Impact of modification on the properties of Eucheuma biochar and its adsorption of phenanthrene from aqueous solution.

Biochar was derived from Eucheuma (EBC) at a temperature of 500 °C and the resulting biochar was modified using NaOH, KOH, NaOH + KOH and HNO + HCl. This study investigated the impact of these modifications on the characteristics of the biochar and its effectiveness in adsorbing phenanthrene (Phe) from an aqueous solution. The results indicated that the surface roughness increased, leading to an increase in the specific surface area, and the development of complex pore structure, leading to a decrease in the polarity and increase in hydrophobicity of biochar modified by a mixture of KOH and HNO + HCl (EBC-K and EBC-H). The EBC-K and EBC-H samples exhibited superior surface areas (272.76 and 289.60 m g) and adsorption capabilities for Phe (removal rates of 99.8% and 99.4%). The pseudo-first order, pseudo-second order and intraparticle diffusion Kinetic model demonstrated that the adsorption process is determined by both physicochemical and intra-particle diffusion. The adsorption process was well described by the Langmuir model. The maximum adsorption capacity of EBC-K and EBC-H was increased by approximately 2.4 times compared with the original biochar. Batch adsorption experiments indicated that the removal rate increases with the increase of dosage. Additionally, EBC-H regenerated from -hexane removed 85.52% of the Phe solution.