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Conducting Polymer Nanostructures as Promising Photocatalysts under Visible-Light

Srabanti Ghosh,1 Natalie A. Kouamé,1 Laurence Ramos,2 Samy Remita,1,3 Alexandre Dazzi,1 Ariane Deniset-Besseau,1 Patricia Beaunier,4, 5 Fabrice Goubard,6 Pierre-Henri Aubert6 and Hynd Remita1, 7*

1Laboratoire de Chimie Physique, UMR 8000-CNRS, Bât. 349, Université Paris-Sud, 91405 Orsay, France 2 Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier 2, Montpellier, F-France. 3Départment CASER, Ecole SITI, Conservatoire National des Arts et Métiers, CNAM, 292 rue Saint-Martin, 75141 Paris Cedex 03, France 4Sorbonne Universités, UPMC Univ. Paris 06, UMR 7197-CNRS, Laboratoire de Réactivité de Surface, F-75005 Paris, France 5CNRS, UMR 7197, Laboratoire de Réactivité de Surface, F-75005 Paris, France 6Laboratoire de Physicochimie des Polymères et Interfaces (LPPI), Université de Cergy-Pontoise, 95031 Cergy-Pontoise Cedex, France 7CNRS, Laboratoire de Chimie Physique, UMR 8000, 91405 Orsay, France *corresponding author, E-mail: [email protected]

Overview.

1. Supplementary materials and methods.

2. Synthesis and Characterization.

3. Supplementary Figures. (Figs. S1‐S13).

4. Supplementary Tables. (Table S1‐S3).

5. Supplementary References.

Conducting polymer nanostructures for photocatalysis under visible light

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NMAT4220

NATURE MATERIALS | www.nature.com/naturematerials 1

© 2015 Macmillan Publishers Limited. All rights reserved

http://dx.doi.org/10.1038/nmat4220

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Materials.

Sodium dodecyl sulfate (SDS), sodium chloride, cyclohexane (> 99%), pentanol (≥ 99%),

ethanol (>98%), acetonitrile (≥ 99% for HPLC), 2-propanol, acetoacetanilide, ammonium

acetate, tris(hydroxymethyl)aminomethane, cupper sulfate (CuSO4, 5H2O), silver perchlorate

AgClO4 (>98%), phenol (C6H5OH) and methyl orange (MO) were purchased from Sigma-

Aldrich. For in-situ polymerization, we used 1,4-diphenylbutadiyne (DPB) (Aldrich) as

monomer and benzoin methyl ether (BME) (Fluka) as catalyst. Titania (P25, a surface area of 50

m2 g_1, 80% Anatase, 20% Rutile) was obtained from Evonik for comparative photo degradation

by polymer nanostructure. N2 gas (purity >99.995%) was purchased from Air Liquide. All

compounds were used as received. Ultrapure water (Millipore System, 18.2 M cm) was used.

All experiments were performed at room temperature.

Methods.

Synthesis of silver modified TiO2.

The photocatalysts were obtained by radiolytic reduction of Ag+ in the TiO2 suspension (2 wt

%). An ethanolic solution containing AgClO4 (2 ×10−3 M) and TiO2 (P25) in suspension was first

sonicated for 3 min, degassed with nitrogen, and irradiated (under stirring) with a 60Co

panoramic gamma source (dose rate = 2.3 kGy h−1). The silver ions were reduced by the solvated

electrons and the alcohol radicals induced by solvent radiolysis and 1 h 20 min exposure time

(3.2 kGy) was necessary to reduce all the silver ions. The modified TiO2 photocatalysts were

separated by centrifugation and dried at 60°C. The modified catalyst (Ag-TiO2) was used for

methyl orange and phenol degradation.


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Hantzsch method for the determination of formaldehyde.

In this method, 1.5 mL of reactant solution was extracted after photoirradiation of organic

pollutants in the presence of PDPB, diluted in 1 mL of 0.2 M acetoacetanilide in ethanol and 2.5

mL of 4 M ammonium acetate. Consequently, a dihydropyridine has been formed having a

maximum absorption wavelength of 368 nm. The absorbance has been measured by a

spectrophotometer.


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Experimental set up for material characterizations.

For nanoIR study, samples were directly deposited on the upper surface of a ZnSe prism that

is transparent in the mid-infrared and the tip of the AFM remained in contact with the object.

High-performance liquid chromatography (HPLC) was used for sample analysis. For elution, an

isocratic mobile phase consisting of 75% H2O and 25% acetonitrile (ACN), at a 1 mL min1 flow

rate, was used, with detection at 270 nm. The column was an Adsorbosphere C18 reverse phase

(5 m, l: 150 mm, ID: 4.6 mm, Alltech) combined with an All-Guard cartridge systemTM

(7.54.6 mm, Alltech). For data acquisition, Star software was used.

