Nanorod bundle-like silver cyanamide nanocrystals for the high-efficiency photocatalytic degradation of tetracycline

Article abstract of DOI:10.1039/d1ra00770j

Silver cyanamide (Ag₂NCN) is a type of functional semiconductor material with a visible-light response. Ag₂NCN nanocrystals with nanorod bundle-like (RB) or straw bundle-like (SB) assemblies were successfully prepared, and it was found that the as-prepared Ag₂NCN nanorod bundle (RB) samples had a narrower bandgap of 2.16 eV, which was lower than those reported. As a result, RB samples demonstrated a higher photocatalytic activity towards tetracycline (TC) degradation. The analyses of active species confirmed that both the photo-generated holes and ˙O₂^?radicals of the RB sample played significant roles during the process of photocatalytic degradation of TC, and the holes were the main active species. These results indicated that effective charge separation could be achieved by adjusting the morphologies of Ag₂NCN nanocrystals. This study provides a new approach to prepare Ag₂NCN nanocrystals with a narrower bandgap and strong visible-light response towards antibiotic degradation.

Full text of DOI:10.1039/d1ra00770j

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Nanorod bundle-like silver cyanamide nanocrystals
for the high-efficiency photocatalytic degradation
of tetracycline†
Cite this: RSC Adv., 2021, 11, 10235
Yulin Li, Chencong Cao, Qing Zhang, Ying Lu, Yanxi Zhao, Qin Li,
Xianghong Li
*
and Tao Huang
Silver cyanamide (Ag2NCN) is a type of functional semiconductor material with a visible-light response.
Ag2NCN nanocrystals with nanorod bundle-like (RB) or straw bundle-like (SB) assemblies were
successfully prepared, and it was found that the as-prepared Ag2NCN nanorod bundle (RB) samples had
a narrower bandgap of 2.16 eV, which was lower than those reported. As a result, RB samples
demonstrated a higher photocatalytic activity towards tetracycline (TC) degradation. The analyses of
ꢀ
active species confirmed that both the photo-generated holes and cO2 radicals of the RB sample
played significant roles during the process of photocatalytic degradation of TC, and the holes were the
main active species. These results indicated that effective charge separation could be achieved by
adjusting the morphologies of Ag2NCN nanocrystals. This study provides a new approach to prepare
Ag2NCN nanocrystals with a narrower bandgap and strong visible-light response towards antibiotic
degradation.
Received 29th January 2021
Accepted 22nd February 2021
DOI: 10.1039/d1ra00770j
rsc.li/rsc-advances
imperative to develop efficient techniques to eliminate TC in
the environment.
Introduction
In recent years, photocatalytic degradation has received
great interest on account of its unique advantages of high effi-
ciency, low energy consumption, and environmental friendli-
ness. Semiconductor photocatalysis has attracted great interest
as a promising strategy for renewable energy generation and
environmental remediation.9–11 Under light irradiation, semi-
conductor photocatalytic materials can be activated by photons
and can produce photo-generated electrons and holes, resulting
in strong oxidation or reduction on their surfaces. However, the
wider energy gap and the fast recombination of photogenerated
electron–hole pairs greatly restrain the photocatalytic efficiency
of the conventional semiconductor photocatalysts.12–14 The
environmentally friendly photocatalysts for TC degradation are
of great signicance for controlling antibiotic pollution. Up to
now, although a series of semiconductor photocatalysts for TC
degradation have been prepared,15–18 it is still a challenge to
explore novel high-efficiency visible-light responsive photo-
catalysts for antibiotic degradation.
