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Hydrogels of Humic Acids
Cihlář, Zdeněk ; Lehocký,, Marián (oponent) ; Pospíšilová,, Lubica (oponent) ; Kučerík, Jiří (vedoucí práce)
Humic acids (HAs) are the main components of the soil organic matter. They are ubiquitous substances with complex chemical and physicochemical structure. In this study, several modifications of HAs were carried out in order to modify their properties. In the first part, the influence of lignite air oxidation on the yield and physicochemical character of regenerated humic acids were studied. In the second step, to stabilize the structure of lignite humic acids and improve the water holding capacity, we applied formaldehyde and carbodiimides crosslinking procedures leading to covalent coupling of humic acids moieties. The production of crosslinked structures was motivated by the attempt to design HAs-based systems resembling hydrogels, with the possibility to modify their reactivity and water retention. Samples were analyzed for their chemical composition and physicochemical properties using various techniques, among the most important were DSC and NMR relaxometry. The chemical composition was studied using FTIR and elemental analysis in order to assess the changes in comparison to pristine humic acids. The stabilities of derivatives were determined by using thermogravimetry. The most important parameter studied in this work was the change in hydration characteristics. For this reason, we developed and applied several new thermoanalytical and NMR relaxometry approaches. In particular, to mimic the situations occurring in nature, we studied sorption of water on humic acids from controlled humidities and monitored qualitative and quantitative aspects of water sorption. Crosslinking by formaldehyde induced a reduction in moisture sorption capacity, which was attributed to the separation of functional groups and a decrease in structural compactness. In addition, the crosslinked humic acids exhibited faster water uptake and approximately three-fold higher water holding capacity than pristine humic acids. In case of carbodiimide coupling (by using water-soluble N-Ethyl-N-(3-dimethylaminopropyl)carbodiimide (EDC)), the derivatives of humic acids contained only between 14–40 % of original free carboxylic groups. Despite that, they exceeded the moisture harvesting ability of parental humic acids around 10–14 % after their equilibration at 100% relative humidity. Although, they showed also more rigid structure, the EDC derivatives showed also faster swelling kinetics and reached almost the same water holding capacity as original sample after 18 days. However, carbodiimides derivatives began to degrade already after 3–9 days during swelling tests, which subsequently decreased their performance. The results suggest that water holding capacity, swelling kinetics and moisture harvesting ability of humic acids are not influenced exceptionally by the amount of free carboxylic groups or other polar functionalities, but also by their spatial arrangement and the distribution of pore sizes on the surface and inside the humic structure. The knowledge gained in this study is beneficial, among others, for the production of soil humic acids-based conditioners, i.e. remediation agents having required and simultaneously adjustable ability to bind and release water into the surrounding environment. Last, but not least, the presented findings improve the fundamental understanding the hydration processes in pristine and modified humic acids, which is beneficial to elucidate the hydration of complex natural systems, and of in particular of natural organic matter.
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Vliv zinku přítomného ve vedlejších surovinách na hydrataci a vlastnosti portlandských směsných cementů
Šilerová, Iva ; Palou, Martin (oponent) ; Rovnaníková, Pavla (oponent) ; Havlica, Jaromír (vedoucí práce)
Tématem této práce je sledování vlivu zinku na vlastnosti portlandských směsných cementů. Zinek byl testován ve formě dvou dobře rozpustných solí: Zn(NO3)22 H2O a ZnCl2 a jedné velmi málo rozpustné sloučeniny ZnO. Směsné cementy byly připraveny s částečnou náhradou jemně mletou vysokopecní struskou, vysokoteplotním a fluidním filtrovým popílkem. U připravených past byly studovány jejich tokové vlastnosti a pomocí isotermální a isoperibolické kalorimetrie pak vliv na průběh hydratačních reakcí. U připravených zkušebních tělísek byly měřeny jejich mechanické vlastnosti – pevnost v tahu za ohybu a v tlaku. Dále bylo studováno fázové složení připravených kompozitů a inkorporace zinečnatých iontů do cementové matrice pomocí vyluhovacích testů a analýzy FTIR. Samozřejmě byl studován i vývoj mikrostruktury cementových vzorků. Posledním studovaným efektem zinku byl jeho vliv na ekotoxicitu.
