Modeling of iron adsorption on HTTA-loaded polyurethane foam using Freundlich,Langmuir and D-R isotherm expressions

The sorption of Fe(III) at low pH range from 1 to 4.5 on open cell polyether type HTTA-loaded polyurethane foam has been carried out using batch technique. The optimum shaking time for 2.5· 10^–4M solution of Fe(III) was found to be 30 minutes. The concept of macropore and micropore nature of polyurethane foam sorbent offers unique advantages of adsorption. Freundlich and Langmuir adsorption isotherms are followed at low concentration range from 1·10^–4 to 3·10^–4M solution of Fe(III). The Freundlich constant (1/n=0.46±0.013 andK=9.16±1.39 mg·g^–1) and Langmuir isotherm constants(M=21.78 mg·g^–1 andb=88.41±9.731·g^–1) were established. The sorption mean free energyE=12.22±0.09 kJ·mol^–1 and loading capacityC _m =145.21±6.1 mg·g^–1 were evaluated using Dubinin-Radushkevich isotherm, which suggested that the adsorption mechanism was chemisorption.     

Adsorption of urea at the mercury—water interface

The adsorption of urea on mercury from aqueous 1 M KNO₃ has been determined from capacity and electrocapillary measurements. A Langmuir isotherm is obeyed with a saturation molecular area of 24 × 10^?10 m² per molecule. The standard free energy of adsorption is a quadratic function of charge with maximum adsorption occurring at a charge of +8 μC cm^?2. These data are interpreted in terms of the partially oriented urea dipole, the contribution of water dipoles and nitrate ions also being considered.     

Optimization of adsorption parameters for Fe (III) ions removal from aqueous solutions by transition metal oxide nanocomposite

Manganese oxide nanocomposite (Mn₂O₃/Mn₃O₄) was prepared by sol-gel technique and used as an adsorbent. Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy (FE-SEM) were used to characterize the adsorbent. The response surface methodology (RSM) was employed to evaluate the effects of solution pH, initial Fe (III) ions concentration, adsorbent weight, and contact time on the removal ratio of the Fe (III) ions. A total of 27 adsorption experimental runs were carried out employing the detailed conditions designed based on the Box-Behnken design (BBD). Results showed that the pH of the solution and initial Fe (III) ions concentration were the most significant parameters for Fe (III) ions removal. In process optimization, the maximal value of the removal ratio of Fe (III) was achieved as 95.80%. Moreover, the corresponding optimal parameters of adsorption process were as: contact time?=?62.5?min, initial Fe (III) concentration?=?50?mg/L, adsorbent weight?=?0.5?g, and pH?=?5. The experimental confirmation tests showed a strong correlation between the predicted and experimental responses (R²?=?0.9803). The fitness of equilibrium data to common isotherm equations such as Langmuir, Freundlich, and Temkin were also tested. The sorption isotherm of adsorbent was best described by the Langmuir model. The kinetic data were analyzed using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models. The adsorption kinetics of Fe (III) ions were well fitted with the pseudo-second-order kinetic model.     

Antibacterial drugs as environmentally-friendly corrosion inhibitors for carbon steel in acid medium

The effect of cefazolin (CZ) and cefotaxime (CT) as corrosion inhibitors for carbon steel in 0.5 M H₂SO₄ solution was investigated by use of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), and scanning electron microscopy (SEM). CZ and CT acted as mixed-type inhibitors. Inhibition increased with increasing inhibitor concentration and decreased with increasing temperature. Adsorption of the inhibitors obeyed the Langmuir adsorption isotherm. SEM confirmed inhibition by the inhibitors. Inhibition by 5 × 10^?4 M CZ and 7 × 10^?4 M CT approached 99.6 % and 90.9 %, respectively. The EIS and EFM results were in good agreement with the potentiodynamic data.     

