Elimination Of Fluoride Research Articles

Sorptive elimination of fluoride from contaminated groundwater in a fixed bed column: A kinetic model validation based study

The current investigation involves a continuous adsorption experiment in a packed bed column for the sorptive elucidation of fluoride from contaminated groundwater using an activated soil-clay mixture. Through the combination of naturally accessible laterite soil with silica enriched clay (3:1 ratio), a low-cost Al–Si heterogeneous material has been developed. Following detailed characterization, the developed materials were employed in a long-time column process to achieve a high degree of fluoride separation from real-world groundwater. In a packed bed column investigation, the effect of bed height, initial fluoride concentration, and flow rate on the breakthrough properties of the adsorption system were investigated. By using a non-linear regression equation, three model kinetics, such as the Thomas Model, Adams-Bohart Model, and Yoon-Nelson Model, were fitted to validate the column-based experimental data, by analysing the breakthrough curves profiles, and distinct kinetic parameters. The Bed Depth Service Time Analysis (BDST) model was tested to express the effect of bed height on breakthrough curves, as well as to predict the time for breakthrough, and material depletion under optimal conditions. The Thomas and Yoon-Nelson models were identified to be the most appropriate ones for describing the entire breakthrough curve, whereas the Adams-Bohart model was only utilised to predict the first half of the dynamic process. With correlation coefficients (R2) 0.96, the experimental results were well suited to Thomas, Yoon-Nelson, and Adams-Bohart models. Finally, regeneration assessment was carried out where even after four cycles of operation, regenerated adsorbent showed a rejection efficacy of 78% to fluoride that proves the viability of the material and methodology.

Removal of dexamethasone by oxidative processes: Structural characterization of degradation products and estimation of the toxicity

Dexamethasone (DEX) belongs to a class of steroid hormones that can potentially be harmful due to their endocrine disrupting properties. The efficient elimination of DEX during the treatment of drinking water is needed to ensure that the health of both human and aquatic species are protected. Thus different oxidative processes were investigated in order to assess the effect of these procedures and conditions on DEX. Aqueous solutions of DEX were treated by conventional chlorination ([NaClO]=10 mg L−1) and advanced oxidative processes (ozonation – [O3]=8 mg L−1; photocatalysis – [TiO2]=120 mg L−1 and UV-C; photolysis – UV-C). The most and least efficient processes for DEX removal were ozonation (95%) and chlorination (54%), respectively. In total, 16 degradation products were identified and characterized by high-resolution mass spectrometry and only two have been proposed in previous reports. Chemical structures of the degradation products were proposed and alcohol oxidation, ozonolysis and decarboxylation were the main chemical transformations observed. The toxicities of DEX and its derivatives were evaluated by following methods: MTT assay (HepG2 cell), ECOSAR (acute and chronic toxicity) and molecular docking (AutoDock). MTT assay results demonstrated that only a mixture DEX and the chlorinated derivative were toxic at high concentrations. ECOSAR analysis showed that products formed from dehydration and fluoride elimination were more toxic than intact DEX, mainly for fish and Daphnid and to a lesser extent for green algae. The docking study revealed that these degradation products were not capable of making hydrogen bonds with residual amino acids GLN570, GLN642 and CYS736, but were stable at the glucocorticoid receptor indicating the possibility of being toxic to humans.

Photoredox Activation of Organozinc Reagents: Barbier-Type Reaction of Alkyl Halides with α-(Trifluoromethyl)styrenes.

Organozinc reagents may be activated under blue light irradiation using an organic photocatalyst to generate alkyl radicals. The radicals are trapped by α-(trifluoromethyl)styrenes leading to gem-difluorinated products after elimination of fluoride. The reaction can be conveniently performed under Barbier conditions starting from organic iodides and bromides and elemental zinc.

