In situ formation of porous TiO2 nanotube array with MgTiO3 nanoparticles for enhanced photocatalytic activity

Accepted Manuscript In situ formation of porous TiO2 nanotube array with MgTiO3 nanoparticles for enhanced photocatalytic activity

Zhizhong Liu, Ping Xu, Hao Song, Jiangwen Xu, Jijiang Fu, Biao Gao, Xuming Zhang, Paul K. Chu PII: DOI: Reference:

S0257-8972(18)30761-8 doi:10.1016/j.surfcoat.2018.07.062 SCT 23628

To appear in:

Surface & Coatings Technology

Received date: Revised date: Accepted date:

31 March 2018 17 July 2018 19 July 2018

Please cite this article as: Zhizhong Liu, Ping Xu, Hao Song, Jiangwen Xu, Jijiang Fu, Biao Gao, Xuming Zhang, Paul K. Chu , In situ formation of porous TiO2 nanotube array with MgTiO3 nanoparticles for enhanced photocatalytic activity. Sct (2018), doi:10.1016/ j.surfcoat.2018.07.062

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Abstract IDs:79

In Situ Formation of Porous TiO2 Nanotube Array with MgTiO3

PT

Nanoparticles for Enhanced Photocatalytic Activity

RI

Zhizhong Liu,a1 Ping Xu,a1 Hao Song,a Jiangwen Xu,a Jijiang Fu,a Biao Gao,a*

State Key Laboratory of Refractories and Metallurgy, Institute of Advanced

NU

a

SC

Xuming Zhang,a,b* and Paul K. Chuc

Materials and Nanotechnology, Wuhan University of Science and Technology, Wuhan,

MA

China

b

State Key Laboratory of High Performance Ceramics and Superfine Microstructure,

c

PT E

D

Shanghai Institute of Ceramics, Chinese Academy of Sciences, China Department of Physics and Department of Materials Science and Engineering, City

the two authors contributed equally to this work.

AC

1

CE

University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China

Corresponding author: [email protected] (B. Gao); [email protected] (X. Zhang)

1

ACCEPTED MANUSCRIPT Abstract:

Heterostructured

semiconductor

photocatalysts

are

desirable

for

applications such as purification of pollutants and water splitting due to the enhanced charge separation.

In this work, porous TiO2 nanotube arrays loaded with MgTiO3

nanoparticles (MgTiO3/P-TiO2 NTAs) are prepared hydrothermally by anodization of TiO2 NTAs in the magnesium acetate (Mg(AC)2) solution.

The photocatalytic (PC)

PT

activity of MgTiO3/P-TiO2 NTAs evaluated by monitoring the degradation of methyl

TiO2.

RI

blue (MB) reveals that the effectiveness is related to the thickness of MgTiO3 layer on The best PC activity is observed from the MgTiO3/P-TiO2 NTAs

SC

hydrothermally treated at 200 oC for 1 h, the degradation rate is twice that of pristine The

NU

anatase TiO2 NTAs and the transient photocurrent is three times higher.

heterostructured MgTiO3/P-TiO2 NTAs with good PC characteristics have large

MA

potential in photoelectrochemical (PEC) water decomposition and solar cell

D

applications.

PT E

Keywords: Photocatalysis; Heterostructure; MgTiO3; TiO2 nanotube arrays;

AC

CE

Hydrothermal reaction.

2

ACCEPTED MANUSCRIPT 1. Introduction Since accelerated fossil energy consumption is causing environmental concerns, renewable energy has generated tremendous interest and photocatalysis utilizing semiconductors is particularly appealing due to the sustainability, environmental Among the various semiconductor

PT

friendliness, and low production cost [1-3].

RI

photocatalysts, titanium oxide (TiO2) is one the most widely studied especially in

SC

light-driven reactions involving organic species oxidation and water splitting because of the strong oxidizing activity, high photosensitivity, as well as biological and TiO2 nano-powders such as Degussa P25 are commonly

NU

chemical stability [4-6].

MA

used photocatalysts because its large surface area benefits surface chemical reactions. However, zero-dimensional (0D) TiO2 suspended in slurry is difficult to recover and Immobilization of TiO2 nanoparticles on different

D

may cause secondary pollution.

