The Function of Cross Linker Carboxylic acid for TiO 2 / Chitosan / SiO 2 Coated as Self Cleaning Fabrics

The chemical compound TiO2/Chitosan/SiO2 is a photocatalyst with a selfcleaning capability against dye contaminations. Morphologically, it has an anatase structure with 13.1 nm of crystallite size, spherical shape, and Eg = 3.209 eV as characterized by X-ray diffraction, TEM, and UV-DRS. The self-cleaning capability of TiO2/Chitosan/SiO2 against the malachite green dye spot was optimized using two carboxylic acid cross-linkers namely 1,2,3,4Buthane Tetra Carboxylic Acid (BTCA) and Chloro Acetic Acid (CAA). The optimization in enhanced the growth of ester covalent interaction with the functional groups of textile fiber was performed gradually in CAA and directly in BTCA to produce a self-cleaning textile. The self-cleaning efficiency of cross-linker under the UV irradiation (536 lux for 60 min.) was 96% and 69.96% in CAA and BTCA, respectively. The FT-IR analysis revealed that the ester covalent interaction among the cross-linker, cotton fiber, and TiO2/Chitosan/SiO2 nanocluster could be determined by the intensity change of C=O stretching of the functional group at1700-1710 cm-1. The intensity was higher in CAA (15.03%) than BTCA cross-link (12.04%). The superficial morphological feature of the cotton fiber as observed by SEM depicted that TiO2/Chitosan/SiO2 particles were dispersed more evenly in the CAA than BTCA. The TiO2/Chitosan/SiO2 nanocluster with a CAA cross-link is reliable to be used indesigning a high-quality self-cleaning textile.


INTRODUCTION
Textile is cer tainly needed infashion industries as well as various medical and office equipments, and other daily needs.The cotton textile is preferable as compared to the other materials due to its ease of maintenance, the strength, absorption, and affordability 1 .However, the higher absorption of cotton fiber makes it easy to be contaminated by dirt and dyes, thus it is also difficult to be removed out 2 .As an alternative solution, some researchers modified the textile cotton fiber to acquire the self-cleaning capability against the dye spots contaminating the textile surface.The self-cleaning textile is practically effective to shorten the contact time of the dirt on the textile.Consequently, the dirt could be easily cleaned and the deterioration of the textile fiber could be maximally prevented 3,4 .
The nano-oxide metals including TiO 2 , ZnO or its composites are commonly used in modifying the cotton fiber due to their functional capability as the sunscreen, self-cleaning agents and antimicrobes [3][4][5] .
The capabilities of the substances are related to their pivotal role as photocatalysts.Hence, they could remove the dye on the fiber by the photocatalytic mechanism.The previous study by Wijesena, applied   this concept to develop the self-cleaning materials by using the TiO 2 and ZnO nanoparticles against the dye spots of methyl orange 4 .Moreover, Pakdel and Doud used TiO 2 and SiO 2 nanocomposites to enhance the functional capability of self-cleaning textile against various dyes including methyl orange 4,6,7 , methylene blue 3,8 , disperse yellow and C.I. reactive red 9 , and acid red 10 .
The coating of nano-oxide metal on the cotton fiber basically requires the cross-link agent, a carboxylic group-consisting compund, in order to promote the covalent interaction with the fiber cellulose and TiO 2 by means the electro statics interaction 11 .The stability of TiO 2 -SiO 2 nanocluster's coating on the cotton fiber is determined by the type of carboxylic acid used as the cross-linker.A study by Karimi demonstrated that the use of succinate acid as across-linker inthe TiO 2 -SiO 2 particle's coating could stand its stability up to 85% against washing, while it was only 11% without a cross-linker 5,11,12 .
Furthermore, our previous study revealed that acrylic acid is an effective cross-linker to develop a textile acquiring the antimicrobe and self-cleaning capability against methylene blue dye 4 .
In this present study, we used two crosslinkers including 1,2,3,4 buthane tetra carboxylic acid (BTCA) and chloroacetic acid (CAA) with two different coating methods by means direct and gradual coating, respectively.It aimed to enhance the self-cleaning capability against the dye spot of malachite green on a textile cotton fiber with a densely TiO 2 /Chitosan/SiO 2 coating.

Synthesis of TiO 2 /Chitosan/SiO 2 nano cluster
The powder of TiO 2 /Chitosan/SiO 2 nanocluster was synthesized using a sol-gel method with the titanium isopropoxide (TIP) and tetra ethyl ortho silicate as precursors.The sol solution consisted of A solution (TIP and DEA in isopropanol solvent; 1:2:2 in M) and B solution (TEOS and HCL 2 M in isopropanol; 1:2:2).The A and B solution Esrter covalent interaction was homogenized separately for 30 min. in RT.
The combination of A and B solution was prepared as a mixed sol with a composition of Ti and Si 3:2.Furthermore, the chitosan/acetic acid suspension (1:20) and CTAB (1:5) were added to the sol.The mixed sol was set at pH 10-11 and homogenized for 8 h followed by the heating at 110-120 o C or 15 h to produce a gel.The gel was then calcinated at 500 o C for 3 h to obtain the powder of TiO 2 /Chitosan/ SiO 2 nanocluster and subsequently morphologically characterized using XRD, UV-Vis DRS, and TEM.

