Defects improved photocatalytic ability of TiO2

Accepted Manuscript Title: Defects improved photocatalytic ability of TiO2 Author: Lei Li Hong-Wei Tian Fan-Ling Meng Xiao-Ying Hu Wei-Tao Zheng Chang Q Sun PII: DOI: Reference:

S0169-4332(14)01825-X http://dx.doi.org/doi:10.1016/j.apsusc.2014.08.078 APSUSC 28531

To appear in:

APSUSC

Received date: Revised date: Accepted date:

28-5-2014 12-8-2014 13-8-2014

Please cite this article as: L. Li, H.-W. Tian, F.-L. Meng, X.-Y. Hu, W.-T. Zheng, C.Q. Sun, Defects improved photocatalytic ability of TiO2 , Applied Surface Science (2014), http://dx.doi.org/10.1016/j.apsusc.2014.08.078 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.

*Highlights (for review)

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Defect improves the photocatalytic ability by band gap narrowing and carrier life prolonging Atomic undercoordination shortens the local bonds, entraps, and polarizes electrons Polarization lowers the local workfunction and lengthens carrier life Entrapment and polarization narrows the band gap tuning the wavelength of absorption

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*Manuscript Click here to view linked References

Defects improved photocatalytic ability of TiO2

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Lei Lia, Hong-Wei Tian a*, Fan-Ling Menga, Xiao-Ying Hub, Wei-Tao Zhenga, and Chang Q Sunc*

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Department of Materials Science and Key Laboratory of Automobile Materials of MOE and State

b c

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College of Science, Changchun University, Changchun 130022, China

School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore

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Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.

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639798.

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*Corresponding author, E-mail: [email protected]; [email protected]

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Abstract ........................................................................................................................................................................ 2 1 Introduction .......................................................................................................................................................... 3 2 Principles .............................................................................................................................................................. 4 2.1 Core level shift: Tight-binding approach ................................................................................................. 4 2.2 BOLS-NEP: Quantum entrapment and polarization ............................................................................... 5 2.3 ZPS: Density-of-states distillation ........................................................................................................... 8 2.4 The mechanism of TiO2 photocatalysis ................................................................................................... 8 3 Results and discussion ........................................................................................................................................ 10

21 22 23 24

3.1 Ti(0001): E2p(0) and ∆E2p(12) ............................................................................................................... 10 3.2 ZPS of defected-TiO2: Ti2p3/2 and O1s core bands .................................................................................. 12 3.3 ZPS of defected-TiO2: Valence band ..................................................................................................... 13 Conclusion.......................................................................................................................................................... 14

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Abstract

3

Defect generation forms an important means modulating the photocatalytic ability of TiO2 with

5

mechanisms that remain yet unclear. Here we show that a spectral distillation clarifies the impact of

6

defect on modulating the band gap, electroaffinity, and work function of the substance. Firstly, by

7

analyzing XPS measurements, we calibrated the 2p3/2 level of 451.47 eV for an isolated Ti atom and

8

its shifts by 2.14 and 6.94 eV, respectively, upon Ti and TiO2 bulk formation. Spectral difference

9

between the defected and the un-defected TiO2 skin revealed then that the 2p3/2 level shifts further

10

from 6.94 to 9.67 eV due to the defect-induced quantum entrapment. This entrapment is associated

11

with an elevation of the upper edges of both the 2p3/2 and the conduction band by polarization. The

12

shortening and strengthening of bonds between undercoordinated atoms densify and entrap the core

13

electrons, which in turn polarize the dangling bond electrons of defect atoms. The entrapment and

14

polarization mediate thus the band gap, the electroaffinity, the work function, and the photocatalytic

15

ability of TiO2.

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Key Words: Photocatalysis, XPS, DFT, TiO2, defect, surface, nanostructures

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1

Introduction

2

Defects are ubiquitous but generally undesired in applications, as they introduce unpredictability and

4

difficulty in understanding. However, if properly controlled, they can form the base of a completely

5

new technology that issue sustainable, scalable applications as a cheap and convenient method.

