Characterization and properties of bioorganoclays - perspective hybrid materials

Knowledge on interactions of microbial organisms and matter with clay minerals, finest inorganic components in soils and sediments, is of great environmental, geological, and technological interest. Generally, soil microorganisms are in active contact with clay minerals in soils and their reactions are a common interfacial phenomenon in geochemical environments. However, fundamental mechanisms governing interactions as well as sorption processes of pollutants are still poorly understood. The objective of the proposed project is to prepare new bioorganoclay materials based on microbial-derived organic matter and selected clay minerals, and to characterize the resulting structures and new specific functional properties as compared to the original compounds. The structure and physicochemical properties will be explored by multiple advanced experimental methods (e.g. X-ray photoelectron spectroscopy, nuclear magnetic resonance spectroscopy,transmissionelectron microscopy,nanoscalesecondary ion mass spectrometry) in a combination with advanced molecular modeling. This approach will lead to complex and detailed (molecular-scale) characterization of the bioorganoclay materials, e.g. arrangement of the bioorganic species in interlayer spaces and on external surfaces of clays. From the physicochemical properties, the special interest will be focused on the variation and changes of the adsorption capacity of the prepared bioorganoclays with respect to the type and amount of the bioorganic material, and used clay minerals. We expect an increasing versatility and applicability of the prepared bioorganoclays in comparison to the parent materials. Formulated hypothesis supposes that depending on the origin, type, and size of the bioorganic molecules and microbial material, and on the difference in the clay matrices, bioorganoclays with different structure and properties can be prepared. Two types will be prepared, i) bioorganoclays having clay particles mostly coated by bioorganic matter with only limited or no penetration into the interlayer galleries (kaolinite-based), ii) bioorganoclays having distributed bioorganic matter in the interlayer galleries and/or external surfaces of clay particles (montmorillonite-based). It is expected that these two types will differ in shape and size of biorganoclay particles, pore volume structure, the stability and binding of the bioorganic coating to clay matrices, and amount and type of active sites on surfaces. To verify this, experiments and computer simulations will be focused to determine the structure, composition, and properties of the prepared bioorganoclays. The successful solution of the tasks defined in the project will be based on the effective and synergistic collaboration between the German (responsible for the experimental part), and the Austrian (responsible for the molecular modeling part) partners, which established a successive collaboration in the framework of an earlier D-A-CH project.

The "BioClay" project was prepared as a bilateral cooperation within the framework of the DACH program including a German partner from the Institute of Soil Science (ISS), Leibniz University, Hannover (Prof. Georg Guggenberger - the project leader, and Dr. Christine Poggenburg - the postdoc collaborator). The Austrian team was composed by the PI Dr. Daniel Tunega and Dr. Peter Grancic as the postdoc collaborator from BOKU university. The general objective of the BioClay project was the preparation, characterization, and modeling new bioorganoclay materials based on the combination of organic matter of microbial origin and clay minerals (bioclays). New materials with specific properties were expected to be prepared (e.g., exhibiting enhanced sorption capacity). The German partner was responsible for the preparation of bioclay materials using bioorganic matter including pure bioorganic molecules, phosphatydilcholine, chitosan and desferrioxamine-B. Two typical clay minerals montmorillonite and kaolinite were selected as inorganic matrix. The German partner also planned to perform multiple experimental measurements for bioclays characterization (e.g., XPS, NMR, TEM, NanoSIMS). To understand the mechanism of preparation and functionality of bioclays at the molecular scale, classical molecular dynamics simulations were performed by the Austrian partner. Based on experimental findings, the modeling group developed representative structural models and suitable molecular modeling algorithms aimed to elucidate the complex mechanisms and forces responsible for the formation of bioclays. This included the detailed characterization of formation, structure, and properties of bioclays looking at i) the determination of possible molecular arrangements of biomolecules in interlayer spaces and/or on external surfaces of clays; ii) the identification of the corresponding binding sites and energies under various physical conditions. The results achieved by molecular simulations of bioclay models showed very promising perspectives for material chemistry in the preparation of new composite materials based on natural biomolecules and clay minerals, mainly of smectite types. These materials could fulfill attributes such as cheap resources (bioorganic matter, clays), environmentally friendly, tuned and enhanced properties (e.g., increasing sorption capacity with respect to organic pollutants); thus, they could be applicable in numerous environmental problems such as remediation of soils or cleaning of water sources. The results achieved during the project were published in several publications and presented at international conferences and institutional seminars.