Potential Military Cotton Textiles by Carbon Quantum Dots

Owing to the sensitivity for color vicissitude by exposing to UV irradiation, manufacturing of uorescent fabrics is widely demanded to be exploited in camping, sensing and military purposes. Pyrimidine based heterocycles were investigated with excellent pharmacological activity, however, their photoluminescence activity was never been investigated till now. The presented approach demonstrate a quite novel route for manufacturing of potential military textiles (uorescent/UV-protective cotton fabrics with micobicide activity) via exploitation of carbon quantum dots (CQDs) nucleated from pyrimidine based heterocycle (4-(2,4-dichlorophenyl)-6-oxo-2-thioxohexahydropyrimidine-5-carbonitrile, Target Molecule, TM). The synthesized TM & CQDs were separately immobilized within both of native and cationized cotton fabrics to obtain TM@cotton, CQDs@cotton, TM@Q-cotton and CQDs@Q-cotton fabrics. The estimated yellowness index, intensity of the uorescence peak, UV-blocking activity and microbicide action, were all followed the order of CQDs@Q-cotton > TM@Q-cotton > CQDs@cotton > TM @cotton. CQDs@Q-cotton showed quite good durability, as after 5 washings, yellowness index was diminished from 26.5 to only 20.3, orescence intensity for CQDs@Q-cotton was decreased from 540 nm to 340 nm and transmission percent was increased from 7 % to 10 %. Moreover, even after 10 washings, microbial inhibition (as a percent) against E. coli, Staphylococcus aureus and Candida albicans was estimated to 63 %, 68 % and 67 %, respectively, while, UV protection factor (UPF) was diminished from 38.2 (very good) to 21.5 (good). The presented unique route was succeeded for manufacturing of durable uorescent textiles that could be superiorly applied as potential military textiles.


