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Electronic Supplementary Information

Nitrogen-rich core/shell magnetic nanostructures for selective

adsorption and separation of anionic dyes from aqueous solution

Bo Chen, Yang Liu, Sijiang Chen, Xuesong Zhao, Wenli Yue, Xuejun Pan*

Faculty of Environmental Science and Engineering, Kunming University of Science and Technology,

Kunming 650500, P.R. China.

*Corresponding author

Tel: +86-871-65920510; Fax: +86-871-65920510; E-mail: xjpan@kmust.edu.cn

Electronic Supplementary Material (ESI) for Environmental Science: Nano.This journal is © The Royal Society of Chemistry 2016

Experimental details

1. Preparation of Fe3O4@NH2@PEI nanomaterials

1.1 Preparation of Fe3O4@NH2 by a solvothermal route

An amount of 2 g FeCl3·6H2O and an amount of 4 g sodium acetate anhydrous were dissolved in

a volume of 60 mL ethylene glycol under magnetic stirring. Then 10 g of 1, 6-hexadiamine was added

and dissolved into the resulting mixture by continuous stirring. After that, the obtained solution was

transferred into a Teflon lined autoclave and reacted for 8 h at 200 °C. After cooling at room

temperature, the resulting Fe3O4@NH2 materials were thoroughly washed with ultrapure water and

ethanol to effectively remove the solvent and unbound 1, 6-hexadiamine, and then dried in the

refrigeration dryer for the following experiments.

1.2 Fabrication of Fe3O4@NH2@PEI composites by a chemical crosslink reaction

0.2 g of Fe3O4@NH2 was fully contacted with 50 mL of PEI in methanol for 30 min by

ultrasonication. For grafting of PEI onto Fe3O4@NH2 surface, 100 mL of 2% (w/v) glutaraldehyde

solution was added dropwise to the mixture and mechanically stirred for 30 min at a speed of 300 rpm

at room temperature. It should be noted that self-crosslinking reaction may occur between free PEI

molecules in the presence of glutaraldehyde. Thus, in order to isolate the PEI-PEI gel from the surface

of Fe3O4@NH2@PEI, it is necessary to fully wash the obtained Fe3O4@NH2@PEI composites with

adequate ultrapure water until the supernatant became clear. In succession, the as-prepared

Fe3O4@NH2@PEI composites were dried in the refrigeration dryer for the following characterization

and adsorption experiments.

2. Adsorption experiments in single-solute system

The solution pH was adjusted by using diluted HCl or NaOH solution. To evaluate the effect of

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pH, an amount of 0.03 g adsorbents was added to 30 mL portions of 100 mg/L each dye with initial pH

ranging from 3.0 to 10.0 and the mixture were continuously shaken in a thermostatic shaker at 25 °C to

reach equilibrium. After adsorption, the liquid/solid phase separation was achieved by a permanent

magnet Nd-Fe-B. The dye concentration in the supernatant part was determined using an UV-visible

absorption spectrophotometry at λmax of 423 nm for ARS and 463 nm for MO. For the kinetics

experiments, at a pH value of 3.0, 0.03 g of Fe3O4@NH2@PEI was mixed with 30 mL of 100 mg/L

dye solution. The flasks containing adsorbents and dye solution were placed in a thermostatic shaker

and shaken for a certain period of time ranging from 1 to 60 min. An aliquot of approximate 30 mL

mixture solution was taken out for dye concentration measurements at different time intervals during

the adsorption process. The adsorption isotherm experiments were carried out by changing the initial

dye concentration from 100 to 300 mg/L at pH of 3.0. And the flasks were shaken at 180 rpm in a

thermostatic shaker at 25 °C for 60 min to reach the equilibrium adsorption. At the same time, the

effect of ion strength and humic acid on adsorption of Fe3O4@NH2@PEI for the two dyes was also

investigated. On the basis of adsorption experiments, the removal efficiency (R, %), adsorption amount

of dyes at time t (qt, mg/g) and equilibrium (qe, mg/g) were calculated by the following equations.

