Adsorption Of Fluoride Ions Research Articles

Mentioned Magnesium Oxide Nanomaterials for Effective Adsorption of Congo Red Dye and Fluoride Ions From Aqueous Solutions

This study investigates the synthesis of nanostructured magnesium oxide (MgO) using the auto-combustion method with urea (MgO-U), glycine (MgO-G), and citric acid (MgO-C) as fuels, followed by subsequent calcination. The selection of fuel plays a crucial role in determining the morphology of the nanostructures.X-ray diffraction (XRD) analysis confirms that the samples exhibit a well-crystallized structure with the desired phase and are free of impurities. Field emission scanning electron microscopy (FESEM) shows that MgO-U nanoparticles have diameters ranging from 10 to 20nm, MgO-C nanoparticles from 60 to 80nm, and MgO-G nanoparticles from 80 to 100nm. These MgO nanomaterials are specifically engineered for adsorption applications, aimed at removing toxic organic dyes and fluoride ions from aqueous solutions. Results demonstrate that MgO-G nanoparticles exhibit superior adsorption activity compared to MgO-U and MgO-C nanoparticles, with maximum uptake capacities of 1429 and 14mg/g, respectively. The adsorption processes adhere to second-order kinetic model. These findings highlight the potential application of the synthesized MgO nanoparticles for mitigating water pollution by adsorbing pollutants from aqueous media.

Mechanism of Enhanced Fluoride Adsorption Using Amino-Functionalized Aluminum-Based Metal–Organic Frameworks

Due to the increasing fluoride concentrations in water bodies, significant environmental concerns have arisen. This study focuses on aluminum-based materials with a high affinity for fluorine, specifically enhancing metal–organic frameworks (MOFs) with amino groups to improve their adsorption and defluorination performance. We systematically investigate the factors influencing and mechanisms governing the adsorption and defluorination behavior of amino-functionalized aluminum-based MOF materials in aqueous environments. An SEM, XRD, and FT-IR characterization confirms the successful preparation of NH2-MIL-101 (Al). In a 10 mg/L fluoride ion solution at pH 7.0, fluoride ion removal efficiency increases with the dosage of NH2-MIL-101 (Al), although the marginal improvement decreases beyond 0.015 g/L. Under identical conditions, the fluoride adsorption capacity of NH2-MIL-101 (Al) is seven times greater than that of NH2-MIL-101 (Fe). NH2-MIL-101 (Al) demonstrates effective fluoride ion adsorption across a broad pH range, with superior fluoride uptake in acidic conditions. At a fluoride ion concentration of 7 mg/L, with 0.015 g of NH2-MIL-101 (Al) at pH 3.0, adsorption equilibrium is achieved within 60 min, with a capacity of 31.2 mg/g. An analysis using adsorption isotherm models reveals that the fluoride ion adsorption on NH2-MIL-101 (Al) follows a monolayer adsorption model, while kinetic studies indicate that the predominant adsorption mechanism is chemical adsorption. This research provides a scientific basis for the advanced treatment of fluoride-containing wastewater, offering significant theoretical and practical contributions.

Adsorption of Fluoride Ions Using Si–Al–Mg Layered Double Hydroxides

ABSTRACT Removal of fluoride ions from water environments has become a research topic because high concentrations of fluoride ions in drinking water are harmful to the human body. The adsorption of fluoride ions by a Si – Al – Mg layered double hydroxide (LDH) was investigated in this study. The prepared adsorbent had a hydrotalcite-like LDH structure, which was decomposed by calcination and reconstructed upon contacting water. The adsorption process followed pseudo-second-order kinetics. Granulation of the adsorbent for application to chromatographic operation decreased the adsorption rate constant. Adsorption of fluoride ions was high at 7 < pHeq <10 and decreased at higher pHs. The adsorption mechanism involved ion exchange between the fluoride ions in aqueous solution and chloride ions in the adsorbent as well as physisorption via van der Waals forces. The adsorbent was selective towards fluoride ions over nitrate and sulfate ions, although the adsorption of fluoride ions was suppressed in the presence of chloride, carbonate, and phosphate ions. Chromatographic operation using the granulated adsorbent with an alumina-based binder was characterized by slow kinetics, necessitating a low flow rate for the feed solution. The prepared adsorbent was also used to selectively adsorb fluoride ions from simulated wastewater produced by the semiconductor manufacturing process.

