Synthesis and Characterization of Transition Metal Oxide and Dichalcogenide Nanomaterials for Energy and Environmental Applications

Transition metal oxides (TMOs) and transition metal dichalcogenides (TMDs) have gained immense interest recently for energy and environmental applications due to their exceptional structural, electronic, and optical properties. For example, titanium dioxide (TiO2) as one of the TMO photocatalysts has been widely studied due to its stability, non-toxicity, wide availability, and high efficiency. However, its wide bandgap significantly limits its use under visible light or solar light. Recent studies also show that semiconducting TMDs could be used as potential supercapacitor electrode materials and platinum (Pt)-free electrocatalysts for economical utilization of renewable energy, because the high cost and scarcity of Pt have impeded the large-scale commercialization of many green technologies. In this dissertation study, various novel TMO and TMD nanomaterials are designed and synthesized, and their catalytic performance is further investigated. First, a facile route for the controllable synthesis of modified TiO2 is designed to improve its photocatalytic efficiency under the visible/solar light. The resulting Ti3+-doped TiO2 with tunable photocatalytic properties using a hydrothermal method with varying amounts of reductant, i.e., sodium borohydride (NaBH4), showed color changes from light yellow, light grey, to dark grey with the increasing amount of NaBH4. The present method can controllably and effectively reduce Ti4+ on the surface of TiO2 and induce partial transformation of anatase TiO2 to rutile TiO2, with the evolution of nanoparticles into hierarchical structures attributing to the high pressure and strong alkali environment in the synthesis atmosphere; in this way, the photocatalytic activity of Ti3+-doped TiO2 under visible-light can be tuned. The band gap of Ti3+-doped TiO2 based on the Kubelka-Munk function is 3.1 eV, which is smaller than that of pristine TiO2 (3.28 eV), confirming that adding NaBH4 as a reductant causes the absorption edge of TiO2 to shift to a lower energy region. After 20 min of simulated sunlight irradiation of photocatalytic reactions for the degradation of methylene blue (MB) aqueous solution, nearly 97.2% of MB was degraded by the sample TiO2-4 (reduced by 12 g of NaBH4 in the hydrothermal reaction), compared with the degradation efficiency of the pristine TiO2 (23.5%). The as-developed strategy may open up a new avenue for designing and functionalizing TiO2 materials with enhanced visible light absorption, narrowed band gap, and improved photocatalytic activity. Second, cobalt sulfide-based (CoSx) nanostructures as one of the TMDs are competitive candidates for fabrication of supercapacitor electrodes due to their high specific surface area, high electrical conductivity, and redox-active structures. However, CoSx materials still suffer from relatively low specific capacitances, degradation of performance over long cycling duration, and tedious synthesis and assembly methods. Hence, metallic vertically-aligned cobalt pyrite (CoS2) nanowires (NWs) are prepared directly on current collecting electrodes, e.g., carbon cloth or graphite disc, for high-performance supercapacitors. These vertically-aligned CoS2 NWs have a variety of advantages for supercapacitor applications. Because the metallic CoS2 NWs are synthesized directly on the current collector, the good electrical connection enables efficient charge transfer between the active CoS2 materials and the current collector. In addition, the open spaces between the vertical NWs lead to a large accessible surface area and afford rapid mass transport. Moreover, the robust CoS2 NW structure results in high stability of the active materials during long-term operation. Electrochemical characterization reveals that the CoS2 NWs enable a large specific capacitance (828.2 F/g at a scan rate of 0.01 V/s) and excellent long-term cycling stability (0-2.5% capacity loss after 4,250 cycles at 5 A/g) for pseudocapacitors. This example of vertically-aligned metallic CoS2 NWs for supercapacitor applications expands the opportunities for transition metal sulfide-based nanostructures in emerging energy storage applications. Third, to combine the advantages of TMOs and TMDs, an aerosol processing method is developed for the facile and green synthesis of reduced graphene oxide (rGO)/tungsten disulfide (WS2)/tungsten trioxide (WO3) ternary nanohybrids, because both TMOs and TMDs are promising candidates for platinum-free electrocatalysts in renewable energy applications. The resulting hybrid material has a spherical structure constructed of crumpled graphene and WS2/WO3 nanorods. The crumpled graphene/WS2/WO3 (CGTH) catalyst showed a superior electrocatalytic activity in the hydrogen evolution reaction (HER), with a Tafel slope of 37 mV/dec and an onset potential of 96 mV. Compared with reported MoS2/WS2-based electrocatalysts, this hybrid material shows one of the highest catalytic activities in HER. The environmentally-friendly synthesis and outstanding performance suggest a great potential of CGTH for noble metal-free electrocatalysts in water splitting. Next, in order to improve the specific capacity of lithium-ion batteries (LIBs)/ potassium-ion batteries (PIBs) and relieve volume expansion of nanoparticles to fulfill the urgent need of reliable energy storage applications, TMD nanomaterials especially MoS2 quantum dots (QDs) have been considered promising anode materials for LIBs owing to their higher theoretical capacity and better rate capability compared with commercial graphite anodes. An exfoliated mesoporous MoS2 QDs-graphite composite anode was designed and investigated. The MoS2 QDs are located in the void spaces between graphite particles, thereby preventing the graphite particles from losing electrical contact with the current collector and enhancing the cycling performance of the MoS2/graphite composite anode. The optimized MoS2 QDs with graphite composites displayed good charge/discharge characteristics and the capacity maintained at 449.8 mAh g-1 after 300 charge/discharge cycles for LIBs. And the MoS2 QDs for PIB cells exhibited a stable capacity of approximately 409 mAh g-1 for 17 cycles. Finally, metal-organic frameworks (MOFs) have attracted substantial research attention owing to their tunable pore size, high pore volume, high specific surface area, and highly ordered crystalline porous networks. Previous studies have mostly focused on sensing, drug delivery, batteries, and selective catalysis; however, their application as photocatalysts has not been thoroughly reported. It is well known that bulk MoS2 is unsuitable for photocatalytic applications due to the insufficient reduction and oxidation ability for the photocatalysis. However, exfoliated MoS2 exhibits a direct band gap of 2.8 eV resulting from quantum confinement, which enables it to possess suitable band positions and to retain good visible-light absorption ability. As a result, it is considered to be a promising candidate for photocatalytic applications. Encapsulating exfoliated MoS2 into MOF exhibits enhanced absorption in the visible light range compared with pure MOF and the highest hydrogen production rate could reach 68.4 μmol h-1g-1, which is much higher than that on pure MOF. With suitable band structure and improved light-harvesting ability, exfoliated MoS2@MOF can be a potential photocatalyst for hydrogen production. This dissertation study suggests that modified TiO2 and exfoliated MoS2@MOF can be efficient photocatalysts with enhanced visible light absorption ability; metallic CoS2 NWs could be active materials with a large specific capacitance and excellent stability; reduced graphene oxide (rGO)/tungsten disulfide (WS2)/tungsten trioxide (WO3) as a ternary nanohybrid offers advantages of TMOs and TMDs, making it an outstanding noble-metal free electrocatalyst in water splitting; and MoS2 QDs with relieved volume expansion are promising anode materials for LIBs/PIBs. The study provides a scientific foundation to design and discover low-cost, efficient and stable TMOs and TMDs candidates for suitable energy and environmental applications

