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A corrosion inhibition test, coupled with aquantification of in-situ H2evolution, can be used to evaluate an organic inhibitor such as Timoho leaf extract (TLE). TLE is a biodegradable and effective corrosion inhibitor because of its potential to protect 304SS against sulfuric acid. TLE corrosion inhibitor was studied through systematic electrochemical experiments and morphological characterization, with a concentration range of 0–6g L−1. Convolutional Neural Network (CNN)-VGG16 was one of the machine learning approaches used to classify and predict physical changes in hydrogen gas bubbles. Constituents of the TLE and 304SS surfaces were analyzed by FT-IR and UV–Vis tests. The results suggested that 3 g L−1 TLE inhibitor was able to reduce the corrosion rate by 99.37 %. The TLE's inhibition mechanism on 304SS was mixed adsorption and mixed type inhibitor that followed the Isothermal Freundlich Equation. The prediction model by CNN-VGG16 for corrosion tests at varied inhibitor doses was 96% accurate. SEM tests revealed that TLE constituent adsorption on the 304SS surface had a smooth surface morphology with few degraded spots.

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Urbanization, armed conflict, and deforestation in African countries have increased the risk of zoonotic infections, which requires a One Health approach focused on the environment, animal health and human health.

Present study deliberates for the surface treatment of15CDV6 steel using electrolytic cadmium and its corrosion resistance behavior by a macromolecular epoxy coating (DGEBA-DAA) using computational and experimental techniques. Electrochemical results demonstrated that presence of the cadmium enhances the interfacial adhesion behavior of the DGEBA-DAA and same conclusion was reinforced through the computational studies carried out by means of density functional theory (DFT) and molecular dynamic (MD) simulations methods. EIS studies conducted at several time intervals varying from 1h to 180 days showed that increase in immersion time results into the corresponding decrease in the corrosion resistance behavior of DGEBA-DAA coating as significant decrease in the values of charge transfer resistance (Rct) and polarization resistance (Rp) were observed on increasing the immersion time. DGEBA-DAA coating showed the highest Rctand Rpvalues of 6.61kΩcm2and 13.52kΩcm2, respectively after 1h immersion time whereas the lowest Rctand Rpvalues of 1.07kΩcm2and 1.80kΩcm2were obsrved after 180 days immersion . Scanning electron microscopy (SEM) analysis coupled with energy dispersive spectroscopy (EDS) showed that increase in the immersion of 15CDV6 steel in electrolyte decreases the corrosion resistance of the DGEBA-DAA coating through the development, deepening and broadening of the micro-pores. DFT study indicated that DGEBA-DAA interacts through charge transfer (donor–acceptor) interactions in which polar functional groups act as sites for the interactions (adsorption). Outcomes of MD simulations studies depicted that DGEBA-DAA, adsorbed on the cadmium (Cd) surface using its flat or nearly flat orientation thereby acts as effective anti-corrosive coating material. Results of EIS, SEM-EDS, DFT and MDS analyses were in good agreement.

Four new 8-hydroxyquinoline derivatives, namely 5-((1H-benzimidazol-2-yl)methyl)quinolin-8-ol (BIMQ), 5-((5-methyl-1H-benzimidazol-2-yl)methyl)quinolin-8-ol (MBMQ), 5-((5-chloro-1H-benzimidazol-2-yl)methyl)quinolin-8-ol (CBMQ) and 5-((5,6-dichloro-1H-benzimidazol-2-yl)methyl)quinolin-8-ol (DCBMQ) were prepared in moderate to good yields through the condensation of 5-(carboxymethyl)-8-hydroxyquinoline and substituted o-phenylenediamine. 1H, 13C NMR and elemental analysis confirm the formation of the desired compounds. The anti-corrosive potential of these heterocyclic compounds has been studied on carbon steel in 2M phosphoric acid (H3PO4) electrolyte by means of electrochemical measurements. The inhibition efficiency of these heterocyclic compounds was strongly linked to the concentration and the structure of the molecules; reached a maximum of 94.7% for DCBMQ at 10−3M. Data generated from potentiodynamic revealed that the investigated 8-hydroxyquinoline derivatives are mixed type inhibitors. The influence of temperature on the corrosion behaviour was assessed. The four quinoline derivatives adsorbed according to the Langmuir's adsorption isotherm. Surface analysis (SEM and XPS) confirmed the formation of a protective layer adsorbed on the steel surface. DFT calculations suggested that 8-hydroxyquinoline derivatives adsorb on the metal via the 8-hydroxyquinoline ring and their corrosion inhibition potential have some linear correlation with the degree of co-planarity of the benzimidazole and hydroxyquinoline rings. Monte Carlo simulations showed that the molecules adsorbed on Fe(110) surface through the 8-hydroxyquinoline in a near-flat mode and the adsorption energies both in the absence and presence of aqueous phosphate ions agree with the observed trends of inhibition efficiencies.

