Effects of silver doping on the optical and photocatalytic properties of Zinc oxide thin mills
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Date
2020
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Publisher
University of Namibia
Abstract
To study the optical and photocatalytic properties of zinc oxide (ZnO or zincite), thin films doped with metallic silver-nanoparticles (Ag-NPs), with various amounts of Ag (20 mol% ≤ n ≤ 80 mol%), were fabricated on a quartz glass substrate at 600°C in air using the molecular precursor method (MPM). The fabricated thin films were analysed and X-ray diffraction (XRD) patterns of Ag nanoparticles, zinc oxide, and composite AgNP/ZnO films were measured using an X-ray diffractometer. XRD patterns of ZnO thin film showed that the pure ZnO is c-axis (002) oriented. The XRD spectrum of pure Ag elucidated that the resultant silver film contains Ag crystallized in the cubic system. UV/Vis absorption spectra of the composite AgNPs/ZnO thin films revealed a surface plasmon resonance (SPR) peak around 410 nm. The 80% Ag film was found to experience the highest SPR. The intensity of wide-range absorption in the visible region increased with an increase in the Ag content in ZnO matrix, hence an increase in the SPR peak. This increase in the SPR absorption is due to the decrease in the amount of ZnO, hence the thin films become more metallic and also hence why the 80% film experiences the highest SPR. The bandgap of ZnO was also determined using the absorption spectra of naked ZnO and composite AgNPs/ZnO thin films and was found to significantly decrease from 3.30 eV for a naked ZnO to 2.30 eV for the composites. The photocatalytic activity of MO decoloration was investigated quantitatively by monitoring the changes between the initial MO absorption spectra and the final MO absorption spectra intensity positions, as well as qualitatively by determining the decoloration rate of MO (nM min−1). The absorption spectra of decoloration of 0.02 × 10−3 M MO aqueous solution tested under visible light irradiation and dark, for 8 h respectively, by employing the naked ZnO thin film, pure Ag-NP, composite thin films and the blank. The decoloration rates monitored by the
absorption intensity of the MO solution indicated that the composite thin films of Ag are effective under visible irradiation. The index of photocatalytic activity (IPCA) values extracted from decoloration rate of 0.02×10–3 M MO solution by photoreaction with each thin film and a blank show that, under visible light irradiation, none of the composite samples exhibits more photoactivity than the 80 % Ag composite thin film. All of the composite samples are more photoactive than pure ZnO under both dark and visible light irradiation. The different results reveal that the photoactive enhancement mechanisms under dark and visible light irradiation are different. Undoped ZnO exhibits no photocatalytic reaction properties. Absorption spectra of the thin films, suggested that the visible responsive activity of the composite thin films is due to SPR of AgNPs. It was also elucidated that the vis-responsive level of the composite thin films corresponds to their change in band gaps depend on the Ag content. On the basis of photo excited electron transfer from AgNPs to the ZnO conduction band, the excellent response to vis-light and major factors affecting the photo response were clarified by SPR
Description
A research thesis submitted in fulfillment of the requirements for the Degree of Master of Science in Chemistry
Keywords
Silver dopinng, Zinc