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Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi
Materials Today: Proceedings xxx (xxxx) xxx
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Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi Nouh Aarab a, Abdelghani Hsini a, Mohamed Laabd a, Abdelilah Essekri a, Toufa Laktif a, Mohamed Ait Haki a, Rajae Lakhmiri b, Abdallah Albourine a,⇑ a b
Analytical Chemistry and Environment Team, Materials and Environment Laboratory, Faculty of Sciences, Ibn Zohr University, B.P: 8106 Agadir, Morocco Laboratory of Chemical Engineering and Valorization of Resources, Faculty of Sciences and Technologies, Abdelmalek Essaadi University, Tangier, Morocco
a r t i c l e
i n f o
Article history: Received 24 June 2019 Accepted 6 August 2019 Available online xxxx Keywords: Adsorption DFT Metronidazole PANi Sodium salicylate
a b s t r a c t The focus of the current research is to evaluate the adsorption mechanisms of sodium salicylate and metronidazole on the polyaniline (PANi) using density functional theory (DFT) at B3LYP/6-31G(d) level of theory. The molecular electrostatic potentials of sodium salicylate, metronidazole and PANi were calculated. The theoretical data show that the oxygenated functional groups of adsorbates and amino groups of PANi are the nucleophilic and electrophilic attack sites, respectively. The structural, electronic and energetic properties of PANi complexed with sodium salicylate and metronidazole were investigated. The adsorption mechanism is due to the formation of hydrogen bond between polymer and adsorbate molecules. The low intermolecular electron transfer at solute/solid interface reveals that the sodium salicylate and metronidazole are physisorbed onto the PANi. In addition, the interaction energies between PANi and adsorbate molecules suggest the stability of the formed complexes, indicating a good adsorbate-adsorbent affinity. All quantum chemical data are in good agreement with the experimental observations. Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Congress: Applied Materials for the Environment CIMAE-2018.
1. Introduction Pollution of aquatic ecosystems by chemicals, commonly generated by human activities, can have harmful effects on human health and environment [1]. Recently, the pharmaceuticals as emerging contaminants have attracted a particular interest of many researchers worldwide [2]. The use of the pharmaceuticals like anti-inflammatory, antibiotics, hormones, antidepressants, disinfectants, anti-epileptic and beta-blockers is hospital, domestic and veterinary [3]. The presence of these compounds at such low concentration in municipal effluents has been associated to chronic toxicity [4]. Therefore, it is greatly desirable to remove pharmaceutical pollutants from wastewaters. In this regard, several wastewater decontamination techniques including advanced oxidation processes, membrane filtration and adsorption were widely applied [5,6]. Amongst all, the adsorption is one of the most
⇑ Corresponding author. E-mail address: [email protected] (A. Albourine).
promising techniques for the treatment of wastewater because of its simplicity and cost-effectiveness [6]. The conductive polymers (i.e. polyaniline, polypyrrole and polytheophene) have attracted a great interest in different research fields such as corrosion inhibition, gas sensors and wastewater decontamination [7]. This is due to their specific physical and chemical proprieties. The PANi is a low-cost, biodegradable and non-toxic conducting polymer. For this reason, the PANi was successfully used as efficient and recyclable adsorbent for removal of organic pollutants such as aromatic acids [8], Congo red [9], sodium salicylate [10] and metronidazole [11] from water. The adsorptive ability of the PANi is mainly related to its doping using acidic solutions (protonation of amine groups) [12]. Thus, the amines of the PANi fulfil a key role in adsorption mechanism. More recently, the density functional theory (DFT) modeling is an important tool for understanding the adsorption mechanisms at solid/solution (i.e. wastewater treatment and corrosion inhibition) and solid/gas (i.e. gas sensors) interfaces [8,13,14]. In this work, we investigate the adsorption of two pharmaceutical pollutants (sodium salicylate and metronidazole) on the PANi from
https://doi.org/10.1016/j.matpr.2019.08.103 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Congress: Applied Materials for the Environment CIMAE-2018.
