Electrodissolution-Coupled Hafnium Alkoxide Synthesis with High Environmental and Economic Benefits
Graphical A green system for hafnium alkoxide synthesis was proposed. Simultaneous heterogeneous Hf dissolution and ethanol dehydrogenation followed by spontaneous solution-based binding of alkoxy with Hf 4+ ions gave Hf(OEt) 4 . After the optimum conditions – electrolyte, temperature, current densities, etc. – had been determined, a proof-of-concept experiment achieved waste-free production of Hf(OEt) 4 with high purity and yield. Besides the system‘s green credentials, it showed a high net profit of 30 477 USD per kg Hf(OEt) 4 and could be extended to the synthesis of other hafnium alkoxides. The conventional thermal method of preparing hafnium alkoxides [Hf(OR) 4 , R=alkyl] – excellent precursors for gate-dielectric HfO 2 on semiconductors – is severely hindered by its unsatisfactory environmental and economic burdens. Herein, we propose a promising electrodissolution-coupled Hf(OR) 4 synthesis (EHS) system for green and efficient electrosynthesis of Hf(OR) 4 . The operational principle of the electrically driven system consists of two simultaneous heterogeneous reactions of Hf dissolution and alcohol dehydrogenation, plus a spontaneous solution-based combination reaction. In applying ethanol as solvent and Hf metal as electrodissolution medium, we achieved waste-free production of high-purity hafnium ethoxide [Hf(OEt) 4 ] with an equivalent “a concomitant” reduction in CO 2 emission of 187.33 g CO 2 per kg Hf(OEt) 4 and a high net profit of 30 477 USD per kg Hf(OEt) 4 . This system is very competitive with the thermal process, which unavoidably releases substantial waste and CO 2 for a net profit of 27 700 USD per kg Hf(OEt) 4 . We anticipate that the environmental and economic benefits of the EHS process could pave the way for its practical application.
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