Initial corrosion protection of Zn-Mn alloys electrodeposited from alkaline solution

The effects of a deposition current density (c.d.) on the corrosion behaviour of Zn-Mn alloy coatings, deposited from alkaline pyrophosphate solution, were investigated by atomic absorption spectrophotometry (AAS), X-ray diffraction (XRD), atomic force microscopy (AFM), optical microscopy, electrochemical impedance spectroscopy (EIS) and measurement of corrosion potential (E(corr)). XRD analysis disclosed that zinc hydroxide chloride was the main corrosion product on Zn-Mn coatings immersed in 0.5 mol dm(-3) NaCl solution. EIS investigations revealed that less porous protective layer was produced on the alloy coating deposited at c.d. of 30 mA cm(-2) as compared to that deposited at 80 mA cm(-2)

Sorption of zinc by novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid

Novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid were applied as adsorbents for the removal of Zn(2+) ions from aqueous solution. In batch tests, the influence of solution pH, contact time, initial metal ion concentration and temperature was examined. The sorption was found pH dependent, pH 5.5 being the optimum value. The adsorption process was well described by the pseudosecond order kinetic. The hydrogels were characterized by spectral (Fourier transform infrared-FTIR) and structural (SEM/EDX and atomic force microscopy-AFM) analyses. The surface topography changes were observed by atomic force microscopy, while the changes in surface composition were detected using phase imaging AFM. The negative values of free energy and enthalpy indicated that the adsorption is spontaneous and exothermic one. The best fitting isotherms were Langmuir and Redlich-Peterson and it was found that both linear and nonlinear methods were appropriate for obtaining the isotherm parameters. However, the increase of temperature leads to higher adsorption capacity, since swelling degree increased with temperature

Hydrogel based on chitosan, itaconic acid and methacrylic acid as adsorbent of Cd2+ ions from aqueous solution

A hydrogel has been synthesized by ionic crosslinking of chitosan (Ch) with itaconic acid (IA), followed by a free radical polymerization and crosslinking of Ch/IA network by adding methacrylic acid and the crosslinker. The resulting material (Ch/IA/MAA hydrogel) was characterized by spectral (Fourier transform infrared (FTIR)), thermal (thermogravimetric analysis (TGA)) and structural (SEM/EDX and atomic force microscopy (AFM)) analyses. The prepared hydrogel was investigated as potential adsorbent for removal of Cd2+ ions from aqueous solution. The effect of various physico-chemical parameters such as pH, adsorbent dosage, adsorbate concentration and contact time was studied in batch experiments. The results of spectral analyses of Cd-loaded hydrogel have shown that active functional groups are -NH2, -OH and -COOH. SEM/EDX analysis and AFM surface topography and phase images indicated that apart from the adsorption on the surface of the hydrogel, sorption takes place in the bulk, as well. The experimental kinetic and equilibrium data were better fitted by pseudo-second order kinetic model and Langmuir adsorption isotherm. The parameters obtained in thermodynamic studies showed that the adsorption of Cd2+ on Ch/IA/MAA hydrogel was spontaneous and exothermic in nature. Desorption studies were carried out using acid leaching (HNO3) and it has been shown that the regenerated hydrogel can be reused three times without any loss of adsorption capacity. The maximum adsorption of 285.7 mg/g has been obtained at pH 5.5 and the results of adsorption/desorption experiments implies that the Ch/IA/MAA hydrogel may be used as efficient sorbent for removal of Cd2+ ions from aqueous solution

Removal of Cu2+ ions using hydrogels of chitosan, itaconic and methacrylic acid: FTIR, SEM/EDX, AFM, kinetic and equilibrium study

A removal of Cu2+ ions from aqueous solutions onto hydrogels of chitosan. itaconic and methacrylic acid has been investigated using batch adsorption technique. The extent of adsorption was investigated as a function of pH, adsorbent dose, initial metal ion concentration, contact time and temperature. The FIR spectra showed that -NH2, -OH and -COOH groups are involved in the Cu2+ ions adsorption. The surface topography changes were observed by AFM, where the phase images indicated that sorption takes place on the surface of the hydrogel and in the bulk. Pseudo-first order, pseudo-second order and intraparticle diffusion models were analyzed and showed that the Cu2+ ions adsorption followed pseudo-second order kinetics. The equilibrium data were analyzed using Langmuir, Freundlich and Redlich-Peterson isotherms and the best interpretation was given by Redlich-Peterson. The adsorption capacity was found to be 122.59 mg/g, based on the non-linear Langmuir isotherm. Based on the separation factor. R-L, the Cu2+ ion adsorption is favorable, while the low activation energies indicate physisorption. Desorption experiments, done with a nitric acid, showed that the investigated hydrogels could be reused without significant losses of the initial properties even after three adsorption-sorption cycles

Formation of oxygen complexes in controlled atmosphere at surface of doped glassy carbon

The effects of boron and phosphorus incorporation in phenolic resin precursor to the oxidation resistance of glassy carbon have been studied. In order to reveal the nature and composition of the oxygen complexes formed at the surface of doped glassy carbon, under controlled atmosphere, the surface of the samples was cleaned under vacuum up to 1273 K. Specific functional groups, subsequently formed under dry CO2 or O-2 atmosphere on the surface of boron-doped and phosphorus-doped glassy carbon samples, were examined using the temperature-programmed desorption method combined with mass spectrometric analysis. Characterization of surface properties of undoped and doped samples has shown that in the presence of either boron or phosphorus heteroatoms, a lower amount of oxygen complexes formed after CO2 exposure, while, typically, higher amount of oxygen complexes formed after O-2 exposure. It has been concluded that the surface of undoped glassy carbon has a greater affinity towards CO2, while in the presence of either boron or phosphorus heteroatoms, the glassy carbon surface affinity becomes greater towards O-2, under experimental conditions