5,915 research outputs found
Classical and quantum algorithms for scaling problems
This thesis is concerned with scaling problems, which have a plethora of connections to different areas of mathematics, physics and computer science. Although many structural aspects of these problems are understood by now, we only know how to solve them efficiently in special cases.We give new algorithms for non-commutative scaling problems with complexity guarantees that match the prior state of the art. To this end, we extend the well-known (self-concordance based) interior-point method (IPM) framework to Riemannian manifolds, motivated by its success in the commutative setting. Moreover, the IPM framework does not obviously suffer from the same obstructions to efficiency as previous methods. It also yields the first high-precision algorithms for other natural geometric problems in non-positive curvature.For the (commutative) problems of matrix scaling and balancing, we show that quantum algorithms can outperform the (already very efficient) state-of-the-art classical algorithms. Their time complexity can be sublinear in the input size; in certain parameter regimes they are also optimal, whereas in others we show no quantum speedup over the classical methods is possible. Along the way, we provide improvements over the long-standing state of the art for searching for all marked elements in a list, and computing the sum of a list of numbers.We identify a new application in the context of tensor networks for quantum many-body physics. We define a computable canonical form for uniform projected entangled pair states (as the solution to a scaling problem), circumventing previously known undecidability results. We also show, by characterizing the invariant polynomials, that the canonical form is determined by evaluating the tensor network contractions on networks of bounded size
Natural and Technological Hazards in Urban Areas
Natural hazard events and technological accidents are separate causes of environmental impacts. Natural hazards are physical phenomena active in geological times, whereas technological hazards result from actions or facilities created by humans. In our time, combined natural and man-made hazards have been induced. Overpopulation and urban development in areas prone to natural hazards increase the impact of natural disasters worldwide. Additionally, urban areas are frequently characterized by intense industrial activity and rapid, poorly planned growth that threatens the environment and degrades the quality of life. Therefore, proper urban planning is crucial to minimize fatalities and reduce the environmental and economic impacts that accompany both natural and technological hazardous events
LIPIcs, Volume 251, ITCS 2023, Complete Volume
LIPIcs, Volume 251, ITCS 2023, Complete Volum
Synthesis and Characterization of Nanoporous Resin Particles for Water Purification
Through progressive industrialization and the relentless consumption of natural raw materials, man is exerting a negative influence on his habitat. In particular, water as the basis of life and almost all processes of our economy is contaminated by various pollutants due to excessive use and insufficient purification. Here, oxyanions, heavy metal ions and organic pollutants pose a high risk to aquatic habitats and ultimately to humans. Due to insufficient removal, they also contribute to the loss of non-renewable raw materials for industrial cycles. Due to a mostly low effect concentration and potential interactions with diverse living organisms, the removal of many contaminants is extremely important to avoid further altering existing ecosystems.
Adsorption represents an energy-efficient method of removal using adsorbents suitable for this purpose. Highly cross-linked resin polymers such as poly(melamine-co-formaldehyde) (PMF) with its excellent chemical resistance, high number of functional groups and ease of preparation, represent promising starting points for adsorbents.
This dissertation describes the colloidal aqueous synthesis of nanoporous resin particles (e.g. PMF) by templating with SiO2 nanoparticles (SiO2 NPs), which are subsequently used to adsorb water pollutants. An overall goal of this work consists of elucidating the mechanism for particle and pore formation by systematically varying various synthesis parameters. Electron microscopy, N2-soprtion and particle size measurement are used to analyze the morphology, size and pore structure of the particles. Comprehensive investigations thus allow to determine the influence of each tested synthesis parameter on these properties.
A very important goal, especially for future large-scale applicability, is the colloidal production of uniform particles, which have both a high ordered porosity and particle diameters in the range of a few micrometers. This enables an application as a fixed-bed adsorber that can be flowed through. This goal is closely linked to the mechanistic elucidation of pore and particle formation in the synthesis.
The prepared nanoporous PMF particles were tested for various adsorption applications after their characterization. In order to obtain a comprehensive picture of the applicability of PMF particles, experiments with oxyanions, with pharmaceuticals as representatives of organic pollutants and with heavy metal ions will be carried out respectively. On the one hand, these experiments will focus on investigating the adsorption performance and mechanism of PMF with the respective pollutant. On the other hand, the influence of the changed porosity on the adsorption mechanism is investigated by using different particles of a varied synthesis parameter.
