Highly Efficient Photo-Reduction of p-Nitrophenol by Protonated Graphitic Carbon Nitride Nanosheets

Article abstract of DOI:10.1002/cctc.201801146

Photocatalytic reduction of p-nitrophenol to p-aminophenol is important because of the high toxicity of p-nitrophenol and the wide application of p-aminophenol. Graphitic carbon nitride (g-CN) is an excellent photocatalyst for various photo-reduction reac

Full text of DOI:10.1002/cctc.201801146

Accepted Article
Title: Highly efficient photo-reduction of p-nitrophenol by protonated
graphitic carbon nitride nanosheets
Authors: Jiajia Qian, Aili Yuan, Chengkai Yao, Jiyang Liu, Benxia Li,
Fengna Xi, and Xiaoping Dong
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Highly efficient photo-reduction of p-nitrophenol by protonated
graphitic carbon nitride nanosheets
Jiajia Qian, Aili Yuan, Chengkai Yao, Jiyang Liu, Benxia Li, Fengna Xi, and Xiaoping Dong*
Abstract: Photocatalytic reduction of p-nitrophenol to p-
aminophenol is of significant importance because of the high toxicity
of p-nitrophenol and the wide application of p-aminophenol.
Graphitic carbon nitride (g-CN) is an excellent photocatalyst for
various photo-reduction reactions, but inefficient for photo-reduction
of p-nitrophenol due to the electrostatic exclusion. In this work, we
control the morphology and surface property of g-CN and achieve
significantly enhanced activity. The obtained protonated g-CN
nanosheet (pg-CNNS) material has positively charged surface that
can adsorb p-nitrophenolate anions, therefore facilitating the transfer
of photo-generated electrons from catalyst to p-nitrophenol. Its
reaction rate is 1626 times higher than that of the pristine g-CN.
Besides the surface charge, the morphology of photocatalyst also
has important effect on activity, which is demonstrated by the
relatively low activity of protonated g-CN in comparison to pg-CNNS.
The pg-CNNS photocatalyst has an excellent stability and superior
catalytic universality for photo-reduction of various nitroaromatic
compounds. This work does not only expand the application of a
well-known material, but also highlights the importance of
As a green and energy-saving technique, semiconductor
photocatalysis using solar irradiation has been extensively
employed to transformation of organic compounds during the
oxidization or reduction process.[25,26] The photo-excited
electrons on conduction band (CB) of photocatalysts with strong
reducible property can also reduce PNP to PAP. Nevertheless,
the correspondingly photo-generated holes on valence band (VB)
are highly oxidizing, which will photo-oxidize organic molecules
including PNP. Additionally, besides the insufficient utilization of
solar light the conventional semiconductor photocatalyst of TiO2
has a low CB potential that results in the photo-induced
electrons cannot efficiently reduce PNP.[27] Modification with
noble metals on TiO2 has been demonstrated which is profitable
for the enhancement of photo-reduction activity.[11] However, the
high cost of noble metal limits the practical application of these
photocatalysts. On the other hand, to improve the photocatalytic
behavior of PNP reduction, the competitive oxidation reaction of
PNP by photo-generated holes must be suppressed. In general,
reactants, such as NaBH4, Na2SO3 and hydrazine, are used as
understanding photocatalytic mechanism for designing photocatalyst. scavengers to quench holes.[28-30]
Graphitic carbon nitride (g-CN) is a fascinating polymeric
organic semiconductor photocatalyst of tri-s-triazine with distinct
advantages, for instance the low-cost precursors, facile synthetic
process, high chemical stability and metal-free nature.[31-39]
Furthermore, g-CN has good visible-light response and a narrow
band gap of 2.6~2.8 eV. The CB position of g-CN is much higher
than those of conventional photocatalysts, meaning it has much
stronger reduction ability. Consequently, g-CN presents
excellent photocatalytic performance for photo-reduction
reactions, such as hydrogen evolution from water splitting and
reduction of CO2 to solar fuels.[31-35] However, it is noteworthy
that the photocatalytic activity of g-CN for reduction of PNP to
PAP is extremely low.[40,41] Moreover, in comparison to the
numerous investigation interests on other photocatalytic
reactions by g-CN or g-CN based composites, fewer studies
have been reported on photo-reduction of PNP. And, in most
cases g-CN was only used as photo-reduction medium or
supporter to prepare or load noble metal catalysts. [40-42]
To obtain high photo-reduction efficiency, the photo-excited
electron-hole pairs should be sufficiently separated and then the
photo-generated electrons must be rapidly transported from g-
CN to PNP. With the co-presence of PNP and conventional
reductants or hole scavengers (NaBH4, hydrazine or Na2SO3),
PNP would be transformed to p-nitrophenolate anion. However,
under such condition the surface of g-CN is negatively charged.
