Efficient activation of peroxydisulfate by a novel magnetic nanocomposite lignin hydrogel for contaminant degradation: Radical and nonradical pathways

A novel magnetic nanocomposite lignin hydrogel (MNLH) was synthesized and applied for peroxydisulfate (PDS) activation in this study. Detailed characterization data indicated that the unique 3-dimensional (3D) structure of the lignin hydrogel is beneficial in dispersing magnetic nanoparticles (nZVI/Ni particles), which enhances the maximum exposure of nZVI/Ni particles. The 3D structure of the lignin hydrogel provides more attachment sites for nZVI/Ni, PDS and contaminants, accelerating the electron transfer between nZVI/Ni and PDS and promoting the degradation of contaminant. Notably, the optimized MNLH0.8 catalyst (where the number 0.8 indicates the mass ratio of [Lignin hydrogel]/[nZVI/Ni] = 0.8) exhibits excellent performance for PDS activation. Under the MNLH0.8/PDS system, 5 mg/L bisphenol A (BPA, 40 mL) can be completely degraded within 15 min with 0.05 g/ L catalyst and 0.66 mM PDS. Quenching experiments and electron spin resonance (ESR) spectra reveal that both radicals (O2 & BULL;?) and nonradicals (1O2) are generated in the MNLH0.8/PDS system as the dominant active species for BPA degradation. In addition, the MNLH0.8 catalyst still shows effectiveness for BPA degradation in the presence of inorganic anions and natural organic matter (NOM). UPLC-Q-TOF-MS system was used to identify the BPA degradation products and four possible pathways for BPA degradation were proposed. According to the results of toxicity prediction, BPA can eventually be transformed into nontoxic products. Additionally, the MNLH/PDS system can effectively degrade different contaminants in water, which highlights promising applications for organic wastewater treatment.