Elimination Of Fluoride Research Articles

SNAr hexafluoroisopropoxylation of electron-rich aryl fluoride with a catalytic electrical input

Abstract Anodic oxidation–promoted SNAr reactions of electron-rich aryl fluoride were developed. The anodic oxidation of 4-fluoroanisole in hexafluoroisopropyl alcohol (HFIP) with K2CO3 led to SNAr-type hexafluoroisopropoxylation, and the reaction was completed with a catalytic electrical input. The results of cyclic voltammetry suggest that the radical cation of 4-fluoroanisole, which would react with the alkoxide of HFIP, is generated. Electron transfer between the intermediate and the starting material constructs the catalytic cycle, and the elimination of fluoride from the Meisenheimer complex produces the desired compound.

IMPACT: Innovative (nano)Materials and processes for advanced catalytic technologies to degrade PFOA in water

We hereby report the development of a novel electrochemical method to degrade perfluorooctanoic acid (C7F15COOH, PFOA). At the center of the approach are bimetallic Pd–Ru nano-catalyst materials called IMPACT: Innovative (nano)Materials and Processes for Advanced Catalytic Technologies. IMPACT uses flavonoid-sequestered Pd–Ru, allowing the development of specialized electrodes with tunable properties to sequentially degrade PFOA in wastewater samples into a sustainable byproduct via an indirect electrochemical method. Electron transfers at RuOxHy species stabilize the Pd component of the nano-catalysts, enabling the degradation process via PFOA deprotonation, chain shortening, decarboxylation, hydrolysis, fluoride elimination, and CF2 flake-off mechanism. IMPACT enabled the observation of redox peaks at −0.26 V and 0.56 V for the first time, with accompanying reduction peaks at −0.5V and 0.29 V, respectively. These redox peaks, which correlated with the concentrations of PFOA (20, 50, 100, 200, and 400.mg L−1), were verified and confirmed using electrochemical simulations. Control experiments did not show degradation of PFOA in the absence of Pd–Ru nano-catalyst. The degradation in wastewater was obtained within 3 h with an efficiency of 98.5%. The electrochemical degradation products of PFOA were identified using High-resolution desalting paper spray mass spectrometry (DPS-MS) and collision-induced dissociation (CID) analysis. The results yielded C2F5COOH, C3F7COOH, and C6F13OH with dissociation losses of CF2O or CO2. IMPACT introduces a novel nano-catalyst with high efficiency and a reliable capability that defluorinates strong C–F bonds that are components of recalcitrant organics in myriad environmental matrices.

Electrochemical elegance: A review on capacitive deionization for fluoride and arsenic mitigation in brackish water

Selective ion extraction from aqueous solutions is crucial for both water purification and resource recovery. This review presents an innovative approach to address the selective removal of fluoride and arsenic in brackish water. In this venture, we explore the elimination of fluoride and arsenic through the integration of tailored electrode materials and electrochemical methods in conjunction with CDI technology. We also describe the future potential of selective CDI, covering aspects such as performance evaluation, objectives, application range, and challenges. This information aims to guide future researchers in addressing knowledge gaps in the development and application of selective CDI systems. The findings of this study set the stage for further exploration and practical implementation of CDI as a robust water purification technique for brackish water sources.

Total synthesis of Comfreyn A and structural analogues via two photochemical key steps.

In this work the influence of o-fluorine substituents on the photo-dehydro-Diels-Alder (PDDA) reaction was investigated and the findings of this study were applied to the total synthesis of natural products. The reactant molecules consisted of two alkyl arylpropiolates, connected by a suberic acid tether and bearing fluorine substituents in each of the o-positions. While quantum chemical calculations suggested that a fluorine substituent prevents an attack of the adjacent carbon atom in the second C-C bond forming step of the PDDA reaction, this attack took place nevertheless. The subsequent fluoride elimination, assisted by protic solvents or trialkylsilanes, resulted in an "Umpolung" of the 4-position of the cycloallene intermediate enabling the introduction of nucleophiles at this position. The nucleophilic replacement of the second fluorine substituent could also be triggered photochemically. After removal of the tether, the two arene moieties stand nearly perpendicular to each other and a selective excitation of the naphthalene moiety was possible. This led to an intramolecular photoinduced electron transfer (PET) followed by a nucleophilic replacement of the fluoride according to a SR+N1Ar* mechanism. The formed phenolic hydroxyl group underwent spontaneous lactonization with the adjacent ester group. Based on these results, the first total synthesis of the lignan Comfreyn A and some structural analogues were developed.

