base tolerant zirconium phosphate nanoflake: Behavior and mechanism

Accepted Manuscript Highly efficient and rapid fluoride scavenger using an acid/base tolerant zirconium phosphate nanoflake: Behavior and mechanism Qingrui Zhang, Yixuan Li, Pikky Phanlavong, Zikang Wang, Tifeng Jiao, Hui Qiu, Qiuming Peng PII:

S0959-6526(17)31060-0

DOI:

10.1016/j.jclepro.2017.05.120

Reference:

JCLP 9659

To appear in:

Journal of Cleaner Production

Received Date: 15 February 2017 Revised Date:

8 May 2017

Accepted Date: 21 May 2017

Please cite this article as: Zhang Q, Li Y, Phanlavong P, Wang Z, Jiao T, Qiu H, Peng Q, Highly efficient and rapid fluoride scavenger using an acid/base tolerant zirconium phosphate nanoflake: Behavior and mechanism, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.05.120. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Highly efficient and rapid fluoride scavenger using an acid/base tolerant zirconium phosphate nanoflake: Behavior and mechanism Qingrui Zhang1,2, Yixuan Li1, Pikky Phanlavong1, Zikang Wang1, Tifeng Jiao*1,2, Hui, Qiu3, and

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Hebei Key Laboratory of Applied Chemistry, School of Environmental and Chemical Engineering,

Yanshan University, Qinhuangdao, 066004, P.R. China 2

State Key Laboratory of Metastable Materials Science and Technology, Yanshan University,

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Qinhuangdao, 066004, P.R. China

Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology

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Qiuming Peng*2,

(CICAEET), School of Environmental Science and Engineering, Nanjing University of Information

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Science & Technology, Nanjing 210044, P. R. China

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5625 words with 7 figures and 1 table

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Graphic Abstract

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Abstracts Zirconium phosphate (ZrP) has been developed as an efficient adsorbent, since the 1960s, but most research involving ZrP focuses on metal cation (e.g. K+/Ca2+/Pb2+/Cu2+) capture. Herein, we synthesized a ZrP nanoflake by simple in-situ precipitation procedures and successfully explored a

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new application area for it: fluoride scavenging. Completely different from the conventional metal oxides, the resultant ZrP exhibits good chemical stability in acidic or basic environments. More

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importantly, preferable fluoride uptake can be achieved at high concentrations of competitive anions (SO42-/Cl-/NO3-) addition, exceeding that of commercial D201, activated Al2O3, manganese sands,

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etc. Kinetic results further demonstrate its efficiency for approaching equilibrium in 5 min. Furthermore, the actual application proves superior treatment capacities of approximately 1800 kg and 3900 kg for groundwater and acidic wastewater treatment, respectively and the exhausted materials can be readily regenerated using 5% NaOH solution for at least five cycles. XPS and

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FT-IR investigation reveal that the preferable fluoride adsorption can be ascribed to strong inner-sphere complexation achieved by Zr-F bonds. All the results demonstrate that the

water.

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representative ZrP nanoflake is an efficient and rapid fluoride-removing candidate for cleaning

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Keywords: Fluoride; zirconium phosphate; adsorbent

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1． ．

Introduction

Fluorine pollution in waters is a world-wide issue, and it mainly arises from geological and hydrogeological structure(Bhatnagar et al., 2011). For instance, fluorine-bearing minerals might bring about dissolution/precipitation at the solid-liquid interface in certain environment and lead to

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fluoride releases(Jagtap et al., 2012b). Excess fluoride ingestion can cause severe harm to human, and lead to mottled enamels, skeletal fluorosis, etc.(Jadhav et al., 2015; Jha et al., 2013; Zhang et al.,

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2016b). So far, many countries and organizations have proposed strict regulations for fluoride levels, particularly in drinking water. The World Health Organization (WHO) and United States

