Surface characterization of oxidized biochar fibers derived from Luffa Cylindrica and lanthanide binding

In the last years, biochar fibers derived from Luffa Cylindrica have emerged as promising adsorbent material for harmful heavy metal ions. Based on their unique vascular structure, they exhibit a large surface area and thus high capability for the adsorption of metal ions. We investigated the structure and chemical surface composition of the carbonized fibers after treatment with 8 M HNO3 prior and after Sm3+ binding in aqueous solutions. We used a large combination of classical analytical methods such as acid-base titration and batch-type adsorption experiments, as well as high-resolution microscopic and spectroscopic techniques like FTIR, XPS/REELS and SEM-EDX. The goal of the chemical oxidation is to functionalize the inner and outer surfaces of the biochar fibers by forming oxygen-containing active surface groups. Titration and spectroscopic data clearly reveal that anhydrides and carboxylic acids are acting as main surface groups to bind metal ions like Sm3+. We will show that the combination of high surface area and high density of carboxylic acid groups results in extremely high capacity of 2.4 mol kg(-1) for the adsorption of Sm3+ ions. Therefore, the functionalization of biochar fibers offers a great potential to design advanced adsorbent materials for polluting heavy metal ions.