Influence of metal halide perovskite modifications on structure and functionality

<p>Metal halide perovskites (ABX₃) represent an important class of materials with respect to optoelectronic applications such as photovoltaic and light-emitting devices. In this thesis, modification of these materials was explored through metal substitutions, halide substitutions and also nanocrystal synthesis. The ability for these modifications to take place was analyzed, and related to the effects on structural and optoelectronic properties. Heterovalent metal substitutions were explored through the substitution of Bi³⁺ into methylammonium lead iodide (MAPbI₃). It was found that a two phase material composed of MAPbI₃ and MA₃Bi₂I₉ forms during these substitutions. This resulted in changes to electron-hole generation in the thin films and separation in photovoltaic devices, as observed through optical absorption and current-voltage measurements. Substitutions of Bi³⁺ and Tl⁺ were also carried out at dopant concentrations of 0.1–1%. Although the bulk crystal structure was maintained here, the power conversion efficiencies of devices decreased, with a bigger effect measured for Bi³⁺ doping. The ability for halide ions in MAPbBr₃ to be substituted with the thiocyanate ion (SCN)⁻ was investigated and compared to previous reports concerning MAPbI₃. From the studies conducted here, it is unlikely that the (SCN)⁻ ion becomes incorporated into the perovskite crystal lattice. This appeared to be primarily due to the reactivity of MA⁺ ion with (SCN)⁻. Finally, Cs₃Bi₂I₉ nanocrystals were synthesized via the hot injection method. This was supported through XRD, TEM and EDS measurements, where the crystals were found to display hexagonal symmetry. Subsequent experiments on the mixed halide nanocrystals (I/Br) revealed the sensitive nature of this synthesis to oxygen contamination.</p>

Influence of metal halide perovskite modifications on structure and functionality

<p>Metal halide perovskites (ABX₃) represent an important class of materials with respect to optoelectronic applications such as photovoltaic and light-emitting devices. In this thesis, modification of these materials was explored through metal substitutions, halide substitutions and also nanocrystal synthesis. The ability for these modifications to take place was analyzed, and related to the effects on structural and optoelectronic properties. Heterovalent metal substitutions were explored through the substitution of Bi³⁺ into methylammonium lead iodide (MAPbI₃). It was found that a two phase material composed of MAPbI₃ and MA₃Bi₂I₉ forms during these substitutions. This resulted in changes to electron-hole generation in the thin films and separation in photovoltaic devices, as observed through optical absorption and current-voltage measurements. Substitutions of Bi³⁺ and Tl⁺ were also carried out at dopant concentrations of 0.1–1%. Although the bulk crystal structure was maintained here, the power conversion efficiencies of devices decreased, with a bigger effect measured for Bi³⁺ doping. The ability for halide ions in MAPbBr₃ to be substituted with the thiocyanate ion (SCN)⁻ was investigated and compared to previous reports concerning MAPbI₃. From the studies conducted here, it is unlikely that the (SCN)⁻ ion becomes incorporated into the perovskite crystal lattice. This appeared to be primarily due to the reactivity of MA⁺ ion with (SCN)⁻. Finally, Cs₃Bi₂I₉ nanocrystals were synthesized via the hot injection method. This was supported through XRD, TEM and EDS measurements, where the crystals were found to display hexagonal symmetry. Subsequent experiments on the mixed halide nanocrystals (I/Br) revealed the sensitive nature of this synthesis to oxygen contamination.</p>

Synthesis and crystal structure of diaquabis(hexamethylenetramine-κN)bis(thiocyanato-κN)cobalt(II)–hexamethylenetetramine–acetonitrile (1/2/2)

The crystal structure of the title solvated coordination compound, [Co(NCS)2(C6H12N4)2(H2O)2]·2C6H12N4·2C2H3N, consists of discrete complexes in which the Co2+ cations (site symmetry \overline{1}) are sixfold coordinated by two N-bonded thiocyanate anions, two water molecules and two hexamethylenetetramine (HMT) molecules to generate distorted trans-CoN4O2 octahedra. The discrete complexes are each connected by two HMT solvate molecules into chains via strong O—H...N hydrogen bonds. These chains are further linked by additional O—H...N and C—H...N and C—H...S hydrogen bonds into a three-dimensional network. Within this network, channels are formed that propagate along the c-axis direction and in which additional acetonitrile solvent molecules are embedded, which are hydrogen bonded to the network. The CN stretching vibration of the thiocyanate ion occurs at 2062 cm−1, which is in agreement with the presence of N-bonded anionic ligands. XRPD investigations prove the formation of the title compound as the major phase accompanied by a small amount of a second unknown phase.

Population improvement and synthetic cultivar production in forage kale (Brassica oleracea L.)

Experimental results are brought together to demonstrate that forage kale population improvement involving full-sib and selfed families can be done on an annual cycle, followed by production of a synthetic cultivar. Furthermore, this new breeding method compares favourably with the two successful methods used to date, namely triple-cross hybrid cultivars from inbreeding and crossbreeding programmes and open-pollinated cultivars from population improvement programmes. The key findings were that natural vernalization of kale in south east Scotland occurred by mid-December so that plants could be pollinated in a glasshouse with heating and lighting by the end of February and seed harvested by the end of May. The resulting full-sib or selfed families could be assessed in a field transplant trial in the same year, from June to November, thus completing an annual cycle. Self-pollination resulted in shorter plants with lower fresh-weight, dry-matter and digestible organic-matter yields, and undesirably higher contents of S-methylcysteine sulphoxide, the haemolytic anaemia factor, and the goitrogenic thiocyanate ion. As a consequence of digestible organic-matter yield being reduced by as much as 22%, the estimated optimum number of selfed parents in a synthetic cultivar was four to eight. Synthetic cultivars are expected to yield as well as triple-cross hybrids as there was no reduction in yield when the latter were open-pollinated.

