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.

Fluoride removal using a rotating anode electro-coagulation reactor: Parametric optimization using response surface methodology, isotherms and kinetic studies, economic analysis and sludge characterization.

The presence of fluoride in drinking water can cause various diseases, such as dental fluorosis and skeletal fluorosis. The present study aims to intensify the fluoride removal using a rotating anode electro-coagulation (EC) reactor with providing the proper hydrodynamics conditions. This fluoride removal is modeled and optimized using Response Surface Methodology (RSM) and central composite design (CCD) with varying operational parameters (rotation speed: 20-80 RPM, current: 0.2-1.0 A, initial fluoride concentration: 8-40 mg/L and time: 15-75 min). The maximum fluoride removal is obtained as 96.87% (predicted) and 95.40% (experimental) for the optimized process parameters, initial concentration of 32 mg/L, 0.8 A current, 60 min, and 60 RPM of rotating speed. Kinetic analysis reveals that the removal process adheres to a second-order kinetic model, suggesting that the rate of fluoride removal is dependent on the concentration of fluoride ions present. Isothermal studies indicate that the effective sorption of fluoride onto the generated flocs follows a sips isotherm. The optimal cost analysis is carried out to determine the operational cost as 0.256 USD/m3 for F removal of 93.49% at initial concentration 24 mg/L, time 50 min, current 0.7 A, and rotation 70 rpm and presenting a cost-effective solution for fluoride mitigation. Further, characterizations of the resultant sludge through X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and the Toxicity Characteristic Leaching Procedure (TCLP) confirmed the safe disposal potential of the sludge. The findings show a promising approach for fluoride removal, combining high efficiency, economic viability, and environmental safety.

Cerium-based metal-organic-frameworks with ligand tuning of the microstructures for fluoride adsorption: linear and nonlinear kinetic and isotherm adsorption models.

We present the synthesis and characterisation of three Ce-based metal-organic frameworks (Ce-MOFs) using fumaric acid (Fu), terephthalic acid (BDC), and trimesic acid (H3BTC) as linkers. The use of different linkers influenced the size of the MOF particles, surface area, crystallinity, and microporous structure. The successful implementation of Ce-Fu, Ce-BDC, and Ce-H3BTC MOFs for fluoride ion removal from wastewater was carried out, in which Ce-Fu MOFs exhibited a maximum adsorption capacity (AC) of 64.2 mg g-1. The study also reveals that the use of ultrasound as a mediator for adsorption study over conventional method gives rapid adsorption rate, in which 85% of the fluoride uptake took place just in 10 min and achieved maximum AC in 30 min. The kinetics data were most accurately explained by the pseudo-second-order model (PSO). The existence of co-ions such as NO3-, Cl-, HCO3-, SO42-, Br-, CO32-, and PO43- has a substantial effect on fluoride removal. The mechanism between the fluoride ions and the MOF surface took place via the electrostatic force and the ion exchange process, confirmed using X-ray photoelectron spectroscopy (XPS) and delsa nano. The material is sustained its relatively higher F- ions removal efficiency up to the five cycles. This research might help in the development of novel microporous Ce-based MOFs since it possesses a highly stable crystalline structure in water, suggesting a promising role in aqueous applications.

Controllable and selective fluoride precipitation from phosphate-rich wastewater.

Industrial wastewater containing high levels of fluoride and phosphate poses significant environmental challenges and results in the waste of non-renewable resources. This study investigates the use of La(OH)3 as a precipitating agent to selectively remove and separate fluoride from phosphate in such wastewater. The findings indicate that fluoride removal efficiency is highly dependent on the pH level and La(OH)3 dosage. Using Response Surface Methodology, the optimal conditions for fluoride precipitation were identified as a pH range of 1.0 to 2.5, a reaction time of 60-80 min, a La/3F molar ratio of 2.0, and reaction temperature of 25 °C. Under these parameters, the fluoride removal efficiency exceeded 96.9 %, while phosphate removal remained around 7.2 %. Further Density Functional Theory calculations and characterization confirmed La(OH)3 has a strong affinity for fluoride than phosphate under acidic conditions, leading to the formation of a LaF3 precipitate without forming LaPO4, effectively separating fluoride from phosphate. These results demonstrate an efficient strategy for treating wastewater with high fluoride and phosphate content, enabling the selective precipitation and recovery of these elements for sustainable management.

