Photocatalytic degradation of methylene blue dye using catalyst based on the gold-containing clusters supported on TiO₂

Abstract

The [Ru₃(μ-AuPPh₃)(μ-Cl)(CO)₁₀] and [Au₉(PPh₃)₈(NO₃)₃] clusters were synthesised according to well-established procedures and their identities were confirmed by NMR, IR, powder XRD, UV-vis and TGA techniques. Atomically precise Ru₃Au cluster was then deposited on dried anatase TiO₂ with the metal loading of 0.08, 0.17. 0.35, 0.50, 0.75, 1.00, 1.50, 2.00 and 5.0 wt%. The metal contents were confirmed by AAS and ICP-MS. The DR UV-vis spectra of the as-made catalyst indicated a successful deposition of the clusters on anatase which was also confirmed by the XPS results. However, the removal of protecting ligands via calcination resulted in agglomeration of clusters as revealed by XPS spectra. The photocatalytic performance in methylene blue dye degradation by the Ru₃Au cluster immobilised on anatase was investigated under UV LED irradiation (λmax = 370 nm) and visible LED irradiation (λmax = 513 nm). Under UV irradiation, an increase in metal loading caused reduced dye conversion. This was due to the adsorbance of UV light by metal clusters which blocked the incident light onto anatase. The 5.0 wt% of metal loading showed the highest conversion due to the synergistic effects from larger surface plasmon resonance-active particles and surviving clusters (confirmed by XPS). The calcined and recycled catalysts exhibited significantly lower activity, most likely due to pronounced sintering of clusters. At 5.0 wt% of metal loading, the deposition of Ru₃Au showed a superior performance in dye degradation as compared to pure Au₉ cluster and Au colloid (~12 nm) under visible light.