Supporting Information

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Supporting Information

Rapid Characterization of Arsenic Adsorption on Single Magnetite Nanoparticles by Collisions at Microelectrodes

Farideh Hosseini Nourei, Daniel Andreescu and Silvana Andreescu*

Department of Chemistry and Biomolecular Science, Clarkson University, Potsdam, NY, 13699- 5810, USA.

E-mail: [email protected]; Tel: +(315) 268 2394

Electronic Supplementary Material (ESI) for Environmental Science: Nano.

This journal is © The Royal Society of Chemistry 2020

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Scheme S1. Preparation and experimental collision measurements of MNPs, As-NPs and As-HA-MNPs.

Storage MNPsAs-MNPs

As-HA-MNPs 1 mg MNPs

redispersed in 1 mL DI

FTIR, XRD, XPS mesurement

Single particle collision electrochemistry (SPCE)

Purge N

2 for 20 min

Pt wire (Counter) Au microelectrode

Ag/AgCl Reference

MNPs, As-MNPs or As-HA-MNPs in PBS 0.1M (pH 7.5)

100 µl

10 ml DI with / without As (0 – 100 µM) HA (0 – 50 ppm) 10 mg Fe3O4

NPs

24 h mixing

-Centrifugation -Washing DI -Filtration

-Driying 80C overnight

30 sec sonication before the transfer in the electrochemical cell in PB (pH: 7.4)

TEM, PSD and zeta potential measurement

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Figure S1. The HRTEM images of Fe3O₄ nanoparticles.

20 30 40 50 60 70

0 10 20 30 40

Intensity

2 theta (degree)

311

220 400222 422 511

Figure S2. X-ray diffraction patterns of Fe₃O₄ nanoparticles.

Table S1. Arsenic removal efficiency by bare Fe₃O₄ and HA- Fe₃O₄ NPs (1 mg/ml) evaluated by AAS.

NPs type Initial As concentration

(µM) Residual As concentration

in supernatant (µM) As removal (%)

1 - > 99

Fe O

5 nm

0.29 nm (220)

0.34 nm (211)

0.29 nm (220)

50 nm

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0 2 4 6 8 10 0.0

0.2 0.4 0.6

Absorbance (a.u.)

Equation y = a + b*x

Intercept -0.00726 ± 0.0034 Slope 0.04883 ± 7.50907E-4 R-Square (COD) 0.99929

As (M)

Figure S3. Arsenic atomic absorption standard calibration curve

.

Figure S4. Zeta potential of magnetite NPs (black) and As-MNPs (red) function of pH.

0 100 200 300 400

0.00 0.02 0.04 0.06

Current (nA)

Time (s)

A

20 pA

5 pA

100 200 300 400

0.00 0.02 0.04 0.06

20 pA

HA

Time (s)

B

Figure S5. Chronoamperometric profile of oxidation spikes of bare Fe₃O₄ (A) and HA- Fe₃O₄ NPs at

2 4 6 8 10 12

-40 -20 0 20 40 60

Zeta potential (mV)

pH

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Figure S6. CV of AuME in 2 mM FcMeOH with 0.1M Na₂SO₄ and 25 mV/s scan rate.

Table S2 Collision characteristics of MNPs exposed to As³⁺ (10µM) at different pH values.

pH The number of oxidation peaks

Average current intensity (pA)

Average charge per spike (pC)

Total charge for 400 s (pC)

As conc / MNP (fM)

4 4 5 2.74 11.0 0.014

5 8 10.8 3.48 27.9 0.018

6 15 15.7 5.52 82.8 0.029

7 10 20.7 6.22 62.2 0.032

8 13 12.5 6.54 84.0 0.034

9 11 10 4.37 48.0 0.024

-0.1 0.0 0.1 0.2 0.3 0.4 0.5

0 10 20 30

Current (nA)

Potential (V)

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Figure S8. The FTIR spectra of MNPs, As-MNPs, HA and AS-HA-MNPs.

Table S3. The influence of HA concentration in SPCE characteristics of As-HA-MNPs (the average value of 3 electrodes).

Humic acid (ppm)

Number of collisions

Charge Transferred

(pC)

As content / particle (fM)

1 11 ± 3 1.66 0.008

2.5 13 ± 4 4.59 0.024

5 13 ± 4 5.72 0.030

10 10 ± 5 3.63 0.022

25 5 ± 3 5.34 0.028

50 2-3 6.41 0.033

MNPs

HA As-MNPs

820841

4000 3500 3000 1500 1000 500

As HA MNPs

Wavenumber (cm-1)

3440 2923 1628

2851 1045 637

1390 585₈11

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Table S4. Relative peak areas of peak components for Fe2p and As3d XPS spectra

Surface elemental mass (%) Electron shell

quantification Fe 2p As 3d

Fe²⁺ Fe³⁺ As³⁺ As⁵⁺

NPs type

As solution

conc.

(mM) As C N O Fe

(%) (%)

Fe³⁺/Fe²⁺

ratio (%) (%)

(Fe₃O₄) MNPs - - 8.2 - 23.2 68.6 43.6 56.4 1.29 - -

As-MNPs 0.1 - 9.2 - 22.7 68.1 45.7 54.3 1.16 - -

As-HA^*-MNPs 0.1 0.5 8.2 0.6 23 67.7 43.8 56.2 1.28 100 -

As-MNPs 10 3.7 8.6 - 22.4 65.3 43.2 56.8 1.31 81 19

As-HA^*-MNPs 10 4.8 7.5 1.0 23 63.7 49.5 50.5 1.02 85 15

^* the humic acid (HA) concentration was 5 ppm

Table S5. The influence of As concentration in SPCE characteristics of As-HA-MNPs collisions As conc in

solution (µM)

Number of collisions

Charge Transferred

(pC)

As content / particle (fM)

0.001 7 2.46 ± 0.36 0.013

0.01 11 3.26 ± 0.78 0.017

0.1 12 3.95 ± 0.61 0.021

1 10 4.94 ± 0.87 0.026

10 17 7.02 ± 1.12 0.036

Fe³⁺

712.7 eV Fe²⁺

710.5 eV Fe 2p

XPS Peak Intensity /a.u.

a

C 1s

O-C=O 288.5 eV

C-O 286.4 eV

284.7 eVC=C

b

O 1s

Carbon-Oxygen bonds 531.2 eV

Metal oxides 529.8 eV

c

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Figure S10. The

As3d and N1s

XPS spectra of As-HA-MNPs (prepared with 10 µM As and 5 ppm HA)

Figure S11. The

As3d

XPS spectra of As-HA-MNPs prepared with 100 µM As in the absence (a) and in the presence (b) of 5 ppm HA.

49 48 47 46 45 44 43 42 41 40

Binding Energy /eV

XPS Peak Intensity /a.u.

As 3d

As³⁺

44.2 eV

a

404 403 402 401 400 399 398 397 396 395

N 1s

C-N 399.9 eV

b

49 48 47 46 45 44 43 42 41 40

As⁵⁺

45.8 eV

As 3d

As³⁺

44.1 eV

a

49 48 47 46 45 44 43 42 41 40

As⁵⁺

45.8 eV

As 3d

As³⁺

44.1 eV