INHIBITING EFFECT OF CRYSTAL VIOLET DYE ON ALUMINUM CORROSION IN ACIDIC AND ALKALINE MEDIA

Crystal violet dye (CV) was studied as a corrosion inhibitor for aluminum in hydrochloric acid (1 mol dm^?3) and potassium hydroxide (0.5 mol dm^?3) solutions in the temperature range 30°–60°C using the gravimetric technique. The effect of iodide ions on the inhibiting efficacy of CV was also assessed. CV was found to inhibit Al corrosion in both aggressive media, exhibiting greater inhibition efficiency in 1 M HCl (83.6%) than in 0.5 M KOH (23.0%). Inhibition efficiency in 0.5 M KOH was, however, synergistically increased in the presence of iodide ions to attain values up to 85.3%. Inhibition efficiency in the acidic and alkaline solutions increased with CV concentration but decreased with rise in temperature, suggesting physical adsorption of CV on the Al surface. The calculated values of activation energy (E_a), free energy of adsorption (ΔG_ads), and heat of adsorption (Q_ads) confirm the physisorption mechanism. The inhibitor adsorption characteristics were approximated by the Freundlich adsorption isotherm.     

Corrosion of the zinc negative electrode of zinc–cerium hybrid redox flow batteries in methanesulfonic acid

Corrosion of zinc in aqueous methanesulfonic acid has been evaluated over a wide range of concentrations of acid (0.5–5 mol dm^?3), dissolved zinc (0.5–2 mol dm^?3), and electrolyte temperature (22–50 °C). The corrosion rate of zinc, in terms of weight loss and the volume of hydrogen evolved, varied with time and it was found to be highly dependent on the surface state and electrolyte conditions. With an initial active layer of zinc present, the corrosion rate rapidly increased following a decline when the proton concentration in the solution decreased to ca. 0.56 mol dm^?3. Organic and inorganic inhibitors were added to the electrolyte to suppress the zinc corrosion in 1 mol dm^?3 methanesulfonic acid. The strong adsorption and blocking effects of cationic organic adsorption inhibitors, such as cetyltrimethyl ammonium bromide and butyltriphenyl phosphonium chloride, led to a significant decrease in zinc corrosion over a 10 h immersion period. With the addition of indium and lead ions inhibitors, the zinc surface showed less activity. Zinc corrosion continued to a smaller extent in the presence of these metallic inhibitors during the first few hours, but the metallic layer of the inhibitors did not cover the surface completely resulting in continued hydrogen evolution and making the inhibitors less effective at longer times.     

CORROSION INHIBITION OF CuNi10Fe ALLOY WITH PHENOLIC ACIDS

The purpose of this study was to investigate the efficiency of two phenolic acids, namely p-hydroxybenzoic acid (HBA) and protocatechuic acid (PCA), as corrosion inhibitors for CuNi10Fe alloy in a 0.5 mol dm^?3 NaCl solution. In these investigations, open circuit potential measurements, potentiodynamic polarization measurements, and the linear polarization method have been used. It was found that both phenolic acids had similar corrosion inhibition effects on the CuNi10Fe alloy dissolution. The inhibition efficiency (IE) increased with increase in inhibitor concentration. The polarization shows that both compounds functioned as cathodic corrosion inhibitors by adsorption on the surface of CuNi10Fe alloy according to the Freundlich adsorption isotherm. The numerical values of free energies of adsorption indicate physical adsorption of the compounds on the electrode surface. DFT-based quantum chemical computations and molecular dynamics (MD) simulations revealed identical electronic and adsorption structures for both HBA and PCA, which could account for the similarities in the experimentally observed inhibiting effects.     

