Nanofibers of chitosan-polycaprolactone blends as active support for photocatalytic nanoparticles: Outstanding role of chitosan in the degradation of an organic dye in water.

Hybrid nanofibers of a chitosan-polycaprolactone blend containing titanium dioxide nanoparticles TiO2NPs, were prepared through electrospinning to study their adsorption and photocatalytic degradation capabilities of the model organic water pollutants, rhodamine B, RhB. To obtain uniform and bead-free nanofibers, an optimization of the electrospinning parameters was performed. The optimization was carried out by systematically adjusting the solution conditions (solvent, concentration, and polymer ratio) and instrumental parameters (voltage, needle tip-collector distance, and flow). The obtained materials were characterized by FT-IR, TGA, DSC, SEM, TEM, mechanical tensile test, and water contact angle. The photoactivity was investigated using a batch-type system by following UV-Vis absorbance and fluorescence of RhB. TiO2NPs were incorporated ex-situ into the polymer matrix, contributing to good mechanical properties and higher hydrophilicity of the material. The results showed that the presence of chitosan in the nanofibers significantly increased the adsorption of RhB and its photocatalytic degradation by TiO2NPs (5, 55 and 80 % of RhB degradation with NFs of PCL, TiO2/PCL and TiO2/CS-PCL, after 30 h of light irradiation, respectively), evidencing a synergistic effect between them. The results are attributed to an attraction of RhB by chitosan to the vicinity of TiO2NPs, favouring initial adsorption and degradation, phenomenon known as "bait-and-hook-and-destruct" effect.

Photothermal motion: effect of low-intensity irradiation on the thermal motion of organic nanoparticles.

The effect of local photo-triggered heat release on the motion of organic nanopartcles (NP), a process that is itself thermal, is largely unexplored under low-intensity irradiation. Here, we develop organic NP specifically tailored for this study and demonstrate, comparing three different irradiation intensity regimes, that indeed the NP undergo "acceleration" upon light absorption (Photothermal Motion). These NP have a well-defined chemical composition and extremely high molar absorbance coefficient, and upon excitation, they deactivate mostly non radiatively with localized heat dissipation. The residual fluorescence efficiency is high enough to allow the detection of their trajectory in a simple wide field fluorescence microscope under low-intensity irradiation, a typical condition for NP bio-applications. The NP were characterized in detail from the photophysical point of view using UV-VIS absorption, steady-state and time-resolved fluorescence spectroscopy and ultra-fast transient absorption (UF-TA). A detailed analysis of the trajectories of the NP reveals a strong dependency of the diffusion coefficient on the irradiation intensity even in a low power regime. This behavior demonstrates the inhomogeneity of the environment surrounding the NP as a result of local heat generation. Upon irradiation, the effective temperature increase, that emerges from the analysis, is much larger than that expected for plasmonic NP. Anomalous diffusion object-motion analysis (ADOMA) revealed that, in the more intense irradiation regime, the motion of the NP is a fractional Brownian motion, which is a simple generalization of Brownian motion where the steps are not independent of each other.

pH Switchable Water Dispersed Photocatalytic Nanoparticles.

Photogeneration of Reactive Oxygen Species (ROS) finds applications in fields as different as nanomedicine, art preservation, air and water depollution and surface decontamination. Here we present photocatalytic nanoparticles (NP) that are active only at acidic pH while they do not show relevant ROS photo-generation at neutral pH. This dual responsivity (to light and pH) is achieved by stabilizing the surface of TiO2 NP with a specific organic shell during the synthesis and it is peculiar of the achieved core shell-structure, as demonstrated by comparison with commercial photocatalytic TiO2 NP. For the investigation of the photocatalytic activity, we developed two methods that allow real time detection of the process preventing any kind of artifact arising from post-treatments and delayed analysis. The reversibility of the pH response was also demonstrated as well as the selective photo-killing of cancer cells at acidic pH.

On the Versatile Role of Electrospun Polymer Nanofibers as Photocatalytic Hybrid Materials Applied to Contaminated Water Remediation: A Brief Review.

