SEM. For MIL-96, HPAM is proven effective in changing the MOF particle morphology as observed in Figure . Generally, starting from the normally reported small hexagonal bipyramidal shaped (HB) crystals, higher HPAM concentrations facilitate incremental increases in the aspect ratio (length : diameter), transitioning from hexagonal spindles (HS) to elongated hexagonal rods (HR), particularly when 20 mL HPAM was used (MIL-96-RHPAM2). Upon closer inspection from out-of-plane PXRD measurements, the apparent HS morphology was revealed to be a hybrid form of two elongated hexagonal pyramids seamlessly connected at the long axis. It was reported that the hydrothermal synthesis conditions for MIL-96 must be strictly controlled given the possibility of forming two larger pore Al trimesates, MIL-100 and MIL-110, in the same reaction system despite all having distinct crystal structures. MIL-100 is the kinetically stable product which forms at short reaction times and low pH condition whereas the thermodynamically favored MIL-96 can be obtained after longer reaction times. MIL-110, on the other hand, crystallizes in a much more acidic or basic medium. Their corresponding crystal morphologies have also been solved with MIL-96, MIL-100 and MIL-110 presenting a flat hexagonal, an octahedral and a hexagonal needle-like habits respectively. Therefore, the influence of HPAM on the crystal morphology agrees well with the stability order of these phases; MIL-96 > MIL-110 > MIL-100.