Mechanistic insights into the enhanced removal of roxsarsone and its metabolites by a sludge-based, biochar supported zerovalent iron nanocomposite: Adsorption and redox transformation

Journal Pre-proof Mechanistic Insights into the Enhanced Removal of Roxsarsone and its Metabolites by a Sludge-based, Biochar supported Zerovalent Iron Nanocomposite: Adsorption and Redox Transformation Bingyu Li, Dongning Wei, Zhuoqing Li, Yimin Zhou, Yongjie Li, Changhong Huang, Jiumei Long, HongLi Huang, Baiqing Tie, Ming Lei

PII:

S0304-3894(20)30077-7

DOI:

https://doi.org/10.1016/j.jhazmat.2020.122091

Reference:

HAZMAT 122091

To appear in:

Journal of Hazardous Materials

Received Date:

14 September 2019

Revised Date:

12 January 2020

Accepted Date:

13 January 2020

Please cite this article as: Li B, Wei D, Li Z, Zhou Y, Li Y, Huang C, Long J, Huang H, Tie B, Lei M, Mechanistic Insights into the Enhanced Removal of Roxsarsone and its Metabolites by a Sludge-based, Biochar supported Zerovalent Iron Nanocomposite: Adsorption and Redox Transformation, Journal of Hazardous Materials (2020), doi: https://doi.org/10.1016/j.jhazmat.2020.122091

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Mechanistic Insights into the Enhanced Removal of Roxsarsone and its Metabolites by a Sludge-based, Biochar supported Zerovalent Iron Nanocomposite: Adsorption and Redox Transformation Bingyu Liabc, Dongning Weiabc, Zhuoqing Liabc ,Yimin Zhouabc, Yongjie Liabc, Changhong Huangd, Jiumei Longe, HongLi Huanga, Baiqing Tieabc, Ming Leiabc* College of Resource & Environment, Hunan Agricultural University, Changsha 410128, P. R.

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a

China b

Hunan Engineering & Technology Research Center for Irrigation Water Purification,

Provincial Key Laboratory of Rural Ecosystem Health in Dongting lake area, Hunan province,

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c

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Changsha 410128, P.R. China

Changsha 410128, P. R. China

College of Resources and Environmental Sciences, China Agricultural University, Beijing

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100193, P. R. China

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d

College of Life Sciences & Environment, Hengyang Normal University, Hengyang, 421008,

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PR China

Corresponding author at: College of Resource and Environment, Hunan Agricultural

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University, Changsha, 410128, PR China, Tel: +86 0731 84617803 E-mail: [email protected](M.Lei)*

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Graphical abstract

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Highlights

nZVI@SBC has been fabricated for the removal of ROX

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Characterization results proved that nZVI spread evenly onto SBC

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Dual-binding affinity for As(V) and benzene rings are effective for ROX capture.

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Synergistic removal pathways have been proposed.

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Abstract

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Roxarsone is a phenyl-substituted arsonic acid comprising both arsenate and benzene rings. Few adsorbents are designed for the effective capture of both the organic and inorganic moieties of ROX molecules. Herein, nano zerovalent iron (nZVI) particles were incorporated on the surface of sludge-based biochar (SBC) to fabricate a dual-affinity sorbent that attracts both the arsenate and benzene rings of ROX. The incorporation of nZVI particles significantly increased

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the binding affinity and sorption capacity for ROX molecules compared to pristine SBC and pure nZVI. The enhanced elimination of ROX molecules was ascribed to synergetic adsorption and degradation reactions, through π-π* electron donor/acceptor interactions, H-bonding, and As-O-Fe coordination. Among these, the predominate adsorption force was As-O-Fe coordination. During the sorption process, some ROX molecules were decomposed into inorganic arsenic and organic metabolites by the reactive oxygen species (ROS) generated

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during the early stages of the reaction. The degradation pathways of ROX were proposed according to the oxidation intermediates. This work provides a theoretical and experimental basis for the design of adsorbents according to the structure of the target pollutant.

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Keywords: Roxarsone (ROX); Adsorption; Degradation; Synergistic removal; nZVI

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1. Introduction

Phenyl-substituted arsonic acids (PSAAs) are a class of veterinary drugs that have been

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widely used in the breeding/husbandry industry because of their various functions, including the control of intestinal parasite, promotion of feed efficiency, and meat pigmentation [1, 2].

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Roxarsone (ROX, 4-hydroxy-3-nitrophenylarsonic acid) is among the most widely used PSAAs

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in the broiler poultry industry in the USA, Canada, China, and other developing countries where the demand for poultry meat is high [3]. ROX has been reported to be chemically stabilized inside chickens and pigs, meaning that animals can only metabolize a few ROX. Therefore, most of the ROX (90%) is excreted in its original form through animal feces, and finally enters the agricultural environment through the land application of feces. Particularly in China, animal manure is often applied to paddy fields and vegetable gardens to improve the fertility of the soil 3

[4]. Despite the relative stability of ROX inside livestock, ROX can be transformed into highly toxic inorganic arsenic (arsenate and arsenite) and other phenyl derivatives via abiotic and biotic reactions in soil or the leachates of feces. These metabolites are highly mobile and can easily accumulate in rice and vegetables or be transported into groundwater, posing a significant threat to the environment. Thus, practical measures must be considered to reduce the hazards

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posed by ROX molecules in soils and surface water/groundwater.

The conventional approaches used to address PSAAs contamination include advanced oxidation processes such as Fenton reaction [5], UV/peroxy-sulfate systems [6] and photolytic

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techniques[7]. These methods are extremely effective for the rapid decomposition and

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mineralization of PSAAs molecules; however, the inorganic arsenic remains in solution or forms metastable arsenic precipitates, which may be reallocated into the environment after the

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reaction.

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In consideration of the above, adsorption may be the best way to deal with the intractable issues related to the elimination of ROX and its metabolites. After adsorption, the spent sorbents

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are easily retrieved from the solutions, and the inorganic arsenic can be subsequently recycled. Nevertheless, several issues need to be addressed. For example, conventional sorbents such as

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iron and aluminum oxides [8] and metal-organic frameworks [9] possess insufficient sorption affinity for PSAAs, while sorbents such as MnO2 [10] and carbon nanotubes [11] have lower sorption capacity for PSAAs compared to inorganic arsenic. Therefore, new sorbents should be designed based on the properties of the target contaminant. In particular, sorbents with a high capacity and strong affinity for ROX need to be fabricated and tested. 4

ROX is a typical organic/inorganic combination molecule; in ROX, the arsenate moiety is directly bound to a benzene ring through an As–C bond, and hydroxyl and nitro groups substituted at the meta- and para-positions of the benzene ring, respectively [8]. Inorganic arsenic species have been shown to bind strongly to iron oxides through inner- or out-sphere complexation reactions [12, 13]; thus, the arsenate moiety on the ROX molecule can coordinate with iron oxides in different configurations (e.g., monodentate-mononuclear, bidentate-

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mononuclear, and bidentate-binuclear) according to the protonation and de-protonation reactions of ROX molecules [8, 14]. Importantly, molecules containing benzene rings have been shown to interact strongly with carbon-based materials (e.g., activated carbon, carbon

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nanotubes, and graphene) through π-π* electron donor/acceptor (EDA) interactions, including

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in phenols [15], levofloxacin [16], and nitroaromatic compounds [17]. ROX molecules are abundant in π-electrons and therefore can react strongly with the π-electron-depleted regions

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on the surfaces of carbon materials. In summary, the structures can render the ROX molecules with a specific binding ability toward iron/aluminum oxides and carbon materials via the Me–

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O–As (where Me refers to Fe or Al) surface complexation and π-π* EDA interactions,

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respectively. Thus, carbon-based iron materials that exhibit dual binding affinity for arsenate moieties and benzene rings might be optimal for the removal of ROX molecules from aqueous

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solutions.

Zero-valent iron (ZVI), especially the nano-zero valent iron has long been regarded as an

efficient solution for the removal of organic and inorganic contaminants such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs), through various mechanisms including surface complexation, Fenton-like degradation, and coprecipitation[18, 19]. 5

Numerous studies have been demonstrated that nZVI can absorb a high level of arsenate and arsenite under laboratory and field conditions on the passivating oxide layer of nZVI [20-22], thus, the arsenate moieties of ROX molecules can also bind strongly to the passivating layer of nZVI through surface complexation reactions[23]. Despite the extraordinary contaminant removal performance of nZVI, the intrinsic weakness of nZVI such as aggregation is greatly impeding the wide applications of nZVI under various conditions. Impregnation of nZVI

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particles in a support matrix such as biochar has gained widely interests because it can not only enhance the stability and dispersion of the nZVI particles but also could bestow the advantages of both biochar and nZVI and exhibit synergistic effects on contaminant removal [18].

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In the present study, nano zerovalent iron on sludge-based biochar (nZVI@SBC) was

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designed as a multifunctional sorbent and fabricated via the in-situ liquid reduction and growth of nZVI on the surface of SBC. The main objectives of this study were to (i) demonstrate the

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successful incorporation of nZVI on the SBC matrix, (ii) evaluate the performance of

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nZVI@SBC for the removal of ROX molecules from aqueous solution in comparison to pristine SBC, and (iii) uncover the mechanism by which nZVI@SBC eliminates ROX and its

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metabolites using a series of analytical techniques. The results demonstrate that materials designed based on the structure of ROX and that exhibit dual affinity for arsenate moieties and

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benzene rings can effectively capture ROX from aqueous solution without the risk of releasing inorganic arsenic.

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2. Materials and methods

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2.1Chemicals and materials

Ferrous sulfate (FeSO4·7H2O, > 99.0%), sodium borohydride (NaBH4, 98%),

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hydrochloric acid (HCl, 37%), absolute ethyl alcohol (CH3CH2OH, ≥ 99.7%), sodium hydroxide (NaOH, ≥ 96%), nitric acid (HNO3, 65%), sodium perchlorate (NaClO4·H2O,

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≥99.0%), and all other analytical grade chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd (China) and used without further purification. The ROX (> 98%) was

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purchased from Adamas-beta Reagent, Ltd. (China). Ultrapure water (≥ 18.2 MΩ-cm)

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obtained using a ZOOMAC-L system (China) (≥18.2 MΩ-cm) was used in all experiments. Stock solutions of ROX (1000 mg·L-1) and working solutions with desired concentrations were prepared using UP water.

