MicrowaveâUltrasonic Synergistically Assisted Synthesis of ZnO

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Microwave-ultrasonic synergistically assisted synthesis of ZnO coated cotton fabrics with enhanced antibacterial activity and stability Hao Yang, Qingxia Zhang, Ying Chen, Yuantao He, Fang Yang, and Zhong Lu ACS Appl. Bio Mater., Just Accepted Manuscript • DOI: 10.1021/acsabm.8b00086 • Publication Date (Web): 03 Jul 2018 Downloaded from http://pubs.acs.org on July 6, 2018

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ACS Applied Bio Materials

Microwave-ultrasonic synergistically assisted synthesis of ZnO coated cotton fabrics with enhanced antibacterial activity and stability Hao Yang a, *, Qingxia Zhang a, Ying Chen a, b, Yuantao He a, Fang Yang a, Zhong Lu a a

Key Laboratory for Green Chemical Process of Ministry of Education, School of Environmental

Ecology and Biological Engineering, Wuhan Institute of Technology, Wuhan, 430205, PR China b

Department of Petrochemical Engineering, Guangzhou Institute of Technology，Guangzhou,

510725, PR China

* Corresponding author: Associate Professor H. Yang, E-mail: [email protected]

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ABSTRACT ZnO nanoparticles (NPs) coated cotton fabrics were prepared via a facile, time-saving and cost-effective microwave-ultrasonic synergistic method. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and inductively coupled plasma (ICP), which demonstrated that uniform ZnO NPs with an average diameter of 34 nm were intensely coated on the cotton fabrics. Compared with the samples prepared by single microwave or ultrasonic method, the as-prepared samples displayed preferable and durable antibacterial activity against Staphylococcus aureus and Escherichia coli. The effects of the samples on inactivating microbial cells were also investigated by atomic force microscopy (AFM). It was found that the size and content of ZnO NPs coated on the cotton fabrics were dependent on the concentration of Zn2+ and microwave-ultrasonic reaction time, which also had a significant influence on the antibacterial activity of the cotton fabrics. In view of the antibacterial activity and synthesis time, the best experimental parameters were obtained. This simple, efficient, and environmentally friendly one-pot synthesis method may have great potential in scale-up production of antibacterial textile. KEYWORDS: antibacterial activity; cotton fabric; ZnO; ultrasonic; microwave; stability

INTRODUCTION With the deterioration of the environment, more and more people concern about public hygiene to avoid infection by bacteria.1 One of the effective way to prevent spread of 2


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bacteria is to use antibacterial fabrics because they can reduce the bioburden by killing microbial cells.2-3 Generally speaking, antibacterial fabrics are prepared by modifying the fabrics with antimicrobial agents, including organic, inorganic and natural antimicrobial agents. Organic antimicrobial agents such as quaternary ammonium salt have been avoided recently because of the multiple drug resistance and adverse side effects.4-5 Natural antimicrobial agents are safe and have good biocompatibility, however, the antibacterial activities are insufficient to kill most bacteria.6 Therefore, inorganic nanoparticles (NPs) would undoubtedly be a good candidate.7-9 Inorganic NPs have proven their effectiveness for treating infectious diseases in vitro as well as in animal models.10-12 Reports have proven that use of inorganic NPs is one of the most promising strategies to overcome the microbial drug resistance.13-15 Among various inorganic antimicrobial agents, zinc oxide (ZnO) has been verified its good antibacterial activity against Gram-positive bacteria and Gram-negative bacteria.16-17 Besides, ZnO has been widely used in food, cosmetics and medicine for its safety and biocompatibility.18 Therefore, the development of ZnO modified antimicrobial textile has attracted much interest in both academic and industrial domains.19-21 It is well known that ZnO NPs with smaller size and larger concentration could achieve better bactericidal response.16,

