A Fe 2 O 3-biochar nano-composite (Fe 2 O 3-BC) was prepared from FeCl 3-impregnated pulp and paper sludge (PPS) by pyrolysis at 750°C. The characteristics and methyl orange (MO) adsorption capacity of Fe 2 O 3-BC were compared to that of unactivated biochar (BC). X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the composite material was nano-sized. Fourier transform infrared (FTIR) spectroscopy revealed the presence of hydroxyl and aromatic groups on BC and on Fe 2 O 3-BC, but Brunauer-Emmett-Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) porosity were lower for Fe 2 O 3-BC than BC. Despite the lower BET surface area and porosity of Fe 2 O 3-BC, its MO adsorption capacity was 52.79 % higher than that of BC. The equilibrium adsorption data were best represented by the Freundlich model with a maximum adsorption capacity of 20.53 mg g-1 at pH 8 and 30 min contact time. MO adsorption obeyed pseudo-second-order kinetics for both BC and Fe 2 O 3-BC with R 2 values of 0.996 and 0.999, respectively. Higher MO adsorption capacity for Fe 2 O 3-BC was attributed to the hybrid nature of the nano-composites; adsorption occurred on both biochar matrix and Fe 2 O 3 nanocrystals. Gibbs free energy calculations confirmed the adsorption is energetically favourable and spontaneous with a high preference for adsorption on both adsorbents. The nano-composite can be used for the efficient removal of MO ([97 %) from contaminated wastewater.

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