MXene (Ti3C2Tx) is a highly protective layered material, but its utilization in solution medium to prevent metal corrosion has been very difficult due to surface oxidation. Thus, it was thought worthy to investigate the role of thiourea in the surface modification of MXene for the effective corrosion mitigation of copper in a chloride solution. This was carried out by the incorporation of thiourea into the MXene matrix via thermal treatment for the effective introduction of nitrogen, sulfur, and oxygen functionalities. N,S codoped Ti3C2TxMXene was characterized using advanced analytical methods, followed by appraising the inhibition efficiency using a combined electrochemical method. Results from the electrochemical analysis revealed that increasing the concentration of N,S codoped Ti3C2TxMXene in the chloride solution increases the inhibition efficiency up to 91% at the maximum inhibitor concentration of 100 ppm compared to pure Ti3C2TxMXene. To support the experimental findings, inter- and intramolecular modeling via density functional theory and molecular dynamics simulation were carried out in the gas and solvation phases. As observed from the molecular modeling, N,S codoped Ti3C2TxMXene shows a flat adsorption orientation with a good total surface coverage. The inhibition mechanism is attributed to the heteroatom doping and formation of a barrier film against the permeation of the corrosive species. This study intends to deepen the functionalization of MXenes for the benefit of corrosion science and applications in the direct solution medium of corrosive agents.

Cost effective inhibition of mild steel corrosion employing eco-friendly materials is a high priority subject for industries these days. Therefore, in this work, a series of N-(benzo[d]thiazole-2-yl)-1-phenylethan-1-imines [N-(benzo[d]thiazole-2-yl)-1-phenylethan-1-imine (BTPEI), N-(benzo[d]thiazole-2-yl)-1-(3-chlorophenyl) ethan-1-imine (BTCPEI), N-(benzo[d]thiazole-2-yl)-1-(m-tolyl) ethan-1-imine (BTTEI), and N-(benzo[d]thiazole-2-ylimino) ethyl) aniline (BTPIA)] for mild steel protection in 1 M HCl were explored by adopting methods like gravimetric analysis, adsorption isotherms, and electrochemical methods, for example, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Different spectral characterization methods such as FTIR and 1H NMR were used to confirm the synthesized derivatives. The experimental results affirmed that all of the inhibitors are proven to be very efficient for combating corrosion for mild steel in acidic media. The determined thermodynamic and activation parameters were used to provide a further understanding of the mechanism of inhibitive activity. The computed Gibbs free energy values suggested strong chemical interaction of inhibitors with the mild steel surface, thereby supporting chemisorption. Potentiodynamic polarization data explained the mixed type nature of all of the inhibitors. Impedance measurements point out that protective film deposits on the mild steel in the presence of the inhibitors. Studies like scanning electron microscope (SEM) with electron dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) further supported the adsorption inhibitive mechanism. The theoretical findings such as density functional theory (DFT), Fukui indices, and molecular dynamics (MD) provided good agreement with different experimental techniques.

Industrial applications of the graphene (G) and graphene oxide (GO) can be further explored by making them more dispersible in the aqueous and organic environments. Several attempts have been performed to enhance the dispersity of the G and GO in which surface functionalization is one of the most effective methods. Recently, surface functionalization of G and GO using ionic liquids is gaining particular emphasis because of their high thermal and chemical stability, low volatility, very high ability to dissolve a wide range of compounds and more importantly their environmental-friendly behaviour. The covalent functionalization of G and GO is mostly being achieved by acylation, esterification, isocyanate formation, nucleophilic ring opening, amide formation, and diazotization and cycloaddition reactions. Non-covalent functionalization mostly involves electrostatic forces, hydrogen bonding, π–πinteractions, van der Waals interaction and donor–acceptor interactions. Because of their high dipolar nature, ionic liquids strongly interact with the sp2-hydrodized carbon networks of G and GO sheets and make them more dispersible as compared to their native networks. In the present review article, we described the collection of reports available on covalent and non-covalent functionalization of G and GO using ionic liquids and their industrial applications. The ionic liquid-functionalized graphene (G-IL) and graphene oxide (GO-IL) are extensively used in pollutants decontamination, sensing and bio-sensing, lubrication, catalysis, and carbon dioxide capturing and hydrogen production. The G-IL and GO-IL represent an essential class of materials for versatile future applications.

