Abstract
Mixed phase TiO2 nanoparticles with element doping by Sm and C were prepared via a facile sol-gel procedure. The UV-Vis light-diffuse reflectance spectroscopy analysis showed that the absorption region of co-doped TiO2 was shifted to the visible-light region, which was attributed to incorporation of samarium and carbon into the TiO2 lattice during high-temperature reaction. Samarium effectively decreased the anatase-rutile phase transformation. The grain size can be controlled by Sm doping to achieve a large specific surface area useful for the enhancement of photocatalytic activity. The photocatalytic activities under visible light irradiation were evaluated by photocatalytic degradation of methylene blue (MB). The degradation rate of MB over the Sm-C co-doped TiO2 sample was the best. Additionally, first-order apparent rate constants increased by about 4.3 times compared to that of commercial Degusssa P25 under the same experimental conditions. Using different types of scavengers, the results indicated that the electrons, holes, and •OH radicals are the main active species for the MB degradation. The high visible-light photocatalytic activity was attributed to low recombination of the photo-generated electrons and holes which originated from the synergistic effect of the co-doped ions and the heterostructure.
Highlights
The preparation and characterization of titanium oxide (TiO2 ) nanopowders have been intensely investigated for applications in air cleaning, sensors, solar cell, gene therapy, and photocatalytic water splitting because of their chemical stability against photocorrosion and chemical corrosion, nontoxicity, and cost-effectiveness [1,2,3]
The high visible-light photocatalytic activity was attributed to low recombination of the photo-generated electrons and holes which originated from the synergistic effect of the co-doped ions and the heterostructure
Average crystallite sizes of the TiO2 samples were measured from X-ray line broadening analysis using the well-known Scherrer equation: d = 0.89λ/Bcosθ where B is the full-width at half maximum (FWHM) in radians, λ is the wavelength of the X-rays in nanometers (1.5406 Å), θ is the angle between the incident and diffracted beams in degrees, and d is the average crystallite size of the powder sample in nanometers [27]
Summary
The preparation and characterization of titanium oxide (TiO2 ) nanopowders have been intensely investigated for applications in air cleaning, sensors, solar cell, gene therapy, and photocatalytic water splitting because of their chemical stability against photocorrosion and chemical corrosion, nontoxicity, and cost-effectiveness [1,2,3]. TiO2 generally shows high activity for the photocatalytic oxidation of organic pollutants [1], more widespread applications of TiO2 as a photocatalyst have been limited due toits low use of solar energy (only active in the ultraviolet region) and its relatively high recombination rate between the photo-generated electrons and holes [4]. To increase the photocatalytic efficiency of TiO2 , various methods have been used to enhance its absorption of the solar energy and to inhibit the recombination of photogenerated electron-hole pairs. A prominent approach is to dope TiO2 with transition metals or nonmetallic elements. Metal ion dopants, such as Fe [5], V [6], Bi [7], and Sm [8], can act as electron or hole traps and, decrease the electro-hole pair recombination rate. Rare-earth metals often serve as catalyst or Materials 2017, 10, 209; doi:10.3390/ma10020209 www.mdpi.com/journal/materials
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