Magnetic Porous Carbonaceous Material Produced from Tea Waste

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Magnetic Porous Carbonaceous Material Produced from Tea Waste for Efficient Removal of As(V), Cr(VI), Humic Acid and Dyes Tao Wen, Jian Wang, Shujun Yu, Zhongshan Chen, Tasawar Hayat, and Xiangke Wang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b00418 • Publication Date (Web): 22 Mar 2017 Downloaded from http://pubs.acs.org on March 27, 2017

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ACS Sustainable Chemistry & Engineering

Authors Information

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The full mailing address of all authors:

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Tao Wen: No.2 Beinong Road, Huilongguan Town, Changping District, School of

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Environment and Chemical Engineering, North China Electric Power University,

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Beijing 102206, P. R. China

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Jian Wang: No.2 Beinong Road, Huilongguan Town, Changping District, School of

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Shujun Yu: No.2 Beinong Road, Huilongguan Town, Changping District, School of

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Zhongshan Chen: No.2 Beinong Road, Huilongguan Town, Changping District,

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School of Environment and Chemical Engineering, North China Electric Power

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University, Beijing 102206, P. R. China

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Tasawar Hayat: NAAM Research Group, Faculty of Science, King Abdulaziz

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University, Jeddah 21589, Saudi Arabia

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Xiangke Wang: No.2 Beinong Road, Huilongguan Town, Changping District, School

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of Environment and Chemical Engineering, North China Electric Power University,

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*: Corresponding authors. [email protected] or [email protected] (X. Wang).

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ACS Paragon Plus Environment


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Magnetic Porous Carbonaceous Material Produced from Tea

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Waste for Efficient Removal of As(V), Cr(VI), Humic Acid and

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Dyes

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Tao Wen,a Jian Wang,a Shujun Yu,a Zhongshan Chen,a Tasawar Hayat,b,c Xiangke

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Wanga,b,d*

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a

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University, Beijing 102206, P.R. China

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b

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21589, Saudi Arabia

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c

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d

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Institutions, School for Radiological and Interdisciplinary Sciences, Soochow

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University, Suzhou 215123, P.R. China

School of Environment and Chemical Engineering, North China Electric Power

NAAM Research Group, Faculty of Science, King Abdulaziz University, Jeddah

Department of Mathematics, Quaid-I-Azam University, Islamabad 44000, Pakistan Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education

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ABSTRACT: Magnetic porous carbonaceous (MPC) materials derived from tea

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waste were synthesized by an integrated biosorption–pyrolysis process and were

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applied as adsorbent for wastewater cleanup. Based on various characterizations, we

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demonstrated that the formation mechanism of γ-Fe2O3 anchored on the porous

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carbonaceous material surface consisted of the adsorption of iron ions and then the

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γ-Fe2O3 nucleation and growth through pyrolysis at alternative peak temperatures

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(300-500 oC). The sample pyrolysed at 300 oC (MPC-300) showed good capacities for

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As(V) (38.03 mg g-1) and Cr(VI) (21.23 mg g-1) adsorption, outperforming that of

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commercial bulk Fe2O3 and many other materials. Moreover, the large available

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positive charge density can facilitate the effective adsorption of anionic dye (MO) and

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humic acid (HA) on γ-Fe2O3 surface while the adsorption performance is sluggish for

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cationic dyes (MB and RhB). Relatively, the adsorption isotherms could significantly

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conform to Langmuir model, and the pseudo-second-order dynamic equation was the

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optimal model to describe the kinetics for the adsorption of As(V), Cr(VI), humic acid

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and dyes pollutants on MPC-300. Kinetic studies show that MPC-300 can efficiently

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remove these pollutants in aqueous solution within 3 h. The presence of HA reduced

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Cr(VI) and As(V) adsorption on MPC-300 at pH < 6.0. The XPS and FTIR analysis

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further demonstrated that ion exchange between surface hydroxyl groups and

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Cr(VI)/As(V) dominated the adsorption while the adsorption mechanism of MO and

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HA was attributed to electrostatic attracted on protonated–OH on γ-Fe2O3 surface.

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The results suggested that the MPC material was a potential material to remove heavy

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metal ions, HA and organic contaminants simultaneously with remarkable adsorption 3



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capacity, fast uptake rate, and easy magnetic separation.

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KEYWORDS: Magnetic Porous Carbonaceous Material, As(V), Cr(VI), Humic Acid,

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Dyes, Adsorption

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INTRODUCTION

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The global occurrence in water resources containing toxic organic or inorganic

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pollutants has raised concerns about potential effects on aquatic ecosystems and

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public health. Wastewaters released by mining, electroplating, paint, metallurgy,

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leather and battery manufacturing industries have resulted in the accumulation of

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persistent organic pollutants and heavy metal ions in the environment. Amongst the

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heavy metal ions, both chromium and arsenic, which are known to be mutagenic,

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teratogenic and carcinogen to human health, pose adverse effects on human life and

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the environment from surface water as well as groundwater.1 At the same time, Cr(VI)

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and As(V) ions inevitably coexist with organic pollutants in aqueous solutions. For

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example, humic acid (HA), one of the principal humic fractions, which is mainly

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produced from the breakdown of animals and vegetables in the environment, is

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widely distributed in soils, lakes and rivers. HA contains many organic functional

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groups such as carboxylic, hydroxyl, amine, phenol, and quinine groups, which

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provide some different potential binding sites for metal ions. Although HA itself is not

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harmful to human health, it can react with halogen-based disinfecting agents during

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water treatment, and thereby producing trihalomethanes, which are associated with an

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increasing risk of cancer. In addition, many dyes (MO, MB, and RhB) are toxic and

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have caused serious issues to aquatic living organisms even at low concentrations.2

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The presence of these dyes in drinking water can give rise to taste, colour, and odour

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problems, while ingestion through the mouth produces a burning sensation and may

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cause nausea, gastritis, and vomit problems.3,4 Therefore, it is critical to eliminate

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organic pollutants and heavy metal ions from wastewater. 5



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Among various treatment technologies, adsorption is regarded as one of the most

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significant methods in fundamental studies and industrial applications owing to its

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easy operation and wide availability of adsorption materials.5 For the sake of low-cost

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and easy-access advantage, biomaterials have great potential as a raw carbon material

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for synthesizing various functional materials. Up to now, a wide variety of

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biomaterials, including enteromorpha prolifera,6 watermelon,7 rice hull ash,8 corn

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stalk,9 cotton,10 have been served as adsorbents to eliminate environmental pollutants.

