This work was supported by the FCI and the DFG (Schu 744/8-2). The authors thank S. Schacht and the group of Dr I. Voigt–Martin (University Mainz) for the TEM micrographs and Dr B. Matthiasch (University Mainz) is acknowledged for his help in the XRF measurements. Additionally we want to acknowledge the BASF AG;
Ludwigshafen for the supply of the non-ionic surfactant;