Supporting Information for AWS
1 Supporting Information for Probing the Dependence of Electron Transfer on Size and Coverage in Carbon Nanotube-Quantum Dot Heterostructures Lei Wang,a Jinkyu Han,b Yuqi Zhu,c Ruiping Zhou,c Cherno Jaye,d Haiqing Liu,a Zhuo-Qun Li,e Gordon T. Taylor,e Daniel A. Fischer,d Joerg Appenzeller,c and Stanislaus S. Wonga,b,* Email: [email protected]; [email protected] a
Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400 b
Condensed Matter Physics and Materials Sciences Department,
Brookhaven National Laboratory, Building 480, Upton, NY 11973 c
Department of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 d
Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20889 e
School of Marine and Atmospheric Sciences,
State University of New York at Stony Brook, Stony Brook, NY 11794-5000
2
Figure S1. TEM images of (A) pristine and (B) purified DWNTs.
3
Figure S2. (A) UV-visible spectra of as-prepared CdSe QDs possessing average diameters of 2.3, 3.0, and 4.1 nm, respectively. (B) XRD patterns of as-prepared CdSe QDs (measuring 3.0 nm in diameter). The corresponding literature database standard (JCPDS #08-0459) is shown immediately below and is highlighted in red.
4
Figure S3. FT-IR spectra of as-prepared and of MTH-capped CdSe QDs, possessing average diameters of 4.1 nm. Comments on IR Characterization. For ‘native’, as-prepared CdSe QDs, a popular surface capping agent typically used is TOPO.1 In our system, the sharp P=O stretch associated with TOPO located near 1147 cm-1 is red-shifted to 1070 cm-1 and is strongly broadened, which could imply the presence of multi-dentate coordination through the occupation of bridging sites on the Cd surface.2, 3 Such distinctive peak is absent in our MTH-capped CdSe QDs, and is replaced by a sharp peak at 1040 cm-1, corresponding to the C-S stretching mode and indicative of a successful ligand substitution process.4 Moreover, the absence of a distinctive S-H peak
5 located near 2400-2500 cm-1 suggests that all of the pendant thiol moieties in these ligands are likely to be completely bound onto the surfaces of the CdSe QDs.5 In terms of other noticeable peaks, the ligand-exchanged MTH-capped QDs are known to give rise to characteristic peaks for aromatic rings near the 1530-1600 cm-1, 1400-1500 cm-1, and 1160-1175 cm-1 regions, and these have been assigned to the C=C asymmetric stretching mode, the C=C symmetric stretching mode, and the C-H bending mode, respectively. As expected, the MTH-capped CdSe QDs highlight the presence of distinctive and broad OH stretching peaks near 3260 cm-1, characteristic of the phenol groups within MTH.
6
Figure S4. C K-edge and O K-edge NEXAFS spectra of pristine and oxidized DWNTs.
NEXAFS Data C K-edge data gave rise to prominent transitions at 285 eV, 292-294 eV, and 301– 309 eV, respectively, corresponding to a sharp C 1s to C=C π* (ring) transition, three C 1s to C-C σ* (ring) transitions,6, 7 as well as broad (π + σ) transitions, respectively.8 After oxidation of the DWNTs, specific transitions at ~288.1 and 289.1 eV, which can attributed to the π* states of carbonyl groups associated with –COOH as well as of σ* states associated with C-O functionalities,9 became more prominent. The corresponding O K-edge data associated with the oxidized DWNTs evinced several distinctive peaks. Specifically, the peak at 531.6 eV corresponds to the C=O π* transition, which originates from the carbonyl oxygen atom, while the peak at 534.8 eV can be assigned to the “-OH” moiety from the carboxylic group. The two broader peaks located at 539.6 and 543.8eV can be ascribed to the presence of non-equivalent σ* C-O bonds within the carboxylic acid group.8, 10
7
Figure S5. Raman D and G-band data of pristine (black) and oxidized (red) DWNTs, respectively.
