Elsevier

Applied Surface Science

Volume 420, 31 October 2017, Pages 303-312
Applied Surface Science

Full Length Article
Bismuth oxychloride homogeneous phasejunction BiOCl/Bi12O17Cl2 with unselectively efficient photocatalytic activity and mechanism insight

https://doi.org/10.1016/j.apsusc.2017.05.076Get rights and content

Highlights

  • BiOCl/Bi12O17Cl2 phasesjunctions are obtained by an one-pot hydrothermal process.

  • BiOCl/Bi12O17Cl2 shows higher degradation activity than BiOCl and Bi12O17Cl2.

  • It shows an universal photocatalytic activity for diverse contaminants degradation.

  • Enhanced charge separation is responsible for the enhanced degradation activity.

Abstract

Fabrication of homo/hetero-junctions by coupling of wide-band gap semiconductor and narrow-band gap semiconductor is desirable as they can achieve a decent balance between photoabsorption and photo-redox ability. Herein, a n-n type bismuth oxychloride homogeneous phasejunction BiOCl/Bi12O17Cl2 was developed by facilely manipulating the basicity in a one-pot hydrothermal process. Compared with BiOCl which only responds to UV light, the photo-responsive range is remarkably extended to visible region. The BiOCl/Bi12O17Cl2 phasejunctions show much higher photocatalytic activity than the single BiOCl and Bi12O17Cl2 toward degradation of methyl orange (MO) under simulated solar light. In particular, it presented a high photo-oxidation ability in degrading diverse industrial contaminants including 2,4-dichlorophenol (2,4-DCP), phenol, bisphenol A (BPA) and tetracycline hydrochloride. Based on a series of photoelectrochemical and photoluminescence measurements, the fortified photocatalytic performance of BiOCl/Bi12O17Cl2 phasejunctions was manifested to be attributed to the efficient separation and transfer efficiencies of photoinduced electron-hole pairs because of the junctional interface formed between BiOCl and Bi12O17Cl2. The study may not only furnish a high-effective photocatalyst in the application of environment purification, but also pave a path to fabricate agnate phase-junctional photocatalyst.

Graphical abstract

BiOCl/Bi12O17Cl2 phasejunctions show much higher photodegradation activity than the single BiOCl and Bi12O17Cl2 and universal photocatalytic activity for treating diverse c ontaminants.

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Introduction

Since 1970s, photocatalysis has gradually developed and occupied an important position in the application of removal of industrial pollutions and production of renewable energy[1], [2], [3]. As an environment-friendly technology, the final degradation product of photocatalysis is harmless CO2, water and inorganic ions. And the photocatalysis technology is also popular for low energy consumption and mild reaction condition, etc[4], [5], [6]. Traditional semiconductor photocatalyst such as TiO2 generally has the wide band that can only absorb the ultraviolet part of the sunlight. Recently, many visible-light-driven phtotocatalysts have been developed. However, there are still some inherent drawbacks for their application, such as the high recombination rate of its photogenerated electron-hole pairs. Therefore, it is necessary to develop effective strategies to improve the charge separation efficiency and enhance the visible-light photocatalytic activity of photocatalysts. Among the various techniques, constructing heterojunctions between different materials could be an effective strategy to boost the visible-light photocatalytic activity by improving the electron–hole pairs separation and interfacial charge transfer efficiency[7], [8], [9], [10], [11], [12], [13], [14].

In recent years, the layered bismuth-based photocatalytic materials have attracted extensive interest among scientists for their good photocatalytic activity under illumination with UV or visible light, as well as their high photochemical stability [15], [16], [17], [18], [19], [20], [21], [22], [23] .These layered bismuth-based photocatalytic materials not only includes the bismuth halides BiOX (X = Cl, Br, or I), but also contains some newly discovered ones by our group, such as Bi2O2[BO2(OH)] [24], Bi2O2(OH)(NO3) [25], MBiO2Cl (M = Sr, Ba) [26], LiBi3O4Cl2 [27], Bi2MO4Cl (M = Eu, Gd) [28], MBiO2Br (M = Sr, Ba) [29], [30], Bi4NbO8Br [31], BiOIO3 and Bi(IO3)3 [32]. Among the bismuth halide photocatalysts, BiOCl, with a bandgap of 3.2–3.5 eV, shows good photocatalytic performance under UV light irradiation [33], [34], [35]. And its special layered structure feature provides the self-built internal static electric fields that can promote the effective separation of the photoinduced electron–hole pairs. Although BiOCl exhibits excellent photocatalytic degradation properties under UV-light, the lights owning long wavelength cannot be absorbed absolutely, such as visible light [36], [37], [38], [39], [40].

