Synthesis of hierarchical wo3 microspheres for photoelectrochemical water splitting application

In this work, hierarchical WO3 microspheres were synthesized using chemical bath deposition. The morphology of the synthesized sample was studied using scanning electron microscopy (SEM). The hierarchical WO3 microspheres formed from spontaneously self-assembled nanosheets have a high specific surface area. Structural characterizations of sample were performed using X-ray diffraction (XRD) and Raman spectroscopy. Analysis of XRD spectra showed that synthesized particles have a monoclinic modification. The optical properties of the sample were studied using UV-Vis diffuse reflectance absorption spectra. The value of the energy gap calculated from the absorption spectra is 2.2 eV, which indicates high light absorption ability. A photocurrent study was done to investigate the photocatalytic activity. The photoelectrode was prepared using hierarchical WO3 microspheres and polymer deposited on fluorine doped tin oxide (FTO) glass via spin coating technique. A remarkable photocurrent density of 18 A/cm2 at 0.5 V was achieved. The elongated structures improved light absorption ability and photocatalytic activity

Synthesis and characterization of pristine and lanthanum modified wo3 nanoparticles for the photocatalytic degradation of organic dyes

Abstract : South Africa is rich in naturally occurring resources including water, coal, oil, land. Individuals and industries use these resources as raw material inputs on a daily basis. However, they create significant amounts of pollution such as persistent organic pollutants (POPs). Such pollutants can be classified as inorganic, microbial and organic. Organic pollutants such as organic dyes are found in textile effluents that escape to the environment. They are designed to have a high degree of stability to fading upon sunlight exposures, chemicals and microbial attack leading to the ineffectiveness of current conventional wastewater treatment methods. Conventional wastewater treatment methods have been reported to be ineffective in the degradation of textile dyes because of their chemical stability. These methods have low effectiveness, with limited flexibility, they require specialized equipment and further handling of the generated waste. These methods are reported to have the ability to effectively remove colour, but for but lack the ability to completely degrade the dye molecules. Developed methods such as advanced oxidation processes (AOPs) use of photocatalytic semiconductors. These semiconductors have been researched and reported to have the characteristics to effectively treat wastewater by completely degrading a diversity of organic pollutants. A widely used semiconductor is monoclinic tungsten trioxide (WO3). It is viewed as an ideal candidate for photocatalytic applications. It is a photocatalyst that is responsive in the visible region, it absorbs light in the region up to 480 nm. WO3 has small band-gap energy which has been reported to range from 2.4−2.8 eV and high oxidation power of valence band (VB) holes and thus displays enhanced photoabsorption in visible-light irradiation. This gives WO3 the advantage to be used as an indoor pollutant treatment as well as outdoor applications. Hence, this project aims to utilize lanthanum-doped WO3 for the photodegradation of refractory vi organic dyes. Lanthanides as dopants are reported to improve the photocatalytic activity of the catalyst by increasing the adsorption capacity for pollutants, as well as, reducing the electron-hole recombination rates. In this study, pristine tungsten trioxide (WO3) nanoparticles were synthesized using the impregnation method with tungstic acid (H2WO4) and nitric acid as precursors, Lanthanum nitrate hydrate was used as a source of lanthanum (La) dopant. The as-synthesized nanoparticles were annealed at 450ºC for 3 hrs. The nanoparticles were characterized using X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), coupled with energy dispersive X-ray (EDX), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, zeta potential, UV-visible spectroscopy (UV-vis), X-Ray photoelectron spectroscopy (XPS) and Ion chromatography (IC). Spectroscopic instruments such as XRD, Raman and FTIR confirmed the nanoparticles were composed of monoclinic polymorphs. The spherical morphology was confirmed by TEM and SEM, with EDX confirming the presence of tungsten, oxygen and lanthanum in the samples. The band gap energy obtained from the DRS measurements were found to be 2.45, 2.42 and 2.57 eV for m-WO3, 1-La-WO3, and 5-La-WO3 nanoparticles respectively. XPS was used to determine the valence band maximum (VBM) which was used to calculate the conduction band and estimate the band edge position. XPS band edge positions were in agreement with the UV-vis band edge positions. Zeta potential confirmed the point of zero charge for the nanoparticles to be at pH 3.8. Ion chromatography confirmed the evolution of the chlorides and sulphate ions from the degradation of Methylene blue and Congo red respectively.M.Tech. (Chemistry

WO3–based photocatalysts: A review on synthesis, performance enhancement and photocatalytic memory for environmental applications

A significant drawback of the traditional photocatalysts such as titanium dioxide (TiO2) is their inability to absorb visible light from the solar spectrum due to their wide band gap energy. They are only photoactive in the ultraviolet (UV) region which is just a little fraction of the solar spectrum and could be harmful with much exposure to it. Due to its abundance in the solar spectrum, visible light needs to be harnessed for environmental applications. However, we lack visible light driven photocatalysts with long-lasting energy storage capacity for “round-the-clock photocatalytic” (RTCP) applications. For this reason, there is a growing need to find new photocatalysts that can mitigate these bottlenecks. It is evident from some carefully selected published articles (1976–2021) that tungsten oxide (WO3) and its composites have attracted popularity in recent years because of its outstanding properties and particularly its smaller band gap energy of 2.8 eV. However, pristine WO3 is limited due to relatively low energy density and smaller specific surface area. These drawbacks can be addressed by developing various WO3 – based materials to improve their performance. This paper reviews and discusses their recent development in surface advancement, morphology control, modification of nanostructured WO3 and its composites, and their RTCP energy storage for photocatalytic activities in visible light and the dark for environmental applications. Specific aspects focused on its nature, structure, properties, synthesis, coatings, deposition, approaches at modifying and enhancing its visible light photoactivity for enhanced performance and energy storage potential