Sulfate and phosphate ions were investigated in the oxyanion class. Extremely high separation rates were demonstrated for both ions, significantly outperforming previous commercially available materials. In experiments concerning a potential selective adsorption and thus separation of both species, the PMF/SiO2 hybrid particles, in which the template had not yet been removed, showed a selective sulfate adsorption.
The immobilization of heavy metal ions was analyzed with special focus on the simultaneous separation of the Cu2+ ions and respective anions used here. Investigations of the adsorbent after the adsorption experiments by means of electron microscopy, X-ray scattering and electron spin resonance spectroscopy elucidated the adsorption mechanism, which had been insufficiently analyzed so far. Here, adsorption and surface-induced precipitation were identified as partially separate subprocesses, both of which are responsible for the separation of both metal and anions from solution. In adsorption experiments with the monovalent ions nitrate and chloride, a two-step uptake process was identified, which was mathematically described for the first time via a new adsorption isotherm.
In the scope of organic water pollutants, the separation of the pharmaceutical diclofenac is being tested. In particular, the adsorption of pharmaceuticals is an urgent issue due to their low effect concentration and ubiquity in surface and tap waters. Pharmaceutical separation using PMF has hardly been investigated worldwide despite its promising properties. In these experiments, particles templated with SiO2 NPs of different sizes and stabilized in different ways were tested. This resulted in pore systems that varied from each other especially in their accessibility of the pore system and in the diameter of the connecting channels between the main cavities. These characteristics significantly affected the adsorption capacity and separation rates in low concentration range.
A final goal is to synthesize a resin network that uses an equally highly functional triazine-based monomer instead of melamine. The monomer 2,4,6-tris(2,4,6-trihydroxyphenyl)-1,3,5-triazine (3PT) possesses nine hydroxyl groups each, whereby a polymer based on it should exhibit strongly modified adsorption properties compared to PMF. This monomer was used in an aqueous polymerization analogous to PMF to produce a previously unknown polymer network, which was designated P(3PT-F). Here, templating was omitted because the newly prepared material already exhibited intrinsic nanoporosity due to the size of the 3PT monomer. In subsequent adsorption experiments, very high separation rates were demonstrated for the toxic metal ions Pb2+, Cd2+ and Ni2+. In realistic initial concentrations, the contamination was reduced to drinking water quality in each case. P(3PT-F) also showed highly selective removal of Pb2+ over the common ions Ca2+, Mg2+, K+ and Fe2+. As fundamental evidence, reusability was also demonstrated by complete desorption with dilute HCl and subsequent re-adsorption without significant reduction in capacity.
Overall, starting from the fundamental study of PMF particle synthesis, a more general understanding of aqueous dispersion polymerization of hydrophobic resins was first derived and templating with hydrophilic SiO2 NPs was implemented. With the help of understanding the particle growth processes and interactions responsible for templating, the properties of the resulting particles could be controlled. Subsequently, the influence of the changed porosity in particular on the separation performance could be investigated in the adsorption studies. In addition, it was possible to analyze which interactions PMF enters into with the respective pollutant types. By replacing the monomer melamine with a hydroxyl-containing monomer, a novel resin polymer could be produced. With its altered porosity and reactivity, this can now serve as a new starting point for adsorption experiments with strongly altered adsorption performance, e.g. towards heavy metal ions.:Abstract 1
