Organic dyes are widely used in various industries,with a production rate of over 7 x 105 tons per year 1,2. It hasbeen estimated that, from all the dyes produced and used, approximately 2%would finally be ended up in the discharged effluents from the relatedindustries 1,2. This has created a serious environmental problem for waterpollution, particularly due to the severe color and the high oxygen demand,causing great harms to the aquatic organisms 1-3. Owing to their highnon-biodegradability, toxicity, as well as carcinogenic potential, dyes areconsidered as the most problematic pollutants and hence their presence in theenvironment should be controlled 1. Although aconsiderable amount of research has been conducted in the past several decadesfor purification of the wastewaters containing dyes, some important issues stillremain, largely because of the process performance limitation and the high costof the available technologies.
For example, physical and chemical processessuch as coagulation 1,3, adsorption 2,4-10, ultrafiltration andnanofiltration 11, etc. have been widely applied to treat dye wastewaters.These methods may be able to reduce the color of the wastewater, but they donot offer the option to degrade the dye molecules ultimately into thenon-harmful ones.
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Even if the biological processes have commonly been used totreat dye wastewaters, they are often ineffective because of thenon-biodegradable feature of many types of the dyes, and of the long processtime and strict operating condition needed for the microorganisms’ growth, inaddition to the large quantity of extra sludge produced in the system requiringfor expensive post-treatment 12,13.Advanced oxidation processes (AOPs) have been alsostudied, for the treatment of recalcitrant organic pollutants. AOPs refer to agroup of technologies that utilize highly reactive species (e.g.
, H2O2,OH· radical) to effectivelyattack and break down those organic pollutants 14,15. Examples of AOPs mayinclude O3/UV, H2O2/UV, Fenton reaction, heterogeneousphotocatalysis, etc 14, 16-22. These technologies have also been attempted indye wastewater treatment either alone 14,15 or in combination of two or moremethods 18,19,23,24. However, the AOPs, in spite of their high degradationpower, often require expensive chemical reagents and/or consume high amounts ofenergy, a factor that makes AOPs costly to use and has so far greatlyrestricted their industrial applications. The decolorization of resistant dyes by aheterogeneous catalytic reaction is one of the most effective methods for thewastewater treatment.
This method consists of using catalysts, such as: TiO2,ZnO, graphene oxide 14,15,25, cation exchange resins 26 or compositematerials 21,27,28, as bulkgels, microgels, or cryogels 29, in the form oftransition metal complexes. The reactivity of the catalysts is correlated withthe redox potential of metal ions, the amount of the complex on catalyticsupport, the type of the support and the structure of the dye.An increasing attention has been paid to the use ofbiopolymers, especially chitosan (CS), for supporting catalytic metals 30-32. CS has been used to stabilize catalytic metals andto prevent both the formation of aggregates (enhancement of the dispersion ofnanoparticles) and the leaching of the metal 30-32. The photocatalyticdegradation rate of MO and rhodamine B has been further enhanced by designingCS-based composites containing SnO2 20, ZnS 21, TiO233, or Cu2O 34.
The aim of this paper is the investigation ofthe degradation process of the MO using novel catalysts obtained by thesorption of Cu2+ ions onto macroporous ion-imprinted ornon-imprinted CS-based composites, namely IICC-Cu2+, and NICC-Cu2+.The catalysts were characterized by Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy (SEM), and energy dispersive X-rayspectroscopy (EDX). The MO degradation by IICC-Cu2+ or NICC-Cu2+catalyst was studied either under ambient light or in a Fenton-like catalyticsystem. The effect of catalyst dose, initial MO concentration, pH, and initial H2O2concentration on the MO degradation was evaluated in detail. The Langmuir–Hinshelwoodkinetic model was used to describe the MO degradation patterns and to calculatethe reaction rate constant. The MO degradation mechanism was evaluated based onthe MS data.