Fluoride Ion Adsorption Effect and Adsorption Mechanism of Self-Supported Adsorbent Materials Based on Desulfurization Gypsum-Aluminate Cement

The adsorption method has the advantages of low cost,high efficiency,and environmental friendliness in treating fluorinated wastewater,and the adsorbent material is the key.This study combines the inherent anion-exchange adsorption properties of layered double hydroxides(LDHs).Self-supported porous adsorbent materials loaded with AFm and AFt were prepared from a composite cementitious system consisting of calcium aluminate cement(CAC)and flue gas desulfurization gypsum(FGDG)by chemical foaming technique.The mineral composition of the adsorbent material was characterized by X-ray diffraction(XRD)and Scanning electron microscopy(SEM).Through the static adsorption experiment,the adsorption effect of the mineral composition of the adsorbent on fluoride ions was deeply analyzed,and the adsorption mechanism was revealed.XRD and SEM showed that the main hydration phases of the composite cementitious system consisting of CAC and FGDG are AFm,AFt,AH_(3),and CaSO_(4)·2H_(2)O.FGDG accelerates the hydration process of CAC and inhibits the transformation of AFt to AFm.The AFt content increased,and the AFm content decreased or even disappeared as the amount of FGDG increased.Static adsorption experiment results showed that AFm and AFt in adsorbent materials could significantly enhance the adsorption of fluoride ions.The adsorption of F^(−)in aqueous solution by PAG tends more towards monolayer adsorption with a theoretical maximum capacity of 108.70 mg/g and is similar to the measured value of 112.77 mg/g.

Effect of fluoride ions on coordination structure of titanium in molten NaCl–KCl

The effects of fluoride ions(F^(-)) on the electrochemical behavior and coordination properties of titanium ions(Ti^(n+)) were studied in this work,by combining electrochemical and mathematical analysis as well as spectral techniques.The α was taken as a factor to indicate the molar concentration ratio of F^(-) and Ti^(n+).Cyclic voltammetry(CV),square wave voltammetry(SWV),and open circuit potential method(OCP)were used to study the electrochemical behavior of titanium ions under conditions of various α,and in-situ sampler was used to prepare molten salt samples when α equal to 0.0,1.0,2.0,3.0,4.0,5.0,6.0,and 8.0.And then,samples were analyzed by X-ray photoelectron spectroscopy(XPS) and Raman spectroscopy.The results showed that F^(-) in molten salt can reduce the reduction steps of titanium ions and greatly affects the proportion of valence titanium ions which making the high-valence titanium content increased and more stable.Ti^(2+) cannot be detected in the molten salt when α is higher than 3.0 and finally transferred to titanium ions with higher valence state.Investigation revealed that the mechanism behind those phenomenon is the coordination compounds(TiCl_(j) F_(i)^(m-)) forming.

A fluorescent probe for fluoride ion based on 2-aminopyridyl-bridged calix[6]arene

An 2-anfinopyddyl-bddged calix[6]arene on the upper rim fixed in cone conformation （3） was successfully synthesized and its highly selective recognition towards fluoride ion was proved by fluorescent and 1H NMR titration experiments.

Dynamic Corrosion Trail of Ti-6Al-4V Alloy in Acid Artificial Saliva Containing Fluoride Ion

The dynamic corrosion behaviors of Ti-6Al-4V alloy in acid artificial saliva containing fluoride ion were traced using electrochemical techniques,optical microscope,scanning electron microscopy,energy dispersive spectrometer and roughness tester.The experimental results indicate that a negative shift of corrosion potential as well as a continuous decrease in impedance for the alloy exists with increasing immersion time,and the degradation rate of the alloy presents the trend of first increase then decrease following the dissolution of passivation film and the formation of corrosion products.The accumulated fluoride ion on the alloy surface accelerates the fracture of passivation film,and the occurrence and development of corrosion of alloy are mainly located at the sites where the formation and shedding of white particles are composed of fluoride compounds,resulting in the decrease of corrosion resisting property of the alloy.A possible model is proposed to elaborate the dynamic corrosion behavior of the alloy.

