Pyrene-functionalized polymeric carbon nitride with promoted aqueous-organic biphasic photocatalytic CO2 reduction

Article abstract of DOI:10.1039/c8ta09801h

We have demonstrated a simple copolymerization process to covalently graft pyrene-functional groups on the polymeric carbon nitride (PCN) surface. The resulting pyrene functionalized carbon nitride (Py-PCN) exhibits unique biphasic photocatalytic activities, which enable efficient CO₂ photoreduction in aqueous solution with simultaneous alkene (C═C) oxidation in the organic phase. The great biphasic activities are attributed to the increased lipophilicity from surface pyrene-functional groups, which allows the hydrophobic alkene molecules to readily approach the PCN surface and react with the hydroxyl radicals created from-OH oxidation by photogenerated holes. In this way, the alkene compounds indirectly consume the photo-holes from excited Py-PCN, promoting the overall photocatalytic process. Our study provides a new strategy for solar fuel production with simultaneous organic synthesis by the oxidation power of photo-holes on amphiphilic metal-free semiconductors.

Full text of DOI:10.1039/c8ta09801h

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Pyrene-functionalized polymeric carbon nitride
with promoted aqueous–organic biphasic
Cite this: DOI: 10.1039/c8ta09801h
photocatalytic CO reduction†
2
Xuezhong Gong, Sijia Yu, Meili Guan, Xianglin Zhu and Can Xue *a
a
a
b
a
We have demonstrated a simple copolymerization process to covalently graft pyrene-functional groups on
the polymeric carbon nitride (PCN) surface. The resulting pyrene functionalized carbon nitride (Py-PCN)
2
exhibits unique biphasic photocatalytic activities, which enable efficient CO photoreduction in aqueous
solution with simultaneous alkene (C]C) oxidation in the organic phase. The great biphasic activities are
attributed to the increased lipophilicity from surface pyrene-functional groups, which allows the
hydrophobic alkene molecules to readily approach the PCN surface and react with the hydroxyl radicals
created from –OH oxidation by photogenerated holes. In this way, the alkene compounds indirectly
consume the photo-holes from excited Py-PCN, promoting the overall photocatalytic process. Our
study provides a new strategy for solar fuel production with simultaneous organic synthesis by the
oxidation power of photo-holes on amphiphilic metal-free semiconductors.
Received 11th October 2018
Accepted 22nd December 2018
DOI: 10.1039/c8ta09801h
rsc.li/materials-a
the PCN surface very difficult. Therefore, some sacricial
1
. Introduction
reagents, such as triethanolamine (TEOA), were commonly used
11
Considering the increasing CO
sphere and overconsumption of fossil fuels, photocatalytic CO
conversion to value-added fuels is believed to be an effective way oxidizing phenol, bisphenol A and some organic dyes by
2
concentration in the atmo- for the photocatalytic CO
2
reduction. Further, in terms of
photocatalytic pollutant degradation, PCN was capable of
2
12
13
1
14
to alleviate the energy crisis and environmental issues. Among hydroxyl radicals and/or superoxide radicals. Considering the
all the semiconductors that are capable of reducing CO
2
, poly- p-conjugated units in the PCN backbones, the p-conjugated
15
meric carbon nitride (PCN) has attracted much research interest molecules (e.g., alkenes, alkynes and aromatics) could be pref-
2
due to its perfect band structure. Specically, its high erably adsorbed via interfacial p–p conjugation. Nevertheless,
conduction band with respect to the CO reduction potentials this requires that the PCN is capable of dispersing in organic
2
provides thermodynamic driving force. And the versatile strat- solvents in order to achieve optimal adsorption of those p-
egies for PCN structure modication, such as copolymeriza- conjugated molecules.
3
4–6
7
tion, introducing a heterojunction, and elemental doping,
can be smoothly applied to functionalize PCN for boosting its (e.g., 2-aminobenzonitrile, aniline, benzonitrile, etc.) was
Co-polymerization of PCN precursors with co-monomers
16–18
photocatalytic activity for CO
2
reduction. Moreover, PCN commonly used to obtain functionalized PCN.
