Biobased Nanographene Oxide Creates Stronger Chitosan Hydrogels with Improved Adsorption Capacity for Trace Pharmaceuticals

A promising green strategy for the fabrication of fully biobased chitosan adsorbents for wastewater purification is presented. Nanographene oxide (nGO)-type carbon dots were derived from chitosan (nGOCS) or from cellulose (nGOCL) through a two-step process including microwave-assisted hydrothermal carbonization and oxidation. Finally, nGO were evaluated as biobased property enhancers in chitosan hydrogel adsorbents. Macroporous chitosan hydrogels were synthesized by cross-linking with genipin, and the incorporation of nGO into these hydrogels was shown to facilitate the cross-linking reaction leading to more robust 3D cross-linked networks. This was evidenced by the increased storage modulus and by the swelling ratio that decreased from 5.7 for pristine chitosan hydrogel to 2.6 for hydrogel with 5 mg/mL nGOCS and 3.3 for hydrogel with 5 mg/mL nGOCL. As a further proof of the concept the hydrogels were shown to be effective adsorbent for the common anti-inflammatory drug diclofenac sodium (DCF). Here, the addition of nGO promoted the DCF adsorption process leading to 100% removal of DCF after only 5 h. The synergistic effect of electrostatic interactions, hydrogen bonding, and π–π stacking could explain the high adsorption of DCF on the hydrogels. The developed biobased CS/nGO hydrogels are thus promising adsorbents with great potential for purification of trace pharmaceuticals from wastewater.