Abstract

Recalcitrant pollutants are challenging to degrade during water treatment processes. Methylene blue (MB), a cationic dye, is particularly resistant to degradation and is environmentally persistent. Heterogeneous photocatalysis has emerged as a suitable strategy for removing such pollutants from water. In this work, ZrO2 thin films were modified with Anderson-type Mn-polyoxometalate (MnPOM) ((NH4)3[MnMo6O24H6]), and the efficiency of MB removal from water was studied. ZrO2 was synthesized by a sol–gel method, with thin films deposited using the doctor blade method, and ZrO2 thin films were modified using chemisorption method. The synthesized materials were characterized using SEM, EDX, UV-Vis diffuse reflectance spectroscopy and FTIR. The adsorption kinetics and isotherms for MB were studied for both bare ZrO2 and ZrO2/MnPOM composites. Optical characterization showed a band gap energy of 4.02 eV for bare ZrO2, while the ZrO2/MnPOM composite exhibited a band gap of 3.7 eV. Furthermore, ZrO2 showed lower MB removal capacity (?8%) than ZrO2/MnPOM thin films (?29%). The isothermal adsorption studies indicated that MB adsorption onto both bare ZrO2 and ZrO2/MnPOM followed the Langmuir adsorption model (qm = 20.6 mg g?1 for ZrO2 and qm = 62.9 mg g?1 for ZrO2/ MnPOM). Furthermore, the adsorption kinetics of MB were well described by a pseudo-second-order model. Photocatalytic testing under UV irradiation showed an apparent rate constant (kap) of 2 × 10?3 min?1 for bare ZrO2 and a value of kap 5.4 × 10?3 min?1 for ZrO2/MnPOM after 100 minutes. TD-DFT calculations revealed an LMCT interaction between the ZrO2 nanoparticle and the MnPOM, which likely contributes to the enhanced photocatalytic activity of the ZrO2/MnPOM composite. © The Royal Society of Chemistry 2025.