Mechanical-assisted preparation and photocatalytic properties of almost-visible light-driven ZnO/ZnFe 2 O 4 nanocomposit
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Mechanical-assisted preparation and photocatalytic properties of almost-visible lightdriven ZnO/ZnFe2O4 nanocomposites Jiaqian Qin1, Yanan Xue2, Xinyu Zhang2, Riping Liu2 1
Metallurgy and Materials Science Research Institute, Chulalongkorn University, Bangkok 10330, Thailand 2 State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, P.R. China ABSTRACT ZnO and ZnO/ZnFe2O4 nanocomposites were synthesized by mechanical-assisted thermal decomposition method. The results show that this method is a simple and low cost method to prepare ZnO and ZnO/ ZnFe2O4 nanocomposites. The nanorod's shape and size have been identified through SEM and TEM. The photocatalytic activity of ZnO and ZnO/ZnFe2O4 nanocomposites were tested by the degradation of methylene blue (MB) in aqueous medium under almost-visible light and the efficiency of the catalyst has been discussed in detail. INTRODUCTION The growing population has led to the increase in contamination of surface and ground water. Organic dyes used in textile and food industries are the important sources of environmental contamination due to their non-biodegradability and high toxicity to aquatic creatures and carcinogenic effects on humans. One of the best ways to reduce the contamination of water is by photocatalytic treatment. Nowadays, researchers have developed many semiconductors that utilize visible light to degrade a high number of recalcitrant materials in aqueous system [1]. ZnO is an important group II-VI semiconductor with a wide band gap (3.37 eV) and a large exciton binding energy of 60 meV at room temperature [2]. ZnO, aside from TiO2, has been considered as a promising material for purification and disinfection of water and air, and remediation of hazardous waste, owing to its high activity, lack of environmental risk and lower cost[3-5]. The biggest advantage of ZnO is that it absorbs a larger fraction of the solar spectrum than TiO2[6, 7]. Previous studies have proved that ZnO can degrade most kinds of persistent organic pollutants, such as detergents, dyes, pesticides and volatile organic compounds, under UV-irradiation [3-5]. Actually, the disadvantage of ZnO is that it absorbs only in the UV region because of its large bandwidth of 3.2 eV (λ=380 nm). The major problem is that only about 4 to 5% of solar spectrum falls in the UV range. Therefore, the effective use of solar energy still remains a challenge in photocatalytic application. Several efforts have been made to enhance the photocatalytic activity of ZnO by various techniques such as modification of ZnO by non-metal doping[8], addition of metals as well as use of coupled semiconductors. Coupling of different semiconductor oxides with two different energy-level systems can play an important role in achieving charge separation. The coupled semiconductor materials can reduce the band gap, extending the absorbance range to visible light region leading to electron-hole pair separation under irradiation and consequently, reaching a higher photocatalytic acti
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