Littérature scientifique sur le sujet « Hydrogen production, Photocatalysis, Photovoltaics, Photosensitizers »

Tremendous amount of research work is going on Titanium dioxide (TiO2) based materials. These materials have many useful applications in our scientific and daily life and it ranges from photovoltaics to photocatalysis to photo-electrochromics, sensors etc.. All these applications can be divided into two broad categories such as environmental (photocatalysis and sensing) and energy (photovoltaics, water splitting, photo-/electrochromics, and hydrogen storage). Synthesis of TiO2nanoparticles with specific size and structural phase is crucial, for solar sell application. Monodispersed spherical colloids with minimum size variation (5% or less) is essential for the fabrication of photonic crystals. When sensitized with organic dyes or inorganic narrow band gap semiconductors, TiO2can absorb light into the visible light region and convert solar energy into electrical energy for solar cell applications. TiO2nanomaterials also have been widely studied for water splitting and hydrogen production due to their suitable electronic band structure given the redox potential of water. Again nanostructured TiO2has extensively been studied for hydrogen storage with good storage capacity and easy releasing procedure. All these issues and related finding will be discussed in this review.

ABSTRACTPhotocatalytic water splitting to form hydrogen can effectively alleviate energy and environmental problems attracting wide attention. However, the current photocatalysts have low photocatalytic efficiencies due to the narrow absorption spectrum, which is far from the actual application requirements. Herein, we use the as-prepared zinc porphyrin self-assemblies to visible-light-drive photocatalytic hydrogen evolution with Pt as the cocatalyst and ascorbic acid (AA) as the sacrificial agent. The results exhibit morphology-dependent performance and hexagonal stacks achieved optimal H2 evolution rate (47.1 mmol/h/g), then followed by nanodiscs, nanorod and tetragonal stacks, meanwhile the nanorods with different aspect ratios show size-dependent properties. The UV-vis absorption and photoluminescence spectra and the shortening of decay time of the corresponding ZnTPyP aggregates reveal that the well-defined self-assembled porphyrin networks are J-aggregation and boost efficient energy transfer with respect to monomer. Such porphyrin self-assemblies are standing for one of the most promising photosensitizers in photocatalysis field and provide an important reference for designing the next generation of hydrogen production.

As the scaling of silicon PV cells and module manufacturing has driven solar energy penetration up and costs down, concentrator photovoltaic technologies, originally conceived as a cost-saving measure, have largely been left behind. The loss of market share by CPV is being locked in even as solar energy development encounters significant obstacles related to space constraints in many parts of the world. The inherently higher collection efficiency enabled by the use of concentrators could substantially alleviate these challenges, but the revival of CPV for this purpose requires substantial reinvention of the technology to actually capture the theoretically possible efficiency gains, and to do so at market-friendly costs. This article will discuss recent progress in key areas central to this reinvention, including miniaturization of cells and optics to produce compact, lightweight “micro-CPV” systems; hybridization of CPV with thermal, illumination and other applications to make use of unused energy streams such as diffuse light and waste heat; and the integration of sun-tracking into the CPV module architecture to enable greater light collection and more flexible deployment, including integration into built structures. Applications showing particular promise include thermal applications such as water heating, industrial processes and desalination; agricultural photovoltaics; building-integrated photovoltaics with dynamic daylighting capabilities; and chemical processes including photocatalysis and hydrogen production. By appropriately tailoring systems to the available solar resource and local energy demand, we demonstrate how CPV can finally achieve real-world efficiencies, or solar resource utilization factors, far higher than those of standard silicon-based PV systems. This makes the argument for sustained development of novel CPV designs that can be applied to the real-world settings where this efficiency boost will be most beneficial.

