Visible light driven photocatalysis mediated via ligand-to-metal charge transfer (LMCT): An alternative approach to solar activation of titania

Visible light harvesting or utilization through semiconductor photocatalysis is a key technology for solar chemical conversion processes. Although titania nanoparticles are popular as a base material of photocatalysis, the lack of visible light activity needs to be overcome. This mini-review is focused on an uncommon approach to visible light activation of titania: the ligand-to-metal charge transfer (LMCT) that takes place between TiO2 nanoparticles and surface adsorbates under visible light irradiation. We discuss a basic concept of photoinduced LMCT and the recent advances in LMCT-mediated visible light photocatalysis which has been applied in environmental remediation and solar energy conversion. Although the LMCT processes have been less investigated and limited in photocatalytic applications compared with other popular visible light activation methods such as impurity doping and dye sensitization, they provide lots of possibilities and flexibility in that a wide variety of organic or inorganic compounds can form surface complexes with TiO2 and introduce a new absorption band in the visible light region. The LMCT complexes may serve as a visible light sensitizer that initiates the photocatalytic conversion of various substrates or the self-degradation of the ligand complexes (usually pollutants) themselves. We summarized and discussed various LMCT photocatalytic systems and their characteristics. The LMCT-mediated activation of titania and other wide bandgap semiconductors has great potential to be developed as a more general method of solar energy utilization in photocatalytic systems. More systematic design and utilization of LMCT complexes on semiconductors are warranted to advance the solar-driven chemical conversion processes.open11144136Ysciescopu

Visible-light promoted bioorthogonal photocatalysis

Traballo Fin de Grao en Química. Curso 2020-2021Biological chemistry deals with the study of the chemical processes that occur inside living beings, from a molecular perspective. Understanding the cellular and molecular mechanisms underlying biological functions is fundamental for the treatment of many diseases. Furthermore, being able to manipulate, monitor and transform cellular behaviour is key to the development of modern medicine. However, interfering with cell’s functioning is not a trivial task and it requires the development of tools to carry out designed transformations under the complex environment of biological habitats. The chemical transformation of exogenous or endogenous substances inside living beings requires bioorthogonality and selectivity. One way to perform biocompatible reactions could be based on the use of photochemically-induced transformations, promoted by visible light. Combining photochemistry and bioorthogonal methods leads to bioorthogonal photochemistry, a new field of research that is still in its infancy. During this TFG, some preliminary work in this area have been carried out.La química biológica consiste en el estudio de los procesos químicos que ocurren en el interior de los seres vivos desde el punto de vista molecular. Entender los mecanismos celulares y moleculares relativos a las funciones biológicas es fundamental para el tratamiento de muchas enfermedades. Es más, ser capaz de manipular, monitorizar y transformar el comportamiento celular es clave para el desarrollo de la medicina moderna. Sin embargo, interferir en las funciones celulares no es una tarea trivial y requiere el desarrollo de nuevas herramientas para llevar a cabo las transformaciones diseñadas bajo el complejo ambiente de los sistemas biológicos. Las transformaciones químicas de sustancias exógenas o endógenas en el interior de los seres vivos requiere bioortogonalidad y selectividad. Un modo de llevarlas a cabo podría basarse en el uso de transformaciones inducidas fotoquímicamente, promovidas por la luz visible. La combinación de la fotoquímica y los métodos bioortogonales abre paso a la química fotobioortogonal, un novedoso campo de investigación que se encuentra todavía en su infancia. Durante este TFG, se ha llevado a cabo trabajo preliminar en este área.A química biolóxica consiste no estudo dos procesos químicos que acontecen no interior dos seres vivos para entender os seres vivos dende o punto de vista molecular. Entender os mecanismos celulares e moleculares relativos as funcións biolóxicas é fundamental para o tratamento de moitas enfermidades. É máis, ser capaz de manipular, monitorizar e transformar o comportamento celular é clave para o desenvolvemento da medicina moderna. Non obstante, interferir nas funcións celulares non é unha tarefa trivial e require o desenvolvemento de novas ferramentas para levar a cabo as transformacións deseñadas baixo o complexo ambiente dos sistemas biolóxicos. As transformacións químicas de substancias exóxenas e endóxenas no interior dos seres vivos require bioortogonalidade e selectividade. Un modo de levalas a cabo podería basearse no uso de transformacións inducidas fotoquímicamente, promovidas pola luz visible. A combinación da fotoquímica e os métodos bioortogonales abre paso a química fotobioortogonal, un novidoso campo de investigación que se encontra aínda na súa infancia. Durante este TFG, levouse a cabo traballo preliminar nesta área

