The Synthesis of a Novel Azo Dyes and Study of Photocatalytic Degradation

Six novel aromatic azo dyes were synthesized from 4-amino-2-nitrobenzoic acid with phenol, catechol, resorcinol, hydroquinone, salicylic acid and acetylsalicylic acid with very good yield. These azo dyes confirm by FTIR, CHNS and study the photo stability used TiO2 and ZnO. The photocatalytic degradation of novel aromatic azo dyes was investigated using TiO2 and ZnO as a catalyst under 125 watts UV lamp. A series of experiments was performed to reaching to the optimum condition of degradation. The photocatalytic degradation of azo dye follows the first order reaction. In all experiments photocatalytic degradation of the azo dye has been studied using different weight of TiO2 and ZnO suspended in an aqueous solution of azo dye irradiated by irradiated by 125–UV lamp in 100 cm3 a vessel reactor at room temperature with 10 cm3/min air bubble has been passed through the solution. In addition, all result was measured using UV-Visible spectrophotometer.


1-Introduction:
Azo dyes are important type of colorant compounds because of their wide application in technology and science (1) . In fact, there are a roughly fifty percent of dyes which used today of industry are azo dye (2) . Usually, these dyes are more stable from natural dye in the wild range of PH; thermally stable and the color don't fade when exposed to oxygen and light (3) . Azo dye compounds contain many application industry like photodynamic therapy, photosensitive and have biological activity due to their use in inflammatory (4,5) anticancer (6,7) antibacterial (8)(9)(10) and antifungal (11)(12)(13)(14)(15)(16) . A few years ago, there are many researchers intense on employing the semiconductors as catalyst. When the aqueous solution irradiated with light equal or greater than band gap of titanium dioxide the electrons rises from the valance band on the semiconductor surface to the conduction band to produce photoelectron in the conduction band of semiconductor leaving positive hole in the valance band .The aim of present work was study the photo activity of titanium dioxide . Photoelectrons in the conduction band react with adsorbed oxygen producing the highly reactive superoxide radical ion. The positive hole in the valance band reacts with adsorbed water to producing hydroxyl radical then reacts with pollutants.

III/ Photo reactor and procedure:
The degradation process of a novel Azo Dyes has been tested in glass photo reactor. Photo degradation of a novel Azo Dyes reactor consisted of two parts. The first part of cooling the suspension solution in which the running water was passed through it. The second part called the reaction vessel solution with (100 ml) capacity. The removal of a novel Azo Dyes was conducted under solar light. All experiments were performed by mixing 0.12 g of the catalyst with 50 mg/L of the dye solution. In order to ensure adsorption equilibrium between surface of catalyst and dye, the suspension solution was kept under stirring in the dark for 30 minutes. The solution of dye was bubbled with air (10 ml/min) during the irradiation. A 2 ml of suspension reaction mixture was withdrawn every 10 minutes, and then centrifuged at 4000 rpm to remove any residual sensitized zinc oxide particles. All samples taken were analyzed at a maximum absorption band by UV-Vis spectrophotometer.

3-Results and Discussion
Six azo dyes were synthesized from 3-nitro-4-benzoicdiazonium chloride (diazonium salt) and phenolic components as a coupling compound. First for all, the diazonium salt was prepared under 0 o C and directly reaction it with coupling compound due to the diazonium salt decomposition above 5-10 o C. The diazonium salt beavers as electrophile with an electron rich coupling compounds. The hydroxyl group of phenolic coupling compounds direct the diazonium ion to the para position unless that position is occupied in this case the ion attaches ortho site of hydroxyl group 24 . The azo dyes were characterized by various techniques. The Fourier-transform infrared spectroscopy (FTIR) is one of the efficient techniques used in the identification of functional groups of organic compounds. FTIR was used in the present study to confirm the presence of functional groups as following, the hydroxyl carboxyl and hydroxyl phenolic groups (COOH & OH) shown at 3500-2500 cm -1 as broad stretching vibration, the carbonyl group (C=O) of carboxylic and ester shown at 1680-1720 cm -1 as broad stretching vibration band, the (C=C) group of aromatic shown around 1600 cm -1 as meddle stretching vibration band, the azo group (N=N) shown at 1490-1520 cm -1 as meddle stretching vibration band, the symmetric stretching vibration of nitro group (NO 2 ) appear at 1350-1300 cm -1 . The photoactivity of titanium dioxide and zinc oxide as a catalyst has been studied using 0.12gm / 100 ml, the light intensity equal to 8.22 mW/cm 2 , and temperature equal to 298 K. The results are plotted in figure 3. The comparison study of the photocatalyst activity of titanium dioxide and ZnO on the degradation of a novel Azo dye was carried out using 0.12g/100ml catalyst with 50ppm of dye for up to 60min. It can be clearly observed that the TiO 2 exhibited a higher photocatalytic activity as compared with zinc oxide that can be attributed to the increase in the effective surface area of the catalyst lead to enhancing its photocatalytic activity for degradation of dye. [20][21][22][23] Fig.2: Comparison between zinc oxide and titanium dioxide using dye.
The optimum photo degradation efficiency which is equal to 87.12% for titanium dioxide whiles the zinc oxide was 54.33% [24][25]

Conclusion
Several aromatic azo dyes were synthesized from 4-amino-2-nitrobenzoic acid with very good yield and confirm these azo dyes by FTIR and CHNS. Photocatalytic degradation process of novel Azo dyes was carried out using 0.12 g /cm 3 and 50 ppm. It was found that TiO 2 is more effective than ZnO with 87.12and 54.33 PDE% respectively.

Acknowledgment
This article was financial support by the University of Babylon, Faculty of Science for Women, for providing the necessary infrastructural facilities during my research.