A novel sludge-based biochar composite adsorbent CS/SBC-H3PO4 for efficient Cr(vi) removal from aqueous solution

In this paper, in order to solve the problem of more impurities and less functional groups on the surface of sludge-based biochar, phosphoric acid and chitosan were used to co-modify sludge-based biochar (CS/SBC-H3PO4) to enhance the removal of Cr(vi). CS/SBC-H3PO4 was characterized using SEM, XRD, FT-IR spectroscopy and XPS. When the initial concentration of Cr(vi) solution was 100 mg L-1, the pH was 2.0, and the dosage of adsorbent was 50 mg, the Cr(vi) removal rate of CS/SBC-H3PO4 was 89.70%. The adsorption process of Cr(vi) by CS/SBC-H3PO4 was spontaneous and heat-absorbing, and was dominated by monolayer chemisorption, which followed the quasi-second-order kinetic model and Langmuir adsorption isotherm model, and its maximum adsorption capacity was 201.93 mg g(-1) at 298 K. The removal mechanism of Cr(vi) by CS/SBC-H3PO4 is electrostatic adsorption, reduction and complexation. In detail, CS/SBC-H3PO4 electrostatically adsorbs Cr(vi) through surface amino protonation, and then reduces Cr(vi) to Cr(iii) through -NH3+ and O-H groups to generate -NO2, C-O and C =O groups. Finally, Cr(iii) is complexed with the C=O group.

Automated summary

In this study, phosphoric acid and chitosan were used to modify sludge-based biochar in order to enhance the removal of Cr(vi). The modified CS/SBC-H3PO4 exhibited high Cr(vi) removal efficiency and spontaneous and heat-absorbing adsorption behavior. The maximum adsorption capacity was found to be 201.93 mg g(-1).