Phosphorus-Doped Cellulose-Derived Carbon Aerogel for Synergistic Adsorption of Congo Red and Cu(II) from Complex Wastewater

Abstract Wastewater produced by dye-related industries commonly contains metal ions, together with organic dyes. Their simultaneous removal is difficult because these pollutants differ in charge, molecular size, and binding behavior. To treat wastewater cocontaminated with copper ions (Cu(II)) and Congo red (CR), phosphorus-doped carbon aerogel (PCA) was fabricated from sodium carboxymethyl cellulose by sol–gel processing, freeze-drying, and one-step carbonization, with phytic acid serving as the phosphorus source and activator. In the single-component systems, Cu(II) and CR are retained by PCA through combined electrostatic attraction, surface complexation, hydrogen-bond formation, and enrichment within the hierarchical pore structure, giving maximum adsorption capacities of 76.40 and 641.86 mg g–1, respectively. The adsorption kinetics follows the pseudo-second-order model, and the equilibrium data are better described by the Langmuir isotherm model. In the Cu(II)–CR binary system, PCA exhibits synergistic adsorption toward both pollutants with CR showing a more pronounced enhancement. The maximum adsorption capacities increase to 87.83 mg g–1 for Cu(II) and 1795.32 mg g–1 for CR, representing 1.15- and 2.8-fold increases, respectively. This synergy is mainly attributed to Cu(II)-mediated local charge regulation and interfacial interactions, which reduce the electrostatic repulsion toward CR and promote its adsorption on the PCA. Regeneration and simulated wastewater experiments further support the applicability of PCA for treating cocontaminated wastewater. This study provides new insights into the design of carbon-based adsorbents for the synergistic removal of heavy metal ions and organic dyes from complex wastewater systems.