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Thesis advisor: James P. Morken / Thesis advisor: Marc L. Snapper / This dissertation will present three projects focusing on the enantioselective synthesis and stereospecific transformation of alkylboronates. The first project describes the development of a nickel-catalyzed enantioselective dicarbofunctionalization of alkenylboronates, which provides a modular route to secondary alkylboronic esters. Intramolecular reaction leads to enantioselective synthesis of exocyclic boronates. The second project depicts a new method for the synthesis of azetidines, pyrrolidines and piperidines via an intramolecular amination of alkylboronic esters. Regioselective amination of vicinal bis(boronates) allows the synthesis of saturated azacycles bearing boronic ester substitutions that can serve as useful synthetic handles. As the transformation is stereospecific, stereodefined cyclic amines can be synthesized from the enantioenriched boronic esters. The method is applied to the synthesis of an intermediate towards a Kras G12C inhibitor. The third project describes the development of a new chiral auxiliary on boron that can be easily synthesized from inexpensive starting materials. The auxiliary is applied to a diastereoselective radical ring-opening/closing [3+2] cycloaddition of cyclopropylanilines with alkenylboron species. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Metal complexes of dipyrromethene (dipyrrins) used as sensitizers in photocatalysis offer a way to harness solar energy in chemical bonds to create new fuels. This offers the dual role of reducing fossil fuel dependence and atmospheric CO2 levels. Traditionally, metal dipyrrin complexes are synthesized using substituted pyrroles, aldehydes, and transition metals. Indoles have a more expanded pi-electron system and their dipyrrin-type complex may exhibit visible light absorption, suggesting that they can act as photosensitizers for CO2 reduction processes. A novel indoledipyrromethene was synthesized using unsubstituted indole and mesitaldehyde. The complex exhibits visible light absorption at 422 nm. Its Zn coordinated complex it likely to exhibit blue-green light absorption making it suitable as a sensitizer for CO2 photoreduction and other applications.

M. Tech. (Chemical Engineering, Faculty of Engineering and Technology), Vaal University of Technology / Acid mine drainage (AMD) is a serious problem associated with mining activities, and it has the potential to contaminate surface and ground water. The aim of this study was to evaluate the performance of constructed wetland and photocatalysis in treating AMD. Three identical unvegetated upflow constructed wetlands packed with natural zeolite (clinoptilolite) and coarse silica sand were made of a cylindrical plastic pipe, and the slurry photocatalyst was prepared using quartz material. A hydro-alcohol thermal method was used to prepare an anatase core-void-shell TiO2 photocatalyst. The results showed that the three unvegetated upflow constructed wetlands (CW) had relatively similar percentage removal of heavy metals despite their varying concentrations within the AMD. The removals were: Fe (86.54 - 90.4%); Cr (56.2 - 64.5%); Mg (56.2 - 67.88%); Ca (77.1 - 100%); and 100% removal was achieved for Be, Zn, Co, Ni, and Mn. The removal of sulphate was also 30%. Heavy metals concentration in CW packing material was significantly higher in the outlet of the constructed wetlands than in the inlet. The adsorption isotherms revealed that the experimental data fitted the Langmuir Isotherms better, which suggested a monolayer coverage of heavy metals on the surface of the adsorbents; thermodynamic studies showed that the nature of adsorption taking place was physical; the kinetics models showed that the adsorption was first order reaction. A higher photocatalytic reduction (62%) of Cr(VI) was obtained at pH 2, 30 mg/l Cr(VI) initial concentration, and three hours of irradiation time. It was also found that the presence of Fe(III) enhanced the reduction of Cr(VI). The core-void-shell TiO2 photocatalyst showed a better activity than the commercial P25 Degussa for the reduction of Cr(VI) to Cr(III). The kinetic studies showed that the reduction of Cr(VI) was first order reaction. Photocatalytic reduction of Cr(VI) in real AMD sample was achieved only for the Douglas North Discharge (DND) sample (68%), and the Fe(III) reduction was found to be 83%. Therefore it was concluded that the combination of constructed wetland and UV/ TiO2 photocatalysis employing anatase core-void-shell TiO2 as a photocatalyst has a potential to reduce the toxicity of Cr(VI)-laden acid mine drainage.

