The Progress of <svg style="vertical-align:-4.50008pt;width:44.5px;" id="M1" height="21.0375" version="1.1" viewBox="0 0 44.5 21.0375" width="44.5"  xmlns="http://www.w3.org/2000/svg">
	<g transform="matrix(1.25,0,0,-1.25,0,21.0375)">
		<g transform="translate(72,-55.17)">
			<text transform="matrix(1,0,0,-1,-71.95,59.7)">
				<tspan style="font-size: 17.93px; " x="0" y="0">T</tspan>
				<tspan style="font-size: 17.93px; " x="10.795666" y="0">i</tspan>
				<tspan style="font-size: 17.93px; " x="15.78104" y="0">O</tspan>
			</text>

			<text transform="matrix(1,0,0,-1,-43.22,55.22)">
				<tspan style="font-size: 12.55px; " x="0" y="0">𝟐</tspan>
			</text>

		</g>
	</g>
</svg> Nanocrystals Doped with Rare Earth Ions

Liu, Hai; Yu, Lixin; Chen, Weifan; Li, Yingyi

doi:https://doi.org/10.1155/2012/235879

Journal of Nanomaterials

On this page

Abstract Introduction Conclusion References Copyright Related Articles

Special Issue

Nanocrystals-Related Synthesis, Assembly, and Energy Applications 2012

View this Special Issue

Review Article | Open Access

Volume 2012 | Article ID 235879 | https://doi.org/10.1155/2012/235879

The Progress of Nanocrystals Doped with Rare Earth Ions

Hai Liu,¹Lixin Yu,¹Weifan Chen,¹and Yingyi Li¹

Academic Editor: William W. Yu

Received29 Sept 2011

Revised03 Nov 2011

Accepted03 Nov 2011

Published15 Mar 2012

Abstract

In the past decades, TiO₂ nanocrystals (NCs) have been widely studied in the fields of photoelectric devices, optical communication, and environment for their stability in aqueous solution, being nontoxic, cheapness, and so on. Among the three crystalline phases of TiO₂, anatase TiO₂ NCs are the best crystallized phase of solar energy conversion. However, the disadvantages of high band gap energy (3.2 ev) and the long lifetime of photogenerated electrons and holes limit its photocatalytic activity severely. Therefore, TiO₂ NCs doped with metal ions is available way to inhibit the transformation from anatase to rutile. Besides, these metal ions will concentrate on the surface of TiO₂ NCs. All above can enhance the photoactivity of TiO₂ NCs. In this paper, we mainly outlined the different characterization brought about in the aspect of nanooptics and photocatalytics due to metal ions added in. Also, the paper mainly concentrated on the progress of TiO₂ NCs doped with rare earth (RE) ions.

1. Introduction

As one of the most popular semiconductors, TiO₂ has attracted lots of interest for its high photodegradation efficiency, high photocatalytic activity, high stability, and other advantages [1–4]. Just for these reasons, it has been used to purify polluted water and air, to solve the environmental problems, to be host in the field of solar cell and other relative areas [5, 6]. It is well known that reduction of particle size of crystalline system can result in remarkable modification of their physical and chemical properties which are different from those of microsized materials, as called bulk, because of surface effect and quantum confinement effect of nanometer materials. Thus TiO₂ NCs have been one of the research central issues. But TiO₂ NCs have the limits of wide band and the trend to transform to rutile from anatase, which has a negative effect to the photocatalytic activity. Some researchers have reported that they could improve the absorption and photocatalytic activity via dye-sensitizing, surface deposition with metal or doping with metal, nonmetal, or their oxides [7–11]. And many nonmetal ions have been successfully doped, such as S, C, F, N, and B [8, 12–16]. Although doping such additives could change the band gap, they will get the oxidative capacity down. Thus, it cannot degrade the adsorption on the surface of nano-TiO₂ absolutely. In addition, the structure stability is not that well. Also, doping metal ions to nano-TiO₂ has also been studied extensively, such as Pt and W [17–20]. Particularly, many studies have been focused on doping RE ions into TiO₂ NCs to improve this situation [21–27]. Because of the perfect ability of titanium oxide to form complexes with the f-orbital from RE, it will adsorb foreign ions around the surface, then enhancing the photocatalytic activity or other optoelectronic characteristics [27, 28]. Among all the RE elements, the Eu/Er ions are considered as the best choice for its excellent physical and chemical performance. The RE ions will form complexation with RE–O–Ti bond on the inner-sphere surface. On the one hand, this bond will inhibit the transformation from anatase to rutile, and on the other hand, the formed complexation will strengthen the ability to absorb foreign ions [27]. In addition, the absorption of TiO₂ NCs doped with RE ions may be adjusted from UV to visible light region because the RE ions have large amounts of energy levels. So it is very necessary for researchers to explore the theory and the experimental results on such field. And now it has been widely known that the photocatalytic reactivity of titanium dioxide depends on microstructure, particle size, preparative route, foreign ions, and so forth [29–31]. In this paper, we introduced the recent development of nanocrystalline TiO₂ doped with RE ions or other additives.

2. The Approaches to Fabricate TiO₂ NCs

The synthesis technique can affect nanocrystalline TiO₂ on the structure, purity, morphology, and other qualities. The soft chemical method, such as sol-gel, hydrothermal method, has many advantages, such as easy, cheaper, preparation processes being controlled and has been applied to prepare TiO₂ NCs extensively. The comparison among these methods was listed in Table 1.