Fluoride removal using electrocoagulation technique

A modest quantity of fluoride can increase the mineralization of teeth and reduce their cavities. But the presomerence of fluoride in excess in water can lead to severe disease infertility. In the past few decades, scientists have thus been preoccupied with developing ways to reduce sewage fluoride concentrations and reduce their effects on human health. The present study is aimed at using the technology of electrocoagulation to remove fluoride from polluted water. Tests have been done to examine the elimination of fluoride with a rectangular electrocoagulation cell and examine the impact of the experimental aspects on fluoride extraction, specifically electrical current, electrode spacing, and pH. The authors found that 93% of the fluoride has been extracted using 5mm spaced electrodes with a current density of 2 mA/cm2 and a level of pH of 7 from the polluted water after 20 min of processing. Experimental factors considerably impact the efficacy of fluoride removal. In the acidic environment, greater effectiveness of fluoride removal is being attained. The elimination effectiveness depends directly on the electric current, whereas the distance between poles is adversely linked to fluoride elimination.

Enhanced fluoride removal from water by nanosized cerium oxides impregnated porous polystyrene anion exchanger

Efficient elimination of fluoride from wastewater is an urgent need for ensuring water safety. In the present study, a stable and reusable nanocomposite (NCO@PAE) was synthesized by impregnating nanosized cerium oxides (NCO) inside a porous polystyrene anion exchanger (PAE) host for efficient fluoride removal from wastewater. The newly fabricated NCO@PAE exhibited excellent resistance to acid and alkali environment, allowing it to be utilized in a wide pH range (2–12). Fluoride uptake onto NCO@PAE was a pH-dependent process, which could reach the maximum capacity at pH 3.0. Compared with its host PAE, NCO@PAE showed conspicuous adsorption affinity towards fluoride in the coexistence of other competing anions at high concentrations. Adsorption kinetics confirmed its high efficiency for achieving equilibrium within 120 min. Fixed-bed adsorption runs demonstrated that the effective processing capacity of NCO@PAE for synthetic fluoride-containing wastewater (initial fluoride 2.5 mg/L) was about ~330 BV (bed volume), while only 22 BV for the host PAE. The exhausted NCO@PAE could be effectively revived by a simple in-situ desorption method for long-term cycle operation without conspicuous capacity loss. All the results indicated that NCO@PAE is a reliable and promising adsorbent for water defluoridation.

Dimerization and Cycloaddition Reactions of Transient Tri-tert-butylphosphacyclobutadiene Generated by Lewis Acid Induced Isomerization of Tri-tert-butylphosphatetrahedrane

Tri-tert-butylphosphatetrahedrane (1) is shown here to act as a synthon of isomeric tri-tert-butylphosphacyclobutadiene in the presence of a Lewis acid or transition-metal complex. When it is combined with a substoichiometric amount of triphenylborane, compound 1 forms a ladderane-type dimer of tri-tert-butylphosphacyclobutadiene in 72% isolated yield. Trapping of a generated intermediate was achieved by repeating the experiment in the presence of excess styrene (20 equiv) or ethylene (1 atm), and the corresponding [4 + 2] cycloadducts of tri-tert-butylphosphacyclobutadiene were isolated in 88% and 74% yields, respectively. The platinum complex (Ph3P)2Pt(C2H4) also reacts with 1 to form an orange η2 complex of tri-tert-butylphosphacyclobutadiene in 80% isolated yield. Additionally, we report a novel method for generating a phosphinidenoid species via fluoride-induced trimethylsilyl fluoride elimination, leading to an improved preparative procedure for 1 (182 mg, 33% isolated yield).

Enhanced biosorption of fluoride by extracted nanocellulose/polyvinyl alcohol composite in batch and fixed-bed system: ANN analysis and numerical modeling.