6

Atomic undercoordination, such as situations of adatoms, atomic defects, terrace edges, monolayer

7

skin of the bulk, and nanostructures, alters the local bond and electronic attributes, including the

8

bond length, bond energy, potential trap depth, charge and energy density [1], electroaffinity, band

9

gap, and work function in terms of entrapment and polarization [2]. These entities determine the

10

performance of a substance at the specific atomic site, such as the catalytic ability, electronic,

11

dielectric, optic, magnetic, mechanical, and thermal properties. Thus, an atomic-scale understanding

12

of the energetic behavior of electrons due to defect becomes increasingly important in systems with a

13

large number of such undercoordinated atoms.

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The photoactivity of the nanoscaled or the highly-defected TiO2 has received extensive attention

16

owing to its tunable band gap and work function [3-8]. The drawbacks of bulk TiO2 stem from its

17

wide band gap and massive photogenerated charge carriers prevent carriers from being generated

18

under visible-light irradiation and from living longer by postponed recombination [9, 10]. Much

19

effort has been made to improve the photovoltaic or photocatalytic ability of TiO2 by introducing

20

defects in past decades. Although the defected-TiO2 containing Ti3+ ions and O2- vacancies could

21

absorb visible light [11, 12], the mechanism of band structure modulation remains inconclusive.

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It has been elegantly accepted that the oxygen-derived Ti 3d states located ~0.85 eV below the Fermi

24

level (EF) narrows the band gap [9, 13]. Such Ti 3d states are conventionally ascribed to the oxygen

25

(Obr) vacancies in bridging two Ti3+ ions across [14-16]. Each Obr vacancy may leave two electrons

26

behind the neighboring Ti atoms during vacating. However, based on their ultra-violet spectroscopy

27

(UPS), scanning tunneling microscopy (STM), and density functional theory (DFT) investigation,

28

Mattinez et al [3] suggested that the Ti 3d defect states at the TiO2(110) surface arise primarily from

29

Ti3+ interstitials in the near-surface region rather than to the surface Obr vacancies. The defected

30

black TiO2 exhibits substantial activity and stability in the photocatalytic production of hydrogen

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1

from water under sunlight [17]. Combining valence band x-ray photoelectron spectroscopy (XPS)

2

and optical absorption spectroscopy, they found that not only the valence band but also the center of

3

the conduction band of the black TiO2 shifts up simultaneously. Therefore, band bending due to

4

defects play important roles in photocatalysis and photochemical processes of TiO2 [18].

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In this communication, we show that a combination of the zone-selective electronic spectroscopic

7

(ZPS) analysis [19] and the bond order-length-strength and nonbonding electron polarization

8

(BOLS-NEP) notation [2, 20] have enabled us to purify and quantify the defect states with

9

clarification of their physical origin.

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2

Principles

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2.1 Core level shift: Tight-binding approach

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According to the tight-binding (TB) theory [21], the integral of the intra-atomic potential, Vatom(r),

15

and the respective electronic eigen wave function at the specific ith atomic site, v, i , determines the

16

νth energy level of an isolated atom, Ev(z = 0). The involvement of the interatomic potential Vcry(r)

17

shifts the Ev(0) to a deeper energy by an amount that is proportional to the cohesive energy per bond

18

at equilibrium, which follows [21],

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ħ        2

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19

ν 0  ν, |   |ν, 

#

%$ ν 12  ν 0  ν,   ν,  !ν,   ν, " 20

 ' (1

%) *

+ ≅ ' ∝ .

#$&

21

(1)

22

The coordination number (CN) z = 0 represents an isolated atom and zb =12 an atom in the fcc bulk

23 24 25 26

as standard reference. The sum is over all z neighbors of the specific ith atom. The parameter α is

the exchange integral and the β the overlap integral. Because v, i v, j = δij with δij being the Kronig function (if i = j, δij = 1, otherwise, δij = 0), the term zβ/α << 1, the β is negligible compared with the

α. Any perturbation to the bond energy Eb will shift the core level accordingly.

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2.2 BOLS-NEP: Quantum entrapment and polarization

3

The BOLS-NEP notation [2] indicates that atomic undercoordination shortens and strengthens the

5

remaining bonds between undercoordinated atoms. Bond contraction raises the local density of the

6

bonding charge, energy, and mass; bond strengthening deepens the local potential well and entraps

7

the electrons with deeper binding energy [1].