TECHNOLOGICAL ADVANCEMENT IN REMOVING HEAVY METALS FROM INDUSTRIAL WASTE WATER

Fluorides are important contaminants found in effluents from a variety of industries, including electroplating and glass. These are extremely harmful to living things and have a negative impact on their health. Thus, removing fluoride with biosorbents is an important step toward environmental conservation. The untreated discharge of industrial waste water into the environment has long had an impact on human, plant, and animal health. These effluents contain harmful compounds that are not degradable through chemical or microbiological processes. However, they are most likely to accumulate in soil, aquatic environments, and plant organs. The present work investigated the elimination of fluoride utilizing an aquatic plant species, Eichhornia Crassipes (Water Hyacinth) by the method of phytoremediation.

Adsorption isotherms and kinetic studies for the defluoridation from aqueous solution using eco-friendly natural adsorbent like Terminalia Chebula

A practical technique for removing fluoride from aqueous solutions by adsorption was created using the natural adsorbent known as Terminalia Chebula with a primary emphasis on adsorption isotherms and kinetic studies. The experimental results showed the best conditions for removing fluorine ions as follows: the dosage of the natural adsorbent: 50 mg/L, contact reaction time: 40 min, shaking speed = 120 rpm, temperature = 32 °C. The amount of removal of fluorine ions was found to be >98 % fluoride within a shorter time and reached adsorption equilibrium within 40 min with a maximum defluoridation capacity of 20.92 mg/g. At lower solution pH (3 to 5), there is higher fluoride adsorption on the adsorbent surface and as the pH becomes alkaline (pH > 7) the adsorption capacity decreased. The two co-ions namely NO3− and Cl− removed the fluoride 79 % whereas, the phosphate ions did not have any marked effect on the defluoridation. The pseudo-second-order kinetic order such Langmuir, Empirical Freundlich, Temkin and Dubinin–Radushkevich isotherms can well predict the adsorption equilibrium rate to be at 0.044 mg/L with contact time (t) of 30 min. In addition to that the adsorption is characterized by SEM, X-ray diffraction and FTIR techniques. This study has ultimately found that the Terminalia Chebula is a workable, natural material for fluoride elimination.

Electrodialysis for fluoride and nitrate removal from synthesized photovoltaic industry wastewater-toward high performance experimental parameters

This study focuses on the use of electrodialysis (ED) process as a mean to treat contaminated ultra-pure water (UPW) from the photovoltaic (PV) industry, for the elimination of two major ions pollutants that are fluoride and nitrate ions. Synthetic solutions, simulating contaminated UPW from the PV cells rinsing step, were used. Both ions were eliminated significantly after 15 min of treatment time with an initial concentration of 140 mgL−1, and 33 min with an initial concentration of 1000 mgL−1 for fluoride and nitrates ions, respectively. The study of the competition between these two ions in their eliminations showed that the presence of fluorides does not disturb the elimination of nitrates (no competition), while the presence of nitrates in the solution strongly affects the elimination of fluorides by delaying the treatment time from 15 to 53 min. In addition, the concentrations of pollutants in the treated solutions are lower than the standards recommended by the World Health Organization (WHO); consequently, the treated UPW can be reused in the process to achieve near Zero Liquid Discharge (ZLD). From a techno-economic standpoint, the ED technique under these experimental conditions could reduce the production price of photovoltaic cells. In effect; the total investment can be amortized in a few years, making this water treatment a viable alternative since UPW is expensive and its consumption is very important in this industry.

