Magnetically recoverable binderless N-doped carbon/Fe3O4/nZVI composite for heavy-metal adsorption and H2O2-assisted phenol removal

A magnetically recoverable binderless N-doped carbon/Fe 3 O 4 /nZVI composite was prepared from technical lignin through activation, nitrogen treatment, binderless granulation, Fe 3 O 4 deposition, and nZVI immobilization for heavy-metal adsorption and H 2 O 2 -assisted phenol removal. Characterization showed a BET surface area of 845 m 2 g⁻ 1 , an average pore diameter of 9.6 nm, and a saturation magnetization of 27.5 emu g⁻ 1 . N 2 adsorption–desorption analysis supported a mesopore contribution but did not establish the coexistence of micro-, meso-, and macropores. The Freundlich model provided a better empirical description of the available Pb(II) and Cd(II) adsorption data than the Langmuir model. Phenol removal reached approximately 75% without added H 2 O 2 and 98% with H 2 O 2 after 120 min, while aqueous-phase total organic carbon removal was approximately 77% in the composite/H 2 O 2 system. These results are consistent with an additional oxidant-assisted contribution, although the degradation pathway and extent of mineralization were not established. Pb(II) removal remained above 91% after five adsorption–desorption cycles. In battery and electroplating wastewaters, Pb(II), phenol, and TOC removal ranged from 90.3–92.5%, 93.8–95.0%, and 70.1–72.0%, respectively. Fixed-bed experiments also demonstrated Pb(II) removal under continuous-flow conditions. The findings support the composite’s potential for combined pollutant treatment, while its individual component contributions, catalytic synergy, and long-term stability require further validation.