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Due to a challenging population growth and environmental changes, a need for new routes to provide required chemicals for human necessities arises. An effective solution discussed in this thesis is industrial heterogeneous catalysis. The development of an advanced industrial heterogeneous catalyst is investigated herein by considering porous carbon nano-material as supports and modifying their surface chemistry structure with heteroatoms. Such modifications showed a significant influence on the performance of the catalyst and provided a deeper insight regarding the interaction between the surface structure of the catalyst and the surrounding phase. This thesis contributes to the few present studies about heteroatoms effect on the catalyst performance and emphasizes on the importance of understanding surface structure functionalization in a catalyst in different phases (liquid and gaseous) and for different reactions (hydrogenolysis, oxidation, and hydrogenation/ polymerization). Herein, the heteroatoms utilized for the modifications are hydrogen (H), oxygen (O), and nitrogen (N). The heteroatoms effect on the metal particle size, on the polarity of the support/ the catalyst, on the catalytic performance (activity, selectivity, and stability), and on the interaction with the surrounding phase has been explored. First hierarchical porous carbon nanomaterials functionalized with heteroatoms (N) is synthesized and applied as supports for nickel nanoparticles for hydrogenolysis process of kraft lignin in liquid phase. This reaction has been performed in batch and flow reactors for three different catalysts, two of comparable hierarchical porosity, yet one is modified with N and the other is not, and a third is a prepared catalyst from a commercial carbon support. The reaction production and analyses show that the catalysts with hierarchical porosity perform catalytically much better than in presence of a commercial carbon support with lower surface area. Moreover, the modification with N-heteroatoms enhanced the catalytic performance because the heteroatom modified porous carbon material with nickel nanoparticles catalyst (Ni-NDC) performed highest among the other catalysts. In the flow reactor, Ni-NDC selectively degraded the ether bonds (β-O-4) in kraft lignin with an activity of 2.2 x10^-4 mg lignin mg Ni-1 s-1 for 50 h at 350°C and 3.5 mL min-1 flow, providing ~99 % conversion to shorter chained chemicals (mainly guaiacol derivatives). Then, the functionalization of carbon surface was further studied in selective oxidation of glucose to gluconic acid using < 1 wt. % of gold (Au) deposited on the previously-mentioned synthesized carbon (C) supports with different functionalities (Au-CGlucose, Au-CGlucose-H, Au-CGlucose-O, Au-CGlucoseamine). Except for Au-CGlucose-O, the other catalysts achieved full glucose conversion within 40-120 min and 100% selectivity towards gluconic acid with a maximum activity of 1.5 molGlucose molAu-1 s-1 in an aqueous phase at 45 °C and pH 9. Each heteroatom influenced the polarity of the carbon differently, affecting by that the deposition of Au on the support and thus the activity of the catalyst and its selectivity. The heteroatom effect was further investigated in a gas phase. The Fischer-Tropsch reaction was applied to convert synthetic gas (CO and H2) to short olefins and paraffins using surface-functionalized carbon nanotubes (CNTs) with heteroatoms as supports for ion (Fe) deposition in presence and absence of promoters (Na and S). The results showed the promoted Fe-CNT doped with nitrogen catalyst to be stable up to 180 h and selective to the formation of olefins (~ 47 %) and paraffins (~6 %) with a conversion of CO ~ 92 % at a maximum activity of 94 *10^-5 mol CO g Fe-1 s-1. The more information given regarding this topic can open wide range of applications not only in catalysis, but in other approaches as well. In conclusion, incorporation of heteroatoms can be the next approach for an advanced industrial heterogeneous catalyst, but also for other applications (e.g. electrocatalysis, gas adsorption, or supercapacitors).
