Property relationship of alginate and alginate–carbon dot nanocomposites with bivalent and trivalent cross-linker ions

Abstract

Synthesis of nanocomposites of biopolymers is the answer to obtaining superior properties which are biocompatible but also possess good mechanical properties. In this work we made an attempt to study the property relationship of alginate and alginate-carbon dot nanocomposites with different bivalent and trivalent cross-linker ions. Biopolymer alginates were crosslinked with five different bivalent and trivalent metal ions and their corresponding carbon-dot (CD) nanocomposites have been prepared successfully. The carbon dots were prepared from commercially available ‘Assam Tea’. The alginate and alginate–carbon dot nanocomposite films were characterized with UV-visible spectroscopy, FTIR, SEM, and fluorescent microscopy. The tensile strength measurements of all the film samples have been carried out. It was observed that alginate films crosslinked by metal ions with larger sizes (Ba²⁺) show higher tensile strength and higher thermostability. Tensile strength values for Ba²⁺ crosslinked alginate films increased from 24.5 MPa to 43.5 MPa and weight loss at 200 °C decreased to 9% on incorporation of 2% CDs. Moreover loading of carbon-dots in the crosslinked alginate system led to higher absorption in the UV region showing the potential use of alginate–carbon dot films as UV blockers. For Ca²⁺ and Ba²⁺ crosslinked films minimum transmittance values significantly reduced to 4 and 5% respectively in the region from 200 to 400 nm for nanocomposite films with maximums of 2% CDs. Some mechanistic aspect of the superior property shown by Ba²⁺ crosslinked alginate and alginate–carbon dot nanocomposites is also discussed.