As consequence, p-nitrophenolate anion cannot be adsorbed
onto the catalyst surface, therefore limiting the transferring
efficiency of photo-induced electrons to PNP. Herein, we report
a significant enhancement of photocatalytic PNP reduction by
pure g-CN during controlling its morphology and surface
property. Positively charged g-CN nanosheet material is
synthesized by H2SO4 exfoliation and meanwhile protonation
process. The obtained protonated g-CN nanosheet (pg-CNNS)
catalyst has a high activity for photo-reduction of PNP under
Introduction
Because of the high toxicity, nocuity, poor biodegradability and
wide application in industries, nitroaromatic compounds have
been considered as priority within harmfully environmental
pollutants.[1,2] Among numerous nitroaromatic compounds, p-
nitrophenol (PNP) is one of the most frequently occurring by-
products in various industries, and its removal from environment
is very important.[3-5] In comparison to the energy-consuming
and inefficient strategies, the catalytic reduction of PNP to low
toxic p-aminophenol (PAP) under mild condition has attracted
enormous attentions.[6-10] More importantly, the reduced product
(PAP) is a vital intermediate for synthesis of many medicines[10-
13] and precursor for various chemicals.[14-17]
The most popular route for reducing nitroaromatic compounds
to corresponding aniline derivatives is catalytic hydrogenation by
heterogeneous catalysts.[18] However, this process is usually
performed at relatively high temperature and is hard to
selectively reduce nitro groups if additional reducible
functionalities are modified on aromatics. Recently, catalytic
reduction of nitroaromatic compounds in mild condition has
achieved significant progress by noble metal catalysts (Au, Ag,
Pt, Pd and so on) using NaBH4 as reductant.[19-23] Especially, the
reaction of PNP to PAP has become a model to evaluate the
activity of catalysts.[24]
J. Qian, A. Yuan, C. Yao, Prof. J. Liu, Prof. B. Li, Prof. F. Xi, Prof. X. Dong
Department of Chemistry
Zhejiang Sci-Tech University
928 Second Avenue, Xiasha Higher Education Zone, Hangzhou, China
E-mail: xpdong@zstu.edu.cn
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Figure 1. (a) Schematic illustration for the delamination of g-CN into pg-CNNS by concentrated H2SO4; (b) Photographs of (A) g-CN, (B) pg-CNNS
suspension and (C) collected pg-CNNS; (c) TEM and (d) AFM images of pg-CNNS. (e) The height profile of colored lines in (d).
visible light irradiation and its reaction rate is 1626 times higher
than that of the pristine g-CN. Furthermore, it has high stability
and reusability, as well as excellent universality that various
substituted nitroaromatic compounds can be efficiently photo-
reduced to their corresponding aminoaromatic compounds.
nitride.[43-46] A nanosheet-like aspect of pg-CNNS is illustrated in
the transmission electron microscopy (TEM) image (Figure 1c).
The size and thickness of the pg-CNNS were examined by
atomic force microscope (AFM, Figure 1d) and its corresponding
height profiles (Figure 1e). It can be seen that uniform
nanosheets have been formed through the exfoliation processes,
which give an average thickness of 1.0 ± 0.2 nm, corresponding
to 3~4 layers of 2D CN skeleton. The change of surface group
was measured by Fourier transform infrared (FTIR) technology,
as revealed in Figure S1. Absorptions at the range of 1200-1600
cm-1 and 810 cm-1 are characteristic peaks of graphitic carbon
nitride.[36, 37] There is no apparent spectral difference between g-
CN and pg-CN, suggesting the protonation does not influence
the skeleton of CN heterocycle. However, some of these
absorptions of 1200-1600 cm-1 change after the H2SO4 treatment.
It should result from the partial oxidation of CN framework by
H2SO4 and the absorption band at ~1600 cm-1 shifting to the low
Results and Discussion
1. Physicochemical properties of pg-CNNS photocatalyst
The 2D pg-CNNS photocatalyst is prepared by delamination of
the pristine g-CN in sulphuric acid under ultrasonic treatment
(Figure 1a). In comparison to the bulky powder of g-CN (Figure
1b), the exfoliated pg-CNNS is stable in a colloidal suspension.
