The corrosion protection and/or adsorption of polyacrylamide (PAA) of number average molecular weight, n M , between 15,000 -1,350,000 g mol -1 on mild steel and iron (99.99 % Fe) in 3 M HCl at room temperature was studied using spectrophotometry (the phenanthroline method), the weight loss method and EIS (Electrochemical Impedance Spectroscopy). It was found that the corrosion protecttion efficiency of the PAA -adsorbed layers strongly depends on both the molar concentration of PAA in the solution and its molecular weight, reaching limiting values between 85 and 96 %. Simultaneously, it was also concluded that a relatively high surface coverage could be obtained with very low PAA concentrations (0.5 -2 ppm), indicating the good adsorption characteristics of PAA on mild steel and iron in hydrochloride acid. The experimentally obtained results follow a Langmuir adsorption isotherm. According to the best fitting parameters, the adsorption coefficient B ranged between 2×10 7 and 4×10 8 mol -1 and depended strongly on the molecular weight of the PAA: B = k α n M (for α ≈ 0.67 and k = 2.95×10 4 ) or the size of the polymer coil. As was found by EIS, the thickness of the adsorbed PAA layer was approx. 1.1 nm (for ε r = 15) and corresponded only to the polymer segments attached to the metal surface. On the other hand, as was found by ellipsometry, the limiting layer of the adsorbed PAA molecules was highly voluminous and relatively thick (100 -200 nm), containing entangled polymer coils.
The presence of phenolic compounds as one of the most common organic pollutants in natural water (surface and ground waters) has been detected as a worldwide problem. Very small concentrations of phenols affect the quality of both environmental and household waters, and directly or indirectly impact lives in aquatic systems and humans, as well. Most of the organic compounds, containing certain functional groups, such as amino, amines, carbonyl, hydroxyl, groups containing sulfur and others, have shown ability of adsorption on metal surfaces from aqueous solutions. Cyclic voltammetry (dE/dt = 100 mV s-1) with simultaneous monitoring of the double layer (dl) capacitance (at 100 Hz and 1 mV ac signal) was used for an adsorption study of phenol on polycrystalline gold from 0.5 mol dm-3 aqueous solutions of NaHCO3. Thus, in this study an effort was made to establish a fast method, an electrochemical procedure for qualitative and quantitative determination of phenols in natural water systems.
Electrochemical synthesis of polypyrrole (PPy) and polypyrrole/activated carbon (PPy/AC)-composite films, with a thickness between 0.5 and 15 μm were performed in a three electrode cell containing 0.1 mol dm-3 Py, 0.5 mol dm-3 NaClO 4 dissolved in ACN, and dispersed particles of AC (30 g dm-3). Electrochemical characterization of PPy and PPy/AC composites was performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The linear dependences of the capacitance (q C), redox capacitance (q red), and limiting capacitance (C L) of PPy and PPy/AC-composite films on their thickness (L), obtained by electrochemical and impedance analysis, indicate a nearly homogeneous distribution of the incorporated AC particles in the composite films (correlation coefficient between 0.991 and 0.998). The significant enhancement of q C , q red and C L , was observed for composite films (for 40±5%) in respect to that of the "pure" PPy. The decreased values of a volume resistivity in the reduced state of the composite film, ρ = 1.3×10 6 Ω cm (for L = 7.5 µm), for two orders of magnitude, compared to that of PPy-film with the same thickness, ρ ≈ 10 8 Ω cm, were also noticed.
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