In Situ Adsorption-Reduction of Chromium(VI) with a Self-Regenerated Intelligent Urea-MOF(Fe): Preparation, DFT Simulation and Mechanism

Abstract

Environmental pollution caused by hexavalent chromium becomes worse and worse, so it is urgent to develop efficient and stable treatments. In this work, urea-doped iron-based metal–organic framework N/MOF(Fe) was prepared via the solvothermal method, and its microstructure was systematically analyzed using characterization techniques, such as SEM, TEM, BET, XRD, FTIR, XPS and so on. Comparison of FTIR spectra with different urea doping amounts revealed the regulation law of amino functional groups and their influence on the construction of Cr(VI) adsorption active sites. Under the optimal conditions (initial Cr(VI) concentration was 5 mg·L^–1, adsorbent dosage was 0.8 g·L^–1, pH value was 5.6, and reaction time was 40 min), N/MOF(Fe) achieved a Cr(VI) removal efficiency of up to 95.23%. Kinetic and thermodynamic analyses showed that the adsorption process followed the pseudo-second-order kinetic model and Langmuir isotherm, with spontaneous exothermic characteristics. N/MOF(Fe) exhibited excellent self-regeneration performance and stability. EPR experiments confirmed the key role of ^•O₂^– in the reduction of Cr(VI). Combined with XPS and FTIR analyses before and after adsorption, a closed-loop pathway of “Cr(VI) adsorption → ^•O₂^–-mediated reduction to Cr(III) → Cr(III) desorption → material regeneration” was proposed, supported by DFT calculations. This work provides a theoretical basis for the design and application of high-efficiency self-regenerating adsorbents through functional group regulation, stability verification, and mechanism investigation.