Surface functionalization of SBA-15 and a nonordered mesoporous silica with a 1,4-diazabicyclo[2.2.2]octane derivative: Study of CuCl2 adsorption from ethanol solution

This work describes the preparation and characterization of postfunctionalized ordered (SBA-15) and nonordered (SMD) mesoporous silicas with n  -propyl-1,4-diazoniabicycle[2.2.2]octane chloride (DbCl) moiety. The main interest is based on the fact that these materials are excellent adsorbents due to the ability of functional groups to retain copper chlorides on their surfaces as anionic complexes CuCl2+nn-. The specific surface areas (SBET) and average pore diameters (dpore) for SBA-15 and SMD are SBA-15, SBET = 944 m2 g−1, dpore = 9.0 nm; SMD, SBET = 710 m2 g−1, dpore = 11 nm. On functionalization with DbCl, reductions in the specific surface areas of the resulting materials (SBA-15/DbCl and SMD/DbCl) are observed and the following functionalization degrees (ϕ) were determined: SBA-15/DbCl, SBET = 247 m2 g−1, ϕ = 0.95 mmol g−1; SMD/DbCl, SBET = 83 m2 g−1, ϕ = 1.2 mmol g−1. The adsorption equilibria of CuCl2 in ethanol were characterized, and the heterogeneous stability constants, β1 and β2, corresponding to formation of CuCl42- and CuCl3- anionic species adsorbed on the surface were found. Also, the effective sorption capacities (tQ) were determined: SBA-15/DbCl, log β1 = 4.46, log β2 = 7.10, tQ = 0.80 mmol g−1; SMD/DbCl, log β1 = 4.95, log β2 = 7.52, tQ = 0.75 mmol g−1. Regeneration of the adsorbents requires a very simple procedure consisting of their immersion in aqueous solution followed by immediate release to the solution phase of the Cu(OH2)n2+ species, followed by chloride anions as the counterions.

Adsorption isotherms of CuCl2 (in ethanol) on mesostructured silicas and an illustrative scheme showing the porous ordering effect on the functionalization and adsorption processes..Figure optionsDownload high-quality image (107 K)Download as PowerPoint slideResearch highlights
► The nonordered mesostructure experienced higher agglomeration of functional groups.
► Higher effective sorption capacity was observed for SBA-15.
► The equilibrium constants for CuCl2 adsorption are similar for both silicas.
► Regeneration of the adsorbents consists only in their immersion in aqueous solution.
► The studied materials are potential adsorbents for ethanol fuel purification.