3rd meeting of young researchers at UP 1 - IJUP - Universidade do ...

Degradation of Sirius ® Blue dye by TiO2 solar photocatalysis
N. Silva, R. Nunes, D. Marques, J. Amaro, C. Botelho, R. Boaventura and V. Vilar
Laboratory of Separation and Reaction Engineering (LSRE), Department of Chemical Engineering
(DEQ), Faculty of Engineering, University of Porto (FEUP), Portugal.
Generally, over 10% of the textile dyes are lost in wastewater stream during their synthesis and
dyeing processes and often cause environmental problems [1]. The main purpose of this work
was to evaluate the decolourization and mineralization of a direct blue textile dye, Sirius ® Blue
K-CFN 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 constituted by 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 30% 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 and mineralization and 100% reduction of aromatic
content after 2.5 days solar exposure (120 kJUV L -1 ). Fig. 1 shows the evolution of colour of the
solution, starting from an intense blue coloured solution, passing to a marine blue colour and
finally to a white coloured solution, which is due to the TiO2 white particles.
a b c
Fig. 1 (a,b,c) Evolution of colour during phototreatment.
The decolourization reaction rate follows a zero-order-kinetic behaviour, with a kinetic
constant (k) and initial reaction rate (ro) of 0.72 mg/kJUV. The mineralization rate presents an
initial slow reaction rate until total decolourization is achieved, followed by a first-order
kinetic behaviour (k = 0.005 L/kJUV, ro = 0.084 mg/kJUV) until 80 kJUV /L and, finally a faster
reaction rate (k = 0.084 L/kJUV, ro = 1.39 mg/kJUV) until 120 kJUV/L. A pH reduction was
observed in the range 40-95 kJUV/L due to molecule dye cleavage and consequently formation
of acid low-molecular-weight carboxylic intermediate compounds, resulting in a decrease of
the absorbance at 254 nm. Experiments were performed in consecutive days, so temperature
rises from morning start-up (20ºC) to an almost constant value (38.5 ºC was the maximum
temperature achieved) and decreases again during the afternoon, depending on the sunlight
intensity.
References:
[1] Forgacs E., Cserhati T., Oros G. (2004), Removal of synthetic dyes from wastewaters: a review,
Env. Int. 30 (7), 953–971.
3 rd meeting of young researchers at UP 31