Ultrasensitive gold nanostar-polyaniline composite for ammonia gas ...
Supplementary Information
Ultrasensitive gold nanostar-polyaniline composite for ammonia gas sensing Vished Kumar 1, Vithoba Patil 2, Amey Apte 1, Namdeo Harale 2, Pramod Patil 2, and Sulabha Kulkarni 1,*
1
Indian Institute of Science Education and Research, Dr.Homi Bhabha Road, Pashan, Pune-
411008, India 2
Thin Film Materials lab, Department of Physics, Shivaji University, Kolhapur-416004, India
*Corresponding author, [email protected]
Page No. S1
Figure S1: Photograph of the Au NS solution depicting the colour progression with respect to heating time (in min), from light green to deep violet.
Figure S2: UV-Vis spectra of the synthesised Au (a) nanospheres, and (b) nanorods respectively.
Fig. S2 shows the UV-spectra of the Au nanospheres and nanorods (synthesised according to Sec. 2.2, 2.3). The positions of the various peaks indicate the localised surface plasmon resonances of the two morphologies (SEM images shown in Fig. 5 (c) and (d)).
Page No. S2
Figure S3: FESEM image of ‘Au NS + PANI’ showing typical stars embedded in the PANI matrix.
Above FESEM image typically shows that, the Au NS are embedded in different layers of the PANI film
Page No. S3
Figure S4: UV-Vis spectra of (a) PANI, (b) Au NS, and (c) Au NS + PANI solutions respectively.
The UV-Vis spectrum of PANI solution shows absorption at 329 nm and 627 nm which can be attributed to the π-π* benzenoid and quinoid exciton transitions respectively 1. The Au NS solution shows peaks at 528 nm and 910 nm, which are due to the transverse and longitudinal surface plasmon resonance modes of the arms of the nanostars. These modes are carried over and seen in the Au NS + PANI solution, although the redshifted values at 579 nm and 1074 nm can be explained due to a change in the local refractive index around the Au NS due to presence of the PANI matrix.
Figure S5: EDAX spectra of (a) Au NS, and (b) Au NS + PANI samples respectively.
Page No. S4
Figure S6: (a-c) Illustrative indication of localised EDAX sampling to adjudicate relative proportion of Au and Cu, in a single nanostar.
Therefore, the percentage of Au in a single nanostar is higher at the centre, whereas the percentage of Cu is higher at the tips. XPS of Au nanostars is shown in Fig. S7. The survey scan can be seen in Fig. S7 (a). Fig. S7 (b) shows the C 1s region having two peaks at 284.8 eV and 281.4 eV. N 1s has B. E. of 399.6 eV, in Fig. S7 (c), whereas Fig. S7 (d) depicts O 1s with two peaks at 532.9 eV and 529.9 eV. Fig. S7 (e) indicates Cu 2p3/2 is at 933.5 eV and Cu 2p1/2 is at 953.3 eV. The satellite appears at 943.3 eV. Finally, in Fig. S7 (f), Au 4f7/2 is at 84.3 eV and Au 4f5/2 is at 88.0 eV binding energy. As can be seen from Fig. S7, the peak positions of Au 4f and Cu 2p do not change; moreover they are very close to binding energy in the pure metallic form. The C 1s 284.8 eV peak appearing in both Au NS and Au NS + PANI is due to graphitic carbon and taken as reference. The peaks at 281.4 eV and 279.9 eV are usually attributed to metal carbon bond 2–4. In Fig. S7 (c), the N 1s peak at 399.6 eV for Au NS shifts to 400.3 eV for Au NS + PANI. Thus there is a shift towards a higher binging energy indicating presence of positive charge on nitrogen. Similarly, the C 1s peak at low binding energy has been reduced and shifted after embedding Au NS in PANI. We also observe that the O 1s peak at 529.9 eV in Au NS is substantially decreased for Au NS + PANI.
