Davide Carboni

Molecularly imprinted La-doped mesoporous titania films with hydrolytic properties toward organophosphate pesticides

The present work is aimed at developing a titania-based mesoporous film with catalytic properties toward organophosphate pesticides by combining two different approaches: the molecular imprinting and the self-assembly with a supramolecular template. The mesoporosity of the material has been obtained by using a tri-block copolymer (Pluronic F127) as a micellar template while the molecular imprinted cavities have been templated by a complex between La3+ and bis-4-nitro-phenyl-phosphate. The template removal allowed opening, in one step, both the mesopores and the imprinted cavities with a simultaneous estimation of the active sites. The catalytic activity of the molecularly imprinted and not imprinted films toward the pesticide Paraoxon® has been evaluated by means of UV-Vis spectroscopy titration of the 4-nitro-phenolate released by the Paraoxon® hydrolysis. The analysis of the initial rates of molecularly imprinted and not imprinted films has shown that the presence of a very low number of molecular cavities improves the catalytic properties of the imprinted film when compared to the not imprinted films and the background hydrolysis.

Smart tailoring of the surface chemistry in GPTMS hybrid organic–inorganic films

Hybrid films prepared from 3-glycidoxypropyltrimethoxysilane have been widely used as organic–inorganic materials for several applications. Tailoring the coating surface should disclose new possibilities of applications in biomaterials as functional interfaces for cells and enzymes. In this work we have designed the synthesis of 3-glycidoxypropyltrimethoxysilane hybrid films to modify the surface properties without additional surface functionalization steps. The pH of the precursor sols has been changed from highly basic to acidic and neutral pH and then the sols have been used to deposit highly transparent films. The analysis by infrared spectroscopy has shown that the synthetic conditions allow tuning the degree of condensation of the silica network and the percentage of epoxide ring opening. A precise control of these two parameters enables the formation of a smart surface library where hydroxyl or epoxide groups or the mixed presence of both change the hydrophobicity of the surface and thus its capability of binding molecules and nano-objects.

Incorporation of graphene into silica-based aerogels and application for water remediation

Graphene/silica nanocomposites in the form of highly porous aerogels are obtained for the first time by integrating a novel approach for the production of low defectivity graphene with a two-step route for the synthesis of a silica-based monolith. Different from the other synthetic methods, the use of co-gelation of a dispersed phase and matrix followed by high temperature supercritical drying leads to well dispersed bilayered graphene inside a high surface area silica matrix with an open texture porosity. Physico-chemical characterization provides evidence that the developed graphene/SiO2 bulk aerogel nanocomposites combine the distinct features of both the dispersed graphene sheets and the porous silica aerogel matrix. It was found that incorporation of graphene in the aerogel, even at low loading, increases significantly the hydrophobic behaviour of the materials. This, combined with the high surface/volume ratio of the aerogel, makes the resulting nanocomposite a suitable candidate as a novel oil sorbent for water remediation. In particular, the developed graphene/silica aerogels selectively and quickly uptake oil, up to more than 7 times the aerogel sorbent mass, from oil–water mixtures, and keeps floating on water after absorbing the oil phase. The suitability of the developed composites as a class of novel sorbents for environmental remediation in the occurrence of flammable liquid spills, where burning represents a major threat, is supported by the specific features of silica aerogels such as a relative fire-resistance, in addition to the high porosity and hydrophobic nature.

Sol‐to‐Gel Transition in Fast Evaporating Systems Observed by in Situ Time‐Resolved Infrared Spectroscopy

The in situ observation of a sol-to-gel transition in fast evaporating systems is a challenging task and the lack of a suitable experimental design, which includes the chemistry and the analytical method, has limited the observations. We synthesise an acidic sol, employing only tetraethylorthosilicate, SiCl4 as catalyst and deuterated water; the absence of water added to the sol allows us to follow the absorption from the external environment and the evaporation of deuterated water. The time-resolved data, obtained by attenuated total reflection infrared spectroscopy on an evaporating droplet, enables us to identify four different stages during evaporation. They are linked to specific hydrolysis and condensation rates that affect the uptake of water from external environment. The second stage is characterized by a decrease in hydroxyl content, a fast rise of condensation rate and an almost stationary absorption of water. This stage has been associated with the sol-to-gel transition.

Design of Carbon Dots Photoluminescence through Organo-Functional Silane Grafting for Solid-State Emitting Devices

Advanced optical applications of fluorescent carbon dots (C-dots) require highly integrated host-guest solid-state materials with a careful design of C-dots – matrix interface to control the optical response. We have developed a new synthesis based on the grafting of an organo-functional silane (3-glycidyloxypropyltrimethoxysilane, GPTMS) on amino-functionalized C-dots, which enables the fabrication of highly fluorescent organosilica-based hybrid organic-inorganic films through sol-gel process. The GPTMS grafting onto C-dots has been achieved via an epoxy–amine reaction under controlled conditions. Besides providing an efficient strategy to embed C-dots into a hybrid solid-state material, the modification of C-dots surface by GPTMS allows tuning their photoluminescence properties and gives rise to an additional, intense emission around 490 nm. Photoluminescence spectra reveal an interaction between C-dots surface and the polymeric chains which are locally formed by GPTMS polymerization. The present method is a step forward to the development of a surface modification technology aimed at controlling C-dots host-guest systems at the nanoscale.