Role of Visible Light-Activated Photocatalyst on the Reduction of Anthrax Spore-Induced Mortality in Mice

BACKGROUND: Photocatalysis of titanium dioxide (TiO(2)) substrates is primarily induced by ultraviolet light irradiation. Anion-doped TiO(2) substrates were shown to exhibit photocatalytic activities under visible-light illumination, relative environmentally-friendly materials. Their anti-spore activity against Bacillus anthracis, however, remains to be investigated. We evaluated these visible-light activated photocatalysts on the reduction of anthrax spore-induced pathogenesis. METHODOLOGY/PRINCIPAL FINDINGS: Standard plating method was used to determine the inactivation of anthrax spore by visible light-induced photocatalysis. Mouse models were further employed to investigate the suppressive effects of the photocatalysis on anthrax toxin- and spore-mediated mortality. We found that anti-spore activities of visible light illuminated nitrogen- or carbon-doped titania thin films significantly reduced viability of anthrax spores. Even though the spore-killing efficiency is only approximately 25%, our data indicate that spores from photocatalyzed groups but not untreated groups have a less survival rate after macrophage clearance. In addition, the photocatalysis could directly inactivate lethal toxin, the major virulence factor of B. anthracis. In agreement with these results, we found that the photocatalyzed spores have tenfold less potency to induce mortality in mice. These data suggest that the photocatalysis might injury the spores through inactivating spore components. CONCLUSION/SIGNIFICANCE: Photocatalysis induced injuries of the spores might be more important than direct killing of spores to reduce pathogenicity in the host

Visible-light-active disinfection of surface water coliform using silver/titanium dioxide/silver bromide(Ag/TiO2/AgBr) as photocatalyst

As human population becomes diverse, the need for sustainable, inexpensive, scalable, and decentralized water treatment technologies to supplement or replace conventional treatment methods are important, especially to satisfy the need of small, rural communities for safe drinking water. These challenges can be somewhat met with the use of semiconductor photocatalysis, especially if the process is driven by visible light energy. Visible-light-active (VLA) photocatalysis can be effectively applied in disinfection of drinking water. In comparison to traditional, energy-intensive, physical and chemical disinfection methods, VLA photocatalysis is capable of providing high disinfection efficiency with the use of cheaper energy, no harmful by-products, and no addition of chemicals. Doped with noble metals, some photocatalysts can be improved to react under visible light, producing in-situ reactive oxidative species (ROS) to disinfect water. In this thesis, experiments show that the noble metal based photocatalyst Ag/TiO2/AgBr is promising in neutralizing coliform bacteria under visible light

Mechanisms of Visible Light Photocatalysis in N-Doped Anatase TiO2 with Oxygen Vacancies from GGA+U Calculations

We have systematically studied the photocatalytic mechanisms of nitrogen doping in anatase TiO2 using first-principles calculations based on density functional theory, employing Hubbard U (8.47 eV) on-site correction. The impurity formation energy, charge density, and electronic structure properties of TiO2 supercells containing substitutional nitrogen, interstitial nitrogen, or oxygen vacancies were evaluated to clarify the mechanisms under visible light. According to the formation energy, a substitutional N atom is better formed than an interstitial N atom, and the formation of an oxygen vacancy in N-doped TiO2 is easier than that in pure TiO2. The calculated results have shown that a significant band gap narrowing may only occur in heavy nitrogen doping. With light nitrogen doping, the photocatalysis under visible light relies on N-isolated impurity states. Oxygen vacancies existence in N-doped TiO2 can improve the photocatalysis in visible light because of a band gap narrowing and n-type donor states. These findings provide a reasonable explanation of the mechanisms of visible light photocatalysis in N-doped TiO2

