Acceptorless Photocatalytic Dehydrogenation of Furfuryl Alcohol (FOL) to Furfural (FAL) and Furoic Acid (FA) over Ti3C2Tx/CdS under Visible Light

Article abstract of DOI:10.1002/asia.202100729

Acceptorless photocatalytic dehydrogenation is not only a promising alternative to photocatalytic water splitting for hydrogen generation but also provides a green and sustainable strategy for the synthesis of value-added organic compounds. In this work, Ti₃C₂T_x/CdS nanocomposites were obtained by self-assembly of hexagonal CdS in the presence of preformed Ti₃C₂T_x nanosheets, which serves as a photocatalyst for acceptorless dehydrogenation of biomass-derived furfuryl alcohol (FOL) to furfural (FAL) and furoic acid (FA) in neutral and alkaline medium respectively, with simultaneous generation of stoichiometric hydrogen under visible light. Ti₃C₂T_x MXene acts as an efficient cocatalyst for the photocatalytic dehydrogenation of FOL over CdS, with an optimum performance achieved over 0.50 wt%Ti₃C₂T_x/CdS nanocomposite. This study provides an economic and sustainable strategy for the simultaneous valorization of biomass-derived FOL to produce FAL and FA as well as the production of clean energy hydrogen under mild condition based on noble metal-free semiconductor-based photocatalysts.

Full text of DOI:10.1002/asia.202100729

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Accepted Article
Title: Acceptorless Photocatalytic Dehydrogenation of Furfuryl Alcohol
(FOL) to Furfural (FAL) and Furoic Acid (FA) over Ti3C2Tx/CdS
under Visible Light
Authors: Jiaqi Wang, Xinyu Liu, and Zhaohui Li
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10.1002/asia.202100729
Chemistry - An Asian Journal
Acceptorless Photocatalytic Dehydrogenation of Furfuryl Alcohol
(FOL) to Furfural (FAL) and Furoic Acid (FA) over Ti3C2Tx/CdS
under Visible Light
Jiaqi Wang, Xinyu Liu and Zhaohui Li
Research Institute of Photocatalysis, State Key Laboratory of Photocatalysis on Energy
and Environment, College of Chemistry, Fuzhou University, Fuzhou 350116, P. R.
China
 Author to whom all correspondences should be addressed. E-mail:
zhaohuili1969@yahoo.com, Tel (Fax): 86-591-22865855
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10.1002/asia.202100729
Chemistry - An Asian Journal
Abstract
Acceptorless photocatalytic dehydrogenation not only is a promising alternative
to photocatalytic water splitting for hydrogen generation, but also provides a green and
sustainable strategy for the synthesis of value-added organic compounds. In this work,
Ti3C2Tx/CdS nanocomposites were obtained by self-assembly of hexagonal CdS in the
presence of preformed Ti3C2Tx nanosheets, which serves as a photocatalyst for
acceptorless dehydrogenation of biomass-derived furfuryl alcohol (FOL) to furfural
(FAL) and furoic acid (FA) in neutral and alkaline medium respectively, with
simultaneous generation of stoichiometric hydrogen under visible light. Ti3C2Tx
MXene acts as an efficient cocatalyst for the photocatalytic dehydrogenation of FOL
over CdS, with an optimum performance achieved over 0.50 wt%Ti3C2Tx/CdS
nanocomposite. This study provides an economic and sustainable strategy for the
simultaneous valorization of biomass-derived FOL to produce FAL and FA as well as
the production of clean energy hydrogen under mild condition based on noble metal-
free semiconductor-based photocatalysts.
Keywords: Acceptorless dehydrogenation • Furfuryl alcohol • Furfural • Furoic acid •
Photocatalysis
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Introduction
Hydrogen is a clean energy carrier and is a promising alternative to traditional
fossil fuels. Photocatalytic water splitting, which utilize the ubiquitous and abundant
solar energy to produce hydrogen from water, is considered to be an ideal strategy to
tackle the ever-increasing worldwide energy shortage and serious environmental
[1-3]
pollution.
