced charge transfer resistance, could be positive driving force for the enhanced PEC activity. Simultaneous PEC reduction of Cr(VI) and degradation of phenol were evaluated under visible light using Fe2O3/NF-TiO2 film as photoanode and Ti sheet as cathode. The calculated rate constants for Cr(VI) and phenol were 4.3 and 3.6 times relative to that on Fe2O3/TiO2-NTs, respectively. Good stability was also confirmed in cyclic runs using the optimized photoanode.

Fluoride-assisted synthesis of anatase TiO2 nanocrystals with tunable shape and band gap via a solvothermal approach

A simple solvothermal approach employing oleic acid has been developed to prepare anatase TiO2 nanocrystals with different shapes, which were tuned from nanorods to nano-ellipsoids by increasing the amount of NaF from 0 to 0.5mmol, and the optical band gap decreased from 3.47eV to 3.29eV accordingly. However, when the fluoride was changed to NH4F, the resultant TiO2 nanocrystals possessed an anatase phase but were made up of smaller-sized nanocrystals and nanorods, and the band gap was increased to 3.53eV. The X-ray photoelectron spectroscopy (XPS) results illustrated an increase of fluorine content with an increasing amount of NaF could account for the variation of the shape and optical band gap of TiO2 nanocrystals. Moreover, the absence of fluorine content brought about less change of shape and increase of optical band gap of the product synthesized in the presence of NH4F. This result may offer another way to alter the shape and band gap of metal oxide nanocrystals with the assistance of fluoride.

Hydrothermal Synthesis of Nanocrystalline Titanium Dioxide for Use as a Photoanode of DSSCs

Nanocrystalline TiO2powder was synthesized using microwave-assisted hydrothermal treatment of titanium oxysulfate in the presence of NH4F. X-ray powder diffraction analysis and Raman spectroscopy were used to determine phase composition and particle size of obtained titanium dioxide. The studies using methods of TEM and EDX spectroscopy have shown that synthesized TiO2powder is a promising functional material for fabrication of photoanode of dye-sensitized solar cells (DSSCs).

Hydrophobic Silica Aerogels by Ambient Pressure Drying

Silica aerogels have been prepared through sol-gel process by polymerization of TEOS in the presence of NH4F and NH4OH as catalysts. The solvent present in the gel is replaced by ethanol followed by a non-polar solvent such as n-hexane prior to solvent modification step. Gels are made hydrophobic by treating them with HMDZ to prevent rupture during drying, which has been confirmed by FTIR. Gels are then washed and dried carefully in a PID controlled oven at atmospheric pressure. The ageing duration and solvent exchange combinations are optimized to yield crack-free gels prior to drying. Aerogels are characterized for density, specific surface area, pore volume, pore size, thermal stability and contact angle. Hydrophobic, high surface area (570 m2/g), low density (0.07 g/cm3) silica aerogels are synthesized by using optimized mole ratio of precursors and catalysts. Silica aerogel granules (1-3 mm) as well as monoliths (Ф~35 mm) could be produced through ambient pressure drying of gels.

A Simple, Low-Cost, and Useful Preconcentration Method for Quantification of Soluble, Insoluble, and Total Oxalate in Selected Vegetables Through Spectrophotometry

The amount of dietary oxalate from food may be an important risk factor in the development of idiopathic calcium oxalate nephrolithiasis. The main aim of this research was to develop an accurate and reliable method by cloud point extraction (CPE) combined with spectrophotometry to measure the oxalate contents of selected vegetables. The method is based on ion association of stable anionic complex, which is produced by the reaction of oxalate with Mo(VI), with Toluidine blue (TBH2+), and then by extraction into micelles of octylphenol ethoxylate (Triton X-45) in the presence of NH4F as a salting-out agent at pH 6.0. Using the optimized conditions, the calibration graph was highly linear in the range of 1.2–240 μg L−1. The detection limit of the method (LOD (3σblank/m) was 0.36 μg L−1, and the relative standard deviation (RSD %) as a measure of precision was in the range of 1.1–5.3 % (n = 5 for 5, 25, and 50 μg L−1). The method was successfully applied to the speciative determination of soluble and total oxalate in vegetables after ultrasonic-assisted extraction and dilution at suitable ratios. The amount of insoluble oxalate was calculated from the analytical difference between total oxalate and soluble oxalate contents of samples with and without acidic extraction under ultrasonic power (300 W, 50 Hz) for 15 min at 60 °C. The accuracy of the method was intrinsically controlled and verified by comparing the results obtained with those of an independent kinetic method as well as recoveries of spiked samples.

Catalytic properties of Pd/HY catalysts modified with NH4F for acetylene hydrochlorination

Ammonium fluoride (NH4F) modified HY zeolite catalysts were prepared by ultrasonic-assisted impregnation and their efficient catalytic behavior in acetylene hydrochlorination reaction was investigated (the conversion of acetylene and the selectivity to vinyl chloride were all achieved above 99%). The results indicate that the presence of NH4F in Pd/HY catalysts can partially enhance the surface acidity of catalysts, and weaken the occurrence of carbon deposition and the loss of Pd active component on the catalyst surface, thus improving the catalytic performance of catalysts.

Solvent-free synthesis of zeolites from anhydrous starting raw solids.

Development of sustainable routes for synthesis of zeolites is very important because of wide applications of zeolites at large scale in the fields of catalysis, adsorption, and separation. Here we report a novel and generalized route for synthesis of zeolites in the presence of NH4F from grinding the anhydrous starting solid materials and heating at 140-240 °C. Accordingly, zeolites of MFI, BEA*, EUO, and TON structures have been successfully synthesized. The presence of F(-) drives the crystallization of these zeolites from amorphous phase. Compared with conventional hydrothermal synthesis, the synthesis in this work not only simplifies the synthesis process but also significantly enhances the zeolite yields. These features should be potentially of great importance for industrial production of zeolites at large scale in the future.

Selective wet etching of Si3N4/SiO2 in phosphoric acid with the addition of fluoride and silicic compounds

Various additives were added to H3PO4 in order to achieve a highly selective wet etching of Si3N4 to SiO2. Fluoride compounds such as HF, NH4F, and NH4HF2 were added to the H3PO4 in order to increase the etch rate of the Si3N4. In addition, silicic compounds, including H2SiF6, TEOS, and Si(OH)4, were added to decrease the etch rate of SiO2. The addition of the fluoride compounds into the H3PO4 increased the etch rate of the Si3N4, but the etch selectivity of the Si3N4 to SiO2 decreased due to the greater increase in the etch rate of the SiO2. Both the etch rate and the selectivity showed strong relationships with the amount of fluorine added in H3PO4. The addition of TEOS and Si(OH)4 increased the etch selectivity by reducing the etch rate of the SiO2. In particular, the addition of Si(OH)4 to H3PO4 in the presence of NH4F and NH4HF2 produced an etch selectivity greater than 104.

Synthesis of titanium nitride by anodic polarization of titanium

Possibility of forming titanium nitride by anodic polarization of the surface of titanium in water-containing organic electrolytes in the presence of NH4F at potentials of 2–14 V was demonstrated and substantiated. The method of cyclic voltammetry was used to study electrochemical processes in electrolytes based on ethylene glycol and glycerol. Results obtained in an analysis of the structural, chemical, and physicomechanical properties of the titanium nitride layers obtained in the study are presented.