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A new adsorbent, Fe 3 O 4 sulfonated magnetic nanoparticle (Fe 3 O 4 -SO 3 H MNP), was developed for heavy metal ions removal from water, which could be effectively separated from the solution owing to the superparamagnetic property. The nanoparticles can be used to remove heavy metal ions due to the additional active site, “sulfo-group”, introduced by the AMPS branches grafted onto the iron oxide. The as-synthesized materials were characterized by SEM, TEM, FT-IR and BET. The FTIR, XPS and Zeta potential were used to describe the adsorption mechanism. The Fe 3 O 4 -SO 3 H MNPs showed rapid removal for Pb 2+ and Cd 2+ with maximum of adsorption capacity of 108. 93 and 80.9 mg/g at 25 °C, respectively. The adsorption isotherms for Pb 2+ and Cd 2+ fitted better with Langmuir than Freundlich models, indicated that the processes of the removal of Pb 2+ and Cd 2+ could follow a kind of similar adsorption manner. The adsorption kinetic was consistent with pseudo-second-order model. Furthermore, the reuse experiments results showed the adsorbent might have potential in treating heavy metal ions pollution in water. [ABSTRACT FROM AUTHOR]

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 93.84 mg/g when the fluoride concentration was 200 mg/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 0.3 mm thickness could reach 1568 L/m 2 when fluoride concentrations were 5 mg/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. [ABSTRACT FROM AUTHOR]

A novel graphitic carbon nitride (g-C 3 N 4 ) nanosheet adsorbent with a large surface area, remarkable hydrophilicity and high adsorption capacity, was presented for the removal of cadmium ions (Cd 2+ ) and methylene blue (MB) from aqueous solution. Adsorption measurements were conducted systematically to study the influences of the contact time, initial concentrations of Cd 2+ and MB, temperature, and pH value. The maximum adsorption capacities of g-C 3 N 4 towards Cd 2+ and MB were 94.4 and 42.1 mg g −1 , respectively, at 318.5 K when the initial concentrations of Cd 2+ and MB were 200 and 20 mg L −1 , respectively. The adsorption kinetics fit a pseudo-second-order model. The high adsorption performance of the g-C 3 N 4 adsorbent can be attributed to the multiple adsorption sites on g-C 3 N 4 , including the π-π conjugate interactions and electrostatic attractions with pollutants in water. In addition, it is significant to achieve high adsorption performance of g-C 3 N 4 nanosheets by efficiently exposing the adsorption sites by adjusting the microstructure surface properties and dispersity in solution. [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]

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 200 mg/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. [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]

Graphical abstract Abstract Consumption of water having excessive arsenic (As) contamination can cause adverse health effects on human beings. In this study, novel ultra-large zirconium oxide (ZrO 2) nanosheets were successfully synthesized using graphene oxide (GO) templates and their adsorption-ability was studied for arsenite (As(III)). Owing to higher values of surface area, numbers of available hydroxyl groups and strong chemisorption binding affinity towards As(III), the synthesized novel ultra-large ZrO 2 nanosheets showed high adsorption-ability for As(III) over a wide pH range. Experimental results demonstrated that the maximum adsorption-ability of the ZrO 2 nanosheets for As(III) reached to 74.9 mg/g at pH 6. BET, zeta potential, effect of initial pH, FTIR and XPS have been used to analyze the As(III) adsorption process on the ZrO 2 nanosheets. The experiments for effects of co-existing ions indicated that ZrO 2 nanosheets possessed good anti-interference ability towards co-existing ions. Furthermore, the ZrO 2 nanosheets demonstrated very fast and excellent treatment of simulated real As(III) polluted water, consequently the effluent concentration met the standard regulated by World Health Organization. This study suggested that the as-prepared ZrO 2 nanosheets could be potentially applied in practical drinking water treatment. [ABSTRACT FROM AUTHOR]

