A facile preparation of cotton fabric containing hybrid poly(sodium methacrylate)/silver nanoparticles for oil removal and water disinfection

Abstract

Water scarcity and pollution has become one of the most serious problems in the world. Generally, both oils and microorganisms exist in polluted water, hence multi-functional materials for the removal of diverse substances from water are desired. We reported a facile method for preparing cotton fabric possessing hybrid poly(sodium methacrylate) (pNaMAA)/silver nanoparticles (AgNPs) for oil/water separation and water disinfection. A crosslinked pNaMAA layer was generated on the cotton surface by ultraviolet-initiated polymerization. By replacing Na⁺ in pNaMAA molecules, Ag⁺ was incorporated into the fabric and then was reduced to AgNPs in situ by photo-thermal reduction. Due to the high underwater oleophobicity and bactericidal effect of the pNaMAA/AgNP hybrid layer, the gravity-driven oil/water separation efficiency of the prepared fabric was higher than 99% and the bacteria killing ratio achieved nearly 100%. Furthermore, AgNPs exhibited relatively good fastness during application. Combining their excellent oil removal and water disinfection effectiveness, these textile-based materials provide a promising future in the field of point-of-use water purification.

Keywords

silver nanoparticles ultraviolet-initiated polymerization water disinfection oil/water separation cotton fabric

Nowadays, world-wide water scarcity and pollution has become one of the most serious problems.^1–3 Due to the fast industry development and population explosion, many people are suffering from a lack of clean and fresh water.^4–7 Several types of contaminants can occur in water, including inorganic chemicals, organic compounds and microorganisms. In recent years, water pollution caused by oil leakage accidents in the ocean and industrial wastewater discharge have attracted extensive attention.^8,9 Meanwhile, waterborne diseases caused by bacteria and viruses in contaminated water have become the main threat to public health in many developing nations.¹⁰ Therefore, technologies for removing oils and bacteria from water are particularly desired to provide safe drinking water. Materials for point-of-use water purification and disinfection can be a challenging topic.¹¹

Water/oil separation technologies include physical adsorption, chemical degradation, gravity separation, biological decomposition, membrane separation and so on.^12–16 Since the separation technology based on materials with special wettability is efficient, reusable and economic, it has been developed rapidly in recent years. In particular, bio-inspired superhydrophilic and underwater superoleophobic materials have aroused great interest.^17–19 For these materials, the highly hydrated polymeric coating on their surfaces can prevent the penetration of oils and allow the passing through of water. Furthermore, they also can protect the surface from oil pollution and prolong the service life of the oil/water separation materials.^20–24

During underwater use, bacteria and organisms could grow on the materials to form biofilms, leading to surface fouling and the loss of separation performance.^11,25 It was reported that the formation of biofilm is one of the key infrastructure rehabilitation challenges for water purification systems.^26–30 Antifouling surfaces, which could inhibit the adhesion of bacteria, are efficient in preventing the formation of biofilms. However, the surface may become invalid once it is partly fouled by organic matter. Furthermore, to supply potable drinking water, the microbiological contamination in water should be inactivated. Currently, disinfectants (e.g. chlorine) are used for water disinfection because of their low cost. However, once the biofilm is formed, it shows remarkable high resistance to chlorine. The use of disinfectant will also result in the production of toxic disinfection byproducts.^31–33 For example, the extensive use of chlorine causes the presence of trichloromethanes in drinking water, which is harmful to human health.

In order to solve the above-mentioned problems, many efforts have been made in developing materials with both antifouling and antibacterial properties, which can be used for oil/water separation and water disinfection simutaneously.^34--36 Liu et al.³⁷ reported that a stainless steel mesh with graphene oxide and titanium dioxide (GO-TiO₂) layer-by-layer assembly coatings presented underwater oleophobicity and bacteriostatic effects. However, materials with nanostructures are expensive and complicated to fabricate, and their durability has rarely been mentioned. Textile is a good candidate for separation material due to its excellent characteristics, including low cost, good softness, flexibility and ease of transport.³⁸ Moreover, high-throughput separation could be achieved since the porosity of textiles is always high.²⁴ These separation processes could be driven by gravity, which is energy-saving and does not require expensive infrastructure. Thus, textile-based multi-functional materials for the deep purification of water have a promising future in underwater applications.