Page No. S5
Figure S7: XPS data for Au NS (upper green plot) and Au NS + PANI (lower blue plot) samples: (a) Survey scans {Peaks marked with * appearing at ~154 eV and ~104 eV correspond to SiO2/Si 2s and 2p peaks respectively 6,7} (b) C 1s (c) N 1s (d) O 1s (e) Cu 2p and (f) Au 4f respectively.
Page No. S6
Table 1 XPS elemental compositions for 'Au NS' and ‘Au NS + PANI’ respectively.
Line Au 4f7/2 Cu 2p3/2 N 1s O 1s C 1s Total
Au NS (%) 1.18 1.19 4.71 22.25 70.67 100.00
Au NS + PANI (%) 1.93 1.58 3.01 12.04 81.44 100.00
For Au NS: Taking only Au 4f7/2 and Cu 2p3/2 peak areas: Au = 49.81%, Cu = 50.19%
For Au NS + PANI: Taking only Au 4f7/2 and Cu 2p3/2 peak areas: Au = 55.04%, Cu = 44.96%
Figure S8: X-ray Diffraction plots of a) Au NS, and b) Au NS + PANI samples respectively. The asterisk in both denotes the (111) reflection peak due to AuCu.
Page No. S7
Table 2 XRD Parameters and calculated lattice constants for 'Au NS' and 'Au NS + PANI' samples (calculations based on data from Fig. S8).
hkl
Au (JCPDS Card 03-065-2870) 2θ (deg)
d1 (Å)
Au NS
Lattice Const
2θ
(Å)
(deg)
d2 (Å)
Au NS + PANI
Lattice Const
(d2-d1)
2θ
(Å)
(Å)
(deg)
d3 (Å)
Lattice Const (Å)
(d3-d1) (Å)
111
38.188
2.356
4.082
38.266
2.352
4.074
-0.005
38.173
2.357
4.083
0.001
200
44.386
2.041
4.082
44.422
2.039
4.078
-0.002
44.422
2.039
4.078
-0.002
220
64.578
1.443
4.081
64.664
1.441
4.077
-0.002
64.612
1.442
4.080
-0.001
311
77.569
1.231
4.081
77.702
1.229
4.076
-0.002
77.571
1.231
4.081
0.000
hkl
Avg Lattice Const: 4.081 Å
Au NS
Au NS + PANI
AuCu (JCPDS Card 01-074-7033) 2θ (deg)
111
Avg Lattice Const: 4.076 Å
40.773
d1 (Å)
2.213
Lattice Const
2θ
(Å)
(deg)
3.833
41.193
d2 (Å)
2.191
Lattice Const
(d2-d1)
2θ
(Å)
(Å)
(deg)
3.795
-0.022
41.121
Page No. S8
d3 (Å)
Lattice Const (Å)
2.195
3.802
(d3-d1) (Å) -0.018
The percentage composition of Au and Cu in the ‘Au NS’ and ‘Au NS + PANI’ samples respectively, can be obtained by referring to Table 1 in Motl et al 5. The authors have calculated the lattice constants (3.882 Å to 4.077 Å) of Au-Cu alloy nanoparticle samples of various percentage compositions, based on their XRD data using Vegard’s Law. Since the lattice constants of AuCu (clusters) in our case are below the minimum value reported by those authors, we fit a linear scaling relation to their values with a very good accuracy (R2 = 0.99):
Figure S9: Linear fit (pink) from data of Table 1 (green) in Motl et al 5. The two points in blue represent the data points from this work that are a result of the extrapolation of the fitted curve (Inset: illustration of the Au nanostar (gold) with localised clusters of Au1-xCux (in green).
