Markovic and colleagues (2016) have used the method of heterogeneous photocatalysis, as an efficient method for degradation and mineralization of pollutants present in water bodies and did some modifications. The materials used to initiate photocatalysis are the semiconductor oxides like TiO2 and ZnO. Researchers modified these semiconductor oxides so that they can become suitable for visible light photocatalysis as these oxides (TiO2 and ZnO) can absorb only UV light from the sunlight which is present in very minute percentage (~3-5%). So, they used Microwave processing (MW) method to introduce lattice defects to modify the absorption properties and visible photocatalytic activity.
The study investigated the influence of PEO molecular weight on the photocatalytic activity of ZnO/PEO nano-structured composites. ZnO nanoparticles of wurtzite structure were synthesized using MW method which generated fast crystallization of spheroidal nano-structured particles with high density of intrinsic crystal defects (oxygen vacancies and zinc interstitials). These defects helped in the absorption of visible light and enhanced the photocatalytic efficiency under direct sunlight irradiation. Further, ZnO nanoparticles composites with polyethylene oxide (PEO, –[CH2CH2O]n–) were prepared, thus creating oxygen interstitials at the composite’s (ZnO/PEO) surface that enhanced the photocatalytic activity of MW processed ZnO.
Researchers used the PEO with molecular weight of 200,000, 600,000 and 900,000 g/mol respectively, to study its influence on photolytic efficiency of ZnO/PEO nano-composites by using the method of de-colorization of methylene blue, under direct sunlight irradiation. They found ZnO/PEO 600,000 was the most efficient composite to enhance the photolytic efficiency because by further increase in the molecular weight particles would get gelled in water suspension.
Further, the researchers investigated the phase purity and crystal structure of the composites by X-ray diffraction and Raman spectroscopy. They also studied the composite’s particles morphology and size distributions by FE-SEM and laser diffraction particle size analyzer, respectively. The optical properties were also analyzed by using UV–Vis diffuse reflectance and photoluminescence spectroscopy. They found that the ZnO and ZnO/PEO composites absorb about 50% of the incident light intensity in the wavelength range 550–800 nm. They also determine the red-shift of band gap energy (0.12–0.15 eV) compared to bulk ZnO.
Calculations based on density functional theory were performed, in order to confirm and further clarify their results. The researchers calculations confirmed that the visible light photolytic efficiency can be enhanced due to the presence of intrinsic defects that caused the band gap narrowing.
Smilja Marković1 , Vladimir Rajić1, Ana Stanković1, Ljiljana Veselinović1, Jelena Belošević-Čavor2, Katarina Batalović2, Nadica Abazović2, Srečo Davor Škapin3, Dragan Uskoković1. Effect of PEO molecular weight on sunlight induced photocatalytic activity of ZnO/PEO composites. Solar Energy, Volume 127, 2016, Pages 124–135.Show Affiliations
- Institute of Technical Sciences of SASA, Knez Mihailova 35/IV, 11000 Belgrade, Serbia
- The Vinča Institute of Nuclear Sciences, University of Belgrade, 11001 Belgrade, Serbia
- Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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