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Environmental Protection Agency (USEPA) implemented a limit of 1.5 mg/L for fluoride ions in drinking water(Jagtap et al., 2012a). China and India also imposed a stricter recommendation of 1.0 mg/L. Therefore, defluoridation of water using efficient technologies has received great attention. To date, various methods, including coagulating sedimentation(Huang et al., 2016),

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adsorption(Kanno et al., 2014), ion-exchange(Wei et al., 2015), electrostatic agglomeration or electrodialysis (Behbahani et al., 2011; Guzmán et al., 2016; Tang et al., 2016) and reverse

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osmosis(Shen and Schäfer, 2014) have been well developed for fluoride sequestration. Among the established methods, adsorption is mostly utilized and regarded as an efficient approach, owing to

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its simple operation and strong adsorptivity of fluorine. Recently, nanosized metal hydroxides have aroused widespread research enthusiasm and interest the environmental sector (Deng et al., 2011; Ma et al., 2014; Wu et al., 2013), as they can form strong metal-F interactions by inner-sphere complexation and exhibit unique nanoscale-dependent high-capacity features that can further enhance efficient fluoride removal, representative compounds include ZrO2(Mohan et al., 2016; Qiu et al., 2015; Zhang et al., 2013a), HFO(Sujana et al., 2013), La(OH)3(Qiu et al., 2017), CeO2(Wang et al., 2013) and AlOOH(Saha et al., 2015) etc. Furthermore, a metal oxide with sufficient active 4

ACCEPTED MANUSCRIPT OH sites can provide bifunctional strong adsorption for both heavy metal cations and fluoride/arsenate/phosphate anions (Zhang et al., 2016a; Zhang et al., 2016c). Such distinguished properties endow the metal hydr(oxide) and its derivatives good prospects in application. Unfortunately, metal oxides are seriously restrained by their lack of chemical stability in acidic or

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organic environments. For instance, the representative HFO can only resist the weak acidic conditions of pH >3, and the high salts surrounding can also produce partly Fe resolution and

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release(Pan et al., 2010); in addition, MnO2 cannot present in EDTA solution safely, the formed EDTA-Mn will lead to the dissolving of given materials and secondary pollution (Wan et al.,

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2016). These drawbacks greatly inhibit the applicability of metal (hydr)oxides in complex environments..

Recently, the metal (IVB) phosphate family, zirconium phosphate (ZrP) being a representative example-exhibiting typical layered mesoporous structures, have found diverse applications in

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adsorbent materials, catalysts and ion conduction (Donnadio et al., 2014; Liao et al., 2014; Wong et al., 2014). As for environmental remediation, in 1960s, the famous scientists G. Alberti and A.

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Clearfield first prepared crystalline zirconium phosphate and its derivatives for alkali or alkaline metal (e.g., Na+, Ca2+, and Mg2+) purification(Alberti et al., 1985; Clearfield and Stynes, 1964) .

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Afterwards, we demonstrated its capacity for efficient adsorption of toxic heavy metals (Pan et al., 2007). However, these works mainly aimed at sequestering cationic pollutants (Du et al., 2016; Wang et al., 2014; Zhao et al., 2016). Given the similar M-O component of metal oxide; it is assumed that zirconium phosphate can also exhibit appreciable fluoride removal with high selectivity. If successful, the metal phosphate will be a second-generation bifunctional adsorbent for both cationic and anionic contaminants. More importantly, completely different from conventional metal oxides, zirconium phosphate exhibits extreme insolubility in waters (Ksp=10-137) and can 5

ACCEPTED MANUSCRIPT resist strong acids (18M H2SO4, 16M HNO3 and 12M HCl), alkaline solutions and most organic agents (Lee et al., 2016; Thakkar and Chudasama, 2009)．Therefore, it is certain that metal (IVB) phosphates will possible provide outstanding performance in replacing traditional metal oxides with more intriguing properties and expanded applications.

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Herein, we succeeded in preparing zirconium phosphate with a nanoflake structure. Its fluoride sorption behavior and stability were well investigated by batch adsorption tests. Commercial ZrO2

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and the ion-exchange resin D201 were studied for comparison. XPS analysis was performed to

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elucidate the possible sorption mechanism.

