Removal of Chromium ( VI ) cation metal using Poly ( N-vinyl-2-pyrrolidone ) / Magnetite nanocomposite from aqueous media

5886 | P a g e F e b r u a r y 2 0 1 7 w w w . c i r w o r l d . c o m Removal of Chromium (VI) cation metal using Poly (N-vinyl-2pyrrolidone)/Magnetite nanocomposite from aqueous media Padmalaya G, Sreeja BS, Radha S, Raamdheep G, Saranya J Department of Electronics and Communication Engineering, SSN College of Engineering, Kalavakkam-603110, India. padmalayag@ssn.edu.in , sreejabs@ssn.edu.in Center for Green Technology, Pondicherry University, Kalapet, Pondicherry-605014, India. raamdheep@gmail.com Department of Electronics and Communication Engineering, Rajalakshmi College of Engineering, Thandalam, Chennai-602105, India. saranyaj@rajalakshmi.edu.in ABSTRACT


INTRODUCTION
Due to rapid increase in industrialization different contaminants are released into environment and pollute ground water.The presence of toxic trace metals like lead (Pb), chromium (Cr), mercury (Hg), Zinc (Zn) and cadmium (Cd) in the ground water have high toxicity and non-degradable properties which can cause severe health hazards to animals and human society.Chromium is one of the most common trace metal found in ground water particularly in industrialized areas.Chromium exists in +II, +III, and +VI states, among these states +VI state is considered to be most toxic and acts as carcinogens, mutagens, and teratogens due to its strong oxidizing properties [1][2][3][4][5].Removal of chromium ions is carried out using methods like chemical precipitation, ion-exchange, membrane filtration/ultrafiltration, solvent extraction, sedimentation, reduction, reverse osmosis, dialysis/electrodialysis and adsorption [6][7][8][9].Among these techniques, adsorption is most popular due to its controlled mechanism, increased ion removal rate, higher regeneration capacity and cost effectiveness [10][11].Activated carbon is the widely used material to remove metal ions.However activated carbon tends to be expensive material and also requires complexing agents to increase removal efficiency.Therefore it is necessary to find alternative adsorbents which are capable of having high metal binding capacities and removal effectiveness at low cost.Compared to traditional adsorbents nanostructured adsorbents exhibited higher efficiency and adsorption capacity at faster rates in ground water treatment.Nano-adsorbents should satisfy few criterions like should be non-toxic, selectivity to low concentration pollutants, easy removal of pollutants and infinitely recycled.Magnetite Nanoadsorbents have attracted researchers due to its multifunctional properties such as super paramagnetic, recyclability, easy processing and low toxicity.Magnetite nanoparticles (MNP) oxidize easily and form aggregates due to dipole-dipole interaction.The stability of the MNP is enhanced by tailoring the surface using natural or synthetic stabilizers like surfactants and polymers with functional groups.The synergistic properties of magnetite nanocomposite containing organic-inorganic materials improve additional properties that cannot be achieved in either single organic or individual inorganic components [17].Research is being carried out in enhancing the trace metal removal efficiency of magnetite nanocomposite using polymers [12][13].Polymers like polypyrrole (PPy), polyaniline (PANI), Chitosan, montmorillonite were incorporated with magnetite nanoparticles are found to be high efficient adsorbent in removal of Cr (VI) ions [18,[22][23]6].These polymers form environmental friendly and are easy to prepare which provides functionalized media for the enhanced removal of chromium ions.Fe NPs are coated with well-defined SiO2 shells were used as suitable adsorbent for removal of chromium ions [2].Magnetite nanoparticles were modified with amorphous FeB alloy and used as efficient adsorbents for chromium removal [19].Surface modification of magnetite nanoparticles with ionic ligands like trimethoxysilane and hydrophilic compounds PEI were also used as good adsorbents for removal of Cr (VI) ions [20][21].Herein we report the novel experimental results that interaction of PVP on magnetite nanoparticles provides 94% of efficiency towards the removal of Cr (VI) ions which was not reported before and it has been achieved with different concentration levels of PVP/Magnetite nanocomposite in aqueous media and analyzed using UVis-Spectroscopy.As poly (N-vinyl-2-pyrrolidone) is a polar polymer, due to its carbonyl group of double group in the pyrrolidone group.It has the active carbonyl or tertiary nitrogen group.It was reported [24] PVP has three compounds (O, N, and carbonyl) that take part in interaction with magnetite nanoparticles.We made comparative study [Table 1] with other nanocomposites efficiency on removing chromium ions.