Experiments were conducted to determine the photocatalytic degradation of three types of gas-phase compounds, NOX, VOCs, and chloramines, by TiO2 impregnated tiles. The oxides of nitrogen NO and NO2 (NOx) have a variety of negative impacts on human and environmental health ranging from serving as key precursors for the respiratory irritant ozone, to forming nitric acid, which is a primary component of acid rain. A flow tube reactor was designed for the experiments that allowed the UV illumination of the tiles under exposure to both NO and NO2 concentrations in simulated ambient air. The reactor was also used to assess NOx degradation for sampled ambient air. The PV values for NO and NO2 were 0.016 cm s-1 and 0.0015 cm s-1, respectively. For ambient experiments a decrease in ambient NOx of ~ 40% was observed over a period of roughly 5 days. The mean PV for NOx for ambient air was 0.016 cm s-1 and the maximum PV was .038 cm s-1. Overall, the results indicate that laboratory conditions generally simulate the efficiency of removing NOx by TiO2 impregnated tiles. Volatile organic compounds (VOC's) are formed in a variety of indoor environments, and can lead to respiratory problems (US EPA, 2010). The experiments determined the photocatalytic degradation of formaldehyde and methanol, two common VOCs, by TiO2 impregnated tiles. The same flow tube reactor used for the previous NOX experiments was used to test a standardized gas-phase concentration of formaldehyde and methanol. The extended UV illumination of the tiles resulted in a 50 % reduction in formaldehyde, and a 68% reduction in methanol. The deposition velocities (or the photocatalytic velocities, PV) were estimated for both VOC's. The PV for formaldehyde was 0.021 cm s-1, and the PV for methanol was 0.026 cm s-1. These PV values are slightly higher than the mean value determined for NO from the previous experiments which was 0.016 cm s-1. The results suggest that the TiO2 tiles could effectively reduce specific VOC levels in indoor environments. Chlorination is a widespread form of water disinfection. However, chlorine can produce unwanted disinfection byproducts when chlorine reacts with nitrogen containing compounds or other organics. The reaction of chlorine with ammonia produces one of three chloramines, (mono-, di-, and tri-chloramine). The production of chloramines compounds in indoor areas increases the likelihood of asthma in pool professionals, competitive swimmers, and children that frequently bath in indoor chlorinated swimming pools (Jacobs, 2007; Nemery, 2002; Zwiener, 2007). A modified flow tube reactor in conjunction with a standardized solution of monochloramine, NH2Cl, determined the photocatalytic reactions over the TiO2 tiles and seven concrete samples. The concrete samples included five different concrete types, and contained either 5 % or 15 % TiO2 by weight. The PV for the tiles was 0.045 cm s-1 for the tiles manufactured by TOTO Inc. The highest PV from the concrete samples was 0.054 cm s-1. Overall the commercial tiles were most efficient at reducing NH2Cl, compared to NOX and VOC compounds. However, the concrete samples had an even higher PV for NH2Cl than the tiles. The reason for this is unknown; however, distinct surface characteristics and a higher concentration of TiO2 in the concrete may have contributed to these findings.

