Tổng quan về các phương chế tạo Fe0 nano Từ các nghiên cứu trong và ngoài nước cho thấy, vật liệu nano sắt có thể được tổng hợp bằng nhiều cách khác nhau như phương pháp cơ học; phương pháp khử pha lỏng; phương pháp khử pha khí; phương pháp điện hóa,… Ngoài ra, các phương pháp biến tính vật liệu nZVI cũng được nghiên cứu nhằm nâng cao độ bền, khả năng phản ứng, giúp vật liệu đạt hiệu suất cao khi xử lý ô nhiễm môi trường.
Colloids and Surfaces A: Physicochem Eng Aspects 457 (2014) 433–440 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Removal of phosphate from aqueous solution using nanoscale zerovalent iron (nZVI) Zhipan Wen a , Yalei Zhang a,∗ , Chaomeng Dai b,∗ a b State Key Laboratory of Pollution Control and Resources Reuse, Tongji University, Shanghai 200092, China College of Civil Engineering, Tongji University, Shanghai 200092, China h i g h l i g h t s g r a p h i c a l a b s t r a c t • nZVI is a suitable and effective material for phosphate removal • pH affected the removal efficiency of phosphate significantly • Ionic strength did not affect phosphate removal • Coexisting anions (except carbonate anion) did not affect phosphate removal • Phosphate is mainly sequestrated within nZVI by adsorption and coprecipitation a r t i c l e i n f o Article history: Received March 2014 Received in revised form June 2014 Accepted 11 June 2014 Available online 18 June 2014 Keywords: Phosphate removal Adsorption Nanoscale zerovalent iron (nZVI) Eutrophication a b s t r a c t Nanoscale zerovalent iron (nZVI) was used to remove phosphate from aqueous solution, and the influence of pH, ionic strength and coexisting anions on phosphate removal was investigated The results agree well with both Langmuir model and Freundlich model, and the calculated maximum adsorption capacity of phosphate was 245.65 mg/g, suggesting significantly higher and excellent uptake of phosphate by nZVI The removal of phosphate obviously decreased with an increasing pH due to the isoelectric point (IEP) of nZVI, but exhibited no change with ionic strength and coexisting anions (except carbonate anion) The microstructure of fresh and reacted nZVI was characterized by FT-IR, XRD and XPS and these results indicated that no redox reaction occurred to the P(V) These observations shed light on the mechanisms of phosphate removal were mainly adsorption and coprecipitation processes The higher uptake of phosphate indicates that nZVI was a suitable and effective material for phosphate removal © 2014 Elsevier B.V All rights reserved Introduction In recent years, nanoscale zerovalent iron (nZVI) has been widely investigated for treatment of environmental contaminants ∗ Corresponding authors at: Tongji University, State Key Laboratory of Pollution Control and Resource Reuse, 1239 Siping Road, Shanghai 200092, China Tel.: +86 21 65985811/+86 21 65980624; fax: +86 21 65986960/+86 21 65989961 E-mail addresses: zhangyalei@tongji.edu.cn, zhangyalei2003@163.com (Y Zhang), daichaomeng@tongji.edu.cn (C Dai) http://dx.doi.org/10.1016/j.colsurfa.2014.06.017 0927-7757/© 2014 Elsevier B.V All rights reserved In previous studies, nZVI has been used for the removal of chlorinated organic compounds, polychlorinated biphenyls (PCBs) [1–3], heavy metals [4–7], and certain inorganic compounds [8,9] from wastewater or groundwater Compared to other bulk materials, nZVI has a larger specific surface area and high reactivity This nZVI can also overcome the narrow limitations of gravitational force and advance Brownian motion movement and dispersion [4] In addition, nZVI is a non-toxic material It is known that when iron reacts with water, it forms a thin oxide layer, which is expressed as oxyhydroxide (FeOOH) and hydrogen gas [10] As a result, nZVI has a core–shell structure with a zerovalent iron core and iron hydroxides as the shell Due to this characteristic core–shell structure, 434 Z Wen et al / Colloids and Surfaces A: Physicochem Eng Aspects 457 (2014) 433–440 nZVI presents unique properties and also a dual redox chemistry capability [6] As a major nutrient in aquatic ecology, phosphate has been regarded as the limiting factor responsible for water eutrophication, which depletes oxygen, affects aquatic life forms and jeopardizes water quality [11] Phosphate pollution includes municipal and industrial wastewater, agricultural drainage, stormwater runoff and household sources Therefore, most of the extra phosphate in wastewater should be removed before being discharged into water bodies, such as rivers or