Synthesis and characterization of structural and photocatalytic properties of MXene/metal-organic framework (MOF) nanocomposites for the degradation of water pollutants

نوع: Type: Thesis

مقطع: Segment: PHD

عنوان: Title: Synthesis and characterization of structural and photocatalytic properties of MXene/metal-organic framework (MOF) nanocomposites for the degradation of water pollutants

ارائه دهنده: Provider: Zahra sangari motlagh

اساتید راهنما: Supervisors: Arash Fattah-alhosseini

اساتید مشاور: Advisory Professors: Minoo Karbasi

اساتید ممتحن یا داور: Examining professors or referees: Omid Imantalab, Ahmad Keyvani, Behzad Koozegar Kaleji

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: سالن کنفرانس دانشکده مهندسی

چکیده: Abstract: Environmental pollution has driven the adoption of photocatalytic processes as a suitable and sustainable solution for removing aqueous pollutants. This research aims to synthesize and evaluate the photocatalytic activity of a composite based on MXene quantum dots (Ti₃C₂Tₓ QDs) and an iron-based metal–organic framework (NH₂-MIL-88B(Fe)). In the first phase, Ti₃C₂Tₓ MXene was synthesized from the MAX phase precursor and characterized using X-ray diffraction and scanning electron microscopy and the synthesis conditions were optimized. The analyses confirmed the complete removal of aluminum. In the second phase, the photocatalytic behavior of the optimized MXene sample was evaluated under visible light irradiation. Its enhanced photocatalytic performance—achieving 49.60% degradation of methylene blue within 4 hours, outperforming the reference P25 photocatalyst—can be attributed to the in situ formation of a heterogeneous structure between the conductive Ti₃C₂Tₓ layers and semiconductor TiO₂ nanoparticles on its surface. The studies revealed that the junction between Ti₃C₂Tₓ and TiO₂ facilitates the generation of electron-hole pairs and suppresses their recombination. In the third phase, MXene was delaminated and converted into quantum dots (MQD) and subsequently composited with NH₂-MIL-88B(Fe) to synthesize a powdered MQD/MOF nanocomposite photocatalyst. Various composites were synthesized with different amounts of MQD (25, 50, and 75 mg). The photocatalytic performance of the synthesized samples was evaluated, and the optimal composite (50MQD/MOF) was selected based on its superior activity. This sample was thoroughly characterized using X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, BET analysis, UV‐Vis diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The optimal composite exhibited a markedly high degradation efficiency of 62.97% for methylene blue, significantly surpassing the negligible activity of the pure MOF. Mott–Schottky analysis indicated a band gap of 1.63 eV for the optimal sample, with the conduction and valence band positions estimated at –0.0493 eV and +1.58 eV, respectively. Scavenger tests identified electrons and superoxide radicals as the primary active species responsible for the degradation process. The proposed mechanism suggests that the heterostructure formed in the nanocomposite results in broad visible-light absorption, enhanced charge carrier separation, and superior electron transport. This study highlights the great potential of MQD/MOF composites as highly efficient materials for the photocatalytic treatment of organic pollutants in wastewater.