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In view of this point, bio-derived carbon materials obtained from waste biomass

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exhibited an enhanced adsorption performance than the commercial activated

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carbons.11 Generally, bio-derived carbon materials have the advantages of superior

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thermal and chemical stability, high surface area, and abundant porosity, which ensure

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interactive sites with organic pollutants and heavy metal ions. Furthermore,

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magnetically functionalized carbon materials bring new prospects for the management

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of environmental pollutants because of its easy separation and fast uptake rate.12-14

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Thus, several research efforts have been made to evaluate magnetic materials as an

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adsorbent in water decontamination for removing various contaminants, including

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heavy metal ions, nutrients, and organic compounds. Zhang et al.15 fabricated

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colloidal γ-Fe2O3 particles embedded in porous biochar matrix from cottonwood for

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the removal of As(V) and methylene blue. Han et al.16 reported that magnetic biochar

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derived from peanut hull biomass showed an extreme capacity for Cr(VI) adsorption

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from aqueous solution. Chen et al.17 synthesized a novel magnetic biochar using

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orange peel powder for highly efficient removal of organic pollutants and phosphate 6


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from water. Unfortunately, most reported magnetic biochar usually exhibited low

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adsorption capacity and poor stability due to the surrounding chemical corrosion of

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their surface in polluted water. Hence, there is still a need to design and fabricate

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high-efficiency adsorbent that presents large capacity, fast adsorption rate, easy

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separation, and long-term stability.

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Due to the great demand of tea products, large amounts of tea waste are generated

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every year in China, which could be reused as an ideal low-cost biomass source for

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wastewater treatment. Herein, we reported a facile, low-cost, and readily scalable

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approach for synthesizing a magnetic porous carbonaceous (MPC) material with

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nanosized γ-Fe2O3 nanoparticles (NPs) embedded in porous carbonaceous matrix

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through thermal pyrolysis of FeCl3 treated tea waste. The presence of diverse

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chemical constituents of tea waste, including sugars, amino acids and phenols, could

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be favorable to γ-Fe2O3 growth and prevent γ-Fe2O3 NPs from aggregating.18 In

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addition, the MPC material was not only an ideal candidate as a high-efficiency

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adsorbent to remove contaminants from water but also could be easily separated from

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solutions. The prepared MPC materials were characterized by scanning electron

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microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction

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(XRD),

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Brunauer–Emmett–Teller (BET) analysis. To achieve a better understanding of the

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pollutants adsorption on MPC material, Fourier transform infrared (FTIR) and X-ray

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photoelectron spectroscopy (XPS) analysis were carried out to explore the possible

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interaction mechanism. The recoverable MPC material derived from tea waste is

thermogravimetric

analysis

(TGA),

magnetic

7


properties,

and


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expected to have potential application in environmental pollution management.

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EXPERIMENTAL SECTION

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Materials. All reagents were of analytical grade and used without any further

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purification.

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Na2HAsO4•7H2O, and K2Cr2O7) were purchased from Sinopharm Chemical

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Reagent Co., Ltd. Humic acid (HA) was extracted from Heilongjiang Province,

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China. The main HA constituents were approximately 60.44% C, 31.31% O, 4.22%

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N, 3.53 H, and 0.50% S. The starting material for the manufacture of biochar used

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in this work was Yellow Mountain Fuzz Tip, a naturally abundant biomass

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obtained from a local plant in Huangshan, China. Soluble and coloured

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components were initially removed from tea by washing with boiling water, and

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then dried in an oven at 85 oC overnight. The dried tea waste was subjected to ball

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milling, resulting in the particle size smaller than 120 mesh. Stock suspensions

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were prepared using Milli-Q water (18.2 M Ω cm-1) throughout the experiments.

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Synthesis of MPC Materials. The MPC material was synthesized by pyrolysis of

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Fe-loaded biomass, which was prepared in a biosorption process using the pristine

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tea leaves as an adsorbent. In a typical synthesis procedure, 6 g of biomass was

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immersed into 600 mL of FeCl3 solution with a concentration of 10 mM and stirred

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for 2 h at ambient temperature. Afterwards, the mixture was washed with Milli-Q

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water and oven-dried at 80 oC overnight. The Fe-loaded biomass was transferred to

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a furnace for pyrolysis under flowing high purity N2 atmosphere (99.999%) and

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heated at the appropriate temperature for 1 h at a heating rate of 2 oC/min. The

The

chemicals

(anhydrous

FeCl3,

NaNO3,

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HNO3,

NaOH,

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final MPC materials obtained at different temperatures-T (300, 400, and 500 oC)

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were denoted as MPC-300, MPC-400, and MPC-500, respectively. Porous

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carbonaceous (PC) material was made by the aforementioned procedure for

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comparison without FeCl3 added.

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Material Characterization. The morphology and microstructure of the samples

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were observed using SEM (JSM-6330F, JEOL, Japan). The TEM images were

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achieved on a Hitachi-7650 microscope transmission electron microscopicwith at

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an accelerating voltage of 100 kV. The XRD patterns were obtained on a Philips

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X’Pert Pro Super X-ray diffractometer equipped with Cu-Kα radiation (λ =

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1.54178 Å) in a scan rate of 2θ = 0.05 o/s. FTIR spectra were obtained on a Nicolet

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Magana-IR 750 spectrometer. The Raman spectra were recorded at room

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temperature in the backscattering configuration on a T64000 Jobin-Yvon (Horiba)

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spectrometer. Magnetic measurements were performed on powder samples using a

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MPMS-XL SQUID magnetometer. The N2-BET (Barrett–Emmett–Teller) surface

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area was measured with a Micromeritics ASAP 2010 system. XPS data were

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performed on a VG Scientific ESCALAB Mark II spectrometer with two ultrahigh

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vacuum (UHV) chambers. Thermogravimetric (TG) analysis was carried out using

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a TG-50 thermal analyzer (Shimadzu Corporation) under air atmosphere at a

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heating rate of 10 oC min-1. Zeta-potential was measured by using a ZETASIEZER

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3000 HSA system.