In our study, a facile way to fabricate multi-functional materials for water disinfection and purification was developed. Crosslinked poly(sodium methacrylate) (pNaMAA) was polymerized onto cotton fabric by ultraviolet (UV) irradiation (Figure 1(a)). In this way, cotton fabrics with high hydrophilicity and underwater oleophobicity were obtained. Then, silver nanoparticles (AgNPs) were incorporated to the pNaMAA-crosslinked fabric through the photo-thermal reduction method (Figure 1(b); the obtained fabric is abbreviated as pNaMAA/AgNP fabric). Finally, the oil/water separation efficiency, antibacterial property and durability were investigated.

Figure 1.

Scheme illustrating the preparation process of poly(sodium methacrylate) (pNaMAA)/silver nanoparticle (AgNP) fabric: (a) pNaMAA-crosslinked fabric was prepared by ultraviolet (UV) irradiation; (b) AgNPs were incorporated to the pNaMAA-crosslinked fabric through the photo-thermal reduction method. NaMAA: sodium methacrylate; MBA: N,N-methylenebis(acrylamide); ITX: 2-isopropylthioxanthone.

Experimental details

Materials

Sodium methacrylate (NaMAA, 99%), N,N-methylenebis (acrylamide) (MBA, 99%) and 2-isopropylthioxanthone (ITX, > 98.09%) were purchased from Aladdin (China). Silver nitrate, acetone (A.R.) and ethyl alcohol (A.R.) were purchased from Hangzhou Shuanglin Chemical Reagent Factory, China. Gram-positive bacteria Staphylococcus aureus (S. aureus, ATCC 6538) was purchased from Taojunzhu Biotechnology Co., Ltd, China. The bacteria were incubated on a nutrient agar plate at 37℃ for 24 h before use. A cotton fabric (plain and woven) was purchased from Zhejiang Furun Printing & Dyeing Co., Ltd (China). It was used after being washed with a surfactant solution twice, rinsed with a large amount of water and dried in an oven at 80℃ for 6 h.

Preparation of pNaMAA-crosslinked cotton fabrics

The preparation process of cotton fabric is shown in Figure 1(a). The cotton fabric was immerged into an acetone solution (30 mL) with 0.036 g ITX, followed by irradiation with UV light (λ = 365 nm) for 5 min in an UV curing machine (HWUV400X, Zhonghe Mechanical Equipment Limited, China). Then, the pre-irradiated fabric was immediately put into an aqueous solution of monomer and crosslinker. It was irradiated with UV light for another 1.2 h. The precursor solution (30 mL) was made of 1.8 g NaMAA and 0.09 g MBA. The fabric needed to be turned over every 30 min to make the polymer coating homogenous on both sides of fabric. Finally, the fabric was soaked in water and shaken for 2 h, and then dried at 80℃ for 6 h.

In situ preparation of silver nanoparticles

AgNPs were loaded on cotton through the impregnation–thermal reduction and photochemical reduction method. pNaMAA-crosslinked fabric was soaked in silver nitrate solution of a certain concentration for 1 h, followed by rinsing with water twice. The fabric was incubated in the oven at 75℃ for 30 min, and then irradiated by UV light for 2 h to produce AgNPs in situ through photochemical reduction.

Characterizations

Grafting ratio

The polymer grafting ratio (G) is the weight growth ratio of polymers on the fabric. It was determined based on the mass measurements of fabrics before and after polymerization. It was calculated using the following equation

Grafting ratio (G) % = (1 - \frac{m_{1}}{m_{2}}) \times 100 %

(1)

where m₁ and m₂ are the weight of raw cotton and pNaMAA-crosslinked cotton, respectively.