Aluminum-Crosslinked Nanocellulose Scaffolds for Fluoride Removal.

Anionic carboxylated cellulose nanofibers (CNF) are effective media to remove cationic contaminants from water. In this study, sustainable cationic CNF-based adsorbents capable of removing anionic contaminants were demonstrated using a simple approach. Specifically, the zero-waste nitro-oxidization process was used to produce carboxylated CNF (NOCNF), which was subsequently converted into a cationic scaffold by crosslinking with aluminum ions. The system, termed Al-CNF, is found to be effective for the removal of fluoride ions from water. Using the Langmuir isotherm model, the fluoride adsorption study indicates that Al-CNF has a maximum adsorption capacity of 43.3 mg/g, which is significantly higher than that of alumina-based adsorbents such as activated alumina (16.3 mg/g). The selectivity of fluoride adsorption in the presence of other anionic species (nitrate or sulfate) by Al-CNF at different pH values was also evaluated. The results indicate that Al-CNF can maintain a relatively high selectivity towards the adsorption of fluoride. Finally, the sequential applicability of using spent Al-CNF after the fluoride adsorption to further remove cationic contaminant such as Basic Red 2 dye was demonstrated. The low cost and relatively high adsorption capacity of Al-CNF make it suitable for practical applications in fluoride removal from water.

Concurrent arsenic, fluoride, and hydrated silica removal from deep well water by electrocoagulation: Comparison of sacrificial anodes (Al, Fe, and Al-Fe).

Some studies have reported the removal of As (As) and fluoride (F-) using different sacrificial anodes; however, they have been tested with a synthetic solution in a batch system without hydrated silica (SiO2) interaction. Due to the above, concurrent removal of As, F-, and SiO2 from natural deep well water was evaluated (initial concentration: 35.5 µg L-1 As, 1.1 mg L-1F-, 147 mg L-1 SiO2, pH 8.6, and conductivity 1024 µS cm-1), by electrocoagulation (EC) process in continuous mode comparing three different configurations of sacrificial anodes (Al, Fe, and Al-Fe). EC was performed in a new reactor equipped with a small flow distributor and turbulence promoter at the entrance of the first channel to homogenize the flow. The best removal was found at j = 5 mA cm-2 and u = 1.3 cm s-1, obtaining arsenic residual concentrations (CAs) of 1.33, 0.45, and 0.77 µg L-1, fluoride residual concentration ( [Formula: see text] ) of 0.221, 0.495, and 0.622 mg L-1, and hydrated silica residual concentration ( [Formula: see text] ) of 21, 34, and 56 mg L-1, with costs of approximately 0.304, 0.198, and 0.228 USD m-3 for the Al, Fe and Al-Fe anodes, respectively. Al anode outperforms Fe and Al-Fe anodes in concurrently removing As, F- and SiO2. The residual concentrations of As and F- complied with the recommendations of the World Health Organization (WHO) (As < 10 µg L-1 and F- < 1 mg L-1). The spectroscopic analyses of the Al, Fe, and Al-Fe aggregates showed the formation of aluminosilicates, iron oxyhydroxides and oxides, and calcium and sodium silicates involved in removing As, F-, and SiO2. It is concluded that Al would serve as the most suitable sacrificial anode.

Process Intensification for Enhanced Fluoride Removal and Recovery as Calcium Fluoride Using a Fluidized Bed Reactor.

