Electrochemical Detection of 4-Nitrophenol by Manganese (II) Scheff Base Complex Modified GCE

Mechanics, Materials Science & Engineering, May 2017

ISSN 2412-5954

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S. Praveen Kumar1, S. Munusamy1, S. Muthamizh1, A. Padmanaban1, T. Dhanasekaran1, G. Gnanamoorthy1, V. Narayanan1,a 1

Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, India

a

vnnara@yahoo.co.in DOI 10.2412/mmse.56.69.941 provided by Seo4U.link

Keywords: manganese (II) Schiff base complex, microwave irradiation, 4-nitrophenol, differential pulse voltammetry, electrochemical polymerization.

ABSTRACT. A selective and sensitive electrochemical determination method was developed for the determination of 4nitrophenol by manganese (II) Schiff base complex modified glassy carbon electrode (GCE). The manganese (II) Schiff base complex was synthesized by a simple green chemical route and it was characterized by FT-IR, Raman, UV-Visible and fluorescence spectral techniques. The electrochemical redox behaviour of manganese (II) Schiff base complex was examined in acetonitrile solution with the aid of cyclic voltammetry. The electrochemical behaviour of 4 -nitophenol at both electrodes were investigated thoroughly in acetate buffer solution at pH-5. The 4-nitrophenol yields an sharp reduction as well as an oxidation peaks at manganese (II) Schiff base complex modified GCE. The well define redox peaks at modified GCE has lower potential and higher peak current than bare GCE. Based on the electrocatalyitc redox observations of 4-nitrophenol we can propose an electrocatalytic sensor for the 4-NP direct determination in real sample analysis. In the electrochemical determination process various kinetic parameters were calculated, such as number of electron and proton transfer, rate constant etc., differential pulse voltammetry technique was utilized for the determination of 4-NP. Under the optimization conditions the peak current various linearly with the concentration of 4-nitrophenol in sensitiv -term stability.

This proposed electrocatalyitc sensor can be used for the determination of 4-NP in real water samples analysis.

Introduction. Phenolic derivatives are mostly used in many industrial synthetic processes and it was released into environment. The phenolic compounds are of primary importance and utilized in the synthesis of pesticides, dyes, pharmaceuticals, paints and petrochemical products. These phenolic compounds were gives undesirable colour to water. They prevent the sunlight penetration and retarding photosynthetic reactions in water. It affects the aquatic life and poses various detrimental e ects to living beings and plants. These compounds are considered as environmental hazards material by USA Environmental Protection Agency, because of its toxicity to humans, animals and plants. Among the phenolic compounds, 4-nitrophenol (4-NP) is the most hazardous substance, it -NP has been reported as a potential carcinogen, mutagen and teratogen, and it also causes headaches, drowsiness, nausea and cyanosis. Hence, there is a necessity for monitoring the 4-NP to avoid adverse e ects on living beings. Therefore, quantification of 4-NP and other phenolic compounds are getting urgent for environmental protection.

There are several methods were reported for the quantification of 4-injection analysis, spectrophotometry, HPLC, capillary electrophoresis, gas chromatography (GC), fluorescence and electrochemical method. Among the reported methods, electrochemical method has great important, because of its cost effect, faster response and simple procedure. Therefore, in the present work we consider the electrochemical method has been utilized for the quantification of 4-NP. In this method, the modified materials play a key role to improving the detection performances, based on this effect 22

The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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manganese(II) Schiff base complex was utilized as a modifier for the 4-NP quantification [1, 2]. The manganese complexes with Schiff base ligands (N,O-donor ligand) getting more attention in the research field, since its significant roles in various fields such as biological, chemical analysis and industrial applications. The manganese complexes possess different types of magnetic behaviors, like ferromagnetic, antiferromagnetic, metamagnetic, and spin flop have been observed. Hence the manganese complexes can play a vital role in material chemistry. The highvalent manganese complexes have been studied mostly in their physical and chemical properties; additionally these complexes provided potential abilities in biological modeling application. The manganese complexes were used as oxygen evolving complexes (OEC) in photosystem II (PS II), water splitting for evolution of fuels. The manganese Schiff base complexes have suitable biometric properties, which can mimic the structural features of the active site in metalloenzymes, redox and non-redox proteins.