Germanium Extraction from Sulfuric Acid Solutions in the Presence of Thiocyanate Ion

The extraction of Ge (IV) from sulfuric acid solutions in the presence of thiocyanate ion with various extractants (caprylic, poly(2-ethylhexyl)phosphonitrile, bis(2,4,4-trimethylpentyl) dithiophosphinic acids, trialkylmethylammonium thiocyanate, etc.) has been studied. In all cases, the thiocyanate ion increases germanium extraction as compared to the extraction from sulfuric acid solutions. During the germanium extraction with bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301, HR), a significant increase in the germanium extraction is due to the formation of a cationic intracomplex compound of the composition [Ge(OH)3-nRn]+[HSO4], where n = 1-3. Due to the large synergistic effect for the extraction of Ge, it is possible to use an extractant with a concentration of 0.1-0.15 mol/l. Trialkylmethylammonium thiocyanate (TAMAR), also shows a high efficiency of germanium extraction from sulfate thiocyanate solutions. For 5-6 stages of extraction with a 0.5 M solution of ТАМАР, the extraction of Ge was 99.5 %. The composition of the extracted complex supposedly corresponds to (R4N)2[Ge(CNS)6]. The use of extraction systems based on Cyanex 301 and ТАМАR in the presence of thiocyanate ion significantly reduces the concentration of extractants and is of undoubted practical interest for hydrometallurgical processes for the germanium extraction

A New Method for the Synthesis of 3-Thiocyanatopyrazolo[1,5-a]pyrimidines

In this article, we demonstrate how an original effective “metal-free” and “chromatography-free” route for the synthesis of 3-thiocyanatopyrazolo[1,5-a]pyrimidines has been developed. It is based on electrooxidative (anodic) C–H thiocyanation of 5-aminopyrazoles by thiocyanate ion leading to 4-thiocyanato-5-aminopyrazoles (stage 1, yields up to 87%) following by their chemical condensation with 1,3-dicarbonyl compounds or their derivatives (stage 2, yields up to 96%). This method is equally effective for the synthesis of 3-thiocyanatopyrazolo[1,5-a]pyrimidines, both without substituents and with various donor (acceptor) substituents in the pyrimidine ring.

Theoretical description of the ligand function for ionoselective electrodes reversible to metal anion complexes. 1. Lower detection limit and its determining factors

Within the framework of the steady-state diffusion model, the theoretical description for the thiocyanate ion lower detection limit (LDL) by the tetrathiocyanatozincate selective electrode, has been presented. The main assumptions of this model are constancy of the ion exchanger concentration along the membrane, traditionally used in various phaseboundary potential diffusion models, and linear profiles of components’ concentrations in diffusion layers. Simple quantitative expressions have been obtained, connecting thiocyanate ion concentration in the solution surface layer (responsible for LDL value) with phase boundary extraction equilibria constants, stability constants for zinc thiocyanate complexes, and diffusion parameters in the membrane and solution phases. Calculated LDL values are in good agreement with experimental data provided in the literature. It has been shown that LDL can be reduced substantially by controlling such easily regulated diffusion parameters as diffusion layer thickness in the membrane phase, which is a function of time, and diffusion layer thickness of the sample solution, which is governed by stirring regime.

Levels of the Thiocyanate in the Saliva of Tobacco Smokers in Comparison to e-Cigarette Smokers and Nonsmokers Measured by HPLC on a Phosphatidylcholine Column

The aim of the study was to estimate the thiocyanate levels in saliva of cigarette smokers in comparison to e-cigarette smokers and nonsmokers. To improve our understanding of the influence of smoking on the oral level of thiocyanate, we conducted an assessment of human saliva, in 24 individuals (eight tobacco smokers, eight e-cigarette smokers, and eight nonsmokers). High-Performance Liquid Chromatography with ultraviolet detection (HPLC-UV) using a unique phosphatidylcholine column was applied in this assay. Thiocyanate ion was detected directly by its absorbance at 210 nm. The method presents a new application of the IAM (Immobilized Artificial Membrane) column for quantification of inorganic anions. The whole process meets the criteria of green chemistry because it was carried out without the use of organic solvents. For compensating matrix effects, an eight-point standard addition protocol was used to quantify the thiocyanate level in saliva samples. The calibration graphs were linear in the range of 5–100 mg L−1 with a correlation coefficient higher than 0.99. The thiocyanate concentrations in the saliva of tobacco smokers, e-cigarette smokers, and nonsmokers were found in the range of 121.25–187.54 mg L−1, 121.24–244.11 mg L−1, 33.03–79.49 mg L−1, respectively. The present study indicates an obvious statistically significant elevation in salivary thiocyanate level in tobacco smokers in comparison to nonsmokers. The phosphatidylcholine-based stationary phase proved to be suitable for the detection and quantification of the thiocyanate ion. The salivary thiocyanate levels in e-cigarette smokers were not significantly different in comparison to tobacco smokers but higher if compared to nonsmokers. The criterion for statistical significance was p < 0.05.