Microwave assisted green chemistry approach of sodium metaborate dihydrate (NaBO2·2H2O) synthesis and use as raw material for sodium borohydride (NaBH4) thermochemical production

In the present study, a novel microwave assisted method has been developed for sodium metaborate dihydrate (NaBO₂·2H₂O) synthesis. Anhydrous NaBO₂, a derivative of borax, is an industrially and technologically important boron compound used as a raw material for the thermochemical production of sodium borohydride (NaBH₄). The effects of different microwave treatment conditions such as microwave power (90, 270 and 360 W) and irradiation time (1, 2, and 5 min) on the synthesis of NaBO₂·2H₂O were examined. After microwave irradiation at 270 W for 1 min, NaBO₂ crystals with 2 molar equivalents of water were formed. Anhydrous NaBO₂ was obtained following incubation at 400 °C for 33 min under calcination conditions. Then the resulting anhydrous NaBO₂ powder was reacted with MgH₂ under 60 bar hydrogen atmosphere at 470 °C, leading to successful production of NaBH₄ with 93% yield.