In addition, manganese complexes were catalyze the disproportionation of hydrogen peroxide, it produced a reactive oxygen species (ROS) in the body. These manganese complexes have different oxidation states, which possess good electrochemical redox activity [3, 4]. By varying the substituent groups in Schiff base ligand, chemists discovered potential manganese complexes for multiple applications with the aid of novel synthetic process. In the present work manganses (II) Schiff base complex was synthesized by microwave irradiation method and utilized for electroctalytic determination of 4-nitrophenol.

Experimental procedure. Manganese (II) Schiff base complex was synthesized by microwave irradiation method using following procedure. One mmol of o-phenylenediamine was added with the 2 mmol of salicylaldehyde under stirring in methanol medium. A yellow colour solution was obtained it was subjected for microwave irradiation at 320 W for 2-3 min. After the irradiation it was kept in normal atmosphere in room temperature for 24 hr. A yellow colour precipitate was obtained, it was collected and recrystallized by hot ethanol. After that 1 moml of manganese (II) chloride was gradually added with 1 mmol of Schiff base ligand under stirring condition in methanol medium. A brown colour solution was obtained it was employed for microwave irradiation at 320 W for 5 min and kept in room temperature for 24 hr. a brown solid was obtained it was collected and recrystallized by hot ethanol (fig. 1).

Fig. 1. Synthesis of manganese(II) Schiff base complex.

Result and Discussion FT-IR spectral analysis. The FT-IR spectrum of the manganese(II) Schiff base complex was recorded in the range of 400-4000 cm-1 and shown Fig. 1a. In the IR absorption band was shifted towards lower frequencies due to the bond formation between the imine nitrogen and manganese(II) metal ion. This peak was appeared at 1633 cm-1. The imine nitrogen forms a bond with manganese(II) ion through its lone pair of electrons. This imine group normally appeared in above 1650 cm-1 frequencies was confirms the complex formation between Schiff base ligand and manganese(II) metal ion. In addition two other peaks due to metal nitrogen and metal oxygen also gives more clarity of MMSE Journal. Open Access www.mmse.xyz

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complex formation in the range of 400-600 cm-1 -Mn)] was appeared -1 -1 at 595 cm -Mn)] peak was appeared at 540 cm . A peak was appeared at 825 cm-1 was due to the presence of phenyl ring in the manganese(II) Schiff base complex. Other characteristic peaks also observed in the IR spectrum, C-C single bond appeared at 2930 cm-1, aromatic C=C double bond exhibits its vibrational peak at 1305 cm-1 and C-N peak was appeared at 1485 cm-1. These IR peaks were confirms the manganese (II) Schiff base complex formation.

UV-Visible spectral analysis. The UV-Visibl spectrum of manganese (II) Schiff base complex was studied in methanol solution at normal ambient condition in the range of 200-800 nm, and it was shown in Fig. 1b. The UV-Visible spectrum of the manganese(II) Schiff base complex shows an absorbance peak at 275 nm is exhibit electronic transition in the aromatic ring. The d-d transition of manganese (II) metal ion is exhibit in visible region 405 and 625 nm. The characteristic transitions suggest the geometry of the manganese (II) Schiff base complexes is octahedral, and it has high spin the measured magnetic momentum is 3.76 BM, it highly matched with the theoretical magnetic momentum of manganese(II) complexes.

EPR spectral analysis. The EPR spectrum of manganese (II) Schiff base complex was studied in methanol solvent at normal atmospheric condition. The EPR spectrum of the manganese complex was shown Fig. 1c. The EPR spectrum of complex manganese (II) complex shows sextet splitting, it clearly indicates that manganese present at +2 oxidation state, since I value is 5/2. The g factor value of all splittings are closed to the free electron value of 2.156, it suggest the absence of spin orbit coupling in the ground state. The g values indicate that the Mn (II) in these complexes are rhombically distorted and the manganese hyperhave agreement with previous reported for similar structure of Mn (II) complex.

Electrochemical studies. The electrochemical redox behaviour of the manganese Schiff base complex was investigated by cyclic voltammetry, in three electrode system. The glassy carbon electrode was used as working electrode, silver and silver chloride (Ag/AgCl) was reference and platinum wire used as counter electrodes. The Voltammetry measurement was carried out in 0.1 M acetonitrile solution of manganese (II) Schiff base complex in presence of tetrabutylammonium perchlorate (TBAP) supporting electrolyte. The obtained cyclic voltammogram shows the electrochemical redox properties the manganese (II) metal ion and it was given in Fig. 2d. The manganese Schiff base complex shows only an oxidation peak, which corresponds to the oxidation of Mn (II) to Mn (III) oxidation state. In the anodic process number of electron transfer was calculated using ip = nFQ /4RT equation, it confirms the one electron transfer in the electrochemical reaction.