This study explored the feasibility of fluoride removal from simulated semiconductor industry wastewater and its recovery as calcium fluoride using fluidized bed crystallization. The continuous reactor showed the best performance (>90% fluoride removal and >95% crystallization efficiency) at a calcium-to-fluoride ratio of 0.6 within the first 40 days of continuous operation. The resulting particle size increased by more than double during this time, along with a 36% increase in the seed bed height, indicating the deposition of CaF2 onto the silica seed. The SEM-EDX analysis showed the size and shape of the crystals formed, along with the presence of a high amount of Ca-F ions. The purity of the CaF2 crystals was determined to be 91.1% though ICP-OES analysis. Following the continuous experiment, different process improvement strategies were explored. The addition of an excess amount of calcium resulted in the removal of an additional 6% of the fluoride; however, compared to this single-stage process, a two-stage approach was found to be a better strategy to achieve a low effluent concentration of fluoride. The fluoride removal reached 94% with this two-stage approach under the optimum conditions of 4 + 1 h HRT combinations and a [Ca2+]/[F-] ratio of 0.55 and 0.7 for the two reactors, respectively. CFD simulation showed the impact of the inlet diameter, bottom-angle shape, and width-to-height ratio of the reactor on the mixing inside the reactor and the possibility of further improvement in the reactor performance by optimizing the FBR configuration.

Enhanced fluoride removal using Mg-Zr binary metal oxide nanoparticles confined in a strong-base anion exchanger.

Generally, the pH of fluorinated groundwater or many industrial wastewater is neutral, while the majority of metal-modified adsorbents can work efficiently only under acidic conditions. In this study, we synthesized a novel hybrid adsorbent, Mg-Zr-D213, by loading nano-Mg/Zr binary metal (hydrogen) oxides in a strong-base anion exchanger, D213, to enhance the adsorption of fluoride from neutral water. Mg-Zr-D213 exhibited a better fluoride-removal capacity in neutral water than monometallic modified resins. Under the interference of competing anions and coexisting organic acids, Mg-Zr-D213 exhibited superior selectivity. The Langmuir model indicated that the fitted maximum sorption capacity of Mg-Zr-D213 was 41.38 mg/g. The results of column experiments showed that the effective treatment volume of Mg-Zr-D213 was 8-16-times higher than that of D213 for both synthetic groundwater and actual industrial wastewater, and that NaOH-NaCl eluent could effectively recover more than 95% of fluoride. Adsorption experiments with Mg/Zr metal (hydrogen) oxide particles and D213 separately demonstrated a synergistic effect between -N+(CH3)3 and Mg/Zr metal (hydrogen) oxide particles. The ligand exchange or metal-ligand interaction of Mg/Zr metal (hydrogen) oxide particles on fluoride was further demonstrated via X-ray photoelectron spectroscopy. Overall, Mg-Zr-D213 has great potential for enhanced fluoride removal in neutral water.

Stratified control of chemical crystallization in a pellet fluidized bed for pH-Adjusted fluoride and phosphate reduction: An experimental study.

Chemical crystallization granulation in a fluidized bed offers an environmentally friendly technology with significant promise for fluoride removal. This study investigates the impact of stratified pH control in a crystallization granulation fluidized bed for the removal of fluoride and phosphate on a pilot scale. The results indicate that using dolomite as a seed crystal, employing sodium dihydrogen phosphate (SDP) and calcium chloride as crystallizing agents, and controlling the molar ratio n(F):n(P):n(Ca) = 1:5:10 with an upflow velocity of 7.52 m/h, effectively removes fluoride and phosphate. Stratified pH control-maintaining weakly acidic conditions (pH = 6-7) at the bottom and weakly alkaline conditions (pH = 7-8) at the top-facilitates the induction of fluoroapatite (FAP) and calcium phosphate crystallization. This approach reduces groundwater fluoride levels from 9.5 mg/L to 0.2-0.6 mg/L and phosphate levels to 0.1-0.2 mg/L. Particle size analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and X-ray diffraction physical characterizations reveal significant differences in crystal morphology between the top and bottom layers, with the lower layer primarily generating high-purity FAP crystals. Further analysis shows that dolomite-induced FAP crystallization offers distinct advantages. SDP not only dissolves on the dolomite surface to provide active sites for crystallization but also, under weakly acidic conditions, renders both dolomite and FAP surfaces negatively charged. This allows for the effective adsorption of PO43-, HPO42-, and F- anions onto the crystal surfaces. This study provides supporting data for the removal of fluoride from groundwater through induced FAP crystallization in a chemical crystallization pellet fluidized bed.

Carbon doping enhances the fluoride removal performance of aluminum-based adsorbents.