Please cite this article as: N. Aarab, A. Hsini, M. Laabd et al., Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.103
2
N. Aarab et al. / Materials Today: Proceedings xxx (xxxx) xxx
aqueous solutions using DFT simulation. The electronic, structural and energetic properties of sodium salicylate, metronidazole and PANi were calculated and discussed. In order to obtain useful information about the adsorption mechanisms, the interactions between adsorbates and adsorbent were investigated. 2. Computational methodology All calculations were performed using Gaussian 09 software package [15]. The output files of the molecules were visualized by employing the GaussView 05 interface program [16]. The unrestricted B3LYP (Becke’s three-parameter and Lee-Yang-Parr) level of theory with 6-31G (d) basis set was used for the geometry optimization of studied molecules. At the same level of the theory, the frequencies were calculated to confirm (by the absence of imaginary frequencies) that the molecular structures obtained corresponded to energy minima. In the present study, a single adsorbate molecule was added to PANI (with two aniline monomer units) emeraldine salt form. As in experimental conditions, the solvation effect (water) was taken into account using conductor-like polarizable continuum model (CPCM) for the optimization of the molecular geometries and the calculation of the interaction energies during the formation of the adsorbent/adsorbate complexes [17]. Molecular electrostatic potential (MEP), Mulliken charges and adsorption energies have been calculated on the sodium salicylate, metronidazole and PANi as well as PANi/sodium salicylate and PANi/metronidazole complexes. The interaction energies (DEint) between adsorbates (sodium salicylate and metronidazole) and PANi were obtained from the following equation:
DEint ¼ EðPANiÞ þ EðAdsorbateÞ EðPANi=AdsorbateÞ
ð1Þ
where E(PANi/Adsorbate) corresponds to the total energy of complex formed during the adsorption process, E(PANi) is the energy of the PANi as adsorbent and E(Adsorbate) is the energy of the sodium salicylate or metronidazole. The charge transfer (Dq) between the adsorbate and the adsorbent during the adsorption process is calculated by the redistribution of electronic charges on the PANi before and after adsorption. The Dq is expressed by Eq. (2):
Dq ¼ qPANibeforeadsorption qPANiafteradsorption
3. Results and discussion 3.1. Molecular electrostatic potential (MEP) MEP is a plot of electrostatic potential mapped onto the molecule surface with constant total electron density, and it gives important information about reactive sites for electrophilic (positive potential region) and nucleophilic (negative potential region) attacks [18]. MEP surfaces of the sodium salicylate, metronidazole and PANi were calculated and illustrated in Fig. 1. The results obtained show that the oxygenated groups of sodium salicylate and metronidazole have a high negative electron density (red color). The negative electron density is localized on the hydroxyl and carboxyl functional groups. This indicates that these groups may be considered as nucleophilic attack sites for molecules of sodium salicylate and metronidazole. In contrast, the amine functional groups of the PANi (dianiline) lead to a high positive electron density (blue color). This suggests that the amine groups are sites of electrophilic attack for PANI. According to these results, the mechanism of adsorption of sodium salicylate and metronidazole on PANi can be carried out through interactions between nucleophilic and electrophilic groups of the adsorbates and PANi, respectively. 3.2. Charge transfer The charge transfer phenomenon between the molecules at the solute/adsorbent interface is examined by an analysis of the net charges of the PANi atoms before and after the complexation/ adsorption (Table 1). The results were obtained after optimization of the complexes formed between di-aniline and metronidazole and sodium salicylate. The redistribution of atomic net charges indicates that metronidazole and sodium salicylate lose the electronic charges Dq of 0.104 and 0.207e, respectively. These losses are transferred to the adsorbent material (PANi) during the complexation process. In addition, the low values of Dq transferred show that the adsorption of metronidazole and sodium salicylate on the PANi is a physisorption process in nature [19]. This is in good agreement with experimental results [10,11]. 3.3. Intermolecular distances
ð2Þ
where qPANi before adsorption and qPANi after adsorption are total net charges of the PANi before and after interaction with the adsorbate, respectively.
From a structural point of view, the intermolecular distances reflect the strength of interactions between molecules. Thus, the affinity of an adsorbate molecule vis-a-vis an adsorbent material surface is inversely proportional to the intermolecular adsorbent/
Fig. 1. MEP surfaces for sodium salicylate, metronidazole and PANi obtained at B3LYP/6-31G(d) level.
