Functional Application of Noble Metal Nanoparticles In Situ Synthesized on Ramie Fibers
© Tang et al. 2015
Received: 19 August 2015
Accepted: 8 September 2015
Published: 17 September 2015
Different functions were imparted to ramie fibers through treatment with noble metal nanoparticles including silver and gold nanoparticles. The in situ synthesis of silver and gold nanoparticles was achieved by heating in the presence of ramie fibers in the corresponding solutions of precursors. The unique optical property of synthesized noble metal nanoparticles, i.e., localized surface plasmon resonance, endowed ramie fibers with bright colors. Color strength (K/S) of fibers increased with heating temperature. Silver nanoparticles were obtained in alkaline solution, while acidic condition was conducive to gold nanoparticles. The optical properties of treated ramie fibers were investigated using UV-vis absorption spectroscopy. Scanning electron microscopy (SEM) was employed to observe the morphologies of silver and gold nanoparticles in situ synthesized on fibers. The ramie fibers treated with noble metal nanoparticles showed remarkable catalytic activity for reduction of 4-nitrophenol (4-NP) by sodium borohydride. Moreover, the silver nanoparticle treatment showed significant antibacterial property on ramie fibers.
Functionalization of textiles with nanoparticles has attracted intensive attentions of scientists and engineers in recent years. A number of strategies have been developed to enhance functions of textiles [1–4], such as antibacterial treatment [1, 5], self-cleaning coating [6, 7], and UV protection enhancement [8, 9]. Semiconductor (e.g., TiO2 and ZnO) nanoparticles have been applied to textiles for functions such as UV-blocking and self-cleaning [10, 11]. Silver nanoparticle as a broad antibacterial agent is widely used for antibacterial finishing of textiles [12, 13]. Besides antibacterial property, noble metal nanoparticles (e.g., silver and gold) possess particular localized surface plasmon resonance (LSPR) property, which leads to bright colors. Some strategies have been developed to utilize noble metal nanoparticles to functionalize different fibers such as cotton, wool, and silk. The coloration of fibers has been achieved through treatment with silver nanoparticles, taking advantage of the LSPR optical property of noble metal nanoparticles [5, 14, 15]. Similarly, gold nanoparticles can also endow fabrics with different functions including colors, UV protection, and antibacterial properties [16–18].
Ramie from a perennial herbaceous plant of the Urticaceae family is one of the most important bast plant fibers and has a silky luster. It is superior to cotton and silk in length and strength [19–21]. Ramie fibers have been applied to an increasing number of textile products including canvas, clothing fabrics, towels, cordages, and garments, due to their high tenacity, excellent thermal conductivity, good comfort, and significant tensile properties [21–23]. China and several other Asian countries are main producing areas of ramie fiber [24, 25]. Functional modification of ramie fibers is one way to promote product value and satisfy the increasing needs from consumers. Regarding modifications of ramie, Zheng et al. coated ramie fabrics with titanium dioxide (TiO2) nanoparticles via a dip-pad-dry process . The ramie fabrics treated with TiO2 showed antibacterial and UV-protective properties. However, the research focused on the functionalization of ramie with nanoparticles is very limited.
In this study, the functionalization of ramie fibers was realized through in situ synthesis of silver and gold nanoparticles. The silver nanoparticle-treated ramie fiber displayed a yellow color, while gold nanoparticles endowed the ramie fiber with red and purple colors. The changes in color strength (K/S) of ramie fibers with pH value of solution were also observed. Antibacterial property of the ramie fibers treated with silver nanoparticles was evaluated. The color fastness to washing of the treated ramie was tested. Moreover, the catalytic ability of ramie fibers treated with silver and gold nanoparticles was determined using reduction of 4-nitrophenol by sodium borohydride as a model reaction.
AgNO3 (>99 %), tetrachloroauric (III) acid (HAuCl4 · 3H2O, >99 %), NaOH (≥97.0 %), acetic acid (>99.7 %), 4-nitrophenol (≥99 %), and sodium borohydride (>98 %) were purchased from Sigma-Aldrich. All chemicals were analytic grade reagents and used without further purification. Ramie fibers and fabrics were kindly provided by Engineering Research Center for Clean Production of Textile Printing in Wuhan Textile University. They were used without pretreatment.
In Situ Synthesis of Silver and Gold Nanoparticles on Ramie Fibers
Ramie fibers were washed for 3 min with hot water (70 °C) followed by rinsing with deionized water at room temperature. The washed fibers were immersed in precursor solutions of metal nanoparticles (AgNO3 for silver nanoparticles and HAuCl4 for gold nanoparticles) with different concentrations. The weight ratio of aqueous solution to fibers was 80. The ramie fibers were immersed in precursor solutions for 15 min at room temperature and the pH values of the solutions were adjusted. After that, the solutions were heated at different temperatures for 60 min in an oscillating water bath. The treated fibers were rinsed with running deionized water and dried at room temperature. The details of the corresponding experimental conditions for in situ synthesis of silver and gold nanoparticles are listed in Additional file 1: Tables S1 and Additional file 1: S2, respectively.