PT E

substrates has been attempted but the compact structure is less effective in harvesting light and adsorbing targeted contaminants [7].

One-dimensional (1D) TiO2

CE

nanotubes composed of nanoparticles constitute a promising platform to overcome the

AC

drawback of condensed nanoparticles by providing a large active surface area and efficient diffusion channels [8, 9].

To

elevate

the

photocatalytic

(PC)

activity of

signal

photocatalyst,

heterostructure photocatalysts have attracted much interest in photodegradation of environmental pollutants, photocatalytic hydrogen evolution and solar cell, because of the synergistic effects rendered by the difference in the potentials of the conduction 3

ACCEPTED MANUSCRIPT band (CB) and valence band (VB) of semiconductors[2, 10-12], such as SrTiO3/TiO2 nanotube arrays [13], CeO2/TiO2 nanobelts [14], ZnO/TiO2 photonic crystals [15], SnO2/TiO2 core/shell nanoparticles [16], and so on.

Magnesium titanate (MgTiO3),

an efficient n-type semiconductor with a bandgap of about 3.4 eV, has the suitable

Meanwhile, the more negative

RI

splitting and hydrogen production [17, 18].

PT

electronic structures and conduction/valence band structure favorable to water

SC

conduction/valence band of MgTiO3 drives the transfer of photogenerated electrons to TiO2 and holes in the opposite direction consequently promoting the charge However, there have been few reports on

NU

separation as well as the PC reaction [19].

MA

the preparation and properties of the heterostructure of MgTiO3/TiO2. Meng et al. [19] prepared MgTiO3/MgTi2O5/TiO2 belt-junctions using a thermally driven

D

magnesium ion doping method by sintering at 700 oC and the materials showed

PT E

excellent charge transportation and enhanced PC reaction.

Jin et al. [20] prepared

Cu-loaded MgTiO3-TiO2 catalyst by calcination at 500 oC and good PC activity was

AC

CE

observed in the reduction of nitrate ions.

Herein, the novel heterostructure of MgTiO3 nanoparticles grown in situ on porous TiO2 nanotube arrays (P-TiO2 NTAs) on Ti substrate is described and evaluated. The heterostructured MgTiO3/P-TiO2 NTAs fabricated by a mild hydrothermal reaction in the presence of high concentration of magnesium acetate (Mg(AC)2) and as-anodized TiO2 NTAs [21, 22] show enhanced light harvesting and high separation efficiency of photogenerated electron and hole for fast photocatalytic degradation of 4

ACCEPTED MANUSCRIPT methyl blue (MB). The degradation rate is twice that of anatase TiO2 NTAs under UV irradiation and the transient photocurrent is three times larger thus boding well for photocatalytic and solar energy conversion applications.

PT

2. Experimental details

RI

The ordered TiO2 NTAs were fabricated by electrochemical anodization of a Ti foil

SC

(1 cm x 1cm x 0.1 cm, Aldrich, USA) at 40 V for 1 h in an ethylene glycol solution containing 5 vol% DI water and 0.5 wt% ammonium fluoride (NH4F).

NU

Anodization was carried out at room temperature in a conventional two-electrode cell

MA

using a direct current power supply (IT 6834, ITECH, Nanjing, China). and graphite foil served as the anode and cathode, respectively.

The Ti foil

The anodized Then

D

samples were rinsed with DI water and annealed at 200 oC for 3 h in air.

PT E

hydrothermal treatment was carried out at 200 oC for different time periods of 0.5 h, 1 h, and 3 h in 40 ml of 0.8 M magnesium acetate (Mg(Ac)2) solution in a 60 mL The as-hydrothermal samples were rinsed with 1 M HCl to

CE

Teflon-lined autoclave.

AC

remove the residual Mg(OH)2 and then annealed in air at 450 oC for 2 hr.

The surface topography, structure, and composition of the products were assessed by field-emission scanning electron microscopy (FE-SEM) (FEI Nova 400 Nano), X-ray diffraction (XRD) (Philips X0 Pert Pro), X-ray photoelectron spectroscopy (XPS) (ESCALABMK-II), and transmission electron microscopy (TEM, TECNAI).

