Effective and Selective Trapping of Volatile Organic Sulfur Derivatives by Montmorillonite Intercalated with a μ-oxo Fe(III)–Phenanthroline Complex

Abstract

The μ-oxo Fe(III)-phenanthroline complex [(OH)(Phen)FeOFe(Phen) (OH)] intercalated in montmorillonite provides a stable hybrid material. In this study, the ability and efficiency of this material to immobilize thiols in gas phase, acting as a trap at the solid-gas interface, were investigated. Aliphatic thiols containing both hydrophilic and hydrophobic end groups were chosen to test the selectivity of this gas trap. DR-UV-vis, IR, elemental analysis, thermal analysis and evolved gas mass spectrometry, X-ray powder diffraction, and X-ray absorption spectroscopy techniques were employed to characterize the hybrid material before and after thiol exposure and to provide information on the entrapping process. Thiol immobilization is very large, up to 21% w/w for heptanethiol. In addition, evidence was obtained that immobilization occurs through the formation of a covalent bond between the iron of the complex and the sulfur of the thiol. This provides an immobilization process characterized by a higher stability with respect to the methods based on physi-adsorption. Thiol immobilization resulted thermally reversible at least for 20 adsorption/desorption cycles. Unlike standard desulfurization processes like hydrotreating and catalytic oxidation which work at high temperatures and pressures, the present system is able to efficiently trap thiols at room temperature and pressure, thus saving energy. Furthermore, we found that the selectivity of thiol immobilization can be tuned acting on the amount of complex intercalated in montmorillonite. In particular, montmorillonite semisaturated with the complex captures both hydrophobic and hydrophilic thiols, while the saturated montmorillonite shows a strong selectivity toward the hydrophobic molecules.

Structural properties of adsorbent phyllosilicates rule the entrapping ability of intercalated iron-phenanthroline complex towards thiols

“…The UV-Vis spectra of Fe 3+ phen in solution, obtained at different concentrations, were reported by Bernini et al [20][21][22]. Fe charge-transfer transition) at λ = 356 nm and two additional bands at 223 and 266 nm attributable to the aromatic ligand.…”

“…In particular the broad band with maximum at λ = 324 nm can be assigned to the above mentioned O 2− (bridge) → Fe 3+ charge-transfer transition, typical for the ferric form of the complex. All the spectra of sepiolite samples treated with Fe 3+ phen and exposed to HPT show a composite band with the maximum at λ = 518 nm, also observed for Fe 2+ -phenanthroline complex in solution [22]. Also in this case, the signal corresponds to the d → π* metal-to-ligand charge transfer band of the Fe 2+ -phenanthroline complex.…”

“…-phenanthroline complex, both on external surfaces and in the interlayer, assumes a bi-dimensional disposition. Montmorillonite treated with Fe 3+ phenanthroline can be used for the removal of sulfur containing phases from waste gasses [22,23], similarly to synthetic phases commonly used for the same purpose [24]. In sepiolite, hosted molecules, such as indigo, are expected to interact with water located inside structural channels due to the absence of layer charge and the needle-like morphology of the mineral, thus defining a linear rather than a bi-dimensional distribution [10,25].…”

Organosulfur adsorbents by self-assembly of titania based ternary metal oxide nanofibers

“…The adsorption capacity of thiols by CuO/La 2 O 3 /TiO 2 nanobers is more than three times than that observed on Au/TiO 2 , 34 and it is comparable with the results of thiol adsorption capacity of an Fe(III) complex supported on nano-clays. 35 The strong adsorption of thiols on the adsorbents was also conrmed by using SEM/EDS analysis (see ESI †).…”

“…In this area of materials research, recently Bernini et al reported the adsorption of thiols on nano-clay modied with Fe(III) phenanthroline complexes; however, the adsorption selectivity of thiols is unknown in the H 2 S and CO 2 containing gas stream. 35 Also recently, our laboratories have reported that commercial Au/TiO 2 products are good potential adsorbents for the selective adsorption of thiols while allowing H 2 S and CO 2 slip through; however, the conversion of the anatase TiO 2 support to rutile TiO 2 caused the material capacity to degrade over several thermal regeneration cycles. 34 In this study, lanthanum was added in the Cu group species doped TiO 2 to promote the thermal stability via a onepot sol-gel route, which is thought to be more amenable for commercialization.…”