Synthesis of highly monodispersed, stable and spherical NZVI of 20

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Synthesis of highly monodispersed, stable and spherical NZVI of 20-30 nm on filter paper for the removal of phosphate from wastewater: Batch and column study Mohammad Arshadi, MK. Abdolmaleki, Hamed Eskandarloo, Morteza Azizi, and Alireza Abbaspourrad ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.8b01885 • Publication Date (Web): 26 Jul 2018 Downloaded from http://pubs.acs.org on August 3, 2018

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ACS Sustainable Chemistry & Engineering

Synthesis of highly monodispersed, stable and spherical NZVI of 20-30 nm on filter paper for the removal of phosphate from wastewater: Batch and column study M. Arshadi, MK. Abdolmaleki, H. Eskandarloo, M. Azizi, A. Abbaspourrad* Department of Food Science, College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853, USA

Corresponding Author; Email: [email protected]

Abstract A nano-biodegradable adsorbent was prepared by stabilizing nanoscale zero valent iron (NZVI) on cellulose filter paper. Characterization of the sample disclosed that the NZVI particles were rounded, well-monodispersed through the paper, and smaller than 30 nm in diameter. We explored this material’s ability to capture phosphate ions in batch and repeated operations, specifically studying the impact of pH, adsorption time, initial phosphate concentration, interference ions, and temperature. The equilibrium results were matched to dissimilar kinds of adsorption isotherms, with the Sips adsorption model displaying the best match. The stabilized NZVI indicated high reusability after 7 adsorption-desorption cycles. We also demonstrated how this nano-biodegradable adsorbent could be applied to eliminate phosphate ions from a real water source (Cayuga Lake). In the continuous system, the results confirmed that an enhancement in the initial phosphate ion concentration improved the phosphate removal ability of the filter-paper-stabilized NZVI, likely due to more motive power for mass transfer by the greater phosphate concentration. However, an enhancement in bed height and flow rate reduced phosphate removal because of the higher flow rate decreasing the reaction time of the solution and adsorbent, while the higher bed height resulted in a channeling effect. Breakthrough curves gained from fixed-bed column tests showed the strong potential of the NZVI for phosphate ion sequestration. An artificial neural network model was used to envision the phosphate ions removal in both batch and continuous systems by this composite. The adsorption mechanism of phosphate onto the filterpaper-stabilized NZVI was further investigated by X-ray spectroscopy, X-ray diffraction, elemental mapping, and zeta potential techniques. Keywords: Cellulose, filter paper, column, phosphate, adsorption, nanoscale zero valent iron, nano-biodegradable.

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Introduction The deposition and aggregation of phosphate ions in still bodies of water, like estuaries and lakes, has gained significant consideration worldwide in the past few years because of the harmful effects of eutrophication in such ecosystems. Phosphate ions are used in the synthesis of special glasses, including glass fibers and fiber-based military grade lasers, for bone scaffolds and degradable tissue in the human body, in sodium lamps, steel, and in other applications, such as pyrotechnics, toothpaste, pesticides, and detergents. Phosphorus is also a critical component in agriculture. However, it is also an insufficient supply, and strong information suggests that present global supplies of phosphorus will run out in 100 years.1 Phosphate ions can be present in aqueous media in various forms, including polyphosphate, organic orthophosphate, and metaphosphates. Among these compounds, orthophosphate is the predominant form found in industrial and municipal wastewater, featuring the following acid ionization constants (pKa1 = 2.1, pKa2 = 7.2, and pKa3 = 12.3). At pH more than 7.2, the primary sorts of orthophosphate that exists in water is HPO-24.2 Wastewater from raw municipal may include phosphorus concentrations that range from 4 to 15 mg/L.3 Nevertheless, some industrial wastewater, e.g., associated with detergent manufacturing and metal-coating processes, may have phosphate values in addition of 10 mg/L.4 When immense phosphate ion amount is found in water, some aquatic plant life like algae will flourish, ultimately causing a significant reduction in dissolved oxygen levels, resulting in decreased photosynthesis and biological productivity.5-6 The U.S. Environmental Protection Agency has suggested that phosphorus levels in water should be smaller than 0.05 mg/L to suppress this eutrophication phenomenon. A current limit of 10 mg/L for phosphorus in aqueous media was also mandated by The Florida Everglades Forever Act.7 NZVI has become a potent tool for the purification of polluted groundwater and soil, targeting chiefly organic contaminants like chlorinated pesticides and solvents and inorganic ones like phosphate, and or metal cations.8 NZVI is especially demanding for water remediation due to its huge surface area to mass ratio, which produces a high solidity of surface active sites. Furthermore, NZVI is magnetic, which can be used to accelerate the fast filtration of nano-iron from water and soil using an external magnetic field, making it a suitable nanoadsorbent for taking off the various contaminants. Unsupported and bare NZVI has many benefits, like high selectivity and reactivity.9 However, the propensity of bare NZVI to aggregate during processing leads to a reduction in reactivity and stability of these nanomaterials,8 which has prohibited their commercialization due to the difficulties come across when trying to separate and regain the unsupported NZVI from solution. Moreover, some industrial issues, like deposition and decay on the reactor walls, are related to the application of bare NZVI. These issues could be minimized by stabilizing NZVI on insoluble solid supports that feature great chemical, mechanical, and thermal stability. The support must also be robust enough to 2

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withstand the rough reaction conditions of NZVI.10 Additionally, cost will always be a factor in the development of such materials. Cellulose-based compounds have gained a great deal of interest for use as structural supports due to these materials’ biodegradability, sustainability, robust mechanical properties, natural abundance, and the inherent functional groups that enable rapid modification and functionalization, all while being low cost.11-13Moreover, cellulosebased composites include the added benefit that they can be valorized as a fuel at the end of their life period much more conveniently than those made of glass-fibers and thermoset resins, which both leave melted glass residues in the recovery boilers.14 For all of these reasons, cellulose has become an important material in purification industries, hastening its commercialization.15 In addition to these factors, cellulose has other attractive features, including its rigidity, high crystallinity, and insolubility in common organic solvents, making it a suitable support for pollution adsorbents.16 More importantly, the wicking properties of cellulose enable water molecules to travel by capillary effect without the need for an external and extra power source.17 The biocompatibility and porosity of cellulose also allows metal nanoparticle compounds (e.g., NZVI) to be stabilized in the paper framework, helping to increase the efficiency of NZVI in removing phosphate ions from aqueous media.18 Additionally, cellulose sheets are inexpensive, accessible in an extent range of thicknesses, feature well-defined pore sizes, are easy to handle, and can be safely discarded. In this work, we explore the feasibility of using cellulose filter paper modified with NaOH as a low-cost biodegradable support for NZVI in the sequestration of phosphate ions from wastewater. All of the used process in this paper for the preparation of NZVI on the surface of the filter paper was performed in water as the solvent instead of ethanol which already being used for synthesis of NZVI on the surface of the cellulose. 17 In fact, by using water as the solvent the size of the monodispersed NZVI decreased to lower than 30 nm instead of ethanol which resulted in the size of the obtained NZVI above 100 nm and they were aggregated together like chain-like structure. 18-19 In order to appraise the application of this nano-biomaterial composite, NZVI stabilized on NaOH activated filter paper (FP-OH-NZVI), we tested its ability at removing phosphate ions in a batch system and a continuous fixed-bed column. The impact of variables, like pH, temperature, contact time, flow rate, bed-height, and initial concentration on the adsorption efficiency of the immobilized NZVI on the filter paper were also studied. Additionally, here, an artificial neural network (ANN) was designed and employed to imitate the phosphate ions removal in both batch and continuous systems by the FPOH-NZVI. ANNs as a very suitable modeling techniques, are able to simulate and predict the experimental data. ANNs modeling are informative in simulating and eventually up–scaling complicated systems because it does not need the mathematical qualification of the phenomena which associated with the studied procedure.20-21 Recently, ANNs modeling technique has been used in different fields for scientific and engineering applications.19 The using of an ANN technique for the modeling of adsorption process can be a suitable strategy, due to the complexity of the reactions involved in adsorption process and mechanism of the process.



