Electronic Supplementary Material (ESI) for Environmental Science: Nano. This journal is © The Royal Society of Chemistry 2015

Electronic Supplementary Information Extremely High Arsenic Removal Capacity for Mesoporous Aluminium Magnesium Oxide Composites Wei Li,‡a Dehong Chen,b Fang Xia,a,c Jeannie Z. Y. Tan,a,b Pei-Pei Huang,d Wei-Guo Song,d Natalita M. Nursama,b and Rachel A. Caruso*a,b a

b

CSIRO Manufacturing, Clayton South, Victoria, 3169, Australia. Particulate Fluids Processing Centre, School of Chemistry, The University of Melbourne,

Melbourne, Victoria, 3010, Australia. c

School of Engineering and Information Technology, Murdoch University, Murdoch, West

Australia, 6150, Australia. d

Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese

Academy of Sciences, Beijing, 100190, P. R. China. ‡ Present address: International Iberian Nanotechnology Laboratory (INL), Avenida Mestre José Veiga, Braga, 4715-330, Portugal.

Corresponding author email: [email protected]

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Table S1 Physical properties of the mesoporous aluminium magnesium oxide composites calcined at 900 °C. Sample

SBET

PSD

Vsp

Phase

[m2 g-1]a [nm]b

[cm3 g-1]c

172.8

10.80

0.45

γ-Al2O3

meso-90Al10Mg-900 174.9

10.84

0.47

γ-Al2O3 & MgAl2O4 spinel

meso-80Al20Mg-900 144.1

12.08

0.41

γ-Al2O3 & MgAl2O4 spinel

meso-70Al30Mg-900 91.6

13.52

0.31

γ-Al2O3 & MgAl2O4 spinel

meso-50Al50Mg-900 121.9

13.41

0.36

MgAl2O4 MgO

spinel

&

cubic

meso-30Al70Mg-900 101.4

8.57

0.27

MgAl2O4 MgO

spinel

&

cubic

meso-Al-900

a

SBET = BET specific surface area obtained from nitrogen adsorption data in the P/P0 range from 0.05 to 0.20. b PSD = pore size distribution determined by using the BJH method from the adsorption branch. c Vsp = single point pore volume calculated from the adsorption isotherm at P/P0 = 0.98.

Table S2 As(V) adsorption kinetic parameters of the mesoporous aluminium magnesium oxide composites calcined at 400 °C. Samples

Pesudo-second-order kinetic parameters k [g mg-1 min-1]

qe [mg g-1]

R2

1.02×10-4

147.71

0.999

meso-90Al10Mg-400 9.25×10-5

125.63

0.996

meso-80Al20Mg-400 7.14×10-5

178.57

0.998

meso-70Al30Mg-400 5.20×10-5

181.82

0.996

meso-50Al50Mg-400 5.76×10-5

165.84

0.998

meso-30Al70Mg-400 2.67×10-4

74.52

0.998

meso-Al-400

meso-Mg-400

1.62×10-4

207.90

0.999

Al-400

1.35×10-4

17.30

0.897

2

Table S3 As(V) adsorption isotherm parameters of the mesoporous aluminium magnesium oxide composites calcined at 400 °C. Sample

meso-Al-400

Highest adsorptionLangmuir isotherm capacity [mg g-1]a qm [mg g-1] b R2

Freundlich isotherm KF

1/n

R2

299.03

271.83

0.4057 0.9716 94.55

0.1806 0.8621

meso-90Al10Mg-400 430.92

333.29

0.2536 0.8485 100.43 0.2100 0.9437

meso-80Al20Mg-400 502.97

422.09

0.0590 0.8902 95.85

0.2456 0.9795

meso-70Al30Mg-400 487.56

438.80

0.0321 0.8916 89.69

0.2531 0.9838

meso-50Al50Mg-400 466.02

416.25

0.0292 0.8778 86.18

0.2486 0.9730

meso-30Al70Mg-400 396.06

587.45

0.0022 0.8630 18.33

0.4482 0.9212

meso-Mg-400

912.32

928.95

0.1296 0.9692 242.32 0.2346 0.8059

Al-400

72.20

72.48

0.0259 0.9120 15.42

0.2362 0.9635

a

The highest adsorption capacity was achieved using an initial arsenic concentration of 1020 mg L-1.