5

ACCEPTED MANUSCRIPT The optical properties of the samples were analyzed by UV-vis diffuse reflectance spectroscopy (UV-vis DRS) (UV-2600, Shimadzu). The PC activity of the TiO2 NTAs and MgTiO3/P-TiO2 NTAs were evaluated with aqueous methyl blue (MB) as the probing molecule.

The sample with a size of 1 cm

The solution was stirred in the dark for 2 h to reach

RI

concentration of 10 mg/mL.

PT

x 1 cm was immersed in 20 mL of the aqueous MB solution with an initial

with air during the PC reaction.

SC

adsorption equilibrium between the photocatalyst and MB and aspirated continuously A high-pressure mercury lamp (500 W, primary

NU

wavelength of 365 nm) was used as the UV irradiation source and the distance The change in the MB

MA

between the light source and sample was about 120 mm.

concentration with PC time was measured by UV–Vis spectrophotometry (TU-

PT E

D

1810SPC, Beijing PGENERAL, Beijing, China).

The PEC characteristics of the TiO2-NTAs and MgTiO3/P-TiO2 NTAs were

The samples were insulated with epoxy resin leaving an exposed area of

AC

irradiation.

CE

evaluated in a 0.5 M Na2SO4 solution using a three electrode PEC cell under the same

1×1 cm2 as the working photoanode.

An Ag/AgCl electrode served as the reference

electrode and platinum foil was the counter electrode.

The current–time curves (I–t)

were obtained at a 0.5 V bias using the same incident light source and recorded on a CHI760e potentiostat (CH Instruments Inc. Shanghai, China).

3. Results and discussion 6

ACCEPTED MANUSCRIPT Fig. 1 shows the morphology of the TiO2 NTAs before and after the hydrothermal treatment at 200 oC in the 0.8 M Mg(Ac)2 solution.

After anodization

at 40 V for 1 h, the TiO2 NTAs with an inner diameter of 90 nm and wall thickness of about 10 nm are fabricated on the Ti foil as shown in Fig. 1A.

When the

PT

hydrothermal treatment is performed for 0.5 h, the nanotube structure is retained The surface

RI

together with smooth wall with a thickness of about 20 nm (Fig. 1B).

SC

become coarse gradually if the hydrothermal time increased to 1 h (Fig. 1C). Many small particles with a size of 10-20 nm are formed and uniformly attached on the tube

MA

NU

surface if the time is increased to 3 hours (Fig. 1D).

Fig. 2 depicts the X-ray diffraction (XRD) patterns of the products after the The main diffraction peaks acquired from the annealed

D

hydrothermal treatment.

PT E

TiO2 NTAs on Ti can be indexed to the anatase TiO2 phase in addition to peaks from the Ti substrate (black line in Fig. 2) [23].

After the hydrothermal treatment in 0.8

CE

M Mg(Ac)2 at 200 oC for more than 1 h, three peaks emerged at 35.5o, 40.6o, and

AC

78.4o can be assigned to the geikielite MgTiO3 (JCPDF:06-0494) [24]. However, only a weak diffraction peak at 35.5o can be observed from the sample reacting for 0.5 h (red line in Fig. 2) due to the small amount of MgTiO3.

The enhanced MgTiO3

diffraction peaks and reduced anatase TiO2 peaks are observed when the reaction time is prolonged indicating that more TiO2 is converted to MgTiO3.

The retained TiO2

suggests that the hydrothermal reaction may not be sufficient and it turns into anatase TiO2 after annealing resulting in the formation of heterostructured MgTiO3/TiO2. 7

ACCEPTED MANUSCRIPT

X-ray photoelectron spectroscopy (XPS) is carried out to determine the chemical states of Mg 1s and Ti 2p in the hydrothermal product obtained at 200 oC for 1 h. The high-resolution Ti 2p spectra obtained from the near surface are shown in Fig. 3A.

PT

The Ti 2p peaks are at 464.2 and 458.6 eV corresponding to Ti in titanate [25] but the

RI

characteristic peak of Ti 2p from TiO2 cannot be observed possibly because of the Fig. 3B shows

SC

high surface concentration of Mg2+ and thick MgTiO3 particle layer.