Double cross-linked chitosan sponge encapsulated with ZrO2/soy protein isolate amyloid fibrils nanoparticles for the fluoride ion removal from water

Fluoride ion pollution in water has become a serious threat to the water environment and human health. Adsorption is a promising means of fluoride removal, but it also faces challenges such as the difficult separation and recovery of powdered particles, the leaching of modified coatings from adsorbents, and the structural disintegration of macroscopic adsorbents. For addressing the above challenges, glutaraldehyde/polyvinyl alcohol co-crosslinked ZrSAF/chitosan spongy composites (ZrS/GPCS) were prepared by utilizing encapsulation strategies and cross-linking. ZrS/GPCS-1, ZrS/GPCS-3 and ZrS/GPCS-4 were prepared due to the different amounts of cross-linking agents. The results showed that their fluoride ion adsorption capacities were 42.02, 44.44 and 39.84 mg/g, respectively. The removal of fluoride ions by ZrS/GPCS was maintained at >80 % in the pH range of 4–10. The addition of glutaraldehyde and polyvinyl alcohol affected the contact efficiency of fluoride ions with chitosan and ZrSAF, influencing the adsorption rate and adsorption effect. Glutaraldehyde, polyvinyl alcohol and ZrSAF improved the thermal stability, mechanical properties and structural integrity of chitosan matrix. Both the chitosan matrix and the internal ZrSAF played an important role in fluoride removal, and the removal mechanisms included electrostatic interaction, hydrogen bonding, and complexation.

Highly efficient removal and real-time visual detection of fluoride ions using ratiometric CAU-10-NH2@RhB: Probe design, sensing performance, and practical applications

The extensive use of fluoride in agriculture, industry, medicine, and daily necessities has raised growing concerns about fluoride residue. To date, real-time visual detection and efficient removal of fluoride ions from water remain greatly desirable. Herein, nano-CAU-10-NH2@RhB is introduced as a ratiometric fluorescent probe and efficient scavenger for the intelligent detection and removal of fluoride ions. CAU-10-NH2@RhB is readily obtained through one-pot synthesis and exhibits high sensitivity and selectivity for real-time fluoride ion detection, with a naked-eye distinguishable color change from pink to blue. A portable device for point-of-care testing was developed based on color hue analysis readout using a smartphone. A quantitative response was achieved across a wide concentration range, with a detection limit of 54.2 nM. Adsorption experiments suggest that nano-CAU-10-NH2@RhB serves as an efficient fluoride ion scavenger, with a fluoride adsorption capacity of 49.3 mg/g. Moreover, the mechanistic study revealed that hydrogen bonds formed between fluoride ions and amino groups of CAU-10-NH2@RhB are crucial for the detection and adsorption of fluoride ions. This analysis platform was also used for point-of-care quantitative visual detection of fluoride ions in food, water, and toothpaste.

Enhancing fluoride ion removal from aqueous solutions and glass manufacturing wastewater using modified orange peel biochar magnetic composite with MIL-53