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2. Material and methods 2.1. Materials The reagents used were of analytical grade and purchased from Tianjin Reagent Station (Tianjin, China). The macroporous polystyrene anion exchanger D-201 (Cl-type), bearing the

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quaternary ammonium ([-CH2-N(CH3)3Cl]) group with an exchange capacity of 3.20 meq/g, was kindly provided by Zhengguang Resin Co. Ltd. (Zhejiang Province, China). It had a globular

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structure with particle diameters ranging from 0.6 to 1.0 mm. Before use, the resins were thoroughly rinsed with 1% hydrochloric acid, 1wt % sodium hydroxide and deionized water to

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remove residue impurities until neutral pH (6.8-7.2) and then vacuum desiccated at 343K for 24h until a constant weight was detected. The commercial ZrO2 powders were purchased from Aladdin Company, China, and used without further purification. 2.2. Preparation of layered ZrP nanoflake

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Layered ZrP was prepared using a simple previously cited in-situ precipitation procedure, with some modification(Trobajo et al., 2000). Specifically, 5 g of zirconyl chloride was first dissolved

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into a 50 mL ethanol solution at room temperature and 0.1 M HCl was added to inhibit possible hydrolysis; The solution thus prepared was introduced into a flask containing 200 mL of a 12 M

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H3PO4 solution gradually and a minute amount of white precipitation (ZrP gels) was formed immediately according to the following reaction: ZrOCl2 (aq)+H3PO4 (aq)→Zr(HPO3)2 (s)+HCl (aq)+H2O (aq) The above mixture was stirred thoroughly for 24 h at 333 K and then centrifuged to eliminate the aqueous portion. The desired ZrP samples were thus obtained, and was sequentially rinsed by deionized water till a neutral pH was achieved. Finally the ZrP samples were freeze-dried for further use. 7

ACCEPTED MANUSCRIPT 2.3. Batch sorption experiments Batch sorption experiments were undertaken in 50 mL glass bottles as follows, and included investigation

of

solution

pH

effects,

competitive

tests,

kinetic

evaluation

and

the

sorption-regeneration cycles.

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Effects of solution pH: 0.05 g portions of the ZrP samples were place in glass flasks containing 50 mL aliquots of 10mg/L fluoride solution with varied pH values (1.0-14.0) and HNO3 (1%) and

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NaOH (1%) solutions were used to adjust solution pH to the desired value. Then the bottles were transferred into an incubator shaker (SHZ85 JINTAN,China) for shaking thoroughly at 200rpm for

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24 h at 298 K, in order to approach sorption equilibrium. Finally the fluoride concentration at equilibrium and corresponding solution pH were determined.

Competing sorption: Similar to the pH experiments, 50 mg of ZrP was introduced to a 50 mL solution containing certain contents fluorine solution and SO42-/NO3-/Cl- were also added as

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coexisting ions, Commercial ZrO2 powder and the ion-exchange resin D-201 were used for reference The sorption equilibrium was then achieved and the final solutions were filtered and

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fluoride concentrations assayed.

Kinetic experiments: Kinetic experiments were carried out using 1000 mL solution of 10mg/L

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fluoride solutions and 0.5 g of ZrP. The solution was sampled at various time intervals and the sampled fluoride contents and corresponding time were determined. Finally, a curve demonstrating the sorption capacity against time was obtained. Sorption-regeneration cycles: Sorption section was performed with 100mL fluoride solution (10 mg/L) coexisting with 200mg/L of SO42-, NO3- and Cl-, respectively, as the background and 0.1g of the ZrP sample. Sorption equilibrium tests were then conducted and the sorption efficiencies for fluoride removal were determined. The above mixtures were then subjected to centrifugal 8

ACCEPTED MANUSCRIPT separation at 8000 rpm/min. Regeneration section: The exhausted ZrP samples were regenerated by 20 mL of a 5% NaOH solution and 24 h of reaction sufficiently stripped the fluoride ions and regenerated the prepared ZrP. Such sorption-regeneration cycles were repeated five times. Note that before the next sorption

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section. Thorough washing with deionized water was necessary to remove residues of the alkaline solution.