PhD (Department of Chemical Engineering, Faculty of Engineering and Technology), Vaal University of Technology / Anaerobic digestion (AD) is usually applied in the treatment of distillery effluent due to the fact that it is effective in chemical oxygen demand (COD) reduction and bioenergy recovery. However, due to the presence of biorecalcitrant melanoidins present in distillery effluent, AD is ineffective in colour reduction. For this reason, ultraviolet (UV) photodegradation, which is effective in melanoidins’ degradation, can be integrated with AD to achieve high efficiency in colour and COD reduction. However, the UV process is energy intensive, majorly due to the electricity requirement of the UV lamp. In contrast, the AD process has high potential of renewable energy production in the form of biomethane, which can be transformed into electrical energy and applied to supplement the energy requirement of the UV process. The aim of this study was to evaluate the efficiency of a combined AD-UV system in colour and COD reduction for the treatment of distillery effluent in fluidised bed reactors. The potential of the application of the bioenergy produced by the AD process to supplement the energy intensive UV process was evaluated and modelled using response surface methodology. In the first place, the optimal hydrodynamic conditions of the fluidised bed reactors were determined using optical attenuation technique. The best homogeneity in the bioreactor, in which zeolite was used as microbial support, was found to be at a superficial liquid velocity of 0.6 cm/s while the best catalyst and gas hold up in the photoreactor were found to be 0.077 and 0.003, respectively. At these conditions, it was found that the initial biological step removed about 90% of COD and only about 50% of the colour while photodegradation post-treatment removed 98% of the remaining colour. Kinetic analysis of the bioreactor showed that ~ 9% of the feed total organic carbon (TOC) was non-biodegradable and this was attributed to the biorecalcitrant melanoidins. Photodegradation post-treatment mineralized the biorecalcitrant melanoidins via a reductive pathway as was indicated by the formation of NH4+ in large quantity compared to NO3-. Kinetic analysis further showed that the rate of substrate utilization in the bioreactor increased with an increase in organic loading rate and it was inversely proportional to the rate of photodegradation post-treatment. Modeling using response surface methodology (RSM) was applied to predict the effects of the operating parameters of the initial AD step on the performance of the photodegradation post-treatment process and the energy efficiency. Energy analysis of the integrated system showed that the AD process could produce 59 kWh/m3 of electricity which could supplement the electricity demand of the UV lamp by 30% leading to operation cost reduction of about USD 4.8/m3. This led to a presumed carbon dioxide emission reduction (CER) of 28.8 kg CO2e/m3.

Water pollution is a major concern in vast countries such as India and other developing nations. Several methods of water purification have been practiced since many decades, Semiconductor photocatalysis is a promising technique, for photodegradation of various hazardous chemicals that are encountered in waste waters. The great significance of this technique is that, it can degrade (detoxify) various complex organic chemicals, which has not been addressed by several other methods of purification. This unique advantage made this field of research to attract many investigators particularly in latter eighties and after. This thesis incorporates the studies on the various semiconductor photocatalysts that have been employed for the detoxification purposes. The fundamental principles involved in the photoelectrochemistry, reactions at the interface (solid - liquid or solid - gas) and photocatalytic reactions on fine particles are briefed. General nature and size quantization in semiconductor particles, photocatalytically active semiconductors, TiCh and ABO3 systems, chemical systems and modifications for solar energy conversions are brought out in the introduction chapter besides giving brief description about photocatalytic mineralization of water pollutants with mechanism involved, formation of reactive species and the factors influencing photomineralization reactions. Scope of the present work is given at the end of the first chapter. Second chapter deals with the materials used for the preparation of photocatalyst, preparative techniques, methods of analysis, instruments employed for the photodegradation experiments and a brief description of material characterization methods such as X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, differential thermal analysis, optical absorption spectro photometry, Electron paramagnetic resonance (EPR), and gas chromatograph - mass spectroscopy (GC - MS). Various preparative routes such as wet chemical and hydrothermal methods for obtaining TiO2 (both rutile and anatase forms), BaTiOs and SrTiO3 fine particles and the chemical analysis of their constituents have been described in brief. Third chapter presents the results of materials characterization. T1O2 (rutile and anatase), BaTiO3 and SrTiO3 have been characterized separately using various techniques. Different routes of obtaining the photocatalyst fine particles, heat treatment at various temperature ranges, experimental procedures and the results of characterization are brought out in this chapter. Fourth and fifth chapters present the details of degradation studies carried out on the photomineralization of chlorophenol, trichloroethylene and formaldehyde. Studies include photodegradation of the pollutants with different catalysts varying experimental conditions to check the effects of change in concentration of pollutants, oxidizer, pH, surface hydroxylation, etc. The most favorable conditions for the complete mineralization of the pollutants have been studied. In case of TiO2, anatase form has shown greater photoactivity when compared to rutile and complete mineralization of chlorophenols has been achieved at low pollutant concentrations, neutral pH, with H2O2 and UV illumination. Retarding effects of surface hydroxylation and the formation of peroxotitanium species during photodegradation have been presented. TCE and HCHO degradation with BaTiO3/SrTiO3 has been studied. Photocatalyst heat-treated at 1100°G-1300°C is found to be highly active in combination with H2O2 as electron scavenger. HCHO is not getting degraded to its completeness in aqueous conditions owing to the strong competition in surface adsorption posed by H2O molecules. Vapour-solid phase reaction however gave good results in the detoxification of HCHO via disproportionation. Summary and conclusions are given at the end of the thesis.

