Search

This study investigates the influence of substrate (AISI M42 tool steel) bias voltage (from −30 to −80 V), on the mechanical properties of magnetron sputtered TiSiN coating derived from Ti and Si targets. Thermal stability, microstructure (crystallite size, microstrain, lattice constant), morphology and mechanical (hardness, Young's modulus, residual stresses) properties, of the deposited TiSiN coatings, were investigated with synchrotron powered X-ray diffraction (SR-XRD), X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and nanoindentation techniques. Rietveld analysis, of the in-situ SR-XRD, in the temperature range of 25–800 °C, demonstrated cubic TiN form in (Ti,Si)N solid solutions, with TiO2 and Ti2O3 identified at lower bias voltages. Density functional theory supplemented the experimental results. Increase in the bias voltage resulted in: (i) a decrease in Si content, (ii) significant smoothening of surface morphology, (iii) change in the phase composition and microstructure, (iv) improved oxidation resistance and thermal oxidation threshold, and (v) hardness and Young's modulus of the coatings increased up to 50% to 33 GPa and 450 GPa, respectively.

This study investigates the influence of substrate (AISI M42 tool steel) bias voltage (from −30 to −80 V), on the mechanical properties of magnetron sputtered TiSiN coating derived from Ti and Si targets. Thermal stability, microstructure (crystallite size, microstrain, lattice constant), morphology and mechanical (hardness, Young's modulus, residual stresses) properties, of the deposited TiSiN coatings, were investigated with synchrotron powered X-ray diffraction (SR-XRD), X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and nanoindentation techniques. Rietveld analysis, of the in-situ SR-XRD, in the temperature range of 25–800 °C, demonstrated cubic TiN form in (Ti,Si)N solid solutions, with TiO2 and Ti2O3 identified at lower bias voltages. Density functional theory supplemented the experimental results. Increase in the bias voltage resulted in: (i) a decrease in Si content, (ii) significant smoothening of surface morphology, (iii) change in the phase composition and microstructure, (iv) improved oxidation resistance and thermal oxidation threshold, and (v) hardness and Young's modulus of the coatings increased up to 50% to 33 GPa and 450 GPa, respectively.

Thermal pretreatment by torrefaction is known to produce improved properties in biomass fuels, but the role of pellet size on key properties in commercially available hardwood derived fuel has not been investigated to date. In this study, densified Australian woody biomass was torrefied over different temperatures (250–300 °C), time (30 and 60 min) and mean pellet size (7 ± 0.5 mm and 15 ± 0.5 mm). Benchmarking, relative to raw fuel properties, is reported in terms of proximate analysis, high heating value (HHV) and water immersion tests as well as FTIR and thermal stability (TGA). Significant differences of 23.55% in mass loss (ML) and 10% in hygroscopic behaviour were observed at varied pellet size. FTIR analysis of the samples identified reduction of polar species such as the hydroxyl (-OH) functional group during torrefaction. This increased the hydrophobicity of torrefied pellets. Torrefaction of larger sized pellets was also accompanied with lower hemicellulose and cellulose degradation. A correlation predicted the HHV of the torrefied pellets which fits well with the actual HHV’s of the wide body of literature with an average difference of less than 1 MJ/kg. Pellet sizing was found to impact the fuel properties only at milder torrefaction conditions. As such, with the increase in torrefaction severity, the effect of pellet size became insignificant. The outcomes emphasise the need to describe pellet size distributions when reporting torrefaction performance indicators, particularly if commercial scale torrefaction is used at higher temperatures and longer times.

Brominated aromatic rings constitute main structural entities in virtually all commercially deployed brominated flame retardants (BFRs). Oxidative decomposition of BFRs liberates appreciable quantities of bromobenzenes (BBzs). This contribution reports experimental measurements for the generation of notorious polybrominated dibenzofurans (PBDFs) and polybrominated diphenyl ethers (PBDEs) from oxidation of monobromobenzene (MBBz). In the light of developed product profiles, we map out reaction pathways and report kinetic parameters for PBDFs and PBDEs formation from coupling reactions of MBBz molecule and its derived ortho-bromophenoxy (o-BPhxy) radical using quantum chemical calculations. The identification and quantitation of product species involve the use of gas chromatograph - triple quadrupole mass spectrometer (GC-QQQMS) operating in the multiple reaction monitoring (MRM) mode. Bimolecular reactions of MBBz and o-BPhxy result in the generation of twelve pre-PBDF intermediates, of which four can also serve as building blocks for the synthesis of PBDEs. These four intermediates are denoted as pre-PBDE/pre-PBDF, with the remaining eight symbolised as pre-PBDF. The resonance-stabilised structure of the o-BPhxy radical accumulates more spin density character on its phenoxy O atom (30.9 %) in reference to ortho-C and para-C sites. Thus, the formation of the pre-PBDE/pre-PBDF structures via O/o-C couplings advances faster as it requires lower activation enthalpies (79.2 – 84.9 kJ mol−1) than the pre-PBDF moieties, which arise via pairing reactions involving o-C(H or Br)/o-C(H or Br) sites (97.2 – 180.2 kJ mol−1). Kinetic analysis indicates that, the O/o-C pre-PBDE/pre-PBDF adducts self-eject the out-of-plane H atoms to produce PBDEs, rather than undergo a three-step mechanism forming PBDFs. However, experimental measurements demonstrate PBDEs appearing in lower yields as compared to those of PBDFs; presumably due to H- and Br-induced conversion of the PBDEs into PBDF

Australia presents a reasonable contribution to the World’s greenhouse gas emissions because of its heavy reliance on fossil fuels for energy production. Coal is the primary founder of energy in Australia with the secondary sourcing from oil, gas, solar, wind, biomass and hydro. Bioenergy currently offers only 1 % of the total energy produced in Australia with anticipated uplift to 8 % by 2030 that demands active research on biofuel resources and production processes. Australia lavishes with land, sunlight, and brackish water, necessary for the growth of algal biomass, the unique composition (carbohydrates, lipids, proteins, nucleic acid and moisture) of which makes it an excellent feedstock for hydrothermal processing. Hydrothermal treatment of algal biomass for the production of biofuels and value-added products is an attractive route towards increasing the bio-energy contribution in Australia to meet the challenges of growing greenhouse gas emissions. Hydrothermal treatment of algal biomass at high temperatures (280 – 700 °C) to produce energy-dense liquid and gaseous fuels are extensively researched for the last three decades with the exceptional attributes achieved in the field. However, the low temperature (180 – 260 °C) hydrothermal carbonisation (HTC) of algal biomass, which essentially serves as an intermediate stage of intense hydrothermal processing, has received less attention. Hydrothermal carbonisation produces hydrochar as a primary product along with biocrude and aqueous phase as co-products, all of which possess exceptional traits to be employed directly or indirectly as biofuels and/or as advanced carbon materials. Despite the rationale research on hydrothermal carbonisation of algal biomass, there are still significant research gaps in assessing the feasibility of hydrothermal carbonisation process for microalgae in the context of an Algal Biorefinery, including (i) the lack of standardised conditions for the characterisation (e.g., proximate anal

Australia presents a reasonable contribution to the World’s greenhouse gas emissions because of its heavy reliance on fossil fuels for energy production. Coal is the primary founder of energy in Australia with the secondary sourcing from oil, gas, solar, wind, biomass and hydro. Bioenergy currently offers only 1 % of the total energy produced in Australia with anticipated uplift to 8 % by 2030 that demands active research on biofuel resources and production processes. Australia lavishes with land, sunlight, and brackish water, necessary for the growth of algal biomass, the unique composition (carbohydrates, lipids, proteins, nucleic acid and moisture) of which makes it an excellent feedstock for hydrothermal processing. Hydrothermal treatment of algal biomass for the production of biofuels and value-added products is an attractive route towards increasing the bio-energy contribution in Australia to meet the challenges of growing greenhouse gas emissions. Hydrothermal treatment of algal biomass at high temperatures (280 – 700 °C) to produce energy-dense liquid and gaseous fuels are extensively researched for the last three decades with the exceptional attributes achieved in the field. However, the low temperature (180 – 260 °C) hydrothermal carbonisation (HTC) of algal biomass, which essentially serves as an intermediate stage of intense hydrothermal processing, has received less attention. Hydrothermal carbonisation produces hydrochar as a primary product along with biocrude and aqueous phase as co-products, all of which possess exceptional traits to be employed directly or indirectly as biofuels and/or as advanced carbon materials. Despite the rationale research on hydrothermal carbonisation of algal biomass, there are still significant research gaps in assessing the feasibility of hydrothermal carbonisation process for microalgae in the context of an Algal Biorefinery, including (i) the lack of standardised conditions for the characterisation (e.g., proximate anal

