Photocatalytic Degradation Of Tetracycline In Aqueous Solution By Zno Quantum Dots/Tio2 Supported Catalysts

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Date
2021-03
Authors
Saidu, Usman
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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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Chemistry
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