Self-nitrogen-doped biochar derived from soybean cake for rhodamine B removal prepared via simple carbonization

Nitrogen-doped biochar performs much better in dye adsorption due to its rich functional groups. Soybean cake, a by-product of soybean oil production, comprises rich contents of cellulose, lignin, and protein. Therein, simple direct carbonization was utilized to prepare self-nitrogen-doped biochar (SCB). The results showed that the N content of SCB was 6.81 wt%, and its specific surface area was 18.8 m2/g. X-ray photoelectron spectroscopic results confirmed that the surface of SCB was rich in pyridine-N, pyrrole-N, graphite-N, and oxidized-N functional groups. The adsorption capacity of SCB for Rhodamine B was 17.2 mg/g, which is higher compared with other unactivated biochars. The results of thermodynamic parameters indicate that Rhodamine B adsorption on SCB is an endothermic, entropy-increasing, and spontaneous process.