Raman spectroscopic studies on surface coordination mechanism of benzotriazole and triphenylphosphine with metals

The complexes of benzotriazole (BTAH) with Ag, Cu, Fe, Zn and Ni were prepared respectively in the non-aqueous solution by the direct electrochemical synthesis and characterized by microanalysis and normal Raman spectroscopy. The influence of the neutral ligand of triphenylphosphine (pph₃) on the coordination process was deduced by the normal Raman spectroscopy and electrochemistry. The metals were classified into two categories. For the first type, such as Cu and Ag, CuBTA and AgBTA were obtained in the solution without pph₃. The introduction of pph₃ led to its participation in the coordination processes of BTAH with Cu or Ag and appeared in the final complex. Fe, Zn and Ni belonged to the second type, there was no influence on the coordination of BTAH with Zn, Ni and Fe, i.e., the final complexes were Fe(BTA)₂, Zn(BTA)₂ and Ni(BTA)₂, respectively, in the solution with/without pph₃. The electrochemical results revealed that the BTAH can inhibit the corrosion of all the above metals, and the introduction of pph₃ resulted in the decrease of inhibition efficiency to Cu surface, while no influence was observed on the Ni surface. The different role of pph₃ was explained in terms of hard/soft acids and bases rule and coordination mechanism was proposed.     

Synthesis and characterization of silica gel microspheres encapsulated by salicyclic acid functionalized polystyrene and its adsorption of transition metal ions from aqueous solutions

The present study was undertaken to develop a novel adsorbent for heavy metal ions, and this paper presents the synthesis and characterization of a composite material-silica gel microspheres encapsulated by salicyclic acid functionalized polystyrene (SG-PS-azo-SA) with a core-shell structure. SG-PS-azo-SA was used to investigate the adsorption of Mn(II), Co(II), Ni(II), Fe(III), Hg(II), Zn(II), Cd(II), Cr(VI), Pd(II), Cu(II), Ag(I), and Au(III) from aqueous solutions. The results revealed that SG-PS-azo-SA has better adsorption capacity for Cu(II), Ag(I) and Au(III). Langmuir and Freundlich isotherm models were applied to analyze the experimental data, the best interpretation for the experimental data was given by the Langmuir isotherm equation with the maximum adsorption capacity for Cu(II), Ag(I), and Au(III) at 1.288 mmol g⁻¹, 1.850 mmol g⁻¹ and 1.613 mmol g^t-1, respectively. Thus, silica gel encapsulated by salicyclic acid functionalized polystyrene (SG-PS-azo-SA) is favorable and useful for the removal of Cu(II), Ag(I) and Au(III) metal ions.     

Raman spectroscopic studies on surface coordination mechanism of benzotriazole and triphenylphosphine with metals

The complexes of benzotriazole (BTAH) with Ag, Cu, Fe, Zn and Ni were prepared respectively in the non-aqueous solution by the direct electrochemical synthesis and characterized by microanalysis and normal Raman spectroscopy. The influence of the neutral ligand of triphenylphosphine (pph₃) on the coordination process was deduced by the normal Raman spectroscopy and electrochemistry. The metals were classified into two categories. For the first type, such as Cu and Ag, CuBTA and AgBTA were obtained in the solution without pph₃. The introduction of pph₃ led to its participation in the coordination processes of BTAH with Cu or Ag and appeared in the final complex. Fe, Zn and Ni belonged to the second type, there was no influence on the coordination of BTAH with Zn, Ni and Fe, i.e., the final complexes were Fe(BTA)₂, Zn(BTA)₂ and Ni(BTA)₂, respectively, in the solution with/without pph₃. The electrochemical results revealed that the BTAH can inhibit the corrosion of all the above metals, and the introduction of pph₃ resulted in the decrease of inhibition efficiency to Cu surface, while no influence was observed on the Ni surface. The different role of pph₃ was explained in terms of hard/soft acids and bases rule and coordination mechanism was proposed.     

