Design magnetic hybrid nanomaterials for molecules harvesting/ delivery

This thesis focuses on magnetic features in single and hybrid nanostructures. Magnetic material based on a spinel iron oxide structure (MeFe2O4; Me: Fe2+; Co2+,) and coated by a mesoporous structure as well as by peculiar molecules (e.g. DNA) and by several types of polymers, have been investigated. The objective of the study is the design of single/hybrid nanoarchitectures with the aim of controlling the magnetic properties as well as their magnetic structure, which may serve as a basis for delivering and harvesting molecules in nanotechnological applications. The magnetic properties of nanoparticles are particularly sensitive to the particle size, being determined by finite size effects on the core properties, related to the reduced number of spins cooperatively linked within the particle, and by surface effects, becoming more important as the particle size decreases physical properties differ greatly from their parent massive materials. Accordingly, the first part of the thesis is dedicated to the study of the different fundamental concepts of magnetism at the nanoscale. We present morpho-structural and magnetic investigation of Fe3O4 and CoFe2O4 nanoparticles. In case of Fe3O4 synthetized with co-precipitation method we have investigated: (i) the temperature effect, (ii) the reaction atmosphere effect and (iii) Cobalt doping effect in tuning specially the magnetic properties. The results reveal a significant change in the magnetic properties (i.e., saturation magnetization and coercive field) due to the Co-doping effect. While in the other cases magnetic properties were independent on the change in the experimental parameters within the experimental error. The effect of surface modification for Fe3O4 nanoparticles with mesoporous silica, DNA molecules and polyacrylic acid, gallic acid, oleic acid and polyethylene glycol was deeply investigated specially from magnetic point of view. The analysis of different cases shows the important role of the functionalization in tuning the properties of the magnetic core. We found that the surface coating has a large influence on changing the saturation magnetization, easy axis orientation in case of oleic acid and mesoporous silica respectively, as compared to the other cases where a change in the interparticle distance by 5% was the main observed change.vi In case of CoFe2O4 prepared with polyol method and coated with mesoporous silica structure also a small but evident decrease in the interparticle interactions is observed. on the other hand, we also introduce a hybrid nanoarchitecture combining crystalline cobalt ferrite and the amorphous parent material, that behaves as an artificial single-phase material with enhanced magnetic anisotropy, well above the values achievable by the individual components. Apart from the experimental investigation micromagnetic modeling is presented as a tool to interpret the magnetic state of the nanocomposite. We compare the simulated result with the experimental one proving the observed large magnetic anisotropy and elucidating the active role of each phase. Finally, we have introduced a theoretical investigation of permanent magnets with cubic geometry disposed in different configurations. Furthermore, experiments have been carried out using a home-made circuit, along with the development of a simple method for data treatment that enable to understand the behavior of the nanoparticles in an applied magnetic field

Galinstan liquid metal as the heat transfer fluid in magnetic refrigeration

Room-temperature magnetic refrigeration is a promising technology in which cooling is achieved by exploiting a special property of some materials, the “magnetocaloric effect” (MCE), i.e., the ability of the material to change its temperature when it undergoes changes in the applied external magnetic field. For magnetic field variations on the order of 1–1.5 T, the MCE results in small adiabatic temperature changes of a few degrees so, in most cases, the designs and prototypes presented by various research groups employ active magnetic regeneration to increase the temperature span required for practical cooling devices. The effectiveness of the regenerator, and thus of the refrigeration device, depends heavily on the properties of the heat transfer fluid, which is usually a water-based mixture. High values of the fluid thermal conductivity greatly affect the heat transfer between the MCE and the fluid allowing faster operation and higher cooling capacity. In this study, the use of a gallium based liquid metal, i.e., Galinstan, is investigated to quantify this improvement. Galinstan was found not to be aggressive to gadolinium at room temperature and it resulted not affected by magnetic induction. The authors report the results of an extensive simulation campaign to characterize the performance of an active magnetic regenerator made of 0.5 mm thick gadolinium sheets using Galinstan as a heat transfer fluid. The results are compared to those of the same device using water; friction is also accounted for since the high density of this liquid metal leads to a high demand for pumping power. On average, a more than tenfold increase in cooling capacity was observed when using Galinstan, but the COP was severely penalized by the higher frictional losses. To avoid this effect, the cycle time and the utilization factor must be adjusted, or the geometry changed by using thicker sheets and ducts for the same Gd weight. In this way a cooling increase of 400% is achieved with the same COP

Metodi di inclusione nella ricerca

The chapter emphasizes the role of Equality, Diversity, and Inclusion (EDI) in enhancing innovation and creativity within scientific research, thereby improving outcomes and societal impact. The authors outline the European Union’s efforts in promoting equality and inclusion in scientific research since the 1990s, initially focusing on gender equality and later broadening to encompass diverse perspectives in Science, Technology, Engineering, Mathematics (STEM) fields, shifting towards an EDI approach. Challenges faced in promoting gender equality and integrating EDI perspectives into research institutions, particularly during research activities, are discussed. Then, scientific initiatives in chemistry and materials science, particularly nanosciences, in Italy, are showcased, emphasizing an EDI -friendly approach. Ultimately, the adoption of EDI perspectives in STEM disciplines could lead to a reduction in unequal access to STEM, including nanotechnologies, and unequal opportunities in research and innovation

Enzyme immobilization on magnetic nanoparticles for polymer synthesis

To satisfy the increasing request for environmentally friendly polymers, in line with the “European green deal”1, the ability of enzymes to transform natural and non-natural compounds into polymers is considered as an environmentally friendly alternative to the traditional chemical synthetic pathways2. Improving enzyme’s activity and stability as well as preserving selectivity is a must and can be achieved by immobilizing the biocatalyst on the surface of metal oxide nanoparticles3. The aim of this work is to design a smart platform consisting of spinel iron oxides (MeFe2O4; Me: Fe2+ and Co2+) nanoparticles (i.e., single magnetic nanoparticles, ordered aggregates of nanoparticles) with optimized morpho structural (i.e., particles size, shape and crystallinity), textural (i.e., high surface area) and magnetic properties. Candida antarctica lipase B (CaLB) was immobilized on nanoparticles’ surface investigating the optimal bioconjugation conditions. Once immobilized on magnetic nanoparticles surface, CaLB was tested for enzymatic polymerization reaction to synthetize polyesters starting from renewable monomers such as adipic acid and 1,8-octanediol. The percentage of conversion of substrate monomers was studied by Nuclear Magnetic Resonance analysis (NMR), and the molecular weights of the polyester products were analyzed by gel permeation chromatography (GPC). As final step, enzyme recyclability over several cycles of condensation reaction was tested