Bioinspired design of inorganic advanced functional materials

Nature offers outstanding examples of multifunctional complex structures able to address different needs by changing the composition or the arrangement of the available materials. In this work, a representative selection of bioinspired materials with functional application is presented. Taking inspiration from biominerals, calcite hybrid crystals including both small molecules and nPs have been synthesized. RA, a small molecule active in cell differentiation, has been included into calcite single crystals and its activity is conserved upon slow dissolution of the matrix. PluS-OH nanoparticles were successfully occluded into calcite without modifying the single crystalline nature of the material. Since different molecules such as drugs or biologically active molecules can be occluded into the PluS-X core, our strategy allows to embed different functions into the additive and make it independent from the nature of the molecule itself. Inverse opal structures able to slow light coupled with plasmonic nanoparticles and the enzyme lipase have been successfully used to obtain laser driven remote and localized control of the catalytic efficiency of the enzyme, thus obtaining a universal platform for catalytical efficiency enhancement. Sea urchin spines whose surface area has been amplified by adsorption of colloidal particles have been successfully used as a template to obtain a silica/titania replica with potential application in the photodegradation of small organic molecules. In conclusion, this thesis shows a selection of functional inorganic materials synthesized using design strategies found in Nature or exploiting natural occurring complex structures as templates, taking advantage of the possibility of using constituents that are not available to biological organisms

Synthesis and Adsorbing Properties of Tabular (001) Calcite Crystals

One of the most common crystal habits of the thermodynamically stable polymorph of calcium carbonate, calcite, is the rhombohedral one, which exposes (10.4) faces. When calcite is precipitated in the presence of Li+ ions, dominantly (00.1) faces appear together with the (10.4), thus generating truncated rhombohedrons. This well-known phenomenon is explored in this work, with the aim of obtaining calcite crystals with smooth (00.1) faces. In order to achieve this objective, the formation of calcite was examined in precipitation systems with different c(Ca2+)/c(Li+) ratios and by performing an initial high-power sonication. At the optimal conditions, a precipitate consisting of thin, tabular (00.1) calcite crystals and very low content of incorporated Li+ has been obtained. The adsorption properties of the tabular crystals, in which the energetically unstable (00.1) faces represent almost all of the exposed surface, were tested with model dye molecules, calcein and crystal violet, and compared to predominantly rhombohedral crystals. It was found that the (00.1) crystals showed a lower adsorption capability when compared to the (10.4) crystals for calcein, while the adsorption of crystal violet was similar for both crystal morphologies. The obtained results open new routes for the usage of calcite as adsorbing substrates and are relevant for the understanding of biomineralization processes in which the (00.1) faces often interact with organic macromolecules

Enhanced Photon–Phonon Interaction in WSe2 Acoustic Nanocavities

Acoustic nanocavities (ANCs) with resonance frequencies much above 1 GHz are prospective to be exploited in sensors and quantum operating devices. Nowadays, acoustic nanocavities fabricated from van der Waals (vdW) nanolayers allow them to exhibit resonance frequencies of the breathing acoustic mode up to f ∼ 1 THz and quality factors up to Q ∼ 103. For such high acoustic frequencies, electrical methods fail, and optical techniques are used for the generation and detection of coherent phonons. Here, we study experimentally acoustic nanocavities fabricated from WSe2 layers with thicknesses from 8 up to 130 nm deposited onto silica colloidal crystals. The substrate provides a strong mechanical support for the layers while keeping their acoustic properties the same as in membranes. We concentrate on experimental and theoretical studies of the amplitude of the optically measured acoustic signal from the breathing mode, which is the most important characteristic for acousto-optical devices. We probe the acoustic signal optically with a single wavelength in the vicinity of the exciton resonance and measure the relative changes in the reflectivity induced by coherent phonons up to 3 × 10–4 for f ∼ 100 GHz. We reveal the enhancement of photon–phonon interaction for a wide range of acoustic frequencies and show high sensitivity of the signal amplitude to the photoelastic constants governed by the deformation potential and dielectric function for photon energies near the exciton resonance. We also reveal a resonance in the photoelastic response (we call it photoelastic resonance) in the nanolayers with thickness close to the Bragg condition. The estimates show the capability of acoustic nanocavities with an exciton resonance for operations with high-frequency single phonons at an elevated temperature

