Synergetic Effect of Facet Junction and Specific Facet Activation of

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Synergetic effect of facet junction and specific facet activation of ZnFe2O4 nanoparticles on photocatalytic activity improvement Jianan Li, Xinyong Li, Zhifan Yin, Xinyang Wang, Hangfan Ma, and Lianzhou Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b11836 • Publication Date (Web): 17 Jul 2019 Downloaded from pubs.acs.org on July 20, 2019

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ACS Applied Materials & Interfaces

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Synergetic effect of facet junction and specific facet activation of

2

ZnFe2O4 nanoparticles on photocatalytic activity improvement

3

Jianan Li a, Xinyong Li *a,b, Zhifan Yin a, Xinyang Wang a, Hangfan Ma a, Lianzhou

4

Wang b

5

a

6

and Environmental Engineering, School of Environmental Science & Technology,

7

Dalian University of Technology, Dalian116024, China

8

b

9

Engineering, The University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia

State Key Laboratory of Fine Chemicals and Key Laboratory of Industrial Ecology

ARC Centre of Excellence for Functional Nanomaterials, School of Chemical

10

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*Corresponding author: Tel: +86 411 84706658.

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E-mail address: [email protected]

13 14

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ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Abstract

2

Crystal facet engineering has been proved as a versatile approach in modulating

3

the photocatalytic activity of semiconductors. However, the facet-dependent

4

properties and underlying mechanisms of spinel ZnFe2O4 in photocatalysis still have

5

rarely been explored. Herein, ZnFe2O4 nanoparticles with different {001} and {111}

6

facets exposed were successfully synthesized via a facile hydrothermal method.

7

Facet-dependent photocatalytic degradation performance towards gaseous toluene

8

under visible light irradiation was observed, where truncated octahedral ZnFe2O4

9

(ZFO(T)) nanoparticles with both {001} and {111} facets exposed exhibited a

10

suppressing performance than the others. The formed surface facet junction between

11

{010} and {100} facets was responsible for the improved activity by separating

12

photogenerated e-/h+ pairs efficiently to reduce their recombination rate.

13

Photogenerated electrons and holes were demonstrated to be immigrated onto {001}

14

and {111} facets, separately. Intriguingly, EPR trapping results indicated that

15

both ·O2- and ·OH were abundantly present in the ZFO(T) sample under the visible

16

light irradiation as major reactive oxygen species involved in the photocatalytic

17

degradation process. Additionally, further investigation revealed that {001} facets

18

played a predominant role in activating photogenerated transient species H2O2

19

into ·OH, beneficially boosting the intrinsic photocatalytic activity. This work has not

20

only presented a promising strategy in regulating photocatalytic performance though

21

the synergetic effect of facet junction and specific facet activation but also broadened

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the application of facet engineering with multiple effects simultaneously cooperated.

23 24 25 26

Keywords: ZnFe2O4; Facet engineering; Photocatalytic activity; Facet junction; H2O2 activation

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1

1. Introduction

2

Photocatalysis technology has attracted much attention in the field of solar

3

energy conversion and environmental purification, due to their unique properties of

4

low cost, energy saving, and mild operation condition.1-2 Activated by suitable light

5

irradiation, the electrons on the valance band (VB) of semiconductor photocatalysts

6

could be excited to jump into the conduction band (CB), leaving corresponding holes

7

on the VB. The photogenerated electrons and holes on the semiconductor surface

8

could play a significant role in the photocatalytic redox reaction. Much effort has been

9

paid into the fabrication of efficient semiconductor photocatalysts, but there is still a

10

long way for the satisfied performance of photocatalysis achieved to meet the

11

practical application requirements. Most commonly the fast recombination of

12

photogenerated e-/h+ pairs will lead to a relatively low charge carriers’ separation

13

efficiency, mostly depressing the photocatalytic activity. Furthermore, a narrow light

14

spectrum absorbed only in the ultraviolet part (5% in the solar spectrum) for some

15

photocatalysts such as TiO2, ZnO also reduced solar light utilization.

16

Structure-reactivity relationships of materials are always the focus of researches

17

in heterogeneous catalysis.3 As photocatalytic reactions are carried out on the surfaces

18

of photocatalysts, the photocatalytic activity is closely related to the surface atomic

19

configuration of semiconductors.4-5 Generally, crystallographic surface structures are

20

determined by exposed facets of semiconductors, and the different enclosed facets

21

could also endow the catalysts with characteristic geometric and electronic structures,

22

showing different physicochemical properties and activity.6-7 Furthermore, surface

23

atom configuration and arrangement intrinsically could bring about a critical effect on

24

the adsorption-desorption of substance molecules and photoinduced chargers’

25

immigration on the surface of semiconductors, resulting in different photocatalytic

26

performances.8-10 Therefore, crystal facet engineering strategy behaves a promising

27

potential in design and modification of some popular photocatalysts in past decades,

28

greatly regulating the photocatalytic reactivity, selectivity, and stability.11-12 For 3



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1

instance, Yang & Sun et al. firstly used theoretical calculation and experiments to

2

demonstrate fluorine ions as an effective morphology controlling agent for TiO2 with

3

variable {001}/{101} ratios.13 Li & Zhang et al. adopted a photoinduced deposition

4

methodology to reveal the spatial separation of photogenerated e-/h+ pairs among

5

{010} and {110} facets of BiVO4, and subsequently constructed dual-cocatalysts on

6

above facets to promote the photocatalytic activity.14-15 Yu & Jaroniec et al. put

7

forward a new surface junction formed between {001} and {101} facets in anatase

8

TiO2 response for its enhanced photocatalytic CO2 reduction activity.16 Although

9

much work about facet-dependent photocatalytic activity has been reported, the facet

10

regulation of semiconductors and underlying mechanisms for excellent performances

11

are still needed to be further explored.

12

Spinel oxides are typically equipped with a general formula of AB2O4, where A

13

and B sites represent divalent and trivalent cations, respectively. They have shown a

14

promising application in the heterogeneous catalytic fields due to their flexible

15

composition, suitable light absorption, and excellent catalytic stability.17-18 As an

16

outstanding member of the spinel oxides family, ZnFe2O4 with a bandgap 1.9~2.1 eV

17

and strong visible light response has been mostly investigated, especially in the fields

18

of solar energy conversion and photocatalysis pollutant remediation.18-19 With the

19

development of nanotechnology, many novel strategies have been adopted in the

20

synthesis

21

solution-combusting method, the electrodeposition method, the sol-gel method, the

22

molten salt method, the solvo/hydrothermal method, etc..20-24 Among them, the

23

solvo/hydrothermal method has been widely used due to the properties of facility,

24

homogeneity, and controllability. To overcome the intrinsic rapid recombination of

25

photogenerated e-/h+, many tactics on modification of ZnFe2O4 catalysts from

26

morphology, composition and even electronic structure have been attempted.25-27 For

27

example, Liu et al. constructed a multiple-shell hollow ZnFe2O4 to enhance the

28

internal light scattering and elevate the photocatalytic performance.28 The carbon

29

quantum dots modified ZnFe2O4 composite photocatalysts were further creatively

30

prepared by Huang et al. to adjust surface redox reaction sites, greatly improving the

of

various

functional

ZnFe2O4

nanoparticles,

4


such

as

the

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1

NO removal efficiency.19 As an effective strategy for activity regulation, however, the

2

facet-engineered modulation on spinel oxides has seldom been considered in the

3

photocatalysis area, mostly mentioned and investigated in the electrochemical

4

domains.29-31 To the best of our knowledge, the facet dependent photocatalytic

5

performance and connotative mechanism of ZnFe2O4 nanoparticles under visible light

6

have never been discussed yet.

7

In this work, different {001} and {111} facets exposed ZnFe2O4 nanoparticles

8

were successfully obtained by adjusting the hydrothermal time and amount of

9

controlling agent NH4F. Facet dependent photocatalytic performances under visible

10

light by these ZnFe2O4 nanoparticles were investigated using gaseous toluene as the

11

target pollutant. As a result, the ZFO(T) nanoparticles simultaneously with {001} and

12

{111} facets exposed behaved a surpassing performance than the cubic ZnFe2O4

13

(ZFO(C)) and octahedral ZnFe2O4 (ZFO(O)) nanoparticles. Experimental and

14

theoretical results pointed out that the facet junction could be established between the

15

anisotropic {001} and {111} facets to facilitate the separation of photogenerated

16

electrons and holes. Photoinduced deposition experiments directly showed the spatial

17

immigration of photogenerated electrons and holes onto the different facets,

18

respectively. The dominant reactive species were also identified by the EPR technique

19

and accordingly, the mechanism was also elucidated to deeply understand the

20

differences present in the photocatalytic activity. Intriguingly, a specific facet

21

dependent activation ability was found on {001} facets, which could contribute to the

22

photocatalytic performance elevation very well. Synergetic cooperation between

23

surface facet junction and specific facet activation was rationally proposed, bringing

24

about some new ideas of facet engineering on the photocatalysis improvement.