2.2 Synthesis and characterization of SBC and nZVI@SBC Municipal sludge was collected from the Xingsha wastewater treatment plant in Changsha 7

City, Hunan Province (N28° 13′28", E113° 03′20"), where the treatment plant employs secondary treatment using an activated sludge system. The obtained sludge was dried to a constant weight in an oven at 90°C and ground to pass through a 100-mesh sieve, and stored in a desiccator for use. To prepare the primary SBC, specific amounts of dried samples (10~20 g) were pyrolyzed at 300°C for 1 hour in a muffle furnace under oxygen-deficient conditions. After cooling to ambient temperature, the SBC was submerged in diluted acid (1mol·L-1 HCl)

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for 12 h (1 g SBC:100 mL HCl) to remove impurities, rewashed with distilled water until neutral, and dried in an oven at 85°C. Finally, the obtained material was ground with an agate mortar, passed through a 100-mesh sieve, and stored as a base material for nZVI loads. The nZVI@SBC

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nanocomposite was fabricated via the in situ reduction and growth of iron nanoparticles on the

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surfaces of biochar [24, 25]. The reduction reaction took place according to the following two equations.

(1)

− 0 𝑆𝐵𝐶@𝐹𝑒(𝐻2 𝑂)2+ 6 + 2𝐵𝐻4 → 𝐹𝑒 @𝑆𝐵𝐶 ↓ +2𝐵(𝑂𝐻)3 + 7𝐻2 ↑

(2)

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2+ 𝑆𝐵𝐶 + 𝐹𝑒(𝐻2 𝑂)2+ 6 → 𝑆𝐵𝐶@𝐹𝑒(𝐻2 𝑂)6

Briefly, 0.756 g of SBC was carefully weighed and soaked in a conical beaker containing

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250 mL of 0.054 mol·L-1 FeSO4·7H2O. The pH of the mixed solution was then adjusted to 5.0±0.2 (NaOH/HCl), and, N2 solution was bubbled through the solution for 1 h. Subsequently,

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250 mL of 0.108 mol·L-1 NaBH4 was added dropwise (8 mL·min-1) under constant vigorous magnetic stirring. The solution was then allowed to react at room temperature (N2 atmosphere) for another 30 min. Subsequently, the materials that formed were allowed to settle, separated from the liquid phase by filtration, and washed three times with 200 mL of ethanol that had been pre-degassed by N2 for 1h to remove H2BO3- and H+. Finally, the product was vacuum 8

dried (DZ-2BCIV, Taisite Instrument) at 95°C. nZVI@SBC samples were prepared with different Fe/C molar ratios (1:1,1:3, and 1:5); the ratio of 1:1 was determined to be optimal (SI). Pure nZVI were also sysentheised alone with the same protocols but without the addition of SBC matrix. A small number of the SBC and nZVI@SBC samples were carefully crushed using a mortar and pestle to confirm the sample homogeneity before conducting various

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characterization. The morphologies of the materials were observed by field-emission scanning electron microscopy (FE-SEM; FEI QUANTA F250 and FEI TECNAI G2 F20). The Brunauer– Emmett–Teller (BET) N2 adsorption/desorption method was used to determine the specific

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surface areas (SSAs) of SBC and nZVI@SBC. X-ray photoelectron spectroscopy (XPS) was

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conducted using an ESCALAB 250Xi spectrometer (Thermo Fisher Scientific, USA). The effect of nZVI loading on the surface functional groups of SBC was evaluated by Fourier

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transform infrared (FTIR) spectroscopy using the KBr-disc method on a Nicolet 5700 FTIR

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spectrometer (USA) over the 400-4000 cm-1 spectral range.

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2.3 Batch adsorption experiments In kinetic experiments, 100 mL of ROX solution (initial concentration= 30, 60 mg·L-1)

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and 0.02 g of biochar, composites materials or nZVI were placed in a 100 ml polyethylene bottle with a cover. To control the ionic strength, 0.01M NaClO4·H2O was added as the background electrolyte, and the pH value was maintained as unchanged. All bottles were sealed tightly, wrapped in tin foil paper to prevent photodecomposition, and then agitated in an oscillating water bath chamber (25±1°C) at an oscillation speed of 180 rpm. At regular time 9

intervals (0 min, 5 min, 10 min, 20 min, 30 min, 40 min, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h and 12 h), aliquots (~2 mL) were removed from the suspension using an Eppendorf pipet. The aliquots were centrifuged (2000 g) and filtered through a 0.22 μm nylon membrane using a syringe. The concentration of ROX in the filtrate was determined using an Agilent liquid chromatography system (HPLC-1260 infinity II, USA). For adsorption isotherm studies, the experimental conditions were kept as the same as

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above except that the initial ROX concentrations ranged from 50 mg·L-1 to 800 mg L-1; the mixtures were shaken in an oscillating water bath chamber at a speed of 180 rpm for 24 h; and the reaction temperature was controlled at 25°C, 35°C, or 45°C. After centrifuge separation, the

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residual ROX concentrations were measured using a liquid chromatography system (HPLC-

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1260 Infinity, USA).

To evaluate the effects of pH on ROX adsorption, additional batch experiments were

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conducted with varying solution pH (3-10). A solution containing 100 mg·L-1 ROX was mixed

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with 0.02 g adsorbents and shaken at 25°C at 180 rpm for 24 h. The residual concentration of ROX in the separated supernatant was detected by high-performance liquid chromatography

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(HPLC). The pH of each solution was adjusted to the desired pH with 0.1 M NaOH and HCl before the addition of adsorbent. All batch experiments were performed in triplicate at the same

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time, and experiments without adsorbent addition served as the control. The results are presented as means with standard deviations, control group without the addition of adsorbents were presented in Table.S6, the concentration of ROX showed tiny changes during 48h reactions.All kinetic data were fitted using pseudo-first-order, pseudo-second-order, intraparticle, and Boyd models (Text-S1). The Langmuir and Freundlich models (Text-S2) were 10

used to describe the isotherm data. Thermodynamic parameters (Text-S3) were calculated according to the equations presented in the supporting information.

2.4 Analytical methods ROX concentrations were determined by HPLC (Agilent Technologies, HPLC-1260 Infinity, USA). The chromatograph was equipped with a Kromasil (Nouryon Separation

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Products, Netherlands) 100-5-C18 column (4.6×250 mm) and a diode array detector (DAD) operating at 262 nm. The mobile phase was composed of formic acid (0.3%) and a mixed solution of 0.05 mol·L-1 potassium phosphate monobasic (KH2PO4) and methanol (80:20, v/v).

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The flow rate of the mobile phase was controlled at 1.0 mL·min-1, and the column temperature

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was set at 30°C. The recovery rate of ROX were ranged between 101.69~111.58%.(Table.S7) The primary degradation intermediates of ROX (arsenate, arsenite) were identified by

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HPLC coupled with atomic fluorescence spectrometer (HPLC-AFS-9530, Haiguang Instrument, China) with a PRP-X100 (Hamilton Company, USA) anion-exchange column. The

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mobile phase was prepared by dissolving KH2PO4 (6.124 g) and Na2HPO4·12H2O (1.7907 g)

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in 1L of deionized water (18.2 MΩ-cm). An isocratic elution flow rate of 1.5 mL·min-1 was applied. The reductant (was freshly prepared) by dissolving 35 g potassium borohydrides

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(KBH4; >97%) in 0.5% KOH (m/v) solution; 10% HCl (v/v) was used as the carrier liquid. The specific operating conditions of HPLC-AFS were conducted according to the detailed illustrated by [26], the primary cathode current was 60 mA and auxiliary cathode current was 30 mA, the carrier gas (argon) flow rate and shielding gas flow rate were set as 600 ml/min and 800 ml/min, respectively; the negative high voltage were using 340 V and the atomizer height 11

were set at 8 mm, the detection wavelength of arsenic was 193.7 nm.

2.5 Mechanistic investigations Subtle changes in the organic moieties during the kinetic reaction were monitored by ultraviolet-visible (UV-VIS) spectrophotometry (Nicolet Evolution-300; Thermo Scientific) over the spectral range of 190-600 nm at regular time intervals of 5 mins to 24 h. After the

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adsorption of ROX, residual samples separated by centrifugation and then freeze-dried for characterization. The surface distributions of adsorbed elements (As, C, O, Fe, and N) after the reaction of ROX with nZVI@SBC were mapped using SEM with energy-dispersive X-ray

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spectroscopy (EDS). The changes in elemental composition and chemical bonds after reaction

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were identified by XPS. The XPS data were processed by using XPS PEAK 4.1 software. FTIR spectroscopy was used to evaluate the types of bonding between the adsorbents and ROX. The

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degradation pathway was explored by ultraperformance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS; Agilent Technologies) with an

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electrospray ion (ESI) source. The mobile phase was composed of water (phase A) and

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acetonitrile (phase B), and the elution flow rate was kept at 0.2 mL·min−1. The mass spectra were collected in negative ion mode in the m/z range of 40–600. High-resolution MS data were

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processed using Mass Hunter qualitative analysis software (Version B.06.00)

3 Results and discussion

3.1 Characterization of SBC and nZVI@SBC The synthesized SBC and nZVI@SBC samples were characterized by FE-SEM, FE-TEM, 12

XRD, BET, and XPS, respectively, to verify that the zerovalent iron nanoparticles have been successfully soldered on the surface of SBC. Fig.1 and Fig.S2 present the SEM and TEM images of SBC and nZVI@SBC samples. As shown in the pictures, SBC had a compact structure with irregularly stacked and fragmentized particles. The enlarged image reveals that pristine SBC had a scabrous surface (Fig.S2). The results of BET surface analysis indicated that pristine SBC had a relatively low SSA of 13.34 m2·g-1 (Fig.S4, Table.S1). However, the rough

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Here is Fig.1

surface of SBC proved beneficial for the in-situ growth of nZVI particles. As shown in Fig.S2, the nZVI@SBC exhibited a fluffy and porous structure with a larger SSA of 43.97 m2·g-1 than