NU

that the Mg 1s peak is at 1303.7 eV which matches with Mg2+ in MgTiO3.

MA

Transmission electron microscopy (TEM) is carried out to characterize the microstructure of the product hydrothermally processed at 200 oC for 1 h. Fig. 4A

The high-resolution TEM image in Fig. 4B reveals lattice fringes with

PT E

of 80 nm.

D

reveals the tubular structure composed of nanoparticles with an approximate diameter

interplanar distances of 0.351 nm and 0.222 nm corresponding to the [101] crystal

CE

plan of anatase TiO2 and [113] crystal plan of MgTiO3 which are in line with the XRD

AC

peaks located at 25.3o and 40.6o, respectively.

Fig. 5 exhibits the UV-Vis diffuse reflectance spectroscopy of TiO2 NTAs before and after the hydrothermal treatment in Mg(Ac)2 solution at 200 oC for 0.5h, 1h and 3h. The TiO2 NTAs has an absorption edge at around 380 nm corresponding to a band gap of 3.2 eV.

After hydrothermal treatment, the absorption edge depicts no

obvious change suggesting the similar band gap energy, however, the adsorption 8

ACCEPTED MANUSCRIPT strengthen gradually increased with the hydrothermal time increased from 0.5 h to 1h because of the enhanced light scattering, but it dramatically decreased after hydrothermal treatment for 3h because the nanotube was clogged with big particles.

PT

Fig. 6A presents PC degradation of MB in the presence of the TiO2 NTAs and After reaching

RI

heterostructured MgTiO3/P-TiO2 NTAs versus UV illumination time.

SC

the adsorption–desorption equilibrium, the concentration of MB in the presence of annealed TiO2 NTAs decreases slowly to 30% after UV irradiation for 3 h.

In

NU

comparison, the photodegradation rate of MO with MgTiO3/P-TiO2 NTAs prepared

irradiation for 3 h.

MA

hydrothermally for 1 h is much faster with almost 90% of MO decomposed after The enhanced PC activity can be attributed to the synergistic However, the

D

effects rendered by the MgTiO3/P-TiO2 nanocomposites.

PT E

MgTiO3/P-TiO2 NTAs hydrothermally treated for 0.5 h and 3 h possess inferior PC activity because of the improper thickness of the MgTiO3 nanoparticle layer which The result is in line with the UV-Vis diffuse reflectance

CE

impedes the reaction.

The

AC

spectroscopy, the enhanced PC activity is related to the light adsorption ability.

MgTiO3/P-TiO2 NTAs hydrothermally treated for 1 h shows structural superiority. Meanwhile, if the MgTiO3 nanoparticle layer is too thick (hydrothermal treatment for 3 h), the photogenerated carriers accumulated in the TiO2 underlayer may not be able to transfer to surface and participate in the PC reactions.

Photodegradation of MB

with MgTiO3/P-TiO2 NTAs obeys the first-order reaction kinetics as shown in Fig. 6B.

9

ACCEPTED MANUSCRIPT The reaction rate (k) observed from the MgTiO3/P-TiO2 NTAs hydrothermally treated for 1 h is twice that of the TiO2 NTAs.

The charge separation efficiency is an important factor determining the PC activity.

PT

Although MgTiO3 found that its band gap energy is similar to anataseTiO2, the

RI

elevated PC activity of coupled MgTiO3/TiO2 nanocomposites is observed and can be

SC

ascribed to the enhanced charge separation derived from the coupling effect in the TiO2 and MgTiO3 nanocomposite, because MgTiO3 has a slightly higher flatband

NU

potential leading to the transfer of photogenerated electrons to TiO2 and holes in the Fig. 7

MA

opposite direction consequently promoting the charge separation.[19, 20, 24]

shows the amperometric I-t curves of the TiO2 NTAs and MgTiO3/P-TiO2 NTAs

D

obtained under UV light turned on and off cycles at a bias of 0.5 V (vs. Ag/AgCl).