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, and different methods have been

developed to immobilize ZnO NPs onto fabrics, for example, the “pad-dry-cure” method,23 bio-approach,24 and layer-by-layer deposition method.25 These techniques are always complicated, time consuming, and the products are not pure and stable. To improve the stability of the materials, cross linking agents are often used,26 which may 3



induce additional waster to the environment. In recent years, sonochemistry opened up new areas of textile finishing process,27-28 because it can dramatically reduce energy, chemicals and time involved in various operations.29 For instance, Perelshtein I. et al. 30 synthesized ZnO NPs with ~30 nm coated on cotton fabrics under ultrasound irradiation for 0.5 h, and the minimum ZnO content for achieving a high antibacterial efficacy was found 0.75% (wt%). Khanjani S. et al. 31 deposited ZnO NPs on silk fabrics by alternate dipping the fabrics in bath of potassium hydroxide and zinc nitrate under ultrasound irradiation. They found that the particle size of ZnO decreased as increasing power of ultrasound irradiation. Besides, microwave irradiation has been extensively utilized to synthesize colloidal inorganic nanocrystals, including single-metal nanocrystals, transition-metal oxides and non-oxide semiconductors.32 Microwave assisted synthesis can not only reduce processing time, but also increase product yields and enhance product purity. For example, Cao X. W. et al.

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deposited Ag NPs on jute fibers by in situ microwave

heating in the absence of reducing reagents, the versatile Ag-jute composites showed superior thermal stability and high crystallinity. Herein, in view of the virtues of ultrasonic and microwave irradiation, the objective of this work is trying to prepare cotton fabric with antibacterial properties by immobilizing ZnO NPs on the fabric via microwave-ultrasonic synergistic method in a shorter time. To prove the advantages of such technique, the antibacterial activities and durability of the ZnO coated cotton fabrics prepared by ultrasonic, microwave and microwave-ultrasonic synergistic method were compared. Furthermore, the effects of 4


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synthesis parameters on antibacterial activity of the cotton fabrics were studied in detail. These results may provide a simple, inexpensive and green approach for scale-up production of antibacterial cotton fabrics.

EXPERIMENTAL SECTION Materials Zinc acetate dihydrate (Zn(Ac)2·2H2O), absolute ethanol and ammonia solution (NH3·H2O, 25%, wt%) were procured from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All the reagents were of analytical grade and used directly without further purification. The cotton fabrics were purchased from local stores and cleaned with ethanol and deionized water. Preparation of ZnO coated cotton fabrics ZnO coated cotton fabrics prepared by microwave-ultrasonic synergistic method were synthesized as following: A certain amount of Zn(Ac)2·2H2O was dissolved in ethanol-water solvent (10:1, v/v) in a 100 mL sonication flask. The pH value of the solution was adjusted to 8~9 by adding NH3·H2O dropwisely. Then, a piece of cotton fabric (2.5 cm×2.5 cm) was immersed in the above solution. The mixture was subsequently transferred to a microwave-ultrasonic reactor (XH-300A, Beijing Xianghu Technology Co., Ltd., China), and heated up to 85 oC under microwave (2450 MHz, 300 W) and discontinuous ultrasonic irradiation (25 kHz, 750 W at 50% efficiency, 2 s insonation and 1 s interruption) for different period. Finally, the coated cotton fabric was washed thoroughly with water to remove traces of ammonia and dried in an oven at 60 °C to obtain the final product. For comparison, samples synthesized by ultrasonic 5



irradiation and microwave irradiation were conducted under the identical conditions except that the microwave or ultrasonic power was set to zero. Hereafter, ZnO coated cotton fabrics prepared by ultrasonic, microwave and microwave-ultrasonic synergistic methods are abbreviated as US, MW and MW-US, respectively. Characterization The crystal structure of ZnO NPs was analyzed by X-ray powder diffraction (XRD, Bruker AXS D8 Discover, USA). The surface morphology of ZnO coated cotton fabrics were observed by scanning electron microscope (SEM, Hitachi S4800, Japan). The antimicrobial effects of the coated fabrics on bacterial cells as well as the high-resolution image of the cotton fabrics were investigated via atomic force microscopy (AFM, Veeco Nanoscope IIIa, USA). The ZnO content on cotton fabric was determined by inductively coupled plasma (ICP, Shimadzu ICPE-9000, Japan). Antibacterial activities of ZnO coated cotton fabrics The antibacterial performances of ZnO coated cotton fabrics were examined against both Gram-positive bacterium Staphylococcus aureus (S. aureus, CCTCC AB 91093) and Gram-negative bacterium Escherichia coli (E. coli, CCTCC AB 93154). To prepare S. aureus and E. coli suspensions, a single colony from the corresponding bacterial stains was used. The bacterial strain was then cultured overnight in Luria-Bertani (LB) medium with required aeration at 37 °C, then it was diluted into a sterile physiological saline solution until 0.1 optical density (OD) at 600 nm was attained, which corresponded to about 1×108 colony forming unit (CFU)/mL. Thereafter, the coated cotton fabrics and the uncoated fabric, which served as a control, were respectively 6


