ZrO(OH)2/Zn-MOF as a Nanocatalyst for Visible-Light-Driven Synthesis of Levulinic Acid from 5-Hydroxymethylfurfural

The organic transformation requires efficient and durable catalysts to drive reactions with high selectivity and efficiency. Herein, we demonstrate the postfunctionalization of a Zn-metal–organic framework (Zn-MOF), derived from trimesic acid building units, with zirconyl hydroxide to produce a nanocatalyst ZrO(OH)₂/Zn-MOF. The parent nanomaterial Zn-MOF is constituted by Zn(II) octahedra aligned parallelly to form a highly porous two-dimensional (2D) paddle-wheel network with dual pores of size 6.41 and 9.60 nm. The porosity of the nanomaterial allows Zr(IV) moieties (size ranging from 2.5 to 3 nm) to percolate and occupy the vacant spaces. Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) analysis, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (PXRD), inductively coupled plasma mass spectrometry (ICP-MS), temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) confirm the formation of ZrO(OH)₂/Zn-MOF with sufficient porosity, thermal stability, and crystallinity. The hydrated form of zirconia (ZrO(OH)₂) provides the active sites for the photocatalytic conversion of levulinic acid to 5-hydroxymethylfurfural via acid-catalyzed hydrolysis. The ZrO(OH)₂/Zn-MOF catalyzes the conversion when irradiated with visible light at room temperature yielding >99% of levulinic acid in 2 h. The selective formation of levulinic acid has been verified by NMR spectroscopy and high-performance liquid chromatography (HPLC-PDA). The reaction kinetics and mechanism are also confirmed by density functional theory (DFT) studies. The catalyst exhibits excellent efficiency, stability, and reusability without any oligomerization over multiple cycles.