Facile synthesis of carbon quantum dots loaded with mesoporous g-C3N4 for synergistic absorption and visible light photodegradation of fluoroquinolone antibiotics

Article abstract of DOI:10.1039/c7dt04360k

The development of facile and efficient synthetic approaches of carbon quantum dots loaded with mesoporous g-C₃N₄ (mpg-C₃N₄/CQDs) is of critical urgency. Here, a facile strategy was developed to synthesize the mpg-C₃N₄/CQDs by using calcinations of the mixture of CQDs, cyanamide, and silica colloid. The obtained composite still retained a considerable total surface area, which could offer a larger population of adsorption sites; therefore enhance the capacity for the adsorption of fluoroquinolones antibiotics (FQs). Under visible light irradiation, mpg-C₃N₄/CQDs demonstrated a higher photocatalytic activity for FQs degradation than did bulk g-C₃N₄ or mpg-C₃N₄. This enhancement might have been ascribed to the high surface area of the mpg-C₃N₄, unique up-converted photoluminescence (PL) properties, and the efficient charge separation of the CQDs. The eradication of FQs followed the Langmuir-Hinshelwood (L-H) kinetic degradation model and absorption pseudo-second-order kinetic model, indicating that surface reactions and chemical sorption played significant roles during the photocatalysis process. The results of electron spin resonance (ESR) technology and reactive species (RSs) scavenging experiments revealed that the superoxide anion radical (O₂^-) and photo-hole (h⁺) were the primarily active species that initiated the degradation of FQs. Based on the identification of intermediates and the prediction of reactive sites, the degradation pathways of ofloxacin (OFX) were proposed. A residual antibiotic activity experiment revealed that mpg-C₃N₄/CQDs provided very desirable performance for the reduction of antibiotic activity.

Full text of DOI:10.1039/c7dt04360k

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Efficient extraction of sulfate from water using
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ARTICLE
Facile synthesis of carbon quantum dots loaded with mesoporous
g-C N for synergistic absorption and visible light
Received 00th
January 20xx,
3
4
photodegradation of fluoroquinolone antibiotics †
a
a
a
a
a
a
b
Yingfei Wang, Fengliang Wang, Yiping Feng, Zhijie Xie, Qianxin Zhang, Xiaoyu Jin, Haijin Liu,
c
a
a
Yang Liu, Wenying Lv, and Guoguang Liu*
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
The development of facile and efficient synthetic approaches of carbon quantum dots loaded with mesoporous g-C
3 4
N
(mpg-C /CQDs) is of critical urgency. Here, a facile strategy was developed to synthesize the mpg-C /CQDs by using
3
N
4
3 4
N
calcinations of the mixture of CQDs, cyanamide, and silica colloid. The obtained composite still retained a considerable
total surface area, which could offer a larger population of adsorption sites; therefore enhance the capacity for the
adsorption of fluoroquinolones antibiotics (FQs). Under visible light irradiation, mpg-C
photocatalytic activity for FQs degradation than did bulk g-C or mpg-C . This enhancement might have been ascribed
to the high surface area of the mpg-C , unique up-converted photoluminescence (PL) properties, and the efficient
3 4
N /CQDs demonstrated a higher
3
N
4
3 4
N
3
N
4
charge separation of the CQDs. The eradication of FQs followed the Langmuir–Hinshelwood (L–H) kinetic degradation
model and absorption pseudo-second-order kinetic model, indicating that surface reactions and chemical sorption played
significant roles during the photocatalysis process. The results of electron spin resonance (ESR) technology and reactive
species (RSs) scavenging experiments revealed that the superoxide anion radical (O ꢀ
−
) and photo-hole (h ) were the
+
2
primarily active species that initiated the degradation of FQs. Based on the identification of intermediates and the
prediction of reactive sites, the degradation pathways of ofloxacin (OFX) were proposed. A residual antibiotic activity
3 4
experiment revealed that mpg-C N /CQDs provided very desirable performance for the reduction of antibiotic activity.
1
0
The synthesis of mesoporous g-C
much attention due to its simplicity and efficiency. The significant
surface and multiple scattering effects of mpg-C can in principle
enhance light harvesting and reactant adsorption capacities.
Moreover, the short diffusion path of electrons from the interior to
the surface of the mpg-C , results in the more easily restrained
recombination of photogenerated electron-hole pairs.
An additional efficient and low cost strategy for the
enhancement of the photocatalytic activity of g-C involves its
3 4 3 4
N (mpg-C N ) has received
4
1
Introduction
3 4
N
Graphitic carbon nitride (g-C
3 4
N ), as a metal-free polymeric
1
1
semiconducting material, has recently been reported to exhibit
1
excellent photocatalytic properties in hydrogen production, CO
2
2
3
3 4
N
reduction, and pollutant degradation, due to its tunable electronic
properties and excellent chemical stability. Unfortunately, the
1
2
3 4
photocatalytic efficiency of bulk g-C N is still far from satisfactory,
2
3 4
N
which is mainly due to the low specific surface area (<10 m /g), high
recombination rates of photogenerated electron-hole pairs, and
5
combination with non-metallic elements. Carbon quantum dots
(CQDs), comprising a novel class of carbon nanomaterials with sizes
of from Ø2-10 nm, have garnered considerable interest due to its
unique optical and electronic properties properties and non-
4
narrow visible-light absorbance. To overcome these limitations,
various approaches have been explored to improve the
3 4
photocatalytic performance of bulk g-C N , including the fabrication
13
4
5
toxicity. With fascinating properties, such as up-conversion
7- photoluminescence (PL) behavior, and excellent photo-induced
electron transfer, CQDs have been widely applied to improve
of micro- and nanostructures, doping with non-metallic elements
6
or metals particles, and compositing with other semiconductors.
14, 15
16
photocatalytic performance.
More recently, Liu et al.
fabricated graphene quantum dots (GQDs)/mpg-C N4 through the
3
pyrolysis of SiO2 and cyanamide, acid removal of the silica
templates, alkali-catalyzed synthesis for graphene quantum dots,
hydroxyl-functionalized of graphene quantum dots, and physical
mixing of GQDs and mpg-C N4
3
.
The hybrid possessed
enhancements photocatalytic performance for the degradation of
organic. However, the synthetic approaches of mpg-C N4/GQDs are
3
time-consuming and the interfacial contacts between the GQDs and
mpg-C N4 are usually weak. In addition, GQDs may block the holes
3
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of mpg-C
3
N
4
by using this synthetic method, leading to an 2.2 Preparation of photocatalysts
undesirable decrease of the total surface area of the composite
2
.2.1 Synthesis of carbon quantum dots
Carbon quantum dots (CQDs) were synthesized via a simple
2
2
from 158.07 m /g to 71.3 m /g. Therefore, the development of
3 4
facile and efficient synthetic approaches of mpg-C N /CQDs is of
5
hydrothermal method according to the previous literature. Citric
acid (1.05 g) was dissolved in 10 ml of water and 0.335 ml of
ethanediamine, and then autoclaved in a Teflon container and
heated at 200 °C for 5 h. After cooling to room temperature, the
solution was centrifuged at 10,000 rpm for 20 min. to remove any
large particles. The aqueous CQDs solution was then dried
overnight at 80 °C to obtain a CQDs powder.
critical urgency.
Fluoroquinolones antibiotics (FQs) are widely employed to
prevent and treat a wide variety of infectious diseases in humans,
17
and as veterinary medications. Currently, a wide range of FQs
have been frequently identified at noticeable concentrations in the
ambient environment, due to their stable chemical structures and
recalcitrance to biological degradation, as well as low degradation
1
8
levels through conventional sewage treatment processes. It has
been demonstrated that antibiotic residues in the environment
could result in the emergence of novel antibiotic resistant bacteria
2
.2.2 Synthesis of mpg-C
3 4
N
1
9
Pure mpg-C N was synthesized via the hard template
3
4
that may ultimately pose a threat to public health. Thus, various
techniques have been extensively studied for the removal FQs from
2
7
method. A 6.0 mL amount of molten cyanamide was added
dropwise into 8 mL of a 12 nm silica colloid, which was used as a
hard template. This mixture was heated at 50 °C with stirring to
evaporate the water and obtain a transparent gel. The resultant
transparent gel was then heated at a rate of 2.8 °C/min. over 3.3 h
to reach a temperature of 550 °C, and then tempered at this
temperature for an additional 3.0 h. The resulting brown-yellow
2
0
aqueous solutions, including adsorption, advanced oxidation
2
1, 22
19
processes (AOPs),
and microbial degradation. The adsorption
method has been widely applied for the removal of organic
23
wastewater due to its convenient operation, lower cost. However,
poor selectivity, small adsorption capacity, secondary pollution, and
other issues might inevitably restrict its practical application. In
recent years, multiple studies have revealed that the combination
of adsorbents and photocatalysts can improve the removal of
4 2
product was treated with NH HF (4.0 M) for 48 h to remove the
silica template. The powder was then centrifuged and rinsed with
distilled water four times, and then twice with ethanol. Finally, the
2
4-26
pollutants.
To the best of our knowledge, the loading of mpg-
mpg-C
3 4
N was dried at 70 °C under vacuum overnight. The bulk g-
3 4
C N
with CQDs as a new form of synergetic absorption and
3 4
C N
was synthesized by the direct heating of 6.0 mL of molten
photocatalysis system to enhance the removal of FQs, has not been
attempted.
cyanamide at a rate of 2.8 °C/min over 3.3 h to attain a
temperature of 550 °C, and then tempered at this temperature for
an additional 3.0 h.
Herein, we report a novel way for the synthesis of mpg-C
CQDs by calcination of the mixture of CQDs, cyanamide, and silica
colloid, and subsequent NH HF removal of the silica templates. The
3 4
N
/
4
2
hybrid was applied to the synergistic absorption and visible light
photocatalytic degradation of FQs. The morphologies, structures,
and optical properties of the prepared hybrid materials were
systematically investigated. The absorption kinetics and
photocatalytic degradation kinetics of FQs was studied. A potential
enhancement mechanism for the absorption and photodegradation
2
.2.3 Synthesis of mpg-C
3 4
N /CQDs
The mpg-C /CQDs were prepared by mixing the molten
3 4
N
cyanamide (6.0 mL), and silica colloid (8 mL) with different amounts
of CQDs at 50 °C under stirring, to evaporate water and obtain a
transparent gel. Subsequently, the mixture was calcined in a
crucible with a cover at 550 °C for 3.3 h, with a ramp rate of
3 4
of the mpg-C N /CQDs was proposed. Finally, the reduction of the
2
.8 °C/min. and tempered at this temperature for an additional 3 h.
Similarly, the silica templates were removed using ammonium
bifluoride, and dried at 70 °C to obtain mpg-C /CQDs powders.
The mpg-C /CQDs photocatalysts were prepared with varied
CQDs contents, and designated at mass percentages of 0.05 %,
antibacterial activity during the photocatalytic process was assessed
through an E. coli inhibition zone test.
3 4
N
3 4
N
2
Experimental
0
.25 %, 0.5 %, 1 %, and 1.5 %.
2
.1 Materials
Ofloxacin (OFX, 98 %), ciprofloxacin (CIP, 98 %), norfloxacin
NOR, 98 %), enrofloxacin (ENR, 98 %), norfloxacin (NOR, 98 %),
lomefloxacin (LOM, 98 %), fleroxacin (FLE, 98 %), cyanamide, and
ammonium bifluoride (NH HF
America). HPLC-grade acetonitrile and methanol were obtained structures of the photocatalysts were recorded by X-ray diffraction
2
.3 Characterization of photocatalyst
(
Transmission electron microscopy (TEM, JEM-2100HR) was
4
2
) were purchased from Aladdin employed to examine the morphologies of all samples. The crystal
(
from CNW Technologies GmbH (Germany). Silicon dioxide (12 nm, (XRD, BRUKER D8 ADVANCE) with Cu Kα radiation Nitrogen
Ludox HS40) was supplied by Sigma-Aldrich Trading Co., Ltd adsorption-desorption isotherms (BET, BECKMAN COULTER SA3100)
(Shanghai). Analytical grade benzoquinone, isopropanol, and were used to calculate the surface areas and pore sizes of the as-
sodium azide were purchased from Taitan (China). Deionized (DI) prepared samples. The compositional analysis of as-prepared
water from a Milli-Q apparatus (Germany) was used throughout this samples were carried out via Fourier transforms infrared spectra
study.
(FT-IR) using a Nicolet 6700 spectrophotometer (Thermofisher). The
ionic characteristics of the as-prepared samples were analyzed by X-
2
| J. Name., 2012, 00, 1-3
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2
ray photoelectron spectroscopy (XPS) using a Thermo VG ESCALAB FED LUMO, and the point charge were determined to predict the
+
ꢀ
− 28, 29
2
50 spectrometer with a monochromatic Al Kα source. Light initial attack sites by h , ꢀOH, and O
absorption properties were obtained through UV-Vis
spectrophotometer (Shimadzu UV 2450), using BaSO powder as 2.4 Residual antibiotic activity test
2
.
a
4
the reflectance standard. Photoluminescence spectra were
monitored with a FluoroMax-4 fluorescence spectrophotometer
The inhibition halo that formed around the sensi-discs on an
agar plate was performed to evaluate the residual antibiotic activity.
(HORIBA Jobin Yvon). Electrochemical measurements were carried
8
Initially, the agar plates were respectively inoculated with 1.2×10
out on a CHI660E electrochemical workstation (CHI Shanghai, Inc.)
with a standard three-electrode cell, which employed an ITO glass
electrode with deposited samples as the working electrode, a
platinum sheet as the counter electrode, and saturated calomel
electrodes (SCE) as the reference electrode. Electron spin
CUF/mL E. coli, and parallel 10 μL reaction samples were separately
spiked on agar plates. The plates were then cultured at 37 °C for 24
h, and the inhibition halo diameter was measured.
resonance (ESR) spectra were conducted on a Bruker model ESR 3 Results and Discussion
JES-FA200 spectrometer. The production of hydroxyl radicals (ꢀOH)
3
.1 Characterization
ꢀ
−
2
and superoxide anion radicals (O ) in the photocatalytic
3
.1.1 Structure and morphology
degradation process was monitored using 5, 5-dimethyl-1-pyrroline
N-oxide (DMPO) as spin-trapping agent. 4-oxo-2, 2, 6, 6-
The TEM images in Fig. 1(a) display the rounded shape of the
tetramethylpiperidine was used as spin-trapping agent for the CQDs, with an average diameter of ~4 nm. The TEM images of g-
1
detection of O
2
.
C
3
N
4
in Fig. S3 show a typical platelet-like morphology with several
g-C N crystallites. As shown in Fig. 1(b), numerous spherical pores
3
4
with a mean diameter of about 12 nm can be observed on the
surface of the mpg-C N , suggesting that the holes of mpg-C N
3 4
2.4 Activity experiments of photocatalysis and adsorption
3
4
The photocatalytic degradation of FQs was conducted in a XPA-
rotary photochemical reactor (Fig. S1, Nanjing Xujiang
were successfully copied by the SiO colloidal solution. After being
2
7
modified with CQDs (Fig. 1(c) (d)), the morphologies of the mpg-
C N /CQDs showed no obvious change. Moreover, certain black
Electromechanical plant). A 350 W xenon lamp with a 420 nm cut-
off filter, a 3 W monochromatic light lamp with a wavelength of 365
nm (Shenzhen lamplic co., LTD.), and a 350 W xenon lamp with a
3
4
dots with an average dimension of about 5 nm were observed,
indicating that the CQDs were successfully introduced into the
matrix of the mpg-C N .
2
90 nm cut-off filter, were employed as the visible light irradiation
3
4
source, the UV light irradiation source, and the simulated sunlight
irradiation source, respectively. A 9 W monochromatic light lamp
with wavelengths of 450 nm, 520 nm, and 660 nm (Shenzhen
lamplic co., LTD.) was used as the blue light, green light, and red
light sources, respectively. The catalysts (0.5 g/L) were introduced
into quartz test tubes, followed by the addition of 50 mL of an
aqueous 8 mg/L FQs solution. Prior to irradiation, the reaction
solution was magnetically stirred in the dark for 5 h in order to
obtain an adsorption-desorption equilibrium of FQs on the
photocatalyst. In addition, the adsorption-desorption experiments
The spectral XRD patterns of g-C N , mpg-C N , and mpg-
3
4
3 4
C N /CQDs composites are shown in Fig. 2(a). The strong diffraction
3
4
peaks at 27.4° might be readily assigned to (002) diffraction planes
JCPDS 87-1526), corresponding to the characteristic interplanar
(
30
stacking structure of the conjugated aromatic system. Other
relatively weak peaks at approximately 12.8° could be indexed to
the (100) diffraction planes, which was close to the relating in-plane
5
structural packing motif of the tri-s-triazine units. Notably, the
mpg-C N and mpg-C N /CQDs peaks were significantly weak, which
3
4
3 4
might have been due to the introduction of the mesoporous
of the mpg-C
3
N
4
and mpg-C
3
N
4
/CQDs were evaluated via magnetic
31
structure. Moreover, the crystal phase of mpg-C N did not
3
4
stirring in the dark for 24 h. During the degradation process,
aliquots of the samples were extracted at predetermined time
intervals, and filtered through 0.22 μm Millipore filters to remove
the photocatalyst. The concentrations of FQs in solution were
analyzed using LC-20A high performance liquid chromatography
change subsequent to coupling with the CQDs, which might have
been due to the low loading amount and high dispersion of the
CQDs.
The nitrogen adsorption-desorption isotherms of g-C N , mpg-
3
4
C N , and mpg-C N /CQDs are shown in Fig. 2(b). The physical
3
4
3 4
(HPLC) (Shimadzu, Japan). Photodegradation intermediates of OFX
adsorption isotherms of mpg-C N and mpg-C N /CQDs show the
3
4
3 4
were identified by liquid chromatography with tandem mass
spectrometry (HPLC–MS/MS). The detailed analytical method is
conveyed in the Text S1.
typical IV with a distinct H1 hysteresis loop, observed in the range
of from 0.6-1.0 P/P , indicating that they existed the mesoporous
0
structures. Further, the pore size distribution in the inset of Fig. 2(b)
revealed that the pores within the mpg-C N and mpg-C N /CQDs
3
4
3 4
2
.5. Theoretical calculations
Molecular orbital calculations and stationary point geometries corresponded to the SiO
were carried out via a hybrid density functional B3LYP method with the mpg-C nanocomposites was determined to be 141.271 m /g,
the 6-311G+ (d, p) basis set (B3LYP/6-311G+ (d, p)). The array of the which was significantly larger than that of g-C
atomic model and atom labeling of the OFX are depicted in Fig. S2. worthy of note that the surface area of the mpg-C
were primarily distributed in the range of from 8-13 nm, which
structure (ca. 12 nm). The surface area of
2
2
N
3 4
2
N
3 4
(16.746 m /g). It is
/CQDs
The frontier electron densities (FEDs) of the highest occupied (133.691 m /g) was much larger than that of previous report (71.3
N
3 4
2
2
16
molecular orbital (HOMO), and the lowest unoccupied molecular m /g). The higher surface area of the mpg-C N /CQDs could offer
3 4
2
2
orbital (LUMO) were calculated. The values of FED HOMO, FED HOMO
+
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additional adsorption and reactive sites, which might enhance its where X represents the electronegativity of the semiconductor (X
3
2
adsorption and photocatalytic capacities.
The FT-IR spectrum was recorded as shown in Fig S4. It may be hydrogen scale (about 4.5 eV). As illustrated in Table S2 and
clearly seen that the vibration of the mpg-C was in good Fig.3(c), the mpg-C presented a significantly reduced band gap
agreement with that of g-C . The spectra exhibited a sharp (2.58 eV) compared with g-C (2.66 eV). This reduction of the
3 4 c
values for g-C N is ca. 4.72 eV). E is the free electron energy on the
4
0
3
N
4
3 4
N
3
N
4
3 4
N
-
1
absorption band at approximately 808 cm , which could be band gap could be attributed to the quantum effect of the
3
3, 34
41
attributed to the tri-s-triazine unit breathing mode.
Several mesoporous structure. In addition, significant positive shifts were
-1
-1
strong vibration peaks, between 1200 cm and 1650 cm
observed in CB following the introduction of CQDs. Accordingly, the
3
3
corresponded to the C=N and CN stretching vibration modes. The fermi levels of CQDs (-0.3 eV) were significantly lower than that of
-1
42
sharp and relatively weaker band around 2178 cm could be g-C
3
N
4
(-0.61 eV). Therefore, the electrons in the Fermi level of
could easily inject into the CQDs. Generally, the
while the wider bands at located at ~3166 cm could be attributed accumulation of electrons inevitably causes the positive shifting of
3
5, 36
assigned to the -C-N triple bond stretching of cyano groups,
3 4
mpg-C N
-
1
3
6
to N–H stretching. We noted that there were no obvious changes the CB, leading to shorter migration paths for photogenerated
4
3
observed following the loading with CQDs, which indicated that the electrons.
CQDs did not alter the chemical structure of mpg-C Generally, the decrease in the electron–hole recombination
The XPS survey spectrum in Fig. S5, Fig. 2(c) and (d) depict that rate gives rise to a lower PL intensity and higher photocatalytic
3 4
N .
6
, 44
the carbon (C1s), nitrogen (N1s) and oxygen (O1s) elements existed activity.
on the mpg-C and mpg-C /CQDs samples. It was shown that at an excitation wavelength of 350 nm. The g-C
the element ratio of C/N (58.1 %) of mpg-C /CQDs was larger strong fluorescence emission peak at ca. 350 nm. However, the PL
than that of mpg-C (56.9 %), indicating that the CQDs affected intensity of the mpg-C decreased significantly in contrast to the
the elemental contents of the complex. The C1s of mpg-C could g-C , which implied that it could significantly inhibit the
be divided into three primary peaks, at 284.6 eV (19.45 %), 285.6 eV recombination of photogenerated charge carriers. After coupling
50.45 %), and 288 eV (60.10 %), corresponding to sp2 C-C bonds, with CQDs, the PL intensity of the mpg-C /CQDs composites
Fig. 3(d) depicts the PL emission spectra of the samples
3
N
4
3
N
4
3 4
N
displayed a
3 4
N
3
N
4
3 4
N
3
N
4
3 4
N
(
3 4
N
3
7
C=O, and N-containing aromatic rings (N-C=N), respectively. decreased significantly, indicating that the CQDs might promote the
Subsequent to doping with CQDs, the peak at 284.6 eV (30.64 %) of transfer of charges and inhibit the electron-hole recombination rate.
3 4 3 4 3 4
the mpg-C N /CQDs was larger than that of the mpg-C N , which Moreover, the emission peak of mpg-C N /CQDs exhibited an
might be attributed to the adventitious carbon or sp2 bonded C-C obvious red-shift, from 454 nm to 470 nm, which was associated
bonds of graphitic carbon from the CQDs. High resolution N1s with the lower band gap energy.
spectra displayed three deconvolution peaks, with binding energies
Transient photocurrent generation and electrochemical
of 398.5 eV, 400 eV, and 400.8 eV, which might be the sp2 impedance spectra (EIS) were conducted to further investigate the
3
8
hybridized aromatic of triazine units (C=N-C)，N-(C)
3
, and N-H.
photo-induced charge transfer and separation behaviors. As shown
in Fig. 3(e), the mpg-C /CQDs exhibited the highest photocurrent
intensity, in contrast to g-C and mpg-C , which revealed the
higher separation and transfer efficiencies of photogenerated
3 4
N
3.1.2 Optical and electrochemical properties
3
N
4
3 4
N
The photoluminescence (PL) spectra of the CQDs are
2
7
electron-hole pairs.
semicircular Nyquist plots for mpg-C
(f)), compared to g-C and mpg-C
separation of the photogenerated electron-hole pairs of mpg-
In addition, an obvious decrease in
/CQDs was observed (Fig.
, which implied the effective
presented in Fig. 3(a). The up-converted emissions of CQDs were
remarkably located in the range of from 400 nm to 700 nm, when
excited by long-wavelength light spanning 650 nm to 900 nm. The
results indicated that CQDs existed the superior up-converted
property.
3 4
N
3
3
N
4
3 4
N
45
C
3
N
4
/CQDs following the introduction of CQDs.
In summary, the characterization results confirmed that the
CQDs were successfully loaded onto the surface of the mpg-C
The high specific surface area of mpg-C might provide additional
adsorption and reaction sites during the degradation process. In
3 4
addition, CQDs could greatly improve the absorbance of mpg-C N
The UV-vis diffuse reflectance spectra (DRS) of g-C
, and mpg-C /CQDs are depicted in Fig. 3(b). The g-C
exhibited a fundamental absorption band at ~466 nm, which was
3 4
N , mpg-
3 4
N .
C
3
N
4
3
N
4
3 4
N
3 4
N
37
consistent with previous reports. An obvious red-shift was
3 4
observed in the spectra of the mpg-C , in contrast to g-C N ,
3
N
4
in the visible region, as well as to enhance its electron charge
carrier separation and transfer capacities. Further, the up-
conversion PL ability of CQDs converted long-wavelength visible
light to shorter wavelengths, leading to the broadening of the broad
spectrum of ambient sunlight. These superior properties of the
CQDs might result in the enhancement of the photocatalytic
which might have been due to the decrease in the conjugation
length, and the strong quantum confinement effect of the pore
39
structure. Following the modification of the CQDs, the light
harvesting capability was improved remarkably in the 450 nm to
8
00 nm range, indicating that the CQDs could improve the light
14
absorption capacity. In order to further investigate the energy
band structure of the composites, the energy gaps (Eg), valence
band (VB), and conduction band (CB) edge potentials were
calculated as following:
3 4
performance of the mpg-C N /CQDs composite.
3.2 Adsorption kinetics of FQ
As shown in Fig. 4(a), the mpg-C
adsorption capacity of FQs than g-C , which may have been
1
/2
(1)
(
ahv) =A(hv-E)
g
3 4
N showed stronger
E
VB = X - E
C
+ 0.5E
g
(2)
(3)
3 4
N
E
CB= EVB -E
g
attributed to its mesoporous structure and high surface area. In
4
| J. Name., 2012, 00, 1-3
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DOI: 10.1039/C7DT04360K
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ARTICLE
addition, the adsorption capacity of the mpg-C
3
N
4
/CQDs was
, which was well initial concentrations of mpg-C
presented in Fig. S6(b). With an increase of initial substrate
The photocatalytic degradation effects of OFX at different
slightly decreased in comparison with mpg-C
coincide with the results of BET (Fig. 2(b)).
3
N
4
3 4
N
/CQDs under visible light are
In order to well understand the adsorption mechanism of FQs concentrations, from 4.0 to 20.0 mg/L, the rate constants of OFX
-1
onto the as-obtained samples, one of the most commonly used FQs, decreased from 0.0489 to 0.0132 min . At higher initial OFX
ofloxacin (OFX), was studied as a representative of FQs. The concentrations, incident light was more liable to be absorbed,
absorption curves of OFX in Fig. 4(b) over the different samples which led to lower population of the activated photons in the mpg-
5
0
revealed that the solution systems almost attained adsorption
equilibrium in 5 h. The pseudo-second-order kinetic model was
C
3
N
4
/CQDs, resulting in a decrease of the degradation rate.
Further, the Langmuir-Hinshelwood (L-H) model was employed
then used to describe the adsorption behavior between mpg- to study the photocatalytic degradation behavior of OFX. The L-H
/CQDs and OFX. The kinetic equations are expressed as the model was described as follows:
3 4
C N
1
1
[OFX]0
following:
=
+
k2
k
LH
K
kLH
t
1
t
(4)
(5)
=
+
2
-1
qt k1qe qe
2 0
where k is the pseudo-first-order rate constant (min ), [OFX]
where q
t e
and q
(mg/g) are the adsorption capacities of OFX at time is the initial concentration of OFX (mg/L), kLH represents the L-H
-1
t and equilibrium time, respectively, and k
1
3 4
(g/(mg·min) is the adsorption constant of OFX over the mpg-C N /CQDs surface (mg ),
pseudo-second-order rate constant. As shown in Fig. 4(b) and Table and K is the intrinsic reaction rate constant (mg/min). From Fig. 4(e),
S3, the pseudo-second-order model exhibited the best alignment it can be observed that the L-H kinetic model of the OFX
2
2
(
R >0.99), suggesting that the sorption between the mpg- degradation had the best fit (R =0.998), indicating that the solid-
3 4
C N
/CQDs and OFX was governed by the chemical bonds at the liquid interface was the dominant site of the photocatalytic
4
6
3 4
catalyst surfaces. The mpg-C N /CQDs contained the π-π bonds on degradation. In other words, the degradation of the OFX primarily
5
1
its surfaces, which might have been the dominating interactive occurred at the surface of the mpg-C
force for the adsorption of chemicals that contained aromatic
3
N
4
/CQDs.
47, 48
rings.
3
.3.3 Photocatalytic activity of mpg-C
3
N
4
/CQDs under irradiation
of different light sources
3.3 Photocatalytic degradation of antibiotics
As shown in Fig. 4(f), the mpg-C
3
N
4
/CQDs composites exhibited
3
.3.1 Enhanced photocatalytic activity of mpg-C
3
N
4
/CQDs under enhanced photocatalytic activity (about 1.7 and 2.7 times higher)
than mpg-C under simulated sunlight (ca. >290 nm) and visible
visible light irradiation
3 4
N
light irradiation (ca. >420 nm), respectively. Interestingly, almost no
enhancement of activity was observed under UV light (ca. 365 nm)
irradiation. This phenomenon might have been attributed to the
low up-converted PL response of CQDs under short wavelengths,
As shown in Fig. 4(c), fluoroquinolones (FQs), including
ofloxacin (OFX), norfloxacin (NOR), ciprofloxacin (CIP), enrofloxacin
(
ENR), lomefloxacin (LOM), and fleroxacin (FLE), underwent much
more highly efficient photodegradation in the presence of mpg-
/CQDs than with mpg-C alone. These results indicated that
which thereby limited the energy transfer from CQDs to mpg-C
In order to further investigate the role of the PL up-conversion
properties of the CQDs, the photocatalytic activity of mpg-C and
mpg-C /CQDs was evaluated using different single wavelength
lamps as light sources. It was observed that the photocatalytic
activity of the mpg-C /CQDs was 3.3, 2.6, and 2.1 times higher
than that of mpg-C under red light (ca. 660 nm), green light (ca.
20 nm), blue light (ca. 450 nm), respectively. The mpg-C /CQDs
3 4
N .
C
3
N
4
3 4
N
the photocatalytic activity was remarkably enhanced following the
introduction of the CQDs. In order to more clearly elucidate the
photocatalytic activity of the as-obtained samples, OFX was
selected as an analog of FQs. A blank experiment in Fig. 4(d)
showed that no appreciable change in degradation efficiency was
observed, suggesting that the self-photolysis of OFX could be
neglected under visible light irradiation. It was obvious that the g-
3 4
N
3 4
N
3 4
N
3 4
N
5
3 4
N
exhibited remarkable photocatalytic activity under long-wavelength
visible light irradiation, indicating that the up-conversion
fluorescent properties of CQDs played a vital role in enhancing the
photoactivity.
C
3
N
4
exhibited weak absorption and photocatalytic activity (8.3 %).
In contrast, the degradation of OFX was significantly increased to
5.6 % when mpg-C was employed as the photocatalyst. The
6
3 4
N
photodegradation efficiency was significantly improved following
the introduction of CQDs. Nearly 90.1 % of the OFX was
decomposed over the same timeline under visible light irradiation.
In addition, the kinetic rate constant gradually improved, from
3
.3.4 Photocatalyst stability
As shown in Fig. 5(a), following four cycles under uniform
-1
-1
0
.0128 min to 0.0350 min , following the increase of CQDs, from 0 conditions, 80.8 % of the OFX was decomposed in 7 h, which was
to 0.5 wt%. However, the photocatalytic activity of the mpg- slightly lower than that of the first round (90.1 %). Simultaneously,
/CQDs composites decreased with excess amounts of CQDs no obvious change was observed in the absorption capacity of the
>0.5 wt%), which might have been attributable to the CQDs mpg-C /CQDs following four cycles. In addition, the FT-IR spectra
competition with mpg-C via the absorption of photons, thereby (Fig. 5(b)) revealed no obvious change in characteristic stretching
reducing the formation of reactive species (Fig. S6(a)).
3 4
C N
(
3 4
N
3 4
N
4
9
subsequent to four cycles. The above results indicated that the
mpg-C /CQDs exhibited high stability and photocatalytic activity,
which might be due to strong π-π stacking interactions between the
3 4
N
3.3.2 Photodegradation kinetics of OFX
5
3 4
CQDs and mpg-C N .
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DOI: 10.1039/C7DT04360K
ARTICLE
Dalton Transactions
charge C43 atom, which led to the cleavage of the heterocyclic ring,
thereby giving rise to m/z 354. m/z 354 may be further oxidized by
3.4 Underlying photocatalyst mechanisms of OFX
RSs to form
a quinolone unit cleavage product m/z 326.
3.4.1 Predominant reactive species
Subsequently, m/z 312 was generated through the demethylation
of m/z 326. Pathway II was considered as the cleavage of
piperazinyl ring via the attack of N9 and N10 atoms of the
piperazine ring by RSs, resulting in an ammonium anion radical. This
An ESR spin trap technique was performed to investigate the
3 4
reactive radicals that were generated during the mpg-C N /CQDs
process. As depicted in Fig. 6(a), (b), and (c), a 1:2:2:1 quartet
pattern signal of DMPO-ꢀOH spin adducts, the four-line
ꢀ
−
1
radical could undergo deprotonation by O
2
2
or O to generate a
ꢀ
−
characteristic signal for DMPO-O
2
species, and characteristic 1:1:1
carbon-centered radical, which could then evolve into keto-groups.
Further, the cleavage of the piperazinyl ring occurred, giving rise to
m/z 391 with keto-groups. The further cleavage of the piperazine
ring through the oxidation of RSs might lead to products with m/z
1
triplet signal of the TEMP- O
, and mpg-C /CQDs, indicating that ꢀOH, O
existed in the photocatalytic system. Moreover, all of these derived
2
adduct were observed in g-C , mpg-
3 4
N
ꢀ
−
1
C
3
N
4
3
N
4
2 2
, and O
mpg-C
mpg-C
3
N
N
4
4
/CQDs signals were significantly stronger than that of the
and g-C , which implied that more RSs could be
3
04 (A), m/z 304 (B), m/z 278, and m/z 260. Pathway III presents
N
4
+
3
3
the demethylation reaction with h attacking the N9 in the
piperazine ring, giving rise to the formation of m/z 348.
Subsequently, the cleavage of the piperazine ring occurred.
Pathway IV was regard as decarboxylation. Reactive site
identification revealed that C30 might preferentially be attacked by
produced following the introduction of the CQDs.
To further differentiate the contributions of various RSs (such
+
−
ꢀ
−
1
as h , e , ꢀOH, O
over mpg-C /CQDs, radical trapping experiments were carried
out through the addition of benzoquinone (BQ, 1.0 mM),
isopropanol (IPA, 10 mM), sodium azide (NaN , 75 mM), sodium
oxalate (Na , 10 mM), and potassium dichromate (K Cr , 50
As shown in Fig. 6(d), IPA induced a modest inhibitory
effect, with inhibition rates of 17.3 %. In addition, the contribution
2 2
, and O ) on the OFX photoreaction process of
3 4
N
ꢀ
−
O
2
due to its more positive point charge. Therefore,
3
decarboxylation might take place at the quinolone groups, leading
to the formation of m/z 318 and m/z 304 (B). A similar reaction was
2
C
2
O
4
2
2 7
O
7
, 52
µM).
54
also reported in previous studies.
1
rates of
45.4 %), which was 28.1 %. On the contrary, BQ, KI, Na
Cr demonstrated obvious inhibitory effects toward the
degradation of OFX, which were found to be 84.0 %, 72.7%, 56.8%,
O
2
could be calculated via the inhibition rate of NaN
3
3
.4.3 Potential photocatalytic mechanisms
(
2
C
2
O
4
, and
5
From the above results and the scientific literature,
a
K
2
2 7
O
potential photocatalytic mechanism over the mpg-C
composite was proposed. As illustrated in Fig. 8, under visible light
irradiation, the surfaces of mpg-C /CQDs were excited by
3 4
N /CQDs
ꢀ
−
2
and 70.8 % of the inhibition rate. These results suggested that O ,
3 4
N
+
−
photo-generated h and e played critical roles in the photocatalytic
absorbing light with a wide wavelength (< 500 nm) range to form
electron-hole pairs. Owing to the confined space effect of the pore
structure, electrons may be rapidly migrated from the interior to
the surface through confined pore channels, leading to the
separation of conduction band (CB) electron and valence band (VB)
−
degradation of OFX. Previous studies have confirmed that e might
contribute to the degradation of organics, via captured oxygen, to
ꢀ
− 5
generate O
2
.
3.4.2 Transformation products and pathways
+ 4
h . Meanwhile, the CQDs can convert light with long wavelengths (>
Using the LC−MS/MS technique, the chemical structures and 500 nm) to shorter wavelengths (< 500 nm) owing to its up-
m/z values of the photocatalytic transformation products (TPs) converted PL properties, which is subsequently absorbed by mpg-
were summarized in Table S4. Ten intermediate products were . Because the CB position of mpg-C /CQDs (2.58 eV) was
detected via mass spectrum analysis HPLC-MS/MS. Among them, more negative than the standard reduction potential of O
TPs with m/z 391, 348, 304(A), 278, and 260 might derived from the 0.33 eV), the excited electrons in the CB could be easily trapped by
C
3
N
4
3 4
N
ꢀ
−
2
/ O
2
(-
ꢀ
− 5
1
cleaved piperazine ring. TPs with m/z 304(B) and 318 might be molecular oxygen to form O
2 2
. Other RSs (e.g. ꢀOH, O
) would
attributed to the cleavage of the carboxyl group, whereas m/z 354, subsequently be generated by the energy or electron transfer of
ꢀ
− 7, 55
.
326, and 312 might be proposed as the heterocyclic ring cleavage
O
2
Notably, due to the high surface area of the mpg-
products of OFX. Frontier electron densities (FEDs) were
3 4
C N /CQDs, as well as the π–π interactions between the catalyst
subsequently calculated to predict the reaction site for RSs attack. and substrate, OFX molecules may be easily absorbed to the surface
ꢀ
−
+ 1
As shown in Table S5, N9 (0.2045) and N10 (0.1718) atoms in the of the mpg-C
3
N
4
/CQDs. Finally, RSs (O
/CQDs surface reacted with the OFX molecule, resulting in its
these two reaction sites were likely to be attacked by h . C24 decomposition.
0.3289), N9 (0.2053) and N10 (0.1755) exhibited a highest values of
2 2
, h , O , ꢀOH) on the mpg-
2
piperazine had higher FED HOMO values than others, indicating that
3 4
C N
+
53
(
2
2
FED HOMO+ FED LUMO, which implied that the addition of a hydroxyl 3.5 Antibacterial activity
radical could occur in the heterocyclic and piperazine rings. Further,
E. coli was employed as the reference organism to assess the
C30 (0.4240) was found to be a more positive point charge than
changes in antibacterial activity during the photocatalytic
others, revealing that C30 might be preferentially attacked by
56
degradation process. Variations in the antibacterial activity of the
ꢀ
− 28, 29
2
O .
treated OFX solution were associated with the inhibition halo
diameter. As shown in Fig. S7, during the photocatalysis process, a
significant decay in antibiotic activity was observed, and the
antibiotic activity disappeared following 120 min visible light
As shown in Fig. 7, three major pathways encompassing the
cleavage of piperazinyl ring, decarboxylation, and the breakdown of
the heterocyclic ring, were involved in the degradation of OFX.
Pathway I was initiated by ꢀOH attack on the most positive point
6
| J. Name., 2012, 00, 1-3
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ARTICLE
irradiation. The elimination of the residual antibacterial activity
might be due to the cleavage of the molecular structure of OFX,
Wang, K. Yao and W. Lv, Applied Catalysis B Environmental,
017, 207, 103-113.
S. Wang, D. Li, C. Sun, S. Yang, Y. Guan and H. He, Applied
Catalysis B Environmental, 2014, 144, 885-892.
G. Li, X. Nie, J. Chen, Q. Jiang, T. An, P. K. Wong, H. Zhang,
H. Zhao and H. Yamashita, Water Research, 2015, 86, 17-
2
1
8
6.
which was confirmed by LC−MS/MS technique (Fig. 8 and Tab. S4).
Thus, it is possible to conclude that mpg-C /CQDs had the
3 4
N
7
.
capacity to satisfactorily reduce the antibacterial activity of OFX,
which may provide for optimal approaches to decrease
antibacterial activity in pharmaceutically contaminated waters.
2
4.
8
9
.
.
Y. Liu, J. Li, B. Zhou, H. Chen, Z. Wang and W. Cai, Chemical
Communications, 2011, 47, 10314-10316.
Q. Chen, J. Li, B. Zhou, M. Long, H. Chen, Y. Liu, W. Cai and
W. Shangguan, Electrochemistry Communications, 2012,
4
Conclusions
3 4
In summary, the mpg-C N /CQDs composite photocatalyst was
2
0, 153-156.
successfully prepared via a thermal polymerization method, using
silica nanoparticles as templates, which enabled the capacity to
efficiently remove (FQs) through the synergistic of adsorption and
1
0.
Y. Liu, H. Zhou, B. Zhou, J. Li, H. Chen, J. Wang, J. Bai, W.
Shangguan and W. Cai, International Journal of Hydrogen
Energy, 2011, 36, 167-174.
photocatalysis. The mpg-C
3
N
4
/CQDs enhanced the adsorption 11.
D. Chen, K. Wang, D. Xiang, R. Zong, W. Yao and Y. Zhu,
Applied Catalysis B Environmental, 2014, 147, 554-561.
X. Gao, X. Jiao, L. Zhang, W. Zhu, X. Xu, T. Chen and H. Ma,
Rsc Advances, 2015, 5, 76963-76972.
Z. Hui, L. Zhao, F. Geng, L. H. Guo, B. Wan and Y. Yu,
Applied Catalysis B Environmental, 2016, 180, 656-662.
X. Yu, J. Liu, Y. Yu, S. Zuo and B. Li, Carbon, 2014, 68, 718-
capacity of FQs, which might have been attributed to the formation
of additional adsorption sites on the surface of the mesoporous
1
1
1
1
2.
3.
4.
5.
structure. In contrast to bulk g-C
3 4 3 4
N and mpg-C N , the mpg-
3 4
C N
/CQDs exhibited enhanced photocatalytic activity under visible
light irradiation toward the degradation of OFX. Results
demonstrated that the up-converted PL properties and efficient
charge separation capacities of the CQDs dramatically enhanced
photoactivity. In addition, the disappearance of OFX followed the
Langmuir-Hinshelwood (L-H) kinetic degradation and absorption
7
24.
S. Zhu, Q. Meng, L. Wang, J. Zhang, Y. Song, H. Jin, K.
Zhang, H. Sun, H. Wang and B. Yang, Angewandte Chemie,
2013, 52, 3953–3957.
pseudo-second-order kinetic models, indicating that the 16.
degradation of OFX occurred primarily at the surface of mpg-
J. Liu, H. Xu, Y. Xu, Y. Song, J. Lian, Y. Zhao, L. Wang, L.
Huang, H. Ji and H. Li, Applied Catalysis B-Environmental,
2017, 207, 429-437.
L. Ge, J. Chen, X. Wei, S. Zhang, X. Qiao, X. Cai and Q. Xie,
Environmental Science & Technology, 2010, 44, 2400-
3 4
C N /CQDs and was mediated by chemical bond sorption. ESR
ꢀ
−
17.
technology and radical scavenger experiments confirmed that O
2
+
−
h , and e played significant roles during the photocatalytic
degradation of OFX. The photocatalytic degradation pathways of
OFX were proposed using the identification of intermediates by
HPLC-MS/MS, and the prediction of reactive sites via FEDs. Further,
a residual antibiotic activity experiment revealed that the antibiotic
activity of the OFX solution could be effectively reduced by mpg-
2
405.
1
1
8.
9.
L. Ge, G. Na, S. Zhang, K. Li, P. Zhang, H. Ren and Z. Yao,
Science of the Total Environment, 2015, s 527–528, 12-17.
M. Sturini, A. Speltini, F. Maraschi, L. Pretali, A. Profumo,
E. Fasani, A. Albini, R. Migliavacca and E. Nucleo, Water
Research, 2012, 46, 5575-5582.
C
3
N
4
/CQDs under visible light irradiation. Hence, the present study 20.
demonstrated that mpg-C /CQDs, which enabled synergistic
absorption and photocatalytic processes, are
promising 21.
C. G. and and K. G. Karthikeyan, Environmental Science &
Technology, 2005, 39, 9166.
D. A. M. Alexandrino, A. P. Mucha, C. M. R. Almeida, W.
Gao, Z. Jia and M. F. Carvalho, Science of the Total
Environment, 2017, 581, 359-368.
3 4
N
a
technology for the elimination of the antibiotic activity of FQs.
2
2
2.
3.
N. Barhoumi, L. Labiadh, M. A. Oturan, N. Oturan, A.
Gadri, S. Ammar and E. Brillas, Chemosphere, 2015, 141,
Acknowledgements
2
50.
This work was supported by the National Natural Science
Foundation of China (No. 21677040 and 21377031), Science and
H. Peng, B. Pan, M. Wu, Y. Liu, D. Zhang and B. Xing,
Journal of Hazardous Materials, 2012, 233-234, 89.
R. K. Sharma, Y. N. Chouryal, S. Chaudhari, J.
Saravanakumar, S. R. Dey and P. Ghosh, Acs Appl Mater
Interfaces, 2017, 9, 11651.
Technology Planning Project of Guangdong Province (No. 24.
017A050506052).
2
2
2
2
2
2
5.
6.
7.
8.
9.
P. Chen, X. Liu, R. Jin, W. Nie and Y. Zhou, Carbohydrate
Polymers, 2017, 167, 36.
W. Wan, S. Yu, F. Dong, Q. Zhang and Y. Zhou, Journal of
Materials Chemistry A, 2016, 4, 7823-7829.
Notes and references
1.
2.
3.
4.
Q. Han, B. Wang, Y. Zhao, C. Hu and L. Qu, Angewandte
Chemie-International Edition, 2015, 54, 11433-11437.
W. Yu, D. Xu and T. Peng, Journal of Materials Chemistry A,
G. Zhang and X. Wang, Journal of Catalysis, 2013, 307,
2
46-253.
H. S. Wahab, T. Bredow and S. M. Aliwi, Surface Science,
009, 603, 664-669.
Y. Ji, L. Zhou, C. Ferronato, X. Yang, A. Salvador, C. Zeng
2
015, 3, 19936-19947.
X. Wang, S. Blechert and M. Antonietti, Acs Catalysis,
012, 2, 1596–1606.
2
2
C. Chang, Y. Fu, M. Hu, C. Wang, G. Shan and L. Zhu,
and J. M. Chovelon, Journal of Photochemistry
Photobiology A Chemistry, 2013, 254, 35-44.
&
Applied Catalysis B Environmental, 2013, s 142–143, 553-
560.
3
0.
H. J. Li, B. W. Sun, L. Sui, D. J. Qian and M. Chen, Physical
5.
F. Wang, P. Chen, Y. Feng, Z. Xie, Y. Liu, Y. Su, Q. Zhang, Y.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
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DOI: 10.1039/C7DT04360K
ARTICLE
Dalton Transactions
Chemistry Chemical Physics Pccp, 2015, 17, 3309.
31.
32.
33.
34.
35.
36.
37.
38.
39.
J. Hong, X. Xia, Y. Wang and R. Xu, Journal of Materials
Chemistry, 2012, 22, 15006-15012.
A. Cai, Q. Wang, Y. Chang and X. Wang, Journal of Alloys &
Compounds, 2016, 692, 183-189.
Y. Zheng, L. Lin, B. Wang and X. Wang, Angewandte
Chemie, 2015, 54, 12868.
Y.-S. Xu and W.-D. Zhang, Chemcatchem, 2013, 5, 2343-
2351.
Y. Zhang, H. Zhao, Z. Hu, H. Chen, X. Zhang, Q. Huang, Q.
Wo and S. Zhang, Chempluschem, 2015, 80, 1139-1147.
C. Shen, C. Chen, W. Tao, Z. Zhao, X. Wang and A. Xu,
Journal of Colloid & Interface Science, 2015, 456, 7-14.
Y. Yuan, L. Zhang, J. Xing, M. I. Utama, X. Lu, K. Du, Y. Li, X.
Hu, S. Wang and A. Genç, Nanoscale, 2015, 7, 12343.
Y. Hou, Z. Wen, S. Cui, X. Guo and J. Chen, Advanced
Materials, 2013, 25, 6291.
Y. Cui, J. Zhang, G. Zhang, J. Huang, P. Liu, M. Antonietti
and X. Wang, Journal of Materials Chemistry, 2011, 21,
13032-13039.
40.
41.
42.
Y. Hong, C. Li, G. Zhang, Y. Meng, B. Yin, Y. Zhao and W. Shi,
Chemical Engineering Journal, 2016, 299, 74-84.
H. M. Zhao, C. M. Di, L. Wang, C. Yuan and Q. H. Xu,
Microporous & Mesoporous Materials, 2015, 208, 98-104.
N. Tian, Y. Zhang, X. Li, K. Xiao, X. Du, F. Dong, G. I. N.
Waterhouse, T. Zhang and H. Huang, Nano Energy, 2017,
38, 72-81.
43.
44.
45.
46.
47.
48.
E. Gao, W. Wang, M. Shang and J. Xu, Physical Chemistry
Chemical Physics, 2011, 13, 2887-2893.
Z. Tong, Y. Dong, T. Xiao, T. Yao and Z. Jiang, Chemical
Engineering Journal, 2015, 260, 117-125.
F. Xiao, F. Wang, X. Fu and Y. Zheng, Journal of Materials
Chemistry, 2012, 22, 2868-2877.
Y. Liu, Colloids
& Surfaces A Physicochemical &
Engineering Aspects, 2008, 320, 275-278.
W. Chen, L. Duan and D. Zhu, Environmental Science &
Technology, 2007, 41, 8295-8300.
S. Gotovac, Y. Hattori, D. Noguchi, J. Miyamoto, M.
Kanamaru, S. Utsumi, H. Kanoh and K. Kaneko, Journal of
Physical Chemistry B, 2006, 110, 16219.
4
5
9.
0.
D. Tan, S. Zhou and J. Qiu, Acs Nano, 2012, 6, 1059.
X. Lei, G. Wang, F. Ma, Y. Zhao, L. Nan, Y. Guo and Y. Xia,
Applied Surface Science, 2012, 258, 7039-7046.
5
5
5
5
5
1.
2.
3.
4.
5.
Y. Li, J. Niu, L. Yin, W. Wang, Y. Bao, J. Chen and Y. Duan,
Journal of Environmental Sciences, 2011, 23, 1911-1918.
H. Xiao, J. Zhu and A. Thomas, Rsc Advances, 2015, 5,
105731-105734.
T. An, H. Yang, G. Li, W. Song, W. J. Cooper and X. Nie,
Applied Catalysis B-Environmental, 2010, 94, 288-294.
Y. Li, J. Niu and W. Wang, Chemosphere, 2011, 85, 892-
897.
Y. Wang, W. Deng, F. Wang, Y. Su, Y. Feng, P. Chen, J. Ma, H.
Su, K. Yao, Y. Liu, W. Lv and G. Liu, Environmental science.
Processes & impacts, 2017, DOI: 10.1039/c7em00111h.
H. S. Ou, J. S. Ye, S. Ma, C. H. Wei, N. Y. Gao and J. Z. He,
Chemical Engineering Journal, 2016, 289, 391-401.
56.
8
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
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DOI: 10.1039/C7DT04360K
Figure Captions
3 4 3 4
Fig. 1. (a) TEM images of (a) CQDs, (b) mpgꢀC N , (c) mpgꢀC N /CQDs; (d)
HRTEM images of mpgꢀC
3 4
N /CQDs.
Fig. 2. (a) XRD spectrum of gꢀC
3
4 3 4 3 4 2
N , mpgꢀC N , and mpgꢀC N /CQDs; (b) The N
adsorption–desorption isotherms of gꢀC N , mpgꢀC N , and mpgꢀC N /CQDs. (Inset:
3
4
3
4
3
4
Pore size distributions of gꢀC
3
N
4
, mpgꢀC
3
N
4
, and mpgꢀC
3
N
4
/CQDs); (c)
Highꢀresolution XPS spectra of C1s; (d) N1s regions of mpgꢀC
mpgꢀC N /CQDs.
3 4
N , and
3
4
Fig. 3. (a) Upꢀconverted photoluminescence spectra of CQDs; (b) UVꢀvis absorption
spectra, (c) Schematic band structure evolution, (d) Photoluminescence spectra, (e)
Transient photocurrent response, (f) Electrochemical impedance spectroscopy of
3 4 3 4 3 4
gꢀC N , mpgꢀC N , mpgꢀC N /CQDs.
Fig. 4. The adsorption capacity of (a) FQs, (b) OFX on to the gꢀ C
mpgꢀC /CQDs (Inset: Pseudoꢀsecond order model of OFX); (c) Kinetic rate
constant of FQs of mpgꢀC N and mpgꢀC N /CQDs under visible light irradiation; (d)
3 4 3 4
N , mpgꢀC N , and
3
N
4
3
4
3
4
3 4 3 4 3 4
Photocatalytic activity of the gꢀC N , mpgꢀC N and mpgꢀC N /CQDs based on the
photocatalytic degradation of OFX under visible light irradiation; (e) The relationship
between 1/K and the initial concentration of OFX; (f) Kinetic rate constant of OFX
over different light sources.
Fig. 5. (a) Recycling runs of the photocatalytic activity of the mpgꢀC
3
N
4
/CQDs; (b)
FTꢀIR spectra of the mpgꢀC
degradation experiments.
3 4
N /CQDs prior and following repeated photocatalytic
ꢀ
−
Fig. 6. (a) ESR spectra of the (a) DMPOꢀO
2
adducts, (b) DMPOꢀꢀOH adducts, and
, mpgꢀC and mpgꢀC /CQDs; (d)
1
(
c) TEMPꢀ O
2
adduct, recorded with the gꢀC
3
N
4
3
N
4
3 4
N
Effects of various actives scavengers on the degradation of OFX over
mpgꢀC /CQDs under visible light irradiation.
3
N
4
3 4
Fig. 7. Possible transformation pathways of OFX in the aqueous mpgꢀC N /CQDs
solution under visible light irradiation.
3 4
Fig. 8. Schematic photocatalytic mechanism for the mpgꢀC N /CQDs under visible
light irradiation

Dalton Transactions
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DOI: 10.1039/C7DT04360K
(a)
(b)
d=12 nm
Holes
(c)
(d)
0.22 nm
mpg-C3N4
CQDs
CQDs
3 4 3 4
Fig. 1. (a) TEM images of (a) CQDs, (b) mpgꢀC N , (c) mpgꢀC N /CQDs; (d)
HRTEM images of mpgꢀC N /CQDs.
3
4

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DOI: 10.1039/C7DT04360K
(a)
(002)
g-C
mpg-C
mpg-C
3
N
4
(b)
0.0075
g-C3N4
3N4
3N4/CQDs
mpg-C
3
N4
N4
224
0
0
.0050
.0025
mpg-C
3
/CQDs
(100)
168
112
0.0000
0
20
40
60
80 100
Pore Diameter (nm)
5
6
0
0
.0
0.2
0.4
0.6
0.8
1.0
10
20
30
40
50
60
Relative Pressure (Ps/P0)
2
theta(degree)
(d)
(c)
N-C=N
mpg-C
N1s
C1s
C=N-C
mpg-C3N4/CQDs
3N4/CQDs
N-(C)
3
C=O
sp2 C-C
N-H
mpg-C3N4
mpg-C3N4
390
395
400
405
410
280
285
290
295
Binding energy (eV)
Binding Energy (eV)
Fig. 2. (a) XRD spectrum of gꢀC
adsorption–desorption isotherms of gꢀC
Pore size distributions of gꢀC , mpgꢀC
3
N
4
, mpgꢀC
3
N
4
, and mpgꢀC
, and mpgꢀC
, and mpgꢀC
3 4 2
N /CQDs; (b) The N
3
N
4
, mpgꢀC
3
N
4
3
N
4
/CQDs. (Inset:
3
N
4
3
N
4
3
N
4
/CQDs); (c)
Highꢀresolution XPS spectra of C1s; (d) N1s regions of mpgꢀC N , and
3
4
3 4
mpgꢀC N /CQDs.

Dalton Transactions
Page 12 of 18
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DOI: 10.1039/C7DT04360K
(
a)
(b)
4
3
2
1
0
500 nm
550 nm
600 nm
650 nm
700 nm
750 nm
800 nm
850 nm
900 nm
2.54 eV
2
.0 2.5 3.0 3.5 4.0 4.5 5.0
hv
g-C
mpg-C
mpg-C
3
N
4
3N4
3
N
4
/CQDs
488 nm
3
00
400
500
600
700
800
320 400 480 560 640 720 800
wavelength(nm)
Emission Wavelength (nm)
(d)
g-C
mpg-C
mpg-C
3
N
4
(
c) -1.11 eV
-1.07 eV
CB
-1.05 eV
CB
3
N
4
4
CB
3N
/CQDs
Quantum
Effect
Additional
Electronic State
400 450 500 550 600 650
Emission (nm)
VB
VB
VB
1
g-C
.55 eV
1.51 eV
mpg-C
1.49 eV
mpg-C3N4/CQDs
3N4
3
N
4
400
450
500
550
600
650
Emission (nm)
(
e)
g-C
mpg-C
mpg-C
3
N
4
(
30
f)
ON
g-C3N4
3
N
N
4
4
12
OFF
mpg-C
3
N4
N4/CQDs
3
/CQDs
mpg-C
3
9
6
3
0
2
0
0
0
1
0
4000
8000
Z'(Ω)
12000 16000
50
100
150
Time(min)
200
250
300
Fig. 3. (a) Upꢀconverted photoluminescence spectra of CQDs; (b) UVꢀvis absorption
spectra, (c) Schematic band structure evolution, (d) Photoluminescence spectra, (e)
Transient photocurrent response, (f) Electrochemical impedance spectroscopy of
3 4 3 4 3 4
gꢀC N , mpgꢀC N , mpgꢀC N /CQDs.

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DOI: 10.1039/C7DT04360K
(
a)
g-C
mpg-C
mpg-C
3
N
4
(b)
56
mpg-C
3N4
mpg-C
3
N
4
/CQDs
3
N
4
8
6
5
3
1
5
3N4/CQDs
8
1
4
7
0
42
28
14
0
180
135
9
0
5
0
4
0
300 600 900 1200 1500
Time (min)
0
300
600
Time (min)
900 1200 1500
OFX NOR CIP ENR LOM FLE
(
c)
(
d)
mpg-C
mpg-C
3N4
3N4/CQDs
0
0
0
0
0
0
.05
.04
.03
.02
.01
.00
1.0
0.8
0
0
0
0
.6
.4
.2
.0
hydrolysis
Photolysis
g-C
mpg-C
mpg-C
3
N
4
3N4
3
N
4
/CQDs
OFX NOR CIP ENR LOM FLE
y=3.5783x+3.0822
-120
0
30
60
90
120
-
300-240 -60
Time (min)
(
e)
(f)
mpg-C
mpg-C
3N
4
1.0 times
8
6
4
2
0
0
0
0
0
0
0
.5
3N4/CQDs
2
R =0.9888
.4
0
0
0
0
.3
.2
.1
.0
1
.7 times
3.3 times
2.6 times
2
.7 times
2
.1 times
Red
Blue
Green
UV Simulated Visible
light (h ) light light (s )
sunlight
light
4
8
12
(mg/L)
16
20
-
1
-1
C
0
light
Fig. 4. The adsorption capacity of (a) FQs, (b) OFX on to the gꢀ C
mpgꢀC /CQDs (Inset: Pseudoꢀsecond order model of OFX); (c) Kinetic rate
constant of FQs of mpgꢀC and mpgꢀC /CQDs under visible light irradiation; (d)
Photocatalytic activity of the gꢀC N , mpgꢀC N and mpgꢀC N /CQDs based on the
3 4 3 4
N , mpgꢀC N , and
3
N
4
3
N
4
3 4
N
3
4
3
4
3
4
photocatalytic degradation of OFX under visible light irradiation; (e) The relationship
between 1/K and the initial concentration of OFX; (f) Kinetic rate constant of OFX
over different light sources.

Dalton Transactions
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DOI: 10.1039/C7DT04360K
(
b)
(a)
Refore
After 4 cycles
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
7
14
21
28 3850 3300 2750 2200 1650-1 1100 550
Time (h)
Wavenumber(cm )
Fig .5. (a) Recycling runs of the photocatalytic activity of the mpgꢀC N /CQDs; (b)
3
4
FTꢀIR spectra of the mpgꢀC
degradation experiments.
3 4
N /CQDs prior and following repeated photocatalytic

Page 15 of 18
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(a)
·-
(
b)
mpg-C3N4/CQDs
mpg-C
3
N
4/CQDs
·
OH
O2
mpg-C3N4
mpg-C3N4
g-C3N4
g-C3N4
3
18.00 318.15 318.30 318.45 318.60
318.08
318.24
318.40
B/mT
318.56
318.72
B/mT
(c)
1
(d)0.04
/CQDs
mpg-C
3
N
4
O2
8
6
4
0
0
0
0.03
0.02
0.01
0.00
mpg-C3N4
g-C
3
N
4
20
Blank IPA KI NaN
3
BQK
2Cr2O
7
Na2C
2O4
333.2 333.3 333.4 333.5 333.6 333.7
B/mT
ꢀ
−
Fig .6. (a) ESR spectra of the (a) DMPOꢀO
2
adducts, (b) DMPOꢀꢀOH adducts, and
, mpgꢀC and mpgꢀC /CQDs; (d)
1
(
c) TEMPꢀ O
2
adduct, recorded with the gꢀC
3
N
4
3
N
4
3 4
N
Effects of various actives scavengers on the degradation of OFX over
mpgꢀC /CQDs under visible light irradiation.
3
N
4

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DOI: 10.1039/C7DT04360K
O
O
O
O
O
O
F
F
I
F
OH
OH
OH
N
N
N
NH
NH2
N
OH
N
OH
N
OH
OH
O
N
m/z 354
m/z 326
m/z 312
O
N
O
O
N
O
O
N
O
II
F
F
O
OH
OH
F
OH
OH
2
9
31
.- 1
N
O
2
/ O
2
O
O
H
2
C
N
N
O
O
N
H N
2
H N
2
6
19
6
O
2
32
H
O
F
18
17
23
O
2
0
21
30 OH
4
O
m/z 304
3
m/z 278
2
m/z 391
m/z 260
4
15
1
N
27
N
10
O
N
2
28
9
46 43
39
3
4
1
O
N
O
O
N
F
F
III
h+
OH
N
N
O
HN
O
HN
N
N
N
m/z 348
m/z 304
N
O2.-
N
deprotonationN
O
.- 1
N
2 2
O / O
F
N
open ring
IV
N
HN
OO
O
II
.-
N
N
OO
O
2
O
N
O
m/z 318
Fig. 7. Possible transformation pathways of OFX in the aqueous mpgꢀC
solution under visible light irradiation.
3 4
N /CQDs

Page 17 of 18
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3 4
Fig. 8. Schematic photocatalytic mechanism for the mpgꢀC N /CQDs under visible
light irradiation

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Table of Contents Entry
Carbon quantum dots loaded with mesoporous g-C N was prepared by using a facile
3
4
synthetic approach and applied for the synergistic absorption and photocatalytic
degradation of FQs.