Preparation of ZnIn2S4/K2La2Ti3O10 composites and their photocatalytic H2 evolution from aqueous Na2S/Na2SO3 under visible light irradiation

ZnIn₂S₄/K₂La₂Ti₃O₁₀ composite photocatalysts were synthesized via a hydrothermal route. The photocatalysts were characterized by the X-ray diffraction, scanning electron microscopy, ultraviolet–visible (UV–vis) diffuse reflection spectra and photoluminescence measurements. The UV–vis results indicated that ZnIn₂S₄/K₂La₂Ti₃O₁₀ has a strong absorption in the visible light region. The compositions of ZnIn₂S₄/K₂La₂Ti₃O₁₀ composite photocatalysts were optimized according to the photocatalytic activity for hydrogen production from aqueous Na₂S/Na₂SO₃. The composite photocatalyst loading 25 wt.% ZnIn₂S₄ exhibited the highest photocatalytic activity, the amount of H₂ production was 6.29 mmol/g after 3 h irradiation under visible light irradiation.     

Photocatalysis and photoelectrocatalysis using nanocrystalline titania alone or combined with Pt,RuO<Subscript>2</Subscript> or NiO co-catalysts

Photocatalytic mineralization of ethanol in the presence of oxygen has been studied in aqueous photocatalyst suspensions by employing either pure nanocrystalline titania or TiO₂ combined with Pt, RuO₂ or NiO co-catalysts. Combined photocatalysts demonstrated a diverse behavior. Highest mineralization rates were obtained with Pt/TiO₂ and lowest with RuO₂/TiO₂ and NiO/TiO₂. These results were related with the photocatalysts’ behavior when used as photoanodes for the production of electricity in a photoactivated fuel cell running with ethanol as fuel. The highest current was obtained with pure titania. The current dropped in the case of Pt/TiO₂ and became much lower in the case of RuO₂/TiO₂ and NiO/TiO₂ photoanodes. Both current and voltage were lower in the presence of oxygen than in its absence. It is concluded that the presence of electron scavengers, like O₂, and/or the use of efficient photocatalysts, like titania-supported Pt, yield less electric power but assist ethanol mineralization process.     

Facile synthesis of ZnBi<Subscript>2</Subscript>O<Subscript>4</Subscript>-graphite composites as highly active visible-light photocatalyst for the mineralization of rhodamine B

Novel highly active visible-light photocatalysts in the form of zinc bismuth oxide (ZnBi₂O₄) and graphite hybrid composites were prepared by coupling via a co-precipitation method followed by calcination at 450 °C. The as-prepared ZnBi₂O₄-graphite hybrid composites were tested for the degradation of rhodamine B (RhB) solutions under visible-light irradiation. The existence of strong electronic coupling between the two components within the ZnBi₂O₄-graphite heterostructure suppressed the photogenerated recombination of electrons and holes to a remarkable extent. The prepared composite exhibited excellent photocatalytic activity, leading to more than 93% of RhB degradation at an initial concentration of 50mg·L^-1 with 1.0 g catalyst per liter in 150min. The excellent visible-light photocatalytic mineralization of ZnBi₂O₄-1.0graphite in comparison with pristine ZnBi₂O₄ could be attributed to synergetic effects, charge transfer between ZnBi₂O₄ and graphite, and the separation efficiency of the photogenerated electrons and holes. The photo-induced h+ and the superoxide anion were the major active species responsible for the photodegradation process. The results demonstrate the feasibility of ZnBi₂O₄-1.0graphite as a potential heterogeneous photocatalyst for environmental remediation.     

Photoreduction of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> using Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> double-layered dense films

Nano-sized bismuth sulfide (Bi₂S₃) and titanium dioxide (TiO₂) with the orthorhombic and anatase tetragonal structures, respectively, were synthesized for application as catalysts for the reduction of carbon dioxide (CO₂) to methane (CH₄). Four double-layered dense films were fabricated with different coating sequences—TiO₂ (bottom layer)/Bi₂S₃ (top layer), Bi₂S₃/TiO₂, TiO₂/Bi₂S₃: TiO₂ (1 : 1) mix, and Bi₂S₃: TiO₂ (1 : 1) mix/Bi₂S₃: TiO₂ (1 : 1) mix—and applied to the photoreduction of CO₂ to CH₄; the catalytic activity of the fabricated films was compared to that of the pure TiO₂/TiO₂ and Bi₂S₃/Bi₂S₃ doubled-layered films. The TiO₂/Bi₂S₃ double-layered film exhibited superior photocatalytic behavior, and higher CH₄ production was obtained with the TiO₂/Bi₂S₃ double-layered film than with the other films. A model of the mechanism underlying the enhanced photoactivity of the TiO₂/Bi₂S₃ double-layered film was proposed, and it was attributed in effective charge separation.     

