Reza Sacourbaravi ,Zeinab Ansari-Asl,,Esmaeil Darabpour

1 Department of Chemistry, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran

2 Department of Biology, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran

Keywords:ZIF-8 Polyacrylonitrile Composites Adsorption Waste treatment Antibacterial agent

ABSTRACT The efficient adsorption of radioactive iodine (129I and 131I) as nuclear waste is of great importance.Polymer nanocomposites consist of metal-organic frameworks(MOFs)developing for various pollutions sorption and separation have attracted much attention.This study reports the fabrication of magnetic polyacrylonitrile (PAN)/zeolitic imidazolate frameworks (ZIF-8) nanocomposites,PAN/ZIF-8(x%)/Fe3O4,x=30 and 50,as iodine capture adsorbents.The PAN/ZIF-8(x%)/Fe3O4 nanocomposite beads were fabricated via the phase inversion method,and their potential for iodine capture and separation in solution and vapor was investigated through UV-vis and weighing methods,respectively.Also,antibacterial activity of the as-prepared beads was assessed against E.coil and S.aureus.The as-fabricated compounds were studied by various techniques such as Fourier-transform infrared,X-ray diffraction,scanning electron microscope,energy-dispersive X-ray spectroscopy mapping,transmission electron microscope,N2 adsorption isotherm,and vibrating sample magnetometer.The iodine capture results showed that the efficiency of nanocomposites is remarkably higher than the pure PAN beads.Additionally,the asprepared nanocomposite adsorbents displayed higher capture capacities for iodine vapor (1524-4345 mg·g-1) than iodine solution (187-295 mg·g-1).The as-obtained magnetic nanocomposites can be successfully separated from polluted media by simple filtration or an external magnet,regenerated through washing with ethanol,and reused.Fast capturing,high sorption capacity,rapid separation,and good reusability make the PAN/ZIF-8(x%)/Fe3O4 nanocomposites highly effective adsorbents for the separation of iodine from wastewater.Additionally,PAN/ZIF-8(50%)/Fe3O4 bead can be considered as a potential new antibacterial agent for water and wastewater treatment.

1.Introduction

The production of some isotopes such as iodine (129I and131I),99Tc,and135Cs is considered the main issue for nuclear technology.Many types of research have been conducted on the successful adsorption of these by-products [1-3].The capture and storage of iodine,a long-lived byproduct,is highly needed to manage nuclear waste.To decrease the impact of these isotopes on health and the environment,various iodine disposal strategies were investigated.Adsorption by organic and inorganic matrices is attracted much attention because of its simplicity,convenience,and easy operation [4-6].Porous adsorbents including zeolites,aerogels,resins,and activated carbons are the most studied porous adsorbents that are used to remove iodine owing to their high sorption capacities and removal efficiency.Activated carbon is the most utilized adsorbent for capturing iodine from polluted wastewater.However,the application of this compound is limited due to its high cost [7-10].

Inorganic nanocomposites are one of the most common adsorbents for I2capturing.However,these materials exhibited low capture capacities,owing to their limited surface area.Recently,new sorbents based on metal-organic frameworks (MOFs) were reported as proper candidates for iodine capture [9,11,12].MOFs are a new class of porous hybrids synthesized of metal ions (or clusters) and organic linkers that contain nano/micro channels and pores.MOFs have been indicated to be potential for application in various fields such as biomedicine,separations,and catalysis [13-15].These structures have some advantages such as tunable pores compare to activated carbon and zeolites[16].Additionally,owing to the strong interaction between iodine (Lewis acid) and nitrogen-containing structures (Lewis base),many nitrogen-containing MOFs have been extensively investigated for capturing I2[17].These materials exhibited higher uptake capacities than other reported adsorbents.For example,El-Shahatet al.[18] have reported MIL-125-NH2@chitosan composite can adsorb iodine with a capacity of 399.68 mg·g-1at room temperature.In another research,a nitrogen-rich MOF,{[Mn2(oxdz)2(tpbn)(H2O)2]·2C2H5OH}n,with high iodine uptake capacity (1.1 g·g-1)was fabricated by Gogiaet al.[19].Nevertheless,the brittleness,poor water stability,and difficulty removal of the MOFs nanoparticles from the polluted mixtures after the adsorption process restrict their applicability.Therefore,dispersion of the MOFs into polymeric matrix and fabrication of their nanocomposites can be conducted for solving this problem [20-22].