Table S4 As(V) adsorption isotherm parameters of the mesoporous aluminium magnesium oxide composites calcined at 900 °C. Sample

meso-Al-900

Highest adsorptionLangmuir isotherm capacity [mg g-1]a qm [mg g-1] b R2

Freundlich isotherm KF

1/n

R2

79.21

76.36

0.5496 0.9748 38.29

0.1203 0.8421

meso-90Al10Mg-900 92.61

87.76

1.9477 0.9732 46.58

0.1134 0.8331

meso-80Al20Mg-900 70.94

58.45

1.4830 0.9254 32.65

0.1090 0.9206

meso-70Al30Mg-900 43.78

35.42

0.7144 0.8900 20.10

0.1036 0.8942

meso-50Al50Mg-900 97.56

91.32

0.5279 0.8189 46.71

0.1163 0.7739

meso-30Al70Mg-900 165.85

159.01

1.079

0.1397 0.7750

0.9087 71.23

a

The highest adsorption capacity was achieved using an initial arsenic concentration of 1020 mg L-1.

Table S5 As(III) adsorption isotherm parameters of the mesoporous aluminium magnesium oxide composites calcined at 400 °C.

3

Highest adsorptionLangmuir isotherm capacity [mg g-1]a qm [mg g-1] b

R2

114.85

120.49

0.1091

0.9815 15.37 0.3171 0.9497

meso-90Al10Mg-400 143.12

157.58

0.0192

0.9901 18.10 0.3336 0.8784

meso-80Al20Mg-400 390.59

424.26

0.0011

0.9320 2.19

0.8137 0.9861

meso-70Al30Mg-400 330.58

416.24

0.0018

0.9452 3.21

0.7288 0.9720

meso-50Al50Mg-400 240.78

394.71

0.0022

0.9919 4.18

0.6243 0.9918

meso-30Al70Mg-400 120.39

196.06

0.0019

0.9731 1.91

0.6264 0.9694

meso-Mg-400

848.72

0.1007

0.9214 162.8 0.2945 0.7509

Sample

meso-Al-400

812.84

Freundlich isotherm KF

R2

1/n

a

The highest adsorption capacity was achieved using an initial arsenic concentration of 820 mg L-1. Table S6 Atomic ratios of the mesoporous aluminium magnesium oxide composites calcined at 400 °C before and after adsorption of 400 mg L-1 of As(V) at pH 3.0 or As(III) at pH 7.0 obtained from XPS analysis. Sample

Atomic ratio Al

Mg

Al/Mg

As

meso-Al-400

16.07

0

0

As(V)-meso-Al-400

25.85

0

4.61

As(III)-meso-Al-400

17.27

0

2.23

Meso-80Al20Mg-400

1.37

6.22

4.54

0

As(V)-meso-80Al20Mg-400

10.31

1.11

9.29

3.07

As(III)-meso-80Al20Mg-400

17.06

1.72

9.92

4.41

meso-Mg-400

0

10.39

0

As(V)-meso-Mg-400

0

20.6

5.9

As(III)-meso-Mg-400

0

13.86

3.38

4

Figure S1 A photoograph of thhe as-preparred mesoporrous aluminnium magneesium oxidees calcined C. at 400 °C

5

F Figure S2 T TEM imagees of (a) m meso-50Al500Mg-400, (bb) meso-30Al70Mg-4000 and (c) m meso-Mg-4400. P Particle sizee distributioon of (d) meso-50Al50 m 0Mg-400, (e) meso-300Al70Mg-4000 and (f) m meso-Mg-4400. T TEM imagees of (g) meso-Al-9000, (h) meeso-90Al100Mg-900, (i) meso-800Al20Mg-9000, (j) meeso770Al30Mg-9900 and parrticle size ddistribution of (k) mesoo-70Al30M Mg-900. Oveer 150 nanooparticles w were aanalyzed forr particle sizze distributioon statistics by using sooftware Nannomeasure 11.25 and Oriigin 9.0.

