Ph.D. project: "Functionalization of layered double hydroxides films for the degradation of pollutants"

Offer Description

Water remediation has become one of the major problems of our modern societies, whether to produce drinking water or to limit polluting discharges into the receiving environment.
Photocatalysis is a promising and sustainable solution based on the ability of materials or molecules to absorb light to produce reactive species (ROS) that can degrade contaminants present in water (antibiotics, hormones and other endocrine disrupters known for their harmful effects on flora and fauna). Because of the technologies used in plants, wastewater treatment is incomplete and these pollutants are often released intact into the environment. The future of photoinduced oxidation-based catalysis as an efficient process of effluent treatment within the framework of a sustainable development policy requires that the scientific community and the manufacturers involved in this field take up several challenges. For fundamental research, the first challenge is the development of a new generation of photocatalytic materials to improve the performance of catalysts used until now in the near UV (UVA), but also specially to develop the catalysts of the future, active in the visible. Additionally, to make photocatalysis economical, sustainable, durable, and environmentally friendly, these materials must be immobilized on a solid support for reuse and material recycling.
Layered double hydroxides (LDH) are lamellar materials made up of positively charged brucite-like sheets with an interlayer region containing charge-compensating anions and solvation molecules. Their general chemical formula can be given as [MII1-xMIIIx(OH)2]x+[An-x/n. m H2O]x- where M(II) and M(III) are respectively divalent and trivalent metal cations and An- is a charge-compensating anion (exchangeable).
Its compositional flexibility and low manufacturing cost make it an attractive material for a wide range of applications. LDH themselves are used as photocatalysts but have moderate activity (absorption mainly in UV, low charge separation and transportation efficiency) [1]. Coupling LDH with either other semiconductors or photosensitizers is a common approach to improve photocatalytic efficiency [2].
Interestingly, these materials can be formed directly from a metallic surface using an in situ growth method leading to particles oriented perpendicular to the substrate allowing the diffusion of species in and out [3]. However, the immobilization of these particles on a substrate can then constrain its functionalisation by anion exchange by limiting the dynamics of the interlayer space [4].
In this context, this thesis will aim to develop LDH films functionalised with photosensitive organic molecules, to study the confinement of these molecules in the interlayer space and the resulting photo-activity, and finally to assess the potential of these surfaces for the degradation of pollutants.
The first part of the work will focus on the synthesis of LDH films using an in situ growth method. These films will then be used for functionalisation by anion exchange. Functionalisation will also be considered using two other methods: direct synthesis of the functionalised film and reconstruction. The influence of the synthesis method on the arrangement of the molecules in the interlayer space will be studied specifically, as this parameter can have a significant influence on photo-activity. The morphology of the films and their structure (film thickness, particle density) will be modulated via the various synthesis parameters. Raman and IR spectroscopies and X-ray diffraction (XRD) will be used systematically to check the structure and functionalisation of the films. Scanning electron microscopy (SEM) will be used to determine morphology. The chemical composition will be determined by SEM-EDX and X-ray photoelectron spectroscopy (XPS).
Grafting of the photo-active anions in the interlayer space may be considered depending on their stability in aqueous solution.

Secondly, the formation of reactive oxygen species (ROS) at the solid-liquid interface will be optimised. To this end, the photophysical properties (fluorescence spectroscopy, singlet oxygen phosphorescence), photochemical properties (use of probe molecules) and photostability of the films will be studied to highlight the formation of ROS under illumination and to be able to quantify these species in solution.
The final part of the work will involve assessing the potential of these surfaces for degrading pollutants. The degradation of a model molecule will be studied in solution and the durability of the coating will be tested via successive adsorption/degradation cycles. Subsequently, the photocatalytic activity towards organic pollutants found in the environment (antibiotics, endocrine disruptors) will be tested. Degradation mechanisms could be studied by coupling with LC-MS analyses or measurements of total organic carbon after degradation.
This thesis is part of the ANR PhotoSurf2D funded project (PHOTOactive SURFaces based on layered double hydroxides for Disinfection and Decontamination) led by the LCPME.
[1] Kim, S.; Fahel, J.; Durand, P.; André, E.; Carteret, C. Eur. J. Inorg. Chem. 2017 (3), 669–678.
[2] Zhang, G.; Zhang, X.; Meng, Y.; Pan, G.; Ni, Z.; Xia, S. Chem. Eng. J. 2020, 392, 123684.
[3] Chen, H.; Zhang, F.; Fu, S.; Duan, X. Adv. Mater. 2006, 18 (23), 3089–3093.
[4] Soulé S., Durand P., El-Kirat-Chatel S., Quilès F., Carteret C., Materials Today Chemistry, 2024, 35, 101897.

Requirements

Research Field Chemistry

Education Level Master Degree or equivalent

Languages ENGLISH

Level Good

Additional Information

Work Location(s)

Number of offers available 1

Company/Institute LCPME

Country France

Where to apply

Website https://emploi.cnrs.fr/Offres/Doctorant/UMR7564-SAMSOU-006/Default.aspx

Contact

City Villers-lès-Nancy

Website http://www.lcpme.cnrs-nancy.fr

Street 405 rue de Vandoeuvre