The present investigation attempted to examine the defluoridation feasibility onto the extracted nanocellulose/PVA polymer composites. Nanocellulose were derived from sugarcane bagasse and blended with PVA (polyvinyl alcohol) polymer matrix. The defluoridation potential of nanocellulose/PVA was observed to be significantly dependent on the various operational factors including pH, time interval, etc. the Temkin isotherm (R2 = 0.989) as well as the Langmuir isotherm equation (R2 = 0.982) could well fit with the investigational data. Following the Langmuir isotherm, the maximum monolayer adsorption capacity for fluoride elimination at 25°C was obtained as 11.363 mg g-1. The nature of rate-limiting steps involved in defluoridation process might be effectively predicted by pseudo-second-order kinetics. Values of thermodynamic state properties achieved as of the thermodynamic analysis showed that the defluoridation process was spontaneous, exothermic, and feasible. The diffusion and mass transfer study were estimated by following the Boyd's model. Average effective diffusion coefficient (De) at various initial fluoride concentrations (4-10 mg L-1) was obtained as 15.3343×10-7 m2s-1 and the estimated magnitude of the mass-transfer coefficient (Kf) was 0.0346×10-9 m s-1 (temperature = 298 K, C0= 6 mgL-1). An ANN (artificial neural network) model applied to optimize and simulate the defluoridation procedure. Furthermore, continuous flow column reactor was conducted to investigate the practical applicability of composites in the defluoridation process. The Yoon-Nelson and the Thomas model exhibited excellent conformity with the breakthrough curves. Nanocellulose/PVA satisfactorily eliminated fluoride from its aqueous solution and can be considered as a suitable bio-sorbent for defluoridation.

Controlled Fabrication of the Biomass Cellulose–CeO2 Nanocomposite Membrane as Efficient and Recyclable Adsorbents for Fluoride Removal

The biomass cellulose nanocomposite membrane is regarded as one of the most promising adsorbents for resource recovery and pollution control owing to the unique physicochemical properties. Herein, a recyclable biomass cellulose–CeO₂ nanocomposite membrane (BCCM) is fabricated by in situ growth of CeO₂ on the cellulose membrane (CM) surface and then employed for the elimination of fluoride from industrial wastewater. Structural characteristics of the BCCM were characterized by XRD and SEM. The adsorption experiment indicated that the maximum fluoride adsorption capacity of the BCCM was 48.0 mg/g. Kinetic and isotherm results elucidated that multilayer chemisorption dominated the BCCM adsorption process. Besides, the adsorption mechanism was also investigated by the energy-dispersive X-ray, FT-IR, and XPS analysis. More importantly, the BCCM has strong acid–base adaptability and can be used in extreme environments. This work provides an effective and environmentally friendly strategy to prepare other biomass nanocomposite membranes, which shows great potential for environmental remediation and chemical separation.

Sono electro-chemical synthesis of LaFeO3 nanoparticles for the removal of fluoride: Optimization and modeling using RSM, ANN and GA tools

The aim of this work was to model, optimize, and compare fluoride removal by LaFeO3-NPs using the RSM (Response Surface Methodology), ANN (Artificial Neural Network), and GA (Genetic Algorithm) techniques.The input variables considered were pH, time, temperature, LaFeO3-NPs dose, and fluoride. The CCD (central composite design) plan was exercised for the analysis of RSM, and ANN to determine their capabilities of prediction of the response. Their performances were evaluated using the regression coefficient (R2), RMSE, SEP, and the AAD. Also, RSM and GA were used to maximize the response and their optimum conditions evaluated. Both RSM (R2 =0.9970, AAD=0.00001, RMSE=0.0037, SEP=0.0042) and ANN (R2 =0.9919, AAD=0.00044, RMSE=0.0066, SEP=0.0074) gave high degree of accuracy. The model equation obtained for the process through RSM was adequate. The GA and RSM gave very close values for the optimization of the fluoride reduction process; RSM gave optimum fluoride removal of 96.35% (at pH 8.6, time=75.03 min, temperature=34.9 °C, dose=0.225 g, and concentration=23.68 mg L−1) while the GA gave 96.30% (at pH 10, time=120.39 min, temperature=28.41 °C, dose=1.030 g, and concentration=16.31 mg L−1). But from the confirmation experiments, RSM and GA data gave 96.52% and 96.63%, respectively. RSM, ANN, and GA were capable of modeling and optimizing the elimination of fluoride using LaFeO3-NPs.

Acid-Catalyzed Hydrothiolation of gem-Difluorostyrenes to Access α,α-Difluoroalkylthioethers.

