Modification of sludge-based biochar using air roasting-oxidation and its performance in adsorption of uranium(VI) from aqueous solutions

作者：Sun, Yiwei; Zeng, Baiyan; Dai, Yatang; Liang, Xiangjing; Zhang, Lijuan; Ahmad, Rashid^*; Su, Xintai^*

来源：Journal of Colloid and Interface Science, 2022, 614: 547-555.

DOI：10.1016/j.jcis.2022.01.138

• Uranium(VI) adsorption
• Sludge-based biochar
• Air roasting-oxidation modification
• Density functional theory (DFT)
• Oxygen-containing functional groups

Modification methods for sludge-based biochar are often complex and generally ineffective. In this study, sludge-based biochars were prepared at low cost using a simple air roasting-oxidation modification method and the adsorption performance on U(VI) was investigated. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) results together indicated that more carbon-oxygen functional groups were formed on the surface of oxidized biochar (OBC) compared to unoxidized biochar (BC). The adsorption performance of 550-OBC (biochar oxidized at 550 degrees C) on U(VI) was explored in batch experiments. The maximum adsorption capacity was up to 490.2 mg/g at 25 degrees C and pH 6, exceeding most of the reported biochars. 550-OBC also showed good adsorption performance at low U(VI) concentration, with 96% removal at pH 6 and an initial U(VI) concentration of 1 mg/L. Density functional theory (DFT) calculations indicated that the H-bond length between the solvated U (VI) and functional groups on the OBC was about 1.7 angstrom, which forms stronger H-bonds between them compared to that between U(VI) and BC (4.21 angstrom), and the adsorption energy value for this complex was highly negative -31.82 kcal/mol. In addition, 550-OBC exhibited high selectivity for U(VI) adsorption and excellent regeneration performance, making it a cost-effective and high-performance adsorbent.