Enhanced visible-light photodegradation of fluoroquinolone-based antibiotics andE. coligrowth inhibition using Ag-TiO2nanoparticles

Article abstract of DOI:10.1039/d0ra10403e

Antibiotics in wastewater represent a growing and worrying menace for environmental and human health fostering the spread of antimicrobial resistance. Titanium dioxide (TiO₂) is a well-studied and well-performing photocatalyst for wastewater treatment. However, it presents drawbacks linked with the high energy needed for its activation and the fast electron-hole pair recombination. In this work, TiO₂nanoparticles were decorated with Ag nanoparticles by a facile photochemical reduction method to obtain an increased photocatalytic response under visible light. Although similar materials have been reported, we advanced this field by performing a study of the photocatalytic mechanism for Ag-TiO₂nanoparticles (Ag-TiO₂NPs) under visible light taking in consideration also the rutile phase of the TiO₂nanoparticles. Moreover, we examined the Ag-TiO₂NPs photocatalytic performance against two antibiotics from the same family. The obtained Ag-TiO₂NPs were fully characterised. The results showed that Ag NPs (average size: 23.9 ± 18.3 nm) were homogeneously dispersed on the TiO₂surface and the photo-response of the Ag-TiO₂NPs was greatly enhanced in the visible light region when compared to TiO₂P25. Hence, the obtained Ag-TiO₂NPs showed excellent photocatalytic degradation efficiency towards the two fluoroquinolone-based antibiotics ciprofloxacin (92%) and norfloxacin (94%) after 240 min of visible light irradiation, demonstrating a possible application of these particles in wastewater treatment. In addition, it was also proved that, after five Ag-TiO₂NPs re-utilisations in consecutive ciprofloxacin photodegradation reactions, only a photocatalytic efficiency drop of 8% was observed. Scavengers experiments demonstrated that the photocatalytic mechanism of ciprofloxacin degradation in the presence of Ag-TiO₂NPs is mainly driven by holes and ˙OH radicals, and that the rutile phase in the system plays a crucial role. Finally, Ag-TiO₂NPs showed also antibacterial activity towardsEscherichia coli(E. coli) opening the avenue for a possible use of this material in hospital wastewater treatment.

Full text of DOI:10.1039/d0ra10403e

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PAPER
Enhanced visible-light photodegradation of
fluoroquinolone-based antibiotics and E. coli
growth inhibition using Ag–TiO2 nanoparticles†
Cite this: RSC Adv., 2021, 11, 13980
bc
a
Jiao Wang,a Ladislav Svoboda,
Jirı Henych,
ˇ´
Zuzana Nemeckova,d Massimo Sgarzi,
ˇ ˇ ´
d
a
a
*
and Gianaurelio Cuniberti
*
Nadia Licciardello
‡
Antibiotics in wastewater represent a growing and worrying menace for environmental and human health
fostering the spread of antimicrobial resistance. Titanium dioxide (TiO2) is a well-studied and well-
performing photocatalyst for wastewater treatment. However, it presents drawbacks linked with the high
energy needed for its activation and the fast electron–hole pair recombination. In this work, TiO2
nanoparticles were decorated with Ag nanoparticles by a facile photochemical reduction method to
obtain an increased photocatalytic response under visible light. Although similar materials have been
reported, we advanced this field by performing a study of the photocatalytic mechanism for Ag–TiO2
nanoparticles (Ag–TiO2 NPs) under visible light taking in consideration also the rutile phase of the TiO2
nanoparticles. Moreover, we examined the Ag–TiO2 NPs photocatalytic performance against two
antibiotics from the same family. The obtained Ag–TiO2 NPs were fully characterised. The results
showed that Ag NPs (average size: 23.9 ꢀ 18.3 nm) were homogeneously dispersed on the TiO2 surface
and the photo-response of the Ag–TiO2 NPs was greatly enhanced in the visible light region when
compared to TiO2 P25. Hence, the obtained Ag–TiO2 NPs showed excellent photocatalytic degradation
efficiency towards the two fluoroquinolone-based antibiotics ciprofloxacin (92%) and norfloxacin (94%)
after 240 min of visible light irradiation, demonstrating a possible application of these particles in
wastewater treatment. In addition, it was also proved that, after five Ag–TiO2 NPs re-utilisations in
consecutive ciprofloxacin photodegradation reactions, only a photocatalytic efficiency drop of 8% was
observed. Scavengers experiments demonstrated that the photocatalytic mechanism of ciprofloxacin
degradation in the presence of Ag–TiO2 NPs is mainly driven by holes and cOH radicals, and that the
rutile phase in the system plays a crucial role. Finally, Ag–TiO2 NPs showed also antibacterial activity
towards Escherichia coli (E. coli) opening the avenue for a possible use of this material in hospital
wastewater treatment.
Received 10th December 2020
Accepted 5th April 2021
DOI: 10.1039/d0ra10403e
rsc.li/rsc-advances
industrial production and the growth of the world's population,
water pollution has become a severe issue that affects human
and environmental health.1–4 In the last years, the presence of
Introduction
Water is essential for life. However, the amount of fresh,
accessible water on Earth is very limited. With the increasing
active pharmaceutical ingredients (API) in water has attracted
increasing attention due to the several damaging effects which
they can cause.5–8 API are “pseudo-persistent” pollutants
because their transformation/elimination rate is balanced by
their continuous input into the environment.7,9 Antibiotics are
a widely studied type of API because they are one of the causes of
the development of multiple resistant bacteria and because they
are detected frequently in the aquatic environment.10,11 The re-
ported levels of antibiotics in wastewater are in the range
of ng Lꢁ1 to mg Lꢁ1. However, the concentration of wastewater
discharged by pharmaceutical factories in some developing
aInstitute for Materials Science, Max Bergmann Centre of Biomaterials and Dresden
Center for Nanoanalysis, TU Dresden, 01062, Dresden, Germany. E-mail: nadia.
licciardello@tu-dresden.de;
tu-dresden.de
nadia.licciardello@inl.int;
gianaurelio.cuniberti@
b
ˇ
IT4Innovations, VSB – Technical University of Ostrava, 17. listopadu 15/2172, 708 33
Ostrava, Czech Republic
cNanotechnology Centre, CEET, VSB-Technical University of Ostrava, 17. listopadu 15/
2172, 708 33 Ostrava, Czech Republic
d
ˇ
ˇ
Institute of Inorganic Chemistry, Czech Academy of Sciences, Husinec-Rez 1001, 250
ˇ
ˇ
68 Rez, Czech Republic
countries has reached mg Lꢁ1 12,13 Therefore, the elimination of
.
antibiotics is an emergent problem to be solved. For example,
ciprooxacin (CIP) and noroxacin (NFX), both belonging to the
uoroquinolone family, have become common antibiotics in
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra10403e
‡ Current address: International Iberian Nanotechnology Laboratory, Avenida
´
Mestre Jose Veiga s/n, 4715-330 Braga, Portugal.
