Monolithic porous silica xerogels were synthesized by the sol-gel process, and their local structure was analysed by vibrational spectroscopy. The silica alcogels were prepared by a two-step hydrolytic polycondensation of tetraethoxysilane (TEOS) in isopropanol, with a water/TEOS molar ratio of 4. The hydrolysis step was catalysed by hydrochloric acid (HCl), with different HCl/TEOS molar ratios (ranging from 0.0005 to 0.009), and the condensation step was catalysed by ammonia (NH(3)), with different NH(3)/HCl molar ratios (ranging from 0.7 to 1.7). After appropriate ageing, the alcogels were washed with isopropanol and subcritically dried at atmospheric pressure. The diffuse reflectance infrared Fourier transform (DRIFT) spectra were analysed in terms of the main siloxane rings that form the silica particles, taking into account the splitting of the nu(as)Sibond;Obond;Si mode into pairs of longitudinal and transverse optic components, by long-range Coulomb interactions. It was proven that the proportion of residual silanol groups (which correlates with hydrophilicity), and the fraction of siloxane 6-rings (which correlates with porosity) may be tailored by adequate catalytic conditions, mostly by the hydrolysis pH. This was explained in terms of the reactions' mechanisms taking place in the two-step sol-gel process followed.
Pectin
and d-limonene were extracted from waste
orange and lemon peel by an innovative eco-friendly process using
only water as dispersing medium and microwaves as energy source. Both
bioproducts were characterized by diffuse reflectance infrared (DRIFT)
spectroscopy, and the pectin samples also by scanning electron microscopy
(SEM). For pectin and essential oils extracted from waste lemon peel,
the results obtained at laboratory and semi-industrial scales are
compared. The high yields obtained, the quality of the bioproducts
and the environmental viability of the process support forthcoming
commercialization of the technology.
Detailed diffuse-reflectance infrared Fourier transform structural analysis of a series of organically
modified silicates (ORMOSIL)-entrapped catalysts, varying the molar percentage and the alkyl chain
length of the organic group, shows that the important factors affording optimal catalytic performance are
two: predominance of six-member siloxane rings (above 80% alkylation) and a low hydrophilicity−lipophilicity balance (HLB). These results provide investigators engaged in developing novel catalysts
based on the sol−gel routean advanced chemical technology for synthetic organic/inorganic chemistrywith general guidelines to prepare optimal catalytic materials for a number of relevant applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.