Fabrication of carboxyalkylated lignin derived microgels for adsorbing heavy metals

Fabricating bio-based materials with various functionalities is crucial in sustainable material production. In the current study, we produced microgels that comprised carboxyalkylated lignin with altered alkyl spacers and studied how these alkyl spacers on the carboxylated lignin impacted the physicochemical properties of lignin-based microgels. The H-1 NMR results indicated that the microgels containing lignin derivatives had similar crosslinking degrees (10.7% for CPr-C vs. 11.1% for CPe-C). Also, the rheological studies suggested that the storage modulus was greater for CPe-C microgel than CPr-C microgel, which might be due to its greater density and compactness. For both samples, the loss modulus was less significant than the storage modulus indicating that the microgels had more remarkable elasticity than viscosity, confirming their solid-like gel structures. With higher hydrophilicity and swelling, CPr-C adsorbed more heavy metals than CPe-C. The adsorption sequence of heavy metals for both lignin-based microgels was Ni+2 >Zn+2 >Cd+2, which could be associated with the smaller radius of Ni+2 than Zn+2 and Cd+2 ions.