Ever since the pioneer work of Fujishima and Honda which show the
[4]
photoelectrochemical hydrogen evolution over a TiO2-based electrode,
intensive
research interest has been devoted to the development of different photocatalytic
systems for hydrogen production under visible light. [5-14] However, only a few systems
ever reported are active for photocatalytic overall water splitting, [3, 15] i.e., generation
of hydrogen and oxygen simultaneously, while most of the photocatalytic systems
require sacrificial electron donors such as alcohols, triethanolamine (TEOA), organic
acids, sulfides and so on to consume the photo-generated holes for an efficient hydrogen
[16-18]
production.
In most cases, these sacrificial agents are oxidized to complicated
products and usually are inseparable from the reaction systems, which makes the
photocatalytic hydrogen evolution process in the presence of the sacrificial agents
neither green nor economic. A promising strategy is to replace the uncontrollable
oxidation of the sacrificial agents with a highly selective oxidation reaction leading to
[19-24]
value added organic compounds.
In this regard, acceptorless photocatalytic
dehydrogenation not only is a promising alternative to photocatalytic water splitting to
produce hydrogen, but also provides green and sustainable strategy for the synthesis of
value added organic compound. [25, 26]
Furfuryl alcohol (FOL), a furan derivative obtained from biomass-derived
hemicellulose, is one of the most promising biomass-derived platform chemicals. FOL
can be converted to a variety of high value added chemicals and fuels. [27] For example,
furfural (FAL) is used in producing diesel/jet fuel range alkanes and is also a crucial
[28, 29]
monomer for the formation of furan resins and plastics,
while furoic acid (FA)
finds value added applications in the fragrance, agrochemicals and pharmaceuticals
production. [30, 31] As compared with the FOL oxidation based on microbial biocatalysis
and traditional thermocatalysis which either requires sensitive biocatalysts or elevated
temperature, [26, 32, 33] the use of visible light to drive photocatalytic dehydrogenation of
FOL is a green and sustainable strategy to produce FAL and FA since it can use the
ubiquitous solar light to realize this reaction under mild condition and generate clean
hydrogen concomitantly. [34-37]
As a binary chalcogenide with relatively narrow band gap (ca. 2.4 eV)
corresponding well to the visible light absorption, CdS has demonstrated promising
activity for photocatalytic hydrogen evolution from water containing sacrificial
reagents under visible light. [38-40] Different cocatalysts, including metals nanoparticles,
transition metal chalcogenides and molecular cocatalysts, which act as catalytic active
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10.1002/asia.202100729
Chemistry - An Asian Journal
sites for hydrogen evolution and to suppress the recombination of the photo-generated
charge carriers, have been deposited on CdS to promote the photocatalytic activity for
hydrogen evolution over CdS. [41-47] As a new type of two-dimensional (2D) transition
metal carbide, Ti3C2Tx MXene (T = -OH, -O and -F) was previously reported to be
[48-52]
active for electrochemical hydrogen evolution.
The use of MXene as efficient
cocatalyst for semiconductor-based photocatalytic hydrogen evolution have also been
demonstrated. [53-55]
In this manuscript, we reported the preparation of Ti3C2Tx/CdS nanocomposites
via self-assembly of hexagonal CdS nanorods in the presence of preformed Ti3C2Tx
nanosheets. The as-obtained Ti3C2Tx/CdS nanocomposites show superior activity for
acceptorless photocatalytic dehydrogenation of FOL to produce FAL and FA in neutral
and alkaline medium, respectively, under visible light. This study provides an economic
and sustainable strategy for the simultaneous valorization of biomass-derived FAL to
produce FOL and FA as well as the production of clean energy hydrogen under mild
condition based on noble metal-free semiconductor-based photocatalysts.