In this study, we developed new adsorbents derived from orange peel biochar (BCOP) and enhanced them with CoFe2O4 magnetic nanoparticles (BCOP/CoFe2O4) and MIL-53(Al) (BCOP/CoFe2O4/MIL-53(Al)). These adsorbents were utilized to remove fluoride (FL) ions from aqueous solutions. We analyzed the properties of these adsorbents using a range of techniques, including FTIR, XRD, SEM, EDX-Map, VSM, Raman spectroscopy, and BET. Our findings indicate that the components interact effectively with one another. Specifically, the BCOP/CoFe2O4/MIL-53(Al) sample exhibited a specific surface area of 196.430 m2/g and a magnetic saturation value of 9.704 emu/g. The maximum FL ion adsorption capacities for BCOP, BCOP/CoFe2O4, and BCOP/CoFe2O4/MIL-53(Al) were 7.618, 16.330, and 37.320 mg/g, respectively, indicating that the modifications significantly enhanced the adsorption capacity. The optimum fluoride ion removal rates using BCOP, BCOP/CoFe2O4, and BCOP/CoFe2O4/MIL-53(Al) were 97.88%, 98.23%, and 99.06%, respectively, at adsorbent doses of 2.5, 1.5, and 0.8 g/L, contact times of 90, 70, and 50 min, pH 4, temperature 50 °C, and a FL concentration of 10 mg/L. Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic, with increased randomness between the adsorbent and fluoride ions. Kinetic analyses showed that fluoride ion adsorption by BCOP/CoFe2O4/MIL-53(Al) followed a pseudo-second-order (PSO) model, while BCOP and BCOP/CoFe2O4 followed a pseudo-first-order (PFO) model. Additionally, the equilibrium data for fluoride ion adsorption on BCOP/CoFe2O4/MIL-53(Al) adhered to the Freundlich model, whereas the other samples conformed to the Langmuir model. The study evaluates the effectiveness of BCOP, BCOP/CoFe2O4, and BCOP/CoFe2O4/MIL-53(Al) in removing FL ions from glass manufacturing wastewater, highlighting the superior performance of the magnetic composite due to its enhanced surface area and functional groups. Notably, the adsorbents demonstrated good regenerative capabilities, maintaining high performance over multiple adsorption cycles.

Adsorption of fluoride ion on Al/La modified acidified attapulgite composite materials

This study developed a novel fluoride ion adsorbent material (Al/La-A) for efficient removal of fluoride ions in water. The crystal structure, elemental composition, surface morphology, specific surface area, thermal stability and surface electronegativity before and after modification were explored using FTIR, XRD, XPS, SEM-EDS, BET, TG-DSC, and zeta potential measurements. Results showed that the fluoride ion adsorption capacity of Al/La-A reached 130.42 mg/g, with the surface area increasing from 65.66 m2/g to 111.68 m2/g, respectively, compared to unmodified attapulgite. Al/La-A maintained excellent fluoride ion removal performance over a wide pH range, with the best adsorption at pH 2. Coexisting ion experiments indicated weak competitive adsorption effects of Cl-, SO42-, and HCO3–, with fluoride ion adsorption remaining above 100 mg/g in the presence of different concentrations of coexisting anions. After 5 adsorption–desorption cycles, Al/La-A exhibited strong adsorption capacity and reusability. The fitting of Langmuir adsorption model and pseudo-second-order kinetic model to the adsorption of fluoride ions on Al/La-A indicated that the adsorption of fluoride ions on Al/La-A was primarily monolayer chemical adsorption. The adsorption mechanism of fluoride ions involved electrostatic interactions, ion exchange, and coordination complexation. This study provides a new research approach for the optimal utilization of attapulgite-based adsorbent materials and the efficient removal of fluoride-containing wastewater.

Simple and modified chitosan gel beads from a natural source as a bio-sorbent for water defluoridation: Experimental and computational perspectives

Water contaminated with fluoride (F -) is widely acknowledged as a major global issue that poses serious health and environmental risks. Adsorption is one of the many fluoride removal treatment methods that has been widely and successfully investigated. In this work, we describe a simple process for making both cross-linked and uncross-linked chitosan gel beads from shrimp waste. SEM, FTIR, XRD and TGA analysis confirmed the successful synthesis of the non-cross-linked chitosan gel beads (Cs beads) and cross-linked chitosan gel (Cs-Ech beads) whose swelling behavior, stability and fluoride removal efficiency were studied. The adsorption conditions were also optimised. An adsorption capacity of 16.59 mg/g was achieved after just 30 min and at pH = 6.8, 10 mg/L and T = 25 °C. It was shown that chitosan gel beads cross-linked with epichlorohydrin removed more fluoride than non-cross-linked chitosan gel beads. The rate of adsorption of fluoride ions is determined by the pseudo-first order kinetic equation. On the other hand, equilibrium data was best described by Langmuir adsorption isotherms. Density functional theory calculations (DFT) based on quantitative analyses were used to explore the interfacial interaction mechanisms, offering valuable perspectives on the inter- and intra-molecular interactions. Further studies on weak interaction were conducted, focusing on the binding contribution of electrostatic interaction and vdW potential. DFT results confirmed the strong adsorption capacity and coordination behavior of F - ions on the cross-linked Cs-Ech, suggesting that the Ech group offers preferred adsorption sites.