However, the
features amphiphilic properties owing to its terminal amine co-polymerization usually inserted the functional group into the
8
groups, enabling excellent affinity for the absorbates in PCN matrix, which signicantly altered the PCN band struc-
aqueous solution for surface reaction.
To date, most photocatalytic CO
tures besides the surface properties. An alternative strategy is
reduction tests have been post-calcination of PCN mixed with functional molecules,
2
carried out in aqueous suspensions, in which H
2
O is expected to which is not effective with non-uniform surface functionaliza-
9,10
serve as the electron donor. In principle, the potential of the tion. The required high temperature calcination restricted the
photohole (Evb ¼ +1.4 V, vs. NHE) of PCN is capable of oxidizing available range of monomers in particular with large conju-
water into O
2
(EH O/O ¼ +1.23 V, vs. NHE). However, the large gated units that may decompose or carbonize.
2
2
overpotential for O evolution makes the real O generation on
According to our previous studies, PCN can be formed
through a solvothermal process, which allows covalent attach-
2
2
19
ment of triazine-based oligomers on the surface. Such oligo-
mers can be further condensed upon mild annealing. These
observations suggest that the conjugated functional groups on
triazine-based molecules can be covalently linked onto the PCN
surface via post-polymerization to modulate the surface
properties.
a
20
School of Materials Science and Engineering, Nanyang Technological University, 50
Nanyang Avenue, 639798 Singapore. E-mail: cxue@ntu.edu.sg
b
Institute for Energy Research, Jiangsu University, 301 Xuefu Road, Zhejiang, 212013,
P. R. China
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c8ta09801h
1
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Specically, in this work, we introduce surface pyrene- treated with the same solvothermal process in acetonitrile with
functionalization on PCN through a solvothermal process by only CC and CA (no PyCC), which is considered as the bare PCN
using 1-(4,6-dichloro-1,3,5-triazin-2-yl)pyrene (PyCC) as the and denoted as 0-PCN.
monomer and pre-synthesized PCN microspheres as the matrix.
The heptazine units in PCN are naturally hydrophilic, which
allows it to readily disperse in water. However the pyrene-moiety
supplies hydrophobic sites that allow affinity for nonpolar
solvents for adsorption and reaction of organic compounds.
Therefore, the pyrene-functionalized polymeric carbon
nitride (Py-PCN) can act as an aqueous–organic biphasic
photocatalyst, which enables photoreduction of bicarbonate in
the aqueous phase and simultaneous oxidation of organic
compounds in a nonpolar solvent. Here, for proof-of-concept,
we demonstrate that the photogenerated holes of PCN can
lead to the oxidation of the C]C bond of alkene compounds,
while the pyrene groups on Py-PCN can greatly enhance the
affinity for alkene compounds in the organic phase and enables
more effective oxidation reaction. This work provides valuable
guidance for the design and preparation of multifunctional
2
.4 Characterization
SEM images were obtained using an FESEM 7600F scanning
electron microscope with the acceleration voltage set at 5 kV.
Fourier transform infrared spectra (FTIR) were obtained from
a Perkin Elmer Fourier Transform Infrared Spectrometer GX.
The XRD patterns of all samples were collected on an XRD-6000
X-ray diffractometer (Cu K source) at a scan rate of 5 min .
UV-Vis diffuse reectance spectra (DRS) were measured with
a Lambda 750 UV/Vis/NIR spectrophotometer (Perkin-Elmer,
USA) using BaSO
spectra were obtained in the solid state with a Shimadzu
RF5301 Spectrouorophotometer. The specic surface area was
calculated from N adsorption–desorption isotherms measured
using a surface area and porosity analyzer (Micromeritics, ASAP
ꢀ
ꢁ1
a
4
as a reference. Photoluminescence (PL)
2
2020) by using the Brunauer–Emmett–Teller (BET) equation.