Solvent Impregnated Resins containing Quinizarin: Preparation and Application to Batch‐mode Separation of Cd(II), Cu(II), Ni(II), and Zn(II) in Aqueous Media Prior to the Determination by Flame Atomic Absorption Spectrometry

Abstract

Preparation of a high stable solvent impregnated resins (SIR) containing 1,4‐dihydroxyanthraquinone (quinizarin, QNZ) was proposed using Amberlite XAD‐16 beads. The SIR was applied for the separation of Cd(II), Cu(II), Ni(II), and Zn(II) in aqueous media prior to the determination by flame atomic absorption spectrometry (FAAS). The optimum conditions for batch mode extraction of the above metal ions were investigated and it was found that the sorption of these metal ions from a 1000‐ml aliquots of the solution on 1.5 g of the SIR can be carried out quantitatively at pH of 9.5 and an ionic strength of 0.01 mol dm^?3. The sorbed metal ions were subsequently eluted with 10 ml 2 mol dm^?3 HCl and the eluent was subjected to FAAS. Beer's law was obeyed in the range of 9×10^?9 ?1×10^?7 mol dm^?3 for Cd(II) and Zn(II), and 9×10^?8 ?1×10^?6 mol dm^?3 for Cu(II) and Ni(II) contents. Significant interference was not observed due to the various ions, which could be found in natural water samples. The practical applicability of the method was confirmed using a synthetic certificated reference material (CRM) and spiked natural water samples.     

Electrochemical determination of malachite green at graphene quantum dots–gold nanoparticles multilayers–modified glassy carbon electrode

A graphene quantum dots–gold nanoparticles–modified glassy carbon electrode was used to investigate the electrochemical behaviors of malachite green (MG). Cyclic voltammetry curves of MG at the modified electrode exhibited a pair of quasi-reversible adsorption-controlled redox peaks at 0.502 V (E _pa) and 0.446 V (E _pc) in a 0.05 mol L^?1 H₂SO₄ solution. Under the optimal conditions, by using differential pulse voltammetry as the detection method, a linear relationship was obtained between the oxidation peak current and the MG concentration in the range of 4.0 × 10^?7 to 1.0 × 10^?5 mol L^?1 with the detection limit as 1.0 × 10^?7 mol L^?1 (signal-to-noise ratio of 3). The modified electrode was applied in the determination of MG in fish samples, and the results were satisfactory with recoveries from 96.25 to 98.00 %. Furthermore, the modified electrode showed very good reproducibility and stability.     

Separation of Electrochemically Generated Ce(IV) from Rare Earths(III) in Nitric Acid Media by TBP Impregnated Resin

Abstract

Electro‐oxidation of Ce(III) to Ce(IV) in nitric acid media at different anode materials with high oxygen evolution overpotential was carried out. Ce(IV) nitrato complexes were adsorbed on a novel resin, based on porous silica beads with immobilized polystyrene/DVB copolymer, that was impregnated with tri‐n‐butyl phosphate (TBP). Under the studied conditions, Ce(IV) sorption increased with increasing nitric acid concentration (0.5–6 mol · dm^?3). Oxidation of sorbent by adsorbed Ce(IV) species resulting in Ce(III) release to the solution was observed and thoroughly evaluated. In spite of problems with TBP leakage (12%), column separation of pure Ce(IV) from Y(III) and La(III) was achieved in 6 mol · dm^?3 HNO₃ at 288 K. Ce(IV) breakthrough capacity was 0.48 mol · kg^?1‐TBP. Column regeneration with 0.1 mol · dm^?3 nitric acid yielded Ce solution with purity higher than 99.99 wt.% with respect to La and Y impurities.     

