A Win–Win Strategy to Fabricate Multifunctional Doping Materials from Cationic Dyes and Negatively Charged Biomass (Cellulose Nanocrystals)

Abstract If optical probes with different sensitivity could be performed simultaneously in their hard states (e.g., film), soft states (e.g., gel), and solution states, their sensing accuracy could be enhanced due to the highly mutual calibration. The biomass of cellulose nanocrystals is less compatible with commonly used organo‐fluorescent dyes and require chemical modification to improve their application performance, but this leads to the less‐effective material cost. In this work, depending on the electrostatic attractions between the negatively charged polymer matrix with cationic dyes, the cellulose nanocrystals (CNCs)‐based emissive membranes were prepared by vacuum filtration method. Then, the resulting materials were transformed into hydrogels, or dispersed into water solutions, or further absorbed into commercially available polymer spheres and filter papers, resulting in the optical devices with different states. It is worth mentioning that this preparation process does not require chemical modification of cellulose nanocrystals or the addition of organic dispersants, thus greatly reducing the material cost. Finally, the sensing behaviors toward several important stimuli, such as temperature, pollutants like Cr (VI) and pH changes, were successfully carried out. Overall, our research works highlighted a processable way to fabricate fluorescent, water‐dispersible, portable, long‐time‐storable, cost‐effective sensors to meet versatile application requirements.