2.1. Hydrothermal Method

The hydrothermal growth of TiO₂ nanowires with using TiO₂ powder in a 5–10 M alkali solution has been extensively applied [33, 34]. However, these films fabricated by this method are very thin, and the processing temperature is too high to be large-scale applications. Still, there are two major controversies about the chemical structure and formation mechanism in the hydrothermal process of TiO₂ NCs doped with RE ions [32]. These chemical structures and their lattice parameters are shown in Table 2. The chemical composition of Na_xH_2−xTi₃O₇ and Na_xH_2−xTi₂O₄(OH) groups are more acceptable. The replacement of Na⁺ by H⁺ during acid washing and the existence of [TiO₆] play a very important role in forming the TiO₂ nanotubes. And rutile is thought to have a better ability to rearrange than anatase phase. The TiO₂ NCs doped with RE ions are usually formed during the sol-gel process [35–38]. After annealing at a relatively high temperature, the RE ions are absorbed on the surface of NCs or enter into the vacancies of lattice just for the theory of solid reaction. Doping of RE ions will inhibit the transformation from anatase to rutile, then it maybe have a high affect on the TiO₂ nanotube growing as thin-and-long state. It is important and interesting that Tong et al. reported that the TiO₂ NCs-doped Ce⁴⁺ ions by hydrothermal method could effectively improve the photocatalytic activity of TiO₂ NCs under both UV light irradiation and visible light irradiation due to the important role 4f electron configuration of Ce⁴⁺ ions played in interfacial charge transfer and elimination of electron-hole recombination [39]. Yan et al. thought that the expansion of the lattice that probably results from the formation of RE–O–Ti bonds [35]. Also they found that the percentage of anatase phase in RE-doped TiO₂ decreasing in the order of Nd³⁺ > Pr³⁺ > Y³⁺ > La³⁺, as is shown in Table 3, but the degree of red shift increases in the order of La³⁺ < Pr³⁺ < Nd³⁺ < Y³⁺-doped samples, in contrast with the ion radii of RE. We can conclude, the doping of RE ion will cause the energy transfer with TiO₂ conduction or valence band, which will lead red shift due to the transition of the electrons situated in the inner 4f orbital to the 5d orbital (4f-5d transition) or to other 4s orbital (f-f transition) [40]. The applied temperature, treatment time, the type of alkali solution, and the Ti precursor during the hydrothermal treatment [32] are considered as the predominant factors affecting the fabrication of TiO₂ doped with RE. So the study on how the RE ions affect the formation of TiO₂ associating with these factors above is very necessary to put the TiO₂ NCs into actual application.

2.2. Sol-Gel Synthesis

Sol-gel approach is one of the most practical manners to prepare inorganic materials for its simpleness and low cost. And we can acquire nanoparticles with dimensions ranging from 5 to 100 nm. The material obtained by this method shows many desirable properties such as high surface area, high homogeneity [41–43]. But because the precursor has a so high reactivity that it is hard to control the structure development during the hydrolysis and condensation, which makes it difficult to fabricate monolithic TiO₂ NCs [44–48]. Chen et al. have reported C-, N-modified porous monolithic TiO₂ NCs through sol-gel technique with average particle size of 7.8 nm [48]. And the reaction rate of decolorization of methyl orange is 0.0026 min⁻¹, which proves that the ratio of the precursors plays an important role in the structure and photo activity. Moreover, Zeng et al. had prepared Eu : TiO₂ with a strong photoluminescence emission with the average particle size of 13 nm [49]. As for the RE ions, it is often doped into the solution of precursor in the form of nitrate or chloride. After several hours of stirring, we can obtain transparent sol with RE. Then the sample must be annealing at a certain temperature for a certain period to ensure Ln(III)-TiO₂ NCs obtained. Stengl et al. studied the affects of RE (La, Ce, Pr, Nd, Sm, Eu, Dy, Gd) on the physical and chemical properties of titania NCs by sol-gel method [50], as is shown in Figure 1. They found that best photocatalytic properties in visible light were the TiO₂ NCs doped with Nd³⁺ ions ( min⁻¹ for UV and 0.0143 min⁻¹ for visible light). Xu et al. also got the similar result that Gd³⁺-doped TiO₂ showing the highest reaction activity among all concerned RE-doped samples (Sm³⁺-, Ce³⁺-, Er³⁺-, Pr³⁺-, La³⁺-, and Nd³⁺-doped TiO₂ NCs catalyst) because of its specific characteristics [23], which was similar with the result from the study of El-Bahy et al., who also thought that Gd³⁺-doped TiO₂ NCs are more effective than La³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and Yb³⁺ just because Gd³⁺/TiO₂ NCs have the lowest band gap and particle size, and also the highest surface area and pore volume [51]. At the meantime, the conclusion that the synthesized Eu/TiO₂ catalyst exhibits strong red emissions under excitation wavelength at 394 and 464 nm from the comparison Eu/TiO₂ and Gd/TiO₂ by Zhou et al. [52]. As can be concluded that, the relationship between RE and luminescent properties or catalytic efficiency needs further research in the field of TiO₂ NCS synthesized by sol-gel technique.

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

2.3. Anodic Oxidation Method

Since Grimes and coworkers first reported the fabrication of titania nanotube array via anodic oxidation of titanium foil in a fluoride-based solution in 2001 [53], the studies on precise control and extension of the nanotube morphology, length and pore size, and wall thickness [54, 55] have obtained extensive attention. As is thought that chemical dissolution and electrochemical etching process play an important role in the conformation of nanotubes. And the electrolyte used in this system is always HF or KF, whose concentration has a strong effect on the dimensions and nanotube arrays [56]. Using the anodic potential from 10 to 20 V, self-organized TiO₂ NCs can be produced with diameters between 15 nm and 200 nm under specific electrochemical condition [57, 58]. The pH value of the electrolyte will also affect the thickness of TiO₂ nanotube layers [58, 59]. Yang et al. used anodization method then obtained TiO₂ nanotube arrays with a high surface area [60], as seen in Figure 2. It can be seen that the length and average outer diameter of this nanotube is 680 nm and 80 nm with a length-to-width aspect ratio about 8.5, which raises the conversion efficiencies to 0.31%, improving surface activities largely. RE ions are usually added into TiO2 NCs during the preparation procedure. After heating at 400°C for a certain time for decomposing the organic compounds brought into during the preparation procedure, the samples are needed to be heated to higher temperature for the insurance of formation of RE compounds in the layers [61]. Graf et al. successfully prepared the TiO₂ doped with cerium and gadolinium ions in the anodic oxidation method, and they found that Gd-doped titanium dioxide showed better photocatalytic activity than cerium-doped sample possibly because Gd³⁺ ions have better stability [62].