Excessive fluoride presence in water poses significant environmental and public health risks, necessitating the development of effective remediation techniques. Conventional aluminum-based adsorbents face inherent limitations such as limited pH range and low adsorption capacity. To overcome these challenges, we present a facile solvent-thermal method for synthesizing a carbon-doped aluminum-based adsorbent (CDAA). Extensive characterization of CDAA reveals remarkable features including substantial carbon-containing groups, unsaturated aluminum sites, and a high pH at point of zero charge (pHpzc). CDAA demonstrates superior efficiency and selectivity in removing fluoride contaminants, surpassing other adsorbents. It exhibits exceptional adaptability across a broad pH spectrum from 3 to 12, with a maximum adsorption capacity of 637.4 mg/g, more than 110 times higher than alumina. The applicability of the Langmuir isotherm and pseudo-second-order models effectively supports these findings. Notably, CDAA exhibits rapid kinetics, achieving near-equilibrium within just 5 min. Comprehensive analyses utilizing Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) offer detailed insights into the mechanisms involving electrostatic attraction, ion exchange, and ligand exchange. Carbon-based groups play a role in ligand exchange processes, synergistically interacting with the unsaturated aluminum structure to provide a multitude of adsorption sites. The exceptional attributes of CDAA establish its immense potential as a transformative solution for the pressing challenge of fluoride removal from water sources.

Synthesis and characterization of functional calcium-phosphate-chitosan adsorbents for fluoride removal from water.

Functional calcium-phosphate-chitosan adsorbents for fluoride (F-) removal from water with different proportions of calcium (0.7 or 1.4 % w/v) were synthesized by: i) ionotropic gelation technique followed by drying in a convection oven (IGA) or freeze drying (FDA); ii) freeze-gelation followed by drying in a convection oven (FGA). Adsorbents were analyzed by SEM-EDX and FTIR- ATR. F- removal percentages higher than 45 % were obtained with calcium-phosphate-chitosan adsorbents for an initial F- concentration of 9.6 mg L-1. Optimal conditions for F- removal were attained, using calcium-phosphate- chitosan adsorbents synthesized by ionotropic gelation with 0.7 % of Ca (IGA0.7). Under these conditions, initial F- concentration of 5 mg L-1, was reduced below the maximum limit of 1.5 mg L-1 established by WHO. Regeneration of IGA0.7 was achieved in acid media. The performance of IGA0.7 was slightly reduced in the presence of coexisting anions (nitrate, carbonate, arsenate). Adsorption kinetics was represented satisfactorily by the pseudo-second order equation; Langmuir isotherm provided the best fit to the equilibrium data and IGA0.7 exhibited a maximum F- adsorption capacity qL = 132.25 mg g-1. IGA0.7 particles were characterized by thermogravimetry coupled to FTIR, XRD, XPS and SEM-EDX. The calcium-phosphate-chitosan adsorbents constitute a suitable and emerging material for water defluorination.

Polyacrylonitrile and polyethersulfone based co-axial electrospun nanofibers for fluoride removal from contaminated stream.

Coaxial electrospun polyacrylonitrile (PAN) and polyethersulfone (PES) based nanofibers were prepared and was used for filtration of fluoride from drinking water for the first time. Well defined fiber geometry was obtained at 1 ml/h of core polymer, i.e., PES flow rate, 1.4 ml/h of shell polymer, i.e., PAN flow rate, voltage of 22 kV, while the distance between the needle tip and the collector was 15-17 cm. Increase in bead like structure in fiber strands was observed with higher PAN concentration, while it decreased for lower PES concentration, thereby giving an optimum composition (6 wt% PAN and 10 wt% PES) for uniform fiber morphology. This nanofiber, abbreviated as N2 acted as an ultrafiltration membrane having permeability in the lower range, i.e., 0.5 × 10-11 m/s Pa and its fluoride removal efficacy was 46%. Fibers were also hydrophilic with considerable porous nature. Uptake of fluoride by this N2 nanofibers were evident from binding energy of 685.2 eV during XPS analysis. It is probable that nitrile and sulfone groups present in the core and shell of the nanofibers played an active in fluoride uptake, which was estimated as 110 mg/g at 298 K. Isoelectric point was in alkaline range which promoted negative fluoride ion uptake on positive nanofiber surface. Lead played higher masking effect in the uptake of fluoride in comparison to arsenic as coexisting ion. Dynamic cross flow filtration was also studied with this nanofiber in both synthetic and real life feed solution.

