Oxidized Ti3C2 MXene nanosheets for dye-sensitized solar cells

Porous TiO2 electrodes were prepared by oxidizing two-dimensional titanium carbide nanosheets (Ti3C2 MXene) and the electrodes were tested in dye-sensitized solar cells. The effects of oxidation temperature and duration time together with various thicknesses on the device performance were investigated. A power conversion efficiency of 2.66% was observed

Role of condensates in modulating DNA repair pathways and its implication for chemoresistance

For cells, it is important to repair DNA damage, such as double-strand and single-strand DNA breaks, because unrepaired DNA can compromise genetic integrity, potentially leading to cell death or cancer. Cells have multiple DNA damage repair pathways that have been the subject of detailed genetic, biochemical, and structural studies. Recently, the scientific community has started to gain evidence that the repair of DNA double-strand breaks may occur within biomolecular condensates and that condensates may also contribute to DNA damage through concentrating genotoxic agents used to treat various cancers. Here, we summarize key features of biomolecular condensates and note where they have been implicated in the repair of DNA double-strand breaks. We also describe evidence suggesting that condensates may be involved in the repair of other types of DNA damage, including single-strand DNA breaks, nucleotide modifications (e.g., mismatch and oxidized bases), and bulky lesions, among others. Finally, we discuss old and new mysteries that could now be addressed considering the properties of condensates, including chemoresistance mechanisms

Chlorophyll derivatives/MXene hybrids for photocatalytic hydrogen evolution: Dependence of performance on the central coordinating metals

Development of efficient photocatalytic hydrogen evolution reaction (HER) with illumination of visible light is challenging. In this work, five chlorophyll derivatives (M-Chls; M = H2/Cu/Ni/Co/Zn) with different central ions in its cyclic tetrapyrrole ring including free base, copper, nickel, cobalt, and zinc were synthesized and employed as the effective visible-light harvester for efficient HER. In addition, two-dimensional (2D) noble metal-free co-catalyst Ti3C2Tx MXene was used as an excellent electron capturer due to its outstanding conductivity property. These M-Chls are modified on the surface of Ti3C2Tx MXene with 2D accordion-like morphology by means of a simple deposition process to form noble metal-free Chl/Ti3C2Tx-based photocatalysts for HER. It is found that the best HER performance as high as 49 μmol/h/gcat was achieved with the Co-Chl@Ti3C2Tx hybrid, which was much higher than those of other M-Chl@Ti3C2Tx composites. This research provides a specific way to synthesize low-cost and environmentally friendly natural Chls for developing highly efficient photocatalytic HER through molecular engineering

Aggregate-forming semi-synthetic chlorophyll derivatives / Ti₃C₂Tₓ MXene hybrids for photocatalytic hydrogen evolution

Chlorophylls (Chls) are the most abundant natural pigments having excellent opt-electrical and semi-conductive properties. Ti3C2Tx MXene, one of the most extensively studied 2D noble metal-free co-catalyst, features outstanding electrochemical properties. This work compares three aggregate-forming chlorophyll derivatives (Chl-n; n = 1–3), namely, zinc methyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (Chl-1), zinc dodecyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (Chl-2) and zinc dodecyl 131-deoxo-3-devinyl-131-dicyanomethylene-3-hydroxymethyl-pyropheophorbide-a (Chl-3), as light-harvesting antenna pigments in the MXene-based photocatalytic system for hydrogen evolution under the white light illumination (λ > 420 nm). The hydrogen evolution reaction (HER) of these Chls depends on the peripheral substituent groups at the C13- and/or C17-positions of the chlorin macrocyclic π-system. Differences among these Chl-n sensitized Ti3C2Tx MXene (Chl-n@Ti3C2Tx) are compared in terms of their light-harvesting ability, morphology, charge transfer efficiency and photocatalytic performance. The best HER performance is found to be as high as 122 μmol/h/gcat with the Chl-3@Ti3C2Tx composite. This work leads the direction in synthesizing Chls in Chl/MXene hybrid structure suitable for highly efficient photocatalytic HER

Chlorophyll based organic heterojunction on Ti3C2Tx MXenes nano‐sheets for efficient hydrogen production