Increasing exposure to arsenic (As) contaminated ground water has become a global health hazard to humanity. Suitable adsorbent for As removal from water, especially for As(III) than As(V), is an urgent but still a challenging task. In this study, waste orange peel (OP) was modified with magnetic nanoparticles followed by calcination as a novel adsorbent and investigated for instantaneous oxidation and adsorption of As(III) from aqueous solutions. The batch adsorption experimental results showed that calcined magnetic orange peel composites (CMOPC) exhibited superior As(III) adsorption capacity (10.3 mg/g) as compared to similar cost effective adsorbents due to its high surface area, large pore size and greater numbers of active sites on its surface. The adsorption equilibrium data obeyed Langmuir model, and kinetic data was well described by the pseudo-second-order model. The adsorption mechanisms for As(III) might be involved ligand exchange of the hydroxyl in CMOPC to form Fe-O-As(III), and partial As(III) oxidation to As(V) followed by instantaneous adsorption on surface of CMOPC. The developed adsorbent has also demonstrated good anti-interference ability to co-existing ions, admirable regeneration ability and pronounced capacity in treating simulated real As(III) contaminated water. This study revealed that waste orange peel, after simple treatment could be used as a potential adsorbent for As(III) from aqueous solutions. [ABSTRACT FROM AUTHOR]

A new uniform-sized CeCO 3 OH nanosphere adsorbent was developed, and tested to establish its efficiency, using kinetic and thermodynamic studies, for fluoride removal. The results demonstrated that the CeCO 3 OH nanospheres exhibited much high adsorption capacities for fluoride anions due to electrostatic interactions and exchange of the carbonate and hydroxyl groups on the adsorbent surface with fluoride anions. Adsorption kinetics was fitted well by the pseudo-second-order model as compared to a pseudo-first-order rate expression, and adsorption isotherm data were well described by Langmuir model with max adsorption capacity of 45 mg/g at pH 7.0. Thermodynamic examination demonstrated that fluoride adsorption on the CeCO 3 OH nanospheres was reasonably endothermic and spontaneous. Moreover, the CeCO 3 OH nanospheres have less influence on adsorption of F − by pH and co-exiting ions, such as SO 4 2− , Cl − , HCO 3 − , CO 3 2− , NO 3 − and PO 4 3− , and the adsorption efficiency is very high at the low initial fluoride concentrations in the basis of the equilibrium adsorption capacities. This study indicated that the CeCO 3 OH nanospheres could be developed into a very viable technology for highly effective removal of fluoride from drinking water. [ABSTRACT FROM AUTHOR]

A novel adsorbent, hydroxyl aluminum oxalate (HAO), for the high efficient removal of fluoride from aqueous solution was successfully synthesized. The adsorbent was characterized and its performance in fluoride (F − ) removal was evaluated for the first time. Kinetic data reveal that the F − adsorption is rapid in the beginning followed by a slower adsorption process; 75.9% adsorption can be achieved within 1 min and only 16% additional removal occurred in the following 239 min. The F − adsorption kinetics was well described by the pseudo second-order kinetic model. The calculated adsorption capacity of this adsorbent for F − by Langmuir model was 400 mg g −1 at pH 6.5, which is one of the highest capabilities of today’s materials. The thermodynamic parameters calculated from the temperature-dependent isotherms indicate that the adsorption reaction of F − on the HAO is a spontaneous process. The FT-IR spectra of HAO before and after adsorbing F − show adsorption mechanism should be hydroxyl and oxalate interchange with F − . [ABSTRACT FROM AUTHOR]

Removing heavy metals from aqueous solutions has drawn more and more attentions these years because of their serious global health challenge to human society. To develop an adsorbent with low-cost and high-efficiency for removal of heavy metals (HMs), β-cyclodextrin (β-CD) polymers crosslinked with rigid aromatic groups were prepared and used for lead (Pb), copper (Cu) and cadmium (Cd) removal for the first time. The negatively charged β-CD polymers with large BET surface area were suitable to be used in HMs adsorption. The adsorption process completed in 5 min was well fit by Freundlich isotherm model and pseudo-second-order model. The intraparticle diffusion model was also appropriate to describe the adsorption of Pb, Cu and Cd on β-CD polymer. The maximum of adsorption capacities at 25 °C for Pb, Cu and Cd were 196.42, 164.43 and 136.43 mg/g when the initial concentration was 200 mg/L. The HMs adsorption process on the surface of β-CD polymer was an endothermic and spontaneous process. Both of the electrostatic interaction and distribution of Pb, Cu and Cd species influenced the adsorption process at different pH values. The order of removal efficiencies in multi-component adsorption for the three metal ions were Pb > Cu > Cd. The adsorption mechanisms were H + ions on hydroxyl groups exchanged with heavy metal ions and electrostatic interactions. This study indicated that β-CD polymers could be developed into effective adsorbents for rapid removal of heavy metals. [ABSTRACT FROM AUTHOR]