25

2. Experimental Section

26

2.1 Materials and Reagents

27

All chemical (Zn(NO3)2·6H2O, FeSO4·7H2O, NH4F, and urea) were purchased 5



1

from Aladdin Reagent Co. LTD. (Shanghai), and directly used without further

2

purification. Deionized water was taken from a water purification machine and used

3

for all solution preparations in this work.

4

2.2 Preparation of ZnFe2O4 nanoparticles

5

The synthesis of ZnFe2O4 nanoparticles was carried out using a hydrothermal

6

method reported by literature with some modifications.31 Briefly, 0.575 g Zn(NO3)2

7

and 1.112 g FeSO4·7H2O were added into 40 ml deionized water with vigorous

8

stirring to obtain a homogeneous yellow solution at room temperature. To control the

9

morphology and facet exposed, different ratio of NH4F and urea were mixed into 30

10

mL deionized water. For ZFO(C) and ZFO(T) nanoparticles, 0.148 g NH4F and 0.600

11

g urea were employed, while 0.296 g NH4F and 0.600 g urea were added for ZFO(O)

12

nanoparticles. After an efficient stirring for about 15 min, the clear solution of NH4F

13

and urea was quickly transferred into the metal ions mixture solution for another 15

14

min stirring. The resulted yellow solution was poured into a 100 mL Teflon-lined

15

stainless steel autoclave and put into the oven at 200 oC. A short reaction time about 2

16

h was set up for ZFO(C) nanoparticles, while a much longer time about 12 h was

17

taken for ZFO(T) and ZFO(O) nanoparticles. When the temperature cooled down to

18

the room temperature naturally, the obtained precipitations were centrifuged with

19

water and ethanol washing several times, respectively, followed by drying in the oven

20

at 70 oC overnight. Finally, the precursors were calcined at 450 oC at air atmosphere

21

in the muffle furnace for 2 h with a heating rate of 1 oC/min.

22

2.3 Characterization

23

Field emission scanning electron microscopy (FE-SEM) images were taken by a

24

HITACHI S4800 scanning electron microscope, and transmission electron

25

microscopy (TEM) images were obtained on an FEI Tecnai G20 transmission electron

26

microscope, both of which were conducted to observe the morphology of the prepared

27

nanoparticles. To give a piece of detailed crystalline information, X-ray diffraction 6


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1

(XRD, Rigaku, Japan) patterns were recorded at 40 mA and 40 kV with a Cu Kα

2

radiation source. The Brunauer-Emmett-Teller (BET) specific surface areas about the

3

prepared samples were conducted on a NOVA1000e Quantachrome volumetric

4

adsorption analyzer. X-ray photoelectron spectroscopy (XPS) analysis was performed

5

on a PHI 5000 Versa Probe machine with an Al Kα X-ray source to investigate the

6

element compositions and chemical states in the samples. The collected XPS spectra

7

were corrected according to the C peak at 284.8 eV. The Fourier transform infrared

8

(FTIR) spectra were measured using a Bruker Vertex 70 spectrometer. The reactive

9

oxygen species were detected by DMPO-capture experiment based on the electron

10

paramagnetic resonance (EPR) technique. Photoelectrochemical tests were measured

11

on a CHI 760e chemical station equipped with a three-electrode system, where Pt

12

plate counter electrode and Ag/AgCl reference electrodes were adopted. The

13

electrolyte used in this system was 0.5 M Na2SO4. The simulated visible light was

14

provided by a Xenon lamp affiliated with a filter (λ > 400 nm) to shield ultraviolet

15

light. An irradiatometer was utilized to measure the effective light intensity shone on

16

the home-made quartz reactor as 33 mW/cm2. The generated H2O2 in the system was

17

analyzed via UV-vis spectrophotometer referring to the metavanadate compleation

18

method.32-34 The terephthalic acid and luminol were used as the chemiluminescence

19

probe for the generated ·OH (a) and ·O2- in the system, respectively.35 The

20

concentration of terephthalic acid was set as 0.5 mM in a 2 mM NaOH solution, and

21

the fluorescent detection was performed at an excitation wavelength of 315 nm.

22

Similarly, the fluorescent detection of ·O2- radicals was proceeded in the 2 mM NaOH

23

solution containing 1.58 mM luminal, with a excitation wavelength at 387 nm.

24

2.4 Photocatalytic Activity Examination

25

The photocatalytic performance for different ZnFe2O4 samples was investigated

26

by using gaseous toluene as target pollutant. This experiment proceeded in a

27

homemade quartz reactor whose volume is about 130 mL. The samples were

28

grounded into uniform powder and placed on the holder equipped in the quartz 7



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reactor. A certain amount of liquid toluene was syringed into the reactor to evaporate

2

into gaseous status. The static adsorption-desorption equilibrium was achieved after

3

about 30 min in the dark condition. Then, turn on the Xenon light source (equipped

4

with UV cutoff filter) to trigger the photocatalytic reaction and measure the

5

concentration change of toluene in the reactor during the photocatalytic process every

6

30 min.

7

2.5 Theoretical calculations

8

The

computational

calculation

was

performed

using

a

plane

wave

9

pseudopotential approach conducting on the Cambridge Serial Total Energy Package

10

(CASTEP) program. To better describe the on-site Coulomb interaction existed in the

11

d orbitals, the exchange and correlation energies was calibrated by using Generalized

12

gradient approximation (GGA) in the parametrization of Perdew-Burke-Ernzerh of

13

(PBE) functional plus U (GGA+U) method. A 3:1:1 Monkhorst–Pack k-points

14

sampling was adopted as the Brillouin zone of ZnFe2O4 crystal structure. An energy

15

cutoff for plane-wave was 350.0 eV to expand electronic wave function during the

16

calculation. The optimized ZnFe2O4 crystal structure was cleaved under the periodic

17

boundary condition to establish different facet exposed structure. The tolerance for

18

SCF, energy, and maximum force were set as 1.0 × 10-5 eV/atom, 1.0 × 10-5 eV/atom

19

and 0.03 eV/Å, respectively.

20

3. Results and Discussion

21

The crystal phase information of these ZnFe2O4 samples is given by the XRD

22

pattern in Figure 1. It reveals that all samples possessed a face-centered cubic (fcc)

23

phase, agreed well with a standard spinel ZnFe2O4 structure (JCPDS No. 22-1012).

24

The peak at 18.19 o, 29.20 o, 35.26 o, 36.87 o, 42.84 o, 53.11 o, 56.63 o, 62.21 o, 70.50

25

and 73.51 o could be ascribed to (111), (220), (311), (222), (400), (422), (511), (440),

26

(620) and (533) crystal planes of ZnFe2O4, respectively. Sharp and strong peaks of 8


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1

three morphological ZnFe2O4 nanoparticles reflect a good crystallization, and except

2

for some unobvious peaks ascribed to a bit of ZnFe2(OH)2CO3 precursor incompletely

3

conversed, no other peaks for impurities found also indicate a relatively high purity of

4

these spinel samples.

5

6 7 8

Figure 1 XRD patterns of different ZnFe2O4 samples.