These nanosheets can be collected by evaporating water, and
the solid sample presents a much more delicate color than g-CN,
which may be related to the protonation effect of carbon
Figure 2. (a) UV-vis spectra of PNP before and after addition of hydrazine; (b) The spectral change of PNP solution with hydrazine by the photocatalytic
treatment of pg-CNNS (λ > 420 nm); (c) Photocatalytic performance under various reaction condition; (d) Photocatalytic performance of pg-CNNS for
reduction of PNP with various hydrazine concentrations.
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wavenumber region in pg-CNNS is ascribed to the presence of
carboxylate groups.[44] Figure S2 compares X-ray diffraction
(XRD) patterns of g-CN, pg-CN and pg-CNNS samples. Two
pronounced diffractions at 13.1o and 27.6o in patterns
respectively correspond to the in-planar (100) diffraction and the
interlayer (002) diffraction of the graphite-like structure of carbon
nitride.[36,37] The pg-CNNS shows a weak broad interlayer (002)
peak, which is attributed to its few-layer structure. Moreover, the
(002) diffraction of pg-CNNS slightly shifts to higher angle
compared to g-CN and pg-CN, reflecting the decreased
interlayer spacing and a structural compaction that is similar to
the reported reference.[45] N2 adsorption-desorption isotherms of
g-CN, pg-CN and pg-CNNS are shown in Figure S3. The pg-
CNNS has a much more marked leap at the high P/P0 range
(0.8~1.0) than g-CN and pg-CN, demonstrating its much more
developed porosity. In general, ultrathin 2D nanosheets have
large surface area. However, once drying them into solids, these
2D nanosheets would re-stack and result in diminishing specific
surface area. Even so, the re-stacked pg-CNNS still presents
much higher specific surface area (25.7 m2 g-1) than g-CN and
pg-CN (8.1 m2 g-1 and 8.8 m2 g-1).
Table 1. Composition analysis of solution after photocatalytic reaction
under different reaction condition by HPLC
Reaction
condition
PNP (retention time of 8.80
min)
PAP (retention time of 2.41
min)
1
2
3
4
5





Essentia LC-15C; detector: SPD-15C; column: WondaSil C18, 4.6 × 200 mm,
5μm; flow:0.9 mL min-1, V (CH3CN/H2O) = 3/7
1: With light + Catalyst + NH2-NH2;
3: Without light; 4: Without catalyst;
2: Without light + Catalyst + NH2-NH2
5: Without NH2-NH2
is also extremely low (< 5%). These results imply that light
irradiation, hydrazine and photocatalyst are necessaries for the
efficient reduction of PNP. The reaction process was also
monitored by high-performance liquid chromatography (HPLC,
Figure S4 and Table 1). The peak at 2.15 min only appears in
the reaction systems with pg-CNNS that is from the adsorbed
sulfate ions. The other two peaks are respectively assigned to
PNP (retention time of 8.80 min) and PAP (retention time of 2.41
min) in these HPLC spectra, which demonstrates that no by-
products were produced. It is found that the signal at the
retention time of 2.41 min does not appear without the condition
of visible light irradiation, photocatalyst or hydrazine, indicating
that these three factors are vital for the photocatalytic reduction
of PNP. With the presence of photocatalyst and hydrazine under
visible light irradiation, all of PNP are reduced to PAP, which is
revealed by the disappearance of PNP peak.
2. Enhanced photocatalytic performance of pg-CNNS for
PNP reduction
The activities of photocatalysts for PNP photo-reduction were
carried out under visible light irradiation (>420 nm). As described
in Figure 2a, aqueous solution of PNP shows an absorption
peak centered at 317 nm. After adding hydrazine into the PNP
solution, the absorption peak shifts to 400 nm, which is ascribed
to the transformation of PNP to p-nitrophenolate ions by the
reaction of acidic phenol hydroxyl group and alkaline hydrazine.
Meanwhile, the color of the solution changes from light yellow to
dark yellow. With the presence of the pg-CNNS sample, the
characteristic peak of the aqueous p-nitrophenolate ion rapidly
declines under visible light illumination, and correspondingly the
solution becomes colorless (Figure 2b). At the meantime, a new
absorption with peak centered at 298 nm that is related to PAP
appears and gradually strengthens with the increase of
irradiation time. The conversion ratio of PNP under various
conditions is presented in Figure 2c. PNP is very stable and
almost no PNP conversion happens without catalyst and
hydrazine in dark. As the single factor (catalyst, hydrazine and
illumination) absences in the reaction, the PNP conversion ratio
Figure 3. (a) Comparison for the photocatalytic activity of pg-CNNS with g-
CN and pg-CN, and (b) their corresponding pseudo-first-order kinetics data
and (c) apparent rate constants; (d) The durability property of pg-CNNS for
photo-reduction of PNP.
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Table 2. Comparison for photocatalytic performance of pg-CNNS with reported photocatalysts
Catalysts
Reducer
Reaction time
(min)
Conversion
(%)
TOF
(10-2 h-1)
Reference
pg-CNNS
g-C3N4-N
hydrazine
NaBH4
18
60
100
0
2
-
This work
[41]
C3N4-ZnS
Na2SO3
alcohol
Na2SO3
Na2SO3
NaBH4
240
160
60
100
25
0.28
0.98
-
[47]
CdS/g-C3N4
Cu2O-rGO-C3N4
CdS
[48]
80
[49]
180
180
70
100
0
0.93
-
[50]
TiO2
[51]
RGO-ZnS
NaBH4
80
0.143
0.80
1
[52]
Fluorinated TiO2
Ce2Zr2O7@rGO
ZrO2-TiO2
Na2SO3
NaBH4
270
120
300
90
[30]
100
100
[53]
Na2SO3
0.27
[54]
Hydrazine is usually used as nucleophilic reagent due to the
existence of lone pairs in nitrogen atoms. This would result in a
possibly competing adsorption of hydrazine with p-
nitrophenolate anion on the positively charged surface of pg-
CNNS. Thus, the concentration of hydrazine is of great
importance for this photocatalytic reaction. As shown in Figure
2d, the photocatalytic activity of pg-CNNS is significantly
improved as increasing the hydrazine concentration from 0.01 M
to 0.02 M, and gradually weakens as the concentration of
hydrazine is increased from 0.02 M to 0.04 M. At a low
hydrazine concentration, the adsorbed hydrazine would be
rapidly oxidized by photo-induced holes to molecular nitrogen
and protons. However, at a high concentration, the adsorbed
hydrazine cannot be immediately oxidized. It would prohibit the
adsorption of PNP onto the surface of pg-CNNS, thus
decreasing the photocatalytic efficiency. We consequently
employed 0.02 M hydrazine as the optimized reaction condition.
The photocatalytic reduction activity of pg-CNNSs is
compared with other graphitic carbon nitride materials, including
g-CN and pg-CN. As exhibited in Figure 3a, g-CN displays very
poor photocatalytic performance and no obvious photo-reduction
happens within 120 min irradiation. By tuning the surface charge
of carbon nitride to positive, the pg-CN sample shows an
apparently improved activity, where ~95 % PNP is transformed
to PAP after 120 min illumination. We attribute this improvement
to the facilitating adsorption of p-nitrophenolate anions on the
positively charged surface of pg-CN. With the increase of
positively charged surface area, the photo-reduction
performance is further enhanced by the pg-CNNS photocatalyst,
and a complete conversion of PNP is realized after 18 min
reaction. A well linear fitting of photocatalytic data (ln C0/C vs. t)
is depicted in Figure 3b, suggesting this photocatalytic reduction
process follows the first-order kinetics. The apparent rate
constant (k) of pg-CNNS is 0.125 min-1, which is about 1626, 7.5
times higher than those of g-CN and pg-CN, respectively (Figure
3c). Additionally, various concentrations of PNP were attempted
in this work, and the result reveals that the pg-CNNS
photocatalyst even can efficiently reduce PNP in high
concentration (20 mg L-1) to PAP (Figure S5). We also compare
the photocatalytic performance of pg-CNNS with these reported
photocatalysts in references (Table 2). The calculated value of
turn over frequency (TOF) is 0.02 h-1 for pg-CNNS that is much
higher than those estimated from reference results. To evaluate
the stability and reusability of pg-CNNS, the successive run was
performed by directly adding a certain amount of PNP in the
post-reacted solution without further treatment of photocatalyst.
Figure 3d illustrates the PNP conversion efficiency of four cycles,
where ~80 % conversion of PNP is retained at the 4th run
Table 3. Photocatalytic activity of pg-CNNS for different group substituted
nitroaromatic compounds.