Tantalum (Ta) and niobium (Nb) have applications in high-technology electronic devices and steel manufacturing, respectively. Africa, South America and Australia collectively provide about 80% of the global supply of Ta-Nb concentrates. In Africa, Sociéte Minière de Bisunzu (SMB) located in the Democratic Republic of Congo (DRC) remains the major supplier of Ta-Nb concentrates containing about 33 wt % Ta2O5 and 5 wt % Nb2O5 as the two oxides of main economic values, associated with uranium (0.14 wt %) and thorium (0.02 wt %). The presence of U and Th complicates the transportation logistics of tantalite to international markets, due to stringent regulation on an allowable limit of U and Th at 0.1 wt %. High radiation levels also hinder further primary beneficiation of the Ta-Nb concentrates at the Bisunzu mine to an extent of at least 50 wt % Ta2O5 and Nb2O5 combined. Digestion of the concentrate using HF is the conventional method to remove U and Th followed by chemical treatment to recover Ta2O5 and Nb2O5. The HF digestion process is hazardous and requires large investments. The main objective of this study is the mineral identification in the ore and concentrates of SMB mine sites, to investigate the possibilities of upgrading the Ta2O5 and the Nb2O5 by weight using physical separation and concentration, and removing U and Th using chemical treatment. The mineral identification analysis conducted on eight concentrates sourced from different mining locations at the Bisunzu mine in DRC has shown that manganocolumbite, manganotantalite and ferrotantalite are the major phases with cassiterite, as well as pyrochlore and microlite group of minerals hosting uranium as minor components. The rare earth minerals, quartz and lepidolite were also identified in the ore and concentrates. The quantitative analysis revealed a chemical composition range of 20 – 47 wt % Ta2O5 and 5.4 – 22 wt % Nb2O5 as the principal oxides, associated with 0.005 – 0.802 wt % U and 0.001 – 0.072 wt

Tantalum (Ta) and niobium (Nb) have applications in high-technology electronic devices and steel manufacturing, respectively. Africa, South America and Australia collectively provide about 80% of the global supply of Ta-Nb concentrates. In Africa, Sociéte Minière de Bisunzu (SMB) located in the Democratic Republic of Congo (DRC) remains the major supplier of Ta-Nb concentrates containing about 33 wt % Ta2O5 and 5 wt % Nb2O5 as the two oxides of main economic values, associated with uranium (0.14 wt %) and thorium (0.02 wt %). The presence of U and Th complicates the transportation logistics of tantalite to international markets, due to stringent regulation on an allowable limit of U and Th at 0.1 wt %. High radiation levels also hinder further primary beneficiation of the Ta-Nb concentrates at the Bisunzu mine to an extent of at least 50 wt % Ta2O5 and Nb2O5 combined. Digestion of the concentrate using HF is the conventional method to remove U and Th followed by chemical treatment to recover Ta2O5 and Nb2O5. The HF digestion process is hazardous and requires large investments. The main objective of this study is the mineral identification in the ore and concentrates of SMB mine sites, to investigate the possibilities of upgrading the Ta2O5 and the Nb2O5 by weight using physical separation and concentration, and removing U and Th using chemical treatment. The mineral identification analysis conducted on eight concentrates sourced from different mining locations at the Bisunzu mine in DRC has shown that manganocolumbite, manganotantalite and ferrotantalite are the major phases with cassiterite, as well as pyrochlore and microlite group of minerals hosting uranium as minor components. The rare earth minerals, quartz and lepidolite were also identified in the ore and concentrates. The quantitative analysis revealed a chemical composition range of 20 – 47 wt % Ta2O5 and 5.4 – 22 wt % Nb2O5 as the principal oxides, associated with 0.005 – 0.802 wt % U and 0.001 – 0.072 wt

Co-pyrolysis of brominated flame retardants (BFRs) with polymeric materials prevails in scenarios pertinent to thermal recycling of bromine-laden objects; most notably the non-metallic fraction in e-waste. Hydro-dehalogenation of aromatic compounds in a hydrogen-donating medium constitutes a key step in refining pyrolysis oil of BFRs. Chemical reactions underpinning this process are poorly understood. Herein, we utilize accurate density functional theory (DFT) calculations to report thermo-kinetic parameters for the reaction of solid polyethylene, PE, (as a surrogate model for aliphatic polymers) with prime products sourced from thermal decomposition of BFRs, namely, HBr, bromophenols; benzene, and phenyl radical. Facile abstraction of an ethylenic H by Br atoms is expected to contribute to the formation of abundant HBr concentrations in practical systems. Likewise, a relatively low energy barrier for aromatic Br atom abstraction from a 2-bromophenol molecule by an alkyl radical site, concurs with the reported noticeable hydro-debromination capacity of PE. Pathways entailing a PE-induced bromination of a phenoxy radical should be hindered in view of high energy barrier for a Br transfer into the para position of the phenoxy radical. Adsorption of a phenoxy radical onto a Cu(Br) site substituted at the PE chain affords the commonly discussed PBDD/Fs precursor of a surface-bounded bromophenolate adduct. Such scenario arises due to the heterogeneous integration of metals into the bromine-rich carbon matrix in primitive recycling of e-waste and their open burning.

Co-pyrolysis of brominated flame retardants (BFRs) with polymeric materials prevails in scenarios pertinent to thermal recycling of bromine-laden objects; most notably the non-metallic fraction in e-waste. Hydro-dehalogenation of aromatic compounds in a hydrogen-donating medium constitutes a key step in refining pyrolysis oil of BFRs. Chemical reactions underpinning this process are poorly understood. Herein, we utilize accurate density functional theory (DFT) calculations to report thermo-kinetic parameters for the reaction of solid polyethylene, PE, (as a surrogate model for aliphatic polymers) with prime products sourced from thermal decomposition of BFRs, namely, HBr, bromophenols; benzene, and phenyl radical. Facile abstraction of an ethylenic H by Br atoms is expected to contribute to the formation of abundant HBr concentrations in practical systems. Likewise, a relatively low energy barrier for aromatic Br atom abstraction from a 2-bromophenol molecule by an alkyl radical site, concurs with the reported noticeable hydro-debromination capacity of PE. Pathways entailing a PE-induced bromination of a phenoxy radical should be hindered in view of high energy barrier for a Br transfer into the para position of the phenoxy radical. Adsorption of a phenoxy radical onto a Cu(Br) site substituted at the PE chain affords the commonly discussed PBDD/Fs precursor of a surface-bounded bromophenolate adduct. Such scenario arises due to the heterogeneous integration of metals into the bromine-rich carbon matrix in primitive recycling of e-waste and their open burning.

