Inverted Photonic Glasses Made of Carbon Nitride as Functional Gradient Materials for Photocatalysis

• Applicants: Professorin Dr. Jannika Lauth; Professor Dr. Sebastian Polarz
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 561333292

Photocatalysis is one of the most important functionalities of semiconductor materials, especially when converting readily available starting compounds such as water or carbon dioxide into more valuable products, which in turn can be used in the chemical value chain. Carbon nitride is considered one of the most promising semiconductors, as it consists of readily available elements and can be produced from simple and inexpensive precursors. To use the sun as an inexhaustible source of energy for photocatalysis, it is advantageous to work with semiconductors that have different electronic band gaps. Depending on the composition, carbon nitride not only offers this option, but the position of the conduction band of graphitic carbon nitride enables the photoreduction of CO2. Another way to increase the yield of photons for photocatalysis is by “slowing down photons”. This refers to two effects: 1. the maximization of scattering in a material and 2. the reduction of the group velocity of the wave packets in certain zones of the photonic band structure. The project aims to synthesize novel CNx materials that can utilize such “slowed photon” effects for photocatalysis. We plan to use an ultracentrifugation-based process to produce photonic glasses with an inverted structure for the first time. Pores of uniform size in a carbon nitride matrix have a short-range order but no long-range order. If the energy of the photonic pseudogap matches the electronic bandgap, an improvement in photocatalytic efficiency is expected, which is being investigated as part of the project. One advantage compared to photonic crystals with a long-range order is that the light can be collected from any angle. The non-crystalline arrangement of the pores also prevents the formation of domains, which allows the creation of gradient materials in which the electronic and photonic band gap varies along a spatial coordinate. The change in the electronic band gap is controlled by a change in the composition of the carbon nitride (doping), whereby we will precisely characterize the optoelectronic properties and the dynamics of the photogenerated charge carriers using various methods, including transient absorption spectroscopy. We envision CO2 can be photoreduced several times in the new gradient metamaterials, as they have a corresponding multi-junction architecture. The project is a collaborative effort between the materials chemistry group led by Dr. Polarz and the group led by Dr. Lauth, which specializes in the physicochemical characterization of optoelectronic properties of semiconductor nanostructures.

• DFG Programme: Research Grants