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pristine SBC (Fig.S2, Fig.S4, Table.S1). Furthermore, the magnified TEM images clearly

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showed that the nZVI nanoparticles were uniformly dispersed on the biochar matrix. The singleparticle size of nZVI was approximately 50 nm, indicating that the incorporation of nZVI in the

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biochar matrix can prevent the particles from aggregating and thus increase the SSA of the nZVI

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incorporated material (Fig.1, Fig.S2). The X-ray energy spectroscopy (EDS) can directly reveal the distribution of elements on the surface of synthetic materials. As is depicted in Fig.S2, the

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iron was evenly distributed on the surface of nZVI@SBC with very strongly fluorescent green color in mapping picture, while the iron on SBC showed dotted distribution patterns with lower

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fluorescent green color intensity. The different intensity of fluorescent green on SBC and nZVI@SBC indicated that the content of Fe on nZVI@SBC is much higher than that on SBC (Fig.S2). Compared with SBC, the Fe content (Wt %: mass percent) on nZVI@SBC is about 22 times higher (48.36% for nZVI@SBC, and only 2.27% for SBC), which further signified that the iron has been successfully loaded on the SBC matrix. The XRD pattern of nZVI@SBC 13

exhibited the characteristic peak of metallic Fe (Fe0) at 2 θ=44.9°, corresponding to a dspacing=2.027 Å (Fig.S1) [24, 27]. Here is Fig.2 Two small shoulder peaks of zerovalent iron were also identified in the XPS spectra at 706.01 eV and 719.26 eV (Fig.2, Fig.S5) [28]. The other two main peaks at binding energy of 724.30 eV (Fe2p1/2), 710.7 eV (Fe2p3/2) match the patterns of maghemite (Fe2O3) and FeOOH

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[29, 30], indicating that nZVI may co-exist with amorphous iron oxides in core-shell structures as reported in previous studies [28, 31]. Together, the characterization results demonstrate that

Adsorption kinetics

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nZVI was successfully loaded onto SBC.

The adsorption kinetics of ROX onto SBC, nZVI@SBC and nZVI were evaluated, as

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shown in Fig.S6 and Fig.S19. The classic pseudo-first-order and pseudo-second-order kinetic models were employed to describe the adsorption kinetics (Fig.3) [32]. All the fitting curves

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were linearized, and all the equations and detailed calculation procedures are presented in SI,

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all the fitting parameters were computed and listed in Table.S2 and Table.S9. As showed in Fig.S6, the adsorption of ROX by both pristine SBC, nZVI@SBC and pure nZVI included two

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processes: fast-initial sorption that happened in the first 40~60 min and followed by a slower sorption processes until equilibrium was reached at 12 h. Thus, the adsorption processes likely involved two stages: surface adsorption and intraparticle pore diffusion between the adsorbate and adsorbent [33]. During the first 40 min, 86.74% and 77.71% of ROX was removed by nZVI@SBC at the initial concentrations of 30 mg·L-1 and 60 mg·L-1, respectively; For the 14

removal of ROX, the corresponding removal rates of the original SBC and nZVI are only 19.67%, 19.17%, 17.36%, and 17.89%, respectively. This suggests that the rapid adsorption that occurred during the early stage (0-40 min), maybe have been facilitated by the abundant available active sites provided by nZVI and the greatly improved reaction activity by the SBC matrix. The goodness of fit of the pseudo-second-order model to the nZVI@SBC adsorption data [correlation coefficient (R2) > 0.99] implies that the adsorption of ROX occurred via

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chemisorption, which involved valence forces through the sharing or exchange of electrons between nZVI@SBC and ROX [34] (Fig.3, Table.S2). The Elovich kinetic model was also applied to verify the chemical interaction between ROX and nZVI@SBC, given the

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circumstances that the heterogeneous surface of adsorbents [35, 36]. As shown in Fig.S7 and

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Table.S3, the adsorption kinetics were well described by the Elovich model with R2 > 0.96. This indicates the nonuniform distribution of adsorption sites along with an adsorption process

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characterized by heterogeneous diffusion rather than a simple first-order reaction [10, 37].

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However, the factor controlling the overall rate of adsorption was not clear. Three consecutive steps have been shown to help define the sorption process of an adsorbate by a porous adsorbent

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[38], (i) external diffusion or film diffusion, (ii) intra-particle diffusion and/or pore diffusion and (iii) adsorption at active sites on the external or internal surface of the sorbent [34]. Step

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(iii) is exceptionally rapid; thus, the fast adsorption of ROX onto nZVI@SBC in the first 40 min was attributed to the abundant active sites on the surface of the sorbent. Therefore, the ratedetermining step is, therefore, related to film or/and particle diffusion. Accordingly, the intraparticle diffusion model and Boyd model (film diffusion) were applied to determine if the rate-restricted step started from film diffusion or pore diffusion [35]. The fitting curves and 15

computed parameters are illustrated in Fig.S8, Fig.S9, and Table.S3. As shown in Fig.S8, the plot of qt vs t0.5 (intraparticle model) could be divided into three linear segments, indicating that the sorption occurred in three stages. The initial steep-sloped stage from 5 to 40 min was attributed to the rapid occupation of adsorption sites. The diffusion rates in this initial stage were 5.077 and 16.34 mg·g-1·min-1/2 at the initial ROX concentration of 30 and 60 mg·L-1, respectively. The second stage from 60 to 240 min, which was associated with intraparticle or

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pore diffusion, had a gentle slope and diffusion rates of 1.62 and 3.63 mg·g−1·min−1/2 for initial ROX concentrations of 30 and 60 mg·L−1, respectively. In the final stage from 240 to 600 min, the diffusion rate declined to 0.12 and 0.63 mg·g−1·min−1/2 for initial ROX concentrations of 30

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and 60 mg·L−1, respectively. This stage was likely the adsorption equilibrium phase. All the

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fitted lines did not pass through the origin, indicating that the rate-limiting step of the adsorption process was not dominated only by intraparticle diffusion. Fig.S9 shows the linear plots of Bt

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v.s. time (Boyd model). Again, the fitted lines did not pass through the origin, indicating that

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sorption was controlled by a film-diffusion mechanism [4, 39, 40]. Based on the above results, intraparticle diffusion and film diffusion may be the critical factors controlling the overall rate of ROX uptake by nZVI@SBC.

Adsorption isotherms and thermodynamic studies

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3.3

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Here is Fig.3

To further understand how ROX molecules interact with the surface sites of the adsorbent

and the ability of nZVI@SBC to remove ROX, batch adsorption isotherms of ROX adsorption on nZVI@SBC, SBC and nZVI were performed at different temperatures (Fig.S10 and Fig.S18). The Langmuir and Freundlich isotherm models were employed to describe the sorption data. 16

The fitting results are shown in Fig.4 and Fig.S18, and the parameter calculated using the two models are listed in Table.S4 and Table.S8. SBC, nZVI@SBC and nZVI exhibited different sorption characteristics. The isotherm data of nZVI@SBC were fitted well by the Langmuir model (R2 = 0.99) but not by the Freundlich model (R2 = 0.76–0.82), Similar results were also observed with pure nZVI treatment that the data are well described by the Langmuir model (R2 = 0.99) which indicates that the sorption of

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ROX on nZVI@SBC and nZVI occurred at uniformly distributed monolayer adsorption sites (Fig.4, Table.S4). Similarly, the sorption isotherms or the sorption of arsenic species on reduced graphite oxide-supported nZVI particles [32] and ZVI-biochar complexes [27] also indicated

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monolayer adsorption at homogeneous active sites. In contrast, the isotherms data for the

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sorption of ROX on SBC was fitted well by both the Langmuir and Freundlich model (R2 >0.92), reflecting the different surface properties of SBC and nZVI@SBC. Similar results were

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reported for the sorption of ROX and 4-hydroxy-3-aminophenylarsonic acid (a degradation

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product of ROX) on soils and anaerobic granular sludge [4] [41] Activated sludge is rich in organic matter and inorganic minerals [42, 43] inorganic minerals such as aluminate silicates

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[44, 45] and iron (oxy) hydroxides [46] are strong scavenger of trace contaminants, particularly those consisting of negatively charged molecules [12, 47]. Thus, the intrinsic physicochemical

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properties of sludge are somewhat convoluted, which conversely provides differently activation moieties to interact with the ROX molecules. Further information can be provided by calculating the Freundlich n values (Table S4), lower n values indicate more nonlinear adsorption and heterogeneously distributed adsorption sites [40, 48]. This explains the contrasting sorption behavior of pristine biochar. However, the incorporation of nZVI into the 17

SBC matrix drastically changed the surface properties of SBC, as discussed earlier. The uniformly distributed nZVI particles on the surface of SBC occupied the inherent sites and provided abundant new active sites, which were primarily responsible for the monolayer sorption of ROX on nZVI@SBC. The sorbent properties play a vital role in determining the sorption capacity and affinity for contaminants [4]. The maximum adsorption capacities (qm) of SBC, nZVI@SBC and nZVI for ROX at different temperatures based on the Langmuir model

ro of

are presented in Table S4 and Table.S8 (qm were calculated using the residual ROX excluded those degraded part). The qm and KL values of nZVI@SBC were higher than those of SBC and nZVI at different temperatures, indicating that the introduction of nZVI into the SBC matrix

-p

significantly improved both the adsorption capacity and affinity of SBC for ROX, and also

re

enhanced the reactivity of nZVI. The remarkably higher removal capability of nZVI@SBC for ROX molecules compared to pristine SBC can be attributed to a combination of two factors.

lP

The first is the direct interaction of ROX molecules with the outer-sphere iron

na

oxides/hydroxides formed on the surface of SBC during the passivation of nZVI particles. The ongoing corrosion of nZVI particles in solution provides a continuous source of active sites for

ur

ROX adsorption [31]. However, it is worth noting that pure zero-valent iron can easily aggregate into agglomerates in solution, which seriously weakens the reactivity of the zero-

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valent iron, as shown in the isotherms sorption data (Fig.S18 and Table.S8). With the support of the SBC matrix, the reactivity and dispersibility of zero-valent iron have been significantly enhanced, thus rendering the higher removal ability for composites materials. Second, the reactive oxygen species (ROS; i.e., hydroxyl radicals) generated during the corrosion of nZVI particles can attack the As–C bonds in the ROX molecules, resulting in ROX decomposition 18

