Adsorption mechanism for removing different species of fluoride by designing of core-shell boehmite

Kinetic analysis and mechanism of nitrate, calcium, and cadmium removal using the newly isolated Pseudomonas sp. LYF26

The co-existence of heavy metals and nitrate (NO3--N) pollutants in wastewater has been a persistent global concern for a long time. A strain LYF26, which can remove NO3--N, calcium (Ca(II)), and cadmium (Cd(II)) simultaneously, was isolated to explore the properties and mechanisms of synergistic contaminants removal. Different conditions (Cd(II) and Ca(II) concentrations and pH) were optimized by Zero-, Half-, and First-order kinetic analyses to explore the environmental parameters for the optimal effect of strain LYF26. Results of the kinetic analyses revealed that the optimal culture conditions for strain LYF26 were pH of 6.5, Cd(II) and Ca(II) concentrations of 3.00 and 180.00 mg L-1, accompanied by Ca(II), Cd(II), and NO3--N efficiencies of 53.10%, 90.03%, and 91.45%, respectively. The removal mechanisms of Cd(II) using strain LYF26 as a nucleation template were identified as biomineralization, lattice substitution, and co-precipitation. The differences and changes of dissolved organic matter during metabolism were analyzed and the results demonstrated that besides the involvement of extracellular polymeric substances in the precipitation of Cd(II) and Ca(II), the high content of humic acid-like species revealed a remarkable contribution to the denitrification process. This study is hopeful to contribute a theory for further developing microbially induced calcium precipitation used to treat complex polluted wastewater.

Phosphogypsum-Modified Vinasse Shell Biochar as a Novel Low-Cost Material for High-Efficiency Fluoride Removal

In this study, vinasse shell biochar (VS) was easily modified with phosphogypsum to produce a low-cost and novel adsorbent (MVS) with excellent fluoride adsorption performance. The physicochemical features of the fabricated materials were studied in detail using SEM, EDS, BET, XRD, FTIR, and XPS techniques. The adsorption experiments demonstrated that the adsorption capacity of fluoride by MVS was greatly enhanced compared with VS, and the adsorption capacity increased with the pyrolysis temperature, dosage, and contact time. In comparison to chloride and nitrate ions, sulfate ions significantly affected adsorption capacity. The fluoride adsorption capacity increased first and then decreased with increasing pH in the range of 3-12. The fluoride adsorption could be perfectly fitted to the pseudo-second-order model. Adsorption isotherms matched Freundlich and Sips isotherm models well, giving 290.9 mg/g as the maximum adsorption capacity. Additionally, a thermodynamic analysis was indicative of spontaneous and endothermic processes. Based on characterization and experiment results, the plausible mechanism of fluoride adsorption onto MVS was proposed, mainly including electrostatic interactions, ion exchange, precipitation, and hydrogen bonds. This study showed that MVS could be used for the highly efficient removal of fluoride and was compatible with practical applications.

The model and mechanism of adsorptive technologies for wastewater containing fluoride: A review

With the continuous development of society, industrialization, and human activities have been producing more and more pollutants. Fluoride discharge is one of the main causes of water pollution. This review summarizes various commonly used and effective fluoride removal technologies, including ion exchange technology, electrochemical technology, coagulation technology, membrane treatment, and adsorption technology, and points out the outstanding advantages of adsorption technology. Various commonly used fluoride removal techniques as well as typical adsorbent materials have been discussed in published papers, however, the relationship between different adsorbent materials and adsorption models has rarely been explored, therefore, this paper categorizes and summarizes the various models involved in static adsorption, dynamic adsorption, and electrosorption fluoride removal processes, such as pseudo-first-order and pseudo-second-order kinetic models, Langmuir and Freundlich isotherm models, Thomas and Clark dynamic adsorption models, including the mathematical equations of the corresponding models and the significance of the models are also comprehensively summarized. Furthermore, this comprehensive discussion delves into the fundamental adsorption mechanisms, quantification of maximum adsorption capacity, evaluation of resistance to anion interference, and assessment of adsorption regeneration performance exhibited by diverse adsorption materials. The selection of the best adsorption model not only predicts the adsorption performance of the adsorbent but also provides a better description and understanding of the details of each part of the adsorption process, which facilitates the adjustment of experimental conditions to optimize the adsorption process. This review may provide some guidance for the development of more cost-effective adsorbent materials and adsorption processes in the future.

