NH2-MIL-100(Fe) Impregnated Amine-Functionalized Magnetic Hydrochar: Synergistic Adsorption Mechanisms for Multiple Heavy Metals and Life Cycle Assessment

The treatment of industrial wastewater containing multiple heavy metals (MHMs) remains challenging, primarily because conventional adsorbents suffer from poor stability, limited adsorption capacity in mixed-metal systems, or high energy consumption during synthesis. To address these issues, this study employed a room-temperature in-situ impregnation method to load NH 2 -MIL-100(Fe) onto amine-functionalized magnetic hydrochar (HBAP). Three highly dispersible magnetic composites, designated as NM-100-HBAP-X (X = 0.75, 1, 1.25), were synthesized by adjusting the mass ratio of NH 2 -MIL-100(Fe) to HBAP. Experimental results demonstrated that the optimal material (NM-100-HBAP-1) exhibited high adsorption capacities for Pb(II), Cd(II), and Cr(VI) in a mixed-metal system. The maximum adsorption capacities determined by the Langmuir model were 181.13, 175.02, and 158.69 mg/g for Pb(II), Cd(II), and Cr(VI), respectively, which are comparable to previously reported values for hydrochars or MOF-based materials. Mechanistic analysis revealed that amino groups facilitate a synergistic process by reducing Cr(VI) to Cr(III), which is then immobilized via complexation and co-precipitation, thereby further enhancing Cd(II) removal. The material also demonstrated good cycling stability, retaining over 50% of its initial adsorption capacity after five regeneration cycles, and maintained effective performance in various real water samples. Furthermore, toxicity tests confirmed its environmental safety, and life cycle assessment quantified the GWP of producing 1 kg of NM-100-HBAP-1 as 41.224 kg CO 2 eq, with electricity and NH 2 -H 2 BDC synthesis as the dominant contributors. This study not only provides an efficient adsorbent for heavy metal removal but also offers a systematic research framework integrating material design, mechanistic investigation, and environmental assessment for pollution remediation.