8 References 1. Qu, L.; Peng, X. Control of Photoluminescence Properties of CdSe Nanocrystals in Growth. J. Am. Chem. Soc. 2002, 124, 2049-2055. 2. Liu, I. S.; Lo, H.-H.; Chien, C.-T.; Lin, Y.-Y.; Chen, C.-W.; Chen, Y.-F.; Su, W.F.; Liou, S.-C. Enhancing Photoluminescence Quenching and Photoelectric Properties of CdSe Quantum Dots with Hole Accepting Ligands. J. Mater. Chem. 2008, 18, 675-682. 3. Katari, J. E. B.; Colvin, V. L.; Alivisatos, A. P. X-ray Photoelectron Spectroscopy of CdSe Nanocrystals with Applications to Studies of the Nanocrystal Surface. J. Phys. Chem. 1994, 98, 4109-4117. 4. Li, R.; Ji, W.; Chen, L.; Lv, H. M.; Cheng, J. B.; Zhao, B. Vibrational Spectroscopy and Density Functional Theory Study of 4-mercaptophenol. Spectrochim. Acta A -Molecular and Biomolecular Spectroscopy, 2014, 122, 698-703. 5. Young, A. G.; McQuillan, A. J.; Green, D. P. In Situ IR Spectroscopic Studies of the Avidin−Biotin Bioconjugation Reaction on CdS Particle Films. Langmuir 2009, 25, 7416-7423. 6. Liu, C.; Lee, S.; Su, D.; Zhang, Z.; Pfefferle, L.; Haller, G. L. Synthesis and Characterization of Nanocomposites with Strong Interfacial Interaction: Sulfated ZrO2 Nanoparticles Supported on Multiwalled Carbon Nanotubes. J. Phys. Chem. C 2012, 116, 21742-21752. 7. Wang, Z.; Wu, L.; Zhou, J.; Cai, W.; Shen, B.; Jiang, Z. Magnetite Nanocrystals on Multiwalled Carbon Nanotubes as a Synergistic Microwave Absorber. J. Phys. Chem. C 2013, 117, 5446-5452. 8. Banerjee, S.; Hemraj-Benny, T.; Balasubramanian, M.; Fischer, D. A.; Misewich, J. A.; Wong, S. S. Surface Chemistry and Structure of Purified, Ozonized, Multiwalled Carbon Nanotubes Probed by NEXAFS and Vibrational Spectroscopies. ChemPhysChem 2004, 5, 1416-1422. 9. Kuznetsova, A.; Popova, I.; Yates, J. T.; Bronikowski, M. J.; Huffman, C. B.; Liu, J.; Smalley, R. E.; Hwu, H. H.; Chen, J. G. G. Oxygen-containing Functional Groups on Single-wall Carbon Nanotubes: NEXAFS and Vibrational Spectroscopic Studies. J. Am. Chem. Soc. 2001, 123, 10699-10704. 10. Leon, V.; Parret, R.; Almairac, R.; Alvarez, L.; Babaa, M. R.; Doyle, B. P.; Ienny, P.; Parent, P.; Zahab, A.; Bantignies, J. L. Spectroscopic Study of Double-walled Carbon Nanotube Functionalization for Preparation of Carbon Nanotube / Epoxy Composites. Carbon 2012, 50, 4987-4994.
Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400 b
Condensed Matter Physics and Materials Sciences Department,
Brookhaven National Laboratory, Building 480, Upton, NY 11973 c
Department of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 d
Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20889 e
School of Marine and Atmospheric Sciences,
State University of New York at Stony Brook, Stony Brook, NY 11794-5000
2
Figure S1. TEM images of (A) pristine and (B) purified DWNTs.
3
Figure S2. (A) UV-visible spectra of as-prepared CdSe QDs possessing average diameters of 2.3, 3.0, and 4.1 nm, respectively. (B) XRD patterns of as-prepared CdSe QDs (measuring 3.0 nm in diameter). The corresponding literature database standard (JCPDS #08-0459) is shown immediately below and is highlighted in red.
4
Figure S3. FT-IR spectra of as-prepared and of MTH-capped CdSe QDs, possessing average diameters of 4.1 nm. Comments on IR Characterization. For ‘native’, as-prepared CdSe QDs, a popular surface capping agent typically used is TOPO.1 In our system, the sharp P=O stretch associated with TOPO located near 1147 cm-1 is red-shifted to 1070 cm-1 and is strongly broadened, which could imply the presence of multi-dentate coordination through the occupation of bridging sites on the Cd surface.2, 3 Such distinctive peak is absent in our MTH-capped CdSe QDs, and is replaced by a sharp peak at 1040 cm-1, corresponding to the C-S stretching mode and indicative of a successful ligand substitution process.4 Moreover, the absence of a distinctive S-H peak
5 located near 2400-2500 cm-1 suggests that all of the pendant thiol moieties in these ligands are likely to be completely bound onto the surfaces of the CdSe QDs.5 In terms of other noticeable peaks, the ligand-exchanged MTH-capped QDs are known to give rise to characteristic peaks for aromatic rings near the 1530-1600 cm-1, 1400-1500 cm-1, and 1160-1175 cm-1 regions, and these have been assigned to the C=C asymmetric stretching mode, the C=C symmetric stretching mode, and the C-H bending mode, respectively. As expected, the MTH-capped CdSe QDs highlight the presence of distinctive and broad OH stretching peaks near 3260 cm-1, characteristic of the phenol groups within MTH.