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Hydration of Humic Substances
Bursáková, Petra ; Šimon, Peter (oponent) ; Slovák,, Václav (oponent) ; Klučáková, Martina (vedoucí práce)
This doctoral thesis studies the character of hydration water in water/humic substances system. The goal is to determine both quantitative and qualitative aspects of hydration of humic substances (HS) in solid and liquid phase and to explore the differences in properties of water surrounding humic matter with the assistance of high resolution ultrasonic spectroscopy (HRUS) and methods of thermal analysis such as differential scanning calorimetry (DSC) and thermogravimetry (TGA). The main aim of this work is to contribute to the knowledge about hydration of humic samples originating from different sources and thus having different properties and composition applying the approaches and techniques already used and reported as being successful for determination and enumeration of hydration water in hydrophilic biopolymers and hydrogels. This thesis investigates the effect of water on humic structure, its way of wetting and penetrating the surface of HS, the possible conformational changes, the retention capacity of HS, and also the influence of origin of individual humic substance on hydration properties with regard to the kinetic of those processes. Moreover, it tries to recognize the influence of degree of humification on hydration processes of humic substances as well as reversibility of these processes. The results of this thesis reveal same parallelism with the properties of non-reversible hydrogels; some similarities between biopolymers and HS were discovered as well.
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Chemical and Physical Transformations of Humic Acids
Vlčková, Zoja ; Pospíšilová, Ľubica (oponent) ; Janoš,, Pavel (oponent) ; Pekař, Miloslav (vedoucí práce)
This work is a pilot study testing the relationships between biological properties and structure of humic acids extracted from original and modified South-Moravian lignite, mine Mír, Mikulčice. In first part of the work, methods suitable for increase of the humic acid yield were explored. Lignite oxidation in gas phase turned out to be relatively instrumentally demanding and insufficiently effective. Therefore, only oxidation in liquid phase was explored further along with modification with short-chained organic acids. Modification with short-chained organic acids was inspired by processes enhancing biological functions in rhizosphere, i.e. the root system produces exudates causing changes in the supramolecular structure of the surrounding organic matter, improving its mobility and cell-walls penetration. Primary structure of humic acids produced in this work was investigated by elemental analysis, solid state NMR, EPR and UV-VIS spectroscopy. Despite the fact that only minor differences were found, conducted assessment of biological activity and genotoxic potential showed that humic acids and their respective humates isolated from lignite with different pre-treatment show different bioactivity. Therefore, supramolecular structure of samples in diluted solutions was investigated by means of HPSEC, HRUS and densitometry measurements. Two counterions – potassium and ammonium – were tested. Obtained results confirm the assumption that observed quality of humates depends on counterion, concen-tration of humate and also on the method of lignite pre-treatment. Both selected pre-treatment methods showed potential to produce humic acids with variable biological properties, applicable in agriculture, environmental chemistry and potencially also in pharmacology.
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Humic Substances Characterization Employing High Resolution Ultrasonic Spectroscopy
Drastík, Martin ; Franců, Juraj (oponent) ; Janoš, Pavel (oponent) ; Pekař, Miloslav (vedoucí práce)
This doctoral thesis deals with the application of high resolution ultrasonic spectroscopy (HRUS) on studying of humic substances (HS). The goal is to obtain deeper insight to the field of relations between primary characteristics (elemental composition and distribution of carbon in functional groups) and aggregation properties. In the literature review the contemporary information about HS and HRUS are presented. Furthermore, basic information about fractal analysis as well as its application on data obtained by various techniques is mentioned. In the first section of the experimental part of this thesis the advantageous application of HRUS in the research of HS is discussed. International Humic Substances Society (IHSS) standards were selected to represent wide spectrum of samples, both humates and fulvates were used. To determine the influence of sodium counterion also fulvic acids in their protonized form were used. Power-based fitting was applied on all samples data and gained empirical parameters were correlated with primary characteristics. Fractal analysis method was developed and applied on the HRUS data. An alternative approach was applied on data gained by HRUS. From a global point of view, the dependency of ultrasonic velocity on concentration shows a linear trend and therefore a linear regression method can be applied. The second purpose of this thesis is to find information about thermal stability of HS aggregates (IHSS standards). Samples at four different concentrations were treated by temperature gradients and aggregation behavior was assessed and discussed. In the third part of thesis the concentration dependencies of the samples were studied. Unlike the first goal, samples originating mainly from locations unaffected by anthropogenic activity were used. Power-based fitting and fractal analysis were applied and acquired parameters were correlated with primary characteristics. To elucidate the extent of hydration shells, the high precision density measurements were performed. As the state-of-the-art research shows, the aggregation properties of humic biomolecules may play an important role in the future designing of humic substances applications, mainly in the agriculture and environmental protection, but even also in medicine.
