Heteroatom-doped magnetic hydrochar to remove post-transition and transition metals from water: Synthesis, characterization, and adsorption studies

Efforts to improve water quality have led to the development of green and sustainable water treatment approaches. Herein, nitrogen-doped magnetized hydrochar (mSBHC-N) was synthesized, characterized, and used for the removal of post-transition and transition heavy metals, viz. Pb2þ and Cd2þ from aqueous environment. mSBHC-N was found to be mesoporous (BET surface area e 62.5 m2/g) and paramagnetic (saturation magnetization e 44 emu/g). Both, FT-IR (with peaks at 577, 1065, 1609 and 3440 cm1 cor- responding to Fe e O stretching vibrations, C e N stretching, N e H in-plane deformation and stretching) and XPS analyses (with peaks at 284.4, 400, 530, 710 eV due to C 1s, N 1s, O 1s, and Fe 2p) confirmed the presence of oxygen and nitrogen containing functional groups on mSBHC-N. The adsorption of Pb2þ and Cd2þ was governed by oxygen and nitrogen functionalities through electrostatic and co-ordination forces. 75e80% of Pb2þ and Cd2þ adsorption at Co: 25 mg/L, either from deionized water or humic acid solution was accomplished within 15min. The data was fitted to pseudo-second-order kinetic and Langmuir isotherm models, with maximum monolayer adsorption capacities being 323 and 357 mg/g for Cd2þand Pb2þ at 318 K, respectively. Maximum Cd2þ (82.6%) and Pb2þ (78.7%) were eluted with 0.01 M HCl, simultaneously allowing minimum iron leaching (2.73%) from mSBHC-N. In conclusion, the study may provide a novel, economical, and clean route to utilize agro-waste, such as sugarcane bagasse (SB),
for aquatic environment remediation.