Polyacrylonitrile (PAN),a promising synthetic polymer,is mainly investigated to fabricate new nanocomposites for various fields such as biomedicine,textile and automobile industries,and electronic applications.PAN and its composites have attracted tremendous attention owing to their unique features,including stiffness,lightweight,high strength [23-25].

The main objective of this study is to modify the PAN beads by zeolitic imidazolate frameworks (ZIF-8) and Fe3O4nanoparticles to enhance their potential as adsorbents for iodine.Structural characterization,iodine sorption efficiency,and magnetic separation of the as-prepared beads were investigated.Antibacterial activity of the as-obtained beads was also assessed againstE.coliandS.aureus.The as-prepared PAN/ZIF-8(x%)/Fe3O4composites owing to their large surface area are proper candidates for adsorption contaminants and after the sorption process,the adsorbents can be separated using a magnetic process.As expected,the PAN/ZIF-8(x%)/Fe3O4composites exhibited high sorption capacity,easy regeneration,and appropriate form to capture iodine in solution and vapor.This method of mixing ZIF-8 and Fe3O4with PAN can provide a new strategy to develop novel adsorbents for radioiodine.

2.Experimental

2.1.Materials and methods

Iron(II) chloride tetrahydrate,Iron(III) chloride hexahydrate,NaOH,polyacrylonitrile,2-methylimidazole,and Zn(II)nitrate hexahydrate were purchased from Merck company.Ethanol (EtOH),methanol (MeOH),cyclohexane,iodine,and dimethyl formaldehyde (DMF) were obtained from Sigma Aldrich.Fe3O4nanoparticles were synthesized using the reported literature method [26].The morphological investigation and energy-dispersive X-ray spectroscopy (EDS) analyses of the as-prepared materials was conducted by scanning electron microscope (SEM,MIRA3 and LEO 1455VP,TESCAN,Czech Republic) and transmission electron microscope (TEM,906E,LEO,Germany) microscope.UV-vis spectra were obtained using a V-730 UV-visible spectrophotometer(JASCO,Japan).X-ray diffraction (XRD) analyses were carried out using an X’Pert PRO instrument (PANalytical,Netherlands).A Fourier-transform infrared (FT-IR) spectrophotometer (Spectrum Two,PerkinElmer,USA) was used for investigation of the asfabricated materials’ chemical structures.The magnetic properties of composites were analyzed using a vibrating sample magnetometer (VSM,LBKFB) at room temperature.The porosity of the PAN/ZIF-8(50%) and PAN/ZIF-8(50%)/Fe3O4was studied by Brunner-Emmet-Teller (BET) technique,Belsorp mini II (Ankersmid,Netherlands).

2.2.Synthesis of ZIF-8 nanoparticles

ZIF-8 nanoparticles were synthesized using a modified synthesis method [27,28].1 ml of zinc nitrate in MeOH (1 mol·L-1) was mixed with a methanolic 2-methylimidazole solution (1 ml,4 mol·L-1).The mixture was magnetically stirred at room temperature for 2 h,then a solution containing 0.1 ml of Et3N and 1 ml of MeOH was added dropwise.After 4 h,the obtained white precipitate was centrifuged,washed with methanol,and dried at 60°C for 12 h.

2.3.Fabrication of PAN, PAN/ZIF-8(x%), PAN/ZIF-8(x%)/Fe3O4 beads

PAN,PAN/ZIF-8(30%),PAN/ZIF-8(50%),PAN/ZIF-8(50%)/Fe3O4,PAN/ZIF-8(50%)/Fe3O4beads were separately fabricated.PAN beads were prepared through the phase inversion method,in which drops of the PAN solution were added into a distilled water bath.To fabricate PAN beads,PAN solution (0.4 g of PAN was dissolved in 3 ml DMF) was placed in a glass burette and then added dropwise to a distilled water bath.Finally,the as-fabricated PAN beads were separated and dried at 50 °C in an oven for 24 h.

