TiO2 Nanotube Arrays

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Fabrication of Heterostructured Metal Oxide/TiO2 Nanotube Arrays Prepared via Thermal Decomposition and Crystallization Yulong Liao,*,†,‡ Botao Yuan,† Dainan Zhang,†,‡ Jin Zhang,§ Xiaoyi Wang,† Peng Deng,† Kaibin Zhang,† Huaiwu Zhang,‡ Quanjun Xiang,†,‡ and Zhiyong Zhong‡ †

Center for Applied Chemistry, University of Electronic Science and Technology of China, Chengdu 611731, China State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China § School of Optoelectronic Engineering, Xi’an Technological University, Xi’an 710032,China Downloaded via DURHAM UNIV on August 7, 2018 at 08:46:57 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: Heterostructured TiO2 materials are of great importance in electronic and photochemical related applications. We report herein a simple, low-cost, and scalable fabrication of metal oxides heterostructured TiO2 nanotube arrays (NTAs) through a combined strategy of thermal decomposition and crystallization. Various MxO y /TiO2 heterostructured films (M = Zn, Ce, Cu, Cr...) were obtained by using TiO2 NTAs as “nano-containers” as well as “nanoreactors”, while using M(CH3COO)x solutions as the precursors. SEM, XRD, EDS results demonstrated that Cu2O/TiO2 NTAs, ZnO/TiO2 NTAs, Cr2O3/TiO2 NTAs, and CeO2/TiO2 NTAs were successfully fabricated. Photocatalytic results revealed that the heterostructured MxOy/TiO2 films could either enhance the UV photocatalytic activities or enable the visible light photocatalytic activities of the TiO2 NTAs. This study provides a facile general approach to prepare MxOy/TiO2 NTAs films, which could be very useful for environmental and energy areas.

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hydrogen or photocatalysts for environmental remediation.16,17 The photochemical activities of nanotubular TiO2 were proved superior to that of its bulk materials, due to large specific surface area and vertical electron transportation provided by the nanotubular architecture.18−21 Nevertheless, their performances were still limited by the inherent materials disadvantages of TiO2. Recently studies showed that coupling with metal oxide semiconductors (especially transition metal oxides: MxOy, M = Zn, Cu, Cr, Ce...) is deemed as an effective strategy.22−24 When metal oxides with proper band gap and band structures coupled with TiO2 NTs, either the lifetime of photogenerated carriers gets increased or the photogenerated electron under visible light irradiation transferred into TiO2 NTs, leading to enhance photochemical performances. So far, research efforts have been prompted to synthesize MxOy heterostructured TiO2 NTs by using various methods, including MBE (Molecular Beam Epitaxy), CVD (Chemical Vapor Deposition), hydrothermal method, template-assisted strategy, and electrodeposition approach.25−27 However, in order to further improve their photocatalytic activities, developing a facile method to load various MxOy nanoparticles (NPs) to the TiO2 NTs is highly desired.

INTRODUCTION In the past two decades, there has been an ever increasing effort to make use of nanomaterials in photocatalytic systems or energy harvesting/storage devices.1−5 Among various materials and technologies, titanium dioxide (TiO2) with chemical stability, environmental friendly, and outstanding photochemical activity has been studied as a promising photocatalyst for organic pollutant degradation and solardriven H2 generation.6−10 However, its feasibility within the visible light region was hindered because of two main disadvantages, including wide band gap (∼3.2 eV) and sluggish charge transfer kinetics.11 For the solar spectrum, the visible light region accounts for approximately 43% of the total energy. To overcome these issues, various approaches such as cocatalysts, doping, noble metals decoration, and integrating narrow band gap semiconductors have been proposed to expand the absorption range of anatase TiO2 to visible and even NIR region.12−15 In another hand, low cost is always favorable for industrialization which is the strongest driving force for the application. Therefore, the quest for materials that are solar light sensitive and fabricated with low cost is of utmost importance. Since self-organized TiO2 nanotubes (NTs) were discovered in 2001, they have been extensively studied as electrodes for photoelectrochemical cells for the production of solar © XXXX American Chemical Society

Received: May 29, 2018

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DOI: 10.1021/acs.inorgchem.8b01483 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. Synthesis flow of MxOy/TiO2 heterostructured films: step 1, anodic growth of empty TiO2 NTs; step 2, loading the TiO2 NTs with M(AC)x solutions (M = Cu, Zn, Ce, Cr...); step 3, precipitations of the M(AC)x salts inside of TiO2 NTs; step 4, formation of MxOy/TiO2 heterostructured films. Schematic diagram of the thermal decomposition of M(AC)x salts (M = Cu, Zn, Ce, Cr...) into metal oxides.