Color Fastness to Washing
Washing fastness was evaluated in accordance with Australian Standard AS 2001.4.15—2006. The ramie fabrics treated with silver or gold nanoparticles were washed for 45 min at 50 °C in the presence of ECE reference detergent (4 g/L) by using a lab dyeing machine (Ahiba, Top Speed Nuance). The CIE Lab color coordinate values (L*, a*, and b*) for each specimen were measured before and after washing. L* represents the lightness/darkness, a* value represents the red or green chroma, and b* represents the chromaticity coordinate for yellow/blue. The color difference (ΔE) was obtained based on the changes in color coordinates (ΔL*, Δa*, and Δb*) with the formula: ΔE = [(ΔL*)2 + (Δa*)2 + (Δb*)2]1/2. The color difference (ΔE) of ramie fabrics before and after washing was measured by spectrophotometer to assess washing fastness of ramie fabrics according to Australian Standard AS 2001.4.A05—2004.
To investigate the catalytic efficiency and reusability of the ramie fibers treated with noble metal nanoparticles, the catalytic conversion of 4-nitrophenol into 4-aminophenol by sodium borohydride (NaBH4) was performed in the presence of untreated and treated ramie. In a typical experiment, 1.0 mL of NaBH4 solution (3.42 M) was added into 40 mL of 4-nitrophenol aqueous solution (0.025 mM). Subsequently, 0.0485 g of untreated ramie fibers or treated ramie fibers (Ag-90-10-1, Ag-90-10-3 and Au-90-5-6) was added into the mixing solution of 4-nitrophenol and NaBH4 under vigorous stirring. UV–visible absorption spectra were monitored during the conversion of 4-nitrophenol into 4-aminophenol.
Antibacterial Test Against Gram-Negative Bacteria
Gram-negative bacteria, Escherichia coli (E. coli) (ATCC 11229), were used as test organisms. Antibacterial test was performed on untreated and silver nanoparticle-treated ramie fibers. The antibacterial test was carried out according to the AATCC 100-2004 (Clause 10.2) test standard with slight modifications. Fifty microliters of bacteria were added to treated samples in separate flasks. After 1.0 min, 50 mL of sterile deionized water was poured into each flask, followed by vigorous shaking. Then, the flasks were incubated for 18 h in a shaker oven at 120 rpm and 37 °C. After that, the fiber samples were collected and the solution left in the flask was further diluted to get countable number of bacterial colonies. A 103 dilution was suitable for obtaining colonies between 30 and 300. One hundred microliters of the 103 dilution obtained was placed on the nutrient agar plates. These plates were then incubated for 18 h in an oven at 37 °C. The bacterial activity was recorded by photography. The test was carried out in triplicate and the entire experiments were repeated three times.
Results and Discussion
Heating may promote the in situ synthesis of noble metal nanoparticles in the presence of ramie fibers. To investigate the influence of heating on synthesis of noble metal nanoparticles, different temperatures were tested when other reaction conditions remained unchanged. Additional file 1: Tables S3 and S4 displays the detailed conditions for synthesis of silver and gold nanoparticles. Additional file 1: Figure S2a shows the K/S curves of ramie fibers treated with silver nanoparticles obtained at different temperatures. The result reveals that the silver nanoparticles can be obtained in situ on ramie fibers at a low temperature (40 °C). The K/S value increased as the reaction temperature increased (Additional file 1: Figure S2b). It is found that high temperature led to high color strength (K/S) of ramie fibers. The gold nanoparticles were also prepared on ramie fibers at 40 °C (Additional file 1: Figure S3a). The K/S value increased when the temperature was increased to 70 from 40 °C. Nevertheless, the maximum K/S value changed slightly when the reaction temperature was between 70 ~ 90 °C (Additional file 1: Figure S3b), implying that nearly all the gold ions were reduced at 70 °C. The trend of change in K/S curves of gold nanoparticle-treated ramie fibers was different from that of silver nanoparticle-treated ramie fibers, which may be due to difference in redox potential of silver and gold.
Content of silver in different ramie fibers treated with silver nanoparticles
Content of Ag (wt%)
Content of Ag (wt%)
Content of gold in different ramie fibers treated with gold nanoparticles
Content of Au (wt%)
Content of Au (wt%)
Color fastness of dyed fabrics is important in practical applications. The same as ramie fibers, the ramie fabrics were colored by in situ synthesized silver and gold nanoparticles. The color fastness to washing of the ramie fabrics treated with noble metal nanoparticles was evaluated. The ramie fabrics were washed for 45 min in the presence of ECE reference detergent at 50 °C under each washing cycle. The color differences (ΔE) of the ramie fabrics before and after washing are shown in Additional file 1: Figure S5. The visible color difference of silver nanoparticle-treated ramie fabrics after the first washing cycle was found with ΔE of 5.2 (Additional file 1: Figure S5). However, the average ΔE value of fabrics treated with silver nanoparticles did not increased notably with further increase in number of washing cycles. Compared with silver nanoparticle-treated ramie fabrics, the gold nanoparticle-treated ramie fabrics showed very good washing color fastness. The average ΔE value of fabrics treated with gold nanoparticles was 2.0 after first washing cycle (Additional file 1: Figure S5), which corresponds to the gray scale rating of 4. The color difference of gold nanoparticle-treated fabrics changed slightly and remained stable as the number of washing cycles increased, which indicates that the ramie fabrics colored by in situ synthesized gold nanoparticles exhibited good washing color fastness.