Facile in-situ Solvothermal Method to synthesize double shell ZnIn2S4 nanosheets/TiO2 hollow nanosphere with enhanced photocatalytic activities

The design and construction of efficient visible light responsive composite photocatalysts with intimate interfacial contacts in photocatalytic field have attracted huge interest. Herein, a double-shelled ZnIn₂S₄ nanosheets/TiO₂ hollow composite single nanosphere (ZIS/TiO₂) was first fabricated by a facile hydrothermal process, where 2D ZnIn₂S₄ nanosheets self-assembled on the external surface of TiO₂ hollow nanosphere to form the double-shelled hollow single sphere. The morphologies, structures, optical properties of as-prepared double-shelled ZIS/TiO₂ hollow nanospheres were characterized in detail. The photocatalytic activities of double-shelled ZIS/TiO₂ nanospheres for the photodegradations of Tetracycline hydrochloride, Levofloxacin and Rhodamine B under visible light irradiation have been investigated. Compared to pure TiO₂ and ZnIn₂S_4, the obtained ZIS/TiO₂ samples have significantly improved photocatalytic performances. The most optimal photocatalytic activity of ZIS/TiO₂-2 nanocomposite with 64 wt% ZnIn₂S₄ nanosheets coated is observed, and its degradation rate constant is 2.32 and 2.14 times as high as those of pure TiO₂ and ZnIn₂S₄. The superior photocatalytic performance of ZIS/TiO₂ nanocomposite can be ascribed to its unique double shell hollow structure and the synergistic effect between ZnIn₂S₄ and TiO₂. Our result provides some guidance for designing novel morphologies of composite photocatalyst with good photocatalytic performance.     

Electrolytic properties of the MeLn<Subscript>2</Subscript>S<Subscript>4</Subscript>-Ln′<Subscript>2</Subscript> S<Subscript>3</Subscript> phases synthesized using the sol-gel and cryochemical technologies

The possibility of synthesizing sulfide-conducting solid electrolytes based on the ternary sulfides MeLn₂S₄ doped with the binary sulfides Ln′₂S₃ has been approved and the influence of dopants on the electrolytic properties of the basic compounds has been investigated for the first time. The influence of the specific features of the method used for synthesizing complex sulfide phases from nanometer-sized oxide precursors on the important functional properties of the solid electrolytes has been analyzed. The samples have been examined using the X-ray powder diffraction analysis, electron scanning microscopy, and electron microprobe analysis. The region of the existence of the solid solutions has been determined, the total electrical conductivity has been studied, and the activation energy for electrical conduction for samples with different dopant contents has been calculated. The ionic and electronic transfer numbers have been determined using the modified versions of the emf method and the Hebb-Wagner polarization method. A possible mechanism of defect formation has been proposed.     

Sulfide ceramic materials based on CaYb<Subscript>2</Subscript>S<Subscript>4</Subscript> with functional electrolytic properties

Phases based on the CaYb₂S₄ compound with hyperstoichiometric compositions of the CaS and Yb₂S₃ sulfides are investigated. The region of solid solutions and the electrolytic temperature range are determined, and the average ion, cation, anion, and electron transport numbers are measured. The pycnometric and X-ray densities are compared. A possible mechanism of defect formation is proposed.     

Photodegradation of benzene,toluene, ethylbenzene and xylene by fluidized bed gaseous reactor with TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> photocatalysts

The photodegradation of BTEX (benzene, toluene, ethylbenzene and xylene) in a photocatalytic fluidized bed reactor with TiO₂/SiO₂ was investigated. The TiO₂ film was prepared using the sol-gel method and coated onto silica-gel powder. The effects of the superficial gas velocity and SiO₂ size on the photodegradation of BTEX were examined in a fluidized bed reactor. At steady-state operation, above 79, 79, 99, 98, and 98% removal efficiencies were achieved for benzene, toluene, ethylbenzene, m, p-xylene and o-xylene, respectively, under optimal conditions (2.0 U _mf of superficial gas velocity and 1.43 of height/diameter ratio). The reaction product such as CO₂ was detected and intermediate products such as benzaldehyde, malonic acid, acetaldehyde, and formic acid were identified from the photocatalytic reaction. Also, small amounts of benzoic acid and benzyl alcohol were found through analyzing the intermediate species adsorbed on the photocatalysts. The experimental results can lead to the development of an efficient photocatalytic treatment system that utilizes solar energy and TiO₂/SiO₂ photocatalysts.     

