Dyeing of cotton fabric materials with biogenic gold nanoparticles

The present work aimed at synthesizing gold nanoparticles in a biological method employing fruit peel waste dumped in the environment. The peels of Garcinia mangostana (Mangostan), were collected from the nearby tourist spot during the season. The collected fruit peels were washed, dried, powder and extracted by using boiling water and acetone. The precipitated extract was dried and powdered for further use. The dried and powdered peel extract was added to the gold solution and boiled to 80 °C and the color change is observed. The color change indicates the completion of the synthesis of gold nanoparticles. The effect of pH, gold ion concentration, peel extract powder concentration, and the temperature was tested by varying the parameters. The biosynthesized nanoparticles were characterized using the UV–Vis spectrophotometer to identify the surface plasmon resonance peaks corresponding to gold nanoparticles. The bio-moieties responsible for the synthesis of gold nanoparticles were identified using the Fourier Transform Infra-Red Spectroscopy. The crystalline nature was detected by using an X-Ray Diffractometer. Atomic Force Microscope viewed the 3D surface image of the gold nanoparticle. The shape and morphology of the nanoparticle were identified by using a Field Emission Scanning Electron Microscope. The active compounds for gold nanoparticle synthesis were identified using Gas Chromatography-Mass Spectrometry. The gold nanoparticle was synthesized in various colors and used for dyeing cotton fabrics. The dyed cotton materials were exposed to various stress conditions to determine the color fastening.

www.nature.com/scientificreports/ antimicrobial property. In the present study, gold nanoparticles were synthesized through a greener method and it was applied for the dyeing process.

Materials and methods
Preparation of fruit peel extract powder. The fruit peels of G. mangostana were collected from Courtallam (8.9342° N 77.2778° E), Tirunelveli, Tamilnadu, India. Collected fruit peels were washed with distilled water and dried in shade to remove adhering dirt and dust. The fruit peels (100 g) were boiled in distilled water at 90 °C for 30 min and crushed by adding 100 ml of distilled water and the resultant extract was filtered through a clean muslin cloth. Equal volumes of chilled acetone were added to filter the precipitate. The resulting precipitate was collected by centrifugation (Eltek RC4100F) at 7000 rpm for 10 min, air-dried in a hot air oven, powdered form, and used for further experiments.
Green synthesis of gold nanoparticles. Chloroauric acid (HAuCl 4 ) in double-distilled water (1 mM) was used as a source of gold nanoparticles throughout the experiments. The reaction mixture contains 10 mg fruit peel extract powder, 2 ml chloroauric acid solution (1 mM). The reaction mixtures were heated at 80 °C in a water bath for 3 min. These were monitored for different time intervals and the nanoparticles and microstructures formed were characterized further.
Synthesis of different colours of gold nanoparticle solution. Gold nanoparticles were synthesized in different colors for dyeing applications. The color of the solution depends on the surface plasmon resonance effect (SPR) of the gold nanoparticle synthesized. The different colors of solution were prepared by increasing the concentration of chloroauric acid solution from 10 -2 , 10 -3 , 10 -4 , 10 -5 , and 10 -6 M.
Characterization of nanoparticles. The reduction of gold ions was monitored by using a double beam UV-vis spectrophotometer (Lambda 25, Perkin Elmer, Singapore) of the reaction medium in the wavelength range of 450-700 nm with a 10 mm quartz cell. FTIR confirmed functional biomolecules associated with the reduction of gold ions into gold nanoparticles (Spectrum two, Perkin Elmer, Singapore). Biosynthesized gold nanoparticles were centrifuged at 7000 rpm for 15 min and the pellets were washed with distilled water. The centrifuging and re-dispersing process were repeated thrice. The samples were dried and analyzed at a wave region of 400-4000 cm -1 . The purified gold nanoparticle structures and compositions were analyzed by XRD (Panalytical X 'Pert Powder X' Celerator Diffractometer). The crystalline nature of the nanoparticles was analyzed at the 2θ ranges of 10-80°. The morphology and size of the gold nanoparticles were found by Field Emission Scanning Electron Microscope (Philip model CM 200). Atomic Force Microscopy analysis (Nanosurf EasyScan 2) was done to examine the shape and size of the nanoparticle synthesized using the biological technique.
Gold nanoparticle as dye. Thermofixing method. The different colored gold nanoparticles were fixed on the wicks (cotton with length 10 cm) material by thermo fixing method. The wicks pieces were dyed by boiling with gold nanoparticle solution at a higher temperature range from 120 to 160 °C. Initially, the dyed wicks were kept at 120 °C for 15 min without alteration in temperature. After 15 min, the temperature of boiling was increased to 160 °C and kept for 1 h. Fabric materials were rinsed with water and then dried Material was again rinsed well after reduction cleaning and then dried in the air 29 .
Colour fastness of the fabrics. The Thermo fixed wick pieces were tested for colorfastness against drastic conditions. Each dyed fabric piece was dried at 45 °C for 24 h and tested for colorfastness against different situations. The color fastness of the colored fabrics was verified by dipping the fabrics in commercial detergent solutions for 24 h and by scouring. Following this process, the pieces were also treated with acid (1% acetic acid), alkali (1% KOH), and hot water with commercial detergent (pH ~ 11) for 1 h. The color fastnesses of the fabrics were also determined by the exposure to sunlight during summer (April-May; average atmospheric temperature 36 °C) at different time scales, i.e. 1-10 days.