9

The morphology of synthesized different ZnFe2O4 nanoparticles was

10

characterized by FE-SEM shown in Figure 2. ZFO(C) nanoparticles with a size of 600

11

nm are illustrated in Figure 2a and 2b, which exposed six {001} planes. Figure 2c and

12

2d show the ZFO(T) nanoparticles enclosed by eight {111} and six {001} planes and

13

their size were about 700 nm. With all {111} planes enclosed, ZFO(O) nanoparticles

14

exhibited a size of 400 nm depicted in Figure 2e and 2f. The morphology regualtion

15

of ZnFe2O4 nanoparticles could be achieved by adjusting the hydrothermal reaction

16

time and addition ratio of urea to NH4F in the system. Based on the Wulff’s model,

17

the crystals’ growth need to minimize the total surface energies to reach an

18

equilibrium, consequently resulting in the process of crystal morphology evolution.6

19

The {001} facets exposed ZFO(C) nanoparticles which possess a more

20

thermodynamically stablity could be obtained with a short hydrothermal reaction time

21

about 2 h. With time prolonged, NH4F began to take over the role of

22

structure-director, obviously limiting the facets exposed in the final products

23

obtained.31 The hydrolysis of urea was benificial to form an alkaline environment to 9



1

induce much more free F- generated in the system.36 The free F- anions tend to

2

coordinate with the unsaturated Zn2+ and Fe3+ on the {111} planes to inhibit the

3

evolution rate perpendicular to these planes during the growth process. According to

4

Cornell and Schwertmann's theory, the close-packed planes behaving a faster growth

5

rate could disappear gradually with the slower-growing planes left.37 Thus, the

6

ZFO(T) with both {001} and {111} facets co-enclosed were achieved. With the

7

amount of NH4F further increased, much more F- anions adsorbed on the {111}

8

planes could greatly depress the growth rate perpendicular {111} planes and form a

9

stronger growth rate difference between {111} and {001} planes, inducing the

10

ZFO(O) nanoparticles entirely with {111} planes disclosed.38 Previous literature have

11

also reported that the ratio of growth rate along [001] to that of [111] has a

12

relationship with the final crystal shape obtained.6,

13

ZFO(C), ZFO(T) and ZFO(O) were 0.58, 1.0, and 1.73, respectively. This all

14

indicated that shape control with different facets unveiled could be realized by

15

regulating the growth rate along facet direction through the adjustment of reaction

16

time and the amount of NH4F.

39

The corresponding ratios for

17

18 19

Figure 2 SEM images of (a, b) ZFO(C), (c, d) ZFO(T) and (e, f) ZFO(O) samples.

20 21

Moreover, TEM characterization was further conducted to give a detailed

22

investigation of morphology and crystal information (Figure 3). As shown in TEM

23

images (Figure 3a, 3b, and 3c), the morphology of the prepared samples are

24

well-defined shapes, in accordance with the corresponding SEM results in Figure 2. A

25

high-resolution TEM (HRTEM) depicted in Figure 3d-f described the fine lattice

26

fringes of the obtained ZnFe2O4 crystals. Thereinto, an obvious lattice fringe with a 10


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1

d-spacing of 0.210 nm was found in ZFO(C) sample, ascribed to the (400) plane. Two

2

crossover lattice fringes displayed in the ZFO(T) sample, which could be assigned to

3

the (111) and (300) crystal facet. Accordingly, the angle of 55o between these two

4

lattice fringes met the featuring angle of {001} and {111} facets. The ZFO(O) sample

5

exhibited the characteristic (222) lattice fringe with a d-spacing of 0.243 nm. Through

6

calculated Fast Fourier Transform (FFT) patterns (Figure 3g-i), it could observe the

7

orderly arranged diffraction spots of the as-obtained ZnFe2O4 samples, demonstrating

8

the single-crystal diffraction properties with these facets indexed in HRTEM results.8,

9

40

10

All these description above could reveal the specific facets ({001} or/and {111})

enclosed in ZFO(C), ZFO(T) and ZFO(O) samples, respectively.

11

12 13 14

Figure 3 TEM, HRTEM, and calculated FFT pattern images of (a, d, g) ZFO(C), (b, c, h) ZFO(T) and (c, f, i) ZFO(O) samples. Scar bar in TEM images: 125 nm.

15 16

FTIR spectroscopy was conducted to further characterize the prepared ZnFe2O4

17

samples. As exhibited in Figure S1, all samples behave two obvious peaks located at

18

548 and 417 cm-1, which were assigned to the typical stretching vibration of the Zn-O

19

bonds in the tetrahedral positions and Fe-O bonds in the octahedral positions of spinel

20

ZnFe2O4, respectively.41-42 There was no peak of impurities detected other than some

21

peaks caused by adsorbed water (1680 and 3400 cm-1) and CO2 (2356 cm-1) in the air,

22

also demonstrating the viewpoint from XRD pattern with a much pure crystalline 11



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1

phase. Brunauer-Emmett-Teller (BET) gas adsorption measurements were measured

2

to examine the specific surface area and porous nature of the obtained ZnFe2O4

3

samples. Figure S2a illustrates the N2 adsorption-desorption isotherm of these

4

obtained samples. All these samples behaved a similar type-III isotherms with a

5

typical H3 hysteresis loop in the relative pressure from 0.0-1.0. The calculated BET

6

specific surface areas of ZFO(C), ZFO(T) and ZFO(O) were 8.2, 7.1, and 6.2 m2/g,

7

respectively. The corresponding pore size distribution characters could be also seen in

8

Figure S2b. Their porous sizes characters of all obtained ZnFe2O4 samples exhibited

9

mainly below 10 nm, indicative of a solid structure of photocatalysts with relatively

10

small surface areas. Though the difference in BET specific surface areas for three

11

samples was small, the photocatalytic performance test in the following part was still

12

calibrated to definitely eliminate the influence brought by their different specific

13

surface areas and solely investigated the intrinsic activity difference caused by the

14

specific facets exposed on ZnFe2O4 nanoparticles.

15

The optical absorption properties of different facets exposed ZnFe2O4 samples

16

were explored by means of UV-vis DRS spectra shown in Figure S3a. All three

17

samples exhibited a strong absorption in the visible light region, which was the typical

18

optical response behavior for spinel ferrites.17, 19 ZFO(C) sample with {001} exposed

19

shows a lower absorption than ZFO(O), while ZFO(T) had an intermediate absorption

20

located between ZFO(O) and ZFO(C) samples. This difference in light absorption

21

could be explained by unequal facets owned in each sample. ZFO(O) with {111}

22

exposed had exhibited a slight red-shift of absorption edge with a considerably large

23

absorption tail. This could be ascribed to the photo enhanced mechanism based on

24

polar {111} surfaces or fast photo-excited electrons migration on this surface.12,

25

According to the Tauc’s plot, the band gap could be calculated based on the equation

26

(αhν)n =A(hν-Eg), where α is the absorption coefficient, h is the Plank constant, ν

27

represents the light frequency, A is the absorption, n is constant dependent on the type

28

of semiconductors (for a direct transition semiconductor n is 2) and Eg represents the

29

band gap energy. As seen in Figure S3b, the band gaps for ZFO(C), ZFO(T) and

30

ZFO(O) were calculated as 1.97, 1.92, and 1.85 eV, respectively. This trend in band 12


43

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1

gap by different facets exposed ZnFe2O4 is similar to previous literature.12 Also from

2

the photograph of these samples, a gradually darkening color change from cubic to

3

octahedral shape was presented both in precursor and calcined samples (in Figure S4),

4

evidenced as an optical behavior of the semiconductor facet effects.44-45 This

5

phenomenon by the visual color change could also reflect the differences in band

6

structure brought up by unequal facets exposed. Transient photocurrent response

7

characterization was consequently conducted to study the photogenerated carriers’

8

transport and separation, as described in Figure S3c. It was observed that there was a

9

fast response by an interval visible light irradiation for these samples, representing for

10

the density and separation efficiency of photogenerated carriers.46 Intriguingly, the

11

photocurrent response of ZFO(T) exhibited an obviously higher intensity than the

12

other two samples, pointing out an improvement in the surface carriers’ enrichment

13

degree. Correspondingly, the EIS technique was additionally used to provide more

14

information about the interfacial transfer of photoinduced carriers under visible

15

inspiration. From EIS Nyquist plots depicted in Figure S3d, all samples could be

16

simulated by a simple Randles circuit, where Rs represents the intrinsic resistance of

17

the system, Rct corresponds the interfacial resistance of the charge transfer, and Cdl is

18

for the capacitance of the space-charge on the sample’s surface.47 The comparison of

19

Rct could be read from simulated data in Table S1 or the semicircle radius in the

20

Nyquist plot. It could be distinctly noted that ZFO(T) had the smallest interfacial

21

resistance, while the difference between ZFO(C) and ZFO(O) was not very obvious.

22

This result also revealed a reduced electron transfer resistance present in the

23

{001}&{111} co-exposed ZnFe2O4 sample, immensely beneficial for the separation

24

and transition of photo-generated carriers to elevate the photocatalytic performance.16

25

The recombination efficiency of photogenerated carriers could also be explored by

26

photoluminescence (PL) characterization, in which a lower PL intensity could reflect

27

less recombination of photogenerated hole-electron pairs in the photocatalyst. From

28

the results displayed in Figure S5, ZFO(T) possesses the weakest PL intensity

29

compared with the other two samples. This could be due to efficient separation of 13



1

hole-electron pairs by the synergetic effect of {001} and {111} facets, similar to the

2

results in the photoelectrochemical characterization above.

