Initial Fluoride Concentration Research Articles

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.

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.

In situ synthesis of MIL-53-type eco-MOF from high-alumina fly ash for efficiently removing fluoride from water

Facing ubiquitous fluoride pollution in aquatic environments and ever-increasing discharge of coal fly ashes, this study aims to in situ synthesize a kind of Al-based metal–organic framework eco-material (eco-MOF) using high-alumina fly ash as metal raw material, and apply the obtained adsorbent to efficiently adsorb fluoride in water. The synthesized eco-MIL-53(Al) exhibits excellent thermal stability, showcasing a consistent morphology of fine columnar crystals and possessing a high specific surface area (353 ​m2·g−1). Moreover, the adsorption isotherm demonstrates a strong agreement with the Langmuir isotherm model, indicative of a maximum uptake quantity of 160 ​mg·g−1 ​at 318 ​K. In addition, fluoride adsorption experiments demonstrate that an increased dosage enhances the adsorption efficiency, the higher water pH value diminishes the removal efficiency, and the impact of coexisting anions is minimal. Also, the adsorption capacity is augmented with increasing temperature at high initial fluoride concentrations, but shows negligible variation at low initial fluoride concentrations. It is worth noting that the desiliconization filtrate can be applied to synthesize ZSM-5 zeolite, realizing the total utilization of fly ash. The present work provides a novel platform that would serve as a mutually beneficial reference for managing the environmental risks of fluoride and waste resource utilization.

Modeling, optimization and comparative study on abatement of fluoride from synthetic solution using activated laterite soil and fly ash

The supply of potable water by proper treatment of fluoride laden ground water is a challenging task. Batch experiments were executed with activated laterite soil and fly ash individually for removal of fluoride. The process parameters such as particle size (100–620 μm), dose of adsorbent (10–60 g/L), initial concentration of fluoride (2–12 mg/L), agitation speed (20–120 rpm), contact time (0.5–10 h) and pH (4.5–9.5) were investigated and it was observed that activated laterite soil had better fluoride removal efficiency than fly ash. At pH 4.5, contact time 10 h, particle size 100 μm, adsorbent dose 60 g/L, initial concentration of fluoride 12 mg/L, and agitation speed 120 rpm, maximum removal efficiencies of fluoride using activated laterite soil and fly ash were found as 85.91 ± 0.62% and 77.1 ± 0.39%, respectively. Kinetic study was performed and Pseudo 2nd order kinetic model was found to fit the kinetic data best. The Freundlich isotherm model fit the equilibrium data fairly well. The values of adsorption equilibrium constant as used in Freundlich isotherm model vis-à-vis adsorption capacity (KF) for activated laterite soil and fly ash were obtained as 0.1331 and 0.0772 ((mgg−1)(Lmg−1)1/n). A thermodynamic analysis was conducted to examine the process behaviour. In order to determine whether the adsorbent may be used for further cases, regeneration of the adsorbents was also done. Generally, two types of adsorption mechanisms happen like electrostatic attraction and ion exchange. The electrostatic force of attraction favours the adsorption of negatively charged fluoride ions on positively charged adsorbent surfaces. In ion exchange, fluoride ions are exchanged by hydroxyl and hydronium ion. Based on experimental data, Multi-Gene Genetic Programming (MGGP) model could accurately predict the removal efficiency of fluoride under various operating situations. Finally, using Genetic Algorithm (GA) optimization the maximum output values for both adsorbents were estimated as 99.14% and 99.02%.