Based on the obtained relation i.e. ‘Cu fraction’ dependence on the ‘lattice constant of AuCu’, we can calculate for our case, the fraction of Cu in the ‘Au NS’ and ‘Au NS + PANI’ samples as 0.596 and 0.581, respectively. Therefore, the fraction of Au in our samples are 0.404 and 0.419, respectively. Owing to the strong intensities of the Au fcc diffraction peaks in the XRD data, it can be hypothesized that there is spread formation of localised AuCu clusters in the Au nanostars, of the form ‘Au1-xCux’, where x = 0.596 for ‘Au NS’ and 0.581 for ‘Au NS + PANI’ samples respectively.
Page No. S9
Figure S10: Enlarged view of the response cycle of the 'Au NS + PANI' sample for 40 ppm NH 3 gas (Fig. 6 in main text, preparation details same as section 2.5.1), indicating “Gas OFF”.
Figure S11: Enlarged view of gas response of the ‘Au NS + PANI’ sensor for various NH 3 gas concentrations (a) 20 ppm to 80 ppm and (b) 100 ppm to 250 ppm, as a function of time, indicating “Gas ON/OFF” (preparation details for both, same as section 2.5.1).
Page No. S10
Figure S12: Typical FESEM images of ‘Au NS + PANI’ (a) before, and (b) after the sensing experiment.
.
Figure S13: UV-Vis spectra of ‘Au NS + PANI’ thin-film sample, before and after the sensing experiments with NH3 gas (preparation given in section 2.5.1).
Fig. S12 shows that the Au NS do not suffer any morphological damage after the NH3 sensing. Au NRs and nanospheres do not suffer any morphological damage either, after NH3 sensing (Fig. 5 (c-d) in main text). Fig. S13 shows the UV-Vis spectra of ‘Au NS + PANI’ sample before and after sensing. It can be seen that there are no remarkable differences in the UV-spectra before and after the sensing, which indicates that the sample is robust and Page No. S11
unchanging with respect to exposure towards NH3 gas, as echoed by the SEM images in Fig. S12.
REFERENCES
(1)
Nguyen, H. D.; Nguyen, T. H.; Hoang, N. V.; Le, N. N.; Nguyen, T. N. N.; Doan, D. C. T.; Dang, M. C. pH Sensitivity of Emeraldine Salt Polyaniline and Poly(vinyl Butyral) Blend. Adv. Nat. Sci. Nanosci. Nanotechnol. 2014, 5, 045001.
(2)
Kim, H.-N.; Yoo, H.; Moon, J. H. Graphene-Embedded 3D TiO2 Inverse Opal Electrodes for Highly Efficient Dye-Sensitized Solar Cells: Morphological Characteristics and Photocurrent Enhancement. Nanoscale 2013, 5, 4200–4204.
(3)
Xie, D.; Wen, F.; Yang, W.; Li, X.; Leng, Y.; Wan, G.; Sun, H.; Huang, N. CarbonDoped Titanium Oxide Films by DC Reactive Magnetron Sputtering Using CO2 and O2 as Reactive Gas. Acta Metall. Sin. (English Lett. 2014, 27, 239–244.
(4)
Dobrzanski, L. a; Zukowska, L. W.; Kubacki, J.; Golombek, K.; Mikuta, J. XPS and AES Analysis of PVD Coatings. Mater. Sci. Eng. 2008, 32, 99–102.
(5)
Motl, N. E.; Ewusi-Annan, E.; Sines, I. T.; Jensen, L.; Schaak, R. E. Au−Cu Alloy Nanoparticles with Tunable Compositions and Plasmonic Properties: Experimental Determination of Composition and Correlation with Theory. J. Phys. Chem. C 2010, 114, 19263–19269.
(6)
Bekkay, T.; Sacher, E.; Yelon, A. Surface Reaction during the Argon Ion Sputter Cleaning of Surface Oxidized Crystalline Silicon (111). Surf. Sci. 1989, 217, L377– L381.
(7)
Cros, A.; Saoudi, R.; Hollinger, G.; Hewett, C. A.; Lau, S. S. An X‐ray Photoemission Spectroscopy Investigation of Oxides Grown on AuxSi1−x Layers. J. Appl. Phys. 1990, 67, 1826–1830.