[49]. relevant reaction processes are discussed later. The thermodynamic parameters (Gibbs free energy ΔG°, enthalpy ΔH°, and entropy ΔS°) for ROX adsorption by nZVI@SBC determined from the Langmuir model-based KL values were calculated and are presented in Table S5 [50]. The increase in ΔG° with increasing temperature indicates that ROX sorption was more favorable at high temperatures (Fig.S10). This can be attributed to the decrease in solution viscosity with increasing solution temperature,

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thereby increasing the rate of diffusion of ROX molecules across the external boundary layer along with the internal pores of the adsorbent particles [51, 52]. Moreover, the positive ΔG° values for ROX sorption at various temperatures revealed the nonspontaneous nature of the

-p

adsorption process, while the negative ΔH° value revealed the exothermic nature of the sorption

re

process. One possible explanation for the increase in exothermicity during the sorption process may be ligand exchange and surface complexation between ROX molecules and nZVI particles

lP

[53].

na

Here is Fig.4

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3.4 Effects of pH on ROX adsorption The pH is an essential factor that can control the removal efficiency of trace contaminants

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in aqueous solution. The pH affects the interfacial properties of the sorbent along with the distributions of the chemical species of pollutants [54]. ROX has three pKa values (Fig. S17), and its protonation and deprotonation at different pH allow ROX to exist as a cationic, zwitterionic, or anionic species under acidic, moderately acidic, or alkaline conditions, respectively. Thus, the pH strongly affects the sorption of ROX onto sorbents such as metal19

organic frameworks [9], Fe3O4@3D graphene nanocomposites [55], and ferric/manganese oxides [54]. To obtain insights into the roles of electrostatic and acid/base interactions during ROX sorption on nZVI@SBC, the ROX sorption performance was investigated in a wide pH range from 3.0 to 10.0 (Fig. 5). As shown in Fig.5, the sorption of ROX onto nZVI@SBC showed a decreased trend, and the qm values were declined with the increasing pH value. The maximum

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sorption capacity (975 mg·g−1) was obtained at pH 3.0, and the sorption capacity decreased sharply at pH > 6. Zeta potential measurements indicated that the isoelectric point of nZVI@SBC was 4.03 (Fig. S11); that is, nZVI@SBC was negatively charged when the pH

-p

value was greater than 4. According to the isoelectric point of nZVI@SBC and the dissociation

re

constants of ROX (3.49, 5.74, and 9.13), the surface charges of nZVI@SBC and ROX under different pH conditions can be summarized as follows:

na

and ROX is neutral

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(i) pH < 3.49 (the first dissociation constant of ROX): nZVI@SBC is positively charged

(ii) pH > 4.03 (the isoelectric point of nZVI@SBC): both nZVI@SBC and ROX are negatively charged

ur

Here is Fig.5

Jo

The electrostatic interactions between the adsorbate and adsorbent explain the adsorption behavior of ROX molecules at different pH values. According to its dissociation constants, ROX predominantly exists as anionic and neutral molecules at pH 3(Fig.S17). In contrast, nZVI@SBC is positively charged at lower pH values, facilitating the sorption of negatively charged molecules. However, as the pH increases, deprotonation occurs, favoring the formation of di-anionic ROX species and negatively charged nZVI@SBC. The data obtained in this study 20

indicate that the reaction between protonated ROX and positively charged nZVI@SBC at low pH was stronger than that between deprotonated ROX and negatively charged nZVI@SBC at high pH. However, it is worth noting that the sorption of ROX by nZVI@SBC still occurred to some extent at elevated pH. Accordingly, other interactions including hydrogen bonding [56], π–π EDA interactions [57] and As–Fe coordination/complexes [58] between nZVI@SBC and ROX molecules cannot be ruled out. The potential mechanisms are discussed further in the

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following section.

3.5 Mechanisms of the enhanced removal of ROX by nZVI@SBC

-p

3.5.1 Sorption mechanism

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The experimental data from the macroscopic adsorption experiments, including the kinetic

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and isotherm data, indicate that nZVI@SBC showed superior removal performance for ROX compared to SBC and nZVI. As mentioned above, this enhanced elimination of ROX might

na

involve several interactions, among which sorption and/or redox pathways predominate[59]. It is well established that the sorption of ionizable and less polar organic compounds (e.g.,

ur

arsanilic acid and ROX) on sorbents such as activated carbon [13] and iron oxides [14] is usually controlled by noncovalent interactions (π–π stacking and hydrogen bonding), or surface

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complexation/coordination, and/or Lewis acid/base interactions [8, 55, 60]. Therefore, to reveal the mutual interactions between the surfaces of nZVI@SBC and ROX molecular. Experiments including SEM-EDS-Mapping, XPS, FTIR were conducted. The high-resolution image of the element mapping image can directly provide us with the distribution of different elements on the adsorbent surface after reaction with the ROX molecule. As shown in Fig.6, the overall 21

surface morphology of nZVI@SBC remained unchanged after ROX loading. Arsenic (indicated by yellow color) was distributed evenly on the nZVI@SBC surface, nearly identical to the distributions of Fe (green) and O (blue). These results are consistent with the Langmuir fitting results which indicating homogeneous sorption, suggesting that Fe or O may participate in the sorption of ROX. Here is Fig.6

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The FTIR spectra of SBC, nZVI@SBC, and nZVI@SBC after ROX sorption are presented in Fig. S12. The spectra of SBC and nZVI@SBC before ROX sorption showed minor differences. The strong peaks at 1643, 1442, 1025, 794, 462, 3415, and 3745 cm−1 were

-p

assigned to aromatic νC=C, νSi–O–Si, FeOOH, νFe–O, and νOH stretching vibrations,

re

respectively. This signifies that SBC and nZVI@SBC contain abundant organic and inorganic functional groups that interact strongly with ROX molecules through π–π EDA interactions

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(between aromatic C=C and benzene ring), hydrogen bonding (C=O and O–H with the hydroxyl

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moieties of ROX), and As–Fe coordination (arsenate moieties with iron oxides). The π-π EDA interactions have long been regarded as a principal driving force for the sorption of sorbates

ur

with benzene rings, such as levofloxacin [16], pentamethylbenzene, naphthalene, and phenanthrene [15], sulfamethazine [61], nitroaromatic compounds [17] on carbon-riched

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sorbents. on carbon-rich sorbents. As ROX molecules contain benzene rings, it is reasonable to predict that ROX will interact strongly with aromatic C=C groups via π–π EDA interactions; hydroxyl-substituted ROX, which possesses a π electron-rich aromatic ring, will act as a πelectron donator, while the π electron-depleted regions on the sorbent surface (aromatic C=C) will act as a π-electron acceptor [62]. This prediction can be verified by the FTIR spectra shown 22

in Fig. S12, in which a slight blue shift of the peaks from 1643 to 1612 cm−1 and peak sharpening were observed after the sorption of ROX on nZVI@SBC. Moreover, a peak characteristic of aromatic C=C stretching vibration completely vanished after ROX sorption on nZVI@SBC, indicating that the aromatic C=C moieties were involved in the sorption process [63]. This π-π interaction further explains the remarkable sorption capacity of SBC (1.37-2.36 mmol·g-1); ); even without the incorporation of nZVI, the sorption performance of SBC is better

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than those of some reported iron oxides (goethite, 0.08 mmol·g−1) [8], manganese oxides (MnO2, 0.07mmol·g−1) [54], and ferrihydrite (0.59–1.07 mmol·g−1, unpublished data).

In addition to the changes in the aromatic C=C moieties upon ROX sorption, the peak

-p

corresponding to the stretching vibration of –OH groups at 3415 cm−1 become broader and was

re

red-shifted to 3445 cm−1, and a new peak associated with the bending vibration of –OH appeared at 1157 cm−1. These changes further indicate that the hydrogen bonds between the

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oxygen-containing functional groups of nZVI@SBC and ROX molecules played a meaningful

na

role during the sorption process. Similar results have been suggested by (T. Chen., et al 2017) [55] and (X. Zhou., et al 2014) [64] who reported that the hydroxyl groups are participated in

ur

the sorption of ROX molecules and Bisphenol A by forming hydrogen bonds. Furthermore, the nitro groups (-NO2) that bound to the benzene rings may also be involved in the sorption of

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ROX onto nZVI@SBC; the incorporation of ROX into soil-derived dissolved organic matter (DOM) was found to enhance the formation of ROX–DOM complexes through the –NO2 groups of ROX [65] In our experiments, this phenomenon was reflected by the appearance of a new C–N bond peak at 1274 cm−1 and the two characteristic peaks of –NO2 groups (N–O bonds) at 1525 cm−1 (asymmetrical stretching vibration) and 1345 cm−1 (symmetrical stretching 23

vibration) [17]. Importantly, as discussed in the introduction part, the arsenate moiety that bound to ROX molecules through As-C bonds also played an indispensable role in determining its sorption behavior towards to soils [4], ferric-manganese binary oxides [54], iron and aluminum oxides [8], and other engineered sorbents and geo-sorbents [9, 13, 14, 55]. Arsenate can bind strongly to the surfaces of iron oxides via surface complexation with surface hydroxyl groups, as

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demonstrated by attenuated total reflectance FTIR spectroscopy [66] and synchrotron-based techniques [67]. Three different arsenic surface complexes are formed on the surfaces of iron oxides: monodentate, bidentate-binuclear, and bidentate-mononuclear complexes. Among them,

-p

the inner-sphere monodentate complexation is the predominated reaction of aromatic arsenic

following three protonation reactions:

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species on the surfaces of iron oxides [68]. The surface complexation can be described by the

(3)

≡ FeOH + AsO3 C6 H6 NO3 3− + 2H+ = ≡ FeHAsO3 C6 H6 NO3 − + H2 O

(4)

≡ FeOH + AsO3 C6 H6 NO3 3− + 3H+ = ≡ FeH2 AsO3 C6 H6 NO3 + H2 O

(5)

na

lP

≡ FeOH + AsO3 C6 H6 NO3 3− + H + = ≡ FeAsO3 C6 H6 NO3 2− + H2 O

ur

where ≡FeOH represents the surface hydroxyl groups of iron oxides [8, 14]. As mentioned earlier, the nZVI particles are surrounded by iron oxides shells (referred to

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as core-shell structures), and the corrosion of nZVI particles continually provides sorption sites and Fe-OH groups for the binding of arsenic species [69]. These abundant reaction sites are reflected in the symmetrical stretching vibration peaks of the Fe–O bond of nZVI@SBC at 539 and 462 cm−1 (Fig.S12); these two peaks are characteristic peaks of Fe2O3. Our XPS scan at Fe2p also proved the presence of Fe2O3 (Fig.2). The core-shell structures of nZVI turn out to 24

be a stronger scavenger towards arsenic species, as depicted in the intense symmetrical stretching vibration of the As-O-Fe bond at 835 cm-1. In the meantime, the increased intensity of the Fe-O bond at 539, and 462 cm-1 after reaction with ROX demonstrated that the nZVI particles were corroded during sorption. The variations in the As-O-Fe and Fe-O bonds may be attributed to the formation of the inner-sphere monodentate complexes with ROX (FeHAsO3C6H6NO3-, FeH2AsO3C6H6NO3, and FeAsO3C6H6NO32-) [66, 70]. Thus, it is

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reasonable to conclude that the Fe-OH groups on the surfaces of Fe2O3 and/or other iron oxides/oxyhydroxides played a vital role in the sorption of ROX [13].