Surface chemistry

Fourier transform infrared (FT-IR) spectra were taken via an infrared spectrometer (Bruker Optics Corporation, Germany) using the attenuated total reflection (ATR) method with 32 scans and at the wavelength of 4000–400 cm⁻¹. The resolution was 0.09 cm⁻¹.

Surface morphology

The surface morphologies of the cotton fabric were observed by scanning electron microscopy (SEM, vltra 55, Carl Zeiss SMT Pte Ltd, Germany) at 4 keV.

Energy dispersive spectrometry

The carbon, oxygen and silver element distribution of the modified cotton fabric was analyzed by energy dispersive spectrometry (EDS) and EDS mapping using SEM (JSM-5610LV, Japan) at 4 keV. Gold was sprayed on the surface of the samples for 40 min using ion sputter apparatus (JFC-1600, Japan).

Surface wettability

A contact angle (CA) measuring instrument (DSA-20, Kruss Corporation, Germany) was employed for CA characterizations. For each test, approximately 3 µL of water was dripped onto the fabric surface and the wicking time was recorded. The underwater oil CA was measured by introducing oil droplets to the fabric surface under water. The mean value of five measurements in different locations was taken as the reported CA data.

Silver content

The silver content of the pNaMAA/AgNP fabric was measured by inductively coupled plasma optical emission spectrometry (ICP-OES, Optima 5300DV, Perkin Elmer, USA).

Zone of inhibition assays

The antibacterial performance of pNaMAA/AgNP fabric was evaluated via zone of inhibition (ZOI) assay according to the FZ/T 73023-2006 standard. Firstly, the suspension of S. aureus (10⁶ cfu/mL) was spread on the agar plate. Then, fabrics were put onto the agar, followed by being incubated in an incubator at 37℃ for 18 h. The experiment was repeated three times and the mean results were reported.

Water/oil mixture separation experiment

The separation experiments were performed in a gravity-driven filtration mode using a home-made unit where the cottons were fixed above the funnel. The prepared mixture was used as the feed solution in this filtration process. The flow rate of the feed solution was controlled by a separatory funnel. The oil/water separation efficiency (E) was calculated according to Equation (2)³⁹

Separation ratio (E) % = (1 - \frac{C_{a}}{C_{b}}) \times 100 %

(2)

where C_a and C_b represent the oil content in the filtrates after and before filtration, respectively, measured by petroleum ether extraction and an ultraviolet visible (UV-Vis) spectrophotometer (Lambda 35, Perkin Elmer, USA) characterization. The relationship between UV absorbance at 232 nm and the oil concentration (mg/mL) is y = 0.5565x–0.0001.

Bactericidal experiment

The suspension of S. aureus was prepared by the following procedure according to FZ/T 73023-2006. Firstly, bacteria were taken out from the agar slant culture medium by an inoculating loop, and then were cultured on nutrient agar plates at 37℃ for 24 h. A bacterial colony picked by the inoculating loop was cultured in nutrient broth medium at 37℃ for 20 h. Then, the inoculum was diluted by phosphate-buffered saline (PBS) solution (pH 7.4) to obtain a bacterial suspension of a certain concentration (10⁶ cfu/mL).

The bactericidal experimental procedure was performed using the same equipment as the oil/water separation. A certain volume of bacterial suspension was added into the separatory funnel. The flow rate of solution passing through the fabric was controlled at 16 mL/min by regulating the opening of the valve. The effluent was collected and diluted 10, 10² and 10³ times, respectively. They were coated on Luria-Bertani plates and colony forming units (CFUs) were determined after incubation at 37 ℃ for 18 h. In this way, the number of residual bacteria in the effluent was calculated. The separation was taken continuously without washing and the maximum volume of bacterial suspension for this test was up to 300 mL.

Antifouling performance of pNaMAA/AgNP fabric

Protein-resistant test

Fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (BSA) (2 mg) was dissolved in 2 mL PBS solution.⁴⁰ Fabrics (1 cm × 1 cm) were immersed in FITC-BSA/PBS solution and incubated for about 1 h. Then, the fabrics were washed with millipore water three times. The samples were shaken in a shaker (TQZ-312, Shanghai, China) for 10 min each time. Finally, the fabric was observed by a confocal laser scanning microscopy (CLSM, Nikon, Japan).

