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Pyrrolidone-based polymers capable of reversible iodine capture for reuse in antibacterial applications
Journal of Hazardous Materials 384 (2020) 121305
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Pyrrolidone-based polymers capable of reversible iodine capture for reuse in antibacterial applications
T
Qinggele Borjihana,b,1, Zhe Zhanga,b,1, Xinyuan Zia,b, Mengxue Huanga,b, Yiqi Chena,b, ⁎ Yanling Zhanga,b, Alideertu Donga,b, a
College of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, People’s Republic of China Engineering Research Center of Dairy Quality and Safety Control Technology, Ministry of Education, Inner Mongolia University, Hohhot 010021, People’s Republic of China
b
A R T I C LE I N FO
A B S T R A C T
Editor: Deyi Hou
Numerous emerging and re-emerging advanced materials have been successful in capturing iodine pollutants that pose an unprecedented global challenge to public health. However, little attention has been paid to the reutilization of the captured iodine. Herein, we report on a pyrrolidone-based polymer capable of reversible iodine capture for reutilization in antibacterial applications. The pyrrolidone-based polymer poly(N-vinyl-2pyrrolidone-co-vinyl acetate), denoted as P(VAc-NVP), was synthesized facilely via a one-step radical copolymerization strategy, and the synthesis was regulated by step-by-step optimization, specifically by tuning the feed ratio of NVP to VAc. The as-synthesized P(VAc-NVP) copolymer functioned as an adsorbent for iodine in various solutions, including water/ethanol, cyclohexane, and petroleum ether, in addition to having the special capability of releasing iodine in the presence of starch or bacteria. This opens up a new horizon for its functional practical use as a flexible adsorbent to capture iodine for safe disposal. Interestingly, the P(VAc-NVP) copolymer, after adsorbing iodine, showed antibacterial ability against pathogenic bacteria, including Staphylococcus aureus and Escherichia coli, when a series of simulated and practical antibacterial assays were conducted. It is believed that this proposed strategy based on the synergism of iodine capture and antibacterial use should have great potential for environmental remediation and public healthcare.
Keywords: Pyrrolidone-based polymer Reversible iodine capture Povidone-iodine Reutilization Antibacterial use
1. Introduction Industrial waste pollution associated with modern productions has become a safety concern and a serious health threat to most living beings. (Li et al., 2017; Jie et al., 2017; Harijan et al., 2018; Ma et al., 2014; Zeng et al., 2019; Hu et al., 2017; Li et al., 2019) Iodine pollutants are some of the most serious, especially those from nuclear power plants, causing great public anxiety due to their toxicity for humans (Geng et al., 2017; Janeta et al., 2018; Du et al., 2016; Zhang et al., 2017; Lin et al., 2017). Accordingly, designing an effective strategy to capture and remove iodine from industrial wastewater is of great importance in environmental governance and public health security. To date, various groups of advanced functional materials developed through molecular chemistry and material science—including zeolites (Pham et al., 2016), metal-organic frameworks (MOFs) (Valizadeh et al., 2018), covalent organic frameworks (COFs) (Wang et al., 2018), aerogels (Gao et al., 2017a), porous organic polymers (POPs) (Xie et al.,
2019), and porous organic cages (Hasell et al., 2011)—have been successful in capturing iodine via complexation (Homendra and Shubhaschandra, 2007), ion-exchange (Yu et al., 2019), host-guest interaction (Brunet et al., 2017), and other means (Yan et al., 2015; Qian et al., 2016). A systematic literature survey demonstrated that most previous studies have devoted themselves to iodine capture, whereas few have been concerned with using the captured iodine in subsequent applications. Given that iodine is a scarce natural resource, the recovery of iodine coupled with its reutilization would be a significant finding in terms of the sustainable harmonic development of modern industry and environmental science. Iodine is an effective and powerful disinfectant adopted throughout the world due to its toxicity for a broad spectrum of living pathogenic bacteria (Hetzel and Dunn, 2003; Chen et al., 2016). However, iodine on its own is unstable and easily volatilized, and it can have a detrimental effect on wounds if applied directly (Burgi, 2010; Atwater et al., 1996; Lamme et al., 1998). Pyrrolidone-based polymers,
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Corresponding author at: College of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, People’s Republic of China. E-mail address: [email protected] (A. Dong). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.jhazmat.2019.121305 Received 4 June 2019; Received in revised form 9 September 2019; Accepted 23 September 2019 Available online 26 September 2019 0304-3894/ © 2019 Elsevier B.V. All rights reserved.
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(VAc-NVP)-I, which endows antibacterial function against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), demonstrated in a series of antibacterial studies. It is believed that with the synergism between iodine capture and its reuse in antibacterial applications, our proposed strategy with a pyrrolidone-based copolymer will be a reliable guide for developing multipurpose advanced materials for environmental remediation and public safety.
polyvinylpyrrolidone (PVP) being the most popular, can absorb and stabilize iodine due to their ability to complex with it (Goodwin et al., 2017; Sriwilaijaroen et al., 2009). In a form of complexation with pyrrolidone-based polymers, iodine rapidly and thoroughly eliminated pathogenic microorganisms (e.g., bacteria, fungi, and viruses) and, more significantly, showed long-term stability under harsh conditions and durability during antimicrobial use (Papadopoulou et al., 2018; AuDuong et al., 2015; Gao et al., 2010). For instance, Papadopouloua et al. complexed antibacterial iodine onto the bioelastomer, which endows sustained povidone-iodine release capabilities for antibacterial use (Papadopoulou et al., 2018). Lee’s group synthesized bactericidal magnetic nanoparticles by complexing iodine with PVP grown at the surface of silica coated magnetic nanoparticles via surface-initiated atom transfer radical polymerization (Au-Duong et al., 2015). According to the Gao’s report, the silica gel particles were functionalized by antibacterial povidone-iodine via a three-step approach: (1) surface modification of silica gel particles; (2) graft polymerization of vinylpyrrolidone on the surface of silica gel particles; (3) complexation between pyrrolidone and iodine (Gao et al., 2010). Nevertheless, these typical synthesis methods listed above are somewhat complicated and cumbersome, which limit the transform of the povidone-iodine into the large-scale practical production. Also, povidone-iodine suffers from low efficacy when it is used in watery environment owing to the high solubility of PVP in water. In response to these challenges above, our group designed and synthesized a series of antibacterial povidone-iodine capable of hydrophilic-hydrophobic regulation via a simple copolymerization strategy (Gao et al., 2017b; Borjihan et al., 2019; Gao et al., 2019). Compared to the complicated and ungeneralizable technologies reported previously, this copolymerization strategy is a convenient and effective way to achieve multifunctional povidone-iodine that meet many actual requirements. Interestingly, the iodine was released from the pyrrolidone-based polymer in the presence of bacteria. Using this reversible interaction with a pyrrolidone-based polymer to recover iodine from environmental pollutants by generating a novel povidone-iodine, coupled with iodine’s reuse in antimicrobial applications, is an eco-friendly strategy with the dual purpose of iodine capture and subsequent reuse. To date, though, the use of pyrrolidone-based polymers to recover iodine for antibacterial utilization has not been reported. In this contribution, we report on the synthesis of a novel pyrrolidone-based copolymer that allows the synergism of iodine capture and antibacterial function against pathogenic bacteria (Fig. 1). With the aim of controlling the hydrophilic–hydrophobic balance so that the pyrrolidone-based copolymer would be useful in different media, PVP was anchored onto hydrophobic polyethylacetate (PVAc) via radical copolymerization using different feed ratios of NVP to VAc. The as-synthesized copolymer P(VAc-NVP) demonstrates good ability to recover iodine from water or organic solvents by generating povidone-iodine P
2. Experimental 2.1. Materials Chemical reagents employed in this work include vinyl acetate (VAc, Adamas Reagent Co., Ltd.), N-vinyl-2-pyrrolidone (NVP, Adamas Reagent Co., Ltd.), azodiisobutyronitrile (AIBN, TCI (Shanghai) Development Co., Ltd.), iodine (I2, Sinopharm Chemical Reagent Co., Ltd.), cyclohexane (Tianjin Fengchuan Chemical Reagent Technologies Co., Ltd.), n-heptane (Tianjin Beilian Fine Chemicals Development Co., Ltd.), and N, N-dimethylformamid (DMF, Tianjin Beilian Fine Chemicals Development Co., Ltd.). Escherichia coli 8099 (E. coli, a Gramnegative bacterium) and Staphylococcus aureus ATCC 6538 (S. aureus, a Gram-positive bacterium) were used as model bacteria in our antibacterial examinations. The culture medium components contained yeast extract powder (Beijing Aoboxing Biotech Co., Ltd.), NaCl (Tianjin Beilian Fine Chemicals Development Co., Ltd.), beef cream (Guangdong Huankai Biotech Co., Ltd.), tryptone (Oxoid Co.), and agar (Biosharp Co., Ltd.), all of biological-reagent grade. Distilled water was supplied by a Millipore system (Millipore Inc.). All the chemical and biological reagents were used without purification. 2.2. Synthesis of P(VAc-NVP) Synthesis of P(VAc-NVP) copolymer was performed via the radical polymerization (Gao et al., 2017b). Typically, NVP and VAc were added into 10 mL of DMF containing 0.1 g of initiator AIBN. The crude copolymer P(VAc-NVP) was obtained after the above mixture was stirred at 65 °C for 24 h under a N2 gas inlet. To remove residual monomers and solvents, the product was dialyzed with distilled water at room temperature for three days, followed by freeze-drying at low temperature, yielding pure P(VAc-NVP) copolymer. In our step-by-step regulation of synthesis, the mole feed ratio of NVP to VAc was tuned to 1:9, 3:7, 5:5, 7:3, and 9:1. As comparative materials, two homopolymers, PVP and PVAc, were synthesized via the same procedure described above. 2.3. Reversible iodine capture Reversible iodine capture of P(VAc-NVP) copolymer was examined as followed. Typically, a total of 0.5 g of P(VAc-NVP) copolymer
Fig. 1. Schematic illustration of P(VAc-NVP) copolymer capable of iodine capture for reuse in antibacterial utilization. 2
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viable colonies was manually counted and expressed as the mean in CFU·mL−1. All colony counts were performed in triplicate. The final sterilizing ratios were calculated based on the following equation:
prepared as above with feed ratios of NVP to VAc of 5:5 and 3:7 was immersed in 50 mL of an iodine solution in different solvents, each with a concentration of 12 g L−1: water/ethanol, cyclohexane, and petroleum ether. After being shaken at room temperature for certain periods, the products were centrifuged and the as-obtained sediments were soaked in n-heptane for 24 h, centrifuged, and washed with n-heptane repeatedly to remove the residual iodine for drying under reduced pressure. The reversibility of iodine capture was evaluated using bacterial suspension (with E. coli as a model) as the extraction medium. When a 1 mL of bacterial suspension (109 CFU·mL−1) was added into 9 mL of P(VAc-NVP)-I suspension (0.05 mg mL-1 in water), the color of the sample changed from yellow to white. After dialyzing for 12 h and drying under vacuum, the obtained P(VAc-NVP)-I copolymer could recapture iodine, showing reversible iodine capture capabilities. After each cycle, the amount of iodine was detected by the iodometry.
