Adsorption Thermodynamic Parameters Research Articles

A composite adsorbent of ZnS nanoclusters grown in zeolite NaA synthesized from fly ash with a high mercury ion removal efficiency in solution

In this study, the nanocomposite adsorbent (ZnS-zeolite NaA) was prepared by a simple ion-exchange method, which modified the zeolite NaA synthesized from fly ash. The removal efficiency, adsorption mechanism of mercury ions by ZnS-zeolite NaA and release of zinc ion into aqueous solution during the adsorption process were determined. The results showed that ZnS nanoclusters were introduced the supercages of zeolite by ion exchange to synthesize the ZnS-zeolite NaA with high removal capacity for Hg2+ in the initial pH 2–7 of solution. Determination of the adsorption kinetics and thermodynamic parameters, in combination with X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy analyses, revealed that the Hg2+ adsorption by ZnS-zeolite NaA was Hg2+ complexed and ion exchanged with ZnS in the ZnS-zeolite NaA to form stable HgS, and then, the released Zn2+ was adsorbed by the zeolite, preventing Zn2+ pollution. The Hg2+ removal rate was greater than 99.90% with the coexistence of either Zn2+ or Cu2+, Cd2+ and Pb2+. After five repetitions, the Hg2+ removal rate by the ZnS-zeolite NaA was only slightly decreased by 2%. Therefore, ZnS-zeolite NaA synthesized using fly ash has potential for broad application as a Hg2+ adsorbent.

Plantago Major Extract as an Environmentally Friendly Inhibitor for the Corrosion of L-80 Carbon Steel in 0.5 M H2SO4 Media

The inhibition impact of Plantago major leaves extract on carbon steel (CS) which immersed in 0.5 M H2SO4 media was ‎investigated by several methods such as mass loss method (ML), electrochemical impedance spectroscopy (EIS), potentiodynamic ‎polarization (PDP), and electrochemical frequency modulation‎ (EFM). Data obtained from different measurements was showed that %IE enhanced with added the Plantago major extract doses also increased with increasing temperature degree. Thermodynamic adsorption and kinetic parameters of the system were also measured and studied. The ‎adsorption of the Plantago major extract on CS is, according to Temkin isotherm. The ‎ curves from PDP explained that the Plantago major extract is considered as a mixed-type inhibitor. The EIS technique's acquired data verified that the studied extract produced a thin layer that covers and protects the CS surface. Atomic ‎Force Microscopy (AFM) and Fourier Transform Infrared (FT-IR) analysis conformed that Plantago major extract was adsorbed on CS surface. The data obtained from unlike measurements were in good accord.

Enhanced adsorptive removal of diclofenac sodium from aqueous solution by bentonite-supported nanoscale zero-valent iron

Nano zero-valent iron-bentonite (B-nZVI) is an excellent composite for treating recalcitrant organic pollutants. In this study, B-nZVI was prepared via NaBH4 reduction method and characterized using different instruments including X-ray diffractometer (XRD), Fourier-transform infrared spectrometry (FTIR), Field emission scanning electron microscope (SEM), Transmission electron microscope (TEM), and UV–Vis spectroscopy. Also, the efficiency of B-nZVI as an adsorbent to remove diclofenac sodium (DCF) from aqueous solution was investigated, and compared with activated carbon (AC) under different experimental conditions such as pH, adsorbent dose, DCF initial concentration, temperature, and contact time. The B-nZVI has successfully removed a high percentage of DCF from aqueous solution (80%) within 50 min, 25 °C, and pH = 3. The maximum adsorption capacity of B-nZVI at equilibrium was 140.8 mg g−1 compared to 107.5 mg g−1 via AC. Furthermore, it was found that the DCF adsorption best fitted the Langmuir isotherm and pseudo-second-order kinetic models (R 2 > 0.987). Also, the thermodynamic parameters of adsorption were estimated and the average values showed that the adsorption of DCF via B-nZVI is an endothermic process and spontaneous with a positive value of entropy at 25 °C. The point of zero charge (PZC) was determined (7.0 ± 0.1) using a salt addition method. Finally, column filtration was demonstrated using a mixture of sand and B-nZVI composite, which showed a significant advantage in comparison with that activated carbon/sand mixture.