For small-angle X-ray scattering (SAXS) measurement, the mesophases were inserted in glass

capillaries of 1.5 mm diameter. A high brightness low power X-ray tube, coupled with aspheric

multilayer optic (GeniX 3D from Xenocs) was employed, which delivered an ultra low divergent

beam (0.5 mrad). Scatterless slits were used to give a clean 0.8 mm diameter X-ray spot with an

estimated flux around 35 Mph/s at the sample position. A transmission configuration was used.

The scattered intensity was collected on a two-dimensional Schneider 2D image plate detector

prototype, at a distance of 1.9 m from the sample. The experimental data were corrected for the

background scattering and the sample transmission. The scattering vector q can be calculated

from the angle of the scattered radiation and X-ray wavelength. The scattering pattern of a

hexagonal phase consists in diffraction peaks whose positions are in the ratio 1:3:2. The first

peak position qo allows a direct determination of the hexagonal lattice parameter a according

to0

2

3

2

qa

the center-to-center distance a between adjacent tubes. We find a =18.4 nm. To

characterize the crystallinity of the synthesized PDPB nanostructures, bulk PDPB powders were

incorporated in glass capillaries of 1.5 mm diameter and probed with the same X-ray scattering

apparatus but with a sample-detector distance of 0.2 m.

The attenuated total reflectance (ATR)-fourier transformed infrared spectroscopy (FTIR) with

diamond ATR attachment (PIKEMIRACLE crystal plated diamond/ZnSe) and MCT detector

with liquid nitrogen cooling system was used. Scanning wavelengths were varied from

4000600 cm-1 with a 4 cm-1 spectral resolution with 100 repetitions scans average for each

spectrum.


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When the sample absorbs the IR laser pulse, it warms via the photothermal effect, resulting in a

rapid thermal expansion of the absorbing region of the sample. The thermal expansion pulse

impacts the tip of the AFM cantilever and causes it to oscillate. As the amplitude of oscillations

is proportional to the absorption, we were able to record infrared absorption spectra at a given

point and to make chemical maps by scanning the surface at a given wavelength. In this study,

drops of ethanolic solution of PDPB powder before and after catalytic degradation were directly

deposited on the upper surface of a ZnSe prism and dried at room temperature. The IR source

was tuned to wavelength 3054 cm-1 to map compositional variations in order to identify further

change of the polymer materials at the specific location after photocatalytic degradation reaction.

In the gel permeation chromatography (GPC), the cross-linked polystyrene gel was packed in

a relatively small column which needed 50 L of sample solution for each run. Calibration of the

system was made with specialized GPC standard of linear polystyrene at room temperature

(30°C) and at a solvent flow rate of 1 mL mm-1. The peak molar mass of the standard ranges

from a few hundred to nearly twenty thousand g mol-1. A detecting wavelength of 280 nm, just

above the absorption edge of the solvent, was used for the UV-visible detector so that the

monomers and dimers as well as longer species can be detected.

The electrochemical setup was a three-electrodes single cell, with a glassy carbon (GC) disk

(2 mm diameter) coated with the sample film as the working electrode, a Pt wire as counter

electrode, and a silver wire pseudo-reference electrode. Ferrocenium/ferrocene (Fc/Fc+) redox

potential was measured at the end of each experiment in order to calibrate the pseudo reference

electrode as recommended by IUPAC. Polymer samples (at a concentration of 1 mg mL-1 in

tetrahydrofuran) were drop-casted onto the GC-electrode and then dried. The GC-electrode was

immersed into the electrochemical cell containing acetonitrile with 0.1 M


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tetrabutylammoniumhexafluorophosphate (TBAPF6). The compounds were electrochemically

reduced prior to being oxidized between −3.0 V and+3.0 V at a scan rate of 20 mV/s.

a b

Figure S1 Scanning electron microscopy (SEM) image of PDPB. Figure shows SEM images of PDPB prepared in (a) cyclohexane (designated as bulk PDPB), and (b) hexagonal mesophases (represented as nano PDPB).


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Figure S2 1H and 13C NMR spectra of bulk PDPB and nano PDPB. (a, d), represents bulk PDPB, (b, e) represents nano PDPB before and after photocatalysis (c, f). The spectra show that the chemical structures of bulk and nano PDPB are similar. Moreover, for nano PDPB, the chemical structure is not affected during the photocatalytic process. Chemical shifts are given in ppm using the residual solvent signals of THF-D8 (3.76 ppm and 1.89 ppm for the proton, 25 ppm and 62 ppm for the carbon) as an internal reference.


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100 200 300 400 500 600 7000

20

40

60

80

100

TGA of PDPB by UV

Temperature (°C)

Wei

gh

t L

os

s (W

t %

)

Figure S3 Thermogravimetric analysis (TGA) profile of solid PDPB nanostructures after extraction from the mesophase. Figure shows onset of decomposition of PDPB nanostructure at about 200C until a major decomposition occurred around 540°C. Further, at higher temperatures, PDPB displays decomposition pattern up to 590°C with a weight loss of about 95 wt%.