Singlet oxygen, the lowest excited state of molecular oxygen, continues to play crucial roles in natural and anthropogenic processes. Singlet oxygen signifies a prominent chemical species in a wide array of prominent chemical and biochemical phenomena. This thesis explores the thermodynamic and kinetic aspects of singlet oxygen-assisted oxidation of biogenic, industrially-valuable, and environmentally-accumulating hydrocarbons. The work embodied in this thesis has elucidated the governing mechanisms of the initiation oxidation reactions of selected organic compounds by the highly reactive singlet oxygen species, as well as characterised the physicochemical implications of the systems. The selected organic substrates include biogenic hydrocarbons such as isoprene (C5) and monoterpenes (C10) that influence the atmospheric chemistry owing to their emission from vegetation; oxazole, an active industrial ingredient whose photo-oxidation holds important implications in syntheses of various pharmaceutical materials; coal surrogate, i.e., pyrrole to shed light and insight into the occurrence of spontaneous fires in coal mines; and notorious toxic environmental pollutants, including dioxins and furans compounds. The method deployed a comprehensive atomistic molecular simulation, employing an unrestricted density functional theory DFT-B3LYP functional in conjunction with the 6-311+G(d,p) basis set, as well as energy refinements based on the approximated spin-projection scheme. Due to the trivial enthalpic requirements of the entrance reaction channels, relatively small at around 100 kJ/mol, the molecular interactions of the selected hydrocarbon with singlet oxygen should be termed as “spontaneous reactions”, contrasting those initiated at higher temperatures by the ground-state molecular oxygen that typically ensures via very sizable entrance barriers in the window of 200 -350 kJ/mol.

Singlet oxygen, the lowest excited state of molecular oxygen, continues to play crucial roles in natural and anthropogenic processes. Singlet oxygen signifies a prominent chemical species in a wide array of prominent chemical and biochemical phenomena. This thesis explores the thermodynamic and kinetic aspects of singlet oxygen-assisted oxidation of biogenic, industrially-valuable, and environmentally-accumulating hydrocarbons. The work embodied in this thesis has elucidated the governing mechanisms of the initiation oxidation reactions of selected organic compounds by the highly reactive singlet oxygen species, as well as characterised the physicochemical implications of the systems. The selected organic substrates include biogenic hydrocarbons such as isoprene (C5) and monoterpenes (C10) that influence the atmospheric chemistry owing to their emission from vegetation; oxazole, an active industrial ingredient whose photo-oxidation holds important implications in syntheses of various pharmaceutical materials; coal surrogate, i.e., pyrrole to shed light and insight into the occurrence of spontaneous fires in coal mines; and notorious toxic environmental pollutants, including dioxins and furans compounds. The method deployed a comprehensive atomistic molecular simulation, employing an unrestricted density functional theory DFT-B3LYP functional in conjunction with the 6-311+G(d,p) basis set, as well as energy refinements based on the approximated spin-projection scheme. Due to the trivial enthalpic requirements of the entrance reaction channels, relatively small at around 100 kJ/mol, the molecular interactions of the selected hydrocarbon with singlet oxygen should be termed as “spontaneous reactions”, contrasting those initiated at higher temperatures by the ground-state molecular oxygen that typically ensures via very sizable entrance barriers in the window of 200 -350 kJ/mol.

This thesis calculates the rate of hydrogen abstraction reactions and the mechanisms of nitrogen oxides (NOx and N2O) reduction, especially those relevant to the oxidation and pyrolysis of nitrogen-rich fuels such as biomass. The dissertation firstly focuses on the interaction of hydrocarbons with the amidogen radical (NH2) and nitrogen dioxide (NO2), before analysing in detail the decomposition of ammonium nitrate (AN) both in gas and liquid media. In addition to this, the moderation of nitrous oxide (N2O) and nitrogen oxides (NOx) via their reaction with a biomass surrogate of catechol was also studied. The underlying aims of the study were to report the mechanisms and kinetic factors controlling the interaction of NH2 and NO2 radicals with a wide array of hydrocarbons, then to map out the prominent reaction pathways prevailing in the decomposition of ammonium nitrate (AN) and conversion of N2O into N2 via dissociative adsorption onto a catechol moiety. Accurate quantum-mechanical calculations probed the hydrogen abstraction reactions from small aliphatic and aromatic hydrocarbons by NH2 and NO2 radicals. Reaction and activation energies for all plausible hydrogen abstraction channels were executed with the accurate chemistry model of CBS-QB3. Reaction rate parameters were obtained based on conventional transition-state theory, accounting for a plausible contribution from tunnelling effects and treating internal rotations as hindered rotors. We established that a linear correlation existed between the strength of the C-H bonds (i.e., primary, secondary, vinylic, and benzylic) and the activation energies for H abstraction channels operated by NH2 and NO2 radicals. Moreover, the meta-hybrid Density Functional Theory (DFT) of M05-2X/6-311+G(d,p) levels elucidated viable systematic conversion routes of N2O into N2 via interaction with a catechol molecule. Two theoretical methodologies were applied to study thermal decomposition of AN in gas and liquid phases. A contin

This thesis presents a series of scientific studies exploring the initiation of various chemical reactions with reactive oxygen species (ROS), mainly singlet oxygen. These studies have revealed new mechanistic insights in environmental, industrial and biological systems, have described the associated set of reactions, have illustrated the detection of new radicals i.e., environmentally persistent free radicals (EPFR), and have provided a new insight explaining the spontaneous fire in coal mines. Comprehensive experimental and quantum-mechanical calculations afforded the investigation of oxidation reactions of singlet oxygen with wastewater organic contaminants, for example, the photodegradation of Phenol and Aniline in water. Detailed experimental studies on modelled surrogates, i.e., Anisole, resolved the fundamentals of thermal interaction of coal with iron oxide Fe2O3 nanoparticles. Along the same line of interest, enhancing the combustion efficiency of fuel constitutes a mainstream strategy in the pursuit of meeting the ever-increasing energy demand. Therefore, this thesis also provides a comprehensive mechanistic and thermo-kinetic accounts underpinning the reaction of fuel surrogates, namely Toluene, with singlet oxygen in the internal combustion (IC) engines. Finally, this work extends insights into biological systems, mapping the Alloxan-Glutathione redox cycle to expose the formation of ROS, species that eventually cause necrosis of the pancreatic insulin-producing beta cells and prompt the insulin-dependent diabetes mellitus (IDDM). The methodology involve customised LED-photoreactors, thermal packed-bed reactor, and various reaction product-monitoring systems, e.g., Fourier transform infrared spectroscopy (FTIR) to quantitate the ignition temperatures of fuel surrogates, in-situ electron paramagnetic resonance (EPR) to elucidate the formation of environmentally-persistent free radicals (EPFR) as well as intermediate radical species, diffuse reflectance in

This thesis describes a number of scientific studies investigating different interesting properties of rare earth metal oxides desired in different applications via combined experimental measurements and accurate density functional theory (DFT) calculations. The electronic, structural, mechanical and thermodynamic properties of cubic lanthanide sesquioxides are first reported, with a particular focus on the most common dioxide in the lanthanide family, ceria (CeO2). This is followed an investigation into the effect of Hf and Zr dopants on the reduction energies of pure ceria. The reduction enthalpies of Ce1-xHfxO2 and Ce1-xZrxO2 and Ce1-2xHfxZrxO2 solid solutions are computed as a function of the reduction extent (x). Alloying with Hf and Zr is found to systematically reduce the energies required to remove oxygen atoms from bulk of ceria. The computed coefficients in the Born-Huang criterion infer a mechanical stability of all cubic lanthanide sesquioxides. Acquired electronic parameters encompass Bader’s atomic charges and Partial Density of States (PDOS). An important part of the thesis focuses on the catalytic capacity of CeO2 in acting as a stand-alone environmental catalyst toward the decomposition of a series of chlorinated volatile organic compounds, namely chloroethene, chloroethane and chlorobenzene. Guided by recent experimental measurements, the pyrolytic and oxidative decomposition of selected chlorinated compounds have been modelled on the most stable ceria surface, CeO2 (111). Dissociative addition (surface-assisted fission of the C-Cl bond) and direct elimination pathways (departure of a stable hydrocarbon entity with the co-adsorption of H and Cl atoms on the surface) assume comparable importance. Fission of the C-Cl bond over oxygen vacancies systematically necessitates lower energy barriers in reference to perfect surfaces. We have illustrated that observed catalytic deactivation in the experiment is attributed to the profound stability of adsorbed

