Polydopamine-Modified Bacterial Cellulose Aerogels for Efficient Elimination and Recovery of Cr(VI): Performance and Mechanism

It is very desirable to explore eco-friendly and sustainable biobased aerogels for the elimination of highly toxic hexavalent chromium (Cr(VI)) from wastewater. Owing to the advantages of rich hydroxyl groups, high porosity, three-dimensional (3D) networks, strong mechanical stability, nontoxicity, and biodegradability, the renewable bacterial cellulose (BC) exhibits potential application prospects in the removal of various heavy metal ions. However, BC shows poor removal ability toward Cr(VI), due to the shortage of specific binding sites on its surface. Herein, we prepared a polydopamine-functionalized bacterial cellulose aerogel (PDA-BC) with a 3D porous network structure and rich surface functional groups for high-efficiency elimination and recovery of toxic Cr(VI) from wastewater. Owing to the 3D interconnected fibrous network, porous structure, and rich functional groups (amino and phenolic hydroxyl groups), the as-prepared PDA-BC exhibited excellent performance for Cr(VI) elimination, including high removal efficiency (>99%), large capacity (350.9 mg·g^-1), excellent selectivity (<i>K</i>_d > 10⁵ mL·g^-1), superior anti-interference ability, and remarkable recyclability. More importantly, PDA-BC could efficiently reduce the levels of Cr(VI) in natural water samples and real wastewater to below the allowable standard for surface water (lower than 0.04 mg·L^-1), even in the presence of a variety of interfering substances. Moreover, by calcining the spent PDA-BC containing the Cr element, high-purity Cr₂O₃ with considerable economic value has been obtained, avoiding the secondary pollution related to the leaching of Cr from the spent PDA-BC adsorbent. The mechanism of Cr(VI) elimination has been elucidated, including electrostatic interaction, complexation, and oxidation-reduction. Taken together, the renewability of raw materials, mild synthetic conditions, excellent Cr(VI) removal properties, antifouling ability, and convenient separation and recovery of spent adsorbents make PDA-BC promising for Cr(VI) elimination from practical wastewater.