2.4. Other Methods

Nowadays, there are also some other routes to fabricate TiO₂ NCs. For example, Liang et al. had studied the effects brought by doping these ions of La, Y, Yb, Eu, Dy into TiO₂ NCs with the plasma way [63]. And they found that the effects of pH, sample flow rate and volume, elution solution, and interfering ions on the separation of analytes all have influence on the photocatalytic activity. Wu et al. systematically explored the effects for lanthanum-ions-doped TiO₂ NCs by plasma spray as well [64].

Template-assisted method is one of the most popular ways to fabricate such material. Attar et al. successfully prepared well-aligned anatase and rutile TiO₂ nanorods and nanotubes with a diameter of about 80–130 nm via sol-gel template method [65]. Also, magnetron sputtering method, electrophoretic deposition (EPD), and many other methods are employed to fabricate TiO₂ NCs doped with RE ions [66–70]. All above methods also could create nanomaterial with perfect morphology and high photocatalytic activity.

3. The Effect Caused by RE Ions

In this section, we mainly discuss the change of optical properties and the morphology caused by the RE ions doped or codoped with RE and other non-RE.

3.1. The Theory of the Effect Caused by RE Ions

The energy transfer from TiO₂ NCs to RE may easily take place since RE ions have a plenty of energy levels. For example, ⁵D₁→⁷F₁, ⁵D₀→⁷F_j transitions of Eu³⁺ ions will cause visible luminescence peaking at 543, 598, 620, 665, and 694 nm [71]. In addition, the RE-doped TiO₂ NCs almost have the capacity to enhance photocatalytic activity due to following properties of as-prepared RE³⁺/TiO₂ composites: (i) quantum size effect; (ii) unique textural properties (mesoporosity with larger BET surface areas and pore sizes); (iii) interesting surface compositions (more hydroxyl oxygen and adsorbed oxygen and some Ti³⁺ species existed at the surface of the products with respect to pure TiO₂) [72], while some thought that the increase in photoactivity is probably due to the higher adsorption, red shifts to a longer wavelength, and the increase in the interfacial electron transfer rate [41, 51].

3.2. The Effect Caused by RE Ions Doped Only

TiO₂ NCs doped with RE ions can concentrate organic pollutants on the semiconductor surface just because lanthanide ions can form complexes with various Lewis bases including organic acids, amines, aldehydes, alcohols, and thiols by the interaction of the functional groups with their f orbital, which can enhance the efficiency of separation between electrons and holes and prohibit the transformation from anatase to rutile [27, 28, 73]. Accordingly, it can prolong the photoresponse in visible region. Du et al. studied the effect of surface OH population on the photocatalytic activity of RE-doped P25-TiO₂ systematically [74], listed in Table 4. It can be seen that Pr, La, Ce, Y, and Sm ions in TiO₂ Ncs have a significant inhibition of phase transformation, especially at 800°C or above. And the anatase fraction follows the decreasing order Pr > La > Ce > Y > Sm. At the meantime, we can also know that the photocatalytic degradation of methylene blue over RE oxide-modified TiO₂ is mainly dependent on the quantity of a specific anatase—OH group. Cacciotti et al. successfully prepared La-, Eu-, and Er-doped TiO₂ NCs via electrospinning technique [75], which also can raise the transformation temperature up to 900°C. Wang et al. also synthesized TiO₂ NCs doped with Eu, Er, Ce, Pr by this method [76]. And the particles obtained had an average diameter of 10 nm with remarkable luminescent properties. It can be clearly seen that most of the RE ions have the ability to inhibit the transformation from anatase to rutile. Li et al. reported that the luminescent intensity can be enhanced through energy transfer from Eu³⁺ to TiO₂ NCs [77]. Jeon and Braun synthesized Er³⁺-doped TiO₂ nanoparticles (−50 nm) through a simple hydrothermal method starting from sol-gel precursors with anatase phase [78]. They observed obviously enhanced luminescence from thin films of the nanoparticles by annealing at 500°C. A sharp emission peak at 1532 nm with a fill width at half maximum (FWHM) of 5 nm was observed, which excludes the possibility that Er³⁺ ions exist under a free oxide form in the TiO₂ matrix, with contrast with the emission band of erbium oxide nanoclusters synthesized through a microemulsion technique centered at 1540 nm with an FWHM of 22 nm [79]. Patra et al. also studied the upconversion luminescence of Er doped into TiO₂ NCs under 975 nm excitation [80].

However, there are two major controversies still exist [81]. One is whether the lifetime of transition metal or RE ions-doped TiO₂ semiconductor NCs can be shortened by orders of magnitude caused by quantum size effects. The other is that lanthanide ions incorporate into the lattice sites of the host or be adsorbed on the surface because of the different radius and valence between RE ions and cationic of host. Chen et al. prepared TiO₂ : Eu anatase NCs (8–12 nm) by a hydrothermal method and proved that Eu³⁺ occupy three sites in NCs host through site selective spectra at 10 K [81], as shown in Figure 3. By means of site selective spectra, at least three kinds of luminescence sites of Eu³⁺ are identified and separated from each other. Two sites (Sites II and IU) exhibit sharp emission and excitation peaks, which are ascribed to the lattice site with ordered crystalline environment (inside). The other site (Site I) associated with the distorted lattice sites near the surface shows significantly broadened fluorescence lines. very strong Eu³⁺ luminescence from major Sites II and III plus other minor sites can be seen under the band gap excitation at 343.1 nm. The energy transfer from the host to Eu³⁺ confirms that Eu³⁺ ions have been effectively incorporated into the TiO₂ NCs. But it should be noted that there may be some RE ions locating at surface sites. So it always has a long way to explore the function caused by lanthanide ions doped.