Experimental Materials Reagents were purchased from Merck used as received. Filter paper (Grade 40, 55 mm in radius) was purchased from Whatman. NZVI synthesis on modified filter paper The in-situ preparation of NZVI stabilized on filter paper begins with the preliminary modification of the cellulose with NaOH to optimize the adsorption of metal ions. First, 5 g of a single cut of filter paper was submerged in 1 L of distilled water at room temperature, followed by adding 0.1 M NaOH (50 ml) and vortex for ~2 h on an orbital shaker. The compound was segregated by filtration, and then purified using distilled water (DI) to remove any NaOH excess. This NaOH activated filter paper (FP-OH) was then dried at 50 oC for 4 h. Next, the FP-OH was impregnated with ferric chloride (FeCl3) accompanied by chemical reduction with NaBH4. Specifically, 0.25 g of FeCl3 anhydrous was dissolved in 90 mL DI, to which the FP-OH was added. Next, the mixture was then shaken for 25 min in order to immobilize the Fe ions on the filter paper (Fe(III)@FP-OH). Afterwards, the paper was removed from solution and air dried, at which point the material turned yellow. 2 g of NaBH4 was then homogenized in 100 mL of the DI. Fe(III)@FP-OH was then dispersed in 15 ml of the borohydride solution while stirring continuously on a shaker, resulting in the formation of visible black solid particles of NZVI in solution. After the complete injection of the NaBH4 solution, the mixture was then shacked for an additional 20 min, followed by separation of the paper composite by filtration, which was washed with water (30 ml) and ethanol (20 ml), resulting in the final product of NZVI stabilized on the FP-OH substrate. Hereafter, the immobilized NZVI on the FP-OH is named FP-OH-NZVI. Characterization techniques Zeta (ζ) potentials of the unmodified filter paper, FP-OH, and FP-OH-NZVI (0.1 mg/ml) samples were determined in NaCl aqueous solution (10−3 M) at neutral pH. Jasco FT/IR-680 plus spectrophotometer was used to record the Fourier transform infrared (FTIR) spectra by preparing 5 mg of each sample in 25 mg KBr pellets. X-ray diffraction (XRD) studies were performed by using a Philips X'PERT MPD diffractometer. Chemical analyses were performed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) via a Shimadzu ARL 34000 instrument (spectro-flamed; frequently, around 30 mg of the sample was dissolved in 4 mL of 4 : 1 HCl : H2SO4 solution and 21 mL H2O). The transmission electron microscopy (TEM) images were taken using an FEI T12 Spirit TEM STEM operating at 120 kV. Scanning Electron Microscope (SEM) images were taken by using a Zeiss Gemini 500 instrument. Samples were analyzed by X-ray photoelectron spectroscopy (XPS) using a Surface Science Instruments SSX-100 at an operating pressure of ~2x10-9 Torr. Monochromatic Al Kα X-rays (1486.6 eV) with 1 mm diameter beam size was used. At 4


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55° emission angle, photoelectrons were collected. A hemispherical analyzer ascertained the electron kinetic energy by using 50 V for high resolution scans and a pass energy of 150 V for wide/survey scans. Non-conductive samples were charge neutralized by using a flood gun. Batch removal of phosphate Adsorption experiments were performed in batch conditions: 1.72 g FP-OH-NZVI which supported 0.1 g NZVI, based on the total mass of the immobilized Fe (5.8 wt%) on the surface of FP-OH-NZVI, was vortexed with 100 ml of the phosphate solution (10.0–1000 mg/L) at 25 ºC. Each trial was carried out triple and the mean amounts in most of the experiments showed a relative standard deviation less than 2.2%. The time needed to reach equilibrium conditions was chosen by initial kinetic tests (results not shown). No meaningful discrepancy in the removal ability of phosphate by FP-OHNZVI was obtained between 0.5–24 h of contact. Finally, the aqueous phase was filtered and then the remained amount of phosphate was ascertained using ICP-AES. The quantity of uptake phosphate (qe) was calculated as: = . − /

(1)

in which V is the volume of the solvent (L); C0 and Ce are the starting and equilibrium liquid-phase values (mg/L) of the adsorbate (i.e., the phosphate ions); and m is the quantity of NZVI (g). This equation estimated that the alter in volume of the solvent was trivial as the volume filled by the adsorbent and the solute concentration were small. The quantity of the phosphate which adsorbed on the NZVI was determined with a calibration curve. We separated the used FP-OH-NZVI adsorbent by filtration after the first phosphate removal test to assess the material’s reusability. To desorb phosphate ions from the modified paper surface, we used various amounts of NaOH to regenerate the active sites of the FP-OH-NZVI. Then the samples were vacuum dried at 70 ºC for reuse under comparable conditions. For real world sample analysis, we collected water from the shore of Cayuga Lake in the city of Ithaca, and filtered it through a 0.45 µm membrane, followed by storage in plastic vials. The amount of phosphate in the real water sample was monitored by ICPAES. The elemental analysis of the Cayuga lake water by ICP-AES was tabulated in Table S1 which showed none phosphorous ions. The removal process was performed by spiking standard amounts of 50 and 100 mg L-1 phosphate ions in the lake water solution prior to exposure to the adsorbent. Column removal of phosphate The breakthrough tests were measured with a glass column (laboratory scale) with a length of 20 cm and an inside diameter of 1 cm. A plastic sieve was fixed at the end of the column with a 2 cm sheet of glass wool. The known amount of phosphate ion solution was injected downwards the column. Then, the column was tested at 3 separate flow rates (0.5, 1.0 and 2 mL min-1) for a phosphate solution amount of 100 mg L-1, pH 4, a bed height of 10 cm, and temperature of 25 oC. The glass fixed bed was loaded with the FP-OH-NZVI (radius 55 mm). The impact of the phosphate ion quantity on the removal potential of FP-OH-NZVI was evaluated using initial phosphate amounts varying from 100 to 300 mg L-1. However, the bed height (3, 6, and 10 cm) was tested at an initial phosphate amount of 100 mg L-1. The amount of FP-OH-NZI in a 10 cm 5 ACS Paragon Plus Environment


column height was about 11.25 g which was filled with 750 papers. Outflow water were gathered at the end of the column at orderly time interlude (0.5 min) and evaluated for phosphate ion amount via ICP-AES. The column curves were figured by graphing the ratio (Ct/C0) of phosphate ion concentration (Ct) at time t to the starting concentration (C0) versus time (t). ANN modeling In this work, for ANN modeling of phosphate removal by FP-OH-NZVI in batch and continuous operations the multilayer perceptron neural net was employed. Multilayer perceptron neural net is known as the most common category of multilayer feed–forward networks. It has an output layer as dependent parameters, an input layer of neuron as independent parameter, and several hidden layers. In designing the ANN– model, the number of output and input neurons was defined by the essence of the issue. The hidden layers can be more than one layer and they operate like feature detectors.22 In addition, a linear transfer function (purelin) at output layer and a three–layered back– propagation algorithm with tangent sigmoid transfer function (tansig) at hidden layer were applied for designing of the ANN–model. MATLAB software, 2016a version, was employed for all ANN calculations in this work. Results and discussion Characterization The successful chemical modification of the filter paper by NaOH and NZVI was confirmed by FT-IR spectroscopy (Figure 1A), in which a broad absorption band at 3250–3500 cm−1 decreased and the bands corresponding to aliphatic bond of the organic support (cellulose fiber) at 2916 and 2854 cm−1were reduced in the FP-OH-NZVI sample compared to the pristine \filter paper. The additional manifestation of a peak at 802 cm−1 after the NaOH/NZVI treatment was ascribed to Fe(0).23-24 The peaks at 709 cm−1 and 447 cm−1 can be ascribed to Fe−O stretching vibrations.25 The structure of the unmodified filter paper and FP-OH-NZVI were also characterized by XRD (Figure 1B). For the filter paper, the diffraction peaks occur at 15.1, 16.8, and 22.5°, equivalent to the cellulose crystalline phase.26When comparing XRD patterns of the pristine filter paper and FP-OH-NZVI samples, the largest diffraction peak that appears after modification occurs at 2θ = 53.0º, which is attributed to the α-Fe phase of the immobilized NZVI.26 It is thought that when the magnitude of the Fe(0) nanoparticle is less than 5 nm, the diffraction bands are remarkably widen and the intensity reduces (Figure 1B).27 Similar results were obtained after amorphous carboxymethyl cellulose was modified with nanosized iron.28-29 We studied the morphology and physical structure of the Fe(0) nanoparticle on the modified filter paper using SEM and TEM (Figures 1C–G). The cellulose strand of the filter paper after treatment with NaOH (FP-OH) was observed through SEM image and 6