Z‐scheme process is a photo‐induced electron transfer pathway in natural oxygenic photosynthesis involving the electron transport from photosystem II (PSII) to PSI. Inspired by the interesting Z‐scheme process, here we demonstrated a photocatalytic hydrogen evolution reaction (HER) employing chlorophyll derivatives, Chl‐1 and Chl‐2, on the surface of Ti3C2Tx MXenes with two‐dimensional accordion‐like morphology forming Chl‐1@Chl‐2@Ti3C2Tx composite. Due to the frontier molecular orbital energy alignments of Chl‐1 and Chl‐2, the sublayer Chl‐1 is a simulation of PSI whereas the upper layer Chl‐2 is equivalent to PSII, and the resultant electron transport can take place from Chl‐2 to Chl‐1. Under the illumination of visible light (> 420 nm), the HER performance of Chl‐1@Chl‐2@Ti3C2Tx photocatalysts was found to be as high as 143 μmol/h/gcat , which was substantially higher than that of photocatalysts of either Chl‐1@Ti3C2Tx (20 μmol/h/g) or Chl‐2@Ti3C2Tx (15 μmol/h/g)

Effect of the Fabrication Method of Chlorophyll-Ti3C2Tx-Based Photocatalysts on Noble Metal-Free Hydrogen Evolution

Composites composed of a chlorophyll-a derivative and Ti3C2Tx MXene recently showed promising results as photocatalysts for the hydrogen evolution reaction. Herein, this type of composites is prepared by using a layered Ti3C2Tx material via an HCl@LiF etching technique, instead of the previously adopted HF etching technique. The performance of H2 evolution, therefore, showed a fourfold increase in this photocatalytic system, compared with the reported data in our previous works. The underlying reason for such a large improvement of the chlorophyll-MXene photocatalyst performance would be attributed to a more suitable surface chemistry, higher conductivity, fewer defects, higher surface area, and larger interlayer space of Ti3C2Tx introduced by the Li+ ions from LiF in the etching process. Herein, it is revealed that the preparation method of MXenes used as the cocatalysts is key to improve the H2 evolution efficiency in photocatalytic water splitting

Study of early transition metal carbides for energy storage applications

La demande urgente d'innovations dans le domaine du stockage de l'énergie est liée au développement récent de la production d'énergie renouvelable ainsi qu'à la diversification des produits électroniques portables qui consomment de plus en plus d'énergie. Il existe plusieurs technologies pour le stockage et la conversion électrochimique de l'énergie, les plus notables étant les batteries aux ions lithium, les piles à combustible et les supercondensateurs. Ces systèmes sont utilisés de façon complémentaire des uns aux autres dans des applications différentes. Par exemple, les batteries sont plus facilement transportables que les piles à combustible et ont de bonne densité d'énergie alors que les supercondensateurs ont des densités de puissance plus élevés et une meilleure durée de vie. L'objectif principal de ces travaux est d'étudier les performances électrochimiques d'une nouvelle famille de matériaux bidimensionnel appelée MXène, en vue de proposer de nouvelles solutions pour le stockage de l'énergie. Pour y arriver, plusieurs directions ont été explorées. Dans un premier temps, la thèse se concentre sur les supercondensateurs dans des électrolytes aqueux et aux effets des groupes de surface. La seconde partie se concentre sur les systèmes de batterie et de capacités à ions sodium. Une cellule complète comportant une anode en carbone et une cathode de MXène a été développées. La dernière partie de la thèse présente l'étude des MXènes pour les supercondensateur en milieu organique. Une attention particulière est apportée à l'étude du mécanisme d'intercalation des ions entre les feuillets de MXène. Différentes techniques de caractérisations ont été utilisées, en particulier la voltampérométrie cyclique, le cyclage galvanostatique, la spectroscopie d'impédance, la microscopie électronique et la diffraction des rayons X.An increase in energy and power densities is needed to match the growing energy storage demands linked with the development of renewable energy production and portable electronics. Several energy storage technologies exist including lithium ion batteries, sodium ion batteries, fuel cells and electrochemical capacitors. These systems are complementary to each other. For example, electrochemical capacitors (ECs) can deliver high power densities whereas batteries are used for high energy densities applications. The first objective of this work is to investigate the electrochemical performances of a new family of 2-D material called MXene and propose new solutions to tackle the energy storage concern. To achieve this goal, several directions have been explored. The first part of the research focuses on MXene behavior as electrode material for electrochemical capacitors in aqueous electrolytes. The next part starts with sodium-ion batteries, and a new hybrid system of sodium ion capacitor is proposed. The last part is the study of MXene electrodes for supercapacitors is organic electrolytes. The energy storage mechanisms are thoroughly investigated. Different characterization techniques were used in this work, such as cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy, scanning electron microscopy and X-ray diffraction

