Phenolation of lignin for polycatecholamines to remove Cr (VI)

Alkaline lignin, a by-product of the paper-pulping process, can undergo phenolation by pyrogallol in the presence of acetone and sulfuric acid to prepare phenolated-alkaline-lignin (PAL). PAL can be further reacted with tetraethylenepentamine (TEPA) to prepare lignin-based catecholamine (PAL-TEPA), which exhibits excellent ability to remove hazardous Cr (VI) from simulated wastewater. In this study, PAL and PAL-TEPA were systematically investigated by SEM, FT-IR, 1H NMR, TGA, and XPS. The conditions for the preparation of PAL and the various variables affecting the adsorption behavior of PAL-TEPA were optimized sequentially. The adsorption process followed the pseudo-second-order model and fitted to the Langmuir isotherm equation. The maximum adsorption amount reached 600 mg g−1 (R = 75 %) under optimized conditions (pH = 2.0, C0 = 200 mg L−1, V = 100 mL, T = 30 °C, dos. = 25 mg, t = 24 h). Toxic Cr (VI) ions were successfully converted to harmless Cr (III) ions and removed by PAL-TEPA adsorbent. This approach opens new avenues for the utilization of lignin and new kinds of adsorbent for Cr (VI) removal.