The present study deals with the corrosion inhibition performance of three 5-aminopyrazole carbonitriles (designated as AHPC, ANPC, and AMPC) on mild steel in 1M HCl medium using gravimetric, electrochemical, surface, and density functional theory (DFT) methods. Gravimetric measurements revealed that inhibition efficiency of the tested compounds increases on increasing their concentration and that AHPC, ANPC, and AMPC showed the highest efficiencies of 90.34%, 92.04%, and 95.45%, respectively, at 7.69 × 10−4M concentration. Electrochemical studies suggest that tested inhibitor molecules act as mixed type corrosion inhibitors and also enhance charge transfer resistance for corrosion process. Surface morphological studies carried out using SEM and AFM studies revealed that AHPC, ANPC, and AMPC molecules adsorb and form surface protective film. DFT study revealed that AHPC, ANPC, and AMPC molecules showed strong interactions with the metallic surface and adsorb strongly.

Enzymes are very important components which are vital for the existence of every cellular life. There is significant interest in the use of structurally stable and catalytically active enzymes in pharmaceutical, food, fine chemicals industries, and in various industrial processes as catalysts. Stem bromelain (BM) is a proteolytic enzyme which is widely used in chemical, medical, and pharmaceutical fields. However, harsh process conditions are the main barriers to the effective use of this enzyme in different applications. To overcome these drawbacks, biocompatible bio-based ionic liquids (ILs), composed of the choline cation (an essential nutrient) and different anions are used. The ILs namely choline chloride [Ch]+[Cl]−, choline acetate [Ch]+[Ac]−, choline dihydrogen phosphate [Ch]+[Dhp]−, choline bitartrate [Ch]+[Bit]−, choline iodide [Ch]+[I]−, and choline hydroxide [Ch]+[OH]−are chosen for the current work. Therefore, in the present study, structural stability and activity of BM have been evaluated in the presence of choline-based ILs using various biophysical techniques at different concentrations. The present work demonstrated that [Ch]+[OH]−is the strongest destabilizer, whereas [Ch]+[Cl]−is the best stabilizer for the native structure of BM among all studied ILs. This work revealed the suitability of some choline-based ILs as potential media for sustained stability and activity of BM.

The present study describes the microwave-induced aqueous phase synthesis, characterization, and corrosion inhibition effect of five heterocyclics containing nitrogen, oxygen, and sulfur (designated by CINH-1 to CINH-5) for mild steel in 1 M HCl. The effectiveness of the newly synthesized heterocyclics has been evaluated using experimental and theoretical methods. Weight loss study revealed an increased effectiveness of the CINH molecules with increase in their concentrations and acquired the highest values of 82.38, 85.79, 88.93, 92.61, and 95.45% for CINH-1, CINH-2, CINH-3, CINH-4, and CINH-5, respectively, at 39.8 × 10−5M concentration. Polarization study revealed that studied CINH molecules as cathodic-type inhibitors. EIS study showed that CINH molecules behave as interface type of corrosion inhibitors and enhance polarization resistances in their presence. Their adsorption at the interfaces obeyed the Temkin adsorption isotherm. The inhibition effect of the investigated CINH molecules was further supported by surface morphological studies using atomic force microscopy and scanning electron microscopy methods. Several DFT parameters such as ∆E, χ, η, σ, µ, and ∆Nbased on the values of frontier molecular energies (EHOMOand ELUMO) have been evaluated and employed to describe the inhibition action of the tested CINH molecules. Using MD simulations, orientation of the CINH molecules and adsorption energies for their interactions with metallic surface have been determined. Experimental and theoretical consequences were in good agreement.

The effect of Holoptelea integrifolialeaf extract (HILE) on corrosive dissolution of mild steel in 1 M hydrochloric acid was investigated using weight loss, surface, electrochemical, and DFT methods. Results showed that corrosion protection capability of HILE increases with increasing its concentration and maximum value of 93.91% was attained at 400 mg/L concentration. Adsorption of phytochemicals present in HILE on metallic surface followed the Langmuir adsorption isotherm. Tafel polarization study revealed that HILE acts as mixed type inhibitor. EIS study revealed that HILE inhibits mild steel corrosion by getting adhered on the mild steel surface. SEM and AFM analyses showed that in presence of HILE, metallic surface becomes smooth because of the formation of inhibitive film over metallic surface. DFT calculations were also performed on the several active phytochemicals. It was found that β-amyrin was the most effective phytochemical for mild steel corrosion among the available constituents present in the extract.

