Surface functionalization of SBA-15 and a nonordered mesoporous silica with a 1,4-diazabicyclo[2.2.2]octane...

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 CuCl(2+n)(n-). The specific surface areas (S(BET)) and average pore diameters (d(pore)) for SBA-15 and SMD are SBA-15, S(BET)=944 m(2) g(-1), d(pore)=9.0 nm; SMD, S(BET)=710 m(2) g(-1), d(pore)=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, S(BET)=247 m(2) g(-1), ϕ=0.95 mmol g(-1); SMD/DbCl, S(BET)=83 m(2) g(-1), ϕ=1.2 mmol g(-1). The adsorption equilibria of CuCl(2) in ethanol were characterized, and the heterogeneous stability constants, β(1) and β(2), corresponding to formation of CuCl(4)(2-) and CuCl(3)(-) anionic species adsorbed on the surface were found. Also, the effective sorption capacities (t(Q)) were determined: SBA-15/DbCl, log β(1)=4.46, log β(2)=7.10, t(Q)=0.80 mmol g(-1); SMD/DbCl, log β(1)=4.95, log β(2)=7.52, t(Q)=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(OH(2))(n)(2+) species, followed by chloride anions as the counterions.