0 50 100 150 200 250 300 350 400

0.70

0.75

0.80

0.85

0.90

0.95

1.00

Time (min)

Ad

so

rpti

on

of

MO

Nano PDPB Bulk PDPB

0 50 100 150 200 250 300 350 4000.70

0.75

0.80

0.85

0.90

0.95

1.00

Time (min)

Ad

so

rpti

on

of

Ph

en

ol

Nano PDPB Bulk PDPB

a b

Figure S4 The dark adsorptions tests of nano PDPB and bulk PDPB. (a) phenol and (b) methyl orange (MO), on nano PDPB (gray circles) and bulk PDPB (blue triangles). The initial

concentrations are C0= 3.7 10-3 mol L-1 for phenol and C0=6 10-5 mol L-1 for MO.


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0

20

40

60

80

100

Nano PDPB

Deg

rad

ati

on

of

MO

(%

)

Ag-TiO 2

P 25 TiO 2

UV VIS

0

20

40

60

80

100

Ag-TiO2

D

egra

da

tio

n o

f P

he

no

l (%

)Nano PDPB

P 25 TiO 2

UV VIS

a b

Figure S5 Comparative photocatalytic activity of commercial TiO2 (P25TiO2), Ag nanoparticle modified TiO2 (Ag-Ti02), and PDPB nanofibers. Figure shows the degradation of (a) MO and (b) phenol under irradiation with UV (45 min) and visible light (240 min for MO and 270 min for phenol).


10

-3 -2 -1 0 1 2 3

-60

-40

-20

0

20

40

60 PDPB nano

PDPB bulk

Potential (V vs. Ag)

Cur

rent

(µ

A)

ferrocene

a

-3 -2 -1 0 1 2 3-10

-8

-6

-4

-2

0

2

4

6

8

10

Beginning ofp -doping

Beginning ofn- doping

PDPB nano

PDPB bulk

Potential (V vs. Ag)

Cur

rent

(µ

A)

b

Figure S6 Cyclicvoltammograms of nano PDPB and bulk PDPB material. (a) The cyclicvoltammograms obtained at 20 mV/s in acetonitrile and 0.1M Tetrabutylammonium Perchlorate. Ferrocenium/ferrocene (Fc/Fc+) redox potential has been measured at the end of each experiment in order to calibrate the pseudo reference electrode (0.63V vs. Ag in the present study). (b) zoom of the voltammogram as shown in (a). The energetic levels of nano PDPB and bulk PDPB are determined as follows: EHOMO (eV) ~ ionization potential = -4.8-e (Eox_onset-0.63) and ELUMO (eV) ~ electronic affinity = -4.8-e (Ered_onset-0.63).


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Figure S7 The representation plot of band gap (Eg = ELUMO-EHOMO) versus 1/n (n= number of repetitive units) of PDPB oligomers. The band gap (Eg) versus 1/n has been calculated by using GAMESS-US Quantum Chemistry software and Density Functional Theory (DFT) with the B3LYP functional.

We performed degradation reactions of the MO in the presence of Cu2+ at a concentration

ranging from 10-6 M to 10-5 M, in the presence of PDPB nanofibers under UV and visible light as

shown in Fig.S8 and S9. We found that the initial degradation rate of MO under visible light

decreases even in the presence of only 10-6 M Cu2+ (see Fig.S8) and is further reduced with

increasing Cu2+concentrations, a total inhibition of the degradation being attained for a 10-5 M

Cu2+ concentration. Similar observations were obtained for degradation of MO under UV light in

presence of Cu2+ (see Fig.S9). These experiments confirm the contribution of excess electrons in

the photocatalytic process.

Cu2+ + e- Cu+ (1)


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0

20

40

60

80

Time of Vis light exposure (min)

Deg

rad

atio

n (

%)

PDPB Nano

PDPB Nano + Cu2+(1x10-6 M)

30 mins

60 mins

120 mins

180 mins

240 mins

Figure S8 Effect of Cu2+ on the photocatalytic activity of PDPB nanofibers. Photocatalytic degradation of methyl orange in the presence of PDPB nanofibers in the presence of Cu2+ under

visible light irradiation. (Initial concentrations C0 for MO is 6 10-5 mol L-1).

0 5 10 15 20 25 30 350.0

0.2

0.4

0.6

0.8

1.0

Time of UV exposure (min)

C/C

0 (M

O)

PDPB Nano




Figure S9 Effect of Cu2+ on the photocatalytic activity of PDPB nanofibers. Photocatalytic degradation of methyl orange (MO) in the presence of PDPB nanofibers at various concentration

of Cu2+ under UV-light irradiation. The initial concentration of MO is C0= 6 10-5 mol L-1.


