Effect of modified multi-walled carbon nanotubes on mechanical properties and microscopic mechanism of lithium slag geopolymers

This study aims to examine the impact of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and micro-mechanisms of lithium slag geopolymer (LSG), a novel environmentally friendly building material. Two distinct dispersion methods, which used ultrasonication or added sodium dodecyl sulfate (SDS) dispersants, were employed to disperse both pristine and modified MWCNTs. Subsequently, these dispersed MWCNT solutions were mixed with waste lithium slag and stirred to prepare LSG. Based on the experiments, it is concluded that all of these demonstrated the most significant enhancement of LSG mechanical properties at a 0.1% mass fraction of modified MWCNTs. In comparison with the reference LSG, the compressive and bending strengths of LSG with modified MWCNTs experienced improvements of 23.29% and 13.76%, respectively, after a curing period of 28 days. This was also evident from a microscopic perspective. The LSGs doped with modified MWCNTs and SDS exhibited stronger Ai-O-Si and Si-O-Si vibrational bands, as well as broader N-A-S-H and C-S-H characteristic peaks compared to the pristine LSGs. The porosity of LSG samples mixed with a mass fraction of 0.1% MWCNTs and SDS was 37.08% lower than that of pristine LSG. FESEM electron micrographs revealed that the modified MWCNTs functioned as fillers, bridges, and extractors of cracks in the hydration products of LSG. The aforementioned results suggest that well-dispersed modified MWCNTs have a beneficial impact on the mechanical properties and microscopic characteristics of LSG. • we used ultrasound and dispersant (SDS) to disperse pristine and modified multi-walled carbon nanotubes (MWCNTs). • we combined multi-walled carbon nanotubes with lithium slag to prepare a new environmentally friendly lithium slag geopolymer (LSG). • 0.1 wt% of modified MWCNTs had the best effect on the improvement of mechanical properties of LSG. • The hydration products of LSG with the addition of modified MWCNTs compared with those of LSG with the addition of pristine MWCNTs.