Kurzfassung 5
List of Publications 9
First-Author Publications 9
Co-Author Publications 10
Patent 12
Conference Proceedings 12
Oral Presentations 12
Poster 12
List of Figures 13
Mesoporous Poly(Melamine-co-Formaldehyde) Particles for Efficient and Selective Phosphate and Sulfate Removal: 14
Tuning the Pore Structure of Templated Mesoporous Poly(melamine-co-formaldehyde) Particles toward Diclofenac Removal: 15
Adsorption vs. Surface Precipitation of CuÂČ+ onto Porous Poly(melamine-co-formaldehyde) Particles: 16
SiO2 Nanospheres as Surfactant and Template in Aqueous Dispersion Polymerizations Yielding Nanoporous Resin Particles: 18
Waterborne Phenolic, Triazine-Based Porous Polymer Particles for the Removal of Nickel, Cadmium, and Lead Ions: 19
List of Tables 21
Mesoporous Poly(Melamine-co-Formaldehyde) Particles for Efficient and Selective Phosphate and Sulfate Removal: 21
Tuning the Pore Structure of Templated Mesoporous Poly(melamine-co-formaldehyde) Particles toward Diclofenac Removal: 21
Adsorption vs. Surface Precipitation of CuÂČ+ onto Porous Poly(melamine-co-formaldehyde) Particles: 22
SiO2 Nanospheres as Surfactant and Template in Aqueous Dispersion Polymerizations Yielding Nanoporous Resin Particles: 22
Waterborne Phenolic, Triazine-Based Porous Polymer Particles for the Removal of Nickel, Cadmium, and Lead Ions: 23
Abbreviations 25
Symbols 26
1. Introduction 1
2. Objectives and Experimental Design 5
3. Scientific Background 11
3.1. Poly(melamine-co-formaldehyde) 11
3.1.1. Polymerization Mechanism 11
3.1.2. Synthesis Strategies for the Preparation of Porous PMF Particles. 13
3.1.3. Fields of Application of PMF 13
3.2. Adsorption 15
3.2.1. Adsorption Isotherms and Mathematical Modeling 16
3.3. Surface Precipitation 20
4. Fundamentals of Instrumental Analytics 23
4.1. Gas Sorption Measurements 23
4.1.1. Determination of Pore Sizes 26
4.1.2. Determination of Specific Surface Area 27
4.2. Transmission Electron Microscopy 29
4.3. Inductively Coupled Plasma Optical Emission Spectroscopy 31
Results and Discussion 33
Chapter Overview 33
5. Mesoporous Poly(Melamine-co-Formaldehyde) Particles for Efficient and Selective Phosphate and Sulfate Removal 37
Graphical Abstract 37
Abstract 37
1. Introduction 38
2. Results and Discussion 39
2.1. Synthesis and Characterization of the PMF Particles 40
2.2. Sorption Experiments 47
3. Materials and Methods 54
3.1. Materials 54
3.2. Methods 54
3.3. Synthesis of the PMF Particles 56
3.4. Water Treatment Experiments 57
4. Conclusions 59
6. Tuning the Pore Structure of Templated Mesoporous Poly(melamine-co-formaldehyde) Particles toward Diclofenac Removal 65
Graphical Abstract 65
Abstract 65
1. Introduction 66
2. Materials 68
3. Methods 68
3.1. Synthesis of the PMF particles 70
3.2. Water treatment experiments with diclofenac solution 72
3.3. Theoretical model 72
3. Results and Discussion 73
3.1. Synthesis and characterization of the PMF particles 74
3.2. Adsorption of Pharmaceutics 80
4. Conclusion 84
7. Adsorption vs. Surface Precipitation of CuÂČ+ onto Porous Poly(melamine-co-formaldehyde) Particles 89
Graphical Abstract 89
Abstract 89
1. Introduction 90
2. Materials and methods 91
2.1. Materials 91
2.2. Synthesis of the Poly(melamine-co-formaldehyde) particles 92
2.3. Methods 93
2.4. Water treatment experiments 96
3. Results and discussion 97
3.1. Synthesis and characterization of the PMF particles 98
3.2. Cu2+ uptake experiments 102
3.3. Mechanism for Cu2+ and Anion Removal 115
3.4. Investigation of other heavy metal salts 116
4. Conclusions 117