Preparation of Fe3O4/NiO Nanomaterials by Electrodeposition and Their Adsorption Performance for Fluoride Ions

The high concentration of fluoride ions in industrial wastewater poses a threat to both human safety and the ecological environment. In this paper, three types of magnetic NiO nanomaterial (MNN) with nickel–iron ratios of 3:1, 2:1, and 1:2 were successfully prepared using the electrodeposition technique to eliminate fluoride ions (F−) from industrial wastewater. The surface morphology, phase composition, and chemical structure of the nanomaterials were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results demonstrate the MNN material’s exceptional adsorption capabilities for fluoride ions (F−) at a nickel–iron ratio of 3:1, with a maximum adsorption capacity of up to 58.3 mg/g. The adsorption process of fluoride on the MNN material was further examined using Langmuir and pseudo-second-order kinetic models, revealing predominantly monolayer adsorption and chemisorption characteristics. When the amount of FeSO4•9H2O added is minimal, only the distinctive peaks of NiO are visible in the product’s spectrum. However, as the Ni/Fe ratio decreases, characteristic peaks of Fe3O4 crystals begin to appear and gradually intensify, indicating an increase in Fe3O4 content within the MNN material. Additionally, the pH level significantly affects the adsorption of fluoride ions (F−) onto the MNN material, with the highest adsorption capacity observed at pH 7.

Performance and mechanism of lanthanum-modified MnO2 for defluoridation from water: The role of MnO2 crystal forms

MnO2 has a large potential for defluoridation, however, the influences of its crystal forms on the performance and mechanism of defluoridation are unknown. The research systematically investigated the defluoridation performance and mechanism of a total of eight materials with different crystal forms of MnO2 (α, β, γ, δ) before and after lanthanum modification, separately. It was indicated that the largest Langmuir adsorption of α-MnO2 and La-γ-MnO2 for fluoride achieved 5.04 mg/g and 42.39 mg/g, correspondingly. The surface hydroxyl group and lanthanum loading of the material proved to be the major contributors to defluoridation. For the adsorption performance of eight materials on fluoride, pH was a significant influencing factor, with the highest adsorption performance at pH 5 ∼ 6. The eight materials showed consistent selectivity for fluoride adsorption in the existence of different anions, with the order of influence on the removal efficiency: CO32–> NO3–> SO42–> Cl–. The studies of FTIR, XPS, and variation of solution pH further illustrated that the adsorption mechanism of the eight materials on fluoride was the ion-exchange interaction and the complexation reaction. In addition, the effect of crystal forms on the adsorption of fluoride ions was further elaborated by DFT analysis. Finally, this study provided an in-depth discussion of the parameters of the dynamic process as well as the nature of the penetration curves by applying the Thomas, Clark, and BDST models.

Adaptive structural modification of Zr-based MOF-808 via solvent and ligand engineering for enhanced fluoride ion adsorption efficiency

The rapid development of industries such as new energy and photovoltaic has led to the generation of a large amount of industrial fluorine wastewater, posing serious threats to water environment and human health. To address this issue, MOF-808 adsorbent was synthesized by controlling the synthesis conditions and modifying the ligand structure. Batch adsorption experiments were conducted by varying experimental conditions, including type of adsorbent, pH, wastewater concentration, adsorption time, temperature, and interfering anions. The adsorption behavior of MOF-808-AA towards fluoride ions was well fitted by the Elovich non-linear kinetic model, as well as the Freundlich and Temkin non-linear isotherm models, indicating that the adsorption behavior was influenced by multiple mechanisms other than just intraparticle diffusion. Thermodynamic results suggested a spontaneous exothermic monolayer chemical adsorption process. Under the conditions of pH 6.0 and T = 298 K, MOF-808-AA exhibited a maximum adsorption capacity of 84.65 mg/g for fluoride ions. Characterization techniques, as well as quantum chemical analysis was employed to analyze the adsorption behavior and predict the reaction sites. The potential mechanism can be summarized as the formation of new bonds between MOF-808-AA and the adsorbed fluoride ions, as well as the weak intermolecular interactions such as hydrogen bonding and vdW forces. Furthermore, MOF-808-AA demonstrated satisfactory reusability and excellent chemical stability during the cyclic process. These findings suggest the potential application of MOF-808-AA for removing fluoride ions from wastewater.