Efficient Fluoride Wastewater Treatment Using Eco-Friendly Synthesized AlOOH

Fluoride ion is essential for health in small amounts, but excessive intake can be toxic. Meeting safety regulations for managing fluoride ion emissions from industrial facilities with both cost-effective and eco-friendly approaches is challenging. This study presents a solution through a chemical-free process, producing a boehmite (AlOOH) adsorbent on aluminum sheets. Utilizing cost-effective Al foil and DI water, rather than typical precursors, yields a substantial cost advantage. The optimized AlOOH adsorbent demonstrated a high fluoride ion removal rate of 91.0% in simulated wastewater with fluoride ion concentrations below 20 ppm and displayed a similar performance in industrial wastewater. Furthermore, the AlOOH adsorbent exhibited excellent reusability through a simple regeneration process and maintained stable performance across a wide pH range of 4 to 11, demonstrating its capability to adsorb fluoride ions under diverse conditions. The efficiency of the AlOOH adsorbent was validated by a high fluoride ion removal efficiency of 90.9% in a semi-batch mode flow cell, highlighting its potential applicability in engineered water treatment systems. Overall, the AlOOH adsorbent developed in this study offers a cost-effective, eco-friendly, and sustainable solution for effectively removing fluoride ion from surface waters and industrial wastewaters.

Remediation of water tainted with noxious aspirin and fluoride ion using UiO-66-NH2 loaded peanut shell

One green adsorbent, UiO-66-NH2 modified peanut shell (c-PS-MOF), was prepared in a green synthetic route for improving the capture level of aspirin (ASP) and fluoride ion (F-). The adsorption properties of c-PS-MOF were evaluated by batch experiments and its physicochemical properties were explored by various characterization methods. The results showed that c-PS-MOF exhibited a wide range of pH applications (ASP: 2-10; F-: 3-12) and high salt resistance in the capturing processes of ASP and F-. The unit adsorption capacity of c-PS-MOF was as high as 84.7 mg·g-1 for ASP as pH = 3 and 11.2 mg·g-1 for F- under pH = 6 at 303 K from Langmuir model, respectively. When the solid-liquid ratio was 2 g·L-1, the content of ASP (C0 = 100 mg·L-1) and F- (C0 = 20 mg·L-1) in solution can be reduced to 0.48 mg·L-1 and 1.05 mg·L-1 separately. The recycling of c-PS-MOF can be realized with 5 mmol·L-1 NaOH as eluent. Analysis of simulated water samples showed that c-PS-MOF could be used to remove ASP and F- from actual water. The c-PS-MOF is promising to bind ASP and F- from rivers, lakes, etc.

Synthesis of Composites for the Removal of F- Anions

This work presents the synthesis of amine and ferrihydrite functionalized graphene oxide for the removal of fluoride from water. The synthesis of the graphene oxide and the modified with amine groups is developed by following the modified Hummer's method. Fourier transform infrared spectrometry, X-ray, Raman spectroscopy, thermogravimetric analysis, surface charge distribution, specific surface area and porosity, adsorption isotherms, and the van't Hoff equation are used for the characterization of the synthesized materials. Results show that the addition of amines with ferrihydrite generates wrinkles on the surface layers, suggesting a successful incorporation of nitrogen onto the graphene oxide; and as a consequence, the adsorption capacity per unit area of the materials is increased.