Revealing the Regularities of Sorption Binding of Cadmium Ions by Pectin Substances from Aqueous Solutions

The complex influence of sorption of cadmium ions on the state of pectin substances was examined using IR spectroscopy of polymer films according to the change of the absorption bands attributed to the stretching vibrations of С–О bond of carboxylic groups of pectates, deformation vibrations of О–Н bond of secondary hydroxyls, and stretching vibrations of carbonyl in ester groups. The isotherms of Cd2+ adsorption were analyzed at 293–308 K. The sorption process on the samples of pectin isolated from the biomass of burdock Arctium lappa L., rhubarb Rheum, citrus cultures, and model substrates of pectinate, pectate, and pectic acid based on them was adequately described using the Langmuir adsorption model. The thermodynamic parameters of adsorption that quantitatively characterize the binding of cadmium with –СООН groups according to the ionic exchange mechanisms, cationic substitution with –СООСа1/2 groups and coordination interactions with alcohol hydroxyls and carbonyl oxygen of methoxylated galacturonate units were determined.

Temperature effect on the efficiency of Eucalyptus Camaldulensis leaves in the acid corrosion of carbon steel

The corrosion phenomenon is greatly affected by temperature. In general, the rate of corrosion increases with rising the temperature. The influence of temperature on the efficiency of Eucalyptus Camaldulensis leaves ( ECl ) have studied using gravimetric method in temperature range 20–60 °C, in the absence and presence of Eucalyptus Camaldulensis leaves ( ECl) at 0.02, 0.04, 0.06 and 0.08 g/ml concentrations. The results indicate that ECl exhibits a great performance as inhibitor to carbon steel in 2 M and 4 M HCl. It can be observed from the experimental results that the inhibition efficiency of Eucalyptus Camaldulensis leaves decreases with rise in temperature which indicates that the inhibition is due to the adsorption of the ECl on carbon steel surface. The highest inhibitor efficiency of 91.56% was obtained at 20 °C in the 2 M HCl and the least inhibitor efficiency of 28.18% was obtained at 60 °C in the 4 M HCl. The adsorption of ECl conforms to Langmuir adsorption isotherm. Kinetics parameters as well as thermodynamic adsorption parameters were calculated and debated.

Anticorrosion activities of polymethacrylic acid and grafted/modified polymethacrylic acid on pure aluminium in acid medium

• The anti-corrosion studies of PMAA and grafted PMAA like PMAA/CAT, PMAA/HQ and PMAA/CAT-HQ were carried out on aluminum in 0.7 M HCl and the inhibition efficiencies were found to be 62%, 82%, 86% and 88% by potentio-dynamic polarizati • The inhibition efficiency of PMAA and grafted PMAA studied by weight loss methods are in good agreement with the results obtained in potentio-dynamic polarization and electrochemical impedance spectroscopic method. • The thermodynamic parameters like standard free energy and equilibrium constant were calculated from the Langmuir curves. Polymethacrylic acid (PMAA) and modified Polymethacrylic acid functionalized with catechol (PMAA/CAT), hydroquinone (PMAA/HQ) and catechol-hydroquinone (PMAA/CAT-HQ) were synthesized by oxidative decarboxylation method using ammonium persulphate as an oxidant and characterized using UV–Visible spectroscopy, FT-IR, XRD, TGA and SEM studies. The percentage of substitution was found to be 81%, 84% and 87% respectively for PMAA/CAT, PMAA/HQ and PMAA/CAT-HQ. The anticorrosion behavior of the synthesized polymers on pure aluminium in 0.7 M HCl was studied by potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and weight loss (WL) methods. As the concentration of the inhibitor increases, the anticorrosion activities increases and reaches the optimum, on further increase in the inhibitor concentration, the anticorrosion activity decreased and remained constant that determines the optimum inhibition efficiency. The increase in the anticorrosion activities at the optimum inhibitor concentration of 300 ppm is found to be in the order: PMAA < PMAA/CAT < PMAA/HQ < PMAACAT-HQ and this may be due to an increase in the substitution. The PDP study indicates that the synthesized polymers act as good cathodic inhibitors on aluminium in 0.7 M HCl. EIS and WL methods have the same trend of inhibitive effect as that of PDP studies which also indicates the formation of a protective layer of polymers on the surface of the pure aluminium. The thermodynamic adsorption parameters like K ads and ΔG ads were calculated using Langmuir adsorption isotherm.