Figure 2. Digital images of a typical loading process when the TiO2 NTAs were immersed into the M(Ac)x solutions; in this case, it was 0.02 mol/ L Zn(AC)2 solution. A large number of bubbles were generated when the empty TiO2 NTAs were immersed into the solution, indicating the air was evacuated out from the TiO2 NTAs, while the M(Ac)x solutions were injected into the TiO2 NTAs.

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Herein, we demonstrate a general method to load the anodic TiO2 nanotubes arrays (NTAs) with MxOy (referred to as MxOy/TiO2), using a combined strategy of optimized immersion technique and thermally induced decomposition. First, the individual anatase TiO2 NTs were adopted as tiny “nano-containers” to load the M(CH3COO)x (noted as M(Ac)x) precursor solutions, then as “nano-reactors” to thermally decompose the M(Ac)x into MxOy. Generally speaking, most MxOy/TiO2 heterostructured films could be obtained by this method, only if their corresponding M(Ac)x precursor solutions are available.

EXPERIMENTAL SECTION

Synthesis of TiO2 Nanotube Arrays. TiO2 NTAs were synthesized by an anodized method surrounded by fluoride ion containing electrolyte (500 mL glycol, 10 mL H2O, and 1.66 g NH4F). Before the anodization process, titanium foils (50 × 15 mm) were washed in foamless eradicator, and then cleaned in an ultrasonic cleaner for 1 h in deionized (DI) water and alcohol, respectively. A constant voltage of 60 V was applied to the two titanium foils for 2 h by using a DC power supply. In order to ensure the tube mouth open, TiO2 NTs were carried out by sonicating in ethanol. Then the assynthesized anodic TiO2 NTs films were annealed at 450 °C for 3 h to crystallize them into anatase phase. Synthesis of MxOy/TiO2 Heterostructured Films. Figure 1 shows a schematical fabrication procedure of MxOy/TiO2 heterostructured films, during which the anodic TiO2 NTs were taken as B

DOI: 10.1021/acs.inorgchem.8b01483 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 3. Typical XRD patterns of the as synthesized MxOy/TiO2 heterostructured films: (a) ZnO/TiO2 heterostructured NTAs, (b) Cu2O/TiO2 heterostructured NTAs, (c) Cr2O3/TiO2 heterostructured NTAs, and (d) CeO2/TiO2 heterostructured NTAs. Characteristic diffraction peaks of anatase TiO2, ZnO(100), Cu2O(111), Cr2O3(110), and CeO2(111) could be clearly observed, indicating the formation of ZnO/TiO2 heterostructured NTAs. thousands of small “nano-containers” to load M(Ac)x solutions (M = Zn, Ce, Cu, Cr...). When the as-anodized TiO2 NTs were immersed into the aqueous solution, the pressure created by the solution would squeeze the air from the individual TiO2 NTs, and the aqueous solutions containing M(Ac) x were injected into TiO2 NTs simultaneously. In this study, the anodic anatase TiO2 NTAs were immersed into Zn(AC)2, Cu(AC)2, Cr(AC)3, and Ce(AC)3 aqueous solutions with concentrations of 1, 0.3, 1, and 1 mol/L according to their solubility, respectively. After a few seconds, the TiO2 NTAs films were taken out. To ensure the uniformity of the film and the consistency of the experiment, the superfluous solution on the surface of the TiO2 NTAs films was cleaned up by a qualitative filter paper. Then the loaded TiO2 NTAs films were dried at 70 °C for 1 h, during which the M(AC)x would precipitate from the solution inside the nanotubes. The M(AC)x loaded TiO2 NTAs were subsequently annealed at a high temperature of 450 °C for 3 h (under air or H2 atmosphere), during which the deposited M(AC)x would be further thermally decomposed into MxOy NPs. Finally, Cu2O/TiO2 NTAs, ZnO/TiO2 NTAs, Cr2O3/TiO2 NTAs, and CeO2/TiO2 NTAs heterostructured films were obtained. All reagents were purchased online from Aladdin Industrial Corporation and all reagents are analytical purity. Characterization. X-ray Diffraction (XRD, D/max 2400 X Series X-ray diffractometer) was applied to characterize the crystal structure of the MxOy/TiO2 heterostructured films. The X-ray radiation source was Cu Kα, and XRD was operated at 40 kV and 30 mA with the speed of 3.6°/min at a step of 0.03° in the range of 10−80°. Scanning electron microscopy (SEM, JSM-7000F, JEOL Inc. Japan) and transmission electron microscopy (TEM, JEOL2100F, Japan) were employed to characterize the microstructure and morphology of the MxOy/TiO2 heterostructured films. Energy dispersive spectrometry (EDS) was applied to characterize the elemental distribution of the

