Synthesis and characterization of anatase TiO 2 nanolayer coating on Ni-Cu-Zn ferrite powders for magnetic photocatalyst
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ung-Wen Liu and Cheng-Hsiung Lin Department of Chemical Engineering, Wu-Feng Institute of Technology, Ming-Hsiung, Chiayi 621, Taiwan (Received 13 May 2009; accepted 10 August 2009)
In the current research, we successfully prepared TiO2/Ni–Cu–Zn ferrite composite powder for magnetic photocatalyst. The core Ni–Cu–Zn ferrite powder was synthesized using the steel pickling liquor and the waste solution of electroplating as the starting materials. The shell TiO2 nanocrystal was prepared by sol-gel hydrolysis precipitation of titanium isopropoxide [Ti(OC3H7)4] on the Ni–Cu–Zn ferrite powder followed by heat treatment. From transmission electron microscopy (TEM) image, the thickness of the titania shell was found to be approximately 5 nm. The core of Ni–Cu–Zn ferrite is spherical or elliptical shape, and the particle size of the core is in the range of 70–110 nm. The magnetic Ni–Cu–Zn ferrite nanopowder is uniformly encapsulated in a titania layer forming core-shell structure of TiO2/Ni–Cu–Zn ferrite powder. The degradation efficiency for methylene blue (MB) increases with magnetic photocatalyst (TiO2/ Ni–Cu–Zn ferrite powder) content. When the magnetic photocatalyst content is 0.40 g in 150 mL of MB, the photocatalytic activity reached the largest value. With a further increase in the content of magnetic photocatalyst, the degradation efficiency slightly decreased. This occurs because the ultraviolet (UV) illumination is covered by catalysts, which were suspended in the methylene blue solution and resulted in the inhibition in the photocatalytic reaction. The photocatalytic degradation result for the relationship between MB concentration and illumination revealed a pseudo first-order kinetic model of the degradation with the limiting rate constant of 1.717 mg/Lmin and equilibrium adsorption constant 0.0627 L/mg. Furthermore, the Langmuir–Hinshelwood model can be used to describe the degradation reaction, which suggests that the rate-determining step is surface reaction rather than adsorption is in photocatalytic degradation.
I. INTRODUCTION
Photocatalysis using semiconductor particles has generated increasing interest in solving the global pollution problem. Compared with other semiconductor photocatalysts, TiO2 has been shown to be the most promising material for practical applications because it is highly photoreactive, low cost, nontoxic, chemically and biologically inert, and photostable.1 TiO2 is regarded as the best photocatalyst for decomposing refractory organic pollutants in water and air.2 The activity of the photocatalyst is significantly dependent on the crystal phase and surface area. Generally, TiO2 has three types of crystal phases: anatase, rutile, and brookite. TiO2 in an anatase is known to be an extremely active photocatalytic material. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0015
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J. Mater. Res., Vol. 25, No. 1, Jan 2010 Downloaded: 12 Mar 2015
Ultrafine anatase powders with large specific areas have g
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