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C: Surfaces, Interfaces, Porous Materials, and Catalysis
Gravimetric, Electrochemical, Surface Morphology, DFT and Monte Carlo Simulation Studies on Three N-Substituted 2-Aminopyridine Derivatives as Corrosion Inhibitors of Mild Steel in Acidic Medium Chandrabhan Verma, Taiwo W Quadri, Lukman O. Olasunkanmi, El-Sayed M. Sherif, and Eno E. Ebenso J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b02740 • Publication Date (Web): 03 May 2018 Downloaded from http://pubs.acs.org on May 5, 2018
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The Journal of Physical Chemistry
Gravimetric, Electrochemical, Surface morphology, DFT and Monte Carlo Simulation Studies on Three N-substituted 2-Aminopyridine Derivatives as Corrosion Inhibitors of Mild Steel in Acidic Medium Chandrabhan Vermaab, Lukman O. Olasunkanmiabc, Taiwo W. Quadriab, El-Sayed M. Sherif de, Eno E. Ebensoab,* a
Department of Chemistry, School of Chemical and Physical Sciences, Faculty of Natural and Agricultural Sciences, North-West University, Private Bag X2046, Mmabatho 2735, South Africa b Material Science Innovation & Modelling (MaSIM) Research Focus Area, Faculty of Natural and Agricultural Sciences, North-West University, Private Bag X2046, Mmabatho 2735, South Africa c Department of Chemistry, Faculty of Science, Obafemi Awolowo University, Ile-Ife 220005, Nigeria d Center of Excellence for Research in Engineering Materials (CEREM), King Saud University, P.O. Box 800, Al-Riyadh 11421, Saudi Arabia *Corresponding author: Email:
[email protected] e (On Leave from): Electrochemistry and Corrosion Laboratory, Department of Physical Chemistry, National Research Centre, El-Behoth St. 33, Dokki, Cairo 12622, Egypt Abstract: Three N-substituted 2-aminopyridine derivatives namely, 6-(2,4-dihydroxyphenyl)-4phenyl-2-(phenylamino)nicotinonitrile (DPPN), 6-(2,4-dihydroxyphenyl)-2-((4hydroxyphenyl)amino)-4-phenylnicotinonitrile (DHPN) and 6-(2,4-dihydroxyphenyl)-2-((4methoxyphenyl)amino)-4-phenylnicotinonitrile (DMPN) were investigated for their inhibitive effects on mild steel corrosion in 1 M HCl solution using electrochemical, surface, chemical and theoretical studies. Results showed that the protection capabilities of inhibitors used in the study increase with increase in their concentrations and attained the maximum numerical values of 95.81 %, 96.24 % and 96.63 % for DPPN, DHPN and DMPN respectively at 20.20 × 10-5 molL-1 concentration. The results of the electrochemical impedance spectroscopy (EIS) studies revealed that DPPN, DHPN and DMPN molecules retard corrosion by adsorbing at the metal/electrolyte interface. Adsorption of the DPPN, DHPN and DMPN molecules on the surface was found to obey the Langmuir adsorption isotherm model. Polarization measurement indicated that DPPN, DHPN and DMPN molecules are mixed-type inhibitors with predominant cathodic inhibitive action. SEM and EDX analyses showed that the corrosion induced surface roughness of mild steel is significantly reduced by the inhibitors due to the development of protective films by DPPN, DHPN and DMPN molecules on the surface. The results of theoretical DFT and Monte Carlo (MC) simulation studies supported experimental studies and posited that the DPPN, DHPN and DMPN molecules adsorbed on mild steel surface as protonated species. Both the experimental and theoretical studies showed that the order of inhibition efficiencies of the studied compounds is DMPN > DHPN > DPPN.
