Kinetics of Tartrazine Photodegradation by Cu-Modified Silicon Nanowires

Abstract

Around 50% of all dye diversity is represented by azo dyes and due to their extensive applications and persistence they pose a clear environmental hazard [1]. Water is an essential natural resource for human being and for all life forms [2,3]. The use of dyes in textile, pharmaceutical, cosmetic and food industries leads to the pollution the wastewaters with different concentrations. Consequently, the reuse of wastewaters has become an absolute necessity. A wide range of methods for the removal of synthetic dyes from wastewaters, including physical adsorption, electrochemical oxidation, and chemical oxidation were proposed. These methods are not destructive and they only transform the pollutant from one phase to another. So, there is an urgent need to develop innovative, more effective and inexpensive techniques for treatment of wastewater [4]. Heterogeneous photocatalytic oxidation, one of the Advanced Oxidation Processes (AOPs), has attracted much attention in recent years and has proved to be a promising technology for remediation of organic pollutants at ambient conditions [5-12]. Photocatalytic oxidation, in the presence of semiconducting materials, of organic compounds with environmental concern was studied extensively during the last 20 years and it was demonstrated that heterogeneous photocatalysis can be an alternative to conventional methods for the removal of organic pollutants from water and wastewater [13]. This process is based on the direct or indirect absorption by a solid, usually a semiconductor, of photons of visible or UV light. When this semiconductor is illuminated, it can generate electron-hole pairs by promoting an electron from the valence band to the conduction band, thus leaving a hole in this band. These holes can react with H 2 O or hydroxyl groups from the reaction medium and produce highly reactive hydroxyl radical species. On the other hand, the electrons promoted to the conduction band, can reduce the molecular oxygen to peroxide anion to form hydrogen peroxide or organic peroxide in presence of organic compounds [14]. Radical hydroxyls are strong oxidizing agents that can degrade organic