Please cite this article as: N. Aarab, A. Hsini, M. Laabd et al., Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.103
N. Aarab et al. / Materials Today: Proceedings xxx (xxxx) xxx
3
Table 1 Atomic net charges of the PANi before and after adsorption of metronidazole and sodium salicylate. N°
Atom
PANi
PANi/Metronidazole
PANi/Sodium salicylate
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
N C C C C C C N C H C C C C C N H H H H H H H H H H H H
0,793 0,393 0,179 0,160 0,356 0,179 0,169 0,741 0,356 0,368 0,160 0,179 0,393 0,169 0,179 0,793 0,369 0,169 0,168 0,179 0,166 0,362 0,168 0,169 0,166 0,179 0,369 0,368
0,790 0,362 0,162 0,143 0,338 0,148 0,144 0,807 0,313 0,340 0,123 0,136 0,364 0,124 0,161 0,782 0,359 0,184 0,157 0,158 0,149 0,399 0,160 0,161 0,160 0,173 0,358 0,339
0,788 0,371 0,167 0,139 0,346 0,152 0,138 0,795 0,322 0,332 0,131 0,141 0,372 0,141 0,171 0,779 0,361 0,179 0,144 0,166 0,152 0,392 0,158 0,155 0,162 0,167 0,360 0,345
adsorbate distances. In this regard, the optimized molecular geometries of PANi complexes with metronidazole and sodium salicylate are calculated and illustrated in Fig. 2. According to this calculation result, we find that the hydrogen atom (10H) of the amine group of the PANi is located at distances of about 1.919 Å and 2.820 Å from the oxygen atoms of metronidazole (36O) and sodium salicylate (32O), respectively. It is also important to mention that long intermolecular distances are observed between the other hydrogen atoms of aromatic ring of PANi and the oxygen atom of metronidazole and sodium salicylate. This indicates that there are weak intermolecular interactions between the studied molecules, and consequently the adsorption mechanism is mainly governed by hydrogen bond formation (physisorption) between the hydroxyl and carboxyl groups of the adsorbates (metronidazole and sodium salicylate) and the amine groups PANi as adsorbent. 3.4. Interaction energies The calculation of the formation/interaction energies (DEint) is very important for studying the interactions between the adsorbent material and the adsorbate molecule in order to evaluate the stability of the obtained complexes [20]. For this purpose, the interaction energies between PANi and adsorbate molecules (metronidazole and sodium salicylate) were calculated. The DEint values of the PANi/Metronidazole and PANi/Sodium Salicylate complexes are 0.218 and 0.095 u.a., respectively. Examination of these values makes it possible to conclude that the adsorbentadsorbate intermolecular interactions during the adsorption of metronidazole and sodium salicylate on the PANi are quite important. This suggests that PANi has good adsorption affinity for metronidazole and sodium salicylate. Also, the energy values obtained show that the adsorption mechanisms are of a physical type. This result is in good agreement with the results obtained previously such as low charge transfer and intermolecular distances.
Fig. 2. The optimized molecular structure of the PANi (di-aniline) complexed with (a) metronidazole and (b) sodium salicylate.
4. Conclusion In this research, the theoretical study of the adsorption mechanism of metronidazole and sodium salicylate from aqueous solution by PANi was successfully investigated using DFT method. All quantum chemical calculations were performed with B3LYP/631G (d) level of theory implemented in Gaussian 09 suite of program. The solvent effect was accounted by CPCM solvation method. The MEP of optimized molecular structures of metronidazole, sodium salicylate and PANi were calculated. As a result, the oxygenated functional groups (hydroxyl and carboxyl) of adsorbates and amine groups of PANi were the nucleophilic and electrophilic attack sites, respectively. In addition, the computational investigation of the PANi/sodium salicylate and PANi/metronidazole complexes formed at solution-adsorbent interface during the adsorption process was carried out. A low electronic charge was transferred from metronidazole and sodium salicylate to PANi, indicating that the adsorption is a physical process. From the structural point of view, intermolecular distances lead to the conclusion that the adsorbate/adsorbent interaction mechanism was governed by the formation of hydrogen bonds. The interaction energies confirm that the metronidazole and sodium salicylate display good affinity with PANi and the adsorption process is physisorption. Finally, the theoretical results are in perfect agreement with the experiments. References [1] A. Arenas-Sánchez, A. Rico, M. Vighi, Sci. Total Environ. 572 (2016) 390–403. [2] J.R. De Andrade, M.F. Oliveira, M.G.C. da Silva, M.G.A. Vieira, Ind. Eng. Chem. Res. 57 (2018) 3103–3127.