3.3. The Effect Caused by Codoped RE Ions and Other Ions

Besides, Xu et al. and Ma et al. had prepared the TiO₂ NCs codoped with RE ions and nonmetal ions by the sol-gel method [82, 83], which had better adsorption activity than those doped with RE ions only. Xu et al. reported that Eu-, N-codoped TiO₂ NCs exhibited a significant red shift to the visible area [82], as shown in Figure 4. It is obvious that Eu-, N-codoped TiO₂ NCs show the highest adsorption activity. And we could also know that Eu-, N-codoped TiO₂ NCs have a smaller particle with a good inhibition from anatase to rutile. Besides, Ma et al. also obtained Sm-, N-codoped TiO₂ NCs by a similar way [83], which was similar to the result of Eu-, N-codoped TiO₂ NCs. Thus, we can conclude the absorption of TiO₂ NCs could be modulated from UV light to visible light because of the addition of RE ions, which can meet the application. It is thought that the metal ions (such as lanthanide ions) doped TiO₂ NCs will expand the photoresponse area. Meantime, the nonmetal ions will inhibit the combination of photogenerated electrons and holes. And it also has the ability to suppress the transformation from anatase to rutile. So it is hopeful to improve the photocatalytic activity by adding the metal ions with nonmetal elements.

4. Conclusion

In conclusion, TiO₂ NCs are chosen as one of the most potential candidates to purify polluted water and air, to solve the environmental problems, and to be host in the field of solar cell and other relative areas for its excellent stability, low cost, and friendliness to environment. Adding RE ions to TiO₂ can suppress the transformation to rutile from anatase, absorb the organic pollutant on the surface of the base, then improving the photocatalytic activity. So RE-doping nano-TiO₂ has been studied extensively, but the application situation is not that affirmative. The author suggested that the development orientation include these aspects below.(1)explore the influent theory about the co-doping ions into nano-TiO₂, such as metal and metal, metal and nonmetal, nonmetal and nonmetal, especially the area of metal and nonmetal coexists, (2)investigate the way to improve the catalytic properties, without sacrificing the oxidation activity, especially adjusting the absorption range,(3)search for the ideal ways to manufacture RE-doped TiO₂ NCs so as to modulate the absorption to visible region and to meet its industrial needs.