Bacteria-resistant test

The fabrics were put into S. aureus suspension (10⁸ cfu/mL) and cultured at 37℃ under shaking (150 rpm) for 24 h. The samples were rinsed with PBS buffer, followed by being fixed with 25% glutaraldehyde solution for 30 min. Then they were sequentially dehydrated using a series of ethanol solutions of different concentrations (30%, 50%, 60%, 70%, 80%, 90%, 95%, 100%, 100% v/v) for 10 min at each step. The samples were put into a vacuum oven (DHG-9140A, Hangzhou, China) and dried at 30℃. Finally, the fabrics were sprayed with gold and observed under SEM.

AgNP fastness

The fastness of AgNPs on the fabric was evaluated by measuring the amount of silver in the filtrates after multiple separations. To mimic the bacteria separation process, PBS buffer was used. In each cycle, 50 mL PBS buffer passed through the pNaMAA/AgNP fabric mounted on the funnel at the speed of 16 mL/min. The content of silver in the filtrate was measured with ICP-OES and atomic absorption spectroscopy (AAS, Sollar M6, Thermo Electron Corporation, USA). The separation was taken continuously up to 300 mL.

Results and discussion

Synthesis and characterization of pNaMAA/AgNP cotton fabric

Surface-initiated photo grafting polymerization was reported in our previous work.⁴¹ ITX was used as the photo initiator. The C-H bonds in cellulose served as hydrogen donors for the initiators. In this way, polymer grew from the substrate under UV irradiation. With the presence of the monomer (NaMAA) and crosslinker (MBA), the crosslinked pNaMAA layer was covalently introduced onto cotton fabrics (Figure 1(b)). The surface chemistry of pNaMAA-crosslinked cotton was confirmed by FT-IR measurements (Figure 2(a)). The peaks at 3300, 1639 and 1108 cm⁻¹ corresponded to O-H stretching vibration, O-H bending vibration and C-O stretching vibration in cellulose molecules, respectively. In the spectra of pNaMAA-crosslinked cotton, new peaks at 1700 and 1550 cm⁻¹ were found and they were attributed to carbonyl groups (C=O) and carboxylate groups (-COO⁻), respectively.⁴² The results confirmed the successful grafting of pNaMAA onto cotton fabric.

Figure 2.

(a) Fourier transform infrared spectrum of pure cotton and poly(sodium methacrylate) (pNaMAA)-crosslinked cotton (the grafting ratio was 20.8%). (b) Silver content in pNaMAA/silver nanoparticle cotton fabrics measured by inductively coupled plasma optical emission spectrometry tests.

AgNPs were incorporated into pNaMAA-crosslinked cotton fabric through the photo-thermal reduction method.⁴³ In order to quantitatively analyze the amount of AgNPs loaded into the fabrics, ICP-OES measurement was used. As the AgNO₃ concentration increased, the content of AgNPs increased almost linearly. The silver content achieved 2% when the AgNO₃ concentration increased to 1.0 g/L (Figure 2(b)). It was suggested that the amount of AgNPs incorporated into cotton fabrics could be well controlled by the AgNO₃ concentration using our method.