Introduction
Military clothes are the rst layer to the soldiers for their protection against combat and environmental hazard effects in military missions. Harsh military terrain extensively exerts harmful effects on the physiological and physical performance of some soldiers to cause hazard health problems. Numerous approaches were world widely reported and proceeded within the military/defense researching laboratories in co-operation with industries for manufacturing of technical textiles by incorporation of suitable smart nishing agents for the alleviation of the dangerous effects associated with combat terrains (Perego et al. 2012; Sahin et al. 2005). For manufacturing of military textiles, fabrics must be characterized by, comfortability, easy cared, and easy to be cleaned. Washing durability (Tao et al. 2017) and sterilization or disinfection should be also considered. It could be newly innovative for working towards weaving cotton fabrics with photoluminescence activities, where it acts in transmitting a color to the user's own uniform, identifying the suspected soldier from the same army, while, the absence of a transmitted color would instantly identify enemy.
Numerous reports were considered with acquirement of textiles with additional functions such like color (Emam and  the development in functionalization of military textiles like tents with enhanced thermal stability, re resistance, water repellent and anti-insects properties is extremely active topic of research. Additionally for protective masks, air-ltration materials for protection against highly toxic gases, that is, chemical warfare agents, is mainly based on the broad and effective adsorptive properties of functionalizing agents such like, the hydrophobic activated carbons (Li et al. 2011b).
According to literature, few reports were considered with the exploitation of some organic compounds for imparting additional functions for textiles such like triclosan for bactericidal activities, benzophenones for ultraviolet (UV) blocking, dimethylol dihydroxy ethylene urea for acquirement of anti-creasing property, uorocarbons for hydrophobic capability, long-chain hydrocarbons and polydimethylsiloxanes for textile softening, etc (Almeida 2006; Hewson 1994). Additionally, citric acid, butane tetra-carboxylic acid, and maleic acid (Yang et al. 1998;Welch 1988;Yang et al. 2010) are applied for imparting anti-creasing property to cotton fabric. On the other hand, pyrimidine compounds were differently studied for their successful applicability in various purposes owing to their excellent pharmacological activity (Abuelela et al. 2016). However, according to our knowledge, few researching reports were considered with their application in textile functionalization.
Carbon quantum dots (CQDs) as spherical nanoparticles with particle size of 1-10 nm were ascribed with advantageous characteristics such as high temperature resistance, outstanding electrical /thermal conductivity, high plasticity, corrosion-resistant, UV-blocking, and high adsorption rate as well as catalytic performance (Dasgupta et al. 2016;Kien Nguyen et al. 2016). CQDs as graphite sheets are composed of sp 2 carbon atoms formed in planes, while, each carbon atom is mainly bound to three nearest neighbors with 120 degrees apart. The implantation of oxygen, sulfur and nitrogen functional groups that could be introduced on sides of graphite sheet is hypothesized to overcome the inter-sheet van der Waals forces that subsequently resulted in enlargement of the interlayered spacing (Sakthivel and Drillet 2018;Delhaes 2000). Few reports were considered with synthesis of CQDs and their applications in various purposes such as battery, fuel cell, super-capacitor, transistor, biosensor..etc.. (Pierson 1993;Wissler 2006;Zhang et al. 2006;). However, according to literature, there is no reports that were investigated the superiority of pyrimidine based heterocyclic compounds as synthesizers for CQDs.
Herein, a new innovative methodology is represented for manufacturing of military textiles. The presented study is concerned with preparation of new uorescent aromatic compound named as 4-(2,4dichlorophenyl)-6-oxo-2-thioxohexahydropyrimidine-5-carbonitrile (target molecule, TM) that in turn exploited for synthesis of carbon quantum dots (CQDs). Sequentially, both of TM & CQDs were successively exploited for preparation of durable cotton fabrics as orescent/antimicrobial /UV-protective fabrics, while, the prepared fabrics was evaluated to be functionalized as potential military textile materials. The synthesized TM & CQDs were rstly synthesized and their chemical formulas were a rmed by FT-IR, 1 HNMR and 13 CNMR spectral mapping data. The synthesized TM&CQDs were immobilized within native and cationized cotton fabrics. Afterwards, the modi ed fabrics were characterized by infrared spectroscopy, scanning electron microscopy, colorimetric measurements, orescence sensitivity, microbicide potency and UV-protective action. The durability of the acquired uorescent, antimicrobial and UV-protective characters for modi ed cotton fabrics was followed up for number of repetitive washings up to 10 cycles. Carbon quantum dots (CQDs) were synthesized from the synthesized TM via hydrothermal technique as follows; 2 g of TM was dissolved in 100 mL DMF and the liquor was transferred to vertical hydrothermal autoclave reactor and then left in oven at 210 ℃ for 6 hr. The reaction liquor with dark brown color was kept to be cooled at room temperature then dialyzed with DMF by using pur-A-lyzer dialysis kits (MWCO 6-8 kDa from Sigma-Aldrich) for 24 hr to obtain highly puri ed/monodispersed/pure CQDs, ready for further analyses.

