Engineering a smart multifunctional UiO-66(Zr)-based metal-organic framework for simultaneous nutrient monitoring and water remediation via spectrophotometric sensing, adsorption, Box-Behnken design, machine learning, and DFT analysis.

The development of multifunctional materials for phosphate detection and removal is crucial for combatting eutrophication and enhancing water quality. We report the preparation of a novel sulfisoxazole-functionalized zirconium-based metal-organic framework (SFX-UiO-66) through glutaraldehyde-assisted modification of NH2-UiO-66(Zr). This framework features various active sites for effective phosphate recognition and adsorption. Characterization confirmed successful functionalization, high crystallinity, and structural stability pre- and post-phosphate uptake. The sensor enabled rapid phosphate detection (response time: 60 s) with a linear range of 0.111-0.200 ppm (R 2 = 0.999), a detection limit of 3.65 × 10-2 ppm, and a quantification limit of 1.11 × 10-1 ppm, while demonstrating excellent selectivity over competing anions. SFX-UiO-66 exhibited a maximum Langmuir adsorption capacity of 202.8 mg g-1 under optimal conditions (pH 5, 0.02 g adsorbent, 100 min, 45 °C), aligning with the Langmuir isotherm and pseudo-second-order kinetics, indicating monolayer chemisorption mechanisms. Response surface methodology based on Box-Behnken design optimized the adsorption process. An artificial neural network (ANN) model achieved R 2 = 0.9815, indicating strong predictive capability for phosphate adsorption. DFT simulations revealed a significant decrease in the HOMO-LUMO energy gap post-phosphate coordination, favoring charge transfer between phosphate ions and active sites. The sensor also demonstrated excellent performance for tap and boiler water samples, with recoveries of 100.29-100.73%, consistent with ion chromatography. These results suggest that SFX-UiO-66 is an effective dual-functional technology for rapid phosphate detection and removal, with potential for environmental monitoring and sustainable water purification.