Multifunctional ZnWO4 nanoparticles for photocatalytic removal of pollutants and disinfection of bacteria

Article abstract of DOI:10.1016/j.jphotochem.2020.112735

Herein, ZnWO₄ nanoparticles (NP_S) with controllable size were synthesized by a facile solvothermal method via changing EG concentration in the solvent. The physicochemical properties of ZnWO₄ NP_S were characterized by XRD, TEM, EDS, BET, XPS, UV–vis DRS, PL and photocurrent. The results shown that the EG concentration has a great influence on the morphology, size and crystallinity of ZnWO₄ NP_S. On the one hand, the photocatalytic activity of ZnWO₄-EG62.5 was obviously better than that of ZnWO₄-EG0 in the removal of hazardous pollutants including Cr⁶⁺, MB, RhB and MO by 71.4, 33.3, 13.5 and 21.3 %, respectively. Moreover, ZnWO₄-EG62.5 displayed excellent photocatalytic stability for Cr⁶⁺ reduction. The ZnWO₄-EG75, on the other hand, exhibited the best antibacterial activity to Bacillus subtilis and Vibrio alginolyticus, and the maximal inhibition zone area of Bacillus subtilis and Vibrio alginolyticus over ZnWO₄-EG75 was 3.4 and 6.8 times than that of ZnWO₄-EG0, respectively. Our work indicated that ZnWO₄ NP_S presented potential future application in water treatment and marine antifouling, and it is a feasible approach to enhance the photocatalytic and antibacterial performance of semiconductor NPs by controlling its size and crystallinity.

Full text of DOI:10.1016/j.jphotochem.2020.112735

JournalofPhotochemistry&PhotobiologyA:Chemistry401(2020)112735
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Multifunctional ZnWO4 nanoparticles for photocatalytic removal of
pollutants and disinfection of bacteria
Hongbo Hea, Zhuangzhu Luoa,*, Changlin Yub,*
a School of Materials Science and Engineering, School of Materials, Sun Yat-sen University, Guangzhou 510000, China
b Faculty of Environmental Science and Engineering, Key Laboratory of Petrochemical Pollution Process and Control, Guangdong Province, Guangdong University of
Petrochemical Technology, Maoming 525000, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
ZnWO4 NPs
Solvothermal synthesis
Photocatalysis
Bacteriostasis
Herein, ZnWO4 nanoparticles (NPS) with controllable size were synthesized by a facile solvothermal method via
changing EG concentration in the solvent. The physicochemical properties of ZnWO4 NPS were characterized by
XRD, TEM, EDS, BET, XPS, UV–vis DRS, PL and photocurrent. The results shown that the EG concentration has a
great influence on the morphology, size and crystallinity of ZnWO4 NPS. On the one hand, the photocatalytic
activity of ZnWO4-EG62.5 was obviously better than that of ZnWO4-EG0 in the removal of hazardous pollutants
including Cr6+, MB, RhB and MO by 71.4, 33.3, 13.5 and 21.3 %, respectively. Moreover, ZnWO4-EG62.5
displayed excellent photocatalytic stability for Cr6+ reduction. The ZnWO4-EG75, on the other hand, exhibited
the best antibacterial activity to Bacillus subtilis and Vibrio alginolyticus, and the maximal inhibition zone area of
Bacillus subtilis and Vibrio alginolyticus over ZnWO4-EG75 was 3.4 and 6.8 times than that of ZnWO4-EG0, re-
spectively. Our work indicated that ZnWO4 NPS presented potential future application in water treatment and
marine antifouling, and it is a feasible approach to enhance the photocatalytic and antibacterial performance of
semiconductor NPs by controlling its size and crystallinity.