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On the other hand, the locally densely entrapped core and bonding electrons will polarize the

10

nonbonding (dangling bond in the present case) electrons and raise their energy close to the Fermi

11

energy or cross. The polarized electrons in turn will split and screen the local potentials, which create

12

polarized states to the core band unless the core band is too deep to be sensitive to the polarization

13

perturbation. These sequential BOLS-NEP events perturb the Hamiltonian of an extended solid.

14

Figure 1 illustrates the BOLS-NEP scheme on the behavior of bonding and nonbonding electrons at

15

sites of undercoordinated atoms. These sequential processes modulate the gap between the

16

conduction and the valence band, electroaffinity or separation between the vacuum level and the

17

bottom edge of the conduction band, work function and tune the photocatalytic ability of the

18

defected-TiO2. The deepening of the conduction band and the polarization of the valence band

19

narrow the band gap for photon absorption; the polarization of the conduction band reduces the work

20

function for electron rejection; and the entrapment of the conduction band enlarges the electroaffinity

21

that represents the ability of holding electrons from being escaped or recombined.

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Figure 1 BOLS-NEP notation indicates that atomic undercoordination shortens the local bond (dz <

3

d0) and deepens the local potential well that densifies and entraps the bonding electrons (T). The

4

densely entrapped electrons polarize the nonbonding electrons to form the polarized states (P)

5

shifting up. The polarized states will screen and split the local potential, which will add polarized

6

states to the core band unless the core band is too deep to be sensitive to the polarization.

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The polarized electrons neither follow the standard dispersion nor occupy the allowed states defined

9

by the Hamiltonian; instead, they generate states in the vicinity of Fermi energy. These electrons are

10

responsible for the size emergence of nanostructures such as the dilute magnetism, catalytic

11

enhancement, Dirac-Fermions for topological insulators, etc. [22, 23].

12 13

Defect formation perturbs the crystal potential in the Hamiltonian with an addition of ∆H:

14

15

16 17 18 19 20

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Where


′  

ħ       21 ∆4 5 2

7%8  % ⁄9 Quantum entrapment  L 1 ∆4  6 D  2E F  E 05⁄2E 12  E 05 Polarization

7%  M% ⁄M9  2⁄N1 OPD212  Q⁄8Q5S (Bond contraction coefficient)

(2)

P is the polarization coefficient to be determined using photoelectron spectroscopy measurement.

The ν x is the spectral peak energy with x representing the T and P components. 7% is the

z-dependent bond contraction coefficient, which varies only with the effective atomic CN and has

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nothing to do with the dimensionality or the structure phase. 9 and M9 are the bond energy and

2

bond length of the bulk standard, respectively. The bond nature indicator m is an adjustable

3

parameter that keeps constant for the same substance.

4

Incorporating the BOLS correlation into the TB approach yields the energy shift of the vth level of

6

z-coordinated atom from that of the isolated atom:

7

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The mean bond energy, 〈% 〉, dominates the core level shift. Eq (3) yileds: % ν Q  ν 0 7 8 Entrapment L   1 ∆4 Q  6 % D 1 Polarization ν 12  ν 0 &

12

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∆ν Q  αQ QβQ ∝ 〈% 〉 Core level shift U α  ν,   1 ∆4 ν,  ∝ 〈% 〉 Exchange integral L β  ν,   1 ∆4 ν, ′ ∝ 〈% 〉 Overlap integral

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where

(3)

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8

∆ν Q  ν Q  ν 0  ∆ν 121 ∆4 Q

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(4)

The bond nature indicator m is to be optimized in decomposing the XPS spectrum. For situations

14

without apparent polarization, the relation evolves,

15

16 17

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  ν Q  ν 0 7%a ν Q  ν 12 7%a 1   b    z c z a  ν Q′  ν0 7% ν Q′  ν 12 7%  1

which yields,

fν 0  e d

   8   ν Q′ 7%a ν Q  7%8 ν Q′ 7% ν Q  7%a  8  8  7%a  7% 7%  7%a L ∆ν 12  2ν Q  ν 057% ν Q  〈ν 0〉 ∆ν 127%8

(5)

(6)

19

One can determine the energy level of an isolated atom and its z-dependent shift by decomposing

20

XPS spectra using constraint of Eq (6) [24].