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Batch Adsorption Experiments. The adsorption of heavy metal ions and various

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organic pollutants on PC-300 and MPC-T material was carried out by batch 9



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method. For Cr(VI) or As(V) adsorption, the MPC stock suspension, the NaNO3

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background electrolyte solution and the Cr(VI) or As(V) solutions were added in

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the polyethylene tubes to obtain the desired concentrations of different

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components. Negligible volumes of Milli-Q water with a given pH (adjusted with

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the dilute HNO3 or NaOH solutions) was added to the susupension to achieve the

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desired pH values. For the kinetic studies, MPC-300 (40 mg) was added to

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Cr(VI)/As(V) solutions (40 mL) with three different concentrations of 2, 5 and 10 mg

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L-1, respectively. The pH of the suspensions was adjusted to 5.0 and withdrawn at

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appropriate time intervals. In the adsorption isotherm studies, the resulting series of

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MPC materias were set as 1.0 g L-1 with different Cr(VI) or As(V) concentrations

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(from 2 mg L-1 to 120 mg L-1) at pH = 5.0. The above suspensions were oscillated for

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24 h to achieve adsorption equilibration and the MPC materials were separated by a

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permanent magnet. The concentrations of heavy metal ions in the supernatant were

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determined using inductively coupled plasma-atomic emission spectroscopy

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(ICP-AES). The adsorption percentage and adsorption capacity were calculated from

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Eqs. (1) and (2), respectively:19,20

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Adsorption(%) =

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qe (mg / g ) =

(C0 − Ce ) × 100% C0

V × (C0 − Ce ) m

(1)

(2)

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where C0 (mg L-1) and Ce (mg L-1) are the initial concentration and the equilibrium

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one after adsorption, respectively, and m (mg) and V (mL) are the dosage of MPC and

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the total volume of the suspension, respectively. The Langmuir isotherm model 10


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assumes homogeneous adsorption surface with the equal adsorbate affinity, which is

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presented as:21

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Langmuir model:

qe =

bqmax Ce 1 + bCe

(3)

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The Freundlich isotherm model is applicable to a multilayer adsorption surface with a

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heterogeneous energetic distribution of active sites, which can be described by the

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following equation:22

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Freundlich model:

qe = kCe1/ n

(4)

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where qe (mg g-1) is the amount of heavy metal ions adsorbed per unit weight of

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adsorbent. qmax (mg g-1) is the saturation adsorption capacity associated with complete

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monolayer coverage, and b (L mg-1) is a Langmuir constant that relates to the energy

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of the adsorbent. 1/n and k (mg g-1) are correlated to the relative adsorption intensity

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and adsorption capacity, respectively.

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For organic pollutants, methylene blue (MB), rhodamine B (RhB), methyl

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orange (MO), and humic acid (HA) were applied as typical organic pollutants. The

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stock suspensions (300 mg L-1) were prepared by dissolution of various organic

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pollutants into Milli-Q water. A certain amount of MPC-300 sample in the

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suspension was mixed with the aqueous soltutions of HA and other organic dyes.

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After gentle shaking for 2 h, the solid phases were separated from the suspension.

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The concentrations of residual MB, MO, RhB or HA were determined on a UV-vis

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spectrophotometer (Hitachi, U-3900, Tokyo, Japan), and the calculation of the

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adsorption percentage and the adsorption capacity was the same as that for the heavy

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metal ions. All experimental data were the average of triplicate determination, and the 11



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relative errors were about 5%.

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RESULTS AND DISCUSSION

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Characterization of MPC Materials.

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Our strategy for the synthesis of MPC sample was schematically described in Scheme

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1. The Fe-loaded precursors were first converted into Fe-hydroxides (FeO(OH))

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composite in the drying process.23 A subsequent pyrolysis step of Fe-preloaded

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biomass at 300-500 oC leads to nucleation and growth of nanoparticles and release

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of porosity, resulting in the metal oxide embedded in the amorphous carbon matrix.

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Details about the morphology of the pristine tea waste and MPC-300 were

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examined by SEM and TEM. The tea waste appeared as bulk stone-like features

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(Figure 1a), and no porous structure was observed in high magnification SEM

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(Figure 1b) and TEM (Figure 1c) images. After the pyrolysis of the as-loaded

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composite, numerous γ-Fe2O3 NPs (Figure 1d) were decorated on the surface of

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biochar where nanometer range (50-80 nm) particles were individually formed

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without obvious aggregations (Figure 1e). The TEM image of MPC-300 (Figure 1f)

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identified the thin layer and the presence of magnetic NPs in the porous carbon

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matrix.

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To further confirm the existence of magnetic iron oxide, the obtained samples of

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MPC-T samples pyrolyzed at different temperatures were characterized by XRD.

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As observed in Figure 2a, typical peaks at 30.1o, 35.5o, 37.1o, 43.1o, 53.5o, 57.0 o, and

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62.5o were assigned to the (220), (311), (222), (400), (422), (511), and (440) facets of

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γ-Fe2O3 (JCPDS No.39-1346), respectively.24 With increasing annealing temperature 12


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to 500 oC, the crystallinity of the powder increased because the intensities of

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diffraction peaks became stronger and sharper than those of the samples prepared at

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300 oC and 400 oC. In addition, three patterns showed a broad and relatively weak

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diffraction peak at 23°, which corresponded to the amorphous carbon, composed of

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aromatic carbon sheets oriented in a relatively random manner. As shown in Figure 2b,

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the FTIR spectra of MPC-T samples showed the characteristic bands at 3407 cm-1

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(stretching vibration of –OH and –NH groups), at 1643 cm-1 (C=O stretching vibration

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conjugate with the NH2 (amide I band)), 1398 cm-1 (the symmetric stretch of C-N) and

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at 1054 cm-1 (C–O stretching vibration).25,26 The band at 588 cm-1 was related to the

