Microgranular cellulose (C6413) was obtained from Sigma-Aldrich (Germany), PET was obtained from Mitsubishi Chemical (Japan), Sodium Hydroxide was obtained from Merck (Singapore), Aluminium Isopropoxide and Heptane were obtained from Aldrich (Germany), Tetra-ethyl ortho-silicate (TEOS) was obtained from Fluka (Switzerland), methanol was obtained from Sigma (USA) and, 3-trimethoxysilylpropyl methacrylate was obtained from Degussa AG. All chemicals were used as obtained without any further purification/treatment.

1.2.1 Synthesis of Zeolite LTA

This zeolite was prepared by the procedure reported by Thompson et al^{[ 11]}. The source materials for silica and alumina chosen were different from the reported materials. First, sodium hydroxide (0.72 g) was dissolved in 80 mL of distilled water. This solution was divided into two parts.One part of the solution was added aluminium isopropoxide (4.13 g). The other part, 16 mL of TEOS was added. Then the two parts were poured simultaneously into a teflon container, resulting in the formation of a thick gel. This teflon container was sealed in an autoclave (hydrothermal bomb) and heated at (100±5)℃ for 4 h. After cooling, the precipitate was collected by filtration. The obtained white precipitate was washed with water thrice and dried to a constant weight in an oven at 80℃.

1.2.2 Synthesis of Mordenite

This zeolite was prepared by the procedure reported by Kim et al^{[ 21]}. The source materials for silica and alumina chosen were different from the reported materials. First, sodium hydroxide (3.33 g) was dissolved in 4 g distilled water. To this solution, we added aluminium isopropoxide (1.43 g). Further, 64.5 g distilled water was added to the solution followed by TEOS (9.8 g). The solution was transferred into a teflon container. This teflon container was sealed in an autoclave (hydrothermal bomb) and heated at (170±10)℃ for 24 h. The container was consecutively cooled and the precipitate was collected by filtration. The obtained white precipitate was washed with water thrice and dried to a constant weight in an oven at 80℃.

Figure 1 shows the SEM images of Mordenite and Zeolite LTA. Typical needle-shaped mordenite could not be obtained from this system and, most crystals formed as plates. Flat and prismatic crystals observed (Fig. 1(a)-(b)), indicate high concentration of silica gel^{[ 21]}. Sparsely distributed needle-shaped morphology for Zeolite LTA was observed, as shown in Fig. 1(c), a high population of flat/square shaped crystals were observed, which is in accordance to the reported literature^{[ 22]}.

Fig. 1

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	Fig. 1 SEM images of Mordenite (a, b) and Zeolite LTA(c, d)

The X-ray diffraction pattern (XRD) of synthesized Zeolite LTA and Mordenite are shown in Fig. 2. The XRD peaks match according to the reported literature. It is to be noted here that the observed XRD peaks for both materials are slightly broader in comparison with the reports, which may be attributed to the choice of different precursors as well as lower crystallization of the materials^{[ 21, 22]}.

Fig. 2

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	Fig. 2 XRD patterns for Zeolite LTA (a) and Mordenite (b)

1.2.3 Fabrication of cellulose:PET fibers

Cellulose:PET:TFA (trifluoro-acetic acid) were taken in 1:3:3 ratios. The solution was stirred at 1000 r/min for 24 h to completely dissolve the polymer and homogenize the solution. The solution was collected in a 10 mL capacity Benton-Dickenson clinical syringe. The electrospinning equipment NANON-01A purchased from MECC (Japan) was used for preparing the fibers. The applied voltage was 30 kV with a flow rate of polymer solution at 1 mL/h. The distance between the needle and collector was kept constant at 12 cm. A rotating drum at 300 r/min was used to ensure uniform deposition of fibers. The humidity was maintained at 50%-60% at all times.

1.2.4 Functionalization of Cellulose:PET fibers by catalysts

The catalysts (Zeolite LTA/Mordenite) (1.5wt%) were dispersed in methanol. This solution was sonicated in a probe sonicator (Vibra-Cell VCX 130 from Sonics, Switzerland) for 30 min with a Pulse On – 10 s, Pulse Off – 5 s, interval. After sonication, 0.05 g of surfactant (3-trimetho- xysilylpropyl methacrylate) was added to prevent agglomeration of the catalyst particles and sonicated for 1 min. This solution was electrosprayed at 12 kV on the cellulose/PET nanofibers.

In the electrospraying technique, small droplets or particles of submicron or nanometer sizes are formed due to the breakup of electrified jet at the capillary tip by the applied voltage. This technique has been successfully applied to deposit wide range of materials such as inorganic, biological, nanoparticles and nanomaterials on the other targets in literature. Recently, much effort has been directed on the deposition of nanoparticles over nanofibers to get the multifunctional membranes^{[ 23, 24, 25, 26, 27]}. To the best of our knowledge, the combinations of electrospraying techniques (to deposit zeolites) with electrospinning technique have not been explored so far in literature. The attachment of Zeolites with nanofibers will open up a new avenue for the exploration of these materials in various applications.

In the present study, coating of zeolite LTA and mordenite were carried out by electrospraying technique on the cellulose/PET nanofiber surfaces. Cellulose has been widely used for the preparation of semi permeable membranes, which own potential applications in the areas of ultra-filtration, dialysis, and reverse osmosis, catalysis, filtration, NEMS, nanocomposites, nanofibrous structures, tissue scaffolds, drug delivery systems, protective textiles, storage cells for hydrogen fuel cells, etc^{[ 28, 29, 30, 31]}. Cellulose possesses hydroxyl functional groups to attach these materials despite having low mechanical stability. In the case of PET membranes, they have excellent mechanical strength, but do not possess any functional groups. The blending of cellulose/PET might increase adhesion stability (by cellulose) and chemical stability (by PET). Thereby the developed composite materials will have enhanced properties. The SEM images of electrospun nanofibers were recorded (not presented here) and the average fibers diameter of the membranes was found to be (525±40) nm.

SEM images of the nanofibers containing Zeolite LTA and Mordenite are shown in Fig. 3(a), 3(b), 3(c), and 3(d), respectively. It has been observed that the morphology of the fibers is more uniform in diameter, smooth and cylindrical in shape. We noticed that some nanofibers were not covered by Zeolite LTA and Mordenite when the coating was carried out for 15 min (Fig. 3). However, when the coating time were increased to 60 min, fully covered nanofibers were obtained (not presented here). This indicates that changing the coating time can control the amount of catalysts coating.

Fig. 3

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	Fig. 3 Cellulose:PET fibers with electrosprayed mordenite (a, b) and cellulose:PET fibers with electrosprayed zeolite LTA (c, d)

Due to toxicity nature of actual nerve agent, we have used paraoxon, a nerve agent stimulant, which is identical in structure to VX. First, the absorbance of the as prepared paraoxon stock solution was noted, which showed an absorbance at 6.8 (not shown in Figure). The decrease in the UV absorbance of paraoxon solution was studied after 15 min and 1 h, when added to the prepared functionalized fibers. The observed decrease in the absorbance (Fig. 4) indicates that the catalyst containing nanofibers are effective in detoxifying the harmful organophosphorous agent.

Fig. 4

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	Fig. 4 UV absorption spectra indicating detoxification of paraoxon at λmax=268 nm