Photocatalytic activity of metal-decorated SiO<Subscript>2</Subscript>@TiO<Subscript>2</Subscript> hybrid photocatalysts under water splitting

We report the fabrication of a metal-decorated hybrid nanocomposite with TiO₂ encapsulation (Metal/SiO₂@TiO₂, Metal=Pt or Ru) using a simple surface-modification chemical process. Metal nanoparticles capped with polyvinylpyrrolidone were successfully assembled on functionalized SiO₂ via electrostatic interactions, after which a thin layer of TiO₂ was coated on the surface by the sol-gel process to avoid agglomeration of the coated silica spheres. Transmission electron microscopy studies confirmed that the metal nanoparticles were uniformly distributed throughout the surface of the SiO₂ with a thin layer of TiO₂. In addition, X-ray diffraction was employed to ensure the crystal structure of the uniformly coated thin TiO₂ layer. Even after calcination at 500 °C, the structure remained intact, confirming high thermal stability. The photocatalytic activity of the metal-decorated SiO₂/TiO₂ nanocomposites was evaluated using the H₂ evolution reaction. The Metal/SiO₂@TiO₂ catalysts show the photocatalytic water splitting efficiency for H₂ generation (i.e., 0.14% for Pt/SiO₂@TiO₂ and 0.12% for Ru/SiO₂@TiO₂), while there is no generation of H₂ on the Metal/SiO₂ without a coating layer. These results indicate that the anatase crystalline coating layer has good thermal and chemical stability and plays a significant role in photocatalytic H₂ production.     

Optical properties of Pt-TiO<Subscript>2</Subscript> catalyst and photocatalytic activities for benzene decomposition

In order to improve the photocatalytic decomposition activity of benzene, which has been regarded as a typical volatile organic compound in air, TiO₂ catalysts modified with metals (Pt, Cu, and Fe) were prepared and tested. Certain correlations between the photocatalytic activities and the optical properties of those catalysts were also found and discussed by using UV-visible spectroscopy and a photoluminescence spectroscopy. Among the metal impregnated TiO₂, the Pt impregnated TiO₂ showed the best activity and it was even better than that of P-25 which is widely used in commercial applications. For the various metal impregnated TiO₂ samples, certain proportional relationships were found between the observed photoluminescence values and photocatalytic activities. On the other hand, in UV-visible spectra for metal impregnated TiO₂ samples, the transmittance value was reduced depending upon the loading of metals. It was thought that photocatalytic activity increases from initial reaction state because the number of photoexcited electrons, which exist at Pt surface augment due to the band gap energy change of Pt and TiO₂ by sintering and light energy-absorbed electrons excited easily to conduction. In conclusion, it was confirmed that the enhanced photocatalytic activity for high metal loading on TiO₂ is related with the high concentration of excited electrons, which could be monitored through UV-visible spectra.     

Photocatalytic Generation of H<Subscript>2</Subscript> Gas from Neat Ethanol over Pt/TiO<Subscript>2</Subscript> Nanotube Catalysts

TiO₂ nanotubes promoted with Pt metal were prepared and tested to be the photocatalytic dehydrogenation catalyst in neat ethanol for producing H₂ gas (C₂H₅OHC₃CHO +H₂). It was found that the ability to produce H₂, the liquid phase product distribution and the catlyst stability of these promoted nano catalysts all depended on the Pt loading and catalyst preparation procedure. These Pt/TiO₂ catalysts with TiO₂ nanotubes washed with diluted H₂SO₄ solution produced 1, 2-diethoxy ethane (acetal) as the major liquid phase product, while over those washed with diluted HCl solution or H₂O, acetaldehyde was the major liquid phase product.     