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wastewater from wastewater treatment plants.14 Being widely nanoparticles using a facile photochemical reduction method.38
present in wastewater, they can threaten the ecological envi- The phase composition and microstructure as well as the
ronment and human health by inducing the increase of bacte- optical properties of the as-obtained Ag–TiO2 NPs were ana-
rial drug resistance.15 Several techniques have been used to lysed. The photocatalytic performance under visible light irra-
remove antibiotics, such as biological treatments,16 membrane diation for the photodegradation of the uoroquinolone-based
processes,17 chemical and electrochemical techniques,18,19 and antibiotics CIP and NFX was explored. The possibility to reuse
adsorption procedures.20 Nevertheless, most of these tech- the same batch of Ag–TiO2 NPs was examined. As a model,
niques are complex or require large spaces and, mostly, they are the photocatalytic mechanism underlying the degradation of
not able to fully eliminate small traces of antibiotics in waste- CIP in the presence of Ag–TiO2 NPs was investigated shedding
water. Advanced oxidation processes (AOPs), and especially some light on it, and taking into consideration the role played
those involving semiconductor photocatalysts, have attracted by the rutile phase. Moreover, qualitative experiments on the
extensive attention.4,21,22 AOPs are processes in which highly antibacterial activity of the Ag–TiO2 NPs against E. coli were also
oxidising species, like hydroxyl radicals and other reactive performed, showing antimicrobial ability and demonstrating
oxygen species, are produced and can degrade target pollutants the potential disinfection properties of these particles in addi-
in wastewater.23 Among AOPs, photocatalysis is one of the most tion to their photocatalytic activity. These ndings not only
studied processes since it usually allows the elimination of contribute to better explain the mechanism behind the photo-
traces of pollutants in water and, ideally, their full catalytic activity of Ag–TiO2 NPs under visible light, but envisage
mineralisation.
the prospective future use of these particles, for instance, in
Among semiconductor materials, TiO2 is one of the most hospital wastewater treatment, where both bacteria and phar-
used photocatalysts because of its large specic surface area, maceuticals might be present.
relatively low toxicity, low cost and high catalytic activity.24 In
1972, Fujishima and Honda were the rst to report the photo-
catalytic activity of TiO2, which was used as the photo-anode in
UV-light induced electrochemical water splitting.25 Ever since,
Experimental section
Materials
this material has been widely explored in photocatalysis for
several applications, including wastewater treatment. However,
TiO2, especially in its more commonly used crystalline phase
anatase, has a wide bandgap (ꢂ3.2 eV), which requires UV light
irradiation for the photo-activation. UV light contribution in
solar irradiance spectrum is limited (5%) compared to visible
(43%) and infrared light (52%), which restricts TiO2 actual
environmental application under visible or solar light
irradiation.26
Titanium dioxide Aeroxide® TiO2 P25 was purchased from
Evonik. Silver nitrate (AgNO3, $99.0%), hydrochloric acid (HCl,
37%), ciprooxacin (CIP, $98.0%), noroxacin (NFX, $98.0%),
methanol (CH3OH, $99.9%), ethylenediaminetetraacetic acid
(EDTA, $99.0%), isopropanol ($99.5%) and Luria-Bertani (LB)
broth were purchased from Sigma-Aldrich. Agar–agar was
purchased from Merck. The strain of Escherichia coli used was
the following: E. coli YFP, MG1655 galK::SYFP2-FRT. The
ultrapure water was produced by a MembraPure Astacus system
(MembraPure GmbH, Hennigsdorf, Germany).
Doping TiO2 with metal or non-metal atoms or modifying
the surface of TiO2 with noble metals are some of the suggested
solutions to overcome this problem.27–31 Noble metals play an
important role in the visible-light-activated photocatalytic
process24,32 by lowering the bandgap, promoting electron–hole
pairs separation and/or introducing additional catalytically
active sites on the surface of TiO2. Among them, Ag is a prom-
ising candidate, owing to its relatively low cost (compared with
gold for instance), easy preparation and particularly high
performance in enhancing the TiO2 photocatalytic activity
under visible light.33 When the TiO2 surface is decorated with Ag
NPs, the photocatalytic response under visible light is enhanced
because of the localised surface plasmon resonance effect of Ag
NPs and the increased separation efficiency of photogenerated
Preparation of Ag–TiO2 NPs
Ag–TiO2 NPs were prepared by a photochemical reduction
method.38 TiO2 P25 (0.2 g) was dispersed in AgNO3 solution
(0.2 mol Lꢁ1, 50 mL) at room temperature. Aer 24 h stirring,
40 mL methanol were added. Subsequently, the system was
irradiated with a 10 W LED chip (lmax ¼ 365 nm) for 30 min to
reduce the Ag+ ions to metallic Ag nanoparticles. Finally, the as-
prepaꢃred samples were washed with ultrapure water and dried
at 70 C for 24 h.
Characterisation of Ag–TiO2 NPs
electron–hole pair, since Ag can act as an electron acceptor.4,34 The morphology and size of Ag–TiO2 NPs were individually
Besides, Ag NPs have a long-time known strong antibacterial examined by high-resolution transmission electron microscopy
activity.4
However,
(HR-TEM). HR-TEM images were acquired using a 200 kV TEM
deep understanding of the photocatalytic microscope FEI Talos F200X, which combines high-resolution
a
mechanism for Ag–TiO2 NPs under visible light irradiation is S/TEM with energy-dispersive X-ray spectroscopy (EDS) signal
oen missing in the literature35,36 and authors usually ignored detection, and 3D chemical characterisation with composi-
the role played by the rutile phase of TiO2 when using tional mapping. As specimen support for TEM investigations,
commercial TiO2 P25.37
a microscopic copper grid covered by a thin transparent holey
In this manuscript, we report on the surface modication of carbon lm was used. Ag–TiO2 NPs were ultrasonicated for few
the commercial Evonik Aeroxide® TiO2 P25 with Ag minutes, and 3 mL of this solution were dropped on the grid and
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evaporated at room temperature. The grid with samples was with negligible UV light content (wavelengths ranging from 400
cleaned by UV light irradiation under vacuum just before the to 1100 nm). The irradiance used during the experiments was
measurement. All measured images were processed by ImageJ 98 W mꢁ2. The distance between the visible light source and the
soware (National Institute of Health, USA). The particle-size surface of the CIP or NFX solution was 9.4 cm. The catalyst
distribution of Ag NPs was statistically evaluated by using particles were added into the CIP or NFX solution under stir-
Origin soware (Northampton, USA). The diffraction patterns of ring. The mixture was kept in dark conditions for 30 min to
Ag–TiO2 NPs were evaluated using Process Diffraction soware establish the adsorption–desorption equilibrium before irradi-
´
´ ´
(Janos L. Labar, Hungary).
ation with visible light. The absorbance changes for CIP and
The chemical composition of Ag–TiO2 NPs was examined via NFX were monitored at 277 nm (for CIP) or 278 nm (for NFX) at
Attenuated Total Reectance-Fourier Transform Infrared (ATR- different times of irradiation by using a UV-Vis spectropho-
FTIR) spectroscopy. ATR-FTIR spectra were recorded on tometer. During the process, samples were withdrawn at times
IRAffinity-1S (Shimadzu, Japan) equipped with GladiATR-10 as 0 min (before irradiation) and aer 5 min, 10 min, 20 min,
ATR accessory. The spectra were acquired in transmission 30 min, 50 min, 70 min, 90 min, 120 min, 150 min, 180 min,
mode, acquiring 32 scans with a resolution of 2 cmꢁ1 in the 210 min, 240 min of visible light irradiation and centrifuged for
wavenumber range from 4000 to 500 cmꢁ1
The crystalline structure of the prepared Ag–TiO2 NPs was nanoparticles.
investigated by X-ray powder diffraction (XRD). XRD patterns A similar procedure was followed for the recycling experi-
were obtained by Bruker D8 Advance diffractometer with lCu ments: aer each CIP photocatalytic degradation, the Ag–TiO2
0.15406 nm. Prepared powder samples were placed into a rota- NPs were recovered by centrifugation (10 min at 20 817g),
.
20 min at 20 817g and 20 ꢃC, in order to remove the suspended
¼
tional holder.
washed once with 0.1 M HCl and twice with ultrapure water,
ꢃ
The measurement of optical absorption and bandgap ener- dried at 40 C in the oven and reused for the subsequent pho-
gies was obtained by diffuse reectance UV-Vis (UV-Vis DRS) tocatalytic degradation of fresh CIP solution.
spectra in the range of 280–800 nm with a Shimadzu spectro-
Besides, in order to study the photocatalytic degradation
photometer UV-2600. The obtained spectra were measured in mechanism of CIP by Ag–TiO2 NPs, different scavengers,
diffuse reectance mode and expressed in terms of absorbance namely EDTA (17 mg), isopropanol (5 mL) and AgNO3 (17 mg),
by means of Kubelka–Munk function.
were introduced into the system (total volume 50 mL) as holes
The Fluorometer FLS920 (Edinburgh Instrument Ltd, UK), (h+) scavenger, cOH radicals scavenger, and electrons (eꢁ)
equipped with a 450 W xenon lamp, was used for the acquisition scavenger, respectively.
of photoluminescence spectra. The excitation wavelength
325 nm was used for all the measurements. All the samples were
measured in powdered form.