1. Introduction
of water, which may weak the photosynthesis of aquatic green plants
and reduce the content of dissolved oxygen in water, and then affecting
In recent decades, the discharge of industrial sewage has been on
the increase due to the rapid development of industrial production, in
which the deleterious and hazardous ingredients have made great
threat and damage to the water resources, as well as to aquatic or-
ganism and human [1–5]. Heavy metal ions are common harmful
substances in industrial sewage, which can be enriched by aquatic or-
ganism, and then transferred to human body through the food chain,
leading to organ dysfunction and a variety of diseases [6–11]. Hex-
avalent chromium Cr (VI), for instance, is a highly toxic heavy metal
ion which can cause cancer to human body [12–16]. Compared with Cr
(VI), however, trivalent chromium Cr (III) possesses less toxicity and
poor mobility, which can be separated from sewage in the form of
hydroxide. Therefore, it is reasonably practicable to reduce the harm of
chromium containing sewage by turning Cr (VI) into Cr (III) [17–20]. In
addition, printing and dyeing sewage is one of the considerable sources
for the deterioration of water environment [21–24]. Most of the chro-
mophores in dyes are difficult to decolorize and degrade due to their
aromatic structure, result in long-lasting environmental hazards
[25–27]. Further, dyes can absorb sunlight and reduce the transparency
the growth of microorganisms and destroying the self-purification ca-
pacity of water [28]. Removal the deleterious and hazardous in-
gredients of industrial sewage has become one of the urgent environ-
mental needs in the world. Besides that, Pathogenic microorganisms in
sewage are the major causes of waterborne diseases [29]. Thus, it is
necessary to clean up pathogenic bacteria of domestic water to protect
our health.
In recent years photocatalysis technology has stood out from many
water treatment methods due to its high efficiency, low consumption,
sustainability, safety and environmental protection, which has become
one of the new sewage treatment technologies with great application
prospects [30–32]. Generally, the physicochemical properties of semi-
conductor materials tightly correlate with that of phases, sizes and
morphologies [33]. Our previous work [34] found that the monoclinic
ZnWO4 prepared by hydrothermal method displays good photocatalytic
activity for Cr (VI) reduction, and the hydrothermal time has a great
influence on its phase, morphology and performance. Lu et al. [35]
fabricated ZnWO4 nanofibers by an electrospinning method and in-
vestigated its size, morphology and photocatalytic performance for
⁎ Corresponding authors.
E-mail addresses: luozhzhu@mail.sysu.edu.cn (Z. Luo), yuchanglinjx@163.com (C. Yu).
https://doi.org/10.1016/j.jphotochem.2020.112735
Received 26 March 2020; Received in revised form 10 June 2020; Accepted 26 June 2020
Availableonline28June2020
1010-6030/©2020ElsevierB.V.Allrightsreserved.

H. He, et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry401(2020)112735
Fig. 1. TEM images of as-prepared samples, (a) ZnWO4-EG0; (b) ZnWO4-EG50; (c, f) ZnWO4-EG62.5 and (d, e) ZnWO4-EG75; (g) STEM images of ZnWO4-EG62.5 and
EDS mapping images of elemental distributions, (h) O, (i) W, (j) Zn.
Fig. 2. (a) XRD patterns and (b) N2 adsorption-sorption isotherms of the as-prepared ZnWO4 samples.
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JournalofPhotochemistry&PhotobiologyA:Chemistry401(2020)112735
Fig. 3. XPS spectra of ZnWO4-EG62.5, (a) whole scanning spectrum and the high-resolution regional spectra of (b) Zn 2p, (c) W 4f and (d) O 1s.
organic dyes. ZnWO4 nanofibers presented excellent photocatalytic
performance in removal of RhB under simulated sunlight irradiation.
In this work, ZnWO4 NPs with controllable size were fabricated by a
facile solvothermal method. The physicochemical properties of as-pre-
pared ZnWO4 NPs were characterized by XRD, TEM, EDS, BET, XPS,
UV–vis DRS, PL and photocurrent. Specifically, which given detailed
investigation to the effects of solvent concentration on crystallinity, size
and morphology of ZnWO4 NPs. The photocatalytic activities of ZnWO4
NPs were investigated by the removal of hazardous pollutants including
Cr6+, MB, RhB and MO. Moreover, the antibacterial performance of
Bacillus subtilis and Vibrio alginolyticus over ZnWO4 NPs were explored
by a modified inhibition zone method.
Na2WO4·2H2O was dissolved in 15 mL of EG solution to obtain S-B.
After that S-B was added into S-A dropwise under vigorous stirring, and
the obtained suspension was sealed in a 100 mL Teflon-lined. After
stirring for 2 h, which was heated at 180 °C for 14 h. Finally, the white
powder was washed several times with water and ethanol. According to
the different x value denoted as ZnWO4-EG0、ZnWO4-EG50、ZnWO4-
EG62.5 and ZnWO4-EG75.