Pore-confined synthesis of mesoporous nanocrystalline La–Ce phosphate films for sensing applications

A new method for the preparation of fluorescent mesoporous La–Ce phosphate films by spin coating is reported here. The structure is obtained by a pore-confined synthesis involving an in situ growth of La0.5Ce0.5PO4 nanoparticles inside the pores of a mesoporous silica thin film and the subsequent partial sintering. The removal of the sacrificial mesoporous silica matrix is achieved by chemical etching, which leaves on the substrate a La0.5Ce0.5PO4 mesoporous film exhibiting good adhesion properties and high fluorescence intensity that can be quenched by a water solution containing organo-phosphate bearing nitrophenyl groups. The sensing capabilities of these materials have been tested for the detection of pesticides in water.

Engineering the surface of hybrid organic–inorganic films with orthogonal grafting of oxide nanoparticles

Superparamagnetic iron oxide nanoparticles of magnetite have been grafted on the surface of a hybrid organic–inorganic film prepared using an organically modified alkoxide, 3-glycidoxypropyltrimethoxysilane, as precursor. A solventless synthesis of the hybrid films at high pH has been employed and the surface chemistry of the deposited films has been processed by controlling the aging time of the sol. The films have been characterized by FTIR, Raman and UV spectroscopy and grazing incidence X-ray diffraction. Films prepared with fresh sols have shown a mixed presence of epoxides and hydroxyls on the surface, which enabled the successful grafting of the iron oxide nanoparticles. Films from aged sols, which contain only hydroxyls, have failed to bind the iron particles but have instead shown the capability of grafting ceria nanoparticles. This method has, therefore, allowed a direct grafting of nanoparticles on the hybrid surface without any post-synthetic functionalization step. Moreover, the phase transition induced in iron oxide nanoparticles by means of a laser beam has been exploited to pattern the film surface creating different domains of magnetite and hematite.

Hard X-rays for processing hybrid organic–inorganic thick films

Hard X-rays, deriving from a synchrotron light source, have been used as an effective tool for processing hybrid organic-inorganic films and thick coatings up to several micrometres. These coatings could be directly modified, in terms of composition and properties, by controlled exposure to X-rays. The physico-chemical properties of the coatings, such as hardness, refractive index and fluorescence, can be properly tuned using the interaction of hard X-rays with the sol-gel hybrid films. The changes in the microstructure have been correlated especially with the modification of the optical and the mechanical properties. A relationship between the degradation rate of the organic groups and the rise of fluorescence from the hybrid material has been observed; nanoindentation analysis of the coatings as a function of the X-ray doses has shown a not linear dependence between thickness and film hardness.

In situ growth of Ag nanoparticles in graphene–TiO2 mesoporous films induced by hard X-ray

The controlled growth of Ag nanoparticles into graphene–TiO2 mesoporous films has been triggered by hard X-ray exposure provided by a synchrotron storage ring. The kinetic process has been studied by UV–visible spectroscopy as a function of the X-ray dose and compared to the nanoparticle growth induced in a bare mesoporous titania matrix. The graphene layers act as a preferential nucleation sites, allowing a faster nucleation of the nanoparticles. Moreover, the growth of larger nanoparticles is also promoted as a function of the exposure dose. The combined bottom-up and top-down approach to fabricate nanocomposites porous films embedding both graphene and plasmonic nanoparticles is expected to be a fundamental tool for the design of new analytical platforms based on the enhancement of the Raman signals.Graphical Abstract

Graphene Oxide-Silver Nanoparticles in Molecularly-Imprinted Hybrid Films Enabling SERS Selective Sensing

A highly sensitive and selective Raman sensor has been developed by combining molecularly imprinted cavities, silver nanoparticles, and graphene oxide into a hybrid organic-inorganic film. The molecular imprinted nanocomposite material is an advanced platform that exhibits Graphene-mediated Surface-Enhanced Raman Scattering. The sensing layers have been prepared via sol-gel process and imprinted with rhodamine 6G to obtain selective dye recognition. Graphene oxide sheets decorated with silver nanoparticles have been incorporated into the matrix to enhance the Raman scattering signal. The template molecule can be easily removed from the films by ultrasonication in ethanol. A 712-fold Raman enhancement has been observed, which corresponds to a 2.15 × 1013 count·μmol−1 signal enhancement per molecular cavity. Besides Raman enhancement, the sensing platform has shown an excellent selectivity toward the test molecule with respect to similar dyes. In addition, the material can be reused at least 10 times without any loss of performance.