Optimising Low Temperature Pyrolysis of Mesoporous Alginate-Derived Starbon® for Selective Heavy Metal Adsorption

In response to the ever increasing need to develop more efficient and sustainable methods for removing heavy metal contaminants from aqueous systems, the following article reports on the design of highly mesoporous alginate-derived materials (Starbon^®) and their application to the adsorption of heavy metals. Using the Starbon^® process to expand, dry and pyrolyse an inherently porous polysaccharide precursor, it was possible to produce mesoporous materials (BJH mesopore volumes 0.81-0.94 cm³ g^-1) with large surface areas (157-297 m² g^-1) across a range of low pyrolysis temperatures (200-300 °C). The mechanisms of thermal decomposition were explored in terms of chemical and structural changes using N₂-sorption porosimetry, thermogravimetric analysis, titration, FT-IR spectroscopy and ¹³C NMR spectroscopy. It was found that, as a result of intermolecular dehydration and crosslinking, sufficient chemical stability is obtained by the intermediate temperature of 250 °C, with limited improvement seen at higher temperatures. In addition, the materials retained large metal adsorption capacities (0.70-1.72 mmol g^-1) as well as strong selectivity for Cu²⁺ ions (over Co²⁺ and Ni²⁺), as compared to commercial petrochemical-derived cation exchange resin Amberlite™ Mac 3H. Thus, highlighting the potential of Starbon^® materials as a sustainable answer to the widespread problem of heavy metal-contaminated wastewaters.