3

4 5 6 7

Figure 4 Photocatalytic degradation of gaseous toluene (a) and corresponding pseudo-first order kinetic fitting curves (b) by different ZnFe2O4 samples under visible light irradiation.

8

The photocatalytic toluene degradation performance of the synthesized ZnFe2O4

9

samples was explored to investigate the activity caused by different facts exposed (in

10

Figure 4(a)). It could be observed that the photocatalytic performance was distinctly

11

differentiated from the facets exposed in the ZnFe2O4 samples. For {001} exposed

12

ZFO(C) nanoparticles, the lowest degradation rate was obtained, which could be due

13

to the fast recombination of photoinduced hole-electron pairs as proved above. In the

14

synchronous presence of {001} and {111} facets, the ZFO(T) displayed an improved

15

degradation performance towards toluene. This might be due to the formation of a

16

surface heterojunction between these adjacent facets, resulting in an efficient

17

separation and migration of photogenerated holes and electrons.8, 16 Thus, much more

18

reactive oxygen species would be produced to involve in the degradation of gaseous

19

toluene. To prove this viewpoint, the terephthalic acid and luminol are usually

20

selected as the chemiluminescence probe for capturing the generated ·OH (a) and ·O2-

21

in different samples, respectively.35 The fluorescence detection results was illustrated

22

in Figure S6, further approving more reactive oxygen radicals present in the ZFO(T)

23

sample for the improved degradation. Comparatively, for the {111} disclosed ZFO(O)

24

nanoparticles, the degradation performance under visible light irradiation was

25

unsatisfied. It was not as good as the results of ZFO(T), just slightly better than that of

26

ZFO(C). In addition, it could be directly observed from Figure 4b that ZFO(T) owned

27

a strongest kinetic rate of 0.1930 h-1, 1.32 and 1.50 times higher than the octahedral 14


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1

and cube one, respectively. As a control, a mixture of cube and octahedron ZnFe2O4

2

photocatalysts was also applied in the degradation of gaseous toluene. The results

3

indicated that the mixed ZnFe2O4 catalyst exhibited an inferior photocatalytic activity

4

than the ZFO(T), further proving a synergetic effect present between {001} and {111}

5

facets. The physically mixed catalysts could not effectively form a facet junction

6

between different facets due to the absence of a close contact, which is always a

7

necessary but not sufficient condition of junction-based photocatalysis enhancement

8

mechanism.48-50 Combining with these results together, a preliminary conclusion

9

could be summarized that there must be some synergetic effect existed between the

10

adjacent facets, which might be the so-called surface junction similar to some

11

previous literature reported.16,

12

some classic facet-engineerd photocatalysts was further conducted. To keep the

13

photocatalytic reactions and conditions consistent in these systems for better

14

comparison, TiO2 with {001}/{101} facets and BiVO4 with {010}/{110} facets were

15

separately synthesized according to the literature reported and applied into the

16

photocatalytic degradation system of gaseous toluene.14,

17

performance comparison of these three photocatalysts with facet regulation (ZnFe2O4,

18

TiO2 and BiVO4) has been summarized and illustrated in Figure S7 and Table S2 in

19

the revised Supporting Information document. The toluene degradation efficiency of

20

BiVO4 was slightly better than the truncated octahedral ZnFe2O4 photocatalysts,

21

where TiO2 behaved a much inferior performance. This phenomenon could be

22

ascribed to the differences in their light response ranges and band structures.14, 16, 52

51

A comparison between the optimal ZnFe2O4 and

16

The photocatalytic

23

To further clarify the reactive oxygen species involved in the photocatalytic

24

degradation process, a series of DMPO capture experiment for ·OH and ·O2- were

25

performed under visible light irradiation by in-situ EPR technology.53 In Figure 5a,

26

EPR spectra for DMPO trapped ·OH in aqueous solution illustrated that the typical

27

quadruple peaks ascribed to DMPO-·OH were detected for both ZFO(C) and ZFO(T)

28

but slightly detected for ZFO(O). Actually, the band gap structure of ZnFe2O4 is not

29

suitable to produce ·OH directly, because its valance band position is not positive

30

enough to directly oxidize H2O or OH- (Eo(H2O/·OH) = 2.38 eV, Eo(OH-/·OH) = 1.99 15



1

eV vs. NHE).54 The present ·OH could be assigned to the protonation process of ·O2-

2

(O2 → ·O2- → H2O2 → ·OH), where Fe element could play an important role in

3

triggering the yield as active sites.19 Intriguingly, the DMPO-·OH signal intensity

4

assigned to ZFO(T) was stronger than that of ZFO(C), which phenomenon would be

5

explained in the latter discussion. Inspired by the previous literature reported,32-33 the

6

transient H2O2 generated in the photocatalytic process was monitored via a UV-vis

7

spectrophotometer method using metavanadate as the complexation reagent. The

8

results measured indicated that the amount of peroxide produced in the ZFO(C),

9

ZFO(T) and ZFO(O) samples were 8.4, 9.0, and 8.5 µmol, respectively, where the

10

difference in the peroxide generation might be assigned to the intrinsic photocatalysis

11

activity. The EPR spectra of DMPO-·O2- trapping results displayed in Figure 5b

12

revealed that there were much stronger characteristic peaks of DMPO-·O2- in the

13

ZFO(T) and ZFO(O) samples than the ZFO(C). The most amount of ·O2- could be

14

achieved on the ZFO(T) sample, similar to the results of the ·OH capture experiment.

15

The different ability to produce reactive oxygen species on these samples indeed

16

elucidated the effect of facets exposed on photocatalytic activity of ZnFe2O4.

17

18 19

Figure 5 In-situ EPR spectra of DMPO capture experiments for ·OH (in water, a) and ·O2- (in

20 21

methanol, b) generated by ZFO(C), ZFO(T) and ZFO(O) samples under visible light, respectively.

22

To explain the mechanism behind the photocatalytic performance and unique

23

EPR results ， both the theoretical calculation and experimental design were put

24

forward. Firstly, rational surface models of ZnFe2O4 exposed with {001} and {111}

25

was constructed, respectively, displayed in Figure 6a and 6b. After a rational

26

configuration and optimized geometry, the calculated density of states on {001} and

27

{111} facets exposed ZnFe2O4 were plotted in Figure 6c. It could be observed that

28

there was a slight upwards shift of the valance and conduction band for {111} facets 16


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1

relative to {001} facets exposed ZnFe2O4. According to previous reports, this kind of

2

band structure condition could be facile to result in a surface heterojunction

3

thermodynamically, advantageously separating the electron-hole pairs spatially.14,

4

Therefore, the photogenerated electrons and holes could be transferred to {001} and

5

{111} facets driven by the facet junction under the inspiration of visible light,

6

separately, formatting the corresponding facets with reduction or oxidation ability. To

7

give better proof of the improved separation of photogenerated electrons and holes

8

with the help of facet junction, we have conducted the fluorescence emission decay

9

spectra and Bode-phase spectra measurement as shown in Figure S8. Time-resolved

10

fluorescence decay spectroscopy is a powerful tool to investigate the photoinspired

11

carrier transfer dynamics of photocatalysts, where a longer lifetime usually means

12

more efficient separation and suppressed recombination of photogenerated

13

electron-hole pairs.55-56 From the results illustrated in Figure S8(a), it could be found

14

that {001} and {111} facets co-existed in ZnFe2O4 photocatalyst effectively

15

prolonged the lifetime of photoinduced carriers. The enhanced emission lifetime of

16

electron-hole pairs was beneficial for the photocatalytic process before their

17

recombination. Furthermore, Bond-phase spectra was also displayed in Figure S8(b)

18

to describe the lifetime of injected electrons through the electrochemical method.7 On

19

the basis of the equation τ = 1/(2πf),57 the lifetime of injected electrons in three

20

ZnFe2O4 samples could be obtained as 7.4, 16.1 and 9.1 ns, respectively. It indicated

21

that the {001} and {111} facets co-exposed ZnFe2O4 photocatalyst exhibited a much

22

superior behavior in the separation of photogenerated electrons and holes, also

23

agreeing with the fluorescence decay spectra analysis above. All these analysis

24

together demonstrated that the presence of facet junction could effectively promote

25

the carriers’ separation and suppress the recombination of photogenerated electrons

26

and holes, much in favor of the photocatalytic performance elevation. Furthermore,

27

Figure S9 also directly gave some additional information about chemical states and

28

valance band position of these two predominant facets exposed samples. From S9(a)

29

and S9(b), it could be found that little difference was found from the high-resolution

30

XPS of Zn 2p and Fe 2p orbits, and the binding energy position confirmed the 17


16


1

presence of chemical states in Zn2+ and Fe3+ in both two samples.58 From the valance

2

band XPS spectrums (Figure S9(c) and S9(d)), the relative valance band edges

3

positions of {001} and {111} facets could be estimated, respectively, verifying the

4

calculation results about their band structure. Combined with electrochemical

5

measurement results (Figure S10 and S11), the relative band structure of {001} facet

6

and {111} facet exposed ZnFe2O4 could be expressed in Figure 6d.