lakes At present, several methods have been widely applied to phosphate removal from wastewater, such as chemical precipitation, bacterial activity and adsorption by materials Chemical precipitation of phosphate with metal cations, such as Ca2+ , Al3+ and Fe3+ , is an effective method of phosphate removal from wastewater but not suitable for wastewater with high phosphate because of the large consumption of chemicals Phosphate removal by phosphateaccumulating bacteria (PCB) in activated sludge is also widely used in conventional sewage treatment plants, but phosphate removal is limited by biological conditions and wastewater composition [12] Furthermore, this approach will produce excess sludge containing high concentrations of phosphate and other pollutants, such as heavy metals, which are notably difficult and costly to treat Among these methods, adsorption seems considered to be one of the most promising technologies for phosphate removal because it is simple to operate, cost-effective, high removal efficiency and versatile for different water streams So numerous adsorbents, such as fly ash, red mud [13–16], steel slag [17,18], iron-based components [11,19–22] and zirconium [23,24] have been widely used to remove phosphate from aqueous solutions However, the serious drawback for those adsorbents was low adsorption capacity of phosphate, which limited the usage of these adsorbents Moreover, certain adsorbents such as natural mineral that contained organic pollutants and heavy metals could release into water during the process of water treatment and cause secondary pollution Despite the widespread use of nZVI in treatment of organic contaminants and heavy metals, to our best knowledge, few paper discuss phosphate removal by nZVI [25] In the present study, nZVI was used to remove phosphate from aqueous solutions, and the influence of certain relevant factors including pH, ionic strength and coexisting anions were investigated The microstructure of the fresh and reacted nZVI was characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to reveal the detailed mechanisms of phosphate removal by nZVI, with the goal of providing a more effective and environmentally friendly method to remove phosphate from water, especially water with high phosphate concentrations Materials and methods 2.1 Materials All reagents were analytical grade and were used without further purification Nanoscale zerovalent iron (nZVI) was synthesized by reduction of ferric iron (FeCl3 ·6H2 O) (Sigma-Aldrich, USA) by sodium borohydride (NaBH4 ) (Sigma-Aldrich, USA) as reported previously [10,26] according to the following reaction: 4Fe3+ + 3BH4 − + 9H2 O → 4Fe0 ↓ + 3H2 BO3 − + 12H+ + 6H2 ↑ Briefly, a 1:1 (v/v) mixture of FeCl3 ·6H2 O (0.05 M) and NaBH4 (0.2 M) was vigorously stirred in flask for 30 The nZVI precipitate was collected with vacuum filtration and washed with deionized water The iron nanoparticles were refrigerated in a sealed container under ethanol at ◦ C to minimize any reaction with water The BET surface area of this obtained nZVI was approximately 27.65 m2 /g, which was consistent with the previous report (30 m2 /g) [5] Standard phosphate stock solution was prepared by dissolving anhydrous potassium orthophosphate (KH2 PO4 ) (Sigma-Aldrich, USA) in appropriate amounts of deionized water, and stored at ◦ C 2.2 Batch phosphate removal and equilibrium experiments The adsorption kinetics experiments were performed in glass bottles (35 mL) containing 30 mL of phosphate solution at 10 mg/L Upon adding a certain amount of adsorbent (30 mg), the bottles were sealed with screw caps and placed in the thermostatic shaker (200 rpm) at 25 ◦ C Individual bottles were sacrificed after certain time intervals (5, 10, 15, 30, 60, 90, 120, 150, 180 min) and immediately filtered by a 0.45 m membrane, and the residual phosphate concentrations of the filtrate were determined Equilibrium experiments were carried out by adding 30 mg adsorbent into a series of 35 mL bottles filled with 30 mL phosphate solutions at different concentrations (10, 20, 50, 100, 200, 400, 600, 800, 1000 mg/L); the bottles were sealed with screw caps and placed in the thermostatic shaker (200 rpm) at 25 ◦ C for h to ensure equilibrium 2.3 Effect of pH The phosphate solutions (30 mL, 100 mg/L) and adsorbent (30 mg) were mixed in the batch bottles, then the pH of the mixed solutions was adjusted to the desired values ranging from 3.0 to 12.0 by adding HCl or NaOH solution The sealed bottles were placed in the thermostatic