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showed no particle in nanometer size on its surface (Figure S1). SEM images revealed that the immobilized NZVI have a nanospherical structure and are well distributed on the surface of the filter paper as single and bi-particles, even after 30 and 70 days (Figures 1C and 1D). The nanosphere sizes after 70 days were in the range of < 50 nm. Furthermore, the TEM images also confirmed that the Fe(0) nanoparticles were welldispersed and decorated on the cellulose strand of the filter paper. The diameters of these nanoparticles were below 30 nm, which increases their mechanical and chemical strength (Figures 1E-G).7 The hydroxyl rich groups of the filter paper’s cellulose fibers can create strong interactions with the prepared NZVI and consequently could prevent the particles from aggregating and deactivating, therefore, increasing their active sites available for interaction with pollutants.29 Using ICP-AES, we determined that the amount of immobilized NZVI on the FP-OH sample was ~14 mg, or 5.8% of the total mass of the FP-OH-NZVI material. Phosphate removal studies The impact of pH on the functional sites of the nano-adsorbent and the phosphate speciation in solution displays a prominent duty in the removal process. To indicate the domination of pH on the elimination ability of FP-OH-NZVI, we ran batch experiments at initial phosphate amounts of 100 and 250 mg L-1 and at pH ranging between 2.0 and 12.0 (Figure 2A). As the initial pH decreased from 7.0 to 3.0, the phosphate removal slowly enhanced from 73.7% to more than 99.9%. The lowest phosphate removal by FP-OH-NZVI (22.6 %) was obtained at a pH of 12.0, due to deprotonation of the -OH groups of the Fe(0) nanoparticles. The removal of phosphate was most significant in the acidic pH, 2.0–6.0. A feasible reason for this behavior is the fact that oxygen bearing functional sites on the surface of the FP-OH-NZVI sample (the dominant active sites are Fe-OH groups) become deprotonated and also negatively charged as the pH increases to the detriment of phosphate removal.30 This is because at basic pH the immobilized NZVI reactive sites are closely correlated with OH- ions, impeding the removal of phosphate ions due to electrostatic repulsion, and thus fewer reactive site of the NZVI are accessible to the bulk solution in order to adsorb phosphate. At acidic pH, the amount of H+ ions is high, which creates an electrostatic interaction between the acidic sites of the NZVI and the phosphate anions (H2PO-4). As the removal capacity of the FP-OH-NZVI at pH 4.0 was 99.8%, this pH was selected as the best value. Zeta (ζ) potentials of the unmodified filter paper, FP-OH, and FP-OH-NZVI (0.1 mg/ml) samples were determined in NaCl solution (10−3 M ) at neutral pH. For unmodified filter paper, the negative value surface charge (ζ = −26.0 ± 0.5 mV) is essentially owing to the hydroxyl sites of the cellulose. After the midification with NaOH and NZVI, the ζ-potential shifted to -38 mV and -18 mV, respectively, acknowledging that the surface of the filter paper was chemically altered after modification and the NZVI was successfully fixed on the FP-OH. Indeed, uncontaminated iron oxides commonly have zero point charges in the pH range of 7– 9.23,24 Therefore, FP-OH-NZVI displayed an increase in the ζ-potential magnitude as a result of substituting for oxygen-containing functional groups on the filter paper. Figure 2B reveals the influence of contact time (0–30 min) on the phosphate removal ions (100 and 250 mg L-1) by the FP-OH-NZVI (0.1 g) at 25 oC in a pH 4 aqueous solution. It is apparent that most of the phosphate is adsorbed in the first 5 min of contact time. The black surface of the FP-OH-NZVI sample was instantly solvated by water molecules and the FP-OH-NZVI reacted quickly with phosphate ions in the water. The highest % of removal of phosphate ions was 99.9% and 89.2% at initial 7 ACS Paragon Plus Environment


phosphate values of 100 and 250 mg L-1, respectively, after 10 min. Truly, the swift removal during the beginning stages of exposure is more likely as a result of the elevated concentration slop between the phosphate ions in water and that on the FP-OHNZVI surface as there are a huge amount of unfilled sites accessible on the NZVI in this era, while the observed lull after 6 min implies that a leisure rate of removal is happening, which may be due to the gathering of phosphate ions on the remaining FPOH-NZVI reactive sites. The adsorption of phosphate ions from water was completed in 10 min. In order to advance the removal process, we evaluated the removal isotherms for all subsequent experiments using a contact time of 10.0 min. To find out the mechanisms of phosphate ion removal by FP-OH-NZVI and the major parameters controlling the adsorption kinetics, we tested the empirical kinetic results of phosphate adsorption using intra-particle diffusion (IPD), pseudo-first-order (PFO), and pseudo-second-order (PSO) models (Table S2). The obtained kinetic variables for removal of phosphate ions by FP-OH-NZVI at different initial amounts of 100 and 250 mg L-1 are shown in Table 1. The perfect fitting model was the PSO model with a R2 of > 0.999. The value of qe,cal determined by this model was also very close to the experimental data (qe,exp). A plot of the linear form of the PSO equation for the removal of phosphate ions is displayed in Figure 2C. The consensus of the experimental data using the PSO kinetic model implied that the sequestration of phosphate ions by FP-OH-NZVI is due to chemisorption as the ratedetermining step of the elimination mechanism by valence forces along with exchange of electrons between the modified paper substrate and the targeted ions. The removal of phosphate by the stabilized NZVI is thought to be consisted of two processes with starting removal rates of 434.7 and 526.3 mg (g min)-1 for 100 and 250 mg L-1, respectively (Table 1), onto FP-OH-NZVI.31 In fact, the adsorption kinetic was correlated to the number of reactive sites on the heterogeneous surface of the FP-OHNZVI.31 Another virtue of the PSO model was that it evaluated the paper composite’s performance over the different phosphate concentrations. The FSO and PSO kinetic models cannot distinguish the diffusion mechanism through intra-particle diffusion. Thus, we also investigated the kinetic data by using the IPD model. For this purpose, the Weber and Moris plot (Table S2; qt versus t0.5) was applied to probe the IPD mechanism. The plots proceed throughout the origin if the diffusion of intra-particle was the only rate-determine step; if not, then border layer diffusion restrained the uptake to some degree. Our results showed that the plots were not linear through the full-time range, indicating that some procedures influenced the removal phenomenon. In order to see the impact of solution temperature on the reactivity of the adsorbent we also analyzed the equilibrium removal ability of phosphate ions by FP-OH-NZVI at different aqueous temperatures (15, 25, 60 and 80 ºC) at pH = 4.0 (Figure 2D). Increasing the temperature of the phosphate solutions from 15 to 80 ºC enhanced the removal ability of the FP-OH-NZVI toward phosphate. The thermodynamic variables 8


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derived from the van’t Hoff plot shown in Figure 2D correlated with the removal of phosphate ions by FP-OH-NZVI, specifically in terms of changes in the enthalpy (∆H), Gibbs free energy (∆G), and entropy (∆S) calculated by the equation: ∆G = −RT ln K (2) in which R (8.314 J (mol·K)-1) is the ideal gas constant, T (K) is the temperature, , and k (L g-1) is the adsorbate distribution coefficient (qe Ce-1). The van’t Hoff equation is explained by: ln K = ∆So/R-∆Ho/RT

(3)

in which the ∆S° and ∆H° values were obtained from the intercept and slope of the linear plot of ln K vs. 1/T, as indicated in Figure 2D. The results confirmed a favorable and spontaneous phosphate removal process by FP-OH-NZVI over the entire used temperature (∆G < 0) (Table 2). The ∆H for the sequestration of phosphate was negative, signifying the exothermic process in nature. The positive number of ∆S implied the enhanced disordering and the degree of freedom increases at the solidsolution interface through the removal of the phosphate ions by the FP-OH-NZVI, which lead to the partial dehydration of the phosphate molecules before uptake from aqueous solution, hence expanding the spontaneity. The result is also in consensus with the negative value of ∆H, in which the negative value of ∆H change for phosphate ion removal shows the removal process is exothermic nature. Additionally, elevating the temperature reduced the value of ∆G, which signified that phosphate elimination by the stabilized NZVI was thermodynamically favorable and spontaneous (Table 2). This behavior could be explained by the increased accessibility of reactive sites of the NZVI and greater activation of the FP-OH-NZVI at higher temperatures, as well as the greater mobility of phosphate ions in the water. In Figure 3A, we demonstrate the influence of various initial phosphate ion concentrations (10–1000 mg L−1) on the removal behavior of the filter paper, FP-OH, and FP-OH-NZVI samples. The obtained maximum capacity adsorption of unmodified NZVI was 232 mg/g at pH 4.0. The sequestration of phosphate decreased in the order of FP-OH-NZVI > NZVI> FP-OH > FP. FP-OH-NZVI was the most efficient system, removing more than 93.5% of phosphate from solution (initial amount of 200 mg L−1) after 10 min, while only 3.23% and 6.24% was removed by the filter paper and FP-OH, respectively. The removal by FP-OH-NZVI was initially swift (i.e., between 10 and 500 mg L−1 over 10 min), reduced slowly, and finally reached equilibrium. Increasing the initial phosphate concentrations in the bulk solutions resulted in decreased removal by FP-OH-NZVI, with phosphate adsorption decreasing from 99.8%, 95.3%, and 42.2 % for 50, 150.0 and 1000 mg L-1 phosphate solution concentrations, respectively (Figure 3A). However, the removal capacity of the FP-OH-NZVI appeared to saturate for phosphate ion amounts greater than 500 mg L−1, which could be due to the agglomeration of NZVI reducing the material’s specific surface area and blocking its active sites.32 The enhancement of phosphate removal with elevating initial phosphate ions amount may be correlated to a raise in electrostatic interactions (comparative to covalent interactions), in which the phosphate groups progressively occupy active sites with lower affinity until saturation is reached. The complete removal potential of FPOH-NZVI at low initial phosphate concentrations ( Na3C6H5O7 > Na2SO4). Higher base strength anions can more firmly bind to metalated adsorbents than lower base strength anions.31 However, the existence of anions can reinforce the influence of electric double layer compression on the active sites of FPOH-NZVI and eventually block the adsorbent surface active sites, as well as causing the release of adsorbed phosphate in the tested condition. The relatively low removal ability of FP-OH-NZVI for phosphate in the existence of NaHCO3 implies that stabilized NZVI has greater affinity to complex with HCO3-, which would reduce the removal of phosphate ions from wastewater.