8. SiOâ Nanospheres as Surfactant and Template in Aqueous Dispersion Polymerizations Yielding Nanoporous Resin Particles 121
Graphical Abstract 121
Abstract 121
1. Introduction 122
2. Materials and methods 123
2.1. Materials 123
2.2. Methods 124
2.3. Synthesis of the PMF particles 125
2.4. Water treatment experiments 128
2.5. Theoretical model 129
3. Results and Discussion 132
3.1. PMF-Std 133
3.2. Influence of the reaction mixture composition 136
3.3. Variation of the process parameters 140
3.4. Conclusion on the templating mechanism for PMF-Std 146
3.5. Acquiring ”m-sized porous PMF particles for adsorption application 149
3.6. Adsorption experiments with K2Cr2O7 solution 151
4. Conclusion 155
9. Waterborne Phenolic, Triazine-Based Porous Polymer Particles for the Removal of Nickel, Cadmium, and Lead Ions 161
Graphical Abstract 161
Abstract 161
1. Introduction 162
2. Materials and methods 163
2.1. Materials 163
2.2. Synthesis 164
2.3. Characterization 166
2.4. Batch adsorption experiments 169
2.5. Calculation and theoretical models 170
3. Results and discussion 172
3.1. Synthesis and characterization of the polymer particles 172
3.2. Adsorption experiments with Ni2+, Cd2+, and Pb2+ onto P(3PT-F)-3L 178
4. Conclusions 184
10. Conclusion and Outlook 191
Contribution to Publications 197
Mesoporous Poly(Melamine-co-Formaldehyde) Particles for Efficient and Selective Phosphate and Sulfate Removal 197
Tuning the Pore Structure of Templated Mesoporous Poly(melamine-co-formaldehyde) Particles toward Diclofenac Removal 198
Adsorption vs. Surface Precipitation of CuÂČ+ onto Porous Poly(melamine-co-formaldehyde) Particles 199
SiOâ Nanospheres as Surfactant and Template in Aqueous Dispersion Polymerizations Yielding Nanoporous Resin Particles 200
Waterborne Phenolic, Triazine-Based Porous Polymer Particles for the Removal of Nickel, Cadmium, and Lead Ions 201
Danksagung 203
Appendix 205
References 207
Eidesstattliche Versicherung 217Durch fortschreitende Industrialisierung und den schonungslosen Verbrauch natĂŒrlicher Rohstoffe ĂŒbt der Mensch negativen Einfluss auf seinen Lebensraum aus. Insbesondere Wasser als Grundlage des Lebens und fast aller Prozesse unserer Wirtschaft wird durch eine ĂŒbermĂ€Ăige Nutzung und unzureichende Reinigung mit diversen Schadstoffen kontaminiert. Hierbei stellen Oxyanionen, Schwermetallionen und organische Schadstoffe ein hohes Risiko fĂŒr aquatische LebensrĂ€ume und letztendlich auch den Menschen dar. Durch unzureichende Entfernung tragen sie auĂerdem zum Verlust nicht-erneuerbarer Rohstoffe fĂŒr industrielle KreislĂ€ufe bei. Durch eine meist geringe Effektkonzentration und potentielle Wechselwirkungen mit diversen Lebewesen ist die Entfernung vieler Verunreinigungen extrem wichtig, um bestehende Ăkosysteme nicht weiter zu verĂ€ndern.
Adsorption stellt eine energieeffiziente Methode zur Entfernung dieser Schadstoffe durch hierfĂŒr geeignete Adsorbentien dar. Hochgradig vernetzte Harzpolymere wie Poly(melamin-co-formaldehyd) (PMF) stellen mit ihrer sehr hohen chemischen BestĂ€ndigkeit, einer hohen Zahl funktioneller Gruppen und einfachen Herstellbarkeit einen vielversprechenden Ausgangspunkt fĂŒr Adsorbentien dar.
Diese Dissertation beschreibt die kolloidale, wĂ€ssrige Synthese nanoporöser Harzpartikel (z. B. PMF) durch eine Templatierung mit SiO2 Nanopartikeln (SiO2 NPs), welche anschlieĂend zur Adsorption von Wasserschadstoffen eingesetzt werden. Ein ĂŒbergeordnetes Ziel dieser Arbeit besteht aus der AufklĂ€rung des Mechanismus zur Partikel- und Porenbildung durch systematische Variation verschiedener Syntheseparameter. Mittels Elektronenmikroskopie, N2-Sorption und PartikelgröĂenmessung wird die Morphologie, GröĂe und Porenstruktur der Partikel analysiert. Umfassende Untersuchungen ermöglichen somit, den Einfluss der einzelnen getesteten Syntheseparameter auf diese Eigenschaften zu bestimmen.