6

mage (a), X XRD patternn (b) and thhe nitrogen gas sorption isotherm (c) of the Figure S3 TEM im s Al-4400 synthesiized in the aabsence of tthe P123 sofft template. control sample

a

0.1

q (Å-1 )

0 0.2

Intensity (a.u.)

Intensity (a.u.) 0.0

meso-Al-900 0 meso-90Al10 0Mg-900 meso-80Al20 0Mg-900 meso-70Al30 0Mg-900 meso-50Al50 0Mg-900 meso-30Al70 0Mg-900 meso-Mg-90 00

b

meso-A Al-900 meso-9 90Al10Mg-900 0 meso-8 80Al20Mg-900 0 meso-7 70Al30Mg-900 0 meso-5 50Al50Mg-900 0 meso-3 30Al70Mg-900 0 meso-M Mg-900

0.3

10

20

30 0

40

50 0

60

70 0

80

2 2-Theta (deg gree)

Figure S4 (a) Syncchrotron SA AXS and (bb) wide angle XRD pattterns of meesoporous aaluminium magnesiium oxide samples withh varying M Mg/Al molarr ratios calciined at 900 °°C.

7

Intensity (a.u.)

Mg

C 1s

Au ge r

O 1s

Mg 1s meso-Mg-400

Mg 2p Mg 2s

Mg 1s meso-80Al20Mg-400

Al 2s O2

s

meso-Al-400

Al 2p

0

200

400

600

800

1000

1200

1400

Binding Energy (eV) Figure S5 The full XPS survey of meso-Al-400, meso-80Al20Mg-400 and meso-Mg-400.

8

Volume Adsorbed (cm 3 g -1 )

a

500 400 300

meso-Mg-900 meso-30Al70Mg-900 meso-50Al50Mg-400 meso-70Al30Mg-900 meso-80Al20Mg-900 meso-90Al10Mg-900 meso-Al-900

200 100 0 0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/P0 ) 0.14

b

dV/dD (cm3g-1 nm-1 )

0.12 0.10 0.08 meso-Al-900 meso-90Al10Mg-900 meso-80Al20Mg-900 meso-70Al30Mg-900 meso-50Al50Mg-900 meso-30Al70Mg-900 meso-Mg-900

0.06 0.04 0.02 0.00 0

20

40

60

Pore Diameter (nm)

80

100

Figure S6 Nitrogen gas sorption isotherms of the mesoporous aluminium magnesium oxides with varying Mg/Al molar ratios calcined at 900 °C and (b) the corresponding pore size distribution derived from the adsorption branches based on the BJH model. Each subsequent curve is shifted up the y axis by 30 cm3 g-1 in (a) and 0.01 cm3 g-1 nm-1 in (b), for clarity.

9

2 200

meso-Al-900 meso-90Al10Mg-900 meso-80Al20Mg-900 meso-70Al30Mg-900 meso-50Al50Mg-900 meso-30Al70Mg-900

As(V) uptake (mg g-1)

150

100

50

0 0

200

400

600

80 00

1000 0

1200 -1

Equilibrium concentrration of As(V) A (mg L ) V) on mesooporous alum minium maagnesium oxxides with Figure S7 Adsorpttion isotherrms of As(V varying Mg/Al mollar ratios caalcined at 9000 °C. Expeerimental coonditions: doose = 0.5 g L-1, initial m 10 to 1000 mg L-1. pH = 3.00, the initiall As(V) concentration rranged from

Figure S8 S Distributtion of As(V V) and As(IIII) species under differrent pH valuues. Reprodduced with permissiion [P. Ravvenscroft, H H. Brammerr, K. Richarrds, Arsenicc Pollution:: A Global Synthesis, Wiley-B Blackwell, U USA 2009, ppp. 25]. Coppyright 20009, John Willey & Sons.

