Direct hydrothermal synthesis of mesoporous Sn-SBA-15 materials under weak acidic conditions

Abstract A direct synthetic route for the preparation of Sn-SBA-15 materials with nSi/nSn ratios ranging from 100 to 10 under milder acidic conditions than normally employed for the preparation of Si-SBA-15 is reported. The changes in the pH conditions of the gel were made through an adjustment of the molar ratio of n H 2 O to nHCl ( n H 2 O to nHCl ratio) results in the location of Sn4+ ions, (a) at the surface of the mesopores (surface of the corona region) as a thin film of SnO2 or small aggregates (loss in mesopore area) depending on the concentration of Sn; (b) at the walls of the mesopore structure, substituting Si4+ ions (some lattice expansion and tetrahedral Sn4+ ions); and/or (c) as a part of the corona region, neutralizing the resulting Si–OH groups (a loss of micropore area and octahedral Sn4+ ions). The studies reveal that the method of preparation, n H 2 O / n HCl ratio and the nSi/nSn ratio (concentration of SnCl4) of the gel significantly influence the type of tin species in the resulting Sn-SBA-15 samples.