1
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
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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).
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-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
PDPB Nano + Cu2+(1x10-6 M)
PDPB Nano + Cu2+(5x10-6 M)
PDPB Nano + Cu2+(1x10-5 M)
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.
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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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