Highly efficient photocatalyst fabricated from the recycling of heavy metal ions in wastewater for dye degradation

Water pollution and energy crisis are becoming global and strategic issues that people are closely concerned about. Green and energy-saving photocatalytic technology is developing rapidly in solving global energy crises and environmental pollution problems. Therefore, we propose the "kill two birds with one stone" strategy to design efficient photocatalysts for dye wastewater treatment by utilizing heavy metal ions in wastewater. The adsorption properties of Mordenite (MOR) were utilized to removal heavy metal ions (Cd2+ and Zn2+) from waste water, and the adsorbed heavy metal ions were dried and sulfurized to obtain CdS/ZnS/MOR(ZnCdM). Then, g-C3N4 was ultrasonically dispersed and composited with ZnCdM by self-assembly, 25 wt% ZnCdCM photocatalytic material was obtained with a degradation rate of 99.8% in 1.5 h for Rhodamine B(RhB). It was found that MOR can provid adequate support for active substances, and the surface of MOR with smaller sizes of CdS nanoparticles, ZnS nanoparticles and g-C3N4 nanosheets, which increased the specific surface area of the materials and improved the reactivity. The porous structure of MOR is favorable for the enrichment of RhB, and the electric field effect of MOR leads to the decrease of the photogenerated carrier complex rate in the semiconductor, which increases the catalytic efficiency. In addition, the double Z charge transfer mechanism formed by CdS, ZnS, g-C3N4 is favorable for separating photogenerated carriers. These synergistic effects improved the photocatalytic efficiency. This strategy will be a green and promising solution to water pollution and energy crisis.

CAZ Composite Photocatalysts for H2 Production and Degradation under Visible Light

g-C3N4/Ag-ZnO (CAZ) composite photocatalysts were synthesized successfully by the hydrothermal method. The photocatalytic performance of photocatalysts was assessed through experiments measuring both hydrogen (H2) production and the degradation of methylene blue (MB). The H2 production rate of 60% CAZ reached 2.450 mmol·g-1·h-1, which was 8.5 times that of g-C3N4. 25% CAZ degraded 99.14% of MB dye within 40 min, and its degradation rate constant was 12.4 times that of g-C3N4. CAZ composite photocatalysts have good synergistic properties in degradation and hydrogen production and exhibit better photocatalytic performance. A Z-scheme photocatalytic system mechanism of CAZ has been proposed for the enhanced H2 production and photocatalytic degradation rate.

Integrating Co(OH)2 nanosheet arrays on graphene for efficient noble-metal-free EY-sensitized photocatalytic H2 evolution

The development of an efficient noble-metal-free cocatalyst is the key to photocatalytic hydrogen production technology. In this study, hierarchical Co(OH)2 nanosheet array-graphene (GR) composite cocatalysts are developed. With Eosin Y (EY) as a photosensitizer, the optimal Co(OH)2-10%GR hybrid cocatalyst presents excellent photocatalytic activity with an H2 production rate of 17 539 μmol g-1 h-1, and the apparent quantum yield for hydrogen production can reach 12.8% at 520 nm, which remarkably surpasses that of pure Co(OH)2 and most similar hybrid cocatalyst systems. Experimental investigations demonstrate that the excellent photocatalytic activity of Co(OH)2-GR arises from its unique nanosheet array architecture, which can collaboratively expose rich active sites for photocatalytic hydrogen evolution and facilitate the migration and separation of photogenerated charge carriers. It is desired that this study would supply a meaningful direction for the rational optimization of the constitute and structure of cocatalysts to achieve efficient photocatalytic hydrogen generation.

More Accurate Method for Evaluating the Activity of Photocatalytic Hydrogen Evolution and Its Reaction Kinetics Equation

Photocatalytic water splitting to hydrogen is a sustainable energy conversion method. However, there is a lack of sufficiently accurate measurement methods for an apparent quantum yield (AQY) and a relative hydrogen production rate (r_H2) at the moment. Thus, a more scientific and reliable evaluation method is highly required to allow the quantitative comparison of photocatalytic activity. Herein, a simplified kinetic model of photocatalytic hydrogen evolution was established, the corresponding photocatalytic kinetic equation was deduced, and a more accurate calculation method is proposed for the AQY and the maximum hydrogen production rate v_H2,max. At the same time, new physical quantities, absorption coefficient k_L and specific activity SA, were proposed to sensitively characterize the catalytic activity. The scientificity and practicality of the proposed model and the physical quantities were systematically verified from the theoretical and experimental levels.

