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The present work concerns the synthesis, the characterization and the study of the light-activated properties (photodegradation, persistent luminescence, sensing) of different inorganic materials and molecular systems. In the first part, the realization of bismuth-based bifunctional materials for the adsorption and photodegradation of organic dyes is presented. Novel procedures for the synthesis of bismuth oxychlorides (BiOCl, Bi24O31Cl10, Bi12O17Cl2) and subcarbonate nanostructures are discussed. By modulating the synthesis parameters (temperature, pH and surfactant) and by means of different treatments (thermal and UV irradiation), a tuning of the chemical composition and consequently of the crystalline phase, morphology and optical properties was obtained. This was reflected in different absorbent properties and photo-degradation activity towards two model dyes: methyl orange and rhodamine B. The most promising nanostructures, based on (BiO)2CO3, are able to adsorb both dyes, from 50 up to 95 %, within 20 minutes. Further, under irradiation with visible light they are able to degrade the dye remained in solution. The second part concerns the study of chromium doped zinc gallate (ZnGa2O4:Cr3+) nanostructures. This material displays interesting emission properties in the red-NIR region (600-900 nm) and, especially, persistent luminescence. Adopting a sol-gel procedure and post-synthesis treatments in the range 500-1000 °C, thin films endowed with homogeneous composition, structure and thickness were obtained. These systems were characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and optical spectroscopy (absorption and emission). A modulation of the emission properties was observed in a wide temperature range from -190 up to 250 °C, evidencing the possibility to employ these materials for the development of temperature sensors. Advanced synchrotron radiation techniques as X-Ray Absorption Spectroscopy (XAS) and X-Ray Excited Optical Luminescence (XEOL) were adopted to get site-specific information and to correlate short-range order to luminescent properties. Lastly, inorganic materials are also employed as substrates and/or hosting matrices for functional molecules. Besides the development of the inorganic system, the study of the molecular unit itself in terms of thermodynamic and kinetic stability, topology, functionality and reactivity is crucial. In this framework, the third part of the thesis describes the study of two lanthanide luminescent antenna complexes characterized by a macrocyclic ligand (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, DO3A) for dysprosium and an acyclic (1,4,7-triazaheptane-1,1,7,7-tetraacetic acid, DTTA) one for europium. The behavior of the couple in aqueous solution was studied in presence of dipicolinic acid (pyridine-2,6-dicarboxylic acid, DPA). In particular, it was investigated the effect of a strongly coordinating agent like DPA on their emission properties and the possibility to develop a ratiometric sensor for small molecules like DPA. To this aim, the dysprosium complex was employed as reference and the europium one as probe for the recognition of DPA which is known as a biomarker for bacterial spores. The modulation of the emission properties (band profile and relative intensity) revealed an interaction between probe complex and dipicolinic acid. NMR and mass spectrometry measurements evidenced that a ligand exchange reaction occurred, with the formation of [EuDPA2]-. This indicates that macrocyclic ligands endowed with a preformed cavity hosting the metal ion insure a better stability over acyclic ligands having the same number and typology of coordination sites. These findings provide crucial information for the future development of solid state sensors, realized by grafting suitable complexes on appropriate solid matrices.

Bi12O17Cl2/(BiO)2CO3 nanocomposite materials were studied as bifunctional systems for depuration of wastewater. They are able to efficiently adsorb and decompose rhodamine B (RhB) and methyl orange (MO), used as model pollutants. Bi12O17Cl2/(BiO)2CO3 nanocomposites were synthesized at room temperature and ambient pressure by means of controlled hydrolysis of BiCl3 in the presence of a surfactant (Brij 76). Cold treatments of the pristine samples with UV light or thermal annealing at different temperatures (370–500 °C) and atmospheres (air, Ar/30% O2) were adopted to modulate the relative amounts of Bi12O17Cl2/(BiO)2CO3 and hence the morphology, surface area, ζ-potential, optical absorption in the visible range, and the adsorption/degradation of pollutants. The best performance was achieved by (BiO)2CO3-rich samples, which adsorbed 80% of MO and decomposed the remaining 20% by visible light photocatalysis. Irrespective of the dye, all of the samples were able to almost complete the adsorption step within 10 min contact time. Bi12O17Cl2-rich composite materials displayed a lower adsorption ability, but thanks to the stronger absorption in the visible range they behaved as more effective photocatalysts. The obtained results evidenced the ability of the employed strategy to modulate sample properties in a wide range, thus pointing out the effectiveness of this approach for the synthesis of multifunctional inorganic materials for environmental remediation.