Synthesis of ZIF-67 composite lignin hydrogel and its catalytic degradation of naphthalene by PMS in wastewater.

The incorporation of ZIF-67 into hydrogels for wastewater pollutant remediation has been widely studied, but the synthesis often requires organic solvents such as methanol or ethanol, which can result in the generation of toxic liquid waste. In this study, a novel hydrogel (ZIF-67@SL) was synthesized by integrating ZIF-67 into a dual-network system of sodium lignosulfonate (SL) and acrylamide (AM) using an in situ precipitation method in water. The material was characterized by XRD, FTIR, XPS, SEM, TEM, BET, and TGA analyses. ZIF-67@SL was used to activate peroxymonosulfate (PMS) for degrading naphthalene (NAP) in aqueous solutions. Results showed that ZIF-67@SL effectively activated PMS, achieving an 85.43 % removal rate of NAP within 60 min at 30 °C, with an initial NAP concentration of 10 mg·L-1, ZIF-67@SL dosage of 800 mg·L-1, PMS concentration of 1000 mg·L-1, and pH 7.0. The catalytic efficiency remained high after five recycling cycles. Quenching experiments and EPR spectra revealed that the degradation of NAP in the ZIF-67@SL/PMS system occurred through both free radical pathways (SO4•-, •OH, and O2•-) and a non-radical pathway (1O2). XPS analysis indicated that the activation of PMS and generation of radicals were influenced by Co2+, Co3+, Co0, nitrogen elements, and adsorbed oxygen in the ZIF-67@SL composite. Furthermore, the ZIF-67@SL/PMS system demonstrated strong resistance to low-concentration anions and humic acid (HA) interference and effectively removed multiple polycyclic aromatic hydrocarbons (PAHs) in mixed wastewater. Maximum removal rates for NAP, ACN, ACT, PHE, and FLU were 95.26 %, 99.9 %, 99.79 %, 99.04 %, and 75.69 %, respectively. This study provides an environmentally friendly strategy for wastewater treatment by synthesizing ZIF-67 hydrogel in water and utilizing it as an efficient catalyst.