Properties of Spartina alterniflora Loisel. Derived-biochar and its effect on cadmiumadsorption

Heavy-metal contamination is an important environmental problem due to the accumulation of toxic metals in humans via the food chain. In recent years, biochar has emerged as an efficient tool for the removal of heavy metals with advantages over other biomaterials. In this study, Spartina alterniflora Loisel.,which is an alien invasive species and grows in Dongtan wetland, Chongming, Shanghai, was used to produce biochar. The optimum temperature for biochar production was selected based on basic properties, adsorption ability for cadmium, and stability at different pyrolysis temperatures. A scanning electron microscope (SEM) and fourier transform infrared spectroscopy (FTIR) were used to observe morphology and to analyze different functional groups involved in cadmium adsorption of prepared biochar, respectively. The results showed that the Cd2+ absorption capacity of biochar prepared at 450 °C was up to 20.576 mg·g^-1 in only 15 min. The adsorption of cadmium by biochar followed the second order kinetic equation, and chemical adsorption was the main adsorption pattern. SEM images showed granular protrusions of cadmium adsorption in Spartina alterniflora biochar, while FTIR revealed remarkable changes in hydroxyl, carboxyl, and other oxygen-containing functional groups in the cadmium adsorbed by biochar. It was also possible that adsorption of cadmium occurred on the surface of biochar due to the formation of a cadmium-biochar compound system. These results demonstrated that Spartina alterniflora biochar is effective for metals adsorption.