Page No. S12
Ultrasensitive gold nanostar-polyaniline composite for ammonia gas sensing Vished Kumar 1, Vithoba Patil 2, Amey Apte 1, Namdeo Harale 2, Pramod Patil 2, and Sulabha Kulkarni 1,*
1
Indian Institute of Science Education and Research, Dr.Homi Bhabha Road, Pashan, Pune-
411008, India 2
Thin Film Materials lab, Department of Physics, Shivaji University, Kolhapur-416004, India
*Corresponding author, [email protected]
Page No. S1
Figure S1: Photograph of the Au NS solution depicting the colour progression with respect to heating time (in min), from light green to deep violet.
Figure S2: UV-Vis spectra of the synthesised Au (a) nanospheres, and (b) nanorods respectively.
Fig. S2 shows the UV-spectra of the Au nanospheres and nanorods (synthesised according to Sec. 2.2, 2.3). The positions of the various peaks indicate the localised surface plasmon resonances of the two morphologies (SEM images shown in Fig. 5 (c) and (d)).
Page No. S2
Figure S3: FESEM image of ‘Au NS + PANI’ showing typical stars embedded in the PANI matrix.
Above FESEM image typically shows that, the Au NS are embedded in different layers of the PANI film
Page No. S3
Figure S4: UV-Vis spectra of (a) PANI, (b) Au NS, and (c) Au NS + PANI solutions respectively.
The UV-Vis spectrum of PANI solution shows absorption at 329 nm and 627 nm which can be attributed to the π-π* benzenoid and quinoid exciton transitions respectively 1. The Au NS solution shows peaks at 528 nm and 910 nm, which are due to the transverse and longitudinal surface plasmon resonance modes of the arms of the nanostars. These modes are carried over and seen in the Au NS + PANI solution, although the redshifted values at 579 nm and 1074 nm can be explained due to a change in the local refractive index around the Au NS due to presence of the PANI matrix.
Figure S5: EDAX spectra of (a) Au NS, and (b) Au NS + PANI samples respectively.
Page No. S4
Figure S6: (a-c) Illustrative indication of localised EDAX sampling to adjudicate relative proportion of Au and Cu, in a single nanostar.
Therefore, the percentage of Au in a single nanostar is higher at the centre, whereas the percentage of Cu is higher at the tips. XPS of Au nanostars is shown in Fig. S7. The survey scan can be seen in Fig. S7 (a). Fig. S7 (b) shows the C 1s region having two peaks at 284.8 eV and 281.4 eV. N 1s has B. E. of 399.6 eV, in Fig. S7 (c), whereas Fig. S7 (d) depicts O 1s with two peaks at 532.9 eV and 529.9 eV. Fig. S7 (e) indicates Cu 2p3/2 is at 933.5 eV and Cu 2p1/2 is at 953.3 eV. The satellite appears at 943.3 eV. Finally, in Fig. S7 (f), Au 4f7/2 is at 84.3 eV and Au 4f5/2 is at 88.0 eV binding energy. As can be seen from Fig. S7, the peak positions of Au 4f and Cu 2p do not change; moreover they are very close to binding energy in the pure metallic form. The C 1s 284.8 eV peak appearing in both Au NS and Au NS + PANI is due to graphitic carbon and taken as reference. The peaks at 281.4 eV and 279.9 eV are usually attributed to metal carbon bond 2–4. In Fig. S7 (c), the N 1s peak at 399.6 eV for Au NS shifts to 400.3 eV for Au NS + PANI. Thus there is a shift towards a higher binging energy indicating presence of positive charge on nitrogen. Similarly, the C 1s peak at low binding energy has been reduced and shifted after embedding Au NS in PANI. We also observe that the O 1s peak at 529.9 eV in Au NS is substantially decreased for Au NS + PANI.
