Preparation, characterization and enhancement of the visible-light photocatalytic activity of In2O3/Na-bentonite composite

doi:10.1016/j.ceramint.2016.02.132

Ceramics International

Volume 42, Issue 7, 15 May 2016, Pages 8850-8855

https://doi.org/10.1016/j.ceramint.2016.02.132 Get rights and content

Abstract

To overcome the drawback of low photocatalytic efficiency brought by electron–hole recombination and low adsorbability of In₂O₃, we successfully synthesized In₂O₃/Na-bentonite composites using a sol-gel method by intercalating In₂O₃ nanoparticles into Na-bentonite matrices. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption measurements and UV–vis diffuse reflectance spectra (UV–vis DRS). The In₂O₃/Na-bentonite composite possesses a wide photoabsorption until 700 nm, which occupies nearly the whole range of the visible light. Compared with bare In₂O₃, the In₂O₃/Na-bentonite composite exhibits significantly enhanced photocatalytic activity for phenol degradation under visible light irradiation. On the basis of the the experimental results, the mechanism of enhanced photocatalytic activity was can be attributed to the effective separation of electron–holes pairs and high adsorbability. The present study provides a new strategy to design composite materials with enhanced photocatalytic performance of In₂O₃.

Introduction

Since Fujishima and Honda reported the evolution of oxygen and hydrogen from a TiO₂ electrode under the irradiation of light in 1972, photocatalysis has been attracting a growing interest because it provides a new promising way for environmental protection and remediation procedures such as water purification [1], [2]. Among various photocatalysts, titanium dioxide (TiO₂) has attracted much attention over the past decades because of its excellent properties such as nontoxicity, chemical and biological stability and the relatively high reactivity for the degradation of organic pollutants and so on [3], [4]. However, the broad band gap of TiO₂ (3.2 eV for anatase) makes it only responsive to high-energy UV light, resulting in low-efficiency in utilization of solar energy, which also limits its large-scale practical applications. In order to efficiently utilize solar light in the visible region, the development of visible light active photocatalysts has attracted a tremendous amount of attention.

In₂O₃, an indirect band gap of 2.8 eV, has been put forwarded as a novel photocatalyst that exhibits extremely high photooxidative capabilities for oxidation of water and photodecomposition of organic dyes under visible-light irradiation [5], [6]. However, the quick recombination of charge carriers is the major limitation in achieving high photocatalytic efficiency. Moreover, the bare In₂O₃ presents photoabsorption properties from UV light to visible light with wavelength of shorter than ca. 450 nm, which occupies a small part of the solar spectrum [7], [8]. Therefore, how to make In₂O₃ to improve the charge separation efficiency and extend the spectral responsive range in photocatalysis becomes an important subject for developing the In₂O₃-based photocatalysts. Very recently, some researcher intended to design a composite photocatalyst systems by coupling In₂O₃ with a narrow bandgap semiconductor or doping with matched band potentials, such as In₂O₃/ZnO [9], TiO₂/In₂O₃ [10], In₂O₃/In₂S₃ [11], Cr-doped Ba₂In₂O₅/In₂O₃ [12], N-doped and C-doped In₂O₃ [13], [14]. The well-established compound semiconductor could be employed to restrict the recombination of the charge carriers and enhance the photoelectrochemical efficiency under visible light. However, the In₂O₃-based photocatalysts has a small surface area and low adsorbability, and its photocatalytic effect is low in very dilute solutions. Hence, enrichment of reactants by adsorption is required for a highly efficient photocatalytic performance.

Recently, pillared clays nanomaterials have attracted growing attention because they can be used as photocatalysts for strong adsorption ability for organic pollutants and favors the charge separation, result in also good degradation property [15], [16], [17], [18]. Among these materials, the bentonite has attracted great attentions in environmental pollution treatment, because of numerous outstanding properties such as large surface area, excellent swelling ability, high sorption capacity, and low-cost [19], [20]. To the best of our knowledge, there is no report related to preparation or photocatalytic properties based on In₂O₃/bentonite composites, and embedding In₂O₃ articles into bentonite matrices is expected to improve the photocatalytic properties of the In₂O₃.

In this study, the In₂O₃/Na-bentonite composite was prepared by a sol-gel method for the first time. The photoactivity evaluation, via the photocatalytic degradation of phenol under visible light, demonstrated that the In₂O₃/Na-bentonite composite exhibits much enhanced photocatalytic activity than bare In₂O₃. On the basis of the room-temperature photoluminescence and the adsorbability of the In₂O₃/Na-bentonite composite, the mechanism of enhanced photocatalytic activity for the In₂O₃/Na-bentonite composite was also discussed in detail.

Section snippets

Preparation

The pristine bentonite (Jianping Liaoning, China) was purified by centrifugal sedimentation with 0.5 mol/L NaCl solution. Composition of Na-bentonite were analyzed by X-ray fluorescence, and the main compounds were SiO₂ 82.55%, Al₂O₃ 12.90%, Fe₂O₃ 2.07%, MgO 0.85%, Na₂O 1.25%, CaO 0.11%, K₂O 0.22%. All the reagents were of analytical purity used in the experiment and were used as received from SCRC, Shanghai Chemical Company. Deionized water was used in the whole experiment.

A typical synthetic

XRD analysis

The crystal structure of the Na-bentonite and the In₂O₃/Na-bentonite samples calcined at different temperatures was investigated by the powder X-ray diffraction (XRD) method, as shown in Fig. 1. From the Fig. 1a, the Na-bentonite exhibits basal (001) diffraction peaks, which are confirmed for Na-bentonite with a highly ordered and oriented silicate layer structure. The D-values of the (001) reflections of the Na-bentonite were 12.1 Å, similar to those reported by Andreola et al. [20]. The (001)

Conclusions

In summary, In₂O₃/Na-bentonite composites was prepared by a simple sol-gel method. The visible absorption edge of the In₂O₃/Na-bentonite composite shows a slight red-shift compared to that of bare In₂O₃. The composite photocatalyst exhibits much enhanced photocatalytic activity in degradation of phenol under visible light irradiation, which is 4.5 times higher than that of bare In₂O₃. On the basis of the experimental results, the mechanism of enhanced photocatalytic activity for the In₂O₃

Acknowledgments

This work was supported by the National Natural Science Foundation of China (21407022, 41362011), the China Postdoctoral Science Foundation (2015M582748XE) and the Science Funds of the Education Office of Jiangxi, China (KJLD13054). The authors thank the anonymous reviewers for their comments.

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Preparation, characterization and enhancement of the visible-light photocatalytic activity of In2O3/Na-bentonite composite

Abstract

Introduction

Section snippets

Preparation

XRD analysis

Conclusions

Acknowledgments

Microporous Mesoporous Mater.

J. Mol. Catal. A – Chem.

Ceram. Int.

Sol. Energy Mater. Sol. Cells

Int. J. Hydrog. Energy

Appl. Catal. A

J. Colloid Interface Sci.

Chem. Eng. J.

Ceram. Int.

Ceram. Int.

J. Alloy. Compd.

Sens. Actuators B – Chem.

J Colloid Interface Sci.

Microporous Mesoporous Mater.

J. Catal.

Microporous Mesoporous Mater.

Preparation, characterization and enhancement of the visible-light photocatalytic activity of In₂O₃/Na-bentonite composite