Pineapple leaf-derived TEMPO-oxidized cellulose nanospheres and graphene oxide composite: a green solution for ciprofloxacin adsorption

Abstract

Graphene oxide (GO) is a promising material for the adsorption of contaminants from wastewater. In this study, a GO-based composite with high adsorption capacity and reduced GO content was synthesized by incorporating TEMPO-oxidized cellulose nanospheres (TO-CNS) derived from pineapple leaves. TO-CNS were effectively integrated into GO via a one-pot reaction based on Hummer’s method. In this process, TEMPO oxidation selectively converted the –CH₂OH groups on cellulose nanospheres into –COOH groups, all while preserving the crystalline structure of cellulose I. Notably, the in situ integration of TO-CNS as a co-support during graphite oxidation significantly enhanced the interlayer spacing of GO sheets, expanding it from 0.34 to 0.85 nm. This increase in spacing, indicative of robust interfacial interactions, was further validated using FTIR spectroscopy. The spectra revealed hydrogen bonding and pronounced shifts in the mode and position of the functional group peaks, underscoring the structural alterations induced by TO-CNS integration. Raman spectroscopy revealed increased graphitic defects, and thermal analysis confirmed structural integration. The composite's average pore size of 40 Å demonstrated a significant enhancement that facilitated adsorption compared to 26 Å in GO. Ciprofloxacin adsorption capacities (35.95 ± 0.54–38.47 ± 0.53 mg/g) were comparable to pure GO (35.08 ± 1.10–36.83 ± 1.12 mg/g) despite a reduced GO content (73.8/26.2 wt%). Zeta potential analysis highlighted the roles of electrostatic attraction, hydrogen bonding, and π–π stacking in adsorption. This GO/TO-CNS composite demonstrates the potential for efficient, sustainable, and biocompatible antibiotic adsorption, offering significant promise for environmental remediation.