Ein sehr wichtiges Ziel, besonders fĂŒr eine zukĂŒnftige groĂtechnische Anwendbarkeit, ist dabei die kolloidale Herstellung uniformer Partikel, welche sowohl eine hohe geordnete PorositĂ€t als auch Partikeldurchmesser im Bereich einiger Mikrometer aufweisen. Dies ermöglicht einen Einsatz als durchströmbaren Festbett-Adsorber. Dieses Ziel ist eng mit der mechanistischen AufklĂ€rung der Poren- und Partikelbildung in der Synthese verknĂŒpft.
Die hergestellten nanoporösen PMF-Partikel wurden nach ihrer Charakterisierung fĂŒr verschiedene Adsorptionsanwendungen getestet. Um ein umfassendes Bild ĂŒber die Einsetzbarkeit von PMF-Partikeln zu erhalten, sollen jeweils Versuche mit Oxyanionen, mit Schwermetallionen und mit Pharmazeutika als Vertreter organischer Schadstoffe durchgefĂŒhrt werden. Bei diesen Versuchen steht zum einen die Untersuchung der Adsorptionsleistung und des Adsorptionsmechanismus des jeweiligen Schadstoffes an PMF im Vordergrund. Zum anderen wird durch die Verwendung verschiedener Partikel, bei welchen ein einzelner Syntheseparameter variiert wurde, der Einfluss der verĂ€nderten PorositĂ€t auf den Adsorptionsmechanismus untersucht.
Sulfat- und Phosphationen wurden in der Klasse der Oxyanionen untersucht. FĂŒr beide Ionen wurden extrem hohe Abtrennraten nachgewiesen, welche bisherige kommerziell erhĂ€ltliche Materialien signifikant ĂŒbertraf. In Versuchen hinsichtlich einer potentiellen selektiven Adsorption und somit Trennung beider Spezies, zeigten die PMF/SiO2-Hybridpartikel, bei welchen das Templat noch nicht entfernt wurde, eine selektive Sulfatadsorption.
Die Immobilisierung von Schwermetallionen wurde mit besonderem Fokus auf die gleichzeitig auftretende Abtrennung der dafĂŒr verwendeten Cu2+-Ionen und jeweiliger Anionen analysiert. Durch Untersuchungen des Adsorbens nach den Adsorptionsversuchen mittels Elektronenmikroskopie, Röntgenstreuung und Elektronenspinresonanz-Spektroskopie wurde der bisher unzureichend analysierte Adsorptionsmechanismus aufgeklĂ€rt. Hierbei wurden Adsorption und oberflĂ€cheninduzierte FĂ€llung als separate Teilprozesse identifiziert, welche beide jeweils fĂŒr die Abscheidung von sowohl Metall- als auch Anionen aus der Lösung verantwortlich sind. Bei Adsorptionsversuchen mit den einwertigen Ionen Nitrat und Chlorid wurde ein zweistufiger Prozess identifiziert, welcher erstmals ĂŒber eine neue Adsorptionsisotherme mathematisch beschrieben wurde.
Im Bereich organischer Wasserschadstoffe wird die Abtrennung des Pharmazeutikums Diclofenac getestet. Insbesondere die Adsorption von Pharmazeutika stellt aufgrund von deren geringen Effektkonzentration und AllgegenwĂ€rtigkeit in OberflĂ€chen- und LeitungswĂ€ssern ein dringliches Thema dar. Die Pharmazeutika-Abtrennung mittels PMF wurde trotz seiner vielversprechenden Eigenschaften weltweit bisher kaum untersucht. Im Rahmen dieser Versuche wurden Partikel getestet, welche mit unterschiedlich groĂen und unterschiedlich stabilisierten SiO2 NPs templatiert wurden. Dadurch entstanden Porensysteme, die besonders in derer ZugĂ€nglichkeit ihres Porensystems und in dem Durchmesser der VerbindungskanĂ€le zwischen den HauptkavitĂ€ten voneinander variierten. Diese Eigenschaften wirkten sich signifikant auf die AdsorptionskapazitĂ€t und die Abtrennraten im niedrigen Konzentrationsbereich aus.
