The effect of oxidative functionalization of carbon nanotubes on the morphological, optical, and photoelectrochemical properties of modified titanium dioxide photoanodes

• Published in: Journal of materials science Vol. 58; no. 12; pp. 5372 - 5388
• Main Authors: Peón-Díaz, Francisco J., del Río, Rodrigo Segura, Hevia, Samuel, Olivares, Fernanda, Expósito-Gálvez, Juan Carlos, Escalante, Renán, Valadez-Villalobos, Karen, Riquelme, Antonio J., Oskam, Gerko, Henríquez, Ricardo
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-03-2023; Springer; Springer Nature B.V
• Subjects: Analysis; Arc lamps; Carbon nanotubes; Characterization and Evaluation of Materials; Chemical synthesis; Chemical vapor deposition; Chemistry and Materials Science; Classical Mechanics; Crystallography and Scattering Methods; Electronic materials; Electrons; Energy Materials; Functional groups; Homogeneity; Materials Science; Morphology; Nanotubes; Optical properties; Optimization; Oxidation; Photoanodes; Polymer Sciences; Solid Mechanics; Substrates; Sulfuric acid; Titanium dioxide; Xenon
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-023-08351-4

In this work, we demonstrate the influence of the oxidative treatment of carbon nanotubes (CNTs) on the morphological, optical, and photoelectrochemical properties of CNTs-TiO
2
photoanodes. CNTs were synthesized by a chemical vapor deposition method (CVD) and subsequently oxidized in a mixture of HNO
3
/H
2
SO
4
to introduce nitrogen- and oxygen-containing functional groups. The oxidation time was varied (45, 90, and 180 min) to obtain CNTs with different oxidation levels (CNTs-ox). Pristine and oxidized CNTs were deposited on ITO and used as substrates to fabricate ITO/CNTs/TiO
2
photoelectrodes by depositing a TiO
2
thin layer using a CVD procedure. The extent of oxidation of the CNTs was found to directly influence the homogeneity and morphology of the TiO
2
overlayer, its physical stability, and the optical and photoelectrochemical properties of the photoelectrodes. An optimum oxidative treatment was achieved for 90 min, leading to a CNTs-ox/TiO
2
electrode with the best performance. Compared to shorter and longer times, this sample showed the smallest bandgap and the best homogeneity of TiO
2
growth on the CNTs' surface. Optimal photoelectrochemical performance was also found for this sample (160 μA/cm
2
at 0 V vs. Ag/AgCl) in KCl (0.1 M) electrolyte (100 mW/cm
2
, Xenon arc lamp).
Graphical Abstract