The effect of anions of transition metal salts on the structure of modified mesostructured silica films and monoliths

Abstract

The structure of the preformed LC mesophase of water:transition metal salt ([M(H 2O) 6]X 2):acid (HX):oligo(ethylene oxide) (or Pluronics):tetramethylorthosilicate (TMOS) mixture during hydrolysis and partial polymerization of the silica source is maintained upon further polymerization and condensation of the silica species in the solid state. The liquid mixture in early stage of the silica polymerization could be casted or dip coated to a surface of a glass or silicon wafer to produce mesostructured silica monoliths and films, respectively. The silica species and ions (metal ions and anions) influence the structure of the LC mesophases (as a result, the structure of silica) and the hydrophilic and hydrophobic balance in the reaction media. The silica structure can be changed from hexagonal to cubic by increasing, for example, the nitrate salt concentration in the nitrate salt systems. A similar transformation takes place in the presence of very low perchlorate salt concentration. The salt concentration in the mesostructured silica can be increased up to 1.1/1.0 salt/SiO 2 w/w ratio, in mesostructured silica materials by maintaining its lamella structure in P123 and cubic in the C n EO m systems. However, the materials obtained from the P123 systems undergo transformation from lamella to 2D hexagonal upon calcinations. The method developed in this work can be used to modify the internal surface of the pores with various transition metal ions and metal oxides that may find application in catalysis.