Defluoridation Capacity Research Articles

Facile fabrication of graphene oxide and rare earth based metal organic frameworks decorated alginate and chitosan biopolymeric hybrid materials for defluoridation studies

Fluorosis disease can be prevented by the defluoridated water. Hence, the present work focused on the fabrication of hybrid materials using graphene oxide (GO) and Ce-based metal organic frameworks namely cerium fumarate (Ce-Fu) which gives GO/Ce-Fu for defluoridation of water. Further, the powdered GO/Ce-Fu was dispersed with alginate (Alg) and chitosan (CS) biopolymeric matrixes to give GO/Ce-Fu/Alg-CS biopolymeric hybrid beads for defluoridation investigations. The developed GO/Ce-Fu and GO/Ce-Fu/Alg-CS beads have defluoridation capacities (DCs) of 4.410 and 4.753 mg/g within 30 min. The fabricated GO/Ce-Fu and GO/Ce-Fu/Alg-CS beads were analyzed by XRD, FTIR, TGA, BET, SEM and EDAX studies. The performance of fluoride adsorption influencing parameters such as dosage, contact time, solution pH, interfering anions and temperature studies were optimized with batch scale. Thermodynamic, adsorption isotherms and kinetic studies were carried out using hybrid materials to find the nature and order of fluoride adsorption. The fluoride adsorption mechanism of GO/Ce-Fu and GO/Ce-Fu/Alg-CS beads was investigated. The performance of recyclability of the hybrid materials was examined. In addition, the field studies of hybrid materials were also explored to identify their field suitability nature.

Removal of Fluoride from Water by using Natural Adsorbent

Abstract: Access to safe drinking water is not only the elementary need of human being but also honored as an mortal right .For overall development of the country , as acceptable nutrition, education, gender equivalency, and particularly the eradication of poverty in developing countries are required , along with that furnishing safe drinkable water is equally important . Fluoride one of the water quality parameters of concern, with redundant( beyond1.5 mg/ l, World Health Organization( WHO) guideline value of what contaminates groundwater coffers in numerous corridors of the world, and renders it not drinkable for mortal consumption, due to affiliated adverse health goods thus, knowledge of its junking, using the stylish fashion with optimum effectiveness demanded . Taking the inflexibility of the problem into consideration, the present paper aims to give a retrospective approach to the use of effective low- cost adsorbents for the junking of fluoride from water . The defluoridation capacity of certain low- cost natural adsorbents like Groundnut shell powder and Soya chunk powder were added in the list and discussed. The effect of pH, adsorbent dose, initial concentration , and contact time also delved . It's set up that the junking of Fluoride ions at optimum parameters like pH, adsorbent dose ,initial concentration and contact time is at 7, 2gm, 5mg/ l, and 100 minutes respectively for groundnut shell powder and 6, 2gm, 5mg/ l, and 100 minutes respectively for Soya chunk powder. For all optimum parameters, the maximum reduction in Fluoride ions observed in the range of 55 to 65% for groundnut shell powder whereas for soya chunk powder it's 40 to 50%

Design and development of rare earth elements anchored pectin/chitosan integrated magnesia hybrid composite for effective defluoridation of water

Fluoride pollution in drinking water is a worldwide concern arises from natural and human actions. The excessive fluoride present in drinking water leads to fluorosis. In this study, dual polysaccharide biopolymers namely pectin and chitosan were incorporated with magnesia followed by imprinted with lanthanum and cerium ions gives PCML (pectin/chitosan/magnesia/lanthanum) and PCMC (pectin/chitosan/magnesia/cerium) hybrid materials for fluoride adsorption investigation. The enhanced defluoridation capacities (DCs) of PCML and PCMC composites were seen as 4.976 and 4.972 mg g−1 by 30 min individually. To decide the impact of various affecting parameters viz., dosage, initial fluoride concentration, pH, contact time and challenging anions were examined in batch method. The pH results show the utmost DCs of PCML and PCMC composites was noted at pH 6 and in co-ions experiments, the significant competition found with bicarbonate ion owing to the superior electronic building of bicarbonate ion. The defluoridation equilibrium data of PCML and PCMC composites follows Langmuir, pseudo-second-order and intraparticle diffusion models. The positive ΔH° value as 3.04 kJ mol−1 for PCML composite and 2.88 kJ mol−1 for PCMC composite were exposed that the endothermic nature of fluoride adsorption occurs onto PCML and PCMC composites. The defluoridation mechanism of PCML and PCMC composites were attained by complexation, ion-exchange and electrostatic interaction. The reusability results shows that the synthesized PCML and PCMC composites can be reused upto six cycles. Field trail result demonstrates the synthesized PCML and PCMC composites were applicable at field conditions by reducing fluoride concentration below 1.5 mg/L.

