Introducing a dual-step procedure comprising microwave and electrical heating stages for the morphology-controlled synthesis of chromium-benzene dicarboxylate, MIL-101(Cr), applicable for CO adsorption.

MIL-101(Cr) crystals were synthesized through a dual-step procedure consisting of a short term nucleation step in which the solution mixture was heated using microwave irradiation (MW phase) followed by a long-term growth step in which conventional electrical heating (CE phase) was used as a source of energy. The primary objective of such segregation is to increase the nuclei population at the end of the nucleation step. As a result of the high population density of nuclei, it is expected that the total time required to grow crystals in the CE phase decreases. The results showed that using the dual-step procedure led to a significant reduction in total synthesis time. The results also revealed that increasing pH from around 1.5 to 3 at the beginning of the CE phase resulted in producing octahedral crystals instead of a multifaceted sphere. Octahedral crystals exhibit higher CO adsorption capacity than the multifaceted ones. Using the dual step procedure, one can not only control the morphology but also reduce the total synthesis time of MIL-101(Cr) crystals.