7

8 9 10 11

Figure 6 Schematic diagram of ZnFe2O4 (a) {001} and (b) {111} facets. (c) DOS calculation results based on {001} and {111} facets. (d) Band structure of {001} and {111} facets formed surface heterojunction.

12 13

To further demonstrate the existence of charge migration and transfer direction

14

between {001} and {111} facets, photo-inspired reduction and oxidation reactions

15

were utilized to selectively deposit Ag and PbO2 on the surface.14-15 ZFO(T)

16

nanoparticles with {001} and {111} co-exposed were chosen as the photocatalyst

17

substrate. SEM images (Figure S12) have clearly shown that when single Ag or PbO2

18

precursor was added in the system, the Ag and PbO2 particles were all solely

19

deposited on the {001} and {111} facets of ZFO(T) substrate, respectively. That was

20

to say the photo-reduced reaction appeared on the {001} facets, and oppositely

21

photo-oxidized reaction happened on the {111} facets. Meanwhile, a dual-precursors

22

deposition experiment was innovatively conducted by the simultaneous occurrence of 18


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1

reduction and oxidation reaction in one system. The results revealed that Ag particles

2

were still reduced on {001} facets and PbO2 oxidized on {111} facets, and

3

corresponding selected area EDS results in Figure S12d also demonstrated it. SEM

4

EDS mapping (Figure S13) and HRTEM (Figure S14) characterizations further

5

proved the Ag and PbO2 deposited on the specific facets of ZFO(T). All of these

6

discussions revealed that a surface junction was indeed established to actuate

7

photogenerated electrons and holes to immigrate apart onto {001} and {111} facets,

8

separately, promoting the reduction and oxidation reaction on the corresponding

9

facets. The mechanism about the photogenerated carriers’ immigration based on facet

10

junction is graphically illustrated in Figure 6d.

11

Although the photogenerated electron-hole pairs’ immigration has been

12

elaborated, there is still one point worth noting that the ·OH signal was detected by

13

EPR technology. As mentioned above, the band structure of ZnFe2O4 could not be

14

feasible to produce ·OH through a direct oxidation, but taken a deprotonation process

15

of ·O2- into account, ZnFe2O4, seen as a kind of Fenton-like catalysts, could also

16

accelerate the production of ·OH by reduction of H2O2.59-60 Different facets exposed

17

catalysts could be also equipped with different ability to activate and decompose

18

hydrogen peroxide to form ·OH.3 Therefore, a hypothesis was proposed that the

19

strong ability of ·OH production for {001}&{111} co-exposed ZnFe2O4 could be

20

attributed to synergetic effect brought by the facet activation and photocatalysis

21

process under visible light irradiation. To prove the viewpoint proposed, FL and EPR

22

trapping experiments were adopted in a Fenton-like system. FL intensity monitor

23

could be established by choosing terephthalic acid as capture reagent which could be

24

complexed with ·OH to form the fluorescent product.61 Several crucial information

25

could be obtained from Figure 7a: 1) Under the dark condition, {001} facets much

26

prefer to heterogeneously catalysis the decomposition of H2O2 to generate ·OH than

27

{111} facets. With more {001} facets occupied, stronger ·OH would be produced by

28

Fenton-like catalytic reaction. The ·OH amount catalyzed by ZFO(C) nanoparticles

29

with all {001} facets enclosed have surpassed other two ZnFe2O4 samples. 2) After

30

visible light irradiation, the amount of ·OH in the system was obviously enhanced 19



1

compared with that obtained under the dark condition. This was due to the

2

participation of the photocatalysis process to accelerate the decomposition of H2O2 to

3

generate free ·OH radicals. 3) The difference in ·OH production between ZFO(C) and

4

ZFO(T) became much reduced under visible light condition. The presence of surface

5

junction was beneficial for photocatalysis enhancement to incur more ·OH formed.

6

The EPR ·OH capture experiments were also carried out to further assist the obtained

7

FL characterization results above, as depicted in Figure 7b. There were characteristic

8

quadruple peaks detected and the trend of their intensity was the same as that of FL

9

characterization. The distinct ability to the catalytic decomposition of H2O2 to

10

form ·OH could be elaborated by the activation difference of facet condition. As

11

literature investigated, H2O2 might be preferentially elongated to form ·OH on {001}

12

facets but tend to dissociate into hydroxyls group on {111} facets to passivate them.62

13

In summary, {001} facets are the dominant crystal plane for catalytic decomposition

14

of H2O2 to form ·OH and photocatalysis process could promote the ·OH production,

15

especially in the presence of surface junction composed by {001} and {111} facets.

16

17 18 19 20 21

Figure 7 Fluorescence spectrum of terephthalic acid (TPA) (a) and EPR spectra of DMPO (b) capture experiments for ·OH (in water) generated by ZFO(C), ZFO(T) and ZFO(O) in dark and visible light condition, respectively.

22

Based on the above analysis, the improved photocatalytic degradation of toluene

23

by {001}&{111} co-exposed ZnFe2O4 nanoparticles could be presumed in Scheme 1.

24

Under visible light inspiration, the electrons on the valance band were excited to jump

25

into the conduction band, meanwhile, corresponding holes were left on the valance

26

band. Due to the unbalanced band structure between {001} and {111} facets, there

27

existed a facet junction as driving force to pump photogenerated electrons to

28

immigrate from {111} to {001} facets with photogenerated holes in the opposite 20


Page 20 of 31

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1

directions. Furthermore, the photogenerated electrons could activate molecular O2 in

2

the air circumstance to yield ·O2- radical. Through a series of transform reaction

3

process (·O2- → H2O2 → ·OH), hydroxyl radical (·OH) which has a strong oxidation

4

ability could also be obtained. In addition to this, {001} facets showed a much

5

dominant ability over {111} facets towards H2O2 activation into ·OH, conducive

6

to ·O2- conversion process. The synergetic effect between efficient e-/h+ pairs’

7

separation lead by the facet junction and prominent H2O2 activation of {001} facets

8

could accelerate the photogenerated charges’ transfer to reduce their recombination

9

probability, boosting the photocatalytic activity by producing more reactive oxygen

10

species. The toluene could be attacked both by strong oxidants such as ·O2-, ·OH and

11

accumulated h+ to be converted into some intermediates (benzaldehyde and benzoic

12

acid) and further small molecules such as CO2 and H2O. Furthermore, the

13

photocatalytic degradation experiment under different trapping agents in an aqueous

14

condition was also conducted to fully investigate the contribution of each active

15

species on degradation efficiency. Both the photocatalytic degradation performance

16

and corresponding degradation efficiencies results were summarized and illustrated in

17

Figure S15, where several trapping agents such as p-Benzoquinone, isopropanol (IPA)

18

and ethylenediaminetetraacetic acid disodium (EDTA-2Na) were utilized to trap

19

reactive ·O2- radiacals, ·OH radicals and photo-excited holes (h+), respectively.63-64

20

After adding IPA and p-Benzonquinone into the system, the substrate degradation

21

efficiency by the ZFO(T) sample decreased from 57.2% to 49.9% and to 36.0%,

22

respectively. Comparatively, the effect of EDTA-2Na on the degradation performance

23

was unobvious, just decreasing from 57.2% to 52.8%. These results revealed that ·O2-

24

and ·OH radicals played a much more dominant role in the photocatalytic degradation

25

process, while photo-excited h+ just made a slight contribution.65 This result also

26

corroborated with other analysis above, indicating the major reactive species involved

27

in the photocatalytic system.