Reversible-deactivation radical polymerization (RDRP) is without any doubt one of the most prevalent and powerful strategies for polymer synthesis, by which well-defined living polymers with targeted molecular weight (MW), low molar dispersity (Ɖ) and diverse morphologies can be prepared in a controlled fashion. Atom transfer radical polymerization (ATRP) as one of the most extensive studied types of RDRP has been particularly emphasized due to the high accessibility to hybrid materials, multifunctional copolymers and diverse end group functionalities via commercially available precursors. However, due to catalyst-induced side reactions and chain-chain coupling termination in bulk environment, synthesis of high MW polymers with uniform chain length (low Ɖ) and highly-preserved chain-end fidelity is usually challenging. Besides, owing to the inherited radical nature, the control of microstructure, namely tacticity control, is another laborious task. Considering the applied catalysts, the utilization of large amounts of non-reusable transition metal ions which lead to cumbersome purification process, product contamination and complicated reaction procedures all delimit the scope ATRP techniques.
Metal-organic frameworks (MOFs) are an emerging type of porous materials combing the properties of both organic polymers and inorganic crystals, characterized with well-defined crystalline framework, high specific surface area, tunable porous structure and versatile nanochannel functionalities. These promising properties of MOFs have thoroughly revolutionized academic research and applications in tremendous aspects, including gas processing, sensing, photoluminescence, catalysis and compartmentalized polymerization. Through functionalization, the microenvironment of MOF nanochannel can be precisely devised and tailored with specified functional groups for individual host-guest interactions. Furthermore, properties of high transition metal density, accessible catalytic sites and crystalline particles all indicate MOFs as prominent heterogeneous catalysts which open a new avenue towards unprecedented catalytic performance. Although beneficial properties in catalysis, high agglomeration and poor dispersibility restrain the potential catalytic capacity to certain degree.
Due to thriving development of MOF sciences, fundamental polymer science is undergoing a significant transformation, and the advanced polymerization strategy can eventually refine the intrinsic drawbacks of MOF solids reversely. Therefore, in the present thesis, a combination of low-dimensional polymers with crystalline MOFs is demonstrated as a robust and comprehensive approach to gain the bilateral advantages from polymers (flexibility, dispersibility) and MOFs (stability, crystallinity). The utilization of MOFs for in-situ polymerizations and catalytic purposes can be realized to synthesize intriguing polymers in a facile and universal process to expand the applicability of conventional ATRP methodology. On the other hand, through the formation of MOF/polymer composites by surface functionalization, the MOF particles with environment-adjustable dispersibility and high catalytic property can be as-prepared.
In the present thesis, an approach via combination of confined porous textures from MOFs and controlled radical polymerization is proposed to advance synthetic polymer chemistry. Zn2(bdc)2(dabco) (Znbdc) and the initiator-functionalized Zn MOFs, ZnBrbdc, are utilized as a reaction environment for in-situ polymerization of various size-dependent methacrylate monomers (i.e. methyl, ethyl, benzyl and isobornyl methacrylate) through (surface-initiated) activators regenerated by electron transfer (ARGET/SI-ARGET) ATRP, resulting in polymers with control over dispersity, end functionalities and tacticity with respect to distinct molecular size. While the functionalized MOFs are applied, due to the strengthened compartmentalization effect, the accommodated polymers with molecular weight up to 392,000 can be achieved. Moreover, a significant improvement in end-group fidelity and stereocontrol can be observed. The results highlight a combination of MOFs and ATRP is a promising and universal methodology to synthesize versatile well-defined polymers with high molecular weight, increment in isotactic trial and the preserved chain-end functionality.
More than being a host only, MOFs can act as heterogeneous catalysts for metal-catalyzed polymerizations. A Cu(II)-based MOF, Cu2(bdc)2(dabco), is demonstrated as a heterogeneous, universal catalyst for both thermal or visible light-triggered ARGET ATRP with expanded monomer range. The accessible catalytic metal sites enable the Cu(II) MOF to polymerize various monomers, including benzyl methacrylate (BzMA), styrene, methyl methacrylate (MMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA) in the fashion of ARGET ATRP. Furthermore, due to the robust frameworks, surpassing the conventional homogeneous catalyst, the Cu(II) MOF can tolerate strongly coordinating monomers and polymerize challenging monomers (i.e. 4-vinyl pyridine, 2-vinyl pyridine and isoprene), in a well-controlled fashion. Therefore, a synthetic procedure can be significantly simplified, and catalyst-resulted chelation can be avoided as well. Like other heterogeneous catalysts, the Cu(II) MOF catalytic complexes can be easily collected by centrifugation and recycled for an arbitrary amount of times.