LOW MOLECULAR WEIGHT STRAIGHT-CHAIN DIAMINES AS CORROSION INHIBITORS FOR SS TYPE 304 IN HCL SOLUTION

The effect of some low molecular weight straight-chain diamines to inhibit the corrosion of SS type 304 in 1 M HCl solution is examined by weight loss and galvanostatic polarization techniques. The inhibition efficiency increases with increasing the number of carbon atoms in the chain up to 8 carbons, but at higher than 8 carbon atoms (12 carbons) it decreases again. These diamine compounds act as mixed-type inhibitors, but the cathode is more polarized than the anode when an external current was applied. The corrosion rate in the presence of the investigated diamine compounds was found to increase with increasing the temperature and decrease with increasing the concentration of these compounds. Activation parameters for the corrosion of SS in 1 M HCl were calculated and showed that corrosion was much reduced in the presence of inhibitors. The adsorption of these compounds on SS from 1 M HCl solution obeys the Langmuir adsorption isotherm. The synergistic effect of KI on the inhibitive efficiency of the investigated diamine compounds was also studied.     

Inhibition of Steel Corrosion in Nitric Acid by Sulfur Containing Compounds

The inhibitive mechanism, thermodynamics, and adsorptive properties of thiobarbituric acid (TBA) and thiourea (TU) on the corrosion of mild steel in 0.5 M HNO₃ solution have been investigated using potentiodynamic, electrochemical impedance spectroscopy techniques, and quantum chemical calculations. Both inhibitors showed good inhibition efficiency in nitric acid solution. TU was the most effective inhibitor and its inhibition efficiency increases with increasing concentration to attain 99% at 6 × 10^?3 mol · L^?1 at 30°C. Theoretical fitting of different isotherms, Langmuir, Flory–Huggins, Temkin, and the kinetic-thermodynamic models were tested to clarify the nature of inhibitors adsorption on mild steel surface. The obtained experimental data fitted all the applied adsorption isotherms except Langmuir. The thermodynamic activation parameters were determined to provide evidence of the inhibitory effect of TBA and TU. To determine the surface charge at the steel surface in nitric acid solution the potential of zero charge was measured using AC measurements at different potentials. Quantum chemical parameters were calculated and explained. The data clarified that the inhibition of steel in nitric acid by TU or TBA takes place through physicochemical adsorption mechanism.     

Potential of Rice Husk for the Decontamination of Silver Ions from Aqueous Media

The sorption behavior of silver ions on rice husk has been investigated in detail. Various physico-chemical parameters were optimized to simulate the best conditions in which this material can be used as an adsorbent. Maximum adsorption was observed at 0.001 mol L^?1 of acid solutions (HNO₃, H₂SO₄ and HClO₄) using 0.5 g of adsorbent for 9.27 × 10^?5 mol L^?1 silver concentration in fifteen minutes equilibration time. The adsorption of silver was decreased with the increase in the concentrations of all the acids used. The kinetic data indicated an intraparticle diffusion process with sorption being pseudo-second order. The determined rate constant k₂ was 14.707 ± 1.832 mol g^?1 min^?1. The adsorption data obeyed the Freundlich, Langmuir, and Dubinin-Radushkevich isotherms over the silver concentration range of 1.85 × 10^?4 to 1.16 × 10^?3 mol L^?1. The characteristic Freundlich constants, that is, 1/n = 0.38 ± 0.033 and K = 0.271 ± 0.104 m mol g^?1 whereas the Langmuir constants Q = (1.504 ± 0.054) × 10^?2 m mol g^?1 and b = (16.582 ± 2.227) × 10³ dm³ mol^?1 have been computed for the sorption system. The sorption mean free energy from the Dubinin-Radushkevich isotherm is 12.16 ± 0.82 kJ mol^?1 indicating ion-exchange mechanism of chemisorption. The uptake of silver increases with the rise in temperature (283–333 K). Thermodynamic quantities, namely, ΔG, ΔS, and ΔH have also been calculated for the system. The sorption process was found to be endothermic. The effect of other cations and anions on the adsorption of silver has also been studied.     

