Colorimetric detection and removal of copper(II) ions from wastewater using a Griess reagent and cellulose nanofibers supported with mesoporous silica nanoparticles: An ImageJ and CIELAB colour space-based analytical approach

• Synthesis and characterization of CNF-MSN composite for removal of copper in real water environment. • The addition of Griess reagent in CNF-MSN composites led to the colour transformation when Cu (II) is present indicating the presence of copper. • The ImageJ approach and UV-Vis were used to detect Cu (II) in water samples. • CNF-MSN composite demonstrated potential for the adsorption of Cu (II) ion from tap, wastewater, and deionised water. • The adsorption results fitted Dubinin-Radushkevich isotherm and pseudo-second order This study presents a green, cost-effective, and dual-function approach for the colorimetric detection and removal of copper ions (Cu(II)) in wastewater, utilizing a cellulose nanofiber–mesoporous silica nanoparticle (CNF-MSN) composite in conjunction with the Griess reagent. The CNF-MSN composite was synthesized via a sol–gel process using cellulose nanofibers derived from natural biomass. Comprehensive characterization using FTIR, SEM, XRD, BET, TEM, and TGA confirmed the successful integration of CNF and MSN, with TEM revealing a web-like nanofiber structure (∼33 nm) and SEM showing mesoporous silica nanoparticles (2–50 nm). Hydrogen bonding between CNF hydroxyl groups and MSN silanol groups was indicated by O–H stretching shifts. For Cu(II) detection, the CNF-MSN composite produced a visible purple color change upon reaction with the Griess reagent across 1–5 mg/L Cu(II) standards. Color intensity and RGB values were quantified using ImageJ, converted to CIEXYZ and CIELAB (Lab) values, resulting in a linear response (R² = 0.9956) over the range of 0.01–5 mg/L, with a detection limit of 0.001521 mg/L. The UV-Vis spectrophotometric method validated the ImageJ approach, yielding an R² value of 0.9993 and a detection limit of 0.006253 mg/L. For Cu(II) adsorption, CNF-MSN removed nearly 100% of Cu(II) within 45 minutes at pH 4–6, outperforming individual CNF and MSN with an adsorption capacity of 0.0978 mg/g and 97.85% removal efficiency. In real samples, removal efficiencies ranged from 94.1% to 99.1%, with a maximum adsorption capacity of 38.9 mg/g. The adsorption data fit the Dubinin–Radushkevich isotherm (R² = 0.980) and the pseudo-second-order kinetics (R² = 0.999). Overall, the CNF-MSN composite offers a sustainable and efficient material for detecting and remediating Cu(II) in water systems.