Recent Advances in Visible-Light Driven Photocatalysis

Semiconductor photocatalysis has been considered a potentially promising approach for renewable energy and environmental remediation with abundant solar light. However, the currently available semiconductor materials are generally limited by either the harvesting of solar energy or insufficient charge separation ability. To overcome the serious drawbacks of narrow light-response range and low efficiency in most photocatalysts, many strategies have been developed in the past decades. This article reviews the recent advancements of visible-light-driven photocatalysts and attempts to provide a comprehensive update of some strategies to improve the efficiency, such as doping, coupling with graphene, precipitating with metal particles, crystal growth design, and heterostructuring. A brief introduction to photocatalysts is given first, followed by an explanation of the basic rules and mechanisms of photocatalysts. This chapter focuses on recent progress in exploring new strategies to design TiO2-based photocatalysts that aim to extend the light absorption of TiO2 from UV wavelengths into the visible region. Subsequently, some strategies are also used to endow visible-light-driven Ag3PO4 with high activity in photocatalytic reactions. Next, a novel approach, using long afterglow phosphor, has been used to associate a fluorescence-emitting support to continue the photocatalytic reaction after turning off the light. The last section proposes some challenges to design high efficiency of photocatalytic systems

Electrochemical Enhancement of Photocatalytic Disinfection on Aligned TiO2 and Nitrogen Doped TiO2 Nanotubes

TiO2 photocatalysis is considered as an alternative to conventional disinfection processes for the inactivation of waterborne microorganisms. The efficiency of photocatalysis is limited by charge carrier recombination rates. When the photocatalyst is immobilized on an electrically conducting support, one may assist charge separation by the application of an external electrical bias. The aim of this work was to study electrochemically assisted photocatalysis with nitrogen doped titania photoanodes under visible and UV-visible irradiation for the inactivation of Escherichia coli. Aligned TiO2 nanotubes were synthesized (TiO2-NT) by anodizing Ti foil. Nanoparticulate titania films were made on Ti foil by electrophoretic coating (P25 TiO2). N-doped titania nanotubes and N,F co-doped titania films were also prepared with the aim of extending the active spectrum into the visible. Electrochemically assisted photocatalysis gave higher disinfection efficiency in comparison to photocatalysis (electrode at open circuit) for all materials tested. It is proposed that electrostatic attraction of negatively charged bacteria to the positively biased photoanodes leads to the enhancement observed. The N-doped TiO2 nanotube electrode gave the most efficient electrochemically assisted photocatalytic inactivation of bacteria under UV-Vis irradiation but no inactivation of bacteria was observed under visible only irradiation. The visible light photocurrent was only a fraction (2%) of the UV response

Indium-Containing Visible-Light-Driven (VLD) Photocatalysts for Solar Energy Conversion and Environment Remediation

Indium-containing visible-light-driven (VLD) photocatalysts including indium-containing oxides, indium-containing sulfides, indium-containing hydroxides, and other categories have attracted more attention due to their high catalytic activities for oxidation and reduction ability under visible light irradiation. This chapter will therefore concentrate on indium-containing nano-structured materials that demonstrate useful activity under solar excitation in fields concerned with the elimination of pollutants, partial oxidation and the vaporization of chemical compounds, water splitting, and CO2 reduction processes. The indium-containing photocatalysts can extend the light absorption range and improve the photocatalytic activity by doping, heterogeneous structures, load promoter, and morphology regulation. A number of synthetic and modification techniques for adjusting the band structure to harvest visible light and improve the charge separation in photocatalysis are discussed. In this chapter, preparation, properties, and potential applications of indium-containing nano-structured materials used as photocatalysis will be systematically summarized, which is beneficial for understanding the mechanism and developing the potential applications

Semiconductor Nanocomposites for Visible Light Photocatalysis of Water Pollutants

Semiconductor photocatalysis gained reputation in the early 1970s when Fujishima and Honda revealed the potential of TiO2 to split water in to hydrogen and oxygen in a photoelectrochemical cell. Their work provided the base for the development of semiconductor photocatalysis for the environmental remediation and energy applications. Photoactivity of some semiconductors was found to be low due to larger band gap energy and higher electron-hole pair recombination rate. To avoid these problems, the development of visible light responsive photocatalytic materials by different approaches, such as metal and/or non-metal doping, co-doping, coupling of semiconductors, composites and heterojunctions materials synthesis has been widely investigated and explored in systematic manner. This chapter emphasizes on the different type of tailored photocatalyst materials having the enhanced visible light absorption properties, lower band gap energy and recombination rate of electron-hole pairs and production of reactive radical species. Visible light active semiconductors for the environmental remediation purposes, particularly for water treatment and disinfection are also discussed in detail. Studies on the photocatalytic degradation of emerging organic compounds like cyanotoxins, VOCs, phenols, pharmaceuticals, etc., by employing variety of modified semiconductors, are summarized, and a mechanistic aspects of the photocatalysis has been discussed