Engineered Nanomaterials and Modified Biochar for Heavy Metal and Organic Contaminant Remediation: A Critical Review

Global environmental contamination by heavy metals, organic pollutants, and emerging contaminants continues to threaten ecosystem and human health. Engineered nanomaterials and modified biochar are widely studied remediation materials because of their high specific surface areas, reactive or sorptive sites, and tunable surface properties. This narrative critical review compares the two material classes in terms of remediation mechanisms, development trajectories, evidence scales, practical applications, technical limitations, environmental risks, sustainability performance, and future research needs. Across the reviewed evidence, engineered nanomaterials often enable rapid contaminant transformation under optimized laboratory conditions, whereas modified biochar more commonly supports contaminant immobilization, soil improvement, and potential carbon storage. The review distinguishes adsorption, degradation, immobilization, mineralization, and detoxification and classifies application evidence from laboratory batch tests to full-scale use. Particular attention is given to nanomaterial–biochar hybrids and to trade-offs involving nanoparticle stability, transformation products, regeneration, and end-of-life management. The available evidence remains dominated by laboratory studies, while comparable life-cycle, techno-economic, chronic-toxicity, and long-term field data are limited. Accordingly, the principal research challenge is to demonstrate not only removal performance, but also durability, ecological safety, economic feasibility, and net environmental benefit under realistic conditions.