A highly charged and porous biochar embedded with hydrated ferric oxide nanoparticles for enhanced removal of Cd(II) and Cu(II) from water

Owing to the limited pore structure and surface charged groups, it is still challenging for biochar (BC) as the host of metallic oxide nanoparticles to achieve the highly efficient treatment of heavy metals in water. To overcome this barrier, a highly porous and charged biochar (LABC) was developed as supporter to load hydrated ferric oxide (HFO), and a new nanocomposite HFO-LABC was acquired for heavy metal decontamination. The increased and enlarged pores from KHCO 3 for LABC activation apparently cut down adsorption equilibrium time of HFO-LABC to Cd(II) and Cu(II) (within 10 min) by reducing pore diffusion resistance of targeted metals. The predicted pore diffusion coefficient D is 2.3 ☓10 –8 and 3.6 ☓10 –8 cm 2 /s for Cd(II) and Cu(II) in HFO-LABC, respectively, about 10 times higher than that in HFO-BC (2.1 ☓10 –9 and 3.7 ☓10 –9 cm 2 /s). The introduced charged groups onto LABC notably enhanced Cd(II) and Cu(II) adsorption on HFO-LABC through promoting the dispersion of the loaded nanoparticles (size < 10 nm) and the potential Donnan membrane effect. Consequently, Fe-normalized adsorption capacities of Cd(II) and Cu(II) on HFO-LABC of 976.23 and 1170.77 mg/g-Fe are much greater than those on HFO-BC (299.50 and 510.92 mg/g-Fe). Moreover, HFO-LABC can achieve advanced treatment for synthetic and real Cd(II) and Cu(II)-polluted wastewater in cyclic batch system, with treatment capacities of 1500, 3500 and 8000, 4500 mL/g-HFO-LABC. In addition, the spent HFO-LABC can achieve complete regeneration using HCl-CaCl 2 binary solution with desorption rate >95 %.