Tailoring TiO2 nanotubes with an iron-based MOF precursor for enhanced photoelectrochemical degradation of methyl red

Abstract

A metal–organic framework (MOF), MIL-88A, was used as a precursor through calcination at 550 °C for hematite (α-Fe₂O₃), which was grown on titania nanotubes (TiO₂ NTs) prepared by anodization from Ti plates. A hybrid material composed of titania nanotubes and hematite (TiO₂ NTs/Fe₂O₃) exhibited a high dispersion of this iron oxide over a titania nanotube array, as demonstrated by FE-SEM, EDS, DRX and Raman spectroscopy characterization. Photocatalysis (PC), electrocatalysis (EC) and photoelectrocatalysis (PEC) with this modified electrode were tested using 15 mg L⁻¹ of methyl red (MR) aqueous solutions dissolved in 0.5 M sulfuric acid. MR discoloration was monitored through UV-vis spectrophotometry at an analytical wavelength of 515 nm. PC experiments performed under irradiation with a 365 nm Hg lamp of 3.5 mW cm⁻² intensity did not produce any discoloration, in contrast to electrocatalysis, performed under a bias voltage of ∼5 V supplied by a commercial photovoltaic cell, which achieved 30% MR removal. PEC experiments, performed under simultaneous irradiation and bias voltage, achieved 67% removal, in contrast to pristine titania nanotubes, which only achieved 50%. The material retained its catalytic activity and was shown to be stable after 5 cycles under the strongly acidic conditions used.