The Cu(II) MOF, composed of photostimulable metal sites, is further used to catalyze controlled photopolymerization under visible light and requires no external photoinitiator, dye sensitizer or ligand. A simple light trigger allows the photoreduction of Cu(II) to the active Cu(I) state, enabling controlled polymerization in the form of ARGET ATRP. More than polymerization application, the synergic effect between MOF frameworks and incorporated nucleophilic monomers/molecules is also observed, where the formation of associating complexes is able to adjust the photochemical and electrochemical properties of the Cu(II) MOF, altering the band gap and light harvesting behavior. Owing to the tunable photoabsorption property resulting from the coordinating guests, photoinduced Reversible-deactivation radical polymerization (PRDRP) can be achieved to further simplify and fasten the polymerization.
More than the adjustable photoabsorption ability, the synergistic strategy via a combination of controlled/living polymerization technique and crystalline MOFs can be again evidenced as demonstrated in the MOF-based heterogeneous catalysts with enhanced dispersibility in solution. Through introducing hollow pollen pivots with surface immobilized environment-responsive polymer, PDMAEMA, highly dispersed MOF nanocrystals can be prepared after associating on polymer brushes via the intrinsic amine functionality in each DMAEMA monomer. Intriguingly, the pollen-PDMAEMA composite can serve as a “smart” anchor to trap nanoMOF particles with improved dispersibility, and thus to significantly enhance liquid-phase photocatalytic performance. Furthermore, the catalytic activity can be switched on and off via stimulable coil-to-globule transition of the PDMAEMA chains exposing or burying MOF catalytic sites, respectively.
Thermoresponsive block copolymers of presumably highly biocompatible character exhibiting upper critical solution temperature (UCST) type phase behavior were developed. In particular, these polymers were designed to exhibit UCST-type cloud points (Tcp) in physiological saline solution (9 g/L) within the physiologically interesting window of 30-50°C. Further, their use as carrier for controlled release purposes was explored. Polyzwitterion-based block copolymers were synthesized by atom transfer radical polymerization (ATRP) via a macroinitiator approach with varied molar masses and co-monomer contents. These block copolymers can self-assemble in the amphiphilic state to form micelles, when the thermoresponsive block experiences a coil-to-globule transition upon cooling. Poly(ethylene glycol) methyl ether (mPEG) was used as the permanently hydrophilic block to stabilize the colloids formed, and polyzwitterions as the thermoresponsive block to promote the temperature-triggered assembly-disassembly of the micellear aggregates at low temperature.
Three zwitterionic monomers were used for this studies, namely 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate (SPE), 4-((2-(methacryloyl- oxy)ethyl)dimethylammonio)butane-1-sulfonate (SBE), and 3-((2-(methacryloyloxy)ethyl)- dimethylammonio)propane-1-sulfate) (ZPE). Their (co)polymers were characterized with respect to their molecular structure by proton nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC). Their phase behaviors in pure water as well as in physiological saline were studied by turbidimetry and dynamic light scattering (DLS). These (co)polymers are thermoresponsive with UCST-type phase behavior in aqueous solution. Their phase transition temperatures depend strongly on the molar masses and the incorporation of co-monomers: phase transition temperatures increased with increasing molar masses and content of poorly water-soluble co-monomer. In addition, the presence of salt influenced the phase transition dramatically. The phase transition temperature decreased with increasing salt content in the solution. While the PSPE homopolymers show a phase transition only in pure water, the PZPE homopolymers are able to exhibit a phase transition only in high salinity, as in physiological saline. Although both polyzwitterions have similar chemical structures that differ only in the anionic group (sulfonate group in SPE and sulfate group in ZPE), the water solubility is very different. Therefore, the phase transition temperatures of targeted block copolymers were modulated by using statistical copolymer of SPE and ZPE as thermoresponsive block, and varying the ratio of SPE to ZPE. Indeed, the statistical copolymers of P(SPE-co-ZPE) show phase transitions both in pure water as well as in physiological saline. Surprisingly, it was found that mPEG-b-PSBE block copolymer can display “schizophrenic” behavior in pure water, with the UCST-type cloud point occurring at lower temperature than the LCST-type one.