Adsorption isotherms and kinetic studies for the defluoridation from aqueous solution using eco-friendly natural adsorbent like Terminalia Chebula

A practical technique for removing fluoride from aqueous solutions by adsorption was created using the natural adsorbent known as Terminalia Chebula with a primary emphasis on adsorption isotherms and kinetic studies. The experimental results showed the best conditions for removing fluorine ions as follows: the dosage of the natural adsorbent: 50 mg/L, contact reaction time: 40 min, shaking speed = 120 rpm, temperature = 32 °C. The amount of removal of fluorine ions was found to be >98 % fluoride within a shorter time and reached adsorption equilibrium within 40 min with a maximum defluoridation capacity of 20.92 mg/g. At lower solution pH (3 to 5), there is higher fluoride adsorption on the adsorbent surface and as the pH becomes alkaline (pH > 7) the adsorption capacity decreased. The two co-ions namely NO3− and Cl− removed the fluoride 79 % whereas, the phosphate ions did not have any marked effect on the defluoridation. The pseudo-second-order kinetic order such Langmuir, Empirical Freundlich, Temkin and Dubinin–Radushkevich isotherms can well predict the adsorption equilibrium rate to be at 0.044 mg/L with contact time (t) of 30 min. In addition to that the adsorption is characterized by SEM, X-ray diffraction and FTIR techniques. This study has ultimately found that the Terminalia Chebula is a workable, natural material for fluoride elimination.

Enhanced defluoridation by nano-crystalline alum-doped hydroxyapatite and artificial intelligence (AI) modeling approach

The study aimed to investigate the defluoridation capacity of nano-hydroxyapatite (HAP) [Ca10(PO4)6(OH)2] and alum-doped hydroxyapatite (AHAP) [Ca8Al(PO4)6.(OH)2] as an environmental friendly adsorbent. The physicochemical characteristics of both the material (HAP and AHAP) were examined using XRD, FE-SEM-EDS, and BET techniques. The batch adsorption study revealed a fluoride removal efficiency of up to 83% (AHAP) and 74% (HAP) under acidic conditions (pH-2). The doping of alum alters the surface chemistry and enhances the affinity of AHAP for fluoride adsorption. The pseudo-second-order kinetic (R2–0.9941) and Langmuir isotherm (R2–0.9425) models best describe the adsorption mechanism and behavior. The thermodynamic analysis indicated the spontaneous and endothermic nature of the adsorption process. The study also tested the applicability of the artificial neural network (ANN) modeling approach using MATLAB R2013a to simulate the simulated absorptive efficiency of AHAP. This study suggests that AHAP proved an effective adsorbent for defluoridation.

Fabrication of covalent organic frameworks incorporated hydroxyapatite based chitosan–gelatin hybrid magnetic beads for fluoride removal