Ein abschlieĂendes Ziel ist die Synthese eines Harznetzwerkes, welches statt Melamin auf einem ebenso hochfunktionellen, triazinbasierten Monomer basiert. Das Monomer 2,4,6-Tris(2,4,6-trihydroxyphenyl)-1,3,5-triazin (3PT) besitzt jeweils neun Hydroxylgruppen, wodurch ein darauf basierendes Polymer stark verĂ€nderte Adsorptionseigenschaften gegenĂŒber PMF aufweisen soll. Mit diesem Monomer wurde in einer analog zu PMF durchgefĂŒhrten wĂ€ssrigen Polymerisation ein bisher unbekanntes Polymernetzwerk hergestellt, welches als P(3PT-F) bezeichnet wurde. Hierbei wurde auf Templatierung verzichtet, da das neu hergestellte Material bereits intrinsische NanoporositĂ€t durch die GröĂe des verwendeten 3PT-Monomers aufwies. In anschlieĂenden Adsorptionsversuchen wurden sehr hohe Abtrennraten fĂŒr die toxischen Metallion Pb2+, Cd2+ und Ni2+ nachgewiesen. In realistischen Ausgangskonzentrationen wurde die Kontamination mit diesen Ionen jeweils auf TrinkwasserqualitĂ€t reduziert. P(3PT-F) zeigte auĂerdem eine sehr selektive Abtrennung von Pb2+ gegenĂŒber den hĂ€ufig vorkommenden Ionen Ca2+, Mg2+, K+ und Fe2+. Als grundlegender Beweis konnte eine Wiederverwendbarkeit durch die vollstĂ€ndige Desorption mit verdĂŒnnter HCl gezeigt werden und eine anschlieĂende erneute Adsorption ohne signifikante Verringerung der KapazitĂ€t.
Insgesamt wurde ausgehend von der grundlegenden Untersuchung der PMF-Partikelsynthese erst ein generelleres VerstĂ€ndnis der wĂ€ssrigen Dispersionspolymerisation hydrophober Harze abgeleitet und die Templatierung mit hydrophilen SiO2 NPs implementiert. Mithilfe des VerstĂ€ndnisses der Partikelwachstumsprozesse und der Wechselwirkungen, welche fĂŒr die Templatierung verantwortlich sind, konnten die Eigenschaften der entstehenden Partikel gesteuert werden. Im Rahmen der Adsorptionsuntersuchungen konnte anschlieĂend der Einfluss insbesondere der verĂ€nderten PorositĂ€t auf die Abtrennleistung untersucht werden. AuĂerdem konnte analysiert werden, welche Wechselwirkungen PMF mit den jeweiligen Schadstoffarten eingeht. Durch den Austausch des Monomers Melamin gegen das hydroxylhaltiges Monomer 3PT konnte ein neuartiges Harzpolymer hergestellt werden. Dieses kann mit seiner verĂ€nderten PorositĂ€t und ReaktivitĂ€t nun als neuer Ausgangspunkt fĂŒr Adsorptionsexperimente mit stark verĂ€nderter Adsorptionsleistung z. B. gegenĂŒber Schwermetallionen dienen.:Abstract 1
Kurzfassung 5
List of Publications 9
First-Author Publications 9
Co-Author Publications 10
Patent 12
Conference Proceedings 12
Oral Presentations 12
Poster 12
List of Figures 13
Mesoporous Poly(Melamine-co-Formaldehyde) Particles for Efficient and Selective Phosphate and Sulfate Removal: 14
Tuning the Pore Structure of Templated Mesoporous Poly(melamine-co-formaldehyde) Particles toward Diclofenac Removal: 15
Adsorption vs. Surface Precipitation of CuÂČ+ onto Porous Poly(melamine-co-formaldehyde) Particles: 16
SiO2 Nanospheres as Surfactant and Template in Aqueous Dispersion Polymerizations Yielding Nanoporous Resin Particles: 18
Waterborne Phenolic, Triazine-Based Porous Polymer Particles for the Removal of Nickel, Cadmium, and Lead Ions: 19
List of Tables 21
Mesoporous Poly(Melamine-co-Formaldehyde) Particles for Efficient and Selective Phosphate and Sulfate Removal: 21
Tuning the Pore Structure of Templated Mesoporous Poly(melamine-co-formaldehyde) Particles toward Diclofenac Removal: 21
Adsorption vs. Surface Precipitation of CuÂČ+ onto Porous Poly(melamine-co-formaldehyde) Particles: 22
SiO2 Nanospheres as Surfactant and Template in Aqueous Dispersion Polymerizations Yielding Nanoporous Resin Particles: 22
Waterborne Phenolic, Triazine-Based Porous Polymer Particles for the Removal of Nickel, Cadmium, and Lead Ions: 23
Abbreviations 25