microscopic region of the materials. Absorption spectra were collected using the UV−vis spectrometry (Ultrospec 2100 pro), and the photoluminescence (PL, FluoTime 300) has been used to characterize carrier lifetime with an excitation wavelength of 320 nm. Photocatalytic activity measurement details are provided in the Supporting Information.

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RESULTS AND DISCUSSION Figure 2 shows a practical loading process, when the TiO2 NTAs were immersed into a 0.2 mol/L Zn(AC)2 solution. After 2 s, a large number of bubbles generated on the surface of the film, indicating the air inside the NTs was ejected out while the Zn(AC)2 solution was injected into the TiO2 NTs film. It took about 20 s to accomplish this loading processing. It should be noted that there might be some residual air inside the TiO2 NTs, which however did not hinder the loading process. The loaded TiO2 NTAs were then dried at 70 °C for 1 h to remove the water from the TiO2 NTAs, leaving the M(Ac)x in the TiO2 NTAs. As illustrated in Figure 1, the last step is to let the M(Ac)x be thermally decomposed into various MxOy inside the “nano-reactors” NTAs. Typical XRD patterns of the loaded TiO2 NTAs after annealing at 450 °C for 3 h are shown in Figure 3. It is noted that high concentrations of M(Ac)x solution were used in this study, due to the detection requirement of XRD (>∼5%). From panels (a)−(d) in Figure 3, the diffraction peaks of TiO2 located at 25.28°, 37.80°, 48.05°, 53.89°, 55.06°, 62.70°, and 68.80° were attributed to the anatase lattice planes (101), (004), (200), (105), (211), (204), and (116), respectively. This indicates that the anodic TiO2 NTAs films have an C

DOI: 10.1021/acs.inorgchem.8b01483 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 4. Morphologies of the MxOy/TiO2 heterostructured films: (a) a schematic diagram, typical SEM images of (b) pure anatase TiO2 NTs, (c) ZnO/TiO2 heterostructured NTAs, (d) Cu2O/TiO2 heterostructured NTAs, (e) Cr2O3/TiO2 heterostructured NTAs, and (f) CeO2/TiO2 heterostructured NTAs.

CeO2 assigned to crystal faces (111), (200), and (311) which were located at 28.55°, 33.08°, and 56.34°, respectively. Therefore, it could be concluded that M(AC)x was loaded into the TiO2 NTAs and thermally decomposed into MxOy inside nanotube arrays, and the MxOy/TiO2 heterostructured NTAs were finally obtained. Morphologies of the above obtained MxOy/TiO2 heterostructured NTAs are shown in Figure 4. As we noted before, the TiO2 NTs were used as “nano-reactors” in this study, and therefore, it is important to maintain their structures when they were decorated with MxOy; see Figure 4a. The initial morphologies of the anodic TiO2 NTAs are shown in Figure 4b. The highly ordered NTs have an average diameter of ∼100 nm, and the open tube mouth of the NTs could be clearly observed. Figure 4c−f shows typical SEM images of the MxOy/ TiO2 heterostructured NTAs, showing a differential top morphology depending on the loaded MxOy. The tubular structure of the anatase TiO2 NTAs could be clearly observed in all samples, indicating that the TiO2 NTAs could serve as a good substrate because of the large specific surface area.30 For ZnO/TiO2 NTAs (see Figure 4c), there are lots of bright white long strips, ZnO nanorods, grown from the tube-pore mouths and on the surface of the TiO2 NTAs, because of the