A Study on the Adsorption of Gold(III) with Macroporous Crosslinked Polyacrylate (MET) Resins. I. Adsorption Equilibrium

Abstract

Equilibrium data for the adsorption of gold tetrachloride from aqueous solutions of four different concentrations of hydrochloric acid (0.250, 0.500, 0.750, and 1.00 mol·dm^?3 HCl) by macroporous crosslinked polyacrylate (MET) resins which have the same functional groups and different structural characteristics have been obtained at a temperature of 25 ± 0.5°C. It was found that the mechanism of adsorption can be regarded as simple ion exchange, and that the adsorption of gold in the resin phase is a “homogeneous” adsorption. The equilibrium constants and the capacities for the adsorption of gold by MET resins were estimated, and the influence of the acidity of the solutions on the equilibrium parameters were discussed.     

Sorption Potential of Styrene‐Divinylbenzene Copolymer Beads for the Decontamination of Lead from Aqueous Media

Abstract

The decontamination of lead ions from aqueous media has been investigated using styrene‐divinylbenzene copolymer beads (St‐DVB) as an adsorbent. Various physico‐chemical parameters such as selection of appropriate electrolyte, contact time, amount of adsorbent, concentration of adsorbate, effect of foreign ions, and temperature were optimized to simulate the best conditions which can be used to decontaminate lead from aqueous media using St‐DVB beads as an adsorbent. The atomic absorption spectrometric technique was used to determine the distribution of lead. Maximum adsorption was observed at 0.001 mol L^?1 acid solutions (HNO₃, HCl, H₂SO₄ and HClO₄) using 0.2 g of adsorbent for 4.83×10^?5 mol L^?1 lead concentration in two minutes equilibration time. The adsorption data followed the Freundlich, Langmuir, and Dubinin‐Radushkevich (D‐R) isotherms over the lead concentration range of 1.207×10^?3 to 2.413×10^?2 mol L^?1. The characteristic Freundlich constants i.e. 1/n=0.164±0.012 and A=2.345×10^?3±4.480×10^?5 mol g^?1 have been computed for the sorption system. Langmuir isotherm gave a saturated capacity of 0.971±0.011 mmol g^?1, which suggests monolayer coverage of the surface. The sorption mean free energy from D‐R isotherm was found to be 18.26±0.75 kJ mol^?1 indicating chemisorption involving chemical bonding for the adsorption process. The uptake of lead increases with the rise in temperature. Thermodynamic parameters i.e. ΔG, ΔH, and ΔS have also been calculated for the system. The sorption process was found to be exothermic. The developed procedure was successfully applied for the removal of lead ions from real battery wastewater samples.     

Potential of Sawdust for the Decontamination of Lead from Aqueous Media

Abstract

The sorption of lead ions on sawdust has been exploited to evaluate its potential for the decontamination of lead ions from aqueous solutions. Various physico‐chemical parameters such as selection of appropriate electrolyte, equilibration time, amount of adsorbent, concentration of adsorbate, effect of diverse ions and temperature were studied in order to simulate the best conditions in which this material can be used as an adsorbent. Maximum adsorption was observed at 0.005 mol · L^?1 acid solutions (HNO₃, HCl, and HClO₄) using 0.2 g of adsorbent for 4.83×10^?5 mol · L^?1 lead concentration in 10 min equilibration time. Studies show that the adsorption of lead decreases with the increase in the concentrations of all the acids. The adsorption data follows the Freundlich isotherm over the lead concentration range of 2.41×10^?5 to 4.83×10^?4 mol · L^?1. The characteristic Freundlich constants, i.e., 1/n=0.49±0.02 and K=0.142±0.0038 m · mol · g^?1 have been computed for the sorption system. The sorption mean free energy from the Dubinin‐Radushkevich isotherm is 11.26±0.31 kJ mol^?1 indicating ion‐exchange mechanism of chemisorption. The uptake of lead decreases with the rise in temperature (293–323 K). Thermodynamic quantities, i.e., ΔG, ΔS, and ΔH have also been calculated for the system. The sorption process was found to be exothermic. The proposed procedure was applied for the removal of lead from battery water samples.     