21

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1 2 3

Based on the BOLS-NEP notation, we can also predict the z-resolved relative atomic cohesive

energy (    Q/ 12  Q% % /Q. .  Q%. 7%8h ) and the local binding energy density 8hkj j j 5⁄2  ) at an atomic site. Therefore, one can obtain ( i  2i Q⁄M % i 12⁄M9 5  7%

comprehensive information regarding the bond order, length, energy, atomic cohesive energy, and the

5

binding energy density (z, dz, Ez, Ec, and Ed) with or without polarization from XPS measurements.

6

These quantities are of fundamental importance to understanding the properties and reaction

7

dynamics pertaining to atoms with any number of neighbors.

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2.3 ZPS: Density-of-states distillation

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Zone-selective photoelectron spectroscopy (ZPS) [19] was invented to purify local and quantitative

12

information on the bonding and electronic dynamics associated with the monolayer skin and atomic

13

defects [25]. The residual spectrum of a ZPS is obtained by differencing two XPS spectra collected

14

from (i) the same undefected surface at different emission angles and (ii) a surface after and before

15

the surface being chemically or physically conditioned (such as defect generation and chemisorption)

16

under the same measurement conditions. Upon background correction and spectral area

17

normalization, the ZPS in (i) discriminates the spectral features of the monolayer skin with least CN

18

from that of the bulk with highest atomic CN. The ZPS removes the commonly shared spectra area.

19

An XPS collects more information from the surface at larger emission angles. Likewise, the ZPS in

20

(ii) purifies merely the spectral features due to the conditioning.

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In the present work, we subtracted the XPS and UPS spectrum of the undefected TiO2 surface from

23

that of the defected-TiO2, the residual spectrum retains only the features due to the defect atoms.

24

Especially, the ZPS removes all artifact backgrounds, such as the charging and the “initial–final

25

states” relaxation effects that exist throughout the course of measurement.

26 27

2.4 The mechanism of TiO2 photocatalysis

28

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As the mostly used photocatalyst, TiO2 has been extensively investigated since 1977 when Frank and

2

Bard [26] firstly proposed TiO2 for decomposing cyanide. Figure 2 illustrates the principle for TiO2

3

photocatalytic reaction. When a TiO2 surface is illuminated by light with energy being equal to or

4

larger than the band gap energy, the radiation photons excite electrons in the ground valance band

5

(VB) to the upper conduction band (CB, e-), leaving a hole (h+) behind the VB. The excited charge

6

carriers (electrons and holes also called excitons) are highly reactive to radicals with robust reducing

7

and oxidizing capacity respectively that may recombine or get trapped in metastable surface states, or

8

react with suitable electron acceptors/donors pre-adsorbed on the catalyst surface.

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Two entities are of concern to enhance the photocatalytic efficiency of TiO2: i) light wavelengths

11

excavating electrons to surpass the band gap of TiO2 in the UV range, which are only accounts for 4%

12

of solar light; ii) in the photocatalytic reaction, when the reduction and oxidation do not proceed

13

simultaneously, there is an electron accumulation in the CB, thereby causing a fast recombination of

14

the e-h pairs. Therefore, improve the utilization rate of sunlight by modulating band gap and raise

15

electrons lifetime by reducing the work function (l) via locally pinning the polarized electrons is

16

essential.

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Reduction

-

e

E0

Φ -

-

e

-

e

-

e

hν

e

CB

Recombination

Excitation

Oxidization

+

h

+

h

+

h

+

h

h

+

VB

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Figure 2 Schematic illustrations of electron transferring in the photocatalytic reaction. The incident

19

light produces e-h pairs that undergo thermalization and then recombination if the excited electrons

20

retain in the conduction band. The excited electrons reserve for catalytic activity. Therefore,

21

modulation of the band gap, electroaffinity (separation between the vacuum level and the bottom

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edge of the CB), and work function (l) are of key factors controlling the photocatalytic behavior.

2 3

3

Results and discussion

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3.1 Ti(0001): E2p(0) and ∆E2p(12)

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In order to calibrate and quantify the electron binding-energy shift of the defected-TiO2, we firstly

8

decomposed the XPS spectra from well-faceted Ti(0001) surface to obtain the energy level of an

9

isolated Ti atom and its bulk shift. Based on the BOLS-TB notation, we decomposed the Ti(0001)

10

2p3/2 spectrum [27] into four components. These components are the bulk (B) and surfaces (Sn , i = 1,

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2, 3) ordered as B, S3, S2 and S1 from higher (closer the EF) to lower binding energy (BE), as shown

12

in Figure 3.