Rational design of MoS2/g-C3N4/ZnIn2S4 hierarchical heterostructures with efficient charge transfer for significantly enhanced photocatalytic H2 production

The rational design of hierarchical heterojunction photocatalysts with efficient spatial charge separation remains an intense challenge in hydrogen generation from photocatalytic water splitting. Herein, a noble-metal-free MoS₂/g-C₃N₄/ZnIn₂S₄ ternary heterostructure with a hierarchical flower-like architecture was developed by in situ growth of 3D flower-like ZnIn₂S₄ nanospheres on 2D MoS₂ and 2D g-C₃N₄ nanosheets. Benefiting from the favorable 2D-2D-3D hierarchical heterojunction structure, the resultant MoS₂/g-C₃N₄/ZnIn₂S₄ nanocomposite loaded with 3 wt% g-C₃N₄ and 1.5 wt% MoS₂ displayed the optimal hydrogen evolution activity (6291 μmol g^?1 h^?1), which was a 6.96-fold and 2.54-fold enhancement compared to bare ZnIn₂S₄ and binary g-C₃N₄/ZnIn₂S₄, respectively. Structural characterizations reveal that the significantly boosted photoactivity is closely associated with the multichannel charge transfer among ZnIn₂S₄, MoS₂, and g-C₃N₄ components with suitable band-edge alignments in the composites, where the photogenerated electrons migrate from g-C₃N₄ to ZnIn₂S₄ and MoS₂ through the intimate heterojunction interfaces, thus enabling efficient electron-hole separation and high photoactivity for hydrogen evolution. In addition, the introduction of MoS₂ nanosheets highly benefits the improved light-harvesting capacity and the reduced H₂-evolution overpotential, further promoting the photocatalytic H₂-evolution performance. Moreover, the MoS₂/g-C₃N₄/ZnIn₂S₄ ternary heterostructure possesses prominent stability during the photoreaction process owing to the migration of photoinduced holes from ZnIn₂S₄ to g-C₃N₄, which is deemed to be central to practical applications in solar hydrogen production.     

A Comparative Study of the Photoconduction,Photocatalytic and Electrocatalytic Performance of g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/ZnS/CuS Heterojunctions with Different Morphologies

Ternary heterojunctions g-C₃N₄/ZnS/CuS with different morphologies were constructed. The g-C₃N₄/ZnS/CuS (hexagonal-nanosheets) exhibited the largest photocurrent, the best photocatalytic and electrochemical activity, which revealed the influence discipline of different morphologies on photoconductivity, photo/electro-catalytic activity. It indicated that this heterojunction can be used as an excellent photoconductor device, a high-efficiency photo/electro-catalyst.

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In situ DRIFTS study of photocatalytic CO<Subscript>2</Subscript> reduction under UV irradiation

Photocatalytic reduction of CO₂ on TiO₂ and Cu/TiO₂ photocatalysts was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under UV irradiation. The photocatalysts were prepared by sol-gel method via controlled hydrolysis of titanium (IV) butoxide. Copper precursor was loaded onto TiO₂ during sol-gel procedure. A large amount of adsorbed H₂O and surface OH groups was detected at 25°C on the TiO₂ photocatalyst after being treated at 500°C under air stream. Carbonate and bicarbonate were formed rapidly due to the reaction of CO₂ with oxygen-vacancy and OH groups, respectively, on TiO₂ surface upon CO₂ adsorption. The IR spectra indicated that, under UV irradiation, gas-phase CO₂ further combined with oxygen-vacancy and OH groups to produce more carbonate or bicarbonate. The weak signals of reaction intermediates were found on the IR spectra, which were due to the slow photocatalytic CO₂ reduction on photocatalysts. Photogenerated electrons merge with H⁺ ions to form H atoms, which progressively reduce CO₂ to form formic acid, dioxymethylene, formaldehyde and methoxy as observed in the IR spectra. The well-dispersed Cu, acting as the active site significantly increases the amount of formaldehyde and dioxymethylene, thus promotes the photoactivity of CO₂ reduction on Cu/TiO₂. A possible mechanism of the photocatalytic CO₂ reduction is proposed based on these intermediates and products on the photocatalysts.     