Coating of textile cotton fiber
The textile cotton of size 64 m 2 was firstly washed using detergent 2 g/L and subsequently rinsed with aquadest and dried up at 80 o C for 5 min.Furthermore, it was dewaxed using Na 2 CO 3 0.01 g in 25 mL aquadest for 5 min.at 100 o C and rinsed with aquadest to adjust the pH 6-7, followed by heating at 80 o C for 5 minute.The textile cotton was directly soaked in 1 M BTCA cross-link for 12 hours.In another treatment, the textile was firstly soaked into 2 M NaOH for 30 min.then into 1 M CAA.After the treatment using BTCA and CAA, the textile was heated at 80 o C for 5 min.then coated using a suspension of 1% TiO 2 /Chitosan/SiO 2 by means dip-spin coating for 90 min.It was then dried up at 80 o C for 15 min.and subsequently analyzed using FT-IR, Photo Optics, XRD, and SEM-EDX.

Self-cleaning test of the textile cotton fiber
The self-cleaning test was carried out by observing the degradation of the malachite green dye spot on the coated cotton fiber under the UV irradiation (536 lux) in 0-2 h time window.The 4x4 cm textile dropped by 50 μL of 150 ppm malachite green was designated for a qualitative test, while the 1x1 cm textile soaked into 20 mL of 5 g/L malachite green was used for a quantitative test.The textile sample was observed in the darkroom for 30 min.and the absorption was subsequently noted as Ao.Furthermore, it was irradiated by UV light in 0-2 h then the absorption was noted as A. The dye degradation rate (Ef) was calculated by the formula as follow: The crystallite size could be modified by adding the dopant of SiO 2 and chitosan.The SiO 2 functions to form the pores and to extend the surface area 15,16 while the chitosan plays a role as a template of porosity during the condensation of the crystallite and enhances the SiO 2 dispersion on TiO 2 surface 16 .It has been demonstrated that when the TiO 2 and SiO 2 were composited, it could inhibit the structural transformation of anatase to rutile phase 15 .Moreover, we have previously reported that the distribution of crystallite size was affected by the sol and gel preparation process 18 .The sol preparation for 8 h and gel polycondensation for 15 h noticeably increased the distributional uniformity of crystallite size of TiO 2 /chitosan/SiO 2 nanocluster.The pattern of UV-DRS spectrum of TiO 2 /chitosan/SiO 2 (presented in Fig. 3, left panel was thenconverted using Plank equation [Eg = ] (Fig. 3, right panel) with Eg (band gap), h (Plank constant, 6.626 x 10 -34 J.s), c (light speed, 3 x 108 m.s -1 ) and (wavelength, in m).It wasrevealed that the maximum wavelength was 386.3 nm and the Eg was 3.209 eV.Hence, the photocatalytic reaction of the TiO 2 /Chitosan/SiO 2 could be induced by the UV light (= 385 nm) with the energy equals the Eg value 19 .
The TEM pattern (Fig. 4) illustrates the 3-dimensional feature of TiO 2 hybridized with SiO 2 and chitosan.It was found that the TiO 2 /Chitosan/ SiO 2 nanocluster has a spherical crystallite shapeand non-agglomerated structure.The SiO 2 and chitosan were amorph, and SiO 2 and TiO 2 formed a core-shell formation with the chitosan functioned as the crosslinker 20 .The TEM-derived picture, in consistent with the XRD spectral pattern,indicated that TiO 2 has the highest crystallite intensity at 2θ = 25.3 o in anatase phase.
different FT-IR spectrum as compared with BTCA cross-link.Interestingly, the absorbance intensity at 3400 cm -1 and 1529 cm -1 was also observed.The occurrance of the absorbance intensity at 3400 cm -1 might be resulted from the combination of carboxylic absorbance and alchoholic -OH stretchings's absorbance.The absorbance intensity at 1529 cm -1 was reported as an absorbance of the carboxylic ionic group 4 .The FT-IR analysis of the cotton fiber coated by TiO 2 /Chitosan/SiO 2 with two cross-linkers (CAA and BTCA) produced the FT-IR spectrum as presented in Fig. 5.The patterns ofthe spectrum indicated that the intensity difference was observed at 1710 cm -1 identified as the covalent ester formation's zone (C=O stretching) 21 .The CAA crosslink has a higher intensity than BTCA, suggesting that the gradual growing of ester group in CAA could enhance the thickness of TiO 2 /Chitosan/SiO 2 coating on the fiber by means the electrostatic interaction 8 .The FT-IR spectrum of the uncoated fiber (Fig. 5a) depicted its absorbance at cm -1 with the intensity 10.1%, while the coated fiber by CAA crosslink (Fig. 5b) indicated the shifted wave number to 1710.04 cm -1 and the increased intensity to 15.03%.Likewise, the coated fiber by BTCA cross-link (Fig. 5c) also demonstrated the shifted wave number to 1708.5 cm -1 and increased intensity to 12.4%.The shiftings of the wave number indicated the chemical esterification'sinteraction between the cellulose of cotton fiber and the carboxylic cross-link as illustrated in Figure 1.
The cotton fiber coated by TiO 2 /Chitosan/ SiO 2 nanocluster with a CAA cross-link depicted the

