Synthesis and Characterization of ZnO Nanoparticles and Their Application on Cotton Fabrics to Obtain Superhydrophobic Surfaces

then reducing the surface


Introduction
Since the discovery of the self-cleaning property in the lotus leaf, extensive research efforts have been made to imitate this phenomenon known as the "lotus effect" by attempting to fabricate surfaces with contact angles higher than 150 ̊ and slide angles less than 10 , which are known as superhydrophobic surfaces 1 .In the last two decades, scientists developed various methods to manufacture superhydrophobic surface structures.Most of these methods are based on creating an appropriate roughness on the surface and then reducing the surface energy 2,3 .The surface of the textiles has a micro-roughness caused by the knitting or weaving process and the threads, which are composed of many microfibers, but it is not enough to obtain superhydrophobic 4 .The most familiar techniques to create roughness on fabric are the deposition of nanomaterials such as TiO2, SiO2, and ZnO by dip-coating methods, spray-coating, chemical vapor deposition (CVD), sol-gel, and plasma processing techniques [5][6][7][8][9] .Zinc oxide nanoparticles have acquired attention in textile Published Online First: January, 2024 https://doi.org/10.21123/bsj.2024.8934P-ISSN: 2078-8665 -E-ISSN: 2411-7986 Baghdad Science Journal finishing processes because of their unique chemical and physical properties, biosafety properties, good stability, and their simple preparation methods with low cost [10][11][12] , further, their multiple functional properties: UV protection, antibacterial, and photolytic self-cleaning properties 13 .Recently several studies used ZnO NPS to develop superhydrophobic properties by creating roughness on the surface of the fabric.Soran et al. offered a method for the fabrication of superhydrophobic cotton textiles using ZnO nano flower/PDMS polymer nanocomposites 14  (HDMS) 15 .Superhydrophobic cotton fabric with a contact angle of 155 ̊ was fabricated by Meng et al. via a two-step: creating roughness on the surface through hydrothermal growth of ZnO nanoparticles and using stearic acid to reduce surface energy the superhydrophobic cotton fabric showed the significant possibility for oil/water separation 16 .This study aimed to produce superhydrophobic cotton fabrics using a simple and low-cost method that can be easily applied in conventional textile finishing processes utilizing a low concentration of ZnO with subsequent modification with stearic acid.The effect of the morphology and size of ZnO NPs and changed stearic acid concentration on the superhydrophobic property of cotton fabrics were studied.

Synthesis of Nano Zinc Oxide
ZnO nanoparticles were prepared at two different temperatures (30, 90) C according to the following method: 100ml of 1 M NaOH, and 100 ml of (0.5 M) ZnCl2 were prepared then two solutions were heated under constant stirring until the required temperature was reached, after that the solution was added drop-wise to the NaOH aqueous solution with continuous stirring (the color of the solution ZnCl2 changed from transparent to white).After completing dripping, the prepared solution was aged for 2 hours.The oxide was left to precipitate, then washed five times with distilled water and dried at a temperature of 150 ̊C for 4 hours.The reactions mechanism is shown in the following: 17 The prepared zinc oxide samples were named as follows: ZnO90 for ZnO NPs synthesis at 90 C, ZnO30 for ZnO NPs synthesis at 30 C

Cotton Fabric Pretreatment
The purpose of the pretreatment is to remove the added and natural impurities from the cotton fabric to make the fabric suitable for the subsequent finishing process.Therefore, the fabric was boiled in a solution containing 4% NaOH and 8% H2O2 for an hour at 100˚C.Then rinsed fabric with water and adjusted with acetic acid, and the fabric was rinsed again with water.Finally, the fabric was left to dry at room temperature.

Deposition Zinc Oxide onto Fabric
A pad-dry-cure technique is used to deposit ZnO NPs onto fabric according to the following steps: First, a colloidal suspension of each ZnO NPs was prepared at a concentration of (1%) by dispersing ZnO powder into ethanol by ultrasound for 30 minutes.Second, the cotton fabric was immersed in the colloidal suspension for 30 min in the ultrasonic bath, then the fabric was squeezed .Finally, the fabric was dried at 80 ˚C for 10min, then cured at 110˚C for 10min.

Surface Modification by Stearic Acid
Different concentrations of stearic acid solution (0.5,1,3,5,7%) were prepared by dissolving stearic acid in ethanol at 70˚C, then immersing the (ZnO NPs cotton fabric) and pristine cotton samples in the stearic acid solutions for 10 minutes, then squeezing the samples and finally drying samples at room temperature.

Characterization
The crystalline structure of the prepared ZnO nanoparticles powder was investigated by the X-ray diffraction patterns obtained using a PHILIPS XRD-PW 1840 Diffractometer using Co-Kα1 radiation at a wavelength of λ =1.78901 Å. Fourier transforms the infrared spectrometer (Jasco FTIR/4100) at the wavenumber region of 4000-400 cm −1 to determine the functional groups of the synthesized ZnO NPs.The morphology of the ZnO NPs was investigated by using Scanning Electron Microscopic (VEGA II XMU).To evaluate the wettability of samples, the water contact angle (CA) was measured using a sessile drop method 18 .A drop (5 µl) of deionized water was set on the surface.The droplet image is taken using a smartphone and processed using the Image J program to measure the CA.Three measurements at different positions on the surface of the sample were made.

X-ray Diffraction (XRD)
Fig. The crystal size of the zinc oxide particles was calculated using Debye-Scherer Equation Eq. 1: Where λ: wavelength of the X-ray (1.78901 Å), β: full width at half maximum peak (radians), and θ: Bragg angle (degree).The average crystalline size of the ZnO Nanopowder was around 19.5 nm at 30 C, which increased to 23 nm when the temperature reaction was raised to 90 C.

