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Today water source pollution is one of the serious problems. Among different kinds of contamination, we can mention heavy metals, radioactive compounds, organic and nano organic compounds. Heavy metals have a significant importance in environment pollution because they can't be analyzed, and have harmful physiological effects on living creatures (1) Copper (II) is one of the important elements for plants and animals; But large amount of it is toxic for all living creatures. Most hazardous human activities like mining, metal melting, domestic and industrial sewage ooze applications in agricultural lands, using copper as a fungicide pesticide cause soil and water pollution to copper. High levels of this metal effect on ecosystem microbial population. Removal of heavy metal ions from water and industrial sewage is very important and has drawn attention of most of researchers (2-4). Nowadays, because of industries improvement and entering waste water of industrial factories to ecosystem, environment and underground water, the pollution risk is developed which has harmful effects on living creatures, soil, also plants and animals of these regions in long and short terms (5-7). Heavy metals are the most common contaminations that are found in high concentration and cause irreparable harms to ecology. Mechanism of toxic effects of heavy metals like copper from bio chemistry prospective is strong tendency of cations of these metals to reaction with sulfur (8-10). Heavy metals which are copper, chrome, cadmium, nickel and zinc have tendency to be gathered in food chain (11-12). Cations of these metals or those molecules which have these metals enter into the body by ingestion and they will attach to Solfhydryl groups which there are plenty of them in body (13). Sulfuric bonds joint effects on those enzymes which control metabolism reaction speed in body; so, these enzymes can't do their normal works and put human health in risk of illnesses that sometimes it is fatal (14-15). Illnesses which are caused by heavy metals like copper are dermatitis, Asthma, Bronchitis and in some sources it is mentioned copper cause cancer. Spreading heavy metals to the environment is happened by different processes and ways such as air, surface water, soil, underground water and plants. When copper is absorbed by mud, it can go a long way and contaminates the surface water and soil. Different ways are used for omission of heavy metal ions from water solution which are ion alternation, reverse osmosis, electro chemical sediment, ion replacement, membranes processes, evaporation and absorption for ion omission of heavy metals from water solution (16-18). Among mentioned methods in recent years, absorption method is important because it is a simple, cheap and an effective way for heavy metals ion omission. Nano fiber is used in this study because of high absorption efficiency, special level and active places. In this research, analytical method for solid phase was used for separating copper cation and measuring was done by flame atomic absorption which has effective factors for efficiency extraction such as pH effect, adsorption supply, cleaning solution type and concentration. Samples' size were checked and optimized by flame atomic absorption spectrometry. Interference effects of other ions and analysis parameters, kinetic and thermodynamic were computed. This method was used effectively for actual samples such as natural water (19).
Aims of the study:
The aim of this research is using electrospun polymer nano fiber coated with ligand for copper ion omission from water solution and industrial wastewater.
 

Materials & Methods

In this study which is an experimental one, absorption rate from industrial waste water was investigated, using polymeric nano fiber absorbent. For preparing mother solution, 1000ppm copper cation from salt Cu(NO₃)₂.3H₂O was used and other necessary. Solution was produced by repeated dilution of primary solution with deionized distilled water. Also, solution of 1000 mgL^-1 used ions in harassment investigation phase were prepared by solving sufficient copper salt in deionized distilled water. Acetate buffer was prepared by Neutralization of hydrogen chloride by sodium hydroxide to reach pH=7. Polystyrene and dithizone complexing agent was prepared by references. Other used solution like Aceton, Tetrahydrofuran, Dimethylformamide, and acids such as nitric acid, acetic acid, sulfuric acid, phosphoric acid which had sufficient analytical purity and all of the mentioned materials were bought in Merck Co. Equipment's which were used in this study were optical microscope, SEM, Electrospinning, device made in Iran for polystyrene fiber production, Flame atomic absorption spectrometer made by Shimadzu, AA-680 model. For measuring copper cation concentration which were used in parameter optimization stage, peristaltic pumps LAMBDACZs.r.o was used for sample solution passing from column containing the adsorbent. For measuring solution pH, pH meter device Lab -827, equipped with compound glass electrode, was used. Ultra sonic bath VGT-173OQTD was used for homogenization.
For preparing absorbent, first pour 500mg polystyrene in a test tube and add Dimethyl formamide and Tetrahydrofuran compound to Polystyrene completely dissolve. Finally, it had obtained viscose solution (20). The final solution was kept in 25c' temperature for three hours. Then, for more homogenization, the final solution was put in Ultrasonic bath for 15 min in 20 degrees Celsius. Then, 30 mg Dithizone was added to the produced solution for complete reaction between polymer and ligand modifier was put in Ultrasonic bath in 20c' for 30 min. We inject the final solution to electrospun machine and nano fiber was obtained in an optimal condition. Obtained nano fiber diameter was investigated by light and electron microscope, see findings in figure1. Polystyrene formation mechanism is shown in figure 2.
 

 

Figure 1) Electron microscope picture of produced nano fiber (a) light microscope picture of nano fiber (b).
 

Figure2) The mechanism of polystyrene formation.
 

In order to optimization of effective factors on absorption before doing this absorbent process, first should recognize effective factors on absorbent then optimize them. For this purpose, pH amount effect, absorbent supply, salt concentration effect, contact time effect was determined for each test. Thus, determined amount of produced nano fiber was put into a micro tube by 5 ml ethanol and deionized distilled water was passed for absorbent compression. Then, prepared solution contains copper with o.2 mg ml-1 concentration passed through pump after that cleaning was done completely. Taken sample was investigated by Flame atomic Absorption spectrophotometer. Four effective parameters for copper absorption were investigated. In way which in each test, three parameters are fixed and one parameter is variable. Thus, it can investigate the effect of variable parameter on copper cation absorption.
 
