Nanowire Photoelectrochemistry.

Recent applications of photoelectrochemistry at the semiconductor/liquid interface provide a renewable route of mimicking natural photosynthesis and yielding chemicals from sunlight, water, and air. Nanowires, defined as one-dimensional nanostructures, exhibit multiple unique features for photoelectrochemical applications and promise better performance as compared to their bulk counterparts. This article reviews the use of semiconductor nanowires in photoelectrochemistry. After introducing fundamental concepts essential to understanding nanowires and photoelectrochemistry, the review considers answers to the following questions: (1) How can we interface semiconductor nanowires with other building blocks for enhanced photoelectrochemical responses? (2) How are nanowires utilized for photoelectrochemical half reactions? (3) What are the techniques that allow us to obtain fundamental insights of photoelectrochemistry at single-nanowire level? (4) What are the design strategies for an integrated nanosystem that mimics a closed cycle in artificial photosynthesis? This framework should help readers evaluate the salient features of nanowires for photoelectrochemical applications, promoting the sustainable development of solar-powered chemical plants that will benefit our society in the long run

Recent advances in the design and photocatalytic enhanced performance of gold plasmonic nanostructures decorated with non-titania based semiconductor hetero-nanoarchitectures

Plasmonic photocatalysts combining metallic nanoparticles and semiconductors have been aimed as versatile alternatives to drive light-assisted catalytic chemical reactions beyond the ultraviolet (UV) regions, and overcome one of the major drawbacks of the most exploited photocatalysts (TiO2 or ZnO). The strong size and morphology dependence of metallic nanostructures to tune their visible to near-infrared (vis-NIR) light harvesting capabilities has been combined with the design of a wide variety of architectures for the semiconductor supports to promote the selective activity of specific crystallographic facets. The search for efficient heterojunctions has been subjected to numerous studies, especially those involving gold nanostructures and titania semiconductors. In the present review, we paid special attention to the most recent advances in the design of gold-semiconductor hetero-nanostructures including emerging metal oxides such as cerium oxide or copper oxide (CeO2 or Cu2O) or metal chalcogenides such as copper sulfide or cadmium sulfides (CuS or CdS). These alternative hybrid materials were thoroughly built in past years to target research fields of strong impact, such as solar energy conversion, water splitting, environmental chemistry, or nanomedicine. Herein, we evaluate the influence of tuning the morphologies of the plasmonic gold nanostructures or the semiconductor interacting structures, and how these variations in geometry, either individual or combined, have a significant influence on the final photocatalytic performance

Novel strategies to design and construct efficient semiconductor-based photocatalyst for enhancing photocatalytic hydrogen evolution and nitrogen fixation under sunlight irradiation