Symbols 26
1. Introduction 1
2. Objectives and Experimental Design 5
3. Scientific Background 11
3.1. Poly(melamine-co-formaldehyde) 11
3.1.1. Polymerization Mechanism 11
3.1.2. Synthesis Strategies for the Preparation of Porous PMF Particles. 13
3.1.3. Fields of Application of PMF 13
3.2. Adsorption 15
3.2.1. Adsorption Isotherms and Mathematical Modeling 16
3.3. Surface Precipitation 20
4. Fundamentals of Instrumental Analytics 23
4.1. Gas Sorption Measurements 23
4.1.1. Determination of
Insights into temperature controls on rockfall occurrence and cliff erosion
A variety of environmental triggers have been associated with the occurrence of rockfalls however their role and relative significance remains poorly constrained. This is in part due to the lack of concurrent data on rockfall occurrence and cliff face conditions at temporal resolutions that mirror the variability of environmental conditions, and over durations for large enough numbers of rockfall events to be captured. The aim of this thesis is to fill this data gap, and then to specifically focus on the role of temperature in triggering rockfall that this data illuminates. To achieve this, a long-term multiannual 3D rockfall dataset and contemporaneous Infrared Thermography (IRT) monitoring of cliff surface temperatures has been generated. The approaches used in this thesis are undertaken at East Cliff, Whitby, which is a coastal cliff located in North Yorkshire, UK. The monitored section is ~ 200 m wide and ~65 m high, with a total cliff face area of ~9,592 mÂČ. A method for the automated quantification of rockfall volumes is used to explore data collected between 2017â2019 and 2021, with the resulting inventory including > 8,300 rockfalls from 2017â2019 and > 4,100 rockfalls in 2021, totalling > 12,400 number of rockfalls.
The analysis of the inventory demonstrates that during dry conditions, increases in rockfall frequency are coincident with diurnal surface temperature fluctuations, notably at sunrise, noon and sunset in all seasons, leading to a marked diurnal pattern of rockfall. Statistically significant relationships are observed to link cliff temperature and rockfall, highlighting the response of rock slopes to absolute temperatures and changes in temperature. This research also shows that inclement weather constitutes the dominant control over the annual production of rockfalls but also quantifies the period when temperature controls are dominant. Temperature-controlled rockfall activity is shown to have an important erosional role, particularly in periods of iterative erosion dominated by small size rockfalls. As such, this thesis provides for the first high-resolution evidence of temperature controls on rockfall activity, cliff erosion and landform development
Studies on the adsorption/absorption-based COâ capture process focusing on implications of process design and adsorbent selection
At COP26 in Glasgow in November 2021, a decisive commitment was made to limit the rise in global temperature to a maximum of 1.5 degrees. Urgent actions are required to achieve the worldwide goal of net-zero carbon emissions by the middle of the century, necessitating a reduction in greenhouse gas emissions. Renewable energy development in the long term and Carbon Capture and Storage (CCS) in the short term are identified as the most effective methods to combat the dramatic increase in COâ emissions from industrial processes and fossil-fuel electricity generation. In this thesis, investigations focus on two industrial emission points with carbon capture technology: integrated gasification combined cycle (IGCC) integrated with pre-combustion COâ capture and conventional coal-fired power plants integrated with post-combustion COâ capture.