 

Results

pH effect
One important parameter in absorption is primary solution pH. The results of pH effect on copper ion absorption are shown in figure 3. By increasing solution pH from 3 to 7, mentioned ion omission increase. So, PH=3 has the lowest absorption and pH=7 has the highest absorption. According to findings, we could mention that, by increasing pH to optimum amount, absorption amount increase. The reason can be explained that, in pHs lower than optimized pH because of ligand protonation and complex tendency deduction with ion, ion absorption and recovery rate decrease. In pHs upper than optimized PH, the percent of recovery decrease because of metal hydroxides formation.

Figure3) pH effect on copper absorption
 
Effect of modified nano fiber
Solid phase column filler is an important parameter and its optimization is necessary. The effect of modified nano fiber absorbent on copper ion absorption was investigated. By increasing absorbent rate, available absorption places for copper increase and absorption was done better. To determine the effect of absorbent rate on copper omission, absorbent rate was determined in 0.002 to 0.01. According to figure 4, by increasing the  absorbent rate to optimized level, the absorption rate increase that results confirm that by increasing absorbent rate to optimized level because abound of rate level, the number of active places for complexion of copper ion increase; thus, increase the absorption process, when absorbents rate reach to it's maximum  performance of 0.006 gr/l, the number of active places and absorbent surface are responsive for copper ion numbers in solution in equilibrium adsorption process. Increasing the absorbent rate to optimized level cause the contact time increase which increase ion absorption percent.

Figure 4) absorbent effect on absorption rate
 
Investigation of salt concentration:
Salt increase has different effects on adsorption efficiency. Maybe, improved adsorption, decrease it or be effect less (20,21). Figure 5 shows the decomposition response changes according to concentration response of potassium nitrate in 0.1 to 2 gr range of this salt. As it can be seen in figure 5, increasing salt concentration to 1.3 gr, increase efficiency extraction, after that extraction decrease. Maybe decomposition response deducted because of that, after a determined concentration of salt, physical properties of extraction layer will change and analyte adsorption rate decrease.

Figure 5) Salt concentration effect on absorption rate.
 
Investigation of contact time effect
The investigation of the contact time is shown in figure 6 that copper ion absorption by modified absorbent has higher velocity, so, 16 percent absorption in 1 min and 62 percent in 60min was seen. According to findings, absorption velocity in first 10 min is higher than other times and after 60 min, desorption take place. It could be related to high sample surface area and abound of active agent groups for copper ion complexion. Absorbent selectivity for heavy metal absorption is related to metal properties. Some properties such as metal ionic radium, atomic weight, electronegativity, fixed hydrolysis and softness are effective on up take efficiency and when they increase, up take efficiency rate increase.

Figure 6) contact time effect on absorption rate
The type and volume of solvent
Absorbing solvent should be able to absorb analytes from absorption level. It doesn’t have damaging effects on species structures. By suitable cleaning of inhibited analytes from column, we can determine repeatability and accuracy of the method. To select the best of washer, 5mL analyte solution, 10ppm copper concentration, 0.006 absorbent rate in pH=7 was passed in column, then absorbed ion cleaning was investigated by 0.5 mL ethanol, methanol and Acetonitrile. According to figure7, findings showed, by methanol as a cleaning solvent, we will reach to the highest rate of absorption. So, methanol solution has higher ability to clean analyte. Recovery level deduction of copper ion with other cleaning solution can contribute to deposit copper ions with existing anionic foundation in structure of these solutions.

Figure 7) copper ion adsorption changes, based on solvent volume variations

Figure 8) Copper ions adsorption changes based on solvent type variation
 
Determine method detection limit
The lowest concentration from sample that the answer of machine is meaningfully different from control signal is the limit of detection. For determining the detection limit (DL), control solution the adsorbent under optimized
 condition and suggested. Solution was investigated by Atomic absorption spectrometry; so, the limit of detection was 2.70 mg/l.
Investigation of repeatability and accuracy of method
Accuracy shows the repeatability rate of method which is shown by relative standard deviation or RSP which is a function of sample concentration. For studying repeatability of method, 8 solutions of 50 ml with 0.2 μgmL^-1 concentration from copper cation were recycled, using solid phase extraction method. Standard deviation was 1.7.
Measurement of copper cation in real samples
For measuring the ability of suggested method to assess heavy metals in water samples with different tissues, this method was used for isolating and measuring of copper ions from different water under optimized condition. To investigate the accuracy of method and it's suitability, standard additional method was used. The extraction and recovery of cation cu²⁺ take place. The result of method accuracy in real sample is seen in table1. As the results showed, samples tissue has a meaningful effect copper cation extraction and the suggested method has a good performance for copper cation extraction from different tissues.

Table 1) copper absorption in real samples

RSD	Recovered (%)	Absorption	Cu2+ (μgL-1)	Piped water
---	---	Not seen	0	Arak
0.60	97.14	97.14±0.01	100
0.80	99.15	198.3±0.01	200
---	---	Not seen	0	Ashtian
1.70	95.16	95.16±0.03	100
2.20	97.13	194.27±0.04	200
---	---	Not seen	0	Farmahin
0.99	96.80	96.8±0.2	100
0.39	96.40	95.16±0.02	200