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A biocompatible and novelly-defined adsorption membrane for rapid removal of fluoride was prepared. Both adsorption and membrane techniques were used in this research. Al(OH) 3 nanoparticles modified hydroxyapatite (Al-HAP) nanowires were developed and made into Al-HAP membrane. The adsorption data of Al-HAP adsorbent could be well described by Freundlich isotherm model while the adsorption kinetic followed pseudo-second-order model. The maximum of adsorption capacity was 93.84mg/g when the fluoride concentration was 200mg/L. The adsorption mechanism was anion exchanges and electrostatic interactions. The contribution rates of HAP nanowires and Al(OH) 3 nanoparticles in fluoride removal were 36.70% and 63.30%, respectively. The fixed-bed column test demonstrate that the Al-HAP was biocompatible and in a good stability during the process of water treatment. The fluoride removal abilities of Al-HAP membrane with 0.3mm thickness could reach 1568L/m 2 when fluoride concentrations were 5mg/L. This study indicated that the Al-HAP membrane could be developed into a very viable technology for highly effective removal of fluoride from drinking water., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Novel ultralong hydroxyapatite (HAP) nanowires were successfully prepared for fluoride removal for the first time. The fluoride adsorption on the HAP nanowires was studied on a batch mode. The results revealed that the adsorption data could be well described by the Freundlich model, and the adsorption kinetic followed the pseudo-second-order model. The maximum of adsorption capacity was 40.65 mg/g at pH 7.0 when the fluoride concentration is 200mg/L. The thermodynamic parameters suggested that the adsorption of fluoride was a spontaneous endothermic process. The FT-IR, XPS and Zeta potential analysis revealed that both anion exchange and electrostatic interactions were involved in the adsorption of fluoride. Furthermore, the HAP nanowires were made into HAP membrane through a simple process of suction filtration. Membrane filtration experiments revealed that the fluoride removal capabilities depended on the membrane thickness, flow rate and initial concentration of fluoride. The as-prepared membrane could remove fluoride efficiently through continues filtration. The filtered water amount could reach 350, 192, and 64 L/m(2) when the fluoride concentrations were 4, 5 and 8 ppm, respectively, using the HAP membrane with only 150 μm thickness. The as-synthesized ultralong HAP nanowires were thus demonstrated to be very effective and biocompatible adsorbents for fluoride removal from contaminated water., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A novel environment friendly adsorbent, micro-nano hierarchical structured flower-like MgO/MgCO3 (MHS-MgO/MgCO3), was developed for fluoride removal from water. The adsorbent was characterized and its defluoridation properties were investigated. Adsorption kinetics fitted well the pseudo-second-order model. Kinetic data revealed that the fluoride adsorption was rapid, more than 83-90% of fluoride could be removed within 30 min, and the adsorption equilibrium was achieved in the following 4 h. The fluoride adsorption isotherm was well described by Freundlich model. The maximum adsorption capacity was about 300 mg/g at pH=7. Moreover, this adsorbent possessed a very wide available pH range of 5-11, and the fluoride removal efficiencies even reached up to 86.2%, 83.2% and 76.5% at pH=11 for initial fluoride concentrations of 10, 20 and 30 mg/L, respectively. The effects of co-existing anions indicated that the anions had less effect on adsorption of fluoride except phosphate. In addition, the adsorption mechanism analysis revealed that the wide available pH range toward fluoride was mainly resulted from the exchange of the carbonate and hydroxyl groups on the surface of the MHS-MgO/MgCO3 with fluoride anions., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Recently, the development of fluorescent sensors to selectively and sensitively detect F− in drinking water has attracted great attention due to the serious harm caused by excessive F− to human bones, kidneys and even DNA. The advantage of a dual emission fluorescent sensor for its fluorescence color change in visualization is well known. In this work, we rationally designed a dual-emitting metal organic framework (MOF) (Eu/Sc)-EBTC, which showed ligand-based emission and Eu3+-based emission and exhibited high selectivity and sensitivity to F− (limit of detection = 16.4 ppb). The sensing mechanism was ascribed to the high affinity between F− and Eu3+ in (Eu/Sc)-EBTC, and was confirmed by PXRD patterns and X-ray photoelectron spectroscopy. Besides, a test strip was made successfully for the practical detection of F−. This study demonstrates the potential of a dual-emission fluorescent MOF sensor for practical applications. [ABSTRACT FROM AUTHOR]