Inhibition effect of environmentally benign Karanj (Pongamia pinnata) seed extract on corrosion of mild steel in hydrochloric acid solution

The inhibition of the corrosion of mild steel in hydrochloric acid solution by the seed extract of Karanj (Pongamia pinnata) has been studied using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization, and linear polarization techniques. Inhibition was found to increase with increasing concentration of the extract. The effect of temperature, immersion time, and acid concentration on the corrosion behavior of mild steel in 1 M HCl with addition of extract was also studied. The adsorption of the extract on the mild steel surface obeyed the Langmuir adsorption isotherm. Values of inhibition efficiency calculated from weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy are in good agreement. Polarization curves showed that Karanj (P. pinnata) seed extract behaves as a mixed-type inhibitor in hydrochloric acid. The activation energy as well as other thermodynamic parameters for the inhibition process was calculated. The adsorbed film on mild steel surface containing Karanj (P. pinnata) seed extract inhibitor was also measured by Fourier transform infrared spectroscopy. The results obtained showed that the seed extract of Karanj (P. pinnata) could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric acid media.     

Cacotheline as an oxidimetric reagent. Determination of Sn(II), Cu(I), Ti(III), Fe(II), V(II) and V(III)

Summary Sn(II), Ti(III), Cu(I), Fe(II), V(III) and V(II) can be titrated potentiometrically with cacotheline in 1–4M hydrochloric acid, 0.5–2M hydrochloric acid, 0.5–1.5M sulphuric acid in presence of 4 ml of 10% EDTA solution in a total volume of 50 ml, 9–10M phosphoric acid, 4–8M acetic acid and 3–8M acetic acid respectively. Cacotheline can be used for the assay of tin plate and solder. The cacotheline undergoes a 2-electron reduction reaction. A cacotheline solution (0.005M) in 0.02M hydrochloric acid is fairly stable for several months. The conditional redox potentials of cacotheline have been determined in sulphuric, phosphoric and acetic acid medium.

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Kakothelin als oxydimetriscbes Reagens. Bestimmung von Sn(II), Cu(I), Ti(III), Fe(II), V(II) und V(III)

Zusammenfassung In 1–4M Salzsäure, in 0,5–2M Salzsäure, 0,5–1,5M Schwefelsäure in Gegenwart von 4 ml 10%iger EDTA-Lösung in einem Gesamtvolumen von 50 ml, in 9–10M Phosphorsäure, in 4–8M Essigsäure bzw. in 3–8M Essigsäure kann man die genannten Kationen potentiometrisch mit Kakothelin titrieren. Dieses eignet sich auch für die Untersuchung von Lötzinn. Kakothelin erleidet dabei eine 2-Elektronen-Reduktions-Reaktion. Seine 0,005M Lösung in 0,02M Salzsäure ist einige Monate beständig. Sein Redoxpotential in Schwefelsäure, Phosphorsäure bzw. Essigsäure wurde bestimmt.

     

The investigation of the adsorptive behaviour of electroactive species by means of admittance analysis: Part II. Anion-induced adsorption of cadmium(II) from bromide and iodide solutions at the dropping mercury electrode

The adsorption of Cd(II) has been studied by measuring the interfacial admittance spectra at different dc potentials of the dropping mercury electrode (DME) in solutions of: (a) 1 M KBr+0.48 mM Cd(NO₃)₂,(b) 1 M KI+0.105 mM CdI₂ and (c) 0.1 M NaI+0.9 M NaClO₄ +0.116 mM CdI₂ The experimental data were analysed using the procedures described in Part I of this series. The frequency dependence of the admittance corresponds to that of a reversible electrode reaction with reactant adsorption. The potential dependence of the resulting adsorption parameters can be mathematically described by a Langmuir isotherm for adsorption of Cd(II) with the adsorption energy being at least a quadratic function of potential. Detailed checks on the consistency of this model have been applied and were found to be satisfactory.     

Organically modified silica gel and flame atomic absorption spectrometry: employment for separation and preconcentration of nine trace heavy metals for their determination in natural aqueous systems