PAN/ZIF-8(x%) beads were obtained by the procedure mentioned above with the difference that at this step,different mass amounts of ZIF-8,30%and 50%,were also added into PAN solution.To the PAN solution,0.170 g or 0.4 g of dispersed ZIF-8 in 2 ml DMF was added and sonicated for 30 min.Afterward,the obtained mixture was added dropwise into a distilled water bath to fabricate the PAN/ZIF-8(30%) and PAN/ZIF-8(50%) beads.

In a similar procedure to the fabrication of pure PAN beads,the PAN/ZIF-8(30%)/Fe3O4beads were obtained as follows: 15 mg of Fe3O4and 170 mg of ZIF-8 nanoparticles were dispersed entirely into 2 ml of DMF by sonication for 1 h.Then,the obtained dispersion was added to PAN solution(0.4 g dissolved in 3 ml DMF),and stirred magnetically for 24 h.The resulted mixture was dropped in a distilled water bath through a burette.The solid PAN/ZIF-8(30%)/Fe3O4beads were prepared immediately by DMF/H2O exchange.The PAN/ZIF-8(30%)/Fe3O4beads were separated and dried at 50 °C for 24 h.

2.4.Iodine capture, release, and recyclability

Iodine adsorption studies were carried for iodine vapor and dissolved iodine in cyclohexane.For capture gaseous iodine studies,20 mg of adsorbent was exposed to iodine vapor in a sealed vial at 75 °C conditions.After different times (2,4,8,11,16,and 24 h),the iodine-adsorbed sample was weighed.The capture capacities were calculated using the bellow equation

whereQ(g·g-1) is iodine uptake capacity,m2andm1represent the mass of the adsorbent after and before iodine capture,respectively[29].

For iodine capture in the solution phase,50 mg of the pure PAN,PAN/ZIF-8(x%),or PAN/ZIF-8(x%)/Fe3O4beads were separately added in 5 ml of iodine solutions in cyclohexane (250,500,1000,1500,2000,and 2500 mg·L-1) and stirred.The adsorbent/iodine contact time was changed from 0 to 4 h for kinetic studies.The used beads were separated from the iodine solution using an external magnet,and the iodine concentration in the solution was determined using a UV-vis spectrophotometer.The sorption capacities were calculated using the following equation

where the sorption capacity (mg·g-1) represents byQt,the iodine concentration (mg·L-1) at initial time andtare given byCiandCt,respectively.W(g)is the mass of the adsorbent,andV(L)is the volume of solution [29].

Regeneration of the as-prepared adsorbents was conducted by immersing into ethanol.50 mg of the adsorbed iodine beads was added in the 5 ml EtOH and stirred magnetically.The iodine-free beads were separated,washed with EtOH,and dried.

2.5.Antibacterial activity test

The microorganism used in this study wasE.coliATCC 25922 andS.aureusATCC 6538.To investigate the antibacterial activity,a suspension ofE.colistrain with a turbidity equivalent to a McFarland standard of 0.5 (corresponding to 1.5 × 108CFU·ml-1) was prepared in 0.9% saline.Then,0.4 g of each nanocomposite bead was added to a test microtube containing the bacterial suspension.Following incubation at 37 °C with shaking (140 r·min-1) for 3 h,colonies were counted and colony forming units (CFU·ml-1) were calculated [30].

3.Results and Discussion

3.1.Preparation and characterization of PAN/ZIF-8(x%)/Fe3O4 composite beads

The fabrication of PAN/ZIF-8(x%)/Fe3O4beads was conducted by the phase inversion process shown in Fig.1.At first,the ZIF-8 nanoparticles and Fe3O4were synthesized separately,then mixed with PAN solution to fabricate PAN/ZIF-8(x%)/Fe3O4beads.Afterward,the adsorbents were exposed to iodine vapor or dispersed in cyclohexane iodine solutions to evaluate their iodine uptake capacities.After iodine capture,the sorbents were separated using an external magnet.The iodine captured samples were immersed in ethanol for recycling purposes.

Fig.1.The schematic fabrication method of PAN/ZIF-8(x%)/Fe3O4 beads.

