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Our research is focused on the targeted synthesis of functional inorganic materials and the development of novel synthetic techniques. Transition metal oxides play an essential role in the development of a future nanotechnology. We aim for their clear-cut, reliable and efficient synthesis as building blocks, such as anisotropic particles with nanoscale dimensions or tailor-made molecular entities. This leads to the synthesis of polyoxometalates (POMs) and their incorporation into organic-inorganic composites. The combination of naturally occurring fibrous bio-inorganic substrates and biomacromolecules with transition metal oxides and POMs open up an unexplored research area.
A wide spectrum of synthetic techniques is applied, including hydrothermal approaches, chimie douce and gas phase methods. It is amended by a large variety of analytical tools, such as different X-ray diffraction and spectroscopic techniques together with electron microscopy. We work in an interdisciplinary environment that is continuously inspired by Organic Chemistry, Bio-Inorganic Chemistry and Physical Chemistry.
Polyoxometalates (POMs) continue to attract intense research interest due to their outstanding structural diversity that gives rise to their vast application potential (including antiviral, catalytic, photochromic, or magnetic properties). We focus on the targeted development of novel POMs for bio-medical and catalytic applications. First, we access new POM motifs and architectures, e.g. through systematic combinations of POM building blocks with cationic linkers. In addition to creating new structural motifs, we tune POMs for catalytic "green chemistry" applications, such as alcohol oxidation or visible-light-driven water oxidation catalysts (WOCs). Research on POM-WOCs as a key component of artificial photosynthesis systems is part of our local SNF-Sinergia network at UZH.
POMs exhibit a wide spectrum of bioactive properties and have thus long been discussed as promising prototypes for innovative and low-cost classes of anticancer and antiviral drugs. However, POM stability and cytotoxicity remain challenging issues on the way to new clinical tests. Most recently, we have developed a novel drug carrier approach to nanocomposites of POMs and chitosan derivatives as biomacromolecular carriers in order to reduce adverse POM effects. For the first time, we directly monitored labeled nanocomposites of bio-active POMs and carboxymethyl chitosan on their way into cells with confocal laser scanning microscopy.
Anisotropic transition metal oxides, such as molybdenum-, vanadium- and tungsten oxide-based fibrous materials, are excellent substrates for the fabrication of functionalized composite materials. In order to control their morphology and to develop efficient synthetic processes for their technical production, we investigate their hydrothermal formation mechanisms within an international network of collaborations. This includes the use of modern in situ spectroscopic techniques, such as in situ EXAFS (Prof. Dr. A. Baiker, PD Dr. J.-D. Grunwaldt, ETH Zürich, Switzerland) and in situ EDXRD (Prof. Dr. W. Bensch, University of Kiel, Germany). The combination of transition metal oxide building blocks into ternary and higher hierarchical architectures is a challenging and rewarding task of modern inorganic synthesis.
Hydrothermal methods are an exceptionally powerful and flexible tool in modern materials chemistry. However, their full synthetic potential still remains to be explored so that they can be applied in a truly predictive manner. This includes the development of novel, cutting-edge combination techniques. We find that microwave-hydrothermal techniques considerably enhance the preparative pathways to oxidic nanomaterials by opening up new approaches to tune their morphology and crystal structure (collaboration with Prof. Dr. S. Komarneni, Pennsylvania State University, USA).
We employ the above-mentioned monitoring strategies and synthesis techniques for targeted oxide production to develop and optimize visible-light-driven oxide photocatalysts for environmental applications. Concerning photocatalytic oxides for wastewater cleaning, we focus on tuning bismuth-containing oxides via structural modifications on the one hand, and surface/morphology engineering as a complementary approach. In parallel, we explore nanoscale mixed oxides as water oxidation catalysts (WOCs). This has recently brought forward a new robust and tuneable type of spinel WOCs.
It is well known that transition metal oxides (TMOs) are intensively investigated materials for diverse applications such as photolysis, selective catalysts and gas sensors for more than a decade. They display outstanding gas sensing properties due to their catalytic behavior in both in oxidation and reduction reactions. Their electrical conduction is explained with oxygen vacancies which induce defect states in the band gap and act as electron donors. In our previous work, we have focused on controlling the morphology and chemical composition of nanoscale MoO3-WO3 mixed oxides. The aforementioned chemical properties exert a tremendous influence on the gas sensing properties. Multi-metal oxide materials can be designed to achieve desired surface to volume ratios and morphologies, which improve gas sensing performance significantly. In addition, varying the composition of the Mo/W-oxides can modify their sensor characteristics as well. Furthermore, nanostructured Mo/W-oxides have outstanding selectivity and sensitivity towards different target gases such as O3, NH3, NO2, H2, CO and CH4 etc. in the temperature range from 200°C to 400°C. In collaboration with Dr. Jorge Cors (PHASIS GmbH, University of Geneva), the gas sensing experimental setup has been constructed for the further investigation of the nanoscale TMOs prepared in our laboratory. In the course of our project, Mo/W-oxides are one of the target TMO systems: we aim for enhanced selectivity and sensitivity towards H2 and O3 by adding alkali additives and adjusting their compositions.
