ZIF-8 and humic acid modified magnetic corn stalk biochar: An efficient, magnetically stable, and eco-friendly adsorbent for imidacloprid and thiamethoxam removal

Neonicotinoids, ones of the most used pesticides extensively present in water environment, are hazardous to environment and human. Herein, a novel magnetic adsorbent ZIF-8-HA@MCSB is designed by modifying ZIF-8 and humic acid (HA) onto the surface of magnetic corn stalk biochar (MCSB) for removing imidacloprid (IMI) and thiamethoxam (THI) from water. MCSB has a superior adsorption performance among magnetic biochars (MBCs); the modification of ZIF-8 creating hierarchically porous structure and HA promoting the crystal growth of ZIF-8 can enhance its adsorption performance. Hence, ZIF-8-HA@MCSB exhibits the high maximum adsorption capacities for IMI (163.9 mg g−1) and THI (123.5 mg g−1). Meanwhile, the HA modification offers a protective shell for magnetic Fe3O4, which endows ZIF-8-HA@MCSB with distinguished magnetic stability. Even in pH = 2 solution, ZIF-8-HA@MCSB still possesses a saturation magnetization value of 13.07 emu g−1, which is beneficial for its separation and reuse. Especially, ZIF-8-HA@MCSB can be repeatedly used 5 times with high removal efficiencies (over 90%). Furthermore, the low Fe (less than 0.3 mg L−1 at pH ≥ 2) and Zn (less than 1.0 mg L−1 at pH ≥ 3) leaching concentrations in a wide pH range guarantee the environmental security of ZIF-8-HA@MCSB. And a promoting effect on wheat growth enables waste ZIF-8-HA@MCSB potentially to be fertilizer for crop production, which agrees with the sustainable concept. Therefore, the advantages of having high adsorption capacities for IMI and THI, resistant to acid, and friendliness to environment indicate that ZIF-8-HA@MCSB has a significant potential for real neonicotinoids removal. In this work, a novel magnetic adsorbent (ZIF-8-HA@MCSB) with the high adsorption capacities of IMI and THI is obtained by simply modifying ZIF-8 and humic acid (HA) onto the magnetic corn stalk biochar (MCSB) surface. Such a magnetic adsorbent has never been reported before. More importantly, compared with various modification methods to increase the adsorption capacity, there are few reports on concerning the acid resistance and environmental friendliness of magnetic adsorbents, especially the corresponding adsorption capacity also increases.