One-pot synthesis of versatile sphere-like nano adsorbent MnAl2O4 (MAO): an optical and magnetic material for efficient fluoride removal and latent finger print detection.

Spherically shaped trimetallic MnAl2O4 (MAO) nanoadsorbent was prepared in an one-pot synthesis process for the removal of excess fluoride from water. The adsorbent was characterized by thermogravimetric analysis (TGA), X-ray diffraction study (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), etc. The adsorption property for fluoride on the MAO was analyzed by batch experiments varying the adsorbent dose, pH, contact time, and initial fluoride concentration. The results showed that the fluoride uptake behavior of the samples could precisely be fitted by the Freundlich model, and the maximum adsorption capacity was estimated to be 39.21 mg/g at room temperature. The pseudo-second-order models accurately described the adsorption kinetics data. The regenerated sample showed excellent reusability along with high removal capacity on real water sample also. The underlying fluoride adsorption mechanism via ion-exchange and electrostatic interaction was established from X-ray photoelectron spectroscopy (XPS) and zeta potential studies. The sample showed excellent luminescence with blue emission with a band gap of 2.6 eV. The materials also showed good elastic behavior exhibiting the Poisson's ratio (σ) 0.32 and excellent latent figure print detection capacity distinguishing the clearly the ridge and furrow regions under UV light. The magnetic behavior was also found to be in long range with antiferromagnetic characteristics.

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.

3D flower-like zirconium magnesium oxide nanocomposite for efficient fluoride removal.

A 3D flower-shaped bimetallic nanocomposite zirconium magnesium oxide (ZMO) was prepared first time by the controlled solution combustion method using triethanolamine (TEA) as a fuel and chelating agent. The composite material was used to remove excess fluoride via adsorption. The thermal stability of the adsorbent was characterized by thermogravimetric analysis (TGA). Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) were used to characterize the adsorbent. The surface charge of the nano adsorbent was determined by Zeta Sizer. The surface area and pore volume of the adsorbent were determined by Brunauer-Emmett-Teller (BET) isotherm and Barrett-Joyner-Halenda (BJH) methods. The adsorption behavior of fluoride was studied systematically varying the pH, contact time, adsorbent dose, and initial fluoride concentration. The adsorption followed the Langmuir isotherm model with a maximum adsorption capacity of 42.14 mg/g. The pseudo-second-order kinetic model was confirmed by the adsorption study. The maximum adsorption efficiency was in the 6-10 pH range. The reaction mechanism was mainly based on ion exchange between hydroxy and fluoride ions which was proven by X-ray photoelectron spectroscopy (XPS). Real water tests indicated that ZMO could be used as a potential defluoridation agent for fluoride containing groundwater treatment.

A novel tri-metal adsorbent used for defluoridation technique from groundwater: performance and mechanism.

In this research article, a novel adsorbent (Zn-Fe-Al) was synthesized successfully by a simple chemical route where three oxides combined to enhance affinity towards fluoride. The physicochemical properties of the adsorbent were used to characterize and assess its effectiveness in defluoridation with both synthetic and groundwater. The TEM results demonstrated the overlapping of metals, and EDX shows the metals present in the adsorbent. The maximum defluoridation efficiency (97%) of Zn-Fe-Al was obtained at an optimized initial pH 7 and adsorbent dose 0.08 g L-1. The fluoride adsorption on Zn-Fe-Al followed the D-R isotherm and intraparticle diffusion. The maximum adsorption capacity of Zn-Fe-Al was found to be 187 mg g-1. The adsorption of fluoride on Zn-Fe-Al was found to be endothermic and spontaneous. The Zn-Fe-Al adsorbent exhibited satisfactory defluoridation performance on real groundwater. The co-existing ions were also investigated. The adsorption mechanisms for fluoride were electrostatic interaction and ion exchange. These results demonstrated that Zn-Fe-Al adsorbent was considered high potential for effective defluoridation of groundwater.

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.

Porous Lanthanum-Zirconium phosphate with superior adsorption capability of fluorine for water treatment.

