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

Hydrochars formed by hydrothermal carbonization of hickory wood, bamboo, and wheat straw at 200 degrees C were modified by potassium permanganate (KMnO4) for the sorption of Pb(II), Cd(II), and Cu(II). The wheat straw hydrochar (WSHyC) modified with 0.2 M KMnO4 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 microparticles. 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 similar to 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.

Automated summary

Hydrochars derived from hydrothermal carbonization of hickory wood, bamboo, and wheat straw were modified with potassium permanganate for effective sorption of heavy metals. The modified wheat straw hydrochar (WSHyC-0.2KMnO(4)) exhibited the highest adsorption capacity, attributed to its large specific surface area, abundant surface oxygenic functional groups, and significant presence of MnOx microparticles. Batch adsorption experiments demonstrated that WSHyC-0.2KMnO(4) had a faster adsorption rate and much higher adsorption capacity (12-17 times) for Pb(II), Cd(II), and Cu(II) compared to WSHyC, due to increased OCFG and MnOx microparticles on its surface facilitating ion exchange, electrostatic interactions, and complexation mechanisms.