Mixed matrix membrane of Pebax-1657 incorporated with H₂O₂-modified ball-milled biochar for enhanced CO₂ separation

Biochar derived from wheat straw was prepared and subsequently modified with hydrogen peroxide through ball milling, yielding ball-milled wheat straw biochar (BMWB). BMWB/Pebax mixed matrix membranes (MMMs) were prepared by incorporating BMWB into Pebax-1657, and their CO₂ separation performance was evaluated. The results showed that ball milling successfully reduced the biochar particle size, increased its specific surface area, and strengthened the intensity of surface functional groups. Furthermore, hydrogen peroxide modification augmented the oxygen-containing functional groups on the biochar surface, enhancing its hydrophilicity and improving its dispersion within the Pebax-1657. Under the experimental conditions of 25 °C and 0.2 MPa, the MMMs loaded with 3 wt% BMWB exhibited significantly enhanced gas separation performance, with a CO₂ permeability of 97.75 Barrer and CO₂/N₂ selectivity of 62.3. These values represent substantial improvements of 38.8 % and 32.8 %, respectively, compared to the pristine Pebax-1657 membrane. This enhanced separation performance can be ascribed to two primary factors: (1) the presence of abundant functional groups (e.g., carboxyl and amino groups) on BMWB significantly improved CO₂ affinity; and (2) the intrinsic gas transport channels within BMWB, combined with the tortuous pathways generated by the effective stacking of BMWB particles, synergistically enhanced both CO₂ permeability and selectivity.