Physical Insights from Frumkin Isotherm Applied to Electrolyte Gated Organic Transistor as Protein Biosensors

Label free biosensors based on electrolyte gated organic transistors (EGOTs) are ultra-sensitive and versatile sensing devices. The dose curve represents the change of the sensor signal as a function of...

Application of Frumkin Isotherm for Carbon Steel Corrosion in Soil Media

This study investigated carbon steel corrosion in three types of soil media (laterite, yellow soil and kaolin). The Frumkin isotherm was used to study the mechanism of the corrosion process. A good linear correlation (y = 3.4x + 3.3) in terms of soil concentration vs. surface coverage was obtained with the value of R2 = 0.996 for carbon steel corrosion in laterite solution at 30oC. A standard weight loss method was used to determine the degree of surface coverage. Investigation on corrosion rate was also carried out on the basis of immersion time and temperature effects. The results showed that yellow soil solution yielded the highest corrosion rate on carbon steel coupon for 5 consecutive days and at various temperatures (30 – 90oC). The thermodynamic properties in terms of heat of reaction and entropy were also investigated in this corrosion study. The results showed that carbon steel coupon was least corroded in the environment of kaolin solution as indicated by its highest endothermic value and lowest entropy. The study showed that the findings are consistent in relation to thermodynamic properties. This work is beneficial for the corrosion study of carbon steel in soil media corresponding to lifetime of buried pipelines and cost safety.

Adsorption of Cytosine on a Mercury Electrode

The electrosorption behavior of cytosine at the mercury electrode/acetic buffer of pH 4 and 5 interfaces was determined from the double-layer differential capacity measurements extrapolated to zero frequency. Solutions of cytosine were prepared to cover the range from 1 × 10-4 to 6 × 10-3 mol dm-3. Adsorption of cytosine was described by the adsorption isotherms constants derived from the surface pressure data as a function of electrode charge density and bulk concentration. The obtained values of the relative surface excesses Γ′ were higher in the acetic buffer of pH 4 than of pH 5. Maximum of cytosine adsorption in the mentioned buffers was at -581 and -551 mV, respectively. The values of the standard Gibbs energy ∆G° obtained from the Frumkin isotherm were higher in the buffer of pH 4 than of pH 5. The values of the interaction parameter A indicated weaker repulsive interaction between adsorbed molecules of cytosine in the former buffer. The adsorption parameters obtained from the virial isotherm confirmed corresponding parameters obtained from the Frumkin isotherm. The dependences of ΦM-2 on the relative surface excess at a constant charge density were analyzed in order to calculate the electrostatic parameters of the inner layer.

Adsorption of Fuchsin Basic on Copper in Citric Acid

The adsorption of Fuchsin Basic (FB) on copper surfaces in citric acid solutions whose concentrations ranged from 0.001 to 0.1 M was investigated using gravimetric measurements. The concentrations of FB studied ranged from 1 × 10−5 to 1 × 10−1 M with adsorption experiments being conducted at temperatures from 298 K to 328 K. The adsorption mechanism is discussed in terms of the applicability of the conventional Frumkin, Bockris–Swinkels and Kastening–Holleck isotherms, amongst others. The best fit was obtained using the Frumkin isotherm model. A thermodynamic/kinetic model of adsorption was also fitted.