To obtain further insights into the chemical bonds formed between ROX molecules and

-p

nZVI@SBC. high-resolution XPS fine scan spectra of C1s, O1sand N1s, were recorded in Fig.7

re

and Fig.S13. As depicted in Fig.8a, the C1s spectra of SBC and nZVI@SBC could be deconvoluted into four peaks: (i) the aromatic carbon-carbon double bond (C=C) at 284.6 eV,

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(ii) carbon singly bonded to carbon (C-C) at 285.16 eV, (iii) carbon singly bonded to

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nitrogen/oxygen (C-N/C-O) at 286.17 eV, and (iv) carbon doubly bonded to oxygen (C=O) at 288.5 eV. After reaction with ROX, the proportions of aromatic C=C bond and C-N/C-O bonds

ur

increased from 48.22% to 61.83% and from 16.83% to 34.62%, respectively. Moreover, a new peak assigned to the π–π* component appeared at 291.2 eV [17, 67]. The variation in the C1s

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chemical state was ascribed to the enhanced sorption of ROX molecules on the nZVI@SBC via π-π* EDA interactions, consistent with the FTIR results. The O1s spectrum of SBC was deconvoluted into three peaks: (i) carbon doubly bonded to oxygen (C=O) at 531 eV; (ii) hydroxyl groups from iron oxides (-OH) at 531.6 eV; and (iii) oxygen atoms from ester groups (C-OH/C-O-C) at 532.6 eV. The new peak appearing at 529.9 eV after nZVI loading was 25

assigned to the O2− species in the crystal structures of iron oxides (Fe-O-Fe) [9, 71]. After reaction with ROX, the proportions of –OH and C–OH/C–O groups decreased from 31.66% to 26.40% and from 23.38% to 10.08%, respectively, while the proportion of aromatic C=O bonds increased substantially from 16.29% to 36.75%. These changes indicate that the oxygencontaining functional groups participated in the sorption of ROX through hydrogen bonding or surface complexation/ligand exchange reactions [13, 55]. The proportion of newly formed Fe-

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O-Fe bonds decreased by a small percentage (1.91%), probably, because of the higher surface coverage of ROX molecules or the formation of inner-sphere monodentate surface complexes depleted some of the O2− species.

-p

Here is Fig.7

The N1s high-resolution XPS fine spectrum of nZVI@SBC after reaction with ROX (Fig.

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S13) exhibited two deconvoluted peaks at 405.9 and 398.9 eV. The peak at 405.9 eV was

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attributed to the -NO2 group of ROX (Fig.S13a), while another newly formed peak was assigned to the C-N bond. The results agree with the FTIR spectrum, in which peaks were observed at

na

1274 cm−1 (C–N) and at 1525 and 1345 cm−1 (–NO2 groups). The XPS results further indicate

ur

that –NO2 groups were involved in the sorption of ROX.

3.5.2 Synergistic degradation mechanisms

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As mentioned above, the redox transformation of zero-valent iron can produce ROS during

the corrosion process, as described by the following reactions [72]: Feo + O2 + 2H+ → Fe2+ + H2 O2

(6)

Feo + H2 O2 → Fe2+ + 2OH−

(7)

Fe2+ + H2 O2 → Fe3+ + OH∙ + OH−

(8) 26

Due to the electron-rich property of ROX, the As–C bonds of ROX molecules are susceptible attack by ROS, leading to ROX decomposition; this may be one reason for the enhanced elimination of ROX on nZVI@SBC compared to on pristine SBC. To explore the oxidative behaviors and identification of intermediates products, UV-VIS scan, Q-TOF-MS, and HPLCAFS techniques were applied. UV-VIS spectrophotometry is widely used to probe the subtle changes in the structures of organic moieties during sorption or/and oxidation reaction [54]. As

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depicted in Fig.S15, the changes in the UV-vis spectra (190-600 nm) during the adsorption of ROX on SBC and nZVI@SBC were recorded over a long time period (5 min-24 h). A standard solution of ROX was also analyzed (Fig.S14). The standard ROX was also analyzed in Fig.S14.

-p

The standard ROX solution showed three broad absorption bands in the UV absorption region

re

(190-380 nm), corresponding to the nitro-groups on aromatic rings (223/340 nm), and hydroxyl groups on aromatic rings (265 nm) [10]. As shown in Fig.S15, the intensities of the two main

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peaks at 265 and 340nm decreased rapidly after ROX was reacted with nZVI@SBC for 5 min.

na

After 24 h of reaction, these two bands nearly disappeared, and a new peak that emerged at 245 nm. This new peak may correspond to, a new oxidation product or a changed structural product

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of ROX molecules. Meanwhile, the intensities of peaks in the ROX spectrum remanined unchanged after reaction with SBC for 24 h, further indicating that the incorporation of nZVI

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particles affected the oxidation ability of SBC. The significantly changes in the UV-Vis spectrum of ROX after reaction with nZVI@SBC indicated the efficient cleavage of the nitro groups, As-C bonds, and/or aromatic rings of ROX. The cleavage of As-C bonds during the oxidation and/or photo- transformation of aromatic arsenical additives is accompanied by the generation of both As(III) and As(V) species [73].In 27

an oxidation system dominated by hydroxyl radicals, the production of arsenic species is expected to involve the following two processes. The first reaction is the disproportionation of As(IV) species. Hydroxyl radical is added to the aromatic ring of ROX followed by the cleavage of the As-C bond, yielding unstable As(IV) species [As(OH)4, As(OH)3O-, HAsO3- and AsO32-] [1]. The As(IV) species are easily transformed into As(III) and As(V) through dismutation reaction in a 1:1 ratio. The dismutation reaction can be described by the followed equations

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[74]. As(OH)4 + HAsO− 3 → As(III) + As(V)

(9)

2As(OH)4 → As(III) + As(V)

(10)

-p

Next, the As(III) is rapidly oxidized to As(V) by free radicals or O2, as illustrated by the

AsIII (OH)3 +∙ OH → As IV (OH)4

lP

− AsIV (OH)4 + O2 → AsV (OH)+ 4 +∙ O2

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following equations [73]:

+ IV AsIII (OH)3 +∙ O− 2 + H2 O + H → As (OH)4 + H2 O2

na

+ AsIV (OH)4 +∙ OH → H2 AsV O− 4 + H3 O

(11) (12) (13) (14)

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The overall content of inorganic arsenic species produced during the reaction was determined using HPLC-AFS at regular time intervals (Fig.8 and Fig.S16). In the HPLC chromatogram of

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arsenic species (Fig.8), the significant peak at the retention time of 2.3 min corresponds to arsenite, while the minor peak at the retention time of 5.5 min represents arsenate. the concentrations of arsenite occupies a more substantial proportion while arsenate constitutes only a small fraction in the whole system. As shown in Fig.S16, the concentrations of As(V) and As(III) in solution increased in the first 5min, indicating the fast decomposition of ROX 28

molecules. As the reaction time increased, the content of arsenic began to decline; among arsenic species, the concentration of As(V) decreased quickly, whereas the content of As(III) decreased relatively slowly. After 1 h, the contents of both As(III) and As(V) remained constant until 24 h. The dynamic changes in inorganic arsenic species during the first hour were consistent with the results of the kinetic experiments, which indicated the rapid occupancy of vacant adsorption sites by As(III) and As(V). However, it is worth noting that the ratio of As(III):

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As(V) in our system was 4.89:1, much larger than that of the theoretical values (1:1) reported by elsewhere. The differences observed between As(III) and As(V) could be attributed to the combined effects of the fast sorption of As(V) onto the passivating layer of nZVI particles [27],

-p

and the intra-particle reduction of As(V) to As(III) [31]. Theoretically, the dismutation reaction

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of As(IV) species generates the same amounts of As(III) and As(V), while in our experiments, the presence of the nZVI particles on the SBC matrix can effectively capture the free arsenic

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species, especially for the arsenate. As the binding affinity of arsenate towards iron oxides was

na

stronger than the arsenite [75]. Therefore, under the same conditions, the As(V) was preferentially sorbed onto nZVI@SBC over As(III), leading to the fast decrease in As(V)

ur

concentration in solution. When As(V) was adsorbed onto the Here is Fig.8

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surface of nZVI particles, the outer layers of the iron oxides acted as a semiconductor to facilitates the transferred of electrons from nZVI to As(V), resulting in the rapid reduction of As(V) to As(III) [69]. These reduced arsenic species could be re-released into solution via aqueous phase extraction, thereby increasing the ratio of As(III) to As(V)[31]. To understand the relationship between adsorption and degradation in detail, the reaction intermediates(As3+ 29

and As5+) during isotherms studies (nZVI and nZVI@SBC) were determined using LC-AFS， and the results were illustrated in Fig.S20 and Table.S10-11. The first thing we need to understand is that adsorption and degradation has happened simultaneously during reaction with NZVI or composite materials. The degradation products could be re-adsorbed to the nZVI/nZVI@SBC surface during the reaction. For ROX, the mass accumulation on nZVI@SBC increased firstly(0~60 min) and then decreased gradually, which is attributed to

