The rechargeable non-aqueous alkali metal-oxygen batteries (also referred to as ‘metal-air’ batteries), such as lithium and sodium-air, offer improved energy storage opportunities over other existing battery systems. Some severe technological problems need to be addressed for the successful development of this system into a commercially viable device. The development of efficient cathode materials and stable electrolytes that allow the reversible electrochemical reduction of oxygen is an area where significant research is necessary. For example, lithium oxygen (Li-O2) cells generate electrical current when lithium ions react with reduced oxygen at the negatively polarised electrode during discharge, the as formed LixO2 reaction products can be reversed during the charging cycle. The problem is that the discharge products (superoxides and peroxides of lithium and sodium) and the metastable intermediates formed are highly reactive, and conventional battery electrolytes easily degrade in their presence. For a greater understanding of the oxygen reduction mechanism and for the direct detection of the intermediates and reaction products formed during the oxygen reduction process, surface sensitive spectroscopy techniques can be utilised. The development of in situ spectroelectrochemical environments for such a purpose is a technical challenge that is unique to each spectroscopy. The information herein has been obtained through in situ surface enhanced Raman spectroscopy (SERS) and UV/Vis spectroscopy in conjunction with common electrochemical techniques. The Raman effect is weak and careful preparation of the surface is necessary to provide enhancement of Raman signals from surface present species during O2 reduction. UV/Vis provides different challenges in the preparation of a sealed electrochemical environment, which the cell and working electrode are transparent to UV/Vis light. Chapter 4 describes the how the size of the supporting salt (tetra alkyl ammonium) cation influences both the electrokinetic and voltage hysteresis between oxygen reduction and evolution reactions (ORR and OER). This was found to be due from the rearrangement of the cation at the electrode interface, under potential control. The use of in situ SERS was used in Chapter 5 to study the effect of solvent on the ORR in the presence of Na+. The findings conclude a solvent dependent mechanism whereby highly solvating solvents like amides and sulfoxides detect only NaO2, and nitriles and glymes detect Na2O2 as respective discharge products. A comparative study of the effect of alkali metal cation size is discussed in Chapter 6 showing the changes in reversibility of O2 with cations of increased ionic radius. Larger cations, such as Na+, K+ and Cs+ display quasi-reversibility, as opposed to the irreversibility of Li+. Finally in Chapter 7 the detection and characterisation of the electronic state of oxygen released from electrooxidised Li2O2, NaO2 and KO2 was obtained through in situ UV/Vis spectroscopy. Li2O2 producing a higher percentage of reactive singlet oxygen per mass of oxidised discharge product compared with NaO2 and KO2. Within this chapter initial findings of a known singlet oxygen sink, 1,4-diazabicyclo[2.2.2]octane (DABCO), is discussed as a possible electrolyte additive.