PCN photocatalysts for not only CO reduction but also simul-
2
The surface hydrophilicity was measured by contact-angle (CA)
measurement (Data Physics, OCA 15 Pro); the samples were
pressed into tablets for measurement.
taneous organic synthesis in nonpolar organic solvents.
2
. Experimental
2.1 Chemicals
2
2.5 Photocatalytic CO reduction in biphase
All the chemical reagents were used as received without further For the photocatalytic activity measurement, 3.0 wt% Pt as
purication. Cyanuric chloride (99%), cyanamide (99%), 1-(4,6- a cocatalyst was loaded through a wetness impregnation
dichloro-1,3,5-triazin-2-yl)pyrene ($85%), sodium bicarbonate process. Typically, the prepared sample (100 mg) was mixed
ꢁ
1
(
99.5%), cyclohexene (>99.7%), 2-methyl-2-butene (>99.0%), with H
2 6
PtCl (1.0 mg mL ) solution, followed by ultrasonic
acetonitrile (anhydrous, 99.8%), and toluene (HPLC Plus, treatment for 5 min to form a slurry. Aer 2 hour impregnation
$
99.9%) were all purchased from Sigma-Aldrich.
under vigorous stirring, excess water was removed by drying at
ꢀ
70 C in an oven. Aerwards, the obtained solid sample was
4
treated by NaBH reduction. The nal product was washed
2
.2 Synthesis of polymeric carbon nitride
thoroughly with distilled water to completely remove ions,
The raw PCN was synthesized through a solvothermal approach.
Typically, 360 mg of cyanuric chloride (CC) and 168 mg of
cyanamide (CA) were dissolved in 15 ml of acetonitrile through
sonication, and the mixture was transferred to a 40 ml Teon-
lined autoclave. Aerwards, the autoclave was sealed, put into
an oven, and maintained at 200 C for 24 h. The obtained
product was washed with acetonitrile, DI water and absolute
ethanol in sequence, and nally dried at 80 C. This raw PCN
sample is denoted as CN0.
ꢀ
separated via centrifugation, and dried at 70 C. In a quartz
reactor, 10 mg of the catalyst was dispersed in a mixture of 1 ml
3
aqueous solution of NaHCO (3 M) and 9 ml cyclohexene (or
9
ml toluene containing 2 mmol of 2-methyl-2-butene). Aer
sonication the mixture became a milky suspension, which was
ꢀ
sealed with rubber and purged with N for 30 min to drive away
2
the inside air. Aerwards, the reactor was placed under illu-
mination of a xenon lamp (300 W, MAX-302, Asahi Spectra,
USA). Reaction kinetics were monitored via analyses of the
withdrawn gaseous samples at a given period using a GC (Shi-
madzu 2010) equipped with FID and TCD detectors. The liquid
product was determined and analyzed at the end of reaction
ꢀ
2
.3 Synthesis of pyrene-functionalized polymeric carbon
nitride (Py-PCN)
The synthesized CN0 (100 mg) was dispersed in acetonitrile to using a GC-MS (Agilent 5977B GC/MSD).
form a homogeneous suspension. Different amounts of 1-(4,6-
dichloro-1,3,5-triazin-2-yl)pyrene (PyCC) were added to the
suspension together with CC and CA. The molar ratio of
PyCC : CC : CA is 1 : 1 : 5. The mixture was transferred to
3
. Results and discussion
3.1 Preparation and characterization of Py-PCN
a Teon-lined autoclave that was placed in an oven maintained The synthetic procedure of Py-PCN is illustrated in Scheme 1.
