MOFs meet loofah: controlled preparation of pH-responsive biosorbent via radiation grafting in situ growth for efficient dyes removal

Abstract

Herein, a novel pH-responsive adsorbent with selective adsorption effect on cationic and anionic dyes was further designed and prepared via radiation grafting in situ growth technique. The cheap, modifiable and benign natural renewable biomass loofah (LFs) was selected as the substrate, and then acrylic acid (AAc) was grafted onto the loofah substrate through electron beam (EB) radiation (grafting rate of 30.5 %). The introduction of –COOH effectively captured and fixed cobalt ions (Co2+), and zeolitic imidazolate framework-67 (ZIF-67) was grown in situ on the loofah surface with Co2+ as a metal center and 2-methylimidazole as the ligand, so a functional loofah-based adsorbent ZIF-67@LFs-AAc was obtained. The introduction of ZIF-67 significantly enhanced the adsorption efficiency and capability of biomass materials, and successfully combined the advantages of biomass and inorganic nanomaterials. The biosorbent is pH-responsive and can specifically adsorb anionic dyes in acidic setting. The equilibrium uptake capacity of Congo red (CR) is 433.9 mg/g at pH = 3. Cationic dyes can be selectively adsorbed under neutral and basic conditions, and the equilibrium uptake capacity of methylene blue (MB) is as high as 554.0 mg/g at pH = 7. When the addition of the ZIF-67@LFs-AAc was 1.0 g/L, the removed rates of MB and CR were 95.9 % and 91.8 %, respectively. With ZIF-67@LFs-AAc, the adsorption of dyes is promoted by electrostatic interaction, pore adsorption, π-π interaction and hydrogen bond. In summary, the integration of MOFs with loofah can lead to the development of a highly efficient biosorbent for treating dye-containing wastewater, thereby offering promising prospects for its application in water treatment.