Microrecycling of spent Zn-C batteries: selective synthesis of nanostructures and hybrid materials for real-field application

In modern life, the usage of batteries in the small/large electronic, industries, automobiles etc. is expanding promptly, which eliminates the necessity of reticulation and/or transportation of power due to the portability, low maintenance, and high energy density characteristics of batteries. Nevertheless, battery technologies undergo from a short life span that causes in a requirement for regular replacement. The propagation of large amount of battery has originated a requirement for an efficient management procedure to safely deal as well as recover valuable materials used in numerous battery manufacturing, which swift the generation of electronics waste (e-waste). Because of the human health and environment concern, recently recycling of e-waste materials is drawing acute attention among the researchers. Thus, the sustainable recycling process of non-rechargeable batteries has become a primary concern, which is now discussed and studied broadly. This research mainly confined into two categories to resolve this issue efficiently. First: the sustainable and adoptable process of synthesizing and characterizing valuable nano-materials (ZnO and MnO) from spent Zn-C battery via microrecycling techniques, where thermal conversion of the black mixture of Zn-C battery to ZnO nanoparticles as well as ZnO ultra-thin film facilitated by the horizontal quartz tube furnace at 900 oC temperature with argon (Ar) gas supply. Whereas, MnO nanoparticles are remained as a residue after condensation. Second: synthetization of hybrid materials by using ZnO for fabricating energy storage and sensing modules for real application. Herein, hybrid material including ZnO, pristine graphene and ethyl-cellulose was used to prepare the sensing materials for fabricating a sensor to detect ethanol efficiently among a set of VOCs at RT. Further, by changing the combination of materials, graphene aerogel decorated with ZnO nanoparticles was synthesized for preparing sensor to detect trace amount of NO2 gas. Later, another composition of microrecycled ZnO and graphene oxide was developed along with ZnO ultra-thin film for fabricating assymetric-supercapacitor. In short, microrecycling of spent Zn-C battery a novel route, presented in this study could be a ground breaking method to synthesize MnO and ZnO nanoparticles simultaneously and synthesized hybrid materials for representing an economic value for industries as well as environmental benefits

Metal oxide nanostructures for sensor applications

Electrorheological fluids have been paying a lot of attention due to their potential use in active control of various devices in mechanics, biomedicine or robotics. An electrorheological fluid consisting of polarizable particles dispersed in a non-conducting liquid is considered to be one of the most interesting and important smart fluids. This work presents the effect of the dopant, camphorsulphonic acid or citric acid, on the electrorheological behaviour of suspensions of doped polyaniline nanostructures dispersed in silicone oil, revealing its key role. The influence of carbon nanoparticle concentration has also been studied for these dispersions. All the samples showed an electrorheological effect, which increased with electric field and nanostructure concentration and decreased with silicone oil viscosity. However, the magnitude of this effect was strongly influenced not only by carbon nanoparticle concentration but also by the dopant material. The electrorheological effect was much lower with a higher carbon nanoparticle concentration and doped with citric acid. The latter is probably due to the different acidities of the dopants that lead to a different conductivity of polyaniline nanostructures. Furthermore, the effect of the carbon nanoparticles could be related to its charge trapping mechanism, while the charge transfer through the polymeric backbone occurs by hopping. Polyaniline/camphorsulphonic acid composite nanostructures dispersed in silicone oil exhibited the highest electrorheological activity, higher than three decades increase in apparent viscosity for low shear rates and high electric fields, showing their potential application as electrorheological smart materials.authorsversionpublishe

Development of electrochemical biosensors and sensors for the determination of interest analytes

Se han puesto a punto varios métodos electroquímicos para la determinación de varios analitos de interés, como lactato, cloruro, bromuro y yoduro utilizando sistemas electródicos serigrafiados (SPEs). Su bajo costo, tamaño pequeño, portabilidad para aplicaciones in situ, así como su facilidad de modificación, les confiere gran versatilidad, para ser usados como transductores en sensores y biosensores electroquímicos con gran precisión y sensibilidad en distintas matrices. Concretamente, se ha desarrollado un biosensor amperométrico para la determinación de lactato, basado en la utilización de la enzima lactato oxidasa. El biosensor ha permitido la determinación de este ácido orgánico en líquidos biológicos como saliva y sudor y en productos alimentarios como vinos. Se incluyen también estudios de los mecanismos de inhibición de las enzimas utilizadas en los biosensores. También se han puesto a punto sensores para la determinación de haluros, que han mostrado su aplicabilidad para su cuantificación en varios tipos de muestras

Enhancing the delivery of poorly water soluble drugs using particle engineering technologies

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Inorganic Fullerene-like Nanoparticles and Inorganic Nanotubes

The subjects of the presented papers cover a wide range of challenges in the area of inorganic fullerene-like nanoparticles and nanotubes. However, it can include only a few comprehensive experimental and theoretical efforts, stepwise evaluating the rationalization of the synthesis, and elucidation of the stability, mechanical, electronic and adhesive properties of these nanostructures. We believe that this thematic issue can be helpful, not only for an advanced researcher to grasp the latest developments in this field, but also to permit a beginner to gain a deeper insight into the field of inorganic fullerene-like nanoparticles and nanotubes

Materials Chemistry of Fullerenes, Graphenes, and Carbon Nanotubes

This Special Issue is intended as a platform for interactive material science articles with an emphasis on the preparation, functionalization chemistry, and characterization of nanocarbon compounds, as well as all aspects of physical properties of functionalized, conjugated, or hybrid nanocarbon materials, and their associated applications. Some recent advances in the field are here collected, providing new ideas for discussion of researchers working in this multidisciplinary scenario

The Sustainable Composite Materials in Civil and Architectural Engineering

This book is a collection of 10 research articles (from 18 submissions) authored by researchers and peer reviewed by professionals in the field to address the use of sustainable composite materials in civil and architectural engineering over the course of more than 2 years. Fiber-reinforced plastic (FRP), geopolymers, and various recycled and repurposed waste materials are among the items addressed, used in a variety of applications from flame retardance to energy consumption. This book is a great resource for both academics and professionals in the field of engineering

Gold Copper Based Catalysts in the Development of Direct Formic Acid Fuel Cells

There is a growing awareness of the need for fundamental and applied research in energy storage and conversion due to the global climate issue with energy sources, environmental and human health challenges. In this work, development of a new synthesis route for catalysts, physicochemical and electrochemical research is reported for direct formic acid fuel cells. The synthesis method is based on the sodium borohydride reduction of (Pd2+, Cu2+, Au3+) precursor, stabilised by polyvinylpyrrolidone for the preparation of a highly stable catalysts with, well-controlled particle size distribution. The surface and bulk properties of the catalysts were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), and electrochemically by cyclic voltammetry and chronoamperometry. The results obtained for Pd-C showed that a uniform XRD estimated the size distribution in a narrow particle size range with an average size of 1.4 ± 0.11 nm. Electrochemical studies for formic acid electrooxidation reveals that Pd-CH3BO3 + NH4F(21wt.%) presents superior catalytic activity (over 44 %) than that of the Pd-CPVP(43.5wt.%) synthesis route. For an equivalent electrode paste, Pd-CPVP(43.5wt.%) exhibited a greater electrochemical surface area (ECSA) than Pd-CPVP(43.5wt.%) but achieved a lower utilisation of palladium. The electrooxidation of the catalyst shows three times higher activity for formic acid oxidation than commercial gold nanoparticles dispersed on the carbon support. The enhanced catalytic performance is attributed to the electronic synergistic effect of copper and the specific gold structure promoting oxidation of adsorbed intermediate species. Overall, these findings have significant implications for practical direct formic acid fuel cells (DFAFCs) technology by the controlled Au-shell Cu-core anode catalysts application. Overall, palladium catalysts demonstrated better electrocatalytic activities for formic oxidation than Au and gold copper catalysts. This work is part of the initial stages of the effort to develop a low-cost gold-catalyst for DFAFCs technology