28

21



1 2 3 4

5

Scheme 1 Illustration of the proposed photocatalytic degradation mechanism by ZnFe2O4 with {001}&{111} formed facet junction.

4. Conclusion

6

In summary, ZnFe2O4 nanoparticles with different {001} and {111} facets

7

exposed were successfully obtained by adjusting the reaction time and amount of

8

NH4F addition in the hydrothermal synthesis process. ZFO(T) nanoparticles disclosed

9

by both {001} and {111} facets exhibited the best photocatalytic performance

10

towards gaseous toluene degradation, surpassing only {001} or {111} facets exposed

11

ZnFe2O4 nanoparticles. DFT calculation and selective photo-deposition results

12

indicated a facet junction established between {001} and {111} facets, separating the

13

photogenerated e-/h+ pairs spatially to suppress their recombination. Integrating EPR

14

and FL trapping characterizations, more reactive oxygen species both ·O2- and ·OH

15

were produced on ZFO(T) nanoparticles under visible light irradiation, where {001}

16

facets also participated a more dominant role in the activation of ·OH production. This

17

work not only emphasized the importance of crystallographic engineering in

18

photocatalyst design but also gave a new understanding of the mechanism behind the

19

enhanced photocatalytic performance.

20

Supporting Information

21

FTIR spectra, N2 adsorption-desorption isotherm and pore size distribution, UV-vis 22


Page 22 of 31

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1

DRS, Tauc’s plot, photocurrent response, EIS Nyquist plot, photographs of different

2

facets exposed ZnFe2O4, Table of resistances and capacitances summarized by the

3

circuit, PL spectra, florescence probe capture experiment for ·OH and ·O2-,

4

photocatalytic degradation comparison of different facet-engineering photocatalysts,

5

Summary of several photocatalytic performance comparison, florescence emission

6

decay spectra and Bode-phase spectra of ZnFe2O4 photocatalysts, XPS spectra for Zn

7

2p and Fe 2p, valence band XPS spectra, Mott-Schottky curves, electrochemical

8

cathodic scan and anodic scan, SEM images of PbO2/ZnFe2O4, Ag/ZnFe2O4 and

9

Ag/PbO2/ZnFe2O4,

SEM-EDS

mapping

images,

HRTEM

images

of

10

Ag/PbO2/ZnFe2O4, trapping experiments for testing the major radical species in the

11

photocatalysis.

12

Acknowledgement

13

This work was supported financially by the Major Program of the National Natural

14

Science Foundation of China (No. 21590813), the National Natural Science

15

Foundation of China (Nos. 21377015 and 21577012), the Key Project of the National

16

Ministry of Science and Technology (No. 2016YFC0204204), the Program of

17

Introducing Talents of Discipline to Universities (B13012), and the Key Laboratory of

18

Industrial Ecology and Environmental Engineering, China Ministry of Education.

19

Conflicts of interest

20

The authors declare no competing financial interest.

21

References

22

(1) Li, H.; Shang, H.; Cao, X.; Yang, Z.; Ai, Z.; Zhang, L. Oxygen Vacancies

23

Mediated Complete Visible Light NO Oxidation via Side-On Bridging Superoxide 23



1

Radicals. Environ. Sci. Technol. 2018, 52 (15), 8659-8665.

2

(2) Jiang, Z.; Wan, W.; Li, H.; Yuan, S.; Zhao, H.; Wong, P. K. A Hierarchical

3

Z-Scheme Alpha-Fe2O3/g-C3N4 Hybrid for Enhanced Photocatalytic CO2 Reduction.

4

Adv. Mater. 2018, 30 (10), 1706108.

5

(3) Zhou, X.; Lan, J.; Liu, G.; Deng, K.; Yang, Y.; Nie, G.; Yu, J.; Zhi, L.

6

Facet-mediated Photodegradation of Organic Dye over Hematite Architectures by

7

Visible Light. Angew. Chem. Int. Ed. 2012, 51 (1), 178-182.

8

(4) Bai, S.; Wang, L.; Li, Z.; Xiong, Y. Facet-Engineered Surface and Interface

9

Design of Photocatalytic Materials. Adv. Sci. 2017, 4 (1), 1600216.

10

(5) Li, J.; Wu, X.; Wan, Z.; Chen, H.; Zhang, G. Full spectrum light driven

11

photocatalytic in-situ epitaxy of one-unit-cell Bi2O2CO3 layers on Bi2O4 nanocrystals

12

for highly efficient photocatalysis and mechanism unveiling. Applied Catalysis B:

13

Environmental 2019, 243, 667-677.

14

(6) Shang, Y.; Guo, L. Facet-Controlled Synthetic Strategy of Cu2O-Based Crystals

15

for Catalysis and Sensing. Adv. Sci. 2015, 2 (10), 1500140.

16

(7) Chen, F.; Huang, H.; Ye, L.; Zhang, T.; Zhang, Y.; Han, X.; Ma, T.

17

Thickness-Dependent Facet Junction Control of Layered BiOIO3 Single Crystals for

18

Highly Efficient CO2 Photoreduction. Adv. Funct. Mater. 2018, 28 (46), 1804284.

19

(8) Zhang, Y.; Han, L.; Wang, C.; Wang, W.; Ling, T.; Yang, J.; Dong, C.; Lin, F.;

20

Du, X.-W. Zinc-Blende CdS Nanocubes with Coordinated Facets for Photocatalytic

21

Water Splitting. ACS Catal. 2017, 7 (2), 1470-1477.

22

(9) He, Y.; Que, W.; Liu, X.; Wu, C. Trapping Behaviors of Photogenerated Electrons

23

on the (110), (101), and (221) Facets of SnO2: Experimental and DFT Investigations.

24

ACS Appl. Mater. Interfaces 2017, 9 (44), 38984-38991.

25

(10) Setvin, M.; Shi, X.; Hulva, J.; Simschitz, T.; Parkinson, G. S.; Schmid, M.; Di

26

Valentin, C.; Selloni, A.; Diebold, U. Methanol on Anatase TiO2 (101): Mechanistic

27

Insights into Photocatalysis. ACS Catal. 2017, 7 (10), 7081-7091.

28

(11) Ghosh, S.; Roy, P.; Karmodak, N.; Jemmis, E. D.; Mugesh, G. Nanoisozymes:

29

Crystal-Facet-Dependent Enzyme-Mimetic Activity of V2O5 Nanomaterials. Angew.

30

Chem. Int. Ed. 2018, 57 (17), 4510-4515. 24


Page 24 of 31

Page 25 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

(12) Chu, C.-Y.; Huang, M. H. Facet-dependent Photocatalytic Properties of Cu2O

2

Crystals Probed by Using Electron, Hole and Radical Scavengers. J. Mater. Chem. A

3

2017, 5 (29), 15116-15123.

4

(13) Yang, H. G.; Sun, C. H.; Qiao, S. Z.; Zou, J.; Liu, G.; Smith, S. C.; Cheng, H.

5

M.; Lu, G. Q. Anatase TiO2 Single Crystals with a Large Percentage of Reactive

6

Facets. Nature 2008, 453 (7195), 638-641.

7

(14) Li, R.; Zhang, F.; Wang, D.; Yang, J.; Li, M.; Zhu, J.; Zhou, X.; Han, H.; Li, C.

8

Spatial Separation of Photogenerated Electrons and Holes among {010} and {110}

9

Crystal Facets of BiVO4. Nat. Commun. 2013, 4, 1432-1439.

10

(15) Li, R.; Han, H.; Zhang, F.; Wang, D.; Li, C. Highly Efficient Photocatalysts

11

Constructed by Rational Assembly of Dual-cocatalysts Separately on Different Facets

12

of BiVO4. Energy Environ. Sci. 2014, 7 (4), 1369-1376.

13

(16) Yu, J.; Low, J.; Xiao, W.; Zhou, P.; Jaroniec, M. Enhanced Photocatalytic

14

CO2-Reduction Activity of Anatase TiO2 by Coexposed {001} and {101} Facets. J.

15

Am. Chem. Soc. 2014, 136 (25), 8839-8842.

16

(17) Chandrasekaran, S.; Bowen, C.; Zhang, P.; Li, Z.; Yuan, Q.; Ren, X.; Deng, L.

17

Spinel Photocatalysts for Environmental Remediation, Hydrogen Generation, CO2

18

Reduction and Photoelectrochemical Water Splitting. J. Mater. Chem. A 2018, 6 (24),

19

11078-11104.

