Upcycling brewer's spent grain waste into activated carbon and carbon nanotubes via two-stage activation for energy and other applications

In this study activated carbon (AC) and carbon nanotubes (CNTs) were synthesised from Brewer’s Spent Grain (BSG); a form of lignocellulosic biomass, more commonly known as barley waste. A novel approach involving two activation steps; firstly, with phosphoric acid (designated BAC-P) and then using potassium hydroxide (designated BAC-K) was proposed for the production of AC and CNTs from BSG. The AC produced showed a surface area as high as 692.3 m2.g-1 with a pore volume of 0.44 cm3.g-1. This can help aid and facilitate the circular economy by effectively up-cycling and valorising waste lignocellulosic biomass to high surface area AC and subsequently, multi-walled carbon nanotubes (MWCNTs). Consequently, MWCNTs were prepared from the produced AC by mixing it with the nitrogen-based material melamine and iron precursor, iron (III) oxalate hexahydrate, where it produced a hydrophilic multi-wall carbon nanotubes (MWCNTs). Both AC and CNTs materials were used in heavy metal removal (HMR), where the maximum lead absorption was observed for sample BAC-K with 77% removal capacity after the first hour of testing. This result signifies that the synthesis of these up-cycled materials can have application in the areas of wastewater treatment or other AC/CNT end uses with a rapid cycle time.