Surface chemistry of bovine serum albumin with hematite nanoparticles and its effect on arsenate adsorption

Environmental context Hematite nanoparticles are efficient adsorbents for proteins and pollutants in environmental and biological systems. Hematite and the protein bovine serum albumin (BSA) were used as models to investigate the surface chemistry and competitive role of BSA in arsenate adsorption. Results show that surface BSA inhibits arsenate adsorption, potentially altering its mobility and bioavailability. Abstract The surface chemistry of metal oxide nanomaterials controls their health impacts and fate in environmental and biological systems. These systems contain proteins capable of binding to nanoparticles, which forms a protein corona that modifies the surface properties of the nanoparticles and reactivity towards pollutants. Using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, we investigate the adsorption of bovine serum albumin (BSA) and quantify the competitive effect of BSA on the adsorption kinetics of arsenate, AsV, to hematite nanoparticles. Experiments were conducted in the flow mode at pH 7. BSA was first adsorbed on hematite, then AsV was allowed to flow over the BSA/hematite thin film. Adsorption kinetic and thermodynamic parameters were calculated using a modified Langmuir adsorption model for both BSA and AsV. The adsorption thermodynamic model showed that BSA binds through two active sites with a binding energy of –41 kJ mol−1, which corresponds to the spontaneous formation of chemisorbed and physisorbed species. When AsV flowed over the BSA/hematite film, only 11 % of surface BSA was desorbed by AsV. This result highlights the inhibitory effect of BSA for AsV adsorption. Structural analysis of BSA revealed changes to the local conformational geometry upon adsorption to and desorption from hematite nanoparticles. Molecular docking simulations showed that the binding free energy of a modelled hematite nanoparticle towards the BSA surface is –6.8 kcal mol−1 (−28.5 kJ mol−1) owing to the formation of various bonds, which agrees with the adsorption kinetics modelling. Overall, surface BSA inhibits arsenate adsorption and therefore increases its mobility and bioavailability.

Energy-Saving and Sustainable Separation of Bioalcohols by Adsorption on Bone Char

The separation of ethanol, propanol, and butanol from aqueous solutions was studied using adsorption on bone char. Adsorption kinetics and thermodynamic parameters of this separation method were studied at different conditions of pH and temperature. Results showed that the maximum adsorption capacities of these bioalcohols were obtained at pH 6 and 20°C. An exothermic separation was identified, which can be mainly associated to hydrophobic interactions between bone char surface and bioalcohols. Binary adsorption studies were also performed using mixtures of these bioalcohols. An antagonistic adsorption was observed for all bioalcohols where the ethanol and propanol separation was significantly affected by butanol. A model based on an artificial neural network was proposed to correlate both single and binary adsorption isotherms of these bioalcohols with bone char. It was concluded that the bone char could be an interesting adsorbent for the sustainable separation and recovery of bioalcohols from fermentation broths, which are actually considered emerging liquid biofuels and relevant industrial chemicals.

Adsorption isotherms, kinetic and thermodynamic studies on cadmium and lead ions from water solutions using Amberlyst 15 resin.

Adsorption isotherms, kinetic and thermodynamic parameters for Cd(II) and Pb(II) ions in water solutions by using Amberlyst 15 resin were performed and evaluated by utilizing solid phase extraction method with the batch system at 298, 308, and 318 K. Flame atomic absorption spectrometry was utilized for absorbance measurements of Cd and Pb in solutions. The Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models, respectively were implemented to equilibrium results obtained. Experimental and theoretical monolayer adsorption capacities of resin for adsorptions of Cd(II) and Pb(II) by the Langmuir isotherm model were approximately the same and they were 120 and 116 mg/g for Cd(II) and Pb(II) ions, respectively at 318 K. Most appropriate kinetic model for adsorption of Cd(II) and Pb(II) on the resin was found as pseudo-second-order. Contact time and temperature for adsorption of analytes on the resin were optimized at 45 min and 298 K. Activation energies (Ea) and thermodynamic values (ΔG°, ΔH° and ΔS°) were determined and assessed. Results showed that adsorptions of Cd(II) and Pb(II) on Amberlyst 15 were spontaneous, exothermic, and chemical ion-exchange processes.