PT E

The annealed TiO2 NTAs show a transient photocurrent of about 1 mA/cm2 and the heterostructured MgTiO3/P-TiO2 NTAs (1 h) is three times larger.

The good PC and

CE

PEC performance provides evidence that the heterostructured MgTiO3/P-TiO2 NTAs

AC

formed by hydrothermal treatment and subsequent calcination are promising photocatalysts.

The cycling stability is also important to a photocatalyst and Fig. 8

presents the long-term stability of the heterostructured MgTiO3/P-TiO2 NTAs evaluated by photogradation of MB under UV illumination.

After 8 cycles, the

photodegradation ratio is maintained at 90% suggesting good stability.

4. Conclusion 10

ACCEPTED MANUSCRIPT Heterostructured MgTiO3/P-TiO2 NTAs are prepared on Ti substrate by electrochemical anodization and hydrothermal treatment.

The PC activity of the

MgTiO3/P-TiO2 NTAs is related to the coated MgTiO3 nanoparticles.

Under

hydrothermal reaction for 1 h, the best PC activity is observed, the degradation rate of

PT

MB observed from the MgTiO3/P-TiO2 NTAs (1 h) is twice that of the pristine anatase The excellent

RI

TiO2 NTAs and the transient photocurrent is also three times larger.

SC

PC activity of the MgTiO3/P-TiO2 NTAs is attributed to the synergistic effects between the MgTiO3 and TiO2 enhancing charge separation due to the favorable Consequently, the heterostructured

NU

conduction and valence band structure.

MA

MgTiO3/P-TiO2 NTAs are promising in PEC water splitting and solar cell

Acknowledgements

PT E

D

applications.

CE

This work was financially supported by National Natural Science Foundation of China (No. 51572100, 61434001 and 31500783), Opening Project of State Key

AC

Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences (SKL201609SIC), City University of Hong Kong Applied Research Grant (ARG) No. 9667122, Hong Kong Research Grants Council (RGC) General Research Funds (GRF) No. CityU 11205617, as well as National Students, Platform for Innovation and Entrepreneurship Training Program (201610488001).

11

ACCEPTED MANUSCRIPT References: [1] W. Wang, M.O. Tadé, Z. Shao, Nitrogen-doped simple and complex oxides for photocatalysis: A review, Prog. Mater. Sci., 92 (2018), pp. 33-63. [2] J. Low, J. Yu, M. Jaroniec, S. Wageh, A.A. Al-Ghamdi, Heterojunction

PT

photocatalysts, Adv. Mater., 29 (2017), Article 1601694.

RI

[3] H. Yu, R. Shi, Y. Zhao, T. Bian, Y. Zhao, C. Zhou, G.I.N. Waterhouse, L.Z. Wu,

SC

C.H. Tung, T. Zhang, Alkali-assisted synthesis of nitrogen deficient graphitic carbon nitride with tunable band structures for efficient visible-light-driven

NU

hydrogen evolution, Adv. Mater., 29 (2017), Article 1605148.

MA

[4] M. Ge, Q. Li, C. Cao, J. Huang, S. Li, S. Zhang, Z. Chen, K. Zhang, S.S. Al-Deyab, Y. Lai, One-dimensional TiO2 nanotube photocatalysts for solar water

D

splitting, Adv. Sci., 4 (2017), Article 1600152.

PT E

[5] J. Schneider, M. Matsuoka, M. Takeuchi, J. Zhang, Y. Horiuchi, M. Anpo, D.W. Bahnemann, Understanding TiO2 photocatalysis: mechanisms and materials,

CE

Chem. Rev., 114 (2014), pp. 9919-9986.

AC

[6] A.E. Wiacek, A. Gozdecka, M. Jurak, Physicochemical characteristics of chitosan– TiO2 biomaterial. 1. stability and swelling properties, Ind. Eng. Chem. Res., 57 (2018), pp. 1859-1870. [7] M.J. Muñoz-Batista, A. Kubacka, M. Fernández-García, Effective enhancement of TiO2 photocatalysis by synergistic interaction of surface species: from promoters to Co-catalysts, ACS Catal., 4 (2014), pp. 4277-4288.