2.3. Characterization
The morphology and micro-structure of ZnWO4 NPs was collected
with the transmission electron microscope (TEM) and high-resolution
TEM (HRTEM) on a TECNAI G2F20 microscope equipment. Powder X-
ray diffraction (XRD) was recorded using a Bruker D8 Advance X-ray
diffractometer to understand the crystalline structure of ZnWO4 NPs.
The Brunauer–Emmett–Teller (BET) specific surface area (SBET) was
measured on a JW-BK200C nitrogen adsorption apparatus. X-ray pho-
toelectron spectroscopy (XPS) has also been conducted on a K-Alpha+
XPS system with a monochromatic Al Kα source and a charge neu-
tralizer to investigate the element composition and chemical state of the
samples. The light response capability of the ZnWO4 NPs was analyzed
by Ultraviolet-visible diffuse reflectance spectra (UV–vis DRS) on a
UV–vis spectrophotometer (UV-2600, Shimadzu) equipment.
Photoluminescence (PL; F-7000, Hitachi, Japan) was used to investigate
the optical properties of the samples. Photocurrent measurements were
performed on a CHI 660E electrochemical workstation in a three-elec-
trode quartz cell. The saturated calomel electrode and Pt wire electrode
are served as reference electrode and counter electrode, respectively.
2. Experimental section
2.1. Materials
All the chemicals were analytical grade and applied without further
purification.
ZnCl2, Na2WO4·2H2O, Na2SO4, K2Cr2O7 and methylene blue (MB)
were purchased from Aladdin. Ethanol, Ethylene glycol (EG), rhoda-
mine B (RhB) and methyl orange (MO) were procured from Sinopharm.
2.2. Synthesis of ZnWO4
In a typical solvothermal process, x mL of EG was mixed with (75-x)
mL of H2O to obtain EG solution (x = 0, 50, 62.5, 75). Then 1.36 g of
ZnCl2 was dissolved in 60 mL of EG solution to obtain S-A, 3.3 g of
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JournalofPhotochemistry&PhotobiologyA:Chemistry401(2020)112735
Fig. 4. (a) UV–vis diffuse reflectance spectra of the as-prepared samples; (b) (αhν)2 versus hν for determining the optical band gap of the as-prepared samples; (c)
Transient photocurrent responses of the as-prepared samples; (d) PL spectra of the as-prepared samples.
The working electrodes were coated with 10 mg of ZnWO4 NPs film on
a 1.0 cm × 1.0 cm ITO. Further, 0.1 mol L−1 Na2SO4 aqueous solution
was used as the electrolyte and 300 W Xenon lamp served as a light
source. The test of the transient photocurrent response with time was
conducted through an alternated test of opening and closing a light
with no bias voltage.
suspension (105–106 CFU/mL) to corresponding medium (LB medium
and 2216E agar medium to Bacillus subtilis and Vibrio alginolyticus, re-
spectively). Then the bacterial suspension was evenly spread on the
surface of medium plate by a sterile coating rod. After that, the as-
prepared disc was placed on the surface of bacteria containing medium
plate using sterile tweezers. Three parallel discs were placed on each
plate to ensure the reliability of the experimental results. Finally, in-
cubated at 36 ℃ for 24 h and recorded the diameter of the inhibition
zone.
2.4. Photocatalysis tests
The photocatalytic degradation tests were conducted on a photo-
chemical reactor with 400 W metal halide lamp as light source. 30 mg
of ZnWO4 sample was added into 30 mL dye solution (such as MB, RhB
and MO, 20 mg/L), the obtained suspension was stirred in the dark for
60 min to achieve the adsorption-desorption equilibrium prior to light
irradiation, and the temperature of suspension was hold at ⁓25 °C with
cyclic cooling water. About 2 mL of suspension was sampled every
10 min and the solid are filtered by centrifugation. Finally, the con-
centration of dyes was analyzed using UV–vis spectrophotometer at its
maximum absorption wavelength. In photocatalytic reduction of Cr
(VI), 50 mg of ZnWO4 sample was added into 50 mL of K2Cr2O7 aqueous
solution (20 mg/L), and the photocatalytic conditions of Cr6+ reduction
were the same as the photocatalytic degradation tests.
3. Results and discussion
3.1. Characterize of materials
The TEM image of ZnWO4-EG0 was illustrated in Fig. 1a, and
ZnWO4-EG0 nanorod about 100 nm by 20 nm. The size of ZnWO4 NPs
decreased with the increase of EG concentration (Fig. 1b–d). Especially,
the diameter of ZnWO4-EG75 sample was about 5 nm. The moral is that
the existence of EG can inhibit the growth of ZnWO4 NPs effectively.