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ν 12 are intrinsic constants for a given material, regardless of their orientations or chemical

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those derived from the same hcp surfaces of Be(0001) [24] and Ru(0001) [28]. The ν 0 and conditions. For simplicity, we refer the energy shift of all surface components to the ν 12 before

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The presently optimized atomic CN (z1 = 3.50, z2 = 4.36, z3 = 6.48 and zB = 12.00) is identical to

knowing the Eν 0 value. There are a total of Ɩ = 4 components involved for the Ti (0001) surface

as shown in Figure 3. One can find the mean o ν 0 p from the C =4!⁄4  2 ! 2!  6 possible

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values of ν 0 from eq (6),

〈Etu⁄v 0〉 ∑| Etu⁄v 0/6  451.47eV,

with the standard deviation of:



&/

σ  6∑ ~u⁄v 0  〈u⁄v 0〉€ //  1‚

= 0.003.

28

The ∆u⁄v 12 = 2.14 eV and the optimized u⁄v 12 = 453.61 eV were thus obtained for the Ti

29

with the following expression for the layer-resolved core level shift:

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u⁄v Q = 〈u⁄v 0〉 ~u⁄v 12  u⁄v 0€ 7%8  451.47 ƒ 0.003 2.147%8….|.

The refinement leads to the bond nature indicator m = 4.6 for Ti. Besides, with the derived Q and m

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values, we elucidate the layer-resolved local strain ( 7%  1 , relative binding energy

density (7%8hkj +, and the relative atomic cohesive energy (Q%. 7%8h ) for each surface component, as

8

featured in Table1.

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Ti(0001)-Ti 2p3/2

M

Expriment Envelope B S3 S2

458

457

456

455

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S1

454

453

452

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BE(eV) 9 10

Figure 3 Decomposition of the Ti(0001) XPS spectrum with derived information featured in

11

Table 1. The energy shift of each component is proportional to the bond energy, which follows this

12 13 14

relation: EE Q⁄EE 12  E% ⁄E†  C%8h .

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Table 1 Information of the effective CNs, bond length, bond energy, relative binding energy density,

16

relative atomic cohesive energy and the layer-dependent core level shift for Ti(0001) surface with

17

bond nature indicator m = 4.6. i

u⁄v

z

dz(Ǻ)

Ez(eV)

C%  1

C%

8hkj

z%. C%8h

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451.47

0

-

-

-

-

-

B

453.61

12.00

2.934

0.4717

0.00

1.00

1.00

S3

454.22

6.48

2.850

0.539

-5.32

1.51

0.69

S2

455.11

4.36

2.718

0.670

-10.91

2.41

0.61

S1

456.00

3.50

2.578

0.855

-15.06

3.63

0.61

1

3.2 ZPS of defected-TiO2: Ti2p3/2 and O1s core bands

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Ti(0001)

atom

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The ZPS in Figure 4 shows the defect-induced Ti 2p3/2 and O1s states. The ZPS was obtained by

6

subtracting the spectrum collected from a undefected TiO2(110) surface as a reference from that of

7

the defected-TiO2(110) surface (defects were obtained by Ar+ bombardment) after background

8

correction and spectral peak area normalization [29]. The ZPS spectra revealed the following:

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(i)

The B valley at 458.41 eV in (a) corresponds to the Ti 2p3/2 bulk component and at 529.83 eV

d

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in (b) to the O1s in the bulk TiO2. According to BOLS-NEP notation, for a surface with

12

undercoordinated atoms, the bulk information is partially annihilated because of

13

undercoordination-induced energy shift, therefore, the differential spectra show a valley, B.

19

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to the polarization effect compared to the Ti 2p orbital.

The interaction between Ti and O substantially magnifies the crystal potential, which results

14

in the Ti 2p3/2 states shifting positively by 4.8 eV compared with that of the bulk Ti.

15 16

(ii)

(P = 456.41 eV). The T is below and the P is above the B (458.41 eV), as we expected.