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Reusability Increasing the solution ionic strength significantly enhanced the phosphate desorption from the active sites of the FP-OH-NZVI (Figure 3C). With a 0.5 M NaOH concentration, 83.0% of the phosphate was released from the paper substrate after 2 h, though only 17.0% was desorbed at a lower NaOH concentrations. The effectiveness of the removal procedure was over 99% when 1.0 M NaOH was used. Additionally, we found that the phosphate removal capacity of the FP-OH-NZVI was almost unaltered after regeneration via NaOH. No loss of removal capacity was detected (11% after 7 runs), representing the high activity and stability of the modified filter paper even after 7 adsorption-desorption cycles (Figure 3D). Real water sample We further investigated the FP-OH-NZVI adsorbent’s ability to remove phosphate by testing it on a real-body of water (Figure 4A). Our outcomes showed that the phosphate removal efficiency in this water sample by FP-OH-NZVI reached up to 99.9% for spiked phosphate ion amounts of 50 and 100 mg L-1 after 5 and 10 min, respectively. However, when the adsorbent was reused after 4 cycles, the removal capacity reached up to 99.9% and 95% for 50 and 100 mg L-1 phosphate ions, respectively, after 30 min. These results implied that FP-OH-NZVI as a nanobiodegradable membrane demonstrates valid and mighty prospective for the phosphate ions removal from real water sources. Column adsorption of phosphate ions by FP-OH-NZVI Influence of the concentration of phosphate ions on the breakthrough curves In order to assess the empirical implementation of FP-OH-NZVI for the continuous phosphate ions removal from aqueous media, we set up a column removal test. It is thought that the amount of phosphate ions can influence the breakthrough curve.9 Thus, we prepared three phosphate solutions with initial amounts of 100, 200 and 300 mg L−1, to analyze the potential of the modified nano-paper-based adsorbent in the continuous system. By graphing the Ct/Co (phosphate concentration in the effluent/phosphate concentration in the influent) against time, the breakthrough curves for the column were estimated (Figure 4B and Table 4). Our results showed that the breakthrough times decreased as the phosphate ion concentration increased, displaying an S-type curve. The column removal efficiency (qe) for phosphate ions by FP-OH-NZVI was 226, 312.1 and 561.1 mg g−1 when the phosphate solutions concentrations were 100, 200, and 300 mg L−1, respectively. The breakthrough times were 28.5, 15.5, and 17 min for phosphate solutions concentrations of 100, 200 and 300 mg L−1, respectively. In the same manner, the exhaustion time reduced by enhancing the initial value of phosphate from 59 min (100 mg g−1) to 48 min (200 mg g−1) and finally 17 min (300 mg g−1), in which faster breakthrough and exhaustion occurred at higher influent phosphate ion concentration, which could be due to the less mass transfer limitation and more concentration gradient at higher initial ion concentrations.33-34 Flow rates influence on the breakthrough curves We measured the influence of different flow rates (0.5, 1, and 2 mL min−1) on the breakthrough curves of the phosphate adsorption for a fixed 100 mg L−1 initial concentration (Figure 4C and Table 4). Based on the results, shorter breakthrough times 11 ACS Paragon Plus Environment


took place at elevated flow rates. Larger volumes of aqueous solutions pass along the bed at higher flow rates, which means that more phosphate ions have attractive interactions with the active sites of FP-OH-NZVI and saturate them faster. Furthermore, a higher removal ability was found at lower flow rate, as a lower flow rate enables longer interaction times for the phosphate ions through the column, allowing equilibrium to be approached before the ions pass through the media.35 Influence of bed height Figure 4D displays the breakthrough curves of various bed heights (3, 6, and 10 cm) when flow rate and phosphate amount were stayed continual at 0.5 mL min-1 and 100 mg L-1 respectively, in which exhaustion time te and breakthrough time tb were enhanced by extending the bed height, whereas the gradient and shape of the breakthrough curves were somewhat changed at diverse bed heights. By rising bed height, the slope of the breakthrough curves reduced, which is related to a extended mass transfer zone. Table 4 displays the removal results obtained from this experiment. With increasing bed height, the column phosphate removal potential decreased. It is thought that channeling effects become enhanced with increased column height, which may be in this case resulting in the deteriorated column performance. This phenomenon could be suppressed by increasing the diameter of the column.35 We applied the Thomas model to forecast the dynamic behavior of column implementation (Tables S1and 4), in which the correlation between concentration and time provide valuable data about the affinity, properties of surface, and adsorption pathways of the adsorbent [36]. The Thomas model was established on the supposition that (1) the removal process is not confined by chemical interactions nevertheless by mass transfer at the interface, and (2) that the experimental results obey second-order kinetics and Langmuir isotherms, where the plots of ln[C0/Ct) / 1] vs. time (t) result in a straight slope (kTh) and intercept (qe) (figure not revealed).9, 36 By increasing the flow rate (0.5 to 2 mL/min) the constant of Thomas rate was also improved (1.45 to 3.72 L/(min mg)) and the removal capacity decreased (226 to 144 mg/g). However, raising the initial phosphate concentration (100 to 300 mg/L) caused an increase in the Thomas rate constant (1.45 to 1.96 mL/(min mg)) and removal ability of the system (226 to 563 mg/g). Enhancing the height of bed (3 to 10 cm) caused in a reduction in the constant of Thomas rate (3.42 to 1.45 mL/(min mg)) as well as removal capacity (311 to 226 mg/g). The higher removal ability at the elevated feed phosphate anion concentration could be related to the higher driving force and greater concentration gradient for the transfer process to suppress the mass transfer limitation.37 For most of the variables studied, the Thomas models correlation coefficients (R2) were over 0.9 (Figures 4B-D). This confirms the succesfully of the Thomas model to apply for the FP-OH-NZVI removal system. It also proposes that the removal procedure of phosphate is not controlled by internal or external diffusion.38 Mechanism study 12


