Magnetron co-sputtered Bi12TiO20/Bi4Ti3O12 composite – An efficient photocatalytic material with photoinduced oxygen vacancies for water treatment application

Abstract

Bi12TiO20/Bi4Ti3O12 composite photocatalyst was investigated as an alternative to the conventionally used titanium dioxide, to tackle the well-known drawbacks of fast charge-carriers recombination and low quantum efficiency of TiO2. Polycrystalline Bi12TiO20/Bi4Ti3O12 thin films were produced by pulsed DC reactive magnetron co-sputtering, a method of high industrial relevance, and compared to titanium dioxide coatings produced with the same technique. Following the deposition process, optimum thermal treatment temperature and length were established, to obtain crystallisation. The synthesised coatings were thoroughly analysed with a range of techniques, including Raman spectroscopy, XRD, SEM, TEM, EDX, XPS and AFM. The photocatalytic properties of Bi12TiO20/Bi4Ti3O12 composite were assessed through methylene blue degradation and E. coli inactivation tests under UV-A irradiation. The results indicated considerably higher efficiency of the composite photocatalyst when compared to TiO2. Moreover, the reusability assessment of Bi12TiO20/Bi4Ti3O12 thin films revealed an incremental performance increase after each consecutive test, leading to a 6-fold increase in photocatalytic activity between the first and 15th cycle. Time-resolved photoluminescence and XPS analysis highlighted an increased presence of oxygen vacancies, forming over repeated usage of bismuth titanate, leading to longer lifetimes of photogenerated species and enhanced photocatalytic performance.