New materials can be fabricated using small scaled building blocks as a repetition unit. Nanoparticles with their unique size-tuneable properties from quantum confinement can especially be utilised to form two- and three-dimensional ordered assemblies to introduce them into what would normally be considered to be incompatible matrices. Furthermore, new collective properties that derive from the ordered arrangement of the building blocks, are accomplished. Additionally, different materials can be combined by mixing different building blocks during self-assembly, so that size ranges and material combinations that are difficult to achieve by other means can be formed. The arrangement of small particles into highly ordered arrangements can be realised via self-assembly. To achieve such assemblies, highly monodisperse nanoparticular building blocks with a size distribution below 5 % have to be synthesised. The production and variation in the size of both lead chalcogenide and noble metal nanoparticles is presented in this work. Moreover, the syntheses of multicomponential nanoparticles (PbSe/PbS and Au/PbS) are investigated. Non-classical crystallisation methodologies with their varyious self-assembly mechanisms are used for the formation of highly symmetrical mesocrystals and supracrystals. Analogous to classical crystallisation methods and their formation processes the interparticle interactions, attractive as well as repulsive, determine the resulting crystalline structure. Variation of the environmental parameters consequently leads to structural variation due to the changing interparticle interactions. In contrast to classical crystallisation the length scale of the interparticle forces stays constant as the size dimension of the self-assembled building unit is changed. Two different non-classical crystallisation pathways are investigated in this work. One pathway focuses on the slow destabilisation of nanoparticles in organic media by the addition of a non-solvent. In this approach optimisation of parameters for the formation of highly symmetrical three-dimensional mesostructures are studied. Furthermore, to shine some light onto the mechanism of self-assembly, the intrinsic arrangement of the building units in a mesocrystal and the steps of non-solvent addition are analysed. The mechanistic investigations explain the differences observed in mesocrystal formation between metal and semiconductor nanoparticles. The lower homogeneity of the building units of the metal nanoparticles leads to smaller and less defined superstructures in comparison to semiconductor building blocks. Another pathway of non-classical crystallisation is the usage of electrostatic interactions as the driving force for self-assembly and supracrystal formation. Therefore, the building blocks are transferred into aqueous media and stabilised with oppositely charged ligands. The well-know procedure for metal nanoparticles was adapted for semiconductor materials. The lower stability of these nanoparticles in aqueous solution induces an agglomeration of the semiconductor nanoparticles without including oppositely charged metal nanoparticles. The destabilisation effect can be increased by the addition of equally charged metal nanoparticles in a salting out type process. In comparison to the slow formation of mesocrystals achieved via destabilisation in an organic media (up to 4 weeks), the salting out procedure takes place within two hours, but the faster agglomeration causes a less well defined assembly of the building units in the mesocrystals. Moreover, the arrangement of semiconductor nanoparticles with organic molecules such as polymers and proteins was investigated in order to use the nanoparticles as a light harvesting component. In combination with the directly bound polymer the charge carrier may be directly transferred to the conductive thiophene-based polymer, so that infrared light can be transformed into an electrical signal for use in further applications such as solar cells. The advantage of the nanoparticle-protein system is the self-assembly across a liquid-liquid interface and additionally a Förster resonance energy transfer can occur at this phase boundary. Hence, it is possible to transfer highly energetic photons directly to biological samples without destroying the biological material.

New materials can be fabricated using small scaled building blocks as a repetition unit. Nanoparticles with their unique size-tuneable properties from quantum confinement can especially be utilised to form two- and three-dimensional ordered assemblies to introduce them into what would normally be considered to be incompatible matrices. Furthermore, new collective properties that derive from the ordered arrangement of the building blocks, are accomplished. Additionally, different materials can be combined by mixing different building blocks during self-assembly, so that size ranges and material combinations that are difficult to achieve by other means can be formed. The arrangement of small particles into highly ordered arrangements can be realised via self-assembly. To achieve such assemblies, highly monodisperse nanoparticular building blocks with a size distribution below 5 % have to be synthesised. The production and variation in the size of both lead chalcogenide and noble metal nanoparticles is presented in this work. Moreover, the syntheses of multicomponential nanoparticles (PbSe/PbS and Au/PbS) are investigated. Non-classical crystallisation methodologies with their varyious self-assembly mechanisms are used for the formation of highly symmetrical mesocrystals and supracrystals. Analogous to classical crystallisation methods and their formation processes the interparticle interactions, attractive as well as repulsive, determine the resulting crystalline structure. Variation of the environmental parameters consequently leads to structural variation due to the changing interparticle interactions. In contrast to classical crystallisation the length scale of the interparticle forces stays constant as the size dimension of the self-assembled building unit is changed. Two different non-classical crystallisation pathways are investigated in this work. One pathway focuses on the slow destabilisation of nanoparticles in organic media by the addition of a non-solvent. In this approach optimisation of parameters for the formation of highly symmetrical three-dimensional mesostructures are studied. Furthermore, to shine some light onto the mechanism of self-assembly, the intrinsic arrangement of the building units in a mesocrystal and the steps of non-solvent addition are analysed. The mechanistic investigations explain the differences observed in mesocrystal formation between metal and semiconductor nanoparticles. The lower homogeneity of the building units of the metal nanoparticles leads to smaller and less defined superstructures in comparison to semiconductor building blocks. Another pathway of non-classical crystallisation is the usage of electrostatic interactions as the driving force for self-assembly and supracrystal formation. Therefore, the building blocks are transferred into aqueous media and stabilised with oppositely charged ligands. The well-know procedure for metal nanoparticles was adapted for semiconductor materials. The lower stability of these nanoparticles in aqueous solution induces an agglomeration of the semiconductor nanoparticles without including oppositely charged metal nanoparticles. The destabilisation effect can be increased by the addition of equally charged metal nanoparticles in a salting out type process. In comparison to the slow formation of mesocrystals achieved via destabilisation in an organic media (up to 4 weeks), the salting out procedure takes place within two hours, but the faster agglomeration causes a less well defined assembly of the building units in the mesocrystals. Moreover, the arrangement of semiconductor nanoparticles with organic molecules such as polymers and proteins was investigated in order to use the nanoparticles as a light harvesting component. In combination with the directly bound polymer the charge carrier may be directly transferred to the conductive thiophene-based polymer, so that infrared light can be transformed into an electrical signal for use in further applications such as solar cells. The advantage of the nanoparticle-protein system is the self-assembly across a liquid-liquid interface and additionally a Förster resonance energy transfer can occur at this phase boundary. Hence, it is possible to transfer highly energetic photons directly to biological samples without destroying the biological material.