anatase crystalline structure in this study, which has been used frequently to obtain the good photocatalytic activity.28 From Figure 3a, the diffraction peaks located at 31.77°, 34.42°, 36.25°, and 56.60° were indexed to lattice planes (100), (002), (101), and (110) of ZnO, respectively. Also from Figure 3b, the diffraction peaks located at 29.55°, 36.42°, 42.30°, and 61.34° were attributed to lattice planes (110), (111), (200), and (220) of Cu2O, respectively. Moreover, the peaks at 43.32° and 50.48° are attributed to Cu. When the heating temperature rises gradually in the thermal decomposition process of Cu(Ac)2 in hydrogen, Cu(II) proceeds in two steps (Cu2+ → Cu+ → Cu), with a possibly appreciable overlap of the consecutive rate processes. The involved chemical reaction is expressed as the following eqs 1 and 2: 2CuO + H 2 → Cu 2O + H 2O

(1)

Cu 2O + H 2 → 2Cu + H 2O

(2)

When the temperature reaches 450 °C, both Cu and Cu2O would appear.29 As shown in Figure 3c, the characteristic diffraction peaks of Cr2O3 could be clearly observed, such as (110), (113), and (300) peaks at 2θ = 36.20°, 41.48°, and 65.10°, respectively. Figure 3d shows the diffraction peaks of D

DOI: 10.1021/acs.inorgchem.8b01483 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry high concentration of Zn(AC)2 solution. By taking a close look, the ZnO nanorods were found attached to the tube wall and tube-pore mouths of the TiO2 NTs, forming a ZnO/TiO2 NTAs heterostructure. Different from the morphology of ZnO/TiO2 heterostructured films, bigger Cu2O particles appeared on the tube mouths, as shown in the Figure 4d. The surface of the TiO2 NTAs is almost covered by Cu2O particles.31 In the similar way, it also can be observed that spherical CeO2 particles with different sizes appear on top of the TiO2 NTAs; see Figure 4f. However, Figure 4e suggests that the Cr2O3 tended to fill into the tube as well as coat the tube wall of the TiO2 NTAs. Although the metal oxides tend to be noticed on the surface of TiO2 NTAs, because when the solution concentration tends to be higher, the metal oxide formed by thermal decomposition retained more easily on the surface of the nanotubes. The corresponding EDS spectra are shown in Figure S1 (Supporting Information), from which the content of Zn, Cu, Cr, Ce besides Ti can be observed. Moreover, Figure S2 (Supporting Information) shows two magnified FESEM images of Cr2O3/TiO2 and ZnO/TiO2 heterostructured NTAs, indicating the metal oxides could grow both inside and outside theTiO2 NTAs to form heterostructured MxOy/TiO2 films. In addition, panels (a) and (c) in Figure S3 (Supporting Information) are two lowmagnification TEM images, which show the morphology of Cu2O/TiO2 and CeO2/TiO2 heterostructured NTAs, respectively. It can be clearly seen that some Cu2O and CeO2 platelike nanoparticles with dozens of nanometers in size are inside the TiO2 nanotube. Also, panels (b) and (d) in Figure S3 are the high-resolution (HR) TEM images taken from the circular region in Figure S3a,c, which shows that the lattice fringe of 0.35, 0.24, and 0.31 nm corresponds to the d spacings of TiO2(101), Cu2O(111), and CeO2(111), respectively, indicating the metal oxides could grow inside the TiO2 NTAs to form heterostructured MxOy/TiO2 films. The above results illustrate that different MxOy NPs were successfully attached to TiO2 NTs arrays, confirming the feasibility of our strategies to fabricate MxOy/TiO2 heterostructured films. Since the TiO2 NTs acted as both “nano-containers” and “nano-reactors” in this study, the loading contents of the MxOy contents in the MxOy/TiO2 heterostructured films could be manipulated by the initial concentration of the M(AC)x precursor solutions. Figure 5 shows XRD patterns of the ZnO/TiO2 heterostructured films with different concentrations of Zn(AC)2 solution ranging from 0.0 mol/L to 1.0 mol/ L. Due to the detection limitation of the XRD spectrometer (∼5%), characteristic peaks of ZnO could be observed when the Zn(AC)2 solution increased above 0.8 mol/L. SEM observation gives a clearer picture of morphological change of the ZnO/TiO2 heterostructured films. When the Zn(AC)2 precursor solution increased to 0.6 mol/L, only few ZnO nanorods started to appear; see Figure 6. Amounts of the ZnO nanorods get increased a lot and could be easily observed, when the Zn(AC)2 precursor solution increased to 0.8 and 1.0 mol/L. The above results demonstrated our synthesis strategy is of convenience and good manipulation. In the field of photocatalysis, the application of TiO2 is hindered by its large band gap and rapid recombination of photogenerated electron−hole pairs.32 The strategy reported in this study provides a facile and general approach to fabricate MxOy/TiO2 heterostructured films. The uppermost attraction of MxOy heterostructured TiO2 is effective electron−hole separation and transportation. In order to ensure electron−