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continuous adsorption and oxidation of the molecules, as indicated by the releases of As(III) and As(V) in Fig.S16. The ROX increased rapidly and plateaued after around 2~4 h for both nZVI and nZVI@SBC which is indicative of no degradation after the rapid reaction stages

-p

(0~60 min). This is because of the continuous oxidation of Zero valent can impede the

re

subsequent reaction. Therefore, under the conditions of our experiment, all the removed ROX and intermediates are considered to be eliminated by adsorption reaction, while all the

lP

remaining degradation products during 12 h reaction in solution were used to probe the

na

degradation rates. Based on these products, we found that during the whole reaction process, the degradation of ROX accounted for only a small part of the entire removal (0~13.81% for

ur

nZVI@SBC and 0~8.72% for nZVI). According to Table.S10 and S11, the degradation rate at different temperatures increased with the increasing initial concentrations while the adsorption

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rate decreased with the increasing initial concentrations. This because at lower concentrations the adsorption reaction can capture most of the ROX in the solution, while with the increasing concentration the available binding sites of nZVI@SBC and nZVI are depleted by the ROX, freer ROX molecules will be exposed under ROS attack, thus resulting in the increasing inorganic arsenic in solution. Interestingly, the degradation rates of ROX by nZVI@SBC at 30

higher concentrations were greater than the nZVI treatments which indicated the enhanced reactivity of the composite material by the SBC matrix. As demonstrated above, the adsorbed ROX on nZVI@SBC was transformed into inorganic arsenic species; however, the changes in the organic moieties of ROX remain unclear. Uncovering the transformations of the organic functional groups of ROX molecules would help reveal the reaction pathways of ROX, which is significant for interpreting the removal

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mechanisms. HPLC/ESI-QTOF-MS was employed to determine the degradation intermediates of ROX molecules during kinetics reactions with nZVI@SBC. The total ion chromatograms (TICs) of the standard ROX solution and the ROX solution after reaction with nZVI@SBC for

-p

different time periods (10 min, 30 min, 1 h, 3 h, 6 h, 12 h, and 24 h) are shown in Fig. 9a.

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Analysis of the TIC and mass spectrum of the standard ROX solution (Figs. 9a and 9b) indicated that the first peak appearing at 10 min corresponded to ROX molecules. After reaction with

na

elimination of ROX.

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nZVI@SBC for 24 h, the intensity of the ROX peak decreased significantly, indicating the

A comparison of the TICs of the ROX solution before and after reaction with nZVI@SBC

ur

also indicated the appearance of three new products after reaction. The first product, which appeared at a retention time of 17 min and showed an intense signal, was assigned to 2-nitro-

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hydroquinone (m/z = 154.01 Da, Fig. 9c) [76] The second product appeared at 17.5 min and was identified as hydroxyquinol (m/z = 124.02 Da, Fig. 9e). The final product was identified as hydroquinone (m/z = 112.84 Da, Fig. 9d). The oxidation intermediates of ROX upon reaction with nZVI@SBC indicated a typical hydroxylation and/or electrophilic addition reaction of aromatic compounds. Hydroxyl groups are known to be highly reactive toward aromatic and 31

heterocyclic compounds and can react with benzene and its substituted derivatives via abstraction, addition, and electron transfer reactions [1]. Several reaction pathways have been proposed to interpret the hydroxyl radical-mediated degradation of phenyl-arsonic acid [1], parsanilic acid [73], and ROX [5]. Hydroxyl radical preferentially adds to the ipso-, meta-, orthoand para-positions of aromatic rings [7], to produce the ipso-, meta-, ortho- and para-isomer adducts as the major products of aromatic arsenic compounds, respectively. Phenol (ipso-

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adduct), catechol (ortho-adduct), and hydroquinone (para-adduct) are the major reaction products of the TiO2 mediated photolytic degradation of phenyl-arsonic acid [7]. Under a UV excited oxidation system, the isomer adducts (catechol, o-nitrophenol and o-benzoquinone) can

-p

be transformed into a series of short-chain carboxylic acids, and finally mineralized to CO2 and

re

H2O [6].

According to the above discussion, the possible transformation pathways of ROX in the

lP

presence of nZVI@SBC were proposed. First, due to the electron density on the ipso-positions

na

of the ROX molecules [73], the ipso-position was preferentially attacked by hydroxyl radicals to form 2-nitro-hydroquinone (ipso-adduct), arsenate, and arsenite. The intense signal of 2-

ur

nitrohydroquinone was still observed after the reaction of ROX with nZVI@SBC for 24 h, indicating that 2-nitrohydroquinone was the main product. Subsequently, the nitro group in the

Jo

aromatic ring continued to be attacked by free radicals, resulting in the formation of metaadducts of hydroxyquinoline [6]. Finally, 2-nitrohydroquinone and hydroxyquinoline were further oxidized by hydroxyl radicals, resulting in the formation of para-adducts of product 3 (hydroquinone) [77]. In consideration of the FTIR and XPS results along with the identified intermediates, a 32

removal mechanism for the elimination of ROX by nZVI@SBC was proposed. The removal of organic compounds by heterogeneous sorbents is dominated by several processes, including sorption and redox transformation [4]. Thus, we divided the removal of ROX by nZVI@SBC into two parts: adsorption and degradation. In the first stage of the reaction, the primary removal mechanism was adsorption, consisting mainly of hydrogen bonding, π–π* EDA interactions, and surface complexation/coordination. Based on the binding energies, the contributions of

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these interactions decreased in the following order: surface complexation > hydrogen bonding > π–π* EDA interactions [55]. As the reaction process continued, ROX removal was enhanced by the corrosion of nZVI particles on the SBC matrix, which generated ROS that decomposed

-p

ROX molecules through electrophilic substitution. However, this degradation only accounted

re

for a minor part of ROX removal based on the content of inorganic arsenic ( Fig.S20, Table.S10-

the production of ROS.

ur

Conclusions

na

Here is Fig.9

lP

11); probably due to the passivating layer of nZVI prevented the corrosion reaction and reduced

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The transformation of PSAAs in aqueous solutions or manure leachates can lead to widespread contamination by toxic inorganic arsenic species. Therefore, the strategies used to eliminate PSAAs should focus on reducing/preventing arsenic leaching. In this study, an nZVI@SBC nanocomposite was designed to simultaneously capture arsenate and the benzene rings of ROX molecules from aqueous solution. The dual-affinity sorbent exhibited superior adsorption performance and affinity for ROX molecules compared to pristine SBC, 33

demonstrating the potential of dual-affinity sorbents to reduce hazards related to arsenic leaching. The coordination and degradation abilities of the nanocomposite toward ROX molecules simultaneously attracted degraded inorganic arsenic species and ROX molecules. The mechanism of ROX removal by nZVI@SBC was proposed based on hydrogen bonding, As–O–Fe coordination, and π–π* EDA interactions. The results shed new light on the design of

na

lP

re

-p

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adsorbents for organic/inorganic molecules.

Jo

ur

Fig. 1. TEM micrographs of SBC (bottom row) and nZVI@SBC (top row).

34

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Fig. 2. Full-survey XPS spectra of SBC (a) and nZVI@SBC (b). Fe2p XPS spectra of SBC (c) and SBC after loading with nZVI (d).

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Fig.3 Adsorption kinetics of ROX onto SBC and nZVI@SBC. The solid lines that pass through the data points represent the fitting by pseudo-first-order kinetic model and pseudo-second-order kinetics model. (a) nZVI@SBC, First kinetics fitting, (b) SBC first kinetics fitting, (c) nZVI@SBC, second-order kinetics fitting, (d) SBC first kinetics fitting.

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Fig.4 Adsorption isotherms of ROX onto SBC and nZVI@SBC. The lines through the data points represent the fitting by Langmuir model and Freundlich model.

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Fig. 5. Effect of pH on the adsorption of ROX onto nZVI@SBC.

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Fig. 6. Elemental maps of nZVI@SBC after ROX sorption.

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Fig. 7. Fine-scan XPS spectra showing the deconvolutions of C1s (a) and O1s (b) for SBC, nZVI@SBC, and nZVI@SBC after ROX adsorption.

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Fig. 8. Oxidation intermediates (arsenate and arsenite) of ROX after reaction with nZVI@SBC for different time periods (5 min – 24 h).

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Fig. 9. UPLC-Q-TOF-MS product identification after the reaction of ROX with nZVI@SBC: (a) TICs of ROX degradation products and mass spectra of (b) ROX, (c) 2-nitrohydroquine, (d) hydroquinone, and (e) hydroxyquinoline. .

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Author Contributions Section Bingyu Li and Ming Lei conceived and designed the study. Dongning Wei, Zhuoqing Li,Yimin Zhou, Yongjie Li, Changhong Huang, and Jiumei Long performed the experiments. HongLi Huang provided the materials.

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Bingyu Li and Ming Lei wrote the paper.

Baiqing Tie reviewed and edited the manuscript. All authors read and approved

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the manuscript.

Declaration of Interest Statement

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On behalf of all the authors, there are no any financial or personal relationships

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Ming Lei

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with other people or organizations in this manuscript.

Conflicts of interest There are no conflicts to declare

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Acknowledgment

The authors are grateful for the financial support provided by the National Natural Science Foundation of China (41671475), the Ministry of Science and Technology of China (2018YFD0800700) and the Excellent Doctoral Dissertation Cultivation Fund of Hunan

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Agricultural University (YB2018004).

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References [1] T. Xu, P.V. Kamat, S. Joshi, A.M. Mebel, Y. Cai, K.E. O'Shea, Hydroxyl Radical Mediated Degradation of Phenylarsonic Acid, The Journal of Physical Chemistry A, 111 (2007) 7819-7824. [2] A. Adak, K.P. Mangalgiri, J. Lee, L. Blaney, UV irradiation and UV-H(2)O(2) advanced oxidation of the roxarsone and nitarsone organoarsenicals, Water Res, 70 (2015) 74-85. [3] J.R. Garbarino, A.J. Bednar, D.W. Rutherford, R.S. Beyer, R.L. Wershaw, Environmental Fate of Roxarsone in Poultry Litter. I. Degradation of Roxarsone during Composting, Environmental Science & Technology, 37 (2003) 1509-1514. [4] Q.L. Fu, J.Z. He, L. Blaney, D.M. Zhou, Sorption of roxarsone onto soils with different physicochemical

ro of

properties, Chemosphere, 159 (2016) 103-112.

