Potassium permanganate modification of hydrochar enhances sorption of Pb(II), Cu(II), and Cd(II).

[Display omitted] • Wheat straw hydrochar modified with 0.2 M KMnO 4 obtained optimal results. • KMnO 4 modification loaded MnOx microparticles on hydrochar surface. • Oxygen-containing surface functional groups increased after modification. • KMnO 4 modification enhanced adsorption of Pb(II), Cd(II), Cu(II) by > 10 times. Hydrochars formed by hydrothermal carbonization of hickory wood, bamboo, and wheat straw at 200 °C were modified by potassium permanganate (KMnO 4) for the sorption of Pb(II), Cd(II), and Cu(II). The wheat straw hydrochar (WSHyC) modified with 0.2 M KMnO 4 resulted in the most promising adsorbent (WSHyC-0.2KMnO 4). Characterization of WSHyC and WSHyC-0.2KMnO 4 revealed that the modified hydrochar features large specific surface area, rich of surface oxygenic functional groups (OCFG), and a significant amount of MnOx micro-particles. Batch adsorption experiments indicated that the adsorption rate by WSHyC-0.2KMnO 4 was faster than for WSHyC, attaining equilibrium after around 5 h. The optimum adsorption capacity (Langmuir) of Pb(II), Cd(II), and Cu(II) by WSHyC-0.2KMnO 4 was 189.24, 29.06 and 32.68 mg/g, respectively, 12 ∼ 17 times greater than by WSHyC. The significantly enhanced heavy metal adsorption can be attributable to the increased OCFG and MnOx microparticles on the surface, thereby promoting ion exchange, electrostatic interactions, and complexation mechanisms. [ABSTRACT FROM AUTHOR]