Photocatalytic characteristics of immobilized SrBi2Nb2O9 film for degradation of organic pollutants

doi:10.1016/j.ceramint.2012.01.042

Ceramics International

Volume 38, Issue 5, July 2012, Pages 3901-3906

https://doi.org/10.1016/j.ceramint.2012.01.042 Get rights and content

Abstract

The use of semiconducting oxide photocatalyst in contaminant purification has recently drawn significant attention in both materials and environmental science. In this study, the compound SrBi₂Nb₂O₉ with layered perovskite-type structure was synthesized by solid state reaction, and the network microstructure film was fabricated by the aerosol deposition method. The compound powder and aerosol-deposited film with SrBi₂Nb₂O₉ were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Ultra violet–visible (UV–vis) spectrophotometry. The photocatalytic activity of the aerosol-deposited film with SrBi₂Nb₂O₉ was evaluated by photo-induced destruction of Rhodamine B under the irradiation of UV and visible light. The aerosol-deposited film with SrBi₂Nb₂O₉ exhibited higher photocatalytic activity than that of SrBi₂Nb₂O₉ powders. This result is attributed not only to the small sized grain, but also to the existence of a network microstructure capable of supporting the enhanced loading of organic contaminants on the aerosol-deposited film.

Introduction

In recent years, semiconducting oxide photocatalysts have attracted extensive attention because of their potential applications in solar energy conversion and environmental purification [1], [2], [3], [4]. There has been a significant amount of research on the decomposition of environmental pollutants and the destruction of bacteria using photocatalytic TiO₂ ever since Fujishima and Handa reported water splitting using a TiO₂ photoelectrode [1]. TiO₂ has been known for its good environmental stability and excellent photocatalytic activity [5], [6]. However, the practical applications of photocatalytic TiO₂ have been hindered primarily by its low quantum yield and lack of visible-light utilization. Therefore, many researchers have focused their efforts on the design and development of single phase oxide photocatalysts working under visible light illumination [7], [8], [9], [10].

Compounds of the general formula A_m−1Bi₂M_mO_3m+3 (m = 1, 2, 3, and 4) were first synthesized by Aurivillius [11]. The crystal structure of Aurivillius-type oxides can be regarded as a regular intergrowth of (Bi₂O₂)²⁺ fluorite layers and (A_m−1M_mO_3m+1)²⁻ pseudo-perovskite slabs. The structure allows a wide variety of chemical substitution at the A and M sites, thereby exhibiting an enormous range of physical properties. Recently, Li et al. reported the photocatalytic activities of Aurivillius-type ABi₂Nb₂O₉ (A = Sr, Ca, Ba) powders on water splitting under UV-light irradiation. In their investigation, SrBi₂Nb₂O₉ showed the highest evolution rate of H₂ and O₂ [12]. Also, Wu et al. studied the photocatalytic activity of microcrystalline ABi₂Nb₂O₉ (A = Sr, Ba) compounds synthesized by a citrate complex method [13]. They reported that SrBi₂Nb₂O₉ exhibited higher photocatalytic activity than that of BaBi₂Nb₂O₉ for the photocatalytic redox reaction of methyl orange under UV light irradiation.

In general, most of the studies on photocatalytic activities have focused on the powder form of photocatalysts. However, there are two practical problems with using powders in photocatalytic processing: (1) it is difficult to separate the catalysts from the suspension after the reaction and (2) particulate suspensions are not easily applicable to continuous processes. Thus, a photocatalyst in film form may be an excellent alternative for resolving these technical problems. The methods available for the fabrication of photocatalytic films include sol–gel [14], sputtering [15], e-beam evaporation [16], and aerosol deposition [17], [18]. Among these, the aerosol deposition (AD) method is an effective technique that enables the fabrication of thin or thick film at room temperature with a high deposition rate and a strong adhesion to the substrate. The aerosol deposition method is based on the impact adhesion of sub- or micron particles accelerated by gas up to a subsonic velocity to a substrate. In addition, operation at room temperature makes it possible to fabricate a film without any phase change.

In this paper, SrBi₂Nb₂O₉ compounds synthesized by a solid-state reaction were used as a source material for aerosol and characterized by XRD and SEM analysis. SiBi₂Ni₂O₉ thin films were successfully fabricated from micron-sized powder at room temperature by aerosol deposition, and their photocatalytic activity was extensively investigated. The photocatalytic performances of the aerosol-deposited film were evaluated by measuring the photo-degradation of a Rhodamine B (Rh-B) aqueous solution with a UV–vis spectrophotometer.

Section snippets

Experimental

The polycrystalline samples of the photocatalysts were synthesized by a conventional solid state method from the starting materials of carbonates (SrCO₃, 99%) and oxides (Bi₂O₃, Nb₂O₅, 99.9%). A mixture of these starting materials in an appropriate molar ratio was finely ground in an agate mortar and pressed into pellets. The pellets were calcined at 900 °C for 15 h, 1000 °C for 15 h, and 1200 °C for 24 h, with intermittent grinding using an attrition mill for 2 h. Fig. 1(a) shows the X-ray

Results and discussion

The XRD analysis on the powders and aerosol-deposited films of the SrBi₂Nb₂O₉ compound are shown in Fig. 1(a) and (b). The peak of the SrBi₂Nb₂O₉ powder was sharp and narrow, indicating a phase with a large crystallite size. Meanwhile, the as-deposited SrBi₂Nb₂O₉ film on Al₂O₃ plate showed small and broad peaks in comparison with the raw powders, despite being deposited at room temperature. According to the Scherrer relation, these broad peaks imply that the film consisted of very small

Conclusion

The SrBi₂Nb₂O₉ compound with perovskite-type layered structure was synthesized by solid state reaction, and network microstructure film was fabricated by aerosol deposition method. The FESEM image of the aerosol-deposited SrBi₂Nb₂O₉ film shows that the submicron particles were uniformly deposited on the Al₂O₃ support, indicating that the fragmentation of SrBi₂Nb₂O₉ powders occurred during the AD method. The average surface roughness (R_a) of the aerosol-deposited SrBi₂Nb₂O₉ film was 3420 Å which

Acknowledgement

This subject is supported by Korea Ministry of Environment as “The Eco-Innovation project (Global Top project), GT-SWS-11-01-004-0”.

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Photocatalytic characteristics of immobilized SrBi2Nb2O9 film for degradation of organic pollutants

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgement

Ceram. Int.

Ceram. Int.

Ceram. Int.

Int. J. Hydrogen Energy

Int. J. Hydrogen Energy

Int. J. Hydrogen Energy

J. Solid State Chem.

Vacuum

Catal. Commun.

Appl. Catal. B

Int. J. Hydrogen Energy

Sens. Actuators A

Appl. Catal. B

Thin Solid Films

Thin Solid Films

J. Membr. Sci.

J. Solid State Chem.

Photocatalytic characteristics of immobilized SrBi₂Nb₂O₉ film for degradation of organic pollutants