Architecture of Biperovskite-Based LaCrO3/PbTiO3 p-n Heterojunction with a Strong Interface for Enhanced Charge Anti-recombination Process and Visible Light-Induced Photocatalytic Reactions

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Architecture of Biperovskite-Based LaCrO /PbTiO p−n

3

Heterojunction with a Strong Interface for Enhanced Charge Anti-

recombination Process and Visible Light-Induced Photocatalytic

Reactions

Lekha Paramanik, K. Hemalata Reddy, Sabiha Sultana, and Kulamani Parida*

Centre for Nanoscience and Nanotechnology, SOA Deemed to be University, Bhubaneswar751030 Odisha, India

*

S Supporting Information

ABSTRACT: Erection of a resourceful p−n heterojunction is a state-of-the-art

tactic to ﬂourish the charge anti-recombination process at the heterojunction

interface and boost the photocatalytic activities under visible light irradiation. In

the present work, we have engineered a new series of PbTiO /LaCrO (PT/LC)

3

p−n heterojunction through a facile two-step combustion process. The structural,

interface, and optical analysis distinctly revealed a strong intact between p-type

LaCrO and n-type PbTiO , elucidating their electronic channelization and

3

substantial reduction of electron−hole recombination at the PbTiO /LaCrO

3

interface, which extend the lifetime and population of photogenerated charges in

the p−n heterojunction material. The asymmetry photocurrent in the opposite

directions and an inverted characteristic V-shape Mott−Schottky plot of the

optimal PT/LC (7/3) material demonstrated the construction of a p−n

heterojunction. The optimal p−n heterojunction possesses excellent photo-

stability, and it revealed the highest photocatalytic activity toward degradation of

phenol, that is, 86% and hydrogen generation, that is, 343.57 μmol in 2 h. The enhanced photocatalytic activities of the p−n

heterojunction materials in comparison to pristine ones are due to the higher separation charge carriers across the p−n

heterojunction interface, which was deeply elucidated by carrying out electrochemical impedance spectroscopy, time-resolved

photoluminescence spectroscopy, and photoluminescence analyses. These materials pave a new way to design the interface

intact photocatalyst with an ultrafast approach for migration of photoexcited electrons across the p−n heterojunction and

enhance the photocatalytic activities.

1

. INTRODUCTION

band gap energy, cost-eﬀective, and additional synergism

between their strongly interacted p-type and n-type semi-

Architecture of heterojunction-based photocatalysts is desired

as a superior photocatalyst for the degradation of organic

pollutants and hydrogen production reaction under visible

light irradiation in comparison to a single semiconductor

system. Among the heterojunctions, the invention of p−n

junction-based photocatalysts provided a greater potential

toward the photocatalytic performance because of their superb

charge anti-recombination process associated with the building

4

conductor components. Till now, a lot of p−n junction-based

photocatalysts have been developed for the photocatalytic

applications, but still there are very limited reports on the

visible light active biperovskite-based p−n junction for the

photocatalytic applications.

1

,2

Perovskites are one of the most popular multifunctional

mixed metal oxides and are also known as ideal materials for

photocatalytic applications because of its high stability, ﬂexible

3

of internal electrostatic ﬁeld across the junction interface.

8

crystal structure, and unique chemical and physical properties.

Theoretically, it has been elucidated that when a p-type

semiconductor contacts with an n-type semiconductor, a p−n

junction is formed between them and the charge carriers move

in opposite directions to create an internal electrostatic ﬁeld at

the junction interface. The created internal electrostatic ﬁeld

facilitates the eﬀective separation of photogenerated charge

carriers at the junction interface and subsequently migrate

from one semiconductor to the other, which is making the

abundance of electron or/and hole on the surfaces of the two

conjoint semiconductors and follow-on to enhance the

As one of the perovskites, PbTiO is a visible light active n-type

3

9

semiconductor with a band gap energy of 2.75 eV. The beauty

of this material is its ferroelectric property with visible light

absorption. The ferroelectric properties of the PbTiO material

3

possess internal dipolar ﬁelds which have force to move the

light-induced charge pairs (i.e. electrons and holes) in reverse

directions and diminish the recombination rate of charge pairs.

The inhibition of charge pair recombination inside the

5

−7

photocatalytic activities.

junction also provides great assurance toward their tunable

Moreover, the constructed p−n

Received: August 21, 2018

©

XXXX American Chemical Society

A

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materials leads to enhance the photocatalytic activities.

Therefore, the ferroelectric properties and narrow band gap

junction semiconductor exhibits outstanding improved photo-

catalytic and photoelectrochemical properties compared to the

single semiconductors, conﬁrming the probability of using p−n

junctions to enhance the photocatalytic activity. Moreover, the

eﬀect of molar ratio of PbTiO and LaCrO in PbTiO /

energy of the PbTiO material makes it as a potential candidate

3

10,11

for the visible light-induced photocatalysis.

After that,

some researchers have reported that the PbTiO -based

3

heterojunction showed excellent photocatalytic performance

LaCrO p−n junction sample toward the photoactivity was

3

in comparison to pristine PbTiO . Rohrer and co-workers

examined comparatively. The possible mechanism for the

enhanced photoactivity was explained on the basis of band

structures and the achieved experimental results. This article

may announce a new signal for the invention of p−n junctions

using biperovskite materials.

3

investigated the visible light-induced photocatalytic activity of

the PbTiO /TiO core−shell heterostructures. They explained

3

2

that, the PbTiO /TiO core−shell heterostructures have

3

2

shown superior photocatalytic performance for methylene

blue (MB) degradation under visible light illumination

12

^c^o^m^p^a^r^e^d^t^o^p^u^r^e^P^b^Tⁱ^O3^.

Very recently, Reddy et al.

2. EXPERIMENTAL SECTION

reported that the prepared CuO/PbTiO₃p−n junction

showed higher photocatalytic performance for degradation of

malachite green under visible light illumination in comparison

to both the neat materials. The abovementioned study aﬀords

strong evidence that instead of using an individual semi-

conductor, the construction of a p−n junction between the p-

type and n-type semiconductors leads to the increase in the

separation of charge pairs at the p−n heterojunction interface

and improve the photocatalytic performance compared to the

individual semiconductors. Till now, there are very limited

2

.1. Fabrication of PbTiO . PbTiO was fabricated by a simple

3 3

combustion method using citric acid as a fuel. Analytical grade

Pb(NO ) , anatase form of TiO , and citric acid were used as

precursor materials. According to a typical synthesis procedure, the

precursors such as Pb(NO ) , TiO , and citric acid were added in a

3

2

3

2

molar ratio of 1:1:2 to the distilled water. The total molar amount of

metal ions in the solution was equal to the molar amount of citric

acid, that is, 1:1. The solution was constantly stirred to get a highly

dispersed suspension. The suspension was gently evaporated at 80 °C

with intensive stirring and subsequently heated up to 130 °C to obtain

a thick viscous gel. The viscous gel was kept at that temperature to

obtain a dry gel. The dry gel was burnt in air to form loose powders.

The loose powder was calcined at 800 °C for 4 h in a muﬄe furnace

reports on the development of PbTiO -based p−n hetero-

3

junctions for photocatalytic applications.

On the other hand, another series of visible light active

perovskites such as rare-earth transition metals also reported

−1 3,10,15

with a heating rate of 10 °C min .

2.2. Fabrication of LaCrO /PbTiO₃p−n Heterojunction.

3

for the photocatalytic applications. Between them, LaCrO is a

Novel LaCrO /PbTiO p−n heterojunctions were synthesized by a

3

renowned p-type visible light active perovskite with a band gap

facile two-step combustion method. According to the stoichiometric

2

heterojunction composition, a speciﬁed amount of La(NO ) ·6H O,

Cr(NO ) ·9H O, and citric acid was dissolved in 250 mL of distilled

water with a molar ratio of the metal ion to citric acid being 1:1 and

kept under continuous stirring to get a blue homogenous solution.

Then, the prepared pure phase PbTiO powder was added to the

energy of 2.6 eV. Moreover, the Cr sites on the LaCrO

3

2

3

surface provides better adsorption centers for atomic oxygen

that endows more favorable characteristics for the photo-

3

2

13

catalytic applications. However, the material showing lower

photocatalytic activity under visible light irradiation is one of

3

above homogenous solution with a molar ratio of PbTiO to LaCrO

14

3

the major drawbacks. Moreover, when this material formed

solid solutions and heterojunctions with other materials, the

photocatalytic activity is greatly enhanced. Recently, Shi et al.

reported that Na La TiO /LaCrO solid solution showed

being 90/10, 70/30, 50/50, 30/70, and 10/90, respectively. The

mixed solution was again stirred for 1 h to well disperse the PbTiO₃

particles in the solution. The resulting dispersed solution was slowly

evaporated from 80 to 130 °C and kept at 130 °C until to get a dry gel

product. Subsequently, the dried gel product on continuous heating

was burnt in a self-propagating combustion manner completely to

obtain the solid dry powder. Finally, the resultant dried powder was

calcined at 800 °C for 4 h with a heating rate of 10 °C min . For a

comparison study, pure LaCrO₃was prepared by following the

abovementioned procedure without the addition of PbTiO precursor

powders.

0

.5 0.5

3

advanced photocatalytic performance for hydrogen evolution

because of their lower band gap energies in comparison to the

neat LaCrO which leads to an increase in the lattice distortion

3

−1

of solid solutions and enhances the generation, separation, and

14

migration of charge pairs inside the material. Nashim and

Parida reported that the photocatalytic activity of the

La Ti O /LaCrO heterojunction increases in comparison to

3

16,17

The PbTiO , LaCrO , and all the prepared p−n

3

2

7

3

heterojunctions were named as PT, LC, PT/LC (9/1), PT/LC (7/3),

PT/LC (5/5), PT/LC (3/7), and PT/LC (1/9), respectively,

afterward.

their individual materials due to establishment of a p−n

junction between the two materials which facilitates to inhibit

the recombination rate of charge pairs and resulting to improve

2

.3. Loading of Pt Cocatalyst. Pt (1 wt %) was loaded over all

18

2

the prepared photocatalysts by the photodeposition method. The

photodeposition method was carried out in a closed gas circulation

chamber. Initially, 1 g of photocatalyst with an appropriate amount of

the metal precursor (H PtCl ) was immersed in 80 vol % methanol

solution, and then the solution was evacuated to completely remove

dissolved air. Finally, the mixed solution was irradiated with a 125 W

high-pressure Hg lamp (UV source) for 3 h. After ﬁltration and

washing with pure water, the resulting powder was dried in an oven at

70 °C for 24 h.

the photocatalytic activity of the p−n junction system. The

abovementioned results motivated that once p-type LaCrO

3

merges with an n-type semiconductor; a signiﬁcantly enhanced

photoactivity may be appreciated due to construction of a p−n

junction between them. Therefore, we have focused the

present article on the building of a PbTiO /LaCrO p−n

2

6

3

heterojunction for the photocatalytic H₂production and

degradation of organic pollutant reactions.

2

^.⁴^.^P^h^o^t^o^d^e^p^o^sⁱ^tⁱ^oⁿ^o^f^A^u^aⁿ^d^Mⁿ^Ox on PT/LC p−n

In this work, we report the fabrication of a novel

biperovskite PbTiO /LaCrO p−n junction by using a two-

Heterojunction. The Au and MnO particles were deposited on the

x

3

surface PT/LC p−n heterojunction by the photodeposition

step calcination method with the goal of improving the

19

method. At ﬁrst, 200 mg of the PT/LC p−n heterojunction was

photocatalytic properties of both pristine PbTiO and LaCrO .

3

suspended in 50 mL of water containing 8 mL of an aqueous solution

Phenol degradation and hydrogen evolution reactions were

employed to determine the photocatalytic properties of the

PbTiO /LaCrO p−n junction. The PbTiO /LaCrO hetero-

of 1 mg/mL MnSO ·H O and 12 mL of an aqueous solution of 0.5

mg/mL HAuCl . The suspension was exposed to a 125 W high-

pressure Hg lamp (UV source) under continuous magnetic stirring for

4

2

4

3

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Figure 1. Mott−Schottky plot of (a) PbTiO , (b)LaCrO , and (c) PT/LC (7/3) heterojunctions.

3

6

h. The photocatalyst sample after photodeposition was washed

several times with deionized water and dried.

.5. Characterization. The as-prepared samples were charac-

absorption equilibrium between the degrading pollutants and the

photocatalysts. After that, the abovementioned suspension was placed

under light irradiation with slow stirring for duration of 2 h. Active

species trapping tests were carried out with the introduction of diverse

quenching agents. The supernatant solution was further subjected to

2

terized by using powder X-ray diﬀraction, diﬀuse reﬂectance UV/vis,

ﬁeld emission scanning electron microscopy (FESEM), transmission

electron microscopy (TEM), photoluminescence (PL) spectroscopy,

time-resolved PL spectroscopy (TRPL), and photoelectrochemical

develop the color by adding 2 mL of 1 M NH Cl and then, the pH

4

was adjusted up to 10 by adding concentrated ammonium hydroxide

solution followed by the addition of 4-aminoantipyrene and

potassium ferricyanide solutions. Lastly, the solution was kept

undisturbed for 15 min to attain equilibrium. Finally, the

(

PEC) measurements. The X-ray diﬀraction (XRD) patterns were

determined by using a Rigaku Ultima IV diﬀractometer with

automatic control. The samples were scanned by a monochromatic

Cu Kα X-ray source in a range of 2θ = 10−80°, wavelength 1.5 Å,

voltage 40 kV, and a current of 40 mA with a scan rate of 5° min .

The FESEM image was conducted on Zeiss Supra 55 to study the

surface morphology of samples. Transmission electron microscopy

concentration of the formed phenol complex was monitored at 510

−

1

20,21

nm in the UV/vis spectrophotometer.

Blank experiments were

carried out without using the photocatalysts.

2.6.2. Photocatalytic Hydrogen Production. Photocatalytic H

2

(

TEM) images were obtained on a Philips Tecnai G2 instrument

production experiments were assessed by using a 100 mL sealed

operated with an accelerating voltage of 200 kV. UV/vis diﬀuse

reﬂectance spectroscopy spectra were carried out by a JASCO 750

UV/visible spectrophotometer in the region of 200−800 nm. By using

JASCO spectroﬂuorometer FP8300, the PL spectrum of as-prepared

materials were recorded at room temperature with an excitation

wavelength of 350 nm. The TRPL spectrum was recorded at 430 nm

by using 375 nm laser as an excitation source assembled with 395 nm

cutoﬀ ﬁlters. X-ray photoelectron spectroscopy (XPS) measurements

were performed on the ESCA+ spectrometer equipped with a

monochromatized aluminum source (Al Kα radiation hν = 1486.7

eV). The binding energy correction was performed using the C 1s

peak of carbon at 284.6 eV as reference.

quartz batch reactor. A 150 W Xenon lamp was used as the visible

light source (λ ≥ 400 nm with 1 M NaNO solution and UV cutoﬀ

2

ﬁlter λ > 420 nm), which was positioned 20 cm away from the

aqueous suspension. The photocatalyst (20 mg) was suspended in 10

vol % methanol solution (20 mL) and stirred continuously to attain

uniformity throughout the reaction mixture. Prior to light irradiation,

N

gas was continuously purged into the batch reactor for 30 min to

2

get rid of all the dissolved oxygen. The amount of H gas evolved was

2

collected through the downward water displacement method and

analyzed by the gas chromatography instrument by using a 5 Å

molecular sieve column with a thermal conductivity detector.

2.6.3. Photoelectrochemical Studies. Typically, all photoelec-

trochemical performances were measured at room temperature with

three electrode conﬁguration using the Ivium n Stat electrochemical

workstation. The sample materials served as the working electrode in

the electrochemical studies, whereas the pure platinum wire was used

as the counter electrode and the commercially available Ag/AgCl

electrode served as the reference electrode, respectively. The working

electrode was prepared by the electrophoretic deposition method.

The ﬂuorine-doped tin oxide (FTO) glass substrate was cleaned with

acetone and ethanol repeatedly, immersed in a parallel manner in a

2

.6. Photocatalytic Reactions. 2.6.1. Degradation of Phenol

and Analysis of Active Species. The photocatalytic activity of the as-

prepared samples was initially monitored by the degradation of

phenol under visible light irradiation (a 150 W Xenon lamp was used

as the visible light source with 1 M NaNO solution as a UV cutoﬀ

2

ﬁlter, λ ≥ 400 nm and a UV cutoﬀ ﬁlter λ > 420 nm) in a well-

equipped quartz batch reactor. Prior to photoreaction, a mixture of 20

mg of the as-prepared photocatalyst and 20 mL of phenol (10 mg

−

1

L ) was continuously stirred in dark for 30 min to guarantee

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Figure 2. Photocurrent responses of (a) PbTiO (PT), (b) LaCrO (LC), and (c) PT/LC (7/3) heterojunction samples.

3

solution (containing 20 mg each of the powder photocatalyst sample

and iodine in 40 mL of acetone solution) with 10−15 mm separation

and a 60 V bias was applied between the two for 6 min under a

potentiostat control. The coated area of the working electrode was 1

cm × 1 cm. All potential values were measured against the Ag/AgCl

reference electrode. Na SO (pH = 6.1) aqueous solution (0.1 M)

that a p−n heterojunction was formed between the two

components with diﬀerent electronic behaviors as shown in

Figure 1c, and these results are well consistent with the PEC

22−24

measurements.

The I−V characteristics curves of PbTiO , LaCrO , and PT/

3

2

4

LC (7/3) p−n heterojunction photoelectrodes under visible

light irradiation (λ ≥ 400 nm) were shown in Figure 2a−c.

From the photocurrent spectra (Figure 2a), it was observed

was used as the electrolyte throughout all measurements. A Newport

3

00 W Xe lamp equipped with a UV light cutoﬀ ﬁlter (λ ≥ 400 nm)

was used as the visible light illumination source. It was noted that bare

FTO did not show any photoresponse in the solution. The

3

that PbTiO initiates to generate the photocurrent at −0.80 V

3

photocurrent measurement was carried out under visible light

irradiation using a 300 W Xenon lamp with a cutoﬀ wavelength of

λ ≥ 400 nm. Electrochemical impedance spectroscopy (EIS)

measurements were performed using a 0.1 M Na SO solution (pH

that sharply increases with the applied positive potential upto

2

+1.0 V and achieved a maximum photocurrent of 8.04 μA/cm

at + 1.0 V.

2

4

Moreover, it was also monitored that PbTiO produced

3

=

6.1) at zero bias potential above a frequency range of 10 to 0.01

anodic photocurrent with the applied bias potential. The

Hz. Mott−Schottky analysis was conducted at 500 Hz with an applied

AC voltage of 25 mV. Both Mott−Schottky analysis and EIS were

performed in absence of light.

invention of anodic photocurrent illustrates that PbTiO is an

3

n-type semiconductor. On the other hand, the LaCrO sample

3

2

produces a cathodic photocurrent that is −25.0 μA/cm at

−

1.0 V with an applied bias potential. The cathodic

3

. RESULTS AND DISCUSSION

photocurrent of LaCrO indicates that it is a characteristic p-

3

Initially, Mott−Schottky analysis and PEC measurements were

performed to conﬁrm the formation of a p−n junction between

PbTiO and LaCrO in the hybrid materials. From the Figure

type semiconductor. In contrast, the PT/LC (7/3) p−n

heterojunction generates diﬀerent photocurrents in the

forward and reverse applied bias directions. The photocurrent

sharply increased with the positive bias potential and achieved

3

1

a, it was clearly observed that the PbTiO polyhedron exhibits

3

2

a positive slope, whereas LaCrO shows a negative slope for

nearly 35 μA/cm at +1 V, while just a small reverse

3

2

the p-type in the linear region of the plot (Figure 1b). The

photocurrent, that is, −30 μA/cm was observed at −1 V.

positive slope of PbTiO and negative slope of LaCrO

The produced asymmetric photocurrent in opposite (forward

and reverse) bias directions demonstrates that the prepared

3

conclusively aﬃrms the n-type and p-type semiconductivity

character of the materials. More interestingly, when PbTiO₃

1

0,25

heterojunction have a p−n junction property.

The p−n

was coupled with LaCrO , an inverted characteristic “V-shape”

junction property of the heterojunction material leads to

promote the separation of photoassisted charge pairs; so that

3

M−S plot {PT/LC (7/3)} was observed which demonstrates

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more charge carriers are participating in the photocatalytic

reactions instead of recombination.

Next, the XRD study was conducted to examine the crystal

phase and phase purity of the as-prepared samples. Figure 3

Figure 3. XRD patterns of (a) PbTiO (PT), (b) PT/LC (9/1), (c)

3

PT/LC (7/3), (d) PT/LC (5/5), (e) PT/LC (3/7), (f) PT/LC (1/

9

), and (g) LaCrO (LC).

3

shows the diﬀraction patterns of the pristine PbTiO , LaCrO ,

3

and PbTiO /LaCrO p−n heterojunction samples prepared

3

Figure 4. FESEM images of (a) PbTiO (PT), (b) LaCrO (LC), and

3

with diﬀerent molar ratios. The peak planes and relative

intensity of all the diﬀraction patterns of pristine PbTiO₃

(c) PT/LC (7/3) p−n heterojunction.

(

indexed by asterisk marks) and LaCrO (indexed by diamond

3

marks) are perfectly assigned to the tetragonal phase of

PbTiO (JCPDS 01-077-2002) and orthorhombic phase of

LaCrO , (JCPDS 00-024-1016), respectively. Moreover, we

have calculated the unit cell parameters of pristine PbTiO (a

shown in Figure 4b. The micrograph of the p−n hetero-

junction sample shows quite rough surface morphology

(Figure 4c). This is due to the assembling of LaCrO₃

nanoparticles with an average particle size of 66.4 nm on the

3

=

b ≠ c) and LaCrO (a ≠ b ≠ c) (as shown in Table S1) and

smooth surface of PbTiO having an average particle size of

3

compared the calculated values with the JCPDS data ﬁle. We

have seen that both the values are nearly same, which again

179.6 nm, indicating that a good heterojunction is created

between the PbTiO and LaCrO interface. Moreover, the

3

concludes the tetragonal phase of PbTiO and orthorhombic

rough surface of a material provides more active sites for

photocatalytic reaction, and the heterojunction-bearing ma-

terial was quite beneﬁcial for the separation of the photo-

generated charge carrier that will lead to the enhancement of

3

phase of LaCrO . The sharp and intense diﬀraction peaks of

3

both PbTiO and LaCrO are concluding their exceeding

3

crystalline nature. Structurally, the PbTiO /LaCrO p−n

3

26

heterojunction samples are clearly showing the presence of

photocatalytic performance.

two sets of XRD peaks that is tetragonal of PbTiO and

In addition, the EDS analysis investigated the elemental

composition of PbTiO₃and LaCrO₃in PT/LC p−n

heterojunction materials, by carrying out the analysis at two

diﬀerent places (Figure 5). The spectrum of PT/LC (7/3)

displayed the presence of Pb, Ti, La, Cr, and O elements in the

p−n heterojunction sample. Further, the calculated elemental

composition conﬁrms the formation of stoichiometric molar

ratio 7:3::PbTiO :LaCrO in the p−n heterojunction. For a

3

orthorhombic phase of LaCrO . Therefore, the PbTiO /

3

LaCrO p−n junctions contain only PbTiO and LaCrO

3

components.

Moreover, the intensities of corresponding diﬀraction peaks

of LaCrO strengthened gradually along with the increase of

3

the LaCrO contents in PbTiO /LaCrO p−n heterojunctions.

3

The diﬀraction peak at 31.6° of all heterojunction materials is

3

broad, and this is because of the peaks of PbTiO and LaCrO

comparison study, the elemental composition of PbTiO and

3

bearing nearly same d-spacing values which were merged

LaCrO is given in Figure S2.

The more in-depth structural information about pristine

3

together because of strong interaction between the pristine

2

materials. A diﬀraction peak of PT/LC (7/3) heterojunction

PbTiO , LaCrO , and PT/LC (7/3) p−n heterojunction

3

composite in 2θ range of 32−33° was deconvoluted using

Gaussian function. The d-spacing value of deconvoluted peaks

reveals the presence of two prominent distinguished peaks with

samples were investigated by TEM and high-resolution TEM

(HRTEM) techniques. From the TEM image (Figure S3a ), it

was detected that the pristine PbTiO consists of polyhedron-

3

2

θ = 32.4° and 32.6° corresponded to the (110) and (002)

shaped particles with an average size of 233.55 nm. Further,

the corresponding HRTEM observation in Figure S3b reveals

plane of PbTiO and LaCrO , respectively (Figure S1).

3

The FESEM was employed to inspect the surface

morphology of the as-prepared materials. Figure 4 shows the

FESEM images of the pristine PbTiO , LaCrO , and PT/LC

the local crystal lattice of PbTiO with a d-spacing of 0.288 nm,

3

attributed to the (101) crystal plane of PbTiO . The SAED

3

pattern shows bright spots without any recognizable halo rings

3

(

7/3) p−n junction samples. Pristine PbTiO₃exhibits

illustrating the single crystalline nature of PbTiO (Figure

3

polyhedral-shaped morphology with neat cut edges having an

average particle size of 234.931 nm (Figure 4a). On the other

hand, pristine LaCrO₃was composed of interconnected

irregular-shaped aggregates with a relative smooth surface as

S3c ). The bright spots in the diﬀraction pattern of the

polyhedron particle are well matched with the (101), (110),

and (002) planes of tetragonal PbTiO . The TEM image of

3

LaCrO showed an irregular-shaped particle with an average

3

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Figure 5. (a) Selected area of the EDS spectrum, (b,c) EDS spectrum

of the PT/LC (7/3) p−n heterojunction.

particle size around 176.57 nm. The HRTEM image showed

the clear lattice fringes with a d-spacing of 0.38 nm and is well

coincided with the (101) lattice plane of LaCrO . Moreover,

3

the dot pattern due to (111) and (002) planes observed from

SAED indicates the single crystalline nature of LaCrO (Figure

Figure 6. (a,b)TEM, (c) HRTEM, (d) SAED pattern, and (e,f)

bright- and dark-ﬁeld images of the PT/LC(7/3) p−n heterojunction.

3

S4 ). The TEM image of the PT/LC (7/3) p−n heterojunction

reﬂected well interaction between the orthorhombic phase of

LaCrO₃particles and the tetragonal phase of pristine

In addition, the SAED pattern further veriﬁes the

coexistence of (111) and (202) planes of the tetragonal

phase of PbTiO₃and (112) and (204) planes of the

polyhedron PbTiO particles as shown in Figure 6a,b. These

3

results were well consistent with those inferred from the

abovementioned XRD analysis. The heterojunction materials

consist of some polyhedron-shaped particles with smooth

surfaces ascribed to the PbTiO₃particles. The irregular

aggregates with smooth surfaces is ascribed to the LaCrO₃

orthorhombic phase of LaCrO in the PT/LC (7/3) p−n

3

heterojunction material (Figure 6d), which again conﬁrms that

the p−n heterojunction sample consists of only PbTiO and

3

LaCrO without any impurities. The bright- and dark-ﬁeld

3

nanoparticles as shown in Figure 6a. PbTiO with an average

particle size of 175.9 nm has been strongly intimated with

images conﬁrmed the deposition of LaCrO particles on the

3

surface of PbTiO . The dark-shaded portion of the image

3

LaCrO particles with a size of 44.6 nm, which is nearly in

close consistency with FESEM results. In addition, some of the

represents PbTiO , whereas the glowing luminescent portion is

3

ascribed to the LaCrO particles (Figure 6e,f).

3

LaCrO particles having size around 10.06 nm are providing a

XPS analysis was further taken to demonstrate the detailed

surface elemental composition, valence state of the elements,

3

strong intimate contact with PbTiO particles at the p−n

3

junction interface (Figure 6b). Furthermore, most of the

and the synergetic electronic interaction between LaCrO and

3

LaCrO nanoparticles have been attached on the surfaces and

PbTiO in the PT/LC (7/3) p−n heterojunction sample.

3

edges of the PbTiO particles. The HRTEM image of the p−n

Figure 7a represents the XPS survey spectrum of PT/LC (7/

3), which exhibits the presence of La, Cr, Pb, Ti, and O

elements in the heterojunction material, and these results are

well consistent with the EDS analysis (Figure 5). Furthermore,

the obtained results again disclose that the p−n heterojunction

sample shows only the presence of PbTiO and LaCrO . The

3

heterojunction material shown in Figure 6c identiﬁed the

lattice fringes with two diﬀerent interplanar distances of 0.28

and 0.38 nm that corresponds to the (101) plane of both

PbTiO₃and LaCrO , respectively. The cleared interface

3

between PbTiO and LaCrO implied the formation of a

3

good heterojunction structure in the PT/LC (7/3) p−n

junction material.

high-resolution XPS spectra of La 3d, Cr 2p, Pb 4f, Ti 2p, and

O 1s, respectively are shown in the Figure 7b−e. Each

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Figure 7. XPS spectra of the PT/LC (7/3) p−n heterojunction: (a) survey spectrum, (b) La 3d, (c) Cr 2p, (d) Pb 4f, (e) Ti 2p, and (f) O 1s.

elemental peak in the spectrum was well ﬁtted by the XPS

software (CASA). Figure 7b displayed typical doublet peaks of

La 3d₃_/₂and La 3d₅_/₂states of lanthanum in the PT/LC (7/3)

p−n heterojunction. The doublet peaks were ascribed to the

from Cr species had migrated from the LaCrO to PbTiO

3 3

crystal lattice through the interface contact after the

equilibration of the Fermi level in the p−n heterojunction.

Further, the appearance of Cr(VI) concentration maintains

electrical neutrality in the material leading to the generation of

more oxygen vacancies, consistent with the previously reported

9

0

9

1

bonding and antibonding states between 3d 4f and 3d 4f L

2

conﬁguration, where L represents the O 2p hole. One

3

0−32

component of the ﬁrst doublet of 3d₅_/₂with a binding energy

of 836.02 eV and another from 3d₃_/₂with a binding energy of

results.

spin−orbit doublet as shown in Figure 7d. The two binding

energy peaks at 139.0 and 144.2 eV for Pb 4f and Pb 4f ,

5/2

The Pb 4f core-level spectrum appeared as a

8

52.77 eV displayed the spin−orbit splitting around 16.6 eV

7

/2

33,34

and undoubtedly veriﬁed that La ions were in the +3 state and

present near the oxygen defect sites.

respectively, corresponds to Pb(II).

Besides the Pb(II)

27−29

In addition, the

signal, two other peaks were observed at 136.6 and 141.6 eV

deconvoluted Cr 2p core-level XPS spectrum (Figure 7c)

for Pb 4f₇_/₂₃and Pb 4f states of reduced metallic lead Pb(0),

5/2

5

reveals the spin−orbit splitting of doublet 2p₁and 2p₃_/₂

respectively. The signiﬁcant variation in the surface state of

/2

excitation states ascribing the existence of Cr in two

independent +3 and +6 oxidation states. The Cr 2p₁_/₂and

Cr 2p₃_/₂peak signal of Cr(III) appeared at a binding energy of

Pb 4f core-levels indicated the surface restructuring of Pb

atoms into Pb ions with oxygen state availability upon second-

36

time combustion. Figure 7e shows the Ti 2p spectrum which

is deconvoluted into four components, two of each were

located at around 459.3 and 464.9 eV, assigned to the core-

levels Ti 2p₃_/₂and Ti 2p₁_/₂peaks of Ti(IV), whereas the other

5

75.5 and 586.08 eV, whereas the Cr 2p₁_/₂and Cr 2p₃_/₂peaks

of Cr(VI) appeared at 578.8 and 588.5 eV, respectively. The

presence of the Cr(VI) state clearly disclosed that electrons

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two peaks were located at around 456.6 and 462.3 eV

consistent with Ti 2p₃and Ti 2p₁_/₂peaks of Ti(III) state in

/2

37,38

PbTiO , respectively .

The Ti 2p₃_/₂and Ti 2p₁_/₂peaks

3

associated with the +3 oxidation state of titanium indicated the

presence of oxygen vacancy (O )-related defects in the

v

37

synthesized material. Oxygen vacancy associated with the

Ti(III) cation suggested to be the key factor to control the

dielectric properties of materials. Besides this, low valence

titanium Ti(III) was also able to inhibit the photoinduced

3

9

charge carrier recombination and promote charge separation.

3

+

Moreover, the observed binding energy of the Ti 2p₃_/₂(Ti )

state is somewhat smaller than the binding energy of the Ti

4

+

2

p₃_/₂(Ti ) state, indicating that the oxidation state of

4+

3+

titanium multipods shifts from Ti to Ti state and this

Figure 8. (a) UV/vis diﬀuse reﬂectance spectra of pristine PbTiO₃

transformation of the oxidation state (Ti⁴to Ti ) in the

+

3+

(

PT), pristine LaCrO (LC), and various PT/LC p−n heterojunction

3

material may be due to the following factor: the electrons

materials.

2+

0

migrated from LaCrO to PbTiO reduce Pb to Pb , and

3

some electrons simultaneously reduce the Ti(IV) state, in

order to balance the charge neutrality oxygen vacancy

generated within the system. Thus, the presence of the Ti(III)

cation will give rise to the colossal permittivity, such as small

PbTiO and LaCrO . The absorption edge of the hetero-

3

junction extended to the visible region suggested an intimate

intact between PbTiO and LaCrO . It has been reported that

3

the shifting of the absorption edge to the visible region

increases the generation of electron−hole pairs on the

photocatalyst surface and results to higher photocatalytic

3+

4+

polarons of electronic hopping of Ti /Ti within the material

3

+

4+

enhancing the electronic conduction associated with Ti /Ti

3

7,40

44

redox couple reaction.

Ohtomo et al. found a similar type

activities. Furthermore, all p−n heterojunction materials

were well investigated by the two characteristic peaks of

LaCrO . In addition, with increasing molar ratio of LaCrO in

41

of observation in LaTiO /SrTiO -mixed heterojunction. The

3

O 1s spectrum was deconvoluted into three components as

represented in Figure 7f. The lower binding energy peak at

3

heterojunction materials, the absorption hump of ∼600 nm

3

+

5

28.1 eV (OI) was aroused because of the metal−oxygen bond

in mixed perovskite, and the higher binding energy peak at

32.2 eV (OIII) was attributed to the chemisorbed O or

gradually enhances due to the d−d transition of Cr in CrO

6

octahedral. From the depth of the literature study, it was well

clariﬁed that as the Cr content increases, an absorption tail

appears in the visible region with wavelength greater than 700

nm and steadily enhanced due to the increase of surface states

5

2

surface hydroxyl bond in the PbTiO /LaCrO heterojunction.

3

The peak corresponding to 530.7 eV (OII) represents

42

45

structural defect oxygen vacancy species. However, the

peak corresponding to the lattice oxygen in binary perovskite

compared to the previous literature has shifted to a lower

energy value due to the existence of oxygen vacancy on the

and defect levels (e.g., oxygen vacancy states). The optical

band gap energies (E ) of PbTiO and LaCrO₃were

g

3

n

determined by using Tauc equation αhν = A(hν − E ) ,

where α, hν, and A are the absorption coeﬃcient, photoenergy,

and proportionality constant, respectively. Meanwhile, the

g

2

7

46

surface. Such oxygen vacancy-related defects were able to

trap the holes on the surface, facilitating the charge carrier

separation and enhance the visible light absorption capability.

In addition, radicals, such as O²^•⁻and OH, with strong

value of n decides the nature of transition in semiconductor

materials, that is, n = 1/2 for direct and n = 1 for indirect

transition. In our case, both pristine materials have shown a

•

n

oxidation ability can also be formed when the adsorbed O or

direct band gap. Figure S5 shows the plot of (αhν) versus

2

−

OH groups trap holes, capable of photodegardation of

(hν), and the intercept of the straight line on the photoenergy

axis estimates its optical band gap. The approximately

organic pollutants. XPS analysis further conﬁrmed that strong

interaction takes place between PbTiO and LaCrO in the

estimated band gap of PbTiO was found to be 2.8 eV, and

3

PT/LC (7/3) heterojunction which results vectorial trans-

formation of electrons from LaCrO to PbTiO .

it was 2.1 and 2.6 eV for LaCrO . The band gap at 2.6 eV for

LaCrO₃is considered to be important for photocatalytic

activity.

3

The optical absorption property of the pristine PbTiO₃,

LaCrO , and PbTiO /LaCrO heterojunction samples were

3

3.1. Photocatalytic Activities. To investigate the photo-

catalytic properties of the p−n heterojunction samples, phenol,

a typical colorless organic pollutant, was chosen as a target

pollutant for the photocatalytic degradation process. The blank

test was performed and found that phenol is stable under

visible light irradiation (λ ≥ 400 nm), indicating that the

photolysis of phenol is negligible. The initial photo-oxidation

of phenol by pristine PbTiO and LaCrO was found to be 63

investigated by using UV/vis diﬀuse reﬂectance spectroscopy

in Figure 8). From the ﬁgure, it was observed that PbTiO₃

(

exhibits a moderate absorption in the visible region with a

steep absorption edge at 454 nm. The steeped edge indicated

that the optical absorption in PbTiO was due to the band gap

3

43

transition rather than a transition from the impurity level. On

the other hand, LaCrO shows strong absorption in the visible

3

region along with the presence of two prominent characteristic

peaks at around 450 and 600 nm attributed to Cr 3d orbital-

and 47%, respectively, which is low due to the high

recombination rate of photogenerated charge carriers. The

photocatalytic activity of the p−n heterojunction materials

such as PT/LC (1/9), PT/LC (3/7), PT/LC (5/5), PT/LC

(7/3), and PT/LC (9/1) shows 70, 73, 83, 86, and 78%,

respectively, for photo-oxidation of phenol within 2 h as shown

in Figure 9a. The enhanced photocatalytic activity of the p−n

heterojunction materials demonstrates that the eﬀective charge

involved transitions in CrO octahedral which expressed the

6

ability to absorb visible light and the results are quite reliable

2

with the previous reports. However, the optical absorption

edges of all PT/LC heterojunction materials lie between that

of pristine PbTiO and LaCrO . It was worth easier to convey

3

that the p−n heterojunctions were a linear combination of

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Figure 9. (a) Photocatalytic degradation rate, (b) pseudoﬁrst-order kinetics, (c) rate constant of pristine PbTiO (PT), pristine LaCrO (LC), and

3

all PT/LC p−n heterojunction materials, and (d) reusability test of the PT/LC (7/3) heterojunction photocatalyst for phenol degradation.

Figure 10. (a) Histograms showing photogenerated carrier trapping during phenol degradation over the PT/LC (7/3) p−n heterojunction and (b)

−

3

ﬂuorescence intensity of PbTiO (PT), LaCrO (LC), and PT/LC (7/3) p−n heterojunction in a 5 × 10 M basic solution of TA.

3

transfer occurred between LaCrO and PbTiO . It was also

degradation rates were calculated using pseudoﬁrst-order

3

C

realized that the optimum proportion of the components

greatly aﬀects the photocatalytic activity of the PT/LC

heterojunction material because of the existence of an eﬀective

synergistic interaction which extends the electron−hole

kinetics ln _C= −kt where C , C, and k stands for the initial

0

concentration, the concentration at time t, and the apparent

pseudoﬁrst-order rate constant, respectively. Figure 9b shows

2

,47

that ln(C/C ) shows a linear relationship with the irradiation

separation eﬃciency.

The photocatalytic oxidation of

0

phenol by optimal PT/LC (7/3) exceptionally showed 1.3-

fold and 1.8-fold higher than PbTiO₃and LaCrO₃,

respectively. In continual to know the kinetics behind phenol

degradation, we have also analyzed the kinetic parameters. The

time. The rate constant (k) of PbTiO

, LaCrO , PT/LC (1/9),

3 3

PT/LC (3/7), PT/LC (5/5), PT/LC (7/3), and PT/LC (9/

−

3

−3

1), respectively, were calculated to be 8 × 10 , 5 × 10 , 9 ×

−

3

−3

−1

10 , 10 × 10 , 14 × 10 , 15 × 10 , and 12 × 10 min ,

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Figure 11. (a) Histograms showing H evolution of pristine PbTiO (PT), LaCrO (LC), and all PT/LC p−n heterojunction materials and (b)

2

3

reusability test of PT/LC (7/3) for H evolution.

2

•

respectively, represented in Figure 9c. From this, it can be

concluded that the rate constant increases for the hetero-

junction photocatalyst compared with pristine materials. The

optimal PT/LC (7/3) heterojunction photocatalyst illustrated

higher photocatalytic activity for phenol oxidation compared to

other materials. Besides activity, the photostability and

reusability of a catalyst were also highly important for its

practical application. Hence, we performed a reusability study

by sequentially monitoring the photodegradation of phenol in

presence of the optimized PT/LC (7/3) p−n heterojunction

material for three repeated cycles. After each cycle, the

photocatalyst was washed with deionized water, dried, and

collected for the next cycle. The rate of photodegradation of

phenol was observed to be nearly same for each cycle as shown

in Figure 9d. This implied that the PT/LC (7/3)

heterojunction photocatalyst exhibits a good stability and

reusability quality.

the formation of OH radicals in all the photocatalysts under

51,52

visible light irradiation.

ﬂuorescence intensity of the PT/LC (7/3) p−n heterojunction

was greater in comparison with other materials that conﬁrm

OH radicals are serving a crucial role in the degradation

mechanism pathway after the formation of the p−n

heterojunction between PbTiO and LaCrO . Thus, we got a

conclusion from the trapping experiments that the photo-

generated OH and hole radicals play major roles, whereas the

radical O₂plays minor roles in the phenol degradation

process under visible light irradiation in the PT/LC (7/3) p−n

heterojunction photocatalyst.

Additionally, the prepared p−n heterojunction materials

were also analyzed for the photocatalytic hydrogen evolution

reaction under visible light illumination (λ ≥ 400 nm), in

presence of methanol as a sacriﬁcial reagent. Blank tests

indicated that no hydrogen gas was generated in absence of

light and a photocatalyst. In contrast, all PbTiO /LaCrO p−n

heterojunction samples produce a higher amount of H gas

within 2 h under visible light in comparison to the pristine

PbTiO₃and LaCrO . Typical plots for the rate of H

production over various photocatalysts are shown in Figure

11a. The pristine PbTiO produced lower amount of hydrogen

gas that is 32.8 μmol in 2 h because of its moderate absorption

in the visible range and higher electron−hole recombination.

In addition, LaCrO has a tendency to absorb light in the

visible regime and is able to produce hydrogen that is 71.4

μmol in 2 h. The combination of both perovskites displayed a

As shown in Figure 10b, the

•

3

•

•−

44

To highlight the roles of active species in the photocatalytic

activities, a series of radical trapping experiments were

implemented in the presence of the PT/LC (7/3) p−n

heterojunction sample with the addition of various radical

trapping agents such as para-benzoquinone (BQ) (1 mM, a

3

2

3

2

•

−

scavenger of O ), methanol (MeOH) (1 mM, a scavenger of

2

+

•

3

h ), and isopropanol (IPA) (1 mM, a scavenger of OH),

4

8

respectively. As shown in Figure 10a, the addition of BQ has

minimal inﬂuence on the photocatalysis oxidation reaction of

phenol. Although the conduction band (CB) edge potential of

PbTiO and LaCrO is located more negative as compared to

the O /O reduction potential (−0.046 eV vs NHE), these

generated O₂radicals readily reacts with H to generate a

3

2

•

−

2

•

−

+

dramatical increase in the hydrogen production activity in 2 h,

•

•−

and the extent of H production over all the constructed p−n

junctions follows the order: PT/LC (1/9) < PT/LC (3/7) <

PT/LC(9/1) < PT/LC (5/5) < PT/LC (7/3). The obtained

results suggested that the proportion of both the PbTiO and

^L^a^C^r^O3 components play a key role in the increased

photocatalytic activity. The highest amount of H production

over the PT/LC (7/3) sample, that is, 343.57 μmol in 2 h.

Further increase in the LaCrO amount and simultaneous

decrease of PbTiO dropped the H production from 343.57 to

289.03 μmol in 2 h suggesting that PT/LC (7/3) is an

optimum ratio for the enhanced photocatalytic activity

compared to other p−n heterojunctions. Further, the enhanced

activity was studied by loading Pt (1%) as a co-catalyst over all

the prepared photocatalysts. Figure S6 shows the presence of

Pt on the optimized PT/LC (7/3) sample has enhanced the

highly reactive OH radical indicating that O₂radicals

2

4

9

provide a minute impact on the photocatalysis reaction. On

the other hand, the phenol degradation eﬃciency was

remarkably reduced by the addition of the methanol radical

scavenger (degradation eﬃciency 14.6%), suggesting that the

hole radical served as the main reactive species for the

process. After the addition of IPA, the rate of photo-

degradation of phenol was also partially reduced (degradation

eﬃciency 30%), as the valence band (VB) edge potential of

both perovskites lies more positive than that of the reduction

potential OH/OH (+1.99 eV vs NHE) and the photo-

generated holes are capable of oxidizing adsorbed OH groups

into OH radicals indicating that OH radicals also contribute

to the degradation process. The ﬂuorescence technique using

terephthalic acid (TA) as a probe agent was used to conﬁrm

3

2

5

0

3

3 2

•

−

•

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Figure 12. (a) PL spectra of PbTiO (PT), LaCrO (LC), and PT/LC (7/3) heterojunction and (b) TRPL spectra of PbTiO (PT) and PT/LC

3

(

7/3) heterojunction.

Table 1. Summary of the Average Lifetime of Charge Carriers

sample

τ1 (ns)

β1 %

τ2 (ns)

β2 %

τ3 (ns)

β3 %

τ_a_v(ns)

PbTiO (PT)

PT/LC (7/3)

0.51

0.79

62.70

84.48

1.63

2.78

34.92

14.44

8.39

23.75

2.36

1.07

2.53

5.79

3

amount of H gas, that is, 847.4 μmol in 2 h, nearly 2.5 times

exciton. Moreover, the shoulder emission peaks in the blue

region around 464 and 525 nm were the aspect to the

existence of oxygen vacancies and localized defect sites in

2

higher in comparison to the PT/LC (7/3) photocatalyst

without cocatalyst loading. Lastly, the stability of the PT/LC

53,54

(

7/3) photocatalyst was veriﬁed by performing the reusability

PbTiO

3

.

LaCrO displayed two nearly equal intense

3

test toward H production under the same reaction conditions.

emission bands around 417 and 437 nm, respectively, wherein

the peak at 437 nm corresponds to near band edge emission of

2

From the experiment, it was observed that there was no

signiﬁcant decline in the photocatalytic activity upto three

subsequent repeated cycles, which indicates that the prepared

heterojunction samples quite withstand stable photocatalysts

for the photocatalysis reactions.

Later on, the photocatalytic performance (phenol degrada-

tion and hydrogen gas production) of all the prepared samples

was also tested using the cutoﬀ ﬁlter λ > 420 nm. The detailed

results have been presented in the Supporting Information

LaCrO . Moreover, the near band edge emission and shoulder

3

peaks of both PbTiO and LaCrO were well resolved in the

3

PT/LC (7/3) p−n heterojunction along with declined

ﬂuorescence intensity (or quenching) compared to the pristine

materials. The declined PL intensity of the PT/LC (7/3)

composite provides unimpeded paths to transfer the photo-

induced electron−hole pairs which signiﬁcantly inhibits the

recombination of the charge carriers, leading to increase in the

3

photocatalytic activity in comparison to the pristine ones. The

(

Figure S7). The comparison study of photocatalytic perform-

ance under both experimental conditions (λ ≥ 400 nm and λ >

20 nm) concluded that the outcome result was nearly the

TRPL spectroscopy was also employed to explore the charge

transfer dynamic characteristics of the prepared PbTiO and

3

4

55

PT/LC (7/3) as shown in Figure 12b. The lifetime of the

same. To justify the eﬃciency of the designed heterojunction,

photogenerated charge carrier was interpreted for PbTiO and

3

we have provided a comparison table containing PbTiO with

3

PT/LC (7/3) samples at 430 nm with a 375 nm laser as an

excitation source assembled with 395 nm cutoﬀ ﬁlters.

The decayed curve was well ﬁtted into a triexponential

other photocatalysts (Table S2 .)

In order to understand the origin accounting for the

improved photocatalytic activity of the PbTiO /LaCrO p−n

3

function

junction material toward phenol oxidation and hydrogen

production in comparison to pristine PbTiO and LaCrO , a

3

Fit = A + β1.exp(−t/τ1) + β2.exp(−t/τ2) + β3

series of supportive characterization was performed.

.

exp(−t/τ3)

3.1.1. PL and TRPL Spectroscopy. The PL spectra of

PbTiO , LaCrO , and PT/LC (7/3) samples were taken to

3

where τ1, τ2, and τ3 are the three decay lifetimes and β1, β2,

and β3 are the relative weights of the decay compounds. The

investigate the rate of recombination of the photogenerated

charge carriers in the material. Figure 12a depicts the PL

emission spectra of pristine PbTiO , LaCrO , and p−n

average lifetimes of PbTiO and PT/LC (7/3) were calculated

3

by using the equation

heterojunctions were taken at room temperature with an

excited wavelength of 350 nm. The PL spectrum of PbTiO₃

displayed various emission peaks over a range of 370−650 nm.

2

β τ + β τ + β τ

3 3

1 1

2 2

(

τ) =

β τ + β τ + β τ

1

2 2

3 3

The intense radiative emission band of PbTiO at 437 nm

3

attributes to the near band edge emission, whereas peaks in the

The multiexponential decay kinetics reveals to the defect

level emission from a charge carrier recombination of a

blue-violet region (∼417 nm) was ascribed to the charge

recombination in diﬀerent surface state defects of PbTiO

localized exciton. The average lifetimes of PbTiO and PT/LC

3

aroused from an electron−hole recombination of a localized

(7/3) were calculated to be 2.53 and 5.79 ns, respectively, as

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shown in Table 1. The prolonged lifetimes of the charge carrier

demonstrate decreased exciton recombination in perovskite.

The increased average lifetime of the heterojunction stipulates

the increased lifetime of charge carriers associated with the

slow recombination process because of the formation of a

for PbTiO and LaCrO were determined to be −0.76 eV

3

versus Ag/AgCl (equivalent to −0.20 eV vs NHE) and 1.60 eV

versus Ag/AgCl (equivalent to 2.16 eV vs NHE), respectively.

As reported, the ﬂat-band potential of a photocatalyst is very

much important to approximate the band edge potential

positions. Generally, in case of metal oxides, the CB for n-type

semiconductors and the VB for p-type semiconductors is

56

stable p−n junction interface. In this material, the interface

facilitates the reduction of defect sites aroused from the

recombination of charge carriers of a localized exciton.

Moreover, the exponential tail of the decay time curve further

reﬂects the lifetime of the exciton emission aroused due to the

radiative recombination of the photoinduced charge carrier in

the materials and this is well consistent with the steady-state

42

located 0.1 eV unit apart to their ﬂat-band potential value.

Therefore, the CB and VB of PbTiO and LaCrO were further

3

evaluated as −0.3 and 2.26 eV versus NHE, respectively.

Accordingly, the VB and CB of PbTiO and LaCrO were

3

calculated by the following equation

57

PL emission study. Combined with the results of PL and

electrochemical studies, it is worth easier to express that the

^ECB ⁼^EVB ⁻^Eg

formation of a p−n heterojunction between the p-type LaCrO

3

and n-type PbTiO greatly facilitates the separation and reduce

where, E represents the band gap of the semiconductor. E of

g VB

3

the recombination rate of photogenerated charge carriers, thus

highly enhancing the photocatalytic activity.

PbTiO and E of LaCrO was calculated to be 2.5 and −0.34

3

CB

3

eV, respectively.

3

.1.2. Electrochemical Impedance Study. To further

Scheme 1 shows the schematic diagram representing the

energy band edge positions of the semiconductors. Before

determine the eﬀective charge separation occurring through

the p−n junction interface in the p−n heterojunction samples,

the electrochemical impedance study also carried out. The

charger transfer-induced interfacial electric ﬁeld between p-

and n-semiconductor materials provides enough energy to

drive the photogenerated charge carriers to separate and

contact, the position of CB and VB edges of LaCrO is located

3

higher than that of the CB and VB of PbTiO . From the MS

3

plots, it was substantiated that LaCrO is a characteristic p-type

3

semiconductor whose Fermi level is located just above the VB,

whereas PbTiO is a characteristics n-type semiconductor with

3

58

transfer in the space charge layer. EIS could provide an

eﬀective route to evaluate the interfacial reaction capability

elucidating the transfer and migration of photogenerated

its Fermi level lying just below the CB. When p-type LaCrO₃

comes in intimate contact with n-type PbTiO to form a p−n

3

junction and the electrons move from n-PbTiO to p-LaCrO ,

3

59,60

charge carriers at semiconductor−electrolyte interfaces.

In

creating a negative charge segment in p-LaCrO region near

3

the EIS Nyquist plot, the arc of the semicircle evidence the

interfacial layer resistance at the electrode surface, and the

smaller arc radius indicates higher charge transfer eﬃciency. As

shown in Figure 13, the PT/LC (7/3) p−n heterojunction

the junction, holes are migrated from p-LaCrO to n-PbTiO ,

3

generating a positive charge segment in the n-PbTiO region

3

adjacent to the junction. At thermal equilibrium conditions,

the Fermi levels of n-PbTiO and p-LaCrO are aligned and

3

induced an internal electric ﬁeld directed from n-PbTiO to p-

3

LaCrO concurrently built to stop the charge carrier diﬀusion

3

from n-PbTiO into p-LaCrO . Meanwhile, the relative energy

3

bands of PbTiO are shifted toward the downward direction

3

along with the Fermi level. Consequently, the relative energy

bands of LaCrO are shifted to the upward direction in this

3

progression. As a result, energy band positions of p-type

LaCrO and n-type PbTiO build up a p−n heterojunction.

3

Accordingly, both CB and VB positions of LaCrO are located

3

higher than the CB and VB positions of PbTiO . Under visible

3

light irradiation, both LaCrO and PbTiO are absorbing

3

photons of energy greater than the band gap energy, exciting

the electrons from the VB to the CB and leaving holes in the

VB. The electrons in the CB of p-type LaCrO are then

3

Figure 13. EIS Nyquist curves of PbTiO (PT), LaCrO (LC), and

PT/LC (7/3) p−n heterojunction.

3

migrated to the lower energetic CB of n-type PbTiO and the

3

holes in the VB of PbTiO ﬂows to the VB of LaCrO . To

3

provide the strong evidence to the directional ﬂow of electrons

from p-LaCrO to n-PbTiO and the holes from n-PbTiO to

p-LaCrO , the FESEM image has been provided. From the

presents a reduced arc radius as compared to the pristine n-

PbTiO and p-LaCrO , and it corresponds to greatly enhance

3

the reaction capability. The combined enhanced photocurrent

response and EIS analysis conﬁrmed a strong interaction

between the n-type PbTiO and p-type LaCrO semiconductor

FESEM image (Figure S8 ), it was observed that during the

photodeposition process, the small dot-shaped Au nano-

particles were deposited on the surface of PbTiO and on

3

interface. In addition, the heterojunction formed with the

strong interface contact is mainly responsible for the inhibition

of the recombination rate of the charge carrier and witnessed

the other hand, MnO with branch-like morphology that

x

assembled to a dense small nanobranch are attached to the

LaCrO particles. This indicates that PbTiO serving as an

3

61

3+

the photodegradation activity study of phenol.

electron source reduced Au into Au. At the same time,

According to the Mott−Schottky analysis (Figure 1a,b), the

LaCrO acting as an hole source present on the surface of

3

2

+

ﬂat-band potential values can be determined by the

LaCrO helps to oxidize Mn into MnO in presence of

3

x

2

extrapolation of 1/C = 0, where C is the space charge

hydroxyl anions. The detailed mechanism has been described

below

62

capacitance of the semiconductor electrode. The E values

fb

L

DOI: 10.1021/acs.inorgchem.8b02364

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Scheme 1. Schematic Diagrams of Formation of the p−n Heterojunction and Proposed Charge Separation Process in PbTiO /

3

LaCrO under Visible Light Irradiation

3

+

−

PT/LC + hν → PT/LC*(h VB + e CB)

present in the VB of LaCrO also participate directly in the

3

64

phenol degradation process. The detailed mechanism is

summarized as

−

LC(e CB) → PT(e CB)

+

−

+

PT/LC + hν → PT/LC*(h VB + e CB)

PT(h VB) → LC(h VB)

−

LC(e CB) → PT(e CB)

Au³+ PT(e CB) → Au

+

−

+

PT(h VB) → LC(h VB)

Mn²+ OH + LC(h VB) → MnO

+

−

+

X

−

•−

PT(e CB) + O → O

2

After this examination, we have concluded that the electrons

migrated from the LaCrO to PbTiO side, and the holes were

migrating from PbTiO to LaCrO after formation of a p−n

junction between them. This movement of photogenerated

charge carries were encouraged by the inner electric ﬁeld

established at the p−n junction interface. Additionally, the Ti

and Cr state at the interface also boosts the separation

eﬃciency of electrons across the junction. Thiel and Ohmoto

et al. have already described that the formed interface in

between two pervoksites not only creates a high-response

internal electric ﬁeld but also enhances the conductivity of the

•

−

+

•

3

O₂+ H → HO

2

3

•

+

−

HO₂+ H + PT(e CB) → H O

2

3

+

−

•

−

H O + PT(e CB) → OH + OH

2

3

+

•

Phenol + OH → intermediate products → CO + H O

2

+

−

•

LC(h VB) + OH → OH

•

41,63

Phenol + OH → intermediate products → CO + H O

produced electrons.

Thus, the photogenerated electrons

2

and holes are eﬃciently separated at the LaCrO /PbTiO p−n

3

+

Phenol + LC(h VB)

→

junction interface, resulting to minimize electron−hole

recombination eﬃciency.

intermediate products

The separated electrons and holes are then free to initiate

the hydrogen production reaction and degradation of phenol

adsorbed on the photocatalyst surfaces with enhanced

photocatalytic activity. For the photo-oxidation of phenol,

the CB of PbTiO and LaCrO were located more negative

→ CO2 + H2O

Similarly to attain H evolution, the CB potentials of both

PbTiO and LaCrO were placed more negative than E (H /

H = 0 eV vs NHE). The available photogenerated electrons

on the CB of PbTiO reacts with H to produce hydrogen gas.

Further, the holes present in the VB of LaCrO also oxidize

aqueous methanol into the oxidizing products. The detailed

mechanism involved in water-splitting involves the following

steps

2

+

3

0

3

•−

2

than the standard reduction potential of O /O₂(−0.046 eV

2

+

3

vs NHE), indicating that the dissolved oxygen can easily be

reduced to O₂^•radicals by the photogenerated electrons

−

3

65

present on the CB of PbTiO . Further, the superoxide radicals

3

abstract the proton from water and electrons from the medium

to produce H O . These H O radicals are responsible for the

2

•

+

−

generation of OH radicals; thereafter, OH eﬃciently

PT/LC + hν → PTLC*(h VB + e CB)

participates in the degradation process. On the other hand,

−

the VB of LaCrO is located more positive than the reduction

LC(e CB) → PT(e CB)

3

•

−

potential of OH/OH (+1.99 eV vs NHE); hence, photo-

generated free holes in the VB of LaCrO reacts with OH to

produce OH radicals that degrade phenol into intermediate

+

−

PT(h VB) → LC(h VB)

3

•

+

−

H + PT(e CB) → H ↑

products and ﬁnally into CO and H O. Moreover, the holes

2

M

DOI: 10.1021/acs.inorgchem.8b02364

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

+

̇

of both ultraviolet and visible light. Dalton Trans. 2016, 45, 13907−

CH OH + LC(h VB) → CH OH + H

3

2

13916.

+

−

(2) Nashim, A.; Parida, K. n-La Ti O /p-LaCrO : a novel

̇

2 2 7 3

CH OH → HCHO + H + e

2

heterojunction based composite photocatalyst with enhanced photo-

+

−

activity towards hydrogen production. J. Mater. Chem. A 2014, 2,

2

H + 2e → H ↑

2

1

8405−18412.

(

3) Reddy, K. H.; Parida, K.; Satapathy, P. K. CuO/PbTiO : A new-

3

fangled p−n junction designed for the efficient absorption of visible

light with augmented interfacial charge transfer, photoelectrochemical

and photocatalytic activities. J. Mater. Chem. A 2017, 5, 20359−

20373.

4

. CONCLUSIONS

In summary, we have successfully fabricated an eﬃcient and

novel biperovskite-based PbTiO /LaCrO p−n heterojunction

3

via a two-step combustion method. The formation of a p−n

heterojunction between the two perovskites was substantiated

by the asymmetric photocurrent nature and inverted V-shaped

Mott−Schottky plot. The construction of a tight p−n junction

interface between PbTiO and LaCrO was demonstrated by

(4) Deng, Y.; Chen, Y.; Chen, B.; Ma, J. Preparation, character-

ization and photocatalytic activity of CuBi2O4/NaTaO3 coupled

photocatalysts. J. Alloys Compd. 2013, 559, 116−122.

(5) Wei, L.; Shifu, C.; Sujuan, Z.; Wei, Z.; Huaye, Z.; Xiaoling, Y.

Preparation and characterization of p−n heterojunction photocatalyst

p-CuBi2 4 n-TiO2 with high photocatalytic activity under visible and

3

the XPS and HRTEM analysis. The prepared PbTiO /LaCrO

O /

3

UV light irradiation. J. Nanopart. Res. 2009, 12, 1355−1366.

p−n heterojunction under optimized concentrations showed

higher photocatalytic activity for the degradation of phenol and

hydrogen production under visible light irradiation. The

superior photocatalytic performance of the biperovskite p−n

junction was mainly attributed due to the eﬀective improve-

ment of the charge anti-recombination process at the p−n

heterojunction interface. This was well explained by the PL,

TRPL, EIS and PEC measurements. The optimized photo-

catalyst can be reused for three consecutive cycles without

change in the photocatalytic activities which speciﬁes the good

stability of the photocatalyst. The designed biperovskite

PbTiO /LaCrO p−n heterojunction triggers various syner-

(6) Reddy, K. H.; Martha, S.; Parida, K. M. Fabrication of Novel p-

BiOI/n-ZnTiO3 Heterojunction for Degradation of Rhodamine 6G

under Visible Light Irradiation. Inorg. Chem. 2013, 52, 6390−6401.

(7) Li, P.; Zhao, X.; Jia, C.-j.; Sun, H.; Sun, L.; Cheng, X.; Liu, L.;

Fan, W. ZnWO4/BiOI heterostructures with highly efficient visible

light photocatalytic activity: the case of interface lattice and energy

level match. J. Mater. Chem. A 2013, 1, 3421−3429.

(8) Pena, M. A.; Fierro, J. L. G. Chemical structures and

̃

performance of perovskite Oxides. Chem. Rev. 2001, 101, 1981−2018.

(9) Arney, D.; Watkins, T.; Maggard, P. A. Effects of particle surface

areas and microstructures on photocatalytic H and O production

2

over PbTiO . J. Am. Ceram. Soc. 2010, 94, 1483−1489.

3

(10) Reddy, K. H.; Parida, K. Fabrication, characterization, and

gistic properties such as boosted light harvesting, creation of

internal electrostatic ﬁeld, resourceful charge separation and

migration, and excellent stability, thus leading to the dramatic

enhancement of photocatalytic performance of the system.

This article provides a new approach to the built-up

biperovskite-based PbTiO /LaCrO p−n heterojunction to

photoelectrochemical properties of Cu-doped PbTiO₃and its

hydrogen production activity. ChemCatChem 2013, 5, 3812−3820.

(11) Yimei, R.; Fengcai, G.; Junzhen, W.; Zhixing, S.; Shulan, Z. The

preparation and photocatalytic ability of lead titanate. Trans. Tianjin

Univ. 1995, 1, 59−62.

(12) Li, L.; Zhang, Y.; Schultz, A. M.; Liu, X.; Salvador, P. A.;

Rohrer, G. S. Visible light photochemical activity of heterostructured

PbTiO3-TiO2 core-shell particles. Catal. Sci. Technol. 2012, 2, 1945−

1952.

3

promote the photocatalytic activity under sunlight.

ASSOCIATED CONTENT

Supporting Information

■

(

13) Wang, Y.; Cheng, H.-P. Oxygen reduction activity on

*

S

perovskite oxide surfaces: A comparative first-principles study of

The Supporting Information is available free of charge on the

ACS Publications website at DOI: 10.1021/acs.inorg-

chem.8b02364.

LaMnO , LaFeO , and LaCrO . J. Phys. Chem. C 2013, 117, 2106−

3

2

112.

(

14) Shi, J.; Ye, J.; Zhou, Z.; Li, M.; Guo, L. Hydrothermal synthesis

−LaCrO solid-solution single-crystal nanocubes for

visible-light-driven photocatalytic H

evolution. Chem.Eur. J. 2011,

7, 7858−7867.

15) Rashad, M. M.; Mohammed, R. S.; Hessien, M. M.; Ibrahim, I.

Deconvoluted XRD peaks, EDS analysis, TEM images,

of Na0.5La0.5TiO

3

SAED pattern, Tauc plot, and Mott−Schottky plots

2

1

(

(PDF)

A.; Kandil, A. T. Synthesis and characterization of lead titanate

nanopowders by organic acid precursor. J. Optoelectron. Adv. Mater.

2008, 10, 1026−1031.

AUTHOR INFORMATION

Corresponding Author

E-mail: paridakulamani@yahoo.com, kulamaniparida@soa.ac.

in . Phone. No. +91-674-2379425. Fax. +91-6 74-2581637.

ORCID

■

*

(16) Shabbir, G.; Qureshi, A. H.; Saeed, K. Nano-crystalline LaFeO

3

powders synthesized by the citrate−gel method. Mater. Lett. 2006, 60,

706−3709.

17) Shen, H.; Cheng, G.; Wu, A.; Xu, J.; Zhao, J. Combustion

3

(

Kulamani Parida: 0000-0001-7807-5561

synthesis and characterization of nano-crystalline LaFeO powder.

3

Notes

Phys. Status Solidi A 2009, 206, 1420−1424.

The authors declare no competing ﬁnancial interest.

(18) Martha, S.; Nashim, A.; Parida, K. M. Facile synthesis of highly

active g-C3N4 for efficient hydrogen production under visible light. J.

Mater. Chem. A 2013, 1, 7816−7824.

ACKNOWLEDGMENTS

The authors are very much thankful to the SOA University

management for their support and encouragement.

■

(19) Liu, G.; Ma, L.; Yin, L.-C.; Wan, G.; Zhu, H.; Zhen, C.; Yang,

Y.; Liang, Y.; Tan, J.; Cheng, H.-M. Selective Chemical Epitaxial

Growth of TiO Islands on Ferroelectric PbTiO Crystals to Boost

2

3

Photocatalytic Activity. Joule 2018, 2, 1095−1107.

(20) Norwitz, G.; Farino, J.; Keliher, P. N. Interference of oxidants

in the determination of phenol by the 4-aminoantipyrine and

ultraviolet ratio spectrophotometric methods. Anal. Chem. 1979, 51,

1632−1637.

REFERENCES

■

(

1) Ao, Y.; Bao, J.; Wang, P.; Wang, C.; Hou, J. A novel p-n

heterostructured photocatalyst for the efficient photocatalytic

degradation of different kinds of organic compounds under irradiation

N

DOI: 10.1021/acs.inorgchem.8b02364

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

(

21) ASTM Designation D-1723-70, Standard Methods of Test for

(38) Nayak, S.; Sahoo, B.; Chaki, T. K.; Khastgir, D. Facile

Phenolic Compounds in Water; American Society for Testing and

Materials: Philadelphia, PA, 1978.

preparation of uniform barium titanate (BaTiO ) multipods with high

permittivity: impedance and temperature dependent dielectric

3

(

22) Zhang, L.; Hu, Y.; Zheng, J. Fabrication of 3D hierarchical

Behavior. RSC Adv. 2014, 4, 1212−1224.

CoSnO @CoO pine needle-like array photoelectrode for enhanced

(39) Jiang, J.; Tang, X.; Zhou, S.; Ding, J.; Zhou, H.; Zhang, F.;

Zhang, D.; Fan, T. Synthesis of visible and near infrared light sensitive

amorphous titania for photocatalytic hydrogen evolution. Green Chem.

2016, 18, 2056−2062.

3

photoelectrochemical properties. J. Mater. Chem. A 2017, 5, 18664−

1

(

8673.

23) Guo, J.; Wang, K.; Wang, X. Photocatalytic reduction of CO₂

with H O vapor under visible light over Ce doped ZnFe O . Catal.

Sci. Technol. 2017, 7, 6013−6025.

(

(40) Kovalevsky, A. V.; Aguirre, M. H.; Populoh, S.; Patrício, S. G.;

Ferreira, N. M.; Mikhalev, S. M.; Fagg, D. P.; Weidenkaff, A.; Frade, J.

R. Designing strontium titanate-based thermoelectrics: insight into

defect chemistry mechanisms. J. Mater. Chem. A 2017, 5, 3909−3922.

(41) Ohtomo, A.; Muller, D. A.; Grazul, J. L.; Hwang, H. Y. Artificial

charge-modulationin atomic-scale perovskite titanate superlattices.

Nature 2002, 419, 378−380.

2

4

24) Kuang, P.-Y.; Ran, J.-R.; Liu, Z.-Q.; Wang, H.-J.; Li, N.; Su, Y.-

Z.; Jin, Y.-G.; Qiao, S.-Z. Enhanced Photoelectrocatalytic Activity of

BiOI Nanoplate-Zinc Oxide Nanorod p-n Heterojunction. Chem.

Eur. J. 2015, 21, 15360−15368.

(

25) Hou, Y.; Li, X.-Y.; Zhao, Q.-D.; Quan, X.; Chen, G.-H.

Electrochemical Method for Synthesis of a ZnFe2O4/TiO2

Composite Nanotube Array Modified Electrode with Enhanced

Photoelectrochemical Activity. Adv. Funct. Mater. 2010, 20, 2165−

(42) Sultana, S.; Mansingh, S.; Parida, K. M. Facile synthesis of

CeO2 nanosheets decorated upon BiOI microplate: A surface oxygen

vacancy promoted z-scheme-based 2D-2D nanocomposite photo-

catalyst with enhanced photocatalytic activity. J. Phys. Chem. C 2017,

122, 808−819.

2

(

174.

26) Niu, F.; Chen, D.; Qin, L.; Zhang, N.; Wang, J.; Chen, Z.;

Huang, Y. Facile synthesis of highly efficient p−n heterojunction

CuO/BiFeO composite photocatalysts with enhanced visible-light

(43) Lv, D.; Zhang, D.; Pu, X.; Li, Y.; Yin, J.; Ma, H.; Dou, J. Facile

synthesis of BiOBr/Bi Sn O heterojunction photocatalysts with

3

2

7

photocatalytic activity. ChemCatChem 2015, 7, 3279−3289.

improved photocatalytic activities. J. Am. Ceram. Soc. 2016, 99,

3973−3979.

(

27) Sennu, P.; Aravindan, V.; Nahm, K. S.; Lee, Y.-S. Exceptional

catalytic activity of hollow structured La Sr CoO perovskite

(44) Wang, M.; Hu, Y.; Han, J.; Guo, R.; Xiong, H.; Yin, Y. TiO₂/

NiO hybrid shells: p−n junction photocatalysts with enhanced

activity under visible light. J. Mater. Chem. A 2015, 3, 20727−20735.

(45) Shi, J.; Zong, S.; Hu, Y.; Guan, X.; Luo, J.; Shang, Y.; Li, G.;

Liu, D.; Wang, X.; Guo, P. Continuous solid solutions of

Na La TiO −LaCrO for photocatalytic H₂evolution under

0

.6 0.4

3‑δ

spheres in aqueous media and aprotic Li-O battery. J. Mater. Chem. A

2

(

017, 5, 18029−18037.

28) Li, T.; Liu, J.; Jin, X.; Wang, F.; Song, Y. Composition-

dependent electro-catalytic activities of covalent carbon-LaMnO3

hybrids as synergistic catalysts for oxygen reduction reaction.

Electrochim. Acta 2016, 198, 115−126.

0

.5 0.5

3

visible-light irradiation. RSC Adv. 2016, 6, 51801−51806.

(46) Behera, G. C.; Biswal, N.; Parida, K. Unexpected rapid photo-

catalytic decolourisation/degradation of organic pollutants over highly

active hetero junction based vanadium phosphate catalyst. Catal.

Today 2017, 284, 84−91.

(

29) Brackmann, R.; Perez, C. A.; Schmal, M. LaCoO perovskite on

3

ceramic monoliths-Pre and post reaction analyzes of the partial

oxidation of methane. Int. J. Hydrogen Energy 2014, 39, 13991−14007.

(

30) Yao, K. P. C.; Lu, Y.-C.; Amanchukwu, C. V.; Kwabi, D. G.;

Risch, M.; Zhou, J.; Grimaud, A.; Hammond, P. T.; Barde,

Horn, Y. The influence of transition metal oxides on the kinetics of

́

F.; Shao-

(47) Qian, D.; Zhong, S.; Wang, S.; Lai, Y.; Yang, N.; Jiang, W.

Promotion of phenol photodegradation based on novel self-assembled

magnetic bismuth oxyiodide core-shell microspheres. RSC Adv. 2017,

7, 36653−36661.

Li O oxidation in Li−O batteries: high activity of chromium oxides.

2

Phys. Chem. Chem. Phys. 2014, 16, 2297−2304.

(

31) Yao, W.; Duan, T.; Li, Y.; Yang, L.; Xie, K. Perovskite chromate

(48) Kumar, S.; Kumar, A.; Kumar, A.; Balaji, R.; Krishnan, V.

Highly efficient visible light active 2D-2D nanocomposites of N-ZnO-

g-C N for photocatalytic degradation of diverse industrial pollutants.

doped with titanium for direct carbon dioxide electrolysis. New J.

Chem. 2015, 39, 2956−2965.

3

4

(

32) Zhang, H.; Pokhrel, S.; Ji, Z.; Meng, H.; Wang, X.; Lin, S.;

ChemistrySelect 2018, 3, 1919−1932.

Chang, C. H.; Li, L.; Li, R.; Sun, B.; Wang, M.; Liao, Y.-P.; Liu, R.;

Xia, T.; Madler, L.; Nel, A. E. PdO doping tunes band-gap energy

levels as well as oxidative stress responses to a Co O p-type

(49) Barrocas, B.; Neves, M. C.; Oliveira, M. C.; Monteiro, O. C.

Enhanced photocatalytic degradation of psychoactive substances

using amine-modified elongated titanate nanostructures. Environ.

Sci.: Nano 2018, 5, 350−361.

̈

3

4

semiconductor in cells and the lung. J. Am. Chem. Soc. 2014, 136,

406−6420.

33) Kumar, R.; Bhuvana, T.; Sharma, A. Nickel tungstate-graphene

6

(

(50) Zhang, H.; Guo, L.-H.; Zhao, L.; Wan, B.; Yang, Y. Switching

oxygen reduction pathway by exfoliating graphitic carbon nitride for

enhanced photocatalytic phenol degradation. J. Phys. Chem. Lett.

2015, 6, 958−963.

nanocomposite for simultaneous electrochemical detection of heavy

metal ions with application to complex aqueous media. RSC Adv.

2

017, 7, 42146−42158.

34) Jasmin, J.-P.; Miserque, F.; Dumas, E.; Vickridge, I.; Ganem, J.-

J.; Cannizzo, C.; Chausse, A. XPS and NRA investigations during the

(51) Tian, N.; Huang, H.; Liu, C.; Dong, F.; Zhang, T.; Du, X.; Yu,

S.; Zhang, Y. In situ co-pyrolysis fabrication of CeO /g-C N n−n

(

2

3

4

́

type heterojunction for synchronously promoting photo-induced

oxidation and reduction properties. J. Mater. Chem. A 2015, 3,

17120−17129.

fabrication of gold nanostructured functionalized screen-printed

sensors for the detection of metallic pollutants. Appl. Surf. Sci.

2

(

017, 397, 159−166.

(52) Padhi, D. K.; Panigrahi, T. K.; Parida, K.; Singh, S. K.; Mishra,

P. M. Green synthesis of Fe O /RGO nanocomposite with enhanced

35) Deepa, M.; Salado, M.; Calio, L.; Kazim, S.; Shivaprasad, S. M.;

3

4

+

Ahmad, S. Cesium Power: low Cs levels Impart Stability to

photocatalytic performance for cr(vi) reduction, phenol degradation,

and antibacterial activity. ACS Sustainable Chem. Eng. 2017, 5,

10551−10562.

perovskite Solar Cells. Phys. Chem. Chem. Phys. 2017, 19, 4069−4077.

(

36) Kumar, G. R.; Savariraj, A. D.; Karthick, S. N.; Selvam, S.;

Balamuralitharan, B.; Kim, H.-J.; Viswanathan, K. K.; Vijaykumar, M.;

Prabakar, K. Phase transition kinetics and surface binding states of

methylammonium lead iodide perovskite. Phys. Chem. Chem. Phys.

(53) Leite, E. R.; Santos, L. P. S.; Carreno, N. L. V.; Longo, E.;

̃

Paskocimas, C. A.; Varela, J. A.; Lanciotti, F.; Campos, C. E. M.;

Pizani, P. S. Photoluminescence of nanostructured PbTiO3 processed

by high-energy mechanical milling. Appl. Phys. Lett. 2001, 78, 2148−

2150.

2

(

016, 18, 7284−7292.

37) Yang, X.; Li, D.; Ren, Z. H.; Zeng, R. G.; Gong, S. Y.; Zhou, D.

K.; Tian, H.; Li, J. X.; Xu, G.; Shen, Z. J.; Han, G. R. Colossal

dielectric performance of pure barium titanate ceramics consolidated

by spark plasma sintering. RSC Adv. 2016, 6, 75422−75429.

(54) Zhang, Y.; Dai, R.; Hu, S. Study of the role of oxygen vacancies

as active sites in reduced graphene oxide-modified TiO . Phys. Chem.

2

Chem. Phys. 2017, 19, 7307−7315.

O

DOI: 10.1021/acs.inorgchem.8b02364

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

(

55) Zhao, P.; Yin, W.; Kim, M.; Han, M.; Song, Y. J.; Ahn, T. K.;

Jung, H. S. Improved Carriers Injection Capacity in Perovskite Solar

Cells by Introducing A-site Interstitial Defects. J. Mater. Chem. A

2

(

017, 5, 7905−7911.

56) Elbanna, O.; Fujitsuka, M.; Majima, T. g-C N /TiO

2

3

4

Mesocrystals Composite for H₂Evolution under Visible Light

Irradiation and Its Charge Carriers Dynamics. ACS Appl. Mater.

Interfaces 2017, 9, 34844−34854.

(

57) Zhang, F.; Sfeir, M. Y.; Misewich, J. A.; Wong, S. S. Room-

temperature preparation, characterization, and photoluminescence

measurements of solid solutions of various compositionally-defined

single-crystalline alkaline-earth-metal tungstate nanorods. Chem.

Mater. 2008, 20, 5500−5512.

(

58) Hou, J.; Wu, Y.; Cao, S.; Liang, F.; Lin, Z.; Gao, Z.; Sun, L. In

Situ Phase-Induced Spatial Charge Separation in Core-Shell Oxy-

nitride Nanocube Heterojunctions Realizing Robust Solar Water

Splitting. Adv. Energy Mater. 2017, 7, 1700171.

(

59) Cheng, X.; Zhang, Y.; Hu, H.; Shang, M.; Bi, Y. High-efficiency

SrTiO /TiO hetero-photoanode for visible-light water splitting by

3

2

charge transport design and optical absorption management. Nano-

scale 2018, 10, 3644−3649.

(

60) Zhou, Y.; Chen, G.; Liu, Y.; He, F. Surface natrotantite phase

induced efficient charge carrier separation and highly active surface of

TaON for superior enhanced photocatalytic performance. Adv. Mater.

Interfaces 2016, 3, 1600429.

(

61) Huang, H.; He, Y.; Du, X.; Chu, P. K.; Zhang, Y. A General and

Facile Approach to Heterostructured Core/Shell BiVO /BiOI p−n

4

Junction: Room-Temperature in Situ Assembly and Highly Boosted

Visible-Light Photocatalysis. ACS Sustainable Chem. Eng. 2015, 3,

3

(

262−3273.

62) Wen, X.-J.; Niu, C.-G.; Zhang, L.; Zeng, G.-M. Novel p-n

heterojunction BiOI/CeO photocatalyst 1 for wider spectrum visible-

2

light photocatalytic degradation of refractory pollutant. Dalton Trans.

2

(

017, 46, 4982−4993.

63) Thiel, S.; Hammerl, G.; Schmehl, A.; Schneider, C. W.;

Mannhart, S. Tunable Quasi-Two-Dimensional Electron Gases in

Oxide Heterostructures. Science 2006, 313, 1942−1945.

(

64) Ren, H.-T.; Jia, S.-Y.; Wu, Y.; Wu, S.-H.; Zhang, T.-H.; Han, X.

Improved photochemical reactivities of Ag2O/g-C3N4 in phenol

degradation under UV and visible light. Ind. Eng. Chem. Res. 2014, 53,

1

(

7645−17653.

65) Guzman, F.; Chuang, S. S. C.; Yang, C. Role of methanol

sacrificing reagent in the photocatalytic evolution of hydrogen. Ind.

Eng. Chem. Res. 2013, 52, 61−65.

P

DOI: 10.1021/acs.inorgchem.8b02364

Inorg. Chem. XXXX, XXX, XXX−XXX

Article Doi

Architecture of Biperovskite-Based LaCrO3/PbTiO3 p-n Heterojunction with a Strong Interface for Enhanced Charge Anti-recombination Process and Visible Light-Induced Photocatalytic Reactions

DOI: 10.1021/acs.inorgchem.8b02364

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Article abstract of DOI:10.1021/acs.inorgchem.8b02364

Full text of DOI:10.1021/acs.inorgchem.8b02364

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