Engineering Nanoparticulate Organic Photocatalysts via a Scalable Flash Nanoprecipitation Process for Efficient Hydrogen Production

Article abstract of DOI:10.1002/anie.202104233

Directly converting sunlight into hydrogen fuels using particulate photocatalysts represents a sustainable route for clean energy supply. Organic semiconductors have emerged as attractive candidates but always suffer from optical and exciton recombination losses with large exciton “dead zone” inside the bulk material, severely limiting the catalytic performance. Herein, we demonstrate a facile strategy that combines a scalable flash nanoprecipitation (FNP) method with hydrophilic soluble polymers (PC-PEG5 and PS-PEG5) to prepare highly efficient nanosized photocatalysts without using surfactants. Significantly, a 70-fold enhancement of hydrogen evolution rate (HER) is achieved for nanosized PC-PEG5, and the FNP-processed PS-PEG5 shows a peak HER rate of up to 37.2 mmol h^?1 g^?1 under full-spectrum sunlight irradiation, which is among the highest results for polymer photocatalysts. A scaling-up production of nanocatalyst is demonstrated with the continuously operational FNP.

Full text of DOI:10.1002/anie.202104233

A Journal of the Gesellschaft Deutscher Chemiker
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International Edition Chemie
www.angewandte.org
Accepted Article
Title: Engineering Nanoparticulate Organic Photocatalysts via a
Scalable Flash Nanoprecipitation Process for Efficient Hydrogen
Production
Authors: Miaojie Yu, Weiwei Zhang, Zhiqian Guo, Yongzhen Wu, and
Weihong Zhu
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202104233
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Angewandte Chemie International Edition
10.1002/anie.202104233
RESEARCH ARTICLE
Engineering Nanoparticulate Organic Photocatalysts via a
Scalable Flash Nanoprecipitation Process for Efficient Hydrogen
Production
‡
‡
Miaojie Yu, Weiwei Zhang, Zhiqian Guo, Yongzhen Wu,* and Weihong Zhu*
[*]
M. Yu, Dr. W. Zhang, Prof. Z. Guo, Prof. Y. Wu, Prof. W. Zhu
Key Laboratory for Advanced Material, Joint International Research Laboratory of Precision Chemistry and Molecular Engineering, Feringa Nobel Prize
Scientist Joint Research Center, Shanghai Key Laboratory of Functional Materials Chemistry, Institute of Fine Chemicals, Frontiers Science Center for
Materiobiology and Dynamic Chemistry, School of Chemistry and Molecular Engineering
East China University of Science & Technology
Shanghai 200237, P. R. China
E-mail: whzhu@ecust.edu.cn; wu.yongzhen@ecust.edu.cn
[‡]
These authors are contributed equally
Supporting information for this article is given via a link at the end of the document.
Abstract: Directly converting sunlight into hydrogen fuels using
particulate photocatalysts represents a sustainable route for clean
energy supply. Organic semiconductors have emerged as attractive
candidates but always suffer from optical and exciton recombination
losses with large exciton “dead zone” inside the bulk material,
severely limiting the catalytic performance. Herein, we demonstrate a
facile strategy that combines a scalable flash nanoprecipitation (FNP)
method with hydrophilic soluble polymers (PC-PEG5 and PS-PEG5)
to prepare highly efficient nanosized photocatalysts without using
water-dominated working system. However, due to the use of
large aromatic building blocks, they are far less polar than
inorganic counterparts, which results in bulky particles in water
with size ranging from microns to millimeters (Figure 1a).[8-9] It is
known that the length scale that light can penetrate organic
photocatalysts is only tens to hundreds of nanometers because of
their high molar extinction coefficient. The bulky particle size can
thus cause apparent optical losses. In addition, due to the limited
photo-generated exciton diffusion length (about 10 nm), many
excitons inside the bulk materials (μm scale) can hardly transport
to the surface of catalyst, leading to the formation of large exciton
“dead zone”.[10] Recently, several groups have independently
revealed that decreasing the particle size of organic
surfactants. Significantly,
a 70-fold enhancement of hydrogen
evolution rate (HER) is achieved for nanosized PC-PEG5, and the
FNP-processed PS-PEG5 shows a peak HER rate of up to 37.2 mmol
-
1
-1
h
g
under full-spectrum sunlight irradiation, which is among the
highest results for polymer photocatalysts. Moreover, a scaling-up
production of nanocatalyst is demonstrated with the continuously
operational FNP, which provides an unprecedented strategy toward
practical applications of particulate photocatalysts for sustainable
energy production.
photocatalysts into a few to tens of nanometers could remarkably
enhance their photocatalytic performance.[
11]
In essence,
nanosized photocatalysts are more dispersible compared to bulk
materials, thus not only enhancing light-harvesting but also
facilitating exciton interception and dissociation at particle
surface.[
8,
11]
The methods for acquiring organic nano-
photocatalysts include physical exfoliation of two-dimensional
crystalline materials (such as g-C
3
[13]
N
4
and CMPs),[12] template-
emulsion polymerization
Introduction
synthesis (g-C
3
N
4
nanorods),
[
14]
(
insoluble CMPs and LCPs) and nanoprecipitation of polymer
Converting sunlight into hydrogen fuel using particulate
photocatalysts represents a facile and low-cost route for clean
and sustainable energy supply.[1] Traditional photocatalysts are
inorganic semiconductors with good solar-to-hydrogen efficiency
while tuning their properties is challenging.[2] Recently, organic
semiconductors have emerged as promising candidates for solar
driven water splitting because of their diverse chemical structures
and highly tunable optoelectronic properties.[3] The widely studied
organic photocatalysts include families of materials known as
[15]
dots (Pdots, soluble LCPs).
The design of water-soluble
polymer and polyelectrolyte is also effective in attaining
nanosized particles.[16] However, these strategies either lack a
fine-control over particle size/morphology or rely on additional
insulate surfactants, and nearly all these methods confront the
difficulty of large-scale production, which criticaly obstructs their
practical implements.
Synthetic modularity of organic semiconductors endows
them with possibility of solution process. Generally, insoluble
photocatalysts have their microstructure “fixed in” during
synthesis, while soluble materials offer chances for post-synthetic
modification. We here present a facile strategy that combines a
couple of rationally designed hydrophilic soluble polymers (PC-
3 4
N
),[4] linear conjugated polymers
graphitic carbon nitrides (g-C
LCPs),[5] conjugated microporous polymers (CMPs),[6] and
(
[7]
covalent organic frameworks (COFs). In spite of numerous
efforts, the photocatalytic performance of organic semiconductors
is still far away from application. As most studies focus on
chemical structure engineering to modulate the absorption and
energy levels of semiconductors, another predominated factor,
the particle size of photocatalyst, was often overlooked.[8]
PEG5 and PS-PEG5) (Figure 1b) with
a scalable flash
In general, learning from inorganic semiconductors, organic
photocatalysts were usually dispersed by bath ultrasonication in
1
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Angewandte Chemie International Edition
10.1002/anie.202104233
RESEARCH ARTICLE
Figure 1. (a) Schematic illustration of photocatalysts processed by bath ultrasonication; (b) Schematic illustration of photocatalysts processed by FNP; (c)
Scanning electron microscope (SEM) image and digital photograph of bulky photocatalysts processed by bath ultrasonication (Ultra) showing micron-sized
aggregates; (d) Transmission electron microscope (TEM) image and digital photograph of colloid solutions prepared by FNP method comprising uniformly
distributed particles of tens of nanometers.
nanoprecipitation (FNP) technique to prepare nanoparticulate
organic photocatalysts. By using FNP technology that implements
a kinetical-control on particles formation, polymer photocatalysts
can be solution-processed into homogenous and stable colloidal
solutions comprising uniformly distributed particles with size of
tens-to-hundred nanometers. Compared to the bulky particles
suspension, a significant 70-fold improvement of hydrogen
evolution rate (HER) was realized for FNP processed PC-PEG5,
and PS-PEG5 even achieves a peak HER of 37.2 mmol h-1 g-1
under full-spectrum light irradiation. The continuous operation and
high reproducibility of FNP render this facile strategy with scale-
up potential for practical application.
tetrahydrofuran (THF) and chloroform, which facilitates further
solution-based processes.
The chemical structures of the as-prepared polymers were
characterized by elemental analysis, 1H NMR and Fourier
Transform Infrared (FT-IR) spectra. In FT-IR spectra, P9-s shows
two characteristic C-H stretching vibration peaks attributed to
-1
alkyl chains at 2800-3000 cm , whereas PC-PEG5 and PS-PEG5
exhibit weak signals for C-H vibration but new asymmetric
stretching vibration peaks attributed to C-O-C in the range of
-1
1000-1170 cm , confirming the presence of PEG side chains
(Figure S1). The molecular weights of PC-PEG5 and PS-PEG5
were estimated by gel permeation chromatography (GPC) and
the results are summarized in Table S1. All polymers exhibited
high thermal stability with a decomposition temperature ranging
2
from 350 to 400 °C under N atmosphere (Figure S2). The powder
X-ray diffraction (PXRD) measurement suggests these polymers
were amorphous in solid state (Figure S3).
The UV-vis absorption and emission spectra of the polymers
were studied in dichloromethane (Figure S4-S6). PC-PEG5
shows an absorption onset at 414 nm, with a slight red-shift
relative to that of P9-s (403 nm). When the DBTO group is
2
introduced, a significant red-shift (57 nm) is observed for PS-
PEG5 due to the enhanced electron-withdrawing property of
Results and Discussion
Grafting PEG side chains for hydrophilic soluble polymeric
photocatalysts
P9-s is a polymer photocatalyst which was firstly developed by
Cooper et. al.[17] The decorated long alkyl chains endow it with
soluble characteristic but meanwhile hydrophobicity. Here we
employed a molecular engineering to introduce a hydrophilic
penta-(ethylene glycol) (PEG) side chain and dibenzothiophene
2
DBTO group. The soluble characteristic of three polymers
2
sulfone (DBTO ) unit into the conjugated backbone, and design
allowed us to investigate their energy levels using cyclic
voltammetry analysis (Figure S7-S8). The highest occupied
molecular orbit (HOMO) levels of P9-s, PC-PEG5 and PS-PEG5
are similar (-5.73, -5.70 and -5.72 eV versus vacuum,
respectively), while the lowest unoccupied molecular orbital
two new polymers of PC-PEG5 and PS-PEG5, respectively. The
synthetic routes are shown in Scheme S1. All of these alternating
co-polymers were synthesized using Pd(0)-catalyzed Suzuki-
Miyaura polycondensation from hydrophobic alkyl or hydrophilic
PEG side chains functionalized carbazole monomers with
diboronic acid ester functionalized comonomers. The crude
products were purified with methanol and acetone, and the
soluble parts were collected using dichloromethane. We note that
these polymers are soluble in common organic solvents like
(
LUMO) levels of PS-PEG5 (-3.09 eV versus vacuum) is more
negative than that of P9-s and PC-PEG5 (-2.66 and -2.71 eV
versus vacuum), which can be attributed to the introduction of
strong electron-withdrawing DBTO unit. The measured LUMO
2
2
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Angewandte Chemie International Edition
10.1002/anie.202104233
RESEARCH ARTICLE
Figure 2. (a) Comparation of average size and poly dispersion index (PDI) of particles for samples processed by bath ultrasonication, traditional
nanoprecipitation and FNP; (b) Dynamic Light Scattering (DLS) results for initial PC-PEG5 nanoparticles and after 14 days (inserts are digital photographs of
samples processed by ultrasonication (Ultra) and FNP kept for 14 days); (c) Zeta potentials of P9-s and PC-PEG5 samples processed by bath ultrasonication
and FNP method at pH 7.4 (inserts are water contact angles of P9-s and PC-PEG5); (d) Cryo-transmission electron microscopy (Cryo-TEM) images of PC-
PEG5 nanoparticles prepared by FNP; (e) Atomic force microscopy (AFM) image of PC-PEG5 nanoparticles prepared by FNP (left image is a height map and
right image is an adhesion map).
levels for all as-prepared polymers are thermodynamically high
enough for proton reduction.
The hydrophilic properties of the three polymers were tested
by water contact angle measurement on their spin-coating films
polydisperse NPs are often generated, and extra filtration is
necessary to exclude the big aggregates, which causes
decreased throughput and unfavorable wastes.[20]
In contrast, FNP technique employs a multi-inlet vortex mixer
(MIVM) system where the organic solvent dramatically mixes with
antisolvent (water) in the range of milliseconds.[21] The τmix in FNP
process is shorter than the characteristic nucleation time of
polymers, and the growth of the NPs is thus a kinetically controlled
process, which could generate nanoparticles with uniform
dispersion and small particle size. Moreover, the particle size can
be modulated by changing the flow rates of different streams.
Here we have for the first time employed FNP technique to
prepare nanoparticulate photocatalysts. As seen from Figure 1d,
it produced a clear colloidal solution with the uniformly dispersed
spherical particles ranging from 40 to 100 nm. The average
particle size and poly dispersion index (PDI) of resulting
nanoparticles were 79.85 nm and 0.281, respectively, as
indicated by Dynamic Light Scattering (DLS) (Figure 2a). As a
contrast, traditional nanoprecipitation method was also performed
by directly injecting the THF solution of PC-PEG5 into water while
ultrasonication. The resulting solution is measured to have
broader size distribution (0.374) with a larger particle size (309.1
nm) relative to FNP (Figure 2a and S10). The stability of the FNP-
produced colloidal solution was evaluated by keeping PC-PEG5
solution unruffled for over 14 days. The solution was found to
remain clear with average particle diameter and size
polydispersity barely changed in DLS measurement (Figure 2b),
indicating that the PC-PEG5 nanoparticles can be stable in water.
When it comes to the alky chains based P9-s, FNP method
can generate a homogeneous dispersion as well. However, the
average particle size reaches 865.3 nm, distinctly larger than PEG
functionalized PC-PEG5 (Figure S11). After removing THF, the
particles gradually aggregated and finally settled out to be
(
Figure 2c and S9). Compared with P9-s (107.35°), the water
contact angles of PC-PEG5 (76.64°) and PS-PEG5 (74.63°) are
largely decreased, indicating that the substitution of alkyl side
chains by PEG side chains can dramatically improve the
hydrophilicity of conjugated polymers. Namely, better interfacial
wettability with water is realized for PEG functionalized polymer
catalysts.
Kinetically controlled production of stable nanoparticulate
colloid via FNP
So far, bath ultrasonication is the most widely used method to
disperse photocatalysts, where the bulky powder materials are
dispersed using fierce conditions for a proper working suspension.
We firstly dispersed the PC-PEG5 with bath ultrasonication, which
generated mixture with naked-eye visible particles, and the
particle sizes are in the range of micrometers (Figure 1c). These
bulky particles are found to quickly sunk to the bottom (Figure 2b),
and the suspension should be kept in stirring to prevent
unfavorable sedimentation during the photocatalytic reaction.[18]
To minimize the particle size of the photocatalyst, some
nanoprecipitation methods were previously reported for preparing
nano-sized catalysts. They were usually conducted by hand
injection of polymer solution into a large amount of water with
vigorous stirring or bath ultrasonication.[15] In this process, the
time scale of solvent mixing (τmix) is much longer than that of
hydrophobic portion nucleation (τN.G.) and hydrophilic portion
aggregation (τagg), resulting in a thermodynamically dictated
nanoparticles (NPs) formation.[19] As
a
consequence,
3
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Angewandte Chemie International Edition
10.1002/anie.202104233
RESEARCH ARTICLE
macroscopic bulk particles (Figure S12). The dispersion stability
was testified by Zeta potentials characterization. As shown in
Figure 2c, the Zeta potential of P9-s particles was -0.334 mV,
while that of the hydrophilic PC-PEG5 was much more negative
facilely produced by altering the velocity of streams and
concentration of polymer in THF. Detailed results are summarized
in Table S4 and Figure S16-S17. As shown in Figure 3a, for 62,
80, 92, and 122 nm-sized photocatalyst, the eventually total
amount of hydrogen generation is 228, 204, 199, 188 μmol in 5
hours operation, respectively. The photocatalytic activity is
increased along with the decrease of particle size. Herein, we
note that the HER variation for particle size changing in nanoscale
is much smaller than that for particle size changing from
micrometer to nanometer (from 0.35 to 25.3 mmol h-1 g ).
(
-31.0 mV), implying that PEG chains can provide electrostatic
stabilization for the nanoparticles. These remarkable differences
manifest that the side chains play a critical role in the formation
and stabilization of organic nanoparticles during FNP. We
consider that the hydrophilic side chains in PC-PEG5 tend to
surround the polymer backbone and closely contact with water,
which block the particle growth and thus result in small particle
size with long-term stability.
-1
(a) 250
(b)
PC-PEG5
PS-PEG5
FNP+Pt
FNP
The self-assembled morphology of nanoparticulate PC-
PEG5 was analyzed by cryo-transmission electron microscopy
1.0
.8
0.6
6
4
2
0
2
1
00
50
0
Ultra
(
cryo-TEM), which can image the samples in an environment that
PC-PEG5
FNP
Ultra
FNP-62 nm
FNP-79 nm
FNP-92 nm
FNP-122 nm
Ultra
is very close to native state.[22] As shown in Figure 2d, an apparent
double-layered sphere structure can be observed for the
nanoparticles, suggesting the different densities between outside
and inside, and this difference is probably related to exposed
hydrophilic PEG side chains on the surface of particles. Further
indicated by atomic force microscopy (AFM), the height map
exhibits that the outer region of the sphere has different height
with the central, and the adhesion mapping also shows
corresponding variation from the outer to central region (Figure
100
50
0
0.4
0.2
0.0
0
1
2
3
4
5
350
400
450
500
(c)
Time (h)
(d)
Wavelength (nm)
8
6
4
00
00
00
4000
3000
2000
1000
0
PS-PEG5
FNP+3t
FNP
FNP+3% Pt >420 nm
FNP >420 nm
Ultra
PS-PEG5-FNP+3wt.%Pt
PS-PEG5-Ultra
2e). The outer layers composed of hydrophilic PEG chains could
200
0
serve as a solvation layer to inhibit unfavorable aggregation of
particles by steric repulsion, thus contributing to the high colloidal
stability. Different from previous fabrication of polymer dots that
additional surfactants were required to prevent aggregation, we
directly prepared stable nanoparticulate organic catalysts via a
combination of molecular engineering with FNP technique.
0
1
2
3
4
5
0
5
10 15 20 25 30
Time (h)
Time (h)
Figure 3. (a) Time-dependent photocatalytic hydrogen evolution for PC-PEG5
nanoparticles with different sizes prepared by FNP and bath ultrasonication
(Ultra) under full-spectral illumination; (b) The absorption spectra (lines) and
AQYs (triangles, squares and diamonds) for PC-PEG5 and PS-PEG5 prepared
by bath ultrasonication and FNP at 365, 405, 420, 450 and 500 nm, respectively;
Enhanced photocatalytic performance of nanoparticulate
catalysts
(c) Time-dependent photocatalytic hydrogen evolution for PS-PEG5 prepared by
FNP and bath ultrasonication under full-spectral illumination; (d) Long-term
photocatalytic hydrogen evolution for PS-PEG5 prepared by bath ultrasonication
and FNP under full-spectral illumination.
Photocatalytic hydrogen production experiments were carried out
with ultrasonication and FNP-processed PC-PEG5 as
photocatalyst, ascorbic acid (AA) as sacrificial agents, and no
additional platinum was loaded as cocatalyst. As exhibited in
Figure 3a, 5 mg ultrasonic-dispersed PC-PEG5 generated 8.8
μmol H in 5 hours under full-spectral illumination, corresponding
2
to a hydrogen evolution rate (HER) of 0.35 mmol h-1 g-1. Under
the same catalytic conditions, remarkably, the FNP processed
To confirm the photocatalytic function with these designed
polymers, control experiments were conducted by removing
irradiation, polymer nanoparticles, or sacrificial agent,
respectively. As shown in Figure S18, no detectable amount of
hydrogen can be observed under these conditions. To exclude
the influence of slight THF residue (in FNP-processed solutions)
on photocatalysis, we also examined the mixture of THF/AA in
2
PC-PEG5 produced 204 μmol H , achieving an average HER of
.2 mmol h-1 g-1. An exceptional HER of 25.3 mmol h-1 g-1 was
2
water without PC-PEG5, and no H was produced for this system
8
under irradiation. All these results indicate that hydrogen
production is photocatalysis rather than the decomposition of
polymers, sacrificial agents, or the residual THF. After a 5 hours
course of continuous photocatalysis experiment, we recycled the
observed in the first hour, which is 72-fold higher than that of
ultrasonic-dispersed samples. The apparent quantum yield (AQY)
of PC-PEG5 nano-photocatalyst was estimated to be 5.3% at 365
nm (Figure 3b and Table S3), which is around 30 times higher
than bulky counterparts (0.18%). Several batches of PC-PEG5
nanoparticles were reproduced by FNP using the same
fabrication parameters, and there were negligible differences in
the average particle size and photocatalytic activity among
1
photocatalyst, and characterized it by UV-vis, H NMR spectra
and FTIR spectroscopy (Figure S19). No apparent change can be
observed compared to pristine material, indicating that the
photocatalyst is chemically stable under the working conditions.
Although PC-PEG5 nanoparticles can achieve
a
different batches (Figure S13-S14), demonstrating
a high
considerable HER under full-spectrum light irradiation, no
photocatalytic activity was observed for this polymer under visible
light. Considering that the UV region comprises only 5% of solar
energy,51 it is highly desirable to expand the absorption range. As
a demonstration, we have designed and synthesized another
repeatability of this effective method. We also tried
triethanolamine (TEOA) as the sacrificial agents and obseved
similar trend between FPN and ultrasonication-based samples
(
Figure S15).
Owing to the fine adjustability of the FNP technique, we
soluble polymer PS-PEG5 that bears
withdrawing unit DBTO , which exhibits a broadened absorption
spectrum (Figure S6). Owing to the solution-processable and
a strong electron-
further investigated the impact of particle sizes on the
photocatalytic activity which was rarely studied. PC-PEG5
nanoparticles with sizes ranging from 60 nm to 120 nm can be
2
4
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Angewandte Chemie International Edition
10.1002/anie.202104233
RESEARCH ARTICLE
intrinsically hydrophilic property, PS-PEG5 was also easily
processed into nanoparticles via FNP method without using
surfactants (Figure S20-S21). Remarkably, 5 mg PS-PEG5 nano-
photocatalyst produced 358 μmol hydrogen during 5 hours
operation under full-spectrum light illumination (Figure 3c),
achieving an average HER of 14.3 mmol h-1 g . Furthermore, the
HER in the first hour reaches 28.1 mmol h-1 g , around 32 times
higher than the ultrasonication based samples (0.87 mmol h-1 g-
generate bound electron-hole pairs (excitons).[11] As depicted in
Figure 4a, when dispersing polymers for same concentration, the
ultrasonically dispersed sample displays a transmittance larger
than 80% in the range of 300 to 450 nm, while less than 10% of
the light can pass through the FNP-processed solution. Namely,
minimizing the particle size from microscale to nanoscale can
significantly enhance the light-harvesting, which can be the
primary reason for the enhanced photocatalysis.
-1
-1
1)
.
We also processed the PS-PEG5 with traditional
Scanning transmission electron microscopy (STEM) imaging
with element analysis were employed to give insights into the
structures of Pt-loaded nano-photocatalysts. As shown in Figure
S25, a number of spherical nanosized particles with a diameter of
around 100 nm can be observed for FNP processed PS-PEG5,
while only bulky particle with size around 10 μm can be found for
ultrasonically dispersed P9-s in the same magnification. The
better dispersion with increased surface area is suposed to be
favorable for cocatalysts loading. On the surface of PS-PEG5
nanoparticles, the Pt cocatalysts were loaded with the sizes
ranging from 5 to 10 nm (bright light parts) which were verified by
element mapping (Figure 4b-4c). The distribution of Pt cocatalysts
is prone to overlap with the signal of element O, which could be
ascribed to the high affinity of oxygen-contained outside PEG
chains with metal Pt.[ Accordingly, PS-PEG5 with PEG chains
exposed at surface might bind more intimately with Pt compared
to alkyl-functionalized polymer, facilitating the charge transfer
from the polymers to the cocatalysts (discuss later).
nanoprecipitation method by directly injecting the THF solution of
polymer into water with ultrasonic bath. As indicated in DLS result
(
1
Figure S20), the resulted solution shows an apparent peak at
000 nm and much increased average particle size and PDI (1439
nm and 0.847), which is consistent with the variable-sized
particles observed in its TEM image (Figure S21). Moreover, the
traditional nanoprecipitation method prepared solution exhibits a
broad and week absorption peak similar to the solid, while the
absorption spectra of FNP sample approximate to the solution
(
Figure S22). Due to the polydisperse particles with larger
diameters, traditional nanoprecipitation method processed PS-
PEG5 shows poorer photocatalytic activity than FNP
a
counterpart, with an average HER of 4.1 mmol h g-1 in the five
hours operation (Figure S23). In view of the high colloidal stability
of FNP-processed PS-PEG5, we made an attempted to remove
the stirring in photocatalytic operation. Interestingly, there is no
deterioration of photocatalytic activity for the static solution with
respect to the stirring one (Figure S24). It is thus the FNP derived
nanoparticulate photocatalyst with uniform dispersion could
-1
24]
(a)
(b)
increase the opportunities for
a
more energy-efficient
1
00
photocatalytic hydrogen evolution system. With addition of 3 wt.%
Pt as cocatalysts, the average HER can be further improved to
FNP
Ultra
FNP
80
2
8.8 mmol h-1 g-1, and a remarkable rate of 37.2 mmol h-1 g-1 for
6
4
0
0
Pt
the initial hour (Figure 3c). This photocatalytic HER activity is
among the highest reported for polymer photocatalysts (Table S5).
particles
Under visible light irradiation (> 420 nm), a notable HER of 11.6
mmol h-1 g-1 was achieved.
20
0
Ultra
Nano-sized
organic photocatalyst
3
00
400
500
600
The AQYs of FNP prepared PS-PEG5 at 405, 420, 435 and
Wavelength (nm)
450 nm were estimated to be 2.20, 1.60, 1.32, and 0.83%,
(
c)
(d)
respectively, about 44, 53, 26 and 17 times higher than that of
ultrasonically dispersed sample, respectively (Figure 3b and
Table S3). With additional 3 wt.% Pt as cocatalyst, these AQYs
can be further increased to 2.92, 2.08, 2.31, and 1.31,
respectively. Previously, it was reported that nano-photocatalysts
often suffer from low stability, and many researches show
deactivation of catalytic reaction after only a few hours.[15a-e] Here,
the longer-term photocatalysis experiments for FNP processed
nano-catalysts were operated up to 30 hours under full-spectrum
light irradiation (Figure 3d). PS-PEG5 shows high stability with an
HER of last hour to be 18.1 mmol h-1 g-1, which is 35-fold higher
than that of the sample prepared by traditional bath
1
00
PS-PEG5-Ultra
PS-PEG5-FNP
IRF
10-1
1
1
1
0-2
0-3
0-4
0
20
40
60
80
Time (ns)
Figure 4. (a) Transmittance spectra of PS-PEG5 processed by bath
ultrasonication and FNP; (b) High-angle annular dark field-scanning
transmission electron microscopy (HAADF-STEM) image for PS-PEG5
nanoparticles prepared by FNP; (c) Element mapping for PS-PEG5
nanoparticles prepared by FNP (all scale bars in C are 50 nm); (d) Time-
resolved photoluminescence (TRPL) spectra for PS-PEG5 in water processed
by bath ultrasonication and FNP (excitation wavelength at 372 nm and
detected wavelength at 470 nm).
-1
-1
ultrasonication (0.52 mmol h g ). The enhanced stability for
FNP-produced nano-photocatalyst can be correlated with the high
colloidal stability of intrinsically hydrophilic polymer with well
dispersion.
The effect of particle size on the charge transfer process was
studied by time-resolved photoluminescence (TRPL) decay with
PS-PEG5 prepared by FNP and bath ultrasonication, respectively.
The decay traces are illustrated in Figure 4d, and the lifetimes
were obtained by fitting the resulting curves with a tri-exponential
model (Table S6). The average PL lifetimes (τ) were calculated to
Insights into the improved photocatalytic activity for FNP-
processed nano-catalysts
We then take insights into the improved photocatalytic
performances for FNP-processed nanoparticles. Light-harvesting
is one of predominated factors for photocatalytic reaction as the
semiconductor firstly absorbs photons with sufficient energy to
5
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Angewandte Chemie International Edition
10.1002/anie.202104233
RESEARCH ARTICLE
be 2.48 and 3.51 ns for FNP and ultrasonication prepared
samples, respectively. The shortening of PL lifetime associated
with the decrease of particle size can be attributed to the
enhanced exciton quenching, which mainly occurs at particle
surface by metal cocatalyst or surrounding water and sacrificial
S27-S28). These results indicate that FNP-produced organic
nanoparticulate photocatalysts is scalable without deterioration of
catalytic activity.
agent.[25] We here attribute the accelerated exciton quenching to Conclusion
both oxygen-contained PEG-chains that facilitate Pt cocatalyst
loading and the smaller size of photocatalyst where the photo-
generated excitons have much larger opportunities to reach the
surface-dominated reaction sites. To sum up, the significantly
improved photocatalytic performance for FNP-produced
nanoparticulate catalyst is ascribed to the following factors: i)
improved light harvesting; ii) facilitated cocatalyst loading as
active sites; iii) enhanced exciton dissociation.
Given the significant optical loss with large exciton “dead zone”
for bulk organic photocatalysts, we have for the first time
introduced an effective strategy combining a scalable flash
nanoprecipitation (FNP) method with hydrophilic soluble polymers
to prepare nanoparticulate organic photocatalysts with boosted
catalytic activity. The rational molecular design afforded two
hydrophilic copolymers (PC-PEG5 and PS-PEG5) that are
soluble in organic solvents and easy for solution-processing. By
using a kinetically controlled FNP method, the homogenous and
stable colloidal solutions comprising uniformly distributed
nanosized organic photocatalysts were successfully prepared
without using surfactants. Significantly, a 70-fold enhancement of
hydrogen evolution rate (HER) was realized for nanoparticulate
PC-PEG5, and PS-PEG5 even achieves a peak HER of 37.2
mmol h-1 g-1 under full-spectrum light irradiation, which is one of
the highest results for polymer photocatalysts. The significantly
improved photocatalytic performance for FNP-produced nano-
catalyst is well ascribed to the improved light-harvesting,
facilitated cocatalyst loading, and enhanced exciton dissociation.
Based on the continuously operational FNP, a preliminary
scaling-up production of photocatalytic solution has been
demonstrated which avoids the traditional disadvantages such as
the discontinuous production, batch to batch sensitivity, and
relatively low production yields, thus offering an attractive protocol
for massive production of nano-catalysts for practical implements.
We expect that the strategy can provide a new platform to
developing efficient nanoparticulate organic photocatalysts for
photocatalytic hydrogen evolution, overall water splitting, and
Scalable production of nanoparticulate photocatalysts with
high reproducibility
Some useful strategies have previously reported for preparing
nano-scaled organic photocatalysts with enhanced catalytic
activity, such as surfactants involved polymer dots (Pdots)
fabrication. However, the scalable production remains a great
challenge for these strategies due to the discontinuous production,
batch to batch sensitivity, and relatively low production yields.
One key advantage of the FNP technique is the continuous
operation, which can work as a promising route toward scalable
production of nano-photocatalysts. The arrangement of FNP
equipment is presented in Figure 5a. Water and polymer solution
are pushed into a multi-inlet vortex mixer (MIVM) through four inlet
streams and the resulting solution can be obtained immediately.
As a demonstration, we multiplied the solution volume from initial
25 mL to 100, 500, 1000 mL using continuous FNP processing on
PS-PEG5 (Figure 5b). DLS results indicate the particles sizes in
these solutions were almost identical (Figure 5c and Table S7),
suggesting a stable production with high reproducibility. When
randomly taking the same amount of solution (25 mL) from these
different batches for photocatalytic hydrogen evolution test, they
exhibited parallel photocatalytic activities (Figure 5d and Figure
other solar-to-chemical energy conversions such as CO
reduction.[
2
26]
(a)
(b)
multi-inlet
vortex mixer
Acknowledgements
Kinetic control
(B)
(MIVM)
This work was financially supported by NSFC/China for Science
Center Program (21788102), NSFC/China (21636002, 822504,
2
1905091),
China
Postdoctoral
Science
Foundation
and
Continuous
production
(No.2019M651418),
Shanghai Municipal
Science
Technology Major Project (2018SHZDZX03), Program of
Introducing Talents of Discipline to Universities (B16017).
(
c)
(d)
2
2
1
1
5
0
5
0
5
0
5
00
2
1
0
Full spectrum
>420 nm
2
1
5
5 mL
00 mL
00 mL
400
Keywords: organic photocatalysts
•
dispersion
•
flash
1000 mL
3
2
1
00
00
00
0
nanoprecipitation • hydrophilic polymers • hydrogen evolution
[
[
1]
2]
a) T. Hisatomi, K. Domen, Nat. Catal. 2019, 2, 387-399; b) Z. Wang, C.
Li, K. Domen, Chem. Soc. Rev. 2019, 48, 2109-2125.
1
10
100
1000
25 mL
100 mL500 mL10
00
mL
Size (d.nm)
Y. Wang, A. Vogel, M. Sachs, R. S. Sprick, L. Wilbraham, S. J. A. Moniz,
R. Godin, M. A. Zwijnenburg, J. R. Durrant, A. I. Cooper, J. Tang, Nat.
Energy 2019, 4, 746-760.
Figure 5. (a) Digital photograph of FNP instrument; (b) Digital photograph of 25,
00, 500 and 1000 mL solutions of PS-PEG5 nanoparticle prepared by FNP; (c)
1
[3]
C. Dai, B. Liu, Energy Environ. Sci. 2020, 13, 24-52.
DLS results and (d) amount of hydrogen evolved evolution and AQYs of 25 mL
solution randomly taken from the initial 25 mL and 100, 500, 1000 mL solutions
by continuous FNP operation on PS-PEG5.
[4]
a) D. J. Martin, K. Qiu, S. A. Shevlin, A. D. Handoko, X. Chen, Z. Guo, J.
Tang, Angew. Chem. Int. Ed. 2014, 53, 9240-9245; b) L. Lin, Z. Lin, J.
Zhang, X. Cai, W. Lin, Z. Yu, X. Wang, Nat. Catal. 2020, 3, 649–655; c)
6
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202104233
RESEARCH ARTICLE
X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson, K.
Domen, M. Antonietti, Nat. Mater. 2009, 8, 76-80; d) W. Jiang, H. Wang,
X. Zhang, Y. Zhu, Y. Xie, Sci. China Chem. 2018, 61, 1205-1213.
[16] a) C. Dai, M. Panahandeh-Fard, X. Gong, C. Xue, B. Liu, Solar RRL 2019,
3, 1800255; b) Z. Hu, X. Zhang, Q. Yin, X. Liu, X.-f. Jiang, Z. Chen, X.
Yang, F. Huang, Y. Cao, Nano Energy 2019, 60, 775-783.
[17] D. J. Woods, R. S. Sprick, C. L. Smith, A. J. Cowan, A. I. Cooper, Adv.
Energy Mater. 2017, 7, 1700479.
[
5]
a) R. S. Sprick, B. Bonillo, R. Clowes, P. Guiglion, N. J. Brownbill, B. J.
Slater, F. Blanc, M. A. Zwijnenburg, D. J. Adams, A. I. Cooper, Angew.
Chem. Int. Ed. 2016, 128, 1824-1828; b) X. Zhang, X. Wang, J. Xiao, S.
Wang, D. Huang, X. Ding, Y. Xiang, H. Chen, J. Catal. 2017, 350, 64-71;
c) Z. A. Lan, G. Zhang, X. Chen, Y. Zhang, K. A. I. Zhang, X. Wang,
Angew. Chem. Int. Ed. 2019, 58, 10236-10240. d) Y. Bai, D. J. Woods,
L. Wilbraham, C. M. Aitchison, M. A. Zwijnenburg, R. S. Sprick, A. I.
Cooper, J. Mater. Chem. A 2020, 8, 8700-8705. e) C. Han, P. Dong, H.
Tang, P. Zheng, C. Zhang, F. Wang, F. Huang, J. X. Jiang, Chem. Sci.
[18] M. Schwarze, D. Stellmach, M. Schroder, K. Kailasam, R. Reske, A.
Thomas, R. Schomacker, Phys. Chem. Chem. Phys. 2013, 15, 3466-
3472.
[19] a) M. Wang, N. Yang, Z. Guo, K. Gu, A. Shao, W. Zhu, Y. Xu, J. Wang,
R. K. Prud’homme, X. Guo, Ind. Eng. Chem. Res. 2015, 54, 4683-4688;
b) Y. Liu, C. Cheng, Y. Liu, R. K. Prud’homme, R. O. Fox, Chem. Eng.
Sci. 2008, 63, 2829-2842.
2
021, 12, 1796-1802
[20] H. Shen, S. Hong, R. K. Prud’homme, Y. Liu, J. Nanopart. Res. 2011, 13,
4109-4120.
[
6]
a) R. S. Sprick, J. X. Jiang, B. Bonillo, S. Ren, T. Ratvijitvech, P. Guiglion,
M. A. Zwijnenburg, D. J. Adams, A. I. Cooper, J. Am. Chem. Soc. 2015,
[21] M. Wang, Y. Xu, Y. Liu, K. Gu, J. Tan, P. Shi, D. Yang, Z. Guo, W. Zhu,
X. Guo, M. A. Cohen Stuart, ACS Appl. Mater. Interfaces 2018, 10,
25186-25193.
137, 3265-3270; b) L. Li, Z. Cai, Q. Wu, W. Y. Lo, N. Zhang, L. X. Chen,
L. Yu, J. Am. Chem. Soc. 2016, 138, 7681-7686; c) Z.-A. Lan, W. Ren,
X. Chen, Y. Zhang, X. Wang, Appl. Catal. B: Environ. 2019, 245, 596-
[22] J. Kosco, M. Bidwell, H. Cha, T. Martin, C. T. Howells, M. Sachs, D. H.
Anjum, S. Gonzalez Lopez, L. Zou, A. Wadsworth, W. Zhang, L. Zhang,
J. Tellam, R. Sougrat, F. Laquai, D. M. DeLongchamp, J. R. Durrant, I.
McCulloch, Nat. Mater. 2020, 19, 559–565.
603; d) X. Gao, C. Shu, C. Zhang, W. Ma, S. Ren, F. Wang, Y. Chen, J.
H. Zeng, J.-X. Jiang, J. Mater. Chem. A 2020, 8, 2404-2411; e) Y. Xu, C.
Zhang, P. Mu, N. Mao, X. Wang, Q. He, F. Wang, J. Jiang, Sci. China
Chem. 2017, 60, 1075-1083. f) A. M. Elewa, M. H. Elsayed, A. F. M. El-
Mahdy, C. L. Chang, L. Y. Ting, W. C. Lin, C. Y. Lu, H. H. Chou, Appl.
Catal. B-Environ. 2021, 285, 119802.
[23] T. Hisatomi, J. Kubota, K. Domen, Chem. Soc. Rev. 2014, 43, 7520-7535.
[24] Z. Hu, Z. Wang, X. Zhang, H. Tang, X. Liu, F. Huang, Y. Cao, iScience
2019, 13, 33-42.
[
7]
a) P. Pachfule, A. Acharjya, J. Roeser, T. Langenhahn, M. Schwarze, R.
Schomacker, A. Thomas, J. Schmidt, J. Am. Chem. Soc. 2018, 140,
[25] M. Sachs, H. Cha, J. Kosco, C. M. Aitchison, L. Francas, S. Corby, C. L.
Chiang, A. A. Wilson, R. Godin, A. Fahey-Williams, A. I. Cooper, R. S.
Sprick, I. McCulloch, J. R. Durrant, J. Am. Chem. Soc. 2020, 142, 14574-
14587.
1423-1427; b) W. Chen, L. Wang, D. Mo, F. He, Z. Wen, X. Wu, H. Xu,
L. Chen, Angew. Chem. Int. Ed. 2020, 59, 16902–16909; c) J. Wang, J.
Zhang, S. B. Peh, G. Liu, T. Kundu, J. Dong, Y. Ying, Y. Qian, D. Zhao,
Sci. China Chem. 2019, 63, 192-197; d) Q. Liao, W. Xu, X. Huang, C. Ke,
Q. Zhang, K. Xi, J. Xie, Sci. China Chem. 2020, 63, 707-714; e) X. Wang,
L. Chen, S. Y. Chong, M. A. Little, Y. Wu, W. H. Zhu, R. Clowes, Y. Yan,
M. A. Zwijnenburg, R. S. Sprick, A. I. Cooper, Nat. Chem. 2018, 10, 1180-
[26] Z. Fu, A. Vogel, M. A. Zwijnenburg, A. I. Cooper, R. S. Sprick, J. Mater.
Chem. A 2021, 9, 4291-4296.
1189.
[
[
8]
9]
C. M. Aitchison, R. S. Sprick, Nanoscale 2021, 13, 634-646.
a) D. J. Woods, S. A. J. Hillman, D. Pearce, L. Wilbraham, L. Q. Flagg,
W. Duffy, I. McCulloch, J. R. Durrant, A. A. Y. Guilbert, M. A. Zwijnenburg,
R. S. Sprick, J. Nelson, A. I. Cooper, Energy Environ. Sci. 2020, 13,
1843-1855; b) Y. Bai, Z. Hu, J. X. Jiang, F. Huang, Chem. Asian J. 2020,
15, 1780-1790.
[
10] O. V. Mikhnenko, P. W. M. Blom, T. Nguyen, Energy Environ. Sci. 2015,
, 1867-1888.
8
[
[
11] C. H. Dai, Y. T. Pan, B. Liu, Adv. Energy Mater. 2020, 10, 2002474.
12] a) L. Wang, Y. Wan, Y. Ding, S. Wu, Y. Zhang, X. Zhang, G. Zhang, Y.
Xiong, X. Wu, J. Yang, H. Xu, Adv. Mater. 2017, 29, 1702428; b) J.
Cheng, L. Liu, G. Liao, Z. Shen, Z. Tan, Y. Xing, X. Li, K. Yang, L. Chen,
S. Liu, J. Mater. Chem. A 2020, 8, 5890-5899; c) B. He, M. Feng, X. Chen,
J.
https://doi.org/10.1016/j.gee.2020.07.011; d) L. Dai, K. Huang, Y. Xia, Z.
Xu, Green Energy Environ. 2020,
https://doi.org/10.1016/j.gee.2020.09.015.
Sun,
Green
Energy
Environ.
2020,
[
[
[
13] X. Li, J. Zhang, X. Chen, A. Fischer, A. Thomas, M. Antonietti, X. Wang,
Chem. Mater. 2011, 23, 4344-4348.
14] Catherine M. Aitchison, R. S. Sprick, A. I. Cooper, J. Mater. Chem. A
2019, 7, 2490-2496.
15] a) L. Wang, R. Fernandez-Teran, L. Zhang, D. L. Fernandes, L. Tian, H.
Chen, H. Tian, Angew. Chem. Int. Ed. 2016, 55, 12306-12310; b) P. B.
Pati, G. Damas, L. Tian, D. L. A. Fernandes, L. Zhang, I. B. Pehlivan, T.
Edvinsson, C. M. Araujo, H. N. Tian, Energy Environ. Sci. 2017, 10,
1372-1376; c) P. J. Tseng, C. L. Chang, Y. H. Chan, L. Y. Ting, P. Y.
Chen, C. H. Liao, M. L. Tsai, H. H. Chou, ACS Catal. 2018, 8, 7766-7772;
d) A. Liu, C.-W. Tai, K. Holá, H. Tian, J. Mater. Chem. A 2019, 7, 4797-
4803. e) M. H. Elsayed, J. Jayakumar, M. Abdellah, T. H. Mansoure, K.
Zheng, A. M. Elewa, C. L. Chang, L. Y. Ting, W. C. Lin, H. H. Yu, W. H.
Wang, C. C. Chung, H. H. Chou, Appl. Catal. B-Environ. 2021, 283,
119659; f) A. Liu, L. Gedda, M. Axelsson, M. Pavliuk, K. Edwards, L.
Hammarstrom, H. Tian, J. Am. Chem. Soc. 2021, 143, 2875-2885.
7
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RESEARCH ARTICLE
Entry for the Table of Contents
This work presents a novel flash nanoprecipitation (FNP) method with rationally designed hydrophilic polymers to prepare
nanoparticulate photocatalysts, which is effective in addressing limitations of bulky particles and greatly improving the photocatalytic
activity. More importantly, this nanostructure engineering is promising for scale-up owing to the continuous operation of FNP, which
presents a vision for the future practical applications of solar-to-chemical energy conversions.
8
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