Antibacterial tests
Specic surface area (ABET) was measured with the surface All the laboratory supplies were sterilised by autoclaving at
ꢃ
area analyser SA9601 (HORIBA Scientic, Japan). The dry 121 C for 20 min. All the experiments were performed under
powdered samples were degassed for 6 hours at 80 ꢃC, and sterile conditions.
subsequently the six-point analysis was applied.
The E. coli suspension culture was prepared as follows.
Firstly, 10 g of LB broth was added to 500 mL of ultrapure water
in a sterile ask under stirring for 15 min. Secondly, the LB
broth was sterilised in the autoclave and subsequently cooled to
Photocatalytic activity measurements
CIP and NFX concentrations were measured via UV-Vis spec- room temperature. Subsequently, 50 mL of LB broth were
trophotometer (Cary 100 UV-Vis) with quartz cuvettes. transferred to a new sterile ask to which 2 mL of the E. coli
The photocatalytic activity of TiO2 P25 and Ag–TiO2 NPs culture were added while working in the laminar ow chamber.
catalysts was evaluated by the chemical degradation of CIP and Finally, this solution was incubated overnight under contin-
ꢃ
NFX antibiotics. In detail, 15 mg of catalyst were added to 50 mL uous shaking at 37 C.
of antibiotic solution (CIP or NFX) to reach a catalyst concen-
In order to prepare the LB agar plate, 10 g of LB broth, 7.5 g
tration of 300 mg Lꢁ1. The antibiotic solution had an initial of Agar–agar were added to 500 mL of ultrapure water in a sterile
concentration of 3 mg Lꢁ1 (pH ¼ 3, adjusted by using 1 M HCl). ask under stirring for 15 min. The medium was aerwards
The selection of pH ¼ 3 for the CIP and NFX solutions was sterilised in the autoclave and subsequently cooled down.
performed to ensure better solubility of the antibiotics in water. Finally, a sufficient volume of the LB-agar was transferred into
According to the literature, indeed, the CIP and NFX have two a sterile Petri dish while working in the laminar ow chamber.
acid dissociation constant (pKa) values of 5.9 and 8.9 for CIP, The as-prepared LB agar plate was stored at 4 ꢃC for future use.
and 6.4 and 8.7 for NFX. Therefore, they are positively charged
The antibacterial activity of Ag–TiO2 NPs against E. coli was
evaluated by a modied streaking method.40,41 The specic
at pH ¼ 3,39 which increases their solubility in water.
As visible light source, an articial lamp was used (Ingen- experimental steps are as follows. The LB agar plate was divided
¨
ieurburo Mencke & Tegtmeyer GmbH, Germany) with Susicon- into two parts by using an antibacterial stick. Five streaks were
trol soware (version 2.9.0) to monitor the light intensity by made for each part. A solution of E. coli in LB broth (20 mL, 108
a silicon irradiance sensor. As reported by the producer, the cells per mL) was placed in each streak on the le part of the
visible light spectrum is similar to the natural solar light, but plate. Ag–TiO2 NPs (0.2 mg) and E. coli in LB broth (20 mL, 108
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cells per mL) were placed in each streak on the right part of the
plate. The obtained plate was incubated in dark conditions at
37 ꢃC for 24 h, and examined for testing the strain inhibition in
the presence of Ag–TiO2 NPs. As a comparison, another LB agar
plate was divided into two parts by using the antibacterial stick.
Five streaks were made for each part. E. coli bacteria in LB broth
(20 mL, 108 cells per mL) were placed in each streak on the le
part of the plate. TiO2 P25 (0.2 mg) and E. coli in LB broth (20 mL,
108 cells per mL) were placed in each streak on the right part of
the plate. The obtained plate was incubated in dark conditions
at 37 ꢃC for 24 h, and examined for testing the strain inhibition
in the presence of TiO2 P25.
Results and discussion
Characterisation of Ag–TiO2 NPs
Fig. 1 Powder XRD patterns of TiO2 P25 and Ag–TiO2 NPs. The blue
lines represent the diffraction peaks positions for the typical Ag XRD
pattern (JCPDS no. 87-0717).
The synthetic path for the preparation of Ag–TiO2 NPs is illus-
trated in Scheme 1. Briey, Ag–TiO2 NPs were prepared using
a photochemical reduction method.38 The Ag NPs were formed
on the surface of the commercial TiO2 NPs through photo-
chemical reduction of AgNO3 under 365 nm LED irradiation.
The ATR-FTIR spectra of TiO2 P25 and Ag–TiO2 NPs are
shown in Fig. S1 (ESI†) and conrm that the Ag NPs did not
modify the chemical structure of TiO2 P25. However, the
concentration of Ag NPs compared with TiO2 NPs in the sample
is very low and it is therefore difficult to conrm their presence
by FTIR spectroscopy. In order to prove the presence of Ag NPs
in the Ag–TiO2 NPs system, the sample was thus characterised
by XRD. The XRD patterns of TiO2 P25 and Ag–TiO2 NPs are
shown in Fig. 1.
The XRD pattern for the TiO2 P25 shows several typical peaks
for both anatase and rutile, as expected. Besides the diffraction
pattern similar to the one of TiO2 P25, the Ag–TiO2 NPs exhibit
four additional main diffraction peaks at 38.116ꢃ, 44.277ꢃ,
64.426ꢃ and 77.472ꢃ. These peaks correspond to the (111), (200),
(220) and (311) planes of Ag (JCPDS no. 87-0717; the blue bars in
Fig. 1).42 These results prove that the obtained Ag–TiO2 NPs
contain Ag. Furthermore, the estimated weight percentages of
anatase, rutile and silver based on the XRD patterns are 82.12%,
12.76% and 5.12% respectively. The morphology and structure
of Ag–TiO2 NPs were characterised by HRTEM measurements.
Fig. 2(a) shows the HRTEM image of Ag–TiO2 NPs, where the Ag
NPs are observed as darker and smaller dots on the TiO2 NPs
surface. As it is shown in Fig. 2(a), the Ag NPs are very nely and
homogeneously dispersed on the TiO2 surface.
The size distribution of Ag NPs is shown in Fig. S2.† The
average size of the Ag NPs is 23.9 ꢀ 18.3 nm. However, these
represent probably the agglomerated primary Ag NPs present in
higher amount and more easily individuated by HRTEM. From
the size distribution graph in Fig. S2(b),† it is clear that the
primary Ag NPs size lies between 10 and 20 nm, although also
smaller particles are visible in the STEM-HAADF micrograph in
Fig. S2(a).† Some Ag NPs agglomerates with size bigger than
100 nm are also present. The EDS elemental maps are shown in
Fig. 2(b) and (c). From these maps, it is even more evident that
Ag NPs are localised mainly at the surface of the TiO2 NPs. The
successfully Ag modication on the surface of TiO2 was
conrmed by EDS analysis, where the weight percentage of Ag is
about 5%, which is a similar result to the one obtained by XRD
patterns.
Fig. 3(a) and (b) clearly show that Ag NPs are evenly
distributed on the surface of TiO2. The SAED image in Fig. 3(c)
shows the crystalline lattice of TiO2 NPs displaying the lattice
spacing of 0.351 nm, 0.175 nm and 0.118 nm, which are char-
acteristics for the crystalline planes (011), (022) and (008),
respectively. Besides, in the SAED image, it is also possible to
individuate the lattice spacing of 0.235 nm for the (111) planes
of Ag NPs.
UV-Vis diffuse reectance spectroscopy was used to investi-
gate optical absorption and bandgap energy of both TiO2 P25
and Ag–TiO2 NPs. Fig. 4(a) shows the DRS spectra of pure TiO2
Scheme 1 Synthetic route for the preparation of Ag–TiO2 NPs.
