Post-activation exposes hidden Fe-N sites in sludge-Chlorella biochar for synergistic tetracycline adsorption: A pore-site decoupling strategy.

Post-activation of sludge-Chlorella biochar exposes hidden Fe3O4 crystallites and pyridinic N sites, boosting tetracycline adsorption capacity to 193.1 mg/g at 25°C.

• Why it matters: Conventional biochar modification faces a pore–site trade-off, where pore-forming steps disrupt metal centers and metal loading blocks pores, limiting adsorption performance.
• What they did: Fe and N were pre-loaded into sludge-Chlorella precursors by co-pyrolysis, then KOH post-activation etched the carbon, increasing specific surface area from 29.3 to 64.2 m2/g.
• The result: The KFe2NSCBC adsorbs tetracycline at 193.1 mg/g (25°C) and 315.8 mg/g (45°C), with DFT and mechanistic analyses indicating pore–site synergy via diffusion and high-affinity binding.

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