Bi12O17Cl2 is a narrow band gap semiconductor, whose band gap is merely 2.22 eV [41]. With a quick charge recombination rate, Bi12O17Cl2 possess poor properties for the degradation of pollutants. Effective approach to enhance the photocatalysis performance of Bi12O17Cl2 is introduced by researchers recently. For instance, the photocatalytic degradation properties of Bi12O17Cl2 are optimized by engineering BiOI/Bi12O17Cl2 heterojunction. In view of the high oxidation ability of BiOCl and benign visible-light absorption ability of Bi12O17Cl2, engineering BiOCl/Bi12O17Cl2 junction is of great interest to gain an efficient photocatalyst.

In this article, we develop the bismuth oxychloride homogeneous phasejunction BiOCl/Bi12O17Cl2 by simply controlling the basicity in one-pot hydrothermal preparation process. The photocatalysis oxidation degradation properties of obtained products are systematically demonstrated by degradation of a series of dyes, pharmaceutical and industrial contaminants, containing methyl orange (MO), 2,4-dichlorophenol (2,4-DCP), phenol, bisphenol A (BPA) and tetracycline hydrochloride. The photocatalytic tests show that the BiOCl/Bi12O17Cl2 junction presents unselectively excellent photocatalytic activity for degrading pollutants under simulated solar irradiation, much higher than those of either individual BiOCl or Bi12O17Cl2. The reactive species for the contaminants degradation were determined by the active species experiments. The mechanism for the improvement of photocatalytic performance over the BiOCl/Bi12O17Cl2 composites was studied in detail. The high separation efficiency for photogenerated electron-hole pairs contributes to the enhanced photocatalytic activity. Our work shed a new light on the synthesis of novel agnate junctional photocatalysts based on bismuth halides.

Section snippets

Synthesis of BiOCl/Bi12O17Cl2 heterojunction

All the reagents used were AR grade and without further purification. BiOCl/Bi12O17Cl2 heterojunction was obtained by a hydrothermal method. In a typical procedure, BiCl3 (3 mmol) was added into 15 ml ethanol and sonicated for 20 min until the BiCl3 was dissolved. Meanwhile, a certain amount of 1 M NaOH was dissolved in 15 ml deionized water to obtain a clear solution. Then the NaOH solution was added dropwise into the BiCl3 ethanol solution under stirring. After being stirred for 1 h under room

Crystal structure, composition and microstructure

The XRD patterns of BiOCl, Bi12O17Cl2 and BiOCl/Bi12O17Cl2 phasejunctions were shown in Fig. 1. The diffraction peaks of BiOCl and Bi12O17Cl2 could be separately ascribed to the tetragonal BiOCl (JCPDS#6-249) and tetragonal Bi12O17Cl2 (JCPDS#37-702). With the increase of NaOH amount, the intensities of characteristic BiOCl (001), (101), and (102) peaks at 12.0°, 25.9° and 33.4° gradually weaken, and the relative peak intensity of Bi12O17Cl2 gradually enhanced. It indicates the increase of the Bi

Conclusions

BiOCl/Bi12O17Cl2 phaseojunctions were fabricated by a one-pot in situ hydrothermal method. The light absorption of as-obtained BiOCl/Bi12O17Cl2 samples is extended to visible light range compared to BiOCl which is only responsive to UV light. The photodegradation of MO of BiOCl/Bi12O17Cl2 under simulated solar irradiation was significantly improved comparing with the pure samples. Particularly, it also exhibited a high photo-oxidation ability in degrading various industrial contaminants

Acknowledgements

This work was jointly supported by the National Natural Science Foundations of China (No. 51672258 and 51572246), the Fundamental Research Funds for the Central Universities (2652015296)

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