Remediation of recalcitrant pollutants in water solution using visible light responsive cerium-doped tungsten trioxide nanoparticles

In order to attain a solar energy-driven photocatalyst for wastewater remediation, cerium-doped WO₃ (W_1-xCe_xO₃ with x = 0, 0.02, 0.04, 0.06, and 0.08) nanoparticles have been synthesized via a chemical co-precipitation technique. X-ray diffraction (XRD) analysis confirmed that W_1-xCe_xO₃ nanoparticles retained their monoclinic structure even after doping. The presence of the vast number of defects produced in the WO₃ lattice was corroborated by Raman spectroscopy. Scanning electron microscopy confirmed the spherical shape of the nanoparticles with particle size range 50-76 nm. The optical band gap of W_1-xCe_xO₃ nanoparticles decreases from 3.07 to 2.36 eV with an increase in x, as confirmed by UV-Vis spectroscopy. Photoluminescence (PL) spectroscopy confirmed that the minimum rate of recombination was observed for W_1-xCe_xO₃ with x = 0.04. Degradation efficiency was explored for methyl violet (MV) and rhodamine-B (Rh-B) with 0.01 g of photocatalyst in a photoreactor chamber having a 200-W xenon lamp as a visible source of light. The results showed that the maximum photo-decolorization towards MV (94%) and rhodamine-B (79.4%) was observed in x = 0.04 sample in just 90 min because of its least recombination rate, highest adsorption capacity, and optimum band edge positions. Intriguingly, it has been observed that the modification with cerium in WO₃ nanoparticles enhances the photocatalytic activity by narrowing the band gap and by efficaciously lowering the recombination rate due to electron entrapment by defects produced in the lattice.

Properties, optimized morphologies, and advanced strategies for photocatalytic applications of WO3 based photocatalysts

The development of WO₃ based photocatalysts has gained considerable attention across the world, especially in the realm of environmental remediation and energy production. WO₃ has a band gap of 2.5- 2.7 eV that falls under the visible region and is thus a potential candidate to utilize in various photocatalytic processes. As an earth-abundant metal oxide, WO₃ discovered in 1976 displayed excellent electronic and morphological properties, good stability, and enhanced photoactivity with diverse crystal phases. Also, it unveils non-toxicity, high stability in drastic conditions, biocompatibility, low cost, excellent hole mobility (10 cm² V^-1s^-1), and tunable band gap. This review provides a comprehensive overview of the different properties of WO₃ inclusive of crystallographic, electrical, optical, thermoelectrical, and ferroelectric properties. The different morphologies of WO₃ based on dimensions were obtained by adopting different fabrication methods including inspecting their effects on the efficiency of WO₃. Numerous strategies to construct an ideal photocatalyst such as engineering crystal facets, surface defects, doping, heterojunction formation explaining specifically type-II, Z-scheme, and S-scheme mechanisms with addition to carbonaceous based WO₃ nanocomposites are summed up to explore the photocatalytic performance. The typical application of WO₃ is deliberated in detail involving the role and efficiency of WO₃ in pollutant degradation, CO₂ photoreduction, and water splitting. Besides, other applications of WO₃ as gas-sensor, bio-sensor, decomposition of VOCs, heavy metals ions adsorption, and antimicrobial property are also included. Moreover, the numerous aspects responsible for the high efficiency of WO₃-based nanocomposites with their challenges, opportunities, and future aspects are summarized. Hopefully, this review may inspire researchers to explore new ideas to boost the production of clean energy for the next generation.

