Nernst equation applied to electrochemical systems and centenary of his Nobel Prize in chemistry

Walther Hermann Nernst received the Nobel Prize in Chemistry in 1920 for the formulation of the third law of thermodynamics, thus celebrating a century in this 2020 year. His work helped the establishment of modern physical chemistry, since he researched into fields, such as thermodynamics and electrochemistry, in which the Nernst equation is included. This paper reports on several experiments that used a Daniell galvanic cell working in different electrolyte concentrations for comparing results with the theoretical values calculated by the Nernst equation. The concentration and activity coefficients values employed for zinc sulfate and copper electrolytes showed activity can replaces concentrations in thermodynamic functions, and the results are entirely consistent with experimental data. The experimental electromotive force from standard Daniell cell, for ZnSO4 and CuSO4, with unitary activity and in different concentrations at room temperature is in agreement with those from theoretical calculations. Cu2+ ion concentrations and temperature were simultaneously varied; however, the cell potential cannot be included in calculations of Nernst equation for different temperatures than 25 °C because the standard potential value was set at 25 °C. The cell potential decreases drastically when the Cu2+ concentration was reduced and the temperature was above 80 oC

Dynamic Luminescent Biosensors Based on Peptides for Oxygen Determination

This chapter summarizes the fundamentals of biosensing techniques based on fluorescence spectroscopy and the protagonism of state-of-the-art luminescent biosensors in a wide range of scientific areas, from environmental monitoring to diagnostics and decease treatment, focusing on the paramount contribution of biosensors based on the Förster Resonance Energy Transfer (FRET) transducing mechanism. State-of-the-art FRET biosensors are specially characterized by outstanding sensitivity toward a number of environmental pollutants and dissolved oxygen in aquatic ecosystems, capable of detecting concentrations in the nano and picomolar scales. These biosensors have also been showing impressive performance over other methods in the study of real-time biological processes in vivo relevant to help understanding decease progression like cancer

Carbon monoxide oxidation on Pt-Ru electrocatalysts supported on high surface area carbon

This find is registered at Portable Antiquities of the Netherlands with number PAN-0000787

Electrochemical Biosensors Containing Pure Enzymes or Crude Extracts as Enzyme Sources for Pesticides and Phenolic Compounds with Pharmacological Property Detection and Quantification

Biosensors are chemical sensors in which the recognition system is based on a biochemical mechanism. They perform the specific component detection in a sample through an appropriate analytical signal. Enzyme-based biosensors are the most prominent biosensors because of their high specificity and selectivity; besides being an alternative to the common immunosensors, they are more expensive and present a limited binding capacity with the antigen depending on assay conditions. This chapter approaches the use of enzymes modified electrodes in amperometric biosensing application to detect and quantify pesticides and phenolic compounds with pharmacological properties, as they have been a promising analytical tool in environmental monitoring. These biosensors may be prepared from pure enzymes or their crude extracts. Pure enzyme-based biosensors present advantages as higher substrate specificity and selectivity when compared to crude extract enzymatic biosensors; nevertheless, the enzyme high costs are their drawbacks. Enzymatic crude extract biosensors show lower specificity due to the fact that they may contain more than one type of enzyme, but they may be obtained from low-cost fabrication methods. In addition, they can contain enzyme cofactors besides using the enzyme in its natural conformation

Elucidation of the surface structure–selectivity relationship in ethanol electro-oxidation over platinum by density functional theory

This article was published by the Royal Society of Chemistry as an Open Access article. It is licensed under a Creative Commons Attribution 3.0 Unported Licence.We have successfully built a general framework to comprehend the structure-selectivity relationship in ethanol electrooxidation on platinum by density functional theory calculations. Based on the reaction mechanisms on three basal planes and five stepped surfaces, it was found that only (110) and n(111) × (110) sites can enhance CO2 selectivity but other non-selective step sites are more beneficial to activity

Platinum–rhodium–tin/carbon electrocatalysts for ethanol oxidation in acid media: effect of the precursor addition order and the amount of tin

Carbon-supported Pt x –Rh y –Sn z catalysts (x:y:z = 3:1:4, 6:2:4, 9:3:4) are prepared by Pt, Rh, and Sn precursors reduction in different addition order. The materials are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques and are evaluated for the electrooxidation of ethanol in acidic media by cyclic voltammetry, chronoamperometry, and anode potentiostatic polarization. The influence of both the order in which the precursors are added and the composition of metals in the catalysts on the electrocatalytic activity and physico-chemical characteristics of Pt x –Rh y –Sn z /C catalysts is evaluated. Oxidized Rh species prevail on the surface of catalysts synthesized by simultaneous co-precipitation, thus demonstrating the influence of synthesis method on the oxidation state of catalysts. Furthermore, high amounts of Sn in composites synthesized by co-precipitation result in very active catalysts at low potentials (bifunctional effect), while medium Sn load is needed for sequentially deposited catalysts when the electronic effect is most important (high potentials), since more exposed Pt and Rh sites are needed on the catalyst surface to alcohol oxidation. The Pt3–Rh1–Sn4/C catalyst prepared by co-precipitation is the most active at potentials lower than 0.55 V (related to bifunctional effect), while the Pt6–Rh2–Sn4/C catalyst, prepared by sequential precipitation (first Rh and, after drying, Pt + Sn), is the most active above 0.55 V.The authors thank the Brazilian National Council of Technological and Scientific Development-CNPq (Grants: 402243/2012-9, 303630/2012-4, 474261/2013-1, 407274/2013-8, and 310282/2013-6) for the scholarships and financial support for this work

Supramolecular Materials for Optical and Electrochemical Biosensors

It is incontestable that the interactions and bonds that keep molecules united to generate unique supramolecular compounds, with individual properties, morphologies and behaviour, are of special dynamics and singular forces. Therefore, it is necessary to discuss and consider the types of interactions that may occur in a determined system, their dynamics and number, which directly act on the energetic balance that strengthen the union between participants and give rise to a supramolecule

Comparative study of gamma-hidroxybutiric acid (GHB) and other derivative compounds by spectroelectrochemistry raman (SERS) on platinum surface.

The electrochemical behaviour of gamma-hydroxybutyric acid (GHB), the cyclic lactone derivative (GBL), 1-butanol, butyric acid and succinic acid on a platinum electrode in acidic medium has been studied by means of Raman spectroelectrochemistry using the SERS effect. Only GHB and 1-butanol were found to be electroactive substances that can form the acid product mainly and other species in minor proportion through the electro-catalytic oxidation reaction of alcohol group. The interaction of all these molecules with the platinum and platinum oxides, generated during the electrodic process has been investigated in a wide interval of potentials. Succinic acid was found to play the role of both intermediate (to produce the conjugate derivative) and product in GHB electrocatalytic oxidation. Likewise, the electrooxidation of 1-butanol produced butyric acid predominantly. The carbon (CH2) and the ring skeletons presented a predominant interaction with the platinum oxide surface for 1-butanol and GBL, respectively