Sterilizing Ratio = (A–B)/A × 100% where A is the number of original cells and B is the number of survival cells. In the inhibition zone test, the sample discs were put onto the surface of agar plates that had been overlaid already with 1 mL of 104 CFU·mL–1 E. coli. After incubation at 37 °C for 12 h, the inhibition zones were measured and pictured. All inhibition zone tests were performed in triplicate. 2.7. Antibacterial use of P(VAc-NVP)-I 2.7.1. Antibacterial additive assay Typically, P(VAc-NVP)-I powders (obtained using a 5:5 feed ratio of NVP to VAc) were incorporated into acrylic pigments with three different colors (green, yellow, and red) by fixing the final P(VAc-NVP)-I’s content in pigments at 2 wt %. Using a surface-coating method, the pigments containing P(VAc-NVP)-I were then coated onto different planar materials: tin foil, glass, and stainless steel. The antibacterial activities of the P(VAc-NVP)-I-modified pigments were then measured using the inhibition zone test with E. coli as the model bacterium.
2.4. Characterization 13 C NMR spectra were recorded on a Bruker AVANCE III-500 NMR instrument with the solvent D2O. FTIR spectra were captured from thoroughly dried samples using a Thermo Nicolet Avatar 370 FTIR spectrometer in the wavenumber range between 400 and 4000 cm–1 using KBr as background. The carbon, nitrogen, and hydrogen contents in the samples were measured using a VARIO EL cube element analyzer. Ultraviolet-visible (UV–vis) spectra were measured with a UV–vis spectrophotometer (U-3900). X-ray photoelectron spectroscopy (XPS) measurements were performed on a Thermo Scientific system with Mg K radiation (1253.6 eV). A field emission SEM (Shimadzu SSX-550) at 15.0 kV was used to examine the morphology, surface state, and elemental information. STEM scanning transmission electron microscopy (STEM, JEM-2100 F) was performed to obtain morphology, EDS, STEMmapping, and STEM-line scanning.
2.7.2. Water purification test The efficiency of P(VAc-NVP)-I (in a 7 : 3 feed ratio of VAc to NVP) at eliminating bacteria from water was examined using the columnpacking method, following a three-step approach (Gao et al., 2019). First, P(VAc-NVP)-I-based filter was fabricated by passing the suspension of P (NVP-VAc)-I through a column containing a piece of cotton fabric. Then, about 20 mL of pristine water was passed through the asprepared filter to ensure that all the active sites inside the column system were occupied by pristine water. Finally, 10 mL of challenge water containing 107 CFU·mL−1 of E. coli was passed through the column, the filtered water was collected, and bacterial survival was examined using the colony-counting method described above. In addition, the reusability of the as-designed P(VAc-NVP)-I-based filter was checked as a function of filtration cycle. After each cycle, 20 mL of deionized water was passed through the P(VAc-NVP)-I filter to ensure there was no residual bacteria-contaminated water in the column system. During the 10 filtration cycles, the as-prepared column did not need to be reloaded with iodine. All tests were done in triplicate.
2.5. Contact angle test The hydrophilic–hydrophobic balances of the copolymers were detected via the contact angle test. Measurements were performed with a CAM 200 static contact angle meter (KSV Instruments Ltd., Helsinki, Finland) at room temperature. Typically, the sample powders were ground and then pressed using a tablet machine to obtain the membrane sample. Water drops were deposited on the top surface of each membrane sample using a manual dosing system holding a 1 mL syringe (0.5 mm diameter needle). Side views of the water drops were photographed at a rate of 10 frames per second, and the corresponding contact angles were automatically calculated by fitting the captured drop shape to the correct one calculated from the Young-Laplace equation.
3. Results and discussion In our synthetic strategy (Fig. S1), the pyrrolidone-based copolymer P(VAc-NVP) was synthesized via one-step radical copolymerization between vinyl pyrrolidone (NVP) and vinyl acetate (VAc). To confirm the success of the copolymerization strategy, the as-obtained copolymer was characterized using 13C NMR analysis (Fig. 2A), with two monomers, NVP and VAc, for comparison. Compared to the two monomers, the copolymer shows two representative peaks at 177.8 ppm and 173.6 ppm, attributed respectively to the eC]O (amide group) in the NVP units and the eC]O (ester group) in the VAc units, suggesting successful copolymerization between NVP and Vac (He et al., 2012). The production of P(VAc-NVP) copolymer was further confirmed by FTIR spectra (Fig. 2B). Copolymer’s spectrum shows two characteristic peaks at 1661 cm−1 and 1742 cm−1, assigned respectively to the amide group in the NVP units and the ester group in the VAc units, again providing evidence of P(VAc-NVP) production (Gao et al., 2010; Liao et al., 2016). On the basis of the above findings, we confirmed the effectiveness of our copolymerization strategy that uses radical copolymerization between NVP and VAc. We also found that the NVP units in the P(VAc-NVP) copolymer can be regulated facilely by tuning the feed
2.6. Antibacterial evaluations The antibacterial activities of iodine-captured P(VAc-NVP) copolymer were evaluated by selecting E. coli and S. aureus as two model strains, and using the colony-counting method combined with the inhibition zone test (Bai et al., 2018, 2016; Dong et al., 2011). Prior to the antibacterial tests, S. aureus and E. coli were inoculated onto separated agar plates and incubated overnight at 37 °C. A single colony of each bacterium from the agar plate was employed to inoculate 5 mL of liquid cultures at 37 °C for 12 h on a rotary shaker at 220 rpm. The culture was expanded by transferring 100 μL of the above bacterial solution to 40 mL of liquid culture and shaking at 37 °C for 3 h. The colony-counting method was performed as follows. Typically, the antibacterial activities of the samples were examined by mixing 107 CFU·mL–1 bacterial suspension with a sample suspension (using final sample concentrations of 0.01, 0.05, 0.1, and 0.5 mg mL–1, respectively) at room temperature for 30 min. Next, the mixed solution was spread on nutrient agar plates and incubated at 37 °C for 12 h. The number of 3
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Fig. 2. (A)
13
C NMR spectra and (B) FTIR spectra of NVP, VAc, and P(VAc-NVP) copolymer.
PVAc homopolymer was exposed to iodine solution, indicating that P (VAc-NVP) anchors iodine by its NVP units rather than its VAc units. In its XPS spectrum (Fig. 3C, black curve), P(VAc-NVP) copolymer shows three strong signals for elemental carbon, oxygen, and nitrogen, while the copolymer after complexation with iodine (Fig. 3C, red curve) presents two additional peaks associated with iodine at 629.5 and 618.0 eV, demonstrating that the copolymer is able to capture iodine (Gao et al., 2019). The magnified XPS spectrum of P(VAc-NVP)-I shows two peaks, at 629.5 and 618.0 eV, associated with the I3− 3d3/2 and 3d5/2 peaks, respectively, further indicating the presence of iodine in an ionic state (Fig. 3D) (Hu et al., 2017; Liao et al., 2016). Additionally, we carried out XPS deconvolution of C 1s, N 1s, and O 1s (Fig. S4) in P (VAc-NVP)-I, as well as 13C NMR (Fig. S5) and FTIR spectra (Fig. S6), to examine the structural stability of the copolymer after iodine capture (i.e., P(NVP-VAc-I). Comparison with the P(VAc-NVP) copolymer shows that the main characteristic peaks remain unchanged after interaction with iodine, suggesting that iodine ions are adsorbed on the surface of the copolymer via complexation without damaging the copolymer molecular framework. After establishing that iodine could be recovered by chemically complexing with P(VAc-NVP), we then looked for other factors (e.g., morphology, surface roughness, etc.) that may have contributed to iodine capture in addition to its complexation with P(VAc-NVP). As seen in Fig. 4A, compared to P(VAc-NVP), P(VAc-NVP)-I shows no difference
ratio of NVP to VAc in our step-by-step regulation strategy. Using the nitrogen content from elemental analysis results, we calculated the NVP units in the P(VAc-NVP) copolymer. As shown in Fig. S2, the NVP units in the P(VAc-NVP) copolymer increased from 0 to 0.12, 0.52, 1.13, 1.55, and 8.40 as the feed ratio of NVP to VAc rose from 0:10 to 1:9, 3:7, 5:5, 7:3, and 9:1. These findings indicate that NVP reacts with VAc in a feed ratio-dependent manner. After confirming the successful synthesis of P(VAc-NVP) copolymer, we examined its ability to capture iodine. In a solid state (Fig. 3A), the white P(VAc-NVP) copolymer turned yellow or brown after capturing iodine from different media, which suggests that P(VAc-NVP) is capable of complexing with iodine in both water and organic media. The UV–vis spectra further confirm that P(VAc-NVP) can recover iodine from different media, as shown in Fig. 3B. The iodine solution in ethanol presented three typical peaks: at 286 and 362 nm, assigned to the characteristic absorption of I3−, and at 445 nm, corresponding to I2. P(VAcNVP) presented no absorption signal within the entire range from 280 to 600 nm, whereas the copolymers, after adsorbing iodine from three media—water/ethanol, cyclohexane, and petroleum ether—showed two intensive absorption peaks at ∼295 and ∼380 nm, both of which are attributed to I3– rather than I2 (He et al., 2012).This reveals that the iodine was chemically adsorbed onto the P(VAc-NVP) copolymer in the form of a polyiodide in an ionic state (Fig. S3). Conversely, we did not find the two characteristic peaks assigned to ionic polyiodide after
Fig. 3. (A) Powder of P(VAc-NVP) before and after iodized in water/ethanol, cyclohexane, and petroleum ether, respectively. (B) UV–vis spectra of iodine, iodized PVAc, P(VAc-NVP), and P(VAc-NVP)-I iodized in water/ethanol, cyclohexane, and petroleum ether, respectively. (C) XPS survey scans of P(VAc-NVP) and P(VAc-NVP)-I. (D) I 3d3/2 and I 3d5/2 spectrum of P(VAc-NVP)-I.