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stretching vibration of Fe–O bond.27 Notably, the absorption bands at 2920-2850 cm-1

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on MPC-300 were attributed to the stretching vibration of –CH and –CH2, while both

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functional groups were disappeared for MPC-400 and MPC-500. Figure S1a show

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Raman spectra of all samples has two strong peaks centered at 1330 and 1600 cm-1,

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which can be ascribed to the D band and G band of carbon material.28 While the peaks

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appeared around 222, 289, 392, and 501 cm-1 were characteristic Raman shifts of

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γ-Fe2O3, respectively.29,30 As the temperature was increased, thermal decomposition of

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original organic residues resulted in the release of the byproducts of H2O, CO2 and CO,

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which was accompanied by the formation of voids because of the volume shrinking at

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high temperature. These results indicated that carboxyl and hydroxyl groups of biochar

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interacted with Fe–O bonds of γ-Fe2O3. From Figure S1b, the surface area of

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MPC-300 calculated by the Brunauer–Emmett–Teller (BET) method was 63 m2 g-1,

259

which was significantly higher than those of PC-300 (16 m2 g-1), MPC-400 (34 m2 g-1) 13



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and MPC-500 (31 m2 g-1). Therefore, the heat-treatment temperature played a crucial

261

role in achieving various functional groups and the chemical bonds between biochar

262

and hematite.

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The TG analysis was conducted to examine the weight percentage of γ-Fe2O3 in

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MPC-T samples (Figure 3a). The weight loss of drying process below 125 oC was

265

considered to the evaporation of free water. The TGA curve of MPC-300 showed a

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slow weight loss of 5.3% from 125 to 260 oC, which could be attributed to the

267

decomposition of residual organic moieties. However, the curves of MPC-400 and

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MPC-500 maintained a stable tendency below 300 oC. Subsequently, the major weight

269

loss (~65%) occurred between 300 and 500 oC indicated a large elimination of

270

oxygen-containing functional groups.31 The DTA curves showed a corresponding

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intense endothermic peak around 400 oC (Figure 3b), which originated from the

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release of H2O, CO2 and CO molecules developed by the combustion of organic

273

carbon framework. The results showed that the mass percentages of γ-Fe2O3 were

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about 19.9% for MPC-300, 27.7% for MPC-400, and 28.8% for MPC-500. Such a

275

difference of γ-Fe2O3 contents can cause diverse magnetization hysteresis curves. The

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magnetic properties of MPC-T samples measured at room temperature (Figure 3c)

277

showed a ferromagnetic behavior with small remnant magnetization and coercivity.

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The specific saturation magnetization (Ms) of MPC-300 was 12.15 emu g-1, which was

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lower than those of MPC-400 (34.81 emu g-1) and MPC-500 (45.25 emu g-1),

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suggesting that the Ms values were related to the heat-treatment temperature and the

14


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load of γ-Fe2O3. Interestingly, the MPC-300 material can be efficiently separated from

282

aqueous solution by using a permanent magnet (Figure 3d).

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Adsorption Isotherms of Cr(VI) and As(V) on the MPC Materials.

284

To evaluate the adsorption performance, the resulting series of MPC-T samples

285

pyrolyzed at different temperatures were expected to probe the uptake of Cr(VI) and

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As(V) ions from aqueous solutions. Two typical isotherm models (Langmuir and

287

Freundlich) were applied to simulate the adsorption isotherms, and the results were

288

shown in Figure 4. Langmuir and Freundlich isotherm constants for Cr(VI) and As(V)

289

adsorption were summarized in Table 1. One can see from the R2 values that the

290

Langmuir model fitted the experimental data better than the Freundlich model,

291

indicating that the binding energy of MPC-T is uniform. In addition, the Freundlich

292

constants n were found to be higher than 1, suggesting the good affinity of

293

as-prepared samples for both Cr(VI) and As(V). According to the results of

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Langmuir model simulation (Figure 4a), the maximum adsorption capacity of Cr(VI)

295

on MPC-300 was 21.23 mg g-1, which was higher than those of Cr(VI) on PC-300

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(8.53 mg g-1), MPC-400 (17.14 mg g-1) and MPC-500 (12.33 mg g-1). Similar

297

results (Figure 4b) were also observed for the adsorption of As(V) on MPC samples

298

pyrolysed at 300-500 oC, which possessed impressive capacities of 9.25, 38.03, 31.67,

299

and 27.81 mg g-1 (still not saturated) for As(V) on PC-300, MPC-300, MPC-400,

300

and MPC-500, respectively. Futhermore, the desorption isotherms were obviously

301

higher than the adsorption isotherms (Figure S2), suggesting the irreversible

302

adsorpiton and the adsorption of Cr(VI) and As(V) on MPC samples was mainly

15



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

303

dominated by strong chemical interaction. As listed in Table S1, all of these values

304

were much higher than previous reported flowerlike CeO2 (5.9 mg/g for Cr(VI) and

305

14.4 mg/g for As(V)),32 surfactant-modified zeolite Y (1.95 mg/g for Cr(VI) and

306

0.93 mg/g for As(V)),33 flowerlike α-Fe2O3 (5.4 mg/g for Cr(VI) and 7.6 mg/g for

307

As(V)) and commercial bulk α-Fe2O3 (0.37 mg/g for Cr(VI) and 0.3 mg/g for

308

As(V)).34 In addition, the poor adsorption performance of MPC-400 and MPC-500

309

may be ascribed to the relatively lower density of adsorptive sites on the γ-Fe2O3.

310

This is because the magnetic nanoparticles obtained at higher temperature have

311

relative higher crystallization degree, larger particles diameter, and are more closely in

312

contact with porous carbon layer.35 Nevertheless, it was expected that MPC-400 and

313

MPC-500 hold a higher magnetic strength for easier separation, which was

314

confirmed by the magnetic hysteresis curves (Figure 3c). Another interesting

315

phenomenon was that MPC-300 showed a greater adsorption capacity for As(V)

316

than Cr(VI), indicating that the surface of MPC-300 held a relatively greater

317

affinity for As(V) rather than Cr(VI). Such type of effects was reported in the

318

formation of an inner-sphere complex between As(V) and iron(hydr-) oxide

319

minerals. While Cr(VI) anion was weakly adsorbed on the surface of iron oxides

320

through outer-sphere surface complex.36,37

321

Kinetic Studies of Cr(VI) and As(V) on MPC-300.