Theoretically, silver cyanamide (Ag2NCN) should demon-
strate good visible-light response and high photocatalytic
performance, and these properties have been conrmed by the
previous reports.19–22 In general, the 2p orbital energy levels of C
and N atoms in Ag2NCN are higher than those of O atoms in
silver oxide, and the valence band energy level formed by the
hybridization of the 2p orbitals of C and N atoms is further
elevated. As a result, the bandgap for Ag2NCN will become
narrower under the premise that the band energy level remains
The environmental pollution and ecotoxicological effects
caused by antibiotics have become one of the major environ-
mental problems in China and even in the world. Antibiotics
have been widely used in anti-infection therapy for humans and
animals. Many antibiotics used in animal husbandry are diffi-
cult to be absorbed by animals, and about 30–90% of them are
excreted directly into the environment in the form of prototypes
or metabolites. Compared to the parent antibiotics, the toxicity
of their metabolites and degradation products is greatly
enhanced, although with lower activities. As one of the most
important antibiotics, tetracycline (TC) is the most widely used
in clinics. It is easy to accumulate in the water environment
because of its good water solubility. It has been detected in
aquatic environments such as surface water and groundwater as
well as the inlets and outlets of sewage treatment plants.1–3 Aer
metabolism, most of TC is excreted in prototype into the envi-
ronment, and it is difficult to degrade since it is nonbiode-
gradable.4 TC antibiotic residues have a profound impact on the
ecological environment and may eventually have harmful
effects on human health and survival.5–8 Therefore, it is
Key Laboratory of Catalysis and Energy Materials Chemistry of Ministry of Education,
College of Chemistry and Materials Science, South-Central University for
Nationalities, Wuhan 430074, China. E-mail: huangt208@163.com
† Electronic supplementary information (ESI) available: TEM, SEM, FT-IR, XRD,
XPS, EDS, Mott–Schottky plots, UV-vis spectra, HPLC-MS and MALDI-TOF-MS.
See DOI: 10.1039/d1ra00770j
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unchanged compared with that of silver oxide. Simultaneously, irradiation with 40 kV and 50 mA. The observations of nano-
the strong energy band dispersion effect facilitates to enhance structures and morphologies were conducted using a eld-
the electron mobility, reduces the electron–hole recombination, emission transmission electron microscope (STEM, Talos
and improves its photocatalytic conversion efficiency.
F200X G2) and a eld-emission scanning electron microscope
In addition, the electronic states of [NCN]2ꢀ in metal cyan- (SEM, SU8010), respectively. The elements of the samples were
amide are more delocalized than O 2p6 states in the metal oxide identied via energy dispersive X-ray spectroscopy (EDS), which
at both the maximum valence band and the minimum was connected with STEM. The chemical composition was
conduction band. In general, [NCN]2ꢀ can exist in the electronic examined by X-ray photoelectron spectroscopy (XPS, VG Multi-
form of symmetrical carbodiimide [N]C]N]2ꢀ (ref. 23–27) or lab 2000). The Brunauer–Emmett–Teller (BET) specic surface
asymmetrical cyanamide [N^C–N]2ꢀ. The inherent dipoles and areas were determined through nitrogen adsorption isotherms
dipolar elds of the asymmetrical [N^C–N]2ꢀ (ref. 28–30) form at 373 K using a Micromeritics ASAP 2020 instrument and
in Ag2NCN should promote photocatalytic activity by assisting calculated from the linear part of the BET plot. FT-IR spectra
the long-range migration of ions with opposite charges in the were recorded on a Nexus-470 spectrometer. UV-vis diffuse
photochemical reactions. Therefore, Ag2NCN has great poten- reection spectra (DRS) were measured on a spectrophotometer
tial application in solar-energy utilization and optoelectric (Cary 5000).
elds. So far, however, the reports on the synthesis and pho-
tocatalytic performances of Ag2NCN with different morphol-
ogies are still limited. In addition, silver cyanamide is mainly
used in the degradation of dyes;19,20 however, its application in
the degradation of antibiotics has not been reported.
Herein, Ag2NCN nanorod bundles as well as other nano-
structures were synthesized with numerous amines as com-
plexing agents by chemical deposition under nonaqueous
conditions, and their photocatalytic activities towards the
degradation of TC were investigated. The as-prepared Ag2NCN
nanorod bundles hold a direct bandgap (Eg) of 2.16 eV, which
was lower than those reported and demonstrated high photo-
catalytic activity for TC degradation.
Photoelectrochemical measurements
Transient amperometric I–t curve and electrochemical imped-
ance spectroscopy (EIS) measurements were carried out on
a CHI-660E electrochemical system with a three-electrode
quartz cell under a LED (3 W) (Shenzhen LAMPLIC Science
Co. Ltd., China). Saturated calomel electrode, platinum wire,
and ITO coated with Ag2NCN samples were used as the refer-
ence electrode, the counter electrode, and the working elec-
trode, respectively. A 0.1 M Na2SO4 solution was used as the
electrolyte.