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Figure 4. (a) UV-vis DRS of g-CN, pg-CN and pg-CNNS; (b) The plots of (αhν)1/2 vs hν. Mott-Schottky curves of (c) g-CN, (d) pg-CN and (e) pg-CNNS.
implying its superior reusability. Other nitroaromatic chemicals
were also employed to estimate the photocatalytic universality of
pg-CNNS. As listed in Table 3, different group substituted
performance of pg-CNNS, we firstly tried to plot the band
alignment of photocatalysts. The optical properties of the as-
prepared g-CN, pg-CN and pg-CNNS samples were examined
using UV-vis diffuse reflectance spectroscope (DRS) technology.
As shown in Figure 4a, the pristine g-CN exhibits an absorption
edge of ~450 nm that represents a band gap (Eg) of 2.64 eV
(Figure 4b). The subsequent protonation treatment makes the
absorption edge slightly shift to the short wavelength region that
is in accordance with the results in published literatures.[44] And
accordingly, the Eg of pg-CN is estimated to 2.68 eV. Due to the
quantum confinement effect of few-layer structure and the
protonation as well, the absorption spectrum of pg-CNNS
nitroaromatic
compounds,
o-nitrophenol,
m-nitrophenol,
nitrobenzene, p-nitrobenzoic acids, p-nitrochlorobenzene and o-
bromonitrobenzene, also present sufficient conversion to
corresponding reductive aminoaromatic products by the
photocatalytic reaction of pg-CNNS under visible light irradiation.
3. Possible photocatalytic mechanism of pg-CNNS for
reduction of PNP
For well understanding the enhanced photocatalytic
Figure 5. (a) EIS curves, (b) transient photocurrent responses and (c) zeta potentials of g-CN, pg-CN and pg-CNNS; Schematic illustration for (d)
electrostatic exclusion of p-nitrophenolate anions by the negatively charged g-CN surface, (e) adsorption of p-nitrophenolate anions on the positively charged
pg-CNNS surface and (f) the possible photocatalytic mechanism of pg-CNNS for photocatalytic reduction of PNP to PAP.
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illustrates a much more obvious blue-shift, and the Eg is
enlarged to 2.85 eV.
holes with strong oxidative ability are captured by hydrazine to
produce N2 and H+. On the other hand, the photo-induced
electrons transfer to the nitro group of PNP that is tightly
adsorbed on the pg-CNNS surface, and subsequently, amination
reaction takes place by absorbing H+ ions from the oxidation of
hydrazine.
The electrochemical Mott-Schottky (MS) technique is an
effective route to determine the conduction behavior of
semiconductor and its flat-band potential (Efb) that can be
regarded as the Fermi level (EF). Similar MS curves of g-CN, pg-
CN and pg-CNNS (Figure 4c-e) suggest their similar electronic
structure and conduction behavior. Also, the
n
type
semiconductor behavior is consistent with these previous
results.[55] The Efb values of g-CN, pg-CN and pg-CNNS are the
X-axis intercepts of prolonging tangents that are evaluated to be
-1.02 eV, -0.90 eV and -1.01 eV vs. Ag/AgCl, respectively. Thus,
associated with their Eg values the band alignment of
photocatalysts is plotted in Figure S6. Compared to the pristine
g-CN, the protonated sample has a low conduction band (CB)
edge potential. This result demonstrates the low activity of g-CN
does not result from the low reduction ability of photo-generated
electrons.
Electrochemical impedance spectroscopy (EIS) was
performed to study the transfer and separation of photo-excited
carriers. As revealed in Figure 5a, the Nyquist plot of pg-CNNS
shows a much smaller semi-cycle than those of pg-CN and g-
CN, which reflects a smaller Rct (charge transfer resistance).[56]
Figure 5b exhibits the photocurrent responses of photocatalysts
during repeated on-off cycles under visible-light irradiation. It is
obviously found that the pg-CNNS sample has the most
strongest photocurrent density, because the ultrathin structure of
pg-CNNS provides short diffusion distance for photo-excited
charges to rapidly transport to surface. Moreover, the small Rct
of pg-CNNS represents a fast interfacial charge transfer, which
may be responsible for the superior performance for PNP
reduction. Besides, surface potential of materials were
measured, and the results are shown in Figure 5c. A zeta
potential of -2.30 mV suggests that g-CN possesses negative
polarity on its surface. With the protonation treatment the
surface charge of pg-CN is changed from negative to positive
(+8.10 mV). As undergoing exfoliation and meanwhile
protonation, the pg-CNNS sample supports much more positive
charges (+14.47 mV) on surface than pg-CN.