The internal structures of ZnWO4-EG62.5 and ZnWO4-EG75 were in-
vestigated with HRTEM as demonstrated in Fig. 1f and e, respectively.
Four lattice spacings were identified, two large interplanar spacings
located at 0.47 and 0.57 nm corresponding to the (100) and (010) facets
of ZnWO4, respectively. Besides that, 0.29 and 0.36 nm could attribute
to the (111) and (110) facets, respectively. The mapping images of O, W
and Zn were displayed in Fig. 1h–j, respectively. Which suggested that
the elements of O, W and Zn were distributed in ZnWO4-EG62.5 uni-
formly (Fig. 1g). The results of TEM analysis shown that controllable
morphology and size of ZnWO4 NPs were synthesized by a simple
2.5. Bacteriostasis tests
The bacteriostatic activities of ZnWO4 were evaluated by a modified
inhibition zone method using Bacillus subtilis and Vibrio alginolyticus as
probes. Firstly, 30 mg of ZnWO4 sample was pressed as a disc with
diameter of 3 mm by a tablet press. Next, adding 200 μL bacterial
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H. He, et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry401(2020)112735
Fig. 5. (a) Photocatalytic performance of as-prepared samples for Cr6+ reduction; (b) Comparison of reaction rates of Cr6+ reduction; (c) Photocatalytic performance
of as-prepared samples for dyes degradation, including MB, RhB and MO; (d) UV–vis absorption spectra of contaminant solution (including Cr6+, MB, RhB and MO)
with different reaction times over ZnWO4-EG62.5.
solvothermal method via changing the concentration of EG in the sol-
vent.
1045.4 eV corresponding to Zn 2p3/2 and Zn 2p1/2, respectively. Sug-
gesting that the presence of Zn2+ states in ZnWO4 [38]. As illustrated in
Fig. 3c, the W region at 35.7 eV and 37.9 were assigned to W 4f7/2 and
W 4f5/2, respectively. Which displayed the existence of W6+ in ZnWO4
[39]. Fig. 3d displayed the high-resolution XPS spectra of O 1s, the
main peak at 531.8 eV corresponding to the lattice oxygen in ZnWO4
[40]. Further, the peaks at 530.7 and 533.3 eV corresponding to eOH
[41] and adsorbed H2O [42], respectively.
The XRD analysis was carried out to investigate the crystal prop-
erties of ZnWO4 NPs as shown in Fig. 2a. The main characteristic peaks
of ZnWO4 NPs at 18.9°, 23.8°, 24.5°, 30.4°, 30.7°, 36.4°, 38.3°, 41.3°,
45.8°, 48.7°, 50.3, 51.7°, 53.6°, 61.7°, 64.7° and 68.2° could be indexed
to the (100), (01-1), (110), (11-1), (111), (002), (200), (121), (211),
(02-2), (220), (130), (20-2), (11-3), (13-2) and (04-1) crystal planes of
ZnWO4 (JCPDS 96-210-1675; lattice constants:
a =4.6830 Å, b
UV–vis DRS and photocurrents were measured to investigate the
light response ability and the photogenerated charge separation and
transfer properties of ZnWO4 NPs, respectively. As displayed in Fig. 4a,
the light absorption area of ZnWO4 samples was mainly in the UV re-
gion. With the increase of EG concentration in the solvent, the light
response ability of ZnWO4 samples in the UV region was enhanced
significantly. Owing mainly to small-sized ZnWO4 NPs have more light
absorption area [43]. The optical band gap energy (Eg) of as-prepared
ZnWO4 NPs could be determined by Tauc plot [44] (Fig. 4b). The Eg of
ZnWO4-EG0, ZnWO4-EG50, ZnWO4-EG62.5 and ZnWO4-EG75 was re-
corded to be 3.87, 3.92, 3.94 and 3.98 eV, respectively, which indicated
that EG concentration had little effect on the Eg of ZnWO4 NPs. Fig. 4c
given the time-based photocurrent responses of as-prepared ZnWO4 NPs
under irradiation in a light on-and-off cycle mode. The ZnWO4 samples
prepared by solvothermal method exhibited a much higher photo-
current intensity than that of ZnWO4-EG0 prepared by hydrothermal
method. Further, ZnWO4-EG62.5 presented the maximal photocurrent
intensity, and it was 2.3 times than that of ZnWO4-EG0. Further,
ZnWO4-EG62.5 illustrated a weaker PL intensity compared with other
ZnWO4 NPs (Fig. 4d). Suggesting a higher efficiency of photogenerated
=5.7210 Å and c =4.9280 Å). Well-defined diffraction peaks, corre-
sponding to good crystallinity, observed in ZnWO4-EG0, ZnWO4-EG50
and ZnWO4-EG62.5 NPs. However, the diffraction peaks of ZnWO4-
EG75 was obviously different from that of other samples. The results of
TEM analysis shown that smaller size of ZnWO4 prepared at higher
concentration of EG. The smaller the size of ZnWO4 NPs, the more likely
it is to cause lattice defects [36]. Therefore, the diffraction peaks of
ZnWO4-EG75 were more blunt than other samples. The BET specific
surface area of ZnWO4 NPs was investigated by N2 adsorption and
desorption isotherm curves as shown in Fig. 2b. The BET specific sur-
face area of ZnWO4-EG0 and ZnWO4-EG75 were 25.4 m2/g and
121.0 m2/g, respectively. Herein, smaller size of ZnWO4 NPs directly
contributed to greater BET specific surface area.