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To elaborate on the interactions of the adsorbed phosphate ions with the NZVImodified filter paper (FP-OH-NZVI@P), we measured the XRD pattern of the paper composite after shaking it for 24 h with a phosphate solution (500 mg/L) (Figure 5A). The XRD results showed the presence of phosphate on the FP-OH-NZVI@P sample. Indeed, the obtained XRD pattern was intricate due to the existence of iron oxides and oxyhydroxides, however, it exhibited a reflections enhancement that were attributed to Fe3(PO4)2·8H2O (vivianite). The 2θ values at 12.1o, 12.5o, 18.5o, 20.3o, 24.85o, 28.1o, 29.1o, and 34.9o were specifically related to the vivianite structure.39 However, the appearance of new peaks at 33.3o, 38.9o, 43.2o, 57.0o, 57.5o, and 53o could be attributed to the oxidation of the immobilized NZVI on the filter paper after exposure to phosphate, indicating the existence of Fe(0) and Fe3O4/γ-Fe2O3.40 The Fe(0) peak after adsorption of phosphate can still be observed and the intensity of XRD reflection for Fe(II) and Fe(III) enhanced, implying that the immobilized NZVI was not oxidized completely by air and water on the surface of the filter paper. Magnetite can induce a conductive situation between the inner electron-rich core and the active species of surface in bulk solution.41 In fact, the generation of both maghemite and hematite, with less conductivity than magnetite, at the surface of FP-OH-NZVI can possibly decrease the oxidation degree and activity of the nano-sized iron. To further study the mechanism of phosphate uptake onto the immobilized NZVI, the FP-OH-NZVI zeta potentials was measured after the capture of phosphate (500 mg/L) (Figure 5B). The surface charge of the FP-OH-NZVI@P sample (after removal of phosphate from solution) was shifted to negative values compared to FP-OH-NZVI. Phosphate ions were adsorbed through the attractive interactions between the anionic phosphate and the immobilized NZVI active sites at pH 7.0,23,24 which increased the negative charge of the FP-OH-NZVI sample. XPS analysis also provided essential information about the mechanism of phosphate adsorption by the modified filter paper. Beginning with the Fe 2p XPS spectrum of FPOH-FeCl3 (the precursor of FP-OH-NZVI), the results showed two main bands at around 708.6 and 721.9 eV along with a satellite peak at 715.3 eV (Figure 5C). The distance, position, and shape of the Fe 2p1/3 and Fe 2p2/3 peaks in the XPS spectrum of the FP-OH-FeCl3 sample and its satellite peak implied that Fe(II) ions were produced through the immobilization of FeCl3 on the functional groups of the filter paper. However, the binding energies (BEs) of 708.6 and 712.8 eV could be marked as Fe(III) in the form of oxide and in chloride, respectively, which might be attributed to the trilayered arrangement of FeCl3, in which the Fe ion is sandwiched between two layers of Cl. In fact, the immobilized Fe(III) ions on the filter paper showed a higher Fe 2p BE than the pure FeCl3, which verified the iron ions interaction with the functional sites of the cellulose substrate. The Fe 2p core level survey of the FP-OH-NZVI sample showed several peaks at 703.2, 707.3, 711.0, 717.2, and 721.1 eV, which could be related to the BEs of the 2p3/2 peaks of Fe(0), Fe (2p3/2), the shake-up satellite 2p3/2, and the overlap of the shakeup satellite of Fe2O3 (2p3/2) and Fe(0) (2p1/2) and Fe (2p1/2), respectively (Figure 5D).42-43 The appearance of a low BE peak of medium intensity (703.2 eV) demonstrated that the thickness of the Fe2O3 shell around the Fe(0) core of the NZVI particles was less than 8 nm (also observed by TEM, Figure 1G). To determine the stability of the FP-OH-NZVI adsorbent, we measured the XPS spectrum again after 60 days, at which point a small Fe(0) peak could still be observed at 702.9 eV (Figure 5E). This implied that the NZVI was protected from complete oxidation and agglomeration after exposure to air by being synthesized in situ on the surface of the filter paper.8 13 ACS Paragon Plus Environment


We also assessed the surface chemical composition of the FP-OH-NZVI composite after the adsorption of phosphate by XPS analysis (Figure 5F). The peak of the metal iron was observed after adsorption of phosphate which could be related to the thickness of the outer shells of the Fe(0) core. It is thought that the adsorbed phosphate on the oxide shells can make a layer that suppresses additional oxidation of the surficial Fe(0).44-45 We also studied the O 1s peak of the filter paper, FP-FeCl3, FP-OH-NZVI, FP-OHNZVI after 70 days, and FP-OH-NZVI@P samples, the results of which are shown in Figures 6A-D. The high-resolution O 1s XPS spectrum of the pristine filter paper demonstrated a peak at 529.5 eV, which might be allocated to the hydroxyl groups of the cellulose (Figure 6A). Upon interaction with FeCl3, the O 1s peak at 529.5 eV shifted to 529.3 eV and the wide peak deconvoluted into three peaks with BEs at 532.2, 529.3 and 528.0 eV (Figure 6B). The appearance of a peak with BEs of 528.0 and 532.3 eV could be associated to the interaction of Fe with -OH groups on the surface of the filter paper (Fe–O)45 and physically or chemically adsorbed water molecule on the surface, respectively.46-47 Furthermore, the O 1s spectrum of FP-OH-NZVI showed three peaks at BEs of about 532.4, 529.0, and 528.2 eV (Figure 6C). The dominant peak at 528.2 eV is attributed to the Fe-O bond, while the two other O1s peaks at around 529.0 and 532.4 eV are attributed to Fe-OH (hydroxyl bonded to metal (Fe-OH and lattice hydroxyl (Fe-OH lattice)) and attached H2O on the surface, respectively. However, the O 1s spectrum of FP-OH-NZVI after aging for 70 days showed that the peak assigned to the Fe-O species at 528.2 eV shifted to 527.4 eV and decreased, while the peak at 529.0 eV shifted to 528.5 eV and increased, indicating that the quantity of iron oxide increased over time (Figure 6D). Finally, the O 1s spectrum of FP-OHNZVI@P in Figure 6E could be fitted by four peaks at BEs of 532.4, 529.9, 528.4, and 526.7 eV, which could be related to adsorbed H2O, P–OH, P–O–Fe, and Fe–O bonds, respectively.45, 48-50 Moreover, the P 2p peak of the adsorbed phosphate was detected at a BE of 133.6 eV for FP-OH-NZVI@P (Figure 6F). Finally, SEM images of the FP-OH-NZVI material after 7 adsorption-desorption cycles of phosphate and its corresponding elemental maps are shown in Figure 6G–K. The SEM image in Figure 6G shows two enlarged immobilized NZVI particles (> 100 nm in diameter) after using the material 7 times for the adsorption of phosphate. The EDS mapping images confirmed that phosphorus and oxygen signals were selective to the NZVI area, which not only confirms adsorption of phosphate by the metal, but also demonstrates that the elements were uniformly spread across the surface of the NZVI nanoparticles (Figure 6I-K). These results confirmed the significant potential of immobilized NZVI on the filter paper as an adsorbent for phosphate from wastewater, even after several cycles of membrane regeneration. From the results of the XRD, zeta potential, elemental mapping, and XPS analysis, it can be concluded that the phosphate ions adsorb on the Fe–OH bond and generate the Fe–O–P bond of Fe3 (PO4)2.8H2O.51 14


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ANN modeling The influences of input parameters on the removal of phosphate by FP-OH-NZVI in batch and continuous operations were simulated by employing a multilayer feed– forward ANN–model. For batch operation, the input parameters of the neural network were contact time, pH, initial amount of phosphate, and solution temperature, and the uptake efficiency of the adsorbent was considered as an output of the neural network. For the continuous system, the input variables of the neural network were flow rate, column height, and initial concentration of phosphate, and the phosphate concentration (Ct) in the effluent was the neural network output. The output and input parameters for the batch and continuous systems are listed in Tables S3 and S4, respectively. The experimental results were segregated into three subsets including; ½ training, ¼ validation, and ¼ test data. The experimental data (Yi) were scaled to a new value xi, as follows, because of the employed sigmoid transfer function in the hidden layer;52 0.6 ( X i − X min ) (4) ( X max − X min ) where Xmin is lowest rate of the input parameter Xi and Xmax is the highest rate. The neurons quantity in the hidden layer can affect the efficiency of the designed network. In order to assess the best quantity of neurons in the hidden layer diverse numbers of neurons (1 to 16) were studied. To avoid random correlation because of the accidental weights initialization, each topology was repeated 3 times. Figure S2 shows the effect of the quantity of neurons in the hidden layer on the performance of designed neural network, in terms of mean square error (MSE). Based on the obtained results, the lowest mean square error was for 8 (Figure S3A) and 6 (Figure S3B) neurons in the hidden layer for the batch and continuous operations, respectively. Accordingly, these quantities of neurons were chosen for the maximum efficiency of the designed ANN– model. The schematics of the designed ANN structures for the batch and continuous systems are illustrated in Figures 7A and 7B. The correlations between ANN–modeled results and experimental data for the test subsets are showed in Figures 7C and 7D. The lines have R2 of 0.97901 and 0.98727 for the batch and continuous systems, respectively, which are very near to one. The rate of R2 confirm the excellence of fit between experimental data and ANN–modeled results. These values allude very acceptable demonstrations of the removal of phosphate by FPOH-NZVI in both batch and continuous operations by the designed ANN–model and showing that the designed ANN–model can accurately simulate the removal of phosphate in both operations. The neural weights provided by ANN-model are given in Tables S5 and S6. Using the neural weight matrix, the relative weight of each input parameter on the output parameter can be evaluated.52 The percentage variation in the output parameter, because of the variation in the input parameter, was estimated for every input parameter, according to Eq. (2);53 Ni m=Nh  ho ih ih    W jm  × W mn W km ∑ ∑  k =1 m =1   I j = k = N m = N (5) Ni i h   ih ih  × W W km  ∑  W km ∑ ∑ k =1  m =1  k =1  x i = 0. 2 +



in which Ni and Nh are the number of inputs and hidden neurons, respectively; Ij is the relative significance of the jth input parameter on the output parameter; W’s are connection weights subscripts ‘n’, ‘m’, and ‘k’, respectively, denote to output, hidden, and input neurons; and the superscripts ‘o’, ‘h’, and ‘i’, respectively, denote to output, hidden, and input layers. Figures 7E and 7F establish an assessment between the influences of every input parameters, as estimate by Eq. (5), on the phosphate removal efficiency of batch and continuous operations. As can be seen in Figure 7E, initial phosphate concentration and solution temperature were found to be the most effective parameters on the removal efficiency of the batch operation, with a relative significance of 38% and 29%, respectively, after them contact time of phosphate and adsorbent with a relative significance of 21%. Initial pH, with a relative significance of 12%, was estimated as having a weak effect on the efficiency of the batch system. As can be seen in Figure 7F, flow rate was found to be the most effective parameters on the removal efficiency of the continuous system, with a relative significance of 51%, followed by column height with a relative significance of 34%. For the continuous system, the initial phosphate concentration had a weak effect (15%) on the efficiency of the uptake process.

