Novel Fluorescent Nanocellulose Hydrogel Based on Nanocellulose and Carbon Dots for Detection and Removal of Heavy Metal Ions in Water

Abstract

Water is an important raw material in the food production process. Maintaining the quality and safety of water is very important in the food field. In this study, a simple novel fluorescent nanocellulose hydrogel (FNH) was prepared for the detection and removal of heavy metals (Fe³⁺ and Pb²⁺) in aqueous solutions based on carbon dots (CDs). The CDs were grafted onto the carboxylated nanocellulose (CNC) by the EDC/NHS coupling method, and then the nanocellulose (NC), CNC, and FNH were characterized by FTIR analysis. The effect of adsorption environment on FNH adsorption capacity was also investigated. After carboxylation and grafting of CDs, the adsorption capacity of nanocellulose to Fe³⁺ and Pb²⁺ was greatly improved, and it was also allowed to make fast visual responses to Fe³⁺ as an optical sensor to determine the concentration of Fe³⁺ through the visual signal. Static adsorption experiment demonstrated that the removal rate of Fe³⁺ and Pb²⁺ by FNH exceeded 69.4% and 98.2%, and the adsorption capacity amount reached 98.3 mg/g and 442.0 mg/g. At the same time, due to the fluorescence quenching effect of Fe³⁺, FNH could also be used for the detection of Fe³⁺ concentration in aqueous solution, and the limit of detection (LOD) could reach 62.5 mg/L.

Keywords: adsorption; fluorescent nanocellulose hydrogel; fluorescent sensor; heavy metals ion; nanocellulose.

Figure 1

FTIR spectrum of NC, CNC and FNH.

Figure 2

SEM images of FNH.

Figure 3

Spectral features of CDs. UV-Vis and PL excitation and emission spectra of CDs (A), and excitation-dependent PL spectra (B).

Figure 4

Appearance and fluorescence behavior of synthesized fluorescent nanocellulose hydrogel (FNH).

Figure 5

Effect of contact time on Fe³⁺ (A) and Pb²⁺ (B) adsorption.

Figure 6

Effect of pH on Fe³⁺ and Pb²⁺ adsorption.

Figure 7

Effect of absorbent dosage on Fe³⁺ (A) and Pb²⁺ (B) adsorption.

Figure 8

Adsorption isotherms of Fe³⁺ (A–C) and Pb²⁺ (D–F) and curves fitted by the Langmuir and Freundlich equation model.

Figure 9

The adsorption capacity and fluorescence behavior of Pb²⁺, Fe³⁺, Ni²⁺, and Cu²⁺ (A). The relationship between the fluorescence behavior of FNH and the gradient fluorescence quenching of Fe³⁺ concentration (B). (C) shows the standard curve.