A 5-formyl-3-(1′-carboxyphenylazo) salicylic acid-bonded silica gel (FCPASASG) chelating adsorbent was synthesized according to a very simple and rapid one step reaction between aminopropyl silica gel (APSG) and 5-formyl-3-(1′-carboxyphenylazo) salicylic acid (FCPASA) and its adsorption characteristics were studied in details. Nine trace metals viz.: Cd(II), Zn(II), Fe(III), Cu(II), Pb(II), Mn(II), Cr(III), Co(II) and Ni(II) can be quantitatively adsorbed by the adsorbent from natural aqueous systems at pH 7.0–8.0. The adsorbed metal ions can be readily desorbed with 1 M HNO₃ or 0.05 M Na₂EDTA. The distribution coefficient, K_d and the percentage concentration of the investigated metal ions on the adsorbent at equilibrium, C_M,_eqm % (Recovery, R%) were studied as a function of experimental parameters. The logarithmic values of the distribution coefficient, logK_d, are 3.7–6.4. Some foreign ions caused little interference in the preconcentration and determination of the investigated nine metals by flame atomic absorption spectrometry (AAS).The adsorption capacity of FCPASASG was 0.32–0.43 meq g⁻¹. C and N elemental analyses of the adsorbent (FCPASASG) allowed us to calculate a surface converge of 0.82 mmol g⁻¹. This value compares well with the best values reported for the azo compounds. The adsorbent and its formed metal chelates were characterized by IR (absorbance and/or reflectance) and UV spectrometry, potentiometric titrations and thermogravimetric analysis (TGA and DTG). The mode of chelation between the FCPASASG adsorbent and the investigated metal ions is proposed to be due to reaction of those metal ions with the salicylic and/or the carboxyphenylazo chelation centers of the FCPASASG adsorbent. Nanogram concentrations (0.07–0.14 ng ml⁻¹) of Cd(II), Zn(II), Fe(III), Pb(II), Cr(III), Mn(II), Cu(II), Co(II) and Ni(II) can be determined reliably with a preconcentration factor of 100.     

Isotherm, kinetic and thermodynamic studies of lead and copper uptake by H2SO4 modified chitosan

The kinetic and thermodynamic adsorption and adsorption isotherms of Pb(II) and Cu(II) ions onto H₂SO₄ modified chitosan were studied in a batch adsorption system. The experimental results were fitted using Freundlich, Langmuir and Dubinin–Radushkevich isotherms; the Langmuir isotherm showed the best conformity to the equilibrium data. The pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models were employed to analyze the kinetic data. The adsorption behavior of Pb(II) and Cu(II) was best described by the pseudo-second order model. Thermodynamic parameters such as free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were determined; the adsorption process was found to be both spontaneous and exothermic. No physical damage to the adsorbents was observed after three cycles of adsorption/desorption using EDTA and HCl as eluents. The mechanistic pathway of the Pb(II) and Cu(II) uptake was examined by means of Fourier transform infrared (FTIR) and Energy dispersive X-ray (EDX) spectroscopy. The equilibrium parameter (R_L) indicated that chitosan–H₂SO₄ was favorable for Pb(II) and Cu(II) adsorption.     

Solid-phase extraction of trace Cu(II) Fe(III) and Zn(II) with silica gel modified with curcumin from biological and natural water samples by ICP-OES

Silica gel was firstly functionalized with aminopropyltrimethoxysilane obtaining the aminopropylsilica gel (APSG). The APSG was reacted subsequently with curcumin yielding curcumin-bonded silica gel (curcumin-APSG). This new bonded silica gel was used for separation, pre-concentration and determination of Cu(II), Fe(III), Zn(II) in biological and natural water samples by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions for effective adsorption of trace levels of metal ions were optimized with respect to different experimental parameters using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the newly sorbent was 4.0. Complete elution of the adsorbed metal ions from the sorbent surface was carried out using 2.0 mL of 0.1 mol L^− 1 of HCl. Common coexisting ions did not interfere with the separation and determination at pH 4.0. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 0.63, 0.46 and 0.37 mmol g^− 1 for Cu(II), Fe(III) and Zn(II) respectively. The time for 95% sorption for Cu(II) Fe(III) and Zn(II) was less than 2 min. The detection limits of the method defined by IUPAC was found to be 0.12, 0.15 and 0.40 ng mL^− 1 for Cu(II), Fe(III) and Zn(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was lower 3.0% (n = 5). The procedure was validated by analyzing the certified reference river sediment material (GBW 08301, China), the results obtained were in good agreement with standard values. This sorbent was successfully employed in the separation and pre-concentration of trace Cu(II), Fe(III) and Zn(II) from the biological and natural water samples yielding 75-fold concentration factor.     