10

& & & &

100

100

80

80 60 60 40 40 20

20 0

-

As(V) only NO3

Cl

-

SO42-

CO 32-

SiO32-

3-

As(V) removal percentage (%)

As(V) uptake (mg g -1)

120

meso-Al-400 meso-80Al20Mg-400 meso-70Al30Mg-400 meso-Mg-400

0

PO4

Co-existing anions

Figure S9 Effect of co-existing anions on the adsorption capacities of meso-Al-400, meso80Al20Mg-400, meso-70Al30Mg-400 and meso-Mg-400 for As(V). Experimental conditions: dose = 0.5 g L-1, initial pH = 6.0, initial As(V) concentration = 50 mg L-1; initial concentration of co-existing anions: 10 mg L-1 of NO3-, 200 mg L-1 of Cl-, 200 mg L-1 of SO42-, 50 mg L-1 of CO32-, 50 mg L-1 of SiO32- or 50 mg L-1 of PO43-.

11

meso-80Al200Mg-400, ((c) and (d) m meso-MgFigure S10 TEM iimages of ((a) meso-All-400, (b) m -1 V) solution at an initial pH of 3.0. 400 afteer adsorptionn of 400 mgg L of As(V

c

After ads sorption of As(III)

After ads sorption of As(V)

After adsorp ption of As(III)

After adsorp ption of As(V)

MgO Mg(OH)2 Unindexed phase p

Intensity (a.u.)

Intensity (a.u.)

b

Intensity (a.u.)

a

After adsorption of As(III)

After adsorption n of As(V)

mes so-Mg-400 meso-80Al20Mg-400

meso-Al-400 20 0

40

60

2-Theta (degree)

8 80

20

40

60

2-Theta (degre ee)

80

20

40

60

80

2-T Theta (degree)

Figure S11 XRD ppatterns of tthe adsorbennts before aand after adsorption of 400 mg L-11 of As(V) and As(III) at the innitial pH off 3.0 and 7.00, respectivvely: (a) meso-Al-400, (b) meso-800Al20MgMg-400. 400 andd (c) meso-M

12

a

O 1s

C 1s

b

O 1s

C 1s

Au ge r

As 2p

Mg 2p

As 2p

As Auger

meso-80Al20Mg-400

As 3d Al 2p meso-Al-400

Mg 1s

Mg

meso-Mg-400

N 1s

Intensity (a.u.)

Intensity (a.u.)

Mg 1s

meso-Mg-400

As Auger

As 3d

meso-80Al20Mg-400

Mg 2p Mg 2s

meso-Al-400

Al 2s Al 2p

0

200

400

600

800

1000

Binding Energy (eV)

1200

1400 0

200

400

600

800

1000

1200

1400

Binding Energy (eV)

Figure S12 The full XPS survey of meso-Al-400, meso-80Al20Mg-400 and meso-Mg-400 after adsorption of 400 mg L-1 of (a) As(V) and (b) As(III). Experimental conditions: dose = 0.5 g L-1, initial pH for As(V) and As(III) adsorption is 3.0 and 7.0, respectively.

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meso-Al-400 after adsorption of As(V) after adsorption of As(III)

74.81 eV 74.75 eV

65

70

75

80

40

85

42

Al 2p

meso-80Al20Mg0-400 after adsorption of As(V) after adsorption of AS(III)

74.83 eV 74.65 eV

65

80

85

45.89 eV As(V)-O

45.8 eV As(V)-O

e

42

44

48

50

40

42

45.9 eV As(V)-O

40

As 3d-Mg 2p

42

f

44

46

48

50

52

54

Binding Energy (eV) 50.6 eV Mg-O

h 44.5 eV

As 3d

44.8 eV As(III)-O

52

50.4 eV Mg-O

40

44

46

48

Binding Energy (eV)

44.96 eV

50

52

As 3d-Mg 2p

44.7 eV As(III)-O 45.6 eV As(V)-O 50.8 eV Mg-O

42

44

46

48

50

52

54

Binding Energy (eV) 49.64 eV

As 3d-Mg 2p 49.4 eV

As(III)-O Intensity (a.u.)

Intensity (a.u.)

75

Binding Energy (eV) As 3d-Mg 2p

g

40

70

46

Intensity (a.u.)

Intensity (a.u.)