Cationization of cotton fabrics
Cationization of cotton fabric was carried out via interaction with quaternary ammonium salt [(3-Chloro-2hydroxypropyl) Trimethyl ammonium chloride] in two steps that could be illustrated as follows; in the rst step that could be ascribed as activation step, cotton fabric was activated using sodium hydroxide, while, in 250 mL Erlenmeyer ask, 2 g of cotton fabric was soaked in 100 mL of distilled H 2 O containing (0.49 g, 12.3 mmol) sodium hydroxide, and then shacked for 2 hr at room temperature. Afterwards, the fabric was removed and washed with distilled H 2 O to eliminate excess of sodium hydroxide. The activated fabric was dried in vacuum oven at 60 °C prior to analysis and application.
In the second step that could be identi ed as cationization step, activated fabric (2 g) was immersed in 50 mL from 60 % of 3-Chloro-2-hydroxypropyl) Trimethyl ammonium chloride. The reaction mixture was shacked in a water bath at 50 ºC for 2 hr. The treated fabric was ltered, washed with distilled water and then dried in vacuum oven at 60 °C and labeled as Q-cotton. Absorption spectra for TM and the generated CQDs were manifested at 250-750 nm using a spectrophotometer (Cary 100 UV-VIS, UV-Vis-NIR Systems, from Agilent). Topographical structures and size average of the synthesized CQDs were estimated by anticipating of High Resolution Transmission Electron Microscope from Japan (JEOL-JEM-1200). The size average of CQDs were evaluated by 4 pi analysis software (from USA) for 50 particles at least. Infrared spectra was obtained by Jasco FT/IR 6100 spectrometer, while, the absorbance spectral data were detected at 500 -4000 cm -1 using 15 points smoothing, 4 cm -1 resolution, 64 scanning times with scanning rate of 2 mm.sec -1 . The spectral mapping data of nuclear magnetic resonance ( 1 H-NMR and 13 C-NMR) were obtained by Jeol-Ex-300 NMR spectrometer (JEOL -Japan). Photoluminescence for the prepared CQDs in ultraviolet-visible range were followed up by spectro-uorometer (JASCO FP8300). The data were estimated at room temperature with excitation at 340 nm.
Material contents in terms of nitrogen content (N%) of the TM & CQDs applied onto cotton fabrics before and after washing cycles were evaluated were measrured according to Kjeldahl method (Emam et al. 2018b). Mixture (a) was preliminary prepared by mixing in powder form of (10 g) CuSO 4 , (90 g) K 2 SO 4 and (1 g) selenium. Indicator was prepared by dissolving both of methyl red (0.125 g) and methylene blue (0.083 g) separately in 50 mL absolute alcohol and subsequently mixed together with equal volumes. Afterwards, solution (b) was prepared by addition of the indicator to 4% boric acid (25 mL). In brief, speci c weight of the samples (100 -150 mg) were digested completely with 1 g of mixture (a) in 10 mL of sulfuric acid via mental heater until cololrelss solution is obtained. Flask content was trasnfered carefully to the Kjeldahl apparatus and then sodium hydroxide solution (0.1 N) was added till violet color was observed. The vapour was received in ask containing solution (b) and then titrated with hydrochloric acid (0.05 N) until the color was changed to violet color. The contents of nitrogen were evaluated as percentage by identifying the titrated volume, then the concentration of HCl and normalized to the weight of sample.
The treated fabrics were investigated under high resolution scanning electron microscope (HRSEM Quanta FEG 250 with eld emission gun, FEI Company -Netherlands). The elemental analysis was also estimated from the energy dispersive X-ray analyzer (EDAX AME-TEK analyzer). The infrared spectra for the modi ed fabrics (CQDs@cotton and CQDs@Q-cotton) were measured by using Jasco FT/IR 6100 spectrometer. The absorbance spectra were ranged in 4000 -400 cm -1 using 4 cm -1 resolution and 64 scanning times with rate of 2 mm/sec.

Optical properties
The digital photos for TM and CQDs were carefully captured inside the box of UV lamp (output 4 W and input 220 V AC). Photos of samples were taken upon excitation at 325 nm by cell phone camera of Oppo A31 model.
The absorbance spectra for TM and CQDs were measured using FLAME-S-UV-VIS spectrometer from USA. Fluorescence were also monitored by Jasco FP-6500 spectro-uorometer (150 W Xenon lamp, with concave holographic grating (1800 grooves/mm emission monochromator and coupled with a second photomultiplier) from Japan. The samples were excited at wavelength of 360 nm and the emission spectra were then detected at room temperature.

