Elsevier

Catalysis Communications

Volume 9, Issue 6, 31 March 2008, Pages 1224-1229
Catalysis Communications

One-step preparation of silver and indium oxide co-doped TiO2 photocatalyst for the degradation of rhodamine B

https://doi.org/10.1016/j.catcom.2007.11.008Get rights and content

Abstract

A novel co-doped TiO2 photocatalyst, Ag/In2O3–TiO2, was developed through a one-step sol–gel process followed by a solvent thermal treatment in the presence of triblock copolymer surfactant. The product showed very small particle size (12 ± 2 nm) with metallic Ag clusters well-distributed on the surface of the product, at the same time, the product was mainly in the anatase phase with high crystallinity. The photocatalytic activity of Ag/In2O3–TiO2 was evaluated by the degradation of an aqueous solution of dye rhodamine B (RB), and the obtained significantly high photocatalytic activity can be ascribed to the simultaneous effects of doped noble metal Ag by acting as electron traps and semiconductor In2O3 as narrow band gap sensitizer. In addition, the unique morphology and nanosize of the product also played an important role in this enhanced photocatalytic activity.

Introduction

Design and preparation of efficient heterogeneous photocatalytic materials still attracts much attention due to their potential activity for total destruction of organic compounds in polluted air and wastewater. For this purpose, various methods have been suggested to enhance the photocatalytic efficiency involving TiO2 (band gap of ∼3.2 eV), which mainly include doping, functionalization of the surface with metal particles, and reduction of particle size to the nanoscale [1]. Therefore, the band gap of TiO2 can be decreased and/or recombination of photogenerated electron-hole pairs (e–h+) can be prevented effectively [2], [3], [4]. Among these methods, doping of two components into anatase TiO2 lattice to produce co-doped TiO2 photocatalysts is one of the most effective ways for enhancing the photocatalytic activity of TiO2 [5]. For example, N–Fe3+-codoped TiO2 photocatalyst demonstrated much higher visible-light photocatalytic activity than that of Fe3+–TiO2 photocatalyst for the decompositions of RB [6]; P–N–codoped TiO2 nanophotocatalyst possessed high photocatalytic activity in visible-light region [7]; Ag-InVO4 co-doped TiO2 composite thin film with Ag doping of 1% exhibited higher visible-light activity for decomposition of dye methyl orange [5]. Motivated by these results, the present work demonstrates a novel co-doped TiO2 nanocomposite, Ag/In2O3–TiO2. Silver is an extremely attractive noble metal to be investigated at nanoscale due to its remarkable catalytic activity [8], [9], [10] and to its size- and shape-dependent optical properties [11], [12], [13], [14]. In the photocatalytic applications, metallic Ag can prevent e–h+ pairs from fast recombination owing to its strong electron trap ability, resulting in enhanced quantum efficiency of the photocatalysts. For this purpose, Ag/TiO2 photocatalysts have been extensively studied [15], [16]. As for the semiconductor In2O3, it can absorb light of wavelength shorter than 480 nm with the band gap of ∼2.5 eV [17]. Doping TiO2 with In2O3 is beneficial to improve the photoactivity of TiO2 due to decreasing its band gap [18].

The reported methods for preparation of Ag/TiO2 mainly are photodeposition and chemical reduction [15], [16], [19]. In current work, Ag/In2O3–TiO2 is prepared by a one-step sol-gel process followed by a solvent thermal treatment in the presence of triblock copolymer surfactant, Pluronic P123 (EO20PO70EO20, where EOdouble bondCH2CH2O, POdouble bondCH2(CH3)CHO). The resulting product exhibits decreased band gap, high crystallinity, and interesting morphology including homogeneous dispersion of Ag on the surface of the product and nearly monodispersed particles with very small particle size (12 ± 2 nm). All of these are crucial factors to improve the photocatalytic activity of TiO2. Here, purpose of adding P123 in the Ag/In2O3–TiO2 preparation process is to lead to well-dispersed product particles rather than to act as soft template for preparation of ordered mesoporous materials. At last, the photocatalytic activity of the Ag/In2O3–TiO2 was evaluated by the degradation of dye RB.

Section snippets

Catalyst preparation

P123 (M = 5800, 2 g) was dissolved in isopropanol (10 ml) under vigorously stirring, and then ice-cooled titanium isoporpoxide (TTIP, 2 ml) was added, followed by further stirring for 30 min (mixture A). Mixture B was consisted of AgNO3 (0.024 g), In(NO3)3 · 4.5H2O (0.04 g), isopropanol (4 ml), and water (0.6 ml). Mixture B was then added dropwise into mixture A under vigorously stirring, and the resulting mixture was continuously stirred until the gel was formed. The gel was transferred into an autoclave

Results and discussion

The determined doping of Ag and In2O3 in the products (2.0 and 1.9 wt%, respectively) by ICP-AES are as expected. The crystalline phase of Ag/In2O3–TiO2 was characterized by XRD measurements. For comparison, as-prepared pure Ag, In2O3, and TiO2 were also tested. As shown in Fig. 1, pure Ag exhibits cubic phase with the peaks at 38.21°, 44.47°, 64.47°, and 77.48°, respectively (JCPDS 03-0921), and pure In2O3 exhibits rhombic phase with the peaks found at 30.97°, 32.57°, 45.57°, 50.24°, 57.35°,

Conclusion

The present work demonstrated a novel and simple route to prepare metallic Ag and semiconductor In2O3 co-doped TiO2 nanocrystal with anatase phase structure, very high crystallinity and extremely small particle size. The product showed interesting morphology and decreased band gap energy compared with anatase TiO2, and it exhibited significantly high UV-light photocatalytic activity towards dye RB degradation compared to as-prepared Ag/TiO2, In2O3–TiO2, P25, pure TiO2, and Ag/In2O3–TiO2 without

Acknowledgements

This work is supported by the Program of New Century Excellent Talents in University (NCET-04-0311) and the Key Project of Chinese Ministry of Education (No. 308008). Also, the work is supported by Analysis and Testing Foundation of Northeast Normal University.

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