Effective charge separation in the rutile TiO2 nanorod-coupled α-Fe2O3 with exceptionally high visible activities

Abstract

Herein, we have fabricated rutile TiO2 nanorod-coupled α-Fe2O3 by a wet-chemical process. It is demonstrated that the visible activities for photoelectrochemical water oxidation and for degrading pollutant of α-Fe2O3 are greatly enhanced after coupling a proper amount of rutile nanorods. The enhanced activity is attributed to the prolonged lifetime and improved separation of photogenerated charges mainly by the transient surface photovoltage responses. Interestingly, the observed EPR signals (with g⊥ = 1.963 and g|| = 1.948) of Ti3+ in the fabricated TiO2-Fe2O3 nanocomposite at ultra low temperature (1.8 k) after visible laser excitation, along with the electrochemical impedance spectra and the normalized photocurrent action spectra, testify evidently that the spacial transfers of visible-excited high-energy electrons of α-Fe2O3 to TiO2 could happen. Moreover, it is confirmed that it is more favorable for the uncommon electron transfers of α-Fe2O3 to rutile than to anatase. This is responsible for the much obvious enhancement of visible activity of Fe2O3 after coupling with rutile TiO2, compared with anatase and phase-mixed P25 ones. This work would help us to deeply understand the uncommon photophysical processes, and also provide a feasible route to improve the photocatalytic performance of visible-response semiconductor photocatalyst for water splitting and pollutant degradation.

Enhanced visible-light activities of porous BiFeO3 by coupling with nanocrystalline TiO2 and mechanism

“…It can be seen clearly, that the fluorescence peaks intensity gradually increases with increase in amount of TiO 2 coupled, and the strongest fluorescence peak intensity is observed for 9T/P-BFO nanocomposite. Therefore, it is suggested that the enhanced visible-light photocatalytic activities of T/P-BFO nanocomposites for acetaldehyde and phenol degradation are mainly attributed to the significant increase in amount of OH -radicals produced [19,32].…”

Doping of TiO2as a tool to optimize the water splitting efficiencies of titania–hematite photoanodes

“…6,31 However, by applying electrochemical impedance spectroscopy, PEC and electron paramagnetic resonance studies, Luan et al evidently confirmed the occurrence of an uncommon transfer of visible-excited high-energy electrons from hematite to rutile TiO 2 . 32 It was suggested that in this process, the excited electrons in hematite populate different energy levels and while low energy electrons recombine with VB holes, high-energy electrons transfer to the CB of rutile. 6,32 Such uncommon electron transfer, leading to improved charge separation and enhanced PEC properties, was also observed in BiVO 3 -ZnO heterojunction photoanodes 33 and recently also for BiVO 3 -TiO 2 heterojunction photoanodes.…”

“…32 It was suggested that in this process, the excited electrons in hematite populate different energy levels and while low energy electrons recombine with VB holes, high-energy electrons transfer to the CB of rutile. 6,32 Such uncommon electron transfer, leading to improved charge separation and enhanced PEC properties, was also observed in BiVO 3 -ZnO heterojunction photoanodes 33 and recently also for BiVO 3 -TiO 2 heterojunction photoanodes. 6,34,35 In addition, the high efficiency could as well be explained on the basis of the formation of a rutile blocking layer.…”

Enhanced visible-light activities for PEC water reduction of CuO nanoplates by coupling with anatase TiO2 and mechanism

“…The photoelectrodes were illuminated with a 500 W Xenon lamp to produce a visible light source with an intensity of 64 mW/cm 2 after utilizing a filter to remove light below the wavelength of 420 nm [15]. The steady-state surface photovoltage spectra (SS-SPS) instrument was a home-built apparatus as discussed elsewhere [20].…”

“…Based on our previous works [14,15], narrow band-gap semiconductors with low conduction band (CB) could be excited by visible light with energy higher than their band-gaps, hence the electrons in the valence band (VB) will be excited to the high energy level over bottom of the CB (high energy electrons). These high energy electrons could be transferred thermodynamically to the CB of another semiconductor.…”