Reaction mass of sodium(E)-6,7'-carbonylbis(azanediyl)bis(4-hydroxy-3-((E)-phenyldiazenyl) naphthalene-2-sulfonate) and disodium 3-[(4-acetamidophenyl)azo]-4-hydroxy-7-[[[[5-hydroxy-6-(phenylazo)-7-sulphonato-2-naphthyl]amino]carbonyl]amino]naphthalene-2-sulphonate and disodium 7,7'-(carbonyldiimino)bis[4-hydroxy-3-(phenylazo)naphthalene-2-sulphonate]

Additional information on environmental fate and behaviour

Administrative data

Endpoint:

additional information on environmental fate and behaviour

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: No GLP, no guidelines followed

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

publication

Title:

Optimization and effects of some electron acceptors on the photocatalytic degradation of Direct Red 23 azo dye

Author:

Débora N. Clausen, Ieda S. Scarminio and Keiko Takashima

Year:

2008

Bibliographic source:

J. Chil. Chem. Soc., 54, Nº 3 (2009)

Materials and methods

Test guideline

Qualifier:

no guideline followed

Deviations:

not applicable

Principles of method if other than guideline:

The photocatalytic degradation of direct red 23 (DR23), was carried out in TiO2 suspension at 30ºC with the use of artificial and solar light sources. The photoreaction followed the first-order behavior with respect to the azo dye as a function of irradiation time. A 2^3 factorial design was carried out, in order to obtain the best experimental conditions, using the rate constant of DR23 degradation as the analytical response. Seven chemical species were determined from the normalized UV-Vis spectra during the DR23 degradation through Imbrie Q mode factor analysis followed by varimax and Imbrie oblique rotations. The addition of electron acceptors, such as H2O2, S2O82-, and ClO3- on the optimized conditions, was carried out to increase the DR23 degradation rate. Comparison of degradation efficiencies under artificial and solar radiation was examined in the presence of oxidants.

GLP compliance:

no

Type of study / information:

Degradation and decolorization

Test material

Test material information

Constituent 1

Reference substance name:

Direct Red 23

IUPAC Name:

Direct Red 23

Results and discussion

Any other information on results incl. tables

Decolorization and degradation of irradiated sample

The highest response of the rate constant (5.59x10^-3 min^-1) was obtained by irradiating 1.50x10^-4 mol/L DR23 in a suspension containing 1.75 g/L TiO2 at the natural pH (6.9) and at 30.0°C. The decrease of the natural pH from 6.9 to 4.4 for the fastest decolorization after 6 h irradiation was attributed to the proton transfer and hydroxyl radical production in the valence band by the water molecule. The most important parameters which affect the decolorization rate constant, were the substrate (DR23) and semiconductor concentrations (TiO2). On the other hand, semiconductor and substrate concentrations showed a significant synergic effect on of the decolorization rate constant (1.72±0.123 x 10^-3 min^-1).

The color remove is attributed to the rupture of the double bond between the two nitrogen atoms (–N=N-) and related as the most active site for oxidative attack. The decrease of the bands with maximum absorptions at 240 and 310 nm indicates the disappearance of the aromatic groups. Results indicate the existence of seven chemical species for the DR23 degradation.

Effect of electron acceptors

In order to enhance the formation of hydroxyl radicals and also inhibit undesired electron/hole pair recombination, and hence permit the degradation of highly toxic wastewater to become faster and easier some electron acceptors were added to the TiO2 suspension containing direct red 23. There is no observable loss of dye, since the rate constants remained practically constant during the irradiation.

Hydrogen peroxide

The initial pH decreased respectively to 6.8 and 6.5 with the addition of H2O2 in this concentration range. This small pH dependence with respect to H2O2 may be due to the simultaneous H+ consumption in the valence band and production in the conduction band 20.

Persulfate ion

The initial pH lowered respectively to 6.7 and 5.7 with the persulfate addition. The gradual and continuous increase of the rate constant is attributed to the reaction of this oxidant with a photogenerated electron, producing a strong oxidant, such as sulfate anion radical. This anion radical produces hydroxyl radical when it reacts with H2O and in subsequent step the molecular oxygen decreasing the medium pH.

Chlorate ion

The addition of this oxidant enhanced the initial pH respectively to 7.4 and 6.0. In contrast to the persulfate case, the rate constant enhancement through the chlorate addition can be attributed to the formation of oxidizing species such as ClO2• radical, that reacts with the azo dye, RH, to produce a radical

Comparison of the irradiation times of the DR23 decolorization in the presence of oxidants

Persulfate ion showed the highest efficiency, because 2.5x10^-4 mol/L decolorized 97.3 % azo dye in 1 min, followed by chlorate ion using 5.0x10^-3 mol/L and 95.7 % also in 1 min and, 97.8 % in 4 h through the addition of 5.0x10^-3 mol/L hydrogen peroxide. In the absence of any oxidant 98.6% was decolorized after 6 h irradiation and resulting in a rate constant of 5.59x10^-3 min^-1. This behavior may be justified in terms of the pH variation during 3 h irradiation as well as the hydroxyl radical production, as it was the case of the hydrogen peroxide and persulfate ion, or of the reduction potential of several oxidant species, as it occurred with the chlorate ion.

Effect of radiation source

When the reaction was performed in the presence of TiO2, the decolorization rate constant increased more than double under solar radiation (15.65x10^-3 min^-1) relative to the value under artificial conditions (5.59x10^-3 min^-1). On the other hand, the rate constant was enhanced by about 30% under solar radiation (0.54x10^-3 min^-1) relative to artificial light (0.41x10^-3 min^-1) in the absence of TiO2.

The rate constant to solar radiation was 0.54 x 10^^-3 min^-1 and to artificial light was 0.41 x 10^^-3 min^-1. the degradation was faster under solar illumination when compared to the artificial one.

Applicant's summary and conclusion

Conclusions:

Direct red 23 azo dye was simultaneously decolorized and degraded in 6 h of artificial irradiation in the presence of titanium dioxide following the 1st order kinetic behavior. Seven chemical species were determined during the DR23 degradation. The addition of oxidants such as persulfate ion, chlorate ion and hydrogen peroxide enhanced the rate constants. Concentrations equivalent to 2.5x10-4 mol L-1 persulfate ion and 5.0x10-3 mol L-1 chlorate showed that the persulfate ion decolorized the dye more rapidly than the others. In addition, the degradation was faster under solar illumination when compared to the artificial one.

Executive summary:

The photocatalytic degradation of aqueous solution of commercial azo textile dye, direct red 23 (DR23), was carried out in TiO2 suspension at 30ºC with the use of artificial and solar light sources. The photoreaction followed the first-order behavior with respect to the azo dye as a function of irradiation time. A 23 factorial design was carried out, in order to obtain the best experimental conditions, using the rate constant of DR23 degradation as the analytical response. Seven chemical species were determined from the normalized UV-Vis spectra during the DR23 degradation through Imbrie Q mode factor analysis followed by varimax and Imbrie oblique rotations. The addition of electron acceptors, such as H2O2, S2O82-, and ClO3- on the optimized conditions, was carried out to increase the DR23 degradation rate. Comparison of degradation efficiencies under artificial and solar radiation was examined in the presence of oxidants.