Abstract
Bismuth oxide has been widely studied as an important oxide with wide application in industry area. Our former work indicates that γ-Bi2O3 presents high visible-light photocatalytic activity. In this paper, a series of γ-Bi2O3/Fe2O3 samples with different content of Fe2O3 were prepared by sol-gel method. The visible-light photocatalytic activity of γ-Bi2O3/Fe2O3 composites was evaluated by degradation of RhB. The result shows that the photocatalytic activity of composite photocatalyst changes with the content of Fe2O3. When the composite content is under 30 wt. %, the photocatalytic activity of the samples is enhanced comparing to γ-Bi2O3. The best composite content is 10 wt. %. In addition, the photocatalytic mechanism of this kind of composite photocatalyst is discussed.
Keywords: γ-Bi2O3/Fe2O3; visible light; photocatalytic
1. Introduction
As an important semiconductor, bismuth oxide has been gotten widely application in the field of gas sensors, superconductors, catalysts, solid-state electrolytes, and so on. [1-4]. Bismuth oxide exist four common polymorphs including monoclinic α-Bi2O3, tetragonal β-Bi2O3, cubic (BCC) γ-Bi2O3, and cubic (FCC) δ-Bi2O3 [4]. Our early research shows that γ-Bi2O3 presents high visible-light photocatalytic activity [5]. So, further research on γ-Bi2O3 is valuable.
Constructing a heterojunction interface between the semiconductors with matching band potentials is a useful method that has been extensively adopted to enhance the photocatalytic activity due to its advantage of promoting the separation of photo-induced electron-hole pairs. So far, variety of Bi2O3 coupled semiconductor systems, including TiO2/Bi2O3 [6], BiVO4/Bi2O3 [7], BiOCl/Bi2O3 [8], SrTiO3/Bi2O3 [9], ZrTiO4/Bi2O3 [10], CeO2/Bi2O3 [11], NiO/Bi2O3 [12], were reported to be efficient photocatalysts under visible light irradiation. In fact, Bi2O3 in all above couples is of monoclinic phase and serves as an assistant catalyst, whose photocatalytic activity is much lower than that of γ-Bi2O3 [5].中国名优茶机械的开发利用与发展
The band gap of Fe2O3 is about 2.2 eV¬, less than that of γ-Bi2O3 [5, 13], which means it can absorb visible-light more efficiently. Thereby Fe2O3 is expected to make up the shortage of γ-Bi2O3 in utilizing visible-light. The preparation of γ-Bi2O3 is difficult because it is a metastable phase material at room temperature [4]. So, study on photocatalytic activity of γ-Bi2O3¬ composites has not been reported. In this paper, γ-Bi2O3/Fe2O3 composites are synthesized successfully and it is expected that the visible-light photocatalytic activity of γ-Bi2O3 can be strengthened via compositing.
2. Experimental
2.1. Materials
Bi(NO3)3•5H2O, NaOH, cetyl trimethyl ammonium bromide (CTAB), nitric acid, FeCl3, hydrochloric acid, absolute alcohol, distilled water, rhodamin B (RhB). All chemicals (Sinopharm Chemical Reagent Beijing Co., Ltd) were of analytic grade and used as received
2.2. Preparation of γ-Bi2O3/Fe2O3(x)
First, γ-Bi2O3 powders with rod-like morphology were prepared using chemical precipitation method [5]. FeCl3 (AR grade) and HCl solution with concentration of 3 mol/L, 0.2 mol/L were prepared respectively. 1.35 ml HCl solution and 133.2 ml deionized water were added into 0.45 ml FeCl3 solution successively, while the solution was vigorously stirred. The resultant solution was stirred at 90 oC for 24 h to form Fe2O3 sol. Then a certain amount of γ-Bi2O3 was added into stoichiometric amount of Fe2O3 sol and the suspension was stirred at 80 oC until it changes into gelatin powders. Finally gelatin powders were heat-treated at 500 oC for 2 h in air to obtain a series of samples γ-Bi2O3/Fe2O3(x), (x: 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, 50 wt.%, 60 wt.%, 80 wt.%). TiO2 (Degussa P25) was annealing at 500 oC for 8 h in nitrogen atmosphere to form TiO2-xNx as reference sample.2377