High capacity and fast removal of Cr(vi) by alkali lignin-based poly(tetraethylene pentamine-pyrogallol) sorbent

In this work, a novel alkali lignin-based adsorption material, alkali lignin-based poly(tetraethylene pentamine-pyrogallol) (AL-PTAP), was prepared using a Mannich reaction and catechol-amine reaction for removal of Cr(vi). It was characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The effects of tetraethylene pentamine (TEPA) dosage, pyrogallol (PL) dosage, contact time, pH, temperature and other factors on the adsorption behavior of the adsorbent were systematically investigated. These experimental data show that the adsorption behavior conforms to the pseudo-second-order kinetic model and the Langmuir isotherm model. The maximum adsorption capacity is 769.2 mg g^-1 at 303 K, which is much higher than that of alkali lignin (AL). AL-PTAP can achieve a removal rate of almost 100% for Cr(vi) solutions with a concentration of less than 90 mg L^-1 at 1 min. Furthermore, the toxic Cr(vi) is partly reduced to nontoxic Cr(iii) during the adsorption process. Therefore, AL-PTAP is a fast and efficient alkali lignin-based adsorbent, which is expected to improve the utilization value of alkali lignin in Cr(vi) wastewater treatment.