Carbon Dots-Functionalized Biosilica from Bamboo Leaves for Adsorption and Optical Detection of Cu(II) Ions

Biosilica extracted from bamboo leaves was functionalized with nitrogen-doped carbon dots to produce a CDs/Si composite and evaluated as both an adsorbent and an optical probe for Cu-(II) ion adsorption and detection. The development of multifunctional and sustainable materials for simultaneous Cu-(II) remediation and monitoring remains an important challenge, as many reported carbon-dot systems are used as dispersed nanoparticles that are difficult to recover after use. The integration of bamboo leaf-derived biosilica with nitrogen-doped carbon dots provides a recoverable biomass-derived platform that combines adsorption and optical sensing functionalities within a single material. The adsorption performance of CDs/Si was optimized, revealing an optimum pH of 5 and a contact time of 60 min, with a maximum Cu-(II) adsorption capacity of 15.15 mg/g. The adsorption behavior was well described by both Langmuir and Freundlich isotherm models, while the adsorption kinetics followed a pseudo-second-order model, indicating that chemisorption was the dominant adsorption mechanism. The CDs/Si composite exhibited distinctive optical properties, with strong fluorescence emission at 550.0 nm upon excitation at 497.5 nm. A linear relationship between Cu-(II) ion concentration and fluorescence quenching was obtained according to the Stern-Volmer equation. In addition, smartphone-based colorimetric detection using the PhotoMetrix PRO application enabled both visual and quantitative analysis of Cu-(II) ions. The fluorescence and smartphone-based approaches showed linear detection ranges of 0.1-50.0 mg/L and 0.2-50.0 mg/L, with limits of detection of 0.03 and 0.05 mg/L, respectively. The optical sensing methods were successfully validated by standard spiking experiments in real water samples, showing excellent accuracy and no statistically significant difference compared with flame atomic absorption spectrometry. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses provided insight into the Cu-(II) binding mechanisms on the CDs/Si surface. Overall, this study demonstrates that the developed CDs/Si composite is a sustainable, simple, and high-performance analytical platform for Cu-(II) ion monitoring and remediation of water.