Synthesis and characterization of three-dimensional graphene oxide-chitosan/ glutaraldehyde nanocomposites: Towards adsorption of crocin from saffron

Despite the unique properties of graphene oxide (GO) as a green adsorbent, its low structural stability presents a drawback. This study aimed to modify the properties of GO through its functionalization with chitosan (CH), cross-linked with glutaraldehyde (GLU), and synthesized via the freeze-drying method (GO-CH/GLU). Microscopic analysis illustrated that covering the GO sheets with CH and nanoparticles (NPs) resulted in a 15.8 % increase in d-spacing and a 600 % increase in sheet thickness. The GO-CH/GLU composite was utilized for the separation/purification of crocin from saffron extract under varying pH (5-9), temperature (298-318 K), stirring rate (100-300 rpm), and crocin concentration (25-200 mg/mL). The Freundlich isotherm and pseudo-second- order kinetic models provided a good fit for crocin adsorption. Thermodynamic analysis revealed that the process was endothermic, spontaneous, and physical. Optimal adsorption conditions in batch mode were pH 7, a stirring rate of 300 rpm, a temperature of 318 K, and a crocin concentration of 100 mg/mL. These conditions were applied in a continuous system, resulting in a crocin separation efficiency of 94.17 % at 180 mL/h. Additionally, HPLC data indicated that the purity of separated crocin exceeded 90 %. So, the GO-CH/GLU composite is a promising and economical adsorbent for the food industry.