SIMS-23 2022 Session SS-ThM2: Environmental

The increasing use of nanomaterials in our lifestyles induce significant problems of pollution in the environment, particularly with respect to microbes and bacteria, which are ubiquitous in ecosystems. However, the mechanisms of interaction between bacteria and nanoparticles are still poorly studied. In particular, the physico-chemical parameters governing the complex processes of degradation of nanoparticulate organic matter and/or the mechanisms of recognition of substrate nanoparticles by bacteria are still unknown². In this project, the study of these parameters is carried out through a multidisciplinary strategy involving a combination of several domains including nanoscience, analytical chemistry and microbiology. In this context, model core-shell hybrid nanoparticles based on hierarchical structure involving gold@silica@gelatin morphologies were designed. Gelatin was used as organic substrate for Alteromonas macleodii, the marine bacteria species selected for this study. The characterization of nanomaterials and the monitoring of enzymatic degradation processes and bacteria/nanoparticle interactions (Fig. 1), were achieved through an innovative combination of surface analysis and mass spectrometry techniques,^3,4 including Time-of-flight secondary ion mass spectrometry (ToF-SIMS Tandem MS), X-ray photoelectron spectroscopy (XPS), Auger microscopy (AES), liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS) and Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). On one hand, SP-ICP-MS and AES analyses allow the quantification of nanoparticle binding mechanisms on cells by following the gold core particles used as markers. On the other hand, ToF-SIMS Tandem MS, XPS and LC-ESI-MS techniques enable to identify peptide fragments originating from the degradation of gelatin on the surface of model nanoparticles. The results obtained and the strategy implemented thus open the way to the determination of key parameters governing the interactions between nanoparticles and bacteria, which are of primary importance in environmental degradation processes but also in the fight against pathogens.

References: [1] F. Ameen, K. Alsamhary, J.A. Alabdullatif, S. AlNadhari, Ecotoxicol. Environ. Saf. 213 (2021), 112027. [2] M. Mansor, J. Xu, Environ. Microbiol. 22(9), (2020), 3633–3649. [3] C. Courreges, M. Bonnecaze, D. Flahaut, S. Nolivos, R. Grimaud, J. Allouche, Chem. Commun. 57 (2021), 5446-5449. [4] L. Yin, Z. Zhang, Y. Liu, Y. Gao, J. Gu, Analyst 144, (2019), 824–845.

Nowadays the presence of pollutants in water represents an ever greater and difficult problem to solve. Efficient removal of contaminants from aqueous solutions requires advanced oxidation processes (AOPs). This can be accomplished by different methods, such as electrocatalysis, photocatalysis and photo-electrocatalysis, involving the use of materials that allow the fast removal of the pollutant with high degradation efficiency. The photo-electrocatalytic approach appears to be among the most promising processes because it combines the advantages of photocatalysis and electrocatalysis [1].

The most used material in this regard is TiO₂ which, however, shows several problems including a band gap around to 3.0-3.2 eV that does not allow the absorption of visible light.

With appropriate surface modifications such as the presence of phosphate anions, it is possible to improve the generated photocurrent [2] to obtain a best performing material in photo–electrocatalysis applications.

In this work the surface of nanostructured TiO₂-based films were chemically modified to improve its electro-, photo-electro and photocatalytic performance. In particular, mesoporous TiO₂ films were engineered using the zirconium phosphate (ZP) modification [3] in order to improve the sensitivity to sunlight, the electrical properties, and the thermal stability of the material.

We used extensively TOF-SIMS for obtaining space-resolved information on the functionalization of the mesoporous oxide, necessary for the engineering and monitoring of the material modification protocol. Moreover, TOF-SIMS allowed to monitor the photocatalytic reactions at the mesoporous oxide surface providing information on the degradation pathway under solar light irradiation. In particular the present study considered, as target molecules, both model dyes such as Rhodamine B and real-world persistent pollutants such as pesticides. Understanding the degradation pathways occurring at the photocatalyst surface, indeed, is an important step for the design of specific functionalization processes aimed to the improvement of the performances of the material.

[1] T.H. Jeon et al. ACS Catal. 8 (2018) 11542–11563.

[2] L. Jing et al. Energy Environ. Sci. 5 (2012) 6552–6558.

[3] S. Vitale et al. J. Vac. Sci. Technol. B. 34 (2016) 03H110.