Catalytic role of Au@TiO 2 nanocomposite on enhanced degradation of an azo-dye by electrochemically active biofilms: a q
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RESEARCH PAPER
Catalytic role of Au@TiO2 nanocomposite on enhanced degradation of an azo-dye by electrochemically active biofilms: a quantized charging effect Shafeer Kalathil • Jintae Lee • Moo Hwan Cho
Received: 18 August 2012 / Accepted: 21 December 2012 Ó Springer Science+Business Media Dordrecht 2013
Abstract A green and sustainable approach to azo dye degradation by an electrochemically active biofilm (EAB) with Au@TiO2 nanocomposite assistance (average size of Au *8 nm) has been developed with high efficiency and mineralization of toxic intermediates. The EAB-Au@TiO2 system degraded the dye more rapidly than the EAB without the nanocomposite, which indicated the catalytic role of the Au@TiO2 nanocomposite on the dye degradation. Toxicity measurements showed that the dye wastewater treated by the EAB-Au@TiO2 system was almost non-toxic while the dye wastewater treated by the EAB without the nanocomposite showed a high toxicity compared to the parent dye. Quantized charging and Fermi level equilibration within the Au@TiO2 nanocomposite may be attributed to the excellent catalytic activity of the nanocomposite on the dye degradation. A mechanism of the catalytic activity is also proposed. Redox behavior and quantized charging of the nanocomposite were confirmed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), respectively. The proposed protocol can be effectively utilized in wastewater treatment applications. Electronic supplementary material The online version of this article (doi:10.1007/s11051-012-1392-5) contains supplementary material, which is available to authorized users. S. Kalathil J. Lee M. H. Cho (&) School of Chemical Engineering, Yeungnam University, Gyeongsan, Gyeongsangbukdo 712-749, South Korea e-mail: [email protected]
Keywords Electrochemically active biofilm Dye degradation Au@TiO2 nanocomposite Quantized charging Fermi level equilibration
Introduction Azo dyes are commonly used in textile industries. Treatment of dye wastewater prior to discharge is one of the daunting tasks as most of the dyes are recalcitrant molecules and highly toxic in nature (Husain 2010). There are many available methods for the degradation of azo dyes including chemical, physical, and biological methods; however, their performances are far from satisfactory (Robinson et al. 2001). Usually, intermediates formed after the degradation of dyes are highly toxic and sometimes even more toxic than the parent dye. Hence, a further treatment is needed for the degradation of the toxic intermediates. There are many metal nanoparticles such as Au, Ag, and Pt which were employed for the degradation of dyes by using various chemical reducing agents such as NaBH4 (Gupta et al. 2011). The major disadvantage of these methods is the use of toxic chemicals which causes a secondary pollution. In recent years, coupling of semiconductors with noble metals has been regarded as an interesting approach to enhance the performance of semiconductor-based nanostructures (Choi et al. 2012; Takai and Kamat 2011).
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