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Fig. 2 (a) HRTEM image of Ag–TiO2 NPs; (b) EDS map of Ag–TiO2 NPs with Ag (red) and Ti (green) atomic distribution; (c) EDS map of Ag–TiO2
NPs with Ag atomic distribution (in red).
P25 and Ag–TiO2. Both materials show the typical absorption contact). The estimated bandgap energy for TiO2 P25 is 3.28 eV,
edge in the UV region around 380 nm. However, in the case of corresponding to an absorption edge around 378 nm, while in
Ag–TiO2 NPs, the spectrum contains a broad band in the visible the case of Ag–TiO2 NPs, the estimated bandgap energy is
region ranging from 385 to 800 nm with the maximum absor- around 3.2 eV (387.5 nm). Thus, the surface decoration of TiO2
bance in the range between 530 and 550 nm, that is ascribable with Ag NPs slightly affected the bandgap energy of TiO2.
to the localised surface plasmon resonance (LSPR) of Ag parti- However, it is evident that the photo-response of the Ag–TiO2
cles.43 The position of the maximum absorbance around 540 nm NPs is greatly enhanced in the visible light region when
could be inuenced by the used Ag precursor in the Ag–TiO2 compared to bare TiO2.
NPs synthesis. Albiter et al.44 studied the synthesis of Ag–TiO2
To investigate the promoted electron–hole pairs separation
NPs in the presence of different Ag precursors, and they found and the recombination of these photo-excited carriers, the
out that the maximum absorbance in the visible light region emission spectra of the samples were acquired (lexc ¼ 325 nm,
strongly depended on the chosen salt for synthesis. Moreover, Fig. 4(b)). A lower emission intensity is desirable as it might
the position of the maximum absorbance is inuenced by indicate a lower probability of electron–hole recombination and
particle size, particles distribution on the surface of TiO2 and an enhanced longer lifetime of the photogenerated charge
chemical interaction between Ag NPs and TiO2.44 The DRS carriers resulting in higher photocatalytic activity. As shown in
spectra also represent an indirect proof of the TiO2 surface Fig. 4(b), both TiO2 P25 and Ag–TiO2 NPs show the maximum
coverage with Ag NPs, since the obtained spectra resemble the photoluminescence (PL) emission intensity around 428 nm, but
plasmon surface absorption typical of Ag NPs.45 Similar effects, the intensity is lowered by 40% for Ag–TiO2 NPs demonstrating
caused by TiO2 NPs' surface decoration with Ag NPs, on the a lower electron–hole recombination rate in this material in
absorption properties of the nal system were already observed respect to TiO2 P25. Similar PL results are reported for Ag/TiO2
in other reported Ag–TiO2 NPs samples.35
(ref. 46) and Ag2O/TiO2 (ref. 47) systems.
Furthermore, Ag NPs at the interface with TiO2 slightly
Finally, the specic surface area (SSA) of TiO2 P25 and Ag–
shied the electronic bandgap of TiO2 to higher wavelength due TiO2 NPs were measured to be 67 and 66 m2 gꢁ1, respectively,
to the creation of a metal–semiconductor junction (Schottky showing that the surface area of pure TiO2 nanoparticles was
Fig. 3 HRTEM images at low magnification (a) and high magnification (b) of Ag–TiO2 NPs; (c) SAED (selected area electron diffraction) pattern of
Ag–TiO2 NPs.
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Fig. 4 (a) UV-Vis absorption spectra of TiO2 P25 and Ag–TiO2 NPs with the inset of Tauc plot and (b) PL spectra of TiO2 P25 and Ag–TiO2 NPs.
practically unchanged by the introduction of Ag NPs. This irradiation. Differently, within the same time, TiO2 P25
indirectly proofs that the photocatalytic activity of Ag–TiO2 NPs degraded only 67% of CIP, a value comparable to previously
under visible light will not be different from the one of pure reported results.15,49 The high visible light photocatalytic activity
TiO2 P25 NPs because of a change in surface area, as shown in of Ag–TiO2 NPs can be attributed to the optical properties of the
the next section.
system induced by the presence of the nely distributed Ag NPs
on the surface of TiO2.
In order to investigate the photocatalytic activity of Ag–TiO2
NPs thoroughly, a kinetic study of the photodegradation
process was performed. The obtained photocatalytic degrada-
tion curve was tted by using a pseudo-rst-order kinetic model
as in eqn (1):32
Photocatalytic activity of Ag–TiO2 NPs towards CIP and NFX
under visible light
Aer thoroughly characterizing the obtained material, the
photocatalytic activity of Ag–TiO2 NPs towards the decomposi-
tion of two of the most used antibiotics belonging to the uo-
roquinolone family, CIP and NFX, was investigated under
visible light irradiation. The chemical structure of CIP and NFX
can be found in Fig. S3 in ESI.†
Ct
ꢁln
¼ kt
(1)
C0
where Ct is the antibiotic concentration at time t, C0 is the
antibiotic concentration at time zero and k is the degradation
rate constant. The slope of the tted curve gave the value of the
degradation rate constant k. The linear relationship of ꢁln(Ct/
C0) vs. time is shown in Fig. S5(a),† and the values of the
degradation rate constants are displayed in Table 1. The results
indicate that the degradation rate constant for Ag–TiO2 NPs, in
the case of CIP, is about 2.1 times higher than that for TiO2
P25.
We selected NFX as a second target compound to evaluate
the visible light photocatalytic activity of Ag–TiO2 NPs. The
concentration of NFX did also not signicantly change under
visible light irradiation in the absence of the photocatalyst
(Fig. S4(b) in ESI†). As for CIP, the photodegradation of NFX
using Ag–TiO2 NPs was studied by acquiring the absorption
spectra of the NFX solution at different times of visible light
irradiation in the presence of the photocatalyst, as shown in
Fig. 6(a). In Fig. 6(b), the variation of NFX concentration over
time shows that aer 240 min of visible light exposure, the
concentration of NFX decreased by 94% in the presence of Ag–
TiO2 NPs and 76% in the presence of TiO2 P25. The pseudo-rst-
order-kinetic tting (Fig. S5(b)† and Table 1) indicates that the
degradation rate constant for Ag–TiO2 NPs is about 1.7 times
higher than that for TiO2 P25. The degradation rate constants
reported for similar catalysts, which were used in the photo-
degradation of CIP under similar irradiation conditions, are in
The photocatalytic performance of Ag–TiO2 NPs was initially
evaluated by measuring the degradation of CIP in aqueous
solution. Moreover, commercial TiO2 P25 was used as a refer-
ence. Before the photocatalytic experiment, photocatalysts were
kept in contact with the antibiotic in dark conditions for 30 min
to reach the adsorption–desorption equilibrium. The results
showed, as expected, that there was no signicant change in the
pollutant concentration in dark conditions, which indicated
that an adsorption–desorption equilibrium was reached aer 30
minutes. Also, the concentration of CIP did not signicantly
change under visible light irradiation in the absence of the
photocatalyst (Fig. S4(a) in ESI†), demonstrating the negligible
photolysis of this molecule under visible light and the crucial
role of the photocatalyst in the degradation of CIP in these
conditions (Fig. 5(b)). Signicant degradation of CIP, as it will
be described more in detail below, occurs in the presence of
both photocatalysts (TiO2 P25 and Ag–TiO2 NPs) under visible-
light irradiation (Fig. 5(b)), as similarly reported in the litera-
ture.48 Nevertheless, from Fig. 5(b) it is already evident that the
degradation of CIP is much faster in the presence of Ag–TiO2
NPs when compared to the TiO2 P25 reference. Fig. 5(a) shows
that the UV-Vis maximum absorbance of CIP decreases with the
increase of the irradiation time with visible light in the presence
of Ag–TiO2 NPs. In particular, the concentration of CIP is
decreased by 92% in the presence of Ag–TiO2 NPs aer 240 min
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Fig. 5 (a) Representative variations of the absorption spectrum of CIP (3 mg Lꢁ1, pH ¼ 3) under visible light irradiation in the presence of Ag–TiO2
NPs (300 mg Lꢁ1); (b) time-dependent variation of the concentration of CIP solution upon exposure to visible light in the presence of TiO2 P25
(300 mg Lꢁ1, black squares) and Ag–TiO2 NPs (300 mg Lꢁ1, red circles); reported values are the mean of 3 replicates.