Morphological analysis using SEM-EDX
The morphological observation by using SEM suggested the difference in the features of cotton fiber treated with a CAA cross-link and BTCA cross-link (Fig. 6a-c).A cross-link plays a pivotal role in th formation of ester covalent interaction with the hydroxyl group of fiber, thereby the coating of the TiO 2 -SiO 2 nanocluster on the textile.Meanwhile, the chitosan in TiO 2 -SiO 2 provides the nitrogen base in order to enhance the amide covalent interaction and thereby trapping the TiO 2 -SiO 2 by means the electrostatic interaction 6 .The difference in the crosslink determines the distributional uniformity of the TiO 2 /Chitosan/SiO 2 nanoparticle on the textile fiber surface.It was found that in the CAA cross-linktreated fiber, the coating particles dispersed more evenly and densely on the surface of the textile as compared with the BTCA cross-link-treated fiber.
Chen et al., reported that cotton fiber coated by TiO 2 depicted the rough surface feature.The roughness of the surface affects the self-cleaning capability of the fiber 22 .The results of SEM analysis (Fig. 6) and the pattern of EDX (Fig. 7), taken together, suggested that the technique of the growing an ester covalent interaction on the fiber determines the amount of TiO 2 -SiO 2 coating, its distributional uniformity as well as the stability of the coating.Based on the EDX analysis, the composition of C, O, Ti and Si elements was equal to the composition of Ti and Si used as the precursors in the TiO 2 -SiO 2 synthesis (3:2 in M).The elements found in the cotton fiber coated by TiO 2 /Chitosan/SiO 2 with a BTCA cross-link consisted of C = 27.6%,O = 17.97%,Ti = 2.36 %, and Si 0.90 %.Otherwise, the elements in the fiber with a CAA cross-link composed of C = 50.73%, O = 38.64 %, Ti = 2.46 %, and Si 1.45%.

Self-cleaning test
The self-cleaning capability of the cotton fiber coated by TiO 2 /Chitosan/SiO 2 nanocluster against malachite green dye spot was evaluated both qualitatively and quantitatively.The qualitative test (Fig. 8) revealed that the cotton fiber coated by TiO 2 / Chitosan/SiO 2 with a CAA cross-link acquired the capability to degrade the malachite green dye spot five times stronger as compared with BTCA crosslink.This result is in accordance with the findings by FT-IR and SEM analysis demonstrating that the CAA cross link noticeably elevated the abundance of TiO 2 /Chitosan/SiO 2 on the textile fiber.The quantitative test for the self-cleaning capability of the cotton textile was conducted by measuring the absorbance of malachite green.The result (Fig. 9) indicated that the efficiency of self-cleaning capability was higher in CAA crosslink (95.59%) as compared with BTCA cross-link (69.96%) under the UV irradiation for 60 minutes.This finding is also in accordance with the previous result by means qualitative test showing the cotton fiber treated by CAA cross-link acquired a higher degradation capability against malachite green as compared with BTCA cross-link.

CONCLUSION
In this recent study, a self-cleaning textile cotton fiber coated by TiO 2 /Chitosan/SiO 2 nanocluster was successfully developed.The TiO 2 /Chitosan/SiO 2 morphologically depicted an anatase structure, with 13.1 mm of crystallite size and a band gap (Eg) = 3.20 eV.This particle acquired the self-cleaning capability against malachite green dye under the UV irradiation (l= 365 nm; 536 Lux).The increase of self-cleaning efficiency was determined by cross-link functionalization in consistent with the abundance of TiO 2 /Chitosan/SiO 2 coating on the cotton fiber.The gradual cross-link functionalization using CAA could highly optimize the self-cleaning efficiency (96.0%) as compared with BTCA (69.96%).The functional optimization of CAA was noticeably correlated with the morphological features revealed by SEM, XRD, and FT-IR analysis.

Fig. 8 .
Fig. 8. Degradation of malachite green dye spot after UV irradiation for 0-8 h on the cotton fiber with (a) uncoated and (b) coated by TiO 2 /chitosan/SiO 2 with BTCA cross link and (c) CAA cross-link

Fig. 9 .
Fig. 9.The relationship curve of between UV radiation time and degradation rate of malachite green (5.0 mg.L -1 ).