THE ROLE OF PHOSPHONATE DERIVATIVES ON THE CORROSION INHIBITION OF STEEL IN HCL MEDIA

The inhibition of corrosion of steel by two P-containing compounds, sodium methyldodecyl phosphonate and sodium methyl (11-smethacryloyloxyundecyl) phosphonate, in hydrochloric acid has been investigated at various temperatures using electrochemical techniques (impedance spectroscopy (EIS), potentiodynamic polarization) and weight loss measurements. Inhibition efficiency (E%) increased with phosphonate concentration. Adsorption of inhibitors on the steel surface in 1 M HCl follows the Langmuir isotherm model. EIS measurements showed that the dissolution process of steel occurred under activation control. Polarization curves indicated that inhibitors tested acted as cathodic inhibitors. The temperature effect on the corrosion behavior of steel in 1 M HCl without and with the inhibitor was studied in the temperature range from 313 to 353 K. The adsorption free energy and activation parameters for the steel dissolution reaction in the presence of phosphonates were determined.     

Separation of Simulated Mixed Mo(VI) and V(V) From HNO3 and HCl Solutions by Selective Extraction and Stripping with Tri-N-Butyl Phosphate as Extractant

Equilibrium study was carried out to determine the optimum conditions required for Mo(VI) extraction from HNO₃ solutions and subsequently, simulated mixed Mo(VI), and V(V) were extracted from HNO₃ (pH = 1.0) and 6.0 mol L^?1 HCl solutions with TBP dissolved in n-hexane. The variation of pH (selective extraction) and selective stripping were investigated as methods of separation of Mo(VI) and V(V). The latter method was found inefficient for separations from HNO₃ solutions (pH = 1.0) except supplemented with selective stripping (back-extraction with 2.0 mol L^?1 H₂SO₄/14.5 mol L^?1 NH₄OH). While from 6.0 mol L^?1 HCl, selective stripping was adequate to quantitatively strip in turns the Mo(VI) and V(V) co-extracted into the TBP phase. About 100% of the co-extracted V(V) from the HCl medium was stripped in a two-stage process, in contrast to a single-stage required for Mo(VI) of the same result. The selective stripping method was found to be better because an initial appreciable co-extraction had occurred prior to stripping separation. Based on analytical and spectra data, the extracted complexes from HNO₃ and HCl media were formulated as ((MoO₂)_7–8n(VO₂)_2n · (NO₃)₁₆) ^(16–18)n- · m TBP (where n>m) and (MoO₂Cl₂ · VO₂ Cl) · xTBP, respectively.     

A Novel Pinus Tabulaeformis Based Adsorbent for the Removal of Malachite Green

Pyrolytic char treated with muffle furnace (TPC), a novel adsorbent, were investigated to enhance its adsorption capacity of malachite green (MG) dye. In addition, the dye adsorption behavior of the TPC in aqueous solution was investigated. The treatment temperature, treatment time, and the particle size of PC had a positive effect on the dye adsorption capacity of TPC. Equilibrium data was fitted well with Langmuir and Redlich-Peterson models with maximum adsorption capacity of 91.24, 111.27, and 119.01 mg g^?1 at 293, 303, and 313 K, respectively. The kinetic of adsorption was found to confirm to the Elovich equation with good correlation and the overall rate of MG uptake was found to be controlled by film diffusion, pore diffusion and particle diffusion. The Boyd plot confirmed that the external mass transfer was the rate-limiting step in the adsorption process. Different thermodynamic parameters have also been evaluated and it was found that the adsorption was spontaneous, feasible, and endothermic in nature. Adsorbents could be regenerated using 0.1 mol L^?1 NaOH solution at least three cycles, with up to 90% recovery. The TPC used in this work proved to be an effective material for the treatment of MG bearing aqueous solutions.     