References

P. V. Kamat, “Meeting the clean energy demand: nanostructure architectures for solar energy conversion,” Journal of Physical Chemistry C, vol. 111, no. 7, pp. 2834–2860, 2007.
View at: Publisher Site | Google Scholar
M. Sleiman, C. Ferronato, and J. M. Chovelon, “Photocatalytic removal of pesticide dichlorvos from indoor air: a study of reaction parameters, intermediates and mineralization,” Environmental Science and Technology, vol. 42, no. 8, pp. 3018–3024, 2008.
View at: Publisher Site | Google Scholar
K. Maeda, K. Teramura, D. L. Lu et al., “Photocatalyst releasing hydrogen from water—enhancing catalytic performance holds promise for hydrogen production by water splitting in sunlight,” Nature, vol. 440, no. 7082, p. 295, 2006.
View at: Google Scholar
X. Chen and S. S. Mao, “Titanium dioxide nanomaterials: synthesis, properties, modifications and applications,” Chemical Reviews, vol. 107, no. 7, pp. 2891–2959, 2007.
View at: Publisher Site | Google Scholar
J. H. Park, S. Kim, and A. J. Bard, “Novel carbon-doped TiO₂ nanotube arrays with high aspect ratios for efficient solar water splitting,” Nano Letters, vol. 6, no. 1, pp. 24–28, 2006.
View at: Publisher Site | Google Scholar
Y. Li, G. Lu, and S. Li, “Photocatalytic transformation of rhodamine B and its effect on hydrogen evolution over Pt/TiO₂ in the presence of electron donors,” Journal of Photochemistry and Photobiology A, vol. 152, no. 1–3, pp. 219–228, 2002.
View at: Publisher Site | Google Scholar
Z. Wang, C. Chen, F. Wu et al., “Photodegradation of rhodamine B under visible light by bimetal codoped TiO₂ nanocrystals,” Journal of Hazardous Materials, vol. 164, no. 2-3, pp. 615–620, 2009.
View at: Publisher Site | Google Scholar
R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, and Y. Taga, “Visible-light photocatalysis in nitrogen-doped titanium oxides,” Science, vol. 293, no. 5528, pp. 269–271, 2001.
View at: Publisher Site | Google Scholar
W. Zhao, W. Ma, C. Chen, J. Zhao, and Z. Shuai, “Efficient degradation of toxic organic pollutants with Ni₂O₃/TiO₂-xBx under visible irradiation,” Journal of the American Chemical Society, vol. 126, no. 15, pp. 4782–4783, 2004.
View at: Publisher Site | Google Scholar
C. Chen, M. Long, H. Zeng et al., “Preparation, characterization and visible-light activity of carbon modified TiO₂ with two kinds of carbonaceous species,” Journal of Molecular Catalysis A, vol. 314, no. 1-2, pp. 35–41, 2009.
View at: Publisher Site | Google Scholar
H. Li, D. Wang, P. Wang, H. Fan, and T. Xie, “Synthesis and studies of the visible-light photocatalytic properties of near-monodisperse Bi-doped TiO₂ nanospheres,” Chemistry—A European Journal, vol. 15, no. 45, pp. 12521–12527, 2009.
View at: Publisher Site | Google Scholar
T. Ohno, T. Mitsui, and M. Matsumura, “Photocatalytic activity of S-doped TiO₂ photocatalyst under visible light,” Chemistry Letters, vol. 32, no. 4, pp. 364–365, 2003.
View at: Google Scholar
S. U. M. Khan, M. Al-Shahry, and W. B. Ingler, “Efficient photochemical water splitting by a chemically modified n-TiO₂,” Science, vol. 297, no. 5590, pp. 2243–2245, 2002.
View at: Publisher Site | Google Scholar
J. C. Yu, J. Yu, W. Ho, Z. Jiang, and L. Zhang, “Effects of F- doping on the photocatalytic activity and microstructures of nanocrystalline TiO₂ powders,” Chemistry of Materials, vol. 14, no. 9, pp. 3808–3816, 2002.
View at: Publisher Site | Google Scholar
R. Nakamura, T. Tanaka, and Y. Nakato, “Mechanism for visible light responses in anodic photocurrents at N-doped TiO₂ film electrodes,” Journal of Physical Chemistry B, vol. 108, no. 30, pp. 10617–10620, 2004.
View at: Publisher Site | Google Scholar
S. C. Moon, H. Mametsuka, S. Tabata, and E. Suzuki, “Photocatalytic production of hydrogen from water using TiO₂ and B/TiO₂,” Catalysis Today, vol. 58, no. 2, pp. 125–132, 2000.
View at: Publisher Site | Google Scholar
M. Kang, S. J. Choung, and J. Y. Park, “Photocatalytic performance of nanometer-sized ${Fe}_{x} O_{y}$ /TiO₂ particle synthesized by hydrothermal method,” Catalysis Today, vol. 87, no. 1–4, pp. 87–97, 2003.
View at: Publisher Site | Google Scholar
T. Hathway, E. M. Rockafellow, Y. C. Oh, and W. S. Jenks, “Photocatalytic degradation using tungsten-modified TiO₂ and visible light: kinetic and mechanistic effects using multiple catalyst doping strategies,” Journal of Photochemistry and Photobiology A, vol. 207, no. 2-3, pp. 197–203, 2009.
View at: Publisher Site | Google Scholar
Y. Ishibai, J. Sato, T. Nishikawa, and S. Miyagishi, “Synthesis of visible-light active TiO₂ photocatalyst with Pt-modification: role of TiO₂ substrate for high photocatalytic activity,” Applied Catalysis B, vol. 79, no. 2, pp. 117–121, 2008.
View at: Publisher Site | Google Scholar
T. S. Yang, M. C. Yang, C. B. Shiu, W. K. Chang, and M. S. Wong, “Effect of N2 ion flux on the photocatalysis of nitrogen-doped titanium oxide films by electron-beam evaporation,” Applied Surface Science, vol. 252, no. 10, pp. 3729–3736, 2006.
View at: Publisher Site | Google Scholar
G. Boschloo and A. Hagfeldt, “Photoinduced absorption spectroscopy of dye-sensitized nanostructured TiO₂,” Chemical Physics Letters, vol. 370, no. 3-4, pp. 381–386, 2003.
View at: Publisher Site | Google Scholar
M. S. P. Francisco and V. R. Mastelaro, “Inhibition of the anatase-rutile phase transformation with addition of CeO₂ to CuO-TiO₂ system: Raman spectroscopy, X-ray diffraction, and textural studies,” Chemistry of Materials, vol. 14, no. 6, pp. 2514–2518, 2002.