Please cite this article as: N. Aarab, A. Hsini, M. Laabd et al., Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.103
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[3] T. Deblonde, C. Cossu-Leguille, P. Hartemann, Int. J. Hyg. Environ. Health 214 (2011) 442–448. [4] R. Rosal, A. Rodríguez, J.A. Perdigón-Melón, A. Petre, E. García-Calvo, M.J. Gómez, A. Aguera, A.R. Fernández-Alba, Water Res. 44 (2010) 578–588. [5] S.O. Ganiyu, E.D. van Hullebusch, M. Cretin, G. Esposito, M.A. Oturan, Sep. Purif. Technol. 156 (2015) 891–914. [6] J. Akhtar, N.A.S. Amin, K. Shahzad, Desalin. Water Treat. 57 (2015) 12842– 12860. [7] T.K. Das, S. Prusty, Polym. Plast. Technol. Eng. 51 (2012) 1487–1500. [8] M. Laabd, A. El Jaouhari, M. Bazzaoui, A. Albourine, H. El Jazouli, J. Polym. Environ. 25 (2016) 359–369. [9] M. Laabd, H. Ait Ahsaine, A. El Jaouhari, B. Bakiz, M. Bazzaoui, M. Ezahri, A. Albourine, A. Benlhachemi, J. Environ Chem. Eng. 4 (2016) 3096–3105. [10] H. Chafai, M. Laabd, M. Elamine, A. Albourine, Desalin. Water Treat. (2017), https://doi.org/10.5004/dwt.2017.21194.
[11] N. Aarab, M. Laabd, M. Bazzaoui, A. Albourine, J. Mater. Environ. Sci. 6 (2015) 1234–1242. [12] M. Laabd, H. Chafai, N. Aarab, A. El Jaouhari, M. Bazzaoui, H. Kabli, H. Eljazouli, A. Albourine, Environ. Chem. Lett. 14 (2016) 395–400. [13] C. Verma, M.A. Quraishi, E.E. Ebenso, I. Bahadur, J. Bio. Tribo. Corros. 4 (2018), https://doi.org/10.1007/s40735-018-0150-3. [14] M. Laabd, A. Hallaoui, N. Aarb, A. Essekri, H. Eljazouli, R. Lakhmiri, A. Albourine, Fibers Polym. 20 (2019) 896–905. [15] , Gaussian, Inc., Wallingford CT, 2009. [16] R. Dennington, T. Keith, J. Millam, Shawnee Mission KS, GaussView, Version 5, Semichem Inc., 2009. [17] M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem. 24 (2003) 669–681. [18] N. Okulik, A.H. Jubert, Internet Electron. J. Mol. Des. 4 (2005) 17–30. [19] O.L.A. Monti, J. Phys. Chem. Lett. 3 (2012) 2342–2351. [20] T.A. Saleh, V.K. Gupta, A.A. Al-Saadi, J. Colloid Interface Sci. 396 (2013) 264–269.