shaker (200 rpm) at 25 ◦ C for h to ensure equilibrium 2.4 Effect of ionic strength The effects of ionic strength on phosphate removal were performed in the same fashion as pH measurement nZVI (30 mg) was added to 30 mL (100 mg/L) sample phosphate solutions containing a known concentration of NaCl (0.005–0.1 M), and mixed in the batch bottles The sealed bottles were placed in the thermostatic shaker (200 rpm) at 25 ◦ C for h to ensure equilibrium 2.5 Coexisting anions The amount of phosphate adsorbed was measured to evaluate the effect of coexisting anions, including chloride, nitrate, sulfate and carbonate, which were often present in the surface water and wastewater Solutions of sodium chloride, sodium nitrate, sodium sulfate and sodium carbonate at a concentration of 0.1 M were added to the phosphate solutions (100 mg/L, 30 mL), and 30 mg adsorbent was later added After h balancing in the thermostatic shaker (200 rpm) at 25 ◦ C, the equilibrium concentration of phosphate was determined 2.6 Analytical methods Samples were filtered through a 0.45 m membrane, and the residual phosphate concentrations were analyzed according to a standard method (ascorbic acid molybdate blue method) The soluble total Fe concentration in the samples at a predetermined reaction time was measured after filtration through a 0.45 m membrane, in which mL filtrate was added to mL deionized water (containing 10% ultrahigh purity HNO3 ) and measured by inductively coupled plasma spectrometry Optical Emission Z Wen et al / Colloids and Surfaces A: Physicochem Eng Aspects 457 (2014) 433–440 435 Spectrometry (ICP-OES, Agilent 720ES, USA) The samples’ pH was determined by a glass potential meter 2.7 Characterization of nZVI Fourier transform infrared (FT-IR) spectroscopy spectra of samples were recorded to monitor changes in the functional group of the ZVI before and after the adsorption tests on a Nicolet 5700 spectrometer using KBr pellets in the range of 4000–400 cm−1 The nZVI before and after adsorption were placed in a glass holder and scanned from 10◦ to 90◦ , with the scanning speed set of 1o min−1 and a step size of 0.02◦ The results were recorded by a Bruker D8 Advance Powder X-ray Diffractometer (XRD, Germany) ˚ radiation source, while the operation using a Cu K␣ ( = 1.54178 A) voltage and current were kept at 40 kV and 40 mA, respectively Fresh and P-loaded nZVI samples were vacuum-dried, sealed under nitrogen and characterized using XPS performed on a Perkin Elmer PHI 5000 ESCA System spectrometer equipped with a rotating Al anode generating Al K␣ X-ray radiation at 1486.7 eV The X-ray beam was monochromatized using seven crystals mounted on three Rowland circles Samples were analyzed in the C 1s, O 1s, Fe 2p and P 2p regions, which accounted for the major elements present at the surface of samples Fig Phosphate removal (mgP/g) and percentage phosphate removal Results and discussion 3.1 Batch phosphate removal and equilibrium experiments The phosphate removal batch study plays an important role for adsorption studies because it can predict the equilibrium time and removal rate of phosphate from aqueous solution by an adsorbent Fig presents the phosphate removal and the soluble total iron concentration in aqueous solution as a function of contact time With an initial concentration of 10 mg/L, the phosphate removal efficiency was more than 99% within and remained constant over 180 min, which agrees with the study published by Chouyyok [11], who used Fe(III)-EDA-SAMMS to remove phosphate, with adsorption equilibrium achieved at just Due to its high surface area, nZVI offered more active binding sites, and phosphate could be adsorbed rapidly and easily The soluble total iron concentration increased in the first 15 and later decreased from 2.64 mg/L to 1.35 mg/L by the end of the reaction Although the surface of the nZVI formed a layer of oxyhydroxide (FeOOH) due to the reaction of iron with water [4,10], part of the Fe2+ and/or Fe3+ was still released from nZVI and formed Fe(OH)2 and/or Fe(OH)3 , which were beneficial to the phosphate removal as a result of a subsequent coagulation/precipitation process [21] Fig shows phosphate removal and percentage phosphate removal versus phosphate equilibrium concentration The results were fitted with the Langmuir model (1) and Freundlich model (2), respectively: Ce Ce = + qe qmax KL qmax ln qe = ln KF + (1) ln Ce n (2) where Ce is the equilibrium concentration of phosphate (mg/L); qe is the equilibrium adsorption capacity (mg/g); qmax