In this work, molecular complexes of transition metals have been synthesised and studied for their CO2 reduction ability, either in an electrochemical or photochemical system, with a focus on complexes of nickel with derivatives of the macrocycle cyclam (cyc, cyc = 1,4,8,11-tetraazacyclotetradecane) which are well-known for being extremely active CO2 reduction electrocatalysts in water. The cyc framework has been modified with functional groups suitable for binding to semiconductor oxides to obtain the new complexes Ni(cycC) and Ni(cycP) (cycC = 1,4,8,11-tetraazacyclotetradecane-6-carboxylic acid, cycP = {[(1,4,8,11-tetraazacyclotetradecan-1-yl)methyl]phosphonic acid}), and their electrochemical activity towards CO2 reduction in water has been evaluated. Modification of the ligand framework in the 6 position with a carboxylic acid does not change the CO2 reduction activity of the complex Ni(cycC) at pH 5, through the use of electrochemical and spectroscopic techniques it was found that there is a large increase in the CO2 reduction activity at pH 2, proposed to be due to the protonated carboxylic acid acting as an internal proton source. When Ni(cycC) was immobilised on TiO2 electrodes it was possible to measure the rate of photoinduced electron transfer by using μs-s transient absorption spectroscopy (TAS) under argon in the presence of a hole scavenger, however the carboxylic acid proved unstable under CO2. Ni(cycP) was synthesised to provide a stronger binding group to the surface. It was found that functionalisation on the 1 position affected the CO2 reduction activity in a negative way, however the complex was able to bind strongly to both TiO2 and ZrO2. ZrO2 nanoparticles modified with Ni(cycP) and a ruthenium dye were able to reduce CO2 to CO in water at pH = 4, with higher rates and turnover numbers compared to the components in solution, when illuminated with visible light. The improvement in activity for the heterogeneous photocatalyst was attributed to a faster electron transfer from the immobilised dye to the immobilised catalyst, calculated through detailed steady-state and transient spectroscopies, which prevented charge recombination. In collaboration with the University of Cambridge, Ni(cycP) has been immobilised on ZnSe quantum dots (QDs) and it has been proven to be an effective photocatalyst for CO2 reduction to CO in water. We have carried out a detailed ultrafast TAS study on suspensions of the modified QDs, and it has been found that in the presence of a hole scavenger, upon illumination the electrons are excited from the VB to the conduction band (CB), however they rapidly decay to trap states close to the CB to generate a long lived signal. When Ni(cycP) is present, faster decay of the trapped electron signal is observed, which is assigned to fast electronic transfer from the QDs to Ni(cycP). The knowledge of the mechanisms for CO2 reduction will allow rational design of better catalysts for CO2 reduction. In collaboration with the Rutherford Appleton Laboratories, we have designed an in situ spectroelectrochemical Sum Frequency Generation (SEC-SFG) technique using the ULTRA laser at the Central Laser facility. We have demonstrated the technique by analysing the redox behaviour of a well-known CO2 reduction catalyst, [Mn(bpy)(CO)3Br]. We were able to observe the redox species at the electrode surface as a Cyclic Voltammogram was carried out, and to propose the orientation of the species at the surface. Furthermore, the same technique has been applied to the study of the absorption mechanism of Ni(cycC) on the mercury surface, the first step in the catalytic cycle.

The transition metal-free reaction conditions that couple haloarenes to benzene using a combination of KOtBu and an organic additive is proposed to be initiated by a single electron transfer (SET) into the haloarene. It was initially believed that KOtBu was the electron donor, however mounting experimental evidence suggests that electron donors are formed in situ. Within this thesis, both of these potential initiation pathways are investigated. Experimental evidence is presented to support the proposal that the electron-rich enolate anion 6 (formed by deprotonation of the additive N,N’-dipropylketopiperazine 5) acts as an electron donor (Scheme 1). When the additive 7 was used in the transition metal-free reactions, the cyclised product 10 was isolated, which arose by SET from the enolate anion 8. Computational analysis has shown that when DMF is used as the additive in these transition metal-free reaction conditions, the electron donors, 13 or 14, can form from the dimerisation of the carbamoyl anion of DMF. This work lead towards the development of new additives for these transition metal-free reaction conditions. Computational analysis and experimental evidence is presented that puts into question the previously proposed mechanism that KOtBu can donate a single electron to CBr4 in the bromination of adamantane (Scheme 2). It is proposed that alkoxides, like 16, form hypobromite intermediates when reacted with CBr4 15 (rather than undergoing SET) and these hypohalites have been shown to successfully achieve this transformation. These transition metal-free reaction conditions have been used to achieve SRN1 reactions to couple aryl halides with enolate anions (Scheme 3). A thorough study of the reaction mechanism and possible selectivity of reaction pathways, between SRN1 and aryl-aryl bond formations, was performed. The conclusion is that neither photoactivation nor transition metal-induced activation is needed, and solvent isshown to influence the product selectivity. (Scheme 1 The proposal of the formation electron donors from N,N’-dipropylketopiperazine 5 and DMF 11 that can donate a single electron to haloarenes, such as 1, in the transitionmetal-free coupling reactions. Scheme 2 The formation of radical species from the reaction of alkoxides, like 16, with tetrabromomethane occurs through the formation of hypobromites like 17, as opposed to SET from alkoxide 16, as previously proposed. Scheme 3 Transition metal-free reaction conditions used to activate haloarenes to form arylradicals in SRN1 cyclisation of substrate 22 and analogues).

