SYNTHESIS, STABILITY AND STATE OF BORON IN BORON-SUBSTITUTED MCM-41 MESOPOROUS MOLECULAR-SIEVES

The boron-substituted MCM-41 was hydrothermally synthesized using Na2B 4O7 and H3BO3 as boron sources. The influence of the nature of the bor on source on the textural properties as well as the stability of MCM-4 1 structure and the state of boron upon different procedures such as N H3 treatment, ion-exchange, and calcination were investigated using XR D, FTIR, TEM, and B-11 MAS-NMR techniques. Na2B4O7 has proven its abil ity to improve uniform long-range ordering compared to the pure silica MCM-41 analogue. The order of the uniform hexagonal mesopores in the MCM-41 products obtained following the same synthesis conditions is B- MCM-41 prepared from Na2B4O7 > B-MCM-41 prepared from H3BO3 > pure sil ica MCM-41. The counterbalancing cations such as Na+ and NH4+ were fou nd to be operative in stabilizing tetrahedral boron while H+ induces u nstability. The ion-exchange procedures were found to be accompanied b y a partial collapse of B-MCM-41 structure. The nature of counterbalan cing cations was also found to play a role in deciding the state of bo ron and its stability during hydration/dehydration process.