[5] A.-Y. Zhang, N.-H. Huang, C. Zhang, P.-C. Zhao, T. Lin, Y.-Y. He, J.-W. Feng, Heterogeneous Fenton decontamination of organoarsenicals and simultaneous adsorption of released arsenic with reduced secondary pollution, Chemical Engineering Journal, 344 (2018) 1-11.

[6] S. Su, C. Cao, Y. Zhao, D.D. Dionysiou, Efficient transformation and elimination of roxarsone and its

-p

metabolites by a new α-FeOOH@GCA activating persulfate system under UV irradiation with subsequent As(V) recovery, Applied Catalysis B: Environmental, 245 (2019) 207-219.

re

[7] S. Zheng, Y. Cai, K.E. O'Shea, TiO2 photocatalytic degradation of phenylarsonic acid, Journal of Photochemistry and Photobiology A: Chemistry, 210 (2010) 61-68. [8] W.R. Chen, C.H. Huang, Surface adsorption of organoarsenic roxarsone and arsanilic acid on iron and

lP

aluminum oxides, J Hazard Mater, 227-228 (2012) 378-385.

[9] Y. Lv, R. Zhang, S. Zeng, K. Liu, S. Huang, Y. Liu, P. Xu, C. Lin, Y. Cheng, M. Liu, Removal of parsanilic acid by an amino-functionalized indium-based metal-organic framework: Adsorption behavior

na

and synergetic mechanism, Chemical Engineering Journal, 339 (2018) 359-368. [10] T.P. Joshi, G. Zhang, H. Cheng, R. Liu, H. Liu, J. Qu, Transformation of para arsanilic acid by manganese oxide: Adsorption, oxidation, and influencing factors, Water Research, 116 (2017) 126.

ur

[11] J. Hu, Z. Tong, G. Chen, X. Zhan, Z. Hu, Adsorption of roxarsone by iron (hydr)oxide-modified multiwalled carbon nanotubes from aqueous solution and its mechanisms, International Journal of Environmental Science and Technology, 11 (2013) 785-794.

Jo

[12] J. Antelo, F. Arce, S. Fiol, Arsenate and phosphate adsorption on ferrihydrite nanoparticles. Synergetic interaction with calcium ions, Chemical Geology, 410 (2015) 53-62.

[13] H.J. Kwon, D.L. Wilson, R. Sammynaiken, Sorptive Uptake Studies of an Aryl-Arsenical with Iron Oxide Composites on an Activated Carbon Support, Materials, 7 (2014).

[14] D. Arts, M. Abdus Sabur, H.A. Al-Abadleh, Surface interactions of aromatic organoarsenical compounds with hematite nanoparticles using ATR-FTIR: kinetic studies, J Phys Chem A, 117 (2013) 2195-2204. [15] D. Zhu, S. Hyun, J.J. Pignatello, L.S. Lee, Evidence for π−π Electron Donor−Acceptor Interactions between π-Donor Aromatic Compounds and π-Acceptor Sites in Soil Organic Matter through pH Effects 44

on Sorption, Environmental Science & Technology, 38 (2004) 4361-4368. [16] B. Yan, C.H. Niu, J. Wang, Analyses of Levofloxacin Adsorption on Pretreated Barley Straw with Respect to Temperature: Kinetics, π–π Electron-Donor–Acceptor Interaction and Site Energy Distribution, Environmental Science & Technology, 51 (2017) 8048-8056. [17] X. Chen, B. Chen, Macroscopic and Spectroscopic Investigations of the Adsorption of Nitroaromatic Compounds on Graphene Oxide, Reduced Graphene Oxide, and Graphene Nanosheets, Environmental Science & Technology, 49 (2015) 6181-6189. [18] S. Wang, M. Zhao, M. Zhou, Y.C. Li, J. Wang, B. Gao, S. Sato, K. Feng, W. Yin, A.D. Igalavithana, Biochar-supported nZVI (nZVI/BC) for contaminant removal from soil and water: A critical review, Journal of hazardous materials, 373 (2019) 820-834. [19] Q. Mao, Y. Zhou, Y. Yang, J. Zhang, L. Liang, H. Wang, S. Luo, L. Luo, P. Jeyakumar, Y.S. Ok,

ro of

Experimental and theoretical aspects of biochar-supported nanoscale zero-valent iron activating H2O2 for ciprofloxacin removal from aqueous solution, Journal of hazardous materials, 380 (2019) 120848. [20] C. Su, R.W. Puls, Arsenate and arsenite removal by zerovalent iron: kinetics, redox transformation, and implications for in situ groundwater remediation, Environmental science & technology, 35 (2001) 14871492.

iron in water, Water Research, 39 (2005) 763-770.

-p

[21] S. Bang, M.D. Johnson, G.P. Korfiatis, X. Meng, Chemical reactions between arsenic and zero-valent

re

[22] F. Fu, D.D. Dionysiou, H. Liu, The use of zero-valent iron for groundwater remediation and wastewater treatment: a review, Journal of hazardous materials, 267 (2014) 194-205. [23] Z. Wu, X. Su, Z. Lin, G. Owens, Z. Chen, Mechanism of As(V) removal by green synthesized iron

lP

nanoparticles, Journal of Hazardous Materials, 379 (2019) 120811. [24] S. Wang, B. Gao, Y. Li, A.E. Creamer, F. He, Adsorptive removal of arsenate from aqueous solutions by biochar supported zero-valent iron nanocomposite: Batch and continuous flow tests, Journal of

na

Hazardous Materials, 322 (2017) 172-181.

[25] D. Wei, B. Li, H. Huang, L. Luo, J. Zhang, Y. Yang, J. Guo, L. Tang, G. Zeng, Y. Zhou, Biochar-based functional materials in the purification of agricultural wastewater: Fabrication, application and future

ur

research needs, Chemosphere, 197 (2018) 165-180. [26] M. Guo, W. Wang, X. Hai, J. Zhou, HPLC-HG-AFS determination of arsenic species in acute promyelocytic leukemia (APL) plasma and blood cells, Journal of Pharmaceutical & Biomedical

Jo

Analysis, 145 (2017) 356.

[27] S. Bakshi, C. Banik, S.J. Rathke, D.A. Laird, Arsenic sorption on zero-valent iron-biochar complexes, Water Research, 137 (2018) 153.

[28] Y.P. Sun, X.Q. Li, J. Cao, W.X. Zhang, H.P. Wang, Characterization of zero-valent iron nanoparticles, Adv Colloid Interface Sci, 120 (2006) 47-56. [29] J.R. Rumble, D.M. Bickham, C.J. Powell, The NIST x‐ ray photoelectron spectroscopy database, Surface & Interface Analysis, 19 (2010) 241-246. [30] C.J. Powell, A. Jablonski, A. Naumkin, A. Kraut-Vass, J.M. Conny, J.R.R. Jr, NIST data resources for surface analysis by X-ray photoelectron spectroscopy and Auger electron spectroscopy, Journal of 45

Electron Spectroscopy & Related Phenomena, 114 (2001) 1097-1102. [31] W. Yan, R. Vasic, A.I. Frenkel, B.E. Koel, Intraparticle Reduction of Arsenite (As(III)) by Nanoscale Zerovalent Iron (nZVI) Investigated with In Situ X-ray Absorption Spectroscopy, Environmental Science & Technology, 46 (2012) 7018-7026. [32] C. Wang, H. Luo, Z. Zhang, Y. Wu, J. Zhang, S. Chen, Removal of As(III) and As(V) from aqueous solutions using nanoscale zero valent iron-reduced graphite oxide modified composites, Journal of Hazardous Materials, 268 (2014) 124-131. [33] T.F. Lin, J.K. Wu, Adsorption of Arsenite and Arsenate within Activated Alumina Grains: Equilibrium and Kinetics, Water Research, 35 (2001) 2049-2057. [34] Y. Zhou, X. Liu, L. Tang, F. Zhang, G. Zeng, X. Peng, L. Luo, Y. Deng, Y. Pang, J. Zhang, Insight into highly efficient co-removal of p-nitrophenol and lead by nitrogen-functionalized magnetic ordered

ro of

mesoporous carbon: Performance and modelling, Journal of Hazardous Materials, 333 (2017) 80.

[35] F.C. Wu, R.L. Tseng, R.S. Juang, Characteristics of Elovich equation used for the analysis of adsorption kinetics in dye-chitosan systems, Chemical Engineering Journal, 150 (2009) 366-373.

[36] Y. Tan, M. Chen, Y. Hao, High efficient removal of Pb (II) by amino-functionalized Fe3O4 magnetic nano-particles, Chemical Engineering Journal, 191 (2012) 104-111.

-p

[37] G.S. Sen, K.G. Bhattacharyya, Kinetics of adsorption of metal ions on inorganic materials: A review, Adv Colloid Interface Sci, 162 (2011) 39-58.

re

[38] X. Fan, D.J. Parker, M.D. Smith, Adsorption kinetics of fluoride on low cost materials, Water Research, 37 (2003) 4929-4937.

[39] M.A. Ahmad, N.K. Rahman, Equilibrium, kinetics and thermodynamic of Remazol Brilliant Orange 3R

lP

dye adsorption on coffee husk-based activated carbon, Chemical Engineering Journal, 170 (2011) 154161.

[40] H. Zhang, J. Wang, B. Zhou, Y. Zhou, Z. Dai, Q. Zhou, P. Chriestie, Y. Luo, Enhanced adsorption of

na

oxytetracycline to weathered microplastic polystyrene: Kinetics, isotherms and influencing factors, Environmental Pollution, 243 (2018) 1550-1557. [41] J.-C. Li, S.-J. Yuan, W. Wang, F. Ji, Z.-H. Hu, Adsorption characteristics of 4-hydroxy-3-

ur

aminophenylarsonic acid (HAPA) onto anaerobic granular sludge, Desalination and Water Treatment, 57 (2016) 20714-20725.