The substitution of hydrogen atoms with fluorine in bioactive molecules can greatly impact physicochemical, pharmacokinetic, and pharmacodynamic properties. However, current synthetic methods cannot readily access many fluorinated motifs, which impedes utilization of these groups. Thus, the development of new methods to introduce fluorinated functional groups is critical for developing the next generation of biological probes and therapeutic agents. The synthesis of one such substructure, the α,α-difluoroalkylthioether, typically requires specialized conditions that necessitate early-stage installation. A late-stage and convergent approach to access α,α-difluoroalkylthioethers could involve nucleophilic addition of thiols across gem-difluorostyrenes. Unfortunately, under basic conditions, nucleophilic addition to gem-difluorostyrenes generates an anionic intermediate that can undergo facile elimination of fluoride to generate α-fluorovinylthioethers. To overcome this decomposition, we herein exploit an acid-based catalyst system to facilitate simultaneous nucleophilic addition and protonation of the unstable intermediate. Ultimately, the optimized mild conditions afford the desired α,α-difluoroalkylthioethers in high selectivity and moderate to excellent yields. These α,α-difluoroalkylthioethers are less nucleophilic and more oxidatively stable relative to nonfluorinated thioethers, suggesting the potential application of this unexplored functional group in biological probes and therapeutic agents.

Acid-mediated intermolecular C-F/C-H cross-coupling of 2-fluorobenzofurans with arenes: synthesis of 2-arylbenzofurans.

Transition-metal-free acid-promoted biaryl construction was achieved via intermolecular C-F/C-H cross-coupling. By treating 2-fluorobenzofurans with arenes in the presence of AlCl3, 2-arylbenzofurans were obtained. This protocol was successfully applied to the short-step orthogonal synthesis of a bioactive 2-arylbenzofuran natural product, which allows independent transformations of C-F and C-Br bonds. Mechanistic studies indicated that α-fluorine-stabilized carbocations, generated via the protonation of 2-fluorobenzofurans, served as key intermediates. The Friedel-Crafts-type C-C bond formation between the α-fluorocarbocations and arenes, followed by hydrogen fluoride elimination, afforded 2-arylbenzofurans.

Removal of fluoride with rice husk derived adsorbent from agro waste materials

Elimination of fluoride from water sample is an imperative stimulus for the betterment of society. Based on WHO policy, the fluoride level superior than 1.5 miligram/litre causes dental and bone scarcity to living entities. In order to prevent these issues, the proper deflouridation technique was chosen. In the present investigations highlighted the elimination percentage of Fluoride from water with the aid of low-cost material, rice husk. Various physical and chemical deflouridation methods were developed to treat high concentrations of fluoride in ground water. Those deflouridation methods need to be built which this will be cost-efficient, and biodegradable. Rice husk is used to detoxify fluoride-rich water and making it safe for human use. 0.5 g/100 mL of adsorbent accomplished 87% of fluoride removal.

Synthesis of Fluorinated 3,6-Dihydropyridines and 2-(Fluoromethyl)pyridines by Electrophilic Fluorination of 1,2-Dihydropyridines with Selectfluor®.

New fluorinated 3,6-dihydropyridines were obtained by the electrophilic fluorination of 1,2-dihydropyridines with Selectfluor®. These 3-fluoro-3,6-dihydropyridines were easily converted to corresponding pyridines by the elimination of hydrogen fluoride under mild conditions. A new approach to the synthesis of methyl 2-(fluoromethyl)-5-nitro-6-arylnicotinates by the fluorination of 3-fluoro-2-methyl-5-nitro-3,6-dihydropyridines or 1,2-dihydropyridines with Selectfluor® has been developed.