This thesis describes a number of scientific studies investigating different interesting properties of rare earth metal oxides desired in different applications via combined experimental measurements and accurate density functional theory (DFT) calculations. The electronic, structural, mechanical and thermodynamic properties of cubic lanthanide sesquioxides are first reported, with a particular focus on the most common dioxide in the lanthanide family, ceria (CeO2). This is followed an investigation into the effect of Hf and Zr dopants on the reduction energies of pure ceria. The reduction enthalpies of Ce1-xHfxO2 and Ce1-xZrxO2 and Ce1-2xHfxZrxO2 solid solutions are computed as a function of the reduction extent (x). Alloying with Hf and Zr is found to systematically reduce the energies required to remove oxygen atoms from bulk of ceria. The computed coefficients in the Born-Huang criterion infer a mechanical stability of all cubic lanthanide sesquioxides. Acquired electronic parameters encompass Bader’s atomic charges and Partial Density of States (PDOS). An important part of the thesis focuses on the catalytic capacity of CeO2 in acting as a stand-alone environmental catalyst toward the decomposition of a series of chlorinated volatile organic compounds, namely chloroethene, chloroethane and chlorobenzene. Guided by recent experimental measurements, the pyrolytic and oxidative decomposition of selected chlorinated compounds have been modelled on the most stable ceria surface, CeO2 (111). Dissociative addition (surface-assisted fission of the C-Cl bond) and direct elimination pathways (departure of a stable hydrocarbon entity with the co-adsorption of H and Cl atoms on the surface) assume comparable importance. Fission of the C-Cl bond over oxygen vacancies systematically necessitates lower energy barriers in reference to perfect surfaces. We have illustrated that observed catalytic deactivation in the experiment is attributed to the profound stability of adsorbed

This thesis presents a series of scientific studies exploring the initiation of various chemical reactions with reactive oxygen species (ROS), mainly singlet oxygen. These studies have revealed new mechanistic insights in environmental, industrial and biological systems, have described the associated set of reactions, have illustrated the detection of new radicals i.e., environmentally persistent free radicals (EPFR), and have provided a new insight explaining the spontaneous fire in coal mines. Comprehensive experimental and quantum-mechanical calculations afforded the investigation of oxidation reactions of singlet oxygen with wastewater organic contaminants, for example, the photodegradation of Phenol and Aniline in water. Detailed experimental studies on modelled surrogates, i.e., Anisole, resolved the fundamentals of thermal interaction of coal with iron oxide Fe2O3 nanoparticles. Along the same line of interest, enhancing the combustion efficiency of fuel constitutes a mainstream strategy in the pursuit of meeting the ever-increasing energy demand. Therefore, this thesis also provides a comprehensive mechanistic and thermo-kinetic accounts underpinning the reaction of fuel surrogates, namely Toluene, with singlet oxygen in the internal combustion (IC) engines. Finally, this work extends insights into biological systems, mapping the Alloxan-Glutathione redox cycle to expose the formation of ROS, species that eventually cause necrosis of the pancreatic insulin-producing beta cells and prompt the insulin-dependent diabetes mellitus (IDDM). The methodology involve customised LED-photoreactors, thermal packed-bed reactor, and various reaction product-monitoring systems, e.g., Fourier transform infrared spectroscopy (FTIR) to quantitate the ignition temperatures of fuel surrogates, in-situ electron paramagnetic resonance (EPR) to elucidate the formation of environmentally-persistent free radicals (EPFR) as well as intermediate radical species, diffuse reflectance in

This thesis calculates the rate of hydrogen abstraction reactions and the mechanisms of nitrogen oxides (NOx and N2O) reduction, especially those relevant to the oxidation and pyrolysis of nitrogen-rich fuels such as biomass. The dissertation firstly focuses on the interaction of hydrocarbons with the amidogen radical (NH2) and nitrogen dioxide (NO2), before analysing in detail the decomposition of ammonium nitrate (AN) both in gas and liquid media. In addition to this, the moderation of nitrous oxide (N2O) and nitrogen oxides (NOx) via their reaction with a biomass surrogate of catechol was also studied. The underlying aims of the study were to report the mechanisms and kinetic factors controlling the interaction of NH2 and NO2 radicals with a wide array of hydrocarbons, then to map out the prominent reaction pathways prevailing in the decomposition of ammonium nitrate (AN) and conversion of N2O into N2 via dissociative adsorption onto a catechol moiety. Accurate quantum-mechanical calculations probed the hydrogen abstraction reactions from small aliphatic and aromatic hydrocarbons by NH2 and NO2 radicals. Reaction and activation energies for all plausible hydrogen abstraction channels were executed with the accurate chemistry model of CBS-QB3. Reaction rate parameters were obtained based on conventional transition-state theory, accounting for a plausible contribution from tunnelling effects and treating internal rotations as hindered rotors. We established that a linear correlation existed between the strength of the C-H bonds (i.e., primary, secondary, vinylic, and benzylic) and the activation energies for H abstraction channels operated by NH2 and NO2 radicals. Moreover, the meta-hybrid Density Functional Theory (DFT) of M05-2X/6-311+G(d,p) levels elucidated viable systematic conversion routes of N2O into N2 via interaction with a catechol molecule. Two theoretical methodologies were applied to study thermal decomposition of AN in gas and liquid phases. A contin

The thesis is composed of two broad themed sections with the underlying aim of understanding on a precise atomic basis, the electronic and structural factors governing the reactive and non-reactive surfaces of two metal oxides belonging to the same group in the periodic table; boron (B) and aluminium (Al). Using accurate density functional theory (DFT) computations, we first elucidate the initial reaction steps of the surface oxidation of elemental boron into its respective oxide; boron trioxide (B₂O₃). The highly exoergic reaction obtained for the dissociative adsorption of molecular oxygen over the boron surface coincides with the widely used boron oxidation reaction as secondary energy source in rockets. The relatively large activation energy for the O-O dissociation step marks the non-spontaneity of elemental boron oxidation at room temperature. Having established routes for the formation of B₂O₃-like precursors, we then investigate the relative stability of four low-index surfaces of the low-pressure B₂O₃ phase; namely the B₂O₃-I configuration. We demonstrate that none of the investigated low-index surfaces have dangling bonds, which reasonably relates to the experimentally observed low reactivity of this compound. The most stable surface terminations of B₂O₃ orientations entail tetrahedral BO₄ units. Such termination incurs a lower surface energy than orientations that consist of only triangular BO₃ units. Electronic and structural factors provide atomic-base elucidation of the observed inertness of B₂O₃. Combined experimental techniques (i.e. diffuse reflectance infrared spectroscopy) and DFT simulation are used to answer some of the most intriguing questions pertinent to factors underpinning the well-documented catalytic inhibition by B₂O₃ and its hygroscopic behaviour. We investigate the adsorption and dissociation mechanisms of two hydrogen chalcogenides, namely water (H₂O) and hydrogen sulfide (H₂S) molecules over B₂O₃-I (101) surfaces. We show that the d

The thesis is composed of two broad themed sections with the underlying aim of understanding on a precise atomic basis, the electronic and structural factors governing the reactive and non-reactive surfaces of two metal oxides belonging to the same group in the periodic table; boron (B) and aluminium (Al). Using accurate density functional theory (DFT) computations, we first elucidate the initial reaction steps of the surface oxidation of elemental boron into its respective oxide; boron trioxide (B₂O₃). The highly exoergic reaction obtained for the dissociative adsorption of molecular oxygen over the boron surface coincides with the widely used boron oxidation reaction as secondary energy source in rockets. The relatively large activation energy for the O-O dissociation step marks the non-spontaneity of elemental boron oxidation at room temperature. Having established routes for the formation of B₂O₃-like precursors, we then investigate the relative stability of four low-index surfaces of the low-pressure B₂O₃ phase; namely the B₂O₃-I configuration. We demonstrate that none of the investigated low-index surfaces have dangling bonds, which reasonably relates to the experimentally observed low reactivity of this compound. The most stable surface terminations of B₂O₃ orientations entail tetrahedral BO₄ units. Such termination incurs a lower surface energy than orientations that consist of only triangular BO₃ units. Electronic and structural factors provide atomic-base elucidation of the observed inertness of B₂O₃. Combined experimental techniques (i.e. diffuse reflectance infrared spectroscopy) and DFT simulation are used to answer some of the most intriguing questions pertinent to factors underpinning the well-documented catalytic inhibition by B₂O₃ and its hygroscopic behaviour. We investigate the adsorption and dissociation mechanisms of two hydrogen chalcogenides, namely water (H₂O) and hydrogen sulfide (H₂S) molecules over B₂O₃-I (101) surfaces. We show that the d

