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

Abstract

The interaction of volatile organic sulfur derivatives, such as 1-heptanethiol (C 7 H 16 S), with clay minerals treated with a μ-oxo Fe 3+-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 Fe 3+-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 Fe 3+-phenanthroline complex and the gas binding process at room temperature. In fact, 1-heptanethiol entrapping occurs via redox reactions between Fe 3+ and a first thiol molecule to give the reduced Fe 2+-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.

The Copper Chemical Garden as a Low Cost and Efficient Material for Breaking Down Air Pollution by Gaseous Ammonia

“…In previous studies [24,25] it was found that the coordination chemistry of the “active” capturing cation – copper(II) in our case – drives the immobilization properties of the whole material: a proper solid functionalized with a Cu(II) complex, effective in the removal of gaseous NH 3 , can successfully work also for the immobilization of heptanethiol and H 2 S, taking advantage of the strong affinity of Cu(II) to both N and S centers. In some cases, the affinity of a metal ion for a gas species is retained also changing the host material [26] …”

“…In some cases, the affinity of a metal ion for a gas species is retained also changing the host material. [26] Experimental Methods…”

Gaseous Heptanethiol Removal by a Fe3+-Phenanthroline–Kaolinite Hybrid Material

“…36 The amount of Fe +3 Phen adsorbed by sepiolite is much closer to that of kaolinite but, as mentioned, it is affected by mineral structural ordering and ranges between 0.0048 and 0.0152 moles per 100 g of sepiolite. 39 This enhanced uptake of HPT by Kt-Fe 3+ Phen can be explained only by considering a continuous catalytic activity of Fe 3+ toward the oxidation of thiol to disulfide according to the following reaction mechanisms (water molecules were omitted in the formula of the iron compounds for the sake of clarity): This reaction mechanism only in part overlaps those already hypothesized for hybrid montmorillonite and sepiolite. Nevertheless, the available data cannot allow to distinguish if the reaction proceeds through steps ( 2) and (3) or through steps (2bis) and (3bis), namely, if the reoxidized complex is mononuclear or dinuclear or else their mixture.…”

“…Different glass containers were prepared to host 50 mg of Kt-Fe 3+ Phen and uniformly spread on the bottom of a Petri dish (diameter = 50 mm), together with a beaker containing 3 mL of HPT. As already experimented with other HCMs, 39,40 this volume is sufficient to ensure vapor saturation even in the case of a high degree of uptake. After fixed times of exposure, ranging between 12 h and 60 days, the samples were removed from the Petri dishes, air-dried for 1 h, and stored in plastic sealed containers.…”

“…36−39 Later, Fe +3 Phen-functionalized montmorillonite was successfully used to selectively capture, also at very low partial pressure of the gas, volatile organic sulfur derivatives, 39,40 hydrogen sulfide, 41 naphthalene, and Cl-naphtalene. 42 Besides, HCMs obtained adsorbing Fe +3 Phen on sepiolite demonstrated a better trapping ability toward thiols than montmorillonite, 39 even if the efficiency of this catalytic process was significantly affected by the structural features of this modulated 2:1 layer silicate. Similarly, high trapping ability toward hydrogen sulfide and ammonia gas was observed also for montmorillonite-based HCMs obtained by intercalation of the Cu 2+ -phenanthroline complex.…”