Electronic Supplementary Information

Environmental performances of hydrochar-derived magnetic carbon

composite affected by its carbonaceous precursor

Xiangdong Zhu, Feng Qian, Yuchen Liu, Shicheng Zhang*, Jianmin Chen

Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), Department of

Environmental Science and Engineering, Fudan University, Shanghai 200433, China

* Corresponding author.

Tel/fax: +86-21-65642297;

E-mail address: zhangsc@fudan.edu.cn.

Electronic Supplementary Material (ESI) for RSC Advances.This journal is © The Royal Society of Chemistry 2015

Fig. S1. HTC temperature and pressure variations as a function of reaction time during the HTC

process.

0 20 40 60 80 100

40

80

120

160

200

240

280

Time (min)

Tem

pera

ture

(o C)

160 oC

0123456789

Pres

sure

(Mpa

)

0 20 40 60 80 100

40

80

120

160

200

240

280

0123456789

200 oC

Tem

pera

ture

(o C)

Pres

sure

(Mpa

)

Time (min)

0 20 40 60 80 100

40

80

120

160

200

240

280240 oC

Tem

pera

ture

(o C)

Pres

sure

(Mpa

)

Time (min)

0123456789

0 20 40 60 80 100

40

80

120

160

200

240

280

0123456789

270 oC

Pres

sure

(Mpa

)

Tem

pera

ture

(o C)

Time (min)

0 20 40 60 80 100

40

80

120

160

200

240

280 300 oC

Tem

pera

ture

(o C)

0123456789

Time (min)

Pres

sure

(Mpa

)

Fig. S2. FTIR spectra for the hydrochar produced at different HTC temperatures.

Abundant FT-IR peaks for hydrochar materials were found, they were similar and different only

in the intensity of some peaks, suggesting that the functional group compositions was not greatly

changed during the HTC reaction. The aromatic C (1616 cm-1) was observed, and the peak

intensity increased with peak temperature of HTC reaction increase, indicating increasing

thermal recalcitrance of hydrochar samples. The hydrochar materials also had the adsorption

bands at 2927 and 2840 cm-1, which were attributed to stretching vibration of aliphatic C-H. The

peak at 1742 cm-1 was assigned to C=O groups, resulted from the acid group (C-OOH).

Obviously, the peaks (2927, 2840 and 1742 cm-1) increased with processing HTC reaction,

indicating that these aliphatic carbons are mainly produced from the HTC reaction. The band at

1512 cm-1 represented the C=C stretching vibration. The peak at 1461 cm-1 was assigned to C-H

deformation vibration. The peak located at 1112 cm-1 was attributed to the C-O stretching

vibration.

4000 3500 3000 2500 2000 1500 1000 500

H-300

H-270

H-240

H-200

Tran

smitt

ance

(%, a

rbita

ry u

nits

)

Wavenumber (cm-1)

1616

H-160

2927 2840

1742 1512

1461

1112

Text S1

As shown in Fig. 1b, the DTG curves contained two general regions of weight loss. The first

region of weight loss was found from 300 to 350°C, resulting from the thermal oxidation of

residual cellulose, hemicellulose and low-boiling products derived from the HTC process. The

second region of weight loss was observed above 400°C, due to the thermal oxidation of the

more recalcitrant organic substances with the structure of lignin or thermally produced

carbonized/aromatic compounds.1 Obviously, the weight loss of hydrochar samples derived from

higher HTC temperatures were focused toward much higher temperatures. Such differences

indicated that hydrochar samples produced at higher peak temperatures would be more

recalcitrant, which was consistent with the qualitative assessment of R50 for those hydrochar

samples.

Fig. S3. Correlations between the yields of magnetic carbon composites and the properties of

hydrochar precursors: R50 index (a), H/C (b) and O/C (c) atomic ratios.

0.36 0.40 0.44 0.48 0.52

4550556065707580

Yiel

d (%

, co

mpo

site)

R50 index

y=201.9x-27.35R2=0.99

a

1.0 1.1 1.2 1.3 1.4 1.5 1.6

4550556065707580

Yiel

d (%

, com

posit

e)

H/C atomic ratio

y=-62.69x+140.8R2=0.98

b

0.2 0.3 0.4 0.5 0.6 0.7

4550556065707580

Yiel

d (%

, com

posit

e)

O/C atomic ratio

y=-69.72x+93.43R2=0.91

c

Fig. S4. Nitrogen adsorption isotherms and pore size distribution for the different hydrochar-

derived magnetic carbon composites.