Investigation of the spectral properties of a squarylium near-infrared dye and its complexation with Fe(III) and Co(II) ions

The spectral features of the squarylium near-infrared (NIR) dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is λ=663 nm in methanol. This value matches the output of a commercially available laser diode (650 nm), thus making use of such a source practical for excitation. The emission wavelength of the dye in methanol is λ_em=670 nm. The addition of either Fe(III) ion or Co(II) ion resulted in fluorescence quenching of the dye. The Stern–Volmer quenching constant, K_SV, was calculated from the Stern–Volmer plot to be K_SV=2.70×10⁷ M⁻¹ for Co(II) ion. The K_SV value for Fe(III) ion could not be established due to the non-linearity of the Stern–Volmer plot and the modified Stern–Volmer plot for this ion. The detection limit is 6.24×10⁻⁸ M for Fe(III) ion and 1.55×10⁻⁵ M for Co(III) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant, K_S, of the metal–dye complex was calculated to be 3.14×10⁶ M⁻¹ for the Fe–dye complex and 2.64×10⁵ M⁻¹ for the Co–dye complex.     

Synthesis and efficiency of poly(acrylamidrazonehydrazide) chelating fiber for preconcentrating and separating trace gold and palladium from solution

A new poly(acrylamidrazone-hydrazide) chelating fiber has been synthesized using polyacrylonitrile fiber as a starting material. An ICP-OES method for applying the fiber to preconcentrate and separate trace Au(III) and Pd(IV) ions in solution has been established. The experiments show that 8 ng/ml Au(III) and 6 ng/ml Pd(IV) in 1000 ml of solution can be enriched quantitatively by the fiber column at a flow rate of 12 ml/min at pH 2. These ions can be desorbed quantitatively with 10 ml of 2.5% CS(NH₂)₂ + 6% H₂SO₄ containing 0.2% Fe(II) from the column at an elution rate of 6 ml/min. A fiber treated with 12M HCl or 15M HNO₃ can be re-used 10 times with above 95% recoveries of Au(III) and Pd(IV), and 120–800-fold excesses of Cu(II), Mn(II), Fe(III), Al(III), Ni(II), Mg(II) and Ca(II) ions cause little interference. The RSDs are 2.0% for 8 ng/ml Au and 3.5% for 6 ng/ml Pd. The recovery of added standard in a solution sample from a metal smelter is 96.2% for Au and 100% for Pd, and the content of each ion in the sample determined by the method is in agreement with the analysed value from the smelter laboratory.     

Linear scan stripping voltammetry of copper(II) at the chemically modified carbon paste electrode

A new chemically modified electrode (CME), -benzoinoxime (CUPRON) modified carbon paste electrode, for determining copper(II) is reported because of its excellent selectivity and sensitivity. The electrode is made by mixing a quantity of CUPRON (25%, w/w) with graphite powder (50%, w/w) and paraffin oil (25%, w/w). The CME preferentially deposits copper from the pH 8.5 NH₃-NH₄Cl buffer solution containing copper(II) under an open circuit and most of metal ions do not interfere with the measurements. The detection limit (S/N of three) for determining Cu(II) is 3 × 10^–10 g/ml after 10 min accumulation in fast linear scan stripping voltammetric measurement. Linear calibration curves are obtained for Cu(II) concentration ranged from 1 × 10^–8 M to 1 × 10^–6 M. The response can be maintained with relative standard deviation of 6.0% in a 5 × 10^–6 M Cu(II) solution after eight accumulation/measurement/ regeneration cycles at the same electrode surface. The effect resulted from carbon paste preparation, reduction potential, electrode renewal, electrolyte and solution pH, preconcentration time, concentration dependence, possible interference and other variables has been evaluated. As for application, the CME demonstrates its high sensitivity and copper-selectivity in complex composition samples, such as anodic mud and polluted water.     