𝑅 =100(𝐶0 ‒ 𝐶𝑒)

𝐶0 (1)

𝑞𝑡 =(𝐶0 ‒ 𝐶𝑡)𝑉

𝑚 (2)

𝑞𝑒 =(𝐶0 ‒ 𝐶𝑒)𝑉

𝑚 (3)

where C0, Ct, and Ce (mg/L) represent the initial, time t, and equilibrium concentration of anionic dye

solution, respectively; V is the volume of anionic solution (L), and m is the mass of adsorbents used (g).

3. Selective adsorption and separation of anionic dyes from binary systems of cationic and

anionic dyes

In present work, a methodology was developed to investigate the selective adsorption and

separation of anionic dyes from mixture containing cationic and anionic dyes, in which a cationic dye,

methylene blue (MB), was chosen as a co-adsorbate. The detailed experimental conditions were as

follows: each dye concentration, 100 mg/L; adsorbent dosage, 30 mg; sample volume, 30 ml; solution

pH, 3.0; contact time, 1-60 min; temperature, 25 °C; and agitation speed, 180 rpm. After adsorption,

the liquid/solid phase separation was achieved by a permanent magnet Nd-Fe-B. The dye

concentration in the supernatant part was determined using an UV-visible absorption

spectrophotometry (UV-754N shanghai, China) at each λmax.

Captions:

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Fig. S1. XRD patterns of Fe3O4@NH2 and Fe3O4@NH2@PEI.

Fig. S2. Zeta potentials of Fe3O4@NH2 and Fe3O4@NH2@PEI as a function of pH.

Fig. S3. N2 adsorption–desorption isotherms of Fe3O4@NH2 and Fe3O4@NH2@PEI.

Fig. S4. Effect of ionic strength on adsorption of ARS by Fe3O4@NH2@PEI. (Conditions: dye

concentration, 100 mg/L; solution pH, 3.0; salt concentration, 0-0.10 mol/L; adsorbent dosage, 1 g/L;

contact time, 60 min; temperature, 25 °C; and agitation speed, 180 rpm.)

Fig. S5. Effect of ionic strength on adsorption of MO by Fe3O4@NH2@PEI. (Conditions: dye

concentration, 100 mg/L; solution pH, 3.0; salt concentration, 0-0.10 mol/L; adsorbent dosage, 1 g/L;

contact time, 60 min; temperature, 25 °C; and agitation speed, 180 rpm.)

Fig. S6. Effect of humic acid on adsorption of ARS and MO by Fe3O4@NH2@PEI. (Conditions: dye

concentration, 100 mg/L; solution pH, 3.0; humic acid concentration, 0-20 mg/L; adsorbent dosage, 1

g/L; contact time, 60 min; temperature, 25 °C; and agitation speed, 180 rpm.)

Fig. S7. Adsorption kinetics curves of ARS and MO by Fe3O4@NH2@PEI. (Conditions: dye

concentration, 100 mg/L; solution pH, 3.0; adsorbent dosage, 1 g/L; contact time, 1-60 min;

temperature, 25 °C; and agitation speed, 180 rpm.)

Fig. S8. Reusability of Fe3O4@NH2@PEI as adsorbents for ARS and MO. (Conditions: initial dye

concentration, 100 mg L-1; amount of eluent, 30 mL of NaOH solution (0.5 mol L-1); desorption time,

10 min (ultrasound); temperature, 25 °C.)

Table S1. The BET surface area, average pore size and total pore volume of Fe3O4@NH2 and

Fe3O4@NH2@PEI.

Table S2. The molecular properties of Methyl blue (MLB)

Fig. S1.

Fig. S2.

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Fig. S3.

Fig. S4.

Fig. S5.

Fig. S6.

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Fig. S7.

Fig. S8.

Table S1. The BET surface area, average pore size and total pore volume of Fe3O4@NH2 and

Fe3O4@NH2@PEI.

Sample SBET (m2 g-1)a Dpore (nm)b Vpore (cm3 g-1)c

Fe3O4@NH2 35.2 8.6 0.08Fe3O4@NH2@PEI 61.8 9.0 0.14

a SBET: BET surface areab Dpore: average pore diameterc V pore: total pore volume

Table S2. The molecular properties of Methyl blue (MLB).

Dyeλmax

a

(nm)M. w. b

(g mol-1)Structure

Methyl blue (MLB) 600 799.80

a maximum absorption wavelength (nm)b Molecular weight(g mol-1)