Photothermal-Assisted Triphase Photocatalysis Over a Multifunctional Bilayer Paper

Article abstract of DOI:10.1002/anie.202110336

Photocatalysis as one of the future environment technologies has been investigated for decades. Despite great efforts in catalyst engineering, the widely used powder dispersion and photoelectrode systems are still restricted by sluggish interfacial mass transfer and chemical processes. Here we develop a scalable bilayer paper from commercialized TiO₂ and carbon nanomaterials, self-supported at gas-liquid-solid interfaces for photothermal-assisted triphase photocatalysis. The photogeneration of reactive oxygen species can be facilitated through fast oxygen diffusion over triphase interfaces, while the interfacial photothermal effect promotes the following free radical reaction for advanced oxidation of phenol. Under full spectrum irradiation, the triphase system shows 13 times higher reaction rate than diphase controlled system, achieving 88.4 % mineralization of high concentration phenol within 90 min full spectrum irradiation. The bilayer paper also exhibits high stability over 40 times cycling experiments and sunlight driven feasibility, showing potentials for large scale photocatalytic applications by being further integrated into a triphase flow reactor.

Full text of DOI:10.1002/anie.202110336

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Accepted Article
Title: Photothermal-assisted triphase photocatalysis over a
multifunctional bilayer paper
Authors: Huining Huang, Run Shi, Xuerui Zhang, Jiaqing Zhao,
Chenliang Su, and Tierui Zhang
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202110336
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RESEARCH ARTICLE
Photothermal-assisted
triphase
photocatalysis
over
a
multifunctional bilayer paper
Huining Huang[a],[c], Run Shi* , Xuerui Zhang[a],[b], Jiaqing Zhao[a],[b], Chenliang Su and Tierui Zhang*
[a]
[c]
[a],[b]
[
a]
Dr. H. Huang, Dr. R. Shi, X. Zhang, J. Zhao, Prof. T. Zhang
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences,
Beijing 100190 (China)
E-mail: shirun@mail.ipc.ac.cn, tierui@mail.ipc.ac.cn
[
[
b]
c]
X. Zhang, J. Zhao, Prof. T. Zhang
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049 (China)
Dr. H. Huang, Prof. C. Su
International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology of Ministry of Education, Institute of Microscale
Optoelectronics, Shenzhen University, Shenzhen 518060 (China)
Supporting information for this article is given via a link at the end of the document.
Abstract: Photocatalysis as one of the future environment
technologies has been investigated for decades. Despite great efforts
in catalyst engineering, the widely used powder dispersion and
photoelectrode systems are still restricted by sluggish interfacial mass
transfer and chemical processes. Here we develop a scalable bilayer
huge step forward has been made in the development of gas-
liquid-solid triphase systems for high performance photo- and
electrocatalysis.[ The triphase systems show much higher
activity than diphase systems, owing to the fast supply of gas
reactants from gas phase instead of dissolved gas molecules from
liquid phase. For triphase photocatalytic ROS generation, the
promotion of full solar spectrum energy utilization will become
more important since the rate-determining step will shift from
interfacial oxygen diffusion to photon energy conversion
process.[ However, there are still challenges in achieving
photocatalysis directly driven by visible and near-infrared light,
which account for ~96% of the total solar energy.[7] Despite limited
5]
2
paper from commercialized TiO and carbon nanomaterials, self-
supported at gas-liquid-solid interfaces for photothermal-assisted
triphase photocatalysis. The photogeneration of reactive oxygen
species can be facilitated through fast oxygen diffusion over triphase
interfaces, while the interfacial photothermal effect promotes the
following free radical reaction for advanced oxidation of phenol. Under
full spectrum irradiation, the triphase system shows 13 times higher
reaction rate than diphase controlled system, achieving 88.4%
mineralization of high concentration phenol within 90 min full spectrum
irradiation. The bilayer paper also exhibits high stability over 40 times
cycling experiments and sunlight driven feasibility, showing potentials
for large scale photocatalytic applications by being further integrated
into a triphase flow reactor.
6]
2
light absorption property, wide bandgap titanium oxide (TiO ) is
still considered as one of the most applicable photocatalysts
owing to its low toxicity and proper band structure for the
generation of energetic electron-hole pairs.[8] Although some
newly developed photocatalysts with narrow bandgap can absorb
more light energies, they usually suffered from reduced excited
state energy of charge carriers and severe charge recombination.
Besides, the mineralization of high concentration aromatics
remains a huge task in currently available photocatalytic systems
due to the gap between the short lifetime of ROS and the slow
Introduction
kinetic process of multi-step free radical reactions involved in the
Industrialization triggered environmental issues have caused
serious threats to the global living things. The usage of toxic
oxidants, adsorbents and antibiotics to deal with waste water in a
large quantity have generated side effects including low efficiency,
reagent residue, secondary pollution and drug resistance,
motivating the development of sustainable ways for sewage
purification.[ Semiconductor-based photocatalytic advanced
oxidation process, as one of the most applicable photocatalytic
technologies investigated so far, has the advantages of low cost,
clean energy input and minimal secondary pollution.[2] Such
photocatalytic process involves the generation of reactive oxygen
species (ROS) from clean oxygen containing sources (oxygen
and water molecules), which has shown special advantages in the
mineralization of chemically stable organic pollutants (such as
phenol and other aromatic compounds) into inorganic carbons.[3]
Currently the overall photocatalytic performance in
photocatalytic reaction.[9]
2
In contrast to TiO -based photocatalytic materials,
photothermic materials (carbon, boron, noble metals, etc.)
intrinsically have the advantage in absorbing and converting low
energy photons into thermal energy. This photothermal effect has
been widely studied in fields of solar energy collection, water
desalination and cancer therapy.[10] Different from conventional
external heating to increase the temperature of the whole system,
local heating induced by the photothermal effect can effectively
accumulate on the surface of nanomaterials.[11] Therefore, we
1]
hypothesize that photon energy utilization and the following
kinetics of photocatalytic reactions can be simultaneously
promoted by incorporating proper photothermic materials into a
well-constructed
triphase
interface.
Besides,
reported
photocatalytic degradation often worked in discontinuous batched
systems with poor stability and scalability, it is of great
significance to construct a highly stable photothermal-assisted
triphase photocatalytic system with broad scalability (easy
recycling, flow reactor, sunlight irradiation, etc.) for potential
conventional
liquid-solid
diphase
systems
(dispersed
nanopowders, under water photoelectrodes, etc.) is still too low to
satisfy the requirement for commercialization, stimulating
[
4]
researchers to seek novel photocatalytic systems. Recently, a
1
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Angewandte Chemie International Edition
10.1002/anie.202110336
RESEARCH ARTICLE
applications.
schematically shown in Figure 1b, the paper self-supports on the
Herein, photocatalytic phenol oxidation was investigated as
a model reaction. A multifunctional bilayer paper consisted of
commercialized TiO and carbon nanomaterials (TiO /C) was
2 2
2
top of water body with TiO layer downward to form a gas-liquid-
solid three phase structure. Light was irradiated from the bottom
of triphase system. Oxygen can diffuse from gas phase to the
developed and self-supported at the air-water interface to form a
triphase system. We demonstrate that the fast oxygen supply and
photothermal effect over this system simultaneously promote the
photochemical ROS generation process, while the fast local
heating process (increased to 55 C from room temperature within
one minute) also improves the following free radical reaction
2
surface of TiO through the porous carbon layer, followed by the
photocatalytic generation of ROS. Phenol in liquid phase will then
be converted and mineralized into inorganic carbons through free
radical reactions.[12] It is known that the morphology and interfacial
wettability of catalyst layers play important roles in regulating
reactant mass transfer over triphase interfaces.[5d,13] Cross-
sectional scanning electron microscope (SEM) image (Figure 1c
and Figure S3) and energy dispersive X-ray spectrum (Figure 1d)
o
2
kinetics. The TiO /C triphase system therefore performs 13 times
higher degradation rate than that of corresponding diphase
system under full spectrum irradiation, showing a mineralization
ratio of 88.4% with an inorganic carbons selectivity of 93.6% in
high concentration phenol (100 ppm) with over 40 times (i.e. 60
h) cycling stability. This bilayer paper also exhibits high
photocatalytic activity under sunlight irradiation and can be
facilely incorporated into a flow reactor, further demonstrating its
potential for scale-up applications.
2
reveal that a TiO layer with thickness of 1.8 ± 0.3 μm was
immobilized onto the carbon layer. Besides, the bilayer paper is
designed to have Janus wettability. The carbon layer side shows
a hydrophobic surface with an apparent water contact angle of
o
147 (Figure 1e), in order to provide sufficient surface tension to
prevent the paper from sinking or being permeated by liquid
phase. On the contrary, the TiO
2
layer side is hydrophilic and
o
exhibits a water contact angle of 18 (Figure 1f). Combining with
abundant mesoporous structures (Figure S4 and Table S1), this
Janus wettability could allow the efficient mass transfer of oxygen
and water molecules from gas and liquid phases, respectively, to
2
the surface of TiO catalysts.
Figure 2. Photocatalytic activity evaluation of diphase and triphase
systems. a Pseudo-first-order kinetic curves of the photocatalytic phenol
reaction process over diphase and triphase systems. Inset in (a) schematically
shows the setup of the two photocatalytic systems. b Phenol mineralization ratio
and inorganic carbons selectivity under different light sources. c-d Time-
dependent temperature distribution diagram of diphase system (c) and triphase
system (d). e-f Schematic illustration of oxygen diffusion and photothermal
effect in diphase system (e) and triphase system (f). PC: photocatalysis. PT:
photothermal effect.
Figure 1. Structural characterization of the TiO
2
/C bilayer paper. a
Photograph of a TiO /C bilayer paper, size: 25 cm  25 cm. b Schematic
2
illustration for the photothermal-assisted triphase photocatalytic phenol
oxidation. c-d Cross-sectional SEM image (c) and EDS mapping (d) of the
TiO
2
/C bilayer paper, scale bar: 10 m. e-f Top-view SEM images of carbon
/C bilayer after TiO immobilization (f), scale bar: 200 nm.
layer (e) and TiO
2
2
Insets in (e-f) show photographs of water droplet on each layer structure.
Evaluation of photocatalytic phenol oxidation. Benzene
compounds, widely used as industrial raw materials, are one of
the main organic pollutants due to their strong toxicity and
chemical stability.[ Therefore, we chose concentrated phenol
aqueous solution (100 ppm) as a model for the photocatalytic
experiments. Experimental setup and details can be found in
Figure S5 and Methods. Full spectrum (300 < λ < 1000 nm, Figure
S6) and ultraviolet (UV, equipped with a λ < 400 nm filter) light
sources were used to evaluate the contribution of photothermal
effect in the phenol oxidation process. Before testing, an
Results and Discussion
14]
Characterization of the TiO
2
/C bilayer paper. In this study, TiO
2
(
P25, Degussa, Germany) solution was deposited onto porous
carbon layer (H14C9, Freudenberg, Germany) to form a TiO
2
/C
bilayer paper (Figure 1a, See Methods for experimental details).
The bilayer paper consists of closely packed TiO and carbon
nanoparticles with diameters of 30-50 nm (Figure S1 and S2). As
2
2
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
o
adsorption step was carried out in the dark for 30 min. Afterwards,
the concentration of phenol solution shows negligible change in
the absence of either catalyst or irradiation at 80 C,
only increased to 35 C. After 10 min of irradiation, the
o
o
temperature finally stabilized at 80 C and 40 C for triphase and
diphase systems, respectively (Figure S10). An obvious
temperature gradient was formed between the edge of catalyst
layer and surrounding liquid phase. Owing to high thermal
conductivity of carbon nanomaterials,[18] the temperature of the
catalyst layer (collected from the thermometer) can be
approximated to the temperature at triphase interfaces, indicating
a higher interfacial reaction temperature of triphase system
compared with nanopowder dispersed diphase system. In
diphase system, except the slow oxygen mass transfer issue, the
photothermal effect can be largely diluted by liquid phase through
the fast heat energy dissipation between dispersed carbon
nanoparticles and surrounding water media (Figure 2e). This
dissipation is energy-wasteful since the heating of bulk liquid
phase contributes little to the interfacial catalysis. In contrast, for
o
demonstrating that phenol cannot be self-degraded (Figure S7).
Time-dependent photocatalytic phenol oxidation over TiO
bilayer-based triphase system and TiO /C nanoparticle
dispersion-based diphase system were performed as shown in
Figure 2a and Figure S8, where C and C represent the
2
/C
2
0
concentration of phenol before and after irradiation, respectively.
Under full spectrum irradiation, the triphase system performs a
phenol conversion ratio of 94.4% after 90 min irradiation, showing
-
a pseudo-first-order kinetic reaction rate constant (k) of 2.98 × 10
2
-1
min , which is 13 times higher than that of the diphase system
Table S2).[
15]
(
The TiO
2
/C triphase system affords excellent
-based
phenol photodegradation efficiency amongst reported TiO
2
photocatalytic systems (Table S3). Besides, when the excitation
wavelength was switched from UV to full spectrum, the k of both
systems increased, in particular about 5 fold enhancement was
achieved in the triphase system. It is worth noting that phenol
oxidation is often accompanied by the formation of incompletely
oxidized side products such as hydroquinone and p-
benzoquinone, resulted in poor mineralization of phenol and
limited photocatalytic selectivity towards inorganic carbons.[16]
Hence, total organic carbon (TOC) tests were then carried out as
the results plotted in Figure 2b. Inorganic carbon selectivity (S) is
defined as follows:
TiO
energy mainly concentrates at the local area of carbon layer
Figure 2f), thus it can be more easily transferred to the adjacent
TiO nanoparticles and contributes to a significantly improved
2
/C bilayer-based triphase system, the photogenerated heat
(
2
triphase photocatalytic activity. The specific function of such
photothermal effect towards ROS generation and the following
phenol oxidation process requires additional investigations.
푀
푅
휌phenol,0 − 휌TOC
푆 =
=
(ꢀ)
휌phenol,0 − 휌phenol,1
Where M and R are the amounts of mineralized carbon and
reacted carbon, respectively. ρphenol,0 and ρphenol,1 refer to the mass
concentration of phenol carbon before and after irradiation,
respectively. ρTOC is the mass concentration of TOC after
irradiation. The diphase systems show phenol mineralization
ratios of only 7.3% and 11.5% under UV and full spectrum
irradiation, respectively, sharing similar inorganic carbons
selectivities of about 59%. For the UV triphase system, although
a slightly increased mineralization of 29.8% is achieved, the
selectivity towards inorganic carbons is still low (67.8%), means
that a large quantity of phenol is incompletely oxidized. In contrast,
the full spectrum triphase system exhibits the highest
mineralization ratio of 88.4%, showing a dramatically increased
2
inorganic carbon selectivity to 93.6%. Since TiO is a wide
bandgap semiconductor showing negligible photocatalytic activity
in visible and near infrared regions, above results indicate that
both the existence of triphase interface and the strong
photothermal effect of carbon nanoparticles play important roles
in enhancing the photocatalytic phenol reaction rate and
selectivity.[17]
In order to explore the photothermal effect over different interface
structures, the time and space-dependent temperature of the two
systems were detected using an infrared imaging camera (Figure
S9 and Movies 1 and 2). As shown in Figure 2c, during the initial
Figure 3. Photo and thermal contributions to the reaction. a EPR spectra of
ROS photogeneration under UV irradiation. b Phenol conversion ratio as a
function of UV intensity and reaction temperature over diphase and triphase
systems. c Photocatalytic phenol reaction rate as a function of UV intensity. The
-
dotted lines show the linear trend observed at intensities less than 60 mW cm
2
.
Only triphase system shows a super-linear relationship between reaction rate
1
min full spectrum irradiation, the temperature of the diphase
and light intensity at higher intensities. d Phenol reaction Arrhenius plots of the
two systems. The dotted lines show two liner regions observed in triphase
system. Error bars represent the standard deviation of three independent
experiments.
o
o
system only rose from 30 C to 37 C. Uniform temperature space
distribution was observed along L axis (perpendicular to the
direction of incident light) as the result of highly dispersed TiO
⊥
2
and carbon nanoparticles in liquid phase. On the contrary, the
triphase system can be quickly heated up under full spectrum
irradiation (Figure 2d). Since the detector was located on the top
of the triphase system, it can provide temperature space
distribution of the irradiated catalyst layer and the surrounding
liquid phase. During irradiation, the catalyst layer was heated from
The function of photothermal effect. Oxygen-containing free
radical capture experiment was performed. Hydroxyl radical (OH)
can effectively catalyze the ring opening reactions of phenol,
therefore it has been considered to be the main oxidant for phenol
oxidation.[19] Here, electron paramagnetic resonance (EPR)
o
o
3
0 C to 55 C within 1 min, while the temperature of liquid phase
3
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
spectra were recorded to characterize the concentration of OH
by using 5,5-dimethyl-1-pyrroline N oxide (DMPO) as a probe
wider absorption ranging from 200 to 2500 nm owing to the
existence of carbon nanoparticles. An inverted absorption peak at
blue light region is observed in both mixed layer and bilayer, which
(
see Methods for details). As shown in Figure 3a, after 20 s UV
irradiation, the signal intensity of OH in triphase system is much
higher than that in diphase system, demonstrating that more OH
radicals were produced in triphase system. Similar OH
generation enhancement was also observed under full spectrum
irradiation (Figure S11). It is reasonable since the rapid supply of
oxygen in a triphase system can promote its reaction with
2
can be ascribed to the reflection effect of TiO nanoparticles layer
(Figure S14).[24] The low energy photons absorbed by carbon
nanoparticles can be converted into heat energy, therefore all the
carbon-containing samples show strong photothermal effects
(
Figure S15).
photogenerated electrons and generate superoxide radicals (O
2
-),
which will then be quickly transformed into OH radicals in
aqueous media.[ While in the diphase system, the restricted
oxygen mass transfer process resulted in a relatively slower
generation of OH.
20]
The influence of photo and thermal effects on the phenol oxidation
reaction were separately investigated by controlled UV irradiation
with an external heating (see Methods for details). As shown in
Figure 3b, the increase of both UV intensity and reaction
temperature attribute to the improved photocatalytic activity.
Besides, triphase system shows higher phenol conversion ratio
compared with diphase system under the same condition (also
see Figure S12 and S13). The difference is not obvious at mild
conditions (low intensity or low temperature), but it can be
gradually enlarged when the UV intensity and reaction
temperature increase at the same time. Therefore, different
charge carriers transfer process and phenol conversion kinetics
might occur between the two systems at high UV intensity and
reaction
temperature.
For
external
thermal-assisted
Figure 4. Evaluation of different catalyst layer structures. a Schematic
illustration of the structure of the TiO layer, carbon layer, TiO /C mixed layer
and TiO /C bilayer. b Diffuse reflectance spectra of the four samples. c
Photocatalytic phenol conversion ratio of the four samples under UV and full
spectrum irradiation. d Photocatalytic cycling stability of TiO /C bilayer paper-
2
based triphase system.
o
photocatalytic tests over triphase system at 80 C, a linear regime
is found between phenol conversion rates and UV intensity below
2
2
2
-2
6
0 mW cm , indicating that energetic electrons mediate the
photocatalytic process (Figure 3c).[21] The transition to the super-
linear regime occurs by further increasing the light intensity. This
increased efficiency can be ascribed to the filling process of the
bulk trap sites in TiO
high, allowing the transfer of photogenerated charge carriers to
the surface of TiO
to be enhanced.[22] On the contrary, the super-
2
when the photo flux becomes sufficiently
Figure 4c shows the corresponding photocatalytic phenol
oxidation activity over these four samples. Owing to the poor
photothermal effect, the TiO layer exhibits similar catalytic
2
2
linear phenomenon is not observed over diphase system owing to
the slow oxygen diffusion process as the potential rate-
determining step. Then, a series of temperature-dependent
photocatalytic tests were carried out at a constant UV intensity of
activities under UV and full spectrum irradiation. Besides,
although the carbon layer has good photothermal effect, it has no
photocatalytic activity in the absence of TiO
For the TiO /C mixed layer, the phenol conversion ratio under full-
spectrum is about 2 times higher than that of under UV irradiation.
But its activity is still lower than the TiO layer mainly due to the
strong blocking effect of carbon nanoparticles, which greatly
hinders the light absorption of TiO in the mixed layer. By layering
2
as photocatalysts.
2
-2
1
20 mW cm . Figure 3d shows the Arrhenius plots of phenol
conversion rate over the two systems. Two linear branches are
observed in triphase system, corresponding to apparent
2
activation energies (E
and high reaction temperatures, respectively.[23] This high
temperature induced apparent E reduction cannot be observed
a
) of 22.8 kJ mol- and 12.2 kJ mol at low
1
-1
2
the TiO and carbon nanoparticles, the TiO /C bilayer shows the
2
2
highest photocatalytic performance under full spectrum irradiation,
since it takes full advantages of the photocatalytic activity of TiO
a
2
in the corresponding diphase system, strongly supporting that the
overall phenol photo-conversion kinetics can be improved by
integrating photothermal effect into a triphase photocatalytic
interface.
Structural regulation of catalyst layer. The composition and
combination mode of the photocatalytic layer structure in triphase
and the photothermal effect of the carbon layer at triphase
interfaces. The photostability of the triphase photocatalysis
system was further investigated. As presented in Figure 4d, under
-2
2
full spectrum illumination (1.2 W cm ), the TiO /C bilayer exhibits
no obvious decrease in activity after 40 test cycles (i.e. 60 h
irradiation in total), and the chemical state and morphological
structure of the catalyst layer were stable after cycling tests
system were then evaluated. Four typical structures, namely, TiO
layer, carbon layer, TiO /C mixed layer and TiO /C bilayer were
2
2
2
(
Figure S16, S17 and S18). The superb photoactivity and stability
selected as controlled samples (Figure 4a, see Methods for
preparation details). The absorption properties of the four
samples were firstly explored and the corresponding diffuse
of the triphase photocatalysis system make it very promising for
large scale applications.
2
reflection spectra are shown in Figure 4b. TiO layer only absorbs
UV light below 400 nm, while the other samples exhibit a much
4
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Angewandte Chemie International Edition
10.1002/anie.202110336
RESEARCH ARTICLE
-1
mL min , the photocatalytic rate gradually increased from 232 mg
-2
-1
-2 -1
m
h to 839 mg m h . This was accompanied by a decrease in
degradation ratio, but it can be offset through multiple cycling
operation. Meanwhile, the degradation performance of high
concentration phenol (100 ppm), bisphenol A (60 ppm) and
salicylic acid (100 ppm) were also explored using this flowing
triphase system, and the results were shown in Figure S23. All
organic species showed over 80% degradation ratios after 2-4
2
flow cycles, respectively. Therefore, TiO /C bilayer with integrated
photocatalytic and photothermal properties at triphase interfaces
shows valuable potentials in dealing with the flowing waste water
in real environment conditions.
Conclusion
In summary,
a
2
TiO /C bilayer paper comprised of
commercialized nanomaterials has been successfully prepared
and evaluated for photocatalytic phenol advanced oxidation. The
bilayer paper exhibits multifunctional properties including Janus
wettability, oxygen diffusion, photogeneration of charge carriers
Figure 5. Characterization of the flow triphase system. a Schematic diagram
of the flow triphase reactor. b Infrared imaging of TiO /C bilayer paper equipped
2
into the flow reactor at a flow rate of 0.5 mL min-1 (MB, 200 ppm) after 1 min full
2
and photothermal effect. The TiO /C bilayer paper-based triphase
system shows a photothermal-assisted photocatalytic phenol
mineralization ratio of 88.4%, of which the rate constant is
approximately 13 times higher compared with nanoparticles
dispersed diphase system. The triphase interface ensures the fast
supply of oxygen reactant and ROS generation at high photon flux,
whilst the photothermal induced local heating promotes the
following phenol free radical reaction kinetics. Discussions on
cycling stability, sunlight feasibility, oxygen concentration
compatibility and flow condition further demonstrate the possibility
of this novel triphase system for large-scale photocatalytic
applications.
spectrum irradiation, scale bar: 1 cm. c Absorption spectra of MB solutions
-
1
before and after two flow cycles at a flow rate of 0.5 mL min . Insets in (c) show
photographs of the initial MB solution and the colorless solution after two flow
cycles. d MB degradation ratio and reaction rate plotted against the liquid phase
flow rate.
Directly using sunlight and air as light and gas sources, which is
of great significance for large scale applications, still remains a
great challenge. Additionally, our results prove the advantage of
triphase photocatalytic system in catalysis recycling, but its
flowing feasibility for large scale applications still needs to be
explored. In our photothermal-assisted triphase photocatalytic
system, over 70% of the initial reaction rate was still maintained
when the gas phase oxygen concentration was reduced from 100
vol.% to 20 vol.% (Figure S19), which meets the requirement of
directly using air as oxygen source. Outdoor experiments were
conducted under reflected sunlight without light focusing (12:00-
Acknowledgements
The authors are grateful for financial support from the National
Key Projects for Fundamental Research and Development of
China (2018YFB1502002), the National Natural Science
Foundation of China (51825205, 51772305, 21902168), the
Beijing Natural Science Foundation (2191002), the Strategic
Priority Research Program of the Chinese Academy of Sciences
1
5:00, 2nd September 2020 in Beijing, China, see Figure S20 for
experiment setup). The result showed a phenol (100 ppm)
conversion ratio of 88.9% after 3 hours irradiation, verifying the
usability of the TiO
2
/C bilayer-based triphase system just in direct
sunlight condition.
Conventional diphase systems always face troubles in the recycle
of nanocatalysts from the liquid phase, making them almost
impossible to be applied in a continuous flow reactor for large-
(
(
XDB17000000), the Royal Society-Newton Advanced Fellowship
NA170422), the International Partnership Program of Chinese
scale waste water treatment (industrial waste water, polluted river, Academy of Sciences (GJHZ201974) and the Youth Innovation
etc.). Thus, it is of practical significance to evaluate the
photocatalytic activity of the as-prepared bilayer paper equipped
into a flow triphase system. As a proof-of-concept study, a flow
triphase reactor with an irradiation area of 3 cm × 3 cm was
developed as shown in Figure 5a and Figure S21. In order to
observe the experimental results more intuitively, blue methylene
blue (MB, 200 ppm) was employed as a model organic pollutant.
Infrared imaging plotted in Figure 5b reveals an obvious
temperature gradient from right side (liquid inlet) to left side (liquid
outlet). The highest surface temperature of the paper reached 70
Promotion Association of the CAS.
Keywords: photothermal • photocatalysis • triphase system •
multifunctional bilayer paper • large scale application
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o
C after 1 min irradiation, indicating an efficient photothermal
heating effect of the triphase local area. Photocatalytic
-1
degradation of MB at a flow rate of 0.5 mL min was performed
and as the results were shown in Figure 5c and Figure S22. The
flow triphase system affords degradation ratios of 69.7% and
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Entry for the Table of Contents
2
We develop a scalable TiO /C bilayer paper for photothermal-assisted photocatalytic phenol oxidation. The triphase interface ensures
the fast supply of oxygen reactant at high photon flux, whilst the photothermal effect promotes the following phenol free radical reaction
kinetics. Cycling stability, sunlight feasibility, oxygen concentration compatibility and flow condition further demonstrate the possibility
for large-scale photocatalytic applications.
7
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