Self-organization is the driving force that led to the evolution of life. Rationalization of the spontaneous self-assembly paradigm will offer tremendous potentialities to obtain a wide variety of complex systems, having specific functionality and properties. Herein, we will propose an overview of the developments in non-covalent syntheses of multi-porphyrin supramolecular species in aqueous solution. This work took inspiration from the pioneering studies aimed at rationalizing the spontaneous aggregation processes, governed by conventional solution properties (i.e. pH, ionic strength, and concentration). The more recent chemical strategies, to hierarchically manipulate the cooperative nature of weak interactions to design and synthesize supramolecular entities having pre-determined structure and properties, demonstrate the feasibility to attain, in a reproducible manner, molecular organization to supramolecular levels. In particular, calixarene–porphyrin species represents concrete evidence of a quantitative complexation, governed by precise hierarchical rules, which together with a rational functionalization of the molecular components leads to supramolecular entities of well-defined and tunable stoichiometry. These systems, thus, represent fertile ground to envisage and implement controlled self-organization strategies as bottom up methodologies to obtain supramolecular nanostructures and smart nanomachines.

For this study, we originally realized ZnO nanofibers (∼50 nm in mean radius) mixed with Pt nanoparticles (∼30 nm in mean radius), prepared by pulsed laser ablation in liquid, and investigated their photocatalytic performance. The material was synthesized by the simple electrospinning method coupled with subsequent thermal treatments. Methylene blue was employed as a representative dye pollutant to evaluate the photocatalytic activity of the nanofibers. It was found that the Pt-ZnO fibers exhibit a photodegradation reaction rate that is ∼40 % higher than the one obtained for reference ZnO fibers. These encouraging results demonstrate that Pt-ZnO nanofibers can be fruitfully applied for environmental applications.

Zn-doped TiO₂ nanofibers shelled with ZnO hierarchical nanoarchitectures have been fabricated combining electrospinning of TiO₂ (anatase) nanofibers and metal–organic chemical vapor deposition (MOCVD) of ZnO. The proposed hybrid approach has proven suitable for tailoring both the morphology of the ZnO external shell as well as the crystal structure of the Zn-doped TiO₂ core. It has been found that the Zn dopant is incorporated in calcined electrospun nanofibers without any evidence of ZnO aggregates. Effects of different Zn doping levels of Zn-doped TiO₂ fibers have been scrutinized and morphological, structural, physico-chemical and optical properties evaluated before and after the hierarchical growth of the external ZnO shell over the electrospun nanofibers. Moreover, doping promotes the incipient transition from the anatase to rutile phase in the core–shell Zn-doped TiO₂–ZnO nanostructures at lower temperature than that observed for pure TiO₂. Finally, the present core–shell hierarchical nanofibers possess a very large surface to volume ratio and exhibit a marked cathodoluminescence with a strong UV and visible emission.