Next Article in Journal
Ocular Drug Delivery: A Special Focus on the Thermosensitive Approach
Previous Article in Journal
Pinch-Off Formation in Monolayer and Multilayers MoS2 Field-Effect Transistors
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Nanomaterials
Volume 9
Issue 6
10.3390/nano9060883
nanomaterials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Ethanol-Quenching Introduced Oxygen Vacancies in Strontium Titanate Surface and the Enhanced Photocatalytic Activity

by
Yang Xiao
1,
Shihao Chen
1,
Yinhai Wang
1,*,
Zhengfa Hu
2,
Hui Zhao
1 and
Wei Xie
3
1
School of Physics & Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, China
2
Synergy Innovation Institute for Modern Industries, Guangdong University of Technology, Dongyuan 517500, China
3
School of Physics Science and Technology, Lingnan Normal University, Zhanjiang 524048, China
*
Author to whom correspondence should be addressed.
Nanomaterials 2019, 9(6), 883; https://doi.org/10.3390/nano9060883
Submission received: 23 May 2019 / Revised: 8 June 2019 / Accepted: 10 June 2019 / Published: 14 June 2019
Browse Figures
Review Reports Versions Notes

Abstract

:
Modification of the surface properties of SrTiO3 crystals by regulating the reaction environment in order to improve the photocatalytic activity has been widely studied. However, the development of a facile, effective, and universal method to improve the photocatalytic activity of these crystals remains an enormous challenge. We have developed a simple method to modify the surface environment of SrTiO3 by ethanol quenching, which results in enhanced UV, visible and infrared light absorption and photocatalytic performance. The SrTiO3 nanocrystals were preheated to 800 °C and immediately quenched by submersion in ethanol. X-ray diffraction patterns, electron paramagnetic resonance spectra, and X-ray photoelectron spectra indicated that upon rapid ethanol quenching, the interaction between hot SrTiO3 and ethanol led to the introduction of a high concentration of oxygen vacancies on the surface of the SrTiO3 lattice. Consequently, to maintain the regional charge balance of SrTiO3, Sr2+ could be substituted for Ti4+. Moreover, oxygen vacancies induced localized states into the band gap of the modified SrTiO3 and acted as photoinduced charge traps, thus promoting the photocatalytic activity. The improved photocatalytic performance of the modified SrTiO3 was demonstrated by using it for the decomposition of rhodamine B and production of H2 from water under visible or solar light.

Graphical Abstract

1. Introduction

Since the discovery of photoelectrochemical water splitting on a titania electrode by Fujishima and Honda in 1972, photocatalysis using semiconductors has been widely studied [1]. Semiconductor-based photocatalysts are capable of directly converting solar energy to chemical energy, which provides a facile approach for environmental protection and H2 production under sunlight irradiation [2,3,4]. Among these semiconductors, titanium dioxide (TiO2) has attracted special interest because of its chemical stability, non-toxicity, and low cost [5,6]. In addition, Strontium titanate (SrTiO3), a perovskite-type oxide, has been classified a wide-band gap (3.1–3.7 eV) semiconductor photocatalyst in the field of light energy exploitation. SrTiO3 possesses various outstanding physical and chemical properties such as good chemical/catalytic stability, suitable band position, and susceptibility to change by other substance. Notably, the conduction band of SrTiO3 is more negative than that of TiO2, which is beneficial for photocatalysis [7]. However, because of its large band-gap, SrTiO3 can be utilized only in the UV region of sunlight, which largely restricts its practical application in photocatalysis [8,9].
Many studies have attempted to expand the spectral response of SrTiO3 by utilizing methods such as doping with a metal/nonmetal, or co-doping with a nonmetal to form a new intermediate gap state between the valence band (VB) and the conduction band (CB) [10,11,12,13,14]. Moreover, mixing of the energy levels of the dopant and host elements can change the position of the VB or CB, resulting in increased visible light absorption [9]. However, the rapid rate of recombination of the electron-hole pairs in SrTiO3 results in poor photocatalytic efficiency. One of the methods to improve the separation efficiency of photogenerated electron-hole pairs involves combination with other noble metals (usually Pt, Au, and Rh) or semiconductors on the surface [15,16,17,18]. In the other hand, the important role played by surface oxygen vacancies in improving the photocatalytic performance is well known. Surface oxygen vacancies can be used as surface adsorption sites and photoinduced charge traps, where the charge shifts to the adsorbed compound, so that the recombination of photogenerated electron-holes is prevented and the photocatalytic performance is improved [19,20]. Therefore, introducing oxygen vacancies on the surface of the SrTiO3 lattice seems to be a feasible process to modify the surface environment of SrTiO3. This process could improve the adsorption capacity of SrTiO3 and inhibit the recombination of photogenerated electron-hole pairs, thus improving the photocatalytic performance of SrTiO3 [21].
In 2011, Mao and co-worker developed black TiO2 by introducing disorder in the surface layer of TiO2 via hydrogenation in a high H2-pressure atmosphere at about 200 °C for 5 days. This modification greatly enhanced the solar light harvesting efficiency and photocatalytic activity of TiO2 [22]. Subsequently, various methods were developed to synthesize hydrogenated or reduced semiconductors such as TiO2, ZnO and WO3 with surface oxygen defects for improving their photocatalytic performance [23,24,25,26]. Unsurprisingly, hydrogenated or reduced SrTiO3 was also synthesized. Tan et al. introduced oxygen vacancies on the SrTiO3 surface by heating it to 300–375 °C under Ar atmosphere, to control any solid-state reaction between NaBH4 and SrTiO3, which improved its photocatalytic activity for H2 generation under UV-vis irradiation [19]. Zhao et al. prepared black SrTiO3 with abundant Ti3+ cations and oxygen vacancies by reduction using molten aluminum at 500 °C. The black SrTiO3 showed enhanced light absorption in the visible and near-infrared region and remarkable photocatalytic performance [27]. However, some questions regarding the photocatalytic practical applications of SrTiO3 remain unanswered. The preparation conditions of these modified SrTiO3 photocatalyst are too complex, hazardous, and costly, thus hindering the extensive application of this compound in photocatalysis.
Supphasrirongjaroen et al. demonstrated that rapid quenching in different media can lead to the formation of Ti3+ self-dopants in TiO2, thus improving the photocatalytic activity of TiO2-based materials [28]. Herein, we report a facile method to prepare SrTiO3 rich in oxygen vacancies, with improved photocatalytic performance in the visible region. SrTiO3 was preheated to a high temperature, followed by rapid submersion in ethanol, resulting in the darkening of the color of SrTiO3. Various structural and electronic analyses revealed the introduction of oxygen vacancies in the quenched SrTiO3 (Q-SrTiO3), resulting in increased photocatalytic activity. The photocatalytic performance of Q-SrTiO3 was evaluated by using it for the degradation of rhodamine B (RhB) dye and the photolysis of water to produce H2, with the original SrTiO3 as a control. The results indicated the enhanced photocatalytic activity of Q-SrTiO3.

