Synthesis of lignin sphere-based carbon-coated nZVI nanocomposites for efficient activation of persulfate to degrade 2,4-dichlorophenol

In this study, taking advantage of the amphiphilic properties of alkali lignin, carbon shell-encapsulated nano-zero-valent iron particles (AL@nZVI) anchored in a porous carbon framework were firstly synthesized by a combination of antisolvent reaction and carbothermal reduction method. AL@nZVI exhibited efficient catalytic performance for the activation of persulfate for the complete removal of 2,4-dichlorophenol at 30 min. The formation of a porous carbon skeleton and carbon shell enhanced the dispersibility and antioxidation of Fe0 nanoparticles and enabled long-term storage of AL@nZVI in air for more than 60 days. Furthermore, oxidation was mainly responsible for the removal of 2,4-dichlorophenol. The adsorption was determined to be 26.9% by analyzing the 2,4-dichlorophenol content in the used material. The generation of O2·−, SO4·−, 1O2 and·OH, was confirmed by EPR and scavenging experiments, and O2·− and 1O2 played dominant roles in the AL@nZVI+ persulfate system. The O2·−-guided free radical pathway was induced by activation of persulfate by Fe0 nanoparticles, while O2·− acted as a precursor to induce the 1O2-guided non-radical pathway. It is worth noting that CO may be favourable for the generation of 1O2. Moreover, the graphitized carbon, micropores, and structural defects contained in AL@nZVI created an electron-rich environment to facilitate the interaction between 2,4-dichlorophenol and reactive oxygen species. Therefore, the free radical and non-radical pathways were coupled to work together to degrade 2,4-dichlorophenol. This work not only develops a new synthesis method for core-shell structured carbon-coated nZVI composites, but also open the way for the high-value utilization of industrial by-products and the advanced oxidation degradation of organic pollutants in environmental remediation.