As shown in the SEM images (Figure 3(a)), the raw cotton fibers are oblate and have natural wrinkle structures. After pNaMAA crosslinking, a thick and homogenous polymeric film was found on the surface, making the cotton fibers much smoother (Figure 3(b)). Silver particles were observed on the surfaces of pNaMAA/AgNP cottons (Figures 3(c) and (d)). These nanoparticles were of the size of tens of nanometers. The elementary composition of the nanoparticles was analyzed by EDS measurements. In the EDS spectrum of pNaMAA-crosslinked cotton, sodium was detected while no silver was found (Figure 4(a)). After the load of AgNPs, the peak of Ag emerged while that of Na disappeared in the spectrum (Figure 4(b)). The results confirmed that AgNPs were successfully incorporated into the fabric. It was deduced that Ag⁺ went into the polymeric layer by replacing Na⁺ in the pNaMAA molecules. Then, Ag⁺ was reduced to AgNPs in the photo-thermal reduction process. The nanoparticles were fastened onto the fabrics via the coordination interaction between silver and carboxylate groups.⁴⁴ Furthermore, in contrast to the AgNPs incorporated into materials prepared by conventional methods, agglomeration was not found on the pNaMAA/AgNP fabric obtained in our work (Figures 4(c)–(f)). EDS mapping results suggested uniform dispersity of AgNPs on the cotton surface (Figure 4(f)). Thus, a facile method was developed to prepare AgNPs incorporated into fabric with narrow size distribution and good dispersity.

Figure 3.

Scanning electron microscopy images of (a) pure cotton fabrics, (b) cotton fabrics crosslinked with 20.8% poly(sodium methacrylate) (pNaMAA), (c) pNaMAA/silver nanoparticle (AgNP) cotton fabrics and (d) AgNPs on fabrics observed at high magnification.

Figure 4.

(a), (b) EDS spectra of (a) poly(sodium methacrylate) (pNaMAA)-crosslinked cotton fabrics and (b) pNaMAA/silver nanoparticle (AgNP) cotton fabrics. (c)–(f) Element mapping results of pNaMAA/AgNP cotton fabrics.

For underwater used materials, surface wettability is a key property.^20,45,46 All fabrics showed high surface hydrophilicity and underwater oleophobicity (Figure 5). The water contact angle (WCA) of each fabric decreased to 0° in a very short time, suggesting that all the fabrics exhibited instant wetting (Figure 5(b)). For fabrics with pNaMAA and AgNPs, the initial WCA (recorded at t = 0 s) was smaller than the raw ones. However, although the raw cotton fabric has a relatively high WCA (∼120 °) and long wicking time (∼5 s), it was hydrophilic as well.^45–48 The underwater oil CAs of the fabrics were also measured. As shown in Figure 5(c), when oil droplets (3 µL) approached the bottom sides of the fabrics in water, the oil droplets were significantly deformed by pressure. Eventually the modified fabrics could not catch the droplets, while the raw cotton stretched the oil droplets, indicating that the modified cotton has an ultralow affinity to oils and an ultrahigh underwater oleophobicity.

Figure 5.

(a) The initial water contact angle. (b) The wicking time of pure cotton, poly(sodium methacrylate) (pNaMAA)-crosslinked cotton and pNaMAA/silver nanoparticle (AgNP) cotton fabrics with different silver contents. (c) The underwater oil contact angles of pure cotton, pNaMAA-crosslinked cotton and pNaMAA/AgNP cotton fabrics (cotton–0.4% Ag).

Oil removing capability

To evaluate the oil removing capability of the as-prepared fabrics, the separation of the layered oil/water mixture was carried out. A mixture of corn oil (stained by oil red) and water was added into the separation apparatus mounted with pNaMAA/AgNP fabric (Figures 6(a)–(d)). The separation was gravity-driven and no external force was applied during the separation process. Since fabrics are highly porous and the pore size is in the micrometer-scale, ultrahigh water flux was obtained. Water quickly passed through the fabric because of the high surface hydrophilicity. The effluent was collected in the underneath beaker. Meanwhile, corn oil was retained above the fabric. The oil content in the effluent was monitored using UV-Vis spectrometry. The oil removing ratio of raw cotton was roughly 30%. A large amount of corn oil passed through the micro-holes and went into the effluent. In contrast, almost no visible oil existed in the effluent after separation by pNaMAA-crosslinked fabric and pNaMAA/AgNP fabric. More than 99% of the oil in the mixture was removed, showing a high oil/water separation efficiency. Furthermore, due to the high underwater oleophobicity of modified fabrics, oils adhered on cottons could be easily cleaned through the rinse of fluid flow. After separating 300 mL oil/water mixture in succession (without washing), the separation efficiency of the textile remained high (>98.5%), indicating a good antifouling performance during application (Figure 6(e)). This was attributed to the highly hydrated pNaMAA layer on the surface of the cotton fibers, which has ultralow affinity to oils.

