Red-Shifted Absorptions of Cation-Defective and Surface-Functionalized Anatase with Enhanced Photoelectrochemical Properties

Abstract

Manipulating the atomic structure of semiconductors is a fine way to tune their properties. The rationalization of their modified properties is, however, particularly challenging as defects locally disrupt the long-range structural ordering, and a deeper effort is required to fully describe their structure. In this work, we investigated the photoelectrochemical properties of an anatase-type structure featuring a high content of titanium vacancies stabilized by dual-oxide substitution by fluoride and hydroxide anions. Such atomic modification induces a slight red-shift band gap energy of 0.08 eV as compared to pure TiO 2 , which was assigned to changes in titanium–anion ionocovalent bonding. Under illumination, electron paramagnetic resonance spectroscopy revealed the formation of Ti III and O 2 – radicals which were not detected in defect-free TiO 2 . Consequently, the modified anatase shows higher ability to oxidize water with lower electron–hole recombination rate. To further increase the photoelectrochemical properties, we subsequently modified the compound by a surface functionalization with N -methyl-2-pyrrolidone (NMP). This treatment further modifies the chemical composition, which results in a red shift of the band gap energy to 3.03 eV. Moreover, the interaction of the NMP electron-donating molecules with the surface induces an absorption band in the visible region with an estimated band gap energy of 2.25–2.50 eV. Under illumination, the resulting core–shell structure produces a high concentration of reduced Ti III and O 2 – , suggesting an effective charge carrier separation which is confirmed by high photoelectrochemical properties. This work provides new opportunities to better understand the structural features that affect the photogenerated charge carriers.

Effects of fluorine on photocatalysis

“…To inhibit the recombination of photo-driven eand h + , and/or to extend its light-response to the visible range, doping TiO2 with metal or non-metal elements has been extensively studied [63][64][65][66][67][68]. Yu et al [69] prepared highly photo-responsive F-doped nanocrystalline TiO2 via the hydrolysis of titanium tetraisopropoxide (TTIP) in NH4F solution.…”

Enhancing Photostability of Complex Lead Halides through Modification with Antibacterial Drug Octenidine

“…On the other hand, the accumulation of bulky cations mostly on the surface of the perovskite grains and at the grain boundaries was frequently reported [ 81 ]. Therefore, the surface and interface effects of OctI 2 can lead to the red shift of the absorption band edge [ 82 ]. In addition, the effect of OctI 2 loading on the optical properties of the perovskite films could be connected to the change in their nanoscale morphology, e.g., the formation of much bigger or smaller grains than in the reference non-modified systems [ 83 ].…”

“…Figure S9 ( Supplementary Materials ) shows the corresponding Tauc plots for the as-prepared reference and modified APbI 3 samples. The observed bathochromic shift of the absorption onset can be explained by the accumulation of bulky organic cations mostly on the surface of the perovskite grains and at the grain boundaries [ 82 ].…”

Preparation of Anatase Titanium Dioxide Nanoparticle Powders Submitting Reactive Oxygen Species (ROS) under Dark Conditions

“…However, their energy levels were smaller than those (3.61 and 3.64 eV) of No. 1 and 2, respectively; this might be due to the co-doping (K and P) effect (this phenomenon is usually called as red shift [26] [27] [41]. In addition, these values of pure anatase (No.1 and No.…”