Effect of Oxidants on the Photocatalytic Degradation of Methylene Blue and Congo Red Under Sunlight

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the dyeing industry needs an effective and cost saving way to treat their waste water. The most conventional cleaning methods produce even more harmful compounds in water, thus research in more effective and cost saving cleaning methods are needed.

There is a wide variety of ways for the removal of dyes. Methods used in the industry include: coagulation and flocculation, bio-sorption, photo-decomposition, ultra-filtration, oxidizing agents, membrane and electrochemical. The advantages and disadvantages of each technique has been widely studied. A very promising solution to the problem is to degrade dyes with the use of a photo catalyst. Sunlight will be used to drive the reaction therefore making it very energy efficient. The addition of an oxidant will improve the efficacy of the photocatalytic degradation. Thus it is important to understand the effect that various oxidants will have on the degradation proses [3] methodology.

A. Materials

The photocatalysts that will be used for the experiments are commercial and Zink oxide (ZnO) powder, supplied by ACE. The concentration that will be used are 0.5 g/L, 1 g/L and 2g/L. The experiments will be conducted with two different dyes; Congo red, a diazo dye and methylene blue, a cationic dye. The oxidants that were chosen are liquid hydrogen peroxide (H2O2, 12%), supplied by Dischem, peroxydisulfate (S2O82-) which will dissociate from the salt, potassium persulfate (Na2S2O8) and Potassium peroxymonosulfate (KHSO5), also referred to as Oxone. The Oxone is supplied as a triple salt with the following formula 2KHSO5·KHSO4·K2SO4. Both salts where supplied by Merck

B. Photocatalytic chamber

The photocatalytic chamber that was used for the degradations of dyes is completely light proof. It also consists of a heating element that will keep the chamber at room temperature i.e. 25oC. The light source consists of three UV lights sources and one LED light source in order to simulate sunlight. The chamber also consists of a magnetic stirrer as well as a 250 ml-Erlenmeyer flask that will be used for the experiment