Figure 5. XRD patterns of the ZnO/TiO2 heterostructured films with different Zn(AC)2 solution concentrations ranging from 0.0 mol/L to 1.0 mol/L. Characteristic peaks of ZnO could only be observed when the Zn(AC)2 solution is above 0.8 mol/L due to the detection limitation of the XRD spectrometer (∼5%).

hole separation and transportation, photoluminescence (PL) spectra of pure TiO2 NTAs and ZnO/TiO2 NTAs are shown in Figure S4 (Supporting Information). Compared with the carriers lifetime of pure TiO2 NTAs (average lifetime τav = 33.00 ns), ZnO/TiO2 NTAs (average lifetime τav = 38.50 ns) have the longer lifetime of carriers, indicating the recombination time of the electron−hole pairs of ZnO/TiO2 NTAs becomes longer and it is easier to separate and transfer electron−hole pairs. The separation of the electron hole pairs will make it produce more hydroxyl and reactive oxygen radicals, leading to decomposition of organic pollutants, which is crucial for various photocatalytic processes. Figure 7a shows several typical MxOy with their relative position of conduction band (CB) and valence band (VB), such as Cu2O (band gap ∼ 2.2 eV), CoO (∼2.6 eV), Ce2O3 (∼2.4 eV), Cr2O3 (∼3.5 eV), and ZnO (∼3.2 eV). When they are rationally coupled with TiO2, the bottom of CB and top of VB of the MxOy (such as ZnO and Cu2O) are slightly higher than those of TiO2, so that electrons are excited to CB of MxOy and transferred to CB of TiO2. As illustrated in Figure 7b, the energy level coupling effect between MxOy and TiO2 suppresses the recombination of electron/hole pairs, which leads to more reactive oxygen species (ROS) produced and a higher photocatalytic degradation efficiency.33 Specifically, Cu2O, owing to a narrow band gap of 2.2 eV, not only enhances the electron−hole pair separation but also enables the visible light photoresponse of the MxOy/TiO2 heterostructured system. In order to explain the spectral broadening of Cu2O/TiO2 heterostructured NTAs, the UV−vis spectrum has been provided as shown in Figure S5 (Supporting Information), indicating the absorption of Cu2O/TiO2 NTAs expands to the visible light range with the increase of Cu2O. We measured the photocatalytic activities of the prepared MxOy/TiO2 heterostructured NTAs through degradation of MO (Methyl orange) solution. Figure 7c shows the degradation kinetics of ZnO/TiO2 heterostructured NTAs, fabricated with different concentrations of Zn(AC)2 solutions, under ultraviolet light irradiation. The photocatalytic activities get enhanced with the increased concentration of Zn(AC)2 precursor solutions. When the concentration of Zn(AC)2 reaches 0.6 mol/L, the corresponding ZnO/TiO2 heterostructured NTAs exhibited the best activity. When the Zn(AC)2 concentration is further increased E

DOI: 10.1021/acs.inorgchem.8b01483 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 6. SEM images of the ZnO/TiO2 heterostructured films with different Zn(AC)2 solution concentrations: (a) 0.6 mol/L, (c) 0.8 mol/L, (e) 1.0 mol/L ((b), (d), and (f) are corresponding zoom-in images with fake color). ZnO nanorods show the shape of the white rodlike, and ZnO nanorods are obviously more and more dense from (b) to (d) and (f). This indicates the ratio of density of ZnO nanorods in the ZnO/TiO2 heterostructured films could be manipulated by controlling the ZnO precursor concentration.