Table 1 Photocatalytic reaction rate constant (k) values for the TiO2
P25 and Ag–TiO2 NPs
NPs can signicantly enhance the photocatalytic activity, under
visible light irradiation, of the TiO2 P25 towards CIP and NFX.
Finally, we performed the recycling photocatalytic experi-
ments to assess the photocatalytic performance of Ag–TiO2 NPs
over different photocatalytic cycles. We chose CIP as a model
pollutant for this experiment since it is the most commonly
used antibiotic of its family and since we further studied the
photocatalytic mechanism for this pharmaceutical in this work.
The results for ve photocatalytic cycles are reported in
Fig. 7. Ag–TiO2 NPs were utilised in the photocatalytic degra-
dation of CIP, recovered, washed once with 0.1 M HCl, twice
with ultrapure water, and dried before being used for another
photocatalytic experiment with a fresh CIP solution. This
procedure was repeated ve times.
Catalyst
kCIP (10ꢁ3 minꢁ1
)
kNFX (10ꢁ3 minꢁ1
)
TiO2 P25
Ag–TiO2 NPs
3.7
7.6
4.6
7.9
the same range or even have lower values when compared with
our ndings.32,50 Higher degradation rate constants were also
reported, but in this case the materials were either exhibiting
different morphologies and/or Ag loading, or were tested under
different irradiation conditions.15,51,52 Concerning NFX, a direct
comparison of our catalysts performance with respect to the
literature is rather difficult since the reported catalysts for the
degradation of NFX possess different morphologies or are used
in different experimental conditions.53,54 Based on our results, it
can be concluded that the decoration of TiO2 surface with Ag
As shown in Fig. 7, the visible-light photocatalytic efficiency
of Ag–TiO2 NPs towards CIP only slightly decreased with the
number of reutilisations. Aer ve cycles, the amount of
degraded CIP decreased only by 8%, namely from 91% to 83%
Fig. 6 (a) Representative variations of the absorption spectrum of NFX (3 mg Lꢁ1, pH ¼ 3) under visible light irradiation by using Ag–TiO2 NPs
(300 mg Lꢁ1); (b) time-dependent concentration of NFX solution upon exposure to visible light in the presence of TiO2 P25 (300 mg Lꢁ1, black
squares) and Ag–TiO2 NPs (300 mg Lꢁ1, red circles); reported values are the mean of 3 replicates.
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Fig. 7 Five photocatalytic degradation reactions of fresh CIP solution
(3 mg Lꢁ1, pH ¼ 3) with reused (for up to 5 cycles) Ag–TiO2 NPs
(300 mg Lꢁ1) under visible light irradiation.
Fig. 8 Visible-light photocatalytic degradation percentage of CIP
(3 mg Lꢁ1, pH ¼ 3) in the presence of only Ag–TiO2 NPs (300 mg Lꢁ1, in
black) or of both Ag–TiO2 NPs (300 mg Lꢁ1) and the scavengers
AgNO3 (in red), EDTA (in green) or isopropanol (in blue).
of the initial CIP amount. The small decrease in the photo-
catalytic efficiency may be due to the loss of active sites caused
by the adsorption on the surface of the catalyst of possibly
unreacted CIP and/or its degradation products. The results
obtained in this work are good and t well with the previously
published ndings for similar catalysts, where comparable or
even larger drops in catalyst efficiency were observed aer
cycling.55–57 Our results indicate that the prepared Ag–TiO2 NPs
possess high stability and durability thus opening the path,
degradation is mainly caused by h+ and cOH, rather than eꢁ
driven reactions taking place on the surface of the photo-
catalyst.58 Therefore, it can be concluded that h+ and cOH are
the main active species of Ag–TiO2 NPs in aqueous solution
under visible light irradiation.
This is in line with our previous ndings for CIP degradation
under visible light in the presence of other similar catalysts,
such as ZnO.59 Based on the experimental results, a possible
mechanism of visible light photocatalytic degradation of CIP in
the presence of the Ag–TiO2 NPs is illustrated in Scheme 2. As
well known, TiO2 P25 is a mixture of anatase and rutile phase in
a ratio of about 80/20,60,61 respectively. D. C. Hurum et al.62 re-
ported that rutile phase, due to its slightly lower bandgap in
comparison to anatase, can be active under visible light irra-
dation. This fact explains why TiO2 P25 can degrade CIP and
NFX under visible light irradiation. However, the rutile phase is
present in a much lower amount than anatase and, therefore,
the photocatalytic activity is low, and the measured bandgap for
TiO2 P25 resembles more the one of anatase. The presence of Ag
NPs on the TiO2 P25 enhances this photocatalytic activity upon
visible light irradiation due to a better electron–hole pairs'
separation. When the Ag–TiO2 NPs are irradiated with visible
aer further studies, for
a possible future industrial
application.
Photocatalytic mechanism of Ag–TiO2 NPs
Once the photocatalytic behaviour was thoroughly investigated,
one of the main scopes of this work was to shed some light on
the photocatalytic mechanism behind the enhanced activity of
Ag–TiO2 NPs under visible light irradiation. CIP was selected as
a model for the study of the photocatalytic degradation mech-
anism of Ag–TiO2 NPs towards the uoroquinolone-based
antibiotics since it is the most commonly used pharmaceu-
tical of this family. Scavengers experiments were performed in
order to determine which were the active species mainly
involved in the photocatalytic degradation process.
Fig. 8 shows that the photocatalytic degradation percentage
of CIP by Ag–TiO2 NPs in the absence and the presence of
different scavengers. When EDTA, a scavenger for holes (h+),
was added into the reaction system, CIP degradation was
signicantly inhibited, and no CIP was degraded aer 240 min
irradiation. Another evident inhibition phenomenon for the
photocatalytic reaction occurred in the presence of isopropanol,
a scavenger for cOH radicals. Indeed, when isopropanol was
added into the reaction system, the degradation efficiency of
Ag–TiO2 NPs towards CIP decreased, resulting in 55% CIP
degradation aer 240 min irradiation. In contrast, in the case of
the addition of AgNO3, a scavenger for electrons (eꢁ), the pho-
tocatalytic degradation of CIP was nearly unchanged compared
Scheme 2 Photocatalytic mechanism scheme of Ag–TiO2 NPs under
with the absence of scavengers. Our study indicates that CIP visible light.
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light, the rutile phase of TiO2 will be activated. The photo- on the right part of the agar plate in Fig. 9(b). Plates were
generated electrons can be then transferred to Ag NPs and to the incubated at 37 ꢃC for 24 h. Fig. 9(a) shows that the growth of E.