Adsorptive removal of methyl orange dye from aqueous solution using populous leaves: Insights from kinetics, thermodynamics and computational studies

Abstract The present investigation reports an effective adsorption of methyl orange dye using the leaves of populous tree in five different forms. The physicochemical properties of all adsorbents were characterized using instrumental analyses such as Fourier transform infrared spectroscopy (FTIR), powder x-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The feasibility of populous leaves for the adsorptive removal of methyl orange dye from aqueous solution was evaluated in a batch process by varying operational parameters such as adsorbent dosage (0.2–0.6 g), solution pH 3–12, initial dye concentration (5–100 ppm), and contact time (10–100 min). The equilibrium data was correlated by both Freundlich and Langmuir isotherms. The maximum Langmuir monolayer adsorptive capacity was found to be 90.44 mg/g at pH 3.0 and 303.15 K with coefficient of determination R2 = 0.9988 for L-arginine treated populous charcoal powder. The kinetic study revealed that the system obeyed pseudo-first order kinetic model for all the adsorbents (R2 > 0.93). The thermodynamic adsorption parameters showed that the adsorption process is exothermic. Using quadrate models and optimizing the conditions, the maximum adsorption capacity for all the adsorbents was observed at initial dye concentration (75 ppm), dosage of adsorbents (0.6 g) and pH (5). The computational chemistry was also used to validate the adsorption of methyl orange dye.

Thermodynamic analysis of aniline adsorption on polyethylene terephthalate with polyethylene glycol

Thermodynamic adsorption parameters of aniline monomer on polyethylene terephthalate (PET) with polyethylene glycol (PEG) were investigated. The standard affinity (-Δμ0 ) decreased when the number of methylene in PEG increased testing from PEG200 to PEG800. According to the changes of the enthalpy (ΔH0 ) and entropy (ΔS0 ), it is found that the aniline molecules embedded into the PET substrates more strongly when adsorbed with lower molecular weight of PEG, but caused more randomness of the PET fibers. After polymerization, the PANI/PET fabric displayed favourable electrical conductivity and the surface specific conductivity (ρs ) reduced to 1.14 × 103Ω. However, the conductivity of PANI/PET fabric was reduced significantly because of the presence of PEG and lower concentration of adsorption solution.

Corrosion Inhibition of Mild Steel in 1 M HCl Solution by Poly(o-aminothiophenol) and Poly(o-aminothiophenol)/CuO Nanocomposites

The chemical oxidative polymerization of poly(o-aminothiophenol) and poly(o-aminothiophenol)/ CuO nanocomposites were performed in aqueous HCl using ammonium persulfate as an oxidant. The synthesized polymer and its CuO nanocomposites were characterized by employing FT-IR, UV-Vis and XRD analysis. Weight loss and electrochemical techniques were used to investigate the inhibitory performance of poly(o-aminothiophenol) and poly(o-aminothiophenol)/CuO nanocomposites on mild steel in 1 M HCl solution. The electrochemical impedance spectroscopic method showed a capacitive loop, revealing that the corrosion reaction is governed by the charge transfer mechanism. The inhibitors were of a mixed type, according to polarization measurements. The adsorption process was obeyed by the Langmuir isotherm. The Langmuir adsorption isotherm was also used to derive thermodynamic adsorption parameters.

Amino acid and cinnamaldehyde conjugated Schiff bases as proficient corrosion inhibitors for mild steel in 1 M HCl at higher temperature and prolonged exposure: Detailed electrochemical, adsorption and theoretical study

Three Schiff bases composing of cinnamaldehyde and three different amino acids, namely glycine (CGSB), histidine (CHSB) and tryptophan (CTSB) have been synthesized and investigated for their anti-corrosion propensity on mild steel in 1 M HCl. Both gravimetric and electrochemical experimentation establish the CTSB as superior inhibitor, while the CGSB as the least effective among the three. Effectiveness of the Schiff bases is tested upto 60 °C for an exposure of 6 h in HCl. Effect of various exposure times, maximum being 96 h, is also investigated at a fixed temperature of 30 °C. All the three inhibitors impart appreciable extent of corrosion inhibition efficiency under these extreme conditions. Thermodynamic adsorption and kinetic parameters ascertain chemisorption of these mixed-type corrosion inhibitors on mild steel. Mode and extent of interaction between Schiff bases and mild steel are evaluated from quantum mechanical calculation and molecular dynamics simulation.