12

ACCEPTED MANUSCRIPT [8] X. Qu, N. Kobayashi, T. Komatsu, Solid nanotubes comprising α-Fe2O3 nanoparticles prepared from ferritin protein, ACS Nano, 4 (2010), pp. 1732-1738. [9] J. Wu, J. Wang, Y. Du, H. Li, Y. Yang, X. Jia, Chemically controlled growth of porous CeO2 nanotubes for Cr(VI) photoreduction, Appl. Catal. B: Environ.,

PT

174-175 (2015), pp. 435-444.

Yin,

T.

Zhang,

Self-assembled

Au/CdSe

nanocrystal

clusters

for

SC

Y.

RI

[10] R. Shi, Y. Cao, Y. Bao, Y. Zhao, G.I.N. Waterhouse, Z. Fang, L.Z. Wu, C.H. Tung,

plasmon-mediated photocatalytic hydrogen evolution, Adv. Mater., 29 (2017),

NU

Article 1700803.

MA

[11] Y. Zhao, B. Zhao, J. Liu, G. Chen, R. Cao, S. Yao, M. Li, Q. Zhang, L. Gu, J. Xie, X. Wen, L.Z. Wu, C.H. Tung, D. Ma, T. Zhang, Oxide-modified nickel

D

photocatalysts for the production of hydrocarbons in visible light, Angew. Chem.

PT E

Int. Edit., 128 (2016), pp. 4287-4291. [12] H. Zhao, X. Ding, B. Zhang, Y. Li, C. Wang, Enhanced photocatalytic hydrogen along

with

byproducts

suppressing

over

Z-scheme

CE

evolution

AC

CdxZn1−xS/Au/g-C3N4 photocatalysts under visible light, Sci. Bull., 62 (2017), pp. 602-609.

[13] X. Zhang, K. Huo, L. Hu, Z. Wu, P.K. Chu, Synthesis and photocatalytic activity of highly ordered TiO2 and SrTiO3/TiO2 nanotube arrays on Ti substrates, J. Am. Ceram. Soc., 93 (2010), pp. 2771-2778.

13

ACCEPTED MANUSCRIPT [14] J. Tian, Y. Sang, Z. Zhao, W. Zhou, D. Wang, X. Kang, H. Liu, J. Wang, S. Chen, H. Cai, H. Huang, Enhanced photocatalytic performances of CeO2/TiO2 nanobelt heterostructures, Small, 9 (2013), pp. 3864-3872. [15] X. Zheng, D. Li, X. Li, J. Chen, C. Cao, J. Fang, J. Wang, Y. He, Y. Zheng,

PT

Construction of ZnO/TiO2 photonic crystal heterostructures for enhanced

RI

photocatalytic properties, Appl. Catal. B: Environ., 168-169 (2015), pp. 408-415.

SC

[16] N.S. McCool, J.R. Swierk, C.T. Nemes, C.A. Schmuttenmaer, T.E. Mallouk, Dynamics of electron injection in SnO2/TiO2 core/shell electrodes for

NU

water-splitting dye-sensitized photoelectrochemical cells, J. Phys. Chem. Lett., 7

MA

(2016), pp. 2930-2934.

[17] N. Zhang, K. Zhang, W. Zhou, B. Jiang, K. Pan, Y. Qu, G. Wang, Pure phase

PT E

106151-106155.

D

orthorhombic MgTi2O5 photocatalyst for H2 production, RSC Adv., 5 (2015), pp.

[18] L. Wang, G. Yang, S. Peng, J. Wang, D. Ji, W. Yan, S. Ramakrishna, Fabrication

CE

of MgTiO3 nanofibers by electrospinning and their photocatalytic water splitting

AC

activity, Int. J. Hydrogen Energ., 42 (2017), pp. 25882-25890. [19] L. Meng, Z. Ren, W. Zhou, Y. Qu, G. Wang, MgTiO3/MgTi2O5/TiO2 heterogeneous belt-junctions with high photocatalytic hydrogen production activity, Nano Res., 10 (2017), pp. 295-304. [20] R. Jin, W. Gao, J. Chen, H. Zeng, F. Zhang, Z. Liu, N. Guan, Photocatalytic reduction of nitrate ion in drinking water by using metal-loaded MgTiO3-TiO2

14

ACCEPTED MANUSCRIPT composite semiconductor catalyst, J. Photochem. Photobiol. A: Chem., 162 (2004), pp. 585-590. [21] K. Huo, H. Wang, X. Zhang, Y. Cao, P.K. Chu, Heterostructured TiO2 nanoparticles/nanotube arrays: in situ formation from amorphous TiO2 nanotube

PT

arrays in water and enhanced photocatalytic activity, ChemPlusChem, 77 (2012),

RI

pp. 323-329.