This contribution reports results from the gas-phase oxidation of 4-bromo-4'-chlorobiphenyl (4,4'-BCB) in order to fathom the formation of toxic species produced during the combustion of mixed halogenated aromatics. In their own right, mixed polybrominated/polychlorinated biphenyls (PXBs) represent a new class of environmental contaminants, recently detected in food and human tissues. Gas chromatography-quadrupole mass spectrometry (GC-QMS), gas chromatography-quadrupole time of flight mass spectrometry (GC-QTOFMS), Fourier transform infrared spectroscopy (FTIR) and ion chromatography (IC) served to analyse the volatile and semi-volatile organic compounds (V/SVOCs), including mixed halogenated dibenzo-p-dioxins and dibenzofurans (PXDD/Fs), and gaseous products including HBr/HCl. The selection of non-ortho substituted PXB as a model species yields a large number of halogenated compounds, including monochloro- and monobromobenzene and higher halogenated benzenes and naphthalenes and derivatives of halogenated benzenes (such as 1-chloro-4-ethynylbenzene). We also detect small amounts of chlorinated and mixed halogenated dibenzofurans. The present study provides insights into the formation of several classes of halogenated and mixed-halogenated pollutants in combustion processes involving both bromine and chlorine sources, such as those of brominated flame retardants and PVC plastics., Bio4Energy

Torrefaction is a thermal pre-treatment technology used to refine biomass, mainly for energy production purposes. However, there is currently a lack of information on the potential formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in the torrefaction process. In this study, torrefaction was conducted using five different types of feedstock: stemwood, bark, wood from a discarded telephone pole, cassava stems and particle board. The feedstock as well as the torrefied biomass (chars) and the volatiles (non-condensable and condensable) generated during torrefaction were analyzed for PCDDs and PCDFs. PCDD concentrations in the torrefaction products were about 2-5 fold of those in the feedstocks. Torrefaction of particle board resulted in extensive formation of PCDDs (7200 ng kg(-1)) compared to the other four feedstocks (13-27 ng kg(-1)). Examination of the homologue profiles suggested that the observed PCDDs in the torrefaction products partly originated from new formation and partly physical transformation from volatilization and re-condensation of PCDDs present in the feedstock. Dechlorination of highly chlorinated compounds (HpCDD and OCDD) in the feedstock to form less chlorinated PCDDs was also observed. Compared to PCDDs, the net formation of PCDFs in the torrefaction process was low, except for the telephone pole sample, for which a dramatic increase (44-fold) of PCDFs was observed. PCDDs and PCDFs were mainly retained in the chars, accounting for 76-96% and 39-74% of the total concentration, respectively. It was also found that the highly chlorinated congeners tended to be retained in the chars, whereas the less chlorinated ones were predominantly volatilized into the gas phase., Bio4Energy

This thesis presents a series of scientific studies exploring the thermal mitigation of nitrogen oxides (NOx) with solid fuel (waste polyethylene) and biomass surrogate (morpholine). These studies have revealed new mechanistic insights, have described the associated set of reactions, and have developed a sustainable means of reducing industrially formed NOx, for example, in combustion processes and during blasting of ammonium nitrate explosive. Comprehensive quantum-mechanical calculations afforded the investigation of low-temperature oxidation of polyethylene (PE) film under representative NOx environments. Investigations of thermal reduction of NOx with recycled PE involved sample characterisation techniques, such as, carbon-hydrogen-nitrogen-sulfur (CHNS) elemental analyses, ion chromatography (IC) and inductively coupled plasma optical emission spectroscopy (ICP-OES), as well as thermogravimetric experiments under practical NOx atmospheres. Innovative application of the on-line Fourier transform infrared (FTIR) spectroscopy and NOx chemiluminescence quantitated the reaction product species and established the removal efficiency of NOx by fragments of pyrolysing PE. Studies on modelled surrogates, i.e., morpholine, resolved the fundamentals of thermal interaction of biomass with NOx. The experiment applied a flow-through tubular reactor coupled with FTIR spectroscopy and chemiluminescence NOx analysis, at constant pressure, reaction time, and representative fuel-rich condition. Furthermore, density-functional-theory (DFT) calculations uncovered new mechanistic insights into initial nitration reactions, and yielded their energetic characteristics, such as exothermic formation of nitro- and nitroso-adducts. Results obtained in this study elucidated, for the very first time, initial products of low-temperature reaction of NOx with polymers and biomass, and determined the rate parameters, from the isoconversional degradation analysis, that are of great practical impo

This thesis presents a series of scientific studies exploring the oxidation chemistry of carbon disulfide (CS2) and its interaction with hydrocarbons in combustion systems. The results illustrate the extreme flammability of CS2 even at low temperature (self-ignition temperature at 363 K under ambient pressure). The thesis proposes a comprehensive oxidation mechanism that works over a wide range of atmospheric and combustion conditions with and without moisture. The thesis also provides experimental validation on the promotion of CS2 on the ignition of methane. Experiments involving CS2 oxidation in combustion processes have been conducted with tubular-flow (TFR) and jet-stirred (JSR) reactors to provide experimental validation for the proposed mechanism. Online Fourier transform infrared (FTIR) spectroscopy served to identify and quantitate the product species and to obtain the detailed species conversion profiles during the combustion process. Low ignition temperature of CS2 of 860 K in TFR and 710 K JSR, with residence time at 0.3 s under ambient pressure, implies the extreme flammability of CS2. The presence of moisture exhibits no effect on the oxidation of CS2 for ignition temperature and species profile at below 1100 K, although moisture converts CO into CO2 at higher temperature (> 1200 K). Co-oxidation experiments of CH4/CS2/O2 in JSR illustrate the promotion effect of CS2 on the ignition of methane. Quantum calculations afford the investigation of primary steps governing the OH-initiated oxidation of CS2 in the atmosphere. We also propose a comprehensive oxidation mechanism of CS2 in combustion systems. The thesis suggests the intersystem crossing (ISC) between triplet and singlet pathways to explain the extreme flammability of CS2, in analogy to the controlling steps operating for other reduced sulfur species. DFT calculations examine the interplay between the SH radical and C1 - C4 hydrocarbons to demonstrate the distinct inhibition and promotion effects

This thesis presents a series of scientific studies exploring the oxidation chemistry of carbon disulfide (CS2) and its interaction with hydrocarbons in combustion systems. The results illustrate the extreme flammability of CS2 even at low temperature (self-ignition temperature at 363 K under ambient pressure). The thesis proposes a comprehensive oxidation mechanism that works over a wide range of atmospheric and combustion conditions with and without moisture. The thesis also provides experimental validation on the promotion of CS2 on the ignition of methane. Experiments involving CS2 oxidation in combustion processes have been conducted with tubular-flow (TFR) and jet-stirred (JSR) reactors to provide experimental validation for the proposed mechanism. Online Fourier transform infrared (FTIR) spectroscopy served to identify and quantitate the product species and to obtain the detailed species conversion profiles during the combustion process. Low ignition temperature of CS2 of 860 K in TFR and 710 K JSR, with residence time at 0.3 s under ambient pressure, implies the extreme flammability of CS2. The presence of moisture exhibits no effect on the oxidation of CS2 for ignition temperature and species profile at below 1100 K, although moisture converts CO into CO2 at higher temperature (> 1200 K). Co-oxidation experiments of CH4/CS2/O2 in JSR illustrate the promotion effect of CS2 on the ignition of methane. Quantum calculations afford the investigation of primary steps governing the OH-initiated oxidation of CS2 in the atmosphere. We also propose a comprehensive oxidation mechanism of CS2 in combustion systems. The thesis suggests the intersystem crossing (ISC) between triplet and singlet pathways to explain the extreme flammability of CS2, in analogy to the controlling steps operating for other reduced sulfur species. DFT calculations examine the interplay between the SH radical and C1 - C4 hydrocarbons to demonstrate the distinct inhibition and promotion effects

