Visible-light-active chlorophyll/flavonoid-sensitized ZnO nanoparticles: preparation and optical and photocatalytic stud
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RESEARCH
Visible-light-active chlorophyll/flavonoid-sensitized ZnO nanoparticles: preparation and optical and photocatalytic studies Azadeh Haghighatzadeh 1 Received: 31 December 2019 / Revised: 17 June 2020 / Accepted: 18 September 2020 # Australian Ceramic Society 2020
Abstract We describe preparation of chlorophyll/flavonoid-sensitized ZnO nanoparticles with visible-light-induced photocatalytic activity. ZnO catalysts were sensitized by an incipient wetness impregnation in which chlorophyll and flavonoid natural pigments were extracted from parsley leaves and Curcuma longa roots, respectively. Structural studies were conducted using characterization techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Diffuse reflectance spectra (DRS) were employed to analyze optical characteristics indicating a decrease in bandgap energies of as-sensitized samples towards visible light absorption compared with nonsensitized ZnO catalysts. The photocatalytic property of chlorophyll/flavonoid-sensitized ZnO nanoparticles was evaluated by measuring photodegradation of methylene blue (MB) as a function of involved operating parameters including irradiation time, photocatalyst concentration, pH, and initial MB concentration in aqueous media. Chlorophyll-sensitized catalysts showed higher photodegradation efficiency in comparison with the flavonoid-sensitized sample relevant to a larger optical absorption edge. The photocatalytic results also indicated less optimum irradiation time in the presence of flavonoid-sensitized catalysts compared with that in the presence of the chlorophyll-sensitized sample due to stronger absorption ability of photons in a region around the optical absorption edge. The kinetic expressions were studied using the Langmuir-Hinshelwood theory, and an appropriate model was presented for the MB photodegradation process. Keywords Dye sensitization . Natural pigments . Zinc oxide . Photocatalyst . Photodegradation
Introduction Living organisms and human health have been seriously threatened by synthetic nitrogen-containing dyes such as rhodamine B (RhB), methyl orange (MO), and methylene blue (MB) as a class of causative agents of water pollution [1]. Tremendous efforts have been dedicated to the development of various treatment techniques, e.g., biological methods, membrane filtration technology, adsorption, electrochemical methods, ozone oxidation, and photocatalytic degradation [2]. Advantages like simple processes, energy savings, and lack of secondary pollutants have led to semiconductor photocatalysis with high oxidation ability and broad applicability being considered a highly efficient technique to
* Azadeh Haghighatzadeh [email protected] 1
Department of Physics, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
eliminate organic dyes from the water [2]. Among reported semiconductor materials, zinc oxide (ZnO) with a hexagonal wurtzite structure has attracted a great deal of attention owning to
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