Abstract
Abstract The interaction of volatile organic sulfur derivatives, such as 1-heptanethiol (C7H16S), with clay minerals treated with a μ-oxo Fe3+-phenanthroline 1:1 complex results strongly affected by crystal chemical properties of pristine mineral phases. In particular, two sepiolite clays with different structural features demonstrated significantly different ability to immobilize the Fe3+-phenanthroline complex at two pH values (pH = 5.4 and pH = 2.3). The most effective binding was obtained with sepiolite with higher structural disorder at pH 5.4. Accordingly, the resulting hybrid material showed also the greatest efficiency in removal of thiol in gas phase. A direct correlation can be established between the adsorption of the Fe3+-phenanthroline complex and the gas binding process at room temperature. In fact, 1-heptanethiol entrapping occurs via redox reactions between Fe3+ and a first thiol molecule to give the reduced Fe2+-phenanthroline complex and disulfide, followed by the binding of further thiols to the reduced metal centre. The extremely high amount of thiol immobilized by the hybrid material also suggests the co-presence of a catalytic mechanism that guarantees the reoxidation of Fe+2 to Fe+3 and the restoration of redox reactions with thiol. Investigation and conclusions were supported by the several experimental techniques: elemental analysis, X-ray powder diffraction analyses, UV–Vis measurements, FT-IR and NMR spectroscopies, thermogravimetric analyses.
Highlights
Volatile organic sulfur derivatives, such as 1-heptanethiol (C7 H1 6S), are smelly pollutants commonly observed in natural environments and as a result of human activities
Elemental analysis shows that C and N increase in sepiolite treated with Fe3 +phen, indicative for adsorption of the iron complex
The data, indicate that the amount of complex adsorbed by sepiolite (0.073, 0.048, 0.152, and 0.087 mol/Kg sepiolite for Sepiolite SP-1 (SP1) Fe3 +phenp H=5.4, SP1 Fe3 +phenp H=2.3, Sepiolite EB (EB)-Fe3 +phenp H=5.4, EB-Fe3 +phenp H=2.3, respectively) is much lower than that immobilized by montmorillonite (0.434 mol/Kg Mt)
Summary
Volatile organic sulfur derivatives, such as 1-heptanethiol (C7 H1 6S), are smelly pollutants commonly observed in natural environments and as a result of human activities. Sepiolite structure (unit cell parameters a × b × c = 13.405 × 27.016 × 5.275 Å3 , α = β = γ = 90°) consists of an alternation of blocks and cavities that grow up along the fibres direction (c-axis). Each block consists of two tetrahedral sheets (T) sandwiching an octahedral sheet (M). The T sheet is continuous, thanks to a periodic inversion in the orientation of the apical oxygen atoms, which point alternatively up and down, bonding either to the upper or to the lower discontinuous M sheet. Tunnels measure approximately 3.7 × 10.6 Å2 in cross section and account in large part for the high specific surface area and excellent sorption properties related to several active sites, i.e., i) OH-anions coordinated to Mg octahedral sites; ii) structural H2 O which completes the Mg octahedral site coordination at the edge of the tunnels; iii) four zeolitic H2 O positions inside sepiolite tunnels [4,5] (Fig. 1).
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