Laser Tailoring of the Hierarchical Titania Towards Ultrafast and Scalable Surface Modification of Photoelectrode Materials
Authors: Siuzdak Katarzyna , Haryński Łukasz , Wawrzyniak Jakub , Kupracz Piotr , Grochowska Katarzyna 
Published: December 2020

Despite wide bandgap energy (3.2 eV) that corresponds to the UV-range, titania materials are still widely used in many processes driven by light. Their doping by non-metal atoms, modification by metal and metal oxide nanoparticles, deposition of conducting polymers or halides, significantly affect the absorption spectra and thus makes the material more useful when exposed to solar light. Most of the undertaken efforts are based on the wet chemistry methods, electrochemical deposition, chemical vapour or atomic layer deposition techniques. Those strategies were also applied for titania nanotubes fabricated via anodization that ensures hierarchical growth of the TiO2 out of the Ti substrate. Such a synthesis method exhibits other important features – the morphology of nanotubes (NTs) can be tuned by changing anodization parameters while any further material immobilization is not required that facilitates titania usage as electrode material or a platform for photocatalytic processes. Nevertheless, one may have impression that some threshold is reached regarding boosting of the optical and electrochemical properties using those procedures and therefore a novel approach towards facile titania NTs modification is needed.
Herein, the rapid and easily scalable method based on the direct laser interaction with the titania NTs covered substrate is proposed. In our experimental works we used pulsed Nd:YAG laser operating at different wavelengths: 266, 355 and 532 nm with optimized fluence and scanning speed. The controlled movement of the sample with the titania nanotubes enables modification within the selected area. The irradiation of the titania nanotubes can be realized: a) just after anodization leading to the phase conversion from the amorphous to the crystalline one [1] or b) after calcination – resulting in partial surface melting [2] or selective encapsulation of hollow tubes. Moreover, laser formation of the metal/metal oxide nanoparticles out of the thin metal layer deposited formerly onto the TiO2NTs surface is also possible. The electrochemical investigations of prepared materials show that intense light-matter interaction leads to the enhancement of the photoactivity defined here as a photocurrent density even by 45% and to increment of donor density by 2 orders of magnitude while the flatband potential shifts positively by 0.74 V. Thus, even without introduction of foreign chemical compounds the significant improvement of electrochemical and photoelectrochemical performance can be achieved while the ordered morphology can be completely preserved or just some side selective tailoring is possible.
This work received financial support from the Polish National Science Centre: grant no 2017/26/E/ST5/00416
[1] Ł. Haryński, K. Grochowska, P. Kupracz, J. Karczewski E. Coy, K. Siuzdak, Nanomaterials 10 (2020) 430
[2] Ł. Haryński, K. Grochowska, J. Karczewski, J. Ryl, K. Siuzdak, ACS Applied Materials and Interfaces 12 (2020) 3225-3235