The block copolymer, which satisfied best the boundary conditions, is block copolymer mPEG114-b-P(SPE43-co-ZPE39) with a cloud point of 45°C in physiological saline. Therefore, it was chosen for solubilization studies of several solvatochromic dyes as models of active agents, using the thermoresponsive block copolymer as “smart” carrier. The uptake and release of the dyes were explored by UV-Vis and fluorescence spectroscopy, following the shift of the wavelength of the absorbance or emission maxima at low and high temperature. These are representative for the loaded and released state, respectively. However, no UCST-transition triggered uptake and release of these dyes could be observed. Possibly, the poor affinity of the polybetaines to the dyes in aqueous environtments may be related to the widely reported antifouling properties of zwitterionic polymers.
The utilization of lignin as renewable electrode material for electrochemical energy storage is a sustainable approach for future batteries and supercapacitors. The composite electrode was fabricated from Kraft lignin and conductive carbon and the charge storage contribution was determined in terms of electrical double layer (EDL) and redox reactions. The important factors at play for achieving high faradaic charge storage capacity contribute to high surface area, accessibility of redox sites in lignin and their interaction with conductive additives. A thinner layer of lignin covering the high surface area of carbon facilitates the electron transfer process with a shorter pathway from the active sites of nonconductive lignin to the current collector leading to the improvement of faradaic charge storage capacity.
Composite electrodes from lignin and carbon would be even more sustainable if the fluorinated binder can be omitted. A new route to fabricate a binder-free composite electrode from Kraft lignin and high surface area carbon has been proposed by crosslinking lignin with glyoxal. A high molecular weight of lignin is obtained to enhance both electroactivity and binder capability in composite electrodes. The order of the processing step of crosslinking lignin on the composite electrode plays a crucial role in achieving a stable electrode and high charge storage capacity. The crosslinked lignin based electrodes are promising since they allow for more stable, sustainable, halogen-free and environmentally benign devices for energy storage applications. Furthermore, improvement of the amount of redox active groups (quinone groups) in lignin is useful to enhance the capacity in lithium battery applications. Direct oxidative demethylation by cerium ammonium nitrate has been carried out under mild conditions. This proves that an increase of quinone groups is able to enhance the performance of lithium battery. Thus, lignin is a promising material and could be a good candidate for application in sustainable energy storage devices.
Photocatalysis is considered significant in this new energy era, because the inexhaustibly abundant, clean, and safe energy of the sun can be harnessed for sustainable, nonhazardous, and economically development of our society. In the research of photocatalysis, the current focus was held by the design and modification of photocatalyst.
As one of the most promising photocatalysts, g-C3N4 has gained considerable attention for its eye-catching properties. It has been extensively explored in photocatalysis applications, such as water splitting, organic pollutant degradation, and CO2 reduction. Even so, it also has its own drawbacks which inhibit its further application. Inspired by that, this thesis will mainly present and discuss the process and achievement on the preparation of some novel photocatalysts and their photocatalysis performance. These materials were all synthesized via the alteration of classic g-C3N4 preparation method, like using different pre-compositions for initial supramolecular complex and functional group post-modification. By taking place of cyanuric acid, 2,5-Dihydroxy-1,4-benzoquinone and chloranilic acid can form completely new supramolecular complex with melamine. After heating, the resulting products of the two complex shown 2D sheet-like and 1D fiber-like morphologies, respectively, which maintain at even up to high temperature of 800 °C. These materials cover crystals, polymers and N-doped carbons with the increase of synthesis temperature. Based on their different pre-compositions, they show different dye degradation performances. For CLA-M-250, it shows the highest photocatalytic activity and strong oxidation capacity. It shows not only great photo-performance in RhB degradation, but also oxygen production in water splitting. In the post-modification method, a novel photocatalysis solution was proposed to modify carbon nitride scaffold with cyano group, whose content can be well controlled by the input of sodium thiocyanate. The cyanation modification leads to narrowed band gap as well as improved photo-induced charges separation. Cyano group grafted carbon nitride thus shows dramatically enhanced performance in the photocatalytic coupling reaction between styrene and sodium benzenesulfinate under green light irradiation, which is in stark contrast with the inactivity of pristine g-C3N4.