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Fig. 4. (A) SEM images of P(VAc-NVP) and P(VAc-NVP)-I, pictured at different magnifications. (B) EDS images, (C) STEM-mapping, and (D) STEM-line scanning of P (VAc-NVP)-I iodized in water/ethanol and in cyclohexane, respectively.
to the N, O, and I signals, stronger C signals were evident for P(VAcNVP)-I iodized in water/ethanol or in cyclohexane; these signals are mainly from the eCH2e units in the copolymer molecular skeleton. When a clear observation was made, N, O, and I presented the same trends, along with extending lines, further proving that the as-captured iodine were fixed tightly onto the NVP units in the copolymer. Strong binding of iodine to P(VAc-NVP) is beneficial for absorbing iodine from pollutants; however, facile desorption of iodine under specific conditions is also essential for its secondary utilization. To understand whether the iodine captured on P(VAc-NVP) was reversible, we investigated the release action of the captured iodine from P(VAcNVP)-I when immersed in starch solution, using an iodometric reaction. As shown in Fig. 5A, the P(VAc-NVP)-I suspension turns from yellow to dark blue after the starch solution is added, suggesting that iodine was released from P(VAc-NVP)-I. The appearance of an iodine–starch complex (yielding the blue suspension), as well as its subsequent fading in the presence of sodium thiosulfate, indicate that the released iodine exists in the original form of I2, which has oxidability toward sodium
in morphology or surface state, which suggests that iodization does not change the structure of P(VAc-NVP). Importantly, unlike adsorbents that recover iodine because of their internal porosity, P(VAc-NVP) copolymer has no holes or cavities on its surfaces, indicating that it captures iodine from media by complexing with iodine on its surface rather than inside it. To obtain elemental information that accords with the corresponding SEM images, EDS patterning was performed on P (VAc-NVP)-I, as shown in Fig. 4B. Whether iodized in water/ethanol or in cyclohexane, the copolymers presented iodine peaks, indicating the existence of P(VAc-NVP)-I within the selected SEM regions. To determine the elemental distributions, we then ran mappings on the STEM images. Presented as small, bright dots in Fig. 4C, the elemental distributions are a good match with the STEM images of P(VAc-NVP)-I iodized in water/ethanol or in cyclohexane, suggesting the as-captured iodine was restricted to the copolymer region through its strong binding with P(VAc-NVP). Since the distributions of N, O, and I provide important evidence for the interaction between P(VAc-NVP) and iodine, we then applied line scanning to the STEM images (Fig. 4D). Compared 5
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Fig. 5. (A) Photographs showing color changes in the P(VAc-NVP)-I suspension involved in the iodometric reaction. (B) Photographs showing reversible iodine capture using P(VAc-NVP) copolymer. (C) Efficiency of iodine capture using P(VAc-NVP) during five iodine loading cycles. (D) Iodine content of P(VAc-NVP)-I as a function of iodization time.
thiosulfate. As further evidenced in Fig. 5B, P(VAc-NVP)-I (brown) returns to P(VAc-NVP) (colorless) after releasing iodine, indicating that iodine captured on P(VAc-NVP) copolymer is reversible and, more importantly, that after desorption of iodine, the copolymer can be regenerated and reused for iodine capture. As shown in Fig. 5C, no decrease in iodine loadings on P(VAc-NVP) copolymer was detected, even after five cycles of re-iodization, demonstrating that iodine can be captured repeatedly by P(VAc-NVP) copolymer. Next, we tried to regulate the iodine loadings on P(VAc-NVP) copolymer by tuning the iodization aging time. As shown in Fig. 5D, iodine loadings rose from 0.29, to 0.49, 0.68, 1.16, 1.22, 1.33, and 1.94% after immersing P(VAc-NVP) prepared with a feed ratio of 5:5 NVP to VAc into iodine solution for different aging times, from 0.5, to 1, 2, 4, 8, 12, and 24 h, respectively. We can therefore confirm that iodine loadings on P(VAc-NVP) copolymer can be regulated simply by extending or shortening the aging period. To determine whether P(VAc-NVP) could have practical, widespread use in different pollutants, its hydrophilic–hydrophobic balance was modulated by regulating the feed ratio of NVP to VAc, then using contact angle measurement to determine the balance. Three samples were selected and used as comparative controls: PVP, PVAc, and P(VAcNVP)-I. As presented in Fig. 6, PVP and PVAc showed average contact angles of 27.6° and 113.0°, placing them within the hydrophilicity and hydrophobicity regions, respectively. The contact angles of P(VAc-NVP) increased from 41.6° to 73.4°, then to 99.1° when the feed ratio of NVP to VAc was changed from 7:3, to 5:5, then to 3:7, indicating that P(VAcNVP) has the potential for widespread use because its hydrophilic–hydrophobic property is adjustable across a wide range, between 27.6° and 113.0°. Comparison of PVP and P(VAc-NVP) suggests that the incorporation of VAc units gave the copolymer hydrophobicity, and
Fig. 6. Contact angles of PVP, PVAc, and P(VAc-NVP) prepared with different feed ratios, and P(VAc-NVP)-I.
such a hydrophilicity→hydrophobicity transformation can be achieved facilely using a radical copolymerization strategy. Obtained by iodine capture on P(VAc-NVP) (copolymerized at a feed ratio of 5:5 NVP to VAc), P(VAC-NVP)-I gives an average contact angle of 76.8°, which is slightly higher than the corresponding value of 73.4° for P(VAc-NVP). This demonstrates that the incorporation of iodine to some extent raises
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Fig. 7. Photographs of the bacterial culture plates of (A) E. coli and (B) S. aureus after treatment with 0.5 mg·mL–1 of P(VAc-NVP)-I for 30 min. (B) Antibacterial activity of P(VAc-NVP)-I against (C) E. coli and (D) S. aureus as a function of sample concentration.
be completely inactivated, Fig. 8B), E. coli cells could no longer keep their original integrity, and some were corrugated or even collapsed. The untreated S. aureus presented a regular spherical shape with a smooth surface (Fig. 8C). After 108 CFU·mL–1 of S. aureus was treated with 5.0 mg·mL–1 of P(VAC-NVP)-I for 60 min, the cytomembrane was damaged and depressed (Fig. 8D). These findings demonstrated that P (VAC-NVP)-I copolymer is capable of bacterial membrane disruption, causing bacterial death. To better understand the practical application of this antibacterial activity, we designed two tests: (i) use as an antibacterial additive and (ii) use for water purification. In our first test, P(VAc-NVP)-I copolymer powders were mixed with acrylic pigments of three different colors (green, yellow, and red), then these three pigments were coated on three different planar materials: glass, stainless steel, and tin foil. One can observe from Fig. 9A that the pigments after incorporation with P (VAc-NVP)-I had good adhesion to the substrates. Visually, in terms of their color, luster, brightness, and surface roughness, the P(VAc-NVP)-Iincorporated pigments look the same as the original pigments without P (VAc-NVP)-I. Interestingly, when their antibacterial powers against E. coli were monitored using the inhibition zone test (Fig. 9B), the unaltered pigments showed the expected robust bacterial growth, with no aseptic rings around the samples. In contrast, aseptic rings appeared around the P(VAc-NVP)-I-incorporated pigments, indicating the effectiveness and potency of P(VAc-NVP)-I-based additives for antibacterial use. Our second exam focused on water purification, using a P(VAcNVP)-I-based self-made filtration system (Fig. 10A) with water containing 107 CFU·mL–1 of E. coli as a model for bacteria-contaminated water. When the contaminated water was passed through the control column without P(VAc-NVP)-I, the corresponding culture plate (left plate in Fig. 10A) showed dense colonies, indicating robust bacterial growth in the absence of P(VAc-NVP)-I. However, the E. coli was completely inactivated after being passed through the P(VAc-NVP)-Ipacked column (right plate in Fig. 10A), demonstrating that the P(VAcNVP)-I effectively decontaminated bacteria-tainted water. To verify the long-term effectiveness and functional repeatability of P(VAc-NVP)-I for water bacterial decontamination, the performance of the P(VAc-
the hydrophobicity of P(VAc-NVP); however, the hydrophilic–hydrophobic balance of P(VAC-NVP)-I depends mainly on copolymer rather than the iodine. Based on our findings, we conclude that the hydrophilic–hydrophobic balance of P(VAc-NVP) and of P(VAcNVP)-I, can be adjusted on demand to meet specific requirements. After confirming that reversible iodine capture can be achieved using P(VAc-NVP) copolymer, we next examined the feasibility of reusing P(VAc-NVP)-I in antibacterial applications, as illustrated in step (ii) of Fig. 1. The antibacterial ability of P(VAc-NVP)-I solution was estimated via the colony-counting method using E. coli and S. aureus as two bacterial models in a bacterial concentration of 107 CFU mL–1 (Fig. 7A and B). In the control culture plate, both E. coli and S. aureus presented dense survival colonies, indicating their robust growth in the absence of the samples. The P(VAc-NVP) copolymer without absorbed iodine had almost no bacteria-killing capability, whereas P(VAc-NVP)-I completely killed both strains under the same conditions, demonstrating that P(VAc-NVP)-I kills bacteria via the release of the captured iodine on the copolymer’s surfaces. This implies that P(VAc-NVP)-I could be reused in antibacterial applications, because after the iodine is released from P(VAc-NVP)-I in the presence of bacteria, iodine-based antibacterial action follows. We then examined the concentration-dependent antibacterial action of P(VAc-NVP)-I against E. coli and S. aureus (Fig. 7C and D). Clearly, P (VAc-NVP) had almost no ability to kill bacteria within the whole sample concentration region of 0.01–0.5 mg·L–1. In comparison, the sterilizing rates of P(VAc-NVP)-I reached ∼32% against S. aureus and ∼24% against E. coli with a sample concentration of 0.01 mg mL–1, while sterilizing rates reached 100% for both E. coli and S. aureus when the sample concentrations were above 0.05 mg mL–1, suggesting that P (VAc-NVP)-I possessed antibacterial capacity, with its efficiency dependent on the concentration of P(VAc-NVP)-I. To ascertain the precise impact of P(VAC-NVP)-I on bacteria, the morphology of E. coli and S. aureus before and after P(VAC-NVP)-I treatment were examined by SEM (see Fig. 8). Clearly, the untreated E. coli displays a rod shape and intact surface without cellular debris (Fig. 8A). After exposing 108 CFU·mL–1 of E. coli to 5.0 mg·mL–1 of P (VAC-NVP)-I for 60 min (under which conditions E. coli was proven to 7
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Fig. 8. SEM images of (A and B) E. coli and (C and D) S. aureus in the (left) absence and (right) presence of P(VAc-NVP)-I.
NVP)-I-packed column after several filtering cycles was tested (Fig. 10B). After 10 cycles, the P(VAc-NVP)-I-packed column maintained 100% antibacterial efficiency, demonstrating that P(VAc-NVP)-I was active enough to combat bacteria in water even after 10 filtration cycles. All these data make it evident that P(VAc-NVP)-I rendered high, stable antibacterial activity for water purification.
including 13C NMR, FTIR, EA, UV–vis, XPS, SEM, STEM, and iodometric reaction, the chemical composition and hydrophilicity–hydrophobicity balance of P(VAc-NVP) were regulated by tuning the feed ratio of NVP to VAc. Interestingly, P(VAc-NVP) copolymer showed the capacity for reversible iodine capture under various different conditions, and the P (VAc-NVP) with captured iodine demonstrated antibacterial activity against E. coli and S. aureus. Subsequently, acrylic pigments containing small amounts of P(VAc-NVP)-I were coated on different planar materials—tin foil, glass sheet, and stainless steel—and the coatings displayed antibacterial function against pathogenic bacteria. We also established that P(VAc-NVP)-I can be used as an effective antibacterial filter for water purification, and a reusability test showed that a P(VAcNVP)-I-based filter could maintain good decontamination performance
4. Conclusions In summary, P(VAc-NVP) copolymer was facilely synthesized via radical copolymerization between NVP and VAc, to achieve the synergism of iodine capture and subsequent antibacterial use of the iodine. After systematic characterization using a series of advanced techniques,
Fig. 9. (A) Photographs showing P(VAc-NVP)-I-modified acrylic pigments coated onto glass, stainless steel, and tin foil, respectively. (B) Inhibition zone images of P (VAc-NVP)-I-modified and unmodified pigments. 8
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Fig. 10. (A) Schematic illustration of the P(VAc-NVP)-I-based filtration system. The inserts are photographic illustrations of the antibacterial activities of the P(VAcNVP)-I-based self-made filtration system. (B) Antibacterial efficiency of P(VAc-NVP)-I-based filtration system toward contaminated water after 10 cycles.
even after 10 filtration cycles. These unique features demonstrate that P (VAc-NVP)-I is an ideal candidate for sanitizing bacteria-contaminated water by filtration. We are sure that this strategy can act as a practical guide for using pyrrolidone-based polymers to recover iodine from pollutants, then reutilizing them in antibacterial-related fields.
