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Adjustments of the curing temperature and silica content were used to improve the corrosion protection properties of an organic–inorganic hybrid (OIH) coating based on a polyurethane-silica (SPU) system. Fourier transform infrared and nuclear magnetic resonance (13C and 29Si NMR) spectroscopy analyses revealed the conversion of urethane groups to secondary amines, with concomitant condensation of Si–R to Si–O–Si, when the curing temperature was increased, while small-angle X-ray scattering analysis showed the formation of denser and less branched aggregates of the inorganic framework. The silica content influenced the roughness and thickness of the coatings, with values in the ranges 1.6–9.6 nm and 1.7–6.5 μm, respectively. All the hybrid coatings deposited on steel presented impedance modulus at the lowest frequency (|Z5|) above 0.1 GΩ cm2throughout the 28 days of analysis. The SPU coating prepared using a TEOS/APTES ratio of 1 and a curing temperature of 167 °C presented the best performance as a corrosion protection barrier, characterized by predominant capacitive behavior and the invariance of |Z5| over 10 GΩ cm2.

In this work, structural and active corrosion inhibition effects induced by lithium ion addition in organic–inorganic coatings based on poly(methyl methacrylate) (PMMA)-silica sol–gel coatings have been investigated. The addition of increasing amounts of lithium carbonate (0, 500, 1000, and 2000 ppm), yielded homogeneous hybrid coatings with increased connectivity of nanometric silica cross-link nodes, covalently linked to the PMMA matrix, and improved adhesion to the aluminum substrate (AA7075). Electrochemical impedance spectroscopy (EIS), performed in 3.5% NaCl aqueous solution, showed that the improved structural properties of coatings with higher lithium loadings result in an increased corrosion resistance, with an impedance modulus up to 50 GΩ cm2, and revealed that the lithium induced self-healing ability significantly improves their durability. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) suggest that the regeneration process occurs by means of lithium ions leaching from the adjacent coating toward the corrosion spot, which is restored by a protective layer of precipitated Li rich aluminum hydroxide species. An analogue mechanism has been proposed for artificially scratched coatings presenting an increase of the impedance modulus after salt spray test compared to the lithium free coating. These results evidence the active role of lithium ions in improving the passive barrier of the PMMA-silica coating and in providing through the self-restoring ability a significantly extended service life of AA7075 alloy exposed to saline environment.

Cement-based products are the synthetic materials most used by humans, with consequent environmental impacts. One strategy that can assist in mitigating the adverse environmental effects of these materials involves the incorporation of multifunctional nanostructured additives. The objective of this work was to demonstrate the efficacy of incorporating mixed oxides (MO) derived from layered double hydroxides (LDH) to control the rheology and porosity of cement-based matrices. Thermal aging of LDH enabled the preparation of MO with different specific surface areas (SSA) for incorporation in different amounts in Portland cement. A low proportion of MO and low SSA increased workability by 22%. In contrast, a high proportion of MO and high SSA led to a 2.4-fold acceleration of cement consolidation and a 36.9% decrease of the porosity of the composite. These features could be attributed to additive–matrix interactions, with the LDH memory effect playing key roles in the cement crystal seed process and in competition for the absorption of free water within the cement paste. Therefore, the unprecedent results obtained suggest that the quantity and SSA of MO are key parameters to fine-tune the paste rheology and structure of hidrated cement. The MO materials showed easy adaptability and excellent potential for use as multifunctional additives in the production of eco-friendly, high-performance cement paste formulations with controllable properties according to the desired application.

The ability of assembling inorganic, organic, and even bioactive components in a single material unfolds an exciting direction in the development of novel multifunctional hybrid materials. Recently, we have observed that the hydrophilic/hydrophobic character of the organic polymeric moieties determines the swelling/diffusion control of the drug release. In this work, the antitumor cisplatin (CisPt) molecules incorporated into the ureasil−PEO (poly(ethylene oxide)) hybrid material was used as a probe for the in situ and simultaneous UV−vis and Raman spectroscopies monitoring of the kinetics of both the water uptake as well as the CisPt release by the hybrid matrix. Drug molecules were incorporated during the hydrolysis and polycondensation steps. The monolithic xerogel were analyzed by X-ray absorption spectroscopy and differential scanning calorimetry, while the drug release properties were monitored by Raman as well as UV−vis spectroscopies. The results show that the molecular structure of the CisPt is preserved in the one pot sol−gel route used in synthesizing the CisPt-loaded PEO1900 hybrid. The in situ monitoring of water uptake clearly points out the key contribution of the osmotic flow on the stepped profile of the CisPt delivered from the PEO1900 hybrid matrix.

