Universal preparation of cellulose-based colorimetric sensor for heavy metal ion detection

A simple and universal strategy was developed to prepare cellulose/dye composite film, as colorimetric sensor for heavy metal ions (HMIs) detection. After regenerating cellulose solution in ethanol, the regenerated films were further soaking in dye/ethanol solution followed by hot-pressing, to obtain cellulose/dye composite films. 1-(2-pyridylazo)-2-naphthol (PAN) was used as an example, and the resultant cellulose/PAN composite films (CPs) possessed robust mechanical property (tensile strength of 52.9 MPa), light transmittance, and thermodynamic stability. PAN distributed uniformly as nanoparticles of 30 nm on cellulose because of the interaction between N of azo group of PAN and cellulose. When used as colorimetric sensor for Zn²⁺ detection, the detection limit of CP was as low as 100 ppb, and the color change was distinguishable after testing with tap water. Moreover, two more dyes including 1-(2-thiazolylazo)-2-naphthol (TAN) and dithizone (Dith) were also immobilized successfully on cellulose, and the resultant films were effective colorimetric sensor for HMIs like Zn²⁺ and Cu²⁺. This work provided a facile and universal method to prepare cellulose-based colorimetric sensor or HMI detection, demonstrating great potential in water treatment and natural resources utilization.