No abstract

Nowadays, the presence of pollutants in water is an urgent problem to solve. The efficient removal of these contaminants from aqueous solutions requires advanced oxidation processes (AOPs). This can be accomplished by various approaches using materials that allow the rapid removal of pollutants with high degradation rates. In this work, we focused on the surface modification of TiO2 films for photocatalytic application in water remediation. In particular, with an appropriate surface functionalization with zirconium phosphate, we have improved the sensitivity to sunlight and the thermal stability of TiO2. The surface functionalization of the samples was verified by using TOF-SIMS, which allows us to obtain spatially resolved chemical information. This information is very helpful for an effective engineering of the material, in order to obtain the best performances for environmental remediation. To our knowledge, this is the first time that TOF-SIMS is used to monitor the evolution of photocatalytic reactions at the photoactive surface, getting information on degradation pathways taking place at the surface of the photoactive material under solar light irradiation. In this work, as a target molecule, we chose rhodamine B, a dye widely used in textile industry, among others. The investigation of the degradation pathways occurring directly at the samples’ surface can provide relevant information about the rate determining step of the reaction and give hints for tailored functionalization of materials for improving their photocatalytic performances.

Surface functionalization with biological molecules, such as peptides or proteins, is a very promising method for developing new biomaterials with many potential applications. However, due to their chemical complexity, the characterization of biological materials is often a very challenging task. In this context, time-of-flight secondary ion mass spectrometry is a very helpful characterization tool due to its ability to provide very detailed spatially resolved chemical information of the topmost layer. The peculiar emission/ion formation mechanisms involved in ToF-SIMS analysis often do not allow the detection of the molecular ion of proteins and peptides, providing a rich fragmentation pattern, which is difficult to be related to the surface composition using a univariate approach, due to the relevant number of peaks in the SIMS spectra of peptides and proteins and the slight differences in intensities between different samples. Therefore, we used multivariate analysis to extract the information contained in the ToF-SIMS spectra of four peptides with high amino acid sequence similarity along the peptide chain. The reference peptide (TAT1) is a 12-unit sequence of six amino acids (GRKKRRQRRRPS). The other three peptides have been obtained by inserting a bAla-H dipeptide (carnosine) in three different positions inside the TAT1 chain, namely, GRKKRRQRRRPS-bAla-H (TAT1-Car), bAla-HGRKKRRQRRRPS (Car-TAT1), and GRKKRRQ-bAla-H-RRRPS (T-Car-T). We show that these peptides can be distinguished by ToF-SIMS combined with multivariate data analysis.