Electrochemical advanced oxidation processes (EAOPs) for dye removal
Different treatment methods, for example filtration , sonolysis , wet land treatment ,adsorption ,electrocoagulation ,photolysis, biodegradation, ozonation ,coagulation , photocatalysis layer filtration and so forth have been utilized for expelling manufactured colors from aqueous arrangement.Advantages and Drawbacks strategies have been mentioned thoroughly((Crini, 2006; Martínez-Huitle and Brillas, 2009; Nidheesh et al., 2013).Based on fundamental mechanism behind the evacuation of dyes,these can be divided into two wide classes : Physical and Chemical methods.The schematic diagram of the dye evacuation process is shown in Fig1. The majority of techniques for dye removal are segregation process and the drawback of these processes is the discarding of dye which contain the sludge as in coaulation process dye sorbed adsorbents and concentrated dye arrangement as in layer forms.In opposed to this complex dye compounds experience a series of degradation in chemical degradation techniques. In case of use of advanced oxidation processes, degradation procedure advance until ultimate oxidation degree, in other words mineralization of organic contaminants. These methods produce water( H2O) carbon dioxide(CO2) as well as other inorganic ions(following heteroatoms present during the starting of organic pollutants ) given that final product.Among different degradation procedures advanced oxidation processes(AOPs) received a great consideration for proficient degradation of dyes during past few years((Martínez-Huitle and Brillas,2009; Oturan and Aaron, 2014)). These methods depend on the creation of highly reactive oxidants, usually hydroxyl radical( ?OH). This radical is the second most effective oxidizing agent(after fluorine) with a redox potential of E?(OH/H2O)=2.8V/SHE. Once these radicals are produced in situ, they attack organic pollutants with high reaction rates through following three different ways (Oturan, 2000; Brillas et al., 2009; Sir_es et al., 2014) electron transfer((Eq1)),dehydrogenation((eq2)),deydroxylation((eq3)).These responses create organic radicals and begin a radical chain incorpating reactions with oxygen and formed reaction intermediates undergo further oxidation reactions with generated agents that are oxidizing until the whole mineralization of organic pollutants.
?OH +RX? RX?? + OH¯ (1)
?OH +RH? R + H2O (2)
?OH+ ?PhX (OH) (3)
Where PhX and RX represents aromatic and aliphatic halogens,respectively.
Among the AOPs , Electrochemical advanced oxidation processes have been produced of great interest in removal of organic pollutants. EAOPs utilize electrolytically produced hydroxyl ions for mineralization. According to hydroxyl ions production EAOPs are divided into two types direct and indirect EAOPs as shown in Fig1.
Fig1; The schematic diagram of dye evacuation methods.