Figure 1. XRD patterns of ZnO synthesis under different temperatures Fourier Transform Infrared Spectroscopy (FT-IR)
FT-IR was used to find out the functional groups in the prepared ZnO.

Figure 2. FTIR spectrum of the synthesis ZnO NPs Scanning Electron Microscope (SEM)
Scanning electron microscopy was used to characterize the morphological structure of zinc oxide nanoparticles prepared at two different temperatures (30 and 90 C) and to descry the difference in the surface morphology before and after treatment with both types of zinc oxide.The SEM images indicate two different types of morphology according to the reaction temperature during the ZnO NPs synthesis.Fig. 3a shows a ZnO nanowire with an average diameter of 30 nm and an average length of 4μm.With the increase in temperature up to 90 C, Fig. 3b, the particles had a spherical shape with an average diameter (41 nm).
The microstructure of the cotton fabric before and after treatment with ZnO NPs also is shown in Fig. 3`.The untreated cotton fabric had smooth surfaces, Fig. 3c, with no solid particles observed.On the other hand, the treated cotton fabrics showed solid white precipitation distributed on the surface, and it was noticed that the spherical shape of the Zinc oxide nanoparticles, Fig. 3(d, d1), provides a roughness on the surface better than ZnO nanowires Fig. 3(e, e1).The effects of changing the content of stearic acid on the hydrophobic properties of ZnO NPs coated cotton fabric with different morphologies were studied.Therefore, different concentrations of stearic acid (0.5, 1, 3, 5, and 7 wt%) were used.
Figure 4 shows the water contact angle results.As Can see from Fig. 4, the quantity of stearic acid markedly influenced the hydrophobic properties of cotton fabric; the contact angle increased at first, then decreased with the increase of stearic acid content.When the concentration of stearic acid was 1wt%, ZnO NPs-coated cotton fabric showed superhydrophobic properties.It is due to the full coverage of the ZnO NPs with the mono-layer of stearate molecules with their hydrophobic tails.On the other hand, any increase in the stearic acid concentration after 1wt% decreases the CA.This is due to the formation of the thick stearic-acid layer on the ZnO surface, which reduces the roughness effect of the ZnO NPs; In addition, the excess carboxylic groups of stearic acid are deposited on the surface, leading to a decrease in CA 23 .

Conclusion
In summary, ZnO NPs were prepared at different reaction temperatures by a simple wet chemical method.The synthesized ZnO NPs were characterized by (XRD), (FTIR), and (SEM).The SEM results confirmed that reaction temperature influences the morphologic structure of ZnO NPs.FTIR results confirmed forming of Zn-O bond.XRD analysis confirmed that ZnO NPs samples had good crystallinity and a hexagonal structure

Fig. 2
shows the infrared transmittance spectrum of zinc oxide prepared at two different temperatures (30°-90°C).The peaks at 3433 cm -1 and 1633 cm -1 indicate the stretchingbond vibration of the O-H, and the bending vibration of the O-H, respectively.The absorption peaks located in the range between 417-517 cm -1 indicate the stretching vibration of the (Zn-O) bond.It is also noted that the Zn-O absorption peaks became sharper with smooth edges, with increasing temperature indicating an increase in the crystallization of nanoparticles19 .These results demonstrate the success of the synthesis of ZnO NP.The change in the shape and position of the IR peaks can be attributed to the structure and size of the particles20,21 .

Figure 3 .
Figure 3. SEM of the ZnO NPs synthesis.(a) 30˚C, (b) 90˚C, (c) untreated cotton, (d, d1) ZnO30 treated cotton fabric, (e, e1) ZnO90 treated cotton fabricContact Angle MeasurementContact angle measurement is a qualitative method of evaluating if a surface is hydrophilic or hydrophobic.For comparison, the contact angle was

Figure 4 .
Figure 4. Effect of stearic acid on contact angleThe effect of the changing morphology of ZnO NPs on the superhydrophobic property of cotton fabrics was studied by comparing the contact angle results of cotton fabric treated with the two different morphology of ZnO NPs and modified with stearic acid.It was established that the cotton samples treated with ZnO90 showed superhydrophobic properties, with CA > 150.while cotton Samples treated with ZnO30 showed hydrophobic properties with CA <150 because ZnO90 with spherical morphology created a rough structure on the cotton surface better than that of ZnO30.

(
wurtzite).To fabricate superhydrophobic cotton surfaces, the cotton fabric was coated with 1% wt of synthesis zinc oxide nanoparticles and modified by different concentrations of stearic acid.Water contact angle (CA)and scanning electron microscopy (SEM) characterized the treated cotton fabric.According to the results, samples treated with ZnO90 showed superhydrophobic, while samples treated with ZnO30 showed only https://doi.org/10.21123/bsj.2024.8934P-ISSN: 2078-8665 -E-ISSN: 2411-7986 Baghdad Science Journal hydrophobic properties after stearic acid modification.
. Gajanan et al. fabricated superhydrophobic cotton fabric with a contact angle of 152 ̊ by coating the surface 1.shows the X-ray diffraction spectra of ZnO NPs prepared at two different temperatures (30˚-90̊ C) in the range (2Ɵ= 35-89).It is noted that all the diffraction peaks in the XRD pattern of the ZnO NPs are identical and correspond to the crystal planes found in the reference card (JCPDS 01-079-0205) which indicates ZnO NPs have a hexagonal structure (wurtzite hexagonal).The sharp and narrow peaks indicate that ZnO NPs samples had good crystallinity.ZnO NPs powder was high purity because there are no peaks indicating impurities.