In-situ hydrothermal synthesis of Bi6O6(OH)3(NO3)3·1.5H2O-BiOCl heterojunction with highly photocatalytic hydrogen evolution activity

Abstract

With the increasing demand and excessive use of fossil energy, energy shortage has become a problem in today’s world [1–2]. Hydrogen is a clean energy source that can reduce the dependency on traditional fossil fuels, and photocatalysis is considered as the most potential hydrogen evolution method [3–5]. Bi6O6(OH)3(NO3)3$1.5H2O (BHN), an incomplete hydrolysate of Bi(NO3)3$5H2O, shows good performance in terms of the photocatalytic degradation due to its non-toxicity and corrosion resistance [6–7]. However, the photocatalytic efficiency of BHN is limited owing to its wide band gap, low quantum efficiency and fast electron–hole recombination [8–9]. Constructing a heterojunction structure between semiconductors can reduce the recombination of photogenerated electron– hole pairs and enhance the quantum efficiency [10–11], which may significantly enhance the photocatalytic activity of semiconductors. At present, some reported composite materials such as BHN/BiOCl [12], BHN/Bi2WO6 [13], BHN/BiVO4 [14] and BHN/BiOBr [15] exhibit high photocatalytic degradation activity. As a promising layered photocatalytic material for environmental remediation, BiOCl (BOC) is characterized with the indirect-transition band gap that makes excited electrons travel a certain k-space distance to reach the valence band, thereby reducing the recombination of electrons and holes [16]. At the same time, the open layered structure composed of [Bi2O2] 2+ layers and Cl layers also can promote the separation of photogenerated electrons and holes [17–18]. However, the wider optical band gap and the higher electron–hole recombination rate may lead to the lower photocatalytic activity of BOC [19– 20]. To solve this problem, heterojunction structures with other semiconductors have been constructed, which effectively improve the photocatalytic activity [21–23], such as Bi2O2CO3/BiOCl [24], ZnIn2S4/BiOCl [25], BiOCl/TiO2 [26–27], BiOCl/Bi2S3 [28] and BiOCl/CdS [29]. Herein, BHN was prepared by a hydrothermal method, and then BHN was used as the Bi source to further synthesize the BHN–BOC composite by the in-situ hydrothermal method. The light absorption range of the prepared composite was obviously broadened, and the separation ability of photogenerated carriers and the migration efficiency of surface electrons were significantly enhanced. Therefore, the hydrogen generation of the composite is clearly higher than that of either pure BHN or pure BOC. Bi(NO3)3$5H2O and KCl were obtained from Shanghai Macklin Biochemical Co., Ltd., China. Ethylene glycol, alcohol and ethanol were purchased from Shanghai Titan Scientific Co., Ltd., China. Triethanolamine (TEOA) was purchased from Xilong Scientific Co., Ltd., China. At first 2 mmol Bi(NO3)3$5H2O was dissolved in 80 mL deionized water under magnetic stirring for 30 min at room temperature. Then, the above solution was transferred into Teflon-lined stainless-steel autoclaves (100 mL) and kept at 180 °C for 12 h. Subsequently it was washed several times with deionized water and ethanol separately, and finally dried at 60 °C for 3 h. The obtained sample was assigned as BHN. 1 College of Materials Engineering, Fujian Agriculture and Forestry