LignoPhot: Conversion of hydrolysis lignin into the photoactive hybrid lignin/BiOBr/BiOBr composite for simultaneous dyes oxidation and Co and Ni recycling.

Valorization of lignin is still an open question and lignin has therefore remained an underutilized biomaterial. This situation is even more pronounced for hydrolysis lignin, which is characterized by a highly condensed and excessively cross-linked structure. We demonstrate the synthesis of photoactive lignin/BiOBr/BiOBr bio-inorganic composites consisting of a lignin substrate that is coated by semiconducting nanosheets. The XPS analysis reveals that growing these nanosheets on lignin instead on cellulose prevents the formation of Bi ions at the surface region, yielding thus a modified heterojunction BiOBr/BiOBr. The material contains 18.9% of BiOBr/BiOBr and is effective for the photocatalytic degradation of cationic methylene blue (MB) and zwitterionic rhodamine B (RhB) dyes under light irradiation. Lignin/BiOBr/BiOBr decreases the dye concentration from 80 mg L to 12.3 mg L for RhB (85%) and from 80 mg L to 4.4 mg L for MB (95%). Complementary to the dye degradation, the lignin as a main component of the composite, was found to be efficient and rapid biosorbent for nickel, lead, and cobalt ions. The low cost, stability and ability to simultaneously photo-oxidize organic dyes and adsorb metal ions, make the photoactive lignin/BiOBr/BiOBr composite a prospective material for textile wastewaters remediation and metal ions recycling.