Design of a solar reactor for the removal of uranium from simulated nuclear wastewater with oil-apatite ELM system

Nuclear wastewater containing uranium ions is a serious threat to the environment. In this study, uranium (VI) ions were adsorbed from the synthesized wastewater by hydroxyapatite nanoparticles (NHAP) in the emulsion liquid membrane (ELM) process. The NHAP was dispersed in the oil, and ELM globules were formed by injecting the NHAP-oil phase into the wastewater. The FT-IR of NHAP, before and after separation process showed the hydroxyl, amine, and phosphoryl groups are important to immobilization of U(VI) ions in oil phase. The morphology of NHAP was identified with FE-SEM, with the NHAP size intially 50 nm, while and at the end the size was about 1 μm. The following optimum conditions were selected: pH = 4, NHAP concentration = 12.4 gL-1, volume of ELM = 43 ml, retention time = 45 min, air flow rate = 0.5 Lmin-1 and impeller rotation speed = 200 rpm. The viscosity of the oil phase decreased with solar radiation and the U(VI) adsorption on the NHAP surface was improved. The oil and air phase distribution within the water phase was simulated. Adsorption isotherms, thermodynamic parameters and kinetic data were investigated.

ISOTHERM, KINETICS AND THERMODYNAMICS ADSORPTION STUDIES OF DYE ONTO Fe3O4-WASTE PAPER ACTIVATED CARBON COMPOSITES

This paper focused on the studying of adsorption properties of Fe3O4-waste paper activated carbon composites for the removal of methylene blue dyes from water. The various parameters were carried out for the adsorption test of the composites, namely; contact time, adsorbent dose, initial MB concentration, pH solution, and temperature. The adsorption of isotherm, thermodynamics and kinetic was used to determine the characteristics of methylene blue adsorption onto the prepared adsorbent. The result indicates that the optimum adsorption capacity has occurred at pH = 6 in water solution. The adsorption capacity increase as the temperature increase until at 315K (45oC). The Langmuir isotherm is more appropriate to be applied as the adsorption model with the maximum adsorption capacity (qm) value of 101 and 93 mg/g for KA HCl-Fe3O4 and KA-Fe3O4 composites, respectively. The value of adsorption thermodynamic parameters was positive for ΔH, negative for ΔGo and positive for ΔSo, meaning the process adsorptions were endothermic, feasibility and spontaneity and randomness, respectively. The pseudo-second-order model was appropriate to predict the kinetic models for methylene blue adsorption onto the composites. The obtained adsorbent composites possess high adsorption efficiency and rapid magnetic separation. They were a promising for practical wastewater treatment for dyes removal from water.

Isolation of biosynthetic crystals by microbially induced calcium carbonate precipitation and their utilization for fluoride removal from groundwater

Biosynthetic crystals (BC) were prepared through microbially induced calcium carbonate precipitation (MICP) for fluoride (F−) removal from the groundwater. Batch experiments were conducted to evaluate the fluoride adsorption capacity and the impacts of critical factors (organic matter, pH, initial fluoride concentration and BC dosage) on defluorination efficiency of BC. The maximum adsorption amount and defluorination efficiency were recorded as 5.10 mg g−1 and 98.24%, respectively. The adsorption kinetics and isotherms studies showed that pseudo-second-order kinetic model and Freundlich isotherm model were best fitting to the reaction. Adsorption thermodynamic parameters indicated a spontaneous, endothermic and thermodynamically favorable adsorption process. Moreover, the mechanism of F− removal by BC was further analyzed by SEM, XPS, XRD and FTIR. The method can cope with the problem of applying the external organic substances in MICP, and avoid the microbial safety risk in the effluent. As an economically and environmentally friendly adsorbent, BC can be used for F− removal from groundwater.