Results and discussion
Green synthesis and characterization of gold nanoparticles. Visual observation. Gold nanoparticle formation was primarily identified by color change visually. The observation of color changes, from colorless solution into purple or pink color, was one of the processes to identify the synthesis of gold nanoparticles in the solution (Fig. 1). The peel powder extract was exposed to gold chloride solution and boiled, the green synthesis of nanoparticles started within few minutes and was identified by color change. Gold nanoparticles show different colors for each concentration of the chosen chloroauric acid solution. The color ranges from yellow, purple, and pink. The color arises because of the excitation of the surface plasmon resonance effect of gold nanoparticles. Previously, the report of Singaravelu et al. 30 and Inbakandan et al. 31 has also shown that the gold nanoparticle www.nature.com/scientificreports/ synthesis by using marine algae Sargassum wightii and the marine sponge Acanthella elongate, respectively. The result color change got in this investigation is very interesting in terms of the identification of potential plants for synthesizing the nanoparticles 32 .

UV-vis spectrophotometer analysis (Effect of gold ion concentrations). UV-vis spectroscopy is an important
preliminary technique used to determine the formation of nanoparticles at different concentrations of gold ions. Figure 2 shows the effect of gold ion concentration in the gold nanoparticles synthesis process by using the peel powder of mangostan. Characteristic surface plasmon absorption bands are observed at 530 nm for the purplecolored gold nanoparticles synthesized from 1 mM (10 -3 M) gold ion concentration. The sharp peak at 530 nm is the characteristic peak of monodispersed spherical nanoparticles. The 1 mM concentration shows a narrow band with increased absorbance, whereas other concentrations like 10 -4 M show a broad peak at 547 nm with low absorbance. It reveals large-sized nanoparticles because of the higher multipole plasmon excitation 33,34 . Single SPR band formation with increased absorbance at lower wavelength reveals the synthesis of the small spherical shape of nanoparticles 35 .
X-ray diffraction analysis. The crystalline size and structure of the gold nanoparticles were determined by XRD in the entire spectrum of 2θ values ranging from 10 to 80°. Peel powder extract mediated synthesized gold nanoparticles using mangostan shows four strong diffraction peaks at the 2θ values of 38.30°, 44.51°, 64.82° and 78.56° (Fig. 3) could be assigned the plane of (1 1 1), (2 0 0), (2 2 0) and (3 1 1), respectively shows the gold  where D is the average crystallite domain size perpendicular to the reflecting planes, λ is the X-ray wavelength (1.5418 Å), β is the width of the XRD peak at half-height, θ is the diffraction angle, and K is the Scherrer coefficient (0.89) shape factor for spherical particles. The calculated average particle size of the synthesized nano gold using mangostan peel powder extract was found to be 128 nm. The present report is well-matched with the standard gold and the report of Singaravelu et al. 30 and Shukla et al. 37 .
Field emission scanning electron microscope. The surface morphology of the synthesized gold nanoparticles was identified on the nanoscale bar by Field Emission Scanning Electron Microscope. FESEM image had shown the shape and distribution of the gold nanoparticles synthesized by using peel extract of mangostan (Fig. 4). FESEM micrographs show synthesized nanoparticles were adsorbed on the surface of peel powder. FESEM image shows individually dispersed gold nanoparticles and several aggregates synthesized with irregular shapes using peel (1) D = K /β cos θ    www.nature.com/scientificreports/ powder extract of mangostan. It illustrates the particles are predominantly spherical and some particles aggregate into larger particles with no well-defined morphology and the size of the gold nanoparticles ranging from 75 to 130 nm. The similar irregular shape of gold nanoparticles with different sizes from 5 to 100 nm was reported by using macerated clove bud's solution 38 .
