Lignin-Chitosan-Vanillin Hydrogels as Sustainable Adsorbents for Wastewater Treatment

Date of Award

5-9-2026

Degree Name

M.S. in Materials Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Erick S. Vasquez

Abstract

The growing emphasis on sustainability and the adoption of eco-friendly methods to address environmental pollution have increased interest in sustainable materials such as bio-based hydrogels. These materials offer advantages such as biocompatibility and low toxicity while effectively removing pollutants through adsorption. Recent advances in green chemistry have introduced the use of natural crosslinkers to enhance the mechanical properties of these adsorbents while avoiding toxic synthetic crosslinkers. In this work, fully bio-based composite hydrogels were synthesized using lignin, chitosan, and vanillin, with vanillin serving as a natural cross-linker in the hydrogel matrix. Structural characterization, such as FTIR analysis, confirmed the successful incorporation of vanillin in the lignin-chitosan hydrogel, with new peaks observed at ~1602 cm⁻¹ corresponding to C=N stretching, indicative of the formation of Schiff base linkages. SEM analysis revealed a reduction in pore size from 124 µm to 95 µm upon vanillin incorporation, likely contributing to the reduced swelling capacity observed in the lignin–chitosan–vanillin hydrogels. Thermogravimetric analysis (TGA) demonstrated an improved thermal stability with the addition of vanillin, with an increase in residual mass from 37% to 43% being observed. Mechanical characterization through rheological and tensile tests showed improvement in the storage modulus, loss modulus, Young’s modulus, and tensile strength, with tensile strength increasing by 32.3% after crosslinking. The hydrogels also exhibited high adsorption performance toward positively and negatively charged dye contaminants, achieving ~95% removal of methylene blue, ~94% removal of rhodamine 590 chloride, and ~93% removal of methyl orange. Adsorption data were well described by the Langmuir model, suggesting monolayer adsorption behavior with adsorption capacities of 6.6 mg/g and 4.7 mg/g being recorded for lignin-chitosan (LC) and lignin-chitosan-vanillin (LCV), respectively. Additionally, the adsorption process followed the pseudo-first-order model, confirming rapid dye uptake. These results show that vanillin acts as a green cross-linker in lignin-chitosan hydrogels, producing a mechanically robust, eco-friendly material suitable for water and wastewater treatment applications.

Keywords

Engineering, Environmental Engineering, Materials Science, Sustainability, Water Resource Management

Comments

OCLC No. 1591626867

Rights Statement

Copyright 2026, author.

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