ꢀ
at 200 C for 24 h. The obtained products were washed with The raw PCN (denoted as CN0) microspheres were synthesized
ꢀ
acetonitrile, DI water and absolute ethanol in sequence and through a solvothermal process at 200 C by using cyanuric
ꢀ

nally dried at 80 C. The nal Py-PCN samples were labelled chloride (CC) and cyanamide (CA) as precursors. The surfaces of
2
.5% Py-PCN, 5% Py-PCN, 10% Py-PCN and 20% Py-PCN based these microspheres are enriched with 1,3,5-triazine based
19
on the mass ratio of PyCC to CN0. As a control sample, CN0 was oligomers that are not fully condensed, which allows PyCC to
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Scheme 1 Illustration of carbon nitride synthesis via solvothermal and
further functionalization.
Fig. 2 XRD patterns of CN0, 0-PCN and Py-PCN.
be graed onto the microsphere surface through further poly-
merization and condensation together with CC and CA in the
secondary solvothermal process. Therefore, the nal pyrene-
moiety is expected to covalently link with the tri-s-triazine
structure on the PCN surface, giving the product Py-PCN.
SEM images (Fig. 1a) indicate that the PCN products from
the rst solvothermal process are irregular spheres with diam-
eters of 0.5–2.5 mm. Aer pyrene-functionalization, the
morphology did not show obvious change, as shown in Fig. 1b.
The XRD patterns (Fig. 2) of the obtained samples show a clear
ꢀ
peak at 27.3 (d z 0.323 nm) corresponding to the (002) inter-
layer of graphitic carbon nitride. It indicates that the PCN
product has a well stacked conjugated hexatomic heterocyclic
21
system. The FT-IR spectra (Fig. S1†) also show the character-
istic peaks of aromatic C–N heterocycles and the s-triazine ring.
However the microspheres do not show the characteristic
ꢀ
peak of in-planar repeat packing at z13 , suggesting the
imperfect and disordered crystal structure of the PCN micro-
13
Fig. 3 Solid-state C NMR spectra of Py-PCN.
19
spheres. Functionalization of pyrene on the PCN surface by
a secondary solvothermal process did not clearly change the
XRD pattern.
3
.2 Photocatalytic CO reduction
2
1
3
The solid-state C NMR spectra (Fig. 3) of Py-PCN show two
PCN based photocatalysts usually have a sufficient conduction
2
peaks at 154.0 and 162.3 ppm corresponding to the sp -
band level for CO reduction into CO and various hydrocarbon
2
2 x 3
hybridized carbon atoms of –CN (NH ) and –CN in the CN
2
products, and have a suitable valence band level, allowing the
network, respectively, which indicates the existence of the
photogenerated holes to oxidize many different organic
compounds in aqueous solution. However, their capability of
initiating reaction with alkenes (C]C) is rarely investigated as
most C]C enriched compounds are not soluble in water. In
this study, the pyrene-functionalized carbon nitride show
affinity for both water and non-polar organic solvents. There-
fore, we carried out photocatalytic tests in an aqueous–organic
biphasic system by using bicarbonate in aqueous solution as
22
characteristic tri-s-triazine structure.
Besides, the weak
shoulder at ꢂ157.6 ppm may be attributed to the junctional
carbon atoms bridging the pyrene-moiety and two nitrogen
22
atoms. The signal at 123.1 ppm can be assigned to the
23
aromatic carbon from pyrene moieties, proving successful
pyrene-functionalization. Elemental analysis results (Table S1†)
also indicate higher C/N ratio for Py-PCN compared to 0-PCN.
2
the source for CO reduction and alkene compounds in the
organic phase for simultaneous reaction of the C]C bond. The
prepared PCN and Py-PCN samples were loaded with 3.0 wt% Pt
through a wetness impregnation process, and suspended in the
24
biphasic liquid for the photocatalytic reactions.
.2.1. Using cyclohexene. As a typical example, cyclohexene
3
was used as both an organic solvent and a reactant. In this case,
CO was the predominant gaseous product. As shown in Fig. 4,
compared to the bare PCN sample (0-PCN), graing with
Fig. 1 SEM images of (a) CN0, (b) 0-PCN and (c) Py-PCN. The scale
bar is 1 mm.
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Fig. 6 Possible pathway of cyclohexene oxidation by hydroxyl radical
addition to the C]C bond.