17

However, the O1s shows only quantum entrapment (T = 531.33 eV) without presence of

18

21

The defected Ti 2p3/2 shows both the entrapment (T = 461.14 eV) and the polarization states

polarization. The 528.83-458.41 = 71.42 eV deeper of the innerest O 1s orbital is insensitive

(iii)

The extents of the entrapment and the polarization increase with the concentration of defects.

22

According to Table 1, the effective CN of the defected-TiO2 should be lower than the ideal

23

surface of 3.5 for the Ti(0001) skin. The ZPS gives polarization coefficient as:

24

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D  ~u⁄v F  u⁄v 0€‰~u⁄v 12 ‡ˆ   u⁄v 0€ = 0.71.

2 3

Because the core level shift is proportional to the equilibrium bond energy, we can also obtain

4

〈. defect〉 2.11 ev/bond in comparison to that of Ti bulk bond energy 〈. Ti〉

ip t

B

461.14 eV

b-a c-a d-a e-a

462

460

456.41 eV

458.41 eV

458 456 BE (eV)

454

452

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T

T

(b) ∆TiO2-O1s

P

B

531.33eV

an

Intensitity(a.u)

(a) ∆TiO -Ti 2p 2 3/2

cr

0.41eV/bond [30].

534

M

6

Intensitity(a.u)

5

the TiO2 bulk bond energy 〈. TiO 〉 1.51 ev/bond and defected bond energy

b-a c-a d-a e-a

529.83eV

532 530 BE(eV)

528

Figure 4 ZPS of (a) the Ti 2p3/2 and (b) O1s of the defected TiO2 with respect to the undefected TiO2

9

under different defect concentrations. The insets show the raw XPS spectra sourced from [29]: a,

10

undefected; b, thermally produced defects; Ar+ bombardment for c, 10 min; d, 30 min; and e, 50 min.

11

B, T, and P denote the bulk, entrapped, and polarized states. The absence of the P states of the O1s

12

indicates that this innerest orbit is insensitive to the polarization.

14 15

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3.3 ZPS of defected-TiO2: Valence band

16

In order to elucidate the relationship between bond contraction and catalytic enhancement of

17

defected-TiO2, we also analyzed the ZPS of the VB when the TiO2(110) surface is reduced by Ar+

18

bombardment (Figure 5)[16]. Results also show the entrapped and the polarized features which are

19

substantially the same as those observed from the 2p core band of the defected-TiO2. Therefore, the

20

valence and the core electrons shift simultaneously in the same fashion because of the screening

21

effect to the core charge, being the same to what happened to AgPd and CuPd alloy catalysts [31],

22

and the Pt and Rh adatoms [2].

Page 14 of 17

∆TiO2-VB(UPS)

Clean Defect Defect-Clean

P

T B Entrapment

12

10

8

6 4 BE(eV)

2

0

cr

1

Polarizaiton

ip t

Intensitity(a.u)

hν = 50eV

Figure 5 Valence ZPS of the defected-TiO2 shows the presence of both the polarization (P) and the

3

entrapment (T) attributes, being consistent to the core band shift. The presence of the P states lowers

4

the work function by locked dipoles, which is beneficial to charge offering in catalytic reaction but

5

prevent combination. The presence of the T states enlarges the electroaffinity, which stabilize

6

electrons hindering combination.

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Conclusion

9

A combination of the BOLS-NEP notation and the ZPS strategy has enabled us to identify the

10

physical origin of the defect-enhanced catalytic ability of TiO2. Atomic undercoordination shortens

11

and strengthens the local bond with local densification, entrapment, and polarization of the valence

12

and the conduction electrons, which revises the band structure. The entrapment deepens the bottom

13

edges and polarization raises the upper edges of all the bands, which narrows the band gap, reduces

14

the work function, and enlarges the electroaffinity of the substance. The reduced gap enables TiO2 to

15

respond to longer wavelength of sunlight for exciting electrons. The increased electroaffinity hinders

16

electron-hole recombination and the lowered work function offers electrons easily in the process of

17

catalysis. Therefore, mechanism for defects modulation to the catalytic ability of TiO2 becomes clear,

18

which can be extended to the understanding of other catalysts such as noble metals.

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Financial support from the NSF (Nos. 51202017 and 51372095) of China, the NSF (No. 20140101107JC) of Jilin Province and Major science and technology project of Jilin Province (No. 11ZDGG010) is highly appreciated.

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