Lignin is one of the most abundant natural polymers and is affordable, has high carbon content and abundant active functional groups. It has been utilized as electrode materials in electrical double-layer supercapacitors and pseudo-supercapacitors.

Chromium(VI) is a well-known highly toxic metal ion that has serious effects on the environment. Herein, novel functional alginate beads were developed cooperatively using polydopamine (PDA)–polyethylenimine (PEI)-modified CaCO₃ composites (solid porogens with amine groups), with PEI acting as a granule interior and surface modification reagent. The hollow cavity structures with high-density reactive sites immobilized favorably into the interior of the alginate capsules and the PEI layers grafted onto the alginate bead surface via cross-linking led to bead-like composites with interior/surface accessible PEI, with the aim of exceptional Cr(VI) removal performance from aqueous conditions. SEM-EDS, TEM, XRD, BET, FT-IR, and XPS analysis were used to characterize these new sorbents. The adsorption properties were investigated using batch adsorption and continuous adsorption processes. The optimally designed adsorbent, namely 0.7-HS-PDA@PEI-SA@PEI, possessed excellent Cr(VI) adsorption capacity, exhibiting a superior experimental uptake capacity of 524.7 mg g⁻¹ for Cr(VI), which was much higher than those of most reported adsorbents. The experimental data fitted well to the Freundlich isotherm and pseudo-second-order kinetic model in a batch experiment. The experimental breakthrough curves obtained under continuous processes were correlated with the Thomas and Adams–Bohart models. Significantly, the reusability experiments showed that 0.7-HS-PDA@PEI-SA@PEI beads exhibited excellent regeneration ability, with no obvious decline in adsorption capacity after five cycles. These results indicated that the newly designed 0.7-HS-PDA@PEI-SA@PEI beads were promising for Cr(VI) removal because of their ultra-high chromium adsorption capacity, rapid adsorption rate, low cost, and facile recovery process.