A novel sustainable and green mechanochemical route from a (HSiO1.5)n polymer to emissive silicon nanocrystals

Abstract

Thermal-induced pyrolysis of the hydrogen silsesquioxane ((HSiO_1.5)_n) polymer has often been applied as a popular straightforward method for the synthesis of silicon nanocrystals (Si NCs), in which the need for high temperature (>1100 °C) and continuous H₂ supply during the time-consuming pyrolysis and cooling processes are the main drawbacks. Herein, we offer a sustainable and green alternative to conventional thermal transformations from the (HSiO_1.5)_n polymer to emissive Si NCs via a room-temperature mechanochemical process with zero H₂ supply. Along with the systematic monitoring of the chemical structure change of the (HSiO_1.5)_n polymer under altered mechanochemical conditions and the detailed characterizations of both solid-state and gas phase products, we derived a novel reaction mechanism from (HSiO_1.5)_n polymer to Si NCs via a mechanochemical route distinct from conventional thermal pyrolysis. It was found that the in-vessel produced H₂via the cleavage of the Si–H bond in (HSiO_1.5)_n molecule facilitates the generation of Si radicals and formation of resultant Si NCs, while the remaining Si–O–Si network transformed into a SiO₂-like matrix through the collapse of the raw (HSiO_1.5)_n structure and bond redistribution during the mechanochemical process. As a practical application, emissive free-standing Si NCs were successfully prepared via further matrix removal by chemical etching and surface passivation by 1-decene. The prepared Si NCs exhibit photoluminescence in the red-light wavelength region and an absolute quantum yield of 9.8%, whose value is comparable to that synthesized by the conventional thermal pyrolysis method. The novel and facile mechnochemical route developed in the present work opens a new avenue for the smart synthesis of functional nanomaterials.