LignoPhot: Photoactive Hybrid lignin/Bi4O5Br2/BiOBr Composite for Complex Pollutants Removal

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 report on photoactive lignin/Bi₄O₅Br₂/BiOBr bio-inorganic composites consisting of a lignin substrate that is coated by Bi₄O₅Br₂/BiOBr nanosheet photocatalysts. The structure of the hybrid material was investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy including energy dispersive X-ray (EDX) spectroscopy, and solid state ¹H−¹³C nuclear magnetic resonance spectroscopy (¹H−¹³C NMR). The material contains 18.9% of Bi₄O₅Br₂/BiOBr and was found to be effective for the photocatalytic degradation of cationic methylene blue (MB) and zwitterionic rhodamine B (RhB) dyes under irradiation with 405 nm light. Lignin/Bi₄O₅Br₂/BiOBr was able to decrease the dye concentration from 80 mg·L^–1 to 12.3 mg·L^–1 for RhB (85%) and from 80 mg·L^–1 to 4.4 mg·L^–1 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 metal ions in aqueous solutions. The highest adsorption capacity was found after 2 hours of phases contact and reached 0.45 mmol·g^–1 for Ni(II) ions (neutral media). The low cost, simplicity of the synthesis, good stability and ability to simultaneously photooxidize organic dyes and to adsorb metal ions, make the developed photoactive lignin/Bi₄O₅Br₂/BiOBr composite a prospective material for textile wastewaters remediation