In this article, we demonstrate that each functional group of ureasil organic–inorganic hybrid (OIH) materials can act as a specific coordination site for a given active guest species, hence allowing the possibility of combining different functional properties. To illustrate this concept, the sol–gel process was used to produce diurea cross-linked siloxane–polyethylene oxide (U–PEO) and siloxane–polypropylene oxide (U–PPO) hybrid host frameworks with similar molecular weights (1900 and 2000 g mol–1for PEO and PPO, respectively), with Li+and Eu3+as active guest ions providing ionic conduction and photoluminescence (PL) properties, respectively. Comparison of Fourier transform infrared spectra and small-angle X-ray scattering results for single-doped (using Li+or Eu3+) and co-doped (using Li+and Eu3+) U–PEO and U–PPO hosts showed that in every case, there was specific coordination of Eu3+by the carbonyl group of the urea bridge and of Li+by ether-type oxygen of the PEO and PPO chains. Optical analyses demonstrated that loading with Li+did not affect the luminescence properties of the Eu3+-loaded OIH. Although loading with Eu3+had a small effect on ionic transport, co-doping with Li+ions ensured macroscopic ion-conduction of the transparent and luminescent hybrid material. The results suggested that the combination of both properties in a transparent elastomeric material could be useful for the development of multifunctional devices. The results suggested that the combination of both properties in a transparent elastomeric material could be useful for the development of multifunctional polyelectrolytes applied in the field of dual luminescent devices such as photoelectrochromic smart windows.

In this work, we report the effects of incorporation of variable amounts (1–20 wt %) of sodium montmorillonite (MMT) into a siloxane–poly(ethylene oxide) hybrid hydrogel prepared by the sol–gel route. The aim was to control the nanostructural features of the nanocomposite, improve the release profile of the sodium diclofenac (SDCF) drug, and optimize the swelling behavior of the hydrophilic matrix. The nanoscopic characteristics of the siloxane-cross-linked poly(ethylene oxide) network, the semicrystallinity of the hybrid, and the intercalated or exfoliated structure of the clay were investigated by X-ray diffraction, small-angle X-ray scattering, and differential scanning calorimetry. The correlation between the nanoscopic features of nanocomposites containing different amounts of MMT and the swelling behavior revealed the key role of exfoliated silicate in controlling the water uptake by means of a flow barrier effect. The release of the drug from the nanocomposite displayed a stepped pattern kinetically controlled by the diffusion of SDCF molecules through the mass transport barrier created by the exfoliated silicate. The sustained SDCF release provided by the hybrid hydrogel nanocomposite could be useful for the prolonged treatment of painful conditions, such as arthritis, sprains and strains, gout, migraine, and pain after surgical procedures.

Herein we discuss in depth the mechanisms of growth of ZnO quantum dots prepared from zinc oxyacetate ethanolic solutions by LiOH addition. The nucleation, growth and aggregation of ZnO nanocrystals were unambiguously unravelled and associated with defined families of quantum dots and well described from two kinetic models: coalescence and Ostwald ripening. The in situmonitoring by X-ray absorption spectroscopy combined with UV–vis spectroscopy allows the determination of the time evolution of the proportions of each family of quantum dots of characteristic sizes from a multivariate data analysis. The aggregation index was calculated from combined UV–vis absorption and small-angle X-ray scattering measurements. The growth of single quantum dot nucleus results from coalescence by pure oriented attachment between themselves, then aggregation occurs through the welding of adjacent coalesced nanocrystals. At the advanced stage the quantum dot coarsening follows the Ostwald ripening mechanism. From the higher oriented attachment efficiency observed here as compared with earlier reported studies using NaOH and KOH, we propose a unified mechanism to describe the coalescence and coarsening of ZnO nanocrystals based on the shielding caused by the adsorption of the alkali solvated cations around the nanocrystals. This latter shielding effect has been also proved to be very efficient for the preparation of quantum dot powder with controlled size as demonstrated by X-ray diffraction and transmission electron microscopy.