Results and Discussion
Ti3C2Tx nanosheets, with its TEM image shown in Supporting Figure S1, were
obtained from Ti3AlC2 and LiF following a previously reported method with slight
modifications. Ti3C2Tx/CdS nanocomposites with different amounts of Ti3C2Tx were
prepared hydrothermally from CdCl2·2.5H2O and thiourea in the presence of performed
Ti3C2Tx nanosheets. The XRD patterns of all the Ti3C2Tx/CdS nanocomposites (take
0.50 wt%Ti3C2Tx/CdS for example) show peaks of 2θ values at 24.8, 26.5, 28.2,
36.6, 43.7, 47.9 and 51.8, which can be assigned to (100), (002), (101), (102), (110),
(103) and (112) crystallographic planes of the hexagonal wurtzite-structure CdS
(JCPDS No. 41-1049) (Figure 1). [56] Although no diffraction peaks corresponding to
Ti3C2Tx was observed in the XRD patterns of 0.50 wt%Ti3C2Tx/CdS nanocomposite,
the presence of Ti was evidenced by its XPS spectra in the Ti 2p region, which can be
deconvoluted into four peaks. The peaks at 458.6 and 454.5 eV can be attributable to
Ti 2p1/2 and Ti 2p3/2 in Ti-C respectively, while the peaks at 460.6 and 455.5 eV can be
assigned to those in Ti-O (Figure 2a). Accordingly, the XPS spectra in the C 1s region
can be deconvoluted into four peaks at 288.7, 286.4, 284.8 and 281.2 eV, ascribable to
C1s in C-F, C-O, C-C and C-Ti, respectively (Figure 2b). Peaks assignable to Cd2+ 3d5/2
and Cd2+ 3d3/2 occurred at 404.4 eV and 411.1 eV as well as S2- 2p3/2 and S2- 2p1/2 at
160.7 eV and 161.9 eV, were also observed (Figure 2c, 2d). [57] The SEM image of 0.50
wt%Ti3C2Tx/CdS nanocomposite show that the sample consists of nanorods, similar to
that of bare CdS, and indicates that the formation of CdS nanorods was not influenced
by the presence of Ti3C2Tx nanosheets (Figure 3a and Figure S2). The TEM image show
that the CdS nanorod with a diameter of ca. 28 nm and a length of ca. 320 nm was
deposited on the Ti3C2Tx nanosheet (Figure 3b). Clear lattice fringes of 0.335 nm,
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10.1002/asia.202100729
Chemistry - An Asian Journal
ascribable to (002) crystallographic plane of hexagonal CdS as well as those of 0.260
nm, matching well with the (0110) crystallographic plane of Ti3C2Tx observed in the
HRTEM image (Figure 3c). All these characterizations demonstrated that robust
Ti3C2Tx/CdS nanocomposites, with CdS nanorods deposited on Ti3C2Tx nanosheets,
have been successful obtained. During the formation of the Ti3C2Tx/CdS
nanocomposites, it is proposed that the negatively-charged Ti3C2Tx nanosheets is
favorable for the electrostatic absorption of Cd2+. [54] Then Ti3C2Tx nanosheets adsorbed
Cd2+ reacted with S2- released from thiourea under hydrothermal conditions to form
CdS nanoclusters, which further grow to CdS nanorods on the Ti3C2Tx nanosheets. As
compared with bare CdS, the UV-vis DRS spectrum of 0.50 wt%Ti3C2Tx/CdS
nanocomposites shows a slight enhanced absorption in the 500–800 nm region, ascribed
to the introduction of Ti3C2Tx nanosheets (Figure 4).
The photocatalytic activity for dehydrogenation of furfuryl alcohol (FOL) was
initially investigated over 0.25 wt%Ti3C2Tx/CdS nanocomposite under visible light in
an aqueous system containing 50 μmol of FOL. It was found that 53.0% of FOL was
converted and 26.2 μmol of FALwas obtained after irradiated for 12 h. In the meantime,
almost quantitative amount of hydrogen (25.9 μmol) was evolved (Table 1, entry 1). No
conversion of FOL was observed either in dark or in absence of 0.25 wt%Ti3C2Tx/CdS
nanocomposite (Table 1, entry 2, 3). Bare CdS showed an inferior activity, with only
15.2% of FOL converted under otherwise similar condition (Table 1, entry 4). These
indicated that the dehydrogenation of FOL to produce FAL is truly induced by
photocatalysis over CdS, while Ti3C2Tx MXene plays a promoting effect for this
reaction.
Since Ti3C2Tx MXene exhibits a positive effect on photocatalytic dehydrogenation
of FOL to produce FAL, the influence of the amount of Ti3C2Tx MXene on the
photocatalytic activity was also investigated. It was found that the conversion of the
FOL first improved with the amount of Ti3C2Tx MXene and then decreased (Table 1,
entry 5, 6), with an optimized performance observed over 0.50 wt%Ti3C2Tx/CdS
nanocomposite, in which 65.6% of FOL was converted and 32.7 μmol of FAL and
quantitative amount of hydrogen (32.3 μmol) were obtained in 12 h (Table 1, entry 5).