Transmission and Ultraviolet Radiation Blocking
Ultra-violet radiation (UVR) transmission spectral results (T %) over native and cationized cotton before and after successive uploading of the prepared TM&CQDs were measured by using JASCO V-750 spectrophotometer from Japan in range of 280−400 nm with 2 nm interval. In addition to, UV protection factor (UPF), blocking in UV- Additionally, the disk diffusion test (inhibition zone technique) was also performed for evaluation of the microbicide effeceincy of the prepared samples. The different tested bacterial strains were grown in the media for preparation of pathogenic suspension.100 μL of bacterial suspension was spreaded onto agar plates corresponding to the broth in which it was maintained. A 10 μL of the tested compounds was placed on the middle of plates and then incubated at 37 °C for 24h. The diameters of the inhibition zones were evaluated in millimeters using slipping calipers according to NCCLS, 1997 (CLSI 2012). In MIC determination, serial dilutions from the tested solutions (0-1000 μL/mL) were prepared and then added to the plates. After incubation at 37 °C for 24 h, the colony forming units (CFU) were counted for each dilution ; CLSI 2012).

Washing durability
Washing durability of the modi ed fabrics was monitored via the repetitive washing cycles up to ve cycles. Washing was carried out according to the AATCC standard method for the home laundry test (AATCC 2010). Washing procedure was performed by using a mixture of 2 g/L of sodium carbonate and

Synthesis of TM
The reaction mechanism for synthesis of TM could be brie y illustrated as in the presence of sodium ethoxide, active carbanion is supposed to be produced within reaction mixture from ethyl cyanoacetate ( Figure 1). Afterwards, nucleophilic addition reaction on carbonyl group of 2,4-dichlorobenzaldehyde with the produced carbanion was subsequently proceeded to give the rst synthetic equivalent (1). Lastly, interaction between thiourea and synthetic equivalent (1) resulted in cyclization with elimination of water and ethanol to produce the desirable TM (2).
The structural formula of the prepared TM was con rmed via different spectral mapping data (IR, 1 HNMR and 13 CNMR) and the data were presented in Figure 2. The represented data showed that, IR spectrum

Synthesis of CQDs
Clustering of CQDs was successively performed via hydrothermal technique from the synthesized TM ( Figure 1). According to literature, the mechanism for synthesis of CQDs could be postulated as follows: the prepared TM is supposed to be hydrolyzed and fragmented under the hydrothermal conditions. Consequently, polymerization, aromatization and afterwards oxidation were proceeded to give aromatic graphite sheets decorated with nitrogen, sulfur and nitrogen containing functional groups, for generation of size and shape regulatable CQDs The topographical features and geometrical shape of TM and CQDs were presented in the micrographs of Transmission Electron Microscope (TEM) from which their size distribution was estimated and plotted. The micrographs showed that, the synthesized CQDs were homogenously/well dispersed and controllably clustered in the reaction medium with quite smaller size rather than TM. TM detected with mean size of 544.6 nm, while, CQDs exhibited quite smaller mean size of 6.5 nm. This could be explained as, under strong alkaline conditions, the hydrothermal technique successively resulted in fragmentation of TM, polymerization and aromatization of the liberated fragments to generate controllably sized CQDs. These could approve the compatibility of the synthesized TM in generation of CQDs under hydrothermal conditions (Figure 3 b & c).

SEM & EDX
The morphological features for the surface of the treated native and cationized cotton fabrics were investigated and plotted in Figure 6. For native cotton, cationized cotton, TM@cotton, CQDs@cotton, TM@Q-cotton and CQDs@Q-cotton, SEM images, EDX signals and elemental analysis were presented. Before treatment with the prepared TM & CQDs, the surface of fabrics was seemed to be smooth, and the characteristic peaks of C & O were only detected native in case of native cotton, while, cationized fabric was characterized with C, O & N bands (Fig.6 a & b). After modi cation, the particles of TM & CQDs were observably distributed on the surface of cotton. For all the modi ed fabrics, EDX analysis showed the four characteristic signals of C, O, N, S & Cl elements, which a rmed the immobilization of the applied TM & CQDs onto the treated fabrics. However, dense masses of the prepared TM & CQDs were observed in case of cationized fabrics rather than the native ones, attributing to the higher accessibility of fabrics with cationization. Moreover, CQDs@Q-cotton were observed with more dense masses on the surface rather than TM@Q-cotton, due to the higher opportunities of entrapping more amounts of smaller sized CQDs rather than TM, that in-turn a rmed the above-postulated mechanism.

