A hierarchical porous carbon – Mn+[FAU] (Mn+ = Ni2+ or Cu2+) adsorbent: Synthesis, characterization and adsorption of salicylic acid from water

• Carbon–zeolite composite modified with Cu2+ or Ni2+ for salicylic acid adsorption.
• Adsorption was influenced by solution pH, carbon presence and metal modification.
• Cu2+ modified composite excelled during salicylic acid adsorption.
• Composite synergistic behavior proved ideal for adsorption-based water remediation.

This work presents the preparation and characterization of a hierarchical porous carbon – Mn+[FAU] or Mn+-CFAU (Mn+ = Ni2+ or Cu2+; FAU = Y zeolite) adsorbent as a potential platform to develop processes for the removal of contaminants of emerging concern (CECs) from water. The impetus for this contribution is the possibility of combining the hydrophobic nature of activated carbons with the unique adsorbent–adsorbate interactions provided by a transition metal based zeolite. A quasi-ordered (CFAU) composite was hydrothermally synthesized and subsequently decorated with extraframework transition metal centers (Ni2+ or Cu2+). The resulting CFAU variants were fully characterized using XRD, XPS, ICP-MS, TGA, zeta potential and nitrogen adsorption to determine chemical, structural and textural properties. Furthermore, these properties were used to assess the performance of the CFAU variants during salicylic acid (a CEC with high occurrence) equilibrium adsorption tests performed at 25 °C and pH in the 7–8 range. In terms of performance, the salicylic acid equilibrium overall adsorption capacities increased as follows: FAU < Activated Carbon < CFAU < Ni2+-CFAU << Cu2+-CFAU. Both transition metal-based composite adsorbents excelled at removing the acid even at concentrations near the 20 ppb levels. Cu2+-CFAU was capable of adsorbing one salicylic acid molecule per zeolite unit cell at the maximum equilibrium loading observed. Thermal treatment tests suggest that spent Mn+-CFAU composites could be regenerated via elimination of the adsorbate in an inert environment without affecting the adsorbent structure.

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