The ratio of FOL to the photocatalyst in the reaction system also influenced the
performance. When the amount of FOL in the reaction system raised from 50 μmol to
100 μmol while the amount of photocatalyst remained unchanged, 75.2% of FOL was
converted in 12 h and the formed FAL increased from the original 32.7 μmol to 74.5
μmol. In addition, the amount of hydrogen evolved increased from the original 32.3
μmol to 73.1 μmol. However, a further increase of the amount of FOL to 150 and 200
μmol resulted in a lowering of the photocatalytic activity, with only 24.3% and 13.8%
of FOL converted, and 33.8 μmol and 25.0 μmol of FAL were obtained, respectively
(Figure 5).
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The time-dependent photocatalytic dehydrogenation of FOL over 0.50
wt%Ti3C2Tx/CdS nanocomposite in a reaction system containing 100 μmol of FOL
show that the amount of FOL decreased with the irradiation time, with the concomitant
generation of FAL and hydrogen. An almost complete conversion of FOL to FAL was
realized after irradiated for 20 h, with 96.2 μmol of FAL and almost stoichiometric H2
(93.9 μmol) obtained (Figure 6). To study the origin of the hydrogen evolved, H2O was
replaced by D2O in the reaction. Instead of D2, only hydrogen was detected in the
gaseous product, indicating that hydrogen evolved in this system comes from FOL
instead of H2O.
The above experimental observations clearly demonstrate that the
dehydrogenation of FOL to produce FAL is a visible light induced photocatalytic
process over CdS, with Ti3C2Tx MXene acting as an efficient cocatalyst to promote the
hydrogen evolution. As already well demonstrated in literature, [19] CdS can be excited
under visible light irradiation to generate electrons and holes. The photogenerated holes
can attack the surface adsorbed FOL to form an alkoxide intermediate, which further
undergoes a cleavage of the C–H bond to form FAL. In the meantime, due to a less
negative CB of Ti3C2Tx (-0.04 V vs NHE) as compared with that of CdS (-1.11 V vs
NHE), a directional transfer of the photo-generated electrons from CdS to Ti3C2Tx
occurs. The released protons can transfer to Ti3C2Tx MXene and are reduced to
hydrogen (Scheme 1). The existence of the interface between Ti3C2Tx and CdS in the
as-obtained Ti3C2Tx/CdS nanocomposite is important for the photocatalytic
acceptorless dehydrogenation reaction, since a mechanical mixture of Ti3C2Tx and CdS
with similar composition to that in 0.50 wt%Ti3C2Tx/CdS show an inferior activity, with
only 32.7% of FOL converted after irradiated for 12 h.
As compared with the transformation of FOL to FAL, the direct synthesis of FA
from FOL is more appealing since FA has many important applications in chemical
industry. Based on the well-known Cannizzaro mechanism, an alkaline reaction
medium is favorable for the disproportionation of the aldehydes to form acids and
[58]
alcohols.
Therefore, the photocatalytic dehydrogenation of FOL over 0.50
wt%Ti3C2Tx/CdS was investigated in an alkaline reaction medium. To our expectation,
when 40 equiv. of NaOH (based on FOL) was introduced into the reaction system, not
only FAL but also FA was obtained. After irradiated for 48 h, 68.8% of FOL was
converted, and 57.7 μmol and 10.2 μmol of FAL and FA were obtained, corresponding
to a selectivity of 85.0% and 15.0% to FAL and FA, respectively (Table 1, entry 7). The
increase of the amount of the base (NaOH) from 40 equiv. to 120 equiv. resulted in an
improved conversion of FOL as well as the selectivity to FA (Table 1, entries 8, 9). 89.0%
of FOLwas converted when 120 equiv. of NaOH was introduced to the reaction system,
with 28.4 μmol of FA obtained, corresponding to a selectivity of 31.9% (Table 1, entry
9). However, a further increase of the amount of NaOH to 400 equiv. led to a slightly
decreased yield to FA (25.3 μmol) (Table 1, entry 10). Although it is not possible to
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10.1002/asia.202100729
Chemistry - An Asian Journal
obtain FA as the only product in the photocatalytic dehydrogenation of FOL over the
current reaction system, this reaction still shows prospect in the direct synthesis of FA
from FOL since the reaction is green and the product can be easily separated by
chromatograph.