View at: Publisher Site | Google Scholar
A. W. Xu, Y. Gao, and H. Q. Liu, “The preparation, characterization, and their photocatalytic activities of rare-earth-doped TiO₂ nanoparticles,” Journal of Catalysis, vol. 207, no. 2, pp. 151–157, 2002.
View at: Publisher Site | Google Scholar
R. Gopalan and Y. S. Lin, “Evolution of pore and phase structure of sol-gel derived lanthana doped titania at high temperatures,” Industrial and Engineering Chemistry Research, vol. 34, no. 4, pp. 1189–1195, 1995.
View at: Google Scholar
G. Garcia-Martinez, L. G. Martinez-Gonzalez, J. I. Escalante-García, and A. F. Fuentes, “Phase evolution induced by mechanical milling in Ln₂O₃:TiO₂ mixtures (Ln=Gd and Dy),” Powder Technology, vol. 152, no. 1–3, pp. 72–78, 2005.
View at: Publisher Site | Google Scholar
C. P. Sibu, S. R. Kumar, P. Mukundan, and K. G. K. Warrier, “Structural modifications and associated properties of lanthanum oxide doped sol-gel nanosized titanium oxide,” Chemistry of Materials, vol. 14, no. 7, pp. 2876–2881, 2002.
View at: Publisher Site | Google Scholar
I. Cacciotti, A. Bianco, G. Pezzotti, and G. Gusmano, “Synthesis, thermal behaviour and luminescence properties of rare earth-doped titania nanofibers,” Chemical Engineering Journal, vol. 166, no. 2, pp. 751–764, 2011.
View at: Publisher Site | Google Scholar
D. W. Hwang, J. S. Lee, W. Li, and S. H. Oh, “Electronic band structure and photocatalytic activity of Ln₂Ti₂O₇ (Ln = La, Pr, Nd),” Journal of Physical Chemistry B, vol. 107, no. 21, pp. 4963–4970, 2003.
View at: Google Scholar
Y. Zhang, A. Weidenkaff, and A. Reller, “Mesoporous structure and phase transition of nanocrystalline TiO₂,” Materials Letters, vol. 54, no. 5-6, pp. 375–381, 2002.
View at: Publisher Site | Google Scholar
D. Vorkapic and T. Matsoukas, “Effect of temperature and alcohols in the preparation of titania nanoparticles from alkoxides,” Journal of the American Ceramic Society, vol. 81, no. 11, pp. 2815–2820, 1998.
View at: Google Scholar
H. Zhang and J. F. Banfield, “Phase transformation of nanocrystalline anatase-to-rutile via combined interface and surface nucleation,” Journal of Materials Research, vol. 15, no. 2, pp. 437–448, 2000.
View at: Google Scholar
H. H. Ou and S. L. Lo, “Review of titania nanotubes synthesized via the hydrothermal treatment: fabrication, modification, and application,” Separation and Purification Technology, vol. 58, no. 1, pp. 179–191, 2007.
View at: Publisher Site | Google Scholar
T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino, and K. Niihara, “Formation of titanium oxide nanotube,” Langmuir, vol. 14, no. 12, pp. 3160–3163, 1998.
View at: Google Scholar
A. Hu, X. Zhang, K. D. Oakes, P. Peng, Y. N. Zhou, and M. R. Servos, “Hydrothermal growth of free standing TiO₂ nanowire membranes for photocatalytic degradation of pharmaceuticals,” Journal of Hazardous Materials, vol. 189, no. 1-2, pp. 278–285, 2011.
View at: Publisher Site | Google Scholar
X. Yan, J. He, D. G. Evans, X. Duan, and Y. Zhu, “Preparation, characterization and photocatalytic activity of Si-doped and rare earth-doped TiO₂ from mesoporous precursors,” Applied Catalysis B, vol. 55, no. 4, pp. 243–252, 2005.
View at: Publisher Site | Google Scholar
K. T. Ranjit, I. Willner, S. H. Bossmann, and A. M. Braun, “Lanthanide oxide doped titanium dioxide photocatalysts: effective photocatalysts for the enhanced degradation of salicylic acid and t-cinnamic acid,” Journal of Catalysis, vol. 204, no. 2, pp. 305–313, 2001.
View at: Publisher Site | Google Scholar
V. Stengl, S. Bakardjieva, J. Šubrt et al., “Sodium titanate nanorods: preparation, microstructure characterization and photocatalytic activity,” Applied Catalysis B, vol. 63, no. 1-2, pp. 20–30, 2006.
View at: Publisher Site | Google Scholar
J. Yu, H. Yu, B. Cheng, X. Zhao, and Q. Zhang, “Preparation and photocatalytic activity of mesoporous anatase TiO₂ nanofibers by a hydrothermal method,” Journal of Photochemistry and Photobiology A, vol. 182, no. 2, pp. 121–127, 2006.
View at: Publisher Site | Google Scholar
T. Tong, J. Zhang, B. Tian, F. Chen, D. He, and M. Anpo, “Preparation of Ce-TiO₂ catalysts by controlled hydrolysis of titanium alkoxide based on esterification reaction and study on its photocatalytic activity,” Journal of Colloid and Interface Science, vol. 315, no. 1, pp. 382–388, 2007.
View at: Publisher Site | Google Scholar
K. Ebitani, Y. Hirano, and A. Morikawa, “Rare-earth ions as heterogeneous photocatalysts for the decomposition of dinitrogen monoxide (N₂O),” Journal of Catalysis, vol. 157, no. 1, pp. 262–265, 1995.
View at: Publisher Site | Google Scholar
F. B. Li, X. Z. Li, M. F. Hou, K. W. Cheah, and W. C. H. Choy, “Enhanced photocatalytic activity of Ce³⁺-TiO₂ for 2-mercaptobenzothiazole degradation in aqueous suspension for odour control,” Applied Catalysis A, vol. 285, no. 1-2, pp. 181–189, 2005.
View at: Publisher Site | Google Scholar
Y. Zhang, H. Zhang, Y. Xu, and Y. Wang, “Significant effect of lanthanide doping on the texture and properties of nanocrystalline mesoporous TiO₂,” Journal of Solid State Chemistry, vol. 177, no. 10, pp. 3490–3498, 2004.
View at: Publisher Site | Google Scholar
M. Saif and M. S. A. Abdel-Mottaleb, “Titanium dioxide nanomaterial doped with trivalent lanthanide ions of Tb, Eu and Sm: preparation, characterization and potential applications,” Inorganica Chimica Acta, vol. 360, no. 9, pp. 2863–2874, 2007.