2. Materials and Methods

2.1. Preparation of Q-SrTiO3

1 g of original SrTiO3 nanoparticles (99.5%, ~100 nm, Macklin Biochemical, Germany) was weighed using an electronic scale, then 1 g of original SrTiO3 was put in a sintering boat (length 6 cm, width 3 cm, height 1.5 cm). When the Muffle furnace heat to 800 °C, the sintering boat along with 1 g of original SrTiO3 was transferred to the Muffle furnace. The SrTiO3 nanoparticles were heated at 800 °C for 20 min, and then open the Muffle furnace door, immediately took out the sintering boat and submerged the SrTiO3 in 45 mL ethanol (AR) at room temperature for rapid quenching. Afterwards, the quenched sample was filtered and then dried at 80 °C for 3 h for further use.

2.2. Characterization

An X-ray diffractometer (XRD, D8 ADVANCE, Bruker, Karlsruhe, Germany) was used to check the phase structures of all the samples. Data were collected between 20° and 80° (2θ) with a 0.02° step size using Cu Kα irradiation, at 36 kV tube voltage and 20 mA tube current. Field-emission transmission electron microscopy (FE-TEM, Talos F200S, FEI, Thermo, Hillsboro, OR, USA) and Field-emission scanning electron microscopy (FE-SEM, SU8220, Hitach, Tokyo, Japan) was used to determine the surface change, particle size and morphology of the samples. Sample specimens for the FE-TEM and the FE-SEM observations were prepared as follows: The powdered sample was dispersed in ethanol in an ultrasonic washing bath, and then, a drop of the suspension was dripped slightly onto a micro grid or a silicon slice and dried before imaging. X-ray Photoelectron Spectroscopy (XPS, Escalab 250Xi, Thermo Fisher, Bremen, Germany) was used to analyze the chemical composition and relative amount of the elements on the surface of the samples, with a reference of C1 s and the excitation source of 150 W Al Kα X-rays. An Electron paramagnetic resonance spectrometer (EPR, EMXplus-10/12, Bruker, Karlsruhe, Germany) was used to detect unpaired electrons in the samples at room temperature. A UV-Vis-NIR spectrophotometer (DRUV-vis, UV-3600 Plus, SHIMADZU, Kyoto, Japan) were used to record the UV-vis diffuse reflectance absorption in the range of 200–2000 nm.