Page No. S5
Figure S7: XPS data for Au NS (upper green plot) and Au NS + PANI (lower blue plot) samples: (a) Survey scans {Peaks marked with * appearing at ~154 eV and ~104 eV correspond to SiO2/Si 2s and 2p peaks respectively 6,7} (b) C 1s (c) N 1s (d) O 1s (e) Cu 2p and (f) Au 4f respectively.
Page No. S6
Table 1 XPS elemental compositions for 'Au NS' and ‘Au NS + PANI’ respectively.
Line Au 4f7/2 Cu 2p3/2 N 1s O 1s C 1s Total
Au NS (%) 1.18 1.19 4.71 22.25 70.67 100.00
Au NS + PANI (%) 1.93 1.58 3.01 12.04 81.44 100.00
For Au NS: Taking only Au 4f7/2 and Cu 2p3/2 peak areas: Au = 49.81%, Cu = 50.19%
For Au NS + PANI: Taking only Au 4f7/2 and Cu 2p3/2 peak areas: Au = 55.04%, Cu = 44.96%
Figure S8: X-ray Diffraction plots of a) Au NS, and b) Au NS + PANI samples respectively. The asterisk in both denotes the (111) reflection peak due to AuCu.
Page No. S7
Table 2 XRD Parameters and calculated lattice constants for 'Au NS' and 'Au NS + PANI' samples (calculations based on data from Fig. S8).
hkl
Au (JCPDS Card 03-065-2870) 2θ (deg)
d1 (Å)
Au NS
Lattice Const
2θ
(Å)
(deg)
d2 (Å)
Au NS + PANI
Lattice Const
(d2-d1)
2θ
(Å)
(Å)
(deg)
d3 (Å)
Lattice Const (Å)
(d3-d1) (Å)
111
38.188
2.356
4.082
38.266
2.352
4.074
-0.005
38.173
2.357
4.083
0.001
200
44.386
2.041
4.082
44.422
2.039
4.078
-0.002
44.422
2.039
4.078
-0.002
220
64.578
1.443
4.081
64.664
1.441
4.077
-0.002
64.612
1.442
4.080
-0.001
311
77.569
1.231
4.081
77.702
1.229
4.076
-0.002
77.571
1.231
4.081
0.000
hkl
Avg Lattice Const: 4.081 Å
Au NS
Au NS + PANI
AuCu (JCPDS Card 01-074-7033) 2θ (deg)
111
Avg Lattice Const: 4.076 Å
40.773
d1 (Å)
2.213
Lattice Const
2θ
(Å)
(deg)
3.833
41.193
d2 (Å)
2.191
Lattice Const
(d2-d1)
2θ
(Å)
(Å)
(deg)
3.795
-0.022
41.121
Page No. S8
d3 (Å)
Lattice Const (Å)
2.195
3.802
(d3-d1) (Å) -0.018
The percentage composition of Au and Cu in the ‘Au NS’ and ‘Au NS + PANI’ samples respectively, can be obtained by referring to Table 1 in Motl et al 5. The authors have calculated the lattice constants (3.882 Å to 4.077 Å) of Au-Cu alloy nanoparticle samples of various percentage compositions, based on their XRD data using Vegard’s Law. Since the lattice constants of AuCu (clusters) in our case are below the minimum value reported by those authors, we fit a linear scaling relation to their values with a very good accuracy (R2 = 0.99):
Figure S9: Linear fit (pink) from data of Table 1 (green) in Motl et al 5. The two points in blue represent the data points from this work that are a result of the extrapolation of the fitted curve (Inset: illustration of the Au nanostar (gold) with localised clusters of Au1-xCux (in green).
Based on the obtained relation i.e. ‘Cu fraction’ dependence on the ‘lattice constant of AuCu’, we can calculate for our case, the fraction of Cu in the ‘Au NS’ and ‘Au NS + PANI’ samples as 0.596 and 0.581, respectively. Therefore, the fraction of Au in our samples are 0.404 and 0.419, respectively. Owing to the strong intensities of the Au fcc diffraction peaks in the XRD data, it can be hypothesized that there is spread formation of localised AuCu clusters in the Au nanostars, of the form ‘Au1-xCux’, where x = 0.596 for ‘Au NS’ and 0.581 for ‘Au NS + PANI’ samples respectively.