L'énergie solaire est la source d'énergie la plus abondante au monde et elle peut être convertie en énergie chimique via des processus photocatalytiques. Au cours des dernières décennies, la photocatalyse sous la lumière du soleil est apparue comme une alternative innovante aux combustibles fossiles afin de résoudre et prévenir des problèmes graves liés à la crise environnementale et énergétique. Actuellement, les matériaux à base de semi-conducteurs (tels que TiO₂, C₃N₄, In₂O₃, WO₃) sont intensivement étudiés pour diverses applications photocatalytiques, y compris la réaction d’évolution d'hydrogène (HER) et la réduction de l'azote en ammoniac (NRR). Par conséquent, diverses approches telles que l'ingénierie structurelle, les hétérojonctions nanocomposites ont été étudiées afin de surmonter les problèmes de ces matériaux et ainsi augmenter l'activité catalytique. Dans le cadre de cette thèse, nous avons développé des nouvelles stratégies pour la synthèse des quatre types de photocatalyseurs efficaces pour la production d'hydrogène et la fixation de l'azote sous la lumière du soleil. Nos matériaux présentent une structure unique, qui favorise l'absorption de la lumière visible, la séparation des charges électrons-trous et l’augmentation du nombre de sites actifs.Pour l'application de la génération d'hydrogène photocatalytique, nous avons d'abord synthétisé les sphères de type éponge CdI₂nS₄ monophasées via une méthode solvothermique suivie d'un traitement au gaz contenant H₂S. La formation du complexe Cd/In avec une distribution uniforme de Cd²⁺ et In³⁺ a joué un rôle crucial dans la formation du spinelle monophasé CdIn₂S₄. L'énergie de la bande interdite s'est avérée être significativement réduite, ce qui permet une absorption étendue de la lumière visible jusqu'à 700 nm, ceci est principalement attribué à la dispersion d'espèce sulfure sur la bande de valence du CdIn₂S₄ monophasé. Avec le dépôt de Ni métallique comme cocatalyseur de réduction, le photocatalyseur hybride Ni-CdIn₂S₄ a montré une efficacité améliorée pour la production d'hydrogène sous la lumière solaire, ce qui représente une augmentation de l’activité d’environ, respectivement, 5,5 et 3,6 fois que celle des échantillons Pt-CdIn₂S₄ et Pd-CdIn₂S₄. Le deuxième système photocatalytique développé implique la préparation de nitrure de carbone graphitique dopé au S (Ni-SCN). Ce dernier est chimiquement ancré au nickel par une technique connue sous le nom de processus de photo-dépôt assisté par sulfuration. L'origine de la structure distinctive du Ni-SCN est dû à l'existence de liaisons chimiques NiS-C-N dans le système, ce qui favorisait la séparation des charges photogénérées et améliorait la capacité d’absorption lumineuse du photocatalyseur. Par conséquent, l’échantillon NiSCN synthétisé présente une excellente activité photocatalytique pour la production d'hydrogène sous la lumière du soleil. En effet, ce système présente une activité beaucoup plus élevée que celle des systèmes g-C₃N₄ dopés au S, Ni supporté g-C₃N₄ et Pt supporté g-C₃N₄ dopés au S. Pour une application photo (électro) catalytique de fixation de l'azote, nos travaux sont les premiers à rapporter la synthèse de nanoparticules d'Au chargées de nanoparticules W₁₈O₄₉ dopées au Fe (notées WOF-Au) par une synthèse solvothermique suivie d'un dépôt in situ des nanoparticules d'Au. L'incorporation de dopants Fe peut non seulement guérir les états de défaut de masse dans les réseaux non stœchiométriques W₁₈O₄₉, mais également favoriser la séparation et la migration interfaciale des électrons du photocatalyseur vers les molécules N₂ chimisorbées; tandis que les nanoparticules Au décorées sur la surface dopée au Fe W₁₈O₄₉ ont fourni les électrons à haute énergie pour la réduction de N₂ via l'effet de résonance plasmonique de surface localisé (LSPR). Le système WOF-Au plasmonique résultant montre un rendement amélioré pour la production de NH₃, beaucoup plus élevé que celui du W₁₈O₄₉ pur ainsi qu'une très grande stabilité. L'amélioration des performances photoélectrocatalytiques est principalement due à l'effet synergique des dopants Fe et des nanoparticules Au dans l'hôte W₁₈O₄₉. Enfin, les cacahuètes creuses de In₂O₃ dopées au Ru (dénotées Ru-In₂O₃ HPN) ont été fabriquées par la nouvelle stratégie d'auto-matrice suivie de la calcination des précurseurs synthétisés. Les nanoparticules uniformes In₂O₃ sont étroitement agglomérées ensemble pour former une structure de cacahuète creuse, ce qui facilite la séparation et le transport des l'électrons-trous photoexcités, améliorant l’absorption de la lumière par multi-réflexion. De plus, l'introduction des dopants Ru induit de nombreuses lacunes en oxygène à la surface et réduit l'énergie de la bande interdite du système photocatalytique. Ces lacunes d'oxygène agissent comme des centres de piégeage, facilitant la séparation des électrons trous photoexcités. Par conséquent, le taux de production d'ammoniac des