All-in-one synthesis of mesoporous silicon nanosheets from natural clay and their applicability to hydrogen evolution

Abstract

Silicon nanosheets have attracted much attention owing to their novel electronic and optical properties and compatibility with existing silicon technology. However, a cost-effective and scalable technique for synthesizing these nanosheets remains elusive. Here, we report a novel strategy for producing silicon nanosheets on a large scale through the simultaneous molten-salt-induced exfoliation and chemical reduction of natural clay. The silicon nanosheets thus synthesized have a high surface area, are ultrathin (~5 nm) and contain mesoporous structures derived from the oxygen vacancies in the clay. These advantages make the nanosheets a highly suitable photocatalyst with an exceptionally high activity for the generation of hydrogen from a water–methanol mixture. Further, when the silicon nanosheets are combined with platinum as a cocatalyst, they exhibit high activity in KOH (15.83 mmol H2 per s per mol Si) and excellent photocatalytic activity with respect to the evolution of hydrogen from a water–methanol mixture (723 μmol H2 per h per g Si). A cost-efficient technique for turning clay minerals into active photocatalysts could benefit solar-based generation of hydrogen fuel. Light-sensitive, two-dimensional (2D) silicon nanosheets have been targeted as catalysts for photoelectrochemical water splitting because their unique geometry enables ample interaction with water molecules. However, most synthetic routes to 2D silicon nanosheets require specialized reagents and conditions. Soojin Park and co-workers in South Korea have developed a strategy based on montmorillonite clay, an abundant mineral that contains 2D layers of silicon, oxygen and aluminum atoms. They found that reacting molten sodium chloride salts with the clay simultaneously exfoliated the natural 2D layers and reduced their chemical structure to produce ultrathin silicon nanosheets with a narrow size distribution. Preliminary tests revealed the 2D photocatalyst generated substantial quantities of hydrogen gas from a water–methanol mixture with a platinum co-catalyst. A novel strategy is demonstrated to produce silicon nanosheets on a large scale through the simultaneous molten-salt-induced exfoliation and chemical reduction of natural clay. The thus-synthesized silicon nanosheets have a high surface area, are ultrathin (~5 nm), and contain mesoporous structures derived from the oxygen vacancies in the clay. These advantages make the nanosheets a highly suited photocatalyst with an exceptionally high activity (723 μmol H2 per h per g Si) for the generation of hydrogen from a water–methanol mixture.