Integrated p-n/Schottky junctions for efficient photocatalytic hydrogen evolution upon Cu@TiO2-Cu2O ternary hybrids with steering charge transfer

Solar-driven photocatalytic H₂ evolution could tackle the issue of fossil fuels-triggered greenhouse gas emission with sustainable clean energy. However, splitting water into hydrogen with high performance by a single semiconductor is challenging because of the poor charge separation efficiency. Herein, a novel ternary Cu@TiO₂-Cu₂O hybrid photocatalyst with multiple charge transfer channels has been designed for efficient solar-to-hydrogen evolution. Indeed, the ternary Cu@TiO₂-Cu₂O hybrid by coupling Cu@TiO₂ with Cu₂O nanoparticles shows highly-efficient photocatalytic hydrogen generation with rate of 12000.6 μmol·g^-1·h^-1, which is 4.4, 2.1, and 1.9 times higher than the pure TiO₂ (2728.8 μmol·g^-1·h^-1), binary Cu@TiO₂ (5595.5 μmol·g^-1·h^-1), and TiO₂-Cu₂O (6076.8 μmol·g^-1·h^-1) composite, respectively. In such a Cu@TiO₂-Cu₂O hybrid, the formed internal electric field in the TiO₂-Cu₂O p-n junction allows the electrons in Cu₂O to migrate to TiO₂, while the electrons in the CB of TiO₂ could flow into Cu via the Schottky junction at the Cu@TiO₂ interface. In this regard, a multiple charge transfer is achieved between the Cu@TiO₂ and Cu₂O, which facilitates promoted charge separation and results in the construction of electron-accumulated center (Cu) and hole-enriched surface (Cu₂O). This p-n/Schottky junctions with steered charge transfer assists the hydrogen production upon the Cu@TiO₂-Cu₂O ternary photocatalyst.

In situ growth of hierarchical phase junction CdS on a H-mordenite zeolite for enhanced photocatalytic properties

A kind of cadmium sulfide (CdS) nanocomposite with different crystalline phases was grown on the surface of H-mordenite zeolite (HMOR) by a chemical liquid-phase co-precipitation method. In this work, 2 wt% CdS@HMOR photocatalytic material with the coexistence phase (hexagonal phase and cubic phase) of cadmium sulfide was grown on the surface of HMOR by controlling the reaction temperature and ammonia concentration. Photocatalytic degradation of methylene blue (MB) was used as an index to detect the photocatalytic performance of materials. The results indicated that the photocatalytic degradation efficiency of the system with HMOR was significantly improved in comparison to that without HMOR (CdS, 40.34%, 0.2578 h^-1). It was found that 2 wt% CdS@HMOR had the best photocatalytic activity. The degradation rate of MB was 84.15% in 2 h, and the degradation rate constant was 0.8884 h^-1. When 1.5 ml H₂O₂ was introduced into the system, the degradation rate of MB was increased to 98.98%, and the degradation rate constant was 1.9976 h^-1. SEM, HRTEM, PL, EIS and photocurrent showed that the cubic and hexagonal phases of CdS were in contact with each other on the HMOR surface, forming a good electron transport. By XRD, XPS and SEM tests, the results of materials after four cycles of reactions showed that the structure of the 2 wt% CdS@HMOR was still stable. Therefore, HMOR may provide a good support for CdS, and the synergistic effect between them is beneficial for the occurrence of photocatalytic reactions. HMOR can act as an electron receptor to inhibit the recombination of carriers. The homo-junction between different phases of CdS on the surface of HMOR is beneficial to the separation of photo-induced carriers. These results indicate that the construction of phase heterojunctions on zeolites and the synergism among them are a method for improving the photocatalytic activity.

Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Core-Shell Nanowires

We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C₃N₅ is a low-band-gap (E_g = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C₃N₅ nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C₃N₅ heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm² V^-1 s^-1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm² V^-1 s^-1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J-V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C₃N₅ in CdS-MHP. C₃N₅, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core-shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.