Synthesis, characterization, and evaluation of fluoride removal capacity of calcium-impregnated Euphorbia neriifolia carbon (Ca-Enc).

Fluoride ions must be removed from drinking water in order to prevent fluorosis. Many conventional techniques have been examined for the defluoridation of water all over the world. As far as fluoride ions are concerned, adsorption is the most promising method for the removal of them from aqueous environments. In the present study, we aim to find out how well Euphorbia neriifolia plants can remove fluoride from water using activated and carbonized adsorbents. The Euphorbia neriifolia plant stem was pulverized, dried, and activated using calcium ions extracted from used eggshells collected nearby. The synthesized adsorbent material before and after adsorption of fluoride ions was systematically characterized using FTIR, XRD, SEM with EDAX, TGA, and zero-point charge. The defluoridation capacity of the as-prepared adsorbent material was investigated using batch adsorption studies. Various influencing factors such as contact time, solution pH, initial fluoride concentration, mass of the adsorbent, temperature, and co-existing ions were systematically investigated towards the removal of fluoride ion on prepared adsorbent material. This study was conducted to identify the optimal conditions of prepared adsorbent for the maximum removal of fluoride ions from aqueous solution. A groundwater sample with fluoride content of more than 1.5ppm was taken and studied in this present work. A basic quality indicator of the synthesized material was examined, and its ability to remove fluoride was determined. The findings provide insight into the selective elimination of fluoride ions from aqueous environment.

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.

Waste bamboo-derived magnetically separable bamboo-activated carbon: from characterization to effective remediation of fluoride (F-) ions from water.

An effective and affordable nanoadsorbent, magnetically separable magnetite-activated bamboo carbon (MABC), was obtained from waste bamboo biomass via pyrolysis of bamboo chunks and the co-precipitation method using ferrous and ferric chloride as iron precursors. The synthesized nanosorbents were characterised using XRD, SEM, and DLS techniques to study the surface characteristics and morphology. Chemical composition, optical absorption, and magnetic properties were studied using FTIR spectroscopy, UV-vis spectroscopy, and VSM, respectively. The BET surface area, porosity and surface charge were determined using N2 adsorption-desorption isotherm and zeta potential technique. The cytotoxicity and antimicrobial properties of BC, ABC and MABC were investigated against prokaryotes and eukaryotes. The result demonstrates the nontoxic nature of BC, ABC and MABC, indicating their significant potential for addressing water treatment using sustainable and eco-friendly nanosorbents. Comparative fluoride ion removal studies were performed using ABC and MABC NPs. About 99.6% of F- ions were adsorbed using MABC and 75.9% were adsorbed using ABC. Thus, MABC NPs were used as sorbents for the rest of the fluoride ion adsorption parameters. The batch fluoride ion sorption was performed at various sorption parameters, such as diverse solution pH (1.0-8.0), temperature (25-45 °C), agitation times (10-60 min), and adsorbent dose (0.01-0.04 g L-1). The pseudo-second-order kinetic model exhibited the best fit with F- ion adsorption (95.96 mg g-1) compared with the pseudo-first-order model (12.30 mg g-1), thereby indicating chemisorption adsorption. The exhausted MABC was recovered from the aqueous solution using a bar magnet. Regeneration studies of exhausted MABC were successfully performed using NaOH (0.1 M) as a desorbing agent.