2.3. Photocatalytic Test

2.3.1. Photocatalytic Degradation of RhB

The photocatalytic degradation activities of Q-SrTiO3 were evaluated by monitoring the rate of decomposition of RhB in an aqueous solution under visible-light or UV-light irradiation from a 500 W Xe lamp equipped with a UV cut off filter (>420 nm) or 500 W Hg lamp, the light intensity of 500 W Xe lamp equipped with a UV cut off filter and 500 W Hg lamp are 6 mW/cm2 and 48 mW/cm2, respectively. A cylindrical Pyrex vessel equipped with a lamp was used as the photocatalytic reactor, with water circulation to keep the reaction temperature at about 27 °C. 40 mL of an aqueous solution of RhB (4 × 10−5 M) and 0.02 g Q-SrTiO3 or SrTiO3 were placed in a quartz tube for the degradation reaction. Before the photodegradation, a dark reaction was conducted for 30 min to ensure adsorption-desorption equilibrium between the photocatalyst and the RhB solution. Continuous magnetic stirring was carried out to keep the photocatalyst suspended in the RhB solution. Next, the mixture was exposed to visible light or UV light. The samples were collected at regular intervals (1.5 h or 1 h), and the concentration of RhB in the solution was determined using a UV-Vis spectrophotometer at 553 nm. The percentage of degradation was recorded as C/C0, and the reaction constant (Kapp) was calculated from the slope of the linear regression obtained from the plot of −ln (C/C0) vs. time, where C0 and C are the absorbance of the RhB solution initially and at a particular time, respectively.

2.3.2. Photocatalytic Evolution of hydrogen

The photocatalytic H2 production experiments were conducted in a 400 mL Pyrex quartz glass reactor at normal pressure and temperature. The photocatalyst (100 mg) was dispersed in 100 mL of 10% aqueous methanol solution (methanol acting as a sacrificial agent) using a magnetic stirrer. Then the reaction mixture was dispersed in an ultrasonic washing bath for 10 min. Before the irradiation by a 300 W Xe lamp (CRL-HXF300, China) as the sunlight source, the reactor was deaerated with nitrogen gas. During the photocatalytic reaction, the reactant solution was maintained at room temperature by using a Low-temperature cooling circulating pump (CEL-CR300, China), and magnetic stirring was continually maintained to keep the photocatalyst suspended in the aqueous methanol solution. The amount of H2 generated was tested using an online Shimadzu GC-2014C gas chromatograph (Shimadzu, Japan) equipped with an MS-5A column. The total reaction time for each sample was 5 h, and the H2 concentration was measured every hour.