An Evaluation of Carbon Nanotube-based and Activated Carbon-based Nanocomposites for Fluoride and Other Pollutant Removal from Water: A Review

Abstract: Water is the most critical component of the earth's ecosystem because it is fundamental to the survival of plants and animals. However, our water supply is continuously polluting. Removing contaminants from water is a crucial part of addressing water scarcity and maintaining a healthy ecosystem for all. This review focuses on adsorption and the CNTs/AC family nano adsorbents and their contribution to the removal of fluoride and other contaminants. Many types of wastewater treatment methods have been employed, including precipitation, ion-exchange, adsorption, membrane filtration, etc. A water technology with great efficiency and low cost, without requiring costly infrastructure, is the most preferred option due to adsorption. Recently, the application of carbon family nanomaterials as adsorbents has been prevalent due to their phenomenal surface properties, simple customization, immense specific surface area, numerous variations in structural type, chemical stability, porosity, low density, ease of regeneration, and the ability to be reused. Hazardous contaminants, such as fluoride, generate major public health risks. Water contamination by heavy metals provides a significant health concern, including an increased chance of getting diseases like cancer, anaemia, carcinogenic effects, and acute effects in children. The increased presence of fluoride in water could cause fluorosis, joint pain, severe anaemia, and other problems. The following review focuses on current findings regarding the utilisation of CNTs and AC nanoparticles in the elimination of harmful contaminants and fluoride.

Divergent Synthesis of Fluoroalkyl Ketones through Controlling the Reactivity of Organoboronate Complexes.

Herein, we report a divergent synthesis of fluoroalkyl ketones through visible-light-induced reactions between readily available organoboronic esters and fluoroalkyl acylsilanes. Selective control of the reactivity of the in situ generated organoboronate complexes is the key to achieving divergent transformations. Under basic conditions, the organoboronate complexes undergo deboronative fluoride elimination, resulting in the formation of enol silyl ethers as intermediates that react with various electrophiles to generate defluorinated ketones as the products. Moreover, in combination with peroxide, a 1,2-shift of fluoroalkyl group is favored over deboronative fluoride elimination to generate ketal intermediates, leading to the formation of ketones as the products. This transition-metal-free reaction is operationally simple, and aryl, alkenyl, and alkyl boronic esters are all suitable substrates. The synthetic potential has been demonstrated by gram-scale reactions and facile synthesis of bioactive molecules including zifrosilone and its fluoroalkyl analogs.

Novel carbohydrate derived nanocomposite materials for efficient arsenic and fluoride elimination

A bottom-up methodology synthesizes the carbohydrate-derived graphene oxide (CGO). Further, the CGO, triiron tetraoxide (TTO) and bentonite (B) synthesizes the carbohydrate- novel composite material (CGO/TTO/B@1:2). The BET surface area of 428.551, 238.645 and 195.814 m2/g, respectively, obtained for the CGO, CGO/TTO and CGO/TTO/B@1:2. The composite material are promising in eliminating of As(III), As(V), and F− under various parametric conditions. The CGO/TTO shows the apparent sorption capacities of 26.59 and 35.97 mg/g for As(III) and As(V), respectively, while the CGO/TTO/B@1:2 exhibits the removal capacity of 17.81 mg/g for F−. Applying an extended Sips equation further elucidated the sorption capacities of 31.88 and 6.57 mg/g for As(V) and F−, respectively, during their simultaneous removal using CGO/TTO. Furthermore, the nanocomposite demonstrated fair stability and exceptional performance in dynamic experiments, including regeneration, repeated operations, natural water, and column studies. The CGO/TTO-Beads show loading capacities of 1.55x102 and 1.15x102 mg/g for As(III) and As(V) removal under the fixed-bed column studies. In contrast, CGO/TTO/B@1:2-Beads shows 1.54 mg/g loading capacity for F− removal.

Preparation of hydroxyapatite and its elimination of excess fluoride from aqueous solution.