322

Based on the above adsorption behavior of as-obtained samples, we investigated a

323

series of kinetic experiments of Cr(VI) and As(V) adsorption on MPC-300. Figure 5a

324

and 5c showed that the adsorption rates of Cr(VI) and As(V) on MPC-300 were

16


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325

considerably fast within the initial contact time of 1 h at three initial concentrations

326

(2, 5, and 10 ppm). The time needed for complete removal of Cr(VI) and As(V) at

327

the low initial concentrations (2 and 5 ppm) was just 1.5 h and the final removal

328

efficiencies were up to ~100%. In comparison, the adsorption efficiencies were

329

found to be 81.8% and 90.7% for Cr(VI) and As(V) on MPC-300 at the initial

330

concentration of 10 ppm. For the concentration of 10 ppm, the equilibrium time of

331

Cr(VI) or As(V) on MPC-300 was longer than that of other concentrations (2 ppm

332

and 5 ppm), indicating that the active sites of γ-Fe2O3 on MPC-300 were gradually

333

occupied by Cr(VI) or As(V) anions. The pseudo-first-order model and

334

pseudo-second-order kinetic model were used to explore the kinetic adsorption

335

processes (e.g., mass transfer or chemical reaction), which were described as:

336

pseudo-first-order model:

337 338

339

ln( qe − qt ) = ln qe − k1t

(5)

pseudo-second-order model:

t 1 t = + 2 qt k 2 qe qe

(6)

340

where qe (mg g-1) and qt (mg g-1) are the amounts of Cr(VI) or As(V) adsorbed after

341

equilibrium and at time t (h), respectively. k1 (h-1) is the Lagergren adsorption rate

342

constant, calculated from the plot of ln(qe - qt) versus t. k2 (g mg-1 h-1) represents the

343

rate constant of the pseudo-second-order rate model. k2 and qe values can be

344

determined experimentally by plotting t/qt versus t. From the adsorption kinetics

345

shown in Figure 5b and 5d, the adsorption rate of Cr(VI)/As(V) on MPC-300

346

depended on its initial concentration, and the higher the concentration, the slower the 17



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

347

adsorption rate. The corresponding detailed kinetic parameters were also tabulated in

348

Table 2 and Table S2. The correlation coefficient values (R2) calculated from

349

pseudo-second-order kinetic model were above 0.999, which were higher than those

350

of pseudo-first-order model. In addition, the calculated qe values were in good

351

agreement with the experimental ones, showing a quite good linearity. Therefore, the

352

Cr(VI) and As(V) uptake onto MPC-300 were favorable by the pseudo-second-order

353

kinetic model, indicating a chemisorption process.38

354

Effect of pH, Humic Acid and Coexisted Ions.

355

Effect of solution pH on Cr(VI) and As(V) adsorption on MPC-300 was also

356

investigated. As shown in Figure 6a and 6b, the tendency of both heavy metal anions

357

adsorption on MPC-300 decreased slowly at pH < 4.0 and quickly at pH 4.0-10.0.

358

Similar effects of pH on Cr(VI) and As(V) adsorption in the presence of HA were also

359

observed. However, the presence of HA slightly decreased Cr(VI)/As(V) adsorption at

360

pH < 6.0. No obvious difference was found for As(V) adsorption in HA+MPC-300

361

system at pH > 6.0. Based on the investigation of zeta-potential (Figure 6c), one can

362

see that the presence of HA slightly influenced the pHzpc values, which decreased from

363

6.8 (absence of HA) to 6.0 (presence of 10 mg/L HA). At pH < pHzpc, HA adsorbed on

364

MPC-300 became more negative and HA occupied the active sites, resulting in the

365

decrease of binding negative charged Cr(VI)/As(V) target ions, whereas at pH > pHzpc,

366

the negative charged Cr(VI)/As(V) and soluble HA were difficult to be adsorbed on

367

negative charged surface of MPC-300 due to the electrostatic repulsion. We speculated

368

that in the case of HA+MPC-300 system, Cr(VI)/As(V) anions might compete 18


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369

against HA molecules for the binding sites of solid particles. Thus, pH-dependent

370

behavior of Cr(VI)/As(V) adsorption onto MPC-300 demonstrated that Cr(VI)/As(V)

371

adsorption was believed to occur via electrostatic interactions.39 Actually, Cr(VI) and

372

As(V) ions inevitably coexist with various electrolyte ions in wastewater, which would

373

influence the migration of pollutants in environmental mediums. Thus, Na+, K+, Mg2+,

374

and Ca2+, as well as Cl-, NO3-, and SO42- anions were the common coexisting ions.

375

From Figure 6d, it was found that the presence of nitrate salts for cations and sodium

376

salts for anions reduced the adsorption capacity of adsorbate on MPC-300. Most

377

coexisting ions had no obvious influence on Cr(VI) and As(V) adsorption. Notably,

378

SO42- anion can significantly reduce both heavy metal ions’ adsorption on MPC-300,

379

which was mainly ascribed to the strongest competition effect with target anions. In

380

view of this point, the coexisting SO42- ions should be removed beforehand to obtain

381

high efficiency of MPC-300 for Cr(VI)/As(V) adsorption.

382

XPS Analysis.