3. Results and Discussion

3.1. Characterization of the Photocatalysts

The peaks in the powder XRD patterns of SrTiO3 and Q-SrTiO3 (Figure 1) matched with the (100), (110), (111), (200), (210), (211), (220) and (310) planes, indicating a characteristic SrTiO3 cubic structure (JCPDS card: 73-6001). Moreover, a small peak for SrCO3 was observed, probably due to the coexistence of SrTiO3 and SrCO3 under the atmospheric operating conditions adopted in the hydrothermal method [29]. No other diffraction peak was observed in the XRD patterns. Comparison with the XRD patterns from the local enlargement of the diffraction peaks (inset of Figure 1) revealed a slight shift (2θ~0.15°) of the (110) peak to a lower angle for Q-SrTiO3. According to the Bragg equation (2d sin θ = λ. where d, θ and λ are the crystal spacing, diffraction angle, and X-ray wavelength, respectively), a shift in the diffraction peaks toward a lower angle suggests an increase in the lattice parameters. This might be attributed to the substitution of Sr2+ (ionic radius Sr2+ > Ti4+) for Ti4+ in Q-SrTiO3 [30].
The UV-visible absorption spectra of SrTiO3 and Q-SrTiO3 (Figure 2a) exhibited an absorption onset at ~400 nm, which corresponds to a band gap of 3.1 eV. In contrast to the SrTiO3, the photoabsorption of Q-SrTiO3 was dramatically enhanced in the both UV, visible and infrared light regions, consistent with the color change of the sample from white to gray (inset of Figure 2a). The improved light absorption was attributed to the formation of surface oxygen vacancies in Q-SrTiO3. Similar results have been observed in other studies [19,31].
EPR is highly sensitive to unpaired electrons; hence, it was used for the detection of oxygen vacancies and Ti3+ species in SrTiO3 and Q-SrTiO3 (Figure 2b) Both SrTiO3 and Q-SrTiO3 showed a distinct EPR signal at g = 1.977 and g = 2.002, which could be ascribed to Ti3+ and oxygen vacancies, respectively. Because of its intrinsic non-stoichiometry, SrTiO3 always contains a fraction of oxygen vacancies and Ti3+ ions [32]. EPR spectra revealed that Q-SrTiO3 exhibited a stronger signal intensity for oxygen vacancies than did SrTiO3, indicating the presence of more oxygen vacancies in Q-SrTiO3, thus favoring enhanced photocatalytic activity of the Q-SrTiO3. Takata and Domen also demonstrated that doping of a cation with a lower valence ion than that of the parent cation (such as Sr2+ in SrTiO3) can introduce oxygen vacancies, thus effectively improving its photocatalytic activity [32]. Thus, based on the XRD results, due to the exists of abundant oxygen vacancies, in order to keep the regional charge balance of the Q-SrTiO3, the Sr2+ ions could substituted for Ti4+ ions, so that lattice expansion occurs (Figure 2c) [32,33].
The high-resolution transmission electron microscopy (HR-TEM) images (Figure 3a,b) revealed the interplanar spacing of SrTiO3 and Q-SrTiO3 crystals to be ~0.27 nm, which is consistent with the d-spacings of the (110) crystallographic planes of cubic SrTiO3. However, Liu et al. have reported that an ice-water quenching TiO2 had introduced a disordered surface layer surrounding the crystalline core, and the surface lattice distortion is related to the generation of oxygen vacancies during the ice-water quenching [34]. In contrast, Q-SrTiO3 prepared in this work used 800 °C ethanol quenching that did not lead to specific disordered surface layer, therefore, the generation of more oxygen vacancies in Q-SrTiO3 have not introduced disordered surface layer. The SEM images (Figure 3c,d) revealed the particle size and particle morphology of Q-SrTiO3 and SrTiO3 show no change, and the average diameters of Q-SrTiO3 and SrTiO3 nanocrystals are ~100 nm, hence, ethanol-quenching can not change the particle size and particle morphology of samples.
XPS was used to investigate the surface chemical composition and VB position of SrTiO3 and Q-SrTiO3. The Sr 3d5/2, Sr 3d3/2, Ti 2p1/2, and Ti 2p3/2 binding energies were 133.2, 134.6, 458.0, and 464.0 eV, respectively, in accordance with the literature values (Figure 4a,b) [35]. The Sr 3d and Ti 2p spectra showed no obvious variation between SrTiO3 and Q-SrTiO3. The Sr/Ti ratio of the samples was estimated according to the peak area and sensitivity factor of Sr 3d and Ti 2p (Table 1). The atomic ratio of Sr to Ti on the surface was about 1.64 and 2.15 for SrTiO3 and Q-SrTiO3, respectively. The larger atomic ratio of Sr/Ti in Q-SrTiO3 than that in SrTiO3 might be due to the substitution of Sr2+ for Ti4+ on the surface of the former.
The O 1s high-resolution X-ray photoelectron spectra of SrTiO3 and Q-SrTiO3 showed two typical components of SrTiO3 (Figure 4c). The two peaks located at 529.2 and 531.5 eV were assigned to bulk oxygen and surface oxygen in the samples, respectively. Based on previous research, it was assumed that the peak intensity of surface oxygen was related to the concentration of oxygen vacancies on the surface of SrTiO3 and Q-SrTiO3 [19,36]. The peak intensity at 531.5 eV become stronger for Q-SrTiO3, indicating that the concentration of oxygen vacancies on the surface of Q-SrTiO3 increased after the ethanol-quenching process. The introduction of more oxygen vacancies on the surface of Q-SrTiO3 lattice resulted in impure/defect states in the band gap, enhancing the visible and near infrared-light absorption of Q-SrTiO3 [27]. Furthermore, the increased amount of oxygen vacancies can improve the efficient charge transport in Q-SrTiO3, followed by the Fermi level shift toward to the CB of the Q-SrTiO3, facilitating the separation of photogenerated electron-hole pairs and resulting in enhanced photocatalytic activity [19,27]. In the VB XPS profile, the VB maxima were estimated by linear extrapolation of the peaks to the baselines (Figure 4d). Both, SrTiO3 and Q-SrTiO3 displayed identical VB band positions at 2.3 eV below the Fermi energy, indicating no shift in the VB edge.