Photocatalytic performance tests
The photocatalytic activities of the as-prepared Ag2NCN nano-
crystals were evaluated with tetracycline hydrochloride as the
simulative pollutant under simulated sunlight irradiation. In
a typical system, 50 mg of the as-prepared Ag2NCN sample was
ultrasonically dispersed into 50 mL of TC aqueous solution
(10 mg Lꢀ1) and then stirred for 30 min to reach the adsorption–
desorption equilibrium in a dark box. A 300 W xenon lamp was
used as the excitation light source. Perpetual circuit water was
supplied to keep the system at room temperature. In the process
of the photocatalytic reaction, 3 mL suspension was taken out
with a syringe at constant time intervals and ltered using
a 0.22 mm organic lter membrane. The resultant clear and
transparent solution was measured using a UV-vis spectropho-
tometer. The cycling stability was also tested under the same
condition. The relative active species during TC degradation
were detected by trapping tests and electron spin resonance
(ESR) on a JES FA-200 spectrometer. The intermediate products
were analyzed by high performance liquid chromatography-
mass spectrometry (HPLC-MS, Agilent LC-Q-TOF-MS 6520).
The degradation products were detected using a matrix-assisted
laser desorption ionization-time of a ight mass spectrometer
(MALDI-TOF-MS, Bruker autoex™ speed MALDI-TOF(TOF)).
Experimental
Materials
Silver nitrate (AgNO3), N,N-dimethylformamide (DMF), cyana-
mide (H2NCN), n-octylamine, t-butylamine, tetracycline (TC),
EDTA-2Na, benzoquinone (BQ), isopropanol (IPA), and all other
chemicals were purchased from Sinopharm Chemical Reagent
Co. Ltd. (Shanghai, China). All reagents were of analytical grade
and used as received without further purication.
Syntheses of Ag2NCN nanocrystals
In a typical synthesis, 0.17 g (1 mmol) of AgNO3 was rst dis-
solved in 3 mL of N,N-dimethylformamide (DMF). Then, 1 mL of n-
octylamine was added. Aer stirring for 30 min, 1 mL of 1 mol Lꢀ1
H2NCN solution in ethanol was injected at room temperature (25
ꢁC), and the solution turned yellow immediately. Aer reaction for
30 min under constant stirring, 2 mL of acetone was added.
Finally, the resultant suspension was centrifugated at 9000 rpm for
10 min, and the collected yellow precipitate was washed 3 times
with DMF, acetone, and water. The obtained bright yellow product
was dried in vacuum at 25 ꢁC for 10 h.
Under the same conditions, Ag2NCN nanocrystals were also
synthesized using t-butylamine instead of n-octylamine.
Results and discussion
Characterization
Characterization of Ag2NCN nanocrystals
The phase analysis was conducted by X-ray diffraction (XRD) on The representative morphologies of Ag2NCN nanocrystals ob-
Bruker D8 Advance diffractometer employing Cu Ka tained with different amines as the capping agents are shown in
a
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Fig. 1 and S1.† TEM images showed that the resulting Ag2NCN
nanocrystals in the t-butylamine system were present in straw-
bundle-like architectures (straw bundles, donated as SB)
assembled with numerous radical nanobelts with an average
length of 1.1 mm (Fig. 1a), while rod bundles (RB) gathered with
nanorods with an average length of 110 nm and a cross-section
of 18 nm in the n-octylamine system (Fig. 1b). SEM images
further conrmed their structural features (Fig. 1c and d).
The crystallographic structures of all the obtained samples
were examined by XRD. It can be seen in Fig. 2a that the char-
acteristic diffraction peaks for RB samples were obtained at 2q
values ¼ 12.5, 19.4, 32.8, 37.9, 39.3, 41.0, and 52.1ꢁ, which can
be well indexed to (100), (110), (202), (300), (220), (022), and
(ꢀ322) lattice planes, corresponding to the monoclinic struc-
ture of Ag2NCN according to the standard diffraction data
(JCPDS no. 70-5232). The sharper diffraction peaks for RB,
compared with those of SB samples (Fig. S2†) suggested its
higher crystallinity.