Primarily, this thesis sought to design and evaluate two process configurations of an IGCC integrated with pre-combustion COâ capture unit (Chapter 4). One IGCC process is configured with sour shift, while the other is based on sweet shift. Incorporating water-gas shift reactors (WGSRs) consuming vast amount of shift steam into an IGCC involves significant alternations to the associated steam cycle, in addition to simply changing the location of the HâS removal step around the shift reactors. Although the sweet shift case requires 4.6 times more shift steam compared to the sour shift case, the energy penalties incurred by carbon capture integration for both configurations were estimated to be almost equal. This similarity is attributed to the water quench requirements of sour shift, leading to a reduction in power generation during the steam cycle. In both cases, the sizes of high and low-temperature water-gas shift reactors were estimated using the reaction rate models reported in literature.
Additionally, this thesis aims to evaluate and compare conventional and emerging porous adsorbents in their applications to an adsorption-based COâ capture processes from the flue gas produced by the conventional coal-fired power plant (15% COâ and 85% Nâ) (Chapter 5). The adsorbent candidates involved in this thesis include zeolites, carbons, MOFs, and triazine-based benzimidazole-linked polymers (TBILPs). The choice of adsorbent material significantly affects process performance in the design of efficient COâ capture processes. It was demonstrated that adsorbents with high COâ recovery did not necessarily correspond to increased productivity. Productivity depends on desorption pressure and COâ isotherm shape. Despite MFI demonstrating the highest COâ recovery among all zeolite candidates, it exhibited the lowest productivity due to its lowest COâ adsorption capacity. Likewise, the adsorption materials with flat COâ isotherms such as BPL AC, UiO-66, MIL-101(Cr)-F, MIL-101(Cr)-OH, and TBILPs also showed better COâ recovery but less productivity compared to the commercial zeolite 13X. In contrast, Mg-MOF-74 showed the highest productivity, attributed to its steepest COâ isotherm during the initial stage of the adsorption. However, a low desorption pressure was required to reach a high COâ recovery, leading to extremely high energy consumption.
To further investigate adsorbents for adsorption-based COâ capture, a two-stage VSA process was simulated by gPROMS upon achieving the desired operational criteria of 90% COâ recovery and 90% COâ purity (Chapter 6). The first stage was packed with MFI, while the second stage employed activated carbon (AC), namely MFI-AC case. As a comparative analysis, an alternative two-stage VSA process utilised zeolite 13X in the first stage and AC in the second stage (zeolite 13X-AC case). As a result, the total productivities for both MFI-AC and zeolite 13X-AC cases were found to be similar, around 6.3 //â. However, it is essential to note that the MFI-AC process exhibited a higher minimum specific energy consumption, estimated at 17.1 /â, in comparison to the zeolite 13X-AC process.
This thesis contributes to an advanced understanding of the process design in pre-combustion IGCC plant integrated with the adsorption-based COâ capture process with a focus on the choice between sour or sweet shift configurations. Besides, this thesis comprehensively evaluates various porous adsorbents for COâ separation from the flue gas using a P/VSA process and provide a systemic guideline for selecting adsorbents
An investigation of entorhinal spatial representations in self-localisation behaviours
Spatial-modulated cells of the medial entorhinal cortex (MEC) and neighbouring cortices are thought to provide the neural substrate for self-localisation behaviours. These cells include grid cells of the MEC which are thought to compute path integration operations to update self-location estimates. In order to read this grid code, downstream cells are thought to reconstruct a positional estimate as a simple rate-coded representation of space.
Here, I show the coding scheme of grid cell and putative readout cells recorded from mice performing a virtual reality (VR) linear location task which engaged mice in both beaconing and path integration behaviours. I found grid cells can encode two unique coding schemes on the linear track, namely a position code which reflects periodic grid fields anchored to salient features of the track and a distance code which reflects periodic grid fields without this anchoring. Grid cells were found to switch between these coding schemes within sessions. When grid cells were encoding position, mice performed better at trials that required path integration but not on trials that required beaconing. This result provides the first mechanistic evidence linking grid cell activity to path integration-dependent behaviour.
Putative readout cells were found in the form of ramp cells which fire proportionally as a function of location in defined regions of the linear track. This ramping activity was found to be primarily explained by track position rather than other kinematic variables like speed and acceleration. These representations were found to be maintained across both trial types and outcomes indicating they likely result from recall of the track structure.
Together, these results support the functional importance of grid and ramp cells for self-localisation behaviours. Future investigations will look into the coherence between these two neural populations, which may together form a complete neural system for coding and decoding self-location in the brain
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