Synthesis and characterization of lignin-modified defective UiO-66-NH₂ for enhanced curcumin adsorption and controlled release in drug delivery applications

This study explores the synthesis and characterization of modulated UiO-66 metal-organic frameworks (MOFs) to enhance curcumin adsorption and controlled release. UiO-66 was synthesized using solvothermal methods with varying linkers and modulating agents to produce non-modulated, defective, and lignin-incorporated variants. Specifically, frameworks were developed using different ratios of terephthalic acid (BDC) and 2-aminoterephthalic acid (ABDC), and lignin was incorporated into a selected defective UiO-66 variant to evaluate its effect on curcumin loading and release. The non-modulated UiO-66 (UiO-66-NM) served as a baseline, while defective UiO-66 samples were prepared with different BDC/ABDC ratios using trifluoroacetic acid (TFA) as a modulator. Among these, UiO-66-D (UiO-66 with 25% ABDC, 75% BDC, and TFA) and its lignin-modified version, L-UiO-66-D (UiO-66 with 25% ABDC, 75% BDC, TFA, and lignin at 10 wt% relative to the combined mass of metal salt and organic linkers), demonstrated superior properties. Curcumin (Cur) loading into L-UiO-66-D was optimized by varying the UiO-66 amount while keeping curcumin and ethanol concentrations constant, achieving a maximum adsorption efficiency of 91.38% and a loading capacity of 49.17 mg g^-1. Release studies were conducted in phosphate-buffered saline (PBS) at 37 °C at different pH levels (1.2, 6.8, and 7.4), where both UiO-66-D and L-UiO-66-D exhibited controlled release behavior over 24 h. Characterization through FT-IR, XRD, SEM, TGA, and BET confirmed successful synthesis and provided insights into the structural and morphological properties of the MOFs. The results highlight the potential of modulating and functionalizing UiO-66 frameworks to improve performance in controlled drug-delivery applications.