Structures of water on the surface of anatase TiO2 studied by diffuse reflectance near-infrared spectroscopy

Structures of adsorbed water on anatase TiO2 (101) were studied using diffuse reflectance near-infrared spectroscopy (DR-NIRS), demonstrating that water is a good NIR spectroscopic probe to show the absorption and the quantity of the absorbate. [Display omitted] •DR-NIRS was used to study the structure of absorbed water on TiO2.•Continuous wavelet transform was used to enhance the resolution of the spectra.•Spectral features of the water absorbed on different sites were observed.•Water was proved to be a probe to show the absorption and the quantity of the absorbates. Investigating the structures of water on metal oxides is helpful for understanding the mechanism of the adsorptions in the presence of water. In this work, the structures of adsorbed water molecules on anatase TiO2 (101) were studied by diffuse reflectance near-infrared spectroscopy (DR-NIRS). With resolution enhanced spectrum by continuous wavelet transform (CWT), the spectral features of adsorbed water at different sites were found. In the spectrum of dried TiO2 powder, there is only the spectral feature of the water adsorbed at 5-coordinated titanium atoms (Ti5c). With the increase of the adsorbed water, the spectral feature of the water at 2-coordinated oxygen atoms (O2c) emerges first, and then that of the water interacting with the adsorbed water can be observed. When adenosine triphosphate (ATP) was adsorbed on TiO2, the intensity of the peaks related to the adsorbed water decreases, indicating that the adsorbed water is replaced by ATP due to the strong affinity to Ti5c. Therefore, there is a clear correlation between the peak intensity of the adsorbed water and the adsorbed quantity of ATP. Water can be a NIR spectroscopic probe to detect the quantity of the adsorbed ATP. A partial least squares (PLS) model was established to predict the content of adsorbed ATP by the spectral peaks of water. The recoveries of validation samples are in the range of 92.00–114.96% with the relative standard deviations (RSDs) in a range of 2.13–5.82%.