Growth mechanism and visible-light-driven photocatalysis of organic solvent dependent WO3 and nonstoichiometric WO3-x nanostructures

Evolving trends in the solvent strategies for preparing semiconducting nanomaterials for multifarious applications

Semiconducting nanomaterials have been widely explored for various applications due to their remarkable coordination between electronic and morphological attributes. The extent of their potential applications transcends from various environmental remediation applications like sensing and photocatalysis to several complex applications like energy storage/production and drug delivery processes. The properties of semiconducting nanomaterials can be effectively tuned by changing the solvent strategies. A solvent can effectively interfere in the nucleation process and hence can significantly influence the shape and size of nanomaterials, which is directly related to other important properties. In this review article, we have holistically discussed and categorized different solvents and encompassed their role in the preparation strategies of different semiconducting nanomaterials. We have tried to explain the evolution of solvent strategies based on the reported literature, that is the evolution from conventional solvents to more advanced and nascent solvent strategies like ionic liquids and deep eutectic solvents. After adequate comparison, we have concluded that the change or rather advancements in the solvent strategies have dramatically enhanced and transformed the properties and potential of several semiconducting nanomaterials in the domains such as photocatalysis, sensing, biomedical and electrochemical applications. We anticipate that this review article will encourage researchers across the globe to explore and develop novel solvent strategies and assess their effect on the properties of different classes of materials.

A review on WO3 photocatalysis used for wastewater treatment and pesticide degradation

The rapid growth in the global population has led to increased environmental pollution and energy demands, exacerbating the issue of environmental contamination. This contamination is significantly impacted by various types of pesticides found in water sources, which pose serious health risks to humans, animals, and aquatic ecosystems. In response, extensive research into water treatment technologies has been conducted, focusing on efficient methods to remove these pollutants, with advanced oxidation processes and the utilization of tungsten trioxide (WO3) as a photocatalyst showing promising results. This paper aims to review WO3-based photocatalytic processes for pesticide degradation, highlighting the potential of modified WO3 structures to improve photocatalytic efficiency and address current environmental challenges. Different WO3 synthesis routes and methods for modification have been discussed. The synthesis of WO3-based photocatalysts encompasses various methods that significantly affect their morphologies, sizes, structures, and thus catalytic performance, cost-effectiveness, and environmental sustainability. Techniques like hydrothermal, solvothermal, co-precipitation, sol-gel, and green synthesis and physical deposition techniques are elaborated, highlighting their unique advantages in producing nanostructures with desired physical and chemical properties. Moreover, enhancement methods aimed at optimizing the photocatalytic activity of WO3 under visible light for pollutant degradation have been discussed. Evaluation of WO3-based photocatalytic systems for pesticide treatment, emphasizing the effectiveness of various catalysts in degrading pesticides including organochlorines, organophosphorus, and chloropyridines have been conducted.

Heterogeneous Photocatalytic Degradation of Selected Pharmaceuticals and Personal Care Products (PPCPs) Using Tungsten Doped TiO2: Effect of the Tungsten Precursors and Solvents

Pharmaceuticals and personal care products (PPCPs) which include antibiotics such as tetracycline (TC) and ciprofloxacin (CIP), etc., have attracted increasing attention worldwide due to their potential threat to the aquatic environment and human health. In this work, a facile sol-gel method was developed to prepare tungsten-doped TiO2 with tunable W5+/W6+ ratio for the removal of PPCPs. The influence of solvents in the synthesis of the three different tungsten precursors doped TiO2 is also taken into account. WCl6, ammonium metatungstate (AMT), and Na2WO4●2H2O not only acted as the tungsten precursors but also controlled the tungsten ratio. The photocatalyst prepared by WCl6 as the tungsten precursor and ethanol as the solvent showed the highest photodegradation performance for ciprofloxacin (CIP) and tetracycline (TC), and the photodegradation performance for tetracycline (TC) was 2.3, 2.8, and 7.8 times that of AMT, Na2WO4●2H2O as the tungsten precursors and pristine TiO2, respectively. These results were attributed to the influence of the tungsten precursors and solvents on the W5+/W6+ ratio, sample crystallinity and surface properties. This study provides an effective method for the design of tungsten-doped TiO2 with tunable W5+/W6+ ratio, which has a profound impact on future studies in the field of photocatalytic degradation of PPCPs using an environmentally friendly approach.

Preparation and Application of Co-Doped Zinc Oxide: A Review

Due to a wide band gap and large exciton binding energy, zinc oxide (ZnO) is currently receiving much attention in various areas, and can be prepared in various forms including nanorods, nanowires, nanoflowers, and so on. The reliability of ZnO produced by a single dopant is unstable, which in turn promotes the development of co-doping techniques. Co-doping is a very promising technique to effectively modulate the optical, electrical, magnetic, and photocatalytic properties of ZnO, as well as the ability to form various structures. In this paper, the important advances in co-doped ZnO nanomaterials are summarized, as well as the preparation of co-doped ZnO nanomaterials by using different methods, including hydrothermal, solvothermal, sol-gel, and acoustic chemistry. In addition, the wide range of applications of co-doped ZnO nanomaterials in photocatalysis, solar cells, gas sensors, and biomedicine are discussed. Finally, the challenges and future prospects in the field of co-doped ZnO nanomaterials are also elucidated.

