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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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.
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