Mesoporous silica microparticles with an average diameter of up to about 50 µm synthesized by a method comprising: preparing a sol from an ammonium catalysed hydrolysis and condensation reaction of a pre-sol solution comprising a silica precursor and a structure directing agent dissolved in a mixed solvent system comprising an alcohol and water; hydrothermally treating the particles to increase the pore size; treating the particles to remove residual structure directing agent; and further increasing the pore size using controlled dissolution.