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Solar photocatalytic decolourization of direct Sirius ® Rubine dye with
TiO2
C. Esteves, A. Cardoso, A. Gouveia, H. Vasconcelos, J. Freitas, J. Melo, C. Botelho, R.
Boaventura and V. Vilar
Laboratory of Separation and Reaction Engineering, Department of Chemical Engineering, Faculty of
Engineering, University of Porto, Portugal.
Textile dyeing is a significant consumer of water and producer of contaminated aqueous waste
streams [1]. The main objective of this work was to evaluate the decolourization and
mineralization of a direct red textile dye, Sirius ® Rubine K-2BL from DyStar, by a
heterogeneous photocatalytic process with TiO2 using solar radiation as UV photon source.
The photocatalytic experiments were carried out in a pilot plant consisting in a unit of
compound parabolic collectors (CPCs) (0.91 m 2 ), two storage tanks (10 and 20 L), two
recirculation pumps (20 L min -1 ) and connecting tubing, being operated in batch mode. The
CPCs have 4 borosilicate tubes connected by plastic junctions and tilted 41º local latitude. The
pilot plant can be operated in two ways: using the total CPCs area (0.92 m 2 ) or using 0.46 m 2
of CPCs area individually (used in this work). The intensity of solar UV radiation is measured
by a global UV radiometer (ACADUS 85-PLS) mounted on the pilot plant at the same angle.
It was observed 16% decolourization of the dye solution after the addition of TiO2, due to the
dye adsorption on the surface of the catalyst. The solar photocatalytic reaction, using 200 mg
TiO2/L, leads to complete decolourization, 83% mineralization and, 100% reduction of
aromatic content after 5.5 days solar exposure (265 kJUV/L). Fig. 1 shows the evolution of
colour of the solution, starting from an intense red coloured solution, passing to a pink colour
and finally to a white coloured solution, which is due to the TiO2 white particles. The UV-Vis
absorption spectrum was performed at different solar energy doses, showing that the red dye
presents a maximum absorption peak at 532 nm, which disappearance during phototreatment
suggests that the chromophore groups responsible for the colour are breaking down.
a b c
Fig. 1 (a,b,c) Evolution of colour during phototreatment.
The decolourization reaction follows a zero-order-kinetic behaviour, with a kinetic constant (k)
and initial reaction rate (ro) of 0.42 mg/kJUV. The mineralization rate presents an initial
induction time of 122 kJUV /L before DOC abatement due to partial oxidation of organics,
followed by a faster reaction rate, showing a first-order-kinetic behaviour (k = 0.012 L/kJUV, ro
= 0.15 mg/kJUV) until 265 kJUV/L. Solar photocatalysis is a promising alternative process for
textile wastewater decolouration, since it can be easily and efficiently applied and employs the
solar radiation as main energy source.
References:
[1] Forgacs E., Cserhati T., Oros G. (2004), Removal of synthetic dyes from wastewaters: a review,
Env. Int. 30 (7), 953–971.
32 3 rd meeting of young researchers at UP