Conclusion This work indicates that FP-OH-NZVI has strong potential as an efficient adsorbent for the phosphate ions sequestration. The batch experiment showed that the phosphate ions elimination from wastewater by FP-OH-NZVI was pH-dependent and pH 4.0 was obtained to be the optimal rate. The kinetic results confirmed that after 10 min the phosphate ions removal reached equilibrium, and this adsorption procedure complies with PSO model. Isotherm results disclosed that the removal equilibrium could be fitted fine by the Sips isotherm with a highest phosphate removal ability of 720 mg/g. FP-OHNZVI showed remarkable adsorption capacity, due to the good synergies of the simple in situ preparation of NZVI on the surface of the filter paper which resulted in a stable, monodispersed NZVI, green and low-cost adsorbent in comparison with the unmodified NZVI and other nanoadsorbents from literature (Table. S7). The obtained thermodynamic variables implied the phosphate ions removal by FP-OH-NZVI was spontaneous and exothermic process in nature. The stabilized NZVI showed high reusability even after 7 cycles of adsorptiondesorption. The prepared nano-biodegradable adsorbent can also be implemented to adsorb the phosphate from a real water taken from Cayuga Lake. Fixed-bed column investigations indicated that the phosphate ions removal by NZVI immobilized on cellulose filter paper was enhanced with increased influent phosphate concentration, while reduced with rising flow rate and bed height. The purification of wastewater by the FP-OH-NZVI column can be well estimated by the Thomas model, as indicated by the high R2 (> 0.95). 16


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The results obtained from the multilayer feed-forward ANN model demonstrated that the initial concentration of phosphate and flow rate predominantly affected the phosphate ions removal from wastewater by FP-OH-NZVI for the batch and continuous systems, respectively. The adsorption mechanism of phosphate onto FP-OH-NZVI was further investigated by XRD, zeta potential techniques, XPS, and elemental mapping, and the results confirmed the preparation of Fe3(PO4)2·8H2O (vivianite) on the surface of FP-OH-NZVI@P. Acknowledgements: This work made use of the Cornell Center for Materials Research's Shared Facilities, which are supported through the NSF MRSEC pro-gram (DMR-1719875). Supporting Information Concentrations of elements in Cayuga lake, SEM images Fe-OH, adsorption isotherm, and kinetics equations, equilibrium absorption of phosphate by FP-OH-NZVI. The ranges of the input and output variables for batch and continuous operations. Effect of the number of neurons in the hidden layer on the performance of the neural network for batch and continuous operations. Weight matrix for operational variables in the batch and continuous operations. References (1) Cordell, D.; Drangert, J.-O.; White, S. The story of phosphorus: Global food security and food for thought. Global Environmental Change 2009, 19 (2), 292-305, DOI: https://doi.org/10.1016/j.gloenvcha.2008.10.009. (2) Snoeyink, V. L.; Jenkins, D. Water Chemistry, Wiley: 1980; p 463 pp. (3) Eilbeck, W. J.; Mattock, G. Chemical processes in waste water treatment, E. Horwood: 1987. (4) Akay, G.; Keskinler, B.; Çakici, A.; Danis, U. Phosphate removal from water by red mud using crossflow microfiltration. Water Research 1998, 32 (3), 717-726, DOI: https://doi.org/10.1016/S0043-1354(97)00236-4. (5) Mayer, B. K.; Baker, L. A.; Boyer, T. H.; Drechsel, P.; Gifford, M.; Hanjra, M. A.; Parameswaran, P.; Stoltzfus, J.; Westerhoff, P.; Rittmann, B. E. Total Value of Phosphorus Recovery. Environmental Science & Technology 2016, 50 (13), 6606-6620, DOI: 10.1021/acs.est.6b01239. (6) Lee, C.-G.; J.J. Alvarez, P.; Kim, H.-G.; Jeong, S.; Lee, S.; Bong Lee, K.; Lee, S.H.; Choi, J. W. Phosphorous recovery from sewage sludge using calcium silicate hydrates, 2017; Vol. 193. (7) Dennison, W. C.; Orth, R. J.; Moore, K. A.; Stevenson, J. C.; Carter, V.; Kollar, S.; Bergstrom, P. W.; Batiuk, R. A. Assessing Water Quality with Submersed Aquatic Vegetation. BioScience 1993, 43 (2), 86-94, DOI: 10.2307/1311969. (8) Crane, R. A.; Scott, T. B. Nanoscale zero-valent iron: Future prospects for an emerging water treatment technology. Journal of Hazardous Materials 2012, 211-212, 112-125, DOI: https://doi.org/10.1016/j.jhazmat.2011.11.073. (9) Wen, Z.; Zhang, Y.; Dai, C. Removal of phosphate from aqueous solution using nanoscale zerovalent iron (nZVI). Colloids and Surfaces A: Physicochemical and 17 ACS Paragon Plus Environment


Engineering Aspects 2014, 457, 433-440, DOI: https://doi.org/10.1016/j.colsurfa.2014.06.017. (10) Arshadi, M.; Faraji, A. R.; Amiri, M. J.; Mehravar, M.; Gil, A. Removal of methyl orange on modified ostrich bone waste--a novel organic-inorganic biocomposite. Journal of colloid and interface science 2015, 446, 11-23, DOI: 10.1016/j.jcis.2014.12.098. (11) Ngo, Y. H.; Li, D.; Simon, G. P.; Garnier, G. Paper surfaces functionalized by nanoparticles. Advances in Colloid and Interface Science 2011, 163 (1), 23-38, DOI: https://doi.org/10.1016/j.cis.2011.01.004. (12) Koga, H.; Kitaoka, T.; Isogai, A. In situ modification of cellulose paper with amino groups for catalytic applications. Journal of Materials Chemistry 2011, 21 (25), 93569361, DOI: 10.1039/C1JM10543D. (13) L., H. M.; N., M. C.; R., N. G. Regioselective Dendritic Functionalization of Cellulose. Macromolecular Rapid Communications 2004, 25 (24), 1999-2002, DOI: doi:10.1002/marc.200400423. (14) Qiu, X.; Hu, S. “Smart” Materials Based on Cellulose: A Review of the Preparations, Properties, and Applications. Materials 2013, 6 (3), 738. (15) Malmstrom, E.; Carlmark, A. Controlled grafting of cellulose fibres - an outlook beyond paper and cardboard. Polymer Chemistry 2012, 3 (7), 1702-1713, DOI: 10.1039/C1PY00445J. (16) Belgacem, M. N.; Gandini, A. The surface modification of cellulose fibres for use as reinforcing elements in composite materials. Composite Interfaces 2005, 12 (1-2), 41-75, DOI: 10.1163/1568554053542188. (17) Boury, B.; Plumejeau, S. Metal oxides and polysaccharides: an efficient hybrid association for materials chemistry. Green Chemistry 2015, 17 (1), 72-88, DOI: 10.1039/C4GC00957F. (18) Datta, K. K. R.; Petala, E.; Datta, K. J.; Perman, J. A.; Tucek, J.; Bartak, P.; Otyepka, M.; Zoppellaro, G.; Zboril, R. NZVI modified magnetic filter paper with high redox and catalytic activities for advanced water treatment technologies. Chemical Communications 2014, 50 (99), 15673-15676, DOI: 10.1039/C4CC06241H. (19) Eskandarloo, H.; Badiei, A.; Behnajady, M. A. Ghodsi , M. Z. Hybrid Homogeneous and Heterogeneous Photocatalytic Processes for Removal of Triphenylmethane Dyes: Artificial Neural Network Modeling. CLEAN – Soil, Air, Water 2016, 44 (7), 809-817, DOI: doi:10.1002/clen.201400449. (20) Elmolla, E. S.; Chaudhuri, M.; Eltoukhy, M. M. The use of artificial neural network (ANN) for modeling of COD removal from antibiotic aqueous solution by the Fenton process. Journal of Hazardous Materials 2010, 179 (1), 127-134, DOI: https://doi.org/10.1016/j.jhazmat.2010.02.068. (21) Eskandarloo, H.; Badiei, A.; Behnajady, M. A. Study of the Effect of Additives on the Photocatalytic Degradation of a Triphenylmethane Dye in the Presence of Immobilized TiO2/NiO Nanoparticles: Artificial Neural Network Modeling. Industrial 18