silica gel particles and bactericidal property. Colloids Surf. B Biointerfaces 79, 446–451. Gao, T., Borjihan, Q., Yang, J., Qu, H., Liu, W., Li, Q., Wang, Y.-J., Dong, A., 2019. Antibacterial povidone-iodine-conjugated cross-linked polystyrene resin for water bacterial decontamination. ACS Appl. Bio Mater. 2, 1310–1321. Gao, R., Lu, Y., Xiao, S., Li, J., 2017a. Facile fabrication of nanofibrillated Chitin/Ag2O heterostructured aerogels with high iodine capture efficiency. Sci. Rep. 7, 4303. Gao, T., Fan, H., Wang, X., Gao, Y., Liu, W., Chen, W., Dong, A., Wang, Y.J., 2017b. Povidone-iodine-based polymeric nanoparticles for antibacterial applications. ACS Appl. Mater. Interfaces 9, 25738–25746. Geng, T., Zhu, Z., Zhang, W., Wang, Y., 2017. A nitrogen-rich fluorescent conjugated microporous polymer with triazine and triphenylamine units for high iodine capture and nitro aromatic compound detection. J. Mater. Chem. 5, 7612–7617. Goodwin, M.J., Steed, B.W., Yufit, D.S., Musa, O.M., Berry, D.J., Steed, J.W., 2017. Halogen and hydrogen bonding in povidone-iodine and related co-phases. Cryst. Growth Des. 17, 5552–5558. Harijan, D.K.L., Chandra, V., Yoon, T., Kim, K.S., 2018. Radioactive iodine capture and storage from water using magnetite nanoparticles encapsulated in polypyrrole. J. Hazard. Mater. 344, 576–584. Hasell, T., Schmidtmann, M., Cooper, A.I., 2011. Molecular doping of porous organic cages. J. Am. Chem. Soc. 133, 14920–14923. He, S., Wang, B., Chen, H., Tang, C., Feng, Y., 2012. Preparation and antimicrobial properties of gemini surfactant-supported triiodide complex system. ACS Appl. Mater. Interfaces 4, 2116–2123. Hetzel, B.S., Dunn, J.T., 2003. The iodine deficiency disorders: their nature and prevention. Annu. Rev. Nutr. 9, 21–38. Homendra, N., Shubhaschandra, S.N., 2007. Effect of an anionic surfactant on the complexation of some nonionic polymers with iodine in aqueous media. J. Phys. Chem. B 111, 4098–4102. Hu, Y.Q., Li, M.Q., Wang, Y., Zhang, T., Liao, P.Q., Zheng, Z., Chen, X.M., Zheng, Z., 2017. Direct observation of confined I−⋅⋅⋅I2⋅⋅⋅I− interactions in a metal-organic framework: Iodine capture and sensing. Chem. Eur. J. 23, 8409–8413. Janeta, M., Bury, W., Szafert, S., 2018. Porous silsesquioxane-imine frameworks as highly efficient adsorbents for cooperative iodine capture. ACS Appl. Mater. Interfaces 10, 19964–19973. Jie, K., Zhou, Y., Li, E., Li, Z., Zhao, R., Huang, F., 2017. Reversible iodine capture by nonporous pillar[6]arene crystals. J. Am. Chem. Soc. 139, 15320–15323. Lamme, E., To, M.U.N., Middelkoop, E., 1998. Cadexomer-iodine ointment shows stimulation of epidermal regeneration in experimental full-thickness wounds. Arch. Dermatol. Res. 290, 18–24. Li, B., Dong, X., Wang, H., Ma, D., Tan, K., Jensen, S., Deibert, B.J., Butler, J., Cure, J., Shi, Z., Thonhauser, T., Chabal, Y.J., Han, Y., Li, J., 2017. Capture of organic iodides from nuclear waste by metal-organic framework-based molecular traps. Nat. Commun. 8, 485. Li, B., Wang, B., Huang, X., Dai, L., Cui, L., Li, J., Jia, X., Li, C., 2019. Terphen[n]arenes and quaterphen[n]arenes (n=3-6): One-pot synthesis, self-assembly into supramolecular gels, and iodine capture. Angew. Chem. Int. Ed. 58, 3885–3889. Liao, Y., Weber, J., Mills, B.M., Ren, Z., Faul, C.F.J., 2016. Highly efficient and reversible iodine capture in hexaphenylbenzene-based conjugated microporous polymers. Macromolecules 49, 6322–6333. Lin, Y., Jiang, X., Kim, S.T., Alahakoon, S.B., Hou, X., Zhang, Z., Thompson, C.M., Smaldone, R.A., Ke, C., 2017. An elastic hydrogen-bonded cross-linked organic framework for effective iodine capture in water. J. Am. Chem. Soc. 139, 7172–7175. Ma, S., Islam, S.M., Shim, Y., Gu, Q., Wang, P., Li, H., Sun, G., Yang, X., Kanatzidis, M.G., 2014. Highly efficient iodine capture by layered double hydroxides intercalated with polysulfides. Chem. Mater. 26, 7114–7123. Papadopoulou, E.L., Valentini, P., Mussino, F., Pompa, P.P., Athanassiou, A., Bayer, I.S., 2018. Antibacterial bioelastomers with sustained povidone-iodine release. Chem. Eng. J. 347, 19–26. Pham, T.C.T., Docao, S., Hwang, I.C., Song, M.K., Choi, D.Y., Moon, D., Oleynikov, P., Yoon, K.B., 2016. Capture of iodine and organic iodides using silica zeolites and the semiconductor behaviour of iodine in a silica zeolite. Energy Environ. Sci. 9,
Acknowledgment This work was supported by the National Natural Science Foundation of China (21304044 and 51663019), the Natural Science Foundation of Inner Mongolia Autonomous Region (2015MS0520), the State Key Laboratory of Medicinal Chemical Biology (201603006 and 2018051), the State Key Laboratory of Polymer Physics and Chemistry (2018-08), and the Program of Higher-Level Talents of Inner Mongolia University (30105-125136). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jhazmat.2019.121305. References Atwater, J.E., Sauer, R.L., Schultz, J.R., 1996. Numerical simulation of iodine speciation in relation to water disinfection aboard manned spacecraft I. Equilibria. J. Environ. Sci. Health A. 31, 1965–1979. Au-Duong, A.-N., Vo, D.-T., Lee, C.-K., 2015. Bactericidal magnetic nanoparticles with iodine loaded on surface grafted poly (N-vinylpyrrolidone). J. Mater. Chem. B Mater. Biol. Med. 3, 840–848. Bai, R., Kang, J., Simalou, O., Liu, W., Ren, H., Gao, T., Gao, Y., Chen, W., Dong, A., Jia, R., 2018. Novel N–Br bond-containing N-halamine nanofibers with antibacterial activities. ACS Biomater. Sci. Eng. 4, 2193–2202. Bai, R., Zhang, Q., Li, L., Li, P., Wang, Y.J., Simalou, O., Zhang, Y., Gao, G., Dong, A., 2016. N-halamine-containing electrospun fibers kill bacteria via a contact/release codetermined antibacterial pathway. ACS Appl. Mater. Interfaces 8, 31530–31540. Borjihan, Q., Yang, J., Q, Song, Gao, L., Xu, M., Gao, T., Liu, W., Li, P., Li, Q., Dong, A., 2019. Povidone-iodine-functionalized fluorinated copolymers with dual-functional antibacterial and antifouling activities. Biomater. Sci. 7, 3334–3347. Brunet, G., Safin, D.A., Aghaji, M.Z., Robeyns, K., Korobkov, I., Woo, T.K., Murugesu, M., 2017. Stepwise crystallographic visualization of dynamic guest binding in a nanoporous framework. Chem. Sci. 8, 3171–3177. Burgi, H., 2010. Iodine excess. Best Pract. Res. Cl. En. 24, 107–115. Chen, Y., Yang, Y., Liao, Q., Yang, W., Ma, W., Zhao, J., Zheng, X., Yang, Y., Chen, R., 2016. Preparation, property of the complex of carboxymethyl chitosan grafted copolymer with iodine and application of it in cervical antibacterial biomembrane. Mater. Sci. Eng. C. 67, 247–258. Dong, A., Lan, S., Huang, J., Wang, T., Zhao, T., Xiao, L., Wang, W., Zheng, X., Liu, F., Gao, G., Chen, Y., 2011. Modifying Fe3O4-functionalized nanoparticles with N-halamine and their magnetic/antibacterial properties. ACS Appl. Mater. Interfaces 3, 4228–4235. Du, X., Fan, R., Fan, J., Qiang, L., Song, Y., Dong, Y., Xing, K., Wang, P., Yang, Y., 2016. Self-assembly of two supramolecular indium (iii) metal–organic frameworks for reversible iodine capture and large band gap change semiconductor behavior. Inorg. Chem. Front. 3, 1480–1490. Gao, B., Wang, Z., Liu, Q., Du, R., 2010. Immobilization of povidone-iodine on surfaces of
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Q. Borjihan, et al.
1039/C8MH01656A. Yan, Z., Yuan, Y., Tian, Y., Zhang, D., Zhu, G., 2015. Highly efficient enrichment of volatile iodine by charged porous aromatic frameworks with three sorption sites. Angew. Chem. Int. Ed. 54, 12733–12737. Yu, X., Cui, W., Zhang, F., Guo, Y., Deng, T., 2019. Removal of iodine from the salt water used for caustic soda production by ion-exchange resin adsorption. Desalination 458, 76–83. Zeng, M., Tan, J., Chen, K., Zang, D., Yang, Y., Zhang, J., Wei, Y., 2019. Guest controlled pillar[5]arene and polyoxometalate based two-dimensional nanostructures toward reversible iodine capture. ACS Appl. Mater. Interfaces 11, 8537–8544. Zhang, X., da Silva, I., Godfrey, H.G.W., Callear, S.K., Sapchenko, S.A., Cheng, Y., Vitorica-Yrezabal, I., Frogley, M.D., Cinque, G., Tang, C.C., Giacobbe, C., Dejoie, C., Rudic, S., Ramirez-Cuesta, A.J., Denecke, M.A., Yang, S., Schroder, M., 2017. Confinement of iodine molecules into triple-helical chains within robust metal-organic frameworks. J. Am. Chem. Soc. 139, 16289–16296.
1050–1062. Qian, X., Zhu, Z.Q., Sun, H.X., Ren, F., Mu, P., Liang, W., Chen, L., Li, A., 2016. Capture and reversible storage of volatile iodine by novel conjugated microporous polymers containing thiophene units. ACS Appl. Mater. Interfaces 8, 21063–21069. Sriwilaijaroen, N., Wilairat, P., Hiramatsu, H., Takahashi, T., Suzuki, T., Ito, M., Ito, Y., Tashiro, M., Suzuki, Y., 2009. Mechanisms of the action of povidone-iodine against human and avian influenza a viruses: its effects on hemagglutination and sialidase activities. Virol. J. 6, 124. Valizadeh, B., Nguyen, T.N., Smit, B., Stylianou, K.C., 2018. Porous metal-organic framework@polymer beads for iodine capture and recovery using a gas-sparged column. Adv. Funct. Mater. 8, 1801596. Wang, P., Xu, Q., Li, Z., Jiang, W., Jiang, Q., Jiang, D., 2018. Exceptional iodine capture in 2D covalent organic frameworks. Adv. Mater. 30, 1801991. Xie, W., Cui, D., Zhang, S.-R., Xu, Y., Jiang, D., 2019. Iodine capture in porous organic polymers and metal-organic frameworks materials. Mater. Horiz. https://doi.org/10.