Rare earth doped metal oxide nanoparticles for photocatalysis: a perspective

Metal oxides are well-known materials that have been considered as the prominent photocatalysts. Photocatalysis is a promising way to address the environmental issues which are caused by fossil fuel the combustion and industrial pollutants. Lot of efforts such as doping of metal oxides with metals, non-metals have been made to enhance their photocatalytic activity. More specifically, in this review we have discussed detailed synthesis procedures of rare earth doped metal oxides performed in the past decades. The advantage of doping metal oxides with rare earth metals is that they readily combine with functional groups due to the 4f vacant orbitals. Moreover, doping rare earth metals causes absorbance shift to the visible region of the electromagnetic spectrum which results to show prominent photocatalysis in this region. The effect of rare earth doping on different parameters of metal oxides such as band gap and charge carrier recombination rate has been made in great details. In perspective section, we have given a brief description about how researchers can improve the photocatalytic efficiencies of different metal oxides in coming future. The strategies and outcomes outlined in this review are expected to stimulate the search for a whole new set of rare earth doped metal oxides for efficient photocatalytic applications.

Rapid and Low-Temperature Molecular Precursor Approach toward Ternary Layered Metal Chalcogenides and Oxides: Mo1-x W x S2 and Mo1-x W x O3 Alloys (0 ≤ x ≤ 1)

Metal sulfide and metal oxide alloys of the form Mo_1-x W _x S₂ and Mo_1-x W _x O₃ (0 ≤ x ≤ 1) are synthesized with varying nominal stoichiometries (x = 0, 0.25, 0.50, 0.75, and 1.0) by thermolysis of the molecular precursors MoL₄ and WS(S₂)L₂ (where L = S₂CNEt₂) in tandem and in various ratios. Either transition-metal dichalcogenides or transition-metal oxides can be produced from the same pair of precursors by the choice of reaction conditions; metal sulfide alloys of the form Mo_1-x W _x S₂ are produced in an argon atmosphere, while the corresponding metal oxide alloys Mo_1-x W _x O₃ are produced in air, both under atmospheric pressure at 450 °C and for only 1 h. Changes in Raman spectra and in powder X-ray diffraction patterns are observed across the series of alloys, which confirm that alloying is successful in the bulk materials. For the oxide materials, we show that the relatively complicated diffraction patterns are a result of differences in the tilt angle of MO₆ octahedra within three closely related unit cell types. Alloying of Mo and W in the products is characterized at the microscale and nanoscale by scanning electron microscopy-energy-dispersive X-ray spectroscopy (EDX) and scanning transmission electron microscopy-EDX spectroscopy, respectively.

Tungsten oxide-based visible light-driven photocatalysts: crystal and electronic structures and strategies for photocatalytic efficiency enhancement

Photocatalysis (PC) technology has received global attention due to its high potential of addressing both environmental and energy issues using only solar light as energy input.

Triplet-Triplet Annihilation Upconversion in Broadly Absorbing Layered Film Systems for Sub-Bandgap Photocatalysis

Upconversion (UC) of sub-bandgap photons extends the effective light absorption range of photovoltaic and photocatalytic devices, allowing them to reach higher conversion efficiencies. Recent advances in polymer host materials make it possible to translate triplet-triplet annihilation (TTA)-UC, the UC mechanism most suitable for this purpose, to solid films that can be integrated into devices. The promise of these films is currently limited by the narrow light absorption of TTA-UC sensitizer chromophores, but incorporating multiple sensitizers into layered film systems presents a promising strategy for producing UC materials with broadened light absorption. This strategy is herein applied for photocatalytic air purification, demonstrating its use in a real-world application for the first time. We superimpose optimized red-to-blue and green-to-blue UC films within dual-layer systems and develop a new photocatalyst compatible with their fluorescence emission. By integrating the dual-layer UC film systems with films of this photocatalyst, we produce the first devices that use TTA-UC to harness both red and green sub-bandgap photons for hydroxyl radical generation and photocatalytic degradation of gaseous acetaldehyde, a model volatile organic compound (VOC). Under white light-emitting diode excitation, the dual-layer film systems' broadened light absorption enhances their devices' photocatalytic degradation efficiency, enabling them to degrade twice as much acetaldehyde as their single-sensitizer counterparts. We show that as a result of the different absorption profiles of the two sensitizers, the film order significantly impacts UC fluorescence and VOC degradation. By probing the influence of the excitation light source, excitation geometry, and chromophore spectral overlap on the film systems' UC performance, we propose a framework for the design of multilayer TTA-UC film systems suitable for integration with a variety of photovoltaic and photocatalytic devices.