13

Figure S10 Effect of oxygen, argon and 0.1 M isopropanol on the photocatalytic activity of PDPB nanofibers. Photocatalytic activities of PDPB nanofibers for the degradation of methyl

orange under UV-visible and visible light (> 450 nm) irradiation in the presence of oxygen, argon and oxygen and 0.1 M isopropanol after 270 minutes exposure to light.

Figure S11 X-ray diffraction pattern of solid PDPB nanofibers and bulk PDPB. The blue line represents PDPB nanofibers and red line represents bulk PDPB.

5 10 15 20 250

200

400

600

800

1000

1200

bulk PDPB nano PDPB

I (a

rb.

un.)

q (nm-1)

0

20

40

60

80

100

O 2 + isopropanol

D

egra

dat

ion

of

MO

(%

)

N 2O 2

UV VIS


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Figure S12 The attenuated total reflectance (ATR)-Fourier transformed infrared spectroscopy (FTIR) spectra of PDPB nanostructures before and after photodegradation. The bottom black spectrum represents PDPB nanofibers before degradation and top blue spectrum represents PDPB nanofibers after five cycles degradation.

Figure S13 Transmission electron microscopy image of PDPB nanostructures after photo degradation. Figure shows PDPB nanostructures after degradation of phenol under visible light irradiation after five cycles.

1000 1500 2000 2500 3000 3500 4000

1000 1500 2000 2500 3000 3500 4000

After catalysis

Inte

ns

ity

(a

.u.) 68

575

991

7

1445 14

8815

95

2858 29

2630

52

Before catalysis

Wavelength (nm)

Inte

ns

ity

(a.

u.)

685 75

991

7

1443 14

9015

95

2856

2923

3054


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Table S1: Determination of electrochemical data, ionization potentials, electronic affinity, energetic levels and electrochemical gap of nano- and bulk PDPB from cyclic voltammograms.

Table S2: Computed data Highest Occupied Molecular Orbital energy level (EHOMO), Lowest Unoccupied Molecular Orbital energy level (ELUMO), Energy gap (Eg) for short PDPB oligomers (n = 1, 2, 4, 6 and 8), showing consistent with theoretical calculated gaps (Fig S7) of oligomeric (n= 2, 4, 6 and 8) PDPB structures by density functional theory (DFT).1-3 The HOMO/LUMO levels (EHOMO ~IP and ELUMO ~EA) have been found to be very similar for both nano versus bulk PDPB as shown in Table S2. Highest occupied Molecular Orbital energy level (EHOMO) and Lowest Unoccupied Molecular Orbital energy level (ELUMO) were obtained and data are given in Table S1 and Table S2. Figure S7 shows the calculated gap (Eg = ELUMO-EHOMO) versus 1/n (n= number of repetitive units) and the extrapolation a 1/n =0 give the value of calculated gap of polymer.

Parameters monomer Dimer tetramer hexamer octamer

Energy -0.06308 -0.0815 -0.09484 -0.095 -0.09774

(hartree) -0.20986 -0.1931 -0.17962 -0.171 -0.16992

LUMO (eV) -1.72 -2.22 -2.58 -2.59 -2.66

HOMO (eV) -5.71 -5.25 -4.89 -4.65 -4.62

Eg(eV) 3.99 3.04 2.31 2.07 1.96

Main peaks ( from Fig S6‐a) Zoomed part (Fig S6‐b)

PDPB

p‐ doping

n‐ doping

IP ~EHOM

O (eV)

EA ~ELUMO

(eV)

E (eV)

p‐ doping

n‐ doping

IP ~EHOM

O (eV)

EA ~ELUMO

(eV)

E (eV)

Eox_onset

(V)

Ered_onset

(V)

E ox_onset (V)

Ered_onset

(V)

Bulk 1.97 ‐1.80 ‐6.14 ‐2.37 3.78 1.26 ‐0.40 ‐5.43 ‐3.77 1.66 Nano 1.91 ‐1.71 ‐6.08 ‐2.32 3.80 1.35 ‐0.45 ‐5.52 ‐3.71 1.81


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Table S3 Determination of formaldehyde use Tris as a probe for hydroxyl radical generation after photodegradation of phenol in the presence of PDPB nanofibers after 240 mins under UV light and visible light.

Supplementary References

1. Kohn, W., Sham, L. J. Phys. Rev.140, A1133 (1965). 2. Becke, A. D. J. Chem. Phys. 98, 5648 (1993). 3. Lee, C. T. Y., W. T., Parr, R. G. Phys Rev B 37, 785 (1988).

Materials Irradiation Formaldehyde concentration ( µM L-1)

PDPB nano UV light 3.0

Visible light 1.2


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