3.2. Photocatalytic Activity

The photodegradation of RhB in aqueous solution under visible-light irradiation was used to evaluate the photocatalytic activity of the Q-SrTiO3, with SrTiO3 as the control (Figure 5a). After adsorption-desorption equilibrium between the photocatalyst and the RhB solution was achieved in the absence of light, even a slight adsorption of RhB over the samples resulted in a slight decrease in the concentration of RhB. During the photodegradation process, SrTiO3 showed no appreciable reduction in the RhB concentration in aqueous solution; however, Q-SrTiO3 showed higher photocatalytic activity than SrTiO3 in reducing the concentration of RhB in aqueous solution. After 370 min of visible-light irradiation in the presence of Q-SrTiO3, RhB was decomposed by about 20%; in contrast, SrTiO3 caused only 3% decomposition of the dye. The reaction constant (Kapp) was calculated from the slope of the linear regression obtained from the plot of −ln (C/C0) vs. time (Figure 5b). These results suggested that Q-SrTiO3 shows better activity than SrTiO3 for the photodegradation of RhB under visible light.
The UV-light photocatalytic activities of Q-SrTiO3 were investigated by monitoring the decomposition of RhB in an aqueous solution, with SrTiO3 as the control (Figure 5c,d). After 270 min of UV-light irradiation, the RhB dye was almost completely decomposed (~90%) by Q-SrTiO3, (Figure 5c). The reaction constant (Kapp) was shown in Figure 5d, this results also suggested that Q-SrTiO3 shows better photocatalytic activity than SrTiO3 for the photodegradation of RhB.
The photocatalytic activity of Q-SrTiO3 for the photolysis of water to produce H2 in 100 mL 10% aqueous methanol solution was also studied under solar irradiation, using SrTiO3 as the control. Figure 5c,d present the time course of H2 generation for SrTiO3 and Q-SrTiO3 under solar light irradiation. Q-SrTiO3 steadily produced H2 gas at the rate of 42.12 μmol g−1 h−1, which was almost 6.2 times higher than that observe with SrTiO3 (6.83 μmol g−1 h−1). All these results demonstrated that Q-SrTiO3 possesses higher photocatalytic activity than SrTiO3.

4. Conclusions

In this paper, a facile and general method has been introduced to modify the surface environment of SrTiO3 through an ethanol-quenching process. Q-SrTiO3 showed higher photocatalytic activity than did SrTiO3 for the degradation of RhB and the photolysis of water to produce H2 under the irradiation by visible, UV or solar light. Results of spectroscopic characterization revealed that after rapid ethanol quenching, a high concentration of oxygen vacancies was introduced on the surface of the Q-SrTiO3 lattice. Consequently, in order to maintain the regional charge balance in Q-SrTiO3, the redundant Sr2+ is likely to substitute for Ti4+. Moreover, oxygen vacancies play an important role in enhancing the photocatalytic performance of Q-SrTiO3 by not only inducing localized states into the band gap of Q-SrTiO3, but also acting as photoinduced charge traps. Consequently, the light absorption ability is increased and the recombination rate of photogenerated electron-hole pairs is decreased, thus enhancing the photocatalytic activity of Q-SrTiO3.

Author Contributions

Y.X.: performed photocatalysts synthesis, XRD, TEM, UV-visible absorption spectra analysis, photocatalytic activity tests and wrote the manuscript, S.C.: supervised rhodamine B and photocatlytic H2 generation analysis in cooperation with Y.X., Y.W.: conceived the concept, designed the experiments, analyzed the data and revised the manuscript, Z.H.: performed EPR analysis, H.Z.: performed XPS analysis, W.X.: performed photocatalytic H2 generation.

Funding

This research received no external funding.