In addition to silver nanoparticle-treated ramie, catalysis ability of the fibers treated with gold nanoparticles was investigated as well. The absorption peak at 400 nm of 4-nitrophenol decreased gradually in the presence of gold nanoparticle-treated ramie fibers (Au-90-5-6) with reaction time (Additional file 1: Figure S6a). The plot of peak intensity at 400 nm versus time proves that the ramie fibers with gold nanoparticles exhibit evident catalytic activity (Additional file 1: Figure S6b). The results indicate that the ramie fibers with noble metal (silver and gold) nanoparticles show effective catalysis cavity.
Silver nanoparticles as antibacterial agents have been used widely for antibacterial finishing of textile products [12, 37]. In the present study, the antibacterial properties of silver nanoparticle-treated ramie fibers were evaluated against the Gram-negative bacteria, E. coli. Additional file 1: Figure S7 shows the photographs of the bacterial colonies on blank (control) sample, untreated ramie fibers, silver nanoparticle-treated fibers (Ag-90-10-3). Plenty of colonies of viable bacteria were seen on agar plates corresponding to the control sample and untreated fibers (Additional file 1: Figure S7a, b). Whereas, no bacteria colonies were found on agar plates of ramie fibers treated with silver nanoparticles (Additional file 1: Figure S7c), revealing that the silver nanoparticles on fibers inhibited the growth of bacteria. Therefore, it is suggested that the in situ synthesized silver nanoparticles endow ramie fiber with strong antibacterial property, which enhances the function of ramie fibers.
Additional file 1: Figure S8 displays the 13C solid-state NMR spectra of ramie fibers before and after treatment with noble metal nanoparticles. It is well-known that the NMR technique probes the signal from the overall sample volume and the NMR intensity is proportional to the number of spins. Therefore, for the present ramie samples, the NMR spectra provide us the structure and dynamics information of the bulk molecules rather than the surface because of its small surface-to-volume ratio. The NMR spectra corresponding to untreated and treated ramie fibers were nearly identical, which indicates that the in situ synthesis of noble metal nanoparticles did not change visibly the chemical structures of the bulk ramie. As an indispensable compensation to NMR, FTIR detects the structure and dynamics of the surface molecules. To understand the surface structure change of the treated ramie fibers, FTIR measurements were performed for all the three samples. Comparing with the FTIR spectrum of untreated ramie (Curve a in Additional file 1: Figure S9), no obvious differences were found in the FTIR spectra of the fabrics after treatment with silver and gold nanoparticles (Curves b and c in Additional file 1: Figure S9). These results suggest that there is no evidence of degradation on the surface of ramie fibers. The main chemical structures of the surface of ramie fibers kept essentially unchanged during the in situ synthesis of silver and gold nanoparticles, which is consistent with the cases of cotton and bamboo treated with noble metal nanoparticles [16, 38]. The ramie is composed mainly of cellulose [39–41]. Cellulose as a reducing agent has been used for synthesis of silver and gold particles because of the presence of hydroxyl groups . Additionally, other components of ramie including lignin, gum, and pectin may reduce silver or gold ions to form nanoparticles, due to their reducibility [43–45]. Further investigation on the mechanism for the reduction of silver and gold ions by ramie is in progress.
Silver and gold nanoparticles were in situ synthesized on ramie fibers at different pH values through heating. Alkaline condition is required to synthesize silver nanoparticle in the presence of ramie. Whereas, acidic condition facilitated the synthesis of gold nanoparticles on ramie fibers. The formation of silver and gold nanoparticle imparted bright colors to ramie fibers. The color strength (K/S) of ramie fibers increased with concentration of precursor ions in solution. UV-vis reflectance absorption spectroscopy and SEM demonstrated that silver and gold nanoparticles were produced on ramie fibers. The contents of silver or gold were analyzed under different conditions. Significantly, the ramie fibers treated with in situ synthesized silver and gold nanoparticles showed remarkable catalytic activity for reduction of 4-nitrophenol. The treated ramie fibers could be separated readily and reused in catalyzed reaction. The ramie fabrics treated with gold nanoparticle had good color fastness to washing. Additionally, the silver nanoparticle-treated fibers showed significant antibacterial property. The finishing of ramie fibers based on the in situ synthesis of noble metal nanoparticles would pave the way for the development of functional ramie fibers.
This research was supported by the National Natural Science Foundation of China (NSFC 51273153 and 51403162).
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