Porous walnut-like Mn2O3 anode derived from the waste graphene production effluent

According to the idea of the circular economy, various wastes should be reasonably managed and recycled for the achievement of the carbon peak and carbon neutralization (double carbon targets). For this purpose, Mn2+ in the waste graphene production effluent was firstly extracted in the form of Mn2O3 powder by the chemical precipitation and the subsequent calcination in air for the different times of 0.5 h, 2 h and 4 h, and the resultant samples were marked as Mn2O3-0.5 h, Mn2O3-2 h, Mn2O3-4 h, respectively. The removal rate and recovery rate of Mn2+ was calculated as about 99.9% and 92.6%, respectively. Furthermore, the effect of the calcination time on the morphology, structure and Li-storage performance of Mn2O3 powder was also further investigated. The results showed that the crystallinity of Mn2O3 increased with the increase of the calcination time, while the walnut-like morphology underwent a process from the integrity to the collapse. Resultantly, 2 h was an optimal calcination time, and Mn2O3-2 h powder exhibited a porous walnut-like morphology with the mean particle size of about 1.0 μm and the largest surface area. Furthermore, Mn2O3-2 h anode delivered the best electrochemical Li-storage performances. For example, the reversible discharge capacity of Mn2O3-2 h anode was about 466 mAh/g for 100 cycles at 1.0 A/g, higher than those of Mn2O3-0.5 h anode and Mn2O3-4 h anode. Obviously, such efforts provide a new strategy for the recovery of graphene production effluent, which may promote the development of the circular economy and the achievement of the double carbon targets.