Ru-In₂O₃ HPNs est 5,6 fois plus élevé que celui des In₂O₃ HPNs purs et largement supérieur au matériau en vrac d'In₂O₃, lorsqu’il est soumis à l’irradiation solaire.Solar energy is the most abundant energy source in the world, and it can be converted into chemical energy via photocatalytic processes. Over the last decades, sunlight-driven photocatalysis has emerged as an innovative alternative to fossil fuels for solving the severe problems related to environmental diseases and the energy crisis. Currently, semiconductorbased materials (such as TiO₂, C₃N₄, In₂O₃, WO₃, BiVO₄) have been intensively studied for diverse photocatalytic applications, including the hydrogen evolution reaction (HER) and the nitrogen reduction reaction (NRR) to produce ammonia. However, the drawbacks of weak visible light absorption, low electron-hole separation with high recombination rate, and lack of surface active-sites have limited the photocatalytic performance of these semiconductorbased photocatalysts. Therefore, various approaches such as structural engineering, nanocomposite heterojunctions have been applied to overcome the limitations of these materials and boosting the catalytic activity. In this thesis, we employed novel strategies to develop four efficient photocatalytic systems for hydrogen production and nitrogen fixation. Our materials possessed a unique structure, which is advantageous to promote the visiblelight absorption, facilitate the separation of charge carrier, and increase the number of surface-active sites. For the photocatalytic hydrogen evolution application, we firstly synthesized the singlephase CdIn₂S₄ sponge-like spheres via solvothermal method followed by H₂S gas treatment. The formation of CdIn-complex with uniform distribution of Cd²⁺ and In³⁺ played a crucial role in achieving the spinel structured-single phase CdIn₂S₄. The bandgap energy was found to be significantly reduced, resulting in the extended visible light absorption up to 700 nm, which was primarily attributed to the sulfide species-mediated modification of the valence band in CdIn₂S₄ single-phase. With the deposition of Ni metal as a reduction cocatalyst, the hybrid Ni-CdIn₂S₄ photocatalyst showed enhanced solar light-driven photocatalytic hydrogen evolution efficiency, which is around 5.5 and 3.6 folds higher than that of Pt-CdIn₂S₄ and Pd-CdIn₂S₄ samples, respectively. The second developed photocatalytic system involved the preparation of chemically bonded nickel anchored S-doped graphitic-carbon nitride (Ni-SCN) through a technique known as sulfidation assisted photo-deposition process. The origin of the distinctive structure of Ni-SCN was due to the existence of Ni-S-C-N chemical bonds in the system, which fundamentally favored the separation of photogenerated electron-hole and improved the light-harvesting capabilities of the photocatalyst. Consequently, the synthesized Ni-SCN exhibited an excellent sunlight-driven photocatalytic activity toward hydrogen evolution, which was several times higher than Sdoped g-C₃N₄, Ni supported g-C₃N₄ and Pt loaded S-doped C₃N₄ systems. For photo(electro)catalytic nitrogen fixation application, our work is the first to report the synthesis of Au nanoparticles loaded Fe doped W₁₈O₄₉ (denoted as WOF-Au) nanorods through a solvothermal synthesis following by in situ deposition of Au nanoparticles. The incorporation of Fe dopants can not only heal the bulk-defect-states in nonstoichiometric W₁₈O₄₉ lattices but also promote the separation and interfacial migration of electrons from photocatalyst to chemisorbed N₂ molecules; while Au nanoparticles decorated on the Fe doped W₁₈O₄₉ surface provided the high energetic electrons for N₂ reduction via the localized surface plasmon resonance effect (LSPR). The obtained plasmonic WOF-Au system shows an enhanced NH₃ yield, which is much higher than that of the bare W₁₈O₄₉, as well as very high stability. The enhancement in photoelectrocatalytic performance is mainly contributed by the synergetic effect of Fe dopants and plasmonic Au nanoparticles on the W₁₈O₄₉ host. Lastly, Ru doped In₂O₃ hollow peanuts (demoted as Ru-In₂O₃ HPNs) were fabricated by the novel self-template strategy followed by the calcination of the as-synthesis precursors. The uniform In₂O₃ nanoparticles were closely packed together to form a hollow peanut structure, which facilitated the separation and transportation of photoinduced electron-hole and favored the light-harvesting ability by the internal multi-reflection process. Furthermore, the introduction of Ru dopants induced numerous surface oxygen vacancies and narrow down the bandgap energy of the photocatalytic system. These oxygen vacancies act as trapping centers, facilitating the separation of photoexcited electrons and holes. Consequently, the ammonia production rate of Ru-In₂O₃ HPNs was 5.6 times and much higher as compared to pure In₂O₃ HPNs and bulk material of In₂O₃ under solar light irradiation

