Tuning the aspect ratio of arrays of silica nanochannels

Arrays of silica nanochannels (ASNCs) are ordered mesoporous silica particles with hexagonal prismatic shape. The entrances of the well-defined one-dimensional nanochannels are located on the base surfaces of the hexagonal prisms. The aspect ratio of the micrometer-sized particles (length-to-diameter ratio) can be tuned in the range of 0.8 to 2.2 by the addition of co-ions (K+ and Ca2+) to the hexadecyltrimethylammonium bromide (CTAB) templated synthesis and by an adjustment of the relative amounts of silica precursor (tetraethoxysilane) and CTAB. The length of the nanochannels can be varied between 2 and 9 μm. Co-ions thereby not only improve the regularity of the hexagonal prismatic particle shape, but also affect the diameter of the nanochannels, which lies at approximately 2.6 nm (with K+ as co-ion) and 3.2 nm (with Ca2+ as co-ion).