This thesis presents a series of scientific studies exploring the thermal mitigation of nitrogen oxides (NOx) with solid fuel (waste polyethylene) and biomass surrogate (morpholine). These studies have revealed new mechanistic insights, have described the associated set of reactions, and have developed a sustainable means of reducing industrially formed NOx, for example, in combustion processes and during blasting of ammonium nitrate explosive. Comprehensive quantum-mechanical calculations afforded the investigation of low-temperature oxidation of polyethylene (PE) film under representative NOx environments. Investigations of thermal reduction of NOx with recycled PE involved sample characterisation techniques, such as, carbon-hydrogen-nitrogen-sulfur (CHNS) elemental analyses, ion chromatography (IC) and inductively coupled plasma optical emission spectroscopy (ICP-OES), as well as thermogravimetric experiments under practical NOx atmospheres. Innovative application of the on-line Fourier transform infrared (FTIR) spectroscopy and NOx chemiluminescence quantitated the reaction product species and established the removal efficiency of NOx by fragments of pyrolysing PE. Studies on modelled surrogates, i.e., morpholine, resolved the fundamentals of thermal interaction of biomass with NOx. The experiment applied a flow-through tubular reactor coupled with FTIR spectroscopy and chemiluminescence NOx analysis, at constant pressure, reaction time, and representative fuel-rich condition. Furthermore, density-functional-theory (DFT) calculations uncovered new mechanistic insights into initial nitration reactions, and yielded their energetic characteristics, such as exothermic formation of nitro- and nitroso-adducts. Results obtained in this study elucidated, for the very first time, initial products of low-temperature reaction of NOx with polymers and biomass, and determined the rate parameters, from the isoconversional degradation analysis, that are of great practical impo

The interaction between biomass and NOx is very important to understand because it can revolutionise the way industrial furnaces are used. The technology that was discussed was re-burning. Re-burning is essentially changing the atmosphere in a furnace where the biomass is being combusted. This zone is known as the re-burning zone. The re-burning zone is a medium where NOx and biomass can interact. The type of biomass that was experimented on was a wood-based biomass. In terms of the characterisation, an ultimate and proximate analysis was done in conjunction with a bomb calorimeter test. The results from the characterisation, when tested with four different sources of biomass, yielded that all the biomass samples have similar properties. The four samples that were tested were pine, eucalyptus, miscanthus and oak. Since they all had similar properties it was safe to perform a test on one of these biomass samples. The test that was being performed was the diffused reflectance infrared fourier transform spectroscopy analysis also know as the DRIFTS analysis and the sample of biomass that was chosen was the miscanthus as seen from the results of the characterisation, it made no difference which biomass sample was picked. The DRIFTS analysis was also done in four different atmospheres to assess the interaction between NOx and biomass. The four different atmospheres included the following; inert atmosphere which would provide data for oxygen-fuel ratio when burning biomass, inert and NOx The conclusion that was drawn due to the DRIFTS analysis is that biomass can interact with NOx in gas-gas and gas-solid reaction. This implies that NOx can interact with wood-based biomass before combustion even occurs. This information is useful as it would help decrease the biomass emissions. The DRIFTS analysis did have its limitations and this was the fact that there no quantifiable data was extracted although this is easily fixed by running the same types of test in a thermogravitime

Current estimations show hydrogen production to be in excess of 55 million tonnes annually. With consumption growing globally by six percent annually, new feedstocks such as ammonia need to be explored to meet demand. Ammonia has many attractive characteristics as a source for hydrogen, such as its product stream when decomposed producing no carbon oxides or sulfurs. Research currently is limited on the decomposition of ammonia to produce hydrogen supported by transitional metal catalysts. This lack of research has suppressed the development of this technology. This thesis project is intended to develop on the original research conducted at the King Abdulaziz University where the development of high surface area molybdenum nitride was researched as a catalyst for the ammonia decomposition reaction to produce hydrogen. The work completed in this thesis aims to capitalise on the findings in the original experiment by accurately determining the mechanisms and kinetics associated with the production of hydrogen. The modelling was separated into three distinct components which investigated the ammonia decomposition on a cobalt-molybdenum catalyst. The first component of the model was focused on optimising the surface which the mechanisms of the decomposition reaction would be situated on. The optimisation calculations found the (111) index to be the most stable of all the surfaces modelled. The data collected displayed a directly proportional relationship between the increasing number of atoms in the structure and its stability. The second component of the project modelled the ammonia decomposition mechanisms on the surface of the optimum (111) indexed surface. Multiple iterations were tested for different locations of the reacting molecule above the surface of the catalyst. The results from the optimised models found the desorption mechanisms were slightly more stable than the adsorption component of the decomposition reaction. The concluding component of the model inve

The combination of graphene nanoplatelets and carbon nanofibers were successfully fabricated by utilizing a one-step solution based on the electrospinning technique. A distinctive morphology was observed in which the platelets were suspended between the fibrous structure that significantly improved the specific capacitance of the nanofiber to 86.11 F g−1, twice the increment from its original structure. Furthermore, all of the graphene nanoplatelets-reinforced samples recorded an optimal performance of over 90% capacitive retention after 1000 continuous charge/discharge cycles, regardless of the GnP concentration. These findings indirectly reflect the potential of CNF as the electrode material in the fabrication of high performance supercapacitor devices.

The combination of graphene nanoplatelets and carbon nanofibers were successfully fabricated by utilizing a one-step solution based on the electrospinning technique. A distinctive morphology was observed in which the platelets were suspended between the fibrous structure that significantly improved the specific capacitance of the nanofiber to 86.11 F g−1, twice the increment from its original structure. Furthermore, all of the graphene nanoplatelets-reinforced samples recorded an optimal performance of over 90% capacitive retention after 1000 continuous charge/discharge cycles, regardless of the GnP concentration. These findings indirectly reflect the potential of CNF as the electrode material in the fabrication of high performance supercapacitor devices.

The present study focused on the development of transition metal oxide and metal nitride based thin film coatings to be utilized as a cost-effective solar selective surface that constitute a new approach in maximizing the power conversion efficiency. Despite many developments on transition metal oxide and metal nitride based selective solar absorbers, these materials are yet to be commercialized for solar thermal conversion applications. Numerous studies on CuCoO and graphene oxide based thin films are dedicated for their optical applications and light harvesting purposes. However to the best of our knowledge, utilization of mixed metal oxide/graphene oxide thin films as solar selective surface is yet to be explored. Both CuCoO and graphene oxide (GO) have generated significant research interest and have widespread applications in clean energy devices due to the good combinations of many important properties. Therefore, in this work we focus on the introduction of GO to the 3d transition metal-based CuCoO coatings and develop the new types optical thin films via dip-coating sol-gel technology to be used as solar selective surfaces. It is believed that use of graphene oxide in wet chemistry based sol-gel derived thin films will explore the new platform of producing highly efficient selective solar surfaces. Generally, 3d transition metal nitride based thin film coatings are studied for structural, mechanical, and electrical applications. However, a very limited number of investigations are directed in search of their optical and solar selective behaviors. With the increasing demand for clean energy alternatives, and economically viable energy devices our endeavor might bring some fruitful breakthroughs in development of 3d transition metal oxide and metal nitride based thin film coatings. Due to its flexibility and numerous technical advantages, the soft chemical sol-gel approach has been adopted to synthesize the metal oxides based thin film coatings. Unbalanced mag

