Facile synthesis of nanoporous nickel phosphates without organic templates under microwave irradiation

The syntheses of two nanoporous nickel phosphates, VSB-1 and VSB-5, have been investigated to elucidate the effect of various synthesis parameters such as pH, type of base, reaction time, and heating method. The pH is found to be the most important factor to direct the structure in the synthesis. These molecular sieves are easily synthesized in a suitable pH range even without organic template molecules. VSB-1 is crystallized only in acidic conditions (pH = 3.5-4.8), while VSB-5 is prepared in weakly basic conditions (pH = 7.5-9.2). The reaction yield of VSB-1 increases with increasing pH, while VSB-5 shows the opposite trend. Compared with conventional hydrothermal synthesis, the microwave irradiation method increases the reaction rates of the two nickel phosphates by about 60 times, and the synthesis of VSB-1 and VSB-5 can be completed within l min at 190 and 180°C, respectively. It is demonstrated that the molecular sieves can be synthesized continuously under microwave irradiation due to these fast crystallizations.