Please cite this article as: N. Aarab, A. Hsini, M. Laabd et al., Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.103
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi Nouh Aarab a, Abdelghani Hsini a, Mohamed Laabd a, Abdelilah Essekri a, Toufa Laktif a, Mohamed Ait Haki a, Rajae Lakhmiri b, Abdallah Albourine a,⇑ a b
Analytical Chemistry and Environment Team, Materials and Environment Laboratory, Faculty of Sciences, Ibn Zohr University, B.P: 8106 Agadir, Morocco Laboratory of Chemical Engineering and Valorization of Resources, Faculty of Sciences and Technologies, Abdelmalek Essaadi University, Tangier, Morocco
a r t i c l e
i n f o
Article history: Received 24 June 2019 Accepted 6 August 2019 Available online xxxx Keywords: Adsorption DFT Metronidazole PANi Sodium salicylate
a b s t r a c t The focus of the current research is to evaluate the adsorption mechanisms of sodium salicylate and metronidazole on the polyaniline (PANi) using density functional theory (DFT) at B3LYP/6-31G(d) level of theory. The molecular electrostatic potentials of sodium salicylate, metronidazole and PANi were calculated. The theoretical data show that the oxygenated functional groups of adsorbates and amino groups of PANi are the nucleophilic and electrophilic attack sites, respectively. The structural, electronic and energetic properties of PANi complexed with sodium salicylate and metronidazole were investigated. The adsorption mechanism is due to the formation of hydrogen bond between polymer and adsorbate molecules. The low intermolecular electron transfer at solute/solid interface reveals that the sodium salicylate and metronidazole are physisorbed onto the PANi. In addition, the interaction energies between PANi and adsorbate molecules suggest the stability of the formed complexes, indicating a good adsorbate-adsorbent affinity. All quantum chemical data are in good agreement with the experimental observations. Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Congress: Applied Materials for the Environment CIMAE-2018.
1. Introduction Pollution of aquatic ecosystems by chemicals, commonly generated by human activities, can have harmful effects on human health and environment [1]. Recently, the pharmaceuticals as emerging contaminants have attracted a particular interest of many researchers worldwide [2]. The use of the pharmaceuticals like anti-inflammatory, antibiotics, hormones, antidepressants, disinfectants, anti-epileptic and beta-blockers is hospital, domestic and veterinary [3]. The presence of these compounds at such low concentration in municipal effluents has been associated to chronic toxicity [4]. Therefore, it is greatly desirable to remove pharmaceutical pollutants from wastewaters. In this regard, several wastewater decontamination techniques including advanced oxidation processes, membrane filtration and adsorption were widely applied [5,6]. Amongst all, the adsorption is one of the most
⇑ Corresponding author. E-mail address: [email protected] (A. Albourine).
promising techniques for the treatment of wastewater because of its simplicity and cost-effectiveness [6]. The conductive polymers (i.e. polyaniline, polypyrrole and polytheophene) have attracted a great interest in different research fields such as corrosion inhibition, gas sensors and wastewater decontamination [7]. This is due to their specific physical and chemical proprieties. The PANi is a low-cost, biodegradable and non-toxic conducting polymer. For this reason, the PANi was successfully used as efficient and recyclable adsorbent for removal of organic pollutants such as aromatic acids [8], Congo red [9], sodium salicylate [10] and metronidazole [11] from water. The adsorptive ability of the PANi is mainly related to its doping using acidic solutions (protonation of amine groups) [12]. Thus, the amines of the PANi fulfil a key role in adsorption mechanism. More recently, the density functional theory (DFT) modeling is an important tool for understanding the adsorption mechanisms at solid/solution (i.e. wastewater treatment and corrosion inhibition) and solid/gas (i.e. gas sensors) interfaces [8,13,14]. In this work, we investigate the adsorption of two pharmaceutical pollutants (sodium salicylate and metronidazole) on the PANi from
https://doi.org/10.1016/j.matpr.2019.08.103 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Congress: Applied Materials for the Environment CIMAE-2018.
