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

Digital representation for assessment of spoken EFL at university level: A case study in Vietnam

Assessing the speaking performance of students who are studying English as a Foreign Language (EFL) has mainly been conducted with face-to-face speaking tests. While such tests are undoubtedly interactive and authentic, they have been criticised for subjective scoring, as well as lacking an effective test delivery method and recordings for later review. Technology has increasingly been integrated into speaking tests over the last decade and become known as computer-assisted or computer-based assessment of speaking. Although this method is widely acknowledged to measure certain aspects of language speaking effectively, such as pronunciation and grammar, it has not yet proved to be a successful option for assessing interactive skills. An effective testing method is deemed to maintain the interactivity and authenticity of live speaking tests, able to deliver tests quickly and efficiently, and provide recordings of performances for multiple marking and review. This study investigated digital representation of EFL speaking performance as a viable form of student assessment. The feasibility of digital representation has previously been examined in relation to authenticity and reliability in assessment of different subjects in Western Australia, including Italian, Applied Information Technology, Engineering Studies, and Physical Education Studies. However, as far as the researcher is aware, no studies have yet assessed EFL speaking performance using digital representation. In an attempt to bridge this gap, this study explored the feasibility of digital representation for assessing EFL speaking performance in a university in Vietnam, the researcher’s home country. Data collection was undertaken in two phases using a mixed methods approach. In Phase 1, data related to English teachers’ and students’ perceptions of Computer- Assisted English Speaking Assessment (CAESA) were collected. Their perceptions were analysed in relation to the outcomes of a digital speaking assessment trial using the Oral Video Assessment Application (DMOVA). In Phase 2, student participants took an English speaking test while being videoed and audio recorded. English teachers invigilated and marked the trial test using the current method, followed by the digital method. Data were collected via Qualtrics surveys, interviews, observations and databases of student performance results. The feasibility of digital representation in assessing EFL speaking performance was analysed according to the Feasibility Analysis Framework developed by Kimbell, Wheeler, Miller, and Pollitt (2007). The findings from Phase 1 indicated that both teachers and students had positive attitudes towards computer-assisted assessment (CAA). They were confident with computer-assisted English assessment (CAEA) and preferred this testing method to the current paper-and-pencil process. Both cohorts believed that CAEA enhanced the precision and fairness of assessments and was efficient in terms of resources. However, some participants were sceptical about the authenticity of computer-assisted EFL speaking tests because it failed to foster conversations and interactions in the same way as face-to-face assessments. In spite of their scepticism, teachers and students indicated their willingness to trial DMOVA. Phase 2 identified the feasibility dimensions of DMOVA. This method of digital assessment was perceived to enhance fairness, reliability and validity, with some correlations between the live interview and digital tests. Teachers found it easy to manage the speaking tests with DMOVA and recognised the logistical advantages it offered. DMOVA was also credited with generating positive washback effects on learning, teaching and assessment of spoken English. In addition, the digital technology was compatible with the existing facilities at the university and required no support or advanced ICT knowledge. Overall, the benefits of the new testing method were perceived to outweigh the limitations. The study confirmed that digital representation of EFL speaking performances for assessment would be beneficial for Vietnam for the following reasons: (a) it has potential to enhance the reliability and accuracy of the current English speaking assessment method, (b) it retains evidence of students’ performance for later assessment and review, and (c) it facilitates marking and administration. These changes could boost EFL teaching, learning, and assessment, as witnessed in the trial, leading to increased motivation of teachers and students, and ultimately, enhancement of students’ English communication skills. The findings of the study also have implications for English speaking assessment policies and practices in Vietnam and other similar contexts where English is taught, spoken and assessed as a foreign language