anatase phase. In particular, Ag clusters deposited on the TiO2 coli is similar in each part (le and right). This indicates that
surface will act as electrons traps avoiding the recombination of TiO2 P25 cannot inhibit the growth of E. coli. Differently, in
electrons and holes and, therefore, enhancing the photo- Fig. 9(b), there is no growth of E. coli on the right part of the
catalytic activity of TiO2. This explains why the mechanism is plate compared to its le part. These ndings mean that the Ag–
mainly hole-driven. Holes and cOH radicals which are produced TiO2 NPs can inhibit the growth of E. coli because of the pres-
by the reaction between the holes and the water molecules ence of Ag NPs, which are known to have a robust antibacterial
adsorbed on the photocatalyst's surface play an important role activity.63 Our previous research64 also showed that the antimi-
in the degradation of CIP to CO2 and H2O. The degradation of crobial activity of Ag NPs-based nanocomposites is closely
CIP due to O2cꢁ radicals is, instead, negligible based on our related to the particle sizes of Ag NPs and their distribution on
experiments with scavengers. Therefore, Ag contributes to the the surface of carrier particles. Smaller Ag NPs guarantee
improvement of the photocatalytic activity of TiO2 under visible a better distribution on the carrier particles' surface, a greater
light, but the role played by the rutile phase in all the process solubility, and a higher concentration of antimicrobial active
seems to be essential and it was widely neglected in previous Ag+ ions released, resulting in an enhanced antimicrobial
studies of TiO2 P25 based-systems under visible light irradia- activity of the nanocomposite. Furthermore, small nano-
tion.37 From the scavenger experiments, it can be estimated that particles can penetrate bacterial cells and induce oxidative
cOH and h+ are the main active species in the photocatalytic stress.64 From HRTEM images presented in this work, it is
degradation of CIP in the presence of Ag–TiO2 NPs in aqueous evident that Ag NPs are very nely distributed on the surface of
solution under visible light irradiation. In other reports about TiO2 and that their sizes are in the range of the Ag NPs pre-
methylene blue degradation under visible light irradiation in sented in our previous work.64 Therefore, the excellent E. coli
the presence of Ag–TiO2 NPs, cOH radicals were found to be the growth inhibition ability of the Ag–TiO2 NPs can be entirely
main active species instead of holes and superoxide radicals.55 justied.
This stresses particularly the importance of the investigation of
the photocatalytic mechanism for each specic pollutant/
catalyst couple under certain selected conditions. However,
Conclusions
one of the main results of this work concerns the importance of In summary, Ag–TiO2 NPs are prepared by using a facile
the rutile phase in the visible-light activation of TiO2 P25-based method. The resulting Ag–TiO2 NPs have an improved visible
systems.
light-harvesting capacity and charge-separation efficiency
compared with TiO2 P25 and thus possess excellent character-
istics for photocatalysis under visible light irradiation. In these
experimental conditions, Ag–TiO2 NPs show improved photo-
catalytic degradation properties towards CIP and NFX in
comparison with those of commercial TiO2 P25. In particular,
the degradation rate constants in the presence of Ag–TiO2 NPs
increased by a factor of 2.1 and 1.7 for CIP and NFX respectively,
compared with the values for commercial TiO2 P25. The recy-
cling experiments showed that it is possible to reutilise the
same Ag–TiO2 NPs batch for ve consecutive CIP photo-
degradation reactions with a drop in efficiency limited to 8%.
Moreover, it was demonstrated that cOH and h+ play a major
role in the photocatalytic degradation of CIP under visible light
irradiation in the presence of Ag–TiO2 NPs and that the rutile
phase in the TiO2 P25-based systems should be not neglected in
the activation mechanism of TiO2 under visible light. Further-
more, Ag–TiO2 NPs can inhibit the growth of E. coli signicantly.
We believe that our manuscript provides important clari-
cations about the possible photocatalytic mechanism under
visible light irradiation for Ag NPs decorated TiO2 P25 systems.
Altogether, the prepared Ag–TiO2 NPs are a viable alternative for
the degradation of uoroquinolone-based antibiotics under
visible light irradiation and, at the same time, for the inactiva-
tion of bacteria in water. It is foreseen that the Ag–TiO2 NPs will
nd practical utilisation and application in water treatment,
especially in that of hospital wastewater, where the removal of
pharmaceuticals and the disinfection from bacteria is a desir-
able nal aim.
Antibacterial activity of Ag–TiO2 NPs
Finally, the antibacterial properties of the Ag–TiO2 NPs towards
E. coli bacteria were qualitatively tested in dark conditions. In
Fig. 9, the results of a modied streaking method used to test
the antibacterial activities of the two materials under study
(TiO2 P25 and Ag–TiO2 NPs) are shown. In Fig. 9, E. coli in LB
broth were added into each streak on the le part of the agar
plates as a control. TiO2 P25 and E. coli in LB broth were added
into each streak on the right part of the agar plate in Fig. 9(a).
Ag–TiO2 NPs and E. coli in LB broth were added into each streak
Fig. 9 Modified streak method demonstrating the inhibitory bacteria
growth potential of TiO2 (a) and Ag–TiO2 NPs (b) against E. coli: (a) E.
coli in LB broth on the left part of the agar plate, TiO2 P25 and E. coli in
LB broth on the right part of the agar plate; (b) E. coli in LB broth on the
left part of the agar plate, Ag–TiO2 NPs and E. coli in LB broth on the
right part of the agar plate.
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chromatography-tandem mass spectrometry, J. Chromatogr.
A, 2014, 1333, 87–98.
Conflicts of interest
¨
8 S. Teixeira, R. Gurke, H. Eckert, K. Kuhn, J. Fauler and
The authors declare no conict of interest.
G.
Cuniberti,
Photocatalytic
present in
degradation
conventional
of
treated
pharmaceuticals
Acknowledgements
wastewater by nanoparticle suspensions, J. Environ. Chem.
Eng., 2016, 4, 287–292.
9 C. Daughton, Environmental stewardship and drugs as
pollutants, Lancet, 2002, 360, 1035–1036.
10 W. Xu, G. Zhang, X. Li, S. Zou, P. Li, Z. Hu and J. Li,
Occurrence and elimination of antibiotics at four sewage
treatment plants in the Pearl River Delta (PRD), South
China, Water Res., 2007, 41, 4526–4534.
11 L. Shi, X. F. Zhou, Y. L. Zhang and G. W. Gu, Simultaneous
determination of 8 uoroquinolone antibiotics in sewage
treatment plants by solid-phase extraction and liquid
chromatography with uorescence detection, Water Sci.
Technol., 2009, 59, 805–813.
12 D. G. J. Larsson, C. de Pedro and N. Paxeus, Effluent from
drug manufactures contains extremely high levels of
pharmaceuticals, J. Hazard. Mater., 2007, 148, 751–755.
13 D. Li, M. Yang, J. Hu, Y. Zhang, H. Chang and F. Jin,
Determination of penicillin G and its degradation products
in a penicillin production wastewater treatment plant and
the receiving river, Water Res., 2008, 42, 307–317.
14 M. Mahdi-Ahmed and S. Chiron, Ciprooxacin oxidation by
UV-C activated peroxymonosulfate in wastewater, J. Hazard.
Mater., 2014, 265, 41–46.
Jiao Wang thanks Xinne Zhao for providing E. coli. The authors
gratefully acknowledge nancial support by the China Schol-
arship Council (CSC), by the European Union's Horizon 2020
Research and Innovation Program under the Marie Sklodowska-
Curie Grant Agreement No. 734381 (CARBO-IMmap), by the
European Regional Development Fund in the IT4Innovations
national supercomputing centre – path to exascale project,
project number EF16_013/0001791 within the Operational
Programme Research, Development and Education, by the
project No. CZ.02.1.01/0.0/0.0/17_049/0008441 “Innovative
therapeutic methods of musculoskeletal system in accident
surgery” within the Operational Programme Research, Devel-
opment and Education nanced by the European Union and
from the state budget of the Czech Republic and by Doctoral
ˇ
grant competition VSB TU-Ostrava grant number CZ.02.2.69/
0.0/0.0/19_073/0016945 of the Ministry of Education, Youth and
Sports of the Czech Republic. The authors gratefully acknowl-
edge the Open Access Funding by the Publication Fund of
¨
Technische Universitat Dresden.
References
1 P. Schwarzenbach, T. Egli, T. B. Hofstetter, U. Von Gunten 15 Z. Jiang, J. Zhu, D. Liu, W. Wei, J. Xie and M. Chen, In situ
and B. Wehrli, Global water pollution and human health,
Annu. Rev. Environ. Resour., 2010, 35, 109–136.
