1. Department of Chemical Engineering, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
2. Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
3. Nanotech Solutions S.L., Ctra. Madrid 23, 40150 Villacastin, Spain
4. Processes, Materials and Solar Energy Laboratory, CNRS-PROMES, 7 Rue du Four Solaire, 66120 Font-Romeu, France
5. Institut de Ciencia de Materials de Barcelona, CSIC, Campus Universitat Autònoma de Barcelona, A08193 Bellaterra, Spain