Page No. S9
Figure S10: Enlarged view of the response cycle of the 'Au NS + PANI' sample for 40 ppm NH 3 gas (Fig. 6 in main text, preparation details same as section 2.5.1), indicating “Gas OFF”.
Figure S11: Enlarged view of gas response of the ‘Au NS + PANI’ sensor for various NH 3 gas concentrations (a) 20 ppm to 80 ppm and (b) 100 ppm to 250 ppm, as a function of time, indicating “Gas ON/OFF” (preparation details for both, same as section 2.5.1).
Page No. S10
Figure S12: Typical FESEM images of ‘Au NS + PANI’ (a) before, and (b) after the sensing experiment.
.
Figure S13: UV-Vis spectra of ‘Au NS + PANI’ thin-film sample, before and after the sensing experiments with NH3 gas (preparation given in section 2.5.1).
Fig. S12 shows that the Au NS do not suffer any morphological damage after the NH3 sensing. Au NRs and nanospheres do not suffer any morphological damage either, after NH3 sensing (Fig. 5 (c-d) in main text). Fig. S13 shows the UV-Vis spectra of ‘Au NS + PANI’ sample before and after sensing. It can be seen that there are no remarkable differences in the UV-spectra before and after the sensing, which indicates that the sample is robust and Page No. S11
unchanging with respect to exposure towards NH3 gas, as echoed by the SEM images in Fig. S12.
REFERENCES
(1)
Nguyen, H. D.; Nguyen, T. H.; Hoang, N. V.; Le, N. N.; Nguyen, T. N. N.; Doan, D. C. T.; Dang, M. C. pH Sensitivity of Emeraldine Salt Polyaniline and Poly(vinyl Butyral) Blend. Adv. Nat. Sci. Nanosci. Nanotechnol. 2014, 5, 045001.
(2)
Kim, H.-N.; Yoo, H.; Moon, J. H. Graphene-Embedded 3D TiO2 Inverse Opal Electrodes for Highly Efficient Dye-Sensitized Solar Cells: Morphological Characteristics and Photocurrent Enhancement. Nanoscale 2013, 5, 4200–4204.
(3)
Xie, D.; Wen, F.; Yang, W.; Li, X.; Leng, Y.; Wan, G.; Sun, H.; Huang, N. CarbonDoped Titanium Oxide Films by DC Reactive Magnetron Sputtering Using CO2 and O2 as Reactive Gas. Acta Metall. Sin. (English Lett. 2014, 27, 239–244.
(4)
Dobrzanski, L. a; Zukowska, L. W.; Kubacki, J.; Golombek, K.; Mikuta, J. XPS and AES Analysis of PVD Coatings. Mater. Sci. Eng. 2008, 32, 99–102.
(5)
Motl, N. E.; Ewusi-Annan, E.; Sines, I. T.; Jensen, L.; Schaak, R. E. Au−Cu Alloy Nanoparticles with Tunable Compositions and Plasmonic Properties: Experimental Determination of Composition and Correlation with Theory. J. Phys. Chem. C 2010, 114, 19263–19269.
(6)
Bekkay, T.; Sacher, E.; Yelon, A. Surface Reaction during the Argon Ion Sputter Cleaning of Surface Oxidized Crystalline Silicon (111). Surf. Sci. 1989, 217, L377– L381.
(7)
Cros, A.; Saoudi, R.; Hollinger, G.; Hewett, C. A.; Lau, S. S. An X‐ray Photoemission Spectroscopy Investigation of Oxides Grown on AuxSi1−x Layers. J. Appl. Phys. 1990, 67, 1826–1830.
Page No. S12
