34,337 research outputs found

    Continuous flow synthesis of colloidal semiconductor nanocrystals: towards autonomous experimentation for accelerated material discovery

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    Colloidal semiconductor nanocrystals (NC) with tunable optical and electronic properties are opening up exciting opportunities for high-performance optoelectronics, photovoltaics, and bioimaging applications. While significant advancements have been made in this area in the past two decades, the vast majority of work has focused on synthesis of semiconductor NCs containing toxic heavy-metal elements such as cadmium and lead. The inherent toxicity of heavy-metal-based colloidal NCs and the associated regulatory constraints have largely impeded their widespread implementation. Therefore, the discovery of efficient synthesis routes to design high quality heavy-metal-free semiconductor NCs is critical to enable their application for various technologies such as solar cells, infrared sensors, and display technologies. Identifying the optimal synthesis and screening of syntheses recipe for these complex NCs, however, remains one of the major bottlenecks for discovery of colloidal NCs. Conventional batch rector-based synthesis screening strategies are often guided by limited understanding of the underlying growth mechanisms. Such approaches are expensive in both time and resources, and thus significantly impede the overall material discovery process. This dissertation focuses on developing an autonomous flow synthesis approach that enables accelerated screening of synthesis recipes, while also providing key kinetic insights into the underlying chemistry. In Chapter 2, a modular millifluidic reactor that leverages precise control over reaction conditions for a fully continuous multi-step synthesis of high quality InP/ZnSeS core-shell NCs exhibiting PL QYs up to 67% is reported. Using the synthesis insights gained from this work, a new pathway for synthesis of InP NCs that exhibit a very rare size-focused growth mechanism is developed in Chapter 3. Molecular insights using NMR and UV-Vis spectroscopy revealed that by addition of trace amounts of water to the reaction mixture, the reactivity of the precursors can be controlled to synthesize NCs with unprecedent control over their size distribution. In Chapter 4, an automated reconfigurable flow reactor platform integrated with inline UV-Vis and PL spectroscopy is designed to develop an efficient shell growth strategy for core/shell NCs. Feeding individual precursors into the reactor channel in a sequential fashion combined with real-time reaction monitoring enabled precise control over layer-by-layer shell passivation of the InP NCs. Further investigation using FTIR, liquid NMR, and solid NMR revealed the origin of interfacial defects and their impact on optical properties of InP-based NCs. In Chapter 5, an Artificial Intelligence-based decision-making feedback module was integrated with the automated flow reactor to develop an autonomous experimentation platform, specifically designed for accelerating screening and discovery of colloidal QDs. The autonomous platform learns the synthesis parameter space through self-driven experiments and synthesizes QDs with user-specified band gap and polydispersity without-any-prior-knowledge of the synthesis chemistry. Using a closed-loop iterative framework, it executed a minimal number of self-driven iterative experiments (28 experiments) through continuous operation (44 hours) to learn the entire synthesis parameter space for predicting the reaction outcomes for more than 100,000 different combinations of synthesis conditions. Finally, in Chapter 6, a summary of insights gained in this dissertation along with a comprehensive proposal for future research directions arising from this dissertation, is provided. Overall, the studies reported in this dissertation provide insights into flow synthesis of indium phosphide nanocrystals as well as provide an artificial-intelligence-guided autonomous experimentation approach that can be utilized to accelerate the discovery of colloidal nanocrystals in future.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    Highly selective PtCo bimetallic nanoparticles on silica for continuous production of hydrogen from aqueous phase reforming of xylose

