Photocatalytic Degradation Of Tetracycline In Aqueous Solution By Zno Quantum Dots/Tio2 Supported Catalysts
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Date
2021-03
Authors
Saidu, Usman
Journal Title
Journal ISSN
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Publisher
Universiti Sains Malaysia
Abstract
In this research, TiO2 nanoparticles (TiO2 NPs) were incorporated with 3%,
5%, 8%, and 10% ZnO quantum dots (ZnO QDs) via sol-gel method. The
photocatalyts (xZnO QDs/TiO2; x= 3%, 5% 8% and 10%) were characterized using Xray
diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force
microscopy (AFM), high resolution transmission electron microscopy (HRTEM), field
emission scanning electron microscopy (FESEM), ultraviolet-visible diffuse
reflectance spectroscopy (UV-vis DRS) Brunauer-Emmett-Teller (BET), X-ray
photoelectron spectroscopy (XPS), and photoluminescence (PL) analyses. The
synthesized photocatalysts' efficiency in suspended form was tested in the
photodegradation of tetracycline (TC) under visible light irradiation. About 95%
degradation of TC was achieved within 90 min of visible light illumination using 8%-
ZnO QDs/TiO2, under the optimized conditions: TC concentration = 40 mg/L, pH = 9,
catalyst dosage = 250 mg/L. The 8%-ZnO QDs/TiO2 nanocomposite photocatalyst was
immobilized on linear low-density polyethylene (LLDPE) polymer using the solution
casting method. The LLDPE supported composite films (ZnO QDs/TiO2@LLDPE),
each with a different amount of 8%-ZnO QDs/TiO2 nanocomposite (2, 5, 8, and 10
wt.%) were characterized by FTIR, XRD, FESEM, UV-vis-DRS, AFM, water contact
angle, differential scanning calorimetry (DSC), and thermogravimetric (TGA)
analyses. Structural and morphological studies revealed that the nanocomposites were
homogenously dispersed and embedded onto the LLDPE matrix. Moreover, the film
photocatalysts exhibited higher surface roughness and enhanced hydrophilicity compared to bare LLDPE film. The photocatalytic activity of the film photocatalysts
was evaluated on the degradation of TC under visible light irradiation. Emphasis was
placed on the effect of catalyst loading, solution pH, film size, light sources, catalyst
reusability, as well as the effects of inorganic ions and natural organic matter (NOM)
on the degradation of TC. All the synthesized photocatalysts exhibited pseudo-firstorder
kinetics with the best film photocatalyst had 89.45% efficiency after 180 min of
visible light irradiation. Moreover, the as-synthesized film photocatalysts could be
easily separated and reused for eight times, showing great potential for practical
applications in environmental wastewater treatment. Finally, TC degradation products
were studied by liquid chromatography/time of flight/mass spectrometry
(LC/TOF/MS) analysis. Based on the identified intermediates, the photocatalytic
degradation pathways of TC were proposed.
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Keywords
Chemistry