Brominated flame retardants (BFRs) are bromine-bearing hydrocarbons added or applied to materials to increase their fire resistance. As thermal treatment or recycling activities are common disposal methods for BFR-laden objects, it is essential to determine the precise decomposition chemistry of BFRs at elevated temperatures, and their transformation pathways into hazardous pollutants. Sunlight can trigger the photodecomposition of BFRs, either during the life cycle of treated objects, or when emitted to the environment after disposal. Therefore, knowledge of the geometric and electronic structures of BFRs is of chief importance when tracking their fate in the ambient environment. Although BFR decomposition mainly occurs in a condensed phase, gas phase reactions also contribute significantly to their overall decay and subsequent fragmentation into brominated pollutants. Thermal degradation of BFRs often proceeds in the presence of bromine atoms which inhibit complete combustion. Therefore, under thermal conditions such as smouldering, municipal waste incineration, pyrolysis, thermal recycling, uncontrolled burning and fires, BFRs degrade to form brominated products of incomplete combustion (BPICs). Thermal degradation of BFRs produces potent precursors to polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs). Co-combustion of BFR-containing objects with a chlorine source (e.g., polyvinyl chlorides) results in the emission of significant concentrations of mixed halogenated dibenzo-p-dioxins and dibenzofurans (i.e., PXDD/Fs; X = Br, Cl). In this thesis, we investigated the thermochemical parameters of bromochlorophenols (BCPhs) and the photodecomposition properties of major BFRs and their derived brominated phenols (BPhs). We scrutinised the formation of brominated and non-brominated products that evolved during the thermal decomposition of major BFR i.e., tetrabromobisphenol A (TBBA), through experimental measurements coupled with accurate quantum chemical cal

Brominated flame retardants (BFRs) are bromine-bearing hydrocarbons added or applied to materials to increase their fire resistance. As thermal treatment or recycling activities are common disposal methods for BFR-laden objects, it is essential to determine the precise decomposition chemistry of BFRs at elevated temperatures, and their transformation pathways into hazardous pollutants. Sunlight can trigger the photodecomposition of BFRs, either during the life cycle of treated objects, or when emitted to the environment after disposal. Therefore, knowledge of the geometric and electronic structures of BFRs is of chief importance when tracking their fate in the ambient environment. Although BFR decomposition mainly occurs in a condensed phase, gas phase reactions also contribute significantly to their overall decay and subsequent fragmentation into brominated pollutants. Thermal degradation of BFRs often proceeds in the presence of bromine atoms which inhibit complete combustion. Therefore, under thermal conditions such as smouldering, municipal waste incineration, pyrolysis, thermal recycling, uncontrolled burning and fires, BFRs degrade to form brominated products of incomplete combustion (BPICs). Thermal degradation of BFRs produces potent precursors to polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs). Co-combustion of BFR-containing objects with a chlorine source (e.g., polyvinyl chlorides) results in the emission of significant concentrations of mixed halogenated dibenzo-p-dioxins and dibenzofurans (i.e., PXDD/Fs; X = Br, Cl). In this thesis, we investigated the thermochemical parameters of bromochlorophenols (BCPhs) and the photodecomposition properties of major BFRs and their derived brominated phenols (BPhs). We scrutinised the formation of brominated and non-brominated products that evolved during the thermal decomposition of major BFR i.e., tetrabromobisphenol A (TBBA), through experimental measurements coupled with accurate quantum chemical cal

Nano-sized materials have promising contemporary and novel technological applications as they possess favourable properties due to quantum effects. The nano-sized graphene material exhibits remarkable electrical, optical, thermal and mechanical characteristics. Adding impurities or doping constitutes an effective way in fine-tuning properties of graphene for specific applications. This study aims to investigate the geometrical aspects of elements adsorption on graphene to produce more accurate models of the electronic structure of graphene as a result of the doping. Previous models investigated mainly the adsorption sites (bridge, hollow, top); however, they could not systematically explain certain phenomena, e.g. nonlinearity of band gaps to atomic ratios in oxygen-adsorbed graphene. We hypothesise that this is attributed to the positions and orientation of the adatoms (adsorbed elements) relative to one another, which is, in essence, a geometrical phenomenon. In the present study, geometrical investigations of elemental adsorption on graphene focused on side (single-, double-sided), site (bridge, hollow, top) and orientation (the position of adatom relative to one another and graphene). The computational simulations were conducted by using the generalized gradient approximation (GGA) functional within the density functional theory (DFT) framework. The VASP (Vienna Ab initio Simulation Package) software was utilised for all simulations. Trends in the elemental adsorption on graphene in terms of sides/sites/orientations are presented in terms of: binding energy (stability); migration (barrier) energy; adatom height; graphene distortion; Fermi energy; magnetization; charge transfer and energy band gap. The calculated results of 10 elements (Na, Mg, Al, Si, P, S, F, Cl, Br and I) adsorbed on pristine graphene indicate that the geometrical combination of side, site and orientation is vital in determining the most stable configuration of the adsorbed systems. This study

Nano-sized materials have promising contemporary and novel technological applications as they possess favourable properties due to quantum effects. The nano-sized graphene material exhibits remarkable electrical, optical, thermal and mechanical characteristics. Adding impurities or doping constitutes an effective way in fine-tuning properties of graphene for specific applications. This study aims to investigate the geometrical aspects of elements adsorption on graphene to produce more accurate models of the electronic structure of graphene as a result of the doping. Previous models investigated mainly the adsorption sites (bridge, hollow, top); however, they could not systematically explain certain phenomena, e.g. nonlinearity of band gaps to atomic ratios in oxygen-adsorbed graphene. We hypothesise that this is attributed to the positions and orientation of the adatoms (adsorbed elements) relative to one another, which is, in essence, a geometrical phenomenon. In the present study, geometrical investigations of elemental adsorption on graphene focused on side (single-, double-sided), site (bridge, hollow, top) and orientation (the position of adatom relative to one another and graphene). The computational simulations were conducted by using the generalized gradient approximation (GGA) functional within the density functional theory (DFT) framework. The VASP (Vienna Ab initio Simulation Package) software was utilised for all simulations. Trends in the elemental adsorption on graphene in terms of sides/sites/orientations are presented in terms of: binding energy (stability); migration (barrier) energy; adatom height; graphene distortion; Fermi energy; magnetization; charge transfer and energy band gap. The calculated results of 10 elements (Na, Mg, Al, Si, P, S, F, Cl, Br and I) adsorbed on pristine graphene indicate that the geometrical combination of side, site and orientation is vital in determining the most stable configuration of the adsorbed systems. This study

The present study focused on the development of transition metal oxide and metal nitride based thin film coatings to be utilized as a cost-effective solar selective surface that constitute a new approach in maximizing the power conversion efficiency. Despite many developments on transition metal oxide and metal nitride based selective solar absorbers, these materials are yet to be commercialized for solar thermal conversion applications. Numerous studies on CuCoO and graphene oxide based thin films are dedicated for their optical applications and light harvesting purposes. However to the best of our knowledge, utilization of mixed metal oxide/graphene oxide thin films as solar selective surface is yet to be explored. Both CuCoO and graphene oxide (GO) have generated significant research interest and have widespread applications in clean energy devices due to the good combinations of many important properties. Therefore, in this work we focus on the introduction of GO to the 3d transition metal-based CuCoO coatings and develop the new types optical thin films via dip-coating sol-gel technology to be used as solar selective surfaces. It is believed that use of graphene oxide in wet chemistry based sol-gel derived thin films will explore the new platform of producing highly efficient selective solar surfaces. Generally, 3d transition metal nitride based thin film coatings are studied for structural, mechanical, and electrical applications. However, a very limited number of investigations are directed in search of their optical and solar selective behaviors. With the increasing demand for clean energy alternatives, and economically viable energy devices our endeavor might bring some fruitful breakthroughs in development of 3d transition metal oxide and metal nitride based thin film coatings. Due to its flexibility and numerous technical advantages, the soft chemical sol-gel approach has been adopted to synthesize the metal oxides based thin film coatings. Unbalanced mag