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Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
Pyrrolidone-based polymers capable of reversible iodine capture for reuse in antibacterial applications
T
Qinggele Borjihana,b,1, Zhe Zhanga,b,1, Xinyuan Zia,b, Mengxue Huanga,b, Yiqi Chena,b, ⁎ Yanling Zhanga,b, Alideertu Donga,b, a
College of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, People’s Republic of China Engineering Research Center of Dairy Quality and Safety Control Technology, Ministry of Education, Inner Mongolia University, Hohhot 010021, People’s Republic of China
b
A R T I C LE I N FO
A B S T R A C T
Editor: Deyi Hou
Numerous emerging and re-emerging advanced materials have been successful in capturing iodine pollutants that pose an unprecedented global challenge to public health. However, little attention has been paid to the reutilization of the captured iodine. Herein, we report on a pyrrolidone-based polymer capable of reversible iodine capture for reutilization in antibacterial applications. The pyrrolidone-based polymer poly(N-vinyl-2pyrrolidone-co-vinyl acetate), denoted as P(VAc-NVP), was synthesized facilely via a one-step radical copolymerization strategy, and the synthesis was regulated by step-by-step optimization, specifically by tuning the feed ratio of NVP to VAc. The as-synthesized P(VAc-NVP) copolymer functioned as an adsorbent for iodine in various solutions, including water/ethanol, cyclohexane, and petroleum ether, in addition to having the special capability of releasing iodine in the presence of starch or bacteria. This opens up a new horizon for its functional practical use as a flexible adsorbent to capture iodine for safe disposal. Interestingly, the P(VAc-NVP) copolymer, after adsorbing iodine, showed antibacterial ability against pathogenic bacteria, including Staphylococcus aureus and Escherichia coli, when a series of simulated and practical antibacterial assays were conducted. It is believed that this proposed strategy based on the synergism of iodine capture and antibacterial use should have great potential for environmental remediation and public healthcare.
Keywords: Pyrrolidone-based polymer Reversible iodine capture Povidone-iodine Reutilization Antibacterial use
1. Introduction Industrial waste pollution associated with modern productions has become a safety concern and a serious health threat to most living beings. (Li et al., 2017; Jie et al., 2017; Harijan et al., 2018; Ma et al., 2014; Zeng et al., 2019; Hu et al., 2017; Li et al., 2019) Iodine pollutants are some of the most serious, especially those from nuclear power plants, causing great public anxiety due to their toxicity for humans (Geng et al., 2017; Janeta et al., 2018; Du et al., 2016; Zhang et al., 2017; Lin et al., 2017). Accordingly, designing an effective strategy to capture and remove iodine from industrial wastewater is of great importance in environmental governance and public health security. To date, various groups of advanced functional materials developed through molecular chemistry and material science—including zeolites (Pham et al., 2016), metal-organic frameworks (MOFs) (Valizadeh et al., 2018), covalent organic frameworks (COFs) (Wang et al., 2018), aerogels (Gao et al., 2017a), porous organic polymers (POPs) (Xie et al.,
2019), and porous organic cages (Hasell et al., 2011)—have been successful in capturing iodine via complexation (Homendra and Shubhaschandra, 2007), ion-exchange (Yu et al., 2019), host-guest interaction (Brunet et al., 2017), and other means (Yan et al., 2015; Qian et al., 2016). A systematic literature survey demonstrated that most previous studies have devoted themselves to iodine capture, whereas few have been concerned with using the captured iodine in subsequent applications. Given that iodine is a scarce natural resource, the recovery of iodine coupled with its reutilization would be a significant finding in terms of the sustainable harmonic development of modern industry and environmental science. Iodine is an effective and powerful disinfectant adopted throughout the world due to its toxicity for a broad spectrum of living pathogenic bacteria (Hetzel and Dunn, 2003; Chen et al., 2016). However, iodine on its own is unstable and easily volatilized, and it can have a detrimental effect on wounds if applied directly (Burgi, 2010; Atwater et al., 1996; Lamme et al., 1998). Pyrrolidone-based polymers,
⁎
Corresponding author at: College of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, People’s Republic of China. E-mail address: [email protected] (A. Dong). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.jhazmat.2019.121305 Received 4 June 2019; Received in revised form 9 September 2019; Accepted 23 September 2019 Available online 26 September 2019 0304-3894/ © 2019 Elsevier B.V. All rights reserved.
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(VAc-NVP)-I, which endows antibacterial function against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), demonstrated in a series of antibacterial studies. It is believed that with the synergism between iodine capture and its reuse in antibacterial applications, our proposed strategy with a pyrrolidone-based copolymer will be a reliable guide for developing multipurpose advanced materials for environmental remediation and public safety.
polyvinylpyrrolidone (PVP) being the most popular, can absorb and stabilize iodine due to their ability to complex with it (Goodwin et al., 2017; Sriwilaijaroen et al., 2009). In a form of complexation with pyrrolidone-based polymers, iodine rapidly and thoroughly eliminated pathogenic microorganisms (e.g., bacteria, fungi, and viruses) and, more significantly, showed long-term stability under harsh conditions and durability during antimicrobial use (Papadopoulou et al., 2018; AuDuong et al., 2015; Gao et al., 2010). For instance, Papadopouloua et al. complexed antibacterial iodine onto the bioelastomer, which endows sustained povidone-iodine release capabilities for antibacterial use (Papadopoulou et al., 2018). Lee’s group synthesized bactericidal magnetic nanoparticles by complexing iodine with PVP grown at the surface of silica coated magnetic nanoparticles via surface-initiated atom transfer radical polymerization (Au-Duong et al., 2015). According to the Gao’s report, the silica gel particles were functionalized by antibacterial povidone-iodine via a three-step approach: (1) surface modification of silica gel particles; (2) graft polymerization of vinylpyrrolidone on the surface of silica gel particles; (3) complexation between pyrrolidone and iodine (Gao et al., 2010). Nevertheless, these typical synthesis methods listed above are somewhat complicated and cumbersome, which limit the transform of the povidone-iodine into the large-scale practical production. Also, povidone-iodine suffers from low efficacy when it is used in watery environment owing to the high solubility of PVP in water. In response to these challenges above, our group designed and synthesized a series of antibacterial povidone-iodine capable of hydrophilic-hydrophobic regulation via a simple copolymerization strategy (Gao et al., 2017b; Borjihan et al., 2019; Gao et al., 2019). Compared to the complicated and ungeneralizable technologies reported previously, this copolymerization strategy is a convenient and effective way to achieve multifunctional povidone-iodine that meet many actual requirements. Interestingly, the iodine was released from the pyrrolidone-based polymer in the presence of bacteria. Using this reversible interaction with a pyrrolidone-based polymer to recover iodine from environmental pollutants by generating a novel povidone-iodine, coupled with iodine’s reuse in antimicrobial applications, is an eco-friendly strategy with the dual purpose of iodine capture and subsequent reuse. To date, though, the use of pyrrolidone-based polymers to recover iodine for antibacterial utilization has not been reported. In this contribution, we report on the synthesis of a novel pyrrolidone-based copolymer that allows the synergism of iodine capture and antibacterial function against pathogenic bacteria (Fig. 1). With the aim of controlling the hydrophilic–hydrophobic balance so that the pyrrolidone-based copolymer would be useful in different media, PVP was anchored onto hydrophobic polyethylacetate (PVAc) via radical copolymerization using different feed ratios of NVP to VAc. The as-synthesized copolymer P(VAc-NVP) demonstrates good ability to recover iodine from water or organic solvents by generating povidone-iodine P
2. Experimental 2.1. Materials Chemical reagents employed in this work include vinyl acetate (VAc, Adamas Reagent Co., Ltd.), N-vinyl-2-pyrrolidone (NVP, Adamas Reagent Co., Ltd.), azodiisobutyronitrile (AIBN, TCI (Shanghai) Development Co., Ltd.), iodine (I2, Sinopharm Chemical Reagent Co., Ltd.), cyclohexane (Tianjin Fengchuan Chemical Reagent Technologies Co., Ltd.), n-heptane (Tianjin Beilian Fine Chemicals Development Co., Ltd.), and N, N-dimethylformamid (DMF, Tianjin Beilian Fine Chemicals Development Co., Ltd.). Escherichia coli 8099 (E. coli, a Gramnegative bacterium) and Staphylococcus aureus ATCC 6538 (S. aureus, a Gram-positive bacterium) were used as model bacteria in our antibacterial examinations. The culture medium components contained yeast extract powder (Beijing Aoboxing Biotech Co., Ltd.), NaCl (Tianjin Beilian Fine Chemicals Development Co., Ltd.), beef cream (Guangdong Huankai Biotech Co., Ltd.), tryptone (Oxoid Co.), and agar (Biosharp Co., Ltd.), all of biological-reagent grade. Distilled water was supplied by a Millipore system (Millipore Inc.). All the chemical and biological reagents were used without purification. 2.2. Synthesis of P(VAc-NVP) Synthesis of P(VAc-NVP) copolymer was performed via the radical polymerization (Gao et al., 2017b). Typically, NVP and VAc were added into 10 mL of DMF containing 0.1 g of initiator AIBN. The crude copolymer P(VAc-NVP) was obtained after the above mixture was stirred at 65 °C for 24 h under a N2 gas inlet. To remove residual monomers and solvents, the product was dialyzed with distilled water at room temperature for three days, followed by freeze-drying at low temperature, yielding pure P(VAc-NVP) copolymer. In our step-by-step regulation of synthesis, the mole feed ratio of NVP to VAc was tuned to 1:9, 3:7, 5:5, 7:3, and 9:1. As comparative materials, two homopolymers, PVP and PVAc, were synthesized via the same procedure described above. 2.3. Reversible iodine capture Reversible iodine capture of P(VAc-NVP) copolymer was examined as followed. Typically, a total of 0.5 g of P(VAc-NVP) copolymer
Fig. 1. Schematic illustration of P(VAc-NVP) copolymer capable of iodine capture for reuse in antibacterial utilization. 2
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viable colonies was manually counted and expressed as the mean in CFU·mL−1. All colony counts were performed in triplicate. The final sterilizing ratios were calculated based on the following equation:
prepared as above with feed ratios of NVP to VAc of 5:5 and 3:7 was immersed in 50 mL of an iodine solution in different solvents, each with a concentration of 12 g L−1: water/ethanol, cyclohexane, and petroleum ether. After being shaken at room temperature for certain periods, the products were centrifuged and the as-obtained sediments were soaked in n-heptane for 24 h, centrifuged, and washed with n-heptane repeatedly to remove the residual iodine for drying under reduced pressure. The reversibility of iodine capture was evaluated using bacterial suspension (with E. coli as a model) as the extraction medium. When a 1 mL of bacterial suspension (109 CFU·mL−1) was added into 9 mL of P(VAc-NVP)-I suspension (0.05 mg mL-1 in water), the color of the sample changed from yellow to white. After dialyzing for 12 h and drying under vacuum, the obtained P(VAc-NVP)-I copolymer could recapture iodine, showing reversible iodine capture capabilities. After each cycle, the amount of iodine was detected by the iodometry.