FLUORIDE IONS REMOVAL EFFICIENCY OF NATURAL/ACTIVATED ZEOLITE AND BENTONITE SORBENTS

Addressing the health concern of fluoride ions contamination in water, that cause such deceases as dental and skeletal fluorosis, requires the development of effective adsorption materials for water treatment. Our research objective was to evaluate the adsorption properties and capacities of zeolite and bentonite, sourced from Ukrainian deposits, and their acid-activated forms in relation to fluoride ions and estimate fitting this data to various adsorption models. Characterization of natural and acid-activated zeolite and bentonite sorbents was performed through X-ray diffraction to determine the phase composition of these substances. Adsorption experiments were carried out at different initial fluoride ions concentrations (3, 5, 10 and 15 mg/l) and pH (3.7; 7.5). Acidification (changing pH from 7.5 to 3.7) increase adsorption capacity of natural zeolite and bentonite more than twice. It was found that natural zeolite removes fluoride ions at the level of 67 % at pH 3.7 and a high dosage of sorbent – 10 g/l and an initial concentration of fluoride ions – 5 mg/l, while its acid‑activated form was more effective - the removal of fluoride ions is 86 % at a lower dosage of sorbent – 1 g/l. Similarly, natural bentonite demonstrated a maximum removal efficiency of 45 % at pH 3.7 and a dosage of sorbent – 10 g/l, and its acid-activated form allowed for the removal of fluoride ions of about 83 % at a dosage of sorbent – 2 g/l at the same fluoride ions concentration. It is shown that the Vagelar-Langmuir (VL) isotherm model is the most accurate for describing the process of fluoride ions adsorption by acid-activated forms of natural sorbents, where the R² values are close to 0.999, indicating monolayer adsorption on homogeneous active centers. The obtained results indicate the greater efficiency of acid-activated forms of natural sorbents and the prospects of their use for the removal of fluoride ions from water.

Soy protein isolate amyloid fibril-coated ZrO2 nanoparticles anchored in the polyurethane sponge for rapid and effective fluoride adsorption in the wide pH range

Fluoride ion contamination remains a key challenge for water scarcity. ZrO2 has a good affinity for fluoride ions, but the narrow pH range of application and agglomeration limit its further development. In this work, soybean isolate protein-coated ZrO2 nanoparticles were immobilized into polyurethane sponge to obtain a macroscopic adsorbent (PU-ZrSAF). PU-ZrSAF exhibited fast kinetics (∼30 min), high adsorption capacity (95.24 mg/g), excellent selectivity and resistance to extreme pH. Especially at pH= 3–8, the PU-ZrSAF could still maintain approximately 100% fluoride removal effectiveness. The complexation, electrostatic interaction, and hydrogen bonding interaction between the oxygen and nitrogen functional groups of amyloid fibrils and fluoride ions were major mechanism of fluoride ions adsorption. The secondary conformation of proteins also changed during synthesis and adsorption. The strategy of synthesizing protein by-product based composites with environmentally friendly in this study can be extended to remove other contaminants from water.

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.

Facile synthesis of bismuth and iron co-doped hydroxyapatite nanomaterials for high-performance fluoride ions adsorption

Fluoride is essential, but excessive intake of it in drinking water can have adverse effects. Thus, it must be removed using routine techniques and novel nanomaterials that are environmentally friendly. In this study, we present a facile synthesis of bismuth and iron co-doped hydroxyapatite nanomaterials for high-performance fluoride ions adsorption. The crystal size and degree of crystallinity of the nanomaterials were controlled by the ratios of iron and bismuth precursors. The morphology analysis confirmed the presence of rod-like structures of variable sizes. Calcium, phosphorous, oxygen, bismuth, and iron were detected with the expected elemental state in the co-doped hydroxyapatite material. Batch adsorption experiments showed excellent fluoride ion adsorption performance for bismuth and iron co-doped hydroxyapatite nanomaterials. Pseudo-second order and Langmuir models better describe the experimental findings. This denotes that fluoride uptake through the synthesized material is a chemical process that forms a monolayer, and the surface is homogenous. Thermodynamic data showed that the defluoridation process absorbs heat energy but is spontaneous. Furthermore, in the regeneration and reuse analysis, 74.3% of 10 mg/L fluoride ions were removed even in the fifth cycle, which ensured the nanomaterial’s reusability. The proposed defluoridation mechanisms were electrostatic interaction and ion exchange. Insertions of bismuth and iron ions into hydroxyapatite structure provided a potent sorbent for fluoride removal. Fluoride adsorption performance and the ease of synthesis make this bismuth and iron co-doped hydroxyapatite nanomaterials attractive for water treatment and environmental remediation applications.

