Potassium citrate-activated hierarchical porous biochar from waste biomass: A promising adsorbent for diclofenac removal with insights into adsorption mechanisms and column adsorption behavior

Biomass-derived biochar is a promising adsorbent for removing organic pollutants from wastewater, yet its performance is often constrained by limited pore development. A novel activation strategy using potassium citrate (KCit) was proposed to convert waste baijiu distillers’ grains (BDGs) into high-performance biochar with a hierarchical porous structure for DCF removal. Unlike conventional activators (e.g., KOH or ZnCl 2 ) that are highly corrosive or rely on single pore-forming mechanisms, KCit serves as a green, low-corrosive, and multifunctional agent that simultaneously enables K⁺-induced etching, gas evolution, and molten-salt templating. Multi-technique characterizations (TG-FTIR, N 2 physisorption, mercury intrusion porosimetry, FESEM, etc.) were applied to reveal the critical role of KCit in pore evolution. Both batch adsorption and column test were used to evaluate the performances of the BDGs-derived biochar. The KCit-assisted pyrolysis promoted the formation of abundant micro–mesopores through K⁺-induced etching, gas evolution, and molten-salt templating effects, significantly improving the textural properties and adsorption capacity of the resulting biochar. The optimized sample exhibited superior performance in both batch and continuous adsorption systems, with rapid uptake and prolonged breakthrough time. The adsorption process was mainly governed by π–π interactions, hydrogen bonding, and pore filling. This work highlights the potential of KCit activation for valorizing biomass waste and developing efficient adsorbents for organic pollutant removal from water.