is the maximum adsorption capacity (mg/g); KL is the adsorption constant (L/mg); KF and 1/n are Freundlich isotherm constants related to adsorption capacity and intensity of adsorption, respectively The calculated isotherms parameters of the Langmuir and Freundlich models for phosphate are summarized in Table The adsorption data of phosphate was better fitted by the Freundlich model (R2 = 0.9818) than by the Langmuir model (R2 = 0.9369) from the correlation coefficients (R2 ), suggesting that phosphate experienced multilayer adsorption on the surface of nZVI The maximum adsorption capacity was 245.65 mg/g, which indicated that nZVI has more potential and was more effective than other reported related adsorbents [21–24,27] The constant KF of Freunlich model, which defined as adsorption capacity which described the arsenic Table Estimated isotherm parameters for phosphate adsorption by nZVI Langmuir isotherm model Fig The adsorption kinetics of phosphate and the total iron concentration Error bars represent standard error of the mean Freundlich isotherm model KL (L/mg) qmax (mg/g) R2 n KF R2 0.0145 245.65 0.9369 3.61 38.11 0.9818 436 Z Wen et al / Colloids and Surfaces A: Physicochem Eng Aspects 457 (2014) 433–440 Fig Effect of pH on phosphate removal Error bars represent standard error of the mean adsorbed on the adsorbent for the unit equilibrium concentration were 38.11, indicating nZVI exhibited higher adsorption capacity for phosphate, which was consistent with the experimental results Moreover, the values of n in Freundlich model for phosphate was greater than 1, suggesting this isotherm is nonlinear, which can be attributed to adsorption site heterogeneity, electrostatic attraction and other sorbent–sorbate interactions The percentage phosphate removal reached nearly 99% at a low initial phosphate concentration (10–50 mg/L) and decreased as the initial phosphate concentration increased to 1000 mg/L Søvik and Kløve [28] reported that chemical precipitation played an important role at a higher initial phosphate concentration; therefore, the phosphate removal mechanism at the high initial phosphate concentrations (100–1000 mg/L) may include adsorption and coprecipitation processes 3.2 Effect of pH The pH of the aqueous solution was an important parameter in the adsorption of cations and anions at the solid–liquid interface [29] The phosphate species present mainly depended on the pH of the aqueous solution H3 PO4 was the predominant species when the pH was lower than 2.1, between 2.1 and 7.2 H2 PO4 − predominated, between 7.2 and 12.3 HPO4 2− predominated, and the main species was PO4 3− when pH was higher than 12.3 [30] The effect of pH on the removal of phosphate from aqueous solution is depicted in Fig The phosphate removal efficiency decreased with increasing pH and dropped sharply between 7.0 and 8.0 This trend agreed with a previous study, which reported that strong phosphate adsorption depended on the solution pH [22] This effect was most likely observed because the isoelectric point (IEP) of the nZVI was approximately 8.0 [31,32]; the surface of the nZVI carries a positive charge when the pH of the solution was lower than the IEP and thus would adsorb the negatively charged phosphate species However, if the pH of the solution was higher than the IEP, the phosphate removal decreased because the nZVI surface carried more negative charges and had a lower affinity toward phosphate species At the same time, there were more OH− ions at high pH, which competed with the phosphate ions for the adsorption sites [27] One notable finding was that even when the pH Fig Effect of ionic strength on phosphate removal Error bars represent standard error of the mean of the solution ranged from 10.0 to 12.0, phosphate removal still reached 35% It was proposed that in this pH range, electrostatic attraction mechanisms may not be predominant, while the coagulation/precipitation process most likely exerted an important role Conversely, the equilibrium pH had an opposite trend compared to the phosphate removal 3.3 Effect of ionic strength Fig demonstrates that the phosphate removal was slightly dependent on the ionic strength, even when the NaCl concentration ranged from 0.005 M to 0.1 M A strong dependence on ionic strength was typical for outer-sphere complexes through electrostatic forces [24], but this result indicated the phosphate most likely formed inner-sphere complexes, which involves appreciable covalent bonding along with ionic bonding at the solid–liquid