Removal Effect of Fluoride Ions by Aluminum Salt in Wastewater

To study a kind of high-efficiency fluoride removal agent based on aluminum salt,through theoretical and experimental research,the influence of different factors(dosage of agent,concentration of fluoride ions,pH,TDS,hardness and alkalinity,etc.)on the removal effect of fluoride ions by fluoride removal agent in industrial wastewater,especially mine water was analyzed.The results show that the fluoride ion removal agent based on aluminum salt could achieve efficient removal of fluoride ions,and the optimal mass ratio of fluoride ion concentration and compound reagent was 1∶130.The concentration of fluoride ions in the water produced after precipitation was≤1 mg/L under the optimal pH condition.As the pH of the solution was 6.5-7.5,the effect of fluoride removal by the agent was the highest.When the pH of the solution was>10.5 or<5,there was no effect of fluoride removal.Under the conditions of optimal pH and reagent dosage,the removal rate of fluoride ions rose with the increase of fluoride ion concentration in wastewater,up to 87.4%.It is also verified that TDS had no obvious effect on fluoride removal,and the smaller the hardness and alkalinity,the better the effect of fluoride removal.

Fluoride ions adsorption from water by CaCO_(3)enhanced Mn-Fe mixed metal oxides

Novel CaCO_(3)-enhanced Mn-Fe mixed metal oxides(CMFC)were successfully prepared for the first time by a simple-green hydrothermal strategy without any surfactant or template combined with calcination process.These oxides were then employed as an adsorbent for adsorptive removal of excess fluoride ions.The adsorbent was characterized by SEM,XPS,XRD,FTIR,and BET analysis techniques.The adsorption property of CMFC toward fluoride ion was analyzed by batch experiments.In fact,CMFC exhibited adsorption capacity of 227.3 mg∙g^(-1)toward fluoride ion.Results showed that ion exchange,electrostatic attraction and chemical adsorption were the main mechanism for the adhesion of large amount of fluoride ion on the CMFC surface,and the high adsorption capacity responded to the low pH of the adsorption system.When the fluoride ion concentration was increased from 20 to 200 mg∙L^(-1),Langmuir model was more in line with experimental results.The change of fluoride ion adsorption with respect to time was accurately described by pseudosecond-order kinetics.After five cycles of use,the adsorbent still maintains a performance of 70.6%of efficiency,compared to the fresh adsorbent.Therefore,this material may act as a potential candidate for adsorbent with broad range of application prospects.

UREA-BASED POLYACETYLENES AS AN OPTICAL SENSOR FOR FLUORIDE IONS

Novel acetylenes carrying urea groups, 1-（4-ethynylphenyl）-3-（4-nitrophenyl） urea （1）, 1-（4-propargyl）-3-（4- nitrophenyl） urea （2）, were synthesized and polymerized with rhodium catalyst. Polymers [poly（1） and poly（2）] with moderate molecular weights were obtained in good yields. The anion sensing ability of poly（1） and poly（2） was estimated using the tetra-n-butylammonium （TBA） salts of a series of anions in DMF. Upon the addition of F, the color of the DMF solution of poly（1） and poly（2） immediately turned to a different color, while the color of solution changed slightly upon addition of C1, HSO4-, Br-, and NO3-, indicating the F- sensing ability of poly（1） and poly（2）. The 1H-NMR titrations of poly（1） revealed that the colorimetric response of poly（1） was triggered by the urea/F interaction through the hydrogen bonding and/or deprotonation process. The absorption spectra titration and Hill plot analysis were carried out to measure the F binding ability, and the Hill coefficient in the poly（1）/F complexation was found to be 5.8. This result clearly indicated that this binding mode between poly（1） and F was based on a positive homotropic allosterism.

Molten salt synthesis of neodynium oxyfluoride in various fluoride media with different fluoride ion activities

Neodymium oxyfluoride has received much attention in the fields of anionic solid electrolytes.luminescent,catalytic and magnetic materials because of its structure combined advantages of rareearth cations with F^(-)and O_(2)^(-)anions.In this work,neodynium oxyfluoride was synthesized by the reaction between neodymium oxide and four fluoride media with different fluoride ion activities.The synthesis processes in molten LiF-CaF_(2)-NdF_(3),LiF-NdF_(3),NaF-CaF_(2)-NdF_(3)and NaF-KF-NdF_(3)are observed in situ by a confocal scanning laser microscope.The expansion of neodymium oxide particle is observed in the LiF-CaF_(2)-NdF_(3),LiF-NdF_(3),and NaF-KF-NdF_(3)melts,and the growth of needle crystals on neodymium oxide particle is clearly observed in molten NaF-CaF_(2)-NdF_(3).Based on scanning electron microscopy(SEM)-energy dispersive X-ray spectroscopy(EDS)and X-ray diffraction(XRD)analyses of products,neodynium oxyfluoride was successfully synthesized in the four fluoride media.The neodynium oxyfluoride generated in the LiF-CaF_(2)-NdF_(3),LiF-NdF_(3),and NaF-KF-NdF_(3)melts is a tetragonal structure.However,in molten NaF-CaF_(2)-NdF_(3),neodynium oxyfluoride with a rhombohedral structure is formed.It is suggested that the substitution of Na(Ⅰ)and Ca(Ⅱ)for Nd(Ⅲ)can transform NdOF from tetragonal structure to rhombohedral structure.The growth rate of needle crystals generated in molten NaF-CaF_(2)-NdF_(3)was calculated based on the result of a confocal scanning laser microscope,and it is found that the reaction kinetics of crystal formation is zero-order reaction.The effect of fluoride media on the structure and morphology of formed NdOF were evaluated by XRD,X-ray photoelectron spectroscopy(XPS)and SEM.The neodymium oxyfluoride prepared in the fluoride media with high fluoride ion activity has low binding energy of F 1 s.The ratio of adsorbed oxygen to lattice oxygen for neodymium oxyfluoride prepared in molten LiF-NdF_(3)is larger than those in the other three fluoride media,so it can have better catalytic performance.

Preparation of CeO_2-TiO_2/SiO_2 and Its Removal Properties for Fluoride Ion

The CeO 2 TiO 2/SiO 2 surface composites were prepared by sol gel method using SiO 2 as substrate and CeO 2 TiO 2 as coating film. The removal capabilities of the composities for fluoride ion and the influences of environment conditions of the preparation on the coating quality and removal capacities of F - were studied by experiments. SEM was used to study the surface morphologies of the films obtained. It is proved that n Ti(OC 4H 9) 4 / n CeCl 3·7H 2O =1, n CH 3COOH / n Ti(OC 4H 9) 4 =4 5, n C 3H 8O 3 / n Ti(OC 4H 9) 4 =0 3, R H=95% and t 110 ℃ are the acceptable conditions to get the surface composite whose adsorbent capacity( q ) and removal ratio( E ) for F - are 21 4 mg/g and 85 6% respectively.

Determination of Fluoride in Various Samples Using a Fluoride Selective Electrode

Fluoride is widespread in the environment, water, air, vegetation and Earth’s crust which can entre ground and surface water by natural process. Fluoride in minute quantities is essential component for human health and help in normal mineralization of bone and formation of dental enamel. The determination of fluoride in some species was performed by using fluoride ion-selective electrode by direct measurement and standard addition method. The concentration of fluoride ion was determined in drinking water (from different place at Kathmandu), toothpaste, various brand of tea and coffees. The range of fluoride concentration in water sample was 0.16 to 0.39 mg/l, tea and coffee samples were 0.011 to 0.084 mg/l and its value of toothpaste was 0.026 to 0.75 mg/l. The concentration of fluoride ion obtain from different sample was compared with the legitimate value given by the world health organization.

REPLACED SITE OF Eu^(2+) ION IN THE COMPLEX FLUORIDES WITH THE PEROVSKITE CRYSTAL STRUCTURE

The replaced site of Eu^(2+) ion is dependent on the electronegativity difference of the cations in complex fluorides.In the mixed fluoride KMgF_3:Eu^(2+),Eu^(2+) ion occupies K^+ site,its emission spectrum is a sharp line and its valence-state is stable.

Two monofluoride-bridged Dy~Ⅲdimers with different magnetization dynamics

As a monoatomic bridge,fluoride ion can transmit efficient magnetic interaction between lanthanide ions but its effect on tuning the magnetization dynamics has not been well understood.Herein,two monofluoride-bridged dinuclear dysprosium complexes[Dy_(2)F(bbpen)_(2)(Et OH)_(2)]Br·Et OH(1)and[Dy_(2)F(bbppy)_(2)]Br·2Et OH(2)with Dy-F-Dy angles of~178°and their diamagnetic-ion diluted analogues 1'and 2'were synthesized.Magnetic studies reveal that 1 and 1'barely show any magnetization dynamics,but 2 and 2'exhibit strong magnetization dynamics.Systematical experimental analysis combined with ab initio calculations reveals that the different magnetization dynamics between 1 and 2 mainly originate from the effect of magnetic anisotropy by terminal ligand and bridging group of the chelating ligand,and the fluoride bridge can effectively suppress the quantum tunneling of the magnetization and turn on Orbach process in 2.

Performance and mechanism of La-Fe metal-organic framework as a highly efficient adsorbent for fluoride removal from mine water

Water fluoride pollution has caused non-negligible harm to the environment and humans,and thus it is crucial to find a suitable treatment technology.In this study,La-Fe@PTA adsorbent was synthesized for the defluoridation of mine water.The results showed that the optimum conditions for defluoridation by La-Fe@PTA were p H close to 7.0,the initial F-concentration of 10 mg/L,the dosage of 0.5 g/L and the adsorption time of 240 min.Compared with SO_4^(2-),Cl^(-),NO_(3)^(-),Ca^(2+)and Mg^(2+),CO_(3)^(2-)and HCO_(3)^(-)presented severer inhibition on fluoride uptake by La-Fe@PTA.The adsorption process fits well with the pseudo-second-order kinetic model and Freundlich model,and the maximum adsorption capacity of Langmuir model was 95 mg/g.Fixed-bed adsorption results indicated that fluoride in practical fluorinated mine water could be effectively removed from 3.6 mg/L to less than 1.5 mg/L within130 bed volume(BV)by using 1.5 g La-Fe@PTA.Furthermore,the adsorbent still had good adsorption capacity after regeneration,which confirms the great application potential of La-Fe@PTA as a fluoride ion adsorbent.The mechanism analysis showed that La-Fe@PTA adsorption of fluorine ions is a physicochemical reaction driven by electrostatic attraction and ion exchange.

Highly Selective Fluoride Recognition by a Simple Carbazole-based Hydrozone Derivative

A simple carbazole hydrozone derivative（l） was synthesized and used as an optical probe for fluoride recognition in CH3CN. Receptor I exhibited colorimetric and fluorescent dual-channel response to fluoride anions. Addition of fluoride to a receptor 1 solution in CH3CN induced a distinct color change from yellow to magenta, the solution also displayed significant fluorescence blue shift. Thus receptor 1 exhibited dual-channel responses to fluo- ride with a hi~.h selectivitv and senitivltv

Novel reusable sulfate-type zirconium alginate ion-exchanger for fluoride removal

It is still a challenge to eliminate efficiently fluoride ion from groundwater,especially to design and synthesis an adsorbent possessing high adsorption capacity,recyclability and wide pH application conditions.Herein we present millimeter-sized sulfate-type zirconium alginate hydrogel beads with 3D network structure(AHB@Zr-SO^(2−)_(4))that exhibited a maximum adsorption capacity of 101.3 mg/g with wide pH applicability(pH 3−9).This material have~2.5 times higher adsorption capacity than that of pure zirconium alginate hydrogel beads(AHB@Zr)and it was ascribed to ion exchange between SO^(2−)_(4)and F−on the surface of AHB@Zr-SO^(2−)_(4),which was verified via ion chromatography measurement coupled with X-ray photoelectron spectroscopy(XPS)and Fourier Transform Infrared Spectrometer(FTIR Spectrometer)analysis.Density functional theory(DFT)calculations indicated that the ion exchange process between SO^(2−)_(4)and F−in AHB@Zr-SO^(2−)_(4)was energetically favorable than OH^(−)and F^(−)in AHB@Zr.In addition,310 bed volumes(BV)of effluent was realized via column adsorption of groundwater containing fluoride on AHB@Zr-SO^(2−)_(4)and indicated that it is a promising candidate for mitigating the problem of fluoride-containing groundwater.

Chromogenic and fluorescent ‘‘turn-on'' chemodosimeter for fluoride based on F~–-sensitive self-immolative linker

A new chromogenic and fluorescent ＂turn-on＂ chemodosimeter 3 was designed and synthesized by using a fluoride-sensitive self-immolative linker, in combination with the fluorescent dyes 7-hydroxy-4-trifluoromethyl coumarin. The chemodosimeter exhibited high selectivity and sensitivity toward fluoride anions through ＂turn-on＂ chromogenic and fluorogenic dual modes.