Sterilizing Ratio = (A–B)/A × 100% where A is the number of original cells and B is the number of survival cells. In the inhibition zone test, the sample discs were put onto the surface of agar plates that had been overlaid already with 1 mL of 104 CFU·mL–1 E. coli. After incubation at 37 °C for 12 h, the inhibition zones were measured and pictured. All inhibition zone tests were performed in triplicate. 2.7. Antibacterial use of P(VAc-NVP)-I 2.7.1. Antibacterial additive assay Typically, P(VAc-NVP)-I powders (obtained using a 5:5 feed ratio of NVP to VAc) were incorporated into acrylic pigments with three different colors (green, yellow, and red) by fixing the final P(VAc-NVP)-I’s content in pigments at 2 wt %. Using a surface-coating method, the pigments containing P(VAc-NVP)-I were then coated onto different planar materials: tin foil, glass, and stainless steel. The antibacterial activities of the P(VAc-NVP)-I-modified pigments were then measured using the inhibition zone test with E. coli as the model bacterium.
2.4. Characterization 13 C NMR spectra were recorded on a Bruker AVANCE III-500 NMR instrument with the solvent D2O. FTIR spectra were captured from thoroughly dried samples using a Thermo Nicolet Avatar 370 FTIR spectrometer in the wavenumber range between 400 and 4000 cm–1 using KBr as background. The carbon, nitrogen, and hydrogen contents in the samples were measured using a VARIO EL cube element analyzer. Ultraviolet-visible (UV–vis) spectra were measured with a UV–vis spectrophotometer (U-3900). X-ray photoelectron spectroscopy (XPS) measurements were performed on a Thermo Scientific system with Mg K radiation (1253.6 eV). A field emission SEM (Shimadzu SSX-550) at 15.0 kV was used to examine the morphology, surface state, and elemental information. STEM scanning transmission electron microscopy (STEM, JEM-2100 F) was performed to obtain morphology, EDS, STEMmapping, and STEM-line scanning.
2.7.2. Water purification test The efficiency of P(VAc-NVP)-I (in a 7 : 3 feed ratio of VAc to NVP) at eliminating bacteria from water was examined using the columnpacking method, following a three-step approach (Gao et al., 2019). First, P(VAc-NVP)-I-based filter was fabricated by passing the suspension of P (NVP-VAc)-I through a column containing a piece of cotton fabric. Then, about 20 mL of pristine water was passed through the asprepared filter to ensure that all the active sites inside the column system were occupied by pristine water. Finally, 10 mL of challenge water containing 107 CFU·mL−1 of E. coli was passed through the column, the filtered water was collected, and bacterial survival was examined using the colony-counting method described above. In addition, the reusability of the as-designed P(VAc-NVP)-I-based filter was checked as a function of filtration cycle. After each cycle, 20 mL of deionized water was passed through the P(VAc-NVP)-I filter to ensure there was no residual bacteria-contaminated water in the column system. During the 10 filtration cycles, the as-prepared column did not need to be reloaded with iodine. All tests were done in triplicate.
2.5. Contact angle test The hydrophilic–hydrophobic balances of the copolymers were detected via the contact angle test. Measurements were performed with a CAM 200 static contact angle meter (KSV Instruments Ltd., Helsinki, Finland) at room temperature. Typically, the sample powders were ground and then pressed using a tablet machine to obtain the membrane sample. Water drops were deposited on the top surface of each membrane sample using a manual dosing system holding a 1 mL syringe (0.5 mm diameter needle). Side views of the water drops were photographed at a rate of 10 frames per second, and the corresponding contact angles were automatically calculated by fitting the captured drop shape to the correct one calculated from the Young-Laplace equation.
3. Results and discussion In our synthetic strategy (Fig. S1), the pyrrolidone-based copolymer P(VAc-NVP) was synthesized via one-step radical copolymerization between vinyl pyrrolidone (NVP) and vinyl acetate (VAc). To confirm the success of the copolymerization strategy, the as-obtained copolymer was characterized using 13C NMR analysis (Fig. 2A), with two monomers, NVP and VAc, for comparison. Compared to the two monomers, the copolymer shows two representative peaks at 177.8 ppm and 173.6 ppm, attributed respectively to the eC]O (amide group) in the NVP units and the eC]O (ester group) in the VAc units, suggesting successful copolymerization between NVP and Vac (He et al., 2012). The production of P(VAc-NVP) copolymer was further confirmed by FTIR spectra (Fig. 2B). Copolymer’s spectrum shows two characteristic peaks at 1661 cm−1 and 1742 cm−1, assigned respectively to the amide group in the NVP units and the ester group in the VAc units, again providing evidence of P(VAc-NVP) production (Gao et al., 2010; Liao et al., 2016). On the basis of the above findings, we confirmed the effectiveness of our copolymerization strategy that uses radical copolymerization between NVP and VAc. We also found that the NVP units in the P(VAc-NVP) copolymer can be regulated facilely by tuning the feed
2.6. Antibacterial evaluations The antibacterial activities of iodine-captured P(VAc-NVP) copolymer were evaluated by selecting E. coli and S. aureus as two model strains, and using the colony-counting method combined with the inhibition zone test (Bai et al., 2018, 2016; Dong et al., 2011). Prior to the antibacterial tests, S. aureus and E. coli were inoculated onto separated agar plates and incubated overnight at 37 °C. A single colony of each bacterium from the agar plate was employed to inoculate 5 mL of liquid cultures at 37 °C for 12 h on a rotary shaker at 220 rpm. The culture was expanded by transferring 100 μL of the above bacterial solution to 40 mL of liquid culture and shaking at 37 °C for 3 h. The colony-counting method was performed as follows. Typically, the antibacterial activities of the samples were examined by mixing 107 CFU·mL–1 bacterial suspension with a sample suspension (using final sample concentrations of 0.01, 0.05, 0.1, and 0.5 mg mL–1, respectively) at room temperature for 30 min. Next, the mixed solution was spread on nutrient agar plates and incubated at 37 °C for 12 h. The number of 3
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Fig. 2. (A)
13
C NMR spectra and (B) FTIR spectra of NVP, VAc, and P(VAc-NVP) copolymer.
PVAc homopolymer was exposed to iodine solution, indicating that P (VAc-NVP) anchors iodine by its NVP units rather than its VAc units. In its XPS spectrum (Fig. 3C, black curve), P(VAc-NVP) copolymer shows three strong signals for elemental carbon, oxygen, and nitrogen, while the copolymer after complexation with iodine (Fig. 3C, red curve) presents two additional peaks associated with iodine at 629.5 and 618.0 eV, demonstrating that the copolymer is able to capture iodine (Gao et al., 2019). The magnified XPS spectrum of P(VAc-NVP)-I shows two peaks, at 629.5 and 618.0 eV, associated with the I3− 3d3/2 and 3d5/2 peaks, respectively, further indicating the presence of iodine in an ionic state (Fig. 3D) (Hu et al., 2017; Liao et al., 2016). Additionally, we carried out XPS deconvolution of C 1s, N 1s, and O 1s (Fig. S4) in P (VAc-NVP)-I, as well as 13C NMR (Fig. S5) and FTIR spectra (Fig. S6), to examine the structural stability of the copolymer after iodine capture (i.e., P(NVP-VAc-I). Comparison with the P(VAc-NVP) copolymer shows that the main characteristic peaks remain unchanged after interaction with iodine, suggesting that iodine ions are adsorbed on the surface of the copolymer via complexation without damaging the copolymer molecular framework. After establishing that iodine could be recovered by chemically complexing with P(VAc-NVP), we then looked for other factors (e.g., morphology, surface roughness, etc.) that may have contributed to iodine capture in addition to its complexation with P(VAc-NVP). As seen in Fig. 4A, compared to P(VAc-NVP), P(VAc-NVP)-I shows no difference
ratio of NVP to VAc in our step-by-step regulation strategy. Using the nitrogen content from elemental analysis results, we calculated the NVP units in the P(VAc-NVP) copolymer. As shown in Fig. S2, the NVP units in the P(VAc-NVP) copolymer increased from 0 to 0.12, 0.52, 1.13, 1.55, and 8.40 as the feed ratio of NVP to VAc rose from 0:10 to 1:9, 3:7, 5:5, 7:3, and 9:1. These findings indicate that NVP reacts with VAc in a feed ratio-dependent manner. After confirming the successful synthesis of P(VAc-NVP) copolymer, we examined its ability to capture iodine. In a solid state (Fig. 3A), the white P(VAc-NVP) copolymer turned yellow or brown after capturing iodine from different media, which suggests that P(VAc-NVP) is capable of complexing with iodine in both water and organic media. The UV–vis spectra further confirm that P(VAc-NVP) can recover iodine from different media, as shown in Fig. 3B. The iodine solution in ethanol presented three typical peaks: at 286 and 362 nm, assigned to the characteristic absorption of I3−, and at 445 nm, corresponding to I2. P(VAcNVP) presented no absorption signal within the entire range from 280 to 600 nm, whereas the copolymers, after adsorbing iodine from three media—water/ethanol, cyclohexane, and petroleum ether—showed two intensive absorption peaks at ∼295 and ∼380 nm, both of which are attributed to I3– rather than I2 (He et al., 2012).This reveals that the iodine was chemically adsorbed onto the P(VAc-NVP) copolymer in the form of a polyiodide in an ionic state (Fig. S3). Conversely, we did not find the two characteristic peaks assigned to ionic polyiodide after
Fig. 3. (A) Powder of P(VAc-NVP) before and after iodized in water/ethanol, cyclohexane, and petroleum ether, respectively. (B) UV–vis spectra of iodine, iodized PVAc, P(VAc-NVP), and P(VAc-NVP)-I iodized in water/ethanol, cyclohexane, and petroleum ether, respectively. (C) XPS survey scans of P(VAc-NVP) and P(VAc-NVP)-I. (D) I 3d3/2 and I 3d5/2 spectrum of P(VAc-NVP)-I.
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Fig. 4. (A) SEM images of P(VAc-NVP) and P(VAc-NVP)-I, pictured at different magnifications. (B) EDS images, (C) STEM-mapping, and (D) STEM-line scanning of P (VAc-NVP)-I iodized in water/ethanol and in cyclohexane, respectively.
to the N, O, and I signals, stronger C signals were evident for P(VAcNVP)-I iodized in water/ethanol or in cyclohexane; these signals are mainly from the eCH2e units in the copolymer molecular skeleton. When a clear observation was made, N, O, and I presented the same trends, along with extending lines, further proving that the as-captured iodine were fixed tightly onto the NVP units in the copolymer. Strong binding of iodine to P(VAc-NVP) is beneficial for absorbing iodine from pollutants; however, facile desorption of iodine under specific conditions is also essential for its secondary utilization. To understand whether the iodine captured on P(VAc-NVP) was reversible, we investigated the release action of the captured iodine from P(VAcNVP)-I when immersed in starch solution, using an iodometric reaction. As shown in Fig. 5A, the P(VAc-NVP)-I suspension turns from yellow to dark blue after the starch solution is added, suggesting that iodine was released from P(VAc-NVP)-I. The appearance of an iodine–starch complex (yielding the blue suspension), as well as its subsequent fading in the presence of sodium thiosulfate, indicate that the released iodine exists in the original form of I2, which has oxidability toward sodium
in morphology or surface state, which suggests that iodization does not change the structure of P(VAc-NVP). Importantly, unlike adsorbents that recover iodine because of their internal porosity, P(VAc-NVP) copolymer has no holes or cavities on its surfaces, indicating that it captures iodine from media by complexing with iodine on its surface rather than inside it. To obtain elemental information that accords with the corresponding SEM images, EDS patterning was performed on P (VAc-NVP)-I, as shown in Fig. 4B. Whether iodized in water/ethanol or in cyclohexane, the copolymers presented iodine peaks, indicating the existence of P(VAc-NVP)-I within the selected SEM regions. To determine the elemental distributions, we then ran mappings on the STEM images. Presented as small, bright dots in Fig. 4C, the elemental distributions are a good match with the STEM images of P(VAc-NVP)-I iodized in water/ethanol or in cyclohexane, suggesting the as-captured iodine was restricted to the copolymer region through its strong binding with P(VAc-NVP). Since the distributions of N, O, and I provide important evidence for the interaction between P(VAc-NVP) and iodine, we then applied line scanning to the STEM images (Fig. 4D). Compared 5
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Fig. 5. (A) Photographs showing color changes in the P(VAc-NVP)-I suspension involved in the iodometric reaction. (B) Photographs showing reversible iodine capture using P(VAc-NVP) copolymer. (C) Efficiency of iodine capture using P(VAc-NVP) during five iodine loading cycles. (D) Iodine content of P(VAc-NVP)-I as a function of iodization time.
