Photocatalytic degradation of phenol and fast green fcf using lithium doped ZnO under fluorescent light irradiation
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Date
2015-09-01
Authors
Noorul Aisyah Md Suhaimi
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Abstract
Zinc oxide (ZnO), plays a main role in this treatment due to its special
characteristic such as, non-toxic, low cost, environmental friendly and stable.
However, modification has to be done to improve its limitation. ZnO photocatalyst
was modified by doping with lithium (Li) using chemical precipitation method. It has been successfully synthesized and synthesized photocatalyst was characterized by Xray diffraction (XRD), scanning electron microscopy (SEM), transmission electron
microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (UV-VIS DRS), and
surface analyzer. Li was found o be a promising metal dopant due to ability for
trapping the photogenerated electron hole pairs from recombine. The photocatalytic
activities of pure ZnO and three Li/ZnO with different Li loading (5 wt%, 7 wt% and
10 wt%) were being evaluated for the degradation of phenol and Fast Green FCF
under fluorescent light irradiation. Results showed that the photocatalytic activities
of all three Li/ZnO were higher than synthesized pure ZnO and commercial TiO2 for
both phenol and Fast Green FCF degradation, especially 7 wt% Li/ZnO which gives
superior photocatalytic performance compare to others. Next, effects of operating
parameters such as initial pollutant concentration, photocatalyst loading and solution
pH towards the photocatalytic degradation of both pollutants were investigated.
Results showed that the best conditions of initial phenol and Fast Green FCF
concentrations were found to be 5 mg/L. Besides, the optimal photocatalyst loading
was found at 2 g/L for both phenol and Fast Green FCF degradation. In addition,
favorable photodegradation of phenol and Fast Green FCF were observed at pH 5.8
and 4.4, respectively. The high reusability and high sedimentation test of 7 wt%
Li/ZnO were achieved suggested its potential usage for practical applications in
wastewater treatment. The actives species involved in phenol and Fast Green FCF
degradation were also investigated by adding certain chemical into the solution
reaction. Then, hydroxyl radical and superoxide anion radical are detected as active
species for phenol and Fast Green FCF degradation, respectively. In addition, several
intermediates product during phenol degradation were detected using high
performance liquid chromatography (HPLC), and its tentative pathway degradation
has been proposed. The kinetics analysis of the degradation of phenol and Fast Green
FCF was over 7 wt% Li/ZnO fitted well by the first-order kinetics represent by the
Langmuir-Hinshelwood model.