Acknowledgments

This work is supported by the National Nature Science Foundation of China (No.21271048), Natural Science Foundation of China (11747074), Guangdong province science and technology plan project public welfare fund and ability construction project (2016A010103041, 2017A010103025), Doctoral Program of Lingnan Normal University (ZL1503), China Spark Program (2015GA780058).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Fujishima, A.; Honda, K. Electrochemical photolysis of water at a semiconductor electrode. Nature 1972, 238, 37–38. [Google Scholar] [CrossRef] [PubMed]
  2. Chen, X.B.; Shen, S.H.; Guo, L.J.; Mao, S.S. Semiconductor-based photocatalytic hydrogen generation. Chem. Rev. 2010, 110, 6503–6570. [Google Scholar] [CrossRef] [PubMed]
  3. Ran, J.R.; Zhang, J.; Yu, J.G.; Jaroniecc, M.; Qiao, S.Z. Earth-abundant cocatalysts for semiconductor based photocatalytic water splitting. Chem. Soc. Rrv. 2015, 46, 7787–7812. [Google Scholar] [CrossRef] [PubMed]
  4. Wang, H.L.; Zhang, L.S.; Chen, Z.G.; Hu, J.Q.; Li, S.J.; Wang, Z.H.; Liu, J.S.; Wang, X.C. Semiconductor heterojunction photocatalysts: Design, construction, and photocatalytic performances. Chem. Soc. Rrv. 2014, 43, 5234–5244. [Google Scholar] [CrossRef] [PubMed]
  5. Dhakshinamoorthy, A.; Navalon, S.; Corma, A.; Garcia, H. Photocatalytic CO2 reduction by TiO2 and related titanium containing solids. Energy Environ. Sci. 2012, 5, 9217–9233. [Google Scholar] [CrossRef]
  6. Pei, Z.X.; Weng, S.X.; Liu, P. Enhanced photocatalytic activity by bulk trapping and spatial separation of charge carriers: A case study of defect and facet mediated TiO2. Appl. Catal. B Environ. 2016, 180, 463–470. [Google Scholar] [CrossRef]
  7. Wu, Z.; Su, Y.F.; Yu, J.D.; Xiao, W.; Sun, L.; Lin, C.J. Enhanced photoelectrocatalytic hydrogen production activity of SrTiO3-TiO2 heteronanoparticle modified TiO2 nanotube arrays. Int. J. Hydrog. Energy 2015, 40, 9704–9712. [Google Scholar] [CrossRef]
  8. Wenderich, K.; Mul, G. Methods, mechanism, and applications of photodeposition in photocatalysis: A review. Chem. Rev. 2016, 116, 14587–14619. [Google Scholar] [CrossRef]
  9. Grabowska, E. Selected perovskite oxides: Characterization, preparation and photocatalytic properties–A review. Appl. Catal. B Environ. 2016, 186, 97–126. [Google Scholar] [CrossRef]
  10. Xie, T.H.; Sun, X.Y.; Lin, J. Enhanced photocatalytic degradation of RhB driven by visible light-induced MMCT of Ti(Ⅳ)–O–Fe(Ⅱ) formed in fe–doped SrTiO3. J. Phys. Chem. C 2008, 112, 9753–9759. [Google Scholar] [CrossRef]
  11. Ouyang, S.; Tong, H.; Umezawa, N.; Cao, J.; Li, P.; Bi, Y.; Zhang, Y.; Ye, J. Surface–alkalinization–induced enhancement of photocatalytic H2 evolution over SrTiO3-Based photocatalysts. J. Am. Chem. Soc. 2012, 134, 1974–1977. [Google Scholar] [CrossRef] [PubMed]
  12. Liu, P.; Nisar, J.; Pathak, B.; Ahuja, R. Hybrid density functional study on SrTiO3 for visible light photocatalysis. Int. J. Hydrog. Energy 2012, 37, 11611–11617. [Google Scholar] [CrossRef]
  13. Yan, J.H.; Zhu, Y.R.; Tang, Y.G.; Zheng, S.Q. Nitrogen-doped SrTiO3/TiO2 composite photocatalysts for hydrogen production under visible light irradiation. J. Alloy. Compd. 2009, 472, 429–433. [Google Scholar] [CrossRef]
  14. Luo, H.M.; Takata, T.; Lee, Y.; Zhao, J.F.; Domen, K.; Yan, Y.S. Photocatalytic Activity Enhanced for Titanium Dioxide by Co-doping with Bromine and Chlorine. Chem. Mater. 2004, 16, 846–849. [Google Scholar] [CrossRef]
  15. Enterkin, J.A.; Setthapun, W.; Elam, J.W.; Christensen, S.T.; Rabuffetti, F.A.; Marks, L.D.; Stair, P.C.; Poeppelmeier, K.R.; Marshall, C.L. Propane oxidation over Pt/SrTiO3 nanocuboids. ACS Catal. 2011, 1, 629–635. [Google Scholar] [CrossRef]
  16. Pan, X.W.; Wang, L.Q.; Ling, F.; Li, Y.H.; Han, D.X.; Pang, Q. A novel biomass assisted synthesis of Au-SrTiO3 as a catalyst for hydrogen generation from formaldehyde aqueous solution at low temperature. Int. J. Hydrog. Energy 2015, 40, 1752–1759. [Google Scholar] [CrossRef]
  17. Iwashina, K.; Kudo, A. Rh-doped SrTiO3 photocatalyst electrode showing cathodic photocurrent for water splitting under visible-light irradiation. J. Am. Chem. Soc. 2011, 133, 13272–13275. [Google Scholar] [CrossRef] [PubMed]
  18. Chambers, S.A.; Engelhard, M.H.; Shutthanandan, V.; Zhu, Z.; Droubay, T.C.; Qiao, L.; Sushko, P.V.; Feng, T.; Lee, H.D.; Gustafsson, T.; et al. Instability, intermixing and electronic structure at the epitaxial LaAlO3/SrTiO3(001) heterojunction. Surf. Sci. Rep. 2010, 65, 317–352. [Google Scholar] [CrossRef]
  19. Tan, H.Q.; Zhao, Z.; Zhu, W.B.; Coker, E.N.; Li, B.S.; Zheng, M.; Yu, W.X.; Fan, H.Y.; Sun, Z.C. Oxygen vacancy enhanced photocatalytic activity of pervoskite SrTiO3. ACS Appl. Mater. Interfaces 2014, 6, 19184–19190. [Google Scholar] [CrossRef]
  20. Wang, G.M.; Ling, Y.C.; Li, Y. Oxygen-deficient metal oxide nanostructures for photoelectrochemical water oxidation and other applications. Nanoscale 2012, 4, 6682–6691. [Google Scholar] [CrossRef]
  21. Thompson, T.L.; Yates, J.T., Jr. TiO2-based photocatalysis: surface defects, oxygen and charge transfer. Top. Catal. 2005, 35, 3–4. [Google Scholar] [CrossRef]
  22. Chen, X.B.; Liu, L.; Yu, P.Y.; Mao, S.S. Increasing solar absorption for photocatalysis with black hydrogenated titanium dioxide nanocrystals. Science 2011, 331, 746–750. [Google Scholar] [CrossRef] [PubMed]
  23. Yan, Y.; Han, M.Y.; Konkin, A.; Koppe, T.; Wang, D.; Andreu, T.; Chen, G.; Vetter, U.; Morante, J.R.; Schaaf, P. Slightly hydrogenated TiO2 with enhanced photocatalytic performance. J. Mater. Chem. A 2014, 2, 12708–12716. [Google Scholar] [CrossRef]