The chemical structures of the as-fabricated materials were first studied using FT-IR spectroscopy (Fig.2).The FT-IR spectrum of PAN shows sharp bands around 2242 and 1247 cm-1corresponding to the C—N bonds stretching vibrations.Furthermore,the absorption bands at 2932,1383,and 1451 cm-1are ascribed to the-CH2vibrations.The characteristic peak for the C=C stretching appears at 1643 cm-1.The peak around 1733 cm-1is ascribed to the C=O vibrations due to the acids and esters monomers used for polymerization [31,32].For ZIF-8 spectra,the peak at 422 cm-1corresponds to the Zn—N absorption.The peaks around 693 and 759 cm-1are corresponded to the aromatic C—H sp2,bending.The peaks at 1147 and 1306 cm-1are ascribed to the C—N stretching vibrations [33,34].In the FT-IR spectrum of Fe3O4,the characteristic absorption bans at 585 and 1655 cm-1are related to the Fe—O stretching vibration and O—H bending stretching vibration,respectively [35-37].This observation confirms the presence of the PAN,ZIF-8,and Fe3O4in the asobtained PAN/ZIF-8(x%)/Fe3O4beads.

Fig.2.FT-IR spectra of PAN,ZIF-8,Fe3O4,PAN/ZIF-8(x%),and PAN/ZIF-8(x%)/Fe3O4 beads.

XRD patterns of the as-prepared PAN,PAN/ZIF-8(x%),and PAM/ZIF-8(x%)/Fe3O4beads are given in Fig.3.XRD pattern exhibits broad peaks for PAN at 16.37° and 27.65° that are assigned to the (100) and (110) planes,respectively,consistent with its amorphous nature[38,39].For ZIF-8,the diffraction peaks at 2θ=12.67°,14.17°,15.32°,18.32°,21.87°,23.52°,26.62°,and 28.22° are ascribed to the (112),(022),(013),(222),(114),(233),(134),and(044)crystallographic planes,respectively[40-42].In the XRD pattern of the Fe3O4,the presence of diffraction peaks at 2θ=30°,36°,43°,57°,and 63° that are corresponded to the (220),(311),(400),(511),and(440)crystalline planes,respectively,confirmed the successful preparation of the Fe3O4nanoparticles [43].The XRD patterns of PAN/ZIF-8(x%) and PAN/ZIF-8(x%)/Fe3O4beads exhibit peaks attributing to the ZIF-8,PAN,and Fe3O4.

Fig.3.XRD patterns of the PAN,ZIF-8,Fe3O4,PAN/ZIF-8(x%),and PAN/ZIF-8(x%)/Fe3O4 beads.

The SEM images of the PAN/ZIF-8(30%),PAN/ZIF-8(30%)/Fe3O4,PAN/ZIF-8(50%),and PAN/ZIF-8(50%)/Fe3O4beads show identical porous morphology(Fig.4),that is good characteristic for an adsorbent.The high porosity and homogeneous attachment of ZIF-8 and Fe3O4into the PAN matrix can be confirmed by the TEM image of the PAN/ZIF-8(30%)/Fe3O4(Fig.5).

Fig.4.SEM images of(a,b)PAN/ZIF-8(30%),and(c,d)PAN/ZIF-8(30%)/Fe3O4 beads,and (e,f) PAN/ZIF-8(50%) beads,and (g,h) PAN/ZIF-8(50%)/Fe3O4 beads.

Fig.5.TEM image of the PAN/ZIF-8(30%)/Fe3O4.

The Zn and Fe elemental EDS analysis was also conducted on the beads,and the obtained results confirmed the distribution of Fe3O4and also ZIF-8 into the PAN matrix.The Zn and Fe elemental mapping of the PAN/ZIF-8(50%)/Fe3O4beads are given in Fig.6.

Fig.6.Zn and Fe elemental mapping of the PAN/ZIF-8(50%)/Fe3O4 beads.

The magnetic characteristics of the as-prepared sample were investigated using a VSM (Fig.7) at room temperature.The VSM hysteresis loop for PAN/ZIF-8(30%)/Fe3O4and PAN/ZIF-8(50%)/Fe3O4nanocomposites confirmed that the as-prepared composites exhibited superparamagnetic characteristics at ambient conditions.The saturation magnetization was found 1.65 emu·g-1(1 emu·g-1=1 A·m2·kg-1) for PAN/ZIF-8(30%)/Fe3O4that is higher than the PAN/ZIF-8(50%)/Fe3O4(1 emu·g-1).

Fig.7.VSM plots for PAN/ZIF-8(30%)/Fe3O4 and PAN/ZIF-8(50%)/Fe3O4.(1 emu·g-1=1 A·m2·kg-1,1 Oe=80 A·m-1).

