Abstract
The combination of TiO2 photocatalyst and magnetic oxide nanoparticles enhances the separation and recoverable properties of nanosized TiO2 photocatalyst. Metal-modified (Me = Pd, Au, Pt, Cu) TiO2/SiO2@Fe3O4 nanocomposites were prepared by an ultrasonic-assisted sol-gel method. All prepared samples were characterized by X-ray powder diffraction (XRD) analysis, Brunauer-Emmett-Teller (BET) method, X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), Mott-Schottky analysis and photoluminescence spectroscopy (PL). Phenol oxidation pathways of magnetic photocatalysts modified with Pt, Pd, Cu and Au nanoparticles proceeded by generation of reactive oxygen species, which oxidized phenol to benzoquinone, hydroquinone and catechol. Benzoquinone and maleic acid were products, which were determined in the hydroquinone oxidation pathway. The highest mineralization rate was observed for Pd-TiO2/SiO2@Fe3O4 and Cu-TiO2/SiO2@Fe3O4 photocatalysts, which produced the highest concentration of catechol during photocatalytic reaction. For Pt-TiO2/SiO2@Fe3O4 nanocomposite, a lack of catechol after 60 min of irradiation resulted in low mineralization rate (CO2 formation). It is proposed that the enhanced photocatalytic activity of palladium and copper-modified photocatalysts is related to an increase in the amount of adsorption sites and efficient charge carrier separation, whereas the keto-enol tautomeric equilibrium retards the rate of phenol photomineralization on Au-TiO2/SiO2@Fe3O4. The magnetization hysteresis loop indicated that the obtained hybrid photocatalyst showed magnetic properties and therefore could be easily separated after treatment process.
Highlights
Degussa (Evonik) TiO2 P25 consisting of a mixture of anatase (∼78%), rutile (∼14%) phases and a minor amount of amorphous phase (∼8%) is a well-known commercial material frequently used to oxidize organic and inorganic compounds in air and water due to its strong oxidative ability and long-term photo-stability [1,2]
X-ray photoelectron spectroscopy (XPS) analysis revealed that the deposition of different metals changed the surface composition of photocatalysts
The magnetic saturation was about 10–12 emu·g−1 and did not depend on the amount and kind of metal deposited on the surface of TiO2
Summary
Degussa (Evonik) TiO2 P25 consisting of a mixture of anatase (∼78%), rutile (∼14%) phases and a minor amount of amorphous phase (∼8%) is a well-known commercial material frequently used to oxidize organic and inorganic compounds in air and water due to its strong oxidative ability and long-term photo-stability [1,2]. Based on practicality, TiO2 -based photocatalysis has some technical limitations that impede its commercialization. Nanomaterials 2018, 8, 28 the separation and recovery of fine TiO2 particles after purification process. Even when the photocatalyst flocculates, there is often some residue of TiO2 nanoparticles in the supernatant. In this regard, the combination of photocatalyst and magnetic particles is a suitable solution for the separation issue, allowing for a complete recovery of
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