The present disclosure relates to a seed-growth based method for the synthesis of metal nanoparticles of controlled shape (cubes, cuboids, octahedrons) and size in an aqueous environment, without the use of shape directing agents. The method involves a first step of preparing a solution comprising water, metal seed growth nanoparticles, a metal salt comprising the same metal as the metal seed growth nanoparticles, and a reducing agent; and a second step of heating the solution to between 9 and 130° C. at a rate of between 1° C./min and 5° C./min and at a pressure of between 1 and 5 atm. The method may also be carried out in a reduced oxygen atmosphere and the concentration of oxygen disclosed in the solution may be less than the concentration of oxygen in an oxygen saturated solution.