TiO2 nanoparticles are one of the most suitable materials for photocatalysis, specifically for water and air treatment and removal of a wide variety of organic pollutants such as dyes, aromatic compounds, and chlorinated aromatic compounds. Methods of synthesis of TiO2 are generally categorized in two main classes of wet chemical, and dry methods. Wet chemical methods generally provide a better control over size, size distribution, and shape; all of which significantly affect photocatalytic performance of the produced nanoparticles. Despite its advantages over other semiconductor photocatalysts, wide band-gap of titania restrains its photocatalytic activity to only UV light, which only makes up to 5% of the light reaching surface of the earth. To induce visible-light activity, titania has been doped by different dopants, including transition metal-dopants such as Fe, and Co and non-metal dopants such as N, and C. Nitrogen has been shown to be a better dopant, providing a suitably placed energy state within the band-gap of TiO2, and not suffering from issues related to transition-metal dopants such as low thermal and physical stability and high electron-hole recombination rates. To dope titania with nitrogen, one could add the nitrogen source together with other precursors during synthesis, referred to as wet chemical doping methods, or anneal the synthesized titania nanoparticles under a flow of ammonia at high temperatures, referred to as dry doping methods. While different doping methods have been studied individually, the author maintains that there has been an absence of research comparing the effectiveness of these methods, on photocatalytic performance of N-doped TiO2 within a consistent experiment. In this research TiO2 nanoparticles were synthesized by a facile, inexpensive sol-gel method, and doping was done by wet chemical methods, dry methods, and a combination of both these methods. Visible-light photocatalytic activity of these nanoparticles was evaluated by their efficiency in degradation of methyl orange. The results show wet doping methods increase the efficiency of titania nanoparticles more than dry doping, or combination of both. Further investigation showed that the main reason for higher activity of wet chemically doped nanoparticles is due to their higher available surface area of 131.7 m2.g-1. After normalizing the available surface area, measured by the BET method, it was shown that a combination of wet chemical doping, and dry doping at 600 °C result in the most active nanoparticles, but high temperature dry doping severely decreases the surface area, lowering the overall efficiency of the product. Additionally, N-doped TiO2 nanoparticles were synthesized using a simple hydrothermal method, in which the nitrogen source was used not only to dope, but also to control shape, size, size distribution, and morphology of the titania nanoparticles, and to induce aqueous colloidal stability. It was shown that addition of triethylamine during the synthesis, results in ultra-small, colloidally stable, cubic TiO2 nanoparticles, while using triethanolamine results in formation of TiO2 pallets, assembled into spherical, rose-like structures. The synthesized nanoparticles show impressive efficiency in visible-light removal of phenol, 4-chlorophenol, and pentachlorophenol, achieving 100% degradation of a 100-ppm phenol solution in 90 min, more than 98% degradation of a 20-ppm 4-chlorophenol solution in 90 min, and 97% degradation of a 10-ppm pentachlorophenol in 180 min with 500 ppm loading of the catalyst in all cases. Moreover, synthesized nanoparticles showed no sign of deactivation after 5 consecutive runs, removing 4-chlorophenol, showing their reusability. / Graduate