View at: Publisher Site | Google Scholar
J. Konishi, K. Fujita, K. Nakanishi, and K. Hirao, “Monolithic TiO₂ with controlled multiscale porosity via a template-free sol-gel process accompanied by phase separation,” Chemistry of Materials, vol. 18, no. 25, pp. 6069–6074, 2006.
View at: Publisher Site | Google Scholar
S. O. Kucheyev, T. F. Baumann, Y. M. Wang, T. Van Buuren, and J. H. Satcher, “Synthesis and electronic structure of low-density monoliths of nanoporous nanocrystalline anatase TiO₂,” Journal of Electron Spectroscopy and Related Phenomena, vol. 144–147, pp. 609–612, 2005.
View at: Publisher Site | Google Scholar
B. Malinowska, J. Walendziewski, D. Robert, J. V. Weber, and M. Stolarski, “The study of photocatalytic activities of titania and titania-silica aerogels,” Applied Catalysis B, vol. 46, no. 3, pp. 441–451, 2003.
View at: Publisher Site | Google Scholar
A. A. Ismail and I. A. Ibrahim, “Impact of supercritical drying and heat treatment on physical properties of titania/silica aerogel monolithic and its applications,” Applied Catalysis A, vol. 346, no. 1-2, pp. 200–205, 2008.
View at: Publisher Site | Google Scholar
C. Chen, W. Cai, M. Long et al., “Template-free sol-gel preparation and characterization of free-standing visible light responsive C,N-modified porous monolithic TiO₂,” Journal of Hazardous Materials, vol. 178, no. 1–3, pp. 560–565, 2010.
View at: Publisher Site | Google Scholar
Q. G. Zeng, Z. M. Zhang, Z. J. Ding, Y. Wang, and Y. Q. Sheng, “Strong photoluminescence emission of Eu:TiO₂ nanotubes,” Scripta Materialia, vol. 57, no. 10, pp. 897–900, 2007.
View at: Publisher Site | Google Scholar
V. Stengl, S. Bakardjieva, and N. Murafa, “Preparation and photocatalytic activity of rare earth doped TiO₂ nanoparticles,” Materials Chemistry and Physics, vol. 114, no. 1, pp. 217–226, 2009.
View at: Publisher Site | Google Scholar
Z. M. El-Bahy, A. A. Ismail, and R. M. Mohamed, “Enhancement of titania by doping rare earth for photodegradation of organic dye (Direct Blue),” Journal of Hazardous Materials, vol. 166, no. 1, pp. 138–143, 2009.
View at: Publisher Site | Google Scholar
W. Zhou, Y. H. Zheng, and G. H. Wu, “Novel luminescent RE/TiO₂ (RE = Eu, Gd) catalysts prepared by in-situation sol-gel approach construction of multi-functional precursors and their photo or photocatalytic oxidation properties,” Applied Surface Science, vol. 253, no. 3, pp. 1387–1392, 2006.
View at: Publisher Site | Google Scholar
D. Gong, C. A. Grimes, O. K. Varghese et al., “Titanium oxide nanotube arrays prepared by anodic oxidation,” Journal of Materials Research, vol. 16, no. 12, pp. 3331–3334, 2001.
View at: Google Scholar
Q. Cai, M. Paulose, O. K. Varghese, and C. A. Grimes, “The effect of electrolyte composition on the fabrication of self-organized titanium oxide nanotube arrays by anodic oxidation,” Journal of Materials Research, vol. 20, no. 1, pp. 230–236, 2005.
View at: Publisher Site | Google Scholar
G. K. Mor, K. Shankar, M. Paulose, O. K. Varghese, and C. A. Grimes, “Enhanced photocleavage of water using titania nanotube arrays,” Nano Letters, vol. 5, no. 1, pp. 191–195, 2005.
View at: Publisher Site | Google Scholar
G. K. Mor, O. K. Varghese, M. Paulose, K. Shankar, and C. A. Grimes, “A review on highly ordered, vertically oriented TiO₂ nanotube arrays: fabrication, material properties, and solar energy applications,” Solar Energy Materials and Solar Cells, vol. 90, no. 14, pp. 2011–2075, 2006.
View at: Publisher Site | Google Scholar
S. Bauer, S. Kleber, and P. Schmuki, “TiO₂ nanotubes: tailoring the geometry in H₃PO₄/HF electrolytes,” Electrochemistry Communications, vol. 8, no. 8, pp. 1321–1325, 2006.
View at: Publisher Site | Google Scholar
J. M. Macák, H. Tsuchiya, and P. Schmuki, “High-aspect-ratio TiO₂ nanotubes by anodization of titanium,” Angewandte Chemie - International Edition, vol. 44, no. 14, pp. 2100–2102, 2005.
View at: Publisher Site | Google Scholar
J. Kunze, L. Müller, J. M. Macak, P. Greil, P. Schmuki, and F. A. Müller, “Time-dependent growth of biomimetic apatite on anodic TiO₂ nanotubes,” Electrochimica Acta, vol. 53, no. 23, pp. 6995–7003, 2008.
View at: Publisher Site | Google Scholar
D. J. Yang, H. Park, S. J. Cho, H. G. Kim, and W. Y. Choi, “TiO₂-nanotube-based dye-sensitized solar cells fabricated by an efficient anodic oxidation for high surface area,” Journal of Physics and Chemistry of Solids, vol. 69, no. 5-6, pp. 1272–1275, 2008.
View at: Publisher Site | Google Scholar
J. M. Macak and P. Schmuki, “Anodic growth of self-organized anodic TiO₂ nanotubes in viscous electrolytes,” Electrochimica Acta, vol. 52, no. 3, pp. 1258–1264, 2006.
View at: Publisher Site | Google Scholar
C. Graf, R. Ohser-Wiedemann, and G. Kreisel, “Preparation and characterization of doped metal-supported TiO₂-layers,” Journal of Photochemistry and Photobiology A, vol. 188, no. 2-3, pp. 226–234, 2007.
View at: Publisher Site | Google Scholar
P. Liang, B. Hu, Z. Jiang, Y. Qin, and T. Peng, “Nanometer-sized titanium dioxide micro-column on-line preconcentration of La, Y, Yb, Eu, Dy and their determination by inductively coupled plasma atomic emission spectrometry,” Journal of Analytical Atomic Spectrometry, vol. 16, no. 8, pp. 863–866, 2001.
View at: Publisher Site | Google Scholar