The elementary composition and valence states of ZnWO4-EG62.5
were investigated by XPS spectra. The XPS survey spectrum indicated
that the existence of Zn, O and W elements as illustrated in Fig. 3a, and
the element of C could originate from the contamination of instrument
itself [37]. Fig. 3b given the high-resolution XPS spectra of Zn 2p, two
obvious peaks with an energy gap of 23.0 eV located at 1022.4 and
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H. He, et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry401(2020)112735
Fig. 6. (a) Stability test of the ZnWO4-EG62.5 in the recycling reactions for Cr6+ reduction; XRD patterns (b) and XPS spectra (c) of ZnWO4-EG62.5 before and after
photocatalytic tests; (d) Schematic of the photocatalytic conversion process for contaminant removal over ZnWO4.
charge separation and transfer on the surface of ZnWO4-EG62.5, which
could largely benefit the boosting of photocatalytic activity [45].
irradiation, and 97.7 % of MO could be degraded over ZnWO4-EG62.5
under the same condition. Compared with ZnWO4-EG0, ZnWO4-EG62.5
increased the photocatalytic removal rate of Cr6+, MB, RhB and MO by
71.4 %, 33.3 %, 13.5 % and 21.3 %, respectively. As shown in Fig. 5d,
with increasing of irradiation time, the UV–vis absorption peaks of
pollutants decreased rapidly over ZnWO4-EG62.5, indicating that
ZnWO4-EG62.5 with excellent photocatalytic activity for the removal of
pollutants including Cr6+, MB, RhB and MO.
3.2. Photocatalytic properties
The photocatalytic performance of ZnWO4 NPs was investigated by
the reduction of Cr6+ in 20 mg/L K2Cr2O7 solution. As presented in
Fig. 5a, the K2Cr2O7 solution displayed good stability under light irra-
diation. After 30 min irradiation, about 20.9 % of Cr6+ was photo-
catalytic reduced over ZnWO4-EG0, while the ZnWO4 NPs prepared by
solvothermal method exhibited better performance in the Cr6+ reduc-
tion. Furthermore, the ZnWO4-EG62.5 presented the maximum photo-
catalytic efficiency of about 92.3 % for Cr6+ reduction. The photo-
catalytic dynamics curves of Cr6+ reduction over ZnWO4 NPs was
illustrated in Fig. 5b, the maximal rate constant of Cr6+ reduction over
ZnWO4-EG62.5 up to 0.0845 min−1, which was 9.8 times than that of
ZnWO4-EG0 (0.0086 min−1).