SC

[22] X. Zhang, B. Gao, L. Hu, L. Li, W. Jin, K. Huo, P.K. Chu, Hydrothermal synthesis of perovskite-type MTiO3 (M = Zn, Co, Ni)/TiO2 nanotube arrays from

NU

an amorphous TiO2 template, CrystEngComm, 16 (2014), pp. 10280-10285.

MA

[23] X. Zhang, K. Huo, H. Wang, W. Zhang, P.K. Chu, Influence of structure parameters and crystalline phase on the photocatalytic activity of TiO2 nanotube

D

arrays, J. Nanosci. Nanotech., 11 (2011). pp. 11200-11205.

PT E

[24] E.A.V. Ferri, J.C. Sczancoski, L.S. Cavalcante, E.C. Paris, J.W.M. Espinosa, A.T. de Figueiredo, P.S. Pizani, V.R. Mastelaro, J.A.

Varela, E. Longo,

CE

Photoluminescence behavior in MgTiO3 powders with vacancy/distorted clusters

AC

and octahedral tilting, Mater. Chem. Phys., 117 (2009), pp. 192-198. [25] N. Zhang, Y. Qu, K. Pan, G. Wang, Y. Li, Synthesis of pure phase Mg1.2Ti1.8O5 and MgTiO3 nanocrystals for photocatalytic hydrogen production, Nano Res., 9 (2016), pp. 726-734.

15

ACCEPTED MANUSCRIPT Figure captions Fig. 1. (A) FE-SEM images of the TiO2 NTAs and MgTiO3/P-TiO2 NTAs hydrothermally prepared at 200 oC for (B) 0.5 h, (C) 1 h, and (D) 3 h. Fig. 2. XRD patterns of the TiO2 NTAs and MgTiO3/P-TiO2 NTAs hydrothermally

PT

prepared for 0.5h, 1h and 3h.

RI

Fig. 3. High-resolution XPS spectra of (A) Ti 2p and (B) Mg 1s obtained from the

SC

surface of the MgTiO3/P-TiO2 NTAs.

Fig. 4. (A) low and (B) high resolution TEM of MgTiO3/P-TiO2 NTAs (1 h).

NU

Fig. 5. UV-Vis diffuse reflectance spectroscopy of the TiO2 NTAs and

MA

MgTiO3/P-TiO2 NTAs hydrothermally prepared for different time (0.5 h, 1 h and 3 h). Fig. 6. (A) Concentration changes of MB in the aqueous solution as a function of UV

D

illumination time (t) in the presence of TiO2 NTAs and MgTiO3/P-TiO2 NTAs; (B)

PT E

Corresponding first-order reaction kinetics curves. Fig. 7. Transient photocurrent curves in the 0.5 M Na2SO4 solution under UV

CE

irradiation of the annealed TiO2 NTAs and MgTiO3/P-TiO2 NTAs (0.5 h, 1 h and 3 h).

for 3 h.

AC

Fig. 8. Photocatalysis cycles of the MgTiO3/P-TiO2 NTAs (1 h) after UV illumination

16

Fig. 1

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

17

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

Fig. 2

18

PT

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

Fig. 3

19

AC

CE

PT E

D

MA

SC

NU

Fig. 4

RI

PT

ACCEPTED MANUSCRIPT

20

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

Fig. 5

21

AC

CE

PT E

D

MA

SC

NU

Fig. 6

RI

PT

ACCEPTED MANUSCRIPT

22

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

Fig. 7

23

AC

CE

PT E

D

MA

NU

Fig. 8

SC

RI

PT

ACCEPTED MANUSCRIPT

24