Surface enhanced Raman scattering (SERS) is a useful tool for the detection of metal ions due to the characteristic vibrational spectra that can be produced. Complexing different metal ions to a single ligand in solution can uniquely alter the SERS spectrum of that ligand, with the changes being specific to each individual metal ion. This approach has been used to research a nanoparticle-based sensor that can detect a number of metalions using SERS for environmental monitoring purposes. Research commenced by studying the small Raman reporter molecules, 4-mercaptobenzoic acid (4-MBA) and 4-mercaptopyridine (4-MPY), which were functionalised onto the surface of AgNPs. Upon addition of different metal ions, the AgNPs would aggregate resulting in an increased SERS response and characteristic frequency shifts in certain bands, which allowed discrimination of different species. The potential of 2,2’-bipyridyl (bipy) as a chelating ligand for the SERS detection of multiple metal ions has also been investigated. It has been shown that coordination of six different metal ions to this ligand produces characteristic changes throughout the entire spectral region, and therefore the presence of a metal ion can be identified with greater confidence. Not only that, the sensitivity is also greatly improved, with both Zn(II)and Cu(II) capable of being detected below the World Health Organisation (WHO) recommended limits of 0.22 and 0.6 ppm, respectively. Finally, the characteristic changes produced in the SERS spectrum of salen by Ni(II), Cu(II), Co(II) and Mn(II) is discussed. Although a smaller range of species can be detected compared to bipy, detection limits are significantly improved and changes produced by the different metal ions are arguably more pronounced. This approach has also been applied to real environmental freshwater samples in order to determine whether it is suitable for environmental sampling. A contaminated water sample known to contain elevated levels of Mn(II) was tested and it has been demonstrated that this method is indeed capable of detecting high levels of metal ions in natural freshwater samples.

Obtaining chemical reaction network experimentally is a time consuming and expensive method. It requires a lot of specialised equipment and expertise in order to achieve concrete results. Using data mining method on available quantitative information such as concentration data of chemical species can help build the chemical reaction network faster, cheaper and with less expertise. The aim of this work is to design an automated system to determine the chemical reaction network (CRN) from the concentration data of participating chemical species in an isothermal chemical batch reactor. Evolutionary algorithm ability to evolve optimum results for a non-linear problem is chosen as the method to go forward. Genetic algorithm’s simplicity is modified such that it can be used to model the CRN with just integers. The developed automated system has shown it can elucidate the CRN of two fictitious CRNs requiring only a few a priori information such as initial chemical species concentration and molecular weight of chemical species. Robustness of the automated system is tested multiple times with different level of noise in system and introduction of unmeasured chemical species and uninvolved chemical species. The automated system is also tested against an experimental data from the reaction of trimethyl orthoacetate and allyl alcohol which had shown mixed results. This had prompted for the inclusion of NSGA-II algorithm in the automated system to increase its ability to discover multiple reactions. At the end of the work, a final form of the automated system is presented which can process datasets from different initial conditions and different operating temperature which shows a good performance in elucidating the CRNs. It is concluded that automated system is susceptible to ‘overfitting’ where it designs its CRN structure to fit the measured chemical species but with enough variation in the data, it had shown it is capable of elucidating the true CRN even in the presence of unmeasured chemical species, noise and unrelated chemical species.