Ti3C2Tx/CdS nanocomposite also show high stability during the photocatalytic
dehydrogenation of FOL in both neutral and alkaline reaction media. The used
photocatalyst after 48 h irradiations even in an alkaline reaction system still show
unchanged XRD patterns as the fresh one (Figure 7). In addition, the photocatalytic
dehydrogenation of FOL to produce FAL can be cycled for ten times without obvious
change of the activity (Figure 8). The reaction can also be scale-up without sacrificing
its activity. Aten-fold scale-up experiment show that 91.7% of FOL was converted after
irradiated for 20 h, with 915.8 μmol of FAL obtained and almost stoichiometric H2
(914.9 μmol) evolved. The possibility to scale-up this reaction and the high stability of
the photocatalyst indicates that it has a promising potential in practical application.
Conclusion
In summary, we reported the fabrication of Ti3C2Tx/CdS nanocomposite, which
act as a photocatalyst for acceptorless dehydrogenation of FOL to FAL and FA under
visible light in neutral and alkaline medium, respectively. The simultaneous generation
of clean energy hydrogen and the valorization of biomass-derived FOL is a green and
sustainable strategy in the synthesis of FAL and FA. This study also highlights the great
potential of semiconductor-based photocatalysis in both the valorization of biomass and
clean energy production.
Experimental Section
Synthesis of Ti3C2Tx/CdS nanocomposites
All the reagents were of analytical grade and were used without further
purifications. Ti3C2Tx nanosheets were prepared from Ti3AlC2 following a previously
reported procedure with slight modifications. [59] Ti3AlC2 powder and LiF powder were
added to HCl solution (6 mol·L-1) and the resultant suspension was stirring vigorously
for 24 h. The resultant product was recovered by filtration and washed with deionized
(DI) water. The thus-obtained black product was re-dispersed in DI water, and was
centrifuged to remove the aggregate. The supernatant was filtered to obtain Ti3C2Tx
nanosheets as a black product, which was dried in a vacuum desiccator.
Ti3C2Tx/CdS nanocomposites were obtained by self-assembly of hexagonal CdS
in the presence of preformed Ti3C2Tx nanosheets. To synthesize Ti3C2Tx/CdS
nanocomposites, different amount of the as-obtained Ti3C2Tx nanosheets were
dispersed in 60 mL of ethylenediamine. CdCl2·2.5H2O (2.28 g, 10 mmol) and thiourea
(3.04 g, 40 mmol) were added to the above suspension under vigorous stirring. The
resultant suspension was sealed in a 100 mL Teflon-lined autoclave and heated at 160
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Chemistry - An Asian Journal
C for 48 h. After cooling to room temperature, the as-obtained yellow product was
collected by centrifugation, washed with ethanol and dried at 60 C. Ti3C2Tx/CdS
nanocomposites with different amount of Ti3C2Tx were labeled as x wt%Ti3C2Tx/CdS
(x is the weight ratio of Ti3C2Tx : CdS, x = 0.25, 0.50 and 1.00). For comparison, bare
hexagonal CdS was synthesized similarly without Ti3C2Tx.
Characterizations
The powder X-ray diffraction (XRD) patterns were conducted on a Rigaku
Miniflex 600 X-ray diffractometer equipped with Cu Kα radiation in a 2θ range of 10 -
90 at a step size of 0.02. X-ray photoelectron spectroscopy (XPS) analysis were
performed on a PHI Quantum 2000 XPS system using a charge neutralizer and a
monochromatic Al Kα as the radiation source. All of the binding energies were
referenced to the C 1s peak at 284.6 eV of the surface adventitious carbon. The
morphology of the samples was obtained by a field-emission scanning electron
microscopy (SEM) (JSM-6700F). The transmission electron microscopy (TEM) and
high-resolution TEM (HRTEM) images were obtained on a FEI Tecnai G2 F20 at an
accelerating voltage of 200 kV. UV–visible diffuse reflectance spectra (UV-vis DRS)
of the samples were recorded on a Varian Cary 500 scan spectrophotometer with BaSO4
as a reference.