Bimetal oxide is a popular defluorinating material. Hexadecyl trimethyl ammonium bromide (CTAB) as a surfactant successfully synthesizes a novel lanthanum-zirconium phosphate to remove fluorine from groundwater. Lanthanum-zirconium phosphate at a Zr/La molar ratio of 2 exhibited a specific surface area of 455.14 m2/g with a wide pore size, which was achieved by incorporating lanthanum into materials and removing CTAB through calcination. The maximum fluoride adsorption capacity is 109.17 mg/g, which is tenfold that of mesostructured zirconium phosphate. Specifically, analysis revealed that mZrP and LamZrP2-1 were amorphous, which is consistent with HAADF-STEM. The fluoride adsorption fitted well with the pseudo-second-order equation model and Langmuir isotherm mode. LamZrP2-1 had potent anti-interference ability without PO43-. Moreover, LamZrP2-1 was reusable for at least six cycles of adsorption-desorption with little influence. The adsorption mechanism of fluoride was discussed by X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR) analysis, and Fourier transform infrared (FTIR) spectroscopy. Fluoride was captured by LamZrP2-1 via charge attraction, ligand exchange of different bond strengths, and ion exchange. Lanthanum-zirconium phosphate is important not only in the research and development of bimetal oxides but also in the treatment of groundwater for fluoride removal.

One-pot solution combustion synthesis of porous spherical-shaped magnesium zinc binary oxide for efficient fluoride removal and photocatalytic degradation of methylene blue and Congo red dye.

A novel porous spherical-shaped magnesium zinc binary oxide (MZO) was successfully prepared for the first time using a chemical process for fluoride removal and photocatalytic methylene blue (MB) and Congo red (CR) dye degradation. XRD, FESEM, and TEM were studied for phase formation, topographic, crystallographic, and detailed structural information. The surface charge and optical properties of the adsorbent were studied by zeta potential and photoluminescence spectra. The synthesized nano-adsorbents showed high fluoride removal capacity (43.10 mg/g) and photocatalytic activity with a degradation efficiency of 97.83% and 78.40% for MB and CR, respectively. The adsorption was strongly pH-dependent and worked well in the range 6-9. The kinetic studies were performed for both fluoride removal and dye degradation and were found to follow pseudo-second-order and first-order rate law, respectively. The samples were found to be extremely reusable and selective for fluoride removal in presence of co-ions such as NO3-, SO42-, and Cl-. The basic fluoride adsorption process of the samples can be related to ion exchange and electrostatic interactions, according to XPS and FTIR data. The detailed mechanistic study of photocatalytic dye degradation showed that the reaction occurred via OH radicals. Thus, MZO could be considered an effective and quick adsorbent for water purification in fluoride-containing groundwater and industrial dye wastewater.

Structure-performance correlation guided cerium-based metal-organic frameworks: Superior adsorbents for fluoride removal in water.

Fluoride in the hydrosphere exceeds the standard, which could be critically hazardous to human health and the natural environment. The adsorption method is a mature and effective way to remove pollutants in water, including fluoride. In this study, we synthesized three kinds of cerium-based metal-organic frameworks (Ce-MOFs) with different structures and properties by modulating the organic ligands (i.e., trimesic acid (BTC), 1,2,4,5-benzenetetracarboxylic acid (PMA), and terephthalic acid (BDC)) via the solvothermal method. The adsorption kinetics of Ce-MOFs on fluoride well fit the pseudo second order model, and their adsorption isotherms also conform to Langmuir isothermal model. The thermodynamic study reveals that the adsorption process is a spontaneous endothermic reaction. The maximum saturated adsorption capacities of Ce-BTC, Ce-PMA, and Ce-BDC are 70.7, 159.6, and 139.5 mg g-1, respectively. Ce-MOFs have stable and excellent adsorption capacity at pH = 3-9. Coexisting anions (Cl-, SO42-, and NO3-) do not affect the performance of Ce-MOFs for fluoride removal. Moreover, Ce-MOFs also show their broad prospect as superior fluoride adsorbents because of their excellent performance and reusability in real water samples. Organic ligands have a remarkable influence on the defluoridation performance of Ce-MOFs. This work will provide a feasible idea for designing MOFs as superiors adsorbents for defluoridation.