Deep-Eutectic-Solvent-Assisted Mechano-Photocatalytic Transformation of Chitosan Films for Green Elimination of Water Pollutants

Chitosan films are emerging as a magnificent alternative to powdered photocatalysts but suffer from issues such as poor mechanical stability and loss of photocatalytic activity. These issues hinder the aspired green rationale for choosing these films over powdered materials. Herein, we have demonstrated how a simple and green Deep Eutectic Solvent (DES) based modification can resolve these problems. The DES, composed of ZnCl2 and urea, induced significant structural and morphological changes on the CN surface, which led to a massive rise in the mechanical strength of the films. Particularly in the CN-6.6 formulation, DES adhered to a unique dendrite arrangement, which enhanced the adsorption capacity of the surface towards pollutants. Besides, DES also affected the electronic properties of the CN surface, which enabled the latter to showcase significant photocatalytic activity. The combined impact of enhanced adsorption and excellent charge transfer with the help of electronic coordination between CN-6.6 film surface and g-C3N4 ensured that CN-g-C3N4-6.6 film not just retains but also exceeds the efficiency of g-C3N4 for all the target pollutants, i.e., methylene blue, tetracycline hydrochloride, and rhodamine B. Mechanistically, the enhanced photocatalytic activity after DES inclusion was a consequence of the direct coordination between DES and photocatalyst due to in situ formation of semiconducting entities, which enhanced the charge separation. Hence, for the first time, we are reporting the application of the solvent as a direct and functional constituent of the photocatalytic pathway. These remarkable structural, morphological, and electronic effects embarked by DES have resolved two of the most notorious problems persisting with CN films in an entirely green framework.