Reusable hybride CoFe 2 O 4 -ZnO hollow nanosphere photocatalysts
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Reusable hybride CoFe2O4-ZnO hollow nanosphere photocatalysts A. Wilson, S. R. Mishra, and B. K. Rai Department of Physics, The University of Memphis, Memphis, TN 38152 R.K. Gupta and K. Ghosh Department of Physics, Materials Science, and Astronomy Missouri State University Springfield, MO 65897 Abstract Magnetically separable and reusable core-shell CoFe2O4-ZnO photocatalyst nanospheres were prepared via hydrothermal synthesis technique using glucose derived carbon nanospheres as template. The morphology and phase of core-shell hybrid structure of CoFe2O4-ZnO was assessed via TEM, and XRD. The UV-vis photocatalytic activity of the composite was assessed via measuring the degradation rate of modeled pollutant methylene blue in water. The magnetic composite showed high UV photocatalytic activity for the degradation of methylene blue. The photocatalytic activity was found to be ZnO shell thickness dependent. Thicker ZnO shells lead to higher rate of photocatalytic activity. Hybrid nanospheres recovered using external magnetic field demonstrated good repeatability of photocatalytic activity. These results promise the reusability of hybrid nanospheres for photocatalytic activity. Introduction In wastewater treatment, nanoparticles loaded slurry reactors may be used as devices because of their high specific surface area and good dispersion [1,2]. However, these slurry reactors find limited application mainly because of difficulty in separating nanoparticles from treated water. To overcome this difficulty various strategies including nanoparticles beads, thin films, nanoparticles loaded porous substrate etc. have been used [3,4,5,6]. However, the activity of nanophotocatalyst is reduced considerably due to immobilization techniques. In order to overcome this problem, recently the use of cores-shell magnetic-photocatalyst particles has been proposed, where photocatalysts particles can be effectively collected using external magnetic field [7,8]. Generally these nanoparitcles use Fe3O4 as a magnetic core, which can easily oxidized to paramagnetic Fe2O3 upon heat treatment while coating it with photocatalyst layer such as TiO2 [9,10]. Thus, it is inherently difficult to produce photocatalyst-coated particles of high photoactivity without loss of magnetic property by an iron oxide phase transition. Although TiO2 is universally considered as the most important photocatalyst, ZnO an n-type semiconductor is also a suitable alternative to TiO2 due to their similar bandgap energy (3.2 eV) and its lower cost. Moreover, in certain case, larger quantum efficiency and higher photocatalytic activity than TiO2 have been reported [11,12]. Some favorable properties of ZnO also include high electron mobility, wide band gap, strong room-temperature luminescence and ability to sustain large electric fields. However, the photocatalytic activity of zinc oxide should be further enhanced from the viewpoint of practical use and commerce. Therefore, various methods have been developed to reduce the e-/h+ recombination rate of ZnO in the photocatal
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