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Catalysis Science & Technology
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solvent, but also enables the synthesis of another value-added To prepare N defects and O dopants co-modified g-C3N4 with
organic chemical.
different crystallinity, the pristine g-C3DNO4I: w10a.1s03a9/nCn9eCaYl0e1d382aBt
different temperature in molten salts (the obtained samples
denoted as CN-T, T=300, 400, 450, 500, and 550, refers to the
post-annealing temperature). The structure of pristine g-C3N4
and functionalized g-C3N4 (CN-T) were analyzed by various
characterization technologies. Fig. 1A shows the X-Ray
Diffraction (XRD) patterns of pristine g-C3N4 and CN-T. The XRD
pattern of the pristine g-C3N4 presents two distinct diffraction
peaks at 13.1° and 27.3° corresponding to the in-planar
packing of s-heptazine units (100) and the layer stacking of the
units (002),43 respectively. It is very interesting to observe that
the XRD patterns of samples obviously change after post-
annealing in molten salts, suggesting obvious changes in the
structure of g-C3N4. A new diffraction peak appears at 8.3o (its
intensity gradually increases when the post-annealing
2. Experimental
Preparation of CN-T. N defects and O dopants co-modified g-
C3N4 with different crystallinity (CN-T) were prepared by
modified salt-melted post-treatment of g-C3N4 in mixture of
KCl and LiCl at different temperature. Typically, the obtained g-
C3N4 powder (600 mg) was mixed and grounded with KCl (3.3
g) and LiCl (2.7 g) (without drying) in air. Then, the mixture was
put in a crucible and annealed at different temperature (300
o
o
o
oC, 400 C, 450 oC, 500 C, and 550 C ) for 4 h with a heating
rate of 5 oC min-1 under an Ar atmosphere in a tubular furnace.
The products (denoted as CN-T, T refers to the annealing
temperature: 300 C, 400 C, 450 oC, 500 C, and 550 C) were
cooled to room temperature spontaneously and washed with
boiling deionized water and ethanol several times, followed by
drying at 60 oC under vacuum.
o
o
o
o
o
temperature is lower than 450 C) with the disappearance of
the peak at 13.1o. It is most likely that K+ (K 2p XPS spectrum in
Fig. S3 shows the existence of K+) with larger atomic size than
C and N incorporates between the in-plane units during the re-
polymerization in molten salts,44,45 which enlarges the packing
distance within the layer planes. Importantly, the diffraction
peak at 27.3o shifts gradually to the higher angle with
increasing the post-annealing temperature, indicating the
decreased interlayer distances due to increased degree of
condensation and packing between the layers. These results
demonstrate that post-annealing g-C3N4 in molten salts leads
to the further condensation of s-heptazine units and thus the
obtained samples present increased crystallinity, which can be
strongly confirmed by TEM results (Fig. 2). Note that upon the
post-annealing at higher temperature, the intensity of both
diffraction peaks at 8.3o and 27.3° decreases along with
increased annealing temperature, which might be due to the
formation of defects in carbon nitride structure during the re-
polymerization in molten salts. These results can be confirmed
by elemental analysis, electron paramagnetic resonance (EPR),
Fourier transform infrared (FTIR), Raman, X-ray photoelectron
spectroscopy (XPS), and solid-state 13C nuclear magnetic
resonance (NMR) results.
Preparation of Pd/CN-T hybrid. Pd NPs supported CN-T (Pd/CN-T)
was prepared via a facile impregnation-reduction method. In a
typical process, 400 mg CN-T powder was dispersed in 40 mL water
under vigorous stirring. Then, 10 mL potassium tetrachloropalladate
(K2PdCl4) aqueous solution with a desired concentration was added
in above suspension under vigorous stirring for 3 h. Thereafter, the
powder product was collected via centrifugation, washed with
distilled water, ethanol, and acetone, respectively, and dried in a
vacuum oven at 40 oC overnight. The obtained Pd modified CN-T
powder was re-dispersed in 40 mL water under vigorous stirring in a
100 mL beaker and NaBH4 solution (10 mL) was added for reduction.
The final product was obtained by centrifugation and washed with
deionized water. 10 mL K2PdCl4 aqueous solution with different
concentration (0.307, 0.614, 1.227, 2.454, and 6.135 mg/mL) was
added for preparation of Pdx/CN-T with different Pd contents (x=
0.25, 0.5, 1, 2, and 5, represents Pd content, Pd wt. % = 0.25%, 0.5%,
1%, 2%, and 5%), respectively.
Photocatalytic activity measurement. The test of photocatalytic
activity was carried out in a Pyrex reactor equipped with a
rubber septum under visible light irradiation at room
temperature. Typically, 15 mg photocatalyst was dispersed in 5
mL acetonitrile, followed by addition of aryl halide (0.2 mmol),
alcohol (0.4 mmol), and K2CO3 (0.5 mmol) in reactor. The
above suspension was degassed with Ar for 15 min under
vigorous stirring to remove air prior to light irradiation. A 300
W xenon lamp (PLS-SXE300UV, Perfectlight) coupled with cut-
off filter (λ ≥ 420 nm) was adopted to provide the visible light
source. After reaction for a certain period of time, the product
and unreacted starting substrate were separated by filtration
and rotary evaporation. Then, the yield of the product was
quantified by Gas Chromatography (Agilent 7890A).
Changes in morphology, microstructure, and crystallinity of
the modified samples during the post-annealing in molten salts
were determined by scanning electron microscopy (SEM) and
transmission electron microscopy (TEM). As shown in Fig. S1,
o
after 300 C annealing, the sheet-like structure of g-C3N4 (SEM
and TEM images are shown in Fig. S1A) is destroyed to form
accumulated irregular fragments (Fig. S1B). Further increasing
temperature leads to reconstruction and sinter of the sample
and the nanotip arrays are formed on the surface of bulk
carbon nitride (Fig. S1C). Then, the nanotip arrays gradually
grow into the nanobelt arrays (length of 100-400 nm and
width of 30-100 nm, inset of Fig. S1D), forming a hierarchical
microarchitecture (Fig. S1D). When the temperature is higher
than 500 oC, the samples (CN-500 and CN-550) become
uniformly dispersed nanobelts with length of 200-400 nm and
width of 40-80 nm (Fig. S1E and F). The HRTEM images (Fig. 2)
of the modified samples (CN-450, CN-500, and CN-550) display
two different typical lattice fringes with d-spacing of ~0.96 nm
3. Results and discussion
Structural characterizations of the CN-T samples.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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Jia, Qiaohui