X. Wu, X. Ding, W. Qin, W. He, and Z. Jiang, “Enhanced photo-catalytic activity of TiO₂ films with doped La prepared by micro-plasma oxidation method,” Journal of Hazardous Materials, vol. 137, no. 1, pp. 192–197, 2006.
View at: Publisher Site | Google Scholar
A. S. Attar, M. S. Ghamsari, F. Hajiesmaeilbaigi, S. Mirdamadi, K. Katagiri, and K. Koumoto, “Synthesis and characterization of anatase and rutile TiO₂ nanorods by template-assisted method,” Journal of Materials Science, vol. 43, no. 17, pp. 5924–5929, 2008.
View at: Publisher Site | Google Scholar
J. Cho, S. Schaab, J. A. Roether, and A. R. Boccaccini, “Nanostructured carbon nanotube/TiO₂ composite coatings using electrophoretic deposition (EPD),” Journal of Nanoparticle Research, vol. 10, no. 1, pp. 99–105, 2008.
View at: Publisher Site | Google Scholar
A. Podhorodecki, G. Zatryb, J. Misiewicz, J. Domaradzki, D. Kaczmarek, and A. Borkowska, “Influence of annealing on europium photoexcitation doped into nanocrystalline titania film prepared by magnetron sputtering,” Journal of the Electrochemical Society, vol. 156, no. 3, pp. H214–H219, 2009.
View at: Publisher Site | Google Scholar
D. Kaczmarek, J. Domaradzki, A. Borkowska, A. Podhorodecki, J. Misiewicz, and K. Sieradzka, “Optical emission from Eu, Tb, Nd luminescence centers in TiO₂ prepared by magnetron sputtering,” Optica Applicata, vol. 37, no. 4, pp. 433–438, 2007.
View at: Google Scholar
B. Liu, X. Zhao, and L. Wen, “The structural and photoluminescence studies related to the surface of the TiO₂ sol prepared by wet chemical method,” Materials Science and Engineering B, vol. 134, no. 1, pp. 27–31, 2006.
View at: Publisher Site | Google Scholar
Y. Zhao, C. Li, X. Liu, F. Gu, H. L. Du, and L. Shi, “Surface characteristics and microstructure of dispersed TiO₂ nanoparticles prepared by diffusion flame combustion,” Materials Chemistry and Physics, vol. 107, no. 2-3, pp. 344–349, 2008.
View at: Publisher Site | Google Scholar
C. W. Jia, E. Q. Xie, J. G. Zhao, Z. W. Sun, and A. H. Peng, “Visible and near-infrared photoluminescences of europium-doped titania film,” Journal of Applied Physics, vol. 100, no. 2, Article ID 023529, 2006.
View at: Publisher Site | Google Scholar
J. Li, X. Yang, X. Yu et al., “Rare earth oxide-doped titania nanocomposites with enhanced photocatalytic activity towards the degradation of partially hydrolysis polyacrylamide,” Applied Surface Science, vol. 255, no. 6, pp. 3731–3738, 2009.
View at: Publisher Site | Google Scholar
R. M. Mohamed and I. A. Mkhalid, “The effect of rare earth dopants on the structure, surface texture and photocatalytic properties of TiO₂-SiO2 prepared by sol-gel method,” Journal of Alloys and Compounds, vol. 501, no. 1, pp. 143–147, 2010.
View at: Publisher Site | Google Scholar
P. Du, A. Bueno-López, M. Verbaas et al., “The effect of surface OH-population on the photocatalytic activity of rare earth-doped P25-TiO₂ in methylene blue degradation,” Journal of Catalysis, vol. 260, no. 1, pp. 75–80, 2008.
View at: Publisher Site | Google Scholar
I. Cacciotti, A. Bianco, G. Pezzotti, and G. Gusmano, “Synthesis, thermal behaviour and luminescence properties of rare earth-doped titania nanofibers,” Chemical Engineering Journal, vol. 166, no. 2, pp. 751–764, 2011.
View at: Publisher Site | Google Scholar
H. Wang, Y. Wang, Y. Yang, X. Li, and C. Wang, “Photoluminescence properties of the rare-earth ions in the TiO₂ host nanofibers prepared via electrospinning,” Materials Research Bulletin, vol. 44, no. 2, pp. 408–414, 2009.
View at: Publisher Site | Google Scholar
L. Li, C. K. Tsung, Z. Yang et al., “Rare-earth-doped nanocrystalline titania microspheres emitting luminescence via energy transfer,” Advanced Materials, vol. 20, no. 5, pp. 903–908, 2008.
View at: Publisher Site | Google Scholar
S. Jeon and P. V. Braun, “Hydrothermal synthesis of Er-doped luminescent TiO₂ nanoparticles,” Chemistry of Materials, vol. 15, no. 6, pp. 1256–1263, 2003.
View at: Publisher Site | Google Scholar
W. Que, Y. Zhou, C. H. Kam et al., “Fluorescence characteristics from microemulsion technique derived erbium (III) oxide nanocrystals,” Materials Research Bulletin, vol. 36, no. 5-6, pp. 889–895, 2001.
View at: Publisher Site | Google Scholar
A. Patra, C. S. Friend, R. Kapoor, and P. N. Prasad, “Fluorescence upconversion properties of Er³⁺-doped TiO₂ and BaTiO₃ nanocrystallites,” Chemistry of Materials, vol. 15, no. 19, pp. 3650–3655, 2003.
View at: Publisher Site | Google Scholar
C. Xueyuan, L. Wenqin, L. Yongsheng, and L. Guokui, “Recent progress on spectroscopy of lanthanide ions incorporated in semiconductor nanocrystals,” Journal of Rare Earths, vol. 25, no. 5, pp. 515–525, 2007.
View at: Publisher Site | Google Scholar
J. Xu, Y. Ao, D. Fu, and C. Yuan, “A simple route for the preparation of Eu, N-codoped TiO₂ nanoparticles with enhanced visible light-induced photocatalytic activity,” Journal of colloid and interface science, vol. 328, no. 2, pp. 447–451, 2008.
View at: Google Scholar
Y. Ma, J. Zhang, B. Tian, F. Chen, and L. Wang, “Synthesis and characterization of thermally stable Sm,N co-doped TiO₂ with highly visible light activity,” Journal of Hazardous Materials, vol. 182, no. 1–3, pp. 386–393, 2010.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2012 Hai Liu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PDF Download Citation

Download other formats

Order printed copies

Views

2539

Downloads

3391

Citations