Supplementary Material

Highly efficient and selective removal of mercury ions

using hyperbranched polyethylenimine functionalized

carboxymethyl chitosan composite adsorbent

Hehua Zeng a, b, d, Lan Wang a*, Dan Zhang a, c, Peng Yan a, Jing Nie a,

Virender K. Sharma e*, Chuanyi Wang a, c*

a Laboratory of Environmental Sciences and Technology, Xinjiang Technical Institute of Physics &

Chemistry; Key Laboratory of Functional Materials and Devices for Special Environments,

Chinese Academy of Sciences, Urumqi 830011, P.R. China

b The Graduate School of Chinese Academy of Science, Beijing, 100049, China

c School of Environmental Science and Engineering, Shaanxi University of Science and

Technology, Xian 710021, P.R. China

d Department of Chemistry and Applied Chemistry, Changji University, Changji 831100, P.R.

China

e Program for the Environment and Sustainability, Department of Environment and Sustainability,

School of Public Health, Texas A&M University, 212 Adriance Lab Rod. College Station Texas

77843, USA

*Corresponding authors. Phone: +86-991-383-5879

Email addresses: wanglan@ms.xjb.ac.cn; cywang@ms.xjb.ac.cn

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2. Experimental

2.1. Materials and characterization

Carboxymethyl chitosan (CCTS, the degree of substitution was not less than

80%, and the average molecular weight was 9000 g/mol) was purchased from

Zhejiang Golden-Shell Biochemical Co. Ltd., Zhejiang, China). Polyethylenimine

[PEI, Mw = 70000 Da, 50wt % aqueous solution, branched polymer (–

NHCH2CH2–)x[–N(CH2CH2NH2)–CH2CH2–]y], polyvinyl alcohol (PVA, analytical

grade, the degree of hydrolysis was 99% and the average degree of polymerization

was 1700) and glutaraldehyde (GLA) with a concentration of 50% were purchased

from Sigma-Aldrich Company. The stock solution of metal ions was prepared from

mercury acetate (CH3COO)2Hg), cadmium acetate (CH3COO)2Cd), lead acetate

trihydrate (CH3COO)2Pb∙3H2O) and copper acetate monohydrate (CH3COO)2Cu∙H2O)

(Sinopharm Group Chemical Reagent Co., Ltd., Shanghai, China) in ultrapure water.

All of the other reagents were of analytical purity and used without further

purification.

FTIR spectra were detected by a Fourier-transform infrared spectrometer

(Nicolet iS50, Thermo, USA), using the KBr pellet method and scanning the range

between 400 and 4000 cm-1. Morphological measurements were recorded by a field-

emission scanning electron microscopy (SEM, SU8020, Hitachi). The X-ray

photoelectron spectroscopy (XPS) measurements were carried out on a

multifunctional X-ray photoelectron spectrometer (PHI-5702, Perkin Elmer, USA)

with Al Ka radiation as the excitation source (14 kV). The specific surface area, total

pore volume, and pore size distribution were calculated by the Brunauer-Emmert-

Teller (BET) equation and the BJH method, respectively. Thermal gravimetry (TG)

was determined with STA 449F3 thermal gravity analyzer (Netzsch, Germany), each

sample was run from 30 to 1000 ºC at a scanning rate of 10 ºC/min under nitrogen

atmosphere.

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2.3. Adsorption studies

The adsorption capacity Qe (mg/g) of HPFC toward metal ions at equilibrium

was calculated as following Eq. (1):

Qe=(C0−C e)×V

m (1)

And the adsorption efficiency (E) was calculated using the Eq. (2):

E¿(C0−C e)

C 0×100 % (2)

where C0 and Ce are the initial and equilibrium concentrations (mg/L) of metal ions in

solution, respectively. V (L) is the volume of solution and m (g) is the mass of HPFC.

2.4. Computational details

All the geometric structures, adsorption energies were carried out on the basis of

DMol3 code [1, 2]. The generalized gradient approximation (GGA) [3] with the

Perdew–Burke–Ernzerhof (PBE) functional [4] and all-electron double numerical

basis set with polarized function (DNP) have been employed. The real-space global

orbital cutoff radius is chosen to be as high as 5.1Å, the convergence tolerance of

energy is 1.0x10-5 Ha (1Ha=27.21eV), and that of maximum force is 2.0x10-3 Ha/Å.

Each atom in the storage models is allowed to relax to the minimum in the enthalpy

without any constraints. Corrugation effects are tested and the results show that all the

atoms are coplanar with each other. The metals Cu, Cd, Hg, and Pb were absorbed

into the model. The adsorption energy (Ead) was calculated according to the following

Eq. (3):

Ead = EA + EB – EA-B (3)

where A represents the selected model; B represents the heavy metal ions.

2.5. Desorption and regeneration

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Desorption and regeneration experiment was carried out in 20 mL of 798.1 mg/L

Hg(II) ions solution at pH 5.5 with 20 mg of HPFC at 30 ºC for 360 min. After

filtration, the Hg(II)-loaded adsorbent was first dispersed into 20 mL of 2 mol/L

HNO3 solution (or 20 mL of 2 mol/L KCl solution) and shaken at 30 ºC for 360 min,

then neutralized in a diluted NaOH solution. Next, the HPFC was filtered and washed

with ultrapure water several times. After freeze-drying, the adsorbent was reused in

the next cycle.