0.0 0.2 0.4 0.6 0.8 1.0200

250

300

350

400

450

500

MC-300MC-270

MC-240

MC-210

Volu

me

adso

rbed

(cm

3 STP

/g)

P/P0

MC-160a

1 2 3 4 5 6

0.0

0.2

0.4

0.6

0.8

MC-300MC-270

MC-240

MC-200

Pore

size

dist

ribut

ion

(cm

3 /g.n

m)

Pore diameter (nm)

MC-160b

Table S1. Regression equation and correlation coefficient of the porosity of magnetic carbon

composite related to the properties of hydrochar

Hydrochar Properties Regression Equation R2

BET Surface Area = –2862R50 + 2403 0.89Micropore Surface Area = –2951R50 + 2367 0.89

Total Pore Volume = –1.30R50 + 1.17 0.88R50

Micropore Volume = –1.44R50 + 1.16 0.91BET Surface Area = 901H/C + 4.53 0.90

Micropore Surface Area = 944H/C – 125 0.93Total Pore Volume = 0.406H/C + 0.0855 0.87

H/C

Micropore Volume = 0.460H/C – 0.0548 0.95BET Surface Area = 1066O/C + 656 0.95

Micropore Surface Area = 1118O/C + 557 0.98Total Pore Volume = 0.476O/C + 0.380 0.90

O/C

Micropore Volume = 0.541O/C + 0.279 0.99

Fig. S5. XRD patterns of the as-prepared magnetic carbon composites.

10 20 30 40 50 60 70 80

MC-300

MC-270

MC-240

MC-200

aa aaa

Inte

nsity

(arb

itary

uni

ts)

2 Theta (degree)

a

a: -Fe2O3, b: -Fe2O3

b

MC-160

Fig. S6. (a) Hysteresis loop of the as-prepared magnetic carbon composites under 300 K (inset

shows the hysteresis loop of MC-300 sample at ± 200 Oe) and (b) photo of magneto separation

for the as-prepared magnetic carbon composite (MC-270).

b

-20000 -10000 0 10000 20000

-15

-10

-5

0

5

10

15

-4 emu/g

Mag

netiz

atio

n (e

mu/

g)

Magnetic field (Oe)

MC-240MC-160MC-300MC-200MC-270

a

4 emu/g

200 Oe-200 Oe

MC-300

Table S2. Ash and Fe2O3 contents, magnetic property and acid resistance for different hydrochar-

derived magnetic carbon composite

a Ms is saturation magnetization determined at room temperature.

b Fe leaching concentration determined at 2000 mg/L magnetic carbon composite with 24 h

contact time at room temperature.

sample ash (%) Fe2O3 (%) Ms (emu/g) a leaching (mg/L, pH 2) b leaching (mg/L, pH 3) b

MC-160 18.1 15.9 ± 0.66 15.2 0.325 ± 0.003 0.0910 ± 0.001MC-200 15.2 13.7 ± 0.35 14.3 0.419 ± 0.018 0.0685 ± 0.001MC-240 17.4 15.3 ± 0.09 16.3 0.387 ± 0.006 0.131 ± 0.004MC-270 13.2 11.4 ± 0.29 13.6 0.524 ± 0.001 0.153 ± 0.006MC-300 14.2 12.4 ± 0.33 15.0 0.549 ± 0.004 0.149 ± 0.002

Fig. S7. Correlations between the Fe leaching concentration and the porosity of magnetic carbon

composites: BET surface area (a), micropore surface area (b), total pore volume (c) and

micropore volume (d).

900 1000 1100 1200 1300 1400 15000.0

0.1

0.2

0.3

0.4

0.5

0.6

pH=3y=-0.00013x+0.26R2=0.66

Fe

leac

hing

(mg/

L)

BET surface area (m2/g)

pH=2y=-0.00039x+0.88R2=0.93

a

800 900 1000 1100 1200 1300 14000.0

0.1

0.2

0.3

0.4

0.5

0.6

pH=3y=-0.00013x+0.25R2=0.69

Fe le

achi

ng (m

g/L)

Micropore surface area (m2/g)

pH=2y=-0.00038x+0.84R2=0.92

b

0.40 0.45 0.50 0.55 0.60 0.65 0.700.0

0.1

0.2

0.3

0.4

0.5

0.6

pH=3y=-0.27x+0.26R2=0.72

Fe le

achi

ng (m

g/L)

Micropore volume (cm3/g)

pH=2y=-0.78x+0.85R2=0.93

d

0.45 0.50 0.55 0.60 0.65 0.70 0.750.0

0.1

0.2

0.3

0.4

0.5

0.6

pH=3y=-0.28x+0.28R2=0.64

Fe le

achi

ng (m

g/L)

Total pore volume (cm3/g)

pH=2y=-0.83x+0.93R2=0.89

c

Text S2

Adsorption kinetics is the most important characteristic in the representation of pollutants’

uptake rates and adsorption efficiency.2, 3 As shown in Fig. S8a, the adsorption reaction

equilibrium was reached quickly, due to abundant adsorption sites for the ROX molecules. This

is important for highly efficient removal of pollutants in the practical application of as-prepared

magnetic carbon composites.

The pseudo-second-order kinetics equation was used to discuss the adsorption characteristics

of ROX:

22

1 +t e e

t tq k q q

where t is the adsorption time, qt (mg/g) is the ROX uptake at time t, qe (mg/g) is the ROX

uptake at equilibrium, and k2 (g/mg·min) is the rate constant of pseudo-second-order adsorption.

As shown in Table 3, the correlation coefficient was 0.99 for all resultant magnetic carbon

composites, and the pseudo-second-order kinetics equation exhibited a good fit for ROX

adsorption, as further confirmed b Fig. S8b.

