Use of titanium dioxide photocatalysis on the remediation of model textile wastewaters containing azo dyes

Abstract

The photocatalytic degradation of two commercial textile azo dyes, namely C.I Reactive Black 5 and C.I Reactive Red 239, has been studied. TiO(2) P25 Degussa was used as catalyst and photodegradation was carried out in aqueous solution under artificial irradiation with a 125 W mercury vapor lamp. The effects of the amount of TiO(2) used, UV-light irradiation time, pH of the solution under treatment, initial concentration of the azo dye and addition of different concentrations of hydrogen peroxide were investigated. The effect of the simultaneous photodegradation of the two azo dyes was also investigated and we observed that the degradation rates achieved in mono and bi-component systems were identical. The repeatability of photocatalytic activity of the photocatalyst was also tested. After five cycles of TiO(2) reuse the rate of colour lost was still 77% of the initial rate. The degradation was followed monitoring the change of azo dye concentration by UV-Vis spectroscopy. Results show that the use of an efficient photocatalyst and the adequate selection of optimal operational parameters may easily lead to a complete decolorization of the aqueous solutions of both azo dyes.

Figure 1

Effect of TiO₂ amount on the complete degradation of 30 mg·L⁻¹.I. Reactive Red 239() and C.I Reactive Black 5 () dyes in 120 min of irradiation with2,60 mW/cm² of irradiation power by a 125 W mercury lamp.

Figure 2

Effect of UV-Irradiation time on the degradation of 30 mg·L⁻¹of the azo dyesC.I. Reactive Red 239 () and C.I Reactive Black 5 () with 0.1 g·L⁻¹ of TiO₂ and 2.60 mW/cm² of irradiation power by a 125 W mercury lamp.

Figure 3

Effect of UV-Irradiation time on the degradation of 30 mg·L⁻¹of the azo dyesC.I. Reactive Red 239 () and C.I Reactive Black 5 () with 1 g·L⁻¹ of TiO₂ and 2.60 mW/cm² of irradiation power by a 125 W mercury lamp.

Figure 4

Photocatalytic degradation under 125 W mercury-vapor lamp irradiation with 0.1 g·L⁻¹ of TiO₂ followed by UV-Vis spectrophotometry from 200 to 900 nm for 30 mg·L⁻¹ of (a) C.I Reactive Black 5 and (b) C.I Reactive Red 239.

Figure 5

TiO₂ (0.1 g·L⁻¹) photodegradation efficiency of 30 mgL⁻¹ C.I Reactive Black 5 at different pH values.

Figure 6

Schematic interaction model of C.I Reactive Black 5 and TiO₂: (a) acid sites and (b) basic sites.

Figure 7

Catalytic yields of 0.1 g·L⁻¹of TiO₂ as a function of its reuse of 30 mg·L⁻¹of C.I. Reactive Red 239 photodegradation.

Figure 8

Effect of the initial concentration of C.I. Reactive Red 239 () and C.I Reactive Black 5 () dyes on the efficiency attained after 2 h of irradiation with 0.1 g·L⁻¹ of TiO₂ and 2,60 mW/cm² of irradiation power by a 125 W mercury lamp.

Figure 9

Effect of the presence of hydrogen peroxideon the photodegradation of C.I. Reactive Red 239 () and C.I Reactive Black 5 () dyes after 60 min of irradiationwith 0.1g−L⁻¹ of TiO₂ and 2,60 mW/cm² of irradiation power by a 125 W mercury lamp.

Figure 10

Photocatalytic degradation under 125 W mercury-vapor lamp irradiation with 0.1 g·L⁻¹ of TiO₂ followed by UV-Vis spectrophotometry from 200 to 900 nm for a 30 mg·L⁻¹ mixture of C.I Reactive Black 5 and C.I Reactive Red 239.

Figure 11

Effect of UV-Irradiation time on the degradation of a 30 mg·L⁻¹mixture of the azo dyesC.I. Reactive Red 239 () and C.I Reactive Black 5 () with (a) 0.1 g·L⁻¹ and (b) 1 g·L⁻¹ of TiO₂ and 2.60 mW/cm² of irradiation power by a 125 W mercury lamp.

Figure 12

Chemical structure of commercial azo dyes: (a) Marine Remazol RGB 150% gran (C.I Reactive Black 5). (b) Ultra Red Remazol gran (C.I. Reactive Red 239).