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1. Introduction The inevitable corrosiveness of industrial environments and an increased use of metals and alloys in all fields of technology have necessitated the enhanced academic and industrial attentions on the study of metallic corrosion and its prevention.1,2 Mild steel is one of the most widely used metal alloys, often for construction purposes in several industries, including the petroleum, food, power production, chemical and electrochemical industries.1-3 Its utilization as constructional material in several industries is connected with its availability at relatively cheap rate and its intrinsic high mechanical strength4-5. However, it reacts with the environment to form relatively more stable corrosion products, resulting into high economic loss and safety threat.6,7 Furthermore, corrosion of mild steel is also brought about by manufacturing and engineering cleaning activities like acid pickling, descaling, industrial acid cleaning and oil well acidification, which utilize highly aggressive acid solutions.4,8 Among the known various methods of retarding metal corrosion, the application corrosion inhibitors, especially, organic molecules containing nitrogen, oxygen, phosphorus and sulphur heteroatoms is considered an efficient and cost effective method.9-12 Corrosion inhibitors are often used as additives to aggressive industrial solutions in order to reduce the corrosiveness of the solutions.13,14 A corrosion inhibitor may be anodic, cathodic or mixed-type in action. Inorganic compounds such as phosphates, molybdates, nitrates and chromates often inhibit anodically, while zinc and polyphosphates often show cathodic inhibitive action. Most organic compounds exhibit mixed-type corrosion inhibition activity. They often inhibit both the anodic metal dissolution and cathodic reduction reactions. Various families of compounds that have been identified to possess corrosion inhibition potentials have one form of limitation or another. For instance, chromates have been reported to be very efficient corrosion inhibitors, but their high toxicity had led to strict restriction of their use as corrosion inhibitors.15 The limitations associated with inorganic inhibitors, such as toxicity, environmental unfriendliness, selective inhibitive behaviour, i.e. anodic or cathodic, high cost of production etc., have necessitated the continuous exploration of organic inhibitors. Most of the industrially useful organic inhibitors are amines, amides, diamines and various other forms of organic compounds that have essential hydrophilic (polar functional groups) and hydrophobic characters. The polar functional groups are responsible for the metalinhibitor interactions (adsorption), while presence of significant hydrophobic character is 2 ACS Paragon Plus Environment
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essential for the separation of metallic surface from aggressive solution. The choice of heterocyclic compounds in corrosion control is related to their good inhibitive performance and their synthesis that can be easily and economically carried out from relatively cheap starting materials.16,17 These heterocyclic compounds effectively impede corrosion by adsorbing on the metal through their functional groups (such as -NO2, -OH, -OCH3, -CN, -NH2, etc.), π-bonds and unshared electrons on the heteroatoms.18-20 Despite the cost-effectiveness and ease of synthesizing heterocyclic compounds, the major challenge confronting the synthesis process is the discharge of environmental unfriendly substances such as organic solvents and intermediate species from the workup into the environment. In order to address this downside, microwave irradiation has been introduced into chemical synthesis research. Microwave irradiation is a powerful alternative heating source for the synthesis of various organic, inorganic, polymeric and nanomaterials.21-23 Unlike conventional heating method that passes heat through the reaction vessels before impacting on reactant molecules, microwave irradiation ensures direct interactions of microwave radiation (energy) with reactant molecules, and brings about fast bond breaking, and consequently speedy product formation.24-26 Furthermore, one step multicomponent reaction (MCR) approach was adopted for the synthesis, thereby avoiding too many work-ups and minimizing organic solvents wastage. Therefore, MCR synthetic approach coupled with microwave irradiation ensures significant green and sustainable synthetic strategy for the development of organic compounds with potential applications in corrosion prevention. The present study is designed to synthesize N-substituted 2-aminopyridine derivatives namely, 6-(2,4-dihydroxyphenyl)-4-phenyl-2-(phenylamino)nicotinonitriles (DPPN), 6-(2,4dihydroxyphenyl)-2-((4-hydroxyphenyl)amino)-4-phenylnicotinonitrile (DHPN) and 6-(2,4dihydroxyphenyl)-2-((4-methoxyphenyl)amino)-4-phenylnicotinonitrile (DMPN) synthesized through microwave irradiation and MCR approach, and to investigate the effect of substituent groups (–OH and –OCH3) on the corrosion inhibition activities of the compounds. The synthesized DPPN, DHPN and DMPN molecules contain several polar functional groups such as –OH, –CN, –N=C