Figure 6.

(a) The apparatus for oil/water separation and bacteria filtration. (b) The mixture of corn oil and water (corn oil was stained by oil red). (c) The residual liquid stayed above the fabrics. (d) The effluent collected in the beaker. (e) The separation efficiency (oil removing ratio) of fabrics. pNaMAA: poly(sodium methacrylate).

Anti-biofouling performance of pNaMAA/AgNP cotton

During the long-term use of fabric in water, proteins, bacteria and microorganisms could attach to the surfaces, leading to the growth of biofilm.⁴⁹ Considering this, the anti-biofouling performance of fabric should be evaluated. In this work, BSA was used as a model protein to study the capability of the protein resistance of fabric. After incubating with FITC-labeled BSA for a certain time, the fluorescence intensities of raw cottons observed under CLSM were the highest comparing to those of pNaMAA-crosslinked and AgNPs/pNaMAA cottons (Figures 7(a)–(c)). It was supposed that the fluorescence intensity correlated to the adsorption amount of BSA on the fabric. Therefore, these results indicated that the raw cotton had little effect on resisting protein adhesion. In contrast, a good antifouling property was found on the fabrics with pNaMAA and AgNPs due to their high surface hydrophilicity.

Figure 7.

(a)–(c) Confocal laser scanning microscopy images of fluorescein isothiocyanate-bovine serum albumin stained (a) raw cotton, (b) poly(sodium methacrylate) (pNaMAA)-crosslinked cotton and (c) pNaMAA/silver nanoparticle (AgNP) cottons. (d)–(f) Scanning electron microscopy images of (d) raw cotton, (e) pNaMAA-crosslinked cotton and (f) pNaMAA/AgNP cottons cultured with S. aureus for 24 h. The loading amount of silver was 0.4%.

The adhesion of bacteria on fabric was investigated by SEM observation (Figures 7(d)–(f)). Different from BSA adsorption results, both raw cotton and pNaMAA-crosslinked cotton fabric showed poor resistance to bacterial adhesion. However, almost no bacteria was found on the surface of AgNP-incorporated fabric, indicating a good performance of biofilm resistance.

Inhibiting the formation of biofilm is a more complex process.^50,51 Bacteria adhere to the surface by secreting exopolysaccharides (EPS) to enhance the attachment. Although surface hydrophilicity is in favor of protein repelling, it is not enough to inhibit the EPS deposition and bacterial attachment during the long-term application.⁵² With the growth of bacterial colonies, the biofilm was developed, causing the biofouling of fabric. Thus, the antibacterial effect is also critical for excellent anti-biofouling properties.

To confirm that the as-prepared silver loaded fabric has antibacterial efficiency, the ZOI size of different fabrics was measured (Figure 8). S. aureus was used as a model bacterium. The raw cotton and pNaMAA-crosslinked cotton fabrics had no antibacterial activity, since bacteria still grew well in the surrounding areas (Figures 8(a)(1) and 8(a)(2)). Their ZOI size was roughly zero. For pNaMAA/AgNP fabric, silver ion leached out and caused the death of bacteria nearby (Figures 8(a)(3–8)). As shown in Figure 8(b), the ZOI size achieved 10 mm. With the increase of AgNP loading, the inhibition zone showed a similar size. It was suggested that the leaching rate of Ag⁺ was insignificantly influenced by the content of AgNPs loaded in fabrics.^53–55 Therefore, with the synergistic effect of protein resistance by hydrophilic polymers and antibacterial effect by silver, pNaMAA/AgNP cotton fabric could effectively resist the formation of biofilm, which is very important during long-term use.

Figure 8.

