A novel ternary Mica/TiO2/Fe2O3 composite pearlescent pigment for the photocatalytic degradation of acetaldehyde

Article abstract of DOI:10.1016/j.jphotochem.2020.112617

A novel ternary mica/TiO₂/Fe₂O₃ composite pearlescent pigment has been designed for the photocatalytic oxidation of gas-phase acetaldehyde in the application of indoor air purification. The mica/TiO₂/Fe₂O₃-x (MTF-x, x = m_Fe2O3 : m_TiO2 = 0.5–2: 100) composites were synthesized by a sol-gel assisted hydrothermal method. The MTF-1.5 composite shows optimal photocatalytic performance, which is 1.8 times photodegradation efficiency and 2.2 times CO₂ mineralization efficiency higher than those of pure TiO₂. The enhanced photocatalytic performance of MTF-x (x = 0.5–2) composites could be associated with enhanced reflectivity of mica, which eventually improved the light absorption properties. Also, the presence of TiO₂/Fe₂O₃ heterostructure facilitated charge separation in the MTF ternary composite. Besides, superoxide radical was proven as the decisive active species for the degradation of gaseous acetaldehyde. This work provides a systematic approach to develop a potential multi-functional pearlescent pigment to purify indoor air.

Full text of DOI:10.1016/j.jphotochem.2020.112617

Journal Pre-proof
A Novel Ternary Mica/TiO /Fe O Composite Pearlescent Pigment for
2
2
3
the Photocatalytic Degradation of Gaseous Acetaldehyde
Xiangming Fang, Guanhong Lu, Asad Mahmood, Zhihong Tang,
Ziwei Liu, Linlin Zhang, Yan Wang, Jing Sun
PII:
S1010-6030(20)30416-0
DOI:
https://doi.org/10.1016/j.jphotochem.2020.112617
JPC 112617
Reference:
To appear in:
Journal of Photochemistry & Photobiology, A: Chemistry
Received Date:
Revised Date:
Accepted Date:
9 February 2020
24 April 2020
3 May 2020
Please cite this article as: Fang X, Lu G, Mahmood A, Tang Z, Liu Z, Zhang L, Wang Y, Sun J,
A Novel Ternary Mica/TiO /Fe O Composite Pearlescent Pigment for the Photocatalytic
2
2
3
Degradation of Gaseous Acetaldehyde, Journal of Photochemistry and amp; Photobiology, A:
Chemistry (2020), doi: https://doi.org/10.1016/j.jphotochem.2020.112617
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Title: A Novel Ternary Mica/TiO
2
/Fe
2
O Composite Pearlescent Pigment
3
for the Photocatalytic Degradation of Gaseous Acetaldehyde
a,b
b
b
a
Authors: Xiangming Fang , Guanhong Lu , Asad Mahmood , Zhihong Tang , Ziwei
b
b
b,*
b,*
Liu , Linlin Zhang , Yan Wang wangyan@mail.sic.ac.cn, Jing Sun
jingsun@mail.sic.ac.cn
Mr. X.M. Fang, Dr. A. Mahmood, Mr. G.H. Lu, Prof. Z.H. Tang, Mrs. Z.W. Liu, Mrs.
L.L. Zhang, Prof. Y. Wang, Prof. J. Sun
a
University of Shanghai for Science and Technology, 516 Jungong Road, Shanghai
2
00093, China.
b
State key Laboratory of High Performance Ceramics and Superfine Microstructure
Shanghai Institute of Ceramics Chinese Academy of Sciences, 1295 Dingxi Road,
China.
*
Corresponding author information:
Prof. Yan Wang
State key Laboratory of High Performance Ceramics and Superfine Microstructure
Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road,
Shanghai 200050, China
Tel: +86-21-52412722
Fax: +86-21-52413122
Prof. Jing Sun

State key Laboratory of High Performance Ceramics and Superfine Microstructure
Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road,
Shanghai 200050, China
Tel: +86-21-52412717
Fax: +86-21-52413122
Highlights:




A novel ternary pearlescent composite is fabricated to photodegrade VOCs.
MTF-1.5 composite shows enhanced photocatalytic activity and stability.
Superoxide radicals (·O
2
–) play a major role in the photodegradation.
The composite is expected to purify indoor air as finish paint additive.
Abstract
A novel ternary mica/TiO
designed for the photocatalytic oxidation of gas-phase acetaldehyde in the application
of indoor air purification. The mica/TiO /Fe
: 100) composites were synthesized by a sol-gel assisted hydrothermal method. The
MTF-1.5 composite shows optimal photocatalytic performance, which is 1.8 times
photodegradation efficiency and 2.2 times CO mineralization efficiency higher than
those of pure TiO . The enhanced photocatalytic performance of MTF-x (x = 0.5-2)
2
/Fe
2
3
O composite pearlescent pigment has been
2
2
3
O -x (MTF-x, x = mFe2O3 : mTiO2 = 0.5–
2
2
2

composites could be associated with enhanced reflectivity of mica, which eventually
improved the light absorption properties. Also, the presence of TiO /Fe
2
2
O
3
heterostructure facilitated charge separation in the MTF ternary composite. Besides,
superoxide radical was proven as the decisive active species for the degradation of
gaseous acetaldehyde. This work provides a systematic approach to develop a
potential multi-functional pearlescent pigment to purify indoor air.
Keywords: Photocatalytic composite pearlescent pigment; Mica-titania pigment;
Gaseous acetaldehyde; Fe
2
3
O .
1
. Introduction
Volatile organic compounds (VOCs) are regarded as the primary source of
indoor air pollution [1-3]. The VOCs i.e., acetaldehyde, is released by the building
materials, which can cause throat irritation, shortness of breath, eye irritation, and
chest tightness [4-6]. Therefore, many air pollutants removal technologies have been
developed [7-9]. The photocatalytic oxidation is regarded as a promising way for
indoor air purification [10, 11]. However, the degradation and CO
2
mineralization
efficiency of semiconductor photocatalyst, such as TiO , have been limited by its poor
2
light harvesting and fast recombination of the photoinduced hole-electron pairs [12].
The constructing of heterojunction with cocatalysts is an effective way to overcome
these issues, such as TiO
Fe is a good cocatalyst due to its availability, chemical stability, and low
bandgap energy (2.2 eV), which has been proved to enhance the visible light
performance of TiO [15-18]. Lin et al. synthesized heterostructured TiO @α-Fe
2
/ZnO and TiO
2
/Fe
2
O
3
[13, 14].
2
O
3
2
2
2
O
3

core–shell nanoparticles, which had good photocatalytic dyes degradation
performance. The band matching of TiO and Fe promotes the migration and
separation of photogenerated electron and hole pairs, thereby improving the
photocatalytic activity [19]. Banisharif et al. synthesized Fe -doped TiO
2
2
O
3
O
2 3
2
photocatalyst by ultrasonic-assisted co-precipitation method and studied the
photocatalytic performance for the photodegradation of trichloroethylene in the air
[
20]. Zhao et al. prepared a TiO
deposition method. The TiO modified by Fe
photocurrent values than those of unmodified TiO
2
/Fe
2
O
3
nanocomposite film by a chemical bath
2
2
O
3
show higher photopotential and
3
+
2
. The optimal Fe is beneficial to
reduce the recombination of photogenerated electrons and holes, also the one-
dimensional nanostructure can enhance the transfer and transport of charge carriers
[21]. Moniz et al. synthesized novel Fe
2
O
3
-TiO nanocomposite by photo-deposition
2
method. Compared with P25, the composite shows better photocatalytic activity for
the complete mineralization of the toxic 2,4-D herbicide. The heterojunction of
Fe
2
O
3
-TiO
2
is confirmed to enhance the separation of photogenerated charge carriers
/Fe heterojunction can
[22]. These results suggest that the construction of TiO
2
2
O
3
obviously improve the photocatalytic activity. In addition, the reflection effect has
proved to be a promising method to increase light harvesting [23]. Mica, a
stoichiometric formula KAl
potential cocatalyst.
2
(AlSi
3
O
10)(OH) , has high reflectivity, which is a good
2
In view of the relationship between structure fabrication and photocatalytic
activity of photocatalyst, we develop a mica/TiO /Fe photocatalytic composite
2
2
O
3

pearlescent pigment (MTF) to photodegrade flowing gaseous acetaldehyde. The
ternary composite is anticipated to improve the light harvesting, charge separation,
and photodegradation efficiency. A sol-gel assisted hydrothermal method was used to
synthesize MTF composite pearlescent pigments. In contrast to pure TiO
demonstrate the obviously increased photodegradation of gaseous acetaldehyde
efficiency and CO mineralization activity. The optical characterizations i.e.,
2
, MTF
2
UV/visible, PL, and photocurrent studies suggest a synergistic effect in the ternary
composite frameworks. The color property of MTF was characterized by the
International Commission on Illumination (CIE) 1976 L*a*b* colorimetry. This work
provides a facile approach to develop stable and efficient ternary photocatalytic
composite pearlescent pigment, which can be exploited to develop a potential
functional pigment for indoor air purification.
2
2
. Experimental
.1. Materials and Reagents
The mica was purchased from Hangzhou Forward Fine Chemicals Co., Ltd,
China. The acetaldehyde gas was purchased from Shanghai Weichuang Standard Gas
Analytical Technology Co., Ltd. Tetrabutyl titanate and ferric chloride were purchased
from Aladdin Industrial Corporation. All other chemicals and solvents were purchased
from Shanghai Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and used
without further purification.
2
.2. Synthesis
A sol-gel assisted hydrothermal method was used to prepare MTF photocatalytic

composite pearlescent pigments. In a typical procedure, absolute ethanol (20 mL),
tetrabutyl titanate (5 mL), and mica (3.9 g) were mixed by continuous stirring at room
temperature (designated as solution A). Similarly, absolute ethanol (19 mL),
concentrated nitric acid (0.1 mL), anhydrous ferric chloride (36 mg) and deionized
water (1 mL) were mixed to form a solution (B). The solution B was slowly dropped
into solution A, which were stirring to form a gel. The as-prepared gel was dried and
homogenously dispersed in 70 mL deionized water by sonication. The suspension was
then transferred into a Teflon-lined autoclave (100 mL) and maintained at 180 °C for
6
h. The final product was collected by centrifugation (6000 rpm) and washed three
times with absolute ethanol and distilled water, which was named as MTF-1.5
Fe2O3 : mTiO2 = 1.5 : 100 = 1.5 wt%). For comparison, the different mass amounts of
FeCl , such as 12 mg, 24 mg, 36 mg, 48 mg, were added to solution B to prepare
MTF-x (mFe2O3 : mTiO2 : mmica= 0.5-2 : 100: 300) composites. Pure Fe was prepared
as the same procedure without mica and tetrabutyl titanate. The mica-titania (MT)
pearlescent pigment was prepared as the same procedure without FeCl
.3. Characterization
The phase development was studied using X-ray diffraction (XRD, BRUKER
(
m
3
2
O
3
3
.
2
AXS GMBH, German) with a Cu Kα radiation source (λꢀ=ꢀ0.154 nm). The surface,
cross-sectional morphology and element mapping scan of composites were
characterized by a Field Emission Scanning Electron Microscope (Magellan 400 FEI)
at 10 kV operating voltage. The Brunauer–Emmett–Teller specific surface area (SBET
)
were investigated by a Micromeritics ASAP 3000 nitrogen adsorption apparatus. All

the composites were degassed at 300 °C for 12 h and then subjected to nitrogen
adsorption measurements. Raman spectra were collected by DXR Raman Microscope
(
Thermo Fisher Scientific) using an excitation wavelength of 532ꢀnm laser at 7ꢀmW
laser power. X-ray photoelectron spectroscopy (XPS) were carried out by a Microlab
10F Scanning Auger Microprobe (VG SCIENTIFIC Ltd). The Perkin–Elmer
3
Lambda 950 spectrometer was applied to record UV–visible spectra of the samples
ranging from 300 to 600ꢀnm. The photoluminescence spectra (PL, Perkin–Elmer
Luminescence spectrometer 55) of all the samples were acquired with an exciting
wavelength of 320ꢀnm. Electron spin resonance (ESR) signals of active radicals were
recorded on a JES-FA200 spectrometer and trapped by 5,5-dimethyl-1-pyrroline N-
oxide (DOJINDO Lab.: >99%) (DMPO). The photocurrent studies were carried out
by a CHI660D electrochemical workstation using a conventional three-electrode cell
configuration, which includes as a Pt counter electrode, Ag/AgCl as a reference
electrode, and FTO coated with samples as a working electrode. The colorimetric
values were evaluated in terms of the Commission Internationale de l’Eclairage (CIE)
1
976 L*a*b* colorimetric method by a Color-Eye automatic differential colorimeter
(XTS).
2
.4. Evaluation of photocatalytic activity
The photodegradation of acetaldehyde was carried out in an automated real-time
gas-flow system coupled with a gas chromatograph (GC-7920). A 120 mL cuboid
quartz vessel was used as the reaction chamber, which can be directly illuminated by
the light source (400 W xenon lamp). The concentration change of gas acetaldehyde

was recorded every 10 minutes. 0.1 g MTF-x (x = 0.5-2) composites for the
photocatalytic reaction was dispersed in 2 mL ethanol, which were uniformly coated
and dried on a glass plate (15 cm × 7.5 cm × 3 mm). The gas acetaldehyde was
diluted one time by compressed air to stabilize the concentration at 500 ppm at 8 sccm
flow rate. Initially, the adsorption-desorption equilibrium was achieved in the dark.
Then, the samples were irradiated and the gas acetaldehyde concentration was
monitored. The removal rate (η) of acetaldehyde was calculated by equation: η =
퐶
(
1 − ) × 1ꢀꢀ%. Where C
0
is the initial concentration, and C is the acetaldehyde
was calculated by
O) in denoted
ꢂ
푖푛
퐶
0
concentration at different times under irradiation. The yield of CO
2
ꢁ
퐶푂2ꢂ표푢푡ꢃꢁ퐶푂 ꢂ
2 푖푛
equation: 푌퐶푂2
=
. Where (CO
2
)
in and (CO
2
)
out, (C
2
H
4
ꢄ 퐶 퐻 푂
ꢁ
2
4
the inlet and outlet concentrations of CO
2
and C
2
4
H O, respectively.
3
3
. Results and Discussion
.1. Phase structure and morphology
Fig. 1 shows the XRD analysis of pure TiO
2
, Fe
2
O , MT, and MTF-x (x = 0.5-2)
3
composites. The characteristic peaks for potassium mica are observed at 2θꢀ=ꢀ17.62°,
2
6.55°, 35.65°, and 45.03°, while the peak at 25.30° corresponds to anatase TiO
2
. The
, whose
contain in the MTF-x (x =
was successfully introduced
o
diffraction peak at 2θ = 33.15 is attributed to (104) crystal plane of α-Fe
O
2 3
intensity increases with the successive increasing of Fe
.5-2) composites [24]. These results indicated that Fe
to MT.
2
O
3
0
2
O
3

Figure 1. (a, b) XRD patterns of pure TiO
2
, Fe
2
3
O , MT and MTF-x (x = 0.5-2)
composites.
The characteristic Raman modes of TiO
2
were observed at 144, 197, 399, 519,
and 639 cm as shown in Fig. 2, which correspond to Eg(1), B1g(1), A1g + B1g(2), and
g(2) of anatase TiO and consistent with its XRD results.
-
1
E
2
Figure 2. Raman spectra of TiO
The FESEM and EDS results of MTF-1.5 composite are illustrated in Fig. 3. The
surface micrographs of pure TiO indicated their average particle size below 30 nm in
2
, MT and MTF-x (x = 0.5-2) composites.
2
Fig. 3a. As shown in Fig. 3b and 3c, the MTF-1.5 composite demonstrated an
irregular flat morphology with dozens of micron particle size and uniformly covered
by nanoparticles. The cross-section morphology of MTF-1.5 composite is presented in

Fig. 3d, whose inner layer is mica with about 300 nm thickness. And the outer layer
of MTF-1.5 is uniform and its thickness is 54±3 nm. To further confirm the presence
of TiO
2
/Fe
2
3
O heterojunction, the element mapping profile of MTF-1.5 composite has
been tested. As shown in Fig. 3e–g, Ti and Fe atoms are uniformly distributed on the
surface of mica. And the content of Fe atom is lower than that of Ti atom.
Figure 3. SEM images of (a) pure TiO
2
and (b-c) MTF-1.5 composite, (d) cross-
section SEM image of MTF-1.5 composite; EDS elemental mapping profiles of MTF-
1
1
.5 composite: (e) Ti-Fe overplay; (f) Ti atoms (purple); (g) Fe atoms (gold).
The HRTEM images were used to reveal the TiO /Fe heterojunction of MTF-
.5 composite (Fig. 4). As shown in Fig. 4b, the d-spacing is 0.35 nm corresponding
2
2
O
3

to the (1 0 1) plane of cubic TiO
plane of Fe . Therefore, TiO /Fe
surface of mica.
2
and the spacing is 0.25 nm belonging to the (1 1 0)
O
2 3
2
O
2 3
with heterostructure uniformly coat on the
Figure 4. (a, b) HRTEM images of MTF-1.5 composite.
The XPS study was used to analyze the chemical composition and elemental
chemical state of the MTF-1.5 composite (Fig. 5). The full range survey XPS
spectrum of MT and MTF-1.5 composite are presented in Fig. 5a. The presence of Fe
element in MTF-1.5 composite has been proved. In the case of Fe 2p (Fig. 5b), two
peaks at 708.93 and 726.01 eV were fitted, which is attributed to Fe 2p3/2 and Fe 2p1/2
respectively. The energy difference between Fe 2p3/2 and Fe 2p1/2 is 17.09 eV,
,
indicating the presence of -Fe
2
3
O in MTF-1.5 composite [25]. For O 1s (Fig. 5c), the
two peaks at 530 and 531.69 eV are attributed to Ti-O and O-H in MTF-1.5
composite. However, the binding energy of O–H bond in MTF-1.5 composite is
higher than that of TiO
the Ti–O–Fe bond [26]. As shown in Fig. 5d, the typical peaks of Ti 2p1/2 and Ti
p3/2 in MT appeared at 464.4 eV and 458.8 eV. These binding energy peaks of
2
, which may provide an indirect evidence for the formation of
2
MTF-1.5 composite were detected at 464.6 eV and 458.8 eV. The energy difference
of Ti 2p1/2 and Ti 2p3/2 peaks in MT and MTF-1.5 composite were 5.6 eV and 5.8

eV, respectively. It is concluded that the energy difference of Ti 2p increase due to the
formation of Ti-O-Fe bond in MTF-1.5 composite [27].
Figure 5. XPS spectra of MT and MTF-1.5 composite: (a) survey spectrum, (b) Fe
2
p, (c) O 1s and (d) Ti 2p.
The MT pearlescent pigment is composed of TiO deposited on mica sheets,
2
which also shows good optical properties. CIE colorimetric analysis was used to
characterize the optical properties of the composites. As can be seen from the data
listed in Table 1, MTF-x (x = 0.5-2) composite pearlescent pigments show light red
color effect (1.29 < a* < 1.65, 4.12 < b* < 4.42). Compared with MT pigment, the L*
(brightness) of the MTF-x (x = 0.5-2) composite pearlescent pigments slightly
increase, and ΔE* also increases with the increasing concentration of Fe . It is
O
2 3

worth noting that the higher L* value of MTF-x (x = 0.5-2) composite pearlescent
pigments maybe imply superior light harvesting to enhance its photocatalytic
performance.
Table 1. The color coordinates of MT and MTF-x (x = 0.5-2) composite pearlescent
pigments.
Samples
Color coordinates
L*
a*
b*
ΔE*
-
MT
57.82
59.74
58.64
59.32
-0.71
1.29
1.28
1.37
1.65
-0.74
4.12
4.24
4.46
MTF-0.5
MTF-1
MTF-1.5
5.56
5.42
5.80
5.46
MTF-2
60.37
4.72
∗
∗ ꢄ
∗ ꢄ
∗ ꢄ
∗
∗
∗
∗
∗
∗
△
E = √ꢁ△ 퐿 ꢂ + ꢁ△ 푎 ꢂ + ꢁ△ 푏 ꢂ , where ΔL , Δa and Δb are the changes of L , a , and b
respectively.
Figure 6. The optical images of (a) MT, (b) MTF-0.5, (c) MTF-1, (d) MTF-1.5, (e)
MTF-2 composites.
3
.2. Photocatalytic activity measurement
The photocatalytic performance of pure TiO , MT and MTF-x (x = 0.5-2)
2
composites are shown in Fig. 7. The photodegradation efficiency of pure TiO
2
is 45%
(
Fig. 7a) and 250 ppm of CO were released at the same time (Fig. 7c). According to
2
ꢁ
퐶푂2ꢂ표푢푡ꢃꢁ퐶푂 ꢂ
2 푖푛
the equation (푌퐶푂2
=
), the CO
2
mineralization efficiency of pure TiO
2
ꢄ 퐶 퐻 푂
ꢁ
ꢂ
푖푛
2
4
is 25%. The photodegradation efficiency of MT increase to 57% and CO
2

mineralization efficiency is 33% (red line). The MTF-1.5 composite (purple line) has
the highest photodegradation efficiency (80%), which is 1.8 times higher than that of
pure TiO
55%) is 2.2 times higher than that of pure TiO
Thus, it can be inferred that the photocatalytic performance of MT can be
significantly enhanced by TiO /Fe heterojunction. A cyclic test of MTF-1.5
composite is further used to study the stability for practical device applications (Fig.
d). The test was performed in two weeks in successive five cycles. The results show
2
and 1.4 times higher than that of MT. And its CO
2
mineralization efficiency
(
2
and 1.8 times higher than that of MT.
2
2
O
3
7
that the MTF-1.5 composite can maintain high photocatalytic stability after the fifth
cycle, ensuring its long-term use.
Figure 7. (a, b) Photocatalytic degradation of flowing gaseous acetaldehyde
(
500ꢀppm, 8ꢀsccm) under 400 W Xenon lamp irradiation; (c) Time profiles of CO
2

concentration of the composites; (d) Cyclic experiments with MTF-1.5 composite.
3
3
.3. Mechanism studies of photocatalytic degradation
.3.1. Optical properties
The optical properties of pure TiO
investigated by UV-visible spectroscopy (Fig. 8). As shown in Fig. 8a, the absorbance
of MT is higher than that of pure TiO ranging from 300 to 600 nm due to the
reflection of mica core. Besides, the absorbance of MTF-x (x = 0.5-2) composite
increase with the increasing content of Fe . Compared with MT, the absorption
2
, MT and MTF-x (x = 0.5-2) composites were
2
2
O
3
band edges of MTF-x (x = 0.5-2) composites demonstrate a red-shift, which extends
light absorption in the visible region. This behavior can be associated with the narrow
energy band of Fe
structures [28]. The bandgap energy of composite was calculated using equation of
αhνꢂꢅ/ꢆ = 퐴ꢁhν − E ꢂ, where α is the absorption coefficient, A is the parameter that
2
O
3
and enhanced optical scattering in the ternary composite
ꢁ
푔
is related to the effective mass associated with the valence and conduction bands, hν
is the absorbed energy and E is the bandgap energy (Fig. 8b). The value of the index
indicates the nature of the electronic transition, either directly or indirectly: the value
of n is 0.5 for direct and 2 for indirect bandgap materials [29]. The E value of MT
3.1ꢀeV) is lower than that of TiO (3.2ꢀeV), which is due to the inter-band electronic
transitions from TiO to mica [30]. The E value of MTF-1.5 composite is 3.0ꢀeV. The
XPS valence band spectra of TiO and Fe have been presented in Figure 8c. The
valence band (VB) of a TiO is 2.91 eV and the conductive band (CB) is -0.29 eV.
While VB of Fe is 2.48 eV and CB is 0.24 eV, respectively.
g
g
(
2
2
g
2
2
O
3
2
2
O
3

Figure 8. (a) UV–vis absorption spectra of pure TiO
composites; (b) The graph of the converted Kubelka-Munk function of light energy;
c) The XPS valence band spectra of TiO and Fe
.3.2. The pollutant adsorption
The corresponding specific surface area (SBET) of composites were employed to
2
, MT and MTF-x (x = 0.5-2)
(
2
2
3
O .
3
estimate the relationship between the adsorption ability of gas and photocatalytic
performance. The bigger specific surface area (SBET) value correspond to the larger
number of adsorbed gas molecules of composites [31]. As shown in Table 2, the SBET
2
value of MTF-x (x = 0.5-2) composites ranging from 41.6 to 44.9 m /g are smaller
2
2
than those of pure TiO
2
(81.3 m /g) and MT (47.1 m /g). It could be assumed that the
introducing of micro flake mica and Fe
2
O
3
is negative for increasing pollutant

adsorption. The temperature programmed desorption (TPD) results of pure TiO
2
,
mica, MT and MTF-1.5 composite are shown in Fig. 9. The peak located at 100-
2
00 °C is related to weak binding for physical absorption of acetaldehyde and the
o
peak located at 300-500 C is ascribed to strong chemical adsorption. The higher TPD
intensity represented stronger adsorptive capacity. As presented in Fig. 9, the order of
gas acetaldehyde physical adsorption is TiO
order of chemical adsorption is TiO ≈MTF-1.5＞MT＞mica. And the quantity of
chemically adsorbed acetaldehyde of the four samples are all stronger than that of
2
＞MTF-1.5≈MT＞mica. While, the
2
physically adsorbed. In contrast to pure TiO
2
, the desorption temperature of MT and
o
o
MTF-1.5 composite both increase from 350 C to 450 C, which indicate the
enhancing of chemical absorbability by introducing mica and Fe
2
3
O . Hence, the
chemical absorbability of photocatalyst could ultimately enhance the photocatalytic
activity [32].
Table 2. The specific surface area of the as-prepared samples calculated by BET
method.
Sample
TiO
2
MT
MTF-0.5 MTF-1
41.6 44.9
MTF-1.5 MTF-2
43.7 43.6
2
S
BET(m /g) 81.3
47.1

Figure 9. TPD spectra of acetaldehyde of pure TiO , mica, MT and MTF-1.5
2
composite.
3
.3.3. Photogenerated electron hole separation
The PL spectroscopy was used to investigate the separation efficiency of charge
carriers in semiconductor [33, 34]. The lower PL intensity represents less
recombination. The emission intensity of MTF-x (x = 0.5-2) composites are much
lower than that of pure TiO
2
(Fig. 10a), which indicates that the TiO
2
/Fe
2
O
3
heterojunction effectively inhibits the recombination of photogenerated charge
carriers. The photocurrent test was used to characterize the generation and separation
of photogenerated electron-hole pairs (Fig. 10b). Compared to MT, MTF-x (x = 0.5-
2
) composites exhibit higher photocurrent density, which means that more
-
+
photoinduced e and h pairs generation and separation were in MTF-x (x = 0.5-2)
composites. It is positive for the increasing of photocatalytic performance [35].
Figure 10. (a) PL spectra and (b) Photo-current response of MT and MTF-x (x = 0.5-
2
) composites.

3
.3.4. The role of radicals
The electron spin resonance (ESR) test was employed to study the role of
superoxide radicals (∙O
2
-) and hydroxide (∙OH) in Fig. 11 [36]. The stronger intensity
-
of radicals presents more radical produced. The intensity order of ∙O
2
and ∙OH are
both MTF-1.5＞MTF-2＞MTF-1＞MTF-0.5＞MT＞pure TiO
2
, which suggests that
the TiO
2
/Fe O
2 3
heterojunction and mica could promote the production of reactive
–
radicals. Also, the intensity of ·O
2
of all samples are higher than that of ·OH.
-
Therefore, it is anticipated that ∙O
2
plays a leading role in the photodegradation of
acetaldehyde of this work.
–
Figure 11. (a) ·O
2
and (b)·OH detection of pure TiO , MT and MTF-x (x = 0.5-2)
2
composites.
The scavenger experiment of MTF-1.5 composite was performed to further
-
-
verify the role of ·O
2
and ·OH [37, 38]. The ·O scavenger is p-benzoquinone (PBQ)
2
and ·OH scavenger is 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). The more
photocatalytic performance decreased, the more important of corresponding radicals
played. As shown in Fig. 12, the photodegradation efficiency of MTF-1.5 composite
sharply decreased from 80% to 60% with PBQ or 42% with TEMPO, when

-
-
photo-·O
2
or ·OH are captured, respectively. Thus, it can be inferred that ·O are
2
more active in acetaldehyde degradation in contrast to ·OH, which is consistent with
the results of ESR.
-
Figure 12. Scavenger experiments using PBQ and TEMO as corresponding ·O
2
and ·OH quenching.
3
.4. Mechanism of enhanced photocatalytic activity
Based on the results, we propose a possible mechanism for the enhanced
photocatalytic performance of MTF ternary composite. As illustrated in Fig. 13, when
TiO contacts Fe to obtain an equalized Fermi level by heterojunction, the
electrons flow from Fe to TiO . There is a positive region adjacent to TiO
heterojunction. While, the holes flow from TiO to Fe , resulting in the formation
of a negative region adjacent to Fe in the heterojunction. Thus, an internal electric
field is constructed between TiO and Fe [39, 40]. The electrons accumulated in
the CB of TiO will react with O
-, while the accumulated holes in the VB
of Fe will react with H
2
2
O
3
2
O
3
2
2
in the
2
2
O
3
O
2 3
2
2
O
3
2
2
to form ·O
2
–
2
O
3
2
O and OH to form ·OH. The adsorbed acetaldehyde was
oxidized on the surface of the photocatalyst. In addition, mica serving as reflection
core can further improve the light harvesting of TiO /Fe shell layer. Therefore, the
2
2
O
3

synergy of mica, TiO
2
and Fe
2
3
O greatly enhances the ternary composite
photocatalytic performance without decreasing its pearlescent effect.
Figure 13. Schematic diagram of the ternary structure of MTF composite.
4
. Conclusion
In this work, a novel MTF-x photocatalytic composite pearlescent pigment was
successfully synthesized by a sol-gel assisted hydrothermal method. The crystal
structure, morphology, and optical properties of the product materials were studied.
The UV-visible results show that the light utilization efficiency can be improved by
introducing the mica core into the ternary composite. Compared with TiO
MTF-x (x = 0.5-2) composite pearlescent pigments exhibited an enhanced
photocatalytic performance. The MTF-1.5 composite demonstrated the highest
photodegradation efficiency for acetaldehyde (80%) and CO mineralization
efficiency (55%) in this work. •O - play a key role in the acetaldehyde photocatalytic
degradation. Also, the photoinduced hole-electron pairs separation can be promoted
by the TiO /Fe heterojunction. This work provides a facile route to develop a
stable and efficient photocatalytic composite pearlescent pigment for acetaldehyde
2
and MT,
2
2
2
2
O
3

degradation, which exhibits a high degradation and conversion efficiency. The MTF
composite pearlescent pigments can also be expected to degrade other VOCs for the
indoor air purification as the functional decorative additive in the finish paint.
Author Statement
We confirm that the manuscript has been read and approved by all named authors and
that there are no other persons who satisfied the criteria for authorship but are not
listed. We further confirm that the order of authors listed in the manuscript has been
approved by all of us.
We confirm that we have given due consideration to the protection of intellectual
property associated with this work and that there are no impediments to publication,
including the timing of publication, with respect to intellectual property. In so doing
we confirm that we have followed the regulations of our institutions concerning
intellectual property.
We understand that the Corresponding Author is the sole contact for the Editorial
process (including Editorial Manager and direct communications with the office). She
is responsible for communicating with the other authors about progress, submissions
of revisions and final approval of proofs. We confirm that we have provided a current,
correct email address which is accessible by the Corresponding Author and which has
been configured to accept email from wangyan@mail.sic.ac.cn.
Signed by all authors as follows: Xiangming Fang, Guanhong Lu, Asad Mahmood,
Zhihong Tang, Ziwei Liu, Linlin Zhang, Yan Wang, Jing Sun
th
Apr. 24 , 2020
Declaration of interests
The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.

Acknowledgment
This work was financially supported by the National Key Research and
Development Program of China (2016YFA0203000), National Natural Science
Foundation of China (Grant No. 51702347) and Shanghai Municipal Committee of
Science and Technology Research Project (Grant No. 19DZ1205102 and
1
8142201700).

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