In den letzten Jahrzehnten ist die Rückgewinnung wichtiger Elemente aus Abfallströmen wie Abwässern, Schlämmen und Abraum. Übermäßiger Bergbau, industrielle Prozesse und Überdüngung in der Landwirtschaft setzen Schadstoffe wie Phosphat, Ammonium und Übergangsmetalle in die Umwelt frei und bringen Ökosysteme aus dem Gleichgewicht. In dieser Dissertation wird die Kristallisation von Übergangsmetallphosphatverbindungen (TMPs) aus wässrigen Lösungen untersucht, darunter M-Struvit, M-Dittmarit und M-Phosphat-Octahydrat (NH4MPO4∙6H2O, NH4MPO4∙H2O, M3(PO4)2∙8H2O mit M = Ni, Co, NixCo1-x). Diese kristallinen Phasen ermöglichen die gemeinsame Ausfällung von PO43-, NH4+ und Übergangsmetallen und bieten einen vielversprechenden Weg zur Rückgewinnung von Phosphat und Übergangsmetallen aus industriellen und landwirtschaftlichen Abwässern. TMPs besitzen vielseitige Eigenschaften wie thermische und mechanische Stabilität, einfache Veränderlichkeit und Multifunktionalität, wodurch sie sich für fortschrittliche Energieumwandlungs- und -speicheranwendungen eignen. Deshalb stellt die Synthese von TMPs eine kombinierte Rückgewinnungs- und Upcycling-Methode für fortschrittliche Funktionsmaterialien dar. Detaillierte Untersuchungen des Bildungsprozesses aus wässriger Lösung wurden mit zeitaufgelösten ex- und in-situ-Elektronenbildern, spektroskopischen, spektrometrischen und beugungsbasierten Methoden durchgeführt. Die in dieser Dissertation enthaltenen Ergebnisse geben neue Einblicke in den nicht klassischen Kristallisationsmechanismus von TMPs, der eine kontrollierte Einstellung der Kristallitgröße und -morphologie ermöglicht. Darüber hinaus führt die thermische Behandlung von TMPs zu thermisch stabilen, mesoporösen und/oder protonenleitenden Materialien für elektrochemische Anwendungen. Die Ergebnisse tragen zum grundlegenden Verständnis von Keimbildung und Kristallisationsphänomenen bei und helfen bei der Entwicklung moderner Funktionsmaterialien für elektrochemische Anwendungen. / A critical issue in the 21st century is the recovery of essential elements from waste streams like wastewaters, sludges, and tailings. Excessive mining, industrial processes, and overfertilization in agriculture release pollutants such as phosphate, ammonium, and transition metals into the environment, unbalancing ecosystems. This dissertation investigates the crystallization of transition metal phosphate (TMPs) compounds from aqueous solutions, including M-struvite, M-dittmarite, and M-phosphate octahydrate (NH4MPO4∙6H2O, NH4MPO4∙H2O, M3(PO4)2∙8H2O with M = Ni, Co, NixCo1-x). These crystalline phases allow for the co-precipitation of PO43-, NH4+, and transition metals, providing a promising route for phosphate and transition metal recovery from industrial and agricultural wastewaters. TMPs possess favorable properties like thermal and mechanical stability, tunability, and multifunctionality, making them suitable for advanced energy conversion and storage applications. Accordingly, the synthesis of TMPs represents a combined recovery and upcycling method towards advanced functional materials. Detailed investigations of the formation process from aqueous solution were carried out using time-resolved ex- and in-situ, electron imaging, spectroscopic, spectrometric, and diffraction-based techniques. The results contained in this dissertation reveal new insights into the non-classical crystallization mechanism of TMPs, allowing for controlled adjustment of crystallite size and morphology. Moreover, thermal treatment of TMPs compounds yields thermally stable, mesoporous, and/or proton-conductive materials for electrochemical applications. The findings, on the one hand, can contribute to the fundamental understanding of nucleation and crystallization phenomena in aqueous solutions in general and specifically for metal phosphates. On the other hand, my findings aid applied materials chemistry in the development of advanced functional materials for electrochemical uses.