Preparation, characterization and activity evaluation of heterostructure In2O3/In(OH)3 photocatalyst
Introduction
Nanoparticles with a uniform size and shape have attracted much attention because of their technological and fundamental scientific importance, novel physical properties and potential applications in the areas such as optoelectronics, information storage, catalysis, and biosensors [1], [2]. The methods to control the synthesis of such nanoparticles have been extensively investigated [3], [4], [5]. As an n-type semiconductor oxide, indium oxide (In2O3) has been used widely as ultra-sensitive toxic gas detectors, transparent conductors, solar cells, flat panel displays, and other optoelectronic devices etc. [6], [7], [8], [9], [10]. Generally speaking, In2O3 can be obtained through the calcination of In(OH)3, which is prepared by hydrolysis of indium nitrate or other indium salts in NaOH aqueous solution or ammonia solution. Meanwhile, it is known that In(OH)3 is a wide-gap semiconductor material with a direct band gap of 5.15 eV and deep absorption in UV region [11]. As the photocatalysts, the preparation method, photocatalytic activity and electrochemical property of single In(OH)3 or In2O3 has been widely investigated. Wang and co-workers successfully synthesized the monodisperse single-crystalline In(OH)3 nanotubes and found it exhibited highly photocatalytic activity through the benzene removal [12]. Sulfur-substituted and zinc-doped In(OH)3 were synthesized and their photoactivity for H2 production under visible light illumination was also investigated [13].
Heterostructure semiconductor materials as the photocatalysts have become a highlight in recent years. It would be a beneficial solution for the disadvantages of the single photocatalyst such as rapid recombination of photogenerated carriers and the relative narrow spectrum response. Composite photocatalysts, such as ZnO/TiO2 [14], SnO2/ZnO, SnO2/TiO2, WO3/TiO2 [15], NiO/TiO2 [16], CuBi2O4/TiO2 [17], ZnO/In2O3 [18] etc. have been investigated extensively. The results showed that nearly all the composite semiconductors had higher photocatalytic activity than single ones. However, to the best of our knowledge, the synthesis and optical properties of the heterostructure In2O3/In(OH)3 photocatalyst have never been reported. Herein, we reported the preparation of the In(OH)3/In2O3 photocatalyst. The structure, morphologies, and optical properties of the In2O3/In(OH)3 were characterized by X-ray power diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectrometry (FT-IR), and transmission electron microscopy (TEM). Rhodamine B was selected as a model substrate to evaluate the photocatalytic activity of the samples under UV-illumination. The possible mechanism was also investigated.
Section snippets
Materials
Indium nitrate (In(NO3)3) was used as the In source. Ammonia solution (NH4OH), terephthalic acid (C8H6O4), sodium hydroxide (NaOH), rhodamine B (RhB) and other chemicals used in the experiments were of analytically pure grade. They were purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd. Deionized water was used throughout the experiment.
Preparation of heterostructure In(OH)3/In2O3
Heterostructure In(OH)3/In2O3 was prepared through programmed thermal treatment of In(OH)3 precursor. In(OH)3 precursor was produced via the
Results and discussion
The XRD patterns of In(OH)3 and In2O3 are shown in Fig. 1. In(OH)3 was prepared by calcination of precursor at 200 °C for 2 h. In2O3 was produced from In(OH)3 precursor through direct thermal treatment at 240 °C for 6 h. The diffraction peaks are in agreement with that reported in the JCPDS database card (No. 89-4595 and No. 85-1338). Fig. 1a shows a well-defined peak at 2θ = 22.26°, corresponding to the (2 0 0) plane of In(OH)3, the peaks at 2θ = 51.16° and 56.46° assigned to the (4 2 0) and (4 2 2) planes,
Conclusion
Heterostructure In2O3/In(OH)3 photocatalyst was prepared via programmed thermal treatment of In(OH)3 precursor. The photocatalytic activity of the heterostructure In2O3/In(OH)3 is higher than that of single In(OH)3 or In2O3. The reason for the increased photocatalytic activity may be attributed to the formation of the heterojunction between In2O3 and In(OH)3, which depresses the recombination of photoexcited electron–hole pairs.
Acknowledgements
This work was supported by the Natural Science Foundation of China (Nos. 20673042, 20973071) and the Key Project of Science and Technology Research of Ministry of Education of China (208062).
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