Enhanced Trace-Level Assay and Excision of Cu(II) Ions via MOF-Cellulose Nanofiber Nanohybrids: A Study of Adsorption Mechanism and RSM Optimization

Metal-organic frameworks (MOFs), synthesized as nano-sized particles, have innumerable applications. However, lower hydrothermal and chemical stability and diminishing structural strength with increasing length of organic ligands have necessitated a suitable substrate for their support, ensuing improved applications and recycling. This study synthesized novel nanohybrids by anchoring Zn-BTC MOFs on the surface of Schiff base cellulose nanofibers (SBCFs) (SBCF@Zn-BTC) using the hydrothermal method. The cellulose nanofibers (CNFs) were derived from waste rice straw to warrant a sustainable bio-economy. The nanohybrids exhibited significant fluorescence quenching in the presence of Cu(II) ions in aqueous medium owing to fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET) mechanisms. Besides, the nanohybrids also showed excellent adsorption of Cu(II) ions due to porous structure of MOF. EDS and XPS results confirmed the synthesis and adsorption of Cu(II) ions. The nanohybrid was highly selective for Cu(II) ions with a detection limit of 0.254mM and negligible interference from competing ions. The removal efficiency was 82.8%, substantially higher than SBCFs and Zn-BTC MOF, respectively. The maximum adsorption capacity was 263.5mg.g⁻¹ (C_o¼400mg.L⁻¹) at pH 8 and after 75minutes of contact time. Facile recovery and recyclability up to 10 cycles with only a 5% descent in adsorption efficiency warranted their efficient performance and potential in wastewater remediation.