In addition, the photocatalytic activities of printing and dyeing
sewage over ZnWO4 NPs were investigated by the degradation of or-
ganic dyes, including MB, RhB and MO. Fig. 5c compared the photo-
catalytic performance of ZnWO4-EG0 and ZnWO4-EG62.5. In the test of
MB, 63.2 % MB could be degraded by ZnWO4-EG0 after 20 min irra-
diation, and ZnWO4-EG62.5 presented better photocatalytic activity
with 96.4 % of MB was removed under the same condition. In the re-
moval of RhB, after 20 min irradiation, 79.5 % and 93.0 % of RhB could
be degraded by ZnWO4-EG0 and ZnWO4-EG62.5, respectively. Further,
Based on the above characterization results, we analyzed the reason
of excellent photocatalytic activity of ZnWO4-EG62.5 NPs. Firstly, the
specific surface area of ZnWO4 NPs gradually increased with the in-
crease of EG concentration. Large specific surface area could effectively
improve the contact probability between ZnWO4 NPs and pollutants,
which would help to improve the photocatalytic efficiency of ZnWO4
NPs. However, the crystallinity of ZnWO4-EG75 decreased significantly
when using pure EG as solvent (XRD analysis), and the low crystallinity
might result in the decrease of its photocatalytic activity in the removal
of pollutants [34]. In addition, the results of photocurrent test shown
that ZnWO4-EG62.5 with faster photogenerated electron transfer effi-
ciency than that of other ZnWO4 NPs. The as-prepared ZnWO4-EG62.5
displayed, on the whole, excellent photocatalytic performance for the
removal of pollutants due to its high crystallinity, large specific surface
area, fast electron migration rate and low carriers recombination
probability.
Further, the recycling experiment of Cr6+ reduction was im-
plemented to explore the stability of ZnWO4-EG62.5. The ZnWO4-
EG62.5 photocatalyst was recycled by centrifugation, and then which
76.4
% MO could be removed over ZnWO4-EG0 after 50 min
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JournalofPhotochemistry&PhotobiologyA:Chemistry401(2020)112735
Fig. 7. Antibacterial activity of as-prepared samples for against Bacillus subtilis: (a, b) ZnWO4-EG0; (c, d) ZnWO4-EG50; (e, f) ZnWO4-EG62.5; (g, h) ZnWO4-EG75; (i)
Inhibition zone diameter of Bacillus subtilis over as-prepared samples; (j) Inhibition zone area of Bacillus subtilis over as-prepared samples.
was reused in the next cycle. ZnWO4-EG62.5 photocatalyst presented
excellent stability as illustrated in Fig. 6a, and the photocatalytic re-
duction efficiency of Cr6+ decreased by 2.3 % after five cycles. No
significant discrepancy observed in the XRD spectrum of the used
ZnWO4-EG62.5, suggesting the crystal texture of ZnWO4-EG62.5 re-
mains stable (Fig. 6b). Fig. 6c compared XPS spectrum of ZnWO4-
EG62.5 before and after the test of Cr6+ reduction. Besides the Zn, O
and W elements, new Cr element observed in the XPS spectrum of the
used ZnWO4-EG62.5. The high-resolution XPS spectrum of Cr 2p was
given in Fig. 6c, the peaks at 586.0 and 577.0 eV corresponding to Cr
2p1/2 and Cr 2p3/2, respectively, indicating that the reduction products
of Cr6+ presented Cr3+ states and precipitated in ZnWO4-EG62.5.
Fig. 6d demonstrated the mechanism of photocatalytic removal pollu-
pollutants (MB, RhB and MO) were degraded by photogenerated oxi-
dative species including ·O2-, ·OH and h+ [45].
3.3. Bacteriostatic properties
The bacteriostatic activities of as-prepared ZnWO4 NPs were eval-
uated by bacterial inhibition zone test using Bacillus subtilis and Vibrio
alginolyticus as probes. Fig. 7 illustrated the bacteriostatic test results of
ZnWO4 NPs against Bacillus subtilis. An unsatisfactory bacteriostatic
effect was observed in ZnWO4-EG0 NPs, and the corresponding in-
hibition zone diameter was 5.3 mm (Fig. 7a and b). Further, the in-
hibition zone diameter of ZnWO4-EG50, ZnWO4-EG62.5 and ZnWO4-
EG75 against Bacillus subtilis was recorded to be 6.6, 8.6 and 9.3 mm,
respectively (Fig. 7c–i). Fig. 7j displayed the inhibition zone area of
ZnWO4 NPs against Bacillus subtilis, the maximal inhibition zone area of
Bacillus subtilis over ZnWO4-EG75 up to 67.89 mm2, which was 3.4
times than that of ZnWO4-EG0 (20.05 mm2).