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2.4 continuous application tests. 1 g of the ZrP nanoflake samples was introduced into a large vessel containing fluoride contaminated waters. Synthetic groundwater and acidic wastewaters were

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employed to evaluate the applicability of the ZrP sorbent. A peristaltic pump (HUXI bl-5, China) and an automatic fraction collector (BS-100A China) were also applied to adjust the feeding flow and effluent collection respectively. The collected samples were determined using an ion selective electrode and the flow history was also determined. Afterwards, regeneration tests were conducted

efficiency determination

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using 5% NaOH as the regenerant and amounts of desorbed fluoride were assayed for regeneration

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2.5 Analysis and characterization

The concentrations of the fluoride ions were determined using an ion selective electrode

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(Orion 720 ion analyzer). The possible Zr(IV) releases were determined by ICP-Ms (Agilent 7800) and the morphology of ZrP samples were obtained using emission scanning electron microscopy (Hitachi S-4800) coupled with energy dispersive spectroscopy with an accelerating voltage of 5–15 kV. Transmission electron microscopy (HRTEM, JEM2010) was also used to detect the lamella structure of ZrP, with the use of a Gatan CCD camera working at an accelerating voltage of 200 kV. The crystalline pattern of ZrP was determined using a Rigaku D/max 2550PC diffractometer (Rigaku Inc., Tokyo, Japan) with CuKߙ radiation of 0.1542 nm under a voltage of 40 kV and a 9

ACCEPTED MANUSCRIPT current of 200 mA. The XPS spectra were obtained on a PHI quantera spectrometer (USA). An Al Ka anode radiation source was conducted as the excitation source. The zeta potentials of the layered ZrP were examined at different solution pH values using Zetasizer Nano (Malvern Instruments Ltd,

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UK) with a laser autocorrelation analyzer.

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3. Results and Discussion 3.1 Characterization The prepared zirconium phosphate samples were investigated by SEM, TEM, XRD, DLS and FT-IR analysis. As shown in Figure 1a, the resultant ZrP had a uniform nanoflake morphology with

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particles size of ∼ 20-40 nm. TEM investigation (Figure 1b) further provided evidence of the nanostructure with particles approximately 40 nm in diameter, which coincides with the SEM

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observation. XRD analysis was performed with the purpose of determining the crystal structure of the prepared ZrP nanoflake; the powder diffraction patterns were recorded in the 2θ range of

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5°-100°, as depicted in Figure 1c. The diffraction peaks at 2θ values of 11.6o, 19.8o, 24.9o and 34.0o were indexed to (200), (-111), (-311), and (-511) planes The representative peaks suggested the presence of α-ZrP crystals on comparison with the standard card (PDF-34-0127) using the software jade 6.5, and an intense first peak corresponded to an interlayer distance of 7.6Å (Kan and

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Clearfield, 2016). DLS results of Figure 1d, further exhibits the particle statistics and the mean diameter is approximately 50-60 nm, which is slightly larger than the SEM observations.

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Furthermore, FT-IR spectra were acquired to identify the possible chemical components. As shown in Figure 2, the representative broad peak at ∼ 3402-3460 cm-1 and the sharp band at ∼ 1641

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cm-1 confirm the presence of external water and the strongly hydrogen-bonded OH respectively(Zhao et al., 2017). An intense band at 1020-1050 cm-1 is attributed to the symmetric stretching vibration of P−O bonds within PO43-. The distinct absorption bands at ∼516 and ∼617 cm−1 obtained for the primitive ZrP nanoflake can be attributed to Zr-O vibrations(Bashir et al., 2016). It is noteworthy that fluoride uptake can bring about obvious intensity decreases and large blue shifts of ∼540 and ∼625cm−1, indicating the possible formation of Zr-F complexation(Pan et al., 2007). In addition the large band shifts (∼24 and 8 cm−1) further prove the possible strong 11