Fig. 4 (a) CO evolution time course over 0-PCN and Py-PCN with C]C bond was rst attacked by the cOH radical that was
ꢁ
1
different contents. Conditions: [Cat.] ¼ 1.0 g L ; 9 ml of cyclohexene
generated through the oxidation of chemisorbed –OH by pho-
as the solvent and 1 ml of 3.0 M NaHCO as the CO source; a 300 W
xenon lamp. (b) The relationship between CO generation rate versus
3
2
togenerated holes on the PCN surface, followed by proton
27
addition. The reactivity of cOH radicals for addition to unsat-
pyrene content.
28,29
urated C]C bonds has been extensively reported.
A possible
reaction pathway for cyclohexene is elucidated in Fig. 6.
The quantication results aer 4 hour irradiation are shown
in Fig. 7. The 10% Py-PCN sample still exhibits a much higher
yield of formic acid (2.2 mmol) and cyclohexanol (3 mmol) than
the bare PCN sample (0.37 mmol of formic acid and 1.1 mmol of
cyclohexanol). Considering the CO evolution amount (0.76
mmol for Py-PCN and 0.3 mmol for the bare PCN), the amount of
pyrene-moieties greatly enhanced the CO evolution rate up to 4
ꢁ1
ꢁ1
times (0.28 mmol h for 10% Py-PCN versus 0.07 mmol h for 0-
PCN). The pyrene-moieties afford the hydrophobic character-
istic and thus allow the Py-PCN surface to be more approach-
able by the cyclohexene molecules for reactions. The enhanced
reaction process of cyclohexene promotes the reduction of
bicarbonate by the photoelectrons in the aqueous phase.
Nevertheless, the excess pyrene-moieties would reduce the
sample affinity for the aqueous phase. Thus we found that 10%
Py-PCN is the optimal sample (Fig. 4b).
photoelectrons that are consumed for reduction (2nCO
nHCOOH) is 5.92 mmol over Py-PCN, which is close to the
amount of photoholes for cyclohexene addition (2ncyclohexanol),
.0 mmol. This indicates that CO reduction and cyclohexene
+
2
6
2
addition are initiated and driven by a photo-induced redox
cycle. The small difference might be attributed to the trace
amount of other liquid products, such as HCHO and CH CHO,
3
which were hardly identied by our GC-MS.
The control experiment (#1) showed no CO evolution over 4
hour irradiation when NaHCO was absent in the aqueous
3
phase. This indicates that the bicarbonate species serve as the
source for CO production. We have also carried out an addi-
tional control experiment (#2) in aqueous solution only. As
shown in Fig. 5, without cyclohexene, the CO evolution rate
dropped more than 10 times, which proved that cyclohexene
has signicant contribution to the overall photocatalytic
process.
3.2.2. Using 2-methyl-2-butene. To further verify the hole
oxidation capability of Py-PCN for the C]C bond, we have
carried out photoreduction of NaHCO3 in aqueous solution
using 2-methyl-2-butene (2M2B) in toluene as the organic
phase. In this case, both CO and CH
products, and no liquid reduction product was detected.
Notably, the yield of CO and CH over 10% Py-PCN is about 4-
4
were the main gaseous
Further, we have examined the liquid products using a GC-
4
MS. Formic acid was the main product in the aqueous phase,
ꢁ
fold and 7-fold higher than that over the bare PCN (Fig. 8). The
main product in the liquid phase was identied as acetone,
which is probably generated through oxidative addition of the
C]C bond in 2M2B to a water molecule by the cOH group
and originates from HCO
3
reduction by photoelectrons via
25,26
a multi-step electron transfer process.
Cyclohexanol was the
main product in the organic phase, and possibly produced
through the addition of water molecules. It is proposed that the
30,31
created by the photogenerated holes on the PCN surface.
Fig. 5 Control experiments over 10% Py-PCN were carried out under
identical conditions except for the absence of NaHCO
hexene, respectively.