Excess fluoride in aqueous solutions can significantly affect dental and bone health. This study used two methods to prepare hydroxyapatite to remove fluoride ions from water. The experiments showed that the adsorption capacity and removal rate of hydroxyapatite (Xq-HAP) prepared by the novel method were higher than for the hydroxyapatite (Yt-HAP) prepared by the conventional method. The maximum fluoride ion trapping capacity of Xq-HAP could reach 29.04 mg g-1 under the conditions of pH = 5 and an F ion concentration of 10 mg L-1. The materials were characterized by SEM, XRD, BET, XPS, and FTIR. An investigation was conducted to examine the impact of contact time, adsorbent dosage, fluoride concentration, solution pH, temperature, and several other parameters on the removal of fluoride. Adsorption equilibrium was reached in approximately 3 h at an initial fluoride concentration of 10 mg L-1. It can be seen that the adsorbent has a faster ability to trap fluoride ions. The adsorption kinetics and Langmuir isotherm indicated that fluoride ion adsorption is a monolayer chemisorption process. Further characterization and kinetic studies indicated that the removal mechanism involves ion exchange, electrostatic interactions, and complexation. After five adsorption cycles, the adsorption capacity reaches 23 mg g-1.

Loss of fluorine during crosslinking by the biarylitide P450Blt proceeds due to restricted peptide orientation.

The biarylitide crosslinking enzyme P450Blt can perform crosslinking between m-F-Tyr-3 and His-5 residues within peptide substrates with concomitant and specific loss of fluorine. Our investigations suggest that a small intrinsic preference for coupling ipso to fluorine is magnified by the binding of the peptide in a specific orientation that enforces the loss of fluorine during peptide crosslinking, likely via a two-step reaction mechanism involving the non-enzyme catalysed reductive elimination of fluoride.

Quaternary ammonium fluorides and difluorosilicates as nucleophilic fluorination reagents.

TBAT (tetrabutylammonium difluorotriphenylsilicate) is an excellent homogeneous nucleophilic fluorination reagent, but a high excess of the reagent was reported to be essential. We hence optimized the reaction conditions and compared its nucleophilic fluorination reactivity with that of other common commercial nucleophilic fluorination reagents, such as anhydrous TBAF and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilicate). As the substrates, we employed a standard set of primary and secondary octyl substrates under identical conditions. To eliminate the possibility of hydrogen fluoride elimination in the above reagents, we prepared four quaternary ammonium fluorides lacking β-elimination possibility in the hydrocarbon chain, transformed them to the corresponding difluorotriphenylsilicates, and compared their reactivity with that of the commercial reagents. Furthermore, attempts to isolate analogous tetrabutylammonium difluoromethyldiphenylsilicate or difluorodimethylphenylsilicate failed, as was confirmed by comparison of the published experimental data with computed 19F NMR spectra. Finally, we studied the transition states of decomposition of various tetramethylammonium methylphenyldifluorosilicates by DFT methods and found that their relative energies increase with an increasing number of phenyl groups. The formation of difluorosilicates is a nearly barrierless process.

A sustainable approach for fluoride treatment using coconut fiber cellulose as an adsorbent

In developing countries like India, an economically viable and ecologically approachable strategy is required to safeguard the drinking water. Excessive fluoride intake through drinking water can lead to dental fluorosis, skeletal fluorosis, or both. The present study has been under with an objective to investigate the feasibility of using cellulose derived from coconut fiber as an adsorbent under varying pH conditions for fluoride elimination from water. The assessment of equilibrium concentration of metal ions using adsorption isotherms is an integral part of the study. This present finding indicates the considerable effect of variation of adsorbent dosages on the fluoride removal efficiency under constant temperature conditions of 25 ± 2 °C with a contact period of 24 h. It is pertinent to mention that maximum adsorption of 88% has been observed with a pH value of 6 with 6 h time duration with fluoride dosage of 50 mg/L. The equilibrium concentration dwindled to 0.4 mg/L at fluoride concentration of 20 mg/L. The Langmuir model designates the adsorption capacity value of 2.15 mg/L with initial fluoride concentration of 0.21 mg/g with R2 value of 0.660. Similarly, the adsorption capacity using Freundlich isotherms is found to be 0.58 L/g and 0.59 L/g with fluoride concentration of 1.84 mg/L and 2.15 mg/L respectively. The results from the present study confirm that coconut fiber possesses appropriate sorption capabilities of fluoride ion but is a pH dependent phenomenon. The outcomes of the study indicate the possible use of cellulose extracted from waste coconut fiber as a low-cost fluoride adsorbent. The present study can be well implemented on real scale systems as it will be beneficial economically as well as environmentally.