Recent advances in Co-based co-catalysts for efficient photocatalytic hydrogen generation

Recent progress in photocatalytic hydrogen generation reaction highlights the critical role of co-catalysts in enhancing the solar-to-fuel conversion efficiency of diverse band-matched semiconductors. Because of the compositional flexibility, adjustable microstructure, tunable crystal phase and facet, cobalt-based co-catalysts have stimulated tremendous attention as they have high potential to promote hydrogen evolution reaction. However, a comprehensive review that specifically focuses on these promising materials has not been reported so far. Therefore, this present review emphasizes the recent progress in the pursuing of highly efficient Co-based co-catalysts for water splitting, and the advances in such materials are summarized through the analysis of structure-activity relationships. The fundamental principles of photocatalytic hydrogen production are profoundly outlined, followed by an elaborate discussion on the crucial parameters influencingthe reaction kinetics. Then, the co-catalytic reactivities of various Co-based materials involving Co, Co oxides, Co hydroxides, Co sulfides, Co phosphides and Co molecular complexes, etc, are thoroughly discussed when they are coupled with host semiconductors, with an insight towards the ultimateobjective of achieving a rationally designed photocatalyst for enhancing water splitting reaction dynamics. Finally, the current challenge and future perspective of Co-based co-catalysts as the promising noble-metal alternative materials for solar hydrogen generation are proposed and discussed.

A "concentration-induced self-assembly" strategy for Ag x H3-x PMo12O40 nanorods: synthesis, photoelectric properties and photocatalytic applications

Polyoxometalates (POMs) as molecule-based metal oxides have exhibited significant application in catalysis and materials science, but the synthesis of pristine POM nanomaterials still remains a challenge. In this work, we find a novel strategy of concentration-induced self-assembly for gaining pristine POM nanorods Ag _x H_3-x PMo₁₂O₄₀ (denoted as AgHPMo₁₂), which are synthesized only from both POMs and silver ion Ag⁺ in an aqueous solution at room temperature. The controllable concentrations of the cationic and anionic components in the aqueous solution become the critical factor for the successful synthesis. In addition, the photoelectric properties of AgHPMo₁₂ nanorods were investigated as compared to those of AgHPMo₁₂ particles, indicating a superior photoelectric performance of AgHPMo₁₂ nanorods to AgHPMo₁₂ particles. Furthermore, AgHPMo₁₂ nanorods/phthalocyanine heterojunction photocatalysts were prepared for evaluating photocatalytic degradation of tetracycline hydrochloride, showing an efficient photocatalytic performance due to the advantages of the nanorods and type II heterostructure.

Co3O4@CdS Hollow Spheres Derived from ZIF-67 with a High Phenol and Dye Photodegradation Activity

The Co₃O₄@CdS double-layered hollow spheres were first prepared by the template-removal method with the assistance of the ZIF-67 material; the structure has been proved by transmission electron microscopy (TEM). The Co₃O₄@CdS hollow spheres calcinated at 400 °C exhibited the highest photodegradation activity. Nearly 90% phenol was degraded after 2 h of visible-light irradiation. More than 80% rhodamine-B (RhB) was degraded within the first 30 min and nearly eliminated after 1 h of irradiation. The mechanism of the photodegradation reaction was investigated. Based on the analysis of electron spin resonance (ESR) spectra and radical trapping test, it was found that superoxide radicals are the major oxidative species for dye degradation and holes and hydroxyl radicals are the major oxidative species for phenol degradation. These results may be used in industrial wastewater treatment. The reaction obeys first-order reaction kinetics, and the rate constant of the Co₃O₄@CdS hollow sphere in dye degradation is 0.05 min^-1 and that in phenol degradation is 0.02 min^-1, which is three times higher than that of CdS nanoparticles. These results indicated the high oxidizing ability of the samples.

