Development of Sustainable Rapid Microwave Assisted Process for Extracting Nanoporous Si from Earth Abundant Agricultural Residues and Their Carbon-based Nanohybrids for Lithium Energy Storage

Bamboo culm (BC), rice husk (RH), and sugarcane bagasse (SB) are the most earth abundant, low-cost, and eco-friendly agricultural residues that contain a substantial amount of biogenic silica (SiO 2 ) in the form of amorphous hydrated silica grains. In this study, we successfully extracted SiO 2 from various agricultural residues such as BC, RH, and SB via rapid microwave assisted solid-state ashing (MW-SS), followed by microwave assisted magnesiothermic reduction (MW-MR) of SiO 2 into crystalline silicon (Si) at <650 °C for 30 min without the need for a reducing gas atmosphere. The MW-MR process further supports the development of an interconnected three-dimensional porous Si network with a pore diameter of 50–80 nm and wall thickness of ∼23 nm. The obtained Si is further decorated with dimensionally modulated carbon-based materials such as carbon (C), graphene nanosheets (GNS), and multiwall carbon nanotubes (MWCNT), which can offer higher delithiation capacities (1997, 1290, and 1166 mAh g –1, respectively) compared to pristine Si (956 mAh g –1 ) extracted from RH at C/5 rate after 200 cycles. These results suggest that the earth-abundant BC, RH, and SB could be sustainable resources for large-scale production of nanoporous crystalline Si, which has been extracted via an energy efficient, low-cost microwave assisted sustainable process for lithium ion battery anodes.