ABSORPTION PROPERTY OF POLYAMIDE NANOFIBROUS MEMBRANE ON DYESTUFF FOR PURIFYING WASTEWATER. Yan WANG, Jacob WIENER, Guocheng ZHU

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1 SORPTION PROPERTY OF POLYMIDE NNOFIROUS MEMRNE ON DYESTUFF FOR PURIFYING WSTEWTER Yan WNG, Jacob WIENER, Guocheng ZHU Technical University of Liberec, Studentska 2, , Liberec, Czech Republic, bstract The aim of this study was to examine the use of polyamide 6 nanofibers as an adsorbent material for removal of dye on textile wastewater. Simulated wastewater of acid dye (namely Color Index cid blue 41) was used for experiment test with concentration of 0.01, 0.02 and 0.03g/L. Two kinds of electrospun polyamide 6 nanofibrous membranes with weight per unit area respectively 1.0 and 2.9g/m 2 were used as the adsorbent material and the dead-end filtration process was performed continuously by self-assembled apparatus with starting flux around 2500L/(m 2 h). The experiments were realized in room temperature. The result of Fourier transform infrared spectroscopy (FTIR) indicated that these two kinds of nanofibrous membranes are the same without any other surface modification, while the scanning electron microscope (SEM) images showed the diameter of nanofibers are respectively around 126 and 178nm. The adsorption results showed the adsorbed amount of adsorbate is related to the specific surface area of the adsorbent as the amount was higher with the larger specific surface area. The concentration of adsorbate has a little effect on the adsorption result due to the fouling of the adsorbent and the interaction between adsorbate themselves. The fouling of the adsorbent was becoming much severer as the concentration of adsorbate increasing, and this trend was more obvious on the adsorbent with larger specific surface area. Keywords: Dead-end filtration; Polyamide nanofibers; Wastewater; Dye removal; Fouling 1. INTRODUCTION The dyestuff released from textile industry in water streams results in a serious environmental impact, many of the dyes cause health problems such as allergic dermatitis, cancer, skin irritation and also mutation in humans. In addition, dyes absorb sunlight within water media resulting in the prevention of photosynthesis of aquatic plants [1-4]. Elimination of very small dust particles, bacteria and viruses from the ambient air and drinking water is becoming increasingly relevant in the present world and is connected with a growing number of respiratory tract diseases in industrial agglomerations and with a threat of various pandemics[5]. esides, many dyestuffs are difficult to be decolorized and decomposed biologically due to complex structure and synthetic origin of dyestuff, which are acidic, basic, disperse, azo, diazo, anthroquinone based, and metal complex dyes[6]. On the other hand, wastewater reuse has become increasingly important in water resource management for both environmental and economic reasons. Nowadays variety of methods is invested into wastewater processing such as application of membrane technologies, ozonization, chlorination, and UV light[7]. Fibrous materials are important for filtration due to which fibrous materials possess good flexibility, compressibility and permeability. Low throughputs from the membrane based filtration processes drive material scientists to explore highly porous media with finer fibers[8]. Polyamide 6 nanofibrous membrane can be used to absorb small particles containing in the wastewater since it has comparatively high specific surface area with normal scale fibrous membranes. This, together with its low density and interconnected open pore structure, make it appropriate for the filtration applications. In this work, dead-end filtration method was applied to study the filtration efficiency which reflects the sorption property of the polyamide 6 nanofibrous membrane as well. ssembled continual filtration

2 equipment was used for the filtration process. The concentration of every 10ml filtrated wastewater was detected, and the flux change was recorded. 2. MTERILS ND METHOD 2.1 Nanofibrous membrane Two kinds of electrospun polyamide 6 nanofibrous membranes with weight per unit area respectively 1.0 and 2.9g/m 2 were purchased and used as the adsorbent material. FTIR result below indicated these two kinds of nanofibrous membranes are original polyamide 6 without any other surface modification. Reflectance 2.9g/m2 nanofiber membrane 1.0g/m2 nanofiber membrane Wave number (cm-1) Fig. 1 dsorbent we have used in our experiments: a) Molecular formula of Polyamide 6 and b) FTIR results of two different membranes. 2.2 Dyestuff Simulated wastewater of acid dye (namely Color Index cid blue 41) showed in Fig. 2 was used for experiment test with concentration of 0.01, 0.02 and 0.03g/L. The molecular Formula is C23H18N3NaO6S and the molecular Weight is [9] Fig. 2 Molecular structure of cid blue 41.[9] 2.3 Dead-end filtration apparatus The assembled apparatus for dead-end filtration shown in fig. 3 was used in this study. This apparatus mainly included a pump whose flow rate can be adjusted from 0 to 60ml/min under the standard