Efficient and Stable Photocatalytic Hydrogen Evolution Activity of Multi-Heterojunction Composite Photocatalysts: CdS and NiS2 Co-modified NaNbO3 Nanocubes

In this study, a NaNbO₃/CdS/NiS₂ ternary composite photocatalyst containing no precious metals was successfully prepared by a simple hydrothermal method. The prepared ternary photocatalyst has a significant improvement in photocatalytic performance of hydrogen production from water splitting under visible light irradiation. The best sample NCN40% hydrogen production rate is 4.698 mmol g⁻¹ h⁻¹, which is about 24.7 times that of pure CdS sample. In addition, the stability of the composite catalyst in the long-term photocatalytic hydrogen production cycle is also improved. The reason for the enhanced hydrogen production performance may be the optimization of the microstructure of the catalyst and the reduction of photogenerated electron-hole recombination. The construction of multi-heterojunctions (NaNbO₃-CdS, CdS–NiS₂, and NaNbO₃-NiS₂) helps to reduce the recombination of carriers. Furthermore, the in-situ-formed NiS₂ nanoparticles can serve as active sites for hydrogen evolution. All of these factors induced the improved photocatalytic activity of the as-prepared ternary photocatalyst.

The influence of the sacrificial agent nature on transformations of the Zn(OH)2/Cd0.3Zn0.7S photocatalyst during hydrogen production under visible light

Photocatalysts based on zinc hydroxide and a solid solution of CdS and ZnS were prepared via the precipitation method and used for photocatalytic hydrogen production from aqueous solutions of inorganic (Na₂S/Na₂SO₃) and organic (ethanol) sacrificial agents. The photocatalysts were tested in cyclic experiments for hydrogen evolution and studied using X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) techniques. Different transformations of the β-Zn(OH)₂ co-catalyst were observed in the presence of inorganic and organic sacrificial agents; namely, ZnS was formed in Na₂S/Na₂SO₃ solution, whereas the formation of ε-Zn(OH)₂ was detected in solution with ethanol. The composite Zn(OH)₂/Cd_1−xZn_xS photocatalysts have great potential in various photocatalysis processes (e.g., hydrogen production, CO₂ reduction, and the oxidation of organic contaminants) under visible light.

The nature of the sacrificial agent affects the transformations of a Zn(OH)₂ co-catalyst during photocatalytic hydrogen production.

Development of core–shell structured Mo2C@BN as novel microwave catalysts for highly effective direct decomposition of H2S into H2 and S at low temperature

Direct decomposition of hydrogen sulfide is an attractive approach for producing CO_x-free H₂ and S from a toxic and abundant waste gas.

PtNixCoy concave nanocubes: synthesis and application in photocatalytic hydrogen generation

PtNi_xCo_y alloy concave nanocubes coupled with CdS nanorods were applied in the H₂ evolution reaction under visible light irradiation.

Highly efficient and stable photocatalytic properties of CdS/FeS nanocomposites

CdS/FeS nanocomposites were successfully synthesized via a liquid-phase thermal decomposition of a single precursor and an ion adsorption method.

Confining Mo-activated CoSx active sites within MCM-41 for highly efficient dye-sensitized photocatalytic H2 evolution

Although transition-metal-based sulfides have been identified as efficient catalysts to replace expensive noble metal catalysts for photocatalytic H₂ evolution reaction (HER), their activities are still unsatisfied and could be further improved by controlling their microstructures and electronic structures. Herein, we present an effective strategy to confine highly active Mo-activated CoS_x (Mo-CoS_x) active sites within MCM-41 frameworks by sulfurization of Co-doped MCM-41 during the in situ photoreduction of [MoS₄]^2- in Erythrosin B-triethanolamine (ErB-TEOA) system. It is found that Co-MCM-41 offers not only abundant coordinatively unsaturated Co sites to be activated by Mo and S but also large surface area to effectively disperse the in situ generated amorphous Mo-CoS_x active sites. Under 520 nm irradiation, the most efficient Mo-CoS_x/MCM-41-100 (Si/Co = 100) catalyst exhibits ~7, 3, and 4 times higher H₂ evolution activity than free MoS_x, free Mo-CoS_x, and CoS_x/MCM-41-100, respectively, and an apparent quantum yield (AQY) of 12.3% for H₂ evolution. Furthermore, when Mo-CoS_x/MCM-41-100 was sensitized with a more stable fluorescein (FL) dye, the photocatalytic system shows a sustainable H₂ evolution activity in a 20 h reaction, showing the good stability of Mo-CoS_x/MCM-41-100 catalyst. This work provides a new insight into the design and development of highly active hybrid H₂ evolution catalysts based on transition metals for highly efficient and large-scale solar energy conversion to clean H₂ energy.

