Surface functionalization of SBA-15 and a nonordered mesoporous silica with a 1,4-diazabicyclo[2.2.2]octane derivative: Study of CuCl sub(2 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 [inline image]. The specific surface areas (S sub(BET) and average pore diameters (d) sub(p)ore) for SBA-15 and SMD are SBA-15, S sub(BET = 944 m[super]2 g[super]-1, d) sub(p)ore = 9.0 nm; SMD, S sub(BET = 710 m[super]2 g[super]-1, d) sub(p)ore = 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 () were determined: SBA-15/DbCl, S sub(BET = 247 m[super]2 g[super]-1, [inline image] = 0.95 mmol g[super]-1; SMD/DbCl, S) sub(B)ET = 83 m[super]2 g[super]-1, [inline image] = 1.2 mmol g[super]-1. The adsorption equilibria of CuCl sub(2 in ethanol were characterized, and the heterogeneous stability constants, beta ) sub(1) and beta sub(2, corresponding to formation of [inline image] and [inline image] anionic species adsorbed on the surface were found. Also, the effective sorption capacities (t) sub(Q)) were determined: SBA-15/DbCl, log beta sub(1 = 4.46, log beta ) sub(2) = 7.10, t sub(Q = 0.80 mmol g[super]-1; SMD/DbCl, log beta ) sub(1) = 4.95, log beta sub(2 = 7.52, t) sub(Q) = 0.75 mmol g[super]-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 [inline image] species, followed by chloride anions as the counterions.