The enhanced performance of Cr(VI) photoreduction and antibiotic removal on 2D/3D TiO2/ZnIn2S4 nanostructures

In this study, 2D/3D TiO₂/ZnIn₂S₄ nanostructures with TiO₂ sheet cluster embedded into ZnIn₂S₄ micro flowers were fabricated via hydrothermal method. The matched band structure, the enlarged surface area and the efficient photo-induced charge transfer offered by effective heterostructures formed between the two components endowed the TiO₂/ZnIn₂S₄ nanoarchitecture with excellent photocatalytic Cr(VI) reduction and tetracycline hydrochloride (TC) degradation performance. Especially, the Cr(VI) photoreduction efficiency of 50% TiO₂/ZnIn₂S₄ was 8.8 times higher compared to pure ZnIn₂S₄. The enhanced separation efficiency of photo-excited charge carriers was induced by the matched band structure, the enlarged surface area and the strong interaction between TiO₂ and ZnIn₂S₄. The key roles of ·O₂^? was confirmed via trapping experiments. Otherwise, the pathway of TC degradation was investigated. The proposed mechanism during photocatalysis process was also discussed according to the photocatalytic and characterization results.     

Electrolytic properties of sulfide-conducting phases based on the BaLn<Subscript>2</Subscript>S<Subscript>4</Subscript> and CaLn<Subscript>2</Subscript>S<Subscript>4</Subscript> compounds of different structural types

The criteria for the choice of objects of investigation that possess sulfide-ion conduction, have the general formula MeLn₂S₄, and crystallize in different structural types are considered. The data obtained on the electrolytic properties of phases based on BaLn₂S₄(Ln = Nd, Sm, Tm); CaFe₂O₄ structural type), CaLn₂S₄(Ln = Y, Yb); Yb₃S₄ structural type), and CaLn₂S₄(Ln = Pr, Nd, Gd); Th₃P₄ structural type) are generalized. The performed comparative analysis of the properties of the synthesized electrolytes has demonstrated that the properties of solid electrolytes depend on the configuration of the f state of lanthanides to a greater extent than on the structure of the electrolytes under investigation. The vacancy mechanism of defects formation and sulfide-ion transfer in phases based on thiolanthanates is proposed reasoning from the data on the dependence of the electrolytic and thermodynamic properties on the composition.     

Preparation of hydrophobic SiO<Subscript>2</Subscript>@(TiO<Subscript>2</Subscript>/MoS<Subscript>2</Subscript>) composite film and its self-cleaning properties

TiO₂/MoS₂ composite was encapsulated by hydrophobic SiO₂ nanoparticles using a sol–gel hydrothermal method with methyltriethoxysilane (MTES), titanium tetrachloride (TiCl₄), and molybdenum disulfide (MoS₂) as raw materials. Then, a novel dual functional composite film with hydrophobicity and photocatalytic activity was fabricated on a glass substrates via the combination of polydimethylsiloxane adhesives and hydrophobic SiO₂@(TiO₂/MoS₂) composite particles. The influence of the mole ratios of MTES to TiO₂/MoS₂ (M:T) on the wettability and photocatalytic activity of the composite film was discussed. The surface morphology, chemical compositions, and hydrophobicity of the composite film on the glass substrate were investigated by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and water contact angle (water CA) measurements. The results indicated that the composite film exhibited stable superhydrophobicity and excellent photocatalytic activity for degradation of methyl orange (MO) even after five continuous cycles of photocatalytic reaction when M/T was 7:1. The water CA and degradation efficiency for MO remained at 154° and 94%, respectively. Further, the composite film showed a good non-sticking characteristic with the water sliding angle (SA) at about 4°. The SiO₂@(TiO₂/MoS₂) composite consisting of hydrophobic SiO₂ nanoparticles and TiO₂/MoS₂ heterostructure could provide synergistic effects for maintaining long-term self-cleaning performance.     

Crystallization Behavior and Corrosion Resistance of Cu<Subscript>50</Subscript>Zr<Subscript>40</Subscript>Ag<Subscript>10</Subscript> Amorphous Alloy

In this study, Cu₅₀Zr₄₀Ag₁₀ amorphous alloy ribbons were prepared by a single roller melt-spinning method. The crystallization behavior of the Cu₅₀Zr₄₀Ag₁₀ amorphous alloy has been investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Moreover, the polarization and passivation behaviors of the as-quenched and as-annealed amorphous alloy have been studied in 1 N H₂SO₄. The surfaces of corroded samples have been examined using scanning electron microscopy (SEM) and the element distribution across the pits has been analyzed using energy dispersive spectrometer (EDS). The results show that the Cu₅₀Zr₄₀Ag₁₀ amorphous alloy has a large supercooled region up to 36 K. The ω-(ZrCu), ZrO₂ and Cu₁₀Zr₇ phases