High cadmium adsorption on nanoscale zero-valent iron coated Eichhornia crassipes biochar

Overgrowth of Eichhornia crassipes, or water hyacinth, in local waters is a major concern, which has caused severe ecological disasters. Moreover, once the E. crassipes biomass is collected from waters, its treatment is difficult because the biomass is highly cellulosic and resistant to bacterial degradation. On the other hand, using biochar adsorbent for water treatment has gained attention because of its low cost and ease of manufacture, but pristine biochar has a low adsorption capacity. Here, a novel nanoscale zero-valent iron (nZVI) coated E. crassipes biochar was synthesized, and the obtained nZVI/biochar was used to remove Cd(II) from aqueous solutions. The deposition of nZVI onto pristine biochar increased specific surface area while retaining functional groups of the carbonaceous surface. Results show that the maximum Cd(II) adsorption capacity based on the Langmuir isotherm is 56.62 mg/g for nZVI/biochar, 2.2-fold of that of pristine biochar. The higher Cd(II) adsorption performance of nZVI/biochar is likely due to the synergistic effects of biochar adsorption and additional nZVI interaction with Cd(II).