Synthesis of tungsten oxide for solar energy conversion and water splitting applications

In this thesis, a range of visible-light-active WO3 electrodes are fabricated by the electrochemical anodization method and studied for its solar energy conversion ability, predominantly as a photoanode for photoelectrochemical (PEC) reactions. The work starts with the synthesis of relatively thick flower-like nanostructured WO3 films by anodizing tungsten foil in fluoride-containing electrolyte under non-stirring static condition. The as-anodized samples comprise of monoclinic hydrated tungstite (WO3 2H2O), while films that were subsequently calcined contain predominantly monoclinic WO3. It was found that the supersaturation condition established during the anodization process favors the formation of the flower-structured WO3 2H2O through an anodization/precipitation-recrystallization process. The flower-structured films also exhibit higher photoresponse as compared to the typical mesoporous structure formed under similar anodization condition with non-static condition. Following the synthesis of these flower-structured WO3 films, a self-photorechargeability phenomenon was discovered with these WO3 films demonstrating simultaneous generation and storage of photo-excited electrons during PEC reactions. By introducing alkali cations such as Na+ and K+ in the electrolyte, the WO3 photoelectrode possessed the ability of storing light energy in the form of trapped electrons. Subsequently, the influence of crystallinity of the flower-structured WO3 films directed towards the optimization of both PEC water splitting and self-photorechargeability performance is also conducted. The effect of crystallinity was found to be crucial in the self-photorecharge property of these films. The last part of the thesis focuses on the development of bismuth tungstate (Bi2WO6) by transforming anodized flower-structured WO3 2H2O films into orthorhombic Bi2WO6 by hydrothermal treatment for PEC water splitting under visible light irradiation. The H2O molecules in the layered anodized WO3 2H2O film are proposed to be substituted by the [Bi2O2]2+ layers during the hydrothermal treatment process. The importance of an initial layered structure is also highlighted by the absence of Bi2WO6 formation in non-layered WO3 films

An electrochromic paper-based device as a diagnostic test for Cystic Fibrosis

Cystic Fibrosis (CF) is an inherited disorder affecting more than 70000 people worldwide, especially Caucasian populations with a carrier prevalence of 1/3000. Currently, it has no cure but an early diagnosis remains a critical issue. Sweat chloride test has been the gold standard to diagnose CF since the affected present sweat chloride concentrations ≥ 60 mM. In this work, a planar electrochromic “point-of-care” device, based on tungsten trioxide nanoparticles produced by microwave assisted hydrothermal synthesis, was developed as a first approach for CF diagnostic testing especially in resource-limited environments. For electrodes patterning, a CO2 laser technology was used in a PET/ITO sheet. The device presents a design that allows the NaCl-based electrolyte deposition, used as artificial sweat, only on time of usage directly on the nanoparticles or in a paper pad. By applying an operating voltage of -3 V, the nanoparticles change their optical properties according to NaCl concentration, presenting a blue colouration with different intensities for different NaCl concentrations. The device was able to differentiate between a positive and negative diagnosis, with a colouration time of only 1 min, using an RGB analysis with a B/R ratio of 1.37±0.03 for 60 mM of NaCl, and a low power consumption

Lithium-Ion Battery and Beyond: Oxygen Vacancy Creation in Tungsten Trioxide and Surface Modification of Lithium Metal

The graphite-based anode material has a low theoretical specific capacity of 371 mAh g-1. The transitional metal oxides (TMOs) are considered a better choice owing to their relatively higher specific capacity. Among TMOs, tungsten trioxide (WO3) is considered promising due to a higher specific capacity of 693 mAh g-1, low cost, mechanically stable, and eco-friendly. It has been a challenge to utilize the TMOs as anode materials as they suffer from poor electronic conductivity and large electrode volume expansion during discharge/charge cycles. In our first project, we demonstrate a unique self-recovery of capacity in reduced WO3 by the incorporation of urea followed by annealing at 500 °C under the N2 environment. The reduced WO3 exhibited a unique cycling phenomenon, where the capacity was significantly self-recovered after an initial sharp decrease. This can be attributed to the activation of oxygen vacancy sites or defects, making the WO3 electrode more electrochemically active with cycling. In our second and third projects, we modify the surface of lithium metal to utilize them as anode because LIBs are approaching their theoretical energy density limit. Lithium metal anodes are expected to drive practical applications that require high energy-density storage. However, the direct use of metallic lithium causes safety concerns, low rate capabilities, and poor cycling performances due to unstable solid electrolyte interphase (SEI) and undesired lithium dendrite growth. To address these issues, in our second project, radio frequency (R-F) sputtered graphite-SiO2 ultrathin bilayer on a Li metal chips was demonstrated, for the first time, as an effective solid-electrolyte interface (SEI) layer. In the third project, we developed a facile, costeffective, and one-step approach to generate an artificial lithium metal/electrolyte interphase by treating lithium anode with an electrolyte containing tin fluoride. The development of artificial SEI on top of lithium metal anode led to a dendrite free uniform Li deposition to achieve a stable voltage profile and outstanding long hours plating/stripping compared to the bare Li. The generated SEI not only ensures fast lithiumion diffusion and suppression of lithium dendrite growth but also brings a synergistic effect of storing lithium via a reversible silicon-lithium or tin-lithium alloy formation and lithium plating