Hierarchically structured biphenylene-bridged periodic mesoporous organosilica

Abstract

Novel composites of highly ordered and stable biphenyl-bridged periodic mesoporous organosilica (PMO) materials confined within the pores of anodic alumina membranes (AAM) were successfully synthesized by evaporation-induced self-assembly (EISA). 4,4′-Bis(triethoxysilyl)biphenyl (BTEBP) was used as a precursor in combination with the ionic surfactant cetyltrimethylammonium bromide (CTAB) or triblock-copolymer F127 as structure-directing agents. The resulting mesophases were characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). With ionic CTAB as a structure directing agent, samples with a mixture of the 2D-hexagonal columnar and a lamellar mesophase were obtained within the AAM channels. When using the nonionic surfactant F127, mesophases with a 2D-hexagonal circular structure were formed in the AAM channels. Additionally, a cubic Imm phase could also be obtained with the same nonionic surfactant after the addition of lithium chloride to the precursor solution. The stability of both the circular and cubic biphenylene-bridged PMO against calcination temperatures of up to 250 °C was confirmed by NMR spectroscopy. Nitrogen sorption in the porous composite membrane shows typical type IV isotherms and narrow pore size distributions. All the biphenyl PMO/AAM composites show fluorescence due to the existence of biphenyl chromophores in the stable organosilica framework.