Synthesis and Characterization of N-Doped Seaweed Biochar and Removal of Cationic Dyes

The development of functional porous carbon materials has attracted great attention in various fields. In this work, N-doped algal biochar (NABc) materials were successfully prepared by an impregnation and calcination methods using Dicyandiamide as a modifier. The specific surface area, average pore volume, and average pore diameter of NABc1%, were 693.92 m²·g^-1, 0.162 cm³·g^-1 and 6.76 nm, respectively. The high efficiency of NABc1% in adsorbing the cationic dyes rhodamine B and methylene blue from water may be attributed to the rich pore structure of NABc1%. The adsorption experiments show that the removal rates of rhodamine B and methylene blue by NABc1% in 90 min are 99.4 and 96.2%, respectively, which are obviously higher than those before modification. The experimental results of adsorption kinetics show that the adsorption process is more consistent with the quasi-second-order kinetic fitting equation (<i>R</i> ² = 0.961, 0.998). The results of isothermal adsorption experiments show that the adsorption process is more consistent with the Langmuir equation (<i>R</i> ² = 0.919, 0.916), indicating that the adsorption of rhodamine B and methylene blue by NABc1% is dominated by a monolayer adsorption process. In addition, the fitting of the intraparticle diffusion model shows that internal diffusion is not the only rate-limiting step. Hence, NABc1% has great potential for practical application as an efficient adsorbent in the field of cationic dye wastewater treatment.