74.51 eV

44

45.0 ev

c

Binding Energy (eV)

Binding Energy (eV)

d

As 3d

45.88 eV As(V)-O

Intensity (a.u.)

b Intensity (a.u.)

Intensity (a.u.)

74.44 eV

Intensity (a.u.)

Al 2p

a

46

48

50

52

Binding Energy (eV)

54

56

40

Mg-O-H 50.3 eV Mg-O

42

44

46

48

50

52

54

Binding Energy (eV)

Figure S13 (a) Al 2p XPS peak of meso-Al-400 before and adsorption of As(V) and As(III), (b) As 3d peak of meso-Al-400 after adsorption of As(V), (c) As 3d peak of meso-Al-400 after adsorption of As(III), (d) Al 2p XPS peak of meso-80Al20Mg-400 before and after adsorption of As(V) and As(III), (e) As 3d and Mg 2p peak of meso-80Al20Mg-400 after adsorption of As(V), (f) As 3d and Mg 2p peak of meso-80Al20Mg-400 after adsorption of As(III), (g) and (h) As 3d and Mg 2p peak of meso-Mg-400 after adsorption of As(V) and As(III), respectively. Experimental conditions: dose = 0.5 g L-1, initial concentration of As(V) or As(III) = 400 mg L-1; initial pH for As(V) and As(III) adsorption is 3.0 and 7.0, respectively.

As shown in Figure S13a and d, for both meso-Al-400 and meso-80Al20Mg-400, the Al 2p peak shifts towards lower binding energy after adsorption of As(V), while the Al 2p peak moves slightly towards higher binding energy after As(III) adsorption. This difference in the Al 2p peak shift after adsorption of As(V) or As(III) over meso-Al-400 and meso-80Al20Mg-400 is likely to be due to the following reasons: 1. The initial pH is different for adsorption of As(V) or As(III) over the samples for the XPS measurement. In this work, the initial pH for As(V) and As(III) adsorption on both meso-Al-400

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and meso-80Al20Mg-400 is 3.0 and 7.0, respectively. The initial pH affects the different dominant arsenic speciation, As(V) (H2AsO4-) and As(III) (H3AsO30), which in turn caused the different shift of the Al 2p peak when forming Al-O-As bonds during the XPS measurement. 2. There are various models of surface complexes for the arsenic (including As(V) and As(III)) immobilization on aluminium oxy-hydroxides and other metal hydroxides/oxides. Most publications proved that arsenic can be adsorbed onto variable-charge adsorbent surfaces by inner-sphere complexation (ligand exchange to form chemical bonding) and/or outer-sphere complexation (electrostatic interaction or hydrogen bonding)(Geoderma 2001, 100, 303–319). The type of sorption mechanism for a particular ion is greatly affected by environmental factors such as pH and ionic strength. For the inner-sphere surface complex, there are four molecular configurations including bidentate binuclear, bidentate mononuclear, monodentate binuclear and monodentate mononuclear (Geochimica et Cosmochimica Acta 2012, 83, 205–216; Geochimica et Cosmochimica Acta 2001, 65, 1211-1217). For each configuration, acid-base or non-dissociative sorption could be included (Journal of Molecular Structure: THEOCHEM 2006, 762, 17–23; Geochimica et Cosmochimica Acta 2012, 83, 205–216). The specific mechanism would be elucidated by X-ray absorption spectroscopy (XAS) including EXAFS and XANES. Generally, the adsorption mechanism is considered to be different for As(V) or As(III) immobilized on the aluminium oxides, although there is no consensus on the exact mechanism applied for either As(V) or As(III). Most publications reported that As(V) predominantly forms inner-sphere bidentate binuclear complexes with the surface of aluminium oxide (Chemosphere 2004, 55, 1259-1270; Journal of Colloid and Interface Science 2001, 234, 204–216; Environmental Science & Technology 2005, 39, 5481-5487; Environmental Toxicology and Chemistry 2006, 25, 3118-3124; Journal of Colloid and Interface Science 2001, 235, 80–88; Applied Geochemistry 2013, 31, 79–83; Environmental Science & Technology 2011, 45, 9687–9692), while some papers claimed the inner-sphere monodentate mononuclear complexes (Environmental Science & Technology 2009, 43, 2537–2543) and co-existing inner-sphere, hydrogen bond and electrostatic interactions would dominate depending on the pH (Journal of Hazardous Materials 254– 255 (2013) 301– 309; Environmental Science & Technology 2006, 40, 7784-7789; Environmental Science & Technology 2005, 39, 3571-3579; Microporous and Mesoporous Materials 2014, 198, 101–114; Geochimica et Cosmochimica Acta 2008, 72, 1986–2004). The dominant complexes debated for As(III)-aluminium oxide surface complexation including outer-sphere (Chemosphere 2003, 51, 1001-1013; Journal of Colloid and Interface Science 2001, 234, 204–216; Soil Science Society of America Journal 70:2017–2027; Environmental Chemistry Letters 2013, 11, 289–294), non-dissociative inner-sphere complexes (Journal of Molecular