Effective defluoridation using lanthanum-organic frameworks encapsulated hydrotalcite based bio-hybrid beads

Herein, hydrotalcite (HT) integrated lanthanum-metal organic frameworks (LaMOFs) cross-linked alginate and chitosan (Alg-CS) biopolymers that are HT-LaMOFs@Alg-CS beads was prepared and successfully utilized for defluoridation investigations. The prepared HT-LaMOFs@Alg-CS beads were evaluated with the help of various instrument analyses. The adsorption capacity of the prepared HT-LaMOFs@Alg-CS beads for fluoride retention was investigated, across a broad choice of pH levels, and in the occurrence of interfering ions identified in water. The batch optimized condition for fluoride adsorption using HT-LaMOFs@Alg-CS beads were contact time (30 min), pH 7, initial fluoride concentration (10 mg/L), dosage (0.1 g) at room temperature. The fluoride adsorption capacity of HT-LaMOFs@Alg-CS beads is 4905 mgF− kg−1 within 20 min. To distinguish the defluoridation behavior on HT-LaMOFs@Alg-CS bio-hybrid beads, the adsorption isotherm, kinetics, and thermodynamic studies were performed. Thermodynamic results suggest that the fluoride adsorption route on the developed HT-LaMOFs@Alg-CS beads was endothermic process with spontaneous nature. The experimental data result of HT-LaMOFs@Alg-CS bio-hybrid beads for fluoride removal was majorly fitted Langmuir isotherm and pseudo-second-order kinetics. The reusability and real water sample examination results of the attained HT-LaMOFs@Alg-CS hybrid beads for defluoridation was demonstrated that the prepared HT-LaMOFs@Alg-CS beads were regenerable nature with more fitting at field level.

Role of starch in one pot fabrication of mesoporous gamma-alumina with excellent fluoride sorption capacity

Green synthesis of mesoporous γ-AƖ2O3, a cutting-edge material for sustainable application in medicine, engineering, energy, and water treatment, is still challenging. Our study used a one-pot strategy for facile synthesis of γ-AƖ2O3 by sol-gel method using starch from cassava waste. AƖ(OH)3 were bound to the O-H groups of the starch molecule to form the AƖ(OH)3-starch complex in a nano-network confined in starch polymer cages. Its calcination at 500 ℃ produced a mesoporous, highly crystalline water stable γ-AƖ2O3 with a pore size of 2.07 nm and an extensive BET surface area (215 cm2/g). Using the response surface methodology (RSM), the as-synthesized γ-AƖ2O3 was optimized for efficient fluoride removal from water. A central composite design (CCD) was used to study the effect of initial fluoride concentration, pH, contact time, and sorbent dose on fluoride removal efficiency and optimization of the process. The relative importance of the sorption process variables to the fluoride removal process was assessed using ANOVA. The quadratic model showed that the predicted response was significantly correlated with the experimental response (R2 = 0.9667), with sorbent dose and pH being the process's most influential factors. Optimum conditions for 93.6% fluoride removal efficiency were sorbent dose of 0.5 g, initial fluoride concentration of 10 mg/L, pH 7, and contact time of 137.5 min. A weakly acidic medium favored fluoride removal from water, while the presence of PO43- and HCO3- retarded the process. The sorption data fitted well in the Langmuir isotherm (0.9783) and pseudo-second-order kinetic model (0.9999), indicative of a chemisorption process. The maximum sorption capacity towards fluoride was 207.5 mg/g. A thermodynamic study indicated that the sorption process was spontaneous and endothermic, with increased randomness at the solid-solution interface. Sorption, desorption, sustainability, and leaching tests showed that the sorbent could be used for sustainable fluoride removal at 8.3 USD/1000 liters of safe drinking water.

Fluoride Removal from Water Sources by Adsorption on MOFs

Fluoride is present in several groundwaters due to natural or anthropogenic origins. Although it is necessary for physiological human functions (in small amounts, i.e., 0.5–1.2 mg/L), it could be very harmful when it exceeds the maximum permissible concentration limit of 1.5 mg/L (according to WHO). Among the numerous technologies for removing fluoride from waters, metal–organic framework (MOF) materials are considered to be promising adsorbents due to their advantages of high porosity, high specific surface area, diverse functions and easy modification. In this study, the synthesis of MOFs and the progress of their application to the removal of fluoride from contaminated water, as published in the recent literature mainly over the past five years, are reviewed. The adsorption mechanism(s) and its main characteristics, such as effect of initial fluoride concentration, adsorbent dosage, solution pH, contact time, adsorption capacity, thermodynamic and regeneration studies, etc., for the removal of fluoride with the addition of different MOFs are compared. According to these comparisons, the hydrothermal/solvothermal synthesis method is most commonly used for the preparation of MOFs, whereas higher BET surface areas are shown by specific MOFs based on aluminum metal ions. The main fluoride adsorption mechanisms were found to be electrostatic attraction and/or complexation. The most common pH for conducting experiments was 7.0, but several examined materials were found to be effective over a wide pH range. Four to six regeneration cycles were successfully applied on average, regarding the MOFs under review, whereas in the majority of these cases, the sorption process was found to be endothermic.