Inhibition of copper corrosion by arylazotriazoles in nitric acid solution

Summary A study has been made to investigate the effect of some azoheterocyclic dyes of the type 3-arylazo 1,2,4-triazole (AT) on the corrosion of copper exposed to 0.5M nitric acid solution at different temperatures and at differentAT concentrations. Using potentiodynamic polarization andTafel electrochemical methods, it can be shown thatAT compounds are good inhibitors of copper corrosion in HNO₃ solution. The kinetic and thermodynamic parameters of the inhibited system were determined. The high inhibition efficiency of these compounds may be due to the adsorption of the additive itself and/or the adsorption of the formed Cu(II)-AT complexes at the polarized electrode interface. Cathodic polarization measurements showed thatAT dyes are predominantly cationic inhibitors.

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Hemmung der Korrosion von Kupfer in salpetersaurer Lösung durch Arylazotriazole

Zusammenfassung Der Effekt einiger azoheterocyclischer Farbstoffe des Typs 3-Arylazo-1,2,4-triazol (AT) auf die Korrosion von Kupfer in 0.5M Salpetersäure bei verschiedenen Temperaturen und unterschiedlichenAT-Konzentrationen wurde untersucht. Potentiodynamische Polarisation und elektrochemische Methoden nachTafel zeigen, daß Verbindungen vom TypAT gute Korrosionsinhibitoren für Kupfer gegenüber HNO₃ sind. Die kinetischen und thermodynamischen Parameter des inhibierten Systems wurden bestimmt. Die hohe inhibitorische Wirksamkeit der untersuchten Verbindungen kann auf die Adsorption des Additivs selbst oder auf jene des Cu(II)-AT-Komplexes an der polarisierten Elektrodenoberfläche zurückzuführen sein. Kathodenpolarisationsmessungen zeigen, daßAT-Farbstoffe vorwiegend kationische Inhibitoren sind.

     

Determination of experimental parameters in the Fe(III)/Fe(II) system in 1 M H2SO4, with a polycrystalline gold electrode, taking advantage of its non-linear behaviour

In this work, the values of the heterogeneous standard rate constant and the transfer coefficient of the electrochemical system Fe(III)/Fe(II) in 1 M H₂SO₄ at a polycrystalline gold electrode were determined. The response spectrum to an ac potential of such amplitude as to make the behaviour of the electrode process non-linear was analysed. The experimental study was complemented by a theoretical study of the Fe(III)/Fe(II) system using numerical methods. Comparison of the experimental and theoretical data enabled the kinetic parameters of this electrode process to be determined.     

Tetrachloroferrate(III)-selective liquid membrane electrode based on crystal violet

An extract of crystal violet-tetrachloroferrate(III) in nitrobenzene was used to prepare a tetrachloroferrate(III)-selective liquid membrane electrode with a poly(vinyl chloride) support. The optimal conditions to determine 2.5 × 10^–5 – 5.0 × 10^–2 M iron(III) as tetrachloroferrate(III) (anionic slope 56 mV/decade, detection limit 7.9 × 10^–6 M) were found to be 4.0–5.5.M total chloride in 0.75–1.5M hydrochloric acid. The electrode was reliably applied to determine iron in human blood, haematite and mineralized vitamin syrup by direct potentiometry, standard and sample additions as well as standard subtraction techniques.     

非水体系中苯并三唑在铜电极上吸附的电化学表面增强拉曼光谱研究

采用电化学现场表面增强拉曼光谱(SERS)研究了非水体系中苯并三唑(BTAH)在铜电极上的吸附及成膜行为, 结果表明非水体系中BTAH的吸附行为随电位变化而不同. 较负电位区间主要以中性分子形式吸附; 中间电位区间主要以BTA^－吸附并不可逆成膜; 而在氧化电位区间主要表现为铜的氧化. 随中性配体三苯基膦(pph₃)的加入, 在中间电位区间, 由于易溶的Cu(pph₃)_n⁺的生成而使铜的溶解速度加快, 最终该阳离子在溶液中和BTA^-作用而生成了多核铜的配合物. 采用直接电化学方法模拟电极表面过程合成了相应的吸附产物, 并对其组成进行了相关表征.