2 A. B. Bhuiyan, M. Mokhtar, M. E. Toriman, M. B. Gasim,
G. C. Ta, R. Elthri and M. R. Razman, The environmental
synthesis of bimetallic Ag/Pt loaded single-crystalline
anatase TiO2 hollow nano-hemispheres and their improved
photocatalytic properties, CrystEngComm, 2014, 16, 2384–
2394.
risk and water pollution: A review from the river basins 16 C. I. Pearce, J. R. Lloyd and J. T. Guthrie, The removal of
around the world, Am.-Eurasian J. Sustain. Agric., 2013, 7,
126–136.
colour from textile wastewater using whole bacterial cells:
A review, Dyes Pigm., 2003, 58, 179–196.
´
´
´
3 J. C. Duran-Alvarez, E. Avella, R. M. Ramırez-Zamora and 17 B. Van Der Bruggen and C. Vandecasteele, Removal of
R. Zanella, Photocatalytic degradation of ciprooxacin
using mono-(Au, Ag and Cu) and bi- (Au-Ag and Au-Cu)
metallic nanoparticles supported on TiO2 under UV-C and
simulated sunlight, Catal. Today, 2016, 266, 175–187.
4 T. Ali, A. Ahmed, U. Alam, I. Uddin, P. Tripathi and
M. Muneer, Enhanced photocatalytic and antibacterial
activities of Ag-doped TiO2 nanoparticles under visible
light, Mater. Chem. Phys., 2018, 212, 325–335.
pollutants from surface water and groundwater by
nanoltration: Overview of possible applications in the
drinking water industry, Environ. Pollut., 2003, 122, 435–445.
18 J. Hollender, S. G. Zimmermann, S. Koepke, M. Krauss,
C. S. McArdell, C. Ort, H. Singer, U. Von Gunten and
H. Siegrist, Elimination of organic micropollutants in
a municipal wastewater treatment plant upgraded with
a full scale post-ozonation followed by sand ltration,
Environ. Sci. Technol., 2012, 43, 7862–7869.
5 C. Carlsson, A. Johansson, G. Alvan, K. Bergman and T. Ku,
Are pharmaceuticals potent environmental pollutants? Part 19 C. Y. Hu, S. L. Lo and W. H. Kuan, Effects of co-existing
I: Environmental risk assessments of selected active
pharmaceutical ingredients, Sci. Total Environ., 2006, 364,
67–87.
anions on uoride removal in electrocoagulation (EC)
process using aluminum electrodes, Water Res., 2003, 37,
4513–4523.
6 W. L. Hough and R. D. Rogers, Ionic liquids then and now: 20 M. Iram, C. Guo, Y. Guan, A. Ishfaq and H. Liu, Adsorption
from solvents to materials to active pharmaceutical
ingredients, Bull. Chem. Soc. Jpn., 2007, 80, 2262–2269.
7 A. S. Maia, A. R. Ribeiro, C. L. Amorim, J. C. Barreiro,
and magnetic removal of neutral red dye from aqueous
solution using Fe3O4 hollow nanospheres, J. Hazard.
Mater., 2010, 181, 1039–1050.
Q. B. Cass, P. M. L. Castro and M. E. Tiritan, Degradation 21 P. S. Saud, B. Pant, A. M. Alam, Z. K. Ghouri, M. Park and
of uoroquinolone antibiotics and identication of
metabolites/transformation products by liquid
H. Y. Kim, Carbon quantum dots anchored TiO2
© 2021 The Author(s). Published by the Royal Society of Chemistry
RSC Adv., 2021, 11, 13980–13991 | 13989

View Article Online
RSC Advances
Paper
nanobers: Effective photocatalyst for waste water
treatment, Ceram. Int., 2015, 41, 11953–11959.
22 E. Friedler and Y. Gilboa, Performance of UV disinfection
composites with different Ag loading and their enhanced
photoelectrochemical and photocatalytic performance, J.
Nanosci. Nanotechnol., 2017, 17, 1942–1949.
´
and the microbial quality of greywater effluent along 37 M. G. Mendez-Medrano, E. Kowalska, A. Lehoux,
a reuse system for toilet ushing, Sci. Total Environ., 2010,
408, 2109–2117.
23 A. O. Ibhadon and P. Fitzpatrick, Heterogeneous
photocatalysis: recent advances and applications, Catalysts,
2013, 3, 189–218.
A. Herissan, B. Ohtani, D. Bahena, V. Briois, C. Colbeau-
´
´
Justin, J. L. Rodrıguez-Lopez and H. Remita, Surface
modication of TiO2 with Ag nanoparticles and CuO
nanoclusters for application in photocatalysis, J. Phys.
Chem. C, 2016, 120, 5143–5154.
24 Y. Ma, X. Wang, Y. Jia, X. Chen, H. Han and C. Li, Titanium 38 K. Chen, X. Feng, H. Tian, Y. Li, K. Xie, R. Hu, Y. Cai and
dioxide-based nanomaterials for photocatalytic fuel
generations, Chem. Rev., 2014, 114, 9987–10043.
25 A. Fujishima and K. Honda, Electrochemical photolysis of
H. Gu, Silver-decorated titanium dioxide nanotube arrays
with improved photocatalytic activity for visible light
irradiation, J. Mater. Res., 2014, 29, 1302–1308.
water at a semiconductor electrode, Nature, 1972, 238, 37– 39 M. E. Roca Jalil, M. Baschini and K. Sapag, Inuence of pH
38.
and antibiotic solubility on the removal of ciprooxacin
from aqueous media using montmorillonite, Appl. Clay
Sci., 2015, 114, 69–76.
26 C. Jia, X. Zhang, K. Matras-Postolek, B. Huang and P. Yang,
Z-scheme reduced graphene oxide/TiO2-Bronze/W18O49
ternary heterostructure towards efficient full solar- 40 A. Eythorsdottir, S. Omarsdottir and H. Einarsson,
spectrum photocatalysis, Carbon, 2018, 139, 415–426.
27 M. Nasr, L. Soussan, R. Viter, C. Eid, R. Habchi, P. Miele and
M. Bechelany, High photodegradation and antibacterial
Antimicrobial activity of marine bacterial symbionts
retrieved from shallow water hydrothermal vents, Mar.
Biotechnol., 2016, 18, 293–300.
activity of BN-Ag/TiO2 composite nanobers under visible 41 S. Gurunathan, V. Umashankar, S. Murugesan and
light, New J. Chem., 2018, 42, 1250–1259.
28 M. Shang, H. Hou, F. Gao, L. Wang and W. Yang,
Mesoporous Ag@TiO2 nanobers and their photocatalytic
activity for hydrogen evolution, RSC Adv., 2017, 7, 30051–
30059.
R. Dhamotharan, 16s rDNA based molecular identication
of Bacteriocin-like inhibitory substance (BLIS/BIS)
producing indigenous phytopathogenic bacteria isolated
from various diseased plant materials, Int. J. Curr. Sci.,
2014, 11, 105–119.
¨
¨
29 A. Yar, B. Haspulat, T. Ustun, V. Eskizeybek, A. Avci, 42 Y. Duan, M. Zhang, L. Wang, F. Wang, L. Yang, X. Li and
H. Kami¸s and S. Achour, Electrospun TiO2/ZnO/PAN
hybrid nanober membranes with efficient photocatalytic
activity, RSC Adv., 2017, 7, 29806–29814.
C. Wang, Plasmonic Ag-TiO2-x nanocomposites for the
photocatalytic removal of NO under visible light with high
selectivity: The role of oxygen vacancies, Appl. Catal., B,
2017, 204, 67–77.
30 V. Keller, P. Bernhardt and F. Garin, Photocatalytic oxidation
of butyl acetate in vapor phase on TiO2, Pt/TiO2 and WO3/ 43 P. V. Kamat, Photophysical, photochemical and
TiO2 catalysts, J. Catal., 2003, 215, 129–138.
31 B. Pal, M. Sharon and G. Nogami, Preparation and
photocatalytic aspects of metal nanoparticles, J. Phys.