Influence of low-frequency vertical vibration on walking locomotion

Walking locomotion has been a subject of studies in diverse research fields, such as computer, medical, and sport sciences, biomechanics, and robotics, resulting in improved understanding of underlying body motion and gait efficiency and pathology (when present). Only recently, a detailed understanding of kinematics and kinetics of the walking locomotion has become an important requirement in structural engineering applications due to an increasing sensitivity of modern, lightweight, low-frequency, and lightly damped footbridges to pedestrian-induced dynamic excitation. To facilitate development, calibration and verification of pedestrian models requires experimental characterization of walking gait parameters and understanding whether and how these parameters are influenced by the structural vibration. This study investigates whether low-frequency vibrations in the vertical direction affect seven walking locomotion parameters: pacing frequency, step length, step width, angle of attack, end-of-step angle, trunk angle, and amplitude of the first forcing harmonic. Three participants took part in a testing program consisting of walking on a treadmill placed on both stationary and vibrating supporting surfaces. The collected data suggest that an increasing level of vibration results in an increase in step-by-step variability for the majority of parameters. Furthermore, the existence of the self-excited force, previously observed only in numerical simulations of walking on pre-excited bridge decks, was confirmed. In addition, the deck vibration tended to have a beneficial effect of reducing the net force induced into the structure when walking at a pacing rate close to the vibration frequency. Finally, it was found that the vibration level perceptible by a pedestrian is one to two orders of magnitude larger than that typical of a standing person, and that the sensitivity to vibration decreases as the speed of walking increases

Experimental characterisation of walking locomotion on rigid level surfaces using motion capture system

Low-frequency structures, such as footbridges and long-span floors, are often sensitive to variations in dynamic loading induced by pedestrians. As a result, the design of these structures using traditional deterministic approaches is being replaced by stochastic load models that can accommodate different styles of walking. To inform development and facilitate wider implementation of the new stochastic approaches, a database of experimental data characterising both inter- and intra-subject variability of gait parameters is required. This study aims to contribute to the development of such a database by providing a set of data for walking over rigid level surfaces. The motion capture system Vicon was used for simultaneous monitoring of the kinematic and kinetic gait parameters. Ten test subjects walking at 13 different speeds participated in the experimental programme. Novel experimental data on pacing rate, step length, step width, angular positions of the legs and the trunk, and the force amplitude were collected and statistically characterised. The acquired data are suitable for calibration of the bipedal pedestrian models intended for civil engineering applications

Experimental and Theoretical Analysis of Cracking Moment of Concrete Beams Reinforced with Hybrid Fiber Reinforced Polymer and Steel Rebars

This study aims at experimentally and theoretically investigating the cracking moment (Mcrc) of hybrid Fiber Reinforced Polymer (FRP)/steel Reinforced Concrete (RC) beams. Six hybrid Glass FRP (GFRP)/steel and three GFRP RC beams with various GFRP and steel reinforcement ratios are tested in four-point bending scheme. Experimental results indicate that both GFRP and steel rebars affect Mcrc, but the effect of steel reinforcement is more significant. When the steel reinforcement ratio increases to 1.17%, Mcrc goes up to 15.9%, while the same value for GFRP is only 9.7%. An analytical method is proposed based on the plain section assumption and nonlinear behavior of materials for estimating Mcrc. The proposed model shows a good agreement with the experimental data conducted in this study and collected from the literature. The results of the parametric study give evidence of the positive effects of hybrid reinforcement ratios and elastic modulus of FRP on Mcrc of hybrid RC beams

Indoor assistance for visually impaired people using a RGB-D camera

In this paper a navigational aid for visually impaired people is presented. The system uses a RGB-D camera to perceive the environment and implements self-localization, obstacle detection and obstacle classification. The novelty of this work is threefold. First, self-localization is performed by means of a novel camera tracking approach that uses both depth and color information. Second, to provide the user with semantic information, obstacles are classified as walls, doors, steps and a residual class that covers isolated objects and bumpy parts on the floor. Third, in order to guarantee real time performance, the system is accelerated by offloading parallel operations to the GPU. Experiments demonstrate that the whole system is running at 9 Hz

Concrete beams using seawater and sea sand reinforced with steel and GFRP rebars exposed to marine environment: An experimental study

Using fresh water and river sand in concrete mix composition makes a lot of negative impacts on resources and the environment while the source of sea sand and sea water is abundant and less harmful to the environment. However, sea sand and seawater in concrete can cause severe corrosion of the reinforcement, reducing the durability and bearing capacity of the structure. This paper illustrates the results of a comparative study on the flexural behavior of six corroded seawater sea-sand concrete (SWSSC) beams. The corrosion process of two concrete beams reinforced with traditional steel bars and four concrete beams reinforced with a combination of glass fiber reinforced polymer (GFRP) and steel bars was coupled by the effect of seawater exposure and sustained load. It was found that after exposure to a marine environment during the period of 60 months the GFRP bar retains surface integrity, meanwhile, the steel bars were significantly corroded with a cross-sectional area loss of approximately 13.93%. The decrease in bending stiffness, yield load, and ultimate load of the RC beams was found due to the deterioration of SWSSC and corrosion of steel bars.