Fe-AC nanocomposites derived from agro-waste biosorbents: a systematic review of synthesis routes, adsorption mechanisms, regeneration, and environmental sustainability.

Heavy metals, synthetic dyes, pharmaceuticals, pesticides, and other persistent contaminants continue to challenge water-treatment systems and require adsorbents that combine high affinity, recoverability, and practical reusability. Iron oxide-grafted agro-waste-derived activated carbon (Fe-AC) composites integrate the porosity and surface chemistry of biomass-derived carbon with Fe2O3/Fe3O4-based binding, redox activity, and magnetic separation. This systematic review evaluates synthesis routes, physicochemical characterization, contaminant-specific adsorption mechanisms, regeneration behavior, and the available evidence on environmental and economic implications. Particular attention is given to differences between inorganic and organic pollutant removal, the molecular-level roles of Fe-OH/Fe-O sites and carbon-surface interactions, and the influence of pH, competing ions, natural organic matter, and experimental conditions on reported adsorption performance. The literature indicates strong laboratory-scale potential, but direct cross-study ranking of adsorption capacities is limited by heterogeneous test conditions. Major barriers to practical translation include iron leaching, loss of capacity during regeneration, matrix interference, limited continuous-flow and real-wastewater validation, and the absence of harmonized quantitative life-cycle and techno-economic assessments. These limitations define priorities for standardized benchmarking, mechanistic validation, long-term cycling, pilot-scale testing, and environmentally robust Fe-AC design.