383

To study the interaction mechanism between the adsorbates and MPC-300,

384

surface sensitive XPS spectra were measured with MPC-300 before and after Cr(VI)

385

and As(V) adsorption. As shown in Figure 7a and 7b, there were four elements in the

386

XPS survey spectrum of MPC-300, including 66.19 atom% of C, 23.44 atom% of O,

387

6.05 atom% of Fe, and 4.32 atom% of N. The fitted high-resolution spectrum of Fe 2p

388

(Figure S3a) revealed that the peak positions located at ~725.8 and ~712.4 eV were

389

assigned to Fe 2p1/2 and Fe 2p3/2 of γ-Fe2O3 rather than Fe3O4,40 which were consistent

390

with the XRD results. In addition, the peak centered at ~719.1 eV was the 19



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

391

characteristic of γ-Fe2O3, which was not obvious in Fe3O4. Deconvolution of C1s

392

(Figure S3b) showed that there were three types of carbon atoms in MPC-300, i.e., the

393

non-oxygenated carbon (284.6 eV), the carbon in C-O bond (286.2 eV), and the

394

carboxylate carbon in O-C=O bond (289.0 eV).41 There were two main types of

395

carbon in MPC-300, i.e., the carbon in C-O and the non-oxygenated carbon. After

396

adsorption, the signals of Cr(VI) and As(V) were found on the MPC-300 sample. The

397

As 3d spectrum of As(V)-adsorbed sample (Figure S3c) showed a characteristic peak

398

located at 45.4 eV, which was attributed to the As-O bonding. While the

399

high-resolution of Cr 2p XPS spectrum (Figure S3d) showed the characteristic Cr 2p

400

peaks at 577.2 and 587.1 eV, which were ascribed to Cr 2p3/2-O and Cr 2p1/2-O

401

bonding, respectively. The complex O 1s spectrum (Figure 7c-e) of MPC-300 can be

402

deconvoluted into four different oxygen containing functional groups: (a) O-H at

403

533.5 eV, (b) C-O at 532.3 eV, (c) C=O at 531.0 eV, and (d) Fe-O 530.0 eV. It was

404

found that the intensities of O-H peaks after As(V) and Cr(VI) adsorption decreased

405

slightly, whereas Fe-O species became significantly higher, suggesting that the partial

406

replacement of hydroxyl groups were exchanged by H2AsO4- or HCrO4-/Cr2O72- (the

407

predominate species in aqueous solution at pH 5, presented in Figure S4). The results

408

were consistent with a recent study, in which Cao et al. found that the O-H groups on

409

flowerlike α-Fe2O3 were replaced by As(V) or Cr(VI) anions, resulting in the decrease

410

ratio of t2g/eg in the synchrotron-based XANES spectra.34

411

Adsorption of Humic Acid and Organic Pollutants

20


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412

The adsorption performance of MPC-300 with various dyes (MB, RhB, and MO)

413

and HA were also studied, followed by UV-vis adsorption examination of the residual

414

solutions (Figure S5). From a kinetic aspect (Figure S6a), MPC-300 can remove ~80

415

wt% of pollutant (10 ppm) from aqueous solution within the contact time of 30 min,

416

exhibiting fast adsorption rate. The high correlation coefficients (Table S3) suggested

417

that the adsorption kinetics of organic pollutants on MPC-300 can be perfectly fitted

418

by a pseudo-second-order model. The total organic carbon (TOC) concentration as a

419

function of contact time (Figure S7) showed clearly that the content of TOC in

420

residual solution was reduced quickly with increase of contact time, demonstrating the

421

strong interaction of organic pollutants with MPC-300. The experimental data of MB,

422

RhB, MO, and HA adsorption were regressively simulated with the Langmuir and

423

Freundlich models (Figure S8) and the relative parameters were tabulated in Table S4.

424

From Table S4, one can see that the isotherms could be described well by the

425

Langmuir model rather than the Freundlich model. This was due to the assumption of

426

an exponentially increasing adsorption amount in the Freundlich model. Moreover,

427

MPC-300 possessed impressive capacities of 95.92 mg g-1 toward HA and 73.12 mg

428

g-1 toward MO, which were higher than those toward MB (45.74 mg g-1) and RhB

429

(31.94 mg g-1) (as shown in Table S4). Obviously (Figure S6d), the adsorption

430

performances of PC-300 toward HA, MO, MB and RhB were 34.14, 25.52, 22.69, and

431

21.36 mg g-1, respectively. Generally, MO and HA are organic molecules with

432

negative charge in aqueous solution, whereas MB and RhB have positive charge.9 The

433

surface of γ-Fe2O3 was positively charged, which was favorable for the binding of the 21



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

434

negatively charged HA and MO targets due to the strong electrostatic. Furthermore,

435

the mutual effects of HA and MO adsorption on MPC-300 were also investigated. As

436

shown in Figure S9a, the presence of HA led to slightly inhibition of MO adsorption

437

on MPC-300, suggesting the stronger coordination of γ-Fe2O3 for HA. The abundance

438

of various organic pollutants adsorbed on MPC-300 can be confirmed by means of

439

FTIR spectroscopy, as shown in Figure S9b. After adsorption of various dyes and HA

440

by MPC-300, the characteristic spectra of MB, RhB, MO and HA were almost

441

recorded in the corresponding spectrum of the adsorptive adduct. From the ring

442

stretching band at 1643 cm-1 and C–O stretching vibration at 1054 cm-1, the organic

443

pollutants adsorbed MPC-300 showed blue shifts to 1617 and 1034 cm-1,42

444

respectively. And the symmetric stretch of C-N at 1384 cm-1 appeared after their

445

adsorption onto MPC-300, implying the interaction between various pollutants and

446

γ-Fe2O3.43

447

CONCLUSIONS

448

To get rid of heavy metal ions and organic pollutants from wastewater, the MPC

449

materials were synthesized via a simple biosorption method followed by heat

450

treatment process. The results showed that the sample prepared at 300 oC (MPC-300)

451

was the best among the series with the maximum adsorption capacities of 38.03 mg

452

g-1 for As(V) and 21.23 mg g-1 for Cr(VI) at pH 5.0. Ion exchange between hydroxyl

453

on the γ-Fe2O3 surface and As(V) or Cr(VI) was the main mechanism of

454

As(VI)/Cr(VI) interaction with MPC-300. Further investigations revealed that the

455

adsorption capacities were in the order of RhB < MB < MO < HA, largely because the

22


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456

MPC-300 can selectively adsorb negatively charged anionic dyes and HA through

457

electrostatic interaction. Therefore, the novel MPC material is practically capable for

458

the efficient separation of heavy metal ions, humic acid and dyes from wastewater in

459

environmental pollution cleanup.