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3. Results and discussion

3.1. Optimization of synthesis conditions

Fig. S1. Influences of synthetic conditions of (a) the impact of the PEI dosage on the N content of

HPFC; (b) the impact of the GLA (5.0%) dosage on the yield of HPFC.

Fig. S2. Effect of PEI amount on Hg(II) ions adsorption.

Except for the investigated parameter, others fixed at C0 = 1596.2 mg/L, pH = 5.5,

sample dosage = 20 mg/20 mL, temperature = 30 ºC, adsorption time = 360 min.

Table S1

The relationship between the N content of the as-products and the adsorption capacity of Hg(II)

ions.

N (mmol/g) 5.65 7.59 8.97 8.89

Hg (mmol/g) 5.20 7.05 7.89 7.90

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3.2. Morphology and structural characteristics

Fig. S3. (a) SEM image of HPFC after Hg(II) adsorption; (b) EDS spectra of Hg(II) loaded HPFC.

Table S2

Surface areas, pore volumes and pore sizes of CCTS and HPFC.

Sample BET surface area (m2/g) pore volume (cm3/g) pore size (nm)

CCTS 1.01 0.0013 106.2

HPFC 22.26 0.0806 11.9

3.3. Adsorption kinetics

Pseudo-first-order model:

Qt=Qf (1−e−k1 t) (4)

Pseudo-second-order model:

tQt

= 1k2Q f

2 +1

Q ft (5)

Intraparticle diffusion model

Qt=k∫ ¿t1 /2+θ¿ (6)

Where k1 (1/min) and k2 [g/(mg·min)] are the rate constants for first-order and

second-order models, respectively; kint [mg/(g·min1/2)] is a constant related to the

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diffusion coefficient in intraparticle diffusion model; θ is the intercept for the

intraparticle diffusion model; Qf is the fitted adsorption value (mg/g) at equilibrium,

and Qt is the experimental value (mg/g) at set time t (min), respectively.

The removal performance of HPFC in the real water sample

The real water sample was taken from a gas field (China), and the main

components are listed in Table S3). Then dried HPFC (20 mg) was immersed into 20

mL of above solution and stirred at room temperature for 24 h. Then the adsorbent

was filtered out and the concentration of the solution was measured by AFFS. The

HPFC could decrease the Hg(II) ions concentration to 0.15 mg/L with a high removal

efficiency of 98.2%. The result suggests that the HPFC has good potential in real

applications.

Table S3

The main components of the real water sample.

Component Hg Na Mg Ca Cl- NO3- SO4

2- HCO3-

C (mg/L) 8.44 9426 685 1624 14574 155 68 201

3.4. Absorption thermodynamics

KC=C Ae

C e

(7)

∆ Go=−RTln KC (8)

lnK C=∆ So

R−∆ Ho

RT(9)

Where KC is distribution coefficient, CAe is the amount of Hg(II) ions adsorbed on

HPFC (mg/L), R is the gas constant (8.314 J / (mol·K)), T is the temperature (K).

3.5. Adsorption isotherms

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Langmuir model

Qe=Qm bLC e

1+bL Ce

(10)

Freundlich model

Qe=K F C e1 /n F

(11)

Langmuir- Freundlich model

Qe=Qm bLF C e

1 /nLF

1+bLF C e1/nLF

(12)

Where Qm is the maximum adsorption capacity (mg/g), Ce is the final equilibrium

mercury concentration (mg/L), bL is the Langmuir constant (L/mg) related to the

adsorption strength. KF is the Freundlich constant related to the adsorption strength

(mg/g) (L/mg), bLF is the Langmuir-Freundlich constant related to the adsorption

strength (L/mg), nF and nLF are the Freundlich and Langmuir-Freundlich constants

related to the adsorption capacity, respectively. Langmuir isotherm describes a

monolayer adsorption which takes place at homogeneous sites within the adsorbent

where all the adsorption sites are energetically identical. Freundlich isotherm

expresses adsorption at multilayer and on the energetically heterogeneous surface and

active sites. Langmuir-Freundlich isotherm suggests that the adsorption of an

adsorbent toward a target is the synergistic effects of the monolayer adsorption and

the multilayer adsorption.

3.8.1. XPS analysis

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Fig. S4. XPS spectra: high-resolution spectra of Pb 4f (a), Cu 2p (b) and Cd 3d (c), (d) survey

spectra after mixed ions adsorption on HPFC.

3.8.3. DFT analysis

Fig. S5. The optimized DFT structures of PEI-GLA-double CCTS monomer.

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(The H, C, N, and O are depicted by white, grey, blue, and red color, respectively).

Fig. S6. HOMO and LUMO plots of PEI-GLA-double CCTS monomer.

References

[1] B. Delley, An all-electron numerical method for solving the local density functional for

polyatomic molecules, J. Chem. Phys. 92 (1990) 508–517.

[2] B. Delley, From molecules to solids with the DMol3 approach, J. Chem. Phys. 113 (2000)

7756–7764.

[3] R.G. Parr, W. Yang, Density-Functional Theory of Atoms and Molecules, Oxford University

Press 1989 127–136.

[4] J.P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple, Phys.

Rev. Lett. 77 (1996) 3865–3868.

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