A detailed study has been made of the electrolyte conductance of a series of salts in methanolic solution. The pressure coefficients of the limiting equivalent conductances were evaluated over the range 2 - 25 x 10-4 moles litre-1, 5 - 45°C and 1 - 2000 atm. In conjunction with a separate study of the compressibility of methanol, these co-efficients were analysed in terms of the Transition State Theory of conductance. The significant variables are temperature and (Pi + P), the sum of the internal and external pressures. From a consistent representation of the transition state theory three principal parameters were evaluated; (i) the isochoric energy of activation, (ii) the volume of activation and (iii) an entropy term related to, but not equal to, the entropy of activation. The variation of these activation parameters with volume, temperature and ion-size is discussed and this leads to an improved conception of ionic migration in methanol and presumably other liquids. The rectilinearity of the isochores is a striking feature of the work and justifies the application of the constant volume principle.

The attenuation of a high amplitude pulse travelling through a column of liquid contained in a rigid tube is measured experimentally with a new type of hydrophone for two liquids, water and sodium chloride solutions over a range of pressure pulses extending from 30 to 700 atmospheres. An expression based on simple shock wave theory for the attenuation of such a pulse in the semi-stable region of propagation is derived and is found to agree with the measurements if a suitable empirical equation of state for the liquid is assumed.

The statistical thermodynamics of sorption in zeolites is studied. The multicomponent sorbate is regarded as a localized assembly of quasi-independent subsystems each contained in a sorption cavity of the microporous sorbent. Molecular exchange among the subsystems as well as between the assembly and the gas phase that is in thermodynamic equilibrium with the sorbate is allowed. Molecular statistics of the sorbate is worked out in detail with respect to a few representative ensembles. In effecting thermodynamic association of theoretical results, a quasi-grand partition function is related to the sorption system which is in complete thermal and material but only in partial mechanical equilibrium with its surroundings. Fundamental thermodynamic equations of the sorbate are derived, and their conditions of integrability with respect to physical variables are interpreted in relation to 'surface effects' and certain operational restrictions connected with the sorption system. A study of small-system thermodynamics further helps to clarify the behaviour of individual subsystems, especially as regards fluctuations. A quantitative theoretical study of the sorption of krypton and methane in Linde molecular sieve 5A is attempted. By means of analytic mathematics and Monte Carlo methods, statistical thermodynamic functions of the subsystems are calculated from relevant physical parameters. Some interesting features of the techniques used are also discussed. Interactions of the sorbate and sorbent, and in particular the effects due to exchangeable cations in the sorption cavities, are investigated. To indicate the degree of localization of the sorbate, probability distribution functions of the sorbate molecules within a specific subsystem, together with their distribution densities among all the subsystems are presented. Thermodynamic functions of the assembly are then calculated and compared with available experimental data. Finally, the usefulness of various approaches to the study of sorption in zeolites is assessed.

No description available.

In this study of combustion under forced convection, the physical process of cigarette smoking has been investigated. The mechanism during the smoking cycle has been studied under a large variety of conditions by varying puff volumes, cigarette sizes and other parameters 0 A simple unidimensional theory of smoulder under forced convection has been derived and tested by experiments with an adiabatic graphite-particle bed. The theory is shown to be correct for the graphite bed but too elementary to represent cigarette combustion, except in differential form. A working hypothesis is suggested for the smoking process, which has been substantiated by experiments including the measurement of consumption patterns and the recording of the external distribution of hot gases by schlieren photography. Temperature distributions and absolute temperature maxima in cigarettes have been determined by two new methods one of which is dependent upon a new device - a high intensity, low energy, x-ray source.. This device was used for the recording of isothermals in opaque materials by the cine-x-radiography of the melting of finely divided inert metal inclusions. The second method is an extension of optical radiation pyrometry applied to the recording of rapid temperature fluctuations. A study of consumption patterns was made by quenching cigarettes in liquid nitrogen at different stages in the smoking process. Measurements on the resulting stubbs enabled amounts of tobacco consumed to be correlated with the parameters of smoking. An elementary diffusion-controlled theory for natural smoulder is developed and compared with practice. Experiments on the heat of co mbustion of tobacco and tobacco/air stoichiometry provide values enabling a theoretical natural smoulder combustion zone temperature to be predicted. This research has resulted in the elucidation of all the principal features of the physical mechanism of smouldering in cigarettes and in the development of new research methods.