A novelly-defined adsorption membrane for rapid removal of fluoride from drinking water was prepared. Both zirconium metal-organic frameworks (Zr-MOFs) adsorbent and membrane with large specific surface area of 740.28 m 2 /g were used for fluoride removal for the first time. For adsorption technique, fluoride adsorption on Zr-MOFs was studied on a batch mode. The adsorption data could be well described by Langmuir isotherm model while the adsorption kinetic followed pseudo-second-order model. The maximum of adsorption capacity was 102.40 mg/g at pH 7.0 when the initial fluoride concentration was 200 mg/L. The FT-IR and XPS analyses of Zr-MOFs revealed that both surface hydroxyl groups and Zr(IV) active sites played important roles in fluoride adsorption process. The as-prepared Zr-MOFs adsorbent was suitable for practical treatment of drinking water and regeneration by sodium hydroxide solution (3 wt%). For membrane experiments, Zr-MOFs membrane supported on Alumina substrate could remove fluoride efficiently through dynamic filtration. The fluoride removal capability of Zr-MOFs membrane depended on flow rate and initial concentration of fluoride. The fluoride removal abilities of Zr-MOFs membrane with 20 μm thickness could reach 5510, 5173, and 4664 L/m 2 when fluoride concentrations were 5, 8 and 10 mg/L, respectively. This study indicated that Zr-MOFs membrane could be developed into a very viable technology for highly effective removal of fluoride from drinking water. [ABSTRACT FROM AUTHOR]

• Recent developments in fluoride removal from water by adsorption are reviewed. • Four technical strategies are proposed for designing of adsorbents. • Transfering the adsorption process to industrial scale is urgently needed. • Fluoride adsorption and desorption in field condition need further investigation. Fluoride contamination in water environment due to natural and artificial activities has been recognized as one of the major problems worldwide. Developing effective and robust technologies for excess fluoride removal from water environment becomes highly important. Among the commonly used treatment technologies applied for fluoride removal, adsorption technique has been explored widely and offers a highly efficient simple and low-cost process for fluoride removal from water. This review reports the recent developments in fluoride removal from water environment by adsorption methods. Studies on fluoride removal from aqueous solutions using various carbon materials are reviewed. It is evident that various adsorbents with high fluoride removal capacity have been developed, however, there is still an urgent need to transfer the removal process to industrial scale. Regeneration studies need to be performed in more extent to recover the adsorbent in field conditions, enhancing the economic feasibility of the process. Based on the review, four technical strategies of adsorption method including nano-surface effect, structural memory effect, anti-competitive adsorption and ionic sieve effect can be proposed. The design of adsorbents through these four strategies can greatly improve the removal efficiency of fluoride in water and provide guidance for the development of new efficient methods for fluoride removal in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel nanoconfinement regulation La-Mg LDH/Ti 3 C 2 T X (T = O, OH) was prepared for the first time. • La-Mg LDH/Ti 3 C 2 T X improved the aggregation of La-Mg LDH and effectively increased the active site. • La-Mg LDH/Ti 3 C 2 T X was made into a membrane which had a good defluorination performance. • Fluoride ions were more easily confined at the interface of La-Mg LDH/Ti 3 C 2 T X. The present study utilized a nanoconfinement-regulated La-Mg LDH/Ti 3 C 2 T X (T = O, OH) adsorbent to achieve efficient fluoride removal. The modified adsorbent effectively increased the surface area and active sites of the material through controlled intercalation of La-Mg LDH into the Ti 3 C 2 T X gaps. The La-Mg LDH/Ti 3 C 2 T X composite was found to exhibit superior suitability for pseudo-second-order kinetics and conformed well to the Langmuir model. Under initial conditions of a fluoride ion concentration of 200 mg/L, pH 7, and a temperature of 298 K, the adsorption capacity was determined to be 139.860 mg/g. The adsorption of fluoride was primarily governed by electrostatic interactions and anion exchange processes. The La-Mg LDH/Ti 3 C 2 T X adsorbent with nanoconfinement regulation had the best adsorption effect on fluoride ions, and fluoride ions were more inclined to be adsorbed at the interface of La-Mg LDH/Ti 3 C 2 T X. Furthermore, facile fabrication of La-Mg LDH/Ti 3 C 2 T X membrane was achievable. Membrane filtration experiments demonstrated that the defluorination efficiency was significantly influenced by the thickness of membrane, water velocity, and solution pH. The membrane processing capacity was 11526 L/m3 when the membrane thickness was 9 mm and the flow rate was 10 mL/min. The present study offers novel insights into the development of defluorinated materials. [ABSTRACT FROM AUTHOR]