Chem. B, 2002, 106, 7729–7744.
characterisation of TiO2/Fe2O3 binary mixed oxides and its 44 E. Albiter, M. A. Valenzuela, S. Alfaro, G. Valverde-Aguilar
´
photocatalytic properties, Mater. Chem. Phys., 1999, 59,
254–261.
and F. M. Martınez-Pallares, Photocatalytic deposition of
Ag nanoparticles on TiO2: Metal precursor effect on the
structural and photoactivity properties, J. Saudi Chem. Soc.,
2015, 19, 563–573.
¨
32 P. Martins, S. Kappert, H. N. Le, V. Sebastian, K. Kuhn,
M. Alves, L. Pereira, G. Cuniberti, M. Melle-Franco and
´
S. Lanceros-Mendez, Enhanced photocatalytic activity of 45 Y. Koo, G. Littlejohn, B. Collins, Y. Yun, V. N. Shanov,
au/TiO2 nanoparticles against ciprooxacin, Catalysts,
2020, 10, 234.
33 Y. C. Yao, X. R. Dai, X. Y. Hu, S. Z. Huang and Z. Jin,
Synthesis of Ag-decorated porous TiO2 nanowires through
M. Schulz, D. Pai and J. Sankar, Synthesis and
characterization of Ag-TiO2-CNT nanoparticle composites
with high photocatalytic activity under articial light,
Composites, Part B, 2014, 57, 105–111.
a sunlight induced reduction method and its enhanced 46 S. P. Lim, A. Pandikumar, N. M. Huang and H. N. Lim,
photocatalytic activity, Appl. Surf. Sci., 2016, 387, 469–476.
34 T. Scott, H. Zhao, W. Deng, X. Feng and Y. Li, Photocatalytic
degradation of phenol in water under simulated sunlight by
Enhanced photovoltaic performance of silver@titania
plasmonic photoanode in dye-sensitized solar cells, RSC
Adv., 2014, 4, 38111–38118.
an ultrathin MgO coated Ag/TiO2 nanocomposite, 47 N. Wei, H. Cui, Q. Song, L. Zhang, X. Song, K. Wang,
Chemosphere, 2019, 216, 1–8.
Y. Zhang, J. Li, J. Wen and J. Tian, Ag2O nanoparticle/TiO2
nanobelt heterostructures with remarkable photo-response
and photocatalytic properties under UV, visible and near-
infrared irradiation, Appl. Catal., B, 2016, 198, 83–90.
35 S. Ko, C. K. Banerjee and J. Sankar, Photochemical synthesis
and photocatalytic activity in simulated solar light of
nanosized Ag doped TiO2 nanoparticle composite,
Composites, Part B, 2011, 42, 579–583.
36 L. Zhang, Y. Ji, D. Wu, S. Du, S. Zhang and S. Zhou,
Controlled synthesis of Ag/TiO2 nanotube arrays
48 Z. Jiang, W. Wei, D. Mao, C. Chen, Y. Shi, X. Lv and J. Xie,
Silver-loaded nitrogen-doped yolk-shell mesoporous TiO2
13990 | RSC Adv., 2021, 11, 13980–13991
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hollow microspheres with enhanced visible light
photocatalytic activity, Nanoscale, 2015, 7, 784–797.
products and antibacterial activity, J. Colloid Interface Sci.,
2019, 557, 236–253.
49 T. Paul, P. L. Miller and T. J. Strathmann, Visible-light- 57 J. Xu, Y. Liu and Y. Zhao, Effect of Ag loading position on the
mediated TiO2 photocatalysis of uoroquinolone
antibacterial agents, Environ. Sci. Technol., 2007, 41, 4720–
4727.
photocatalytic performance of TiO2 nanocolumn arrays,
Beilstein J. Nanotechnol., 2020, 11, 717–728.
58 W. Li, S. Seal, E. Megan, J. Ramsdell, K. Scammon, G. Lelong,
L. Lachal and K. A. Richardson, Physical and optical
properties of sol-gel nano-silver doped silica lm on glass
substrate as a function of heat-treatment temperature, J.
Appl. Phys., 2003, 93, 9553–9561.
59 A. Ulyankina, T. Molodtsova, M. Gorshenkov, I. Leontyev,
D. Zhigunov, E. Konstantinova, T. Lastovina, J. Tolasz,
J. Henych, N. Licciardello, G. Cuniberti and N. Smirnova,
Photocatalytic degradation of ciprooxacin in water at
nano-ZnO prepared by pulse alternating current
electrochemical synthesis, J. Water Process. Eng., 2021, 40,
101809.
50 Y. Tang, H. Sun, Y. Shang, S. Zeng, Z. Qin, S. Yin, J. Li,
S. Liang, G. Lu and Z. Liu, Spiky nanohybrids of titanium
dioxide/gold nanoparticles for enhanced photocatalytic
degradation and anti-bacterial property, J. Colloid Interface
Sci., 2019, 535, 516–523.
51 Z. Liu and Z. Ma, Ag-SrTiO3/TiO2 composite nanostructures
with enhanced photocatalytic activity, Mater. Res. Bull.,
2019, 118, 110492.
´
´
´
52 J. C. Duran-Alvarez, E. Avella, R. M. Ramırez-Zamora and
R. Zanella, Photocatalytic degradation of ciprooxacin
using mono-(Au, Ag and Cu) and bi-(Au-Ag and Au-Cu)
metallic nanoparticles supported on TiO2 under UV-C and 60 D. M. Tobaldi, R. C. Pullar, M. P. Seabra and J. A. Labrincha,
simulated sunlight, Catal. Today, 2016, 266, 175–187.
Fully quantitative X-ray characterisation of Evonik Aeroxide
53 H. Salazar, P. M. Martins, B. Santos, M. M. Fernandes,
TiO2 P25®, Mater. Lett., 2014, 122, 345–347.
´
A. Reizabal, V. Sebastian, G. Botelho, C. J. Tavares, 61 F. Amano, M. Nakata, A. Yamamoto and T. Tanaka, Rutile
J. L. Vilas-Vilela and S. Lanceros-Mendez, Photocatalytic
and antimicrobial multifunctional nanocomposite
membranes for emerging pollutants water treatment
applications, Chemosphere, 2020, 250, 126299.
titanium dioxide prepared by hydrogen reduction of
Degussa P25 for highly efficient photocatalytic hydrogen
evolution, Catal. Sci. Technol., 2016, 6, 5693–5699.
62 D. C. Hurum, A. G. Agrios, K. A. Gray, T. Rajh and
M. C. Thurnauer, Explaining the enhanced photocatalytic
activity of Degussa P25 mixed-phase TiO2 using EPR, J.
Phys. Chem. B, 2003, 107, 4545–4549.
63 P. Gong, H. Li, X. He, K. Wang, J. Hu, W. Tan, S. Zhang and
X. Yang, Preparation and antibacterial activity of Fe3O4@Ag
nanoparticles, Nanotechnology, 2007, 18, 285604.
54 Z. Lin, Y. Lu and J. Huang, A hierarchical Ag2O-nanoparticle/
TiO2-nanotube composite derived from natural cellulose
substance with enhanced photocatalytic performance,
Cellulose, 2019, 26, 6683–6700.
55 T. Ali, A. Ahmed, U. Alam, I. Uddin, P. Tripathi and
M. Muneer, Enhanced photocatalytic and antibacterial
´ˇ
´
´
´
activities of Ag-doped TiO2 nanoparticles under visible 64 L. Svoboda, J. Bednar, R. Dvorsky, Z. Rybkova, K. Malachova,
ˇ
ˇ
´
´
light, Mater. Chem. Phys., 2018, 212, 325–335.
J. Henych, D. Matysek and Z. Nemeckova, Novel synthesis of
56 A. Kaur, W. A. Anderson, S. Tanvir and S. K. Kansal, Solar
light active silver/iron oxide/zinc oxide heterostructure for
Ag@AgCl/ZnO by different radiation sources including
radioactive
isotope
60Co:
Physicochemical
and
photodegradation
of
ciprooxacin,
transformation
antimicrobial study, Appl. Surf. Sci., 2020, 529, 147098.
© 2021 The Author(s). Published by the Royal Society of Chemistry
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