Recent Advances in Endocrine Disrupting Compounds Degradation through Metal Oxide-Based Nanomaterials

Endocrine Disrupting Compounds (EDCs) comprise a class of natural or synthetic molecules and groups of substances which are considered as emerging contaminants due to their toxicity and danger for the ecosystems, including human health. Nowadays, the presence of EDCs in water and wastewater has become a global problem, which is challenging the scientific community to address the development and application of effective strategies for their removal from the environment. Particularly, catalytic and photocatalytic degradation processes employing nanostructured materials based on metal oxides, mainly acting through the generation of reactive oxygen species, are widely explored to eradicate EDCs from water. In this review, we report the recent advances described by the major publications in recent years and focused on the degradation processes of several classes of EDCs, such as plastic components and additives, agricultural chemicals, pharmaceuticals, and personal care products, which were realized by using novel metal oxide-based nanomaterials. A variety of doped, hybrid, composite and heterostructured semiconductors were reported, whose performances are influenced by their chemical, structural as well as morphological features. Along with photocatalysis, alternative heterogeneous advanced oxidation processes are in development, and their combination may be a promising way toward industrial scale application

Novel Nanostructured Materials for Solar Fuel Production and Advanced Rechargeable Batteries

Non-renewable fossil fuels are the major sources to meet the energy, electricity and transportation demands of today\u27s world. The over consumption of fossil fuels will lead to the increasing energy crisis and disastrous effects such as air pollution, global warming etc. The primary greenhouse gas is CO2 mainly emits from the combustion of fossil fuels. Photocatalytic reduction of CO2 using sunlight as the energy input is a promising way to reduce CO2 level in the atmosphere and in the meantime produce alternative fuels such as CO, methane, methanol, etc. Among the various photocatalyst materials reported, nanomaterial TiO2 is the most widely studied due to its suitable band positions, high chemical stability, non-toxic nature, and low cost. However, the energy conversion efficiency using TiO2 for CO2 photoreduction is still low, mainly due to the reasons of (1) high probability of recombination of photo-induced electron-hole pairs, (2) fast backward reaction of hydrogen and oxygen to form water, and (3) limited ability of visible light utilization. Another efficient way to decrease CO2 emissions is to reduce fossil fuels consumption. The invention of hybrid electric vehicles (HEVs) and electric vehicles (EVs) are great promise of replacing traditional gasoline driven automobiles. As one of the new generation high energy density batteries, lithium-sulfur (Li-S) battery is very attractive because sulfur has a high theoretical capacity of 1,675 mA h g-1. However, the practical realization of Li-S batteries is limited by several problems: (1) poor electrical conductivity of sulfur (2) dissolution of the lithium polysulfide intermediates into the electrolyte, and (3) large volume expansion of sulfur during cycling. One objective of this study is to demonstrate high-efficiency photocatalysts using innovative hybird nanostructures that consist of Ce doped TiO2 dispersed on mesoporous silica (SBA-15) or noble-metal nanoparticles Ag supported on TiO2 or MgAl-LDOs (layered double oxides) grafted on TiO2 (TiO2-MgAl LDOs). The use of Ce doping could result in smaller TiO2 nanocrystals and facilitate electron-hole separation, while SBA-15 provides good dispersion of TiO2 and a strong interaction between TiO2 and the substrate. And Ag species on TiO2 facilitate electron trapping and transport to the catalyst surface, and thus, can potentially enhance multi-electron transfer processes. TiO2-MgAl LDOs is favorable for CO2 species adsorption on the photocatalyst, therefore, compensating the weakened CO2 adsorption ability at higher temperature in the presence of H2O vapor. The other objective of this study is to find alternative materials as anode for Li-ion battries and demonstrate high-performance Li-S battery electrodes using hybrid nanomaterials consist of sulfur infiltrated porous micrsophere carbon (PMC). Carbon/TiO2 was found to be promising as anode alternative to replace graphite materials to avoid safety issues for Li-ion batteries. Cathodes made of sulfur infiltrated in such a multi-modal porous carbon framework provide advantageous properties that guaranttee the superior electrochemical performance. Ce-doped TiO2 on SBA-15, Ag deposited TiO2 (Ag/TiO2) and MgAl-LDOs grafted on TiO2 (TiO2-MgAl LDOs) were synthesized and characterized for applications in CO2 photoreduction with H2O. Ce-doped TiO2 were synthesized using sol-gel method and SBA-15 was then added to the sol to prepare Ce-doped TiO2 on SBA-15 nanocomposites. Modification of TiO2 with Ce significantly stabilized the TiO2 anatase phase and increased the specific surface area, which contributed to an improvement of CO production from CO2 reduction. Dispersing Ce-TiO2 nanoparticles on the mesoporous SBA-15 support further enhanced both CO and CH4 production. The superior catalytic activity may be related to the partially embedded Ce-TiO2 nanoparticles in the ordered 1-D pores in SBA-15 that form synergies between the different components of the catalysts and enhance the diffusion and adsorption of CO2. Ag/TiO2 nanocomposites were synthesized by spray pyrolysis technique. This work has demonstrated the feasibility of syngas (H2 and CO) production from a gas mixture of CO2, H2O and CH3OH hrough a photocatalytic reduction process on Ag/TiO2 nanocomposite catalysts under solar irradiation.The material property analysis and photocatalytic activity results showed that the ultrasonic spray pyrolysis method is much superior to conventional wet impregnation process with the advantages of smaller Ag nanoparticles, a better Ag dispersion on TiO2, and a higher fraction of metallic Ag species, which facilitate charge transfer and improve photocatalytic activity. TiO2-MgAl LDOs were synthesized by hydrothermal and coprecipitation method. As the MgAl LDOs concentration increases, TiO2 crystal size was increased. MgAl LDOs grafting on TiO2 cuboids may help improve the adsorption ability of CO2 onto TiO2 which improves the photocatalytic activity of CO2 reduction. Our work also entails the synthesis and characterization of carbon coated TiO2 for the application of Li-ion batteries and sulfur infiltrated porous microsphere carbon (PMC/S) for the application of Li-S batteries. Carbon decorated on commercial TiO2 nanoparticles (P25 and P90) composites with optimized carbon concentration and structure were fabricated by a facile process employing carbonization method. The electrochemical performance of C-P90 was superior to C-P25 because of its higher specific surface area and larger anatase fraction that can accommodate more lithium ions. 1.9% carbon was found to form an optimized carbon layer on TiO2 that can improve the electronic conductivity. The PMC was synthesized by spray pyrolysis method. Then PMC/S was fabricated via a liquid phase infiltration. The novel-structured porous carbon microspheres possess a controllable multi-modal pore size distribution, i.e., a combination of interconnected micropores, mesopores and macropores, which is beneficial for Li-S batteries electrochemical performance. Future work includes further improvement of PMC/S composites to inhibit shuttle effect and improve the electrode performance including the cyclability and rate capability