Niobium doped tungsten oxide mesoporous film with enhanced electrochromic and electrochemical energy storage properties

Exploring high performance cathode materials is of great means for the development of bi-functional electrochromic energy storage devices. Herein, Nb-doped WO₃ mesoporous films as integrated high-quality cathode are successfully constructed via a facile sol-gel method. Chemical state and crystallinity of the WO₃ based films are significantly influenced by doping concentration. Compared with the pure WO₃, the optimal Nb-doped film shows improved optical-electrochemical properties with high specific capacity (74.4 mAh g^-1 at 2 A g^-1), excellent high-rate capability, large optical contrast (61.7% at 633 nm), and ultra-fast switching speed (3.6 s and 2.1 s for coloring and bleaching process, respectively). These positive features suggest the potential application of Nb-doped WO₃ mesoporous cathode. Our research paves the way for the development of multifunctional photoelectrochemical energy devices.

The effect of cerium alteration on the photocatalytic performance of WO3 in sunlight exposure for water decontamination

In an effort to enhance the photocatalytic activity of cubic WO₃ in sunlight exposure, its surface was modified by impregnating the Ce³⁺ ions ranging from 1% to 25% with a step of 5% with respect to the weight of WO₃.

Co2+ and Ho3+ doped CuS nanocrystals with improved photocatalytic activity under visible light irradiation

Co²⁺ and Ho³⁺ doped CuS nanostructures have been synthesized by a hydrothermal method. The nature of dopants influence the morphology, photocatalytic performance and the band gap values.

Surface modification of InVO4 nanoparticles on WO3 plate array films for improved photoelectrochemical performance

Surface modification of InVO₄ nanoparticles on WO₃ plates array films using a dipping–annealing method.

Bi-functional Mo-doped WO3 nanowire array electrochromism-plus electrochemical energy storage

Metal-doping is considered to be an effective way for construction of advanced semiconducting metal oxides with tailored physicochemical properties. Herein, Mo-doped WO3 nanowire arrays are rationally fabricated by a sulfate-assisted hydrothermal method. Compared to the pure WO3, the optimized Mo-doped WO3 nanowire arrays exhibit improved electrochromic properties with fast switching speed (3.2s and 2.6s for coloration and bleaching, respectively), significant optical modulation (56.7% at 750nm, 83.0% at 1600nm and 48.5% at 10μm), high coloration efficiency (123.5cm(2)C(-1)) and excellent cycling stability. In addition, as a proof of concept, the Mo-doped WO3 nanowire arrays are demonstrated with electrochemical energy storage monitored by the electrochromism. This electrode design protocol can provide an alternative way for developing high-performance active materials for bi-functional electrochromic batteries.

In situ synthesis of g-C3N4/WO3 heterojunction plates array films with enhanced photoelectrochemical performance

g-C₃N₄/WO₃ heterojunction plate array films with enhanced photoelectrochemical (PEC) performance were successfully synthesized through a combination of hydrothermal and dipping-annealing methods.

Synthesis of Mo-doped WO3 nanosheets with enhanced visible-light-driven photocatalytic properties

Ion doping provides a powerful means for the fabrication of a functionalized photocatalyst that is both active and stable.

ZnO nanoparticle-functionalized WO3 plates with enhanced photoelectrochemical properties

ZnO nanoparticle-functionalized WO₃ plates were prepared via an electrodeposition and an electrochromism reaction of WO₃, and the composites improve the separation of photogenerated electrons and holes.

Self-assembled macro porous ZnS–graphene aerogels for photocatalytic degradation of contaminants in water

This work demonstrates the facile green synthesis of ZnS–graphene aerogels with superior photocatalytic performance.