Truncated octahedral bipyramidal TiO2/MXene Ti3C2 hybrids with enhanced photocatalytic H2 production activity

MXene Ti₃C₂/TiO₂ hybrids were successfully synthesized through a simple calcination of F-terminated Ti₃C₂. The resultant Ti₃C₂/TiO₂ composite photocatalysts retained a 2D multilayer structure like MXene Ti₃C₂, and TiO₂ exhibited a truncated octahedral bipyramidal structure with exposed (001) facets under the participation of fluorine ions. The residual Ti₃C₂ could act as a co-catalyst to enhance the photocatalytic H₂ production activity by capturing photogenerated electrons from TiO₂ because of its electron reservoir feature and suitable Fermi level. The (101)-(001) surface heterojunction of the truncated octahedral bipyramidal TiO₂ further accelerated the separation of photogenerated carriers. As a result, the Ti₃C₂/TiO₂ hybrids with calcining F-terminated Ti₃C₂ exhibited photocatalytic hydrogen production that is twofold higher than that of Ti₃C₂/TiO₂ hybrids with calcining OH-terminated Ti₃C₂. This work presented a new strategy to prepare MXene Ti₃C₂/TiO₂ hybrids for photoconversion applications.

In situ photodeposition of amorphous NixP on CdS nanorods for efficient visible-light photocatalytic H2 generation

Noble metal-free amorphous Ni_xP modified CdS with superior photocatalytic H₂ evolution activity has been successfully fabricated.

One-step facile synthesis and high H2-evolution activity of suspensible CdxZn1-xS nanocrystal photocatalysts in a S2-/SO32- system

For a CdS-based photocatalyst, both the photocorrosion resistance and the rapid H₂-production reaction are highly required for improving its photocatalytic H₂-production performance. In this study, a facile strategy was reported to simultaneously realize an improved photocorrosion resistance and rapid interfacial H₂-evolution reaction of Cd_xZn_1-xS solid-solution photocatalysts in a sulfur-rich S^2-/SO₃^2- solution. Here, the suspensible Cd_xZn_1-xS nanocrystal photocatalysts are prepared by a one-step co-precipitation route through the direct introduction of Zn²⁺/Cd²⁺ mixing ions in a sulfur-rich Na₂S-Na₂SO₃ solution, and the resultant Cd_xZn_1-xS nanocrystals (ca. 5 nm) display a suspensible structure owing to the numerous and selective adsorption of S^2-/SO₃^2- on the surface of these Cd_xZn_1-xS nanocrystals. It is found that the bandgap structure of Cd_xZn_1-xS (from 2.25 to 3.52 eV) nanocrystals can be easily controlled by adjusting the Cd²⁺/Zn²⁺ molar ratio. The photocatalytic experimental results suggested that the suspensible Cd_xZn_1-xS nanocrystal photocatalysts clearly displayed an excellent photocatalytic H₂-production performance, and the suspensible Cd_0.6Zn_0.4S nanocrystals exhibit the highest photocatalytic H₂-generation performance of 717.19 μmol h^-1, a value higher than that of the sole CdS (320.99 μmol h^-1) and ZnS (5.89 μmol h^-1) by a factor of 2.2 and 121.8 times, respectively. Based on the experimental results, a possible S^2- active site-mediated mechanism accounted for the high H₂-production activity of the suspensible Cd_xZn_1-xS nanocrystals, namely the numerous adsorbed S^2- ions not only function as efficient hole scavengers to rapidly consume the photogenerated holes, resulting in an improved photocorrosion resistance of suspensible Cd_xZn_1-xS nanocrystals, but also serve as effective H⁺-capturing active sites to accelerate the interfacial H₂-production reaction. Meanwhile, an optimum bandgap structure of suspensible Cd_xZn_1-xS nanocrystals is also extremely required for promoting the photocatalytic H₂-production activity. This research may provide advanced insights for developing stable and high-activity photocatalytic materials.