ACCEPTED MANUSCRIPT affinity between Zr-O and fluoride species and the detailed mechanism is further elucidated by XPS investigation. 3.2 Solution pH effect on adsorption and remarkable stability The effects of solution pH on fluoride sorption were determined and the results were shown in

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Figure 3. As seen in Figure 3a，the ZrP nanoflake exhibit efficient adsorption capacities at low pH region (1 to 3) and then follow a nonlinear falling curve with increasing solution pH values. It is

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speculated that the phenomenon is related to the charged species of ZrP and different F components (Figure 3b). Specifically, in acidic surroundings, the ZrPs are protonated with positively charged

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species, according to the zeta potential analysis (pHzpc = ∼3.10, Figure 3c), which favors negatively charged fluoride adsorption. Interestingly, at pH < ∼2.0, the F- ions will transform into neutral HF completely (Figure 3b), while the obtained robust F adsorption suggests possible present strong inner-sphere complexation between ZrP and HF species, a similar phenomenon was also seen in our

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previous study(Zhang et al., 2013b). Comparatively, at a higher pH region, the observed sorption decreases (pH > ∼3.2), which can be ascribed to the deprotonation process and the negatively

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charged ZrP surface strongly rejects the F- ion accessibility. It is noteworthy that the negligible F adsorption in alkaline conditions (approximately pH > 12), indicates possible regeneration using the

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NaOH solution. It is seems that the acidic wastewater might be more effective than drinking water purification, based on the pH-dependent adsorption. Additionally, he detailed sorption-regeneration tests are further evaluated in Section of 3.5. In addition, extremely low zirconium release at wide pH conditions (Figure 3a) further reveals the distinguished chemical stability of the ZrP nanoflake, similar results has been proved by Lee and Thakkar’s work (Lee et al., 2016; Thakkar and Chudasama, 2009). Such a property is far beyond the typical metal oxides or hydroxides adsorbents reported (Anderson and Rubin, 1981). 12

ACCEPTED MANUSCRIPT 3.3 Strong fluoride sorption selectivity Sorption selectivity is a crucial factor for ideal adsorbent assessment. Most sorbents usually exhibit large capacities, but inefficient working performances. Such phenomena can be attributed to possible strong competing interferences from the similarly charged SO42-, Cl- and NO3- ions, which

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always coexist at higher concentration in natural waters or industrial wastewaters. In this study, the influences of SO42-, Cl- and NO3- ions on fluoride adsorption by nano-ZrP, commercial ZrO2 and

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D201 were investigated. D201 was selected here for comparison，as ion exchange is a classical technique for fluoride ion removal from water while commercial ZrO2 is a representative material

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for fluoride removal. As shown in Figure 4a-c, the prepared ZrP nanoflake exhibits better defluoridation efficiency as compared to the referred sorbents. Interestingly, competitive ion addition can bring about a gradual sorption enhancement rather than suppression. As aforementioned, the preferential adsorption implies strong inner-sphere complexation between ZrP

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and fluoride species and the enhanced removal might ascribe to the possible anionic ligand-complex from SO42-, Cl- species. In addition, the nanosized structure within ZrP can also reveal abundance of

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active sorption sites, further enhancing the target fluoride sequestration enhancement. Comparatively, favorable fluoride uptake can be also realized by the commercial ZrO2

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particles, but its performance is still inferior to adsorption onto ZrP nanoflake. However, the ion exchange resin D201, is completely paralyzed at identical conditions and the competing anions greatly occupy the ion-exchange sites of the quaternary ammonium groups (-CH2N+(CH3)3Cl), within the D201 matrix. In particular, greater 16 times foreign ions additions can completely suppress its adsorption capability toward fluoride ions, implying non-specific fluoride adsorption. Considering the chemical component of quaternary ammonium groups, it is believed that fluoride adsorption onto D201 mainly originates from weak electrostatic forces; consequently, the high 13

ACCEPTED MANUSCRIPT concentration of common ions will significantly compete with trace fluoride removal. Next, we compared the ZrP nanoflake sample with four representative commercial adsorbents for defluoridation (Figure 4d), i.e. activated aluminum (AA), granular ferric hydroxides (GFH),

demonstrates its applicability and feasibility.