Modification of PVC with 1-Vinylimidazole for CO2/CH4 Separation: Sorption, Permeation and DFT Studies

To improve the gas separation performance of poly (vinyl chloride) membrane, 1-vinyl imidazole was grafted onto the poly (vinyl chloride) by free radical graft copolymerization. The synthesized of the graft copolymer was characterized by the elemental analyzer technique (CHN). The prepared membrane morphology was surveyed by Scanning Electron Microscope (SEM). The properties of thermodynamics of CO2 adsorption were investigated at various temperatures and pressures by quartz crystal microbalance (QCM). The experimental data were correlated by the dual-mode model. The calculated thermodynamics parameters of CO2 adsorption display that CO2 adsorption has the nature of exothermic. Also, methane and carbon dioxide gas permeability was measured. The effects of variation of temperature and feed pressure on the membrane performance were surveyed. The increment in temperature cause to decrement the selectivity of membrane for carbon dioxide/methane gases; whiles, the selectivity of the membrane was incremented by incrementing feed pressure. The outcomes indicate that the permeation selectivity of the grafted copolymer is more than those of the poly (vinyl chloride) membrane for CO2/CH4 gasses. Moreover, Density functional theory (DFT) computes corroborated that the interaction energy of grafted copolymer with CO2 is stronger than this of CH4.

Thermodynamic Analysis of Trisiloxane Surfactant Adsorption and Aggregation Processes.

The trisiloxane polyether surfactant (3-[3-(hydroxy)(polyethoxy)propyl]-1,1,1,3,5,5,5 -heptamethyltrisiloxane) (TS-EO12) was successfully synthesized by a hydrosilylation reaction in the presence of Karstedt catalyst. The structural analysis of the surfactant was done by 1H-NMR, 13C-NMR, 29Si-NMR and FT-IR analysis. In addition the thermal stability of TS-EO12 was studied by the thermogravimetric measurements. On the one hand the surface properties of TS-EO12 at the water-air interface were investigated by surfactant aqueous solutions surface tension measurements carried out at 293 K, 303 K and 313 K, and on the other the aggregation properties were analyzed based on the solubilization properties of TS-EO12 aggregates at different temperatures. On the basis of the obtained thermodynamic parameters of adsorption and micellization of studied surfactant the temperature impact on its surface and volume properties were deduced. It was proved that the tendency of the studied surfactant molecules to adsorb at the water-air interface and to form micelles weakens with decreasing temperature. It was also concluded that the structure of the adsorption layer changes with temperature. Optical microscopy measurements were used for the TS-EO12 micelle morphology determination.

Inhibition of Aluminium Corrosion in 1M HCl by Pyridoxine Hydrochloride: Thermodynamic and Quantum Chemical Studies

Currently, research in the area of corrosion inhibition is focussed on the development of green corrosion inhibitors. It is with this in mind that pyridoxine hydrochloride, which is vitamin B6, has been tested as a corrosion inhibitor of aluminium in 1M HCl by mass loss, Density Functional Theory (DFT) and Quantitative Structure-Property Relationship (QSPR) methods. The results obtained show that the inhibition efficiency increases with concentration but decreases with increasing temperature. This vitamin is adsorbed on aluminium according to the modified Langmuir isotherm and occurs in two modes: physisorption and chemisorption. Thermodynamic adsorption and activation parameters have been determined and discussed. Finally, QSPR approach was used to find the best set of parameters in order to determine the theoretical inhibition efficiencies from the experimental data. Experimental measurements were found in good collaboration with the theoretical results.

Expired amoxicillin and cefuroxime drugs as efficient anticorrosives for Sabic iron in 1.0 M hydrochloric acid solution

The effects of two expired antibacterial drugs, amoxicillin (Amo) cefuroxime (Cef), on the corrosion behavior of Sabic iron in 1.0 M HCl solution were examined using weight loss, galvanostatic polarization (GAP), potentiodynamic anodic polarization, and electrochemical impedance spectroscopy techniques. The outcomes showed that the inhibition efficiency increased with increasing concentrations of Amo and Cef and decreased with temperature. The activity of inhibition of these compounds was elucidated by adsorption on Sabic iron surfaces. The adsorption process obeyed the Langmuir isotherm. The activation and adsorption thermodynamic parameters have been determined and clarified. GAP studies indicated that expired Amo and Cef served as mixed inhibitors. The impedance data showed capacitive loop which indicates that charge transfer governs corrosion reactions. Expired Amo and Cef drugs are good pitting inhibitors by positively shifting the pitting potential. There is a complete agreement between the inhibition efficacies obtained from the different measurements