Material synthesis:
Magnetite nanoparticles were synthesized using Chemical Co-Precipitation technique.Fig ( ) shows the schematics on preparation of magnetite nanoparticles.In this technique, precursors of ferric chloride and ferrous sulphate were taken in the ratio of (2:1) and stirred well for 20mins.With the continuous stirring, 10% of Ammonium Hydroxide (NH4OH) was added in drop wise and black precipitate is formed indicating the formation of magnetite nanoparticles.Formed Magnetite nanoparticles were collected using decanted with magnet and washed three times with double distilled water (ddH2O).In order to form hybrid nanocomposite, 0.5% PVP was added along with magnetite nanoparticles and stirred for 1hour and made into powder form by drying in hot air oven at 80°C.The final product in the powder form was used for further analysis.

Adsorption of Cr
6+ ions were performed in batch mode with desired concentration of PVP/magnetite nanocomposite.The studies were performed by shaking predetermined adsorbents in 50mL of metal ion solution containing desired concentration of adsorbents (0~1.5g/L)The efficiency in removal of heavy metal using PVP and PVPmagnetite nanocomposites were evaluated using UV-visible spectroscopy.The removal efficiency is calculated using the equ (1).

E= (Co -Ce /Co)/100 -----(1)
Where Co is the initial Cr (VI) concentration of the Solution and Ce represents the remaining Cr (VI) existing in solution after the adsorption process.

S.No. Materials used
-1 confirms the C-N stretching vibration and C=O stretching vibration of PVP, respectively [17].The narrow absorption peak centered at 1285 and 686 cm -1 were occurred due to the C-N bonding and Fe-O vibrations [21] of PVP and magnetite nanoparticles attributed to coordinate bond between nitrogen-carbon atoms of PVP and Fe-O ions.As a consequence, the FTIR qualitatively confirms the formation of PVP-Magnetite nanocomposites.

Effect of initial concentration and metal removal mechanism:
The PVP/Magnetite nanocomposite is employed for Cr 6+ removal using the UV-visible absorption spectrophotometer (JASCO V 650) with the 10mg/L in 50mL of Cr 6+ solution and alternatives after treatment with PVP/Magnetite nanocomposite under ultrasonication for 5min.The evaluation of Cr (VI) removal in the solution was using the colorimetric method with a characteristic peak at 350nm in the U-Vis absorption curve.The higher the Cr (VI) focus in the perfect solution, the better peak intensity was noticed.The solution of Cr 6+ containing 10mg/L showed greatest absorbance at 2.18, on treating with PVP/Magnetite nanocomposite at different concentrations (0~2.5g/L)under ultrasonication for 5 min, the peak intensity reduced little by little with increasing the adsorbent concentration indicating the reduced Cr(VI) amount in the solution.Fig. 3. Shows the kinetics of adsorbent that describes the Cr (VI) uptake rate is one of the important characteristics which controls the property of absorbate moments uptake at the solid-solution interface.Hence, in our study, the kinetics of Cr (VI) removing was accomplished to understand the adsorption behavior of the prepared PVP/Magnetite nanocomposite.On the basis of above experimental results, it is believed that PVP-Magnetite nanocomposite shows high adsorption towards the Cr (VI) ions.Chromium (VI) exists in aqueous solutions as Cr2O7 2-and HCr2O7 - [23,46].So, here high adsorption of 94% of PVP-Magnetite nanocomposite was believed to come from strong interaction between functional groups (eg.C=O and C-N) of PVP [24] and metal ions which provides lots of adsorption sites for removal of Cr (VI) ions.Moreover, it is clear that chromium uptake by PVP-Fe3O4 nanocomposite is a physicochemical process, which carries electrostatic interaction.

Conclusion
Magnetite nanoparticles were prepared by coprecipitation of Fe 2+ and Fe 3+ with NH4OH, and then surface is grafted with polyvinyl pyrrolidone polymer.Powder X-ray diffraction shows the spinel structure for these nanoparticles.FT-IR spectra indicate that C-N and C=O molecules have been bound onto the surface of the magnetite nanoparticles through Fe-O.Then they could be used successfully as a magnetic cation exchanger with the possibility of removal of chromium (VI) cationic metal from water solution through grafted polymerization with polyvinyl pyrrolidone.The effect of concentration on cation separation was investigated too.From the results, it is obvious that the grafted nanocomposite shows high removal efficiency about 94%.Subsequently, the removal of chromium (VI) cationic metals using PVP-magnetite nanocomposite is highly efficient.
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Fig. 1 .
Fig.1.X-Ray diffraction patterns of PVP/Magnetite nanocompositeCrystallite size of 10.7nm was calculated by using Scherrer formula for preferential orientation plane of (311).Lattice constant values of nanocomposite were calculated (a, b=8.386, 8.375) of inverse spinel structure and were in good agreement with literature.
u m e 1 3 N u m b e r 1 0 J o u r n a l o f A d v a n c e s i n c h e m i s t r y 5889 | P a g e F e b r u a r y 2 0 1 7 w w w .c i r w o r l d .c o m HCrO 4-, CrO4