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placed into a conical flask containing 9.99 mL of LB liquid medium, then 10 µL of above bacteria suspension was added into the conical flask, respectively, so the initial bacterial concentration in the conical flask was approximately 1×105 CFU/mL. The suspensions were then incubated at 37 °C with agitation at 180 rpm. An aliquot (10 µL) was taken at different time intervals (0.5, 1, 2, 3h) and transferred onto LB agar plates, which were allowed to grow overnight at 37 °C. The viable bacteria were monitored by counting the number of CFU on LB agar plates. The inhibition rates of the samples can be calculated by the following formula: Inhibition rates (%)= (N0 - N) / N0 × 100 where N0 and N stand for the average number of CFU of the uncoated and coated fabrics, respectively. The antibacterial assays were repeated at least three times for each bacterium. Durability of ZnO coated cotton fabrics Ultrasonic water bath was used to test the durability of ZnO NPs on cotton fabrics. In a typic procedure, ZnO coated cotton fabric was put in an ultrasonic cleaner (Ningbo Scientz Biotechnology SB-3200, China). It was washed in deionized water under ultrasonic irradiation at 40 kHz for 30 min, then it was dried in an oven at 60 °C for 2 h. This process was repeated several times, and the antibacterial activities of the pristine samples and washed samples inactivating S. aureus and E. coli for 3 h were measured to verify the strong adhesion of ZnO NPs on fabrics.

RESULTS AND DISCUSSION Comparison of US, MW, and MW-US 7



Fig. 1 depicted XRD patterns of ZnO NPs prepared by ultrasonic, microwave and microwave-ultrasonic synergistic methods when the concentration of Zn2+ was 1.0 mM and reaction time was 15 min. The ZnO NPs were gathered from the precipitates of the microwave-ultrasonic reactor. All the patterns showed the main peaks at 31.8o, 34.5o, 36.3o, 47.6o, 56.6o, 62.9o, 68.0o, 69.1o, which were corresponded to (100), (002), (101), (102), (110), (103), (112) and (201) crystal planes of hexagonal phase of ZnO (JCPDS No. 36-1451), respectively. However, ZnO NPs synthesized by ultrasonic and microwave methods had some impurities. The peaks of ZnO prepared by ultrasonic method at 20.2o, 27.4o, 40.9o, 55.4o and 59.5o could be ascribed to (110), (111), (121), (222) and (421) crystal planes of Zn(OH)2 (JCPDS No. 1-360). Meanwhile, the minor peak at 20.2o also emerged in ZnO prepared by microwave method, which indicated that only under microwave-ultrasonic synergistic method, the as-prepared nanoparticles were pure ZnO nanocrystals. Besides, some differences could still be observed among the samples. The preferential growth lattice plane of ZnO prepared by ultrasonic was (100) plane, while that of ZnO prepared by microwave and microwave-ultrasonic were both (101) plane as the standard atlas. The difference of preferential growth lattice plane may lead to the diverse morphology of ZnO.34

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Fig. 1. XRD patterns of ZnO NPs prepared by ultrasonic, microwave and microwave-ultrasonic synergistic methods.

Fig. 2 showed the corresponding SEM images of US, MW and MW-US. ZnO prepared by ultrasonic method was aggregated with non-specific topography on the surface of cotton fabrics, as shown in Fig. 2 (a, b). However, when prepared by microwave and microwave-ultrasonic, ZnO NPs with spherical shape about 30 nm were formed. This is agreed with the analysis of XRD. Compared with ZnO NPs prepared by microwave, those prepared by microwave-ultrasonic showed more uniformity, and nearly all the surface of the cotton fabrics was coved by ZnO NPs. The content of ZnO on the fabrics prepared by ultrasonic, microwave and microwave-ultrasonic synergistic methods were 0.14%, 0.13% and 0.31%, respectively (Table 1). Usually, microwave irradiation could better regulate ZnO formation and enhance product quality and yield by dielectric heating, which could produce efficient internal volumetric heating and reduce “wall effects” as compared with conventional conductive heating.35-37 Moreover, ZnO NPs could be well dispersed on the surface of cotton fabrics by shock waves and 9



ultrasonic microjets resulting from the collapse of the sonochemical bubbles (or called acoustic cavitation).38 The acoustic cavitation mechanical effect of ultrasound and the flash dielectric heating effect of microwave are different in nature, and they could form a novel environment with high temperature and pressure, fast mass and heat transfer in the reaction medium, therefore, synergistic effect could be expected under this condition. In our study, microwave-ultrasonic synergistic method had significantly increased the ZnO NPs yield and enhanced their uniformity on cotton fabrics.