460

ASSOCIATED CONTENT

461

Supporting

462

Adsorption-desorption isotherms of Cr(VI) (a) and As(V) on MPC-300, The X-ray

463

photoelectron spectroscopy (XPS) spectrum of Fe 2p and C 1s for MPC-300, XPS

464

spectrum of As 3d and Cr 2p of MPC-300 after As(V) and Cr(VI) adsorption. The

465

relative distribution of As(V) and Cr(VI) species in aqueous solutions. The UV-vis

466

spectra of MB, RhB, MO, and HA adsorption on MPC-300 as a function of reaction

467

time. Kinetic parameters of As(V), Cr(VI), MB, RhB, MO and HA adsorption on

468

MPC-300. Dyes and humic acid adsorption on MPC-300. Langmuir and Freundlich

469

adsorption isotherm fitting and parameters for MB, RhB, MO and HA sorption on

470

MPC-300. TOC concentrations as a function of reaction time.

471

AUTHOR INFORMATION

472

Corresponding Author

473

*X.K.Wang. E-mail: [email protected]. Phone: +86-10-61772890. Fax:

474

+86-10-61772890.

475

Notes

476

The authors declare no competing financial interest.

477

ACKNOWLEDGEMENTS

Information.

N2

adsorption–desorption

23


isotherms,


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

478

The financial support from NSFC (21225730, 91326202, 21377132, 21577032), the

479

Fundamental Research Funds for the Central Universities (JB2015001), the Jiangsu

480

Provincial Key Laboratory of Radiation Medicine and Protection and the Priority

481

Academic Program Development of Jiangsu Higher Education Institutions are

482

acknowledged. X. Wang acknowledged the CAS Interdisciplinary Innovation Team of

483

Chinese Academy of Sciences.

484

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485

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synthesis of flowerlike α-Fe2O3 nanostructures for heavy metal ion removal:

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adsorption property and mechanism. Langmuir 2012, 28, 4573-4579.

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(35) Wu, Z.; Li, W.; Webley, P. A.; Zhao, D. General and controllable synthesis of

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novel mesoporous magnetic iron oxide@carbon encapsulates for efficient arsenic

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removal. Adv. Mater. 2012, 24, 485-491.

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(36) Müller, K.; Ciminelli, V. S.; Dantas, M. S. S.; Willscher, S. A comparative study

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of As(III) and As(V) in aqueous solutions and adsorbed on iron oxy-hydroxides by

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Raman spectroscopy. Water Res. 2010, 44, 5660-5672.

587

(37) Williams, A. G. B.; Scherer, M. M. Spectroscopic evidence for Fe(II)-Fe(III) 28


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electron transfer at the iron oxide-water interface. Environ. Sci. Technol. 2004, 38,

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4782-4790.

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(38) Gong, J. M.; Liu, T.; Wang, X. Q.; Hu, X. L.; Zhang, L. Z. Efficient removal of

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heavy metal ions from aqueous systems with the assembly of anisotropic layered

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double hydroxide nanocrystals@carbon nanosphere. Environ. Sci. Technol. 2011, 45,

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6181-6187.

594

(39) Wang, P.; Lo, I. M. C. Synthesis of mesoporous magnetic g-Fe2O3 and its

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application to Cr(VI) removal from contaminated water. Water Res. 2009, 43,

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3727-3734.

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(40) Agrawal, P.; Bajpai, A. K. Dynamic column adsorption studies of toxic Cr(VI) ions

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onto iron oxide loaded gelatin nanoparticles. J. Dispersion Sci. Technol. 2011, 32, 1353.

599

(41) Chandra, V.; Park, J.; Chun, Y.; Lee, J. W.; Hwang, I. C.; Kim, K. S.

600

Water-dispersible magnetite-reduced graphene oxide composites for arsenic removal.

601

ACS Nano 2010, 4, 3979-3986.

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(42) Ramesha, G. K.; Vijaya Kumara, A.; Muralidhara, H. B.; Sampath, S. Graphene

603

and graphene oxide as effective adsorbents toward anionic and cationic dyes. J.

604

Colloid. Interf. Sci. 2011, 361, 270–277.

605

(43) Zhou, K. Q.; Zhang, Q. J.; Wang, B.; Liu, J. J.; Wen, P. Y.; Gui, Z.; Hu, Y. The

606

integrated utilization of typical clays in removal of organic dyes and polymer

607

nanocomposites. J. Clean. Prod. 2014, 81, 281-289.

608

29



609 610 611 612

Scheme 1 Schematic illustration of the synthesis of magnetic porous carbonaceous (MPC) materials.

613 614

Figure 1. Low-magnification and high-magnification SEM images of biomass waste

615

(a-b) and MPC-300 (d-e). The corresponding TEM images of biomass waste (c) and

616

MPC-300 (f).

(220) (222)

(b)

MPC-300 MPC-400 MPC-500

(311)

(400)

3407

(511)(440) (422)

Intensity (a.u.)

(a) Intensity (a.u.)

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

Page 30 of 35

Amorphous carbon

MPC-500

1054 1643 1398

588

MPC-400

MPC-300 2920-2850

JCPDS No.39-1346

20

617 618 619

30

40 50 2 Theta (degree)

60

70

4000

3500

3000

2500 2000 1500 -1 Wavenumber (cm )

1000

500

Figure 2. (a) XRD patterns and (b) FTIR spectra of MPC-T (300, 400, and 500 oC).

30


Page 31 of 35

620 621 622

Figure 3. (a) TGA and (b) the corresponding DTA curves of MPC-T (300, 400, and

623

500 oC). (c) Hysteresis curves of MPC-T at 300 K, the corresponding close view of

624

the hysteresis loops of MPC-T (300, 400, and 500 oC) and (d) MPC-300 material

625

dispersed water solution and magnetic separation. 20

(a)

18

Cr(VI)

(b)

25

MPC-300

16

As(V)

MPC-300

20

14

MPC-400

15 -1

qe (mg g )

MPC-400

12 qe (mg g )

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


10 MPC-500

8 6

10

MPC-500

5

PC-300

PC-300

4

0

2 0

20

40 60 -1 Ce (mg L )

80

0

100

626

20

40 60 -1 Ce (mg L )

80

100

627

Figure 4. Adsorption isotherms of Cr(VI) (a) and As(V) (b) on PC-300 and MPC-T

628

(300, 400, and 500 oC). m/V = 1.0 g L-1, pH = 5.0 ± 0.1, I = 0.01 M NaNO3.