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Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


& Engineering Chemistry Research 2014, 53 (17), 6881-6895, DOI: 10.1021/ie500253q. (22) Pareek, V. K.; Brungs, M. P.; Adesina, A. A.; Sharma, R. Artificial neural network modeling of a multiphase photodegradation system. Journal of Photochemistry and Photobiology A: Chemistry 2002, 149 (1), 139-146, DOI: https://doi.org/10.1016/S1010-6030(01)00640-2. (23) Nakamoto, K.; Editor. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part A: Theory and Applications in Inorganic Chemistry, Sixth Edition, John Wiley & Sons, Inc.: 2009; p 419 pp. (24) Soleymanzadeh, M.; Arshadi, M.; Salvacion, J. W. L.; SalimiVahid, F. A new and effective nanobiocomposite for sequestration of Cd(II) ions: Nanoscale zerovalent iron supported on sineguelas seed waste. Chem. Eng. Res. Des. 2015, 93, 696-709, DOI: 10.1016/j.cherd.2014.06.006. (25) Arshadi, M.; Gholtash, J. E.; Zandi, H.; Foroughifard, S. Phosphate removal by a nano-biosorbent from the synthetic and real (Persian Gulf) water samples. RSC Advances 2015, 5 (54), 43290-43302, DOI: 10.1039/C5RA03191E. (26) Peng, H.; Meng, L.; Niu, L.; Lu, Q. Simultaneous Reduction and Surface Functionalization of Graphene Oxide by Natural Cellulose with the Assistance of the Ionic Liquid. The Journal of Physical Chemistry C 2012, 116 (30), 16294-16299, DOI: 10.1021/jp3043889. (27) Hono, K.; Ping, D. H.; Ohnuma, M.; Onodera, H. Cu clustering and Si partitioning in the early crystallization stage of an Fe73.5Si13.5B9Nb3Cu1 amorphous alloy. Acta Materialia 1999, 47 (3), 997-1006, DOI: https://doi.org/10.1016/S1359-6454(98)003929. (28) Wang, Q.; Snyder, S.; Kim, J.; Choi, H. Aqueous Ethanol modified Nanoscale Zerovalent Iron in Bromate Reduction: Synthesis, Characterization, and Reactivity. Environmental Science & Technology 2009, 43 (9), 3292-3299, DOI: 10.1021/es803540b. (29) Ge, S.; Zhang, L.; Zhang, Y.; Lan, F.; Yan, M.; Yu, J. Nanomaterials-modified cellulose paper as a platform for biosensing applications. Nanoscale 2017, 9 (13), 43664382, DOI: 10.1039/C6NR08846E. (30) Soejoko, D. S.; Tjia, M. O. Infrared spectroscopy and X ray diffraction study on the morphological variations of carbonate and phosphate compounds in giant prawn (Macrobrachium rosenbergii) skeletons during its moulting period. Journal of Materials Science 2003, 38 (9), 2087-2093, DOI: 10.1023/a:1023566227836. (31)Ho, Y. S.; McKay, G. Pseudo-second order model for sorption processes. Process Biochemistry 1999, 34 (5), 451-465, DOI: https://doi.org/10.1016/S00329592(98)00112-5. (32) Liu, H.; Sun, X.; Yin, C.; Hu, C. Removal of phosphate by mesoporous ZrO2. Journal of Hazardous Materials 2008, 151 (2), 616-622, DOI: https://doi.org/10.1016/j.jhazmat.2007.06.033. (33) Xu, X.; Gao, B.; Wang, W.; Yue, Q.; Wang, Y.; Ni, S. Adsorption of phosphate from aqueous solutions onto modified wheat residue: Characteristics, kinetic and column studies. Colloids and Surfaces B: Biointerfaces 2009, 70 (1), 46-52, DOI: https://doi.org/10.1016/j.colsurfb.2008.12.006. (34) Nguyen, T. A. H.; Ngo, H. H.; Guo, W. S.; Pham, T. Q.; Li, F. M.; Nguyen, T. V.; Bui, X. T. Adsorption of phosphate from aqueous solutions and sewage using zirconium loaded okara (ZLO): Fixed-bed column study. Science of The Total Environment 2015, 523, 40-49, DOI: https://doi.org/10.1016/j.scitotenv.2015.03.126. 19 ACS Paragon Plus Environment


(35) Paudyal, H.; Pangeni, B.; Inoue, K.; Kawakita, H.; Ohto, K.; Alam, S. Adsorptive removal of fluoride from aqueous medium using a fixed bed column packed with Zr(IV) loaded dried orange juice residue. Bioresource Technology 2013, 146, 713-720, DOI: https://doi.org/10.1016/j.biortech.2013.07.014. (36) Jain, M.; Garg, V. K.; Kadirvelu, K. Cadmium(II) sorption and desorption in a fixed bed column using sunflower waste carbon calcium–alginate beads. Bioresource Technology 2013, 129, 242-248, DOI: https://doi.org/10.1016/j.biortech.2012.11.036. (37) Foo, K. Y.; Lee, L. K.; Hameed, B. H. Preparation of tamarind fruit seed activated carbon by microwave heating for the adsorptive treatment of landfill leachate: A laboratory column evaluation. Bioresource Technology 2013, 133, 599-605, DOI: https://doi.org/10.1016/j.biortech.2013.01.097. (38) Sun, X.; Imai, T.; Sekine, M.; Higuchi, T.; Yamamoto, K.; Kanno, A.; Nakazono, S. Adsorption of phosphate using calcined Mg3–Fe layered double hydroxides in a fixed-bed column study, 2014; Vol. 20, p 3623-3630. (39) Chen, S.; Yue, Q.; Gao, B.; Li, Q.; Xu, X.; Fu, K. Adsorption of hexavalent chromium from aqueous solution by modified corn stalk: A fixed-bed column study. Bioresource Technology 2012, 113, 114-120, DOI: https://doi.org/10.1016/j.biortech.2011.11.110. (40) Heiberg, L.; Koch, C. B.; Kjaergaard, C.; Jensen, H. S.; Hans Christian, B. H. Vivianite Precipitation and Phosphate Sorption following Iron Reduction in Anoxic Soils. Journal of Environmental Quality 2012, 41 (3), 938-949, DOI: 10.2134/jeq2011.0067. (41) Cornell, R. M.; Schwertmann, U. The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses, Wiley: 2006. (42) Hamoudi, S.; Saad, R.; Belkacemi, K. Adsorptive Removal of Phosphate and Nitrate Anions from Aqueous Solutions Using Ammonium-Functionalized Mesoporous Silica. Industrial & Engineering Chemistry Research 2007, 46 (25), 8806-8812, DOI: 10.1021/ie070195k. (43) Taha, M. R.; Ibrahim, A. H. Characterization of nano zero-valent iron (nZVI) and its application in sono-Fenton process to remove COD in palm oil mill effluent. Journal of Environmental Chemical Engineering 2014, 2 (1), 1-8, DOI: https://doi.org/10.1016/j.jece.2013.11.021. (44) Li, X.-q.; Zhang, W.-x. Sequestration of Metal Cations with Zerovalent Iron NanoparticlesA Study with High Resolution X-ray Photoelectron Spectroscopy (HRXPS). The Journal of Physical Chemistry C 2007, 111 (19), 6939-6946, DOI: 10.1021/jp0702189. (45) Kim, E.-J.; Kim, J.-H.; Azad, A.-M.; Chang, Y.-S. Facile Synthesis and Characterization of Fe/FeS Nanoparticles for Environmental Applications. ACS Applied Materials & Interfaces 2011, 3 (5), 1457-1462, DOI: 10.1021/am200016v. (46) Cao, Z.; Liu, X.; Xu, J.; Zhang, J.; Yang, Y.; Zhou, J.; Xu, X.; Lowry, G. V. Removal of Antibiotic Florfenicol by Sulfide-Modified Nanoscale Zero-Valent Iron. 20


