Enhanced photocatalytic activity of direct Z -scheme Bi 2 O 3 /g-C 3 N 4 composites via facile one-step fabrication
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Difa Xu,b) Xiangchao Zhang, and Mengyao Shen Hunan Key Laboratory of Applied Environmental Photocatalysis, Changsha University, Changsha 410022, People’s Republic of China (Received 26 January 2018; accepted 12 March 2018)
Coupling oxidation type semiconductors is a feasible strategy to improve the photocatalytic activity of reduction type g-C3N4 photocatalysts. In this work, Bi2O3 was used as an oxidation type semiconductor to construct direct Z-scheme Bi2O3/g-C3N4 photocatalysts by a one-step calcination method. The obtained Bi2O3/g-C3N4 composites exhibited excellent photocatalytic activity and stability toward methylene blue degradation under visible light irradiation. The composite with 1% weight content of Bi2O3 to g-C3N4 exhibited the highest photocatalytic activity with an apparent rate constant of 0.063 min1, which was 3.0 and 3.7 times higher than that of pure Bi2O3 and g-C3N4, respectively. The enhanced photocatalytic activity of the Bi2O3/g-C3N4 composite was mainly attributed to the improved charge separation efficiency and stronger redox ability. This work gave a new insight in developing g-C3N4-based Z-scheme heterojunction photocatalysts with enhanced photocatalytic activity.
I. INTRODUCTION
Photocatalytic degradation is a promising purification technology for the organic pollutant elimination in water.1–5 Under light irradiation, the excited photocatalysts produce photogenerated electrons (e) and holes (h1). Subsequently, some of the separated carriers can be converted into hydroxyl radicals (_OH) and superoxide radicals (_O2) with strong oxidation ability. These oxidizing species, such as h1, _OH, and _O2, play important roles in photocatalytic degradation. However, the photocatalytic activity of the photocatalysts is generally limited by two facts of weak visible light response and rapid charge carrier recombination. It is crucial to construct a photocatalytic system with wide spectral response and high charge carrier separation efficiency. Meanwhile, the expected photocatalysts must be stable, inexpensive, easily available, and environment friendly.2 Bismuth oxide (Bi2O3) is one of the chemically stable metal oxides with six different polymorphs including a-, b-, c-, d-, x-, and e-polymorph.6,7 Among them, a- and b-Bi2O3 are mostly investigated due to their visible light response ability and high thermal stability.8–10 The band gap of a- and b-Bi2O3 is about 2.8 and 2.5 eV corresponding to the absorption band edge of Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2018.67
440 and 500 nm, respectively. Moreover, Bi2O3 is one of the representative oxidation type semiconductors. The conduction band (CB) and valance band (VB) of b-Bi2O3 is 10.33 and 13.17 V versus NHE,6 respectively, suggesting its strong oxidation and weak reduction ability due to the relatively positive CB and VB position. Recently, metal-free graphite carbon nitride (g-C3N4) has attracted a broad attention since Wang et al. first find that g-C3N4 can gene
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