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Structure: THEOCHEM 2006, 762, 17–23), inner-sphere bidentate binuclear (Geochimica et Cosmochimica Acta 2012, 83, 205–216; Microporous and Mesoporous Materials 2014, 198, 101–114), a combination of inner-sphere bidentate binuclear and bidentate mononuclear (Chemosphere 2014, 113, 151–157), as well as co-existing mixtures of several surface innersphere complexes and outer-sphere complexes (Journal of Colloid and Interface Science 2001, 235, 80–88). Because of the different kinds of surface complexes obtained through chemical bonding (innersphere configurations) and possible discernable intervention from electrostatic outer-sphere complexes, the XPS peak shift is likely different between As(V) at pH 3.0 and As(III) at pH 7.0, even if the As(V) and As(III) species are chemisorbed onto the surface of meso-Al-400 and meso-80Al20Mg-400 forming As-O-M bonds. The different kinds of surface complexes have been reported to cause either a positive or negative Al 2p peak shift in the Fe/Al hydroxide when adsorbing different speciations of As(V), indicating that the Al 2p peak shift is not necessarily consistent even though an As-O-Al bond is formed. (Journal of Hazardous Materials 2015, 293, 97–104)

b

After adsorption of 400 ppm of As(V)

After adsorption of 400 ppm of As(III)

meso-Mg-400

c

meso-80Al20Mg-400

After adsorption of 400 ppm of As(V)

Transmittance

meso-Al-400

Transmittance

Transmittance

a

After adsorption of 400 ppm of As(V)

After adsorption of 400 ppm of As(III)

After adsorption of 400 ppm of As(III)

819 cm-1

3700 cm -1

4000

3500

3000

2500

2000

1500

1000

Wavelength Number (cm-1 )

500

4000

3500

3000

2500

2000

1500

1000

Wavelength Number (cm-1 )

500

4000

3500

841 cm -1

3000

2500

2000

1500

1000

500

Wavelength Number (cm -1 )

Figure S14 FTIR spectra of the vacuum-dried samples before and after adsorption of arsenic: (a) meso-Al-400, (b) meso-80Al20Mg-400 and (c) meso-Mg-400. Experimental conditions: dose = 0.5 g L-1, initial concentration of As(V) or As(III) = 400 mg L-1; initial pH for As(V) and As(III) adsorption is 3.0 and 7.0, respectively.

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300

As(V) uptake (mg g-1)

250 200 150 100 50 0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Dose (g L-1) Figure S15 Effect of the adsorbent dose on the As(V) adsorption capacity of meso-Al-400. The mass of meso-Al-400 was 0.02 g, the initial pH was 3.0 ± 0.1 and the initial As(V) concentration is 420 mg L-1. The volume of As(V) solution was varied from 10 to 100 mL, resulting in the dose ranging from 0.2 g L-1 to 2.0 g L-1. Please note that the adsorbent dose was 0.5 g L-1 throughout the work. Figure S15 demonstrates that 0.5 g L-1 is the optimal adsorbent dose with the highest adsorption capacity (260 mg g-1) for As(V). When the dose was increased to 1.0 and 2.0 g L-1, the adsorption capacity was decreased by 25.4% and 42.3%, respectively.

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