In contrast, the syntheses of mesoporous elemental semiconductor materials are highly limited. For common mesoporous crystalline metal oxide materials, numerous preparation methods have been reported utilizing many different synthesis techniques after the discovery of mesoporous materials in the 1990s (refs 16, 17, 18, 19, 20). More generally, the preparation of porous, especially mesoporous crystalline materials is a big challenge in material chemistry 15, 16. However, the Si unit in these materials is not porous, although the overall structure is porous and shows good electrochemical performance as a Li-ion battery anode 5. A few porous Si/C composite materials have been reported using a chemical vapour deposition method 5, which is considered an effective bottom-up way to prepare nano-Si materials 5, 14. Both reduction processes, however, need pre-formed porous materials as the precursor, which makes the syntheses complicated. Another approach utilizing sodiothermic reduction of zeolite NaY was reported to obtain higher surface area than the magnesiothermic method 13.
At elevated temperature, porous silica precursor is reduced by magnesium vapour, leaving the pore structure unchanged. One type is magnesiothermic reduction of silica 11, 12. In recent years, a few alternative preparations have been reported. Therefore, high Si mass loss and the need for large quantities of toxic hydrofluoric acid (HF) make these methods high cost and inefficient. However, both are top-down methods and suffer from low yield because of their corrosion nature, which generate pores by sacrificing Si. After decades of development, there are two well-established methods to produce porous Si materials, namely, anodisation and stain etching 10. Porous Si is also considered a promising candidate for hydrogen-generating materials because of its chemical and photocatalytic/photoelectrochemical reactivities towards water 7, 8, 9. For example, porous Si has been deeply investigated in optoelectronics and sensors owing to its light-emitting properties, drug/gene delivery research has benefited from its high porosity and bio-compatibility 2, 3, 4 and in recent years, porous Si has also been evaluated as a Li-ion battery anode 5, 6. Porous silicon (Si) has long been studied in many fields because of its special physical and chemical properties 1. These also make the mesoporous silicon a potential candidate for other applications, such as optoelectronics, drug delivery systems and even lithium-ion batteries.
The advantages of these materials, such as their nanosized crystalline primary particles and high surface areas, enable increased photocatalytic hydrogen evolution rate and extended working life.
The chemical synthesis utilizes salt by-products as internal self-forming templates that can be easily removed without any etchants. Here we demonstrate a bottom-up synthesis of mesoporous crystalline silicon materials with high surface area and tunable primary particle/pore size via a self-templating pore formation process. A few alternative routes have been reported, including magnesiothermic reduction however, pre-formed porous precursors are still necessary, leading to complicated syntheses. Conventional preparations suffer from high mass loss because of their etching nature. 206 (2008) 2769.As an important material for many practical and research applications, porous silicon has attracted interest for decades. Smart, Physical Chemistry Chemical Physics, 14 (2012) 2434. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp, Eden Prairie, MN, 1992. Rumble, NIST Standard Reference Database 20, Version 3.4 (Web Version) (http://xps/) 2003. Grant (Eds.), Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, IM Publications, Chichester, UK, 2003, pp. Shirley (Ed.), Proceedings of an International Conference held at Asilomar, Pacific Grove, California, USA, 7-10 September, 1971, North-Holland, Amsterdam, 1972, p. Positions, Madelung constants) of the bonded atoms. Structures, bond directionality) and structural parameters (e.g. These shifts are related to the electronic states (e.g. Understood to represent the “chemical shift” as a result of ground stateĮlectronic structure and are a function of the valence structure of the coreĪtom, which is in turn is a function of bonding to neighboring atomic valence Δε, initial state contributions, and Δ R, final state contributions, result