The changes in ROX adsorption capacity as a function of ROX concentration in the solution at

equilibrium are shown in Fig. S9a. The Langmuir model was used to fit the adsorption data:

e e

e m m

1C Cq bq q

where Ce (mg/L) is the equilibrium concentration of the ROX in the solution, qm (mg/g) is the

maximum adsorption capacity, and b (L/mg) is the Langmuir constant.

The linear forms of the Langmuir equation for the adsorption data were shown in Fig. S9b. As

shown in Table 3 a high regression coefficient (0.99) for all cases revealed that Langmuir

equation was well fitted to the adsorption of ROX. In addition, the as-prepared magnetic carbon

composites exhibited a large adsorption capacity for ROX removal, indicating that this material

can be an excellent candidate for the ROX removal.

Fig. S8. (a) Adsorption of ROX onto as-prepared magnetic carbon composites as a function of

time (ROX initial concentration: 400 mg/L). (b) Pseudo-second-order kinetics for ROX

adsorption onto the as-prepared magnetic carbon composite: markers are experimental data and

lines are the data predicated by the pseudo-second-order kinetics model.

0 200 400 600 800 1000 1200 14000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

t (min)

t/qt (

g/m

g m

in)

MC-300MC-270MC-240MC-200MC-160

b

0 200 400 600 800 1000 1200 1400

0.50

0.55

0.60

0.65

0.70

0.75

MC-160 MC-200

MC-240MC-270

MC-300

Contact time (min)

C t/C

0 B D F H J

a

Fig. S9. (a) Adsorption isotherms of ROX onto as-prepared magnetic carbon composites. (b)

Linear Langmuir equation for ROX adsorption onto as-prepared magnetic carbon composites:

markers are experimental data and lines are the data predicated by the Langmuir model.

0 50 100 150 200 250 300100

200

300

400

500

600

MC-270

MC-300

MC-240MC-200

q e (

mg/

g)

Ce (mg/L)

MC-160a

0 50 100 150 200 250 3000.00.10.20.30.40.50.60.70.8 MC-300

MC-270MC-240MC-200MC-160

C e/qe (g

/L)

Ce (mg/L)

b

Fig. S10. Correlations between adsorption uptake at equilibrium (qe, obtained from the pseudo-

second-order kinetics equation at an initial ROX concentration of 400 mg/L) and porosity of

magnetic carbon composites: BET surface area (a), micropore surface area (b), total pore volume

(c) and micropore volume (d).

900 1000 1100 1200 1300 1400 1500

390

420

450

480

510

q e (

mg/

g)

BET surface area (m2/g)

y=0.225x+195R2=0.86

a

800 900 1000 1100 1200 1300 1400

390

420

450

480

510

q e (m

g/g)

Micropore surface area (m2/g)

y=0.214x+223R2=0.83

b

0.45 0.50 0.55 0.60 0.65 0.70 0.75

390

420

450

480

510

q e (m

g/g)

Total pore volume (cm3/g)

c

y=501x+152R2=0.89

0.40 0.45 0.50 0.55 0.60 0.65 0.70

390

420

450

480

510

q e (m

g/g)

Micropore volume (cm3/g)

d

y=446x+217R2=0.84

Fig. S11. Correlations between the maximum adsorption capacity (qm, obtained from the

Langmuir equation) and the porosity of magnetic carbon composites: BET surface area (a),

micropore surface area (b), total pore volume (c) and micropore volume (d).

900 1000 1100 1200 1300 1400 1500400

440

480

520

560

600

q m

(mg/

g)

BET surface area (m2/g)

y=0.293x+171R2=0.96

a

800 900 1000 1100 1200 1300 1400400

440

480

520

560

600

q m (m

g/g)

Micropore surface area (m2/g)

y=0.282x+204R2=0.94

b

0.45 0.50 0.55 0.60 0.65 0.70 0.75400

440

480

520

560

600

Total pore volume (cm3/g)

q m (m

g/g) y=642x+121

R2=0.96

c

0.40 0.45 0.50 0.55 0.60 0.65 0.70400

440

480

520

560

600

q m (m

g/g)

Micropore volume (cm3/g)

y=585x+197R2=0.95

d

Fig. S12. Correlations between adsorption uptake at equilibrium (qe, obtained from the pseudo-

second-order kinetics equation at an initial ROX concentration of 400 mg/L) and properties of

hydrochar: R50 index (a), H/C (b) and O/C (c) atomic ratios.

0.36 0.40 0.44 0.48 0.52

390

420

450

480

510

R50 index

q e (m

g/g)

y=-705.7x+762.1R2=0.92

a

1.0 1.1 1.2 1.3 1.4 1.5 1.6

390

420

450

480

510

q e (m

g/g)

H/C atomic ratio

y=216.7x+177.6R2=0.89

b

0.2 0.3 0.4 0.5 0.6 0.7

390

420

450

480

510

q e (m

g/g)

O/C atomic ratio

y=237.6x+342.6R2=0.80

c

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