Facile synthesis of lignin Schiff base-copper complex as a catalyst for methylene blue and 4- nitrophenol removal

Abstract Recently, biopolymer-based catalysts have been reported frequently due to the advantages of biodegradability, highly efficiency, and low cost. In this work, novel catalyst lignin Schiff base-copper complex (L-SB-Cu) was synthesized, and this catalyst was used for methylene blue (MB) and 4-nitrophenol (4-NP) reduction in aqueous solutions. The results of characterization from elemental analysis, Fourier-transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), and proton nuclear magnetic resonance (1H NMR) proved that lignin Schiff base (L-SB) was synthesized successfully. X-ray photoelectron spectroscopy (XPS), and EDS-mapping proved that copper ions was coordinated with L-SB, thus forming L-SB-Cu catalyst. The catalyst showed highly catalytic reduction ability towards organic pollutants MB and 4-NP with sodium borohydride (NaBH4) as a reducing agent even after three times of recycling. The catalyst ability of reducing MB and 4-NP was evaluated by UV-Vis spectroscopy, and the mechanisms were explored. This work showed a new strategy of utilizing bio-based material as a highly efficiency catalyst to degrade organic pollutants.