Martina Salzano de Luna

Chitosan hydrogels embedding hyper-crosslinked polymer particles as reusable broad-spectrum adsorbents for dye removal

The removal of dye and toxic ionic pollutants from water is an extremely important issue that requires systematic and efficient adsorbent preparation strategies. To address this challenge, we developed composite chitosan (CS)-based hydrogels containing hyper-crosslinked polymer (HCP) particles to be used as broad-spectrum adsorbents. The goal is to efficiently combine the dye adsorption ability of chitosan and the capacity of the porous particles of trapping pollutant molecules. The HCP particles are well distributed and firmly embedded into the chitosan matrix and the composite hydrogels exhibit improved mechanical properties. Adsorption experiments reveal a synergistic effect between CS and HCP particles, and the samples are able to remove both anionic and cationic dyes (indigo carmine, rhodamine 6G and sunset yellow) from water. The maximum dye uptake is higher than that of comparable biosorbents. Moreover, the mechanical properties of the composite hydrogels are enhanced respect to pure CS, and the samples can be regenerated and reused keeping their adsorption ability unaltered over successive cycles of adsorption, desorption, and washing.

Long‐Lasting Efficacy of Coatings for Bronze Artwork Conservation: The Key Role of Layered Double Hydroxide Nanocarriers in Protecting Corrosion Inhibitors from Photodegradation

Abstract The photodegradation kinetics of 2‐mercaptobenzothiazole (MBT), a corrosion inhibitor for copper‐based alloys, is studied in high amorphous polyvinyl alcohol coatings subjected to either UV irradiation or indoor light exposure. The photodegradation process proceeds rapidly, thus compromising the anticorrosion ability of the coating. The encapsulation of MBT into layered double hydroxide (LDH) nanocarriers slows down its decomposition kinetics by a factor of three. Besides preserving the corrosion inhibitor, such a strategy allows a controlled release of MBT triggered by corrosion‐related stimuli, for example, presence of chloride species and acid pH. The developed coating guarantees long‐lasting corrosion protection even at low amounts of inhibitor‐loaded LDH nanocarriers (ca. 5 wt %). This also reflects in a high transparency, which makes the protective coating suitable for demanding applications, such as the conservation of high‐value metal works of art.

Linear viscoelasticity of polymer-graphite nanoplatelets (GNPs) nanocomposites

We prepare well dispersed nanocomposites based on Graphite Nanoplatelets (GNPs) and polystyrene (PS) through a combination of solution and melt mixing techniques. The samples are subjected to morphological, electrical, and rheological investigations. Electron microscopy analyses show that GNPs are well dispersed, and the presence of few nanometers thick GNPs is noticed. The electrical conductivity of the polymer dramatically increases at a critical content of particles of Φ∼4 wt.%, indicating that electrical percolation has occurred. The existence of a percolating network induces a marked elastic connotation in the melt state. We show that the elasticity of GNP networks in samples at different composition can be scaled on a single master curve. This allows for the accurate estimation of the rheological percolation threshold. In addition, using the master curve we can infer the elasticity of GNP networks which are too tenuous to be appreciated via conventional rheological measurements.

Preparation optimization of chitosan/graphene oxide aerogels: Tailoring of dye adsorption ability and mechanical properties

Chitosan (CS)/graphene oxide (GO) nanocomposite aerogels have been prepared by freeze-drying and investigated as possible adsorbents for the removal of water-soluble dyes. The preparation procedure has been optimized in terms of CS and GO mixing procedure, crosslinking conditions and freezing protocol. The ultimate goal is to properly select the process-related parameters in order to maximize the performances of the CS/GO aerogels, specifically focusing on dye uptake capacity and mechanical properties. The obtained results suggest that the fine tuning of the preparation process allows to efficiently combine the ability of chitosan in binding anionic species and the capacity of GO nanoparticles of adsorbing cationic pollutants. In addition, compression tests reveal that the composite aerogels exhibit improved mechanical properties, which is highly attractive from a practical point of view since facilitate their handling and recovery after the adsorption process.Chitosan (CS)/graphene oxide (GO) nanocomposite aerogels have been prepared by freeze-drying and investigated as possible adsorbents for the removal of water-soluble dyes. The preparation procedure has been optimized in terms of CS and GO mixing procedure, crosslinking conditions and freezing protocol. The ultimate goal is to properly select the process-related parameters in order to maximize the performances of the CS/GO aerogels, specifically focusing on dye uptake capacity and mechanical properties. The obtained results suggest that the fine tuning of the preparation process allows to efficiently combine the ability of chitosan in binding anionic species and the capacity of GO nanoparticles of adsorbing cationic pollutants. In addition, compression tests reveal that the composite aerogels exhibit improved mechanical properties, which is highly attractive from a practical point of view since facilitate their handling and recovery after the adsorption process.