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Příprava a vlastnosti románského cementu
Opravil, Tomáš ; Palou, Martin (oponent) ; Škvára, František (oponent) ; Havlica, Jaromír (vedoucí práce)
Disertační práce se zabývá přípravou vysoce hydraulických pojiv na bázi románského cementu. Románský cement (přírodní cement) není v současné době u nás běžně dostupný na trhu vzhledem k neekonomičnosti produkce takto specifického pojiva. Výjimkou je několik importovaných románských cementů z Polska, Francie a USA. V současné době odborníci v oblastech restaurování, památkové péče, historici, umělci a výzkumníci z oblasti materiálů přijali nové zásady hodnocení kvality a tak se potýkáme s nedostatkem fundovaných informací o přípravě těchto hydraulických pojiv, která by splňovala všechna kritéria. A tak při opravách historických budov či jiných monumentů vystavěných z materiálů takového typu často nemůže být splněn základní princip moderních přístupů v restaurování těchto památek - a to, že materiály, které jsou k těmto pracím používány by měly být kompatibilní s materiálem originálním. Cestou k řešení tohoto problému je detailní poznání procesů přípravy románského cementu opírající se o moderní metody studia, které mohou poskytnout řadu nových informací pro zefektivnění výběru jiných zdrojů surovin než byly tradičně využívány. Naskytují se tak další možnosti pro architektonická řešení nebo dokonce pro netradiční využití pro umělecká díla. Proto se také tato disertační práce zabývá studiem orientovaným na výběr surovin a-to jak přírodních zdrojů, tak vhodných druhotných surovin, jako je např. antuka. Hlavním motivem práce je příprava vysoce hydraulických pojiv na bázi románského cementu.
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Vliv pH záměsové vody na hydrataci a mechanické vlastnosti cementových kompozitů.
Bezděk, Ondřej ; Krátký, Josef (oponent) ; Šiler, Pavel (vedoucí práce)
Tato diplomová práce se zabývá vlivem pH záměsové vody na hydrataci a mechanické vlastnosti cementových kompozitů na bázi portlandského cementu. Výchozím materiálem byl CEM I 42,5 R. Průběh hydratace byl analyzován pomocí isoperibolické kalorimetrie, rentgenové difrakční analýzy a diferenční termické analýzy. Z mechanických vlastností byla sledována pevnost v tahu za ohybu a pevnost v tlaku. Mikrostruktura vzorků byla pozorována pomocí skenovací elektronové mikroskopie. Byl prokázán vliv pH záměsové vody na jednodenní pevnost v tahu za ohybu a pevnost v tlaku, zpomalení hydratace a poměr jednotlivých fází.
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Možnosti redukce šestimocného chromu při hydrataci portlandského cementu
Mončeková, Miroslava ; Koplík, Jan (oponent) ; Šoukal, František (vedoucí práce)
Problematika toxicity šestimocného chromu při hydrataci portlandského cementu je v dnešní době velmi aktuální. Vynakládá se mnoho úsilí na získání cementů s obsahem Cr(VI) pod 2 ppm. Cílem této práce bylo vyhledání vhodných redukčních činidel, upřesnění jejich účinnosti a snaha o optimalizaci jejich dávkování. V této práci byly jako redukční látky zkoumány siřičitany a cínaté soli. Vliv použitých redukčních činidel na hydrataci a vlastnosti cementu byl prověřen pevnostními zkouškami, kalorimetrickým měřením a měřením objemových změn. Zkoumány jsou také změny mikrostruktury hydratačních produktů portlandského slínku po nahrazení sádrovce siřičitanovými ionty. Studium mikrostruktury je založené na metodách SEM a XRD.
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Hydration and structure of humic acids studied by thermal analysis
Grebíková, Lucie ; Šmejkalová, Daniela (oponent) ; Kučerík, Jiří (vedoucí práce)
The aim of this work was to use thermal analysis and namely temperature-modulated differential scanning calorimetry (TMDSC) to reveal the changes in humic acids (HA) structure caused by regular wetting of HA by water and its repeated drying. The total number of rewetting cycles was five because further rewetting did not bring any other observable structural changes. Experiments carried out in this work have shown that water plays a role not only in swelling of the HA matrix and disruption of van der Waals forces but it also plays a role in disrupting of some hydrogen bonds, thus it had greater effect on reduction of the glass transition temperature, Tg. The changes in the glass transition temperatures were only of minor scale, so that water influenced predominantly the close proximity of amorphous domains (responsible for glass transition) than the domains themselves. The next task was to shed light on the role of free lipids in the stability of HA physical structure with respect to the repeated wetting and drying. Water periodically stabilized and destabilized HA structure, in the lipid free HA sample the effect of water was short-term, water required less time to cause changes in the sample, whereas in the HA sample the changes induced by water were continuous. The rewetting induced a decrease in the phase transition temperatures in every following cycle in comparison with the previous one and influenced especially kinetic processes, namely crystallization/crystalline reorganization. Furthermore, the rewetting caused redistribution and washing out of the hydrophilic molecules and thus making the HA structure more hydrophobic with every other cycle.
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