QIN Liqin, TAO Pingfang, ZHU Ligang, PEI Yuanjiao

(Guangxi Key Laboratory of Agricultural Resources Chemistry and Biotechnology, College of Chemistry and Food Science, Yulin Normal University, Yulin 537000, Guangxi, China)

Extended abstract:

[Background and purposes] Photocatalysis based on semiconductor catalysts is an effective method to treat environmental pollutants, so that the technology of photocatalysis has become one of the most important topics to solve environmental pollution. However, the limited utilization of sunlight and the recombination of photogenerated electron-hole pairs of typical photocatalysts limit their application. Indium oxide (In₂O₃) is an important n-type semiconductor and a photocatalyst with visible light activity, but it shows poor photocatalytic activity, owing to the recombination of photogenerated carriers. Construction of In₂O₃-based heterostructures is one of the most effective methods to suppress the recombination of photogenerated electrons and holes. g-C₃N₄, as a conjugate polymer photocatalyst, has excellent light absorption capacity, physical and chemical stability, environmental friendness, easy synthesis and low cost. The position of the conduction band and valence band of g-C₃N₄ is higher than that of In₂O₃, while the energy of g-C₃N₄ and In₂O₃ can match well, which can easily form a heterojunction.

[Methods] In this paper, microspheres of In₂O₃ photocatalyst were synthesized by using a one-step solvent method with ethanol and ethylamine as mixed solvents. Porous cubic In₂O₃ was prepared by using hydrothermal method, while g-C₃N₄ was prepared by using high-temperature solid-phase method. A series of In₂O₃/g-C₃N₄ microsphere composite photocatalysts and porous In₂O₃/-C₃N₄ cube composite photocatalysts with different compositions were synthesized by using physical mixing method. Structure, morphology and properties of the products were characterized by using XRD, SEM, DRS and PL. Photocatalytic activity of In₂O₃/-C₃N₄ composite photocatalysts were evaluated by using Rhodamine B (RhB) solution as a simulated dye.

[Results] XRD peaks of In₂O₃/-C₃N₄ well matched with those of the standard data of cubic phase In₂O₃ (PDF No 65-3170) and C₃N₄ (No 87-1526), confirming the formation of In₂O₃/-C₃N₄ composite photocatalyst with microsphere morphology. UV absorption edge of the In₂O₃/-C₃N₄ microsphere composite photocatalysts with different contents of In₂O₃ shifts relatively to g-C₃N₄, among which the redshift of sample R-IC-10 is most obvious. When the content of R-In₂O₃ is 10%, fluorescence intensity of the In₂O₃/-C₃N₄ microsphere composite photocatalyst is the lowest, indicating that the degree of e⁻ and h⁺ combination is reduced. When the content of In₂O₃ microspheres is 10%, the In₂O₃/-C₃N₄ composite photocatalyst has the highest photocatalytic activity. After visible light irradiation for 80 min, photocatalytic degradation rate of 0.1g In₂O₃/-C₃N₄ composite photocatalyst for Rhamine B is 95.7%.

[Conclusions] When the mass fraction of In₂O₃ microspheres is 10, the In₂O₃/-C₃N₄ composite photocatalyst has the strongest photocatalytic activity. After visible light irradiation for 80 min, photocatalytic degradation rate of the 0.1g In₂O₃/-C₃N₄ composite photocatalyst for Rhamine B reached 95.7%, which is 2.3, 1.6 and 1.2 times of the degradation rate of single phase In₂O₃, microspheres g-C₃N₄ and porous cubic In₂O₃/-C₃N₄ , respectively. The degradation process of Rhodamine B by the In₂O₃-C₃N₄ composite photocatalyst obeyed the pseudo-first-order kinetic model, where the photocatalytic degradation of RhB was mainly contributed by h⁺ and·O₂⁻, while ·OH played a minor role.

Key words:In₂O₃; g-C₃N₄; composite photocatalyst; photocatalytic properties