Insights on the interaction of calcein with calcium carbonate and its implications in biomineralization studies

The effects of calcein, a fluorescent marker commonly used to assess mineral growth in calcifying organisms, on calcite and aragonite structure have been investigated. Calcein is entrapped within calcite and aragonite and modifies the shape and morphology of both polymorphs. Moreover, in the presence of Mg2+, it inhibits aragonite formation in favor of magnesium calcite

Synthesis of calcium carbonate in trace water environments

Calcium carbonate (CaCO3) was synthesized from diverse water- free alcohol solutions, resulting in the formation of vaterite and calcite precipitates, or stable particle suspensions, with the dimensions and morphologies depending upon the conditions used. The obtained results shed light on the importance of solvation during crystallization of CaCO3 and open a novel synthetic route for its precipitation in organic solvents

Effect of Surface Chemistry on Incorporation of Nanoparticles within Calcite Single Crystals

Inclusion of additives into calcite crystals allows one to embed non-native proprieties into the inorganic matrix and obtain new functional materials. Up to now, few parameters have been taken into account to evaluate the efficiency of inclusion of an additive. Taking inspiration from Nature, we grew calcite crystals in the presence of fluorescent silica nanoparticles carrying different functional groups (PluS-X) to investigate the effect of surface chemistry on the inclusion of additives. PluS-X allowed us to keep constant all the particle characteristics, including size and morphology, while changing exposed functional groups and thus zeta potential. The effect on crystal morphology and structure, the loading, and distribution of PluS-X within the crystals have been evaluated with different microscopy and diffractometric techniques. Our data indicate that hydroxyl functionalized particles are entrapped more efficiently inside calcite single crystals without distortion of the crystal structure and inhibition of the growth

Preparation and Surface Functionalization of a Tunable Porous System Featuring Stacked Spheres in Cylindrical Pores

<p>A geometrically tunable nanoporous system featuring enhanced active surface area by stacking of spheres in cylindrical pores is fabricated. Highly ordered arrays of straight, constricted pores are obtained by anodization of metallic aluminum. Polystyrene (PS) spheres are assembled inside the pores by flowing their suspension through the porous membrane, whereas the construction serves as a filter. After surface functionalization with a noble metal catalyst, these model electrocatalysis systems exhibit functional properties (capacitance in electrochemical impedance spectroscopy) that mirror their geometric parameters. A systematic investigation of the system's geometry as it depends on the surface chemistry of the pores, on the one hand, and the physical parameters of the infiltration procedure, on the other hand, shows that mechanical stacking prevails over surface chemical interactions to determine the stacking density. The highest values of surface area are obtained when PS spheres are put in contact with HfO2 followed by ZnO according to adsorption measurements. Surface derivatization with organic layers does not improve stacking any further. However, choosing the proper concentration of PS spheres and flow rate are crucial for obtaining densely packed sphere assemblies without clogging of the pore entrance.</p&gt

Preparation and Surface Functionalization of a Tunable Porous System Featuring Stacked Spheres in Cylindrical Pores

Abstract A geometrically tunable nanoporous system featuring enhanced active surface area by stacking of spheres in cylindrical pores is fabricated. Highly ordered arrays of straight, constricted pores are obtained by anodization of metallic aluminum. Polystyrene (PS) spheres are assembled inside the pores by flowing their suspension through the porous membrane, whereas the construction serves as a filter. After surface functionalization with a noble metal catalyst, these model electrocatalysis systems exhibit functional properties (capacitance in electrochemical impedance spectroscopy) that mirror their geometric parameters. A systematic investigation of the system's geometry as it depends on the surface chemistry of the pores, on the one hand, and the physical parameters of the infiltration procedure, on the other hand, shows that mechanical stacking prevails over surface chemical interactions to determine the stacking density. The highest values of surface area are obtained when PS spheres are put in contact with HfO2 followed by ZnO according to adsorption measurements. Surface derivatization with organic layers does not improve stacking any further. However, choosing the proper concentration of PS spheres and flow rate are crucial for obtaining densely packed sphere assemblies without clogging of the pore entrance