Chlorosome‐Like Molecular Aggregation of Chlorophyll Derivative on Ti₃C₂Tₓ MXene Nanosheets for Efficient Noble Metal‐Free Photocatalytic Hydrogen Evolution

Efficient photocatalytic hydrogen evolution reaction (HER) in the visible‐to‐near infrared region at a low cost remains a challenging issue. This work demonstrates the fabrication of organic‐inorganic composites by deposition of supramolecular aggregates of a chlorophyll derivative, namely, zinc methyl 3‐devinyl‐3‐hydroxymethyl‐pyropheophorbide a (Chl) on the surface of Ti3C2Tx MXene with 2D accordion‐like morphology. This composite material is employed as noble metal‐free catalyst in photocatalytic HER under the white light illumination, where Chl serves as a small molecule organic semiconductor component instead of ordinary inorganic and polymer organic semiconductors such as TiO2 and g‐C3N4, and Ti3C2Tx serves as a co‐catalyst. Different composition ratios of Chl/Ti3C2Tx are compared for their light‐harvesting ability, morphology, charge transfer efficiency, and photocatalytic performance. The best HER performance is found to be as high as 52 ± 5 µmol h−1 gcat−1 after optimization. Such a large HER activity is attributed to the efficient light harvesting followed by exciton transfer in Chl aggregates and the resultant charge separation at the interface of Chl/Ti3C2Tx

Ideias para germinar novos mundos : Educação Ambiental como subsídio para o ensino de Geografia

O presente trabalho se propõe a refletir sobre a relação da Educação Ambiental com a Geografia, a partir do debate sobre desastres naturais e mudanças ambientais globais. O debate aqui colocado critica as formas como se dá o desenvolvimento no Antropoceno, além de ansiar por novos mundos em comunidade, a exemplo do Bem-Viver. O primeiro capítulo do texto traz um panorama geral acerca das problemáticas ambientais globais em sua primeira parte, seguido de uma reflexão sobre nossa posição no mundo frente às mudanças ambientais globais, criticando o desenvolvimento e suas formas de progresso no que chamamos de Antropoceno. No segundo capítulo, aborda-se perspectivas da Geografia Escolar, relacionando-a com a Educação Ambiental e sua importância nos debates com os jovens atualmente. Por fim, no último capítulo, foi elaborado um exemplo de vivência para ser realizada em espaços escolares, com os alunos dos anos finais do Ensino Fundamental. A proposta foi baseada na metodologia de Nunes e Castrogiovanni (2018). Diante disso, o trabalho pretendeu colaborar com as discussões em torno da Educação Ambiental, um tema tão importante em tempos de crise climática em nossa Terra, em nossa casa.This work reflects about the relation between Environmental Education and Geography from the debates about natural disasters and global environmental changes. The debate criticises the ways the development exists in the Anthropocene, proposing new worlds in community, as an example of the Bem-Viver. The first chapter brings a general panorama about global environmental problematics, followed by a reflection about our position in the world ahead of global environmental changes, criticizing the development in its forms of progress in the Anthropocene. The second chapter approaches perspectives of Scholar Geography, in relation with environmental education and its value in debates with young people nowadays. Finally, in the last chapter, an example of activity was elaborated to be realized in school spaces with students in elementary school. The activity was based in the metodologie of Nunes and Castrogiovanni (2018). Thus, this work intended to collaborate with the discussions about Environmental Education, a so important subject nowadays in the climathical crises in our land Earth, our home