tants over ZnWO4 NPs. Photogenerated electrons (e−) and holes (h+
)
were rapidly separated over ZnWO4 NPs upon light irradiation. Then
photogenerated electrons and holes migrated to the surface of ZnWO4
NPs under the action of internal electric field [46]. On the one hand,
Cr6+ could be reduced to Cr3+ by photogenerated electrons due to its
excellent reducing activity [34]. On the other hand, the electrons and
holes in the surface of ZnWO4 would be trapped by O2 and H2O to
produce ·O2- and ·OH radicals, respectively. After that organic
Fig. 8 given the bacteriostatic test results of ZnWO4 NPs against
Vibrio alginolyticus. ZnWO4-EG0 sample displayed good bacteriostatic
effect for Vibrio alginolyticus, and the corresponding inhibition zone
diameter was 9.9 mm (Fig. 8a and b). Further, the inhibition zone
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JournalofPhotochemistry&PhotobiologyA:Chemistry401(2020)112735
Fig. 8. Antibacterial activity of as-prepared samples for against Vibrio alginolyticus: (a, b) ZnWO4-EG0; (c, d) ZnWO4-EG50; (e, f) ZnWO4-EG62.5; (g, h) ZnWO4-EG75;
(i) Inhibition zone diameter of Vibrio alginolyticus over as-prepared samples; (j) Inhibition zone area of Vibrio alginolyticus over as-prepared samp.
diameter of ZnWO4-EG50, ZnWO4-EG62.5 and ZnWO4-EG75 against
Vibrio alginolyticus was recorded to be 11.1, 11.3 and 17.2 mm, re-
spectively (Fig. 8c–i). ZnWO4 NPs shown, on the whole, better anti-
bacterial activity to Vibrio alginolyticus than that of Bacillus subtilis. Si-
milarly, ZnWO4-EG75 also displayed the best bacteriostatic effect on
Vibrio alginolyticus, and the maximal inhibition zone area of Vibrio al-
ginolyticus over ZnWO4-EG75 up to 232.23 mm2, which was 6.8 times
than that of ZnWO4-EG0 (34.19 mm2) (Fig. 8j). The size of as-prepared
ZnWO4 NPs decreased with the increase of EG concentration, and the
specific surface area increased from 25.4 m2/g to 121.0 m2/g. Which
was conducive to the release and migration of antibacterial substance
Zn2+ [47,48]. ZnWO4-EG75 demonstrated, therefore, better anti-
bacterial activity than that of other ZnWO4 NPs.
Zn2+, and therefore ZnWO4-EG75 shown the best photocatalytic ac-
tivity to Bacillus subtilis and Vibrio alginolyticus. Although small size and
large specific surface area of ZnWO4-EG75 could be obtained by using
pure EG as solvent. ZnWO4-EG75 displayed, however, defective crys-
tallinity and low carrier separation efficiency than that of ZnWO4-
EG62.5. Thus ZnWO4-EG62.5 shown excellent photocatalytic activity
for the removal of Cr6+, MB, RhB and MO. Further, excellent stability
for photocatalytic performance of ZnWO4-EG62.5 was also affirmed by
Cr6+ reduction. Our work proved that controlling the size and crys-
tallinity of ZnWO4 was a feasible approach to enhance its photo-
catalytic and antibacterial properties, and which given a new realm of
possibilities for the rational design of functional semiconductor NPs for
applications in water treatment and marine antifouling.
4. Conclusion
CRediT authorship contribution statement
Herein, Multifunctional ZnWO4 NPs with controllable size were
prepared by a facile solvothermal method via changing EG concentra-
tion in the solvent. Increasing EG concentration could effectively inhibit
the growth of ZnWO4 NPs and increase the specific surface area. Which
was propitious to the release and migration of antibacterial substance
Hongbo He: Conceptualization, Methodology, Investigation, Data
curation, Writing - original draft. Zhuangzhu Luo: Resources, Writing -
review & editing, Visualization, Project administration, Funding ac-
quisition. Changlin Yu: Resources, Supervision, Writing - review &
editing, Funding acquisition.
8

H. He, et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry401(2020)112735
Declaration of Competing Interest
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This work was supported by the National Natural Science
Foundation of China (NSFC) (No.51575504, 21567008), Project
Supported by Guangdong Province Universities and Colleges Pearl
River Scholar Funded Scheme (2019), Guangdong Basic and Applied
Basic Research Foundation (2019A1515011249), Key Research Project
of Natural Science of Guangdong Provincial Department of Education
(2019KZDXM010).
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