Fixed-bed column adsorption modeling using Zr biocomposites for fluoride removal

ABSTRACT This research involved conducting continuous adsorption experiments to assess fluoride elimination from drinking water achieved by utilizing biocomposites created from the peels of oranges and apples, which were impregnated with zirconium (Zr), to form BOP-Zr and BAP-Zr, respectively. The findings from the experimental data indicate that BOP-Zr and BAP-Zr are effective biosorbents with a solid ability to remove fluoride selectively. Additionally, these biosorbents were found to be stable, as they do not release Zr into the treated water. Notably, these environmentally friendly biosorbents are derived from renewable sources and enhance the value of waste materials. The study employed various empirical models, including Bohart-Adamas, Thomas, Yoon-Nelson, BDST, Clark, Yan, and Woolborska, to elucidate the mechanisms and crucial parameters involved in fluoride adsorption within packed bed columns. The Yan model demonstrated the highest correlation among these models, indicating a chemical adsorption process with kinetics following a pseudo-second-order pattern. BOP-Zr and BAP-Zr exhibited a maximum adsorption capacity of 59.3 and 47.5 mg/g, respectively, under a flow rate of 4 mL/min and an inlet fluoride concentration of 25 mg/L. The analysis of mass transfer coefficients revealed that the primary step governing the adsorption procedure was diffusion through pores. Consequently, the study conclusively establishes that BOP-Zr and BAP-Zr biocomposites, originating from lignocellulosic biomass remains, present a practical and competitive choice for eliminating fluoride from water. These materials surpass waste materials in performance and rival more expensive options in efficiency and performance.

Facile synthesis of Aluminium fumarate metal–organic framework and hydroxyapatite composite with improved adsorption characteristics for efficient fluoride removal from water

An aluminium fumarate (AlFu)-hydroxyapatite (HAP) composite (AlFu-HAP) with numerous functional groups for fluoride binding was synthesised by a simple solid–solid mixing process. The produced AlFu-HAP composite with numerous functional groups results in outstanding adsorption capability in the sequence AlFu-HAP > AlFu > HAP. This composite was studied under different pH, initial fluoride concentrations, temperatures, and contact times. The adsorption kinetics and isotherms were pseudo-second-order model and Freundlich adsorption isotherm, respectively. XRD, SEM, FTIR, Raman spectroscopy, and XPS analysis of the samples before and after the adsorption reaction indicate that the fluoride removal mechanism was controlled by anion exchange of the OH– group in AlFu-HAP and F- in water. At high concentrations (150–200 mg F-/L) in groundwater and industrial effluent, the AlFu-HAP showed > 90 % fluoride removal. Thus, the current study will provide an effective strategy for developing an AlFu-HAP composite adsorbent to be used for the effective elimination of fluoride from wastewater.

Copper-Catalyzed Regio- and Enantioselective Hydroboration of Difluoroalkyl-Substituted Internal Alkenes.

Catalytic asymmetric hydroboration of fluoroalkyl-substituted alkenes is a straightforward approach to access chiral small molecules possessing both fluorine and boron atoms. However, enantioselective hydroboration of fluoroalkyl-substituted alkenes without fluorine elimination has been a long-standing challenge in this field. Herein, a copper-catalyzed hydroboration of difluoroalkyl-substituted internal alkenes with high levels of regio- and enantioselectivities is reported. The native carbonyl directing group, copper hydride system, and bisphosphine ligand play crucial roles in suppressing the undesired fluoride elimination. This atom-economic protocol provides a practical synthetic platform to obtain a wide scope of enantioenriched secondary boronates bearing the difluoromethylene moieties under mild conditions. Synthetic applications including functionalization of biorelevant molecules, versatile functional group interconversions, and preparation of difluoroalkylated Terfenadine derivative are also demonstrated.

