Bio-Based Phenolic Aldehyde Functionalization of Cellulose Acetate–Polyethyleneimine Membranes for Enhanced Ni2+ and Cu2+ Retention

Abstract

The increasing occurrence of heavy metal ions in water and wastewater streams represents a serious concern for both the environment and human health. The efficient removal of such contaminants requires the development of stable and functional membrane materials capable of combining separation performance with specific metal-binding interactions. This work proposes the use of bio-sourced phenols alongside branched polyethyleneimine and cellulose acetate to develop advanced membranes for the retention of Ni2+ and Cu2+ ions from aqueous solutions. The chemical modification of the cellulose acetate membrane was confirmed by structural and thermal analysis. Improved thermal resistance between 50–200 °C suggests that chemical interactions as well as hydrogen bonds were developed within the functionalized membranes. The effect of aldehyde modification on membrane chemistry, morphology, thermal behavior, mechanical properties, and filtration performance was systematically investigated. The vanillin-modified membrane showed the best mechanical response, likely due to improved matrix cohesion promoted by its methoxy-substituted aromatic structure. In contrast, the salicylaldehyde-modified membrane exhibited the highest metal-ion retention, reaching approximately 73% for Ni2+ and 67% for Cu2+ after five filtration cycles. These findings highlight the potential of bio-based phenolic aldehydes as active compounds for designing membranes with tailored morphology, stability, thermal, mechanical, and metallic ion-removal performances.