Figure 7. (a) Energy levels of common metal oxides, (b) electron transfer pathway and coupling effects between TiO2 and other proper metal oxides, (c) photocatalytic degradation kinetics diagram of ZnO/TiO2 NTs heterostructured films under UV irradiation, and (d) photocatalytic degradation kinetics diagram of Cu2O/TiO2 NTs heterostructured films under visible light irradiation.

F

DOI: 10.1021/acs.inorgchem.8b01483 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry to 0.8 and 1 mol/L, the photocatalytic activity of the asprepared ZnO/TiO2 NTAs becomes deteriorated, which could be attributed to excessive ZnO nanorods blocking the tube mouth of TiO2 NTAs as shown in Figure 6. Moreover, simulation results show how the excessive ZnO nanorods on the tube mouth would hinder the molecular transportation inside the TiO2 NTs; see Figure S6 (Supporting Information). In addition, in order to ensure the stability of the as-prepared MxOy/TiO2 NTA films, the cycling experiments were carried out. Figure S7 (Supporting Information) shows that the ZnO/ TiO2 NTAs sample kept its high photocatalytic activity after 4 cycles. Also as shown in Figure S8 (Supporting Information), when the Cu2O/TiO2 films were immersed into the deionized water for 36 h, there is no color change though Cu2O shows a reddish color. These results indicate the MxOy were firmly attached to the TiO2 NTAs and thus successfully immobilized. Figure 7d shows the degradation kinetics of Cu2O/TiO2 heterostructured NTAs fabricated with different concentrations of Cu(AC)2 solutions, under visible light irradiation. All the Cu2O/TiO2 heterostructured NTAs exhibited visible light photocatalytic activities (>480 nm), due to the coupling effect between Cu2O and TiO2. When the concentration of Cu(AC)2 reaches 0.3 mol/L, the corresponding Cu2O/TiO2 heterostructured NTAs exhibited the best activity. The comparative data for the photocatalytic activities of the heterostructured MxOy/TiO2 films and the pure TiO2 NTAs are shown in Figure S9 (Supporting Information). The photocatalytic results further confirm the formation of M x O y /TiO 2 heterostructures, and the MxOy/TiO2 NTAs fabricated by our strategies could serve as a facile low-cost protocol for highly efficient photocatalysts.

Quanjun Xiang: 0000-0002-4486-7429 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National R&D Program of China under No. 2017YFA0207400, the National Key Research and Development Plan under No. 2016YFA0300801, the National Natural Science Foundation of China under Nos. 51502033, 61571079, 61131005, and 51572042, the National Basic Research Program of China under Grant No. 2012CB933104, the 111 Project No. B13042, International Cooperation Projects under Grant No. 2015DFR50870, and the Science and Technology Project of Sichuan Province No. 2017JY0002.

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CONCLUSION Over all, we successfully demonstrated a very simple and general approach to prepare MxOy/TiO2 heterostructured films (M = Zn, Ce, Cu, Cr...) by using TiO2 NTAs as “nanoreactors” while using M(AC)x solutions as the precursors. This simple and general synthetic approach may offer an avenue for preparation of MxOy/TiO2 heterostructured films with different morphologies and improved photochemical properties for vast environmental applications.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01483. EDS spectra, magnified FESEM images, TEM image of Cu2O/TiO2 heterostructured NTAs, TEM image of CeO2/TiO2 heterostructured NTAs, PL spectra of TiO2 NTAs and ZnO/TiO2 NTAs and UV−vis spectra of TiO2 NTAs and Cu2O/TiO2 NTAs, the simulation results of ZnO nanorods, the photocatalytic activity of ZnO/TiO2 NTAs after 4 cycles, and photocatalytic testing details (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86-028-83201440. Fax: +86-028-83202556. ORCID

Yulong Liao: 0000-0003-3761-7170 G

DOI: 10.1021/acs.inorgchem.8b01483 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.inorgchem.8b01483 Inorg. Chem. XXXX, XXX, XXX−XXX