Recent progress on upconversion luminescence enhancement in rare-earth doped transparent glass-ceramics

The upconversion（UC） of the rare earth doped glass-ceramics has been extensively investigated due to their potential applications in many fields, such as color display, high density memories, optical data storage, sensor and energy solar cell, etc. Many series of them, especially the oxyfluorides glasses containing Ba2 LaF 7 nanocrystals were studied in this review work, due to the thermal and mechanical toughness, high optical transmittance from the ultraviolet to the infrared regions, and a low nonlinear refractive index compared to the other commercial laser glasses. Moreover, the energy transfer（ET） between the rare earth ions and transition metals plays an important role in the upconversion process. The cooperative ET has been researched very activly in UC glasses due to applications in the fields of solar cells, such as in the Er/Yb, Tm/Yb, Tb/Yb, Tb/Er/Yb and Tm/Er/Yb couples. The present article reviews on the recent progress made on：（i） upconversion materials with fluoride microcrystals in glasses and the mechanisms involved, including the UC in double and tri-dopant RE ions activated fluoride microcrystal, energy transfer process; and（ii） the effect of the metal Mn and nanoparticles of Au, Ag, Cu on the enhancement of UC emissions. Discussions have also been made on materials, material synthesis, the structural and emission properties of glass-ceramics. Additionally, the conversion efficiency is still a challenge for the spectra conversion materials and application; challenge and future advances have also been demonstrated.

β-Cyclodextrin-modified AuBi metallic aerogels enable efficient peroxidase mimicking for colorimetric sensing of urease-positive pathogenic bacteria

The detection of pathogenic bacteria with improved accessibility,reduced analysis time,and increased sensitivity is of great importance for diagnosing the infected disease.Nanozymes have attracted rising attention in the bioassay field.Designing a model nanozyme needs the combined merit of sensible nanostructures and a large specific surface area to guarantee exceptional enzyme-mimic activity.Herein,aβ-cyclodextrin modified AuBi aerogel is prepared by a one-pot reduction strategy.The introduction ofβ-cyclodextrin(featured with a hydrophobic cavity and hydrophilic surface)enhances the catalytic activity of AuBi aerogels by engendering host-guest complex and improving dispersity/stability.Based on the specific urea hydrolysis,which could produce NH_(3)to raise pH by urease,the pH up-regulation would inhibit the peroxidase-mimicking performances ofβ-cyclodextrin/AuBi aerogels.Therefore,the sensitive colorimetric detection platform for urease activity could be constructed.Moreover,the sensing platform can detect straightforwardly urease-positive Proteus mirabilis in urine circumstances with a wide detection range and a low limit of detection(LOD)of 4 colony-forming unit(CFU)·mL^(-1).The reproducibility,stability,and specificity of this approach are verified to be satisfactory.Also,as an inhibitor of urease activity,the fluoride ion could be detected by the constructed sensing platform sensitively and specifically.Overall,this work provides a blueprint for designing an ideal nanozyme and paves a new roadway for detecting pathogenic bacteria.

Electrochemical behavior of open-cellular structured Ti-6Al-4V alloy fabricated by electron beam melting in simulated physiological fluid:the significance of pore characteristics

The cellular structured titanium alloys have attracted significant attention for implants because of their lower Young’s modulus,which is comparable to human bone and has the capability of providing space for bone tissue in-growth.However,there is a gap in the knowledge in regard to the relationship between the pore characteristics and the electrochemical performance of open-cellular structured titanium alloys.In this study,we elucidate the influence of pore characteristics on the electrochemical performance of open-cellular structured Ti-6Al-4V alloys produced by electron beam melting(EBM).Intriguingly,the passive film formed on cellular structured Ti-6Al-4V alloy with a larger pore size was more stable and protective,and the corrosion performance was superior compared to the samples with a smaller pore size in phosphate buffered saline(PBS),mainly because of relatively smaller exposed surface area and unlimited flow of electrolyte.However,in acidic PBS containing fluoride ions,the pore characteristics did not play an important role in the corrosion resistance.It was considered that the protective film breaks down such that the corrosion performance of cellular structured alloys was comparable to each other in this harsh environment.