Hierarchical camellia-like metal–organic frameworks via a bimetal competitive coordination combined with alkaline-assisted strategy for boosting selective fluoride removal from brick tea

Developing an efficient and easy scale-up adsorbent with excellent fluoride adsorption and selectivity from brick tea is urgently desired. However, the separation of fluoride from tea is particularly challenging due to it contains abundant active compounds. Herein, we report ultrahigh fluoride adsorption from brick tea by a hierarchical camellia-like bimetallic metal-organic frameworks (MOFs). The hierarchical camellia-like Ca₂Al₁Fu is fabricated via a Ca/Al competitive coordination combined with alkaline-assisted strategy to tailor the morphology and porous structure. Subsequently, we systematically explore how the kinetic, thermodynamic, pH, and coexisting ions parameters employed during fluoride adsorption influence the resulting uptake behavior of Ca₂Al₁Fu. Further, sensory evaluation of the tea after adsorption is explored to determine the optimal dose that makes Ca₂Al₁Fu as a practical adsorbent for application. Importantly, the fluoride adsorption capacity of optical CaAlFu with mixed CaAl metals molar ratio of 2:1 is 3.15 and 2.11 times higher than that of pristine CaFu and AlFu, respectively. Theoretical results reveal that the boosting selective fluoride removal can be ascribed to the specific interactions between fluoride and CaAl coordinatively unsaturated bimetallic centers. These results present an effective design strategy for the construction of bimetallic MOFs with hierarchically porous structures for broad prospect in adsorption-based applications.

Facile synthesis of nanostrip-structured pseudo-boehmite "nest" for nano-TiO2/γ-Al2O3construction to remove tetracycline hydrochloride in water

A particular bird's nest-like pseudo-boehmite (PB) composed of cohesive nanostrips was prepared by a novel and facile approach based on the reaction of Al-Ga-In-Sn alloy and water, together with ammonium carbonate. The PB possesses a large specific surface area (465.2 m²g^-1), pore volume (1.0 cm³g^-1), and pore diameter (8.7 nm). Subsequently, it was utilized as a precursor to form the TiO₂/γ-Al₂O₃nanocomposite for tetracycline hydrochloride removal. The removal efficiency can reach above 90% at TiO₂:PB = 1:1.5 under the Sunlight irradiation simulated by a LED lamp. Our results indicate that the nest-like PB is a promising carrier precursor for efficient nanocomposite catalysts.

Comparison of Adsorption Capacity and Removal Efficiency of Strontium by Six Typical Adsorption Materials

The rapid development and application of nuclear technology have been accompanied by the production of large amounts of radioactive wastes, of which Sr is a typical nuclide. In this study, six typical materials with strong adsorption properties, namely activated carbon, kaolin, montmorillonite, bentonite, zeolite, and attapulgite, were selected. Their adsorption mechanisms were investigated by analyzing their adsorption isotherms, adsorption kinetics, micromorphologies, element contents, specific surface areas, crystal structures, and functional groups. The results showed that the adsorption efficiency of Sr by the six adsorbents can be ranked as zeolite, bentonite, attapulgite, montmorillonite, activated carbon, and kaolin, among which the maximum adsorption capacity of zeolite was 4.07 mg/g. Based on the adsorption kinetic and thermodynamic fitting results, the adsorption of Sr by zeolites, bentonite and attapulgite is consistent with Langmuir model, the pseudo-first-order and pseudo-second-order model, and the adsorption process of Sr (II) by montmorillonite, activated carbon and kaolinite is consistent with the Freundlich model and corresponds to non-uniform adsorption. The main mechanisms of the six materials are physical adsorption, ion exchange and complexation. In summary, zeolite, bentonite, and attapulgite, especially zeolite, are highly effective for the treatment of radioactive wastewater containing strontium and have great application value in the treatment of radioactive wastes.