A wide variety of materials, strategies, and methods have been proposed to face the challenge of wastewater pollution. The most innovative and promising approaches include the hybrid materials made of polymeric nanofibers and photocatalytic nanoparticles. Electrospun nanofibers with unique properties, such as nanosized diameter, large specific surface area, and high aspect ratio, represent promising materials to support and stabilize photocatalytic nanosized semiconductors. Additionally, the role performed by polymer nanofibers can be extended even further since they can act as an active medium for the in situ synthesis of photocatalytic metal nanoparticles or contribute to pollutant adsorption, facilitating their approach to the photocatalytic sites and their subsequent photodegradation. In this paper, we review the state of the art of electrospun polymer/semiconductor hybrid nanofibers possessing photocatalytic activity and used for the remediation of polluted water by light-driven processes (i.e., based on photocatalytic activity). The crucial role of polymer nanofibers and their versatility in these types of procedures are emphasized.

The Photophysics and Photochemistry of Melanin- Like Nanomaterials Depend on Morphology and Structure.

Melanin-like nanomaterials have found application in a large variety of high economic and social impact fields as medicine, energy conversion and storage, photothermal catalysis and environmental remediation. These materials have been used mostly for their optical and electronic properties, but also for their high biocompatibility and simplicity and versatility of preparation. Beside this, their chemistry is complex and it yields structures with different molecular weight and composition ranging from oligomers, to polymers as well as nanoparticles (NP). The comprehension of the correlation of the different compositions and morphologies to the optical properties of melanin is still incomplete and challenging, even if it is fundamental also from a technological point of view. In this minireview we focus on scientific papers, mostly recent ones, that indeed examine the link between composition and structural feature and photophysical and photochemical properties proposing this approach as a general one for future research.

Extending photocatalysis to the visible and NIR: the molecular strategy.

Photocatalysis exploits light to perform important processes as solar fuel production by water splitting, and CO2 reduction or water and air decontamination. Therefore, photocatalysis contributes to the satisfaction of the increasing needs for clean energy, environmental remediation and, most recently, sanification. Most of the efficient semiconductor nanoparticles (NP), developed as photocatalysts, work in the ultraviolet (UV) spectral region and they are not able to exploit either visible (Vis) or near infrared (NIR) radiation. This limitation makes them unable to fully exploit the broad band solar radiaton or to be applied in indoor conditions. Recently, different approaches have been developed to extend the spectral activity of semiconductor NP, like for example band-gap engineering, integration with upconversion NP and plasmonic enhancement involving also hot-electron injection. Nevertheless, the use of organic molecules and metal complexes, for enhancing the photoactivity in the Vis and NIR, was one of the first strategies proposed for sensitization and it is still one of the most efficient. In this minireview we highlight and critically discuss the most recent and relevant achievements in the field of photocatalysis obtained by exploiting dye sensitization either via dynamic or static quenching.

Bio-Applications of Multifunctional Melanin Nanoparticles: From Nanomedicine to Nanocosmetics.

Bioinspired nanomaterials are ideal components for nanomedicine, by virtue of their expected biocompatibility or even complete lack of toxicity. Natural and artificial melanin-based nanoparticles (MNP), including polydopamine nanoparticles (PDA NP), excel for their extraordinary combination of additional optical, electronic, chemical, photophysical, and photochemical properties. Thanks to these features, melanin plays an important multifunctional role in the design of new platforms for nanomedicine where this material works not only as a mechanical support or scaffold, but as an active component for imaging, even multimodal, and simple or synergistic therapy. The number of examples of bio-applications of MNP increased dramatically in the last decade. Here, we review the most recent ones, focusing on the multiplicity of functions that melanin performs in theranostics platforms with increasing complexity. For the sake of clarity, we start analyzing briefly the main properties of melanin and its derivative as well as main natural sources and synthetic methods, moving to imaging application from mono-modal (fluorescence, photoacoustic, and magnetic resonance) to multi-modal, and then to mono-therapy (drug delivery, anti-oxidant, photothermal, and photodynamic), and finally to theranostics and synergistic therapies, including gene- and immuno- in combination to photothermal and photodynamic. Nanomedicine aims not only at the treatment of diseases, but also to their prevention, and melanin in nature performs a protective action, in the form of nanopigment, against UV-Vis radiations and oxidants. With these functions being at the border between nanomedicine and cosmetics nanotechnology, recently examples of applications of artificial MNP in cosmetics are increasing, paving the road to the birth of the new science of nanocosmetics. In the last part of this review, we summarize and discuss these important recent results that establish evidence of the interconnection between nanomedicine and cosmetics nanotechnology.