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    Hydrogen (H2) is a promising energy vector for mitigating greenhouse gas emissions. Lignocellulosic biomass waste has been introduced as one of the abundant and carbon-neutral H2 sources. Among those, xylose with its short carbon chain has emerged attractive, where H2 can be catalytically released in an aqueous reactor. In this study, a composite catalyst system consisting of silica (SiO2)-supported platinum (Pt)-cobalt (Co) bimetallic nanoparticles was developed for aqueous phase reforming of xylose conducted at 225 °C and 29.3 bar. The PtCo/SiO2 catalyst showed a significantly higher H2 production rate and selectivity than that of Pt/SiO2, whereas Co/SiO2 shows no activity in H2 production. The highest selectivity for useful liquid byproducts was obtained with PtCo/SiO2. Moreover, CO2 emissions throughout the reaction were reduced compared to those of monometallic Pt/SiO2. The PtCo bimetallic nanocatalyst offers an inexpensive, sustainable, and durable solution with high chemical selectivity for scalable reforming of hard-to-ferment pentose sugars

    Master Class 4. Chemostat

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    Quantum dots based superluminescent diodes and photonic crystal surface emitting lasers

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    This thesis reports the design, fabrication, and electrical and optical characterisations of GaAs-based quantum dot (QD) photonic devices, specifically focusing on superluminescent diodes (SLDs) and photonic crystal surface-emitting lasers (PCSELs). The integration of QD active regions in these devices is advantageous due to their characteristics such as temperature insensitivity, feedback insensitivity, and ability to utilise the ground state (GS) and excited state (ES) of the dots. In an initial study concerning the fabrication of QD-SLDs, the influence of ridge waveguide etch depth on the electrical and optical properties of the devices are investigated. It is shown that the output power and modal gain from shallow etched ridge waveguide is higher than those of deep etched waveguides. Subsequently, the thermal performance of the devices is analysed. With increased temperature over 170 ÂșC, the spectral bandwidth is dramatically increased by thermally excited carrier transition in excited states of the dots. Following this, an investigation of a high dot density hybrid quantum well/ quantum dot (QW/QD) active structure for broadband, high-modal gain SLDs is presented. The influence of the number of QD layers on the modal gain of hybrid QW/QD structures is analysed. It is shown that higher number of dot layer provides higher modal gain value, however, there is lack of emission from QW due to the requirement of large number of carriers to saturate the QD. Additionally, a comparison is made between “unchirped QD” and “ chirped QD” of hybrid QW/QD structure in terms of modal gain and spectral bandwidth. It is showed that “chirped” of the QD can improve the “flatness” of the spectral bandwidth. Lastly, the use of self-assembled InAs QD as the active material in epitaxially regrown GaAs-based PCSELs is explored for the first time. Initially, it is shown that both GS and ES lasing can be achieved for QD-PCSELs by changing the grating period of the photonic crystal (PC). The careful design of these grating periods allows lasing from neighbouring devices at GS ( ~1230 nm) and ES (~1140 nm), 90 nm apart in wavelength. Following this, the effect of device area, PC etch depth, PC atom shape (circle or triangle or orientation) on lasing performance is presented. It is shown that lower threshold current density and higher slope efficiencies is achieved with increasing the device size. The deeper PC height device has higher output power due to more suitable height and minimal distance to active region. The triangular atom shape has slightly higher slope efficiency compared to triangular atom shape which is attributed to breaking in-plane symmetry and increase out-of-plane emission

    A review of process intensified CO2 capture in RPB for sustainability and contribution to industrial net zero

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    Carbon dioxide (CO2), a significant greenhouse gas released from power plants and industries, substantially impacts climate change; minimizing it and achieving carbon net zero is essential globally. In the direction of reducing CO2 emissions into the atmosphere, post-combustion carbon capture from large point CO2 emitters by chemical absorption involving the absorption of this gas in a capturing fluid is a commonly used and efficacious mechanism. Researchers have worked on the process using conventional columns. However, process intensification technology is required because of the high capital cost, the absorption column height, and the traditional columns’ low energy efficiency. Rotating packed bed (RPB) process intensification equipment has been identified as a suitable technology for enhanced carbon capture using an absorbing fluid. This article reviews and discusses recent model developments in the post-combustion CO2 capture process intensification using rotating packed beds. In the literature, various researchers have developed steady-state mathematical models regarding mass balance and energy balance equations in gas and liquid phases using ordinary or partial differential equations. Due to the circular shape, the equations are considered in a radial direction and have been solved using a numerical approach and simulated using different software platforms, viz. MATLAB, FORTRAN, and gPROMS. A comparison of various correlations has been presented. The models predict the mole fraction of absorbed CO2 and correspond well with the experimental results. Along with these models, an experimental data review on rotating packed bed is also included in this work

