High-performance polyethylenimine-functionalized lignin/silica porous composite microsphere for the removal of hexavalent chromium, phosphate and Congo red from aqueous solutions

Based on lignin derived from nature, polyethylenimine-functionalized lignin/SiO2 porous composite microspheres (LSPGs) were prepared by inverse emulsion polymerization in this article. The experimental parameters were optimized via orthogonal experiments, and the removal performance of LSPGs for common anionic pollutants was comprehensively investigated. The equilibration times required for the adsorption of Cr(VI), PO43- and Congo red by LSPGs were 2.0 h, 0.75 h and 3.0 h, respectively. The removal process of these pollutants mainly relied on chemical adsorption. The highest adsorption capacity of LSPGs for Cr(VI), PO43- and Congo red calculated by Langmuir model were 355.21 mg g−1, 313.48 mg g−1 and 588.24 mg g−1, respectively. In the presence of different anions, LSPGs showed good selectivity for Cr(VI), while SO42- had a strong inhibitory effect on the enrichment of PO43-. Electrostatic attraction adsorption mechanism played an important role in the removal of pollutants. In addition, redox, hydrogen bonding and π-π interactions also had irreplaceable abilities in the removal of Cr(VI), PO43- and Congo red, respectively. For the three target ions, the LSPGs that underwent five adsorption-desorption cycles still retained more than 80% adsorption capacity. The results showed that composite microspheres LSPGs can effectively remove PO43--containing, Cr(VI)-containing and organic dye wastewater.