Inorganic Control of Interfacial Charge-Transfer Transitions in Catechol-Functionalized Titanium Oxides Using SrTiO₃, BaTiO₃, and TiO₂

Abstract

Charge-transfer transitions at the interface between wide band gap semiconductors and organic compounds have new potentialities in optical functions such as chemical sensing and solar energy conversion. A feature of interfacial charge-transfer (ICT) transitions is the flexible wavelength controllability based on the combination of various organic and inorganic materials. The organic control of ICT transitions in the visible to near-IR region has been demonstrated with chemical modification of organic compounds. On the other hand, the inorganic control of ICT transitions has not yet been studied systematically. In order to demonstrate the inorganic control of ICT transitions, we comparatively study ICT transitions in catechol (CA)-functionalized titanium oxides using SrTiO3, BaTiO3, and anatase TiO2 nanoparticles. It has been reported that SrTiO3 and BaTiO3 have the higher-energy conduction band edge by ca. 0.4 and 0.3 eV, respectively, than that of anatase TiO2. CA-functionalized SrTiO3 and BaTiO3 show a broad ICT band in the visible region. The ICT bands are blue-shifted by 0.29 and 0.24 eV as compared to that of TiO2–CA. Ionization potential measurements reveal that the highest occupied molecular orbital level of CA chemisorbed on SrTiO3 and BaTiO3 is higher in energy by ca. 0.1 eV than that on TiO2, which gives no explanation of the blue shift observed for SrTiO3 and BaTiO3. From the experimental results, the blue shift of the ICT band in SrTiO3 and BaTiO3 is attributed to the higher-energy conduction band edges of SrTiO3 and BaTiO3 than that of TiO2. Our research demonstrates the inorganic controllability of ICT transitions based on the energy position of the conduction band edge of inorganic semiconductors.

Establishing Interfacial Charge-Transfer Transitions on Ferroelectric Perovskites: An Efficient Route for Photoelectrochemical Bioanalysis

“…Therefore, the energy level difference between the CB energy level of PbTiO 3 and HOMO energy level of PCA was about 1.71 eV, this value agreeing well with the absorption onset energy (726 nm, 1.71 eV) obtained from the UV–DRS spectrum. Together, these results validated that the new absorption feature in PbTiO 3 /PCA was caused by the ICTT transitions from the HOMO of PCA to CB of PbTiO 3 . Additional studies about the charge transfer characteristics of PbTiO 3 before and after PCA chelation were also performed using electrochemical impedance spectra (EIS) and surface photovoltage (SPV) spectra (Figure S4a and b).…”

“…Together, these results validated that the new absorption feature in PbTiO 3 / PCA was caused by the ICTT transitions from the HOMO of PCA to CB of PbTiO 3 . 15 Additional studies about the charge transfer characteristics of PbTiO 3 before and after PCA chelation were also performed using electrochemical impedance spectra (EIS) and surface photovoltage (SPV) spectra (Figure S4a and b).…”

Interfacial charge-transfer transitions in SnO2 functionalized with benzoic acid derivatives

“…However, inorganic semiconductors available for ICTT are quite limited to a few kinds of wide band-gap semiconductors (TiO 2 , SrTiO 3 , BaTiO 3 , ZnO). [37][38][39][40] Particularly, the exploration of ICTT in inorganic semiconductors with a lower-energy conduction band such as SnO 2 is a high-priority issue to realize the absorption of visible light with organic adsorbates possessing the deep highest occupied molecular orbital (HOMO) such as benzoic acid derivatives. In addition, SnO 2 is an important semiconductor for electronic and optoelectronic devices and chemical sensors due to the high electron mobility.…”

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

“…In this case, the position of the absorption band of the complex depends on the relative energy levels of the ligand's HOMO and the semiconductor's CB edge. It should be underlined that the HOMO and LUMO potentials of organic ligands are not absolute values, but the result to vary according to the semiconductor they are bound to [98,99].…”

“…Titanates, wide bandgap semiconductors with the perovskite crystal structure, also show interesting photocatalytic properties. Studies on the effect of catechol, salicylic acid, and 2,3-dihydroxynaphthalene on interfacial CT on TiO 2 , SrTiO 3 , and BaTiO 3 have been performed in relation to their band edge potentials [99,113], underlying a broad shift of the absorption onset and enhancement of the photoelectrochemical and photocatalytic properties, not only under visible light but also with UV irradiation. Orthoferrites are less known as perovskite materials in the photocatalysis field; ErFeO 3 functionalized with tartrate ligands was found to show multiple photoluminescence and a considerable photocatalytic activity [150].…”