Rationally designed and hierarchically structured functionalized aluminium organic frameworks incorporated chitosan hybrid beads for defluoridation of water

In this present investigation, aluminium (Al³⁺) fabricated 2-aminobenzene-1,4-dicarboxylic acid (ABDC) namely Al@ABDC metal organic frameworks (MOFs) was developed for defluoridation studies. The unique advantages of developed MOFs possess high selectivity, high porosity and enhanced surface area but the developed powder form of Al@ABDC MOFs has several limitations in field applications like slow filtration and column blockage. To prevail over these troubles, biopolymer namely chitosan (CS) supported Al@ABDC MOFs namely Al@ABDC-CS beads were developed for effective fluoride adsorption from water. The synthesized Al@ABDC-CS beads were employed for the retention of fluoride in batch level. The defluoridation capacities (DCs) of Al@ABDC MOFs and Al@ABDC-CS beads were found to be 4880 and 4900 mgF^- kg^-1 respectively. The influencing parameters of adsorption method namely agitation time, adsorbent dosage, initial fluoride concentration, pH, co-existing anions and temperature were exploit to get utmost defluoridation capacity (DC) of Al@ABDC-CS beads. The experimental data of Al@ABDC-CS beads have been evaluated utilizing Langmuir, Fruendlich and Dubinin-Radushkevich (D-R) isotherms. The defluoridation nature of Al@ABDC-CS beads was determined by the thermodynamic parameters. The order of reaction of Al@ABDC-CS beads was studied using various kinetic models. The regeneration and field water studies of Al@ABDC-CS beads were also carried out to check their reusability and suitability at field conditions.

Multi-step Phase Transformation from Metal-Organic Frameworks to Inorganic Compounds for High-Purity Th(IV) Generation

The generation of high-purity thorium is the precondition for next-generation nuclear energy; however, this remains a challenging task. To this end, we present herein an ultrasimple technique with the combination of crystallization plus phase transformation. Crystallization into ECUT-68 is found to show almost 100% selective uptake of Th(IV) over rare earth and UO₂²⁺ ions, while multistep phase transformation from metal-organic frameworks (MOFs) to inorganic compounds is found to directly generate inorganic Th(IV) compound and then Th(IV) solution, suggesting its superior application in the generation of high-purity thorium.

Antimicrobial nanocomposite adsorbent based on poly(meta-phenylenediamine) for remediation of lead (II) from water medium

In this study, poly(m-phenylenediamine)@ZnO (PmPDA@ZnO) nanocomposite was fabricated by in-situ chemical oxidative polymerization for the effective lead(II) removal from aqueous solutions. PmPDA@ZnO was characterized by several instrumental methods like FTIR, XRD, EDX, TGA, FESEM, TEM, zeta potential, and BET. The TEM images showed a core–shell-like structure for the PmPDA@ZnO nanocomposite. TGA results showed that the thermal stability of the PmPDA@ZnO nanocomposite was higher than the PmPDA. The maximum adsorption of lead (II) onto PmPDA@ZnO nanocomposite was obtained at pH 6, adsorbent dosage 60 mg, lead(II) ion concentration 90 mg/L, and agitation time 90 min. Langmuir and Freundlich's isotherm models were evaluated to simulate the lead(II) sorption via empirical data. Langmuir's model was in good agreement with empirical data with a maximum adsorption capacity (Q_max) of 77.51 mg/g. The kinetic data adsorption fitted best the pseudo-second-order model. The values of thermodynamic parameters of ΔS° and ΔH° were obtained 0.272 J/mol K, and 71.35 kJ/mol, respectively. The spontaneous and endothermic behavior of the adsorption process was confirmed by the negative and positive response of ΔG° and ΔH°, respectively. Moreover, the addition of coexisting cations e.g. cobalt (II), nickel (II), calcium (II), and copper (II) had no significant effect on the removal efficiency of lead(II). Adsorption–desorption studies showed that the PmPDA@ZnO nanocomposite can be remarkably regenerated and reused after three sequential runs without a significant decline in its adsorption performance. The antimicrobial activities of PmPDA@ZnO nanocomposite were evaluated against Escherichia coli and Staphylococcus aureus bacteria species. These results confirmed that the PmPDA@ZnO nanocomposite could be a good candidate for water decontamination.