3 configuration, and a connection device which used for fixing filter between pipes without air leaking. The filter was used to support filter membrane. 2.4 UV spectrophotometer Fig. 3 Continual filtration apparatus used in this study. Thermo Scientific Helios Epsilon UV-Visible Spectrophotometer and 1cm 1cm curvettes were used to test the concentration of the acid dye solution during all the experiments. The absorbances of three concentrations (0.01, 0.02, 0.03g/L) were plotted in below figure with R 2 linear fitting. 0.3 bsorbance Concentration (g/l) Fig. 4 Linear fitting of absorbanes versus three concentrations of solution cid lue Method SEM images of two nanofibrous membranes were taken for checking the diameter of fibers and calculating the specific surface area of the membranes. The continual filtration was performed with the apparatus showed in fig. 3 with starting flux around 2500L/(m 2 h). The concectration after filtration were examed every 10ml, and the time taken by every 10ml filtration was recorded meanwhile. The accumulated mass of dyes absorbed by the membrane and the flux during the filtration were calculated in this study. 3. EXPERIMENT ND RESULTS 3.1 Specific surface area calculation

4 Fig. 5 Images of nanofibrous membranes surface: a) membrane surface image with weight per unit area 1.9g/m 2 ; b) membrane surface image with weight per unit area 1.0g/m 2. From the surface images we can obtain the diameter of the fibers in each membrane. 5 times each were measured and the average value was calculated as 126 and 178nm respectively. The specific surface area of these two nanofibers membranes were calculated using following equation under the assumption that the membrane is only a single fiber whose length is L. 2 r L 2 r L 2 S 2 (1) m r L r s the r=63 and 89nm respectively, the density of P6 is around 1.14g/cm 3, the specific surface area (S) are 20m 2 /g for 2.9g/m 2 weight per unit area and 28m 2 /g for 1.0g/m Effect of specific surface area of the membrane Fig. 6 shows the effect of specific surface area on the filtration property and the fouling phenomenon. With the 0.02g/L concentration, the filtration was performed on two membranes with different specific surface area. The accumulated mass of dye absorbed by membranes according to the filtration volume has been plotted as shown in the fig. 6(a) which shows a dramatic difference between two filtration processes. oth mass of dye per mass of fiber was increasing along with the filtration process, and got the equilibrium after around 200ml simulated wastewater filtrated. 280 and 126mg/g are the maximum mass of dye absorbed by the membrane with specific surface area of 28 and 20m 2 /g. The flux reduced along with the filtration process until nearly 1000L/(m 2 h) and the values of flux for the higher specific surface area membrane was always lower than the other which is shown in fig. 6(b). dsorption capacity (mg/g) m 2 /g 20m 2 /g Flux (L/(m2*h)) m 2 /g 20m 2 /g Fig. 6 ccumulated mass per mass of fibrous membrane and flux changing during the filtration with wastewater concentration 0.02g/L: a) adsorption capacity of membranes versus filtrated volume; b) flux versus filtrated volume.

5 Higher specific surface area creates more surface area of fibers for absorbing dyestuff which caused much higher adsorbed mass of dye. Due to the quick increasing of the dye absorption, the flux reduced more at the beginning of the filtration process. 3.3 Effect of concentration of the wastewater ccording to the filtration result showed by fig. 7, the accumulated masses absorbed by the membrane were around 0.06mg after 300ml filtration with lower concentration and nearly 0.08mg with 0.03g/L concentration. 94% reduction of flux with wastewater concentration 0.03g/L was detected while 47% and 14% reduction were found with 0.02 and 0.01g/L concentration ccumulated mass (mg) g/L 0.02g/L 0.01g/L Flux (L/(m2*h)) g/L 0.02g/L 0.01g/L Fig. 7 ccumulated mass and flux changing during the filtration by membrane with 1.0g/m 2 weight per unit area: a) accumulated mass versus filtrated volume; b) flux versus filtrated volume. The accumulated mass absorbed by the fibrous membrane increased slightly with the concentration increasing while a dramatic flux reduction showed especially for the highest concentration of the simulated wastewater. 4. CONCLUSIONS The nanofibrous membranes were characterized by FTIR and SEM images. FTIR result showed the materials are polyamide 6 and SEM images showed the diameter of the nanofibers. The specific surface area was calculated by through the diameter and the density of the material under an assumption. Filtration process was performed with two nanofibrous membranes with different specific surface area and three different concentration simulated wastewater of cid lue 41. The filtration result showed membrane with higher specific surface area can absorb over two times dyestuff amount under the same condition. The higher concentration of simulated wastewater caused much severer fouling problem during the filtration process. CKNOWLEDGEMENTS The authors acknowledge the kindly help from Prof. Jiri Militky and the financial support of Department of Material Engineering, Technical University of Liberec.

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