Bio-friendly fluorescent polyvinyl alcohol/gelatin/chitosan hydrogel membranes strengthened by g-C3N4/CQDs nanocomposite: Preparation, investigation of UV-absorption, mechanical and rheological properties

This study's purpose is to synthesize fluorescent hydrogel membranes using polyvinyl alcohol, chitosan and gelatin as bio-friendly substances, and to analyze the strengthening effect of graphitic carbon nitride/carbon quantum dots nanocomposite (g-C3N4/CQDs) on optical, mechanical and rheological properties of the synthesized hydrogel membranes (HMs). A two-step pyrolysis of the mixture of starch as a natural resource and urea as a nitrogen resource with 1:10 weight proportion was utilized to synthesize g-C3N4/CQDs nanocomposite via microwave -assisted system. Water absorption value in the synthesized samples was calculated 237-275%. UV absorbance and fluorescence features were investigated by UV-visible and photoluminescence spectroscopy. Results indicated that adding 0.5 wt% and 1 wt% g-C3N4/CQDs to HMs matrix led to UV absorption in 225, 275 and 395 nm wavelengths and strong fluorescence emission in 515 nm (green region). Samples flexibility was figured 22-56% by tensile test results so that by an increase in filler content, flexibility was driven down but tensile strength was driven up. Rheometry test findings confirmed that g-C3N4/CQDs adding resulted in improvement of rheological properties of the HMs like storage modulus and loss modulus, and growth of complex viscosity. [Graphical abstract]