Rahman, M. M., Ibrahim, K., Taha, H., Amri, A., Zhao, X., Kabir, H., . . . Jiang, Z. -. (2019). Studies of annealing impact on the morphological, opto-dielectric and mechanical behaviors of molybdenum-doped CrN coatings. Thin Solid Films, 677, 119-129. Available here

Rahman, M. M., Jiang, Z. T., Zhou, Z. F., Xie, Z., Yin, C. Y., Kabir, H., ... & Altarawneh, M. (2016). Effects of annealing temperatures on the morphological, mechanical, surface chemical bonding, and solar selectivity properties of sputtered TiAlSiN thin films. Journal of Alloys and Compounds, 671, 254-266. Available here

Rahman, M. M., Awaltanova, E., Amri, A., Altarawneh, M., Hossain, M. A., Zhao, X., . . . Jiang, Z. -. (2019). A holistic analysis of surface, chemical bonding states and mechanical properties of sol-gel synthesized CoZn-oxide coatings complemented by finite element modeling. Ceramics International, 45(8), 10882-10898. Available here

Rahman, M. M., Jiang, Z. T., Munroe, P., Chuah, L. S., Zhou, Z. F., Xie, Z., ... & Haque, M. M. (2016). Chemical bonding states and solar selective characteristics of unbalanced magnetron sputtered Ti x M 1− x− y N y films. RSC Advances, 6(43), 36373-36383. Available here

The pyrolysis of Tetrabromobisphenol A (TBBPA) mixed with Electric Arc Furnace Dust (EAFD) was studied using thermogravimetric analysis (TGA) and theoretically analysed using thermodynamic equilibrium calculations. Mixtures of both materials with varying TBBPA loads (1:1, and 1:3) were prepared and pyrolyzed in a nitrogen atmosphere under dynamic heating conditions at heating rates of 5 and 10 ⁰C/min. The mixtures degraded through several steps including decomposition of TBBPA yielding mainly HBr, bromination of metal oxides, followed by their evaporation in the sequence of CuBr3, ZnBr2, PbBr2, FeBr2, MnBr2, KBr, NaBr, CaBr2 and MgBr2, and finally reduction of the remaining metal oxides by the char formed from decomposition of TBBPA. Thermodynamic calculations suggest the possibility of selective bromination of zinc and lead followed by their evaporation leaving iron in its oxide form, while the char formed may serve as a reduction agent for iron oxides into metallic iron. However, at higher TBBPA volumes, iron bromide forms, which can be also evaporated at a temperature higher than those of ZnBr2 and PbBr2. Results from this work provide practical insight into selective recovery of valuable metals from EAFD while at the same time recycling the hazardous bromine content in TBBPA.

The pyrolysis of Tetrabromobisphenol A (TBBPA) mixed with Electric Arc Furnace Dust (EAFD) was studied using thermogravimetric analysis (TGA) and theoretically analysed using thermodynamic equilibrium calculations. Mixtures of both materials with varying TBBPA loads (1:1, and 1:3) were prepared and pyrolyzed in a nitrogen atmosphere under dynamic heating conditions at heating rates of 5 and 10 ⁰C/min. The mixtures degraded through several steps including decomposition of TBBPA yielding mainly HBr, bromination of metal oxides, followed by their evaporation in the sequence of CuBr3, ZnBr2, PbBr2, FeBr2, MnBr2, KBr, NaBr, CaBr2 and MgBr2, and finally reduction of the remaining metal oxides by the char formed from decomposition of TBBPA. Thermodynamic calculations suggest the possibility of selective bromination of zinc and lead followed by their evaporation leaving iron in its oxide form, while the char formed may serve as a reduction agent for iron oxides into metallic iron. However, at higher TBBPA volumes, iron bromide forms, which can be also evaporated at a temperature higher than those of ZnBr2 and PbBr2. Results from this work provide practical insight into selective recovery of valuable metals from EAFD while at the same time recycling the hazardous bromine content in TBBPA.

The pyrolysis of Tetrabromobisphenol A (TBBPA) mixed with Electric Arc Furnace Dust (EAFD) was studied using thermogravimetric analysis (TGA) and theoretically analysed using thermodynamic equilibrium calculations. Mixtures of both materials with varying TBBPA loads (1:1, and 1:3) were prepared and pyrolyzed in a nitrogen atmosphere under dynamic heating conditions at heating rates of 5 and 10 ⁰C/min. The mixtures degraded through several steps including decomposition of TBBPA yielding mainly HBr, bromination of metal oxides, followed by their evaporation in the sequence of CuBr3, ZnBr2, PbBr2, FeBr2, MnBr2, KBr, NaBr, CaBr2 and MgBr2, and finally reduction of the remaining metal oxides by the char formed from decomposition of TBBPA. Thermodynamic calculations suggest the possibility of selective bromination of zinc and lead followed by their evaporation leaving iron in its oxide form, while the char formed may serve as a reduction agent for iron oxides into metallic iron. However, at higher TBBPA volumes, iron bromide forms, which can be also evaporated at a temperature higher than those of ZnBr2 and PbBr2. Results from this work provide practical insight into selective recovery of valuable metals from EAFD while at the same time recycling the hazardous bromine content in TBBPA.

The pyrolysis of Tetrabromobisphenol A (TBBPA) mixed with Electric Arc Furnace Dust (EAFD) was studied using thermogravimetric analysis (TGA) and theoretically analysed using thermodynamic equilibrium calculations. Mixtures of both materials with varying TBBPA loads (1:1, and 1:3) were prepared and pyrolyzed in a nitrogen atmosphere under dynamic heating conditions at heating rates of 5 and 10 ⁰C/min. The mixtures degraded through several steps including decomposition of TBBPA yielding mainly HBr, bromination of metal oxides, followed by their evaporation in the sequence of CuBr3, ZnBr2, PbBr2, FeBr2, MnBr2, KBr, NaBr, CaBr2 and MgBr2, and finally reduction of the remaining metal oxides by the char formed from decomposition of TBBPA. Thermodynamic calculations suggest the possibility of selective bromination of zinc and lead followed by their evaporation leaving iron in its oxide form, while the char formed may serve as a reduction agent for iron oxides into metallic iron. However, at higher TBBPA volumes, iron bromide forms, which can be also evaporated at a temperature higher than those of ZnBr2 and PbBr2. Results from this work provide practical insight into selective recovery of valuable metals from EAFD while at the same time recycling the hazardous bromine content in TBBPA.

The pyrolysis of Tetrabromobisphenol A (TBBPA) mixed with Electric Arc Furnace Dust (EAFD) was studied using thermogravimetric analysis (TGA) and theoretically analysed using thermodynamic equilibrium calculations. Mixtures of both materials with varying TBBPA loads (1:1, and 1:3) were prepared and pyrolyzed in a nitrogen atmosphere under dynamic heating conditions at heating rates of 5 and 10 ⁰C/min. The mixtures degraded through several steps including decomposition of TBBPA yielding mainly HBr, bromination of metal oxides, followed by their evaporation in the sequence of CuBr3, ZnBr2, PbBr2, FeBr2, MnBr2, KBr, NaBr, CaBr2 and MgBr2, and finally reduction of the remaining metal oxides by the char formed from decomposition of TBBPA. Thermodynamic calculations suggest the possibility of selective bromination of zinc and lead followed by their evaporation leaving iron in its oxide form, while the char formed may serve as a reduction agent for iron oxides into metallic iron. However, at higher TBBPA volumes, iron bromide forms, which can be also evaporated at a temperature higher than those of ZnBr2 and PbBr2. Results from this work provide practical insight into selective recovery of valuable metals from EAFD while at the same time recycling the hazardous bromine content in TBBPA.