Hierarchical hollow manganese-magnesium-aluminum ternary metal oxide for fluoride elimination

Rational designs and syntheses for advanced structures are of immense importance to enhance adsorption performances toward a variety of materials. In this study, the synthesis of a novel hierarchical hollow manganese-magnesium-aluminum ternary metal oxide (MMA) via a green hydrothermal strategy coupled with a calcination process serves as a robust adsorbent for fluoride elimination. Combining the strong affinities Mn, Mg, and Al species have toward fluoride into a 3D-hierarchical hollow structure with an adequately accessible adsorption surface can remarkably boost the migration and diffusion of fluoride and provide more mass diffusion pathways for fluoride elimination. Remarkably, the adsorption process follows the pseudo-second-order model and the Langmuir isotherm model with a considerable performance of 63.05 mg/g. Moreover, the adsorbent retained outstanding selectivity and recyclability. Overall, the results from the universal characterization techniques and batch experiments validate that the potential adsorption mechanisms were electrostatic attraction and ion exchange, and complexation. As such, the present method expands the current adsorbent toolbox by providing a rational design and synthesis of a highly efficient adsorbent material for use in managing environmental pollution.

Stereoselective Synthesis of Terminal Monofluoroalkenes from Trifluoromethylated Alkenes.

Herein we report the hydrodefluorination reaction of trifluoromethylated alkenes to access terminal monofluoroalkenes. The use of LiAlH4 allowed the stereoselective synthesis of the terminal monofluoroalkenes in good to excellent yields with good to excellent diastereoselectivities. Mechanistic studies suggested a hydroalumination reaction followed by a stereoselective fluoride elimination.

Arsenic Elimination from Water Solutions by Adsorption on Bone Char. Effect of Operating Conditions and Removal from Actual Drinking Water

Consuming drinking water contaminated with As(V) represents a hazard to human health. Adsorption of As(V) onto bone char (BC) has been studied previously, but a detailed study is required for applying BC to remove arsenate present in drinking water. The effect of the operating conditions, water matrix, and presence of fluoride onto the adsorption capacity of BC toward As(V) were thoroughly investigated. The XRD examination confirmed the presence of hydroxyapatite in BC, and the TEM examination of BC showed the random piling of the layers of hydroxyapatite. The BC adsorption capacity was contrasted with that of reagent-grade hydroxyapatite, and it was found that the BC capacity was mainly attributed to its hydroxyapatite content. The BC capacity is augmented by diminishing the solution pH because of the rise of the electrostatic attraction between the arsenate in water and the positive charge of the BC surface. The adsorption capacity was improved by incrementing the temperature so that the adsorption of As(V) was endothermic. The adsorption mechanism of As(V) on BC comprised electrostatic attraction and ion exchange. The simultaneous elimination of fluoride and arsenate in drinking water samples in San Luis Potosi, SLP, Mexico, revealed that both pollutants could be effectively removed by adsorption on BC, and the presence of As(V) did not affect the adsorption capacity of BC toward fluoride. In contrast, the capacity of BC for adsorbing As(V) was enhanced in the drinking water compared with that of deionized water, and this synergistic behavior was due to a screening effect.

Removal of fluoride and hydrated silica from underground water by electrocoagulation in a flow channel reactor.

This paper concerns simultaneous removal of fluoride and hydrated silica from groundwater (4.08mgL-1 fluoride, 90mgL-1 hydrated silica, 50mgL-1 sulfate, 0.23mgL-1 phosphate, pH 7.38 and 450μS cm-1 conductivity) by electrocoagulation (EC), using an up-flow EC reactor, with a six-cell stack in a serpentine array, opened at the top of the cell to favor gas release. Aluminum plates were used as sacrificial electrodes. The effect of current density (4≤j≤7mAcm-2) and mean linear flow rate (1.2≤u≤4.8cms-1), applied to the EC reactor, on the elimination of fluoride and hydrated silica was analyzed. The removal of fluoride followed the WHO guideline (<1.5mgL-1), while the hydrated silica was abated at 7mAcm-2 and 1.2cms-1, with energy consumption of 2.48kWh m-3 and an overall operational cost of 0.441 USD m-3. Spectroscopic analyses of the flocs by XRD, XRF-EDS, SEM-EDS, and FTIR indicated that hydrated silica reacted with the coagulant forming aluminosilicates, and fluoride replaced a hydroxide from aluminum aggregates, while sulfates and phosphates were removed by adsorption process onto the flocs. The well-engineered EC reactor allowed the simultaneous removal of fluoride and hydrated silica.