Fig. 2. SEM images of (a, b) US, (c, d) MW and (e, f) MW-US.

The antibacterial activities of US, MW and MW-US were recorded in Fig. 3. It was found out that no matter how long inactivation took, MW-US exhibited the highest 10


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inhibition rates against both S. aureus and E. coli, while US displayed the lowest values (Fig. 3a, b). On one side, both MW and MW-US had the similar particle size, the larger content of ZnO of MW-US showed higher inhibition rate. On the other side, the content of ZnO of US was slightly higher than MW, but its inhibition rates were the smallest among all the samples. The reason could be ascribed to the impurities, different morphology and size of ZnO NPs.39-40 It is believed that ZnO NPs with smaller size could easily penetrate into bacterial membranes due to their large interfacial area.41 Meanwhile, smaller ZnO NPs with larger surface area would induce higher concentration of oxygen species on the surface and release more Zn2+ ions, which could obtain greater antibacterial activity.42-43 Therefore, excellent antibacterial activity of the cotton fabrics requires pure ZnO NPs with more uniform morphology, smaller size and larger loading capacity.

Fig. 3. Antibacterial activities of US, MW and MW-US against (a) S. aureus and (b) E. coli, respectively.

The topography changes of bacterial cells of S. aureus and E. coli treated with uncoated cotton fabrics and ZnO coated fabrics for 3 h were investigated by AFM. As

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depicted in Fig. 4, the cells of S. aureus treated with uncoated cotton fabrics had smooth surfaces with perfect spherical morphology, which suggested that the uncoated cotton fabrics had no obvious effect on the bacteria. After contact with US, only a few bacterial cells began to collapse. That is because US had the lowest antibacterial activity. When the bacterial cells treated with MW, a big hole appeared on most of the cells surface, and some bacterial fragments emerged. Furthermore, when the cells contacted with MW-US, almost all the bacterial cells were ruptured. The spherical-shape cells could hardly be seen, and their surface became rough. This can be ascribed to the damages of the cell walls, thus induced the leakage of intracellular content, and finally resulting in bacterial death.44 Similarly, the cells of E. coli treated with uncoated cotton fabrics were full, which had relatively smooth surface with rod-shaped morphology. After contact with US, the height of the cells decreased while their width increased, and some small protuberances emerged on the cells surface, which implied that the cell walls collapsed. When E. coli treated with MW, the boundary of the cells became blurred and large protuberances appeared on the cells. Moreover, after E. coli contacted with MW-US, the cells merged together and lost their original shape, which illustrated that the structure of the bacteria cells could be heavily destroyed by MW-US.45 It seemed that the degree of destructions on both S. aureus and E. coli was in the following sequence: US < MW < MW-US, which was in accordance with the sequence of antibacterial activities.

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Fig. 4. 3D AFM images of S. aureus (left column) and E. coli (right column) treated with uncoated cotton fabrics and ZnO coated cotton fabrics.

To compare the durability of ZnO coated cotton fabrics prepared by different methods, the antibacterial activities of the pristine samples and those washed for 3, 10 times were evaluated. As shown in Fig. 5, the inhibition rates of all the samples reduced slightly after they were washed for 3 times. However, there was dramatic decreases in inhibition rates after they were washed for 10 times. In terms of S. aureus (Fig. 5a), the average inhibition rates of US, MW and MW-US decreased by 26%, 28% and 23%,

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respectively after washed for 10 times. As for E. coli (Fig. 5b), their average inhibition rates decreased by 15%, 17% and 13% respectively under the identical condition. It appeared that the stability of antibacterial activities of MW-US was the best, and the sample which had been washed for 10 times still had preferable antibacterial activity as compared with other reports.27-28 This result indicated that the binding force between ZnO and the cotton fabrics of MW-US was the strongest. The reason could be attributed to the synergistic effects of microwave and ultrasonic irradiation.

Fig. 5. Antibacterial activities of ZnO coated cotton fabrics before and after washed 3, 10 times against (a) S. aureus and (b) E. coli, respectively.