The FT-IR spectra of RB showed strong absorption bands at
3451.49 and 1383.98 cmꢀ1 wavenumbers (Fig. S3†), corre-
sponding to N–H stretching vibration and in-plane bending
vibration. The absorption bands at 2927.41 and 2857.38 cmꢀ1
wavenumbers were indexed to C–H (CH2 and CH3) stretching
vibrations. Moreover, the absorption bands at 2133.80, 1978.68,
and 1511.09 cmꢀ1 wavenumbers were identied as C^N, NCN,
and C–N stretching vibrations, revealing the existence of both
symmetrical carbodiimide [N]C]N]2ꢀ and asymmetrical
cyanamide [N^C–N]2ꢀ electronic structures. In addition, the
FT-IR data also indicated the existence of the ligand amine on
the surface of Ag2NCN nanocrystals.
Fig. 2 (a) XRD patterns of RB samples. (b) XPS spectra of the Ag 3d
region for RB samples.
impurity peak was observed, revealing a high purity. Among
them, the characteristic peaks at 374.7 and 368.7 eV were
observed for Ag 3d spectrum, corresponding to the binding
energies of 3d3/2 and 3d5/2 of Ag+ ions, as shown in Fig. 2b. It
was noteworthy to mention that the Ag 3d peaks of RB shied
towards higher binding energies compared with SB, implying
a deviation in the electron cloud of Ag+ ion to other elements,
which may be ascribed to different [NCN]2ꢀ structures.
The chemical compositions of the as-prepared Ag2NCN
samples were further determined by EDS. The EDS mapping and
spot analyses for RB and SB as well as BP (prepared by the method
in ref. 19) are shown in Fig. S5 and S6.† Compared with BP, it was
found that the carbon contents in RB and SB were higher, which
may be ascribed to the presence of ligand amines on the surface of
the particles, as shown in the data listed in ESI.†
The elemental compositions and chemical states of the as-
prepared Ag2NCN samples were measured by XPS. The results
showed that the surface compositions consisted of four
elements, namely C, N, Ag, and O (Fig. S4†). No other obvious
The formation mechanism of Ag2NCN nanocrystals
To further understand the formation of Ag2NCN nanocrystals,
the effects of reaction temperature and time on the formation of
RB and SB nanocrystals were investigated. Fig. S7 and S8† show
the TEM images of Ag2NCN nanocrystals prepared in n-octyl-
amine and t-butylamine systems, respectively, at different
temperatures. Compared with RB samples obtained at 25 ꢁC
(Fig. S7b†), no obvious difference either in length or in cross-
section of the nanorod was observed for rod bundle-like nano-
structures obtained at 0 ꢁC (Fig. S7a†), while the same nanorod
bundles were obtained at 60 ꢁC and no obvious increase in the
cross-section of the nanorod but an increased length was
observed (Fig. S7c†). Similarly, no obvious change was observed
for the straw bundle-like nanostructures obtained at different
temperatures in the presence of t-butylamine except for the
Fig. 1 (a and b) TEM and (c and d) SEM images of Ag2NCN nano-
crystals. (a) SB; (b) RB; (c) SB; (d) RB.
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length of the nanostraw bundles. Compared with SB samples demonstrated not only an obviously enhanced photocurrent
obtained at 25 ꢁC (Fig. S8b†), straw bundles with an average signal but also a slight increase during the light on–off cycling,
length of 550 or 2000 nm were produced at 0 or 60 ꢁC (Fig. S8a whereas the photoresponse of the SB sample was relatively
and c†), respectively. Thus, it can be seen that straw bundle-like strong at the moment of light on and then decreased immedi-
nanostructures cannot transform to rod bundle-like nano- ately. This may be attributed to the more electronic structure
structures. The experiment at a higher temperature was not forms of asymmetrical cyanamide [N^C–N]2ꢀ ions for the RB
conducted because of the reduction of silver ions.
sample, in which the inherent dipoles and dipolar elds facil-
Fig. S9† shows the TEM images of products obtained in the t- itate the long-distance migration of the opposite charge carries
butylamine system at different reaction times. As the reaction in optical activities, resulting in an increase in the effective
time extended to 1 to 2 h, there was no signicant change in the charge migration. In addition, stronger electronic resonance
straw bundle-like nanostructures except for a little increase in existing in RB would be another reason for its enhanced
aggregation. Therefore, by changing the temperature or pro- photocurrent.
longing the time, the nanostraw bundles cannot change to
nanorod bundles. Similarly, no obvious change was observed Compared with SB and BP samples, the RB sample showed the
for RB nanostructures by extending the reaction time. lowest charge transport resistance and the highest charge
Moreover, EIS results displayed similar phenomena (Fig. 3d).
Furthermore, it was found that the use of different amines transfer efficiency due to its smallest semicircle of the Nyquist
has a signicant effect on the morphology of Ag2NCN nano- plots. This result was consistent with the narrowest bandgap of
crystals. Instead of n-octylamine or t-butylamine, one of the the RB sample.
other amines such as ethylamine, n-butylamine, or oleylamine
In order to investigate the properties of the as-prepared
were also introduced into the reaction systems. It can be seen in Ag2NCN nanocrystals, the energy band structures were deter-
Fig. S10† that Ag2NCN bulk nanocrystals were produced using mined via Mott–Schottky plots by electrochemical tests. As
ethylamine (Fig. S10a†), while Ag2NCN rod-like nanocrystals shown in Fig. S12,† the positive slope of the curve indicated that
were generated using n-butylamine (Fig. S10b†). Moreover, either the RB sample (Fig. S12a†) or other samples (Fig. S12b†)
2ꢀ
Ag2NCN nanorods with less aggregation were formed when were typical n-type semiconductors. For Csc ¼ 0, the at-band
oleylamine was used (Fig. S10c†). These results implied that the potential obtained by the extrapolating Mott–Schottky equation
increase in the carbon chain length of amines was benecial to was approximately equal to the conduction band potential. The
the formation of Ag2NCN nanorods accompanied with less CB position of the RB sample was determined to be ꢀ0.59 V
aggregation, while the branched chain structure was benecial versus SCE. Combined with bandgap, the VB position of the RB
to the formation of long slender nanostructures. It can be seen sample was calculated to be +1.57 V via the empirical formula:
that in the presence of n-octylamine Ag2NCN nanorods were EVB ¼ ECB + Eg. The band structure diagram of RB is shown in
formed and assembled into rod bundles, which may be ascribed Fig. S12c.† Similarly, the VB position of the SB sample was
to fewer adsorptions of n-octylamine on the surface of nano- calculated to be 1.77 V, and the details are shown in ESI.†
rods. In the presence of t-butylamine, however, a signicant
number of thinner and longer straw-like nanostructures were
generated and gathered into straw bundles due to a large
number of adsorbed t-butylamine. Thus, the formation of
nanorod bundles or nanostraw bundles was dependent upon
the carbon chain length and structure of amines. Accordingly,
the formation process of RB and SB samples can be illustrated
as in the scheme (Fig. S11†).
BET analyses
In general, the photocatalytic activity is essentially dependent
upon the separation efficiency of the photoinduced electron–
hole pairs as well as the adsorption of antibiotic molecules in
the photocatalytic degradation system. The BET specic surface
areas of the RB and SB samples were investigated to charac-
terize their adsorption abilities. Fig. 4a shows the nitrogen
adsorption–desorption isotherms of RB and SB samples as well
as that of the BP sample. It can be seen that a type H3 hysteresis
loop for RB and SB samples suggested the type IV adsorption–
desorption isotherm, which was different from that of BP. These
distinctive characteristics may be ascribed to the layered
assembly structures in RB and SB. The specic surface areas of
DRS analyses and photoelectrochemical measurements
Furthermore, DRS was conducted to determine the bandgap of
the as-prepared Ag2NCN samples. As shown in Fig. 3a and b, the
band gaps of RB and SB samples were estimated to be 2.16 and
2.24 eV, respectively, which were lower than those of the re-
ported BP sample (2.30 eV).19 The narrower bandgap of the RB
sample implied a stronger visible-light response. These results
showed that the effective charge separation could be achieved
by adjusting the morphologies of Ag2NCN nanocrystals.
The photo-induced electron–hole pair separation and
transfer efficiency of RB and SB samples were investigated by
transient amperometric I–t curves and EIS measurements. It
can be seen in Fig. 3c that photocurrent responses under visible
RB and SB were measured to be 22.41 m2 gꢀ1 and 12.39 m2 gꢀ1
,
respectively, which are larger than that of the BP sample (1.2 m2
gꢀ1). Fig. 4b shows their relative pore size distribution, which
demonstrated typical mesoporous characteristics. In addition,
the biggest pore size of the RB sample implied that it was more
benecial for the adsorption of TC molecules.
Photocatalytic performances for TC degradation
light irradiation could be observed over all the RB and SB The photocatalytic activities of the as-prepared Ag2NCN nano-
samples as well as BP samples. Among them, the RB sample crystals with different morphologies were evaluated by the
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Fig. 3 (a) and (b) DRS spectra of RB and SB samples, respectively; (c) transient photocurrent response of the RB, SB, and BP samples irradiated
under visible light; (d) EIS of the samples. The insets in (a) and (b) show the corresponding (A ꢂ hn)2–hn curves.
degradation of TC under visible light. As shown in Fig. 5a, both the optimal degradation efficiency reached 96% in 120 min.
RB and SB exhibited strong photocatalytic activity towards the Since Ag2NCN nanocrystals would dissolve in a strongly acidic
degradation of TC. Compared with the SB sample, obviously, environment, the photocatalytic degradation of TC was carried
the RB sample demonstrated a higher photocatalytic perfor- out under a weak acidic condition. It can be seen that a weakly
mance since more than 96% of TC was removed within 120 min acidic aqueous solution was helpful for the degradation of TC in
under the optimum conditions. Nevertheless, the degradation the rst 40 min (Fig. S14b†). Fig. 5b shows the kinetic curves of
performance of the BP sample was close to that of the SB TC degradation over different Ag2NCN samples. A linear rela-
sample. Though the corresponding UV-vis absorption spectra tionship between ln(C/C0) and illumination time revealed
showed that the main characteristic peak of TC at 357 nm a pseudo-rst-order reaction for TC degradation. In addition,
gradually decreased with time for all the three samples the pseudo-rst-order rate constant K derived from the kinetic
(Fig. S13a†), the degree of degradation corresponding to the curve of the RB sample was the highest compared with other
peak at 275 nm demonstrated signicant differences, implying samples (Fig. 5c). These results indicated that the photocatalytic
different degradation pathways. Moreover, the effects of other performance of the nanorod bundle-like Ag2NCN nanocrystals
factors such as the catalyst dosage and pH value on the pho- was higher than that of the straw bundle-like Ag2NCN assembly
tocatalytic degradation process were also investigated. As or BP sample, which may be attributed to the optimal charge
shown in Fig. S14a,† the degradation of TC increased with the separation–adsorption equilibrium in the RB sample. These
increase in the amount of RB. As the dosage of RB was 50 mg, results were coincident with their specic surface areas.
Fig. 4 (a) Nitrogen adsorption–desorption isotherms and (b) relative pore size distribution of RB, SB, and BP samples.
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Fig. 5 (a) Photocatalytic degradation of TC over different samples (RB, SB, and BP) in 120 min (the optimum conditions: 50 mg of sample,
20 mg Lꢀ1 of TC solution, pH 9.62, 350 W of the light intensity); (b) the kinetic curves of TC degradation over different samples; (c) the apparent
rate constants for TC degradation with different samples; (d) the cyclic degradations of TC over RB samples.
ꢀ
Furthermore, the cyclic degradation of TC was conducted to cO2 adducts over the RB samples (Fig. 6b), which was consis-
examine the stability of the catalyst. It can be seen in Fig. 5d that tent with trapping tests, conrming the existence of active
ꢀ
the degradation rate of TC over the RB sample showed a slight oxygen species. Thus, cO2 radicals were one of the active
decline aer four consecutive cycles, which may be ascribed to radicals for the effective photocatalytic degradation of TC.
the loss of the collected catalyst. Compared with the original RB
sample, no obvious variations were observed in XRD and XPS
(Fig. S15†) as well as TEM measurements for RB aer 4 cycles
(Fig. S16†), indicating a strong structural stability of the RB
sample in the process of photocatalytic degradation. SB
samples showed the same catalytic stability in the photo-
catalytic degradation of TC. Their stability should be attributed
to their aggregated bundle structures.