Studying the effects of Aspergillus niger (MF431834) dead biomass on water defluoridation in batch and bed column: Adsorption kinetics, characterization, genotoxicity studies

Fluoride pollution in water caused by biological and anthropogenic activities has been recorded as a significant global issue, posing severe risks to the ecosystem. The present study focuses on the isolated fungus Aspergillus niger (MF431834)-dead biomass served as novel adsorbents for defluorination. The dead fungal mycelium of A. niger was used to study the biosorption of fluoride from an aqueous medium while varying the pH, fluoride concentrations, bio-sorbent concentrations, temperatures, contact periods, and coexisting ions. After the batch experimentation, the maximum fluoride adsorption capacity of 93.85 % was achieved by 0.2 g dosage, a 50-min equilibrium time was predicted as a contact time, considerable fluoride adsorption was observed at 15 mg/L of initial fluoride concentration, the maximum fluoride adsorption of 92 % was achieved by pH 2.0, and NaOH was the best desorption agent. The biosorption of fluoride ion well pseudo-second-order (R20.99) compared to pseudo-first-order and the biosorption equilibrium data were more suited by the Langmuir isotherm than the Freund isotherm model. Thermodynamic parameters such as ΔG°, ΔS°, and ΔH° the biosorption of fluoride ions by endothermic nature. Energy Dispersive Spectroscopy (SEM-EDX) and Fourier transform infrared (FTIR) spectroscopy examine the biosorption of fluoride by fungal bio-sorbent. Fluoride removal was also significantly attained in the column study with bio-sorbent. The findings demonstrated that A. cepa subjected to untreated polluted fluoride water exhibited chromosome abnormalities, including disorganized, disturbed metaphase, chromosomal displacement in anaphase, aberrant telophase, spindle disturbances, and binucleate cells. The highest chromosomal aberrations and mitotic inhibition were found in roots exposed to contaminated fluoride water. The novelty of this research can be used as a biomarker to identify the genotoxic effects of fluoride water contamination on biota. Hence, the native fungus A. niger exhibits as an effective adsorbent for fluoride elimination, being valuable in the theory and practical management of environmental pollution.

Synthesis and application of alginate-nanocellulose composite beads for defluoridation process in a batch and fluidized bed reactor

Electronegative Fluorine has great reactivity and it exists as organic or inorganic fluoride compounds. Biosorption feasibility of fluoride onto alginate-cellulose composites was investigated in this study. Extracted cellulose has been utilized to synthesize calcium alginate impregnated composite beads for fluoride remediation process in batch and fluidized-bed reactors. Physiochemical characteristics were analyzed by FTIR, SEM, TGA and BET. From the BET properties analysis, the surface area of prepared composite beads was 87.13 m2/g. The point zero charge (PZC) value of composite beads was attained at pH 7.32. The relationship between biosorption efficiency and independent variables have been observed to evaluate the effects on the fluoride biosorption efficiency of composites and its components. The hypothetical development of the removal technique has been explained using various nonlinear model-fitting methods to evaluate Isotherm study, bio-sorption Kinetics, Thermodynamic parameters and Mass transfer study. Maximum monolayer adsorption capacity (qm) obtained by following Langmuir model for fluoride removal was found to be 23.809 mg/g at 30 °C using adsorbent dosage of 2 g/L for an initial fluoride concentration of 6 mg/L. The optimized condition for fluoride adsorption experiment was observed by evaluating response surface methodology (RSM) was pH-5.67, dose 1.89 g/L and time 85.71 min and removal was found as 82.79%. Experimental data of fluidized-bed study were evaluated by designing mathematical modeling. Fluidization velocities was adjusted in between Umf and 2Umf for optimizing external mass transfer and adsorbent loss. Regeneration study of fluoride loaded biosorbent and cost analysis of composite production have been estimated.

Improved defluoridation and energy production using dimethyl sulfoxide modified carbon cloth as bioanode in microbial desalination cell

In the present study, carbon cloth (CC) was functionalized using dimethyl sulfoxide (DMSO) and employed as an excellent bioanode for improving defluoridation efficiency, wastewater treatment, and power output from a microbial desalination cell (MDC). The Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis of DMSO modified carbon cloth (CCDMSO) confirmed the functionalization of CCDMSO, and the water drop contact angle of 0° ensured its superior hydrophilicity. The presence of –COOH (carboxyl), SO (sulfoxide) and O–CO (carbonyl) functional groups on CCDMSO aids in enhancing the performance of the MDC. Besides, cyclic voltametric and electrochemical impedance analysis revealed that CCDMSO had an excellent electrochemical performance with low charge transfer resistance. Replacing CC with CCDMSO as anode in MDC, the time required for 3,10 and 20 mg/L of initial fluoride (F−) concentrations in the middle chamber was reduced from 24 ± 0.75 to 17 ± 0.37, 72 ± 1 to 48 ± 0.70, and 120 ± 0.5 to 96 ± 0.53 h, respectively to meet the prescribed standards (1.5 mg/L). Furthermore, using CCDMSO, the anode chamber of MDC exhibited a maximum of 83% substrate degradation, and simultaneously, the power output is increased by 2–2.8 times. CCDMSO improved the power production from 0.009 ± 0.003, 1.394 ± 0.06 and 1.423 ± 0.15 mW/m2 to 0.020 ± 0.07, 2.748 ± 0.22 and 3.245 ± 0.16 mW/m2, respectively, for initial F− concentrations of 3,10, and 20 mg/L. Modifying CC with DMSO thus proved to be an efficient and simple methodology for enhancing the overall performance of MDC.

Fluoride Adsorption from Aqueous Solution by Modified Zeolite-Kinetic and Isotherm Studies.

Fluorine is a very common element in the Earth's crust and is present in the air, food, and in natural waters. It never meets in the free state in nature due to its high reactivity, and it comes in the form of fluorides. Depending on the concentration of fluorine absorbed, it may be beneficial or harmful to human health. Similar to any trace element, fluoride ion is beneficial for the human body at low levels, but as soon as its concentration becomes too high, it is toxic, inducing dental and bone fluorosis. The lowering of fluoride concentrations that exceed the recommended standards in drinking water is practiced in various ways around the world. The adsorption process has been classified as one of the most efficient methods for the removal of fluoride from water as it is environmentally friendly, easy to operate, and cost-effective. The present study deals with fluoride ion adsorption on modified zeolite. There are several influential parameters, such as zeolite particle size, stirring rate, solution pH, initial concentration of fluoride, contact time, and solution temperature. The maximum removal efficiency of the modified zeolite adsorbent was 94% at 5 mg/L fluoride initial concentration, pH 6.3, and 0.5 g modified zeolite mass. The adsorption rate increases accordingly with increases in the stirring rate and pH value and decreases when the initial fluoride concentration is increased. The evaluation was enhanced by the study of adsorption isotherms using the Langmuir and Freundlich models. The Langmuir isotherm corresponds with the experimental results of the fluoride ions adsorption with a correlation value of 0.994. The kinetic analysis results of the fluoride ions adsorption on modified zeolite allowed us to demonstrate that the process primarily follows a pseudo-second-order and then, in the next step, follows a pseudo-first-order model. Thermodynamic parameters were calculated, and the ΔG° value is found to be in the range of -0.266 kJ/mol up to 1.613 kJ/mol amidst an increase in temperature from 298.2 to 331.7 K. The negative values of the free enthalpy ΔG° mean that the adsorption of fluoride ions on the modified zeolite is spontaneous, and the positive value of the enthalpy ∆H° shows that the adsorption process is endothermic. The ∆S° values of entropy indicate the fluoride adsorption randomness characteristics at the zeolite-solution interface.

Development of a Point-of-Use Drinking Water Purifier Using Aluminum Oxide-Based Flocculent-Disinfectant Composite

One in every three people in the world still lacks access to clean drinking water. Aside from microbiological pollution, high fluoride content in drinking water is one of the most serious problems in African countries. This study aimed to contribute to the availability of clean water by developing a point-of-use drinking water purifier using an aluminum oxide-based flocculent-disinfectant composite. Batch experiments were conducted to determine factors affecting fluoride removal efficiency (FRE) and E. coli log reduction efficiency. AO of 75 mg/L, 800 mg/L alum, lime (35% alum dose), and 1.5 mg/L Ca(OCl)₂ doses achieved 95% FRE and 5 log10 reductions of E. coli using 15 mg/L as initial fluoride concentration ([F−]0), and 105 CFU/100 mL E. coli concentration. [F−]0 affected FRE but showed no effect on E. coli log reduction. The optimum pH of the solution for both FRE and E. coli log reduction was found to be in the range of 4–8. Three prototypes in powder form were developed. The prototypes were tested on real water samples from the Ethiopian Rift Valley, and the results were found to be within the drinking water standards, thus indicating the capability of the developed products to purify contaminated water for human consumption.

Mesoporous cellulose assemblage Al-doped ferrite for sustainable defluoridation process based on parameters optimization through RSM

In this work, we present defluoridation studies of Mesoporous Cellulose assemblage Al-doped ferrite (MCAF). The characteristic changes in the material were observed by Fourier transform infrared spectroscopy, Scanning electron microscopy, Energy dispersive X-ray spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area analysis and thermal gravimetric analysis. Scaffolds formed due to introduction of aluminium and iron oxides shows collaborative effect on the material. It increases the stability of the material and makes the material mesoporous. Magnetic behavior contributes towards effortless handling of the material. Collective impact of the different parameters on adsorption process were optimized by availing the response surface methodology (RSM). Design of experiments based on 48 runs was formulated and accordingly experiments were conducted. Process optimization was carried out as next step and based on the optimized condition 98 % adsorption was achieved for 20 mg/L initial fluoride concentration. From contour and surface plots between the three independent variables, the optimized adsorption time was 30 min, pH at 6.27 and adsorbent dose at 0.25 g. The optimization condition had a composite desirability of 1. Isotherm studies have revealed that the adsorption process fit well to Freundlich model. The composite displayed maximum absorption capacity of 42.52 mg g-1for fluoride adsorption. Pseudo second order followed for the adsorption of fluoride. Adsorption process found to be spontaneous and exothermic as revealed from thermodynamic studies. Applicability of composite at field conditions was tested with real samples from fluoride endemic areas through column studies. It was found that approximately 5 L of water sample having fluoride concentration 4.81 mg/g was purified with 1 g of the adsorbent. The used adsorbent had been regenerated by 5 % (w/V) sodium nitrate solution. Adsorption desorption cycles shown that up to fourth cycle the % removal of fluoride was more than 90 %.

Enhancement of surface area of iron oxide modified by natural moieties towards defluoridation from water and antibacterial properties

A novel adsorbent has been developed by modifying iron oxide (Fe2O3) surface using humic acid (HA) biopolymer and reduced graphene oxide (rGO), resulting in a highly efficient composite rGO/HA-Fe2O3 with magnetic property for removal of fluoride. The surface area of the composite is found to be 455.6 m2/g which has been enhanced around five times after modification with rGO and HA. Batch adsorption experiments were conducted to determine the optimal conditions for fluoride adsorption. The study found that the maximum fluoride adsorption occurred at adsorbent dose of 0.3 g/L, pH 7, contact time of 120 min. Equilibrium adsorption study data best fitted for the freundlich isotherm model, whereas, kinetic studies follow second-order kinetics which demonstrates multilayer adsorption on a heterogeneous surface with chemisorption type interaction. The adsorption process was found to be feasible, spontaneous, endothermic in nature and also the adsorbent was capable of removing around 99% of fluoride at 100 ppm initial fluoride concentration. The composite demonstrated a fluoride removal capacity of 376.46 and 395.32 mg/g at 30 and 50 °C, respectively, at pH 7, and also exhibited antibacterial properties. The composite was successfully regenerated using a 0.1 M alkaline solution with 98% efficiency and can be reused up to four cycles with an efficiency of 83.1%. The antibacterial property of the composite was assessed using solutions of Escherichia coli in water. This study is unique in its use of humic biopolymer in fluoride adsorption studies with graphene oxide, incorporating iron oxide to maintain a neutral pH during the adsorption process. The high surface area of the rGO/HA-Fe2O3 facilitates for removal of fluoride up to a very high-level fluoride concentration broadening its practical applications in various aspects. Moreover, this adsorbent is cost-effective as the precursors are easily and abundantly available in the natural environment.

Fabricated design of hydrotalcite embedded lanthanum organic frameworks for defluoridation of water

AbstractThe surplus fluoride in drinking water leads to diseases namely fluorosis (dental, skeletal, and non‐skeletal). Hence, to overcome these problems, in this study, hydrotalcite (HT) integrated La‐based metal‐organic frameworks (LaMOFs) namely HT‐LaMOFs was fabricated for fluoride removal. The fabricated HT‐LaMOFs material was well characterized by various characterization methods (x‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Energy‐dispersive X‐ray spectroscopy (EDAX), thermogravimetric analysis (TGA), and differential thermal analysis (DTA)) to find the structural properties and stability of HT‐LaMOFs. To find the fluoride adsorption nature, the batch studies were employed towards fluoride adsorption such as reaction time, co‐ions, HT‐LaMOFs dosage, pH, initial fluoride concentration, selectivity, pHzpc, and temperature studies. The contact time studies results reveals that the defluoridation capacity (DC) of HT‐LaMOFs was towards fluoride was found as 4451 mgF− kg−1 at 30 min than HT (1030 mgF− kg−1 at 50 min). The DC had little influences in the presence of HCO3− ion compared to other ions. Fluoride adsorption mechanism of HT‐LaMOFs was initiated to be electrostatic interaction, ion‐exchange and complexation. Fluoride adsorption onto HT‐LaMOFs was well matched and followed with Langmuir model. Thermodynamic investigations exposed that the adsorption of fluoride onto HT‐LaMOFs followed by spontaneous and endothermic nature. Kinetic studies of HT‐LaMOFs on fluoride capture followed with pseudo‐second‐order and intraparticle diffusion models. Defluoridation by HT‐LaMOFs was followed endothermic with spontaneous nature of adsorption system. The regeneration study results of HT‐LaMOFs revealed that the developed HT‐LaMOFs was regenerable up to six cycles. In addition, field study outcomes revealed that the developed HT‐LaMOFs diminished fluoride concentration under the acceptable limit as 1.5 mg/L.

Fabrication of Ce-La-MOFs for defluoridation in aquatic systems: A kinetics, thermodynamics and mechanisms study

Ce-La-MOFs composites was fabricated via the hydrothermal method, and considered an adsorbent to remove fluoride from aqueous solutions, and its property for defluoridation was discussed in this work. This study evaluated the ideal preparation molar ratio, adsorption period, and initial fluoride concentration. The adsorption mechanism was deduced from the analysis of thermodynamics, kinetics models, and characterization (SEM, XRD, FTIR, EDS, BET, TG). Furthermore, the impact of co-existing ions on the removal efficiency and regeneration of adsorbents was investigated. The studies have shown that the optimum conditions for defluoridation by Ce-La-MOFs were pH close to 3.0, the molar ratio of lanthanum-nitrate, cerium-nitrate, and 2-aminoterephthalic acid (La: Ce: ATPA) equal to 3:1:2, the initial F− concentration of 10 mg L−1, and the adsorption time of 120 min. Under these conditions, the removal efficiency can exceed 90%. The interference experiments suggested that the adsorbent material was highly selective for F−. The existence of most additional ions has a limited influence on the adsorption capacity, with only a minimal amount having an inhibitory effect. Kinetic and thermodynamic studies unveiled that the adsorption procedure is well-fitted with the Langmuir and pseudo-second-order models, and reaches a maximum Langmuir adsorption capacity of 138.64 mg g−1 at 50 °C. The adsorption process involved the integration of ion exchange and electrostatic interaction mechanisms. The regeneration cycle experiments showed that the Ce-La-MOFs composites had a favorable regeneration ability. After four regenerations, the adsorption capacity still reached 36.25 mg g−1 with 73% removal efficiency at C0 = 10 mg L–1.

Facile synthesis and characterization of multi-walled carbon nanotubes decorated with hydroxyapatite from cattle horns for adsorptive removal of fluoride

Developing a new adsorbent for fluoride removal from cattle horn waste materials by a facile chemical method has shown great potential for fluoride removal. This paper reports the synthesis of multi-walled carbon nanotubes decorated with hydroxyapatite from cattle horns (MWCNT-CH) using a facile chemical method. Characterization studies using standard techniques showed that the composite is mesoporous with a rough morphology and contained MWCNTs uniformly encapsulated by the hydroxyapatite forming a crystalline MWCNT-CH composite. Optimization of fluoride adsorption by the as-synthesized composite using Response Surface Methodology (RSM) showed that a maximum fluoride removal efficiency of 80.21% can be attained at initial fluoride concentration = 10 mg/L, pH = 5.25, adsorbent dose = 0.5 g and a contact time of 78 min. ANOVA indicates contribution of the process variables in descending order as pH > contact time > adsorbent dose > initial fluoride concentration. Langmuir isotherm (R2 = 0.9991) best described the process, and the maximum adsorption capacity of fluoride onto the as-synthesized MWCNT-CH composite was 41.7 mg/g. Adsorption kinetics data were best fitted in the pseudo-second-order kinetic model (R2 = 0.9969), indicating chemisorption. The thermodynamic parameter (Δ H = 13.95 J/mol and Δ S = 65.76 J/mol/K) showed that fluoride adsorption onto the MWCNT-CH composite was a spontaneous, endothermic, and entropy-driving process. Moreover, the adsorption mechanism involves ion exchange, electrostatic interaction, and hydrogen bonding. Fluoride was successfully desorbed (using 0.1 M NaOH) from the composite in four cycles, retaining fluoride removal efficiency in the fourth cycle of 57.3%.

Adsorption of Fluoride from Aqueous Solution using Eggshell Pretreated with Plasma Technology

Fluoride is a toxic substance that can cause adverse effects on human health such as dental and skeletal fluorosis. Therefore, the objective of this study was to investigate the adsorption potential of fluoride from aqueous solution using eggshell pretreated with plasma technology and compare to untreated eggshell. The batch adsorption experiments of fluoride from aqueous solution using pretreated eggshell and untreated eggshell were carried out to compare their performances on fluoride removal efficiency, adsorption capacity and isotherm. The effects of adsorption factors of contact time (5 - 360 min), adsorbent dosage (10 - 35 g/L) and particle size of adsorbent (mesh sieve no.12 - 20 or 0.85 - 1.70 mm sieve opening) were studied. The results showed that with the initial fluoride concentration of 10 mg/L, the optimum condition for the adsorption of fluoride from aqueous solution was obtained with pretreated eggshell at contact time of 180 min, adsorbent dosage of 25 g/L and adsorbent size of Sieve no.16 (≤1.18 mm in diameter). With this optimum condition, the maximum fluoride removal efficiency increased from 59.88 % with untreated eggshell to 90.34 %, which was due to an increase in adsorption sites after surface modification process of eggshell. Moreover, the results clearly showed that adsorption isotherm was fitted by Langmuir model, which indicate a monolayered adsorption. The maximum adsorption capacity was 0.341 mg/g for pretreated eggshell, while this was 0.202 mg/g for untreated eggshell. This study showed that eggshell pretreated with plasma technology has potential for the application of the adsorption of fluoride from aqueous solution in the future and needs further investigation on the continuous adsorption column. HIGHLIGHTS Eggshell pretreated with plasma technology (EPPT) was applied for fluoride removal Effects of contact time, adsorbent dosage and size were examined by batch method Maximum fluoride (F) removal efficiency was 90.34 % with EPPT at optimum condition F adsorption on EPPT fitted Langmuir isotherm with maximum capacity of 0.341 mg/g GRAPHICAL ABSTRACT

Fluoride removal from drinking water (Metlaoui, Tunisia) using untreated and treated natural clays

AbstractBACKGROUNDFluorosis is an endemic disease due to an excess of fluoride intake via drinking water. In some regions of the world, removing fluoride from drinking water is a severe problem that is still to be solved. The present study focuses on the use of a natural clay to reduce fluoride concentration in Tunisian contaminated drinking water under relevant working conditions.RESULTSAdsorption experiments were performed in batches using a fluoride aqueous solution. The Box–Behnken model design was used to define the working conditions in which three factors were controlled: clay dosage, contact time and agitation speed. The fixed parameters were the initial fluoride concentration and water pH as observed in Metlaoui, Tunisia in 2021, and experiments were performed at room temperature. Results show that 4 g(50 mL)−1 of clay dosage, 10 min of contact time and 280 rpm of agitation speed could provide 51% fluoride removal using an untreated natural clay. Then, various adsorbents based on this clay were synthesized (chitosan–clay, C6H17NO3Si–clay and thermally treated clays purified using different methods) and tested using the same approach. Among the adsorbents tested, the thermally treated purified clays were the most effective in removing fluoride under ambient conditions with a fluoride removal of 97.5%. Tests performed on drinking water showed that the safety fluoride concentration could be achieved without modifications of the water pH.CONCLUSIONSThe thermally treated clays investigated in this study were effective for fluoride removal under relevant conditions, which can pave the way for future field applications. © 2023 Society of Chemical Industry (SCI).

Removal of fluoride from water using aluminum‐modified activated carbon prepared from khat (Catha edulis) stems

AbstractThis study investigated the fluoride removal efficiency and adsorption of a low‐cost adsorbent prepared using aluminum‐modified activated carbon from khat (Catha edulis) in a batch‐mode reactor. The operating factors, including pH, adsorbent dose, and fluoride initial concentration, were optimized using the Box Behnken design of response surface methodology. The correlation coefficient (R2) for the removal of fluoride was found to be 0.93, showing the validity of the developed quadratic model. The results showed that, under optimized conditions of an adsorbent dose of 2.47 g/L, an initial fluoride concentration of 2.1 mg/L, an initial pH 6.08, and 60 min, 90% fluoride reduction was achieved. Meanwhile, the adsorption isotherm and kinetics followed the Langmuir adsorption model and the Pseudo second model, respectively, with a monolayer adsorption capacity of 0.3065 mg/g. On the other hand, Fourier transform infrared spectroscopy and scanning electron microscopy analyses revealed the formation of major peaks of components such as hydroxyl and carboxylic acids. The same optimum treatment conditions (adsorbent dose of 2.47 g/L, initial pH 6.08, and treatment time of 60 min) managed to remove low initial fluoride concentrations of 3.67 and 4.33 mg/L from real groundwater by 72.84% and 70.37%, respectively. The modified adsorbent prepared in this study successfully treat the low fluoride concentration to a level recommended by WHO for drinking water.