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Functional materials are key to master the challenges of modern society in the 21th century. This work comprises publications on novel synthetic approaches and applications of two promising classes of functional materials that contribute to numerous present and future key technologies.
Graphitic carbon nitride (g-CN), a metal free semiconductor, is one of the most extensively studied materials in research over the last two decades. The application of g-CN as a functional material led to numerous synthetic approaches to control its structure and dimensionality at the nanoscale to optimize the performance. The publication “From 1D to 3D Graphitic Carbon Nitride (Melon): A Bottom-Up Route via Crystalline Microporous Templates” expands the field of structure directing approaches for g-CN materials. The growth characteristics of isolated 1D melon strands in microporous silica templates are investigated. The results offer a novel experimental perspective on structure directing approaches of g-CN at a molecular level. Removal of the silicate template via etching goes along with the self-assembly of 1D melon strands to stacked 3D g-CN materials, which offer a high potential in catalytic applications.
Another promising class of functional materials are transition metal phosphates (TMPs). Based on unique structural and physicochemical features, TMPs play an important role for clean and efficient power generation and energy storage. The publication “Facile synthesis of novel, known, and low-valent transition metal phosphates via reductive phosphatization” presents a novel synthesis pathway for first-row (Ti, V, Cr, Mn, Fe) TMPs. The presented approach, denoted as reductive phosphatization, allows the syntheses of novel and known low-valent TMPs, which are not producible by conventional methods. Key feature of the new route is the reductive character of a hypophosphite salt melt, which acts as reaction medium and enables to direct the oxidation state of the transition metal. In particular, the publication involves the synthesis and characterization of two novel crystalline titanium phosphate materials, which have been coined with notations Ti(III)p and Ti(IV)p.
Structure-property correlations of the novel Ti(III)p and Ti(IV)p materials are discussed with respect to various applications in key technologies. Investigations on crystal structures, thermal stabilities, and proton conductivities of Ti(III)p and Ti(IV)p are presented in the publication “Crystal Structures of Two Titanium Phosphate-Based Proton Conductors: Ab Initio Structure Solution and Materials Properties”. The results reveal proton conductivities under hydrated conditions in the range of 10-3 S/cm, which belong to the highest ever reported for this class of materials.
In the context of heterogeneous catalysis, TMPs are of great interest due to the combination of acid-base properties and redox activity. The catalytic conversion of n-butane to maleic acid with molecular oxygen is by far the most demanding partial selective oxidation reaction industrially applied and the only one, converting a rather inert alkane to a multi-functionalized molecule. The publication “Partial selective oxidation of n-butane to maleic acid using titanium phosphate catalysts” presents titanium phosphate materials as environmentally friendly and cost-efficient alternative to established vanadium based catalytic systems for a key process in the chemical industry. Conversion rates above 50% resulted in 20% overall selectivity for maleic acid with 90% oxygenate selectivity. Correlations of catalytic results and characterization data of the titanium phosphate catalysts reveal the potential of environmental compatible TMPs as alternative catalytic systems for complex partial selective oxidation reactions under industrial relevant conditions.
