"HelioClean"
Within the framework of the BMBF-funded HelioClean project, the University of Kassel is working on two subprojects in the field of materials for construction and construction chemistry and one subproject in the field of chemistry of mesoscopic systems.
The first objective is to develop and adapt existing detection methods in order to be able to measure the effectiveness and efficiency of photocatalytically modified building materials. Both national and international standards that track the oxidative degradation of dyes, nitrogen oxides, etc. on ceramic materials serve as a starting point here.
The simulation of different influencing factors such as temperature, humidity and UV radiation intensity makes a decisive contribution to the development and assessment of the validity of such methods. Equally important are the properties of the material itself, which differ significantly from already established systems such as photocatalytically active window glass. Porosity plays an important role and complicates various measurements by sorption processes or even makes them impossible for some materials. The pH of cement-based systems must also not be ignored. In addition, a distinction must be made between different model pollutants, which can be present in both, solid, liquid and gaseous form. Here, the development and extension of the test methods to the special conditions of building materials as well as the measurement on larger and more practical samples is required. Only the possibility to compare and evaluate different materials in a meaningful way creates the prerequisite for the improvement of existing materials.
The development of more efficient photocatalysts represents the second subproject of the Materials of Construction and Construction Chemistry working group. To increase efficiency, the required proportion of photocatalytically active titanium dioxide is being reduced. For this purpose, composite materials consisting of an inert core and a thin enveloping shell of the active material are synthesized with the aim of obtaining a high specific surface area of the photocatalyst while saving material. These materials are called core-shell particles. The aim is to produce core-shell materials from the most cost-effective starting materials possible in order to enable their broad application in building materials and to increase their enforceability compared to conventional systems, where price is a decisive factor in addition to self-cleaning and the degradation of pollutants.
The aim of the subproject in the field of "Chemistry of Mesoscopic Systems" is the synthesis of hybrid particles of nanoparticulate TiO2 (np-TiO2) and peripherally functionalized porphyrazines. The hybrid particles will be investigated with respect to their wavelength-dependent photocatalytic properties, which can serve an oxidative pollutant degradation. While np-TiO2 generates reactive superoxide and hydroxyl radicals after excitation with high-energy UV (wavelength 200 - 300 nm) in air, porphyrazines generate reactive singlet oxygen after long-wavelength excitation (wavelength 600 - 900 nm).
In this project, synergistic photocatalytic properties of innovative hybrid particles will be induced and demonstrated to increase the efficiency of photooxidative processes over the entire visible light spectrum.
In the first phase of this subproject, suitably functionalized porphyrazines with polar binding sites for np-TiO2 will first be prepared in multi-step synthesis procedures. This will be followed by the "doping" of np-TiO2 with porphyrazines and the characterization of the nanoparticles thus produced. In the last phase, the photocatalytic properties of the hybrid particles are investigated. For this purpose, several dye assays, an NIR measuring station for the measurement of singlet oxygen and the methyl stearate degradation detectable by GC-MS coupling are available.