Facile and green carboxylation of never-dried bacterial cellulose produced from low-cost substrates: structural characterization and copper binding performance

Abstract

In this study, bacterial cellulose production was optimized using molasses and cheese whey via response surface methodology, a central composite design approach. Using Gluconacetobacter hansenii, the effects of sugar, protein, pH, and acetic acid were evaluated, resulting in a 6.85-fold yield increase from 0.9 (HS media) to 6.17 g L⁻¹. The produced BC was hydrolyzed with sulfuric acid to generate bacterial cellulose nanocrystals (BCNC), followed by functionalization through the Fenton reaction to synthesize carboxylated BCNC (BCNC-H). Structural analyses using FTIR and XPS confirmed successful carboxylation, with the O/C ratio increasing from 0.55 (BC) to 0.68 (BCNC-H). Zeta potential measurements demonstrated a significant increase in the absolute negative surface charge (−22.53 mV for BC vs. −37.46 mV for BCNC-H). SEM images revealed a substantial reduction in fiber diameter after sulfuric acid treatment and the Fenton reaction (BC > BCNC > BCNC-H). Thermal and crystallinity properties were also evaluated. Finally, BCNC-H exhibited excellent Cu²⁺ adsorption capacity (164 ± 8.07 mg g⁻¹), representing a 173% increase over unmodified BC, highlighting its potential as a sustainable and efficient biopolymer-based adsorbent for water and wastewater treatment.