Interfacially-Located Nanoparticles Anticipate the Onset of Co-Continuity in Immiscible Polymer Blends

The addition of nanoparticles has recently emerged as a clever tool to manipulate the microstructure and, through it, the macroscopic properties of immiscible polymer blends. Despite the huge number of studies in this field, the underlying mechanisms of most of the nanoparticle-induced effects on the blend microstructure remain poorly understood. Among others, the origin of effect of nanoparticles on the transition from distributed (drop-in-matrix) to co-continuous morphology is still controversial. Here we address this issue through a systematic study on a model blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) filled with small amounts of nanoparticles (organo-modified clay) selectively located at the polymer–polymer interface. Extraction experiments with selective solvents prove that the nanoparticles significantly anticipate the onset of co-continuity with respect to the unfilled blend. Morphological analyses reveal that such an effect is a consequence of the interconnection of nanoparticle-coated polymer domains. Such “ginger-like” clusters get into contact at low content due to their irregular shape, thus anticipating the onset of co-continuity.

Morphology stabilization of co-continuous polymer blends through clay nanoparticles

The influence of plate-like nanoparticles on the morphology evolution of co-continuous polymer blends during quiescent annealing is investigated thorugh viscoelastic analysis. Contextually, the effect of the molten polymer phases on the assembly dynamics and ultimate structure of the filler is also studied. A model co-continuous blend of polystyrene and poly(methyl methacrylate) (45/55 wt/wt) has been selected, and different amount of clay nanoparticles preferentially adsorbing at the polymer-polymer interface are added to this system. The filler inhibits the typical phase coarsening of the co-continuous morphology during thermal treatments even at extremely low filler volume fractions (Φ=0.4 vol.%). In addition, the time evolution of the rheological response of the filled blends resembles that of homopolymer-based nanocomposites, suggesting that the fluid phases do not appreciably alter the nanoparticle dynamics. Exploiting a simple two-phase model, the main elastic features of the filler network that bu...

Chitosan-based hydrogel for dye removal from aqueous solutions: Optimization of the preparation procedure

The efficacy of chitosan-based hydrogels in the removal of dyes from aqueous solutions has been investigated as a function of different parameters. Hydrogels were obtained by gelation of chitosan with a non-toxic gelling agent based on an aqueous basic solution. The preparation procedure has been optimized in terms of chitosan concentration in the starting solution, gelling agent concentration and chitosan-to-gelling agent ratio. The goal is to properly select the material- and process-related parameters in order to optimize the performances of the chitosan-based dye adsorbent. First, the influence of such factors on the gelling process has been studied from a kinetic point of view. Then, the effects on the adsorption capacity and kinetics of the chitosan hydrogels obtained in different conditions have been investigated. A common food dye (Indigo Carmine) has been used for this purpose. Noticeably, although the disk-shaped hydrogels are in the bulk form, their adsorption capacity is comparable to that rep...

Protection of bronze artefacts through polymeric coatings based on nanocarriers filled with corrosion inhibitors

Protective coatings based on polymers synthesized from renewable sources (chitosan or an amorphous vinyl alcohol based polymer) have been prepared for the protection of bronze artifacts from corrosion. Besides acting as an effective barrier against corrosive species present in the environment, the efficiency of the coatings has been improved by adding corrosion inhibitor compounds (benzotriazole or mercaptobenzothiazole) to the formulations. The liquid medium of the formulations has been carefully selected looking at maximizing the wettability on the bronze substrate and optimizing the solvent evaporation rate. The minimum amount of inhibitor compounds has been optimized by performing accelerated corrosion tests on coated bronze substrates. The inhibitors have been directly dissolved in the coating-forming solutions and/or introduced by means of nanocarriers, which allow to control the release kinetics. The free dissolved inhibitor molecules immediately provide a sufficient protection against corrosion. O...

Melt state dynamics of plate-like nanoparticles in immiscible polymer blends

The dynamics of assembly of lamellar (clay) nanoparticles in a molten blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with drop-matrix morphology are studied combining viscoelastic measurements and morphological analyses. The goal is studying how the preferred polymer-polymer interface alters the melt state dynamics of the filler and the structures resulting from particle self-assembly. The PMMA drops anchor the lamellae, frustrating their peculiar mobility in the polymer melt, at least until saturation of the available polymer-polymer interface. On the other hand, the clay radically affects the blend morphology, inducing irregularly-shaped drops and drop clustering phenomena even in case of partial coverage of the drop surface.