Carbon nanotubes (CNTs) and graphene oxide (GO) have been used to reinforce PMMA-siloxane-silica nanocomposites considered to be promising candidates for environmentally compliant anticorrosive coatings. The organic–inorganic hybrids were prepared by benzoyl peroxide (BPO)-induced polymerization of methyl methacrylate (MMA) covalently bonded through 3-(trimethoxysilyl)propyl methacrylate (MPTS) to silica domains formed by hydrolytic condensation of tetraethoxysilane (TEOS). Single-walled carbon nanotubes and graphene oxide nanosheets were dispersed by surfactant addition and in a water/ethanol solution, respectively. These were added to PMMA-siloxane-silica hybrids at a carbon (CNT or GO) to silicon (TEOS and MPTS) molar ratio of 0.05% in two different matrices, both prepared at BPO/MMA molar ratios of 0.01 and 0.05. Atomic force microscopy and scanning electron microscopy showed very smooth, homogeneous, and defect-free surfaces of approximately 3–7 μm thick coatings deposited onto A1020 carbon steel by dip coating. Mechanical testing and thermogravimetric analysis confirmed that both additives CNT and GO improved the scratch resistance, adhesion, wear resistance, and thermal stability of PMMA-siloxane-silica coatings. Results of electrochemical impedance spectroscopy in 3.5% NaCl solution, discussed in terms of equivalent circuits, showed that the reinforced hybrid coatings act as a very efficient anticorrosive barrier with an impedance modulus up to 1 GΩ cm2, approximately 5 orders of magnitude higher than that of bare carbon steel. In the case of GO addition, the high corrosion resistance was maintained for more than 6 months in saline medium. These results suggest that both carbon nanostructures can be used as structural reinforcement agents, improving the thermal and mechanical resistance of high performance anticorrosive PMMA-siloxane-silica coatings and thus extending their application range to abrasive environments.

The influence of benzoyl peroxide (BPO) on the synthesis of polysiloxane thin films doped with Ce(III) deposited onto Sn coated steel as well as their anticorrosion properties are reported. The addition of BPO, whose role is polymerize the film, showed an increase in |Z| values due to the fact that augments the crossed link bonds and therefore improves the protective feature of the film. Ce(III) does not act in the polymerization process and thus is essential the addition of BPO to obtain more resistant polysiloxane films.

The processes of formation, aggregation, and growth of ZnO quantum dots (Qdot) induced by the addition of KOH solution ([OH]/[Zn] = 0.5) to the zinc oxy-acetate ethanolic solution at 40 °C were examined in depth by in situ and simultaneous time-resolved monitoring of UV−vis absorption spectra combined with small-angle X-ray scattering (SAXS) and with X-ray absorption fine structure (XAFS) measurements. XAFS results recorded at the Zn K-edge evidence the presence of both the zinc oxy-acetate precursor and the ZnO nanocrystals. Each XAFS spectrum could be described by a linear combination of each reference spectra, the composition evolving from ∼47% to ∼82% of ZnO from the beginning to the end of time monitoring. The time evolution of the UV−vis spectra shows a pronounced red shift of the excitonic peak during the first 100 min of reaction, characterizing the ZnO Qdot growth. The SAXS curves obtained simultaneously with the UV−vis spectra follow the Porod law at the large q-range, indicating the presence of well-defined smooth surface particles. At the intermediate q-range, the SAXS profiles evolve from a Guinier pattern, typical of diluted sets of aggregates, to a power law dependence characteristic of fractal structures. For reaction times higher than 400 min, the slope of the fractal region of SAXS curves reaches a value characteristic of diffusion controlled cluster−cluster aggregation process. The results of this in situ and combined techniques investigation show that the kinetic of formation of colloidal ZnO nanocrystal is a step process composed of four main stages: (i) ZnO Qdot nucleation and growth; (ii) growth of compact ZnO Qdot aggregates; (iii) growth of fractal aggregates; and (iv) secondary nucleation and fractal aggregates growth.