Chemical sensing platform for the Zn+2 ions based on poly(o-anisidine-co-methyl anthranilate) copolymer composites and their environmental remediation in real samples

A novel nanostructure of poly(o-anisidine-co-methyl anthranilate) (poly(Ani-Co-MA) copolymer has been synthesized by chemical oxidative in situ polymerization technique with equal molar proportion of monomers in the presence of sodium dodecylbenzene sulfonic acid (SDBS) surfactant. The synthesized copolymers were characterized by scanning electron microscope (SEM) and X-ray crystallography (XRD), Fourier transform infrared (FTIR), UV-Vis, thermo-gravimetric analysis (TGA), and simultaneous X-ray photoelectron spectroscopy (XPS) study. The ultraviolet visible spectrum shows the π to π∗ transition and n to π∗ transition. XRD diffraction pattern confirms the amorphous nature of poly(Ani-Co-MA)-SDBS composites. The scanning electron microscope image shows the morphology of the copolymer matrix. For the selective detection of Zn⁺² cation in neutral phosphate buffer, it was fabricated Zn⁺² cation sensor based on glassy carbon electrode (GCE) coated with poly(Ani-co-MA)-SDBS composites as a thin layer with conducting coating binders. The proposed cation sensor has been found to exhibit the inertness in air and chemical environment, long-term stability with good sensitivity, a broad linear dynamic range practically, a reliable reproducibility, short response time, and high electrochemical activity. The sensitivity (0.3560 μA μM^-1 cm^-2) of Zn⁺² cation sensor has been calculated from the slope of the calibration curve. The linearity of the calibration curve is found over the linear dynamic range (LDR) 0.1 nM~0.01 M, and detection limit (DL) is 27.0 ± 1.35 pM at the signal to noise ratio of 3. This novel effort may be considered quite reliable and effective to detect Zn⁺² cation in environmental and biomedical sectors on a broad scale. Simultaneously, SDBS doped poly(o-anisidine-co-methyl anthranilate) copolymer composites were measured against medically important organisms Escherichia coli. E. ludwigi, and Bacillus subtilis. Graphical abstract ᅟ.

Characterizations and morphology of sodium tungstate particles

A solid-state reaction technique was used to synthesize polycrystalline Na₂WO₄. Preliminary X-ray studies revealed that the compound has a cubic structure at room temperature. The formation of the compound has been confirmed by X-ray powder diffraction studies and Raman spectroscopy. Electrical and dielectric properties of the compound have been studied using complex impedance spectroscopy in the frequency range 209 Hz-1 MHz and temperature range 586-679 K. The impedance data were modellized by an equivalent circuit consisting of series of a combination of grains and grains boundary. We use complex electrical modulus M* at various temperatures to analyse dielectric data. The modulus plots are characterized by the presence of two relaxation peaks thermally activated. The morphologies and the average particle size of the resultant sodium tungstate sample were demonstrated by atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The thicknesses and optical constants of the sample have been calculated using ellipsometric measurements in the range of 200-22 000 nm by means of new amorphous dispersion formula which is the objective of the present work. The results were obtained for Na₂WO₄ particles from experimental (EXP) and measured (FIT) data showed an excellent agreement. In addition, the energy gap of the Na₂WO₄ sample has been determined using ellipsometry and confirmed by spectrophotometry measurements.

Light-assisted synthesis MoSx as a noble metal free cocatalyst formed heterojunction CdS/Co3O4 photocatalyst for visible light harvesting and spatial charge separation

In this paper, a novel photocatalyst with visible light harvesting and spatial charge separation is reported, in which cobalt oxide (acting as a hole trap) and molybdenum sulfide (acting as an electron trap) are assembled on the surface of cadmium sulfide nanorods. The MoSx/CdS/Co3O4 composite photocatalyst shows a high H2 evolution with a yield of 537.51 μmol in 5 h, which is 35.53 times greater than over pristine CdS (15.13 μmol). The detailed underlying reason was comprehensively studied and understood by means of SEM, TEM, XRD, XPS, UV-vis DRS, BET; in particular, investigation of their photoelectrochemical properties with photocurrent, voltammetric scanning, fluorescence spectra etc. The high photocurrent response, the lower overpotential (-0.37 V vs. SCE), the faster electron transfer rate constant (ket = 4.23 × 109 s-1) and the short fluorescence lifetime (0.457 ns) supported the efficient spatial charge transfer between CdS and MoSx as well as Co3O4. The simultaneous loading of bicocatalysts can significantly improve the photo-induced spatial charge separation of CdS because MoSx nanoparticles act as an electron trap to rapidly transfer electrons from CdS while Co3O4 acts as a hole trap to quickly transfer holes, enhancing its photocatalytic performance as well.