Fibre optic oxygen sensor for long term use in jet fuel, featuring phosphorescent dye chemically bonded to functionalised silica

Five new compounds, termed “metallo-porphyrin silicas”, have been synthesised by the reaction of functionalised silicas with platinum (II) meso tetrakis (pentafluorophenyl) porphyrin. The reaction resulted in the elimination of hydrogen fluoride to create a covalent bond between a functional group of the silica and the para carbon atom of a pentafluorophenyl group. Four out of the five new compounds exhibited phosphorescence under irradiation with u.v. light at ~400 nm, and in all four cases the phosphorescence was quenched by molecular oxygen. Stern Volmer plots of the four phosphorescent compounds showed that the aminopropyl derivative gave the largest response at 400 nm over a concentration range of 0–20% oxygen. Further tests were undertaken on this compound that showed that the output was dependant not only on oxygen concentration but also temperature (−17 °C–40 °C). A prototype probe suitable for testing oxygen content in aviation fuels was developed using an optical fibre. It was possible to detect changes in oxygen concentration in jet fuel. The results demonstrate the potential of this approach to provide a low cost, low power resilient probe for the detection of oxygen in aviation fuel.

Elimination of Fluoride, Arsenic, and Nitrate from Water Through Adsorption onto Nano-adsorbent: A Review

Fluoride, arsenic, and nitrate are considered as major pollutants of water around the world, affecting millions of people mainly through the potable groundwater. Presence of these contaminants in drinking water can cause health issues like dental fluorosis, skeletal fluorosis, blackfoot disease, blue-baby syndrome, reproductive disorders, skin cancer, thyroid dysfunction, hypertension etc. The removal of fluoride, arsenic, and nitrate is mainly carried out through ion-exchange, membrane, adsorption, and other chemical treatments. Owing to the cost competitiveness, energy consumption and customized operating procedure, adsorption has been a popular choice for the removal of these contaminants. The adsorbent based on natural material either in native form or modified at the surface, have gained the momentum to be utilized for fluoride, arsenic, and nitrate free drinking water because of their adequate disposability. Recently, adsorbent of nanomaterial has shown the significant potential for water treatment because of their higher surface area and tailored selectivity. Nanoadsorbents prepared by wet-chemical precipitation, co-precipitation, sol-gel, electro-coextrusion, hydrothermal, thermal refluxing methods etc. can be effectively employed at comparatively lower concentration for water treatment. The adsorption capacity, durability, recyclability, and toxicity of nano-adsorbent are further explored particularly, at commercial scale. The present article is mainly aimed to provide a comprehensive review about the applicability and challenges associated with the use of nano-adsorbents for the removal of fluoride, arsenic, and nitrate with a brief discussion on options and future perspective to meet the challenges of complexity for the selection of environmentfriendly adsorbents.

Removal of fluoride ions (F−) from aqueous solutions using modified Turkish zeolite with quaternary ammonium

ABSTRACT The natural Turkish zeolite has been modified with hexadecyltrimethylammonium bromide (CTAB) for the elimination of fluoride (F−) from aqueous solutions. The parent natural zeolite (NZ) and modified zeolite (MZ) have been characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), zeta potentials and Brunauer-Emmett-Teller (BET) method. The effect of pH, adsorbent dose, contact time, initial concentration and temperature on adsorption of fluoride ions onto modified zeolite (MZ) has been determined in batch experiments. Fluoride concentration can be reduced to 1.5 mg/L under the optimum condition (pH = 5, adsorbent dose = 20 mg/L, contact time = 60 min and T = 293 K) when initial fluoride concentration of 10 mg/L is employed. The fluoride adsorption on MZ has been described by the Langmuir isotherm and the maximum fluoride adsorption capacity was found as 2.994 mg/g. Kinetics data were best described by the pseudo-second-order model. The thermodynamic studies proved that the adsorption was exothermic and spontaneous.