Supporting nanoscale zero-valent iron onto shrimp shell-derived N-doped biochar to boost its reactivity and electron utilization for selenite sequestration

Nanoscale zero-valent iron (nZVI) has been widely used in the reductive removal of contaminants from water, yet it still fights against the inherent passive cover and the raise of medium pH. In this study, nZVI was supported onto a nitrogen-doped biochar (NBC) that was prepared by pyrolyzing shrimp shell for efficiently sequestrating aqueous selenite (Se(IV)). The resultant composite (NBC-nZVI) revealed a higher reactivity and electron utili-zation efficiency (EUE) than the bare nZVI in Se(IV) sequestration because of the positive charge, the buffering effect and the good conductivity of NBC. The kinetic rate and EUE of NBC-nZVI were increased by 143.4% and 15.3% compared to the bare nZVI, respectively, at initial pH of 3.0. The high removal capacity of 605.4 mg g-1 for NBC-nZVI was obtained at Se(IV) concentration of 1000 mg L-1, initial pH of 3.0, NBC-nZVI dosage of 1.0 g L-1 and contact time of 12 h. Moreover, NBC-nZVI exhibited a strong tolerance to solution pHs and coexisting compounds (e.g., humic acid) and could reduce the Se(IV) concentration from 5.0 mg L-1 to below the limit of drinking water (50 mu g L-1) in real-world samples. This work exemplified a utilization of shrimp shell-derived NBC to simultaneously enhance the reactivity and EUE of nZVI for reductively removing contaminants.

Automated summary

In this study, nitrogen-doped biochar supported nanoscale zero-valent iron (NBC-nZVI) was used to efficiently remove aqueous selenite (Se(IV)) contaminants from water. The NBC-nZVI exhibited higher reactivity and electron utilization efficiency (EUE) compared to bare nZVI due to its positive charge, buffering effect, and good conductivity. The removal capacity of NBC-nZVI was 605.4 mg g-1 at Se(IV) concentration of 1000 mg L-1, initial pH of 3.0, NBC-nZVI dosage of 1.0 g L-1, and contact time of 12 h. Moreover, NBC-nZVI showed strong tolerance to solution pHs and other coexisting compounds, and could effectively reduce Se(IV) concentration in real-world samples.