Organic dyes are one of the largest groups of pollutants in wastewaters and most of
them are produced from the textile industry, which use them in conjunction with a wide
range of auxiliary chemicals for various dyeing and finishing process. It is estimated that
approximately 12% of dyes are lost annually during manufacturing and the processing
operations. The discharge of these colored wastewaters in the ecosystem without treatment
can cause serious problems due to the toxicity of some dyes to the aquatic life and damaging
to the aesthetic nature of the environment1.
Several techniques such as activated carbon and other adsorbents2-6 have been used
to solve the problems caused by the toxic substance contained in these colored wastewaters.
However, all of these treatments mentioned above have a major disadvantage of simple
transferring the pollutants from one phase to another phase rather than destroying them,
which consequently leads to secondary pollution. Semiconductor photocatalytic oxidation is912 A. M. Algubili et al.: Photocatalytic Degradation of Remazol….
a famous modern water treatment technology. It has many advantages such as high
efficiency, low energy-consumption, moderate condition, extensive applicability and
decrease in secondary pollution. It can be used as catalyst and photocatalyst under the
ultraviolet radiation (? ? 368 nm) to resist bacteria, eliminate odor, disinfect, refine and
protect the environment. Therefore, ZnO will play an important role in the treatment of
contamination7.
Therefore, many research groups have paid attention to the degradation of these
colored wastewaters in recent years8-11. The photocatalytic mechanism of AOPs employing
ZnO was investigated in details elsewhere. Briefly, when aqueous ZnO suspension is
irradiated in light energy greater than the band gap energy of the semiconductor
(Eg > 3.2 eV), conduction band electrons (e?) and valance band holes (h+) are generated. If
charge separation is maintained, the electrons and holes may migrate to the catalyst surface
where they participate in redox reaction with the adsorbed species. The photogenerated
electrons react with the adsorbed molecule O2 on the Zn(II)-site and reduce it to superoxide
radical anion (O2•?), while the photogenerated holes can oxidize the H2O or OH? ions
adsorbed at the ZnO surface to OH• radicals. These radicals together with other highly
oxidant species (e.g. peroxide radicals) will act as strong oxidizing agents that can easily
attack the adsorbed organic molecules or these located close to the surface of the catalyst,
thus resulting in their complete degradation into small inorganic species. The dye derivative
Remazol Brilliant Blue has been widely used in textile industry and its structure is presented
in Fig. 1. To the best of our knowledge few efforts have been made to investigate the
photocatalytic degradation of this dye. Therefore, a detailed investigation on the
photodegradation of Remazol Brilliant Blue (RBB) was carried out in the present study.
In the present work, we report the photocatalytic degradation of RBB dye with ZnO
and the effect of operational parameters such as catalyst loading, the initial dye
concentration, and light intensity on the decolorization were studied to optimize the pro