The developed biocompatible materials like covalent organic frameworks (COFs) and hydroxyapatite acquire significant defluoridation capacity (DC). But because of their powder nature, creates column blockage, pressure drop during field investigations and difficult in separation after fluoride adsorption. To address these problems, COFs and hydroxyapatite were fabricated in the usable form of beads using chitosan, gelatin and iron oxide materials as magnetic chitosan–gelatin/hydroxyapatite/covalent organic frameworks (MCGHCOF) bio-beads were developed and it was potentially applied for the removal of fluoride from water. The MCGHCOF bio-beads surface and their properties were described with FTIR, EDAX, SEM and XRD analysis. The adsorption studies were performed under the batch method. The HCO3– ion has a vital inhibitory effect on DC and this may be because of the similar ionic size of fluoride and HCO3–. The enhanced DC of MCGHCOF beads was found to be 4992 mgF-.kg−1 in 30 min at pH 7. Isotherm experimental data of fluoride adsorption was apt with Langmuir isotherm than Fruendlich and D-R isotherm models. The defluoridation system is endothermic and its spontaneous nature was demonstrated with thermodynamic studies. Kinetic studies of experimental data of fluoride adsorption were well-fitted with pseudo-second-order and intraparticle diffusion. The complexation and electrostatic interaction play a predominant role in fluoride adsorption by MCGHCOF beads. The MCGHCOF bio-beads are stable and are reusable upto six cycles. The collected field water sample was examined using MCGHCOF beads and it reduced the fluoride concentration to the tolerable drinking water threshold as recommended by WHO (1.5 mg L−1).

Oxidative Polymerization of Aniline on the Surface of Sisal Fibers (SFs) as Defluoridation Media for Groundwater

Chemical modification of sisal fibers via in situ oxidative polymerization of aniline was conducted to examine their defluoridation capacity for fluoride from drinking water. The effects of polyaniline modifications have shown significant changes on the chemical moieties and defluoridation capacity of sisal fibers (SFs). FTIR peaks at 1440 cm−1 and 1560 cm−1 revealed the presence of benzoid and quinoid structures together with sisal fiber (SF). Thermal profiles confirmed the enhancement of thermal stability of polyaniline-modified sisal fibers (PAniMSFs). SEM microstructure also proved the surface roughening of SFs as a result of polyaniline modifications. Optimal batch adsorption parameters (pH, contact time, adsorbent dose, and initial concentration) were found to be 5, 60 min, 1 g, and 10 mg/L, respectively. Adsorption kinetics proved that the removal of fluoride follows pseudo-second-order model (K2 = 0.18 g. (mg·min)−1), while the adsorption isotherm well described by the Langmuir and Freundlich model with an experimental adsorption capacity of 2.49 mg/g. Hence, modifications and improvements are required to reduce the amount of fluoride to a permissible level and enhance the longevity and activity of adsorbent materials.

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.

Effect of calcination temperature on hydroxyapatite in fluoride removal from groundwater: Process optimization and kinetic study

The present study investigates the defluoridation capacity of calcium hydroxyapatite as an efficient and environmentally safe adsorbent material. Calcium hydroxyapatite was synthesized by co-precipitation route using Ca/P = 1.76 ratio followed by calcination at various temperature ranges (30–900 °C) and termed as CaHAP-T. The physical and chemical properties of CaHAP-T samples were analyzed by TGA, SEM, BET, XRD, TEM, UV-DRS, FTIR, and NMR techniques. The CaHAP-900 sample exhibited exceptionally excellent thermal stability, crystallinity and ion-exchange capacity. Furthermore, the parametric studies revealed 98.12 ± 1.03 % fluoride removal efficiency at 30 °C temperature and 30 min contact time at neutral pH using 1 g/50 mL of adsorbent dose. The well-fitted pseudo-second-order and intraparticle diffusion model indicates the chemisorption combined with diffusion control of fluoride ions sorption on CaHAP-900 adsorbent. This work offers a deep understanding of the removal of fluoride ions from contaminated groundwater in prevalent areas and the calcium hydroxyapatite (CaHAP-900) can be utilized as an efficient cost-effective adsorbent material.