thiosulfate. As further evidenced in Fig. 5B, P(VAc-NVP)-I (brown) returns to P(VAc-NVP) (colorless) after releasing iodine, indicating that iodine captured on P(VAc-NVP) copolymer is reversible and, more importantly, that after desorption of iodine, the copolymer can be regenerated and reused for iodine capture. As shown in Fig. 5C, no decrease in iodine loadings on P(VAc-NVP) copolymer was detected, even after five cycles of re-iodization, demonstrating that iodine can be captured repeatedly by P(VAc-NVP) copolymer. Next, we tried to regulate the iodine loadings on P(VAc-NVP) copolymer by tuning the iodization aging time. As shown in Fig. 5D, iodine loadings rose from 0.29, to 0.49, 0.68, 1.16, 1.22, 1.33, and 1.94% after immersing P(VAc-NVP) prepared with a feed ratio of 5:5 NVP to VAc into iodine solution for different aging times, from 0.5, to 1, 2, 4, 8, 12, and 24 h, respectively. We can therefore confirm that iodine loadings on P(VAc-NVP) copolymer can be regulated simply by extending or shortening the aging period. To determine whether P(VAc-NVP) could have practical, widespread use in different pollutants, its hydrophilic–hydrophobic balance was modulated by regulating the feed ratio of NVP to VAc, then using contact angle measurement to determine the balance. Three samples were selected and used as comparative controls: PVP, PVAc, and P(VAcNVP)-I. As presented in Fig. 6, PVP and PVAc showed average contact angles of 27.6° and 113.0°, placing them within the hydrophilicity and hydrophobicity regions, respectively. The contact angles of P(VAc-NVP) increased from 41.6° to 73.4°, then to 99.1° when the feed ratio of NVP to VAc was changed from 7:3, to 5:5, then to 3:7, indicating that P(VAcNVP) has the potential for widespread use because its hydrophilic–hydrophobic property is adjustable across a wide range, between 27.6° and 113.0°. Comparison of PVP and P(VAc-NVP) suggests that the incorporation of VAc units gave the copolymer hydrophobicity, and
Fig. 6. Contact angles of PVP, PVAc, and P(VAc-NVP) prepared with different feed ratios, and P(VAc-NVP)-I.
such a hydrophilicity→hydrophobicity transformation can be achieved facilely using a radical copolymerization strategy. Obtained by iodine capture on P(VAc-NVP) (copolymerized at a feed ratio of 5:5 NVP to VAc), P(VAC-NVP)-I gives an average contact angle of 76.8°, which is slightly higher than the corresponding value of 73.4° for P(VAc-NVP). This demonstrates that the incorporation of iodine to some extent raises
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Fig. 7. Photographs of the bacterial culture plates of (A) E. coli and (B) S. aureus after treatment with 0.5 mg·mL–1 of P(VAc-NVP)-I for 30 min. (B) Antibacterial activity of P(VAc-NVP)-I against (C) E. coli and (D) S. aureus as a function of sample concentration.
be completely inactivated, Fig. 8B), E. coli cells could no longer keep their original integrity, and some were corrugated or even collapsed. The untreated S. aureus presented a regular spherical shape with a smooth surface (Fig. 8C). After 108 CFU·mL–1 of S. aureus was treated with 5.0 mg·mL–1 of P(VAC-NVP)-I for 60 min, the cytomembrane was damaged and depressed (Fig. 8D). These findings demonstrated that P (VAC-NVP)-I copolymer is capable of bacterial membrane disruption, causing bacterial death. To better understand the practical application of this antibacterial activity, we designed two tests: (i) use as an antibacterial additive and (ii) use for water purification. In our first test, P(VAc-NVP)-I copolymer powders were mixed with acrylic pigments of three different colors (green, yellow, and red), then these three pigments were coated on three different planar materials: glass, stainless steel, and tin foil. One can observe from Fig. 9A that the pigments after incorporation with P (VAc-NVP)-I had good adhesion to the substrates. Visually, in terms of their color, luster, brightness, and surface roughness, the P(VAc-NVP)-Iincorporated pigments look the same as the original pigments without P (VAc-NVP)-I. Interestingly, when their antibacterial powers against E. coli were monitored using the inhibition zone test (Fig. 9B), the unaltered pigments showed the expected robust bacterial growth, with no aseptic rings around the samples. In contrast, aseptic rings appeared around the P(VAc-NVP)-I-incorporated pigments, indicating the effectiveness and potency of P(VAc-NVP)-I-based additives for antibacterial use. Our second exam focused on water purification, using a P(VAcNVP)-I-based self-made filtration system (Fig. 10A) with water containing 107 CFU·mL–1 of E. coli as a model for bacteria-contaminated water. When the contaminated water was passed through the control column without P(VAc-NVP)-I, the corresponding culture plate (left plate in Fig. 10A) showed dense colonies, indicating robust bacterial growth in the absence of P(VAc-NVP)-I. However, the E. coli was completely inactivated after being passed through the P(VAc-NVP)-Ipacked column (right plate in Fig. 10A), demonstrating that the P(VAcNVP)-I effectively decontaminated bacteria-tainted water. To verify the long-term effectiveness and functional repeatability of P(VAc-NVP)-I for water bacterial decontamination, the performance of the P(VAc-
the hydrophobicity of P(VAc-NVP); however, the hydrophilic–hydrophobic balance of P(VAC-NVP)-I depends mainly on copolymer rather than the iodine. Based on our findings, we conclude that the hydrophilic–hydrophobic balance of P(VAc-NVP) and of P(VAcNVP)-I, can be adjusted on demand to meet specific requirements. After confirming that reversible iodine capture can be achieved using P(VAc-NVP) copolymer, we next examined the feasibility of reusing P(VAc-NVP)-I in antibacterial applications, as illustrated in step (ii) of Fig. 1. The antibacterial ability of P(VAc-NVP)-I solution was estimated via the colony-counting method using E. coli and S. aureus as two bacterial models in a bacterial concentration of 107 CFU mL–1 (Fig. 7A and B). In the control culture plate, both E. coli and S. aureus presented dense survival colonies, indicating their robust growth in the absence of the samples. The P(VAc-NVP) copolymer without absorbed iodine had almost no bacteria-killing capability, whereas P(VAc-NVP)-I completely killed both strains under the same conditions, demonstrating that P(VAc-NVP)-I kills bacteria via the release of the captured iodine on the copolymer’s surfaces. This implies that P(VAc-NVP)-I could be reused in antibacterial applications, because after the iodine is released from P(VAc-NVP)-I in the presence of bacteria, iodine-based antibacterial action follows. We then examined the concentration-dependent antibacterial action of P(VAc-NVP)-I against E. coli and S. aureus (Fig. 7C and D). Clearly, P (VAc-NVP) had almost no ability to kill bacteria within the whole sample concentration region of 0.01–0.5 mg·L–1. In comparison, the sterilizing rates of P(VAc-NVP)-I reached ∼32% against S. aureus and ∼24% against E. coli with a sample concentration of 0.01 mg mL–1, while sterilizing rates reached 100% for both E. coli and S. aureus when the sample concentrations were above 0.05 mg mL–1, suggesting that P (VAc-NVP)-I possessed antibacterial capacity, with its efficiency dependent on the concentration of P(VAc-NVP)-I. To ascertain the precise impact of P(VAC-NVP)-I on bacteria, the morphology of E. coli and S. aureus before and after P(VAC-NVP)-I treatment were examined by SEM (see Fig. 8). Clearly, the untreated E. coli displays a rod shape and intact surface without cellular debris (Fig. 8A). After exposing 108 CFU·mL–1 of E. coli to 5.0 mg·mL–1 of P (VAC-NVP)-I for 60 min (under which conditions E. coli was proven to 7
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Fig. 8. SEM images of (A and B) E. coli and (C and D) S. aureus in the (left) absence and (right) presence of P(VAc-NVP)-I.
NVP)-I-packed column after several filtering cycles was tested (Fig. 10B). After 10 cycles, the P(VAc-NVP)-I-packed column maintained 100% antibacterial efficiency, demonstrating that P(VAc-NVP)-I was active enough to combat bacteria in water even after 10 filtration cycles. All these data make it evident that P(VAc-NVP)-I rendered high, stable antibacterial activity for water purification.
including 13C NMR, FTIR, EA, UV–vis, XPS, SEM, STEM, and iodometric reaction, the chemical composition and hydrophilicity–hydrophobicity balance of P(VAc-NVP) were regulated by tuning the feed ratio of NVP to VAc. Interestingly, P(VAc-NVP) copolymer showed the capacity for reversible iodine capture under various different conditions, and the P (VAc-NVP) with captured iodine demonstrated antibacterial activity against E. coli and S. aureus. Subsequently, acrylic pigments containing small amounts of P(VAc-NVP)-I were coated on different planar materials—tin foil, glass sheet, and stainless steel—and the coatings displayed antibacterial function against pathogenic bacteria. We also established that P(VAc-NVP)-I can be used as an effective antibacterial filter for water purification, and a reusability test showed that a P(VAcNVP)-I-based filter could maintain good decontamination performance
4. Conclusions In summary, P(VAc-NVP) copolymer was facilely synthesized via radical copolymerization between NVP and VAc, to achieve the synergism of iodine capture and subsequent antibacterial use of the iodine. After systematic characterization using a series of advanced techniques,
Fig. 9. (A) Photographs showing P(VAc-NVP)-I-modified acrylic pigments coated onto glass, stainless steel, and tin foil, respectively. (B) Inhibition zone images of P (VAc-NVP)-I-modified and unmodified pigments. 8
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Fig. 10. (A) Schematic illustration of the P(VAc-NVP)-I-based filtration system. The inserts are photographic illustrations of the antibacterial activities of the P(VAcNVP)-I-based self-made filtration system. (B) Antibacterial efficiency of P(VAc-NVP)-I-based filtration system toward contaminated water after 10 cycles.
even after 10 filtration cycles. These unique features demonstrate that P (VAc-NVP)-I is an ideal candidate for sanitizing bacteria-contaminated water by filtration. We are sure that this strategy can act as a practical guide for using pyrrolidone-based polymers to recover iodine from pollutants, then reutilizing them in antibacterial-related fields.
