Adsorption patterns of caffeic acid on titania: affinity, charge transfer and sunscreen applications

ABSTRACT

Several photo-induced processes contribute to titania-catalysed photodegradation of organic UV-absorbing compound, caffeic acid (CA), utilised as skin photoprotector in sunscreens containing titania. Optical transitions, channels of photoexcitations, and charge transfer state formation in anatase TiO₂ nanowire sensitised by CA are computed and analysed. Trends of charge transfer state formation are explored through modelling of non-adiabatic dynamics using reduced density matrix approach combined with density functional theory with Perdew–Burke–Ernzerhof functional, in the basis of plane waves, using Vienna Ab initio Simulation Package software. The electronic structure of the explored model shows signatures of quantum confinement of TiO₂ nanowire. A change of excitation energy provides control of either one of the possible channels for photoexcitations: (1) local excitation at either nanowire or CA-adsorbate or (2) photo-induced electron transfer from CA-adsorbate to titania. The conclusions obtained from this computational modelling deliver further understanding of the adsorption of catechol groups on the surface of titania nanowire that will help in designing titania-based materials least damaging to CA and skin.

KEYWORDS:

• TiO₂
• caffeic acid
• non-adiabatic molecular dynamics
• charge transfer
• sunscreen
• dye-senitised titania

Acknowledgments

We acknowledge discussions and editorial help from computational group members at The University of South Dakota: Stephanie Jean Jensen, Dayton Vogel, Wendi Sapp, Adam Erck, Mariah Hoffman, and Yulun Han.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Khaled Rashwan appreciates Joseph F. Nelson and Martha P. Nelson Scholarship Endowment for the support. We thank dean's opportunity fund of USD Arts and Science for supporting travel of Khaled Rashwan to the Sanibel Symposium. Authors acknowledge help of USD High Performance Computer cluster operated by Douglas Jennewein. The use of computational resources of National Energy Research Scientific Computing Center (NERSC) allocation award 88777 ‘Computational Modeling of Photo-Catalysis and Photo-Induced Charge Transfer Dynamics on Surfaces’, supported by the Office of Science of the DOE [contract No. DE-AC02- 05CH11231] is gratefully acknowledged. Dmitri Kilin acknowledges financial support NSF [grant number CHE-1413614] for method's development.