Nanocomposites and nanomaterials
Photocatalytic decomposition of azo dyes using zinc (II) oxide
Hutsul K.R., Ivanenko I.M.
 National Technical University of Ukraine
“Igor Sikorsky Kyiv Polytechnic Institute”
37, Prosp. Peremohy, Kyiv, 03056, Ukraine. 
E-Mail: x_gucul1997@ukr.net

The efficiency of the photocatalytic method using semiconductor photocatalysts is a relatively new but very promising method of wastewater treatment from pollutants of different nature. Dyes are a big problem, as today there is virtually no technology for their complete removal. Therefore, improving the conditions for photocatalytic processes and developing new effective photocatalysts is an urgent practical task.
In the presented work, zinc (II) oxide was synthesized by the method of precipitation, and its photocatalytic activity in relation to dyes, both anionic and cationic in nature, was studied under static and dynamic conditions.
Under ultraviolet irradiation of Congo red initial concentration of 8 mg/dm3 in static conditions in the presence of the synthesized sample of zinc (II) oxide in 2 minutes the degree of degradation in 99,6% is reached. In contrast to Congo red, for the cationic dye methyl blue, only 35% degree of degradation is achieved in 2 minutes and is 95% after 15 minutes of irradiation. The cationic methylene green dye decomposed by 85% in 30 minutes of irradiation, and by 99% after 60 minutes of ultraviolet irradiation. This indicates a greater affinity of the ZnO surface for cations than for anions.
At ultraviolet irradiation of Congo red initial concentration of 25 mg/dm3 in dynamic conditions its almost complete discoloration is observed. The degree of decomposition is 90% after 10 minutes and 98% after 30 minutes of UV irradiation under dynamic conditions. Methyl blue initial concentration of 15 mg/dm3 under dynamic conditions is discolored by ~80% with the duration of irradiation for 120 min, but for the first 10 minutes, the degree of extraction is only 35%. Interestingly, when reused, the photocatalytic activity of ZnO increases by 10-30%.
The obtained data testify to the high activity of the synthesized zinc (II) oxide in relation to azo dyes, even in highly concentrated solutions, both in static and dynamic conditions.