Design and preparation of CaFe layered double hydroxides for efficient treatment of fluorinated water deduced by tailored sustained-release of Ca2+

The pollution from fluorinated wastewater is increasingly severe, and its excessive intake can cause significant harm to human health. CaFe-LDH (Layered Double Hydroxides, LDH) is susceptible to hydrolysis, releasing Ca2+ that can cause secondary pollution to water sources, resulting in limited attention from researchers regarding its application in water treatment. This research explored the application of CaFe-LDH in fluorinated water treatment, harnessing its distinct properties for combined defluoridation through precipitation and adsorption. Various CaFe-LDHs with different Ca/Fe ratios were prepared using inexpensive raw materials and calcined to obtain various CaFe-CLDHs (Calcined Layered Double Hydroxides, CLDH). The calcination temperature and the Ca/Fe ratios influence the composition of CaFe-CLDH, thereby determining its hydrolysis capacity. The key intermediate product of CaFe-LDH/CLDH hydrolysis, CaFe2O4, was discovered for the first time, which slow hydrolysis provides crucial sustained-release capacity for Ca2+, increasing the utilization rate of free Ca2+ and significantly enhancing the defluoridation capacity. CaFe-LDH/CLDH exhibits excellent defluoridation capacity, which increases with the rise in Ca/Fe ratio and calcination temperature. The defluoridation capacity of Ca2Fe-LDH was 234.76 mg g−1, while Ca10Fe-CLDH-800 °C exhibited an astonishing defluoridation capacity of 463.16 mg g−1. The defluoridation of CaFe-LDH/CLDH involves a complex coupling reaction process, incorporating precipitation, coagulation, and adsorption, while the hydrolysis process encounters resistance, as confirmed by DFT simulation results that also verify the adsorption capacity of CaFe2O4 for F. This work provides guidance for the treatment of fluorinated water.

Ultrasonically assisted synthesis of g-C3N4-activated carbon composite for enhanced defluoridation of water

Fluoride contamination in drinking water poses a health threat. Activated carbon suffers from low fluoride adsorption capacity, which can be enhanced by loading with nitrogen-rich compounds. In this study, graphitic carbon nitride (g-C3N4) nanosheets were loaded onto activated carbon using ultrasonic irradiation to synthesize a g-C3N4-activated carbon composite. The ultrasonically synthesized composite exhibited significantly higher fluoride removal capacity of 92.7 mg/g compared to 2.1 mg/g for activated carbon alone. The adsorption followed the Langmuir isotherm model. Thermodynamic analysis revealed the adsorption was spontaneous and exothermic. Characterization confirmed the role of surface complexation between fluoride ions and C-N/CN groups in g-C3N4 for the enhanced adsorption. The composite achieved 82–90% defluoridation of real wastewater samples containing initially 8.7–12 mg/L fluoride. The composite could be regenerated using NaOH and reused for multiple cycles. The study demonstrates the potential of a simple ultrasonic irradiation method for synthesizing a g-C3N4-activated carbon composite with remarkably enhanced defluoridation capacity. The composite is promising for practical decentralized water defluoridation applications, especially in regions affected by high fluoride levels.

Design and fast uptake of fluoride using hybrid biopolymers encapsulated magnetic hydroxyapatite beads

AbstractHydroxyapatite is the one of the promising defluoridating material. For easy separation and to enhance defluoridation capacity (DC), magnetic iron oxide cum β‐cyclodextrin functionalized hydroxyapatite was prepared and because of its powder form it cannot be used in column studies. To make functionalized magnetic hydroxyapatite in usable bead form it was encapsulated using hybrid biopolymers chitosan and gelatin named as magnetic iron oxide/gelatin‐chitosan/hydroxyapatite/β‐cyclodextrin (MGCHC) composite beads were fabricated and utilized for rapid fluoride removal. The obtained MGCHC hybrid beads exhibited DC of 4985 mgF− kg−1 within 30 min. In co‐anions studies, Cl−, SO42− and NO3− had little influence on fluoride adsorption, whereas HCO3− had major influence on fluoride adsorption. The isotherm and kinetic data of MGCHC beads toward fluoride removal was effectively portrayed with Langmuir and pseudo‐second order model respectively. Defluoridation mechanism of MGCHC beads were mainly followed by electrostatic attraction, ion‐exchange and complexation. This investigation using MGCHC beads affords cost‐effective and eco‐friendly for fluoride removal which gives a practicable way for the fluoride treatment from field water.