  24. Wang, G.M.; Wang, H.Y.; Ling, Y.C.; Tang, Y.C.; Yang, X.Y.; Fitzmorris, R.C.; Wang, C.C.; Zhang, J.Z.; Li, Y. Hydrogen-treated TiO2 nanowire arrays for photoelectrochemical water splitting. Nano Lett. 2011, 11, 3026–3033. [Google Scholar] [CrossRef] [PubMed]
  25. Wang, G.M.; Ling, Y.C.; Wang, H.Y.; Yang, X.Y.; Wang, C.C.; Zhang, J.Z.; Li, Y. Hydrogen-treated WO3 nanoflakes show enhanced photostability. Energy Environ. Sci. 2012, 5, 6180–6187. [Google Scholar] [CrossRef]
  26. Lu, X.H.; Wang, G.M.; Xie, S.L.; Shi, J.Y.; Li, W.; Tong, Y.X.; Li, Y. Efficient photocatalytic hydrogen evolution hydrogenated ZnO nanorod arrays. Chem. Commun. 2012, 48, 7717–7719. [Google Scholar] [CrossRef] [PubMed]
  27. Zhao, W.L.; Zhao, W.; Zhu, G.L.; Lin, T.Q.; Xu, F.F.; Huang, F.Q. Black strontium titanate nanocrystals of enhanced solar absorption for photocatalysis. CrystEngComm 2015, 17, 7528–7534. [Google Scholar] [CrossRef]
  28. Supphasrirongjaroen, P.; Kongsuebchart, W.; Panpranot, J.; Mekasuwandumrong, O.; Satayaprasert, C.; Praserthdam, P. Dependence of quenching process on the photocatalytic activity of solvothermal-derived TiO2 with various crystallite sizes. Ind. Eng. Chem. Res. 2008, 47, 693–697. [Google Scholar] [CrossRef]
  29. Dong, W.J.; Li, X.Y.; Yu, J.; Guo, W.C.; Li, B.J.; Tan, L.; Li, C.R.; Shi, J.J.; Wang, G. Porous SrTiO3 spheres with enhanced photocatalytic performance. Mater. Lett. 2012, 67, 131–134. [Google Scholar] [CrossRef]
  30. Feng, L.L.; Zou, X.X.; Zhao, J.; Zhou, L.J.; Wang, D.J.; Zhang, X.; Li, G.D. Nanoporous Sr-rich strontium titanate: a stable and superior photocatalyst for H2 evolution. Chem. Commun. 2013, 49, 9788–9790. [Google Scholar] [CrossRef]
  31. Tan, H.; Zhao, Z.; Niu, M.; Mao, C.; Cao, D.; Cheng, D.; Feng, P.; Sun, Z. A facile and versatile method for preparation of colored TiO2 with enhanced solar-driven photocatalytic activity. Nanoscale 2014, 6, 10216–10223. [Google Scholar] [CrossRef] [PubMed]
  32. Takata, T.; Domen, K. Defect engineering of photocatalysts by doping of aliovalent metal cations for efficient water splitting. J. Phys. Chem. C 2009, 113, 19386–19388. [Google Scholar] [CrossRef]
  33. Hofman, W.; Hoffmann, R.W. Dopant influence on dielectric losses, leakage behaviour, and resistance degradation of SrTiO3 thin films. Thin Solid Film 1997, 305, 66–73. [Google Scholar] [CrossRef]
  34. Liu, B.S.; Cheng, K.; Nie, S.C.; Zhao, X.J.; Yu, H.G.; Yu, J.G.; Fujishima, A.; Nakata, K. Ice–water quenching induced Ti3+ Self-doped TiO2 with surface lattice distortion and the increased photocatalytic activity. J. Phys. Chem. C 2017, 121, 19836–19848. [Google Scholar] [CrossRef]
  35. Wagner, C.D. Handbook of X-ray Photoelectron Spectroscopy; Perkin-Elmer Corporation: Waltham, MA, USA, 1979. [Google Scholar]
  36. Schaub, R.; Thostrup, P.; Lopez, N.; Lægsgaard, E.; Stensgaard, I.; Nørskov, J.K.; Besenbacher, F. Oxygen vacancies as active sites for water dissociation on rutile TiO2(110). Phys. Rev. Lett. 2006, 87, 266104-1–266104-4. [Google Scholar] [CrossRef] [PubMed]
Nanomaterials 09 00883 g001 550
Figure 1. XRD patterns of SrTiO3 and Q-SrTiO3 samples.
Figure 1. XRD patterns of SrTiO3 and Q-SrTiO3 samples.
Nanomaterials 09 00883 g001
Nanomaterials 09 00883 g002 550
Figure 2. UV-vis absorption spectra of SrTiO3 and Q-SrTiO3 (a), the insert is a photograph of SrTiO3 and Q-SrTiO3; EPR spectra of SrTiO3 and Q-SrTiO3 (b). Schematic illustration of lattice change of Q-SrTiO3 after solvent-quenching (c).
Figure 2. UV-vis absorption spectra of SrTiO3 and Q-SrTiO3 (a), the insert is a photograph of SrTiO3 and Q-SrTiO3; EPR spectra of SrTiO3 and Q-SrTiO3 (b). Schematic illustration of lattice change of Q-SrTiO3 after solvent-quenching (c).
Nanomaterials 09 00883 g002
Nanomaterials 09 00883 g003 550
Figure 3. High-resolution TEM images and SEM images of SrTiO3 (a,c) and Q-SrTiO3 (b,d).
Figure 3. High-resolution TEM images and SEM images of SrTiO3 (a,c) and Q-SrTiO3 (b,d).
Nanomaterials 09 00883 g003
Nanomaterials 09 00883 g004 550
Figure 4. Sr 3d XPS spectra (a), Ti 2p XPS spectra (b), O1s Spectra (c), XPS valence band spectra of SrTiO3 and Q-SrTiO3 samples (d).
Figure 4. Sr 3d XPS spectra (a), Ti 2p XPS spectra (b), O1s Spectra (c), XPS valence band spectra of SrTiO3 and Q-SrTiO3 samples (d).
Nanomaterials 09 00883 g004
Nanomaterials 09 00883 g005 550
Figure 5. Photodecomposition of RhB aqueous solution with SrTiO3 and Q-SrTiO3 under visible light (a) and UV light (c). −ln (C/C0) of the RhB concentration as a function of visible light (b) or UV light (d) irradiation time. Time-course of photocatalytic water splitting for H2 generation in 100 mL 10% aqueous methanol solution under solar light (e). The rate of hydrogen generation for SrTiO3 and Q-SrTiO3 under solar light (f).
Figure 5. Photodecomposition of RhB aqueous solution with SrTiO3 and Q-SrTiO3 under visible light (a) and UV light (c). −ln (C/C0) of the RhB concentration as a function of visible light (b) or UV light (d) irradiation time. Time-course of photocatalytic water splitting for H2 generation in 100 mL 10% aqueous methanol solution under solar light (e). The rate of hydrogen generation for SrTiO3 and Q-SrTiO3 under solar light (f).
Nanomaterials 09 00883 g005
Table
Table 1. Summary of the XPS data for the SrTiO3 and Q-SrTiO3.
Table 1. Summary of the XPS data for the SrTiO3 and Q-SrTiO3.
SampleAtomic Concentration (%)Atomic Ratio
TiSrOCSr/Ti
SrTiO33.736.1431.3658.761.64
Q-SrTiO32.836.1029.7561.322.15