31



10

14

(a)

Cr (VI) 10 ppm 5 ppm 2 ppm

Ce (mg L )

8

8

-1

t/qt (h g mg )

-1

4

6 4 2 0

0

(c)

As (V) 10 ppm 5 ppm 2 ppm

8

12

(d)

As (V) 10 ppm 5 ppm 2 ppm

10 8

-1

-1

t/qt (h g mg )

6

Ce (mg L )

Cr (VI) 10 ppm 5 ppm 2 ppm

10

6

10

(b)

12

2

4 2

6 4 2

0

0 0

3

6

9

12

15

18

21

24

0

3

6

9

Time (h)

629

12

15

18

21

24

Time (h)

630

Figure 5. Effect of initial Cr(VI) (a) and As(V) (c) concentration (2, 5, and 10 ppm)

631

on the Cr(VI) and As(V) removal efficiency of MPC-300. Pseudo-second-order linear

632

plots for the removal of Cr(VI) (b) and As(V) (d) by MPC-300. m/V = 1.0 g L-1, pH =

633

5.0 ± 0.1, I = 0.01 M NaNO3. (a)

100

Cr(VI)

80

Adsorption percentage (%)

Adsorption percentage (%)

90

70 60 50 40 30 10 mg/L HA, MPC-300 MPC-300

20

(b)

As(V)

80 60 40 20

10

10 mg/L HA, MPC-300 MPC-300

0

0 2

40

3

4

5

6 pH

7

8

9

10

2

(c)

7

30

10 mg/L HA, MPC-300 MPC-300

20

3

4

5

6 pH

7

8

(d)

9

10

Cr(VI) As(V)

6 5 qe (mg g )

10

-1

Zeta potential (mV)

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

Page 32 of 35

0

4 3 2

-10

1

-20

0

2

634

3

4

5

6

7

8

9

10

None

+

Na

+

K

2+

Mg

2+

Ca

-

Cl

-

NO3

2-

SO4

pH

635

Figure 6. Effect of humic acid on the adsorption of Cr(VI) (a) and As(V) (b) on

636

MPC-300. (c) Zeta potential of MPC-300 and HA+MPC-300 as a function of pH. (d) 32


Page 33 of 35

637

Effect of coexisting ions on the adsorption of Cr(VI) and As(V) by MPC-300. m/V =

638

1.0 g L-1, I = 0.01 M.

639 80

C 1s

(a)

O 1s

70

Fe 2p

Intensity (a.u.)

N 1s

(b)

MPC-300 MPC-300 + As(V) MPC-300 + Cr(VI)

60

30 20

1000

800

M P C -3 0 0

As3d

Cr2p

0

600 400 200 Binding Energy (eV)

(c )

(d )

0

C1s

O1s

M P C -3 0 0 + A s(V )

Fe2p

(e )

N1s

M P C -3 0 0 + C r (V I)

P eak Su m O -H C -O C =O F e -O

538 536 534 532 530 528

640

10

2.63 %

Cr 2p

40

3.96 %

At. (%)

50 As(A) As 3d

MPC-300 MPC-300 + As(V) MPC-300 + Cr(VI)

Intensity (a.u.)

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


538 536 534 532 530 528 B in d in g E n e r g y (e V )

538 536 534 532 530 528

641

Figure 7. (a) XPS spectra and (b) elemental compositions of MPC-300 before and

642

after As(V) and Cr(VI) adsorption. And the corresponding O1s spectrum of MPC-300

643

(c) before adsorption, (d) after As(V) adsorption, and (e) after Cr(VI) adsorption.

644 645 646 647

33



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

Page 34 of 35

648

Table 1. Langmuir and Freundlich adsorption isotherm parameters for Cr(VI) and

649

As(V) on PC-300 and MPC-T (300, 400, and 500 oC). Species

Sample name

Cr(VI)

As(V)

Langmuir qmax( mg g-1)

Freundlich

b (L mg-1)

R2

k

n

R2

PC-300

8.53

0.042

0.973 1.06

2.38

0.927

MPC-300

21.23

0.117

0.964 5.47

3.35

0.867

MPC-400

17.14

0. 071

0.979 3.18

2.82

0.893

MPC-500

12.33

0.051

0.998 1.81

2.55

0.953

PC-300

9.25

0.049

0.908 1.34

2.56

0.815

MPC-300

38.03

0.029

0.925 2.56

1.83

0.855

MPC-400

31.67

0.012

0.958 0.87

1.41

0.922

MPC-500

27.81

0.008

0.965 0.79

1.27

0.907

650 651 652 653

Table 2. Kinetic parameters calculated from pseudo-second-order model. Species C0 (mg L-1) Cr(VI) 2 5 10 As(V) 2 5 10

qe,exp (mg g-1) 1.88 4.96 8.18 1.91 4.86 9.07

qe,cal (mg g-1) 1.90 4.98 8.21 1.91 4.88 9.12

654 655 656 657 658 659 660 34


k2 (g mg-1 h-1) 10.05 3.20 1.25 15.39 5.77 0.96

R2 0.999 0.999 1 0.999 0.999 0.999

Page 35 of 35

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661

For Table of Contents Use Only

662

Magnetic Porous Carbonaceous Material Produced from Tea

663

Waste for Efficient Removal of As(V), Cr(VI), Humic Acid and

664

Dyes

665

Tao Wen, Jian Wang, Shujun Yu, Zhongshan Chen, Tasawar Hayat, Xiangke

666

Wang

667

Synopsis

668

A sustainable magnetic material derived from tea waste was developed to remove

669

heavy metal ions (As(V) and Cr(VI)) and organic contaminants (humic acid and

670

various dyes) simultaneously with remarkable adsorption capacity.

671 672

35


Magnetic Porous Carbonaceous Material Produced from Tea Waste

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