3
and cyclo- Fig. 7 Comparison of gaseous and liquid products obtained over 0-
PCN and Py-PCN when using cyclohexene as the substrate.
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Fig. 8 CO (a) and CH (b) evolution time course over 0-PCN and 10%
ꢁ1
Py-PCN, respectively. Conditions: [Cat.] ¼ 1.0 g L ; 0.1 ml of 2-
methyl-2-butene in toluene and 1 ml of 3 M NaHCO
3 2
as the CO
source; a 300 W xenon lamp.
Fig. 11 The BET surface area calculated from nitrogen adsorption–
desorption isotherms.
The process should have generated acetaldehyde simulta-
neously with the same molar amount of acetone, but acetalde-
hyde could not be accurately quantied in our GC-MS. In this
2
ꢁ1
Py-PCN was estimated as 2.11 m g , which is lower than that
reaction, the total amount of electrons for reduction (2nCO
+
2
ꢁ1
of 0-PCN (5.49 m g ). The decrease of surface area aer the
attachment of pyrene-moieties can be attributed to the reduced
surface roughness. The results further prove that the enhanced
activity of Py-CN in the biphasic photocatalytic reaction is
attributed to the surface pyrene-moieties, rather than the effect
of surface area.
4n
CH4) is almost equal to that of holes for addition (2nacetone)
aer 20 h irradiation (Fig. 9). Hence, it is reasonable to deduce
such a reaction pathway as shown in Fig. 10.
The above photocatalytic experiments demonstrate that the
C]C bond in organic alkenes can be indirectly reacted by the
photogenerated holes of PCN when the photoelectrons are
ꢁ
To clarify the effect of phase affinity on the photocatalytic
activity, we have implemented a comparison experiment of
reducing HCO3 . Moreover, the pyrene-moiety graed onto the
PCN surface can promote adsorption of the hydrophobic
organic alkenes as well as their addition with water, which
enhances the overall photocatalytic activity.
Brunauer–Emmett–Teller (BET) surface areas of 0-PCN and
Py-PCN are measured by using liquid nitrogen adsorption–
desorption isotherms (Fig. 11). The specic surface area of the
photocatalytic H
0% TEOA as a hole scavenger, which is one of the most
common reactions for identifying photocatalytic activity.
2
generation in pure aqueous solution with
1
Interestingly, the H generation rate over the bare PCN was
2
obviously higher than that over Py-PCN (Fig. 12), which is an
opposite trend to the activities for bicarbonate reduction in
the biphasic system. The lower photocatalytic activity of Py-
PCN in pure aqueous solution could be ascribed to the
pyrene-moieties that restrict the free access of hydrophilic
species, such as protons and TEOA, to the PCN surface, which
reduces the rate of their redox reactions. The contact angle
measurement conrmed that Py-PCN is more resistant to
water (Fig. S2†). Therefore, we believe that the better perfor-
mance of Py-PCN in the biphasic system would be more likely
Fig. 9 Comparison of gaseous and liquid products obtained over 0-
PCN and Py-PCN using methyl-butene as the substrate. The products
were accumulated after 20 h irradiation.
2
Fig. 12 Photocatalytic H generation over 0-PCN and Py-PCN in
ꢁ1
Fig. 10 The oxidation pathway of 2-methyl-2-butene by hydroxyl aqueous solution. [Cat.] ¼ 1.0 g L with 3.0 wt% Pt via impregnation;
radicals.
10% TEOA as the scavenger. Light source: a Xe lamp, 300 W.
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Fig. 13 (a) UV-Vis diffuse reflectance spectra of 0-PCN and Py-PCN. Fig. 15 Illustration of photocatalytic simultaneous CO reduction and
2
(
b) Plot of transformed Kubelka–Munk function versus energy of light. organic alkene (C]C) oxidation.
due to the increased hydrophobicity by the incorporated
pyrene-moieties, rather than the improvement of electronic
properties.