Fabrication of biocompatible graphene oxide layered zirconium-organic frameworks entrapped magnetic bio-hybrid beads for defluoridation of water

Fluorine in the form fluoride is one the few elements that could cause healthiness trouble with together its insufficiency and surplus intake. For instance, the surplus fluoride in potable water leads to fluorosis. In this present study, magnetic iron oxide/graphene oxide/alginate/zirconium-organic frameworks (MGOAZ) based hybrid beads were fabricated and it was applied for defluoridation experiments. Several instrumental characterization techniques like EDAX, XPS, FTIR, SEM and XRD were studied to find the surface properties (physical and chemical) of fabricated MGOAZ beads material. Batch fluoride adsorption tests were performed to notice the fluoride adsorption action. The maximum defluoridation capacity (DC) of developed MGOAZ beads was attained at pH 7. Adsorption kinetics and isotherm equilibrium data for fluoride adsorption of the developed MGOAZ beads were vitally followed by pseudo-second-order/intraparticle and Langmuir isotherm model. Thermodynamic exploration exhibited that the adsorption route by MGOAZ beads was endothermic with spontaneous nature. Moreover, electrostatic attraction and complexation mechanism possess substantial role during fluoride adsorption onto the developed MGOAZ beads. Moreover, the regeneration performance and field suitability of MGOAZ beads was discussed in detail.

Study of Modified Magnesium Phosphate Cement for Fluoride Removal.

In this study, we used a novel composite material based on magnesium phosphate cement (MPC) to explore the retention of fluoride from used water. Dead-burned magnesium oxide (MgO), ammonium dihydrogen phosphate (NH4H2PO4), and a few retarders were used to create this particular substance. Several studies have corroborated the performance of using aluminum in the capture of fluoride. From this perspective, we attempted to reinforce our matrix with different quantities of aluminum, which increased the resistance of the composite in water. The optimal conditions that were obtained were evaluated and scrutinized using a range of techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transforms infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). The adsorbents demonstrated a powerful ability to remove fluoride from contaminated water and the defluoridation capacity was evaluated at 4.84 mg/g. Equilibrium modeling was carried out, and the experimental data were expressed in accordance with the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms.

Uptake of Fluoride from Water Using Recycled Raw Beef Bone as an Environmently Freindly Waste

Excessive intake of fluoride, mainly through drinking water is a serious health hazard affecting humans worldwide. In this study, the defluoridation capacities of locally available raw waste beef bones have been estimated. Several experimental parameters including contact time, pH, bone dose, fluoride initial concentration, bone grains size, agitation rate, and the effect of co-existence of anions in actual samples of wastewater were studied for fluoride removal from aqueous solutions. Results indicated excellent fluoride removal effeciency up to 99.7% at fluoride initial concentration of 10 mg F/L and 120 min contact time. Maximum fluoride uptake was obtained at neutral pH range 6-7. Fluoride removal kinetic was well described by the pseudo-second order kinetic model. Both, Langmuir and Freundlich isotherm models could fit the experimental data well with correlation coefficient values > 0.99 suggesting favorable conditions of the process. Furthermore, it was found that the co-existing anions had no significant effect on fluoride removal. Ion exchange and fluoride precipitation are the modes of fluoride removal.

Construction of magnetic particles sprayed hydroxyapatite based bio-ceramic beads for selective fluoride removal

The current study concentrates on the fabrication of hydroxyapatite in an exploitable bead form with enhance defluoridation capacity (DC) and quick separation. Hence, magnetic iron oxide/alginate-gelatin/hydroxyapatite/β-cyclodextrin based beads (MAGHC bio-ceramic beads) were prepared and constructively utilized for fluoride retention from water. The responsible parameter for fluoride removal was performed by batch mode. The physic-chemical properties of the developed MAGHC bio-ceramic beads were characterized with different sophisticated instrumental methods namely EDAX, SEM and FTIR studies. The different adsorption kinetic and isotherms studies were carried out to fit experimental data of fluoride adsorption onto MAGHC bio-ceramic beads. The fluoride adsorption method was thermodynamically feasible and endothermic nature. Defluoridation by MAGHC bio-ceramic beads was majorly governed by electrostatic interaction and complexation. The reusable and actual real water sample test also investigated using developed MAGHC bio-ceramic beads. The results revealed that MAGHC bio-ceramic beads could reusable and efficiently remove fluoride from drinking water at field condition.