20

(18) Lan, Y.; Liu, Z.; Guo, Z.; Li, X.; Zhao, L.; Zhan, L.; Zhang, M. ZnO/ZnFe2O4

21

Uniform Core-shell Heterojunction with Tubular Structure Modified by NiOOH for

22

Efficient Photoelectrochemical Water Splitting. Dalton Trans. 2018, 47, 12181.

23

(19) Huang, Y.; Liang, Y.; Rao, Y.; Zhu, D.; Cao, J. J.; Shen, Z.; Ho, W.; Lee, S. C.

24

Environment-Friendly

25

Characterization, Biocompatibility, and Mechanisms for NO Removal. Environ. Sci.

26

Technol. 2017, 51 (5), 2924-2933.

27

(20) Aghazadeh, M.; Karimzadeh, I. Fabrication of High-performance Metal Ion

28

Doped Iron Oxide Electrode for Supercapacitor Applications through a Novel

29

Platform. Mater. Res. Express 2017, 4 (10), 105505.

30

(21) Tabari, T.; Singh, D.; Jamali, S. S. Enhanced Photocatalytic Activity of

Carbon

Quantum

Dots/ZnFe2O4

25


Photocatalysts:


Page 26 of 31

1

Mesoporous ZnFe2O4 Nanoparticles towards Gaseous Benzene under Visible Light

2

Irradiation. J. Environ. Chem. Eng. 2017, 5 (1), 931-939.

3

(22) Liu, C.; Ni, Y.; Zhang, L.; Guo, F.; Wu, T. Simple Solution-combusting

4

Synthesis of Octahedral ZnFe2O4 Nanocrystals and Additive-promoted Photocatalytic

5

Performance. RSC Adv, 2014, 4 (88), 47402-47408.

6

(23) Xing, Z.; Ju, Z.; Yang, J.; Xu, H.; Qian, Y. One-step Hydrothermal Synthesis of

7

ZnFe2O4 Nano-octahedrons as a High Capacity Anode Material for Li-ion Batteries.

8

Nano Res. 2012, 5 (7), 477-485.

9

(24) Ji, G.; Lin, X.; Sun, Y.; Trimizi, S. A. A.; Su, H.; Du, Y. Molten Salt Growth and

10

Magnetic Properties of Octahedral CoFe2O4 Crystals: Effects of Synthesis Conditions.

11

CrystEngComm 2011, 13 (21), 6451-6456.

12

(25) Guo, Y.; Zhang, N.; Wang, X.; Qian, Q.; Zhang, S.; Li, Z.; Zou, Z. A Facile

13

Spray

14

Photoelectrochemical Water Splitting. J. Mater. Chem. A 2017, 5 (16), 7571-7577.

15

(26) Zhu, X.; Guijarro, N.; Liu, Y.; Schouwink, P.; Wells, R. A.; Le Formal, F.; Sun,

16

S.; Gao, C.; Sivula, K. Spinel Structural Disorder Influences Solar-Water-Splitting

17

Performance of ZnFe2O4 Nanorod Photoanodes. Adv. Mater. 2018, 30 (34), 1801612.

18

(27) Sahu, T. K.; Shah, A. K.; Gogoi, G.; Patra, A. S.; Ansari, M. S.; Qureshi, M.

19

Effect of Surface Overlayer in Enhancing the Photoelectrochemical Water Oxidation

20

of in situ Grown One-dimensional Spinel Zinc Ferrite Nanorods Directly onto the

21

Substrate. Chem. Commun. 2018, 54 (74), 10483-10486.

22

(28) Liu, B.; Li, X.; Zhao, Q.; Hou, Y.; Chen, G. Self-templated Formation of

23

ZnFe2O4 Double-shelled Hollow Microspheres for Photocatalytic Degradation of

24

Gaseous o-Dichlorobenzene. J. Mater. Chem. A 2017, 5 (19), 8909-8915.

25

(29) Yan, Y.; Li, K.; Chen, X.; Yang, Y.; Lee, J. M. Heterojunction-assisted

26

Co3S4@Co3O4 Core-Shell Octahedrons for Supercapacitors and Both Oxygen and

27

Carbon Dioxide Reduction Reactions. Small 2017, 13 (47), 1701724.

28

(30) Zhou, X.; Liu, Z.; Wang, Y.; Ding, Y. Facet Effect of Co3O4 Nanocrystals on

29

Visible-light Driven Water Oxidation. Appl. Catal. B-Environ. 2018, 237, 74-84.

30

(31) Zhong, X.-B.; Jin, B.; Yang, Z.-Z.; Wang, C.; Wang, H.-Y. Facile Shape Design

Pyrolysis

Method

to

Prepare

Ti-doped

26


ZnFe2O4

for

Boosting

Page 27 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

and Fabrication of ZnFe2O4 as an Anode Material for Li-ion Batteries. RSC Adv.

2

2014, 4 (98), 55173-55178.

3

(32) Yi, H.; Jiang, M.; Huang, D.; Zeng, G.; Lai, C.; Qin, L.; Zhou, C.; Li, B.; Liu, X.;

4

Cheng, M.; Xue, W.; Xu, P.; Zhang, C. Advanced Photocatalytic Fenton-like Process

5

over Biomimetic Hemin-Bi2WO6 with Enhanced pH. J. Taiwan Inst. Chem. E. 2018,

6

93, 184-192.

7

(33) Yi, H.; Yan, M.; Huang, D.; Zeng, G.; Lai, C.; Li, M.; Huo, X.; Qin, L.; Liu, S.;

8

Liu, X.; Li, B.; Wang, H.; Shen, M.; Fu, Y.; Guo, X. Synergistic Effect of Artificial

9

Enzyme and 2D Nano-structured Bi2WO6 for Eco-friendly and Efficient Biomimetic

10

Photocatalysis. Appl. Catal. B-Environ. 2019, 250, 52-62.

11

(34) Nogueira, R. F.; Oliveira, M. C.; Paterlini, W. C. Simple and Fast

12

Spectrophotometric Determination of H2O2 in Photo-Fenton Reactions Using

13

Metavanadate. Talanta 2005, 66 (1), 86-91.

14

(35) Nosaka, Y.; Nosaka, A. Y. Generation and Detection of Reactive Oxygen

15

Species in Photocatalysis. Chem. Rev. 2017, 117 (17), 11302-11336.

16

(36) Lv, B.; Liu, Z.; Tian, H.; Xu, Y.; Wu, D.; Sun, Y. Single-Crystalline

17

Dodecahedral and Octodecahedralα-Fe2O3 Particles Synthesized by a Fluoride

18

Anion-Assisted Hydrothermal Method. Adv. Funct. Mater. 2010, 20 (22), 3987-3996.

19

(37) Cornell, R. M.; Schwertmann, U. The Iron Oxides: Structure, Properties,

20

Reactions, Occurrences and Uses, John Wiley & Sons: 2003.

21

(38) Zhang, D.-F.; Zhang, H.; Guo, L.; Zheng, K.; Han, X.-D.; Zhang, Z. Delicate

22

Control of Crystallographic Facet-oriented Cu2O Nanocrystals and the Correlated

23

Adsorption Ability. J. Mater. Chem. 2009, 19 (29), 5220-5225.

24

(39) Xiao, X.; Liu, X.; Zhao, H.; Chen, D.; Liu, F.; Xiang, J.; Hu, Z.; Li, Y. Facile

25

Shape Control of Co3O4 and the Effect of the Crystal Plane on Electrochemical

26

Performance. Adv. Mater. 2012, 24 (42), 5762-5766.

27

(40) Chauhan, M.; Reddy, K. P.; Gopinath, C. S.; Deka, S. Copper Cobalt Sulfide

28

Nanosheets Realizing a Promising Electrocatalytic Oxygen Evolution Reaction. ACS

29

Catal. 2017, 7 (9), 5871-5879.

30

(41) Zhu, H.; Fang, M.; Huang, Z.; Liu, Y. G.; Chen, K.; Tang, C.; Wang, M.; Zhang, 27



1

L.; Wu, X. Novel Carbon-incorporated Porous ZnFe2O4 Nanospheres for Enhanced

2

Photocatalytic Hydrogen Generation under Visible Light Irradiation. RSC Adv. 2016,

3

6 (61), 56069-56076.

4

(42) Zhang, P.; Lo, I.; O'Connor, D.; Pehkonen, S.; Cheng, H.; Hou, D. High

5

Efficiency Removal of Methylene Blue Using SDS Surface-modified ZnFe2O4

6

Nanoparticles. J. Colloid. Interf. Sci. 2017, 508, 39-48.

7

(43) Liu, B.; Ma, L.; Ning, L. C.; Zhang, C. J.; Han, G. P.; Pei, C. J.; Zhao, H.; Liu, S.

8

Z.; Yang, H. Q. Charge Separation Between Polar {111} Surfaces of CoO

9

Octahedrons and Their Enhanced Visible-light Photocatalytic Activity. ACS Appl.

10

Mater. Interfaces 2015, 7 (11), 6109-6117.

11

(44) Chen, Y. J.; Chiang, Y. W.; Huang, M. H. Synthesis of Diverse Ag2O Crystals

12

and Their Facet-Dependent Photocatalytic Activity Examination. ACS Appl. Mater.

13

Interfaces 2016, 8 (30), 19672-19679.

14

(45) Huang, W. C.; Lyu, L. M.; Yang, Y. C.; Huang, M. H. Synthesis of Cu2O

15

Nanocrystals from Cubic to Rhombic Dodecahedral Structures and Their

16

Comparative Photocatalytic Activity. J. Am. Chem. Soc. 2012, 134 (2), 1261-1267.

17

(46) Long, B.; Huang, Y.; Li, H.; Zhao, F.; Rui, Z.; Liu, Z.; Tong, Y.; Ji, H. Carbon

18

Dots Sensitized BiOI with Dominant {001} Facets for Superior Photocatalytic

19

Performance. Ind. Eng. Chem. Res. 2015, 54 (51), 12788-12794.

20

(47) Li, J.; Li, X.; Zhao, Q.; Jiang, Z.; Tadé, M.; Wang, S.; Liu, S.

21

Polydopamine-assisted Decoration of TiO2 Nanotube Arrays with Enzyme to

22

Construct a Novel Photoelectrochemical Sensing Platform. Sensor. Actuat. B-Chem.

23

2018, 255, 133-139.

24

(48) Wang, X.; Xu, Q.; Li, M.; Shen, S.; Wang, X.; Wang, Y.; Feng, Z.; Shi, J.; Han,

25

H.; Li, C. Photocatalytic Overall Water Splitting Promoted by an α-β Phase Junction

26

on Ga2O3. Angew. Chem. Int. Edit. 2012, 51 (52), 13089-13092.

27

(49) Moniz, S. J.; Shevlin, S. A.; Martin, D. J.; Guo, Z.-X.; Tang, J. Visible-light

28

Driven Heterojunction Photocatalysts for Water Splitting-A Critical Review. Energ.

29

Environ. Sci. 2015, 8 (3), 731-759. 28


Page 28 of 31

Page 29 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

(50) Bai, S.; Wang, L.; Li, Z.; Xiong, Y. Facet-engineered Surface and Interface

2

Design of Photocatalytic Materials. Adv, Sci, 2017, 4 (1), 1600216.

3

(51)

4

Multiheterojunction Film Photocatalyst with Enhanced Photocatalytic CO2-Reduction

5

Activity. ACS Appl. Mater. Interfaces 2019, 11 (6), 5581-5599.

6

(52) Li, H.; Yu, H.; Quan, X.; Chen, S.; Zhao, H. Improved Photocatalytic

7

Performance of Heterojunction by Controlling the Contact Facet: High Electron

8

Transfer Capacity between TiO2 and the {110} Facet of BiVO4 Caused by Suitable

9

Energy Band Alignment. Adv. Funct. Mater. 2015, 25 (20), 3074-3080.

Meng,

A.;

Zhang,

L.;

Cheng,

B.;

Yu,

J.

TiO2-MnOx-Pt

Hybrid

10

(53) Qi, W.; An, X.; Zhang, F.; Liu, H.; Qu, J. Facet-dependent Intermediate

11

Formation and Reaction Mechanism of Photocatalytic Removing Hydrophobic

12

Anthracene under Simulated Solar Irradiation. Appl. Catal. B-Environ. 2017, 206,

13

194-202.

14

(54) Zhang, F.; Li, X.; Zhao, Q.; Zhang, D. Rational Design of ZnFe2O4/In2O3

15

Nanoheterostructures: Efficient Photocatalyst for Gaseous 1,2-Dichlorobenzene

16

Degradation and Mechanistic Insight. ACS Sustain. Chem. Eng. 2016, 4 (9),

17

4554-4562.

18

(55) Jiang, D.; Zhu, Y.; Chen, M.; Huang, B.; Zeng, G.; Huang, D.; Song, B.; Qin, L.;

19

Wang, H.; Wei, W. Modified Crystal Structure and Improved Photocatalytic Activity

20

of MIL-53 via Inorganic Acid Modulator. Appl. Catal. B-Environ. 2019, 255, 117746.

21

(56) Shi, Y.; Huang, J.; Zeng, G.; Cheng, W.; Yu, H.; Gu, Y.; Shi, L.; Yi, K. Stable,

22

Metal-free, Visible-light-driven Photocatalyst for Efficient Removal of Pollutants:

23

Mechanism of Action. J. Colloid. Interf. Sci. 2018, 531, 433-443.

24

(57) Kern, R.; Sastrawan, R.; Ferber, J.; Stangl, R.; Luther, J. Modeling and

25

Interpretation of Electrical Impedance Spectra of Dye Solar Cells Operated under

26

Open-circuit Conditions. Electrochim. Acta 2002, 47 (26), 4213-4225.

27

(58) Guo, J.; Wang, K.; Wang, X. Photocatalytic Reduction of CO2 with H2O Vapor

28

under Visible Light over Ce Doped ZnFe2O4. Catal. Sci. Technol. 2017, 7 (24),

29

6013-6025.

30

(59) Wang, F.; Chen, Y.; Zhu, R.; Sun, J. Novel Synthesis of Magnetic, Porous 29



1

C/ZnFe2O4 Photocatalyst with Enhanced Activity under Visible Light Based on the

2

Fenton-like Reaction. Dalton Trans. 2017, 46 (34), 11306-11317.

3

(60) Nguyen, X. S.; Zhang, G.; Yang, X. Mesocrystalline Zn-doped Fe3O4 Hollow

4

Submicrospheres: Formation Mechanism and Enhanced Photo-Fenton Catalytic

5

Performance. ACS Appl. Mater. Interfaces 2017, 9 (10), 8900-8909.

6

(61) Xiao, Q.; Si, Z.; Zhang, J.; Xiao, C.; Tan, X. Photoinduced Hydroxyl Radical and

7

Photocatalytic Activity of Samarium-doped TiO2 Nanocrystalline. J. Hazard. Mater.

8

2008, 150 (1), 62-67.

9

(62) Dai, C.; Tian, X.; Nie, Y.; Lin, H. M.; Yang, C.; Han, B.; Wang, Y. Surface

10

Facet of CuFeO2 Nanocatalyst: A Key Parameter for H2O2 Activation in Fenton-Like

11

Reaction and Organic Pollutant Degradation. Environ. Sci. Technol. 2018, 52 (11),

12

6518-6525.

13

(63) Yang, Y.; Zhang, C.; Huang, D.; Zeng, G.; Huang, J.; Lai, C.; Zhou, C.; Wang,

14

W.; Guo, H.; Xue, W. Boron Nitride Quantum Dots Decorated Ultrathin Porous

15

g-C3N4: Intensified Exciton Dissociation and Charge Transfer for Promoting

16

Visible-light-driven Molecular Oxygen Activation. Appl. Catal. B-Environ. 2019,

17

245, 87-99.

18

(64) Yi, H.; Huang, D.; Zeng, G.; Lai, C.; Qin, L.; Cheng, M.; Ye, S.; Song, B.; Ren,

19

X.; Guo, X. Selective Prepared Carbon Nanomaterials for Advanced Photocatalytic

20

Application in Environmental Pollutant Treatment and Hydrogen Production. Appl.

21

Cataly. B-Environ. 2018, 239, 408-424.

22

(65) Yi, H.; Qin, L.; Huang, D.; Zeng, G.; Lai, C.; Liu, X.; Li, B.; Wang, H.; Zhou,

23

C.; Huang, F. Nano-structured Bismuth Tungstate with Controlled Morphology:

24

Fabrication, Modification, Environmental Application and Mechanism Insight. Chem.

25

Eng. J. 2018, 358, 480-496.

26 27

30


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