In der vorliegenden Arbeit werden Wege zur Gewinnung verschiedener phenolischer Substanzen wie Lignin, Diarylheptanoide und 4-(3-Oxobutyl)phenol (Himbeerketon) aus dem Stamm der Hängebirke (Betula pendula) aufgezeigt. Durch Methacrylierung des 4-(3-Oxobutyl)phenols wurde ein Monomer erzeugt, welches mittels freier radikalischer Masse- und Lösungspolymerisation, sowie enzymatischer Polymerisation polymerisiert werden kann.
Eine erste Isolierung von Bestandteilen wurde durch Extraktion von Innenholz bzw. Rinde mit Methanol erzielt. Die in Methanol unlöslichen Bestandteile des Innenholzes und der Rinde wurden anschließend mit ausgewählten ionischen Flüssigkeiten extrahiert. Es wurde ein Verfahren zum selektiven Trennen der mit diesen ionischen Flüssigkeiten extrahierten Bestandteile in Cellulose, Hemicellulose, Lignin und mit Ethylacetat extrahierbare Bestandteile entwickelt. Hierdurch war es möglich, sowohl die verwendeten ionischen Flüssigkeiten als auch das Innenholz und die Rinde hinsichtlich ihres Extraktionsverhaltens miteinander zu vergleichen.
Ferner wurden verschiedene Strategien aufgezeigt, um insgesamt drei Spezies an Diarylheptanoiden aus dem methanolischen Extrakt der Rinde zu isolieren. Eines der gefundenen Diarylheptanoide (5 Hydroxy-1,7-bis(4-hydroxyphenyl)-3-heptanon) wurde via Retroaldolreaktion in 4 (3 Oxobutyl)phenol (Himbeerketon) und 3 (4 Hydroxyphenyl)propanal gespalten.
Es wurde die Verwendung des 4-(3-Oxobutyl)phenol als Monomerbestandteil untersucht. Hierfür wurde 4-(3-Oxobutyl)phenylmethacrylat synthetisiert und Wege zur Reinigung mittels Säulenchromatographie und Umkristallisation aufgezeigt. Anschließend wurde Poly(4-(3-oxobutyl)phenylmethacrylat) (PObMA) und Polybenzylmethacrylats (PBzMA) aus Massen- und Lösungspolymerisation hergestellt. Die Ausbeuten an PObpMA im Vergleich zum PBzMA liegen bei gleichen Reaktionsbedingungen auf gleichem Niveau. Im Kontrast hierzu ist der Polymerisationsgrad aus freier radikalischer Polymerisation in Masse des PObpMA im Vergleich zum PBzMA um den Faktor 3,7 größer. Die Glasübergangstemperaturen des PObpMA liegen bei gleichen Reaktionsbedingungen sowohl bei freier radikalischer Polymerisation in Masse, als auch bei Lösungspolymerisation über denen des PBzMA. Darüber hinaus wurde die Polymerisation von 4-(3-Oxobutyl)phenylmethacrylat und Benzylmethacrylat mit einem Initiatorsystem bestehend aus Meerrettichperoxidase, Acetylaceton und Wasserstoffperoxid bei Raumtemperatur beschrieben. Die mit enzymatischem Initiatorsystem erzeugten Produkte zeigten starke Übereinstimmung mit Produkten aus Lösungspolymerisationen, welche mit Azobis(isobutyronitril) initiiert wurden.