Synergistic removal of fluoride from groundwater by seed crystals and bacteria based on microbially induced calcium precipitation

A new hypothesis that seed crystals (SC) and bacteria based on microbially induced calcium precipitation (MICP) synergistically remove fluoride (F^-) from groundwater was proposed, with a focus on evaluating the defluoridation potential of this method and revealing its F^- removal mechanism. The crucial conditions were optimized to reduce preparation and operation costs. SC furnished more available binding sites due to the existence of bacteria, and the reuse experiments showed that the defluoridation efficiency of SC still remained a high level after 14 cycles (70.10%), with a residual F^- concentration of 0.96 mg L^-1. The SEM-EDS, FTIR and XRD analyses indicated the predominant F^- removal mechanism of SC could be ascribed to the chemisorption, ion exchange, and co-precipitation. Moreover, ion exchange and co-precipitation (PO₄^3- involvement) were validated more contributive than chemisorption (CaCO₃ and CaSO₄ involvement). As a feasible, reusable, and eco-friendly technique, SC suggests promising applications in the treatment of fluoride-contaminated groundwater.

Parallel-slipped π-π electron-donor-acceptor in adsorption process: Molecular dynamics simulation

Molecular dynamics simulation was used to study the adsorption of single wall carbon nanotubes (SCNT) in levofloxacin (LEV) solutions of different concentrations by Radial distribution function, mean square displacement and interaction energy. The results showed that levofloxacin molecules were adsorbed around the carbon nanotubes. The adsorption effect of large concentration solution was not as good as that of low concentration solution because of agglomeration. LEV molecules with different concentration were free diffusion within 15ns, and gradually agglomerated under the influence of adsorption. The energy change is proportional to the concentration of the molecule. The distance between benzene rings corresponding to the agglomeration effect of levofloxacin molecules was 0.4 nm, which should be the effect of parallel-slipped π-π electron-donor-acceptor (EDA) interactions. The simulation results are valuable to study the adsorption and removal of benzenes by adsorbent.

Insight into the ion exchange in the adsorptive removal of fluoride by doped polypyrrole from water

In this study, the polypyrrole (PPy) samples doped with Cl^- (PPy-Cl), SO₄^2- (PPy-SO4) and SO₄^2-+Cl^- (PPy-SO4+Cl) were synthesized by chemical polymerization for the adsorptive removal of fluoride ion from water. The structure and morphology of the as-prepared PPy samples were characterized by FT-IR, BET, SEM, XPS, and zeta potential. The adsorption experiments revealed that the PPy-Cl exhibited faster kinetics and higher adsorption capacity (13.98 mg/g), more than 4 times that of PPy-SO4 (3.08 mg/g) and PPy-SO4+Cl (3.17 mg/g). The kinetics of the adsorption followed the pseudo-second-order model and the adsorption isotherm data fitted well to the Langmuir model. FT-IR, EDX, and XPS tests for PPy samples before and after fluoride adsorption demonstrated that anion exchange between F^- and Cl^- or SO4^2- was the prior mechanism for fluoride ion removal from water. Cl^- was more favorable than SO₄^2- in the ion exchange with F^-. Meanwhile, the Cl^- or SO₄^2- exchanged with F^- was mainly bound to the active nitrogen that accounts for 6% of the total nitrogen in PPy molecular matrix. Further study of zeta potential and pH influence experiment demonstrated the electrostatic interaction is auxiliary interaction for the fluoride removal by doped PPy samples.

