The PhD thesis in Engineering:

"Photocatalytic degradation of azo dyes in aqueous solutions

by nanosized TiO_2"

  ABSTRACT:

Nanosized powders of TiO₂ have been prepared from ilmenite ore by the sulfate process, in which the thermal hydrolysis stage carried out with microwave heating. The properties of titania concerning with photocatalytic applications, such as: specific surface area, particle size, crystallinity…, were controlled by the concentration of Ti(IV) in hydrolysis solution and the calcination temperature of titania. Among the prepared powders, sample calcined at 700⁰C (with pure anatase, highly crystallinity, anatase-phase crystallite size of 20 nm, average particle size of 25nm and specific surface area of 30m²/g) was shown to have the photoactivity comparable with the commercial TiO₂ (P-25 Degussa).

The prepared TiO₂ was used for the photocatalytic degradation of commercial azo dyes such as Orange G (OG), Yellow 2G (Y2G), Amido Black 10B (AB10B), Congo Red (CR) and Remazol Black B (RBB). The effects of catalyst loading, initial concentration of the dyes, pH, inorganic anions and hydrogen peroxide was investigated. The experimental data followed Langmuir–Hinshelwood rate form and the kinetic parameters were obtained.

The prepared TiO₂ was also used for the photocatalytic degradation of a simulated textile effluent containing various dissolved azo dyestuffs and associated auxiliary chemicals.

RESEARCH RESULTS:

1.     The new preparation method of nanosized TiO₂ with high photoactivity from Viet Nam ilmenite ore.

2.     The dependency of the photoactivity on the crystallite size of prepared titania was confirmed: TiO₂ with  crystallite size around 20nm showed the highest photoactivity in photocatalytic decolourization of OG in water.

3.     In photocatalytic degradation of studied azo dyes, the rates of decolourization are in accordance with the rates of mineralization and both were  decrease in the following order: Y2G > OG > CR ~ RBB > AB10B.

4.     With an addition of 10mM of H₂O₂, the pseudo-first order rate constants of photocatalytic degradation of RBB and AB10B were increased by 1.76 and 3.25 times, respectively.

5.     The decolourization of simulated wastewater was completed within 77 minutes of photocatalytic treatment. With the decolorization, 71%COD and 21%TOC were removed and the biodegradability of the wastewater was enhanced enough for further biotreatment.

POSSIBLE PRACTICAL VALUES AND RECOMMENDATION FOR THE FURTHER RESEARCH:

-       The preparation method of nanosized TiO₂ can be developed for production of TiO₂ for application in environmental technology and other fields.

-       Results in this dissertation can be developed for further research of dyeing wastewater treatment technology.

Based on prepared TiO₂, the recommendation for further research is as follows:

-       Photocatalytic treatment of textile wastewater using solar on pilot scale.

-       Integration of photocatalytic process with biotreatment in treatment technology of textile wastewater.

-       Photocatalytic degradation of non-biodegradable pollutants in water.