ZnO NPs were formed via the hydrolysis reaction 30: Zn2+ + 4NH3 H2O [Zn (NH3)4]2+ + 4H2O (1) [Zn (NH3)4]2+ 2OH- + 3H2O ZnO +4NH3·H2O (2) In this process, ammonia acted as a catalyst and ZnO was formed through the ammonium complex Zn (NH3)42+. Generally, NH3·H2O dissociated into NH4+ and OHions. NH4+ ions tended to get adsorbed on ZnO NPs to form a monolayer and prevent subsequent loading of ZnO NPs as a result of charge repulsion,46 therefore, the size of 14


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ZnO NPs could be controlled in a small range. The dispersed ZnO NPs created high-speed microjets in form of bubbles collapsing on the cotton fabrics under ultrasonic irradiation, which might cause a local welding of the fabrics at the contact sites, and thus result in well dispersed and robust coating of ZnO NPs. The similar phenomenon was also reported elsewhere.47-49 Meanwhile, microwave dielectric heating provided much more energy during the reaction. It can accelerate the reaction very fast and promote the form of crystal structure, boost ZnO NPs impacting the fabrics and make them strongly adhere to the fabrics. All the results illustrated that MW-US possessed the best antibacterial activity and stability towards both S. aureus and E. coli for the uniform morphology, small size, large loading capacity and strong adhesive force. Hence, microwave-ultrasonic synergistic method is more excellent than microwave and ultrasonic methods.

Optimization of microwave-ultrasonic reaction For scale-up production of MW-US, a more detailed work was conducted by studying the effects of synthetical conditions on antibacterial activities of the fabrics. Generally speaking, the antibacterial activity of ZnO coated cotton fabrics depends on the particle size and content of ZnO, which is strongly related to the concentration of the reagents and the growth rate and time of the particles. That was why experimental parameters such as the concentration of Zn2+ and reaction time were selected as the major factors for the optimization of the reaction. The synthesis parameters of different samples were listed in Table 1.

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Table 1. The effect of synthesis parameters on size and content of ZnO NPs coated on cotton fabrics. sample

a b

ultrasound microwave concentration reaction time particle size ZnO content power (W) power (W) of Zn2+ (mM) (min) (nm) (wt %)

US

750

0

1.0

15

-a

0.14

MW

0

300

1.0

15

27

0.13

MW-US1

750

300

0.2

15

52b

0.16

MW-US2

750

300

1.0

15

34

0.31

MW-US3

750

300

2.0

15

36

0.74

MW-US4

750

300

20.0

15

1920

3.47

MW-US5

750

300

2.0

5

30

0.45

MW-US6

750

300

2.0

30

92

1.04

“-” indicated that the size of ZnO NPs cannot be measured. the morphology of the ZnO NPs was ellipse, and the size was the long distance between two ends.

The surface morphology of MW-US prepared by different precursor concentrations were presented in Fig. 6. When the concentration of Zn2+ was 0.2 mM (MW-US1), uniform ZnO nanomaterials with rice-shape were coated on the cotton fabrics (Fig. 6a, b). With increasing the concentration to 1 mM (MW-US2), the morphology of ZnO changed from rice-shape to nanoparticles (Fig. 2e, f). Further increasing the concentration to 2 mM (MW-US 3), the morphology and size of ZnO NPs had hardly changed (Fig. 6c, d). The size of ZnO NPs was further determined to be 36 nm by high resolution of AFM 3D image (Inset of Fig. 6d). When the concentration of Zn2+ was raised to 20 mM (MW-US4), the size of ZnO NPs increased dramatically to 1.92 µm (Fig. 6e, f). According to the results of inductively coupled plasma (ICP), as shown in Table 1, the content of ZnO on cotton fabric increased gradually as the concentration of Zn2+ increased from 0.2 to 20 mM. Therefore, the concentration of the precursor played an important role on the morphology and size of ZnO, as well as the content of ZnO

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coated on the cotton fabrics, which could affect their antibacterial activities.

Fig. 6. SEM images of MW-US prepared by using (a, b) 0.2 mM, (c, d) 2 mM and (e, f) 20 mM of Zn2+, respectively. The reaction time was 15 min.

