Study on Efficient Depolymerization of Sodium Lignosulfonate Using N-Cqds/Mgin2s4 Composite Photocatalyst

Abstract

In this thesis, the optimization of photocatalytic performance of metal sulfide MgIn2S4 was achieved by direct loading of nitrogen-doped carbon quantum dots (N-CQDs). The comparison of the optical properties revealed that the N-CQDs possessed superior photocatalytic activity than pure CQDs. Then the N-CQDs were directly loaded on the surface of MgIn2S4, and a series of N-CQDs/MgIn2S4 composite materials (x-C/MIS composite materials, x is the loading amount of N-CQDs) were prepared. The composition, structure, morphology, and specific surface area were analyzed characterization, which proved the successful composite of the two. The UV-Vis diffuse reflectance spectra, Mott-Schottky curves, transient photocurrent response, electrochemical impedance spectra, and photoluminescence spectra confirm that the N-CQDs can effectively modulate the energy band structure of MgIn2S4, enhance the light absorption performance, reduce the charge transfer impedance, and promote the separation of photogenerated carriers. The photocatalytic performance test confirmed that 0.4% (mass percent) was the optimal loading amount of N-CQDs, and the optimized photocatalyst was able to depolymerize 60.9% of sodium lignosulfonate (SLS) within 150 min, while the highest depolymerization rate of the original photocatalyst was only 40.2%.

Keywords: photocatalysis, lignin depolymerization, metal sulfides, Carbon quantum dots