Oriented Self-Assembled Monolayer of Zn(II)-Tetraphenylporphyrin on TiO 2 Electrode for Photoelectrochemical Analysis

• Published in: Analytical chemistry (Washington) 2019-02, Vol.91 (4), p.2759-2767
• Main Authors: Zhou, Yue, Shi, Yi, Wang, Feng-Bin, Xia, Xing-Hua
• Format: Article
• Language: English
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.8b04478

The photoelectrochemical performance of a zinc porphyrin sensitized TiO photoelectrode fabricated through the axial-coordination strategy has been studied. Zinc(II) tetraphenylporphyrin (TPPZn) was immobilized on the TiO electrode through the axial coordination reaction with surface premodified methyl 4-(1 H-imidazol-1-yl)benzoate (PhImMe). Spectral characterizations were carried out to confirm the robust interaction between TPPZn and PhImMe, while the chemical bonding of PhImMe on TiO surface has been evidenced by XPS measurement. The modified TiO electrode produces a stable and enhanced photocurrent signal under 410 nm irradiation at a bias of 0.2 V in phosphate buffer solution, compared with pristine TiO . A sensitive increment of the photocurrent is observed with the addition of l-glutathione. A possible mechanism for this photoelectrochemical process includes the photoexcitation of the porphyrin, electron injection from porphyrin toward the TiO , and the hole-scavenging process by the reductants. The "lying-low" surface conformation of the porphyrin plane might facilitate the PEC process owing to the enhanced electronic coupling between the porphyrin plane and the TiO substrate. A PEC analysis on l-glutathione has been carried out to evaluate the photoelectrochemical performance of the modified TiO electrode, which presents the wide linear ranges of 5-80 μM and 80-5000 μM, with a lower detection limit of 3.21 μM at an S/N ratio of 3. This work reports for the first time on the PEC performance of metalloporphyrin axially coordinated on a semiconductor surface and could lead to the designing of more efficient photoelectrochemical sensors and devices based on similar electrode structures.