silica gel particles and bactericidal property. Colloids Surf. B Biointerfaces 79, 446–451. Gao, T., Borjihan, Q., Yang, J., Qu, H., Liu, W., Li, Q., Wang, Y.-J., Dong, A., 2019. Antibacterial povidone-iodine-conjugated cross-linked polystyrene resin for water bacterial decontamination. ACS Appl. Bio Mater. 2, 1310–1321. Gao, R., Lu, Y., Xiao, S., Li, J., 2017a. Facile fabrication of nanofibrillated Chitin/Ag2O heterostructured aerogels with high iodine capture efficiency. Sci. Rep. 7, 4303. Gao, T., Fan, H., Wang, X., Gao, Y., Liu, W., Chen, W., Dong, A., Wang, Y.J., 2017b. Povidone-iodine-based polymeric nanoparticles for antibacterial applications. ACS Appl. Mater. Interfaces 9, 25738–25746. Geng, T., Zhu, Z., Zhang, W., Wang, Y., 2017. A nitrogen-rich fluorescent conjugated microporous polymer with triazine and triphenylamine units for high iodine capture and nitro aromatic compound detection. J. Mater. Chem. 5, 7612–7617. Goodwin, M.J., Steed, B.W., Yufit, D.S., Musa, O.M., Berry, D.J., Steed, J.W., 2017. Halogen and hydrogen bonding in povidone-iodine and related co-phases. Cryst. Growth Des. 17, 5552–5558. Harijan, D.K.L., Chandra, V., Yoon, T., Kim, K.S., 2018. Radioactive iodine capture and storage from water using magnetite nanoparticles encapsulated in polypyrrole. J. Hazard. Mater. 344, 576–584. Hasell, T., Schmidtmann, M., Cooper, A.I., 2011. Molecular doping of porous organic cages. J. Am. Chem. Soc. 133, 14920–14923. He, S., Wang, B., Chen, H., Tang, C., Feng, Y., 2012. Preparation and antimicrobial properties of gemini surfactant-supported triiodide complex system. ACS Appl. Mater. Interfaces 4, 2116–2123. Hetzel, B.S., Dunn, J.T., 2003. The iodine deficiency disorders: their nature and prevention. Annu. Rev. Nutr. 9, 21–38. Homendra, N., Shubhaschandra, S.N., 2007. Effect of an anionic surfactant on the complexation of some nonionic polymers with iodine in aqueous media. J. Phys. Chem. B 111, 4098–4102. Hu, Y.Q., Li, M.Q., Wang, Y., Zhang, T., Liao, P.Q., Zheng, Z., Chen, X.M., Zheng, Z., 2017. Direct observation of confined I−⋅⋅⋅I2⋅⋅⋅I− interactions in a metal-organic framework: Iodine capture and sensing. Chem. Eur. J. 23, 8409–8413. Janeta, M., Bury, W., Szafert, S., 2018. Porous silsesquioxane-imine frameworks as highly efficient adsorbents for cooperative iodine capture. ACS Appl. Mater. Interfaces 10, 19964–19973. Jie, K., Zhou, Y., Li, E., Li, Z., Zhao, R., Huang, F., 2017. Reversible iodine capture by nonporous pillar[6]arene crystals. J. Am. Chem. Soc. 139, 15320–15323. Lamme, E., To, M.U.N., Middelkoop, E., 1998. Cadexomer-iodine ointment shows stimulation of epidermal regeneration in experimental full-thickness wounds. Arch. Dermatol. Res. 290, 18–24. Li, B., Dong, X., Wang, H., Ma, D., Tan, K., Jensen, S., Deibert, B.J., Butler, J., Cure, J., Shi, Z., Thonhauser, T., Chabal, Y.J., Han, Y., Li, J., 2017. Capture of organic iodides from nuclear waste by metal-organic framework-based molecular traps. Nat. Commun. 8, 485. Li, B., Wang, B., Huang, X., Dai, L., Cui, L., Li, J., Jia, X., Li, C., 2019. Terphen[n]arenes and quaterphen[n]arenes (n=3-6): One-pot synthesis, self-assembly into supramolecular gels, and iodine capture. Angew. Chem. Int. Ed. 58, 3885–3889. Liao, Y., Weber, J., Mills, B.M., Ren, Z., Faul, C.F.J., 2016. Highly efficient and reversible iodine capture in hexaphenylbenzene-based conjugated microporous polymers. Macromolecules 49, 6322–6333. Lin, Y., Jiang, X., Kim, S.T., Alahakoon, S.B., Hou, X., Zhang, Z., Thompson, C.M., Smaldone, R.A., Ke, C., 2017. An elastic hydrogen-bonded cross-linked organic framework for effective iodine capture in water. J. Am. Chem. Soc. 139, 7172–7175. Ma, S., Islam, S.M., Shim, Y., Gu, Q., Wang, P., Li, H., Sun, G., Yang, X., Kanatzidis, M.G., 2014. Highly efficient iodine capture by layered double hydroxides intercalated with polysulfides. Chem. Mater. 26, 7114–7123. Papadopoulou, E.L., Valentini, P., Mussino, F., Pompa, P.P., Athanassiou, A., Bayer, I.S., 2018. Antibacterial bioelastomers with sustained povidone-iodine release. Chem. Eng. J. 347, 19–26. Pham, T.C.T., Docao, S., Hwang, I.C., Song, M.K., Choi, D.Y., Moon, D., Oleynikov, P., Yoon, K.B., 2016. Capture of iodine and organic iodides using silica zeolites and the semiconductor behaviour of iodine in a silica zeolite. Energy Environ. Sci. 9,
Acknowledgment This work was supported by the National Natural Science Foundation of China (21304044 and 51663019), the Natural Science Foundation of Inner Mongolia Autonomous Region (2015MS0520), the State Key Laboratory of Medicinal Chemical Biology (201603006 and 2018051), the State Key Laboratory of Polymer Physics and Chemistry (2018-08), and the Program of Higher-Level Talents of Inner Mongolia University (30105-125136). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jhazmat.2019.121305. References Atwater, J.E., Sauer, R.L., Schultz, J.R., 1996. Numerical simulation of iodine speciation in relation to water disinfection aboard manned spacecraft I. Equilibria. J. Environ. Sci. Health A. 31, 1965–1979. Au-Duong, A.-N., Vo, D.-T., Lee, C.-K., 2015. Bactericidal magnetic nanoparticles with iodine loaded on surface grafted poly (N-vinylpyrrolidone). J. Mater. Chem. B Mater. Biol. Med. 3, 840–848. Bai, R., Kang, J., Simalou, O., Liu, W., Ren, H., Gao, T., Gao, Y., Chen, W., Dong, A., Jia, R., 2018. Novel N–Br bond-containing N-halamine nanofibers with antibacterial activities. ACS Biomater. Sci. Eng. 4, 2193–2202. Bai, R., Zhang, Q., Li, L., Li, P., Wang, Y.J., Simalou, O., Zhang, Y., Gao, G., Dong, A., 2016. N-halamine-containing electrospun fibers kill bacteria via a contact/release codetermined antibacterial pathway. ACS Appl. Mater. Interfaces 8, 31530–31540. Borjihan, Q., Yang, J., Q, Song, Gao, L., Xu, M., Gao, T., Liu, W., Li, P., Li, Q., Dong, A., 2019. Povidone-iodine-functionalized fluorinated copolymers with dual-functional antibacterial and antifouling activities. Biomater. Sci. 7, 3334–3347. Brunet, G., Safin, D.A., Aghaji, M.Z., Robeyns, K., Korobkov, I., Woo, T.K., Murugesu, M., 2017. Stepwise crystallographic visualization of dynamic guest binding in a nanoporous framework. Chem. Sci. 8, 3171–3177. Burgi, H., 2010. Iodine excess. Best Pract. Res. Cl. En. 24, 107–115. Chen, Y., Yang, Y., Liao, Q., Yang, W., Ma, W., Zhao, J., Zheng, X., Yang, Y., Chen, R., 2016. Preparation, property of the complex of carboxymethyl chitosan grafted copolymer with iodine and application of it in cervical antibacterial biomembrane. Mater. Sci. Eng. C. 67, 247–258. Dong, A., Lan, S., Huang, J., Wang, T., Zhao, T., Xiao, L., Wang, W., Zheng, X., Liu, F., Gao, G., Chen, Y., 2011. Modifying Fe3O4-functionalized nanoparticles with N-halamine and their magnetic/antibacterial properties. ACS Appl. Mater. Interfaces 3, 4228–4235. Du, X., Fan, R., Fan, J., Qiang, L., Song, Y., Dong, Y., Xing, K., Wang, P., Yang, Y., 2016. Self-assembly of two supramolecular indium (iii) metal–organic frameworks for reversible iodine capture and large band gap change semiconductor behavior. Inorg. Chem. Front. 3, 1480–1490. Gao, B., Wang, Z., Liu, Q., Du, R., 2010. Immobilization of povidone-iodine on surfaces of
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Journal of Hazardous Materials 384 (2020) 121305
Q. Borjihan, et al.
1039/C8MH01656A. Yan, Z., Yuan, Y., Tian, Y., Zhang, D., Zhu, G., 2015. Highly efficient enrichment of volatile iodine by charged porous aromatic frameworks with three sorption sites. Angew. Chem. Int. Ed. 54, 12733–12737. Yu, X., Cui, W., Zhang, F., Guo, Y., Deng, T., 2019. Removal of iodine from the salt water used for caustic soda production by ion-exchange resin adsorption. Desalination 458, 76–83. Zeng, M., Tan, J., Chen, K., Zang, D., Yang, Y., Zhang, J., Wei, Y., 2019. Guest controlled pillar[5]arene and polyoxometalate based two-dimensional nanostructures toward reversible iodine capture. ACS Appl. Mater. Interfaces 11, 8537–8544. Zhang, X., da Silva, I., Godfrey, H.G.W., Callear, S.K., Sapchenko, S.A., Cheng, Y., Vitorica-Yrezabal, I., Frogley, M.D., Cinque, G., Tang, C.C., Giacobbe, C., Dejoie, C., Rudic, S., Ramirez-Cuesta, A.J., Denecke, M.A., Yang, S., Schroder, M., 2017. Confinement of iodine molecules into triple-helical chains within robust metal-organic frameworks. J. Am. Chem. Soc. 139, 16289–16296.
1050–1062. Qian, X., Zhu, Z.Q., Sun, H.X., Ren, F., Mu, P., Liang, W., Chen, L., Li, A., 2016. Capture and reversible storage of volatile iodine by novel conjugated microporous polymers containing thiophene units. ACS Appl. Mater. Interfaces 8, 21063–21069. Sriwilaijaroen, N., Wilairat, P., Hiramatsu, H., Takahashi, T., Suzuki, T., Ito, M., Ito, Y., Tashiro, M., Suzuki, Y., 2009. Mechanisms of the action of povidone-iodine against human and avian influenza a viruses: its effects on hemagglutination and sialidase activities. Virol. J. 6, 124. Valizadeh, B., Nguyen, T.N., Smit, B., Stylianou, K.C., 2018. Porous metal-organic framework@polymer beads for iodine capture and recovery using a gas-sparged column. Adv. Funct. Mater. 8, 1801596. Wang, P., Xu, Q., Li, Z., Jiang, W., Jiang, Q., Jiang, D., 2018. Exceptional iodine capture in 2D covalent organic frameworks. Adv. Mater. 30, 1801991. Xie, W., Cui, D., Zhang, S.-R., Xu, Y., Jiang, D., 2019. Iodine capture in porous organic polymers and metal-organic frameworks materials. Mater. Horiz. https://doi.org/10.
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