6
Figure S4. C K-edge and O K-edge NEXAFS spectra of pristine and oxidized DWNTs.
NEXAFS Data C K-edge data gave rise to prominent transitions at 285 eV, 292-294 eV, and 301– 309 eV, respectively, corresponding to a sharp C 1s to C=C π* (ring) transition, three C 1s to C-C σ* (ring) transitions,6, 7 as well as broad (π + σ) transitions, respectively.8 After oxidation of the DWNTs, specific transitions at ~288.1 and 289.1 eV, which can attributed to the π* states of carbonyl groups associated with –COOH as well as of σ* states associated with C-O functionalities,9 became more prominent. The corresponding O K-edge data associated with the oxidized DWNTs evinced several distinctive peaks. Specifically, the peak at 531.6 eV corresponds to the C=O π* transition, which originates from the carbonyl oxygen atom, while the peak at 534.8 eV can be assigned to the “-OH” moiety from the carboxylic group. The two broader peaks located at 539.6 and 543.8eV can be ascribed to the presence of non-equivalent σ* C-O bonds within the carboxylic acid group.8, 10
7
Figure S5. Raman D and G-band data of pristine (black) and oxidized (red) DWNTs, respectively.
8 References 1. Qu, L.; Peng, X. Control of Photoluminescence Properties of CdSe Nanocrystals in Growth. J. Am. Chem. Soc. 2002, 124, 2049-2055. 2. Liu, I. S.; Lo, H.-H.; Chien, C.-T.; Lin, Y.-Y.; Chen, C.-W.; Chen, Y.-F.; Su, W.F.; Liou, S.-C. Enhancing Photoluminescence Quenching and Photoelectric Properties of CdSe Quantum Dots with Hole Accepting Ligands. J. Mater. Chem. 2008, 18, 675-682. 3. Katari, J. E. B.; Colvin, V. L.; Alivisatos, A. P. X-ray Photoelectron Spectroscopy of CdSe Nanocrystals with Applications to Studies of the Nanocrystal Surface. J. Phys. Chem. 1994, 98, 4109-4117. 4. Li, R.; Ji, W.; Chen, L.; Lv, H. M.; Cheng, J. B.; Zhao, B. Vibrational Spectroscopy and Density Functional Theory Study of 4-mercaptophenol. Spectrochim. Acta A -Molecular and Biomolecular Spectroscopy, 2014, 122, 698-703. 5. Young, A. G.; McQuillan, A. J.; Green, D. P. In Situ IR Spectroscopic Studies of the Avidin−Biotin Bioconjugation Reaction on CdS Particle Films. Langmuir 2009, 25, 7416-7423. 6. Liu, C.; Lee, S.; Su, D.; Zhang, Z.; Pfefferle, L.; Haller, G. L. Synthesis and Characterization of Nanocomposites with Strong Interfacial Interaction: Sulfated ZrO2 Nanoparticles Supported on Multiwalled Carbon Nanotubes. J. Phys. Chem. C 2012, 116, 21742-21752. 7. Wang, Z.; Wu, L.; Zhou, J.; Cai, W.; Shen, B.; Jiang, Z. Magnetite Nanocrystals on Multiwalled Carbon Nanotubes as a Synergistic Microwave Absorber. J. Phys. Chem. C 2013, 117, 5446-5452. 8. Banerjee, S.; Hemraj-Benny, T.; Balasubramanian, M.; Fischer, D. A.; Misewich, J. A.; Wong, S. S. Surface Chemistry and Structure of Purified, Ozonized, Multiwalled Carbon Nanotubes Probed by NEXAFS and Vibrational Spectroscopies. ChemPhysChem 2004, 5, 1416-1422. 9. Kuznetsova, A.; Popova, I.; Yates, J. T.; Bronikowski, M. J.; Huffman, C. B.; Liu, J.; Smalley, R. E.; Hwu, H. H.; Chen, J. G. G. Oxygen-containing Functional Groups on Single-wall Carbon Nanotubes: NEXAFS and Vibrational Spectroscopic Studies. J. Am. Chem. Soc. 2001, 123, 10699-10704. 10. Leon, V.; Parret, R.; Almairac, R.; Alvarez, L.; Babaa, M. R.; Doyle, B. P.; Ienny, P.; Parent, P.; Zahab, A.; Bantignies, J. L. Spectroscopic Study of Double-walled Carbon Nanotube Functionalization for Preparation of Carbon Nanotube / Epoxy Composites. Carbon 2012, 50, 4987-4994.
