Hydroxylation-induced defect states and formation of a bidentate acetate adstructure of TiO2 catalysts with acetic acid variation for catalytic application

Abstract

Abstract TiO2 is considered a promising candidate for catalysis applications. The addition of acetic acid and its variation creates a strong bond with oxide surfaces, which generates various oxidizing agents. X-ray diffraction analysis of the prepared TiO2 nanoparticles reveals their semicrystalline nature. The results show that holes are captured by the surface and subsurface, producing ≡ T i IV − O H . , ≡ T i IV − O . − − T i IV ≡ and the reducing agent = T i III − , which act as active oxidizers during photocatalysis, thus confirming the occurrence of an OH radical via an advanced oxidation process. Increasing the acetic acid amount leads to disordered structural defects below the conduction band (CB). X-ray photoelectron spectroscopy analysis shows the induction of hydroxylation of surface defects, such as Ti–OH. The results indicate that an oxygen vacancy is favourable due to a large number of surface defects. Detailed discussion of the energy band structure with the concept of a valence band (VB) and a CB maximum is implemented. The electron-withdrawing carboxylic group can affect oxygen vacancies and acetate ligands on the photocatalyst surface. The formation of a bidentate acetate adstructure with a lower acetic acid concentration leads to an explanation for higher visible-light-driven methylene blue degradation. The mechanism for the formation of an additional Ti–O–Ti bond by a condensation process is also illustrated elaborately. Theoretical calculations of the potentials of the VB and CB show the effects of active sites on degradation and can be associated with redox reactions for water splitting abilities. A possible model of sensitized photocatalysis for hydrogen production with hydrogen and oxygen evolution sites is also proposed in this article. Thus, TiO2 nanoparticles with acetic acid variation are promising sources for photocatalytic/catalytic applications.