Synthesis of Pr3+-doped WO3 particles: correlation between photoluminescent and photocatalytic properties

The WO3 and WO3:Pr3+ particles were successfully synthesized by the co-precipitation method. The XRD analysis with Rietveld refinement revealed the formation of a monoclinic phase for WO3 and for doped samples, this result was later confirmed by Raman spectroscopy studies. The presence of Pr3+ in the WO3 crystalline lattice induced structural and optical changes in the particles, increasing the crystallite size, distorting the clusters (shortening of the W-O bonds), favoring the crystallinity and changing the optical gap. The predominant morphology of the particles of WO3 and WO3:Pr3+ obtained was nanocubes constituted by the superposition of plates of nanometric thicknesses. The photoluminescence of WO3 and WO3:Pr3+ was produced by the existence of surface defects in the particles. The increase in the concentration of Pr3+ promoted an increase in the intensity of PL, due to the increase in the rate of recombination of electron/hole charges. The WO3 sample exhibited emission in the white region due to the adjustment of simultaneous electronic transitions in the blue, green and red regions, characteristic of the broadband spectrum. The interval of the 2.65 eV gap band and the high efficiency in the separation of the photogenerated charges (e-/h+) with the low recombination rate contributed to the photocatalytic degradation of Crystal Violet (CV) by the catalyst. The WO3:4% Pr3+ sample showed the best photocatalytic efficiency, degrading 73% of the CV dye in 80 minutes. This result was associated with a reduction in particle size and density of oxygen vacancies on the material surface.

Hydrothermal construction of WO3.0.33H2O/g-C3N4 nanocomposites with enhanced adsorption and photocatalytic activity

Tungsten trioxide has attracted extensive attention for photocatalytic applications owing to its unique structure and intrinsic merits; however, small specific surface area and rapid electron-hole recombination still limit its adsorption...

Unique Cd0.5Zn0.5S/WO3-x direct Z-scheme heterojunction with S, O vacancies and twinning superlattices for efficient photocatalytic water-splitting

Photocatalytic water-splitting employing the Z-scheme semiconductor systems mimicking natural photosynthesis is regarded as a promising way to achieve efficient soalr-to-H₂ conversion. Nevertheless, it still remains a big challenge to design high-performance direct Z-scheme photocatalysts without the use of noble metals as electron mediators. Herein, a unique Cd_0.5Zn_0.5S/WO_3-x direct Z-scheme heterojunction was constructed for the first time, which consisted of smaller O-vacancy-decorated WO_3-x nanocrystals anchoring on Cd_0.5Zn_0.5S nanocrystals with S vacancies and zinc blende/wurtzite (ZB/WZ) twinning superlattices. Under visible-light (λ > 420 nm) irradiation, the Cd_0.5Zn_0.5S/WO_3-x composites exhibited an outstanding H₂ evolution reaction (HER) activity of 20.50 mmol h^-1 g^-1 (corresponding to the apparent quantum efficiency of 18.0% at 420 nm), which is much superior to that of WO_3-x, Cd_0.5Zn_0.5S, and Cd_0.5Zn_0.5S loaded with Pt. Interestingly, the introduced O and S vacancies contributed to improving the HER activity of Cd_0.5Zn_0.5S/WO_3-x significantly. Moreover, the cycling and long-term HER measurements confirmed the robust photocatalytic stability of Cd_0.5Zn_0.5S/WO_3-x for H₂ production. The excellent light harvesting and efficient spatial charge separation induced by the ZB/WZ twinning homojunctions and defect-promoted direct Z-scheme charge-transfer pathway are responsible for the exceptional HER capability. Our study could enlighten the rational engineering and optimization of semiconductor nanostructures for energy and environmental applications.

Z-scheme heterojunction based on NiWO4/WO3 microspheres with enhanced photocatalytic performance under visible light

The green treatment of dye wastewater has always been a research hotspot in the environmental field. The photocatalytic technology is considered to be a simple and effective strategy to remove dyes in wastewater. A new type of NiWO₄/WO₃ Z-scheme heterojunction microspheres were synthesized by a simple hydrothermal method and impregnation-calcination process. The crystal structure, microscopic morphology, optical and electrochemical properties of the samples were systematically characterized. The photocatalytic activity of methylene blue (MB) was studied by visible light irradiation. The results show that the direct Z-scheme heterojunction formed by NiWO₄/WO₃ effectively reduces the transfer resistance of photogenerated carriers and improves the separation efficiency of photogenerated carriers. The degradation rates of NiWO₄/WO₃-4 Z-scheme heterojunction microspheres to MB dye are 1.8 and 3.2 times higher than that of pure WO₃·2H₂O and WO₃ microspheres, respectively. Combined with the Mott-Schottky curve and the active species capture experiments, a possible Z-scheme photogenerated carrier transfer mechanism is proposed. This study provides a method for the development and design of Z-scheme heterojunction photocatalysts in the field of wastewater purification.