interface Furthermore, inner-sphere complexes (chemical bonds) were more stable than outer-sphere complexes (ion pairs) 3.4 Coexisting anions Several common anions, which could potentially interfere in the removal of phosphate, often coexisted in the surface water and wastewater Therefore, it was notably important to estimate their influence on removal efficiency during the process of phosphate removal from surface water or wastewater The results in Table indicated that the presence of 0.1 M chloride, nitrate or sulfate (a Table Effect of coexisting anions on phosphate removal by nZVI Matrix Initial pH Final pH % Phosphate removal Phosphate Phosphate + 0.1 M sodium chloride Phosphate + 0.1 M sodium nitrate Phosphate + 0.1 M sodium sulfate Phosphate + 0.1 M sodium carbonate 5.14 4.97 4.95 5.06 11.29 9.25 9.09 9.18 9.13 11.11 78.49 76.36 77.97 81.56 14.70 Z Wen et al / Colloids and Surfaces A: Physicochem Eng Aspects 457 (2014) 433–440 437 Fig XRD analysis of fresh nZVI and reacted nZVI Fig The FT-IR spectra of fresh nZVI (a), P (10 mg/L)-loaded nZVI (b) and P (100 mg/L)-loaded nZVI (c) concentration in approximately 30-fold molar excess of the phosphate) had only a small effect on phosphate adsorption However, carbonate strongly influenced phosphate adsorption, and the percentage of phosphate removal in this case was only 14.70% This phenomenon was due to the initial pH of the solutions The initial pH of the solution containing 100 mg/L phosphate and 0.1 M sodium carbonate was 11.29, phosphate removal decreased sharply due to OH− ions at high pH, which competed with the phosphate ions for adsorption sites [27], and electrostatic repulsion between the phosphate and the nZVI, the surface of which carried more negative charges at this pH value, which result in the decrease of phosphate removal This result indicated that common anions in surface water and wastewater did not affect the phosphate removal by nZVI 3.5 Characterization of nZVI Fig 5a is the FT-IR spectrum of fresh nZVI, and b and c represent the FT-IR spectra between 4000 and 400 cm−1 , of the nZVI that adsorbed 10 mg/L and 100 mg/L phosphate, respectively Broad and strong peaks at ∼3400 cm−1 (O H stretching vibration) and peaks at ∼1640 cm−1 (O H bending vibration) indicated the presence of physisorbed interstitial water molecules on the surface of the nZVI [33] The peak at 1327 cm−1 (O H bending vibration) indicated the presence of surface hydroxyls on nZVI After adsorption, a portion of hydroxyl groups were replaced by PO4 3− , and this peak was shifted to a higher wavenumber (1384 cm−1 ) and weakened [24] New peaks at 1090 cm−1 and 1060 cm−1 appeared on the spectra of P-loaded nZVI (In Fig 5b and c) compared to the fresh nZVI, which were attributed to the bending vibration of adsorbed phosphate P O, revealing some phosphate ions had been adsorbed the surface of nZVI It was worth noting that some extra peaks were also observed at 496, 543 and 568 cm−1 , which may be attributed to the lattice vibrations of Fe O Fe and Fe O iron–oxygen bonds [34,35] Fig compares the XRD patterns of fresh nZVI and reacted nZVI in the 2Â range of 10–90◦ For fresh nZVI, the three characteristic peaks that appeared at 44.6◦ , 65.2◦ and 82.3◦ could be indexed to (1 0), (2 0), and (2 1) (JCPDS No 06-0696), in which the crystal structure was a regular ␣-Fe crystalline state [36,37] The same peaks for Fe(0) also appeared on the reacted nZVI but the related peaks weaken; however, the reacted sample also contained additional P mineral phases, such as vivianite (Fe3 (PO4 )2 ·8H2 O) (JCPDS No 30-0662), which indicated phosphate was adsorbed on the surface of nZVI Vivianite was also formed while the nZVI was exposed to the HPO4 2− anions month [38] and appeared as a secondary mineralization product from the bioreduction of lepidocrocite (␥FeOOH) [39] In this present study, vivianite was the predominant mineral product X-ray photoelectron spectroscopy (XPS) is a versatile analysis technique that was used to investigate the composition and chemical state of nZVI before and after phosphate adsorption Fig presents the full-range survey spectra of fresh nZVI and P-loaded nZVI Based on photoelectron peaks, the major elements of fresh nZVI were consisted mainly of iron (Fe), oxygen (O) and carbon (C) The small amounts of carbon appearing on the spectra was due to exposure to air and water during the sample preparation and reaction [4] The P 2p spectra on the full-range survey of P-loaded nZVI indicated that the phosphate species