Tunable wettability of Chitosan-Biochar composites for Oil-Water separation and noble metal recovery.

As wastewater discharge issues in the petrochemical industry become increasingly severe, billions of tons of wastewater containing emulsified oil and trace platinum group metals (PGMs) is discharged annually, causing significant environmental pollution and resource loss. To address this challenge, biomass resources have been extensively studied for conversion into biochar via pyrolysis as an adsorbent material for wastewater treatment. Despite biochar's abundant availability and low cost, its limited specific surface area and functional groups constrain treatment efficiency. In recent years, research on biochar modification or composite materials has emerged as an effective strategy to enhance performance. Herein, we report a unified material strategy based on a chitosan-Prussian blue-biochar precursor that can be divergently processed into two distinct forms with antagonistic wettability: a hydrophilic hydrogel for PGM capture and a superhydrophobic sponge coating for oil separation. The silanized sponge composite (CPBBSM-P) exhibits excellent superhydrophobicity (water contact angle = 168.4°) and high adsorption capacities for oils and organic solvents (up to 81 g/g), enabling selective and continuous separation from water. The hydrogel composite (CPBBHM) demonstrates exceptional adsorption capacities for Pd(II) (290 mg/g) and Pt(IV) (593.67 mg/g), far surpassing many reported adsorbents. The adsorption mechanism was elucidated through systematic characterization, revealing the synergistic effect of coordination, electrostatic interaction, and reduction deposition. This work provides a novel "one-precursor-for-two-tasks" paradigm, offering a cost-effective and integrated solution for the complex challenge of petrochemical wastewater remediation.