The porous structure assessment of PAN/ZIF-8(50%) and PAN/ZIF-8(50%)/Fe3O4beads was investigated by nitrogen adsorption-desorption at -196 °C (Fig.8).It showed steep nitrogen absorption in the low-pressure range (P/P0=0-0.05) and an obvious hysteresis in the high-pressure range.The corresponding data calculated from the BET analysis,including BET surface area,pore volume,and average pore size,are given in Table 1.The BET surface areas were 13.069 and 217.27 mg2·g-1for PAN/ZIF-8(50%) and PAN/ZIF-8(50%)/Fe3O4,respectively.Adding the Fe3O4nanoparticles improved the surface area of composites.As presented in Fig.8,it is obvious that PAN/ZIF-8(50%) and PAN/ZIF-8(50%)/Fe3O4beads exhibited type-II and type III isotherms,confirming their nonporous structure.

Table 1 BET results of the PAN/ZIF-8(50%) and PAN/ZIF-8(50%)/Fe3O4

Fig.8.Nitrogen adsorption and desorption isotherm of PAN/ZIF-8(50%) and PAN/ZIF-8(50%)/Fe3O4.

To study the aqueous stability of ZIF-8,the as-prepared sample was immersed in distilled water for 1,3,and 7 days.The samples were separated,dried,and analyzed using FT-IR spectrometer.The FT-IR spectra of the soaked samples (Fig.9) were identical to the as-synthesized ZIF-8,confirming that ZIF-8 possesses a proper stability in the aqueous media.Therefore,this property make ZIF-8 an outstanding candidate for removing aquatic contaminants from polluted water.To confirm the iodine sorption property of the asprepared PAN/ZIF-8(50%)/Fe3O4,iodine EDS mapping (Fig.10)was conducted after I2uptake.

Fig.9.FT-IR spectra of ZIF-8 after immersing in distilled water for 1,3,and 7 days.

Fig.10.EDS-mapping of I in (a) vapor and (b) liquid phase for the as-prepared PAN/ZIF-8(50%)/Fe3O4.

3.2.Capture and release of iodine

3.2.1.Iodine vapor capture

The iodine vapor uptake capacities of the as-prepared beads are given in Fig.11.The PAN,PAN/ZIF-8(30%),PAN/ZIF-8(30%)/Fe3O4,PAN/ZIF-8(50%),and PAN/ZIF-8(50%)/Fe3O4have exhibited the capacity around 160,1872,1524,4345,and 3606 mg·g-1respectively,which were superior to some reported adsorbents.These capacities are comparable with the highest reported values for some adsorbents(Table 2);such a proper uptake ability can correspond to the porosity and affinity of the ZIF-8 toward iodine,and also the presence of the nitrogen-containing organic linkers[19,56,57].The iodine vapor uptake capacity of the pure PAN was low,which proved that the adsorption of iodine by the asfabricated composites was related to the ZIF-8 incorporated into the PAN matrix.

Table 2 The iodine vapor adsorption capacities of the as-fabricated samples compare to some reported adsorbents

Fig.11.Iodine vapor uptake capacities of the as-prepared samples (inset:photographs of color changing of the PAN/ZIF-8(50%) after iodine vapor capture).

3.2.2.Iodine capture in solution

The obtained nanocomposites exhibit proper chemical stability,which enables their utilization and recyclability for iodine uptake under ambient conditions.Iodine adsorption investigations were carried out through immersing the PAN,PAN/ZIF-8(x%),or PAN/ZIF-8(x%)/Fe3O4beads to iodine solution in cyclohexane using UV-vis spectroscopy [58].Iodine in the cyclohexane shows the absorption band around 530 nm.As can be seen in Fig.12,the uptake of iodine by the as-prepared adsorbents caused to decrease in iodine amount.In agreement with these results,a color change from white to brown was observed for the as-fabricated adsorbents after their iodine capturing,owing to the iodine diffusion to the pores and surface of the adsorbents (Fig.13).

Fig.12.The UV-vis spectra and color change of iodine solution (1500 mg·L-1) by (a) the PAN/ZIF-8(30%) and (b) the PAN/ZIF-8(50%).