3
.3 Proposed reaction mechanism
The above results demonstrate that in the aqueous–organic
biphasic system, the pyrene-functionalization of PCN provides
certain lipophilic capability that enables the C]C bond of
alkene compounds in the organic phase to readily approach the
carbon nitride surface. Subsequently, the alkene molecules can
sacrice the cOH radicals that are formed from oxidation of
surface adsorbed –OH by the photogenerated holes (Fig. S5†).
This process promotes hole consumption, and consequently
the charge separation efficiency is greatly improved, which
allows the photoelectrons to be more effectively accumulated on
the attached Pt catalyst surface for reduction of HCO3
Therefore, Py-PCN showed much better activity in the photo-
catalytic reduction of HCO
To verify this, we have identied the band energy levels for
Py-PCN and bare PCN (0-PCN). Fig. 13 shows the absorption
spectra of 0-PCN and Py-PCN. According to the K–M plot, the
bandgap energies are estimated as 2.27 and 2.31 eV for the bare
PCN and Py-PCN, respectively. The Mott–Schottky plot (Fig. S3†)
was used to estimate the atband potential of 0-PCN and
Py-PCN as ꢁ0.85 V (vs. Ag/AgCl) and ꢁ0.94 V (vs. Ag/AgCl),
respectively, which could be approximately regarded as the
32
conduction band. The detailed energy levels of the conduction
band and valence band (vs. NHE) are listed in Table S2.† There
is not much difference in the band structure between Py-PCN
and bare PCN. And their conduction band potential is much
ꢁ
.
ꢁ
3
in the biphasic system. In
comparison, the bare PCN naturally has a more hydrophilic
surface covered with a water layer, which inhibits adsorption of
hydrophobic alkenes (Fig. 15). However, the capability of holes
for water oxidation towards oxygen evolution is very limited,
resulting in low overall photocatalytic activity. So the role of the
pyrene-moiety is to optimize the interface of the photocatalyst–
organic solvent to promote the oxidation reaction, resulting in
high charge separation efficiency for bicarbonate reduction. In
addition, the cycling test (Fig. S6†) indicates very good stability
of Py-PCN for bicarbonate reduction.
more negative than that of the CO
thermodynamically favorable to produce different products
Fig. S4†).
The PL spectra (Fig. 14, excitation at 360 nm) reveal a slight
2
reduction, and thus it is
(
blue shi for the emission peak of Py-PCN (479 nm) compared
to that of the bare PCN (485 nm), which is consistent with the
33
slightly larger bandgap of Py-PCN. Though the pyrene-CC
precursor shows an intensive emission band at 488 nm, it is
quenched in the Py-PCN sample, suggesting that strong p–p
stacking exists between the pyrene and PCN. The results indi-
cate that the pyrene-functionalization on the PCN surface
resulted in little change in the PCN band structure, and had 4. Conclusions
almost no effect on the charge separation and recombination
on PCN.
We have successfully graed pyrene-functional groups on the
PCN surface through post co-polymerization strategy.
a
Compared to the original bare PCN, the product, Py-PCN,
exhibits greatly enhanced photocatalytic activities in an
aqueous–organic biphasic environment, which enable efficient
photoreduction of bicarbonate in the aqueous phase and
simultaneous oxidation of alkenes in the organic phase. The
enhancement is attributed to the increased lipophilicity from
the surface pyrene-functional groups, which allows the hydro-
phobic organic molecules to readily approach the PCN surface,
react and get converted to other molecules. This work is
signicant because of the unique promising advantages of
biphasic photocatalytic reactions. Our study demonstrates
a new strategy for solar fuel production with effective utilization
of the oxidation power of photo-holes for organic synthesis with
convenient separation of the product in the organic phase and
economical solvent recovery.
Fig. 14 PL spectra of 0-PCN, Py-PCN and PyCC at an excitation
wavelength of 360 nm.
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5 J. Low, J. Yu and W. Ho, J. Phys. Chem. Lett., 2015, 6, 4244–
Conflicts of interest
4251.
There are no conicts to declare.
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