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 Fe-0 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 O-2(center dot-), SO4 center dot-, O-1(2) and center dot OH, was confirmed by EPR and scavenging experiments, and O-2(center dot-) and O-1(2) played dominant roles in the AL@nZVI+ persulfate system. The O-2(center dot-)-guided free radical pathway was induced by activation of persulfate by Fe-0 nano-particles, while O-2(center dot-) <inverted exclamation> acted as a precursor to induce the O-1(2)-guided non-radical pathway. It is worth noting that C=O may be favourable for the generation of O-1(2). 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.