Please cite this article as: N. Aarab, A. Hsini, M. Laabd et al., Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.103
2
N. Aarab et al. / Materials Today: Proceedings xxx (xxxx) xxx
aqueous solutions using DFT simulation. The electronic, structural and energetic properties of sodium salicylate, metronidazole and PANi were calculated and discussed. In order to obtain useful information about the adsorption mechanisms, the interactions between adsorbates and adsorbent were investigated. 2. Computational methodology All calculations were performed using Gaussian 09 software package [15]. The output files of the molecules were visualized by employing the GaussView 05 interface program [16]. The unrestricted B3LYP (Becke’s three-parameter and Lee-Yang-Parr) level of theory with 6-31G (d) basis set was used for the geometry optimization of studied molecules. At the same level of the theory, the frequencies were calculated to confirm (by the absence of imaginary frequencies) that the molecular structures obtained corresponded to energy minima. In the present study, a single adsorbate molecule was added to PANI (with two aniline monomer units) emeraldine salt form. As in experimental conditions, the solvation effect (water) was taken into account using conductor-like polarizable continuum model (CPCM) for the optimization of the molecular geometries and the calculation of the interaction energies during the formation of the adsorbent/adsorbate complexes [17]. Molecular electrostatic potential (MEP), Mulliken charges and adsorption energies have been calculated on the sodium salicylate, metronidazole and PANi as well as PANi/sodium salicylate and PANi/metronidazole complexes. The interaction energies (DEint) between adsorbates (sodium salicylate and metronidazole) and PANi were obtained from the following equation:
DEint ¼ EðPANiÞ þ EðAdsorbateÞ EðPANi=AdsorbateÞ
ð1Þ
where E(PANi/Adsorbate) corresponds to the total energy of complex formed during the adsorption process, E(PANi) is the energy of the PANi as adsorbent and E(Adsorbate) is the energy of the sodium salicylate or metronidazole. The charge transfer (Dq) between the adsorbate and the adsorbent during the adsorption process is calculated by the redistribution of electronic charges on the PANi before and after adsorption. The Dq is expressed by Eq. (2):
Dq ¼ qPANibeforeadsorption qPANiafteradsorption
3. Results and discussion 3.1. Molecular electrostatic potential (MEP) MEP is a plot of electrostatic potential mapped onto the molecule surface with constant total electron density, and it gives important information about reactive sites for electrophilic (positive potential region) and nucleophilic (negative potential region) attacks [18]. MEP surfaces of the sodium salicylate, metronidazole and PANi were calculated and illustrated in Fig. 1. The results obtained show that the oxygenated groups of sodium salicylate and metronidazole have a high negative electron density (red color). The negative electron density is localized on the hydroxyl and carboxyl functional groups. This indicates that these groups may be considered as nucleophilic attack sites for molecules of sodium salicylate and metronidazole. In contrast, the amine functional groups of the PANi (dianiline) lead to a high positive electron density (blue color). This suggests that the amine groups are sites of electrophilic attack for PANI. According to these results, the mechanism of adsorption of sodium salicylate and metronidazole on PANi can be carried out through interactions between nucleophilic and electrophilic groups of the adsorbates and PANi, respectively. 3.2. Charge transfer The charge transfer phenomenon between the molecules at the solute/adsorbent interface is examined by an analysis of the net charges of the PANi atoms before and after the complexation/ adsorption (Table 1). The results were obtained after optimization of the complexes formed between di-aniline and metronidazole and sodium salicylate. The redistribution of atomic net charges indicates that metronidazole and sodium salicylate lose the electronic charges Dq of 0.104 and 0.207e, respectively. These losses are transferred to the adsorbent material (PANi) during the complexation process. In addition, the low values of Dq transferred show that the adsorption of metronidazole and sodium salicylate on the PANi is a physisorption process in nature [19]. This is in good agreement with experimental results [10,11]. 3.3. Intermolecular distances
ð2Þ
where qPANi before adsorption and qPANi after adsorption are total net charges of the PANi before and after interaction with the adsorbate, respectively.
From a structural point of view, the intermolecular distances reflect the strength of interactions between molecules. Thus, the affinity of an adsorbate molecule vis-a-vis an adsorbent material surface is inversely proportional to the intermolecular adsorbent/
Fig. 1. MEP surfaces for sodium salicylate, metronidazole and PANi obtained at B3LYP/6-31G(d) level.