In order to further clarify the mechanism of the photo-
catalytic TC degradation, EDTA-2Na, benzoquinone (BQ), and
isopropanol (IPA) were added into the RB-catalytic system to
ꢀ
capture holes, cO2 radicals, and cOH radicals, respectively,
under the same conditions. The kinetic curves and the degra-
dation rates of the corresponding photocatalytic degradation
process are shown in Fig. 6a and S17,† respectively. It can be
seen that the photocatalytic degradation of TC was nearly
inhibited completely under visible light in the system with
EDTA-2Na. Besides, the degradation rate of TC decreased from
96% in 120 min without BQ to 66.7% in 120 min aer adding
BQ (Fig. S17†), while no obvious effect was observed with the
addition of IPA. These results suggested that both the photo-
ꢀ
generated holes and cO2 radicals over the RB sample played
signicant roles during the photocatalytic degradation of TC,
and the holes were the main active species. In addition, using
dimethyl pyridine N-oxide (DMPO) as the trapping agent, ESR
measurements showed typical characteristic peaks for DMPO-
Fig. 6 (a) The photocatalytic activity of RB samples with different
quenchers; (b) ESR spectra of DMPO-cO2 adducts under light irra-
diation and in dark.
ꢀ
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In addition, the intermediates produced in the process of
RSC Advances
antibiotic resistance genes and bacterial communities in
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photocatalytic degradation were analyzed via HPLC-MS and
MALDI-TOF-MS, respectively. According to the HPLC-MS
(Fig. S18†) and MALDI-TOF-MS (Fig. S19†) spectrograms,
a possible pathway for the photocatalytic degradation of TC is
ꢀ
provided in Fig. S20.† Under the attacks of cO2 radicals and
holes in the process of photocatalytic degradation, TC mole-
cules were gradually oxidized and degraded to small molecule
organics aer a series of deamination, dealkylation, and ring-
opening reactions.15,31 Finally, these small molecule organics
generated during the degradation process were mineralized
into CO2 and H2O.
6 C. Q. Chen, L. Zheng, J. L. Zhou and H. Zhao, Persistence and
risk of antibiotic residues and antibiotic resistance genes in
major mariculture sites in Southeast China, Sci. Total
Environ., 2017, 580, 1175–1184.
Conclusions
In summary, Ag2NCN nanocrystals with nanorod bundle-like
(RB) or straw bundle-like (SB) assemblies were successfully
prepared using n-octylamine or t-butylamine, respectively, as
the complexing agents by chemical deposition in DMF, and
their photocatalytic activities for the degradation of TC were
investigated. The results indicated that the effective charge
separation could be achieved by adjusting the morphologies of
Ag2NCN nanocrystals. The as-prepared Ag2NCN nanorod
bundles (RB samples) demonstrated higher photocatalytic
activity towards TC degradation due to the narrowest bandgap
of the RB samples (2.16 eV) to date for Ag2NCN semiconductors.
The analyses of active species conrmed that both the photo-
generated holes and cO2ꢀ had signicant roles during the
7 J. Sun, L. Jin, T. He, Z. Wei, X. Liu, L. Zhu and X. Li, Antibiotic
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material with a strong visible-light response for antibiotic
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Conflicts of interest
There are no conicts to declare.
12 H. G. Kim, D. W. Hwang and J. S. Lee, An undoped, single-
phase oxide photocatalyst working under visible light, J.
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Acknowledgements
Y. Li and C. Cao contributed equally to this work and should be
regarded as co-rst authors. This work was supported by the
National Nature Science Foundation of China (Grant 21273289) 14 S. Misra, L. Li, D. Zhang, J. Jian, Z. Qi, M. Fan, H.-T. Chen,
and the Fundamental Research Funds for the Central Univer-
sities (CZZ20002).
X. Zhang and H. Wang, Self-assembled ordered three-
phase Au-BaTiO3-ZnO vertically aligned nanocomposites
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