Optimizing the precursor of sulfur source for hydrothermal synthesis of high performance CdS for photocatalytic hydrogen production

Although the CdS photocatalyst has been extensively investigated, a rational hydrothermal synthesis route is still required to prepare highly active CdS for H2 evolution reaction (HER). To optimize the precursor of the sulfur source, three prevalent organic sulfur sources of thiourea (TA), thioacetamide (TAA) and l-cysteine (l-Cys) were used for hydrothermal synthesis of CdS. Their effects on the crystallographic structure, morphology, optical property, band structure, and photocatalytic HER performance of the products were then investigated systematically. The results indicated that hexagonal branched dendritic structure CdS (S-TA) could be produced in TA solution and showed the highest HER activity due to the branched 1D structure, the smallest interfacial electron transfer resistance and the most negative conduction band bottom (E cb). Whereas in TAA, spherical CdS (S-TAA) with a mixed phase of hexagonal and cubic was obtained. The mixed phase structure and the more positive E cb of S-TAA lead to a considerably lower HER activity than that of S-TA. Poorly crystallized hexagonal CdS nanoparticles (S-Cys) were prepared in l-Cys and showed the lowest HER performance as its E cb is very near to H+ reduction potential. Thus, compared to T-AA and l-Cys, TA is a more suitable sulfur source for hydrothermal preparation of highly active CdS for HER.

A new mechanism for improving electromagnetic properties based on tunable crystallographic structures of FeCoNiSixAl0.4 high entropy alloy powders

Mechanical grinding method was employed to prepare FeCoNiSi_xAl_0.4 high entropy alloy powders, which present a simple solid solution structure (FCC and BCC). After annealing at 673 K, a large amount of BCC phase precipitate and a small amount of CoFe₂O₄ phase generate. The change of crystal structure may lead to an increase in M_s (from 100.3 emu g⁻¹ to 124.2 emu g⁻¹) and a decrease in H_c (from 107 Oe to 59.5 Oe for FeCoNiSi_0.3Al_0.4). The silica content has a significant effect on the electromagnetic parameters of the as-milled and as-annealed alloy powders, presenting the trend of first increase and then decrease. And the dielectric constant is obviously improved after annealing (e.g. from 8.48 to 11.21 and from 0.15 to 2.84 for the ε′ and ε′′ of FeCoNiSi_0.3Al_0.4 at 18 GHz, respectively), while the permeability is reduced. Compared with those of the as-milled samples, the μ′ of as-annealed FeCoNiSi_xAl_0.4 (x = 0.1, 0.3, 0.4) remain unchanged or even increase due to the formation of CoFe₂O₄. Meanwhile, the relative content of the precipitated BCC to FCC for FeCoNiSi_0.3Al_0.4 enhance with the annealing temperature increase from 573 K to 773 K, and then reduce. And the ε′ and μ′ at 2 GHz present the same trend as the content ratio (A_BCC/A_FCC), while the ε′′ improve obviously after annealing, corresponding to the elevation of conductivity.

Mechanical grinding method was employed to prepare FeCoNiSi_xAl_0.4 high entropy alloy powders, which present a simple solid solution structure (FCC and BCC).

Multidirectional-charge-transfer urchin-type Mo-doped W18O49 nanostructures on CdS nanorods for enhanced photocatalytic hydrogen evolution

The urchin shaped Mo doped W₁₈O₄₉ greatly enhances the charge transfer and photocatalytic efficiencies.

Non-covalent polyhedral oligomeric silsesquioxane-polyoxometalates as inorganic–organic–inorganic hybrid materials for visible-light photocatalytic splitting of water

Hydrophilic to hydrophobic conversion of polyoxometalate by integration of POSS-NH₂via non-covalent interactions for sustainable photocatalytic hydrogen production reactions.