Development of a TiO2 nanotube photoanode decorated with MIL-53(Fe) for the photoelectrochemical degradation of 2,4-dimethylaniline

Metal-organic frameworks (MOFs) based on Fe exhibit great potential as highly effective photocatalysts for water treatment applications. TiO2 nanotube photoanodes decorated with 170–370 μg cm−2 of MIL-53(Fe) and Fe-MOF (i.e., melamine-modified MIL-53(Fe)) were synthesized and evaluated in the photoassisted electrochemical degradation of 2,4-dimethylaniline (2,4-DMA) under visible light irradiation. The morphological, optical, and electrochemical properties of the photoanodes were evaluated by SEM, TEM, FTIR, XPS, BET, PL, XRD, DRS, zeta potential, linear voltammetry, EIS, and Mott-Schottky technique, respectively. The absorption band of the carboxyl groups coordinated to the iron centers is observed by FTIR at 1550 cm−1, whereas a peak at 538 cm−1 is related the formation of metal-oxo bonds between the carboxylic group of terephthalic acid and Fe3+. The modification of MIL-53(Fe) through the insertion of melamine led to a reduction in the formed nanoparticles. The photoelectrochemical activity of MIL-53(Fe) at pH 3.0 was optimized using a central composite design (CCD) experimental plan, with H2O2 concentration, applied anode potential (Ean) and reaction time as variables under study. Upon addition of 10 mg L−1 H2O2, a degradation of 74.4% of 2,4-DMA was achieved at Ean = 1.0 V after 110 min, outperforming the 57% reached using an unmodified TiO2 nanotube photoanode. Further modification of the MIL-53(Fe) with melamine allowed obtaining an almost total degradation. A plausible degradation pathway for 2,4-DMA is discussed from NMR and HPLC-MS/MS results. This work demonstrates the promising photoelectrocatalytic activity of TiO2 photoanodes decorated with Fe-based MOFs.