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manganese sand and magnetite. The favorable fluoride sequestration onto the ZrP nanoflake further

To further quantify the sorption selectivity, the distribution ratio Kd (mL/g) was using the

(C0 - Ce ) V C0 m

（1）

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Kd =

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following equations with the results of Table 1.

where C0 (mg/L) represents the initial fluoride concentration of the solution, V (L) is the volume of the solution, and m (g) is the mass of the adsorbent. Evidently, the substantially large Kd values (Table1) for ZrP samples further verifies its preferential sorption performances. It

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approximately equates to 7000 times greater than that of the commercial ion-exchange resin D201 and 5 times larger than the performances of ZrO2 materials. 3.4 Rapid sorption kinetics and sorption isotherms

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Sorption kinetics was also conducted as shown in Figure 5a-b. An extremely rapid fluoride

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uptake can be achieved in less than 5 min for equilibrium. The favorable adsorption can be partly ascribed to the nanosized morphology and the strong fluoride sorption affinity. Similar phenomenon was also reported by our previous study(Pan et al., 2007). In addition, the representative sorption models are also employed to describe the kinetic results with the following equations (Table S1).: ሺ‫ݍ‬௘ − ‫ݍ‬௧ ሻ = log ‫ݍ‬௘ − ௧ ௤೟

ଵ

௧

= ௞ଶ௤మ + ௤ ೐

௞ଵ ଶ.ଷ଴ଷ

‫ݐ‬

Pseudo-first-order model

(2)

Pseudo-second-order model

(3)

೐

Evidently, the sorption process can be well described by the pseudo-second-order model. In 14

ACCEPTED MANUSCRIPT addition, sorption isotherms can also provide fundamental information for F adsorption at different temperatures (Figure 5c-d,). The lower temperature favors adsorption of fluoride, suggesting a possible exothermic reaction. The representative Langmuir and Freundlich models are employed to

Q max KLCe 1 + KLCe

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Langmuir model

Freundlich model

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Qe =

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describe the sorption behaviors using the following equations

(5)

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where Ce is the fluoride contents at equilibrium, Qe is the adsorption capacity, and Qmax is the maximum sorption capacity for fluoride ions. KL (L/g) is a binding constant and Kf is the Freundlich constant to determine the kinetics; n is a parameter to evaluate the adsorption favorability. The detailed sorption parameters are shown in Table S2. The high correlation coefficients of R2>0.92

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suggest efficient description according to the Langmuir model with a maximum capacity of 55.8 mg/g, which can be well compared to the literature reported by the capacity and sorption rates

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survey (Table2).

3.5 Sorption mechanism elucidation

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XPS investigation was also performed to elucidate the possible sorption mechanism. Figure 6 a displays the binding energy onto the ZrP nanoflake and F-loaded samples. The distinct F1s peak located at ~685 eV, suggests the favorable fluoride adsorption. Next, the F1s peak was analyzed in detail: the binding energy of F1s for fluoride-loaded ZrP samples was located at ~685.7 eV; in contrast, the F 1s peak, originating from pure NaF, was centered at ~684.9 eV(Pan et al., 2013). The distinct band shift of 0.8 eV to a higher binding energy suggests strong sorption affinity between the obtained ZrP sample and target F ions (Figure 6 b). 15

ACCEPTED MANUSCRIPT Similar results were also deduced from the Zr 3d spectra. The representative Zr 3d signals for primitive ZrP samples display two doublet satellite peaks (Figure 6c), located at ∼183.3eV (Zr 3d5/2) and ∼185.6eV (Zr 3d3/2) respectively(Hua et al., 2013; Qiu et al., 2015). The presence of satellite peaks at higher energies is often observed in La or Zr based oxides, which is interpreted as the

