Facile and scalable synthesis of Ti6Mn2 oxo-cluster nanocrystals with flower-like morphology and excellent photocatalytic properties

Abstract

Three new phenylphosphonate (PhPO₃) and salicylate (Sal) substituted heterometallic titanium-oxo clusters (ST-M), namely [Ti₆Mn₂O₄(OEt)₄(PhPO₃)₂(Sal)₆(EtOH)₂] (ST-Mn), [Ti₆Zn₂O₄(OEt)₄(PhPO₃)₂(Sal)₆(EtOH)₂(H₂O)₂] (ST-Zn) and [Ti₆Tb₂O₄(OⁱPr)₄(PhPO₃)₂(Sal)₆Cl₂(ⁱPrOH)₂]·ⁱPrOH (ST-Tb), were synthesized. The most impressive structural feature of these compounds is the calixarene-type carboxylate endpoint in the Ti₆-oxo core, which can readily capture metal ions with different radii and coordination geometries, for example, Mn²⁺, Zn²⁺ and Tb³⁺ ions in this case, to generate neutral mixed-metal Ti₆M₂-oxo clusters. Flower-like ST-Mn (denoted as FST-Mn) nanocrystals formed by nanosheets can be facilely obtained in gram-scale quantities from a simple solution reaction using Triton X-100 as a conditioning agent. The catalytic activity of these materials was evaluated by photocatalytic degradation of rhodamine B (RhB), among which FST-Mn showed the highest catalytic activity. Under visible light, 93.0% of RhB (50 ppm, 100 mL) was decomposed within 30 min catalyzed by FST-Mn without adding hydrogen peroxide, which is quite preeminent among Ti based catalysts. The catalytic decomposition efficiency under the same experimental conditions was 80.0% for ST-Mn, 24.6% for ST-Zn and 17.6% for ST-Tb. Investigation of the degradation mechanism showed that h⁺ and ·OH were the dominant active species in the decomposition of RhB. Moreover, the reusability and stability of FST-Mn were also verified.