[42] P. Zhang, S. Zheng, J. Liu, B. Wang, F. Liu, Y. Feng, Surface properties of activated sludge-derived

Jo

biochar determine the facilitating effects on Geobacter co-cultures, Water Research, 142 (2018) 441451.

[43] O. Das, A.K. Sarmah, D. Bhattacharyya, Biocomposites from waste derived biochars: Mechanical, thermal, chemical, and morphological properties, Waste Management, 49 (2016) 560-570.

[44] M. Ruyter-Hooley, A.-C. Larsson, B.B. Johnson, O.N. Antzutkin, M.J. Angove, The effect of inositol hexaphosphate on cadmium sorption to gibbsite, Journal of Colloid and Interface Science, 474 (2016) 159-170. [45] H. Du, W. Chen, P. Cai, X. Rong, X. Feng, Q. Huang, Competitive adsorption of Pb and Cd on bacteria– montmorillonite composite, Environmental Pollution, 218 (2016) 168-175. 46

[46] C. Tiberg, J.P. Gustafsson, Phosphate effects on cadmium(II) sorption to ferrihydrite, Journal of Colloid and Interface Science, 471 (2016) 103-111. [47] N.K. Niazi, E.D. Burton, Arsenic sorption to nanoparticulate mackinawite (FeS): An examination of phosphate competition, Environmental Pollution, 218 (2016) 111-117. [48] L. Ji, Y. Wan, S. Zheng, D. Zhu, Adsorption of Tetracycline and Sulfamethoxazole on Crop ResidueDerived Ashes: Implication for the Relative Importance of Black Carbon to Soil Sorption, Environmental Science & Technology, 45 (2011) 5580-5586. [49] Z.-H. Diao, W. Qian, Z.-X. Lei, L.-J. Kong, J.-J. Du, H. Liu, J.-W. Yang, S.Y. Pu, Insights on the nitrate reduction and norfloxacin oxidation over a novel nanoscale zero valent iron particle: Reactivity, products, and mechanism, Science of The Total Environment, 660 (2019) 541-549.

wastewaters, Bioresource Technology, 160 (2014) 24-31.

ro of

[50] X. Liu, D.-J. Lee, Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from

[51] Y.J. Yao, F.F. Xu, M. Chen, Z.X. Xu, Z.W. Zhu, Adsorption behavior of methylene blue on carbon nanotubes, Bioresource Technology, 101 (2010) 3040.

[52] Z. Wang, X. Yu, B. Pan, B. Xing, Norfloxacin Sorption and Its Thermodynamics on Surface-Modified Carbon Nanotubes, Environmental Science & Technology, 44 (2010) 978-984.

-p

[53] J. Romero-González, J.R. Peralta-Videa, E. Rodrıǵ uez, S.L. Ramirez, J.L. Gardea-Torresdey, Determination of thermodynamic parameters of Cr(VI) adsorption from aqueous solution onto Agave

re

lechuguilla biomass, The Journal of Chemical Thermodynamics, 37 (2005) 343-347. [54] T.P. Joshi, G. Zhang, W.A. Jefferson, A.V. Perfilev, R. Liu, H. Liu, J. Qu, Adsorption of aromatic organoarsenic compounds by ferric and manganese binary oxide and description of the associated

lP

mechanism, Chemical Engineering Journal, 309 (2017) 577-587.

[55] T. Chen, Z. Jian, Z. Jing, S. Chu, D. Zhi, L. Zhang, B. Xing, T. Chen, Z. Jian, Z. Jing, Enhanced removal of roxarsone by Fe 3 O 4 @3D graphene nanocomposite: synergistic adsorption and mechanism,

na

Environmental Science Nano, 4 (2017).

[56] A. Wang, S. Li, Y. Teng, W. Liu, L. Wu, H. Zhang, Y. Huang, Y. Luo, P. Christie, Adsorption and desorption characteristics of diphenylarsenicals in two contrasting soils, Journal of Environmental

ur

Sciences, 25 (2013) 1172-1179.

[57] H. Tang, Z. Ying, S. Sujie, Y. Xiaonan, L. Dongmei, C. Fuyi, X. Baoshan, Theoretical Insight into the Adsorption of Aromatic Compounds on Graphene Oxide, Environmental Science Nano, 5 (2018)

Jo

10.1039.C1038EN00384J-.

[58] Y. Du, H. Fan, L. Wang, J. Wang, J. Wu, H. Dai, α-Fe2O3 nanowires deposited diatomite: highly efficient absorbents for the removal of arsenic, Journal of Materials Chemistry A, 1 (2013) 7729-7737.

[59] W. Liu, Z. Ai, R.A. Dahlgren, L. Zhang, X. Wang, Adsorption and reduction of roxarsone on magnetic greigite (Fe3S4): Indispensable role of structural sulfide, Chemical Engineering Journal, 330 (2017) 1232-1239. [60] C. Chang, F. Lian, L. Zhu, Simultaneous adsorption and degradation of gamma-HCH by nZVI/Cu bimetallic nanoparticles with activated carbon support, Environ Pollut, 159 (2011) 2507-2514. [61] M. Teixidó, J.J. Pignatello, J.L. Beltrán, M. Granados, J. Peccia, Speciation of the Ionizable Antibiotic 47

Sulfamethazine on Black Carbon (Biochar), Environmental Science & Technology, 45 (2011) 1002010027. [62] W. Chen, L. Duan, L. Wang, D. Zhu, Adsorption of Hydroxyl- and Amino-Substituted Aromatics to Carbon Nanotubes, Environmental Science & Technology, 42 (2008) 6862-6868. [63] F. Wang, W. Sun, W. Pan, N. Xu, Adsorption of sulfamethoxazole and 17β-estradiol by carbon nanotubes/CoFe2O4 composites, Chemical Engineering Journal, 274 (2015) 17-29. [64] X. Zhou, J. Wei, K. Liu, N. Liu, B. Zhou, Adsorption of Bisphenol A Based on Synergy between Hydrogen Bonding and Hydrophobic Interaction, Langmuir, 30 (2014) 13861-13868. [65] Q.-L. Fu, J.-Z. He, L. Blaney, D.-M. Zhou, Roxarsone binding to soil-derived dissolved organic matter: Insights from multi-spectroscopic techniques, Chemosphere, 155 (2016) 225-233. [66] S. Depalma, S. Cowen, T. Hoang, H.A. Al-Abadleh, Adsorption Thermodynamics of p-Arsanilic Acid

1922-1927.

ro of

on Iron (Oxyhydr)Oxides: In-Situ ATR-FTIR Studies, Environmental Science & Technology, 42 (2008)

[67] C. Tian, J. Zhao, X. Ou, J. Wan, Y. Cai, Z. Lin, Z. Dang, B. Xing, Enhanced Adsorption of p-Arsanilic Acid from Water by Amine-Modified UiO-67 as Examined Using Extended X-ray Absorption Fine Structure, X-ray Photoelectron Spectroscopy, and Density Functional Theory Calculations,

-p

Environmental Science & Technology, 52 (2018) 3466-3475.

[68] M. Chabot, T. Hoang, H.A. Al-Abadleh, ATR-FTIR Studies on the Nature of Surface Complexes and

Technology, 43 (2009) 3142-3147.

re

Desorption Efficiency of p-Arsanilic Acid on Iron (Oxyhydr)oxides, Environmental Science &

[69] L. Ling, X. Huang, M. Li, W.-x. Zhang, Mapping the Reactions in a Single Zero-Valent Iron Nanoparticle,

lP

Environmental Science & Technology, 51 (2017) 14293-14300.

[70] D. Fu, Z. He, S. Su, B. Xu, Y. Liu, Y. Zhao, Fabrication of α-FeOOH decorated graphene oxide-carbon nanotubes aerogel and its application in adsorption of arsenic species, Journal of Colloid and Interface

na

Science, 505 (2017) 105-114.

[71] R. Yang, J. Tao, Q. Huang, B. Tie, M. Lei, Y. Yang, H. Du, Co-adsorption of Cd(II) and Sb(III) by ferrihydrite: a combined XPS and ITC study, Journal of Soils and Sediments, (2018) 1-9.

ur

[72] M. Auffan, W. Achouak, J. Rose, M.-A. Roncato, C. Chanéac, D.T. Waite, A. Masion, J.C. Woicik, M.R. Wiesner, J.-Y. Bottero, Relation between the Redox State of Iron-Based Nanoparticles and Their Cytotoxicity toward Escherichia coli, Environmental Science & Technology, 42 (2008) 6730-6735.

Jo

[73] T. Sun, Z. Zhao, Z. Liang, J. Liu, W. Shi, F. Cui, Efficient degradation of p-arsanilic acid with arsenic adsorption by magnetic CuO-Fe3O4 nanoparticles under visible light irradiation, Chemical Engineering Journal, 334 (2018) 1527-1536.

[74] U.K. Klaening, B.H.J. Bielski, K. Sehested, Arsenic(IV). A Pulse-radiolysis study, Inorganic Chemistry, 28 (1989) 2717-2724. [75] B. Li, S. Zhou, D. Wei, J. Long, L. Peng, B. Tie, P.N. Williams, M. Lei, Mitigating arsenic accumulation in rice (Oryza sativa L.) from typical arsenic contaminated paddy soil of southern China using nanostructured α-MnO2: Pot experiment and field application, Science of The Total Environment, 650 (2019) 546-556. 48

[76] T. Yang, Y. Liu, L. Wang, J. Jiang, Z. Huang, S.Y. Pang, H. Cheng, D. Gao, J. Ma, Highly effective oxidation of roxarsone by ferrate and simultaneous arsenic removal with in situ formed ferric nanoparticles, Water Res, 147 (2018) 321-330. [77] J. Fan, Z. Ding, Z. Zhao, J. Liu, Degradation of p-arsanilic acid and simultaneous in-situ removal of arsenic species with ferrate(VI): Kinetics, intermediate and degradation pathway, Chemical Engineering

Jo

ur

na

lP

re

-p

ro of

Journal, 350 (2018) 453-462.

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