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Supporting information

Adsorptive denitrogenation of model fuels with porous metal-organic frameworks (MOFs): effect of acidity and basicity of MOFs

Imteaz Ahmed, Zubair Hasan, Nazmul Abedin Khan and Sung Hwa Jhung*

1. Materials:

p-Xylene, n-octane and chromium (VI) oxide were purchased from Junsei chemical

company. Ethanol, hydrochloric acid (HCl, 35.0%), hydrofluoric acid (HF, 48.0%) and n,n-

dimethylformamide (DMF) were obtained from OCI company Ltd. Benzothiophene (BT),

quinoline (QUI), indole (IND), trimesic acid (H3BTC) and acetone were obtained from

Sigma-Aldrich Co. Ethylenediamine (ED), chromium (III) nitrate nonahydrate were

purchased from Samchun pure chemical Co. Ltd. Copper (II) nitrate trihydrate was obtained

from Wako pure chemicals industry Ltd. Aminomethanesulfonic acid was purchased from

Alfa-Aesar Co. Terepthalic acid (TPA) and toluene were collected from Samsung

Petrochemical Co. Ltd. and Duksan pure chemicals Co. Ltd., respectively. All the chemicals

required in this study were used without further purification.

2. MOFs synthesis:

The MOFs used in this study were prepared under autogeneous pressure similar to the

reported methods [1-3]. For the synthesis of Cu-BTC, an exact amount of H3BTC (2.0 mmol)

and copper (II) nitrate trihydrate (3.65 mmol) were dissolved in 24 mL of a 1:1 (wt./wt.)

mixture of water and ethanol, and stirred magnetically for 10 min. The resulting reactant

mixture was loaded into a Teflon-lined autoclave, sealed and placed in a microwave oven

(Mars-5, CEM, maximum power of 1200W) to take advantage of rapid synthesis under

microwaves. MIL-101(Cr) was prepared by hydrothermal synthesis process. In this case,

chromium (III) nitrate, TPA, HF and H2O were mixed with a molar ratio of 1:1.5:1:280 and

further heated for 10 h at 220 oC. Finally, for the preparation of MIL-100(Cr); chromium (VI)

oxide, HF, H3BTC and H2O were mixed with a molar ratio of 1:1:0.67:265. The mixture was

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then transferred to a Teflon-lined autoclave and heated in a conventional electric oven for 96

h at a temperature of 220 oC. After synthesis, all the MOFs were filtered, washed and purified

with solvents and dried in a drying oven at 100 oC. MIL-101(Cr) was purified by

solvothermal method. DMF (30 mL) and 1 g of MIL-101(Cr) was mixed and heated

overnight at a temperature of 225 oC. Then it was filtered and dried in a vacuum oven at 150 oC for the complete removal of DMF. Cu-BTC and MIL-100(Cr) were purified by mixing

with ethanol and magnetically stirring at 65 oC for 5 h followed by filtering.

3. Adsorption isotherms:

Langmuir isotherm:

The maximum adsorption capacity was calculated using the Langmuir adsorption isotherm [4, 5] after adsorption for 2 h. The adsorption isotherms in various conditions have been plotted to follow the Langmuir equation [4, 5]:

1

bQQ

C

q

C

oo

e

e

e

Where,

Ce : equilibrium concentration of adsorbate (mg/L)

qe : amount adsorbed at equilibrium (mg/g)

Q0 : Langmuir constant (maximum adsorption capacity) (mg/g)

b : Langmuir constant (L/mg)

The maximum adsorption capacity Qo, therefore, can be obtained from the reciprocal of the slope of a plot of Ce/qe against Ce.

Freundlich isotherm:

Linear form of Freundlich isotherm equation [6] can be expressed as:

eFFe CbKq ln)(lnln

Where,

Ce : equilibrium concentration of adsorbate (mg/L)

qe : amount adsorbed at equilibrium (mg/g)

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KF, bF = constants for a given adsorbate and adsorbent at a particular temperature.

Temkin isotherm:

The linearized expression of Temkin isotherm [6] is:

Where,

Ce : equilibrium concentration of adsorbate (mg/L)

qe : amount adsorbed at equilibrium (mg/g)

R : gas constant (8.316 JK-1mol-1)

A : Temkin isotherm constant (L/g)

b : Temkin constant (J/mol)

T : absolute temperature (K)

Separation factor:

Separation factor (RL) was calculated using the following equation which suggests describing the adsorption process [7].

Where,

RL: separation factor

b: Langmuir constant (L/mg)

Co: initial concentration of adsorbate (mg/L)

1

1

oL bC

R

ee Cb

RTA

b

RTq ln)()ln()(

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References

[1] N.A. Khan, E. Haque and S.H. Jhung, Phys. Chem. Chem. Phys. 12 (2010) 2625–

2631.