present in aqueous solution had been adsorbed on the surface of nZVI, and the photoelectron peaks were more obvious if the phosphate initial concentration was higher The O 1s narrow scans in fresh nZVI and P-loaded nZVI can be deconvoluted into three overlapped peaks corresponding to oxide oxygen (O2− ), hydroxyl groups (OH− ) and adsorbed water (H2 O) From Fig 7a–c and Table 3, it was found that the O 1s spectra were quite different before and after adsorption M O (where M represents a metal oxide substrate) increased from 37.41% to 40.53% and 44.56%, this increase may be attributed to the new oxygen which from P O after phosphate was adsorbed on the surface of nZVI Moreover, P (100 mg/L)-loaded nZVI has relative high percentage of M O due to the more phosphate on the surface of nZVI In contrast, OH− decreased from 45.90% to 43.27% and 40.93%, respectively It was known that high concentration of Fe–OH was proposed as the main reason for the high phosphate adsorption capacity of nZVI However, by increasing the phosphate adsorbed on the surface of nZVI, some OH− would be replaced by phosphate, so the percentage 438 Z Wen et al / Colloids and Surfaces A: Physicochem Eng Aspects 457 (2014) 433–440 Fig Full-range XPS spectra of Fresh nZVI and P-loaded nZVI, O 1s spectra with three deconvolutions of Fresh nZVI (a), P (10 mg/L)-loaded nZVI (b) and P (100 mg/L)-loaded nZVI (c) of OH− decreased after P-loaded nZVI More than 2% percentage of OH− decreased compared P (100 mg/L)-loaded nZVI to P (10 mg/L)loaded nZVI, suggesting more phosphate had been adsorbed on the surface of nZVI Detailed XPS surveys on the Fe 2p and P 2p of nZVI are shown in Fig 8a and b The binding energies at 711.4 eV and 725.0 eV were assigned to Fe 2p3/2 and Fe 2p1/2 in Fig 5, and the separation of the Fe 2p3/2 and Fe 2p1/2 spin–orbit levels was 13.6 eV, which was attributed to Fe(III) ions However, the binding energies of 2p3/2 and 2p1/2 for fresh nZVI were 711.0 eV and 724.5 eV, Table Relative contents of O 1s in various chemical states Samples Fresh nZVI P (10 mg/L)-loaded nZVI P (100 mg/L)-loaded nZVI Chemical states Binding energy (eV) Percent (%) O2− OH− H2 O O2− OH− H2 O O2− OH− H2 O 529.99 531.32 532.71 530.06 531.29 532.36 529.86 531.24 532.69 37.41 45.90 16.69 40.53 43.27 16.20 44.56 40.93 14.51 respectively It was found that the binding energies of Fe were shifted to the higher binding energy after phosphate had been adsorbed on the surface of nZVI, suggesting the possibility that Fe atoms was involved in the adsorption In addition, the fresh nZVI yielded a small peak at 707.0 eV compared to the P-loaded nZVI, suggesting the presence of zerovalent iron (Fe(0) 2p3/2 ) [4] The missing metallic iron peaks in the P-loaded nZVI implied that surface corrosion occurred [40]; the nZVI core shrank, and the concomitantly thickness of the iron oxide shell increased after reaction [41] At the same time, a relatively small amount of zerovalent iron indicated that the surface of nZVI was nearly all iron oxyhydroxide, which could be expressed as FeOOH [10] High-resolution P 2p deconvoluted spectra are shown in Fig 8b Only one P 2p peak appeared at 133.4 eV, attributable to the P(V) O bonding, after phosphate adsorption, suggesting the phosphate ions present in aqueous solutions had been adsorbed on the surface of nZVI and no occurrence of redox reaction between phosphate ions and nZVI, although the latter always was realized to a strong reducing agent It was also obvious that the photoelectron peak at an initial phosphate concentration of 100 mgP/L was much greater than at 10 mgP/L, which was consistent with high-resolution O 1s deconvoluted spectra analysis that was discussed before Z Wen et al / Colloids and Surfaces A: Physicochem Eng Aspects 457 (2014) 433–440 439 Fig XPS survey on the Fe 2p (a) and P 2p (b) of nZVI Conclusions Nanoscale zreovalent iron (nZVI) was synthesized and characterized for removal of phosphate The adsorption results agree well with the Langmuir model and Freundlich model, and the phosphate removal is highly pH-dependent but only slightly dependent on the ionic strength The coexisting anions chloride, nitrate and sulfate did not affect phosphate removal, but removal efficiency was significantly impacted by the carbonate anion due to its initial pH value in solution The results of FT-IR, XRD and XPS indicate that the mainly mechanism of phosphate removal includes adsorption and coprecipitation and no occurrence 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