Please cite this article as: N. Aarab, A. Hsini, M. Laabd et al., Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.103
N. Aarab et al. / Materials Today: Proceedings xxx (xxxx) xxx
3
Table 1 Atomic net charges of the PANi before and after adsorption of metronidazole and sodium salicylate. N°
Atom
PANi
PANi/Metronidazole
PANi/Sodium salicylate
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
N C C C C C C N C H C C C C C N H H H H H H H H H H H H
0,793 0,393 0,179 0,160 0,356 0,179 0,169 0,741 0,356 0,368 0,160 0,179 0,393 0,169 0,179 0,793 0,369 0,169 0,168 0,179 0,166 0,362 0,168 0,169 0,166 0,179 0,369 0,368
0,790 0,362 0,162 0,143 0,338 0,148 0,144 0,807 0,313 0,340 0,123 0,136 0,364 0,124 0,161 0,782 0,359 0,184 0,157 0,158 0,149 0,399 0,160 0,161 0,160 0,173 0,358 0,339
0,788 0,371 0,167 0,139 0,346 0,152 0,138 0,795 0,322 0,332 0,131 0,141 0,372 0,141 0,171 0,779 0,361 0,179 0,144 0,166 0,152 0,392 0,158 0,155 0,162 0,167 0,360 0,345
adsorbate distances. In this regard, the optimized molecular geometries of PANi complexes with metronidazole and sodium salicylate are calculated and illustrated in Fig. 2. According to this calculation result, we find that the hydrogen atom (10H) of the amine group of the PANi is located at distances of about 1.919 Å and 2.820 Å from the oxygen atoms of metronidazole (36O) and sodium salicylate (32O), respectively. It is also important to mention that long intermolecular distances are observed between the other hydrogen atoms of aromatic ring of PANi and the oxygen atom of metronidazole and sodium salicylate. This indicates that there are weak intermolecular interactions between the studied molecules, and consequently the adsorption mechanism is mainly governed by hydrogen bond formation (physisorption) between the hydroxyl and carboxyl groups of the adsorbates (metronidazole and sodium salicylate) and the amine groups PANi as adsorbent. 3.4. Interaction energies The calculation of the formation/interaction energies (DEint) is very important for studying the interactions between the adsorbent material and the adsorbate molecule in order to evaluate the stability of the obtained complexes [20]. For this purpose, the interaction energies between PANi and adsorbate molecules (metronidazole and sodium salicylate) were calculated. The DEint values of the PANi/Metronidazole and PANi/Sodium Salicylate complexes are 0.218 and 0.095 u.a., respectively. Examination of these values makes it possible to conclude that the adsorbentadsorbate intermolecular interactions during the adsorption of metronidazole and sodium salicylate on the PANi are quite important. This suggests that PANi has good adsorption affinity for metronidazole and sodium salicylate. Also, the energy values obtained show that the adsorption mechanisms are of a physical type. This result is in good agreement with the results obtained previously such as low charge transfer and intermolecular distances.
Fig. 2. The optimized molecular structure of the PANi (di-aniline) complexed with (a) metronidazole and (b) sodium salicylate.
4. Conclusion In this research, the theoretical study of the adsorption mechanism of metronidazole and sodium salicylate from aqueous solution by PANi was successfully investigated using DFT method. All quantum chemical calculations were performed with B3LYP/631G (d) level of theory implemented in Gaussian 09 suite of program. The solvent effect was accounted by CPCM solvation method. The MEP of optimized molecular structures of metronidazole, sodium salicylate and PANi were calculated. As a result, the oxygenated functional groups (hydroxyl and carboxyl) of adsorbates and amine groups of PANi were the nucleophilic and electrophilic attack sites, respectively. In addition, the computational investigation of the PANi/sodium salicylate and PANi/metronidazole complexes formed at solution-adsorbent interface during the adsorption process was carried out. A low electronic charge was transferred from metronidazole and sodium salicylate to PANi, indicating that the adsorption is a physical process. From the structural point of view, intermolecular distances lead to the conclusion that the adsorbate/adsorbent interaction mechanism was governed by the formation of hydrogen bonds. The interaction energies confirm that the metronidazole and sodium salicylate display good affinity with PANi and the adsorption process is physisorption. Finally, the theoretical results are in perfect agreement with the experiments. References [1] A. Arenas-Sánchez, A. Rico, M. Vighi, Sci. Total Environ. 572 (2016) 390–403. [2] J.R. De Andrade, M.F. Oliveira, M.G.C. da Silva, M.G.A. Vieira, Ind. Eng. Chem. Res. 57 (2018) 3103–3127.
Please cite this article as: N. Aarab, A. Hsini, M. Laabd et al., Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.103
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Please cite this article as: N. Aarab, A. Hsini, M. Laabd et al., Theoretical study of the adsorption of sodium salicylate and metronidazole on the PANi, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.103