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Condensed clusters of hydrolyzed tetramethylorthosilicate (TMOS), methyltrimethoxysilane (MTMS) and vinyltrimethoxysilane (VTMS), as single precursors or in combination, were studied using complementary approaches: (i) Fourier transform infrared (FTIR) spectroscopy; (ii) solid-state NMR spectroscopy, and (iii) density functional theory calculations of energies, structural and vibrational and 29Si NMR chemical shift data of pertinent TMOS, MTMS and VMTS hydrolysis products, and species with different numbers of silicon atoms and different structures/conformations (linear, cyclic, and cage), performed at the B3LYP/6-311+G(d,p) and B3LYP/IGLO-III (for NMR) levels of theory. The calculated versus experimental (FTIR and solid-state NMR spectra) analysis of the aerogel derived from a single precursor shows that: (i) the TMOS-derived aerogels are mostly made of linear and/or cyclic elements with silicon environments of types Q4, Q3 and Q1, which have four, three and one Si–O–Si bridges, respectively; (ii) the MTMS-derived aerogels are mainly based on cyclic and/or cage structures with silicon of types T3, T2 and T1; (iii) VTMS-based aerogels exhibit the same type of silicon environments as MTMS (T3, T2 and T1), but incorporate structures that can be linear/cyclic/cage-like. The 29Si NMR spectra of the aerogels prepared with the mixtures of TMOS, MTMS and VTMS allowed the quantification of the relative percentages of the constitutive precursor components in the gels, i.e. the final composition of the aerogel is in line with the composition of the prepared solutions. This result is of utmost importance as the composition of the gel affects its final properties. The integrated experimental and computational investigation on the targeted nanostructured materials reported here provides a new understanding of both the microstructures of aerogels and the condensation stage of sol–gel polymerization. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) nanoparticles are extremely attractive materials for numerous applications, especially in the anatase form. We have made these shaped, ＜10 nm anatase nanoparticles (NPs) via the supercritical (SC) drying of a titania sol, made by a “green” aqueous sol–gel nanosynthesis route. The SC drying was carried out in alcohol at 255–260 °C, and no further heating or processing of the NPs was required. The true phase composition (crystalline and amorphous phases) and the microstructure of the NPs was thoroughly characterised by the advanced X-ray methods, such as Rietveld-reference intensity ratio (RIR) and the whole powder pattern modelling (WPPM) technique, and HR-TEM analysis. Furthermore, the NPs were also characterised by Raman, FT-IR and optical spectroscopy. These anatase NPs showed themselves to exhibit a truncated tetragonal bipyramidal shape, exposing the {101} (side) and {001} (top) faces. They had a euhedral crystal habit, with sharply defined and easily recognised faces, and were very homogeneous and monodisperse in both shape and size. The photocatalytic activity (PCA) of the samples was assessed in gas–solid phase by monitoring the degradation of nitrogen oxides (NOx), a major atmospheric pollutant. Results showed that the particular shape of these anatase NPs played a key role in their photocatalytic behaviour. In fact, these truncated tetragonal bipyramidal nanocrystals exhibited an enhanced photocatalytic activity, double that of spherical anatase NPs of a similar size reported previously by the authors. This was attributed to the exposure of mainly the {101} and, to a lesser extent, {001} crystal faces, which are more reactive under photocatalysis for redox reactions. [ABSTRACT FROM AUTHOR]

Mechanically reinforced polymer–silica aerogels have been successfully prepared by using surface-initiated reversible addition-fragmentation chain transfer polymerization. With this approach, well-defined polystyrene (PSt) and poly(butyl acrylate) (PBA) with low polydispersities grew on the silica surface and improved the mechanical strength in relation to native aerogels. Moreover, it allowed establishing a structure–property relationship between the grafted polymer molecular weight and physical properties of the hybrid aerogels, thereby enabling the preparation of composites with tailored properties. The aerogel composites here obtained exhibited a low density of 0.13–0.17 g cm−3, high thermal insulation performance of 0.03–0.04 W m−1 K−1 and a high specific surface area of 350–780 m2 g−1, with approximately one order of magnitude improvement in the compression strength over the non-reinforced aerogels. [ABSTRACT FROM AUTHOR]

Petroleum comprises the monoaromatic and polycyclic aromatic hydrocarbons, which exhibit acute toxicity towards living animals. Consequently, their removal from natural environment is a priority challenge. On the other hand, biomaterials are increasingly being used as adsorbents. Pectin and chitosan are well-known polysaccharides able to form coacervate hydrogels. Aiming an increase of sorption ability by hydrophobic compounds, pectin was also functionalized with two amphiphilic compounds: β-cyclodextrin (β-CD) and poly(vinyl alcohol) (PVA). Both the modified pectin and the hydrogels were evaluated using nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The hydrogels were further characterized in terms of thermogravimetric analysis (TGA) and swelling kinetics. The interaction between the hydrogel and mix solutions containing six different aromatic compounds (BTXs and the following PAHs: pyrene, benzo(b)fluoranthene and benzo(a)pyrene) has been evaluated through sorption isotherms and kinetics. The mechanism of sorption interaction and the selectivity of the adsorbents towards different aromatic compounds were discussed. The results clearly show that the presence of β-CD and PVA into gel leads to an increase in the removal efficiency of both, BTXs and PAHs. The gels were subjected to two sorption/desorption cycles to have an assessment of the capability of adsorbents for re-use. Finally, the sorption quantification of those six aromatic compounds from a real gasoline sample onto gels has been tested., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

This work reports an efficient method for the preparation of aqueous dispersions of superparamagnetic iron oxide nanoparticles (SPIONs), involving the use of an amphiphilic block copolymer, poly(ethylene glycol)-block-poly(4-vinyl pyridine) (mPEG-b-P4VP). The iron oxide nanoparticles are easily and efficiently dispersed due to the strong direct interaction of the hydrophobic P4VP segments, through complexation with pyridine units of the copolymer. Well-defined block copolymers, having different compositions and molecular weights, were prepared by atom transfer radical polymerization (ATRP). The aqueous self-assembly behavior of each system has been compared based on the method of preparation. The results revealed that the addition of ionic species has a significant effect on the size and type of formed nanostructures, the magnitude of which is dependent on the block copolymers' molecular design. When similar self-assembly strategies were used in the presence of SPIONs, the same type of nanostructures was formed. The hybrid SPION nanoaggregates were investigated using NMR relaxometric techniques, whereby high r 2 /r 1 relaxivity ratios were achieved, making these materials potentially efficient T 2 -weighted MRI contrast agents.