Unraveling the molecular mechanisms of Cd sorption onto MnOx-loaded biochar produced from the Mn-hyperaccumulator Phytolacca americana

Wu, Ping; Cui, Peixin; Zhang, Ying; Alves, Marcelo Eduardo; Liu, Cun; Zhou, Dongmei; Wang, Yujun

Unraveling the molecular mechanisms of Cd sorption onto MnOx-loaded biochar produced from the Mn-hyperaccumulator Phytolacca americana

2022

Engineered biochar represents a promising material for green remediation practices. In this paper, we present an innovative approach to produce MnOₓ-loaded biochars by pyrolyzing the biomass of a Mn-hyperaccumulator species (Phytolacca americana). Batch sorption and stirred-flow kinetic experiments were combined with spectroscopic techniques to elucidate the mechanisms behind the Cd sorption onto those biochars, named here as PABCs. The incorporation of MnOₓ into the PABCs increased their surface densities of oxygen-containing functional groups. The average Mn leaching (< 9%) from PABCs was lower than that measured for the non-pyrolyzed biomass of P. americana (30–43%). PABCs pyrolyzed at 500 °C had Cd sorption capacities as high as 212–337 mg/g, which achieved by far the best performance reported for biochar materials. The stirred-flow experiments showed that MnOₓ loading was instrumental in increasing both the Cd sorption onto PABCs as well as its irreversibility. Extended X-ray absorption fine structure spectroscopy revealed that the Cd immobilization occurred mainly through its association with organic matter (Cd-OM) and, to a lesser extent, with carbonate (CdCO₃) and MnOₓ (Cd-MnOₓ). In short, MnOₓ-loaded biochar prepared from the biomass of a Mn-hyperaccumulator species proved to be an effective, sustainable, and eco-friendly material for remediating Cd-contaminated waters.

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