Green synthesis of chitosan/glutamic acid/agarose/Ag nanocomposite hydrogel as a new platform for colorimetric detection of Cu ions and reduction of 4-nitrophenol.

In this study, the green synthesis of chitosan/glutamic acid/agarose/Ag (Chi/GA/Aga/Ag) nanocomposite hydrogel was obtained via in situ reduction of Ag ions during the crosslinking process of chitosan-agarose double network hydrogels. The rich hydroxyl, carboxyl and amino groups in both agarose, chitosan, and glutamic acid can effectively control the growth, dispersion and immobilization of nearly spherical Ag nanoparticles (70 nm) in the Chi/GA/Aga/Ag composite hydrogel. Glutamic acids can act as the structure-directing agents to induce the formation of chitosan/glutamic acid hydrogel. The mechanical strength of the Chi/GA/Aga/Ag composite hydrogel can be enhanced by the introduction of chitosan-agarose double network hydrogels, which guarantees that it can be directly used as a visual test strip of the Cu ions with a lower detection limit of 1 μM and an active catalyst for the reduction of 4-nitrophenol within 18 min. The quantitative and semi-quantitative measurement of Cu ions can be carried out by UV-visible absorption spectroscopy and visual measurement, which provided a convenient, portable, and "naked-eye" solid-state detection methodology.