Fig.13.The color change of the as-fabricated adsorbents (a) before iodine adsorption,(b) after adsorption of iodine solution,and (c) after iodine vapor capture.

The equilibrium capacities of the PAN,PAN/ZIF-8(x%),and PAN/ZIF-8(x%)/Fe3O4beads for iodine uptake in the solution phase(1500 mg·L-1) were given in Fig.14.The PAN,PAN/ZIF-8(30%),PAN/ZIF-8(30%)/Fe3O4,PAN/ZIF-8(50%),and PAN/ZIF-8(50%)/Fe3O4beads exhibited the maximum iodine capture capacities around 85,230,187,295,and 270 mg·g-1,respectively.As can be seen,the iodine capture capacity of PAN/ZIF-8(x%) and PAN/ZIF-8(x%)/Fe3O4beads increases with increasing the ZIF-8 into the PAN matrix.According to these results,it can be seen that the PAN/ZIF-8(50%) exhibited the maximum iodine uptake capacity(295 mg·g-1).

Fig.14.The iodine uptake isotherms by the as-fabricated adsorbents under different concentrations of iodine in cyclohexane.

3.2.3.Iodine adsorption isotherm

The iodine adsorption isotherm of the PAN/ZIF-8(x%) and PAN/ZIF-8(x%)/Fe3O4beads was studied using iodine solutions at room temperature.50 mg of the adsorbents was added into 5 ml of iodine with different initial concentrations (250,500,1000,1500,2000,and 2500 mg·L-1).UV-vis spectroscopy was used to determine the iodine concentration after the adsorption process at different intervals.To determine the iodine adsorption mechanism of the as-fabricated beads,the obtained data were fitted to the Temkin,Langmuir,and Freundlich models [59,60].The obtained parameters for these models are tabulated in Table 3.According to these parameters,the Langmuir isotherm withR2=0.976-0.996 was considered as the iodine capturing mechanism for all of the as-prepared adsorbents.The iodine monolayer adsorption process is also can be concluded by these results[61].Furthermore,fitting of the experimental data of iodine adsorption by the PAN/ZIF-8(50%)and PAN/ZIF-8(50%)/Fe3O4with the Langmuir and Freundlich models is given in Fig.15.

Table 3 Parameters of the isotherm models for the as-prepared adsorbents

Fig.15.Langmuir and Freundlich models of the iodine capture by the PAN/ZIF-8(50%) and PAN/ZIF-8(50%)/Fe3O4.

3.2.4.Iodine adsorption kinetics studies

An essential factor of a proper adsorbent for practical application is its kinetic information.The kinetics studies of iodine adsorption in cyclohexane (1500 mg·L-1) by the PAN/ZIF-8(x%)and PAN/ZIF-8(x%)/Fe3O4beads were conducted using a UV-vis spectrophotometer at room temperature.The kinetic of iodine adsorption was investigated using the PFO (pseudo-first-order),PSO (pseudo-second-order),and intra-particle models by the following equations:

where the mass of adsorbed iodine (mg) per amount of adsorbent(g) at equilibrium and timetis represented byqe(mg·g-1) andqt(mg·g-1),respectively,and equilibrium rate constants are given byk1(min-1) andk2(g·mg-1·min-1) [62,63].The intra-particle infiltration model is the function oft0.5which expressed using the following equation [64].

where,Candkpare calculated from intercept and slope values ofqt vs t0.5.

The obtained parameters of the intra-particle,PFO,and PSO models were given in Table 4.The obtainedR2values for the asfabricated adsorbents (0.997-0.999) suggested the PSO kinetic model for iodine uptake that describes the chemical adsorption(chemisorption) process.Similar results have been reported for iodine adsorption by some porous adsorbents [65,66].Furthermore,fitting of the experimental data of iodine adsorption by the PAN/ZIF-8(50%) and PAN/ZIF-8(50%)/Fe3O4with PFO and PSO kinetic models is given in Fig.16.

Table 4 The obtained parameters of kinetic models for the iodine adsorption process

Fig.16.PFO and PSO kinetics of the PAN/ZIF-8(50%) and PAN/ZIF-8(50%)/Fe3O4 for capturing iodine (1500 mg·L-1).

Fig.17.Antibacterial activity of PAN/ZIF-8(x%) and PAN/ZIF-8(x%)/Fe3O4 beads against E.coli.