Conclusions
In summary, we have realized the efficient conversion of
PNP to PAP by an inactive photocatalyst of graphitic carbon
nitride for this reaction. The pristine g-CN shows poor
photocatalytic ability for PNP reduction because its bulky
morphology results in the high charge recombination rate
and the negatively charged surface will exclude p-
nitrophenolate anions. After exfoliating it into 2D
nanosheets by sulphuric acid, the 2D pg-CNNS sample
presents an ultrathin morphology and its surface loads
plentiful positive charges, where the photo-excited charges
are sufficiently separated, fast transport to the surface, as
well as subsequently transfer onto the adsorbed p-
nitrophenolate anions to form reduced PAP. Its photo-
reduction rate is 1626, 7.5 times higher than those of g-CN
and pg-CN, respectively. Moreover, the pg-CNNS has well
photocatalytic reusability and also has superb activity for
reduction of other functionalized nitroaromatic chemicals.
This work indicates the surface property of photocatalysts is
of vital importance to photocatalytic reaction, especial to the
reduction process because photo-excited electrons are only
able to transfer to the adsorbed molecules. Additionally, this
work will inspire us to attempt other photo-reduction
reactions for negative substrates using this protonated
carbon nitride nanosheet photocatalyst, such as
transforming Cr (VI) to Cr (III).
Experimental Section
In view of above results, we propose a possible mechanism of
pg-CNNS for photo-reduction of PNP with hydrazine. As an
alkaline compound, hydrazine will react with PNP to produce p-
nitrophenolate anion that cannot be adsorbed onto the
negatively charged surface of g-CN (Figure 5d), therefore
suppressing the transfer of photo-induced electron to substrate
molecules. Becuase the exfoliation of pristine g-CN is carried out
in a sulphuric acid system, the terminal amino groups on the
obtained pg-CNNS would accept protons to form positive
amminium ions. Consequently, p-nitrophenolate anions facilely
access to the surface of pg-CNNS and are reduced to PAP with
hydrazine (Figure 5e). The detailed photocatalytic process is
illustrated in Figure 5f. Under visible light illumination, electrons
on the VB of pg-CNNS are excited and transmitted to its CB,
meanwhilely leaving holes on the VB. These photo-generated
charges can fastly diffuse to the surface due to the extremely
thin morphology of pg-CNNS, which is favarable for diminishing
the bulk recombination of eletron-hole pairs. Then, these surface
1 Synthesis of photocatalysts
The g-CN was obtained by thermal polycondensation of melamine, which
was reported in our previous literatures.[43] And protonated g-CN (pg-CN)
was synthesised by treating 3 g g-CN with 60 mL HCl aqueous solutions
(12 mol L−1), similar with reported method.[44] The pg-CNNS was
prepared by the treatment of g-CN with H2SO4. Typically, 2 g g-CN
powder was added into 40 mL of H2SO4 (98 wt%) and stirred for 10 h at
room temperature. Then, the mixture was slowly poured into 100 mL of
deionized water and sonicated with 8h for exfoliation. After pouring off
the clear supernatant, the sediments were rinsed by water again and
again. As most of the deposition could not be separated from the
suspension by centrifugation at 12000 rpm, we achieved the stable
colloidal suspension of pg-CNNS. Finally, the pg-CNNS powder was
obtained by drying at 70 oC overnight.
2 Characterizations
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Transmission electron microscope (TEM) image was taken on a JEOL-
2100 electron microscope operating at an accelerating voltage of 200 kV.
The samples were characterized by X-ray powder diffraction (XRD) by a
DX-2700 diffractometer (Dandong Haoyuan Instrument Co. Ltd. China).
The thickness was assessed using a tapping mode atomic force
microscope (AFM) (Multimode-8; Bruker; USA). Fourier transform
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The pg-CNNS photocatalyst prepared
by sulphuric acid exfoliation of g-C3N4
possesses 2D ultrathin morphology
that is favorable for efficient
separation of photo-excited charges
and then fast diffusion to surface of
Jiajia Qian, Aili Yuan, Chengkai Yao,
Jiyang Liu, Benxia Li, Fengna Xi,
Xiaoping Dong*
Page No. – Page No.
Highly efficient photo-reduction of p-
nitrophenol by protonated graphitic
carbon nitride nanosheets
catalyst.
Furhtermore,
plentiful
positive charges on surface promote
adsorption of p-nitrophenolate anions
and subsequently rapid reduction of
PNP to PAP by photo-generated
electrons. Additionally, the pg-CNNS
has well photocatalytic reusability and
superb activity for reduction of other
functionalized
chemicals.
nitroaromatic
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