Towards Green, Enhanced Photocatalysts for Hydrogen Evolution

This book gathers selected research on the preparation, characterization and application of new organic/inorganic composites endowed with photo(electro)catalytic properties for the photocatalytic production of H2. In these pilot studies, the photoactive materials were tested under either UV-visible or, even more conveniently, under visible light for H2 evolution in “sacrificial water splitting” or “photoreforming” systems. In addition, a review article on the use of 2D materials and composites as potential photocatalysts for water splitting is included

Role of Graphene in Photocatalytic Solar Fuel Generation

One of the most promising methods for conversion and storage of solar energy is in the form of the chemical bonds of an energy carrier, such as hydrogen or light hydrocarbons. However, the traditional methods to harness and store solar energy are simply too expensive to be implemented on a large scale. It has been documented that the recombination of photo-induced charge carriers is the greatest source of inefficiency in photocatalytic systems. In the last decade, graphene derivatives and their functionalized nanostructures were extensively utilized for various roles to improve the efficiency of photocatalytic solar fuel generation. These include photocatalyst/redox active sites via band gap and defect density engineering, charge acceptor due to their excellent carrier mobility, a solid-state charge mediator by electronic band alignment, and light absorber by taking advantage of their photoluminescence characteristics at the nanoscale. This chapter aims to provide an authoritative and in-depth review on the properties and application of graphene derivatives, as well as the recent advances in the design of graphene-based photocatalytic systems. The knowledge extracted from the presented materials can be applied to other applications dealing with surface chemistry, interfacial science, and optoelectronic device fabrication

Synthesis and Applications of Nanomaterials for Photocatalysis and Electrocatalysis

This book supplies fundamental aspects regarding the use of different nanostructures as heterogeneous catalysts for energy and environmental applications. In recent decades, the attention of both scientific and industrial communities has become increasingly focused on the implementation of groundbreaking nanomaterials in all fields of human activity, especially toward improving energy efficiency and fulfilling environmental demands. Energy and environment represent a perfect blend: energy-saving environmental remediations and promising energetic devices meeting environmental concerns represent potential future challenges that humankind will face. In this context, the fine control of the nanosized species is the real tool to overcome the current issues and to improve the final performances. Herein, from an energetic point of view, oxygen evolution and reduction reactions (OER and ORR) are keys to deeply understanding the behaviour of water splitting devices and fuel cells as well as zinc/air batteries, respectively. Zinc tantalum oxynitride-based photoanodes and nitrogen-modified carbon doped with different metals will be presented and fully characterised. Concurrently, bismuth titanate nanosheets and noble metal core-shell nanoparticles can be adopted to enhance hydrogen evolution through photocatalytic water splitting, exploiting solar energy. Instead, for what concerns the environmental remediation, the use of pure (black, modified, and faceted TiO2, Ga2O3) and composite (graphene/titanate, Zn2\u2013SnO4/BiOBr, g-C3N4/Nb2O5, MnO2/TiO2 and CaIn2S4/ZnIn2S4) nanomaterials allow for air and water purification, especially under solar irradiation. Particularly, the complete photodegradation of noxious species (benzylic acid), organic dyes (rhodamine B, methylene blue and alizarin red), heavy metals (chromium), recalcitrant pharmaceutical active principles (cinnamic acid, ibuprofen and tetracycline), and VOCs (ethanol) will be thoroughly discussed. Finally, we would like to acknowledge all the authors who have contributed to this book with their scientific expertise, and we hope that the readers will find the arguments both useful and interesting