The phenomenon of global warming, coupled with the progressive depletion of feedstocks, demands a rapid replacement of fossil fuels with renewable energy sources. Among them, solar energy appears very appealing since it is abundant, ubiquitous and practically inexhaustible. Furthermore, this kind of energy can be exploited in several different ways, since it can be converted both to electricity (photovoltaics) and fuels, overcoming the problem of storage and distribution. In this, H2 seems to be one of the best candidates since it is carbon-free, can be produced from water and has a high energy content. Contrary to traditional electrolysis, photocatalytic H2 production can be considered a promising and cheap alternative to produce H2 in a green and sustainable way. The main project explicated during this Ph.D. career focused on the Dye-Sensitized Photocatalysis (DSP), a relatively new method to convert sunlight into a fuel, such as H2. In this approach, the photoactive system is made with by Pt0/TiO2 nanoparticles decorated by colored dyes capable to extend the active spectral range to the Vis wavelengths, so to increase the efficiency of the catalytic process. The mechanism of such devices involves an electron flow from the photo-excited sensitizer to the Pt hydrogen evolution catalyst, while a molecule of sacrificial electron donor (SED) is required to regenerate the dye. The required optical and electrochemical properties of the dyes employed in DSP are very similar to those required for dye-sensitized solar cells (DSSC), as a result, the classes of compounds most commonly employed in DSP are those that have shown the highest efficiencies in DSC. Nevertheless, it’s still not clear how the dye structure affects the efficiency of catalysis in H2 production experiments. Thus, the aim of this research project has been to find a reliable guideline for the synthesis of D-π-A dyes with optimized structures for hydrogen production. The activity of such dyes in DSSC application has been also investigated. In order to prepare a wide-ranging family of D-π-A dyes optimized for H2 production, we decided to face the two most critical issues: hydrophilicity and bulkiness. In this sense, we explored sensitizers with increasing hydrophilicity in the donor moiety, to promote dye-SED interaction, and increasing bulkiness of the backbone, to shield the TiO2 surface and avoid dye leaching and negative recombination processes. We selected a class of compounds containing the 2,1,3-benzothiadiazole moiety, a scaffold that was already shown to have impressive power conversion efficiencies in DSSC, even if no systematic study on their structural optimization were carried out. Furthermore, to date, there are only a few reports concerning their use in DSP. Here, the preparation and application in photocatalytic H2 production of several D-π-A benzothiadiazole-based dyes will be reported. The design of the structures proposed has been optimized in order to tune the photophysical and chemical properties by a proper choice of terminal groups, π-spacers and side chains. All the new structures have been synthesized and fully characterized and used to build the corresponding DSSC, which showed good efficiencies. Photocatalytic tests were conducted by varying the SED nature, as well as the dyes concentration in the system and the type of TiO2 exploited, leading to very interesting results in terms of H2 production rate and TONs and highlighting an actual correlation between dyes architectures and catalytic efficiencies.

Skin aging is classified into chronological aging and photoaging, involving ultraviolet radiation (UV), visible light, and others. UVA and UVA-photosensitizers (involving photocatalysis) contribute to the production of chronically induced skin damage that results in photoaging, especially wrinkles that are associated with histopathological actinic elastosis in the dermis. Hydrogen peroxide produced by the photosensitization involving photocatalysis, such as flavin, has been proposed as a risk factor for photoaging. It was also revealed that hydrogen peroxide production by UVA is amplified through the following reactions. The photosensitization of type I and type II by riboflavin as an initiator oxidizes coexisted amino acids and vitamins. The oxidized amino acids and vitamins produce reactive oxygen species (ROS), including hydrogen peroxide, through secondary UVA-photosensitization. Finally, we proposed a screening method for detecting the effects of antioxidants on UVA-photosensitization. In our previous study, histidine and other antioxidants did not inhibit UVA-photosensitized by riboflavin, even though they have been reported to scavenge singlet oxygen and superoxide. In contrast, we demonstrated that ergothioneine suppressed the production of hydrogen peroxide by UVA-photosensitization. The purpose of this report is to provide new findings for the prevention of photoaging by discussing the characteristics of UVA-photocatalysts in the skin.