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Environmental Science & Technology 2017, 51 (19), 11269-11277, DOI: 10.1021/acs.est.7b02480. (47) Moulder, J. F.; Chastain, J. Handbook of X-ray Photoelectron Spectroscopy: A Reference Book of Standard Spectra for Identification and Interpretation of XPS Data, Physical Electronics Division, Perkin-Elmer Corporation: 1992. (48) Liu, A.; Liu, J.; Pan, B.; Zhang, W.-x. Formation of lepidocrocite ([gamma]FeOOH) from oxidation of nanoscale zero-valent iron (nZVI) in oxygenated water. RSC Advances 2014, 4 (101), 57377-57382, DOI: 10.1039/C4RA08988J. (49) Liu, F.; Yang, J.; Zuo, J.; Ma, D.; Gan, L.; Xie, B.; Wang, P.; Yang, B. Graphenesupported nanoscale zero-valent iron: Removal of phosphorus from aqueous solution and mechanistic study. Journal of Environmental Sciences 2014, 26 (8), 1751-1762, DOI: https://doi.org/10.1016/j.jes.2014.06.016. (50) Pecheva, E.; Pramatarova, L.; Toth, A.; Hikov, T.; Fingarova, D.; Stavrev, S.; Iacob, E.; Vanzetti, L. Effect of nanodiamond particles incorporation in hydroxyapatite coatings. ECS Trans. 2009, 25 (3, Analytical Techniques for Semiconductor Materials and Process Characterization 6 (ALTECH 2009), 2009), 403-410, DOI: 10.1149/1.3204431. (51) Usha, N.; Viswanathan, B.; Murthy, V. R. K.; Sobhanadri, J. X-ray photoelectron spectroscopic study of some pure stages of graphite ferric chloride intercalation compounds. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 1997, 53 (11), 1761-1765, DOI: https://doi.org/10.1016/S1386-1425(97)00072-3. (52) Kasiri, M. B.; Aleboyeh, H.; Aleboyeh, A. Modeling and Optimization of Heterogeneous Photo-Fenton Process with Response Surface Methodology and Artificial Neural Networks. Environmental Science & Technology 2008, 42 (21), 79707975, DOI: 10.1021/es801372q. (53) Garson, G. D. Interpreting neural-network connection weights. AI Expert 1991, 6 (4), 46-51.



Figures

Figure 1. A) FT-IR spectra of unmodified filter paper (FP) and FP-OH-NZVI. B) XRD patterns of FP and FP-OH-NZVI. SEM images of FP-OH-NZVI after C) 30 days and D) 90 days. (E–G) TEM images of the FP-OH-NZVI sample at various magnifications. 22


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Figure 2. A) Effect of pH on phosphate ion removal by FP-OH-NZVI from aqueous solutions (pH = 4.0, adsorbent dosage = 0.1 g/100 ml, contact time = 30 min, T = 25 o C). B) The removal kinetics, C) pseudo-second order plot of phosphate ion removal by FP-OH-NZVI at various phosphate concentrations, and D) a Van’t Hoff plot for the determination of thermodynamic variables of phosphate on the FP-OH-NZVI (pH = 4.0, adsorbent dosage = 0.1 g/100 ml, contact time = 30 min, T = 25 oC).



Figure 3. A) Equilibrium removal of different concentrations of phosphate by the filterpaper (FP)-based materials at (pH = 4.0, C0 = 250 mgL-1, adsorbent dosage = 0.1 g/100 ml FP and FP-OH and 1.72 g/100 ml FP-OH-NZVI, contact time = 30 min, T = 25 oC). B) The effect of chloride, nitrate, bicarbonate, sulfate, and citrate on the removal of phosphate by FP-OH-NZVI (pH = 4.0, C0 = 250 mgL-1, adsorbent dosage = 1.72 g/100 ml FP-OH-NZVI, contact time = 30 min, T = 25 oC). C) The impact of NaOH concentration on the desorption of phosphate from FP-OH-NZVI (C0 = 250 mgL-1, adsorbent dosage = 1.72 g/100 ml FP-OH-NZVI, contact time = 30 min, T = 25 oC), and D) the removal capacity of FP-OH-NZVI after repeated regeneration. Each trial was performed three times and the relative standard deviation was lower than 2.2% (pH = 4.0, C0 = 250 mgL-1, adsorbent dosage = 1.72 g/100 ml FP-OH-NZVI, contact time = 30 min, T = 25 oC).

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Figure 4. A) Phosphate ion removal from Cayuga Lake water on FP-OH-NZVI at diverse times. Breakthrough curves for phosphate ion removal by FP-OH-NZVI at various B) initial amount of phosphate ions, C) flow rates, and D) column heights. Solid lines imply the fitting curve through the Thomas model (pH = 4.0, adsorbent dosage = 1.72 g/100 ml FP-OH-NZVI, contact time = 30 min, T = 25 oC).



Figure 5. A) Wide-range XRD of FP-OH-NZVI@P (P = 100 mg L-1, FP-OH-NZVI = 0.10 g). B) Zeta potential of FP-OH-NZVI@P. C) Fe2pigh-resolution spectra of FPFeCl3, D) FP-OH-NZVI, E) FP-OH-NZVI after 60 days and F) FP-OH-NZVI@P. 26


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Figure 6. High resolution O 1s XPS spectra of A) filter paper, B) FP-FeCl3, C) FP-OHNZVI, D) FP-OH-NZVI after 70 days, and E) FP-OH-NZVI@P. F) P 2p high resolution spectrum of the adsorbed phosphate ions. G) SEM image of FP-OH-NZVI@P after 7 cycles of adsorption/desorption, and H-K) corresponding elemental mapping.



Figure 7. Schematic illustration of the optimized ANN structure for the A) batch and B) continuous systems. Comparison between the predicted and experimental values for the test sets of the C) batch and D) continuous systems, and the relative importance (%) of the input variables on the efficiency of the E) batch and F) continuous systems.

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Table captions

Table 1. Kinetic variables for the uptake of phosphate by FP-OH-NZVI. Table 2. Thermodynamic parameters for the removal of phosphate by FP-OH-NZVI. Table 3. Isotherm parameters for phosphate absorption by FP-OH-NZVI in the batch system. Table 4. Isotherm parameters for phosphate absorption by FP-OH-NZVI in a fixed-bed system.



Table 1. Kinetic variables for the adsorption of phosphate by FP-OH-NZVI. Initial concentration First-order model (mg/L) k1(1/min) q1 (mg/g) 100 0.289 384.6 250 0.575 434.7 Second-order model k2 (mg/(g min)) q2 (mg/g) h (mg/(g min)) 100 0.0426 101.0 434.7 250 0.0097 232.5 526.3 Inter-particle model Kint (mg/(g min1/2)) 100 11.699 250 41.453

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R2 0.5335 0.8003 R2 0.9999 0.9997

R2 0.537 0.7562

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Table 2. Thermodynamic parameters for the removal of phosphate by FP-OH-NZVI. Initial -∆Ho ∆So -∆Go (kJ·mol-1) -1 -1 concentration (J mol ) (J (mol K) ) 288 298 312 (mg/L)

353

100

75.81

296.3

76.53

88.38

98.75

104.6

250

52.92

190.5

49.22

56.84

63.51

67.33

700

4.198

16.73

4.320

4.990

5.575

5.910

1000

5.289

14.94

3.860

4.457

4.980

5.279

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Table 3. Isotherm parameters for phosphate absorption by FP-OH-NZVI in the batch system. System FP-OH-NZVI

FP-NaOH

Filter paper

qm 437.7

KL 4.34× 10−2 −1

720 7.58

1.48× 10 3.03× 10−2

8.96 3.58

−2

9.95× 10 7.63× 10−2

4.20

9.05× 10−2

KF

n

119

4.67 2.63

2.08

5.09 1.69

1.58

7.80 1.07

32


R2 0.9584 0.9728 0.9795 0.9704 0.9646 0.9916 0.9918 0.9387 0.992

Sorption model Langmuir Freundlich Sips Langmuir Freundlich Sips Langmuir Freundlich Sips

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Table 4. Isotherm parameters for phosphate adsorption by FP-OH-NZVI in a fixed-bed system. System condition

Flow rate

Bed depth

Co

Co (mg L-1)

100 100 100 100 100 100 100 200 300

Q (ml min-1)

0.5 1.0 2.0 0.5 0.5 0.5 0.5 0.5 0.5

H (cm)

tb (min)

te (min)

qe (mg g-1)

10 10 10 3 6 10 10 10 10

28.5 17 10 10 21.5 28.5 28.5 15.5 7.0

59 51 24 26.5 47 59 59 48 17

226 187.2 144.8 311.7 286.2 226 226 312.1 563

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Thomas model KTH (L (mg min)-1)

q0 (mg g-1)

R2

1.45 1.77 3.72 3.42 1.80 1.45 1.45 1.69 1.96

212.5 186.4 138.0 294.7 272.2 212.5 212.5 308.4 561.1

0.9689 0.9548 0.9719 0.9681 0.9592 0.9689 0.9689 0.9613 0.9614


Graphical abstract

Well mono-dispersed NZVI was prepared in situ on the surface of the modified filter paper in water instead of ethanol and it was used for phosphate capture from water.

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Synthesis of highly monodispersed, stable and spherical NZVI of 20

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