Share and Cite

MDPI and ACS Style

Xiao, Y.; Chen, S.; Wang, Y.; Hu, Z.; Zhao, H.; Xie, W. Ethanol-Quenching Introduced Oxygen Vacancies in Strontium Titanate Surface and the Enhanced Photocatalytic Activity. Nanomaterials 2019, 9, 883. https://doi.org/10.3390/nano9060883

AMA Style

Xiao Y, Chen S, Wang Y, Hu Z, Zhao H, Xie W. Ethanol-Quenching Introduced Oxygen Vacancies in Strontium Titanate Surface and the Enhanced Photocatalytic Activity. Nanomaterials. 2019; 9(6):883. https://doi.org/10.3390/nano9060883

Chicago/Turabian Style

Xiao, Yang, Shihao Chen, Yinhai Wang, Zhengfa Hu, Hui Zhao, and Wei Xie. 2019. "Ethanol-Quenching Introduced Oxygen Vacancies in Strontium Titanate Surface and the Enhanced Photocatalytic Activity" Nanomaterials 9, no. 6: 883. https://doi.org/10.3390/nano9060883

APA Style

Xiao, Y., Chen, S., Wang, Y., Hu, Z., Zhao, H., & Xie, W. (2019). Ethanol-Quenching Introduced Oxygen Vacancies in Strontium Titanate Surface and the Enhanced Photocatalytic Activity. Nanomaterials, 9(6), 883. https://doi.org/10.3390/nano9060883

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop