Selective valorization of 5-hydroxymethylfurfural to 2,5-diformylfuran using atmospheric O2 and MAPBBr3 perovskite under visible light

Article abstract of DOI:10.1021/acscatal.0c04330

Selective production of value-added platform chemicals from renewable biomass feedstocks and their derivatives has attracted tremendous attention with high potential in addressing global problems of energy and sustainability. In this work, a lead-halide perovskite (MAPbBr₃, MA = methylammonium) is utilized as a photocatalyst for selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) using atmospheric O₂ upon visible-light irradiation. Under minimally optimized conditions, the photocatalytic conversion of HMF in acetonitrile solvent reaches 100% with a DFF selectivity of over 90%, achieving an overall furanic carbon yield of over 96%. A detailed catalytic mechanism was proposed based on various spectroscopic and experimental results, revealing that the atmospheric O₂, photogenerated electrons (e^?), holes (h⁺), ^?O₂^?, and ¹O₂ species together play crucial roles in the effective and selective photo-oxidation of HMF to DFF. In addition, our present photocatalytic system is also applicable for photo-oxidation of benzyl alcohol with approximately 100% conversion and benzaldehyde selectivity, providing insights for future exploration of the present catalytic system.

Full text of DOI:10.1021/acscatal.0c04330

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Research Article
Selective Valorization of 5‑Hydroxymethylfurfural to 2,5-
Diformylfuran Using Atmospheric O2 and MAPbBr3 Perovskite under
Visible Light
Mo Zhang, Zheng Li, Xing Xin, Junhao Zhang, Yeqin Feng, and Hongjin Lv*
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ABSTRACT: Selective production of value-added platform chemicals from
renewable biomass feedstocks and their derivatives has attracted tremendous
attention with high potential in addressing global problems of energy and
sustainability. In this work, a lead-halide perovskite (MAPbBr3, MA =
methylammonium) is utilized as a photocatalyst for selective oxidation of 5-
hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) using atmospheric O2
upon visible-light irradiation. Under minimally optimized conditions, the
photocatalytic conversion of HMF in acetonitrile solvent reaches 100% with a
DFF selectivity of over 90%, achieving an overall furanic carbon yield of over 96%.
A detailed catalytic mechanism was proposed based on various spectroscopic and
experimental results, revealing that the atmospheric O2, photogenerated electrons
•
1
(e−), holes (h+), O2−, and O2 species together play crucial roles in the effective
and selective photo-oxidation of HMF to DFF. In addition, our present photocatalytic system is also applicable for photo-oxidation
of benzyl alcohol with approximately 100% conversion and benzaldehyde selectivity, providing insights for future exploration of the
present catalytic system.
KEYWORDS: lead-halide perovskite, heterogeneous photocatalysis, atmospheric O2, 5-hydroxymethylfurfural, selective oxidation,
visible-light irradiation
transformations of organic compounds due to the advantages of
cost-effectiveness and sustainability, consistent with the concept
of green chemistry and sustainable development.16−18 To date,
there are several reports on photocatalytic oxidation of HMF to
DFF and FDCA8,19,20 using different semiconductor photo-
catalysts; however, low yields or selectivity was usually
achieved.21−30 In this regard, the exploration of efficient and
selective oxidation of HMF to target products under mild
photocatalytic conditions still remains substantially challenging
and attracting.
As a rising star among various semiconductor materials,
organic−inorganic halide perovskites (MAPbX3; MA =
CH3NH+3, X = Br− or I−) have been attracting tremendous
attention and widely investigated due to their outstanding
photovoltaic and optoelectronic properties,31−34 including
strong and broad photon absorption efficiency and excellent
charge transport ability.35,36 Compared to their wide application
INTRODUCTION
■
As important renewable carbon feedstocks, biomass has recently
attracted tremendous attention as one of the potential
alternatives to petroleum resources to generate sustainable
fuels and value-added fine chemicals. The effective trans-
formation and utilization of biomass or biomass-derived
intermediates could play a crucial role in solving energy,
ecological, and environmental problems.1−5 The biomass-
derived chemical 5-hydroxymethylfurfural (HMF), widely
produced via the dehydration of C6 carbohydrates, is considered
as a versatile platform compound with high industrial
potential.6,7 As shown in Scheme 1, HMF could be oxidized
to various furanic products. Among them, 2,5-furandicarboxylic
acid (FDCA) and 2,5-diformylfuran (DFF) are regarded as most
valuable starting reagents for furan-based polyesters, pharma-
ceutical intermediates, antibacterial agents, and furanic poly-
Schiff bases.8
Under thermal catalytic conditions, many works have been
recently reported on HMF oxidation by various catalysts,
including homogeneous manganese and cobalt salts,9 poly-
oxometalates,10 and supported noble metals like Au, Pt, and
Pd.11−15 However, most of these catalytic systems require high
temperature, and/or high O2 pressure, or the addition of a noble
metal cocatalyst. In contrast, photocatalysis driven by light and
O2 has attracted enormous attention in promoting oxidative
Received: October 6, 2020
Revised: November 17, 2020
https://dx.doi.org/10.1021/acscatal.0c04330
© XXXX American Chemical Society
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Scheme 1. Schematic Illustration of Various Oxidation Products from HMF
in solar cells,35 the use of perovskite-based photocatalysts for
light-driven catalytic organic transformations has achieved
significant advances only in recent few years,37−42 such as
benzylic alcohol oxidation,43 C(sp3)−H bond activation,44 C−
C bond cleavage, and hydrocarbons oxidation.45 However, to
our knowledge, there is no report on the photocatalytic selective
oxidation of HMF by a perovskite-based photocatalyst.
Herein, we report the use of MAPbBr3 perovskite as a
photocatalyst for visible-light-driven selective oxidation of HMF
to DFF with atmospheric O2 as an oxidant under mild and base-
free conditions. Specifically, under minimally optimized
conditions, the photocatalytic conversion of HMF reaches
100% with a DFF selectivity of over 90% after 10 h irradiation by
a 450 nm blue light-emitting diode (LED) light in acetonitrile
solvent, which to our knowledge belongs to one of the high
values among literature reports on photocatalytic oxidation of
HMF to DFF using semiconductor-based photocatalysts.
Moreover, our present photocatalytic system can also be
extended to selective photo-oxidation of benzyl alcohol to
benzaldehyde with approximately 100% conversion and
selectivity.
possibility of using MAPbBr3 perovskite to photocatalyze
HMF oxidation.
The photocatalytic oxidation of HMF tests were performed
using MAPbBr3 perovskite as a photocatalyst and atmospheric
O2 as an oxidant in CH3CN at 15 °C under the irradiation of a
blue LED light (450 nm). The amount of MAPbBr3 photo-
catalyst used was first optimized in Figure S7, revealing that 40
mg of MAPbBr3 is sufficient to promote complete photo-
oxidation of HMF in 10 h. Figure 1a shows the high-
RESULTS AND DISCUSSION
■
Powders of MAPbBr3 perovskite were synthesized according to
a modified literature method as described in the Experimental
Section32 and systematically characterized by a series of
spectroscopic techniques, including scanning electron micros-
copy (SEM), UV−vis diffuse reflectance spectroscopy (UV−
vis−DRS), powder X-ray diffraction (PXRD), and photo-
luminescence spectroscopy (PL) (see the Supporting Informa-
tion for details, Figures S1−S5). SEM images reveal the smooth
surface of MAPbBr3 perovskite formed by small crystalline
particles (Figure S1). The UV−vis diffuse reflectance spectra
show a good visible-light absorption of MAPbBr3 perovskite
with an absorption edge at around 575 nm (Figure S2). Analysis
of the UV−vis spectra with the Kubelka−Munk plot yields an
estimated band gap of 2.15 eV for MAPbBr3 (Figure S3),
consistent with the literature report.46 PXRD profile confirms
good crystallinity and phase purity of MAPbBr3 perovskite
(Figure S5). Also, the presence of HMF substrate leads to
significant photoluminescence quenching of MAPbBr3 perov-
skite, indicating the efficient transportation of charge carriers
between them which would be beneficial for a good photo-
catalytic performance (Figure S4). Chopped-light chronoam-
perometric measurements in CH3CN solvent were performed to
investigate the charge separation property of MAPbBr3
perovskite upon visible-light irradiation (Figure S6). Obvious
photocurrent response was observed under 450 nm blue LED
light illumination. Addition of HMF substrate into the system
increased the photocurrent density, further revealing the
Figure 1. (a) HPLC traces of photocatalytic reaction solution over
reaction time and (b) the corresponding calculated HMF conversion
and product selectivity over time. Reaction conditions: 5 mM HMF, 40
mg of MAPbBr3 photocatalyst, 10 mL CH3CN, 15 °C, air, and a 450 nm
blue LED light.
performance liquid chromatography (HPLC) traces of various
species during photocatalytic reaction. It is clear that no product
is formed in the dark. After exposure to light, the HPLC signals
clearly show the decrease of HMF and rise of DFF over time,
suggesting the effective conversion of HMF to DFF. After
photocatalysis for 10 h, the HPLC traces of HMF disappeared,
while that of DFF increased to the maximum, indicating the
complete conversion of HMF. It is noted that a HPLC signal
belonging to MAPbBr3 perovskite appears during the photo-
catalytic reaction, which might be attributed to the slight
dissolution of the photocatalyst. To check whether the dissolved
MAPbBr3 photocatalyst had a significant contribution to the
photo-oxidation of HMF, we conducted a control experiment
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a
Table 1. Comparison of Literatures on Photocatalytic Oxidation of HMF to DFF
photocatalyst
MAPbBr3
CoPz/g-C3N4
Nb2O5-800
WO3/g-C3N4
P-ZnxCd1−xS
TMADT
reaction solution
MeCN
potassium biphthalate buffer
HMF (mM)
time (h)
conv. (%)
sel. (%)
yield (%)
refs
5.0
20
0.1
0.1
16
10
14
6
6
8
12
16.3
4
24
48
5
100
84
19.2
27.4
40
87.7
50
26
90 1.2
85
90.6
87.2
65
76.5
26
88
90 1.2
71.4
17.4
23.9
26
this work
19
BTF
21
22
23
24
25
26
27
28
MeCN/BTF (3/2)
water
MeCN/6 M HBr
water
water
water
DMF
water
MeCN/Mn(NO3)2
60
67.1
13
TiO2
0.5
0.5
16
10
0.5
25
MCN-TE-H2O2
Zn0.5Cd0.5S/1% MnO2
SGCN/Pt
TEO
CdS
22.9
46.6
38.4
33.4
99
46.6
38.4
47
100
99
71
29
30
48
99
99
a
Abbreviations: MeCN = acetonitrile, HMF = 5-hydroxymethylfurfural, DFF = 2,5-diformylfuran, CoPz = cobalt thioporphyrazine, BTF =
benzotrifluoride, TMADT = tetramethylammonium decatungstate, MCN-TE-H2O2 = a thermally etched polymeric carbon nitride-hydrogen
peroxide adduct, SGCN/Pt = mesoporous carbon nitride with 2.96 wt % Pt as the cocatalyst, and TEO = thermally etched polymeric carbon nitride
treated with H2O2.
containing the dissolved MAPbBr3 photocatalyst and the freshly
prepared HMF solution. After 10 h of photocatalysis under
otherwise identical conditions, only 0.97% conversion of HMF
was detected, excluding the significant contribution of the
dissolved MAPbBr3 to the overall photo-oxidation of HMF to
DFF. The calculated percentage of HMF conversion and DFF
selectivity is shown in Figure 1b. Similar to the HPLC traces, the
percentage of HMF conversion gradually increased over time. In
the meanwhile, the DFF selectivity reached approximately 100%
after first 2 h irradiation and then decreased slightly over time,
which is ascribed to the transformation of a small portion of DFF
to FFCA. After photocatalytic reaction for 10 h, HMF has been
completely oxidized with the selectivity of DFF and FFCA
reaching 90 1.2 and 6.5 0.3%, respectively, corresponding to
an apparent quantum efficiency (AQE) of 0.123%. Table 1
summarizes different photocatalytic systems for HMF oxidation
to DFF in the presence of various photocatalysts, including
unfunctionalized metal oxides, heterojunction semiconductors,
polymeric carbon nitride modified with precious metal or redox
mediators, and polyoxometalates. By comparing to these known
systems, our present photocatalytic system, in terms of both
HMF conversion and DFF selectivity, belongs to one of the high
values among literature reports. Also, it works under noble-
metal-free and base-free conditions simply using atmospheric O2
as an oxidant at ambient temperature, agreeing with the concept
of green chemistry.
Table 2. Catalytic Oxidation of HMF under Different
Conditions
a
light
HMF
DFF sel.
(%)
FFCA sel.
(%)
entry
1
catalyst
source
conv. (%)
MAPbBr3
LED
450 nm
100
90 1.2
6.5 0.3
2
3
MAPbBr3
MAPbBr3
dark
LED
365 nm
0
100
0
3.8
0
0
4
5
MAPbBr3
H2O2
Xe lamp
LED
450 nm
100
0
6.4
0
0
0
b
6
7
8
9
MAPbCl3
no
LED
100
100
0.05
0
0
0
365 nm
LED
365 nm
LED
450 nm
LED
450 nm
0
0
no
36.6
0
0
MAPbI3
0
c
10
MABr + PbBr2 LED
450 nm
MABr
60.41
49.82
0
41.82
30.83
0
25.26
15.36
0
c
11
LED
450 nm
LED
450 nm
c
12
PbBr2
a
Reaction conditions: 5 mM HMF, 40 mg of photocatalyst, 10 mL of
b
CH3CN, 15 °C, air, and 10 h. Reaction conditions: 5 mM HMF, 10
mM H2O2, 10 mL of CH3CN, 15 °C, air, and 10 h. Reaction
c
Then, a series of control experiments have been conducted to
better understand the photocatalytic system. As shown in Table
2, no oxidation product was generated in the dark (entry 2),
indicating the crucial role of visible-light irradiation. In the
absence of MAPbBr3 photocatalyst, only 0.05% of HMF has
been converted due to its self-decomposition under light,
yielding a DFF selectivity of 36.6% (entry 8). In addition,
different light sources have a significant effect on the photo-
oxidation and product distribution of HMF. While using a 365
nm LED and a Xe lamp as light sources, the DFF product was
obtained with a very low yield (entries 3 and 4) even at 100%
conversion of HMF, which is probably attributed to the self-
decomposition of HMF by UV light irradiation (entry 7). Such
hypothesis is confirmed by the self-decomposition curve of
HMF under a Xe lamp; a similar behavior is also observed while
using 365 nm LED light irradiation (Figure S8). In the
meanwhile, we also checked the performance of other similar
conditions: 5 mM HMF, same molar equivalent of MABr + PbBr2
(1:1), MABr, or PbBr2 as that of MAPbBr3, 10 mL of CH3CN, 15 °C,
air, and 10 h.
lead-halide perovskites with different anions; the experimental
results reveal that the replacement of MAPbBr3 with MAPbCl3
or MAPbI3 does not lead to the formation of any products
(entries 6 and 9) due to the self-decomposition of HMF under
365 nm LED light irradiation. In the case of using MAPbI3 as a
photocatalyst, it is observed that MAPbI3 perovskite decom-
poses under 450 nm LED light illumination, thereby resulting in
no conversion of HMF. To investigate the robustness of the
photocatalytic system, we have isolated and reused the
MAPbBr3 photocatalyst for new reactions. There is a slight
decrease in the catalytic performance after three successive
cycles (Figure 2), which could be ascribed to the loss of the
MAPbBr3 catalyst during isolation or the slight dissolution of the
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Then, various control experiments have been performed to
further investigate the photocatalytic mechanism by changing
the gas atmosphere (air, O2, or N2) or adding different
scavengers. No obvious difference in both photocatalytic
HMF oxidation and DFF selectivity was observed while running
the catalysis under air or pure O2 atmosphere; in contrast, HMF
could not be photo-oxidized under a N2 atmosphere, proving the
necessity of O2 for catalytic HMF oxidation (Table S1). To
identify the reactive oxygen species in our catalytic system, a
remarkable scavenger, 4-chloro-2-nitrophenol (CN),19 for
singlet oxygen (1O2) was added into the photocatalytic system.
The experimental results showed that the presence of CN
species dramatically decreased the percentage of HMF
Figure 2. Reusability tests using the isolated MAPbBr3 photocatalyst.
Reaction conditions: 5 mM HMF, 40 mg of MAPbBr3, 10 mL of
CH3CN, 15 °C, air, and a 450 nm blue LED light (the reaction time of
each cycle is 10 h). Legend: black bar, HMF conversion; red bar, DFF
yield.
1
conversion to 39.8% (Figure 4), indicating that O2 is very
catalyst in the solvent, consistent with the HPLC signal shown in
Figure 1a.
The isolated MAPbBr3 photocatalyst was further evaluated by
SEM, UV−vis DRS, and PXRD techniques; the results are in
agreement with that of pristine MAPbBr3 before photocatalysis
(Figures S1, S2, and S5), confirming the phase purity and
robustness of MAPbBr3 under photocatalytic conditions. As
suggested by an anonymous reviewer, we have conducted
additional control experiments using other potential catalysts
including physically mixed MABr + PbBr2, MABr, and PbBr2
under otherwise identical conditions. Experimental results show
that the use of MABr + PbBr2 or MABr as photocatalysts also
leads to certain photo-oxidation of the HMF substrate, but the
yield of DFF is very low compared to that of the MAPbBr3
photocatalyst (Table 2, entries 10 and 11). Notably, the system
using PbBr2 as a potential catalyst shows no catalytic activity
(Table 2, entry 12). All of these experimental results
demonstrate that MAPbBr3 represents a very promising
photocatalyst for the selective photo-oxidation of HMF to
DFF under our testing conditions (entry 1).
Figure 4. Effect of different scavengers, 4-chloro-2-nitrophenol (CN),
superoxide dismutase (SOD), HCOONa, K2S2O8, catalase (CAT), and
5 mM HMF, under the following conditions: 40 mg of MAPbBr3, 10
mL of CH3CN, 15 °C, air, 10 h, and a 450 nm blue LED light.
likely one of the reactive oxidants for the selective photo-
oxidation of HMF. To further confirm the formation of singlet
oxygen (1O2), we have also used NaN3 1as another singlet oxygen
scavenger; the addition of NaN3 as a O2 scavenger leads to a
decreased conversion of 50.3% with DFF selectivity of only
25.8%, strongly demonstrating the active role of singlet oxygen
(1O2) in the oxidation process (Figure S9). By adding K2S2O8
and superoxide dismutase (SOD) as an electron scavenger and
superoxide (•O2−) scavenger, the conversion significantly
decreased to 18.9 and 35.5%, respectively, demonstrating the
important role of photogenerated electrons in activating the
molecular oxygen to generate the reactive oxidant species •O2−
during the catalytic process. Meanwhile, addition of a hole
scavenger, sodium formate (HCOONa), to the catalytic system
also inhibited the HMF conversion to 42.1% (Figure 4),
revealing the active role of the photogenerated hole (h+)
species.47,48
To unveil the transformation process of HMF under
photocatalytic conditions, we have performed the in situ diffuse
reflectance infrared Fourier transform spectroscopy (DRIFTs)
measurements as shown in Figure 3. Upon 450 nm LED light
Furthermore, the reactive oxygen species (e.g., 1O2 and •O2−)
was spin-trapped by electron paramagnetic resonance (EPR)
measurements.49 When using 2,2,6,6-tetramethylpiperidine
(TMP) as a spin-trapping reagent, a characteristic 1:1:1 triplet
EPR signal (g = 2.0064) was detected (Figures 5a and S14),
which is assigned to the signal of TMP−1O2 produced through
Figure 3. DRIFTs spectra of HMF transformation during photo-
catalytic process.
1
the reaction of O2 and TMP under experimental conditions.
Moreover, the formation of superoxide •O2−, as another reactive
oxygen species, has also been confirmed using 5,5-dimethyl-1-
pyrroline N-oxide (DMPO) as a spin-trapping agent, leading to
the formation of a characteristic EPR signal of DMPO−•O2− (g =
2.0069) (Figures 5b and S14).50,51 Such EPR signals of either
TMP−1O2 or DMPO−•O−2 can also be detected under light
irradiation in the absence of HMF substrate (Figure S10),
further confirming the formation of both •O2− and 1O2 species by
the MAPbBr3 photocatalyst. It is noted that no characteristic
irradiation, the intensity of peaks at 3349, 875, and 750 cm−1
belonging to the vibrational modes of the hydroxyl (OH) group
in HMF decreased significantly, while the intensity of peak
signals at 1670 and 1534 cm−1 belonging to the vibrational
modes of the CO group continued to increase obviously,
indicating the effective conversion of HMF to DFF product
during the photocatalytic processes.
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Figure 5. EPR signals of the reaction solution in the dark (black line) and 450 nm LED light illumination (red line) in the presence of (a) TMP and (b)
DMPO as spin-trapping reagents under experimental conditions.
Scheme 2. Proposed Catalytic Mechanism on the Selective Oxidation of HMF Using MAPbBr3 Photocatalyst and Atmospheric
O2
EPR signal is detected in both situations in the dark. In addition,
we also tried to check whether hydroxyl radical (•OH) is a
reactive species using 5,5-dimethyl-1-pyrroline (DMPO) as a
spin-trapping reagent;19 however, no characteristic EPR signal
of the DMPO−•OH adduct was detected, excluding the
product. During either proposed catalytic cycle, the important
side product H2O2 should be produced. To confirm our
hypothesis, an excess amount of saturated NaI was added into
the post-photocatalytic reaction solution, where triiodide (I−3 )
species with a characteristic UV−vis absorption peak at 350 nm
will be formed through the reaction of H2O2 with excess amount
of I−.52 Such expectation is fully consistent with our
experimental observation (Figure S12). It is noted that the
control experiment in the absence of HMF substrate does not
lead to the formation of H2O2 under otherwise identical
conditions (40 mg of MAPbBr3, 10 mL of CH3CN, 15 °C, air, 10
h, a 450 nm blue LED light), further supporting the catalytic
routes in our proposed mechanism. In addition, the KMnO4
titration method54 was performed to quantitatively analyze the
amount of generated H2O2. Two parallel measurements yielded
•
participation of OH in our photocatalytic process (Figures
S11 and S14).
Based on all above analyses, we concluded that the selective
photo-oxidation of HMF in the present system is achieved
through combined contribution from atmospheric O2, photo-
•
1
generated electrons (e−), holes (h+), O2−, and O2 species.
Therefore, the following mechanism was proposed to better
illustrate the catalytic pathway during photocatalysis (Scheme
2). Upon irradiation by a 450 nm blue LED light, charge carriers
of h+ and e− are generated on the surface of the MAPbBr3
photocatalyst. On the one hand, the photogenerated e− could
activate molecular O2 into its reactive superoxide form (•O2−),
which further helps deprotonate the HMF substrate, producing
alkoxide anion intermediate and hydroperoxyl radical (•OOH)
species. The alkoxide anion intermediate is further oxidized by
the photogenerated h+ into an anionic radical, which is
that 4.2
0.18 mM H2O2 was produced after 10 h of
photocatalytic reaction. The amount of produced H2O2 is
slightly lower than the calculated value (∼4.5 mM) based on the
yield of DFF, which is probably attributed to the slight
disproportionation of H2O2 to O2 and H2O or the very slow
consumption of H2O2 to oxidize DFF to FFCA (6.5% selectivity
after 10 h of photocatalysis) during the reaction. Considering
the possibility that H2O2 may also act as a potential oxidant for
the oxidation reaction, two additional control experiments were
conducted. The addition of up to 10 mM H2O2 to the catalytic
solution in the absence of MAPbBr3 does not cause any
oxidation of HMF after 10 h irradiation (Table 2, entry 5). An
additional control experiment in the presence of catalase (CAT)
as a H2O2 scavenger does not obviously decrease the efficiency
of the selective photo-oxidation of HMF to DFF (Figure 4).
These results clearly revealed that the generated H2O2 did not
•
subsequently oxidized by OOH into desirable DFF as the
final product following a similar route to the literature-reported
alcohol oxidation mechanism.52 On the other hand, the singlet
oxygen (1O2) could also work as a reactive species to participate
in the catalytic cycle, which can be formed through either the
energy transfer from the excited photocatalysts to molecular O2
53
•
or the oxidation of O−2 by photogenerated holes (h+). The
reactive 1O2 participates in the catalytic transformation of HMF
by abstracting one proton, leading to the formation of an anionic
•
radical that is further oxidized by OOH to the final DFF
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play a crucial role in the photocatalytic oxidation process, further
radicals by adding 2,2,6,6-tetramethylpiperidine (TMP) as a
spin-trapping reagent in the photocatalytic reaction.
•
1
confirming the importance of O−2 and O2 as reactive oxidant
species in our proposed catalytic mechanism.
Synthesis of MAPbBr3 Perovskite. MAPbBr3 was
synthesized from an aqueous solution by dissolving MABr and
PbBr2 in a molar ratio of 1:1 according to a modified literature
method.32 Specifically, 15 g of PbBr2 was dissolved in 50 mL of
HBr acid (47 wt % in water), and then 4.57 g of MABr was slowly
added into the solution with vigorous stirring under 60 °C. The
solution with excess orange powder was heated to 90 °C, kept
for 1 h to crystallize and reach dynamic equilibrium, and then
cooled down to room temperature. The precipitates were dried
in a vacuum oven at 80 °C to obtain the MAPbBr3 powder.
Photocatalytic HMF Oxidation Reaction. In a typical
experiment, the photocatalytic oxidation of HMF was
performed in a custom-built reactor containing 40 mg of
MAPbBr3 perovskite and 5 mM HMF in 10 mL of CH3CN at 15
°C under air conditions. The reactor was illuminated by a 450
nm blue LED light with a light intensity of 170 mW cm−2 of the
PCX50C instrument, Beijing Perfectlight Technology Co., Ltd.
For every 2 h, 1 mL of aliquot of the catalytic reaction solution
was collected and analyzed with a Shimadzu LC-20A liquid
chromatograph (LC) equipped with an Aminex HPX-87H 300
mm × 7.8 mm column. The eluent containing H2SO4 solution
(pH = 2.0) was used as mobile phase with a flow rate of 0.5 mL
min−1 at 40 °C. The identification and quantification of the
products were confirmed according to standard calibration
curves achieved using commercially available furanic products
(e.g., HMF, DFF, and FFCA). The amount of generated H2O2
was determined by the KMnO4 (0.2 mM) redox titration
method54 with the addition of 5 mL of 1 M H2SO4 solution. The
concentration of H2O2 was calculated based on the amount of
consumed KMnO4 at the end of the titration when the color of
the titration solution turned light pink after the addition of
KMnO4 and remained in the same color for 30 s.
Finally, it is worth mentioning that our present photocatalytic
HMF oxidation system could also be applicable for photo-
oxidation of other alcohol substrates (e.g., benzyl alcohol).
Under otherwise identical conditions, benzyl alcohol can be
selectively oxidized to benzaldehyde with approximately 100%
selectivity after only 6 h of 450 nm blue LED light irradiation
(Figure S13), providing the possibility of expanding the present
catalytic system to the oxidation of other alcohol substrates. The
related research on this specific research topic is ongoing in our
lab.
In summary, we demonstrated a viable and environmentally
benign approach to selectively convert an important biomass-
derived chemical (HMF) to a value-added DFF product using
MAPbBr3 as a photocatalyst and atmospheric O2 as an oxidant
under visible-light irradiation. Under minimally optimized
conditions, the photocatalytic conversion of HMF in CH3CN
solvent reaches 100% with a DFF selectivity of over 90%; the
overall furanic carbon yield reaches over 96%. Detailed
mechanistic studies reveal that the photogenerated electrons
(e−), holes (h+), •O2−, and 1O2 species together play crucial roles
in the efficient and selective oxidation of HMF to DFF. Also, our
present photocatalytic system is applicable for photo-oxidation
of benzyl alcohol with approximately 100% conversion and
benzaldehyde selectivity. The present study reveals a new
approach of using a perovskite-based photocatalyst to achieve
HMF and benzyl alcohol oxidation and may also provide
insightful guidelines on photocatalytic production of value-
added chemicals from various biomass derivatives under mild
conditions.
EXPERIMENTAL SECTION
■
Chemicals. 5-Hydroxymethylfurfural (HMF), 2,5-diformyl-
furan (DFF), and 2-formyl-5-furancarboxylic acid (FFCA) were
purchased from Aladdin. Benzyl alcohol and benzaldehyde were
purchased from Macklin. PbBr2 with purity >99% was purchased
from Alfa Aesar. Methylammonium bromide (MABr) with
purity >99% was purchased from Macklin. HBr acid (47 wt % in
water) was purchased from Macklin. 2,2,6,6-Tetramethylpiper-
idine (TMP) was purchased from Energy Chemical. All
chemicals were used as received without further purification.
Instrumentation. Phase purity of as-obtained catalysts was
characterized by powder X-ray diffraction (PXRD) recorded on
a Shimadzu XRD-6000 diffractometer. Morphologies and
microstructures of the catalysts were characterized by scanning
electron microscopy (SEM) (JSM-7500F). The UV−vis diffuse
reflectance spectroscopy (UV−vis−DRS) of the products was
recorded by a Techcomp UV 2600 spectrophotometer equipped
with an integrating sphere. The steady-state luminescence
quenching spectra were recorded on an Edinburgh FS50
spectrofluorometer (PL) at 395 nm laser excitation at room
temperature. Chopped-light chronoamperometric measure-
ments were performed by a CHI 660E instrument. The in situ
diffuse reflectance infrared Fourier transform spectroscopy
(DRIFTs) spectra were recorded on a Bruker Tensor II FT-IR
spectrometer equipped with a diffuse reflectance accessory
(Sharp X); the spectra were recorded by accumulating 50 scans
with a resolution of 4 cm−1. All DRIFTs spectra were displayed
in Kubelka−Munk units using Omnic software. The electron
paramagnetic resonance (EPR) measurement was carried out
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acscatal.0c04330.
SEM images; UV−vis spectra and PXRD profiles of
MAPbBr3 perovskites before and after photocatalysis; PL
spectra; chopped-light chronoamperometric test; opti-
mization of photocatalytic reaction conditions; photo-
oxidation of benzyl alcohol; the determination of H2O2;
and EPR tests (PDF)
AUTHOR INFORMATION
■
Corresponding Author
Hongjin Lv − MOE Key Laboratory of Cluster Science, School of
Chemistry and Chemical Engineering, Beijing Institute of
Technology, Beijing 102488, P. R. China; orcid.org/0000-
0002-9212-7572; Email: hlv@bit.edu.cn
Authors
Mo Zhang − MOE Key Laboratory of Cluster Science, School of
Chemistry and Chemical Engineering, Beijing Institute of
Technology, Beijing 102488, P. R. China
Zheng Li − MOE Key Laboratory of Cluster Science, School of
Chemistry and Chemical Engineering, Beijing Institute of
Technology, Beijing 102488, P. R. China
1
using a spectrometer (Germany MS-5000) to detect the O2
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ACS Catal. 2020, 10, 14793−14800

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Junhao Zhang − MOE Key Laboratory of Cluster Science,
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Institute of Technology, Beijing 102488, P. R. China
Yeqin Feng − MOE Key Laboratory of Cluster Science, School of
Chemistry and Chemical Engineering, Beijing Institute of
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Author Contributions
H.L. and M.Z. designed the project, analyzed the data, and wrote
the paper; Z.L. and M.Z. conducted liquid chromatography
measurements; X.X., J.Z., and Y.F. participated in the project
discussion and TOC drawing.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors gratefully acknowledge the financial support from
the National Natural Science Foundation of China (21871025
and 21831001), the Recruitment Program of Global Experts
(Young Talents), and the BIT Excellent Young Scholars
Research Fund.
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