A pencil graphite electrode was modified with poly(crystal violet) film and characterized using cyclic voltammetric method (CV). The film coated electrode exhibited excellent electrocatalytic properties towards electrochemical detection of hydroquinone (HQ) and catechol (CC) and the process was found to be adsorption-controlled. A linear relationship was observed between the peak current response and concentration for both HQ and CC by using differential pulse voltammetry (DPV) technique and the detection limits of 30.35 nM and 27.76 nM were obtained for HQ and CC respectively. The redox potentials were observed to be pH dependent and confirms transfer of the same protons and electrons number in the oxidation and reduction mechanisms. Furthermore, successful selective separation of HQ and CC in a binary mixture was achieved.

The potentials of three carbazole derivatives, namely 2,3,4,9-tetrahydro-1H-carbazole-8-carboxylic acid (THCZCA), 6-methyl-2,3,4,9-tetrahydro-1H-carbazole (MTHCZ) and 9-methyl-9H-carbazole-3-carboxylic acid (MCZCA) as anticorrosion agents for mild steel in abiotic, 1 M HCl and biotic, Desulfovibrio vulgaris(D. vulgaris) media have been investigated by electrochemical and weight loss techniques. The compounds were found to suppress mild steel corrosion in both 1 M HCl and D. vulgarismedia. Potentiodynamic polarization data suggested that the presented carbazoles exhibit mixed-type inhibitive behaviour with hugely cathodic effect. Adsorption of the compounds was best described by Langmuir (for THCZCA) and Frumkin (for MTHCZ and MCZCA) isotherms. Scanning electron microscopy analyses indicated that the studied carbazoles formed protective film on mild steel surface both in the 1 M HCl and SRB media. The N and O heteroatoms and aromatic π-electron fragments of the molecules interact chemically with the mild steel as suggested by FTIR spectra. Quantum chemical calculations also suggested that the N and O atoms are the most susceptible sites of interactions with mild steel and the trends of the derived reactivity indices correlate fairly well with experimental inhibition efficiencies. Monte Carlo simulations also showed that the carbazole molecules have a great tendency to displace water from metallic surface and adsorb strongly on the steel surface as revealed by the high magnitudes of adsorption energies in the Fe(110)/inhibitor/50 H2O systems.

Three N-substituted 2-aminopyridine derivatives, namely, 6-(2,4-dihydroxyphenyl)-4-phenyl-2-(phenylamino)nicotinonitrile (DPPN), 6-(2,4-dihydroxyphenyl)-2-((4-hydroxyphenyl)amino)-4-phenylnicotinonitrile (DHPN), and 6-(2,4-dihydroxyphenyl)-2-((4-methoxyphenyl)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 the 20.20 × 10–5mol L–1concentration. The results of the electrochemical impedance spectroscopy 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 because of the development of protective films by DPPN, DHPN, and DMPN molecules on the surface. The results of theoretical DFT and Monte Carlo simulation studies supported experimental studies and posited that the DPPN, DHPN, and DMPN molecules adsorbed on the 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.

The electrochemical response of serotonin on the modified electrode based on multiwalled-carbon-nanotube (MWCNT) doped respectively with nickel, zinc and iron oxide nanoparticles coating on glassy carbon electrode (GCE) at physiological pH7 was determined using cyclic voltammetry (CV) and square wave voltammetry (SWV). The modified GCE/MWCNT-metal oxide electrodes exhibited excellent electrocatalytic activity towards the detection of serotonin at large peak current and lower oxidation potentials compared to other electrodes investigated. The dynamic range for the serotonin determination was between 5.98×10−3μM to 62.8μM with detection limits 118, 129 and 166nM for GCE/MWCNT-NiO, GCE/MWCNT-ZnO and GCE/MWCNT-Fe3O4sensors respectively. GCE-MWCNT-NiO was the best electrode in terms of serotonin current response, electrode stability, resistance to fouling and limit of detection towards the analyte. The developed sensors were found to be electrochemically stable, reusable, economically effective due to their extremely low operational cost, and have demonstrated good limit of detection, sensitivity and selectivity towards serotonin determination in urine samples.