FTIR
The unmodi ed and modi ed cotton fabrics were characterized by FTIR as presented in Figure 7. The Material contents & Color data Table 1 represented the nitrogen contents estimated for TM & CQDs, in addition to native and cationized fabrics before and after uploading of the prepared TM & CQDs. Moreover, the effect of washing on the estimated values of material contents was followed up for all the treated sample. The data showed that, material contents was signi cantly higher in case of cationized fabrics rather than native ones, in addition to, fabrics treated with CQDs exhibited higher material contents rather than that treated with TM. From the evaluated data, CQDs@Q-cotton showed the highest material content percent of 7.56 %, while, after ten repetitive washings, the material content percent was diminished to 4.92 %, to give more a rmation for higher accessibility of fabrics with cationization in more e cient preservation of the uploaded CQDs. The color data for the modi ed fabrics were presented in Table 2 & Figure S1 in supplementary le. From the estimated data, the cotton fabrics were acquired yellowish color after modi cation owing to the yellow color of TM. YI (yellowness index) was extremely higher in case cationized cotton compared cotton fabrics. In addition to, fabrics modi ed with CQDs exhibited higher yellowness degree rather than that modi ed with TM. The modi cation of cationized cotton fabric with CQDs showed the highest yellowness index and lowest whiteness index. The strength of yellow color was ordered as follows; CQDs@Q-cotton > TM@Q-cotton > Q-cotton > CQDs@cotton > TM@cotton > cotton.   The excited CQDs uniquely showed with greatly higher intensed peak at more than 1000 nm, that could be attributed to extensive higher aromatic character of CQDs with their decorative substituents which extensively shared in extension of conjugation resulted signi cantly observable jumping in their uorescence intentsity. Figure 8b, represented the uorescence intensity for cotton and cationized cotton after modi cation with both of TM & CQDs. The spectral data a rmed that, uorescence intensity was corresponding to the following order; CQDs@Qcotton > CQDs@cotton > TM@Q-cotton > TM @cotton. Meanwhile, cationization of cotton fabrics resulted in higher a nity for successive impregnation of CQDs in greater quantities within cotton matrix, leading to CQDs@Q-cotton extinesively exhibit the highest uorescence intensity (560 nm) corresponding to yellow emission.
In textile industrialization, washing durability is highly demanded to be acquired and hence it must be well-considered in the current approach. The uorescence spectra were measured for the modi ed cotton fabrics after 5 and 10 washing cycles, while the data were shown in Figure 8c & d. The uorescence spectra similar to that of the unwashed fabrics, while, the uorescence intensity was observably decreased with washing due to leaching out the applied uorescent active TM & CQDs. Increment in the number of washing cycles logically resulted in further diminishing in the uorescence intensity of the modi ed fabrics. However, even after 10 washing cycles the modi ed fabrics still exhibited uorescent character with good washing fastness with sequential laundry. highly actively uorescent textiles with substantial washing fastness rather than that previously reported in literature which were interested in preparation of photoluminescent textiles.