Atomic force microscope. Atomic force microscopy (AFM) was also known as scanning force microscopy (SFM). AFM is a basic technique and inevitable for all nanoscopic research. The AFM image of gold nanoparticles synthesized using the peel extract powder of mangostan is shown in Fig. 5. The particles synthesized www.nature.com/scientificreports/ agglomerated with each other to form a sheet-like form 39 . The particles were viewed at 2 and 4 µm distances and also in a 3D pattern. The particles synthesized using mangostan formed layers and are smaller.
Fourier transform infra-red spectroscopy. The FTIR spectrum of gold nanoparticles synthesized using the peel extract powder of mangostan is presented in Fig. 6. The functional groups responsible for the synthesis of nanoparticles are denoted by the corresponding peaks arising due to the infrared radiations. The functional groups corresponding to the peak in the gold nanoparticles are presented in Table 1.
Gas chromatography mass spectrum analysis. The GC-MS analysis revealed that eleven major constituents were present in the mangostan peel extract ( Table 2). The compounds were first identified by Gas Chromatography and then the mass spectrum of the analyzed sample was matched with the NIST-2008 libraries. The analyses of mangostan peel extract indicate the presence of eleven major compounds with significant matches to 1, 3, 3 trimethyl, diaziridine (23.063%) followed by 2, 3 dimethyl, 1-pentanol (15.337%) and 11, 18-Diacetoxy-5, 6,  www.nature.com/scientificreports/ 12, 17-Trinaphthylenetetrone (12.658%) major peak area. The compound names, molecular weight, empirical formula, retention time, peak area percentages, and structure of the identified compounds are given in Table 2.
Dye fixing. Synthesis of various coloured gold nanoparticles. The variety of attractive colors will be produced by altering the concentration of the gold ion solution as 10 -2 , 10 -3 , 10 -4 , 10 -5 , and 10 -6 M solutions. They exhibit reddish-brown, purple, pink, pale yellow and colorless solutions respectively containing nanoparticles (Fig. 7). The particles exhibit different colors due to surface plasmon resonance effects in the visible region with the collective plasmon oscillations at the metal surface 40 . The rising of colors was based on the size of the gold nanoparticles. The colors of the cotton wicks were mainly various shades of brown, blue-purple, and shade blue colored fabrics produced.
Dyeing of cotton wicks. The different colored gold nanoparticles can be readily attached to cotton wicks. Figure 8 shows the cotton wicks before and after the dyeing process. Purple and red-colored gold nanoparticle colloids were successfully attached with cotton wicks samples.
Colour fastness. Generally, some colors were degraded while exposed to UV light. So, the color fastness determines the quality of fibers 41 . Figure 9 shows the stable color of cotton wicks treated with gold nanoparticles after exposure to various conditions like acid, alkali, commercial detergent, and direct sunlight. The nanoparticles are embedded in the interspaces between the cross-linked fabric materials. This result indicates the dye is attached to fabrics and showed positive colorfastness because most dyes were still in a negative phase for colorfastness. Hence these results show that the cotton wicks are colorfast and stable so would be a viable alternative to current synthetic dyes.
Scanning electron microscope. The SEM characterization technique is used to determine the morphology and physical properties of nanomaterials. The distribution of nanomaterials on the solid surface can also be attained using the SEM technique. SEM image (Fig. 10) visualizes the green synthesized gold nanoparticles which are deposited on the surface of cotton fabrics. Cotton fabrics are immobilized in gold nanoparticles prepared at different concentrations. Figure 10 shows  www.nature.com/scientificreports/

Conclusion
Gold nanoparticles impart different colors depending on their (Localized Surface Plasmon Resonance) LSPR in solution. The colors imparted by the nanoparticle solution were employed to dye cotton fabrics and the stability of the dyes on the fixed fabric was tested. These tests showed a positive result in the dyeing process. In summary, this paper presents an innovative approach to the synthesis and use of gold nanoparticles as novel stable colorants utilizing the surface plasmon resonance coloring effect of nanogold. www.nature.com/scientificreports/