[2] T.K. Trung, N.A. Ramsahye, P. Trens, N. Tanchoux, C. Serre, F. Fajula, and G. Férey,

Micropor. Mesopor. Mater. 134 (2010) 134–140.

[3] N.A. Khan and S.H. Jhung, Crystal Growth Des. 10 (2010) 1860–1865.

[4] B.H. Hameed and A.A. Rahman, J. Hazard. Mater. 160 (2008) 576–581.

[5] S.-H. Lin and R.-S. Juang, J. Environ. Manag. 90 (2009) 1336–1349.

[6] T. Karthikeyan, S. Rajgopal, L.R. Miranda, J. Hazard. Mater. 124 (2005) 192–199.

[7] T.W. Weber and R.K. Chakkravorti, AIChE J. 20 (1974) 228–238.

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Table S1. R2 values for the three adsorption plots.

Adsorbent Adsorbate Langmuir R2

Freundlich R 2

Temkin R 2

BT 0.999 0.934 0.954

MIL-100(Cr) QUI 0.998 0.976 0.996

IND 0.999 0.967 0.996

BT 0.999 0.955 0.973

ED-MIL-100(Cr) QUI 0.996 0.992 0.994

IND 0.995 0.948 0.988

BT 0.998 0.992 0.993

AMSA-MIL-100(Cr) QUI 0.998 0.948 0.905

IND 0.996 0.993 0.993

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Figure S1. XRD patterns of the three MOFs used in this study.

5 10 15 20

0

2500

5000

7500

Inte

nsity

(a.

u.)

2 theta (deg)

CuBTC MIL-100(Cr) MIL-101(Cr)

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Figure S2. FTIR spectra of the virgin and modified MIL-100(Cr)s: (a) MIL-100(Cr); (b) ED-MIL-100(Cr) and (c) AMSA-MIL-100(Cr).

1800 1200 600

80

120

160

1034

1074

1594

1033

Tra

nsm

itanc

e (%

)

Wave number (cm-1)

MIL-100(Cr) ED-MIL-100(Cr) AMSA-MIL-100(Cr)

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0 500 1000 1500 2000

20

40

60

80(a)

MIL-100(Cr) ED-MIL-100(Cr) AMSA-MIL-100(Cr)

Ce/

q e

Ce (ppm)

-250 0 250 500 750 1000

0

3

6

9

12

(b)

Ce/

q e

Ce (ppm)

0 200 400 600 800

3

6

9

12

(c)

Ce/

q e

Ce (ppm)

Figure S3. Langmuir plots for (a) BT; (b) QUI and (c) IND adsorption over virgin and grafted MIL-100(Cr)s.

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5.5 6.0 6.5 7.0 7.5

2.70

2.85

3.00

3.15

3.30

MIL-100 (Cr) ED-MIL-100 (Cr) AMSA-MIL-100 (Cr)

ln(q

e) (

ppm

)

ln(Ce) (ppm)

3 4 5 6 7

3.2

4.0

4.8

5.6

ln(q

e) (

ppm

)

ln(Ce) (ppm)

Figure S4. Freundlich plots for (a) BT; (b) QUI and (c) IND adsorption over virgin and grafted MIL-100(Cr)s.

4.5 5.0 5.5 6.0 6.5 7.03.0

3.5

4.0

4.5

5.0

ln(q

e) (

ppm

)

ln(Ce) (ppm)

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5.5 6.0 6.5 7.0 7.5

15

18

21

24

27

MIL-100 (Cr) ED-MIL-100 (Cr) AMSA-MIL-100 (Cr)

q e (p

pm)

ln(Ce) (ppm)

2 3 4 5 6 70

100

200

300

q e (p

pm)

ln(Ce) (ppm)

Figure S5. Temkin plots for (a) BT; (b) QUI and (c) IND adsorption over virgin and grafted MIL-100(Cr)s.

5 6 720

40

60

80

q e (p

pm)

ln(Ce) (ppm)

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0 500 1000 1500 2000

0.1

0.2

0.3

0.4(a)

RL

Co (ppm)

MIL-100 (Cr) ED-MIL-100 (Cr) AMSA-MIL-100 (Cr)

0 250 500 750 10000.15

0.30

0.45

0.60

0.75(c)

RL

Co (ppm)

Figure S6. Effect of initial concentrations on the separation factor RL for (a) BT; (b) QUI and (c) IND adsorption over virgin and grafted MIL-100(Cr)s.

0 250 500 7500.0

0.2

0.4

0.6

0.8(b)

RL

Co (ppm)

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Figure S7. FTIR spectra of the fresh and regenerated AMSA-MIL-100(Cr)s.

1800 1200 600

90

120

150

180

1034

Tra

nsm

itanc

e (%

)

Wave number (cm-1)

AMSA-MIL-100(Cr) AMSA-MIL-100(Cr) (regenerated)