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

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

Steering Electron Density of Zr Sites Using Ligand Effect in Bio‐Beads for Efficient Defluoridation

AbstractBecause of spontaneous agglomeration effect and undesirable electronic state of Zr sites on the surface, zirconium (hydro)oxides generally exhibit suboptimal defluoridation capacity. Herein, a template confinement‐ligand anchoring strategy is developed by utilizing confined growth of zirconium hydroxide (ZH) inside chitosan hydrogel beads (CHB) and subsequent anchoring of fumaric acid (fm) on its surface Zr sites in a monodentate mononuclear coordination mode. This technique leads to uniform dispersion of ultrafine fmZH (≈3.4 nm) and tunable electron density at the Zr sites. Due to the electron‐withdrawing ability of fm, electron‐delocalized Zr sites increase the orbital energy level matching and vacate Zr 4d orbitals to promote hybridization with the F 2p orbitals. Ultimately, robust ZrF bond can be formed as a result of reduced the adsorption energy toward fluoride ions. The defluoridation capacity shows positive linear relationship with the electron extraction ability of ligands. The saturation adsorption capacity and dynamic treatment capacity of CHB@fmZH are 10.8 and 45.9 times higher than that of CHB@ZH, respectively, owing to high electron extraction (0.098 e−) of fm. This study offers a novel insight into the design and synthesis of high‐efficiency metal oxide adsorbents by steering its surface metal sites’ electronic state through ligand effect.

Synthesis and Characterization of New Composite Materials Based on Magnesium Phosphate Cement for Fluoride Retention.

In this research work, new composite materials based on magnesium phosphate cement (MPC) were developed to evaluate the retention of fluorine from wastewater. This material was prepared with dead burned magnesia oxide (MgO), ammonium dihydrogen phosphate (NH4H2PO4), and some retarding agents. We chose to synthesize with hydrogen peroxide instead of water; alumina and zeolite were also added to the cement. The obtained optimal conditions were studied and analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), BET, and thermogravimetric analysis (TGA). The adsorbents showed a strong ability to remove fluoride from contaminated water, and the best defluoridation capacity was evaluated as 2.21 mg/g for the H2O2 cement. Equilibrium modeling was performed, and the experimental data were presented according to the isotherms of Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich.

Enhanced water defluoridation using ion channel modified hydroxyapatite: Experimental, mechanisms and DFT calculation

Hydroxyapatite (HAP) is one of the fluoride adsorbents to remove fluoride in water, but F- is hard to enter the lattice of HAP caused by spatial confinement and competitive adsorption, which leads to low defluoridation efficiency. In this study, Ca-deficient regulation method was used to create ion channels during HAP synthesis to overcome the inhibition caused by spatial confinement effect, which increased the defluoridation capacity by 50 % from 1.56 to 2.34 mg/g (Initial F- concentration: 5 mg/L). The effects of dosage, pH, initial F- concentration and co-existing ions on defluoridation process were evaluated and the dosage of 1.4 g/L under neutral condition was the economic condition. The adsorption performance followed the Pseudo-second-order kinetic model and Freundlich isotherm model, which was a spontaneous and endothermic process. The results of molecular mechanics and density functional theory (DFT) calculations showed ion channels near the F- adsorption sites on HAP surface were generated due to the calcium deficiency, which effectively promoted F- into the lattice. The defects also changed the adsorption energy and sites of HF and F-, which reduced the competitive adsorption. In addition, the catalytic decomposition of HF molecules occurred on the surface of HAP was discovered for the first time.