Highly efficient fluoride removal from water using 2D metal-organic frameworks MIL-53(Al) with rich Al and O adsorptive centers

In this study, metal-organic framework MIL-53(Al) was synthesized and studied to understand the different mechanisms between normal MIL-53(Al) and 2D metal-organic framework MIL-53(Al) for removing fluoride. Comparatively, the 2D MIL-53(Al) had two-dimensional linear morphology rather than block shape, indicating more expose adsorptive sites than normal MIL-53(Al). The batch adsorption experiments were applied to investigate the performance of 2D MIL-53(Al), including pH, adsorption kinetics, and thermodynamics. The 2D MIL-53(Al) (75.50 mg/g) showed better adsorption capacity than normal MIL-53(Al) (35.63 mg/g). The adsorption process of 2D MIL-53(Al) followed the pseudo-first-order model and Langmuir model. The adsorption mechanism of this material was further studied by using experimental characterization and density functional theory calculations in detail. The main adsorptive sites were Al and O in the 2D MIL-53(Al), and the relationship between fluoride binding with Al and O was HF₂ ^- > HF > F^-. The species of fluoride were HF₂ ^-, HF, F at different pH and concentrations. Hence, this study provides a significant way on the application of two-dimensional materials for removing fluoride.

Microbially induced calcium precipitation based simultaneous removal of fluoride, nitrate, and calcium by Pseudomonas sp. WZ39: Mechanisms and nucleation pathways

A simultaneous denitrifying and mineralizing bacterium, Pseudomonas sp. WZ39 was isolated for fluoride (F^-), nitrate (NO₃^--N), and calcium (Ca²⁺) removal. Strain WZ39 exhibited a remarkable defluoridation efficiency of 87.49% under a pH of 6.90, F^- and Ca²⁺ concentration of 1.99 and 201.88 mg L^-1, respectively. EEM, SEM-EDS, XRD, and FTIR analyses elucidated the chemical adsorption and co-precipitation with calcium salt contributed to the removal of F^-. The mechanisms of biomineralization were also investigated by determining the role of bound and unbound extracellular polymeric substances (EPS), cell wall, and calcium channel in nucleation. The results showed that bacteria can promote nucleation on the templates of cell walls or EPS through the electrostatic effect. The presence of the calcium channel blocker inhibited the transport of intracellular Ca²⁺ to the extracellular environment. The outcome of the present research can provide a theoretical basis for the understanding of MICP phenomenon and the efficient treatment of F^- containing groundwater.

A novel ICT-based chemosensor for F- and its application in real samples and bioimaging

A novel colorimetric and fluorescent chemosensor MQS-Si with intramolecular charge transfer character has been designed and synthesized. The chemosensor shows exclusively "off-on" fluorescence response toward F^- at 620 nm in HEPES (pH 7.4): DMSO solution (7:3, v/v), which is attributed to the specific cleavage of Si-O bond. The ultrasensitive detection limit for F^- in the fluorescence measurement is down to 30 nM. Application of the chemosensor has been demonstrated by selective detection of F^- in drinking water, urine and serum samples and fluorescence imaging of F^- in living cells and zebrafish, which proves that MQS-Si has a promising application in vitro and in vivo detection of F^- and may be utilized for the diagnosis of fluorosis and esteofluorosis.

Removal of fluoride from industrial wastewater by using different adsorbents: A review

Many industries such as iron and steel metallurgy, copper and zinc smelting, the battery industry, and cement manufacturing industries discharge high concentrations of fluoride-containing wastewater into the environment. Subsequently, the discharge of high fluoride effluent serves as a threat to human life as well as the ecological ability to sustain life. This article analyses the advantages and drawbacks of some fluoride remediation technologies such as precipitation and flocculation, membrane technology, ion exchange technology, and adsorption technology. Among them, adsorption technology is considered the obvious choice and the best applicable technology. As such, several adsorbents with high fluoride adsorption capacity such as modified alumina, metal oxides, biomass, carbon-based materials, metal-organic frameworks, and other adsorption materials including their characteristics have been comprehensively summarized. Additionally, different adsorption conditions of the various adsorbents, such as pH, temperature, initial fluoride concentration, and contact time have been discussed in detail. The study found out that the composite synergy between different materials, morphological and structural control, and the strengthening of their functional groups can effectively improve the ability of the adsorbents for removing fluoride. This study has prospected the direction of various adsorbents for removing fluoride in wastewater, which would serve as guiding significance for future research in the field.