Fig.18.Antibacterial activity of PAN/ZIF-8(x%) and PAN/ZIF-8(x%)/Fe3O4 beads against S.aureus.

3.3.Antibacterial assay

The viability ofE.coliandS.aureuscells after treatment with the PAN,PAN/ZIF-8(x%) and PAN/ZIF-8(x%)/Fe3O4beads are shown in Figs.17 and 18.The pure PAN bead did not cause any reduction in the number of viableE.coliandS.aureuscells,whereas the PAN/ZIF-8(x%) and PAN/ZIF-8(x%)/Fe3O4beads caused a significant reduction in viable count of the tested strains (＞4 CFU·ml-1).Also,the results indicated that there was no significant difference in the antibacterial activity between the PAN/ZIF-8(x%) and PAN/ZIF-8(x%)/Fe3O4beads.Based on the results,the antibacterial activity of these beads againstE.coliandS.aureusis depended on the concentration of ZIF-8.The Zinc-based MOFs exhibit attractive antibacterial effects due to the release of Zn2+ions,which have good antimicrobial activity against various bacteria [67].The asprepared magnetic beads presented bactericidal activity againstE.coliandS.aureuswithin 3 h,suggesting their potential application for the fast and efficient treatment of water and wastewater treatment [68-70].

3.4.Reusability study

Reversible iodine adsorption by adsorbents is essential for their applications,and therefore,recyclability of the PAN/ZIF-8(50%)beads was also investigated [71].Iodine release was conductedby immersing the iodine-captured adsorbents in EtOH.The supernatant that showed different colors,from colorless to brown owing to iodine release,was investigated by UV-vis spectroscopy.UV-vis spectrum of the supernatant exhibited two absorption peaks at 295 and 365 nm (Fig.19) indicate the existence of iodine anions.The captured iodine was released from adsorbents in the 80 min of immersing the adsorbents in EtOH.The PAN/ZIF-8(50%) exhibited a useful ability to desorption captured iodine (100%) suitable for adsorption recyclability.Additionally,the PAN/ZIF-8(50%)didn’t exhibit a significant decrease capture activity after five runs(Fig.20).

Fig.19.UV/vis absorption spectra of the iodine released from the loaded PAN/ZIF-8(50%) in 5 ml of EtOH.

Fig.20.Reusability of the PAN/ZIF-8(50%) for capturing iodine (250 mg·L-1).

4.Conclusions

Porous and magnetic adsorbents are considered efficient adsorbents because of their potential to eliminate inorganic and organic pollutants with considerable efficiencies and their facile separation using an external magnet.Nitrogen-rich nanocomposites,the PAN/ZIF-8(x%) and PAN/ZIF-8(x%)/Fe3O4beads were fabricated through the phase inversion method.The as-fabricated materials were characterized by FT-IR,XRD,SEM,TEM,VSM,BET,and EDSmapping techniques.This study investigated the utilization of the PAN/ZIF-8(x%) and PAN/ZIF-8(x%)Fe3O4beads as iodine adsorbents.In iodine sorption studies,the PAN/ZIF-8(50%) beads exhibited the highest capacities,around 295 and 4345 mg·g-1for solution and vapor phase,respectively.Furthermore,the kinetic data exhibited well-fitting with the PSO model,and the isotherm parameters fit better to the Langmuir model.The PAN/ZIF-8(x%)and PAN/ZIF-8(x%)/Fe3O4beads adsorbents could be reused for five cycles while maintaining 100% iodine capture capacity.Moreover,the PAN/ZIF-8(x%)/Fe3O4beads have both heterogeneous and magnetic properties that result in their simple separation.Also,PAN/ZIF-8(50%)/Fe3O4bead can be used as a potential novel antibacterial agent for water and wastewater treatment.

CRediT Authorship Contribution Statement

Reza Sacourbaravi:Conceptualization,Methodology,Formal analysis,Investigation,Resources,Visualization.Zeinab Ansari-Asl:Writing-original draft,Conceptualization,Methodology,Formal analysis,Investigation,Resources.Esmaeil Darabpour:Conceptualization,Methodology,Formal analysis,Investigation,Writing -original draft.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors gratefully acknowledge financial support (SCU.SC1400.29011) from the Shahid Chamran University of Ahvaz.