In this paper, the thermo-reversible sol−gel transition of titanium poly oxo building blocks dispersed in a solution of p-toluene sulfonic acid (PTSH) in isopropanol is reported. The sol formed by the thermo-hydrolysis at 60 °C of titanium tetraisopropoxide (Ti(OiPr)4) reversibly changes into a gel upon cooling. A large domain of formulations (β-domain) presenting this thermo-reversible behavior has been obtained for samples containing different nominal acidity (A= [PTSH]/[Ti]) and hydrolysis (H= [H2O]/[Ti]) ratios. The EXAFS study of the β-domain evidences the formation of different titanium poly oxo building blocks, depending on the formulation, for which the local-order structure does not change upon sol−gel transition. This result points out that the thermo-reversible behavior is linked to interfacial properties of these building blocks. SAXS results indicate that the thermo-reversible gelation is associated to a reversible aggregation of a disperse set of building blocks. The presence of both immobilized and free PTSH species was revealed by Raman and 1H NMR spectroscopies. Furthermore, NMR clearly evidences the significant decrease of free PTSH amount during the sol−gel transition. In the light of the different structural investigations, we propose that the thermo-reversible gelation is induced by the formation of a supramolecular network, in which the protonated surface of building blocks and/or aggregates are interconnected through cooperative bonds between the PTSH molecules.

Excitation and dynamic emission spectra of Eu3+ ions were simultaneously used with FTIR and Raman spectroscopy to study the structural evolution during SnO2 sol ? gel ? xerogel conversion. Results make evident an increase of the surroundings symmetry for the Eu3+ ions dissolved in SnO2 matrix and a decrease of the amount of hydroxo groups (Sn-OH) during drying. These phenomena were associated to the pursuit of the condensation reaction after gelation.

In order to determine structural changes during drying of inorganic gels, the local and long-range order structure of SnO2-x(OH)2x xerogels resulting from drying hydrogels with different concentrations of electrolyte (Cl− and NH+4) have been measured by extended X-ray absorption fine structure (EXAFS), X-ray diffraction (XRD) and N2 adsorption techniques. EXAFS measurements performed at the Sn K edge on the hydrogels and xerogels show the existence of microcrystallites with the cassiterite structure. Two drying modes have been used: freeze drying and drying by evaporation at 45°C. It is shown that the microcrystallite size determined by XRD and EXAFS techniques on the drying mode and on the electrolyte concentrations. The microcrystallite size measured on the freeze dried xerogels is similar to that of their parent hydrogels, whatever the concentration of electrolyte; however, during drying by evaporation, a preferential growth of microcrystallites along the c-axis of the cassiterite structure is observed. The size of these crystallites is enhanced with a decrease of the electrolyte concentration. Specific surface areas calculated by the Brunauer-Emmett-Teller method indicate that this preferential growth is related to the improvement of the network connectivity. The comparison of both drying processes indicates that crystallization and polycondensation are independent phenomena.

Acetaldehyde is an important chemical commodity and a building block for producing several other high-value products in the chemical industry. This has motivated the search for suitable, efficient, stable, and selective catalysts, as well as renewable raw materials such as ethanol. In this work, supported copper catalysts were prepared from CuZnAl layered double hydroxides (LDHs) with different copper contents (5, 10, and 20 wt %) for application in the ethanol dehydrogenation reaction (EDR). The samples were thoroughly characterized by a series of techniques, which allowed for analysis of all of the copper and zinc species involved in the different catalyst preparation steps and during the EDR. The results obtained by in situ quick extended X-ray absorption fine structure (EXAFS) measurements, combined with multivariate data analysis, showed that the copper content in the pristine LDH influenced the phase composition of the mixed oxide support, which consequently affected the dispersion of copper nanoparticles. The higher the copper content, the higher are the ZnAl2O4and zinc tetrahedral prenuclei (TPN) contents, to the detriment of the ZnO content. All the samples showed high selectivity (>97%) and stability in the catalytic reactions at 300 and 350 °C, with no observed deactivation during 6 h on-stream. Although the samples with lower copper content presented higher copper dispersion and reactivity, the sample containing 20 wt % of copper outperformed the others, with greater conversion and higher activity toward acetaldehyde.

The influence of benzoyl peroxide (BPO) on the synthesis of polysiloxane thin films doped with Ce(III) deposited onto Sn coated steel as well as their anticorrosion properties are reported. The addition of BPO, whose role is polymerize the film, showed an increase in |Z| values due to the fact that augments the crossed link bonds and therefore improves the protective feature of the film. Ce(III) does not act in the polymerization process and thus is essential the addition of BPO to obtain more resistant polysiloxane films.