Defluorination by ion exchange of SO42- on alumina surface: Adsorption mechanism and kinetics

Electrostatic and complexation effects have been considered as the primary adsorption mechanisms for defluorination using aluminum based materials, while the effect of ion exchange between anions and fluorine ion has been mostly ignored, although synthesized alumina materials usually contain a large amount of anions, such as SO₄^2-, NO₃^-, and Cl^-. In this study, the effect of anions exchanges and its key role on defluorination were systematically investigated for adsorption by aluminas loaded with various typical anions (SO₄^2-, NO₃^- and Cl^-). Experimental results showed that SO₄^2-- loading alumina had the best defluorination performance (94.5 mg/g), much higher than NO₃^- (45.0 mg/g) and Cl^- (19.1 mg/g). The contribution ratio of ion exchange between SO₄^2- and F^- was as high as 20-60% in all potential defluorination mechanisms. By using Density Functional Theory calculation, the detailed mechanism revealed that the ion exchange process was mainly driven by the tridentate chelation of SO₄^2- which reduced the exchange energy ( [Formula: see text] 4.8 eV). Our study clearly demonstrated that ion exchange between SO₄^2- and F^- is a critical mechanism in defluorination using aluminum-based materials and provides a potential alternative method to enhance the adsorption performance of modified alumina.

Iron Oxide (Fe3O4)-Supported SiO2 Magnetic Nanocomposites for Efficient Adsorption of Fluoride from Drinking Water: Synthesis, Characterization, and Adsorption Isotherm Analysis

This research work reports the magnetic adsorption of fluoride from drinking water through silica-coated Fe3O4 nanoparticles. Chemical precipitation and wet impregnation methods were employed to synthesize the magnetic nanomaterials. Moreover, the synthesized nanomaterials were characterized for physicochemical properties through scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray powder diffraction. Screening studies were conducted to select the best iron oxide loading (0.0–1.5 wt%) and calcination temperature (300–500 °C). The best selected nanomaterial (0.5Fe-Si-500) showed a homogenous FeO distribution with a 23.79 nm crystallite size. Moreover, the optimized reaction parameters were: 10 min of contact time, 0.03 g L−1 adsorbent dose, and 10 mg L−1 fluoride (F−) concentration. Adsorption data were fitted to the Langmuir and Freundlich isotherm models. The Qm and KF (the maximum adsorption capacities) values were 5.5991 mg g−1 and 1.869 L g−1 respectively. Furthermore, accelerated adsorption with shorter contact times and high adsorption capacity at working pH was among the outcomes of this research work.

Enhanced fluoride adsorption from aqueous solution by zirconium (IV)-impregnated magnetic chitosan graphene oxide

In this study, zirconium (IV)-impregnated magnetic chitosan graphene oxide (Zr-MCGO) was synthesized for removing fluoride from aqueous solution in batch mode. Characterization approaches (pH_pzc, FTIR, SEM, XRD, VSM, Raman, BET, and XPS) proved the successful incorporation of Zr into the adsorbent. Zr-MCGO exhibited a relatively favorable and stable capacity of defluoridation at lower pH with a wide range of pH from 4.0 to 8.0, while there was slightly negative effect of ionic strength on adsorption. In addition, Elovich kinetic model and Koble-Corrigan isotherm model could describe the uptake of fluoride well. The adsorption capacity was 8.84 mg/g at 313 K and Zr-MCGO was easily separated from mixtures using external magnet. Based on the experiments and XPS, electrostatic force, ligand exchange, and Lewis acid-base interaction might be potential adsorption mechanisms. Pseudo-second-order model was more compatible with the desorption process by 0.01 mol/L NaHCO₃ solution. Therefore, Zr-MCGO was a promising candidate for defluoridation on wastewater pollution remediation.