This work describes and compares the electron transport and electrocatalytic properties of chemically synthesised cobalt oxide (Co3O4) and nickel oxide (NiO) nanoparticles grafted onto graphene oxide (GO)/acid treated multi-walled carbon nanotubes decorated glassy carbon electrode. Successful synthesis of these nano materials was confirmed using microscopic and spectroscopic techniques. Successful modification of electrode was confirmed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Results showed that the GCE-fMWCNT-NiO and GCE-fMWCNT- Co3O4 nanocomposite modified electrodes gave faster electron transfer process in both 5 mM Ferri/Ferro ([Fe(CN)6]3−/4−) redox probe and 0.1 M phosphate buffer solution (PBS). GCE-fMWCNT-NiO and GCE-fMWCNT-Co3O4 electrodes also gave enhanced Pyrene oxidation current compared with bare GCE and other electrodes studied. The charge transfer resistance, electron transfer rate constant (ks), Tafel value, limit of detection (LoD), sensitivity, adsorption equilibrium constant (β), Gibbs free energy change due to the adsorption (ΔGoads) of Pyrene onto the GCE-fMWCNT-Co3O4 are established and discussed. The LoD and ΔGoads for Pyrene were 1.62 nM and -15.8 kJ/mol, respectively, over a linear dynamic range of 1.0 x 10-9 – 100 x 10-9 M. The electro-oxidation of Pyrene was a diffusion dominated process, but demonstrated adsorption thought to be as a result of a combination of the strong pi-pi electron interactions between Pyrene and the MWCNT, thus the thin film formed on the surface of the electrode by the analyte and its reaction intermediates. The LoD compared favourably with literature reported values. GCE-fMWCNT-Co3O4 gave better performance to Pyrene electrooxidation, good resistance to electrode fouling, higher catalytic rate constant and lower limit of detection. The sensor is easy to fabricate, cost effective and could be used for routine determination of Pyrene in food and environmental matrices.

Effects of electron donating (−CH3and −OH) and electron withdrawing (−NO2) substituents on the corrosion inhibition efficiency of four glucosamine-based, substituted, pyrimidine-fused heterocycles (CARBs) on mild steel corrosion in 1 M HCl have been investigated using gravimetric, electrochemical, surface morphology (SEM, AFM, and EDX), and computational techniques. Gravimetric studies showed that protection performances of the compounds increase with increase in concentration. Both electron withdrawing (−NO2) and electron donating (−CH3and −OH) groups were found to enhance the inhibition efficiency, but the effect is more pronounced with electron-donating substituents. The compounds were found to be cathodic-type inhibitors as inferred from the results of potentiodynamic polarization studies. EIS studies suggested that the studied compounds inhibit metallic corrosion by adsorbing on metallic surface. The adsorption of the inhibitor molecules on steel surface was further supported by SEM, AFM, and EDX analyses. Adsorption of CARBs on a mild steel surface obeyed the Langmuir adsorption isotherm. Theoretical studies using quantum chemical calculations and molecular dynamics simulations provided additional insights into the roles of the −OH, −CH3, and −NO2substituents on the corrosion inhibition performances of the studied inhibitors.

The corrosion inhibition efficiencies of three novel naphthyridines namely, 5-amino-9-hydroxy-2-phenylchromeno[4,3,2-de][1,6]naphthyridine-4-carbonitrile (N-1), 5-amino-9-hydroxy-2-(p-tolyl)chromeno[4,3,2-de][1,6]naphthyridine-4-carbonitrile (N-2), and 5-amino-9-hydroxy-2-(4-methoxyphenyl)chromeno[4,3,2-de][1,6]naphthyridine-4-carbonitrile (N-3) have been investigated for mild steel in 1 M HCl solution by using weight loss, electrochemical impedance spectroscopy, and potentiodynamic polarization methods. All three compounds show high inhibition activities at 6.54 × 10–5M : N-1, 94.28%; N-2, 96.66%; and N-3, 98.09%. Electrochemical impedance spectroscopy analysis reveals an increase in polarization resistance due to the adsorbed inhibitor molecules on metal surface. Potentiodynamic polarization analysis reveals that all three compounds act as mixed-type inhibitors but of predominantly cathodic type. The adsorption of the studied compounds on mild steel surface follows the Langmuir adsorption isotherm. Surface morphology examined by using scanning electron microscopy and atomic force microscopy analysis shows a smoother surface for mild steel in the presence of naphthyridines in acidic solution. Quantum chemical parameters correlate well with the experimental results, which support higher inhibition efficiencies of N-3 and N-2 due to the electron-donating effects of −OCH3and −CH3substituents, respectively, than of N-1, which is devoid of substituents. The magnitudes of the adsorption energies obtained from Monte Carlo simulations also agree with the trend of the experimental inhibition efficiency.