Novel MOF(Zr)-on-MOF(Ce) adsorbent for elimination of excess fluoride from aqueous solution

Herein, we used a one-pot method to fabricate a novel MOF-on-MOF adsorbent, namely MOF(Zr)-on-MOF(Ce). The adsorbent demonstrated a high maximum fluoride-ions capture capacity of 164.47 mg g−1. The morphology, elemental distribution, pore size distribution, and thermal stability were studied using SEM-EDS, XRD, BET, and TGA. The influence of the temperature, solution pH, fluoride concentration, and coexisting ions was explored using intermittent experiments. The results suggested that MOF(Zr)-on-MOF(Ce) had a fast capture rate for fluoride. MOF(Zr)-on-MOF(Ce) maintained an excellent fluoride removal performance over a wide pH range with an initial fluoride concentration of 20 mg L−1. The optimal effect was obtained at a pH of 4, but a high removal efficiency of 94% was maintained even at a pH of 9. Interference experiments showed that only the PO43– had an adverse inhibition influence. The field experiments demonstrated that MOF(Zr)-on-MOF(Ce) can keep the safety threshold levels of fluoride in drinking water. The Langmuir and pseudo-second order kinetic models were well fitted for the defluoridation process, demonstrating that the adsorption of fluoride ions on MOF(Zr)-on-MOF(Ce) was dominated by monolayer chemisorption. With the further characterization and kinetic thermodynamic studies indicates that the removal mechanism involves ion exchange, electrostatic interactions and complexation effect.

Electron-Transfer-Enabled Concerted Nucleophilic Fluorination of Azaarenes: Selective C-H Fluorination of Quinolines.

Direct C-H fluorination is an efficient strategy to construct aromatic C-F bonds, but the cleavage of specific C-H bonds in the presence of other functional groups and the high barrier of C-F bond formation make the transformation challenging. Progress for the electrophilic fluorination of arenes has been reported, but a similar transformation for electron-deficient azaarenes has remained elusive due to the high energy of the corresponding Wheland intermediates. Nucleophilic fluorination of electron-deficient azaarenes is difficult owing to the identity of the Meisenheimer intermediate after fluoride attack, from which fluoride elimination to regenerate the substrate is favored over hydride elimination to form the product. Herein, we report a new concept for C-H nucleophilic fluorination without the formation of azaarene Meisenheimer intermediates through a chain process with an asynchronous concerted F--e--H+ transfer. The concerted nucleophilic aromatic substitution strategy allows for the first successful nucleophilic oxidative fluorination of quinolines.

The efficiency of nano metakaolin modified with zirconium oxide for fluoride adsorption from aqueous solution

Groundwater pollution by fluoride is a global issue that has health implications for humans. Thus, it is important to have an understanding of how to efficiently remove it using the most effective and sustainable technique. In this research, a novel and economical adsorbent, zirconium-modified nano metakaolin (Zr@NMK), was synthesized through a chemical precipitation process and was explored in the adsorption technique for fluoride from water. Analytical techniques including FTIR, XRD, SEM, EDX, TGA, as well as BET were employed to analyze Zr@NMK. The response surface methodology was utilized to obtain the optimal crucial factors that affect fluoride adsorption. The adsorption process reaches equilibrium and follows the pseudo-second-order whereas fluoride isotherm fits the Langmuir and Freundlich model. The optimum fluoride adsorption capacity of Zr@NMK is 6.42 mg/g, corresponding to 96.4% fluoride removal efficiency, significantly higher than that of the unmodified nano metakaolin (NMK), under the optimum condition according to Response Surface Methodology (RSM); (pH∶ 6, dose of adsorbent∶ 3 g/L, fluoride level∶ 20 mg/L, at 38 °C in 80 min). Additionally, the influence of concurrent anions in water on the elimination of fluoride was assessed, and it was determined that the existence of Cl− and NO3− had a minor influence on removal efficiency, whereas the existence of SO42− and CO32− in water led to its substantial drop. However, the positive sign of ΔH° and ΔS°, and the negative sign of ΔG° indicate that the fluoride capture was spontaneous and endothermic on Zr@NMK. Moreover, desorption of Zr@NMK is possible for subsequent utilization and can be utilized for up to eight cycles. Zr@NMK offers a promising solution for fluoride removal and has the potential to promote a more sustainable future.