A new material based on montmorillonite and Cu(II)-phenanthroline complex for effective capture of ammonia from gas phase

Abstract

The intercalation of [Cu(Phen)(H 2 O) 2 ] 2+ (CuPhen) in montmorillonite (Mt) produces a stable hybrid material that is very efficient in removing NH 3 from gas phase even at extremely low pressures.The process was studied by elemental analysis, X-ray powder diffraction, thermal analysis coupled with evolved gas mass spectrometry and DR UV-Vis, NMR and X-ray absorption spectroscopy. The adsorption of CuPhen on Mt consists of two consecutive steps. During the first one, CuPhen intercalates alone into Mt through a cation exchange process, afterwards CuPhen and SO 4 2− ions entry jointly into the mineral interlayer. The two-steps adsorption process is described by a VI-type isotherm, successfully fitted by two independent Frumkin isotherms. NH 3 trapping is long-lasting, easy, fast even at extremely low gas pressure and reversible under mild conditions. Mt containing CuPhen always results well performant in removing ammonia from gas phase, but an appreciably higher adsorption capacity of NH 3 is obtained when SO 4 2− ion is absent from the interlayer. This hybrid montmorillonite is thus a promising material to be used in industrial or environmental contexts, as an efficient air-cleaner.

Interlayer-Confined Cu(II) Complex as an Efficient and Long-Lasting Catalyst for Oxidation of H2S on Montmorillonite

“…The XRPD patterns (3 ≤ 2θ( • ) ≤ 40) of Mt-CuPhen before and after exposure are shown in Figure 4. As discussed previously [11,15], the diffraction peaks of Mt-CuPhen with respect to Mt show: (i) a shift towards higher d values of d 001 reflection (d 001 Mt = 1.51 nm; d 001 Mt-CuPhen = 1.71 nm), suggesting that CuPhen species coordinated by sulfate groups, which are about 0.71 nm thick, that occupy the interlayer positions; (ii) higher order XRD reflections, which are approximate multiples of the 2θ angle of the 001 reflection [19], suggesting the presence of more ordered domains.…”

“…The same chemicals and procedures described by the authors in a previous study were used [11]. Specifically, CuSO 4 •5H 2 O was dissolved at room temperature in a well-stirred phenanthroline (Phen) solution in order to obtain a 6 mM solution of Cu(II)Phen; Mt (50 mg) was dispersed in 10 mL of this solution, shaken for 1 h at 250 rpm at room temperature, and then separated from the liquid phase via centrifugation at 14,000× g for 1 min.…”

“…The resulting material, Mt-CuPhen, contains large amounts of Cu ions in the interlayer, 0.651 Cu 2+ moles/kg. An extensive characterization of Mt-CuPhen material was described in detail elsewhere [11].…”

“…The diffuse-reflectance (DR) UV-Vis spectra of Mt-CuPhen in the range 200 ≤ λ ≤ 1000 nm before and after exposure to H2S are shown in Figure 2. As described previously [11], when compared to Mt, Mt-CuPhen shows: (i) the appearance of a signal at λ=270 nm corresponding to the overlap of Mt (λ = 256 nm) and Cu(II)Phen (λ = 272 nm) signals; (ii) a band at λ = 300 nm (π → π* transition of phenanthroline bond to Cu 2+ ); (iii) three shoulders at λ = 316, 332, and 350 nm (related to phenanthroline transitions); (iv) a large band at about λ = 780 nm, due to Cu The H 2 S capture proceeds without reaching completion, following a pathway that differs from that reported for Mt intercalated with the µ-oxo binuclear Fe(III)-phenanthroline 1: [14]. For the latter, the H 2 S removal process occurs into two distinct steps: the former, lasting for about 20 h, is fast in the first 4 h and then slows down, while the latter is completed within about 110 h. Overall, the process lasts 110 h; eventually the exhaust material must be regenerated by a thermal treatment at 295 • C for reuse.…”

“…The diffuse-reflectance (DR) UV-Vis spectra of Mt-CuPhen in the range 200 ≤ λ ≤ 1000 nm before and after exposure to H 2 S are shown in Figure 2. As described previously [11], when compared to Mt, Mt-CuPhen shows: (i) the appearance of a signal at λ = 270 nm corresponding to the overlap of Mt (λ = 256 nm) and Cu(II)Phen (λ = 272 nm) signals; (ii) a band at λ = 300 nm (π → π* transition of phenanthroline bond to Cu 2+ ); (iii) three shoulders at λ = 316, 332, and 350 nm (related to phenanthroline transitions); (iv) a large band at about λ = 780 nm, due to Cu 2+ d → d transition); and (v) a band at λ = 920 nm, most likely associated to H 2 O molecules (overtone) related to Cu 2+ , due to the adsorbed Cu(II)Phen.…”