Adsorption behavior of Cr(VI) by magnetically modified Enteromorpha prolifera based biochar and the toxicity analysis

Enteromorpha prolifera (EP) biomass collected from a lake in China was employed for biochar production. The EP biochar was magnetically modified by loading γ-Fe₂O₃ particles on the surface, and Cr(VI) adsorption behavior and mechanism were evaluated. The magnetic biochar had higher surface polarity, specific surface area and exhibited a higher Cr(VI) adsorption capacity of 95.23 mg/g biochar compared with pristine EP biochar. The pronounced electron spin resonance (ESR) signals showed that the environmental persistent free radicals (EPFRs) preferred to form at lower pyrolysis temperature and lower transition metal concentration. The g factors of BC400, BC800 and BCF400 were 1.8959, 1.7955 and 1.7954, respectively, indicating that the EPFRs mainly used carbon atom as center. In addition, biological toxicity of magnetic EP biochar was tested using the microalga Scenedesmus obliquus. Exposure of S. obliquus cells to magnetic biochar led to the accumulation of reactive oxygen species (ROS) and oxidative stress. The leaching solution toxicity of BCF400 was stronger than BCF800. Thus, the magnetic EP biochar prepared at higher temperature (such as BCF800) provide better Cr (VI) performance with low biologic toxicity. And the EP biomass could be a promising low-cost feedstock for biochar production.