    Optimization of physico-chemical parameters for the production of phycobilin protein blue pigment, phycocyanin from the cyanobacterial strain Pseudanabaena limnetica (Lemmermann) Komarek

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    Pseudanabaena limnetica, the cyanophycean microalga, like other members of Cyanophycea, is an excellent source of pigments such as phycocyanin, proteins, carotenoids and polysaccharides. These strains also form a large proportion of algal biomass. The P.limnetica strain can grow in the extreme environmental conditions and it grows well in SW-BG 11 medium under laboratory conditions. In the present investigation, this cyanobacteria strain was isolated from the salt pans of Mulund Mumbai areas and it was cultivated in the lab under controlled conditions of light and temperature with optimum parameters of nitrate and carbonate concentrations. The culture was cultivated in the 60L photo bioreactor systems with the (65,000-85,000 lux) at 45?C in the SW-BG11 medium. The optimization experiments were carried out at the indoor and outdoor conditions. The nitrate and carbonate concentrations were optimized for obtaining maximum amount of algal biomass along with the blue-green phycocyanin pigment. The phycocyanin pigment was lyophilized for its further incorporation into the food and cosmetics products. The spectroscopic calculations of phycocyanin, allophycocyanin and phycoerythrin was done at 620, 650 and 562 nm using the Bennett and Bogorad equation. From the results obtained, it was concluded that 0.1gms/L and 1.5gms/L of the carbonate and nitrate concentrations, respectively, were the ideal concentrations for the further experiments for the cost effective production of P. limnetica in the SW-BG 11 medium. The outdoor conditions were found to be favorable for obtaining the maximum biomass and phycocyanin pigment production which would - make it more cost effective, commercially

    Metagenomic assessment of nitrate-contaminated mine wastewaters and optimization of complete denitrification by indigenous enriched bacteria

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    Nitrate contamination in water remains to be on the rise globally due to continuous anthropogenic activities, such as mining and farming, which utilize high amounts of ammonium nitrate explosives and chemical-NPK-fertilizers, respectively. This study presents insights into the development of a bioremediation strategy to remove nitrates (NO3−) using consortia enriched from wastewater collected from a diamond mine in Lesotho and a platinum mine in South Africa. A biogeochemical analysis was conducted on the water samples which aided in comparing and elucidating their unique physicochemical parameters. The chemical analysis uncovered that both wastewater samples contained over 120 mg/L of NO3− and over 250 mg/L of sulfates (SO42-), which were both beyond the acceptable limit of the environmental surface water standards of South Africa. The samples were atypical of mine wastewaters as they had low concentrations of dissolved heavy metals and a pH of over 5. A metagenomic analysis applied to study microbial diversities revealed that both samples were dominated by the phyla Proteobacteria and Bacteroidetes, which accounted for over 40% and 15%, respectively. Three consortia were enriched to target denitrifying bacteria using selective media and then subjected to complete denitrification experiments. Denitrification dynamics and denitrifying capacities of the consortia were determined by monitoring dissolved and gaseous nitrogen species over time. Denitrification optimization was carried out by changing environmental conditions, including supplementing the cultures with metal enzyme co-factors (iron and copper) that were observed to promote different stages of denitrification. Copper supplemented at 50 mg/L was observed to be promoting complete denitrification of over 500 mg/L of NO3−, evidenced by the emission of nitrogen gas (N2) that was more than nitrous oxide gas (N2O) emitted as the terminal by-product. Modification and manipulation of growth conditions based on the microbial diversity enriched proved that it is possible to optimize a bioremediation system that can reduce high concentrations of NO3−, while emitting an environmentally-friendly N2 instead of N2O, that is, a greenhouse gas. Data collected and discussed in this research study can be used to model an upscale NO3− bioremediation system aimed to remove nitrogenous and other contaminants without secondary contamination

