Vanadium-based materials as photocatalysts for the degradation of methylene blue

Yan, Wenxuan (2026) Vanadium-based materials as photocatalysts for the degradation of methylene blue. MSc(R) thesis, University of Glasgow.

Abstract

The performance of metal-organic framework (MOF) photocatalysts cannot be assessed from surface area alone, because dye removal in aqueous media also depends on molecular accessibility, mass transfer, light-source-dependent response, and framework stability. Three vanadium-based MOFs constructed from distinct tetratopic carboxylate ligands V-MOF-10, V-TBAPy, and V-TCPB were synthesized solvothermally and evaluated using methylene blue (MB) as a model pollutant. Their structural and physicochemical properties were characterized by PXRD, SEM, FT-IR, nitrogen sorption, TGA, and V K-edge XAS. Dark adsorption followed by light-induced removal was investigated at different catalyst dosages under ultraviolet and AM 1.5G simulated solar irradiation.

All three materials formed crystalline vanadium–carboxylate frameworks, but their accessible porosity differed markedly. The BET surface areas of V-MOF-10, V-TCPB, and V-TBAPy were 1300, 485, and 314 m² g⁻¹, respectively, but this order was not reproduced in aqueous adsorption of MB. V-MOF-10 showed slower site utilization, consistent with diffusion limitations within its narrow micropores; V-TBAPy exhibited the fastest initial adsorption response; and V-TCPB provided a more favourable balance between accessible sites and mass transfer. At a catalyst dosage of 5 mg, total MB removal after dark adsorption and subsequent ultraviolet irradiation was approximately 37%, 57%, and 95% for V-MOF-10, V-TBAPy, and V-TCPB, respectively. Under simulated solar irradiation, the corresponding values were 99%, 94%, and 97%, shifting the performance order in favor of the porphyrin-based V-MOF-10. This reversal may reflect a better match between the light-response characteristics of its TCPP-based framework and the broader spectral distribution of the simulated solar source. PXRD comparison of the fresh, post-adsorption, and post-UV-photocatalysis samples showed that the principal framework reflections were retained after treatment, with V-TCPB exhibiting the strongest structural retention.

Ligand selection therefore regulates the combined effects of pollutant pre-enrichment, pore accessibility, light-source-dependent performance, and structural persistence. Under the tested conditions, the most effective framework depended on the irradiation environment rather than on porosity alone. Because the two light sources were not photon-flux matched, their comparison reflects overall performance under the applied irradiation conditions rather than intrinsic spectral efficiency. These structure–function relationships provide a basis for designing vanadium-based MOFs for integrated adsorption–photocatalytic treatment of dye-contaminated water.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Keywords: Vanadium-based metal–organic frameworks, ligand structure, methylene blue, adsorption–photocatalysis, wastewater treatment.
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Supervisor's Name: Forgan, Professor Ross
• Date of Award: 2026
• Depositing User: Theses Team
• Unique ID: glathesis:2026-86265
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 23 Oct 2026 09:55
• Last Modified: 23 Oct 2026 14:01
• Thesis DOI: 10.5525/gla.thesis.86265
• URI: https://theses.gla.ac.uk/id/eprint/86265