Band gap coupling in photocatalytic activity in ZnO–TiO2 thin films

Abstract

Zinc oxide and titanium dioxide composite thin films were prepared on Corning 7059 glass substrates by co-sputtering. The reactive gas-surroundings used was ultrahigh purity oxygen. To analyze the structural, optical and photocatalytic properties of the ZnO-TiO 2 samples, X-ray diffraction (XRD), atomic force microscopy (AFM), optical absorption, Raman spectroscopy and methylene blue bleaching were carried out at room temperature. XRD patterns indicate the presence of TiO 2 (anatase and rutile phases), ZnO, ZnTiO 3 , and Zn 2 TiO 4 crystalline structures. AFM images allow the observation of non-homogeneous surface in the ZnO-TiO 2 system, suggesting the separation of different crystalline phases in the composite. Raman studies exhibit different spectra in the films depending on the area analyzed, which can be interpreted as a result of the existence of well separated crystalline regions as seen in AFM images. The photocatalytic activity (PA) of TiO 2 -ZnO-ZnTiO 3 -Zn 2 TiO 4 composite, as expected for adequate coupling semiconductors, is larger than PA of ZnO and TiO 2 oxides, used as references. A simple proposal about the probable alignment of the conduction band, the valence band, and the Fermi level is included. E. García-Ramírez · M. Mondragón-Chaparro ESIME Azcapotzalco, Instituto Politécnico Nacional,

Atomic layer deposition of TiO2-nanomembrane-based photocatalysts with enhanced performance

“…In present case, we consider 6, 115113 (2016) that the enhancement of the photocatalytic performance is due to the band gap coupling among the different materials in the composite leading to a better charge separation and transportation, which in turn increases the lifetime of charge carriers by reducing their recombination-rate. 8,9,41 Correspondingly, the diffusion length of electrons and holes to reach the interface oxide-organic material is increased. 8 Additional factor that can contribute to the increase of photocatalytic activity is the presence of a high electric conductive phases of ZnO with a better conductivity property, which leads to an increase of the probability of the carriers reaching the photocatalyst/solution interface.…”

“…8 Additional factor that can contribute to the increase of photocatalytic activity is the presence of a high electric conductive phases of ZnO with a better conductivity property, which leads to an increase of the probability of the carriers reaching the photocatalyst/solution interface. 8 In addition, the evolution of photocatalytic activities of the TZO composites with different ZnO concentrations (TZO1: TiO 2 (10)/ZnO(1), 20 loops, TZO2: TiO 2 (10)/ZnO(5), 15 loops, and TZO3: TiO 2 (10)/ZnO(10), 11 loops) is exhibited in Fig. 5(c).…”

“…[1][2][3][4][5][6] Especially, oxides semiconductor such as titanium dioxide (TiO 2 ), zinc oxide (ZnO) and related structures have attracted attention for applications in photocatalysis, gas sensing, and photovoltaic cells. [7][8][9][10][11][12] The enhancement of photocatalytic properties of the TiO 2 -ZnO composite structure, in comparison with TiO 2 oxide has been reported. 8,9,13 It is believed that the coupling of anatase and rutile TiO 2 with ZnO can achieve a more efficient electronhole pair separation under illumination and, consequently, a higher reaction rate.…”

“…[7][8][9][10][11][12] The enhancement of photocatalytic properties of the TiO 2 -ZnO composite structure, in comparison with TiO 2 oxide has been reported. 8,9,13 It is believed that the coupling of anatase and rutile TiO 2 with ZnO can achieve a more efficient electronhole pair separation under illumination and, consequently, a higher reaction rate. 14,15 Specifically, the electronic properties modification of the composite materials is invoked to explain this behavior: the electron transfer from the conduction band of ZnO to the conduction band of TiO 2 under illumination and, conversely, the hole transfer from the valence band of TiO 2 to the valence band of ZnO give rise to a decrease of the pairs recombination rate, i.e., to an increase of their lifetime.…”

Characterization and photocatalytic activity of Ti/TinOm ∙ ZrxOy coatings for azo-dye degradation

“…The effective way to increase the spectral sensitivity of the material is doping the semiconductor nanostructures with transition metal oxides in the quantity of 1-10% wt. [8][9][10][11][12][13].…”