Carbon sponge nanostructure derived from cellulose as an adsorbent for enhanced removal of organic contaminants

Developing advanced carbonaceous adsorbents with engineered porosity is critical for addressing the global challenge of water contamination by persistent organic micropollutants (OMPs). In this study, we synthesized a series of 3D carbon nanostructure sponges (CS) derived from microcrystalline cellulose via a two-step carbonization and potassium hydroxide (KOH) activation process. By systematically varying the cellulose-to-KOH ratio from 1:1–1:4, we engineered the pore architecture from a strictly microporous framework to a highly hierarchical micro-mesoporous system. Extensive characterization using nitrogen adsorption–desorption isotherms, X-ray diffraction (XRD), Raman spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM) revealed that the optimal material (CS4) exhibits an exceptional Brunauer-Emmett-Teller (BET) specific surface area of 3007 m ² g ⁻¹ and a total pore volume of 1.37 cm ³ g ⁻¹. Structural analysis resolved a crystallographic paradox: while XRD indicated a loss of long-range order, Raman spectroscopy and TEM confirmed the preservation of local graphitic domains within a highly crumpled, exfoliated nanosponge morphology. This unique structure proved decisive in the adsorption of diverse OMPs, including pharmaceuticals, phenols, and dyes. Adsorption assays demonstrated a strong structure-function relationship governed by size exclusion; while all adsorbents effectively removed small phenolic compounds (capacities ∼ 200 mg g ⁻¹), only the hierarchically porous CS4 could accommodate bulky dye molecules such as Direct Red 80 (60.6 mg g ⁻¹) and Reactive Green 19 (46.8 mg g ⁻¹), which were sterically hindered on the microporous CS1. The results establish cellulose-derived carbon nanosponges as sustainable, high-performance adsorbents with tunable porosity, offering a scalable solution for the remediation of complex wastewater matrices containing pollutants of varying molecular dimensions.