UV-protection
Transmission percent (T %) as a key factor for monitoring the ultraviolet blocking capability for all tested specimens was estimated and plotted in Figure 9. It could be clearly observed that, T% was greatly diminished for all the tested fabrics by modi cation with both of TM & CQDs compared to the untreated specimens. Unmodi ed cotton fabric showed the highest transmission percent (60 % at 400 nm).
Diminishing in T% was much higher in cationized cotton, owing to its inter-composition with greater amounts of TM & CQDs. The results showed that, T% was decreased from 15% for cationized cotton to 6% and 5% for TM@Q-cotton and CQDs@Q-cotton, respectively. After 5 washing cycles, T% was insigni cantly increased to 40% for CQDs@cotton. With cationization of fabric, the uploaded CQDs were more retained against washings, as T% was increased un-sensibly up to 10% for CQDs@Q-cotton. So it could be depicted that, cationization is superiorly affected in more stably and stronger interaction of CQDs with fabric building blocks. features. For all tested fabrics, UV protection in B-region was relevantly lower than that in A-region. Ultraviolet protection factor (UPF) was detected from T% results (Table 3), and it was 1.3 and 8.1 for native cotton and cationized cotton fabrics, whereas it was estimated to increase up to 5.2, 5.5, 29.4 and 38.2 for TM@cotton, CQDs@cotton, TM@Q-cotton and CQDs@Q-cotton, respectively. Referring to materials contents (Table 1), the highest UPF value was estimated for CQDs@Q-cotton to a rm the prior cationization effect in more e cient uploading and higher amounts of CQDs within fabric matrix. In addition to approving the higher compatibility of CQDs for re ecting more radiation rather than TM.
Moreover, after washing, UPF values were diminished for the cationized fabrics after ten cycles, as it was lowered from 38.2 to 21.5 for CQDs@Q-cotton that re ected the washing durability of the prepared samples, to give more con rmation for the effect of cationization in stronger and more e cient immobilization of CQDs within fabric polymeric blocks.
From the above-illustrated results it could be mentioned that, comparing with other reports for preparation of UV-protective cotton via direct deposition of metals on cotton fabrics, UV protection properties for CQDs@Q-cotton was considerably higher, regardless to the metal type (Ag, Au, Zn, Cu or Ti) ( Table 4 Table 5 represented the antimicrobial potentiality of the unmodi ed and modi ed fabrics, before and after 5 & 10 washing cycles. From the evaluated results, it could be depicted that, the synthesized TM & CQDs showed to acquire the cotton fabrics superior antimicrobial activity. CQDs@Q-cotton showed to exhibit the highest antimicrobial performance, with inhibition percentage of 71.0 ± 1.1 %, 82.0 ± 1.0 % and 62.0 ± 0.9 % against E. coli, S. aureus and C. albicans, respectively, relating to the effect of cotton cationization in increment of the immobilization a nity for CQDs, CQDs@Q-cotton. Moreover, by monitoring the washing durability of the modi ed fabrics for their antimicrobial performance, the tabulated data revealed that, even after 10 washing cycles, CQDs@Q-cotton fabric still exhibited good microbicide potency, whereas, microbial inhibition percent was evaluated to be 55.0 ± 0.9%, 61.0 ± 1.1% and 32.0 ± 0.6% against the tested microbes.

Conclusion
In the current approach, uorescent 4-(2,4-dichlorophenyl)-6-oxo-2-thioxohexahydropyrimidine-5carbonitrile (Target Molecule, TM) was newly synthesized and exploited in nucleation of carbon quentum dots (CQDs). The strucutral formulas for both TM & CQDs were a rmed by IR and NMR spectral analyses. The synthesized TM & CQDs were uploaded onto native and cationized cotton fabrics and the modi ed fabrics were characterized by yellowish color. Under UV lamp at 325 nm, all of the modi ed fabrics were exhibited green emission. After excitation at 440 nm, the modi ed cationized fabrics were showed an intense emission peak at 540 nm by modi cation with CQDs. The yellowness degree, uorescence intensity, UV-protection and microbicide actions were followed the order of CQDs@Q-cotton > TM@Q-cotton > CQDs@cotton > TM@cotton. Durability for all prepared samples were monitored for the washing for 10 repetitive washing cycles, while CQDs@Q-cotton showed to superior retaining for the acquired orescent sensitivity, UV-protection and antimicrobial actions with good durability which was explained by the effect of cotton cationization in stronger and stably immobilization of the applied CQDs within fabric matrix.
The current work opened unique/novel challenge in the textile industry to obtain durable photoluminescent/UV-protective textiles with excellent microbicide activity by using the prepared CQDs. Moreover, the synthesized CQDs could also be promising for several purposes such as smart labeling, anti-counterfeiting, sensors/biosensors, bio-imaging and tissue engineering.

Declarations
Compliance with ethical standards: The authors declare that they have no competing nancial interest Con ict of interest: There is no con ict of interest Ethical approval: Not applicable