The inhibition rates of MW-US prepared by different precursor concentrations against S. aureus and E. coli were shown in Fig. 7. MW-US1 exhibited the minimum inhibition rates for both S. aureus and E. coli owing to the lowest content of ZnO. When the concentration was higher than 0.2 mM, the antibacterial activities of the samples improved notably. Comparing MW-US2 and MW-US3, both had the similar particle size, the higher content of ZnO endowed MW-US3 a superior antibacterial activity. It is 17



worth noting that the ZnO content of MW-US4 was almost five times as much as that of Z3, but its inhibition rate was smaller than MW-US3, which indicated that the particle size of ZnO had a great influence on its antibacterial activity. The inhibition rates of MW-US3 were over 99% for both S. aureus and E. coli after the treatment for 3h. Thus, MW-US prepared by the precursor concentration of 2 mM had the best antibacterial activity against both S. aureus and E. coli.

Fig. 7. Antibacterial activities of MW-US prepared by using 0.2 mM, 1 mM, 2 mM and 20 mM of Zn2+ against (a) S. aureus and (b) E. coli, respectively. The reaction time was 15 min.

Keep the precursor concentration at 2 mM, the surface morphology and antibacterial activities of MW-US prepared under different reaction time were also investigated. When the reaction time was only 5 min (MW-US5), the ZnO NPs with an average diameter of 30 nm aggregated on the surface of cotton fabrics (Fig. 8a, b). Prolonging the reaction time to 15 min, the size of ZnO NPs didn’t have an obvious change, but ZnO NPs were dispersed uniformly on the cotton fabrics (Fig. 6c, d). When the reaction time was 30 min (MW-US6), the size of ZnO NPs increased to 92 nm, as presented in Fig. 8 c and d. The content of ZnO of MW-US5, MW-US3, and MW-US6 were 0.45%,

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0.74%, and 1.04%, respectively, which revealed that the reaction time influenced both the size and content of ZnO coated on the cotton fabrics.

Fig. 8. SEM images of MW-US prepared by (a, b) 5 min and (c, d) 30 min. The concentration of Zn2+ was 2 mM.

Fig. 9 showed the inhibition rates of MW-US prepared by different reaction time against S. aureus and E. coli, respectively. MW-US5 exhibited inferior antibacterial activity for its low ZnO content. Its inhibition rates were less than 40% for both S. aureus and E. coli after 0.5 h treatment. However, its inhibition rates raised up to over 90% for both bacteria after 3 h treatment. The increase of the inhibition rates may be ascribed to the slow release of zinc ion by the nanoparticles.50 Additionally, MW-US3 and MW-US6 showed similar inhibition rates. Although the ZnO content of MW-US6 was higher than that of MW-US3, a larger particle size of MW-US6 declined the antibacterial activity. Considering the time consumption of the synthesis, the reaction time of 15 min was chosen for the optimum reaction condition. 19



Fig. 9. Antibacterial activities of MW-US prepared by 5 min and 30 min against (a) S. aureus and (b) E. coli, respectively. The concentration of Zn2+ was 2 mM.

CONCLUSIONS In summary, we have successfully grown ZnO NPs on cotton fabrics by microwave-ultrasonic synergistic method. Compared with ZnO coated cotton fabrics prepared by ultrasonic or microwave irradiation, the products prepared by microwave-ultrasonic possessed higher antibacterial activity and durability for their high purity, uniform morphology, small size, large loading capacity and strong adhesive force of ZnO NPs. The optimum parameters for the preparation of ZnO coated cotton fabrics via microwave-ultrasonic synergistic method were as follows: the concentration of Zn2+ was 2 mM, and reaction time was 15 min. Under this condition, 36 nm ZnO NPs were well dispersed on the cotton fabrics without significant damage to the structure of the cotton, and the content of ZnO was 0.74 wt %. The as-prepared sample exhibited the best antibacterial activity against both S. aureus and E. coli, which could reach over 99% reduction in viability after treatment for 3h. AFM results further revealed the bactericidal effects of the samples on cells of S. aureus and E. coli. This work 20


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demonstrates that microwave-ultrasonic combined method affords a simple, time-saving and environmentally benign coating technique, which could be further explored in scale production of antibacterial multifunctional fabrics.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]. Phone: +86-13377876683.

ORCID Hao Yang: 0000-0003-3325-1378

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (Grant No. 21201135 and 31701604). Thank Prof. Shantang Liu for providing instruction on AFM characterization.

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MicrowaveâUltrasonic Synergistically Assisted Synthesis of ZnO

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MicrowaveâUltrasonic Synergistically Assisted Synthesis of ZnO