Rozina Khattak

By Murtaza Sayed, Luqman Ali Shah, Javed Ali Khan, Noor S. Shah, Rozina Khattak and Hasan M. Khan

In this chapter, free radical kinetics with the help of competition kinetics and some experimental results calculated by competition kinetics to find out the rate constant of reactive species (●OH, eaq−, ●H) with target compound, which is used by radiation chemists is briefly discussed. The competition kinetics method is well validated by taking ciprofloxacin, norfloxacin and bezafibrate as example compounds. The bimolecular rate constants of hydroxyl radical, hydrate electron and hydrogen atom has been calculated for example solute species (ciprofloxacin, norfloxacin and bezafibrate).

Part of the book: Advanced Chemical Kinetics

By Rozina Khattak, Murtaza Sayed, Muhammad Sufaid Khan and Hamsa Noreen

Part of the book: Redox

By Rozina Khattak

The sensitizer-mediator redox reaction is a vital component of the dye-sensitized solar cells (DSSCs). The efficiency and stability of dye-sensitized solar cells are aided by the kinetics of this redox process. Several reaction parameters influence the kinetics of a reaction, and if those parameters are controlled, the rate of the process and its results can be controlled. One of the most important aspects of the sensitizer-mediator interaction is the reaction medium. Aqueous DSSCs are unquestionably a good replacement when it comes to taking a green approach to avoiding toxic, flammable, and volatile organic solvents and their mixtures, which are commonly used in DSSCs and are known to harm the environment while also reducing the lifetime and stability of the DSSCs. The catalytic role of a small volume fraction of organic solvent in the aqueous electron transfer kinetics of a few putative sensitizer-mediator reactions is discussed in this chapter. In binary solvent media including dilute tertiary butyl alcohol (TBA)-water and dilute 1,4-dioxane-water, the reduction of dicyanobis(2,2′-dipyridyl)iron(III) and dicyanobis(1,10-phenanthroline)iron(III) was investigated. The reactions were carried out in a 10% TBA or dioxane to water media with a volume-volume fraction of both solvents using iodide as a reducing agent. The effect of several parameters on the rate constant was also calculated and analyzed.

Part of the book: Recent Advances in Chemical Kinetics

By Rozina Khattak

This chapter discusses the catalytic effect of extended π-conjugation on the electron transfer process between ferricyphen-ferrocyanide and ferricypyr-ferrocyanide in an aqueous medium. Ferricyphen and ferricypyr may be feasible options for the sensitizer in dye-sensitized solar cells due to their high reduction potential, stability, capability as an outer-sphere oxidant, and photosensitivity. Meanwhile, ferrocyanide could be used as a mediator in DSSCs instead of iodide to avoid iodate production and achieve a similar reduction potential and stability. This chapter compared the ability of competent putative sensitizers to oxidize the likely mediator in water. In contrast to the 2,2′-dipyridyl chelate, the extended π-conjugation in 1,10-phenanthroline accelerated the redox process by increasing the electron affinity of ferricyphen as compared to ferricypyr. The reactions had the same kinetics but different rate constants, indicating that the ferricyphen-ferrocyanide reaction was several times faster than the ferricypyr-ferrocyanide reaction, revealing and confirming the catalytic influence of extended π-conjugation on the redox process.

Part of the book: Recent Advances in Chemical Kinetics

By Muhammad Sufaid Khan, Rozina Khattak and Abbas Khan

The global need for energy is growing every day. In this situation, looking for alternative energy sources should be a priority. Alternative energy comes in a variety of forms. One of the most promising technologies to partially address the energy deficits is fuel cell technology, or FCT. Fuel cells can be classified according to their design and the electrolyte that was used to build them. The FCT is regarded as one of the most promising technologies for alternative energy sources since it has so many advantages over other forms of energy sources. The oxygen reduction reaction (ORR), which occurs on the fuel cell’s cathode, is the primary electrochemical process in fuel cell technology. Pt catalyst is used to increase ORR, which improves a fuel cell’s (FC’s) stability and performance. The use of platinum (Pt) metal is not without its problems, though; among them is the metal’s high cost and scarcity. Therefore, the challenge for researchers is to identify low-cost, easily accessible substitute electrocatalysts. These are some of the challenges or barriers that will need to be overcome in the future. Two major barriers to the commercialization of FCT are the stability of the catalytic materials and the availability of a substitute material for Pt. The FCT and technological research used to enhance it are summarized in this chapter.

Part of the book: Chemical Kinetics and Catalysis

By Rozina Khattak

Solvent plays a significant role in the kinetics of any reaction in solution. The reactions that occur between ions of similar charges, ions with dissimilar charges, ion and neutral molecules, and-or, between neutral molecules/compounds, solvent or solvent-solvent mixture, and-or, reaction media show a distinct effect in each case. The solvent or solvent-solvent mixture, and-or, reaction media may either increase the rate of reaction or decrease it or may not even affect it when the rate constant is measured as a function of the dielectric constant of the reaction media. The transition state theory of reactions in solution correlates the rate constant with the dielectric constant, and provides a straight-line formulation. The charges on the reactants help to predict whether the rate of the reaction will be increased or decreased or will stay constant as the dielectric constant of the reaction media is varied. However, this is not always the case. There is no simple correlation of the rate constant and the dielectric constant of reaction media as described by the transition state theory. This chapter reveals the facts beyond this correlation. The kinetics of the redox reaction between Fe(III) based metal complex and iodide was studied in four different reaction media. The effect of the ionic strength was also revealed to identify the reactive species that are involved in the rate-determining step of the reaction to surface the role of the solvent or the mixture of solvents in the redox kinetics and mechanism. This study showed a prominent effect of the solvents on the kinetics and mechanism of the reaction.

Part of the book: Chemical Kinetics and Catalysis