CORROSION INHIBITION OF CARBON STEEL IN ACIDIC MEDIA BY BIFURCARIA BIFURCATA EXTRACT

The effect of extract of brown alga Bifurcaria bifurcata (Bb) on the corrosion of steel in 1 M HCl solution was studied using weight loss, potentiodynamic, and polarization resistance measurements. Experimental data revealed that Bb extract acted as an inhibitor in the acid environment. The extract was a mixed-type inhibitor, predominating as an anodic inhibitor at higher concentration. It was found that the inhibition efficiency increased with an increase in Bb extract concentration. The corrosion inhibition of Bb extract on carbon steel in 1 M HCl solution was also investigated by infrared and UV-visible spectrophotometry to obtain information on bonding mechanism between the metallic surface and the inhibitor. The process of inhibition is attributed to the adsorption of the extract molecules, the precipitation of Fe-chelates, and/or formation of complex at the electrode surface.     

INHIBITION OF ACIDIC AND PITTING CORROSION OF NICKEL USING NATURAL BLACK CUMIN OIL

The inhibition effect of natural black cumin oil on the corrosion of nickel in 0.1 M HCl solution was studied using galvanostatic and potentiodyanmic anodic polarization techniques. It was found that the inhibition efficiency increased with an increase in the inhibitor concentration of this oil. The inhibitive action of black cumin oil was attributed to the adsorption on metal surface. The adsorbed layer acts as a barrier between the metal surface and aggressive solution, leading to a decrease in the corrosion rate. The adsorption process follows the Langmuir adsorption isotherm. It was found also that black cumin oil provides good protection to nickel against pitting corrosion in sodium chloride solutions.     

Recovery of Gold from Hydrochloric Acid by means of Selective Coagulation with Persimmon Extract

Abstract

Gold was selectively precipitated with solution of persimmon extract which contains persimmon tannin, a kind of polyphenol. Quantitative recovery of gold was achieved in the concentration range of hydrochloric lower than 0.5 mol · dm^?3. X-ray diffraction analysis and a digital micrograph of the filtered cake indicated the formation of gold particle during recovery process. High selectivity of persimmon extract is ascribed to the reduction of Au(III) to elemental form.     

INHIBITION OF MILD STEEL CORROSION IN SULFURIC ACID MEDIUM BY HYDROXYETHYL CELLULOSE

The inhibitive effect of hydroxyethyl cellulose (HEC) on mild steel corrosion in aerated 0.5 M H₂SO₄ solution was studied using gravimetric and electrochemical techniques. The effect of temperature on corrosion and inhibition was also investigated. The results show that hydroxyethyl cellulose functioned as a good inhibitor in the studied environment and inhibition efficiency increased with concentration of inhibitor. Potentiodynamic polarization measurements revealed that HEC inhibited both the cathodic and anodic partial reactions of the corrosion processes. Impedance results clearly show that HEC inhibited the corrosion reaction by adsorption onto the metal/solution interface by significantly decreasing the double layer capacitance (C _dl ). This result was greatly pronounced in the presence of the inhibitor system (HEC + KI) that contains halide additive. Temperature studies revealed an increase in inhibition efficiency with rise in temperature. The adsorption behavior was found to obey the Freundlich isotherm. The values of activation energy, heat of adsorption, and standard free energy suggest that there was transition from physical to chemical adsorption mechanism of HEC on the mild steel surface. Quantum chemical calculations using the density functional theory (DFT) was employed to determine the relationship between molecular structure and inhibition efficiency.     

羧甲基壳聚糖在酸性溶液中缓蚀性能

采用失重及电化学方法（EIS 和 Tafel曲线）研究了羧甲基壳聚糖（CM-chitosan）作为一种绿色缓蚀剂,在1 mol·L-1 HCl 和0.5 mol·L-1 H2SO4溶液中对碳钢的缓蚀作用。结果表明,CM-chitosan是一种良好的缓蚀剂,且在1 mol·L-1 HCl 溶液中的缓蚀作用要优于在0.5 mol·L-1 H2SO4溶液中的缓蚀作用。在HCl和H2SO4两种酸性溶液中,CM-chitosan在碳钢表面的吸附都遵循修正的Langmuir吸附等温式。