Photocatalytic reactions
The photocatalytic reactions were conducted in a gas-tight Pyrex reaction tube
under visible light with a 3 W blue LED lamp (GeAoLEDs, H106064). In a typical
reaction, 10 mg of photocatalyst in a 10 mL schlenk tube was evacuated and purged
with N2. FOL (8.64 μL, 100 μmol) in H2O (4 mL) was pre-degassed with N2 to remove
any dissolved O2 and was injected into the above schlenk tube. The suspension was
irradiated with a 3 W blue LED lamp with a wavelength centered at ca. 420 nm. After
the reaction, the gaseous products were analyzed by GC-TCD (Shimadzu GC-2014)
with a TDX-01 packed column. The filtrate was analyzed by high-performance liquid
chromatography (HPLC, Waters 2695) equipped with a photodiode array detector using
a SunFire column (5 µm × 4.6 mm × 250 mm). For FOLand FAL, a mixture of methanol
and water (v/v = 30/70) was used as the eluent, with the wavelength for the detection
of FOL and FAL to be 218 and 274nm, respectively. As for furoic acid (FA), an eluent
containing methanol and ammonium acetate (v/v = 40/60) was used as the mobile phase.
The wavelength for the detection of FAis 245 nm. The scale-up experiment was carried
out in a 50 mL schlenk tube containing 100 mg of 0.50 wt%Ti3C2Tx/CdS
nanocomposite, FOL (86.4 μL, 1000 μmol) and H2O (40 mL).
Acknowledgements
This work was supported by the NSFC (21872031 and U1705251). Z. Li thanks
the Award Program for Minjiang Scholar Professorship for financial support.
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Chemistry - An Asian Journal
Conflict of Interest
The authors declare no conflict of interest.
Appendix A. Supplementary data
Supplementary material including the TEM image of Ti3C2Tx and the SEM image
of CdS can be found in the online version.
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Captions for Figures
Figure 1 XRD patterns of 0.50 wt%Ti3C2Tx/CdS and CdS.
Figure 2 XPS spectra of 0.50 wt%Ti3C2Tx/CdS in (a) Ti 2p, (b) C 1s, (c) Cd 3d and (d)
S 2p region.
Figure 3 Images of Ti3C2Tx/CdS nanocomposite (a) SEM; (b) TEM and (c) HRTEM.
Figure 4 UV–vis DRS of bare CdS and 0.50 wt%Ti3C2Tx/CdS nanocomposite.
Figure 5 Influence of the amount of FOL on the photocatalytic dehydrogenation of
FOL to produce FAL over 0.50 wt%Ti3C2Tx/CdS nanocomposite.
Figure 6 Time-dependent conversion of FOL and the yield to FAL over 0.50
wt%Ti3C2Tx/CdS nanocomposite.
Figure 7 XRD patterns of fresh and used Ti3C2Tx/CdS.
Figure 8 Cycling runs for photocatalytic conversion of FOL over 0.50
wt%Ti3C2Tx/CdS nanocomposite.
Scheme 1 Proposed mechanism for photocatalytic dehydrogenation of FOL over
Ti3C2Tx/CdS nanocomposite under visible light.
Table 1 Photocatalytic dehydrogenation of FOL to produce FAL and FA under different
reaction conditions.
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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Figure 8
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Scheme 1
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Table 1
Yield
FA
FOL
(μmol)
Entry
Catalyst
NaOHc Conv. (%) Time (h)
FAL (μmol)
H2 (μmol)
25.9
-
(μmol)
Select. (%)
1
2a
3b
4
0.25 wt%Ti3C2Tx/CdS
0.25 wt%Ti3C2Tx/CdS
-
50
-
-
53.0
-
12
12
12
12
12
12
48
48
48
48
26.2
-
-
-
50
-
-
-
-
50
-
-
-
-
CdS
50
-
15.2
65.6
46.0
68.8
72.4
89.0
90.2
7.5
-
-
7.1
5
0.50 wt%Ti3C2Tx/CdS
1.00 wt%Ti3C2Tx/CdS
0.50 wt%Ti3C2Tx/CdS
0.50 wt%Ti3C2Tx/CdS
0.50 wt%Ti3C2Tx/CdS
0.50 wt%Ti3C2Tx/CdS
50
-
32.7
22.8
57.7
56.0
60.6
64.0
-
-
32.3
22.4
55.1
53.7
58.5
62.0
6
50
-
-
-
7
100
100
100
100
40
80
120
400
10.2
16.2
28.4
25.3
15.0
22.4
31.9
28.3
8
9
10
Reaction conditions: Catalyst (10 mg), H2O (4 mL), N2, blue LED. aIn absence of light. bIn absence of photocatalyst. cThe molar ration
of NaOH/FOL.
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Graphical Abstract
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