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result of charge transfer from the valence band of the ligand atom to the 4f orbital of the Zr atom. Fluoride uptake can lead to obvious disappearance of the satellite peaks, instead of a broad band

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with an expanded full width at half maximum (FWHM) value of ∼4.06 eV (Figure 6c), implying the emergence of new fluoride-complex. Therefore, the peaks should be classified into two groups

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of satellite peaks, i.e. the original Zr3d5/2 (∼183.3eV) and Zr3d3/2 (∼185.6eV) peaks and the peaks for the newly formed complex at ∼184.4eV and ∼186.8 eV respectively. The large band shift of ∼1.1 eV suggests strong affinity and the formation of a new Zr-F complex(Mohan et al., 2016), further proving preferable F adsorption. Such a powerful interaction is probably ascribed to a

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so-called inner-sphere complexation and similar results have been reported and verified in recent study(Zhang et al., 2013c). In contrast, negligible peak variations were also obtained for Cl- loaded

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ZrP materials, further reflecting the weak adsorption. It also implies efficient selective adsorption toward fluoride against that of the common Cl- at high concentrations.

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3.6 Actual application evaluation

To examine the applicability of the ZrP nanoflake, continuous feedings of synthetic groundwater and industrial wastewater were selected to evaluate its adsorption performance towards fluoride ions. the main water compositions are listed in Table S3. Atractively, the applicability results (Figure 7) reveal that the prepared nano-sized ZrP materials display efficient adsorption capability for both groundwater and acidic wastewater. Based on the drinking water standard recommended by WHO (1.5 mg/L), remarkable application performances of 1800 kg and 16

ACCEPTED MANUSCRIPT 3900 kg respectively can be well approached before significant breakthough. In addition, the exhausted ZrP materials can be amenable to efficient regerenation by diluted alkaline solutions (5% NaOH) with the efficiency higher than 95 %. Prior to the next adsorption, the 0.1 % HCl and deionized water were used to buffer the extra OH- in regeneration until a netrual surroundings was

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achieved. The OH-, if released into water, is unfavorable for fluoride sequestration. Sorption-regeneration cycles further verify the material’s outstanding stability(Figure 7a- insert

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Figure). The negligible capacity loss over five cycles implies its efficient regeneration and repeated

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use.

4. Conclusion

Herein, we prepared a zirconium phosphate nanoflake by a simple in-situ precipitation procedure and successfully applied it towards anionic fluorides scavenging. The prepared ZrP

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material exhibits distinguished chemical stability against acids and bases over a wide range of pH values, better than reported metal oxide counterparts. More importantly, it exhibits efficient sorption

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selectivity for common anions additions and its performance exceeded that of commercial D201, activated Al2O3 and manganese sand. Such satisfactory sequestration can be ascribed to strong

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inner-sphere complexation formation, as confirmed by XPS investigation; continuous application tests further prove its applicability and superior treatment capacities of approximately 1800 kg and 3900 kg can be reached for groundwater and acidic wastewater treatment, respectively. In addition, the exhausted ZrP can be well regenerated for repeated use. All the results demonstrate that ZrP is a new adsorbent with good stability for trace fluoride sequestration in water.

Acknowledgments This work was financially supported by NSFC (grant Nos. 51578476, 21607080, 21473153, 17

ACCEPTED MANUSCRIPT 51422105), NSF of Hebei Province (grant No. B2016203056, E2015203404,), the China Postdoctoral Science Foundation (No. 2015M580214), Science and Technology Support Program of

Appendix A. Supplementary data

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Supplementary data related to this article can be found at

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Hebei Province (No. 15273626).the Support Program for the Top Young Talents of Hebei Province.

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Figure 1

Figure 1 (a) SEM image of the prepared ZrP nanoflake; (b) TEM of ZrP nanoflake;(c) XRD pattern

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for ZrP samples; (d) DLS analysis for particle size statistics onto ZrP nanoflake.

