The research activity of the Photocatalysis & Photoconversion axis deals with investigations on controlled synthesis and design of nanomaterials for photocatalytic, photoconversion and low-temperature catalysis processes. These materials are designed to have optimized properties for applications in the fields of Environment, Health and Life Sciences and Renewable energies.

Synthesis and characterization of functional nanomaterials

Synthesis and nanostructuration of semiconductors (SC). This topic explores the material synthesis from the nano-scale to its macroscopic shaping for applications. The two mains objectives are: (i) shift the material photo-response from UV-A to longer wavelength for a better use of the solar energy and (ii) limit the photo-generated charges recombination for a better efficiency of the photo-chemical reactions. To improve photocatalytic and photoconversion yield, different strategies are carried out such as:

Nanostructuration and architecturation approaches
Specific 1D-morphologies elaboration
Physico-chemical modifications (Functionalization, chemical doping, metal/SC interfaces, hetero-junction between SCs)
Exaltation of light absoprtion through plasmonic effects

Bottom-up preparation of metal nanoparticles and hybrid nanostructures. It consists in metal, alloy or metal-oxide nanoparticles synthesis and their subsequent deposition on hydroxyl-terminated, oxygenated, alkyl-terminated or graphitic surfaces. To decorate surfaces with nanoparticles of controlled size and composition, methods of chemical or thermal reduction of metal precursors (complexes, salts) have been developed. They can be achieved in solution, directly on the surface or within a porous network. A special effort has been devoted to the synthesis of gold nanoparticles, which exhibits a much lower melting point than the other noble metals. Indeed, functional gold nanoparticles (diameters < 5 nm) are much harder to synthesize and maintain divided even at low loadings. Recently, we have moved the effort towards tackling the eco-efficiency aspect of these syntheses, aiming at maximizing both deposition yields and metal dispersion.

Bioorganic Synthesis. The aim of this project is to develop novel chemical, biochemical or nanochemical approaches for the efficient reactivation of phosphylated and inhibited choline esterases ChEs. In particular, acetylcholine esterase is an important protein of the brain that is responsible for the transmission of nerve influx, through the metabolisms of the neurotransmitter acetylcholine. This serine protease is inhibited by organophosphorus nerve agents suchs VX, sarin, tabun, soman and pesticides (paraoxon). Our goals are to find innovative medical countermeasures and biocompatible antidotes able to reactivate, with high efficiency, inhibited AChE restoring its activity in the plasma and in the central nervous system. Besides this, all the other related aspects such as decontamination, protection, and detection of organophosphorus nerve agents are also deeply investigated, by developing challenging approaches and functional technologies.

Environmental applications

Pollution control. Air and water treatment. Amongst the targeted chemical pollutants, one may mention VOCs (Volatile Organic Compounds) molecules, like methylethylketone, methanol, toluene, acetone, ethylene and models for chemical warfare agents. In addition, some inorganic compounds have also been targeted like CO, NH₃ and H₂S. A part of the research activity is focused on industrial, hospital and domestic waste waters. The targeted pollutants are orange II, methylene blue, Diuron® pesticide as well as standard pollutants found in water. A new approach has been initiated concerning the elimination of endocrine disruptors known as emerging pollutant in domestic and hospital waste waters.

Elaboration of functionalized surfaces. With a double goal, (i) elaboration of surfaces (textiles, polymers, paints, walls…) providing self-decontaminating, self-cleaning, biocidal functionalities and (ii) also able for air treatment at their contact.

Green, eco-efficient chemical processes. The main motivation of this research is to minimize energy consumption and waste production, in particular by developing highly selective, low temperature heterogeneous catalytic processes. The considered reactions include the gas phase oxidative dehydrogenation of ethane, the liquid phase aerobic epoxidation of higher alkenes (e.g. cyclohexene, stilbene…), and the selective oxidation of CO in hydrogen-rich feeds. In these reactions, recurring challenges include maximizing selectivity and stability of known active phases at a given conversion level, as well as developing new composites with enhanced catalytic efficiency at low temperature.

Interface with Life Sciences and Health

TiO₂-based photosensors for artificial retina. We aim to develop a new kind of artificial retina containing pixellized architectures of vertically aligned TiO₂-based nanotubes, acting as artificial photoreceptors in replacement of degenerated natural ones when the neuronal network of retina is partially maintained. The idea is to activate the TiO₂-based semiconductor to create photo-generated charges able to be used by the neuronal system to generate a signal for useful vision. The two main challenges of this project are to enhance absorption in the visible part of the solar spectra and to increase charge transfer from the SC to the interface on which neuronal cells are in contact.

Photocatalytic decontamination of bioaerosols. As photo-oxidation processes are known to oxidize at room temperature a large variety of organic molecules, they are also efficient for the oxidation of the organic constituents of micro-organisms to lead to their death. It has been demonstrated that photo-catalysis is very efficient for the inactivation of bacteria, viruses and spores, notably in form of bioaerosols. This research area, for which we were pioneers in 2005, will be continued by now focusing on a fundamental approach concerning the understanding of the involved reaction mechanisms.

Biocidal and self-decontaminating surfaces. The same approach is also devoted to the elaboration of TiO₂-functionalized surfaces providing micro-organism elimination properties aiming also at the limitation of biofilms. The case of textiles, paints, glasses and steel represents a special interest.

Solar photo-conversion for energy applications

Production of hydrogen by photo-(electro)catalytic water splitting. H₂ production from water photodissociation could be an interesting alternative for the production of fuel directly from solar light. For this purpose, two complementary approaches are studied in parallel: (i) Photocatalysis; using suspensions of photo-catalysts SC in water. The approach investigated consists in the elaboration of new composites associating gC₃N₄/TiO₂ semiconductors. This part also includes the influence of different kinds of sacrificial agents on the overall H₂ production yield. (ii) Photoelectrochemistry; using two separate compartments for O₂ and H₂ evolution, respectively on a nanostructured-based TiO₂ photoanode and on a Pt cathode. The overall efficiency is evaluated both through the measurement of the photocurrent and the quantification of the O₂ and H₂ evolved gazes. In both configurations, a focus has been put on the enhancement of activity by inducing exalted plasmonic effects due to the addition of Ag or Au nanoparticles.

Hybrid Solar Cells. Recently, a part of the research activity of the group in the domain of Energy applications has been focused on the concept of Dye-sensitized solar cells (DSSC). The novelty and the innovation lie in the association of efficient nanostructured TiO₂ photoanodes grafted with tailored specific dyes molecules (Bodipy dyes).

Reaction kinetics and mechanisms

A pre-requisite to the design of tailor-made structures is to understand the molecular processes (those occurring at the interface between the (photo-)catalyst and the reactants/products, as well as those taking place in the bulk of the (photo-)catalyst triggered by the (photo-)catalytic reaction, in particular those involved in the activation of molecular oxygen. A great effort is thus devoted to kinetic studies of the reaction. For low –temperature catalysis applications, these are performed on model catalysts, which contains only one or two components of the active site, but also on more complex systems, in which the core active site is in interaction with other components which potentially affect the expression of its function. Establishment of structure-activity relationships then mostly depends either on the development of synthetic methods to selectively produce only a specific part of the active site or on the extent of the characterization of the composite to identify the functional structure and composition of the active site.