    L’Asie du Sud-Est 2023 : bilan, enjeux et perspectives

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    Chaque annĂ©e, l’Institut de recherche sur l’Asie du Sud-Est contemporaine (IRASEC), basĂ© Ă  Bangkok, mobilise une vingtaine de chercheurs et d’experts pour mieux comprendre l’actualitĂ© rĂ©gionale de ce carrefour Ă©conomique, culturel et religieux, au cƓur de l’Indo-Pacifique. Cette collection permet de suivre au fil des ans l’évolution des grands enjeux contemporains de cette rĂ©gion continentale et archipĂ©lagique de plus de 680 millions d’habitants, et d’en comprendre les dynamiques d’intĂ©gration rĂ©gionale et de connectivitĂ©s avec le reste du monde. L’Asie du Sud-Est 2023 propose une analyse synthĂ©tique et dĂ©taillĂ©e des principaux Ă©vĂ©nements politiques et diplomatiques, ainsi que des Ă©volutions Ă©conomiques, sociales et environnementales de l’annĂ©e 2022 dans chacun des onze pays de la rĂ©gion. Ce dĂ©cryptage est complĂ©tĂ© pour chaque pays par un focus sur deux personnalitĂ©s de l’annĂ©e et une actualitĂ© marquante en image. L’ouvrage propose Ă©galement cinq dossiers thĂ©matiques qui abordent des sujets traitĂ©s Ă  l’échelle rĂ©gionale sud-est asiatique : les ressorts institutionnels de l’approche de santĂ© intĂ©grĂ©e One Health, le vieillissement de la population et sa prise en compte par les politiques publiques, les cĂąbles sous-marins au cƓur de la connectivitĂ© sud-est asiatique, l’amĂ©nagement du bassin du MĂ©kong et ses multiples acteurs, et les enjeux politiques et linguistiques des langues transnationales. Des outils pratiques sont Ă©galement disponibles : une fiche et une chronologie par pays et un cahier des principaux indicateurs dĂ©mographiques, sociaux, Ă©conomiques et environnementaux

    A critical review of the production of hydroxyaromatic carboxylic acids as a sustainable method for chemical utilisation and fixation of CO2

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    Hydroxyaromatic carboxylic acids (HACAs) such as salicylic acids, hydroxynaphthoic acids and their halogenated derivatives are essential feedstocks for the pharmaceutical, dye, fragrance, cosmetic and food industries. Large-scale production of HACAs is currently based on the Kolbe–Schmitt reaction between CO2 and petroleum-based phenolic compounds. This batch reaction is carried out at ∌125 °C, ∌85 bar and reaction times of up to 18 hours to achieve high conversions (≈99%). The long reaction times and dependence on fossil-derived phenols have negative sustainability implications. However, as a CO2-based process, HACA production has the potential for large-volume anthropogenic CO2 sequestration and contributes to net zero. A big challenge is that the current global production capacity of HACAs uses only about 41 450 tonnes per year of CO2 which is just ≈0.00012% of the annual anthropogenic emissions. Therefore, significant efforts are needed to increase both the sustainable production and demand for such CO2-based products to enhance their economic and environmental sustainability. This review covers the basic kinetic and thermodynamic stability of CO2. Thereafter, a comprehensive coverage of early and current developments to improve the carboxylation of phenols to make HACAs is given, while discussing their industrial potential. Moreover, it covers new propositions to use biomass-derived phenolic compounds for sustainable production of HACAs. There is also a need to expand the uses and applications of HACAs and recent reports on the production of HACA-based recyclable vinyl polymers point in the right direction