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Figure 2 FT-IR analysis of the ZrP nanoflake and fluoride loaded samples

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Figure 3 (a) Solution pH effects for fluoride removal and chemical stability in acid/base using the ZrP nanoflake (b) fluoride species distribution at various solution pH; (b) zeta potential analysis for

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Figure 4 (a-c) effects of SO42-, Cl- and NO3-ion addition on fluoride removal by D201, commercial ZrO2 and prepared ZrP nanoflakes respectively (conditions: 0.5 g/L sorbent, initial fluoride

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concentration of 10 mg/L at 298K) ; (d) fluoride sorption performance comparison of commercial

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activated aluminum (AA), granular ferric hydroxides (GFH), manganese sands and magnetite.

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Figure 5 (a-b) Fluoride uptake kinetics onto ZrP nanoflake. (a) The pseudo-second -order model; (b) the pseudo-first -order model (Conditions: dose of 1g/L, initial fluoride concentration of 10mg/L at

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298K) (c-d) Sorption isotherms t different temperatures, (c) Langmuir model; (d) Freundlich model.

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Figure 6 High-resolution XPS spectra of obtained ZrP nanoflake samples. (a) XPS spectra survey

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of ZrP nanoflake and fluoride loaded samples; (b) F 1s spectra of fluoride adsorbed ZrP and pure NaF; (c) Zr 3d spectra of primitive ZrP and F loaded ZrP samples as well as Cl-adsorbed ZrP samples.

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Figure 7 Continuous applicability evaluations for the ZrP nanoflake. (a) Synthetic groundwater, the insert figure reveals the sorption-regeneration cycles; (b) synthetic acidic wastewater; the insert figure is the regeneration curve.

(Regenerant: 5% NaOH solution; the influent components are

shown in Table S3) 30

ACCEPTED MANUSCRIPT Table 1 Evaluation of the selective coefficient Kd for adsorption on the ZrP nanoflake, commercial ZrO2 and D201 resin with different concentrations of added SO42-/ NO3-/ Cl- ions.

ZrP

2075

2246

2617

ZrO2

742

651

632

D201

71

14

ZrP

3149

2708

ZrO2

577

D201

6.2

ZrP

2922

ZrO2

1615

D201

491

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64

128

2617

3741

648

739

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12

8.3

0.5

2922

3386

2748

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Cl-

8

584

491

480

512

5.3

5.8

3.63

4.9

4194

3911

3958

5504

2274

1766

2095

2132

332

190

170

125

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NO3-

Kd (mL/g) at different ratios of M/F ions

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SO42-

Adsorbents

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4

Titanium/lanthanum oxides activated carbon (TLAC) Zr loaded fibrous protein

5

Al-humic acid-La aerogel

6

Monetite bundles inlaid chitosan beads Iron nanoparticles loaded tea

9 10

8.83

180 min

(Velazquez-Jimenez al., 2013) (Kanno et al., 2014)

27.2

30 min

(Jing et al., 2012)

57.9

100 min

(Deng and Yu, 2012)

50.0

40 min

(Liu et al., 2016)

50.1

120 min

(Shen et al., 2016)

@

in

Sulfate doped Fe3O4/Al2O3 nanoparticles lanthanum-loaded magnetic cationic hydrogel Zirconium phosphate nanoflake

2.18 70.4

et

4 min

(Ali et al., 2015)

200 min

(Chai et al., 2013)

60.9

120 min

(Dong and Wang, 2016)

55.7

< 5 min

Our work

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50 min

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7.42

Zirconium-Carbon Hybrid Sorbent Novel Apatite-Based Sorbent

References

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Kinetics (min)

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Sorption capacity (mg/g)

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Adsorbent

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Highlighted We develop the new applicability of ZrP towards F in waters ZrP exhibits a good chemical stability against acid or base environments

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Superior capacity can be attached with 3900Kg acidic wastewaters/Kg ZrP Its capability exceeds the commercial D201, AA, GFH, Manganese and Magnetite

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Fast Fluoride uptake can be achieve in below 5 mins