The anodic peak was appeared at 0.439 V as a broad peak. From the cyclic voltammogram we conclude that Mn (II) Schiff base complexes were electrochemically active and show response in the potential range of 0 to 0.9 V vs Ag/AgCl. The redox potential of the Mn (III)/Mn (II) is dependent on number of factors such as coordination number of the complex, bulkiness and hard/soft nature of the ligand. The manganese (II) Schiff base complex shows good electrochemical redox properties due to the electron transfer between two stable oxidation states Mn (II) to Mn (III).

Electrochemical polymerization. The electropolymeriztion was done in the potential range of 0 to 0.9 V at the scan rate of 50 mVs-1 and 20 cycles. The cyclic voltammogram for electropolymerization of manganese(II) Schiff base complex was shown in the Fig. 2a. The poly-manganese Schiff base complexes (poly-MnSBC) were deposited on the surface GC electrode. The modified electrode was dried and stored at 10 0C when it was not used for the sensing process. The poly-MnSCB coverage

of the electrode (A = 0.0707 cm2). The calculated modified electrode surface coverage concentration -11 mol cm-2. This modified electrode was used for the electrocatalytic sensing of 4NP. The Mn (II) Schiff base complex electrochemical polymerization follows the stacked polymerization process [5].

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Fig. 2. (a) FT-IR spectrum, (b) UV-Visible spectrum, (c) EPR spectrum and (d) Cyclic voltammogram in 0.1 M TBAP at the scan rate of 50 mVs-1 of manganese(II) complex.

Electrocatalytic sensing of 4-nitrophenol. The electrocatalytic sensing behavior of bare GCE and manganese (II) Schiff base complex modified GCE towards 4-NP determination in 0.1 M phosphate bu er was estimated by cyclic voltammetry in the sweeping potential of 0.8 V to -0.8 V and it was shown in Fig. 3b. The 4-NP was determine in the oxidation processes, which is monitoring after the reduction of NO2 group to NH2, followed by oxidation of NH2 group. For bare GCE, the 4-NP oxidation was appeared at 0.375 V with anodic peak current 2.67 A. IT is attributed to the irreversible oxidation of the NH2 group. The modified GCE shows the same anodic process at 0.379 V with peak current of 5.25 A. The modified GCE exhibits a sharp anodic peak when compare with bare GCE, Besides with it has more peak current double the amount of bare GCE. It explains that the modified GCE has enhanced sensing activity for the 4-NP determination, it was attributed by the polymerized manganese (II) Schiff base complex. The presence of Mn (II) ion in the active surface will leads better electrochemical redox process of 4-NP, which gives better activity in the quantification process [6, 7]. These results of 4-NP determination shows that manganese (II) Schiff base complex incerase the activity and it can be a good electrocatalytic sensor. This manganese (II) Schiff base complex can utilized for the determination of 4-NP in real samples.

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Fig. 3. (a) Cyclic voltammogram of Mn(II) Schiff base complex polymerization in 0.1 M TBAP, (b) Cyclic voltammogram of Electrocatalytic sensing of 4-NP in PBS at the scan rate of 50 mVs-1.

Summary. Manganese (II) Schiff base complex was synthesized by microwave irradiation method and it was characterized by FT-IR, UV-Vis and EPR spectral techniques. All the spectral techniques were confirms the Mn (II) Schiff base complex formation. The electrochemical behaviour of Mn (II) Schiff base complex was studied by cyclic voltammetry it shows an oxidation process of Mn(II) state to Mn(III) and the manganese(II) Schiff base complex was subjected to electrochemical polymerization. The polymerized Mn (II) Schiff base complex was deposited on the GCE surface and the modified electrode was successfully studied for the detection of 4-NP. The modified electrode shows a better result than bare GCE. Hence it can be used for quantification of 4-NP in real samples.

Acknowledgment One of the authors (S.P.K) wishes to thank Department of Science and Technology (DST), Government of India for the financial assistance in the form of INSPIRE fellowship (Inspire Fellow no: 130032) under the AORC scheme.

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