CO₂ Adsorption on Aluminosilicate Single-Walled Nanotubes of Imogolite Type

Abstract

Adsorption of CO 2 at subatmospheric pressure at temperatures about ambient has been studied on three materials: (i) imogolite (IMO, chemical formula (OH) 3 Al 2 O 3 SiOH)) a hydrated alumino-silicate occurring as nanotubes (NTs) with bridged AlOHAl groups at the outer surface and Si−OH groups at the inner surface; (ii) an imogolite-like material (Me-IMO, chemical formula (OH) 3 Al 2 O 3 SiCH 3 ) with Si-CH 3 groups replacing Si−OH at NTs inner surface; (iii) a material (Me-IMO-NH 2 ) obtained by grafting 3-aminopropylsilane at the outer surface of Me-IMO. All materials, being in the form of NTs, exhibit rather high specific surface area values (355−665 m 2 g −1 ) and are accessible to CO 2 molecules. Infrared spectroscopy shows that carbon dioxide may interact in a variety of ways. At the inner surface of IMO, linear molecular species are reversibly formed by interaction with silanols, whereas at the outer surface carbonate-like species are given rise with partial reversible character. With Me-IMO, no interaction takes place at the inner surface: linear species are formed in the intertube nanopores as well as carbonate species as in the case of IMO. Finally, with Me-IMO-NH 2 , all species present in Me-IMO are found, as well as reversible carbamate species arising from the reaction with amino groups. Optical isotherms concerning molecular adsorption have Langmuir character, whereas those for the reversible formation of carbonates/carbamates are of Henry-type. Volumetric isotherms are interpreted as due to two independent families of adsorption sites, respectively Langmuir and Henry: comparison between optical isotherms (measured at ca. 33 °C) and volumetric isotherms (measured at 0 °C) allows a semiquantitative estimate of the adsorption enthalpy for molecular species, corresponding to ca. −20 kJ mol −1 , for linear species reversibly formed by interaction with inner silanols in IMO, and to a relatively high adsorption enthalpy for molecular species formed in the larger intertube nanopores of Me-IMO (ca. −32 kJ mol −1 ).

The Role of Cation-Vacancies for the Electronic and Optical Properties of Aluminosilicate Imogolite Nanotubes: A Non-local, Linear-Response TDDFT Study

“…The growing research in the photo-catalytic potential of 3D nano- and meso-porous silicates (Sastre et al, 2012a,b; Alarcos et al, 2017; Murcia-López et al, 2017), and parallel substantial progress in the synthesis and characterization of 1D-structured aluminosilicate (AlSi) nanotubes (NTs) based on the imogolite (Imo) structure (Wada et al, 1979; Barron et al, 1982; Theng et al, 1982; Mukherjee et al, 2005, 2007; Levard et al, 2008, 2010; Kang et al, 2010, 2011, 2014; Bottero et al, 2011; Yucelen et al, 2011, 2012b; Zanzottera et al, 2012a,b; Bonelli et al, 2013; Amara et al, 2015; Monet et al, 2018), have prompted recent exploratory computational studies of the potential of Imo-NTs for photo-catalytic applications (Teobaldi et al, 2009; Zhao et al, 2009; Poli et al, 2015, 2016; Elliott et al, 2016).…”

Hybrid, Tunable-Diameter, Metal Oxide Nanotubes for Trapping of Organic Molecules

“…38 In both cases, an enhanced adsorption towards CO 2 and methane was evidenced, which could find applications in molecular separation, gas storage or catalysis. 35,37,38 While all these studies concern only silicon-based imogolite nanotubes, no data have been reported so far on germanium and Si/Ge modified nanotubes.…”

Large-scale density functional theory simulation of inorganic nanotubes: a case study on Imogolite nanotubes

“…In addition, the creation of double-walled (DW) AlGe NTs has also been achieved. [34][35][36][37] Important advances have been made in the post-synthetic, selective functionalisation of the outer or inner surface of AlSi NTs, [38][39][40] and in the direct creation of methylated (AlSiMe) 41,42 or aminated (AlSiAm) 43 AlSi NTs derivatives, with methyl (ZCH 3 , Fig. 1) or amine (ZNH 2 ) functions in the NT cavity, instead of silanol groups.…”

“…Further selective amination of the outer surface of AlSiMe NTs by post-synthesis grafting, yielding hybrid AmAlSiMe derivatives, has also been shown to be possible. 39,40 Exploration of the surface properties of these hybrid materials has revealed superior performances for chemical separation, [39][40][41][42][43][44] and results on their beneficial role as support for (photo)catalysts 45,46 as well as in hybrid nanocomposites 47 have started to appear in the literature.…”