(a) Images of the inhibition zone of different fabrics: (1) raw cotton; (2) poly(sodium methacrylate) (pNaMAA)-crosslinked cotton; (3–8) pNaMAA/silver nanoparticle cotton with 2.03%, 1.1%, 0.4%, 0.23%, 0.12% and 0.03% silver, respectively. (b) The size of the inhibition zone for different fabrics.

Bactericidal capability during separation

A simple gravity-driven filtration experiment was carried out to test the disinfection performance of the fabric. As shown in Figure 9(a), a large number of bacteria still existed in the effluents after the bacterial suspension was filtrated by the raw cotton and pNaMAA-crosslinked fabric. It was suggested that the silver-free fabric had a low antibacterial effect. The number of bacteria in the effluents reduced by only 30%, which may be a result of the physical interception by fabrics. In comparison, AgNP-incorporated fabric presented high bactericidal efficiency (Figure 9(a)(4)). Approximately 100% of bacteria could be killed when they passing through the fabric and no bacterium was detected in the effluent. After separating 300 mL bacterial suspension in succession (without washing), the fabrics with different Ag content showed different bactericidal capabilities. For cotton fabrics with 0.12% and 0.23% AgNPs, the antibacterial ratio decreased to roughly 50%. The long-term antibacterial performance enhanced as the silver loading increased. When the silver loading was 0.4% or higher, the fabric could keep a high biocidal efficiency during the whole separation process for 300 mL bacteria solution (Figure 9(b)).

Figure 9.

(a) The images of bacteria cultured on Luria-Bertani plates from effluents of (1) unfiltered suspension, (2) raw cotton, (3) poly(sodium methacrylate) (pNaMAA)-crosslinked cotton fabric and (4) pNaMAA/silver nanoparticle cotton fabric. (b) The calculated antibacterial ratio of different fabrics.

The durability of pNaMAA/AgNP cotton fabric

Since the toxicity of metal ions and nanoparticles is still a question of wide concern, the content of silver in the effluent should be strictly controlled. In this study, the silver contents measured by AAS and ICP-OES are as shown in Figure 10. The AAS and ICP-OES results showed were highly consistent with each other. The content of silver in the effluent was less than 6 ppm. The value measured by AAS was lower than that determined by ICP-OES, since only Ag⁺ could be detected by AAS. Actually, a certain number of AgNPs may come off from the fabric, which could also be detected by ICP. With the prolongation of the operation time (the increase of the separation volume), the silver content decreased slightly. These results confirmed that the silver content in the effluent was low, indicating that the fastness of AgNPs was high. Our method guarantees a high bacteria killing ratio with high stability. At the same time, the silver content in the filtrate is very low under long-term operation.⁵⁶

Figure 10.

Silver content in the filtration measured by (a) atomic absorption spectroscopy (AAS) and (b) inductively coupled plasma optical emission spectrometry (ICP-OES) tests.

Conclusion

In summary, synthesis of pNaMAA coating on cotton fabrics has been successfully carried out by the photo grafting method. Then, AgNPs were produced in situ and incorporated to pNaMAA-crosslinked cottons by the reduction method. The SEM and EDS results implied that AgNPs with narrowly distributed size were uniformly dispersed on the cotton surface. ICP-OES tests showed that the silver loading in the fabric could be well controlled by AgNO₃ concentration. The pNaMAA/AgNP fabric showed an excellent oil/water separation performance (>99%) due to the high oil repellence. The disinfection capability was evaluated against S. aureus. The pNaMAA/AgNP fabrics showed significant bacterial removal efficiency, which may be attributed to the contacting antibacterial activity of AgNPs incorporated into cotton fabrics. In addition, a low content of silver was detected in the effluent (less than 6 ppm) and the amount decreased with repeating cycles, confirming the high durability and fastness of AgNPs during application. Taken together, the results reveal that pNaMAA/AgNP fabrics with high oil removing capacity and efficient biocidal activity are promising to be used for water disinfection and purification.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Key R&D Program of China (2017YFB0309600), National the Natural Science Foundation of China (Grant No. 21604072) and the Zhejiang Provincial Top Key Academic Discipline of Chemical Engineering and Technology.

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