POM-132@MOF-801 HYBRID FOR PRESSURE-DEPENDENT NOX CAPTURE: SYNTHESIS, STRUCTURAL CHARACTERIZATION AND STATIC-PRESSURE ADSORPTION PERFORMANCE

Nitrogen oxides (NOx) are important atmospheric pollutants generated predominantly by combustion and industrial processes and are associated with ozone formation, secondary particulate matter, acid deposition, and adverse environmental and health effects. The development of porous materials capable of capturing nitrogen oxides therefore remains an important research objective. Metal–organic frameworks (MOFs) provide structurally tunable porous environments, while polyoxometalates (POMs) offer oxygen-rich surfaces together with distinctive acid–base and redox properties. Their integration provides an attractive route toward multifunctional adsorption materials. In this study, a Mo132-containing MOF composite, denoted Mo132@MOF-801, was synthesized and investigated for static-pressure NOx uptake. MOF-801 was prepared from zirconium tetrachloride and fumaric acid using N, N-dimethylformamide/water and acid modulation, while boric acid was also employed during synthesis. The Mo132-containing POM was prepared from ammonium molybdate, ammonium acetate, and hydrazine sulfate under acidic aging conditions. The resulting POM/MOF hybrid was subsequently prepared by thermal treatment in ethanol. Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were employed to characterize the materials. The composite exhibited a distinct FTIR fingerprint and retained crystalline features after hybridization. SEM revealed a heterogeneous, aggregated morphology, while EDS detected O, Cl, Zr, and Mo, with normalized mass fractions of 33.71, 13.45, 20.39, and 32.45%, respectively.  Static-pressure NOx measurements at 273 K yielded reported uptake values of 10, 14, 19, 21 and 21 mmol g⁻¹ at 0.5, 1.0, 1.5, 2.0 and 2.5 bar, respectively. The uptake increased by 110% between 0.5 and 2.0 bar and exhibited an apparent plateau between 2.0 and 2.5 bar. The results indicate that the Mo132@MOF-801 architecture can accommodate substantial NOx uptake under the reported static conditions. Nevertheless, because the adsorbent mass was varied systematically across the pressure measurements and the exact NOx composition, activation procedure, replicate measurements, and uncertainty were not reported, the data should be interpreted as pressure-dependent static uptake rather than as a rigorously resolved equilibrium isotherm. The study establishes a promising POM/MOF design concept while identifying the experimental requirements necessary for quantitative validation and practical evaluation.