Synthesis and characterization of zinc oxide nanocomposite for fluoride ion removal from aqueous solution.

In India, the problem of fluorosis has arisen in semi-urban and rural areas due to the intake of groundwater. The development and application of zinc oxide nanocomposite recently received a lot of attention for fluoride ion removal. Nanotechnology and nanocomposites are widely used by researchers to treat wastewater and control water pollution. Rice husk is extensively found in rice-producing countries such as India that contributes about twenty-two percent of worldwide rice production. Rice husk is used to synthesize nanocellulose using chemical and mechanical approaches. To increase the effectiveness, nanocellulose was modified and coated with a zinc oxide layer to form nanocomposite by chemical precipitation method. Functional groups and morphological, structural, and surface area analysis were characterized by FTIR, FESEM, XRD, and BET. Results revealed that zinc oxide modification on nanocellulose was observed at 440.29 cm-1 and 616.94 cm-1. Maximum fluoride ion removal was achieved at varied initial ion concentrations 2 ppm (86%), 5 ppm (84%), 8 ppm (82%), 10 ppm (80%), 13 ppm (76%), and 15 ppm (75%) at pH 5 using 0.8 g/50 ml at 30°C in 60 min using zinc oxide nanocomposite in the batch study. The isotherm model's best-fitted order was Langmuir (R2=0.999) > Sips (R2=0.996) > Baudu (R2=0.993) > Fritz-Schluender (R2=0.992) > Freundlich (R2=0.986). A pseudo-second-order kinetic model (R2=0.989) fitted well with fluoride ion adsorption data showed chemical adsorption. The thermodynamic study showed the adsorption of fluoride ions due to physical adsorption.

Understanding fluoride adsorption from groundwater by alumina modified with alum using PHREEQC surface complexation model

Fluoride is recognized as a vital ion for human and animal growth because of the critical role it plays in preventing skeletal and dental problems. However, when it is ingested at a higher concentration it can cause demineralization of teeth and bones resulting in fluorosis, therefore, the production of high-adsorptive capacity material which is also cost-effective is necessary for the treatment of fluorides. In this study, aluminium foil is valorised into alumina nanoparticles. The as-prepared alumina was modified with alum in two different ratios of 1:0.5 and 1:1 (alumina to alum w/w%) and later used as adsorbents for the removal of fluoride from groundwater. The adsorbents were characterized by Fourier transform infrared spectroscopy, point of zero charge and X-ray diffraction. Different factors that influence the removal efficiency of fluorides such as pH, initial concentrations, contact time and adsorbent dosage were studied and optimized using a simulated fluoride solution. The optimum conditions obtained were used to test real groundwater. The static experiment conditions were used to calibrate a PHREEQC geochemical model which was later used to simulate the fluoride sorption onto the modified alumina at different conditions. PHREEQC was also coupled with parameter estimation software to determine equilibrium constants for the surface reactions between the fluoride species and the adsorbent in a way that the simulations accurately reflect the outcomes of laboratory experiments. Isotherm studies were carried out on the adsorbents. Both Langmuir and Freundlich's non-linear models fitted well for the equilibrium data. However, with a higher coefficient of regression and low chi-square test values, the adsorption process was more of chemisorption on a monolayer surface. Kinetic studies were also carried out by using the non-linear equations from the pseudo-first-order and pseudo-second-order models. The pseudo-second-order model fitted well for the equilibrium data. The mechanism for the fluoride ion adsorption was also studied by the intraparticle (IP) diffusion model and was found that IP was not the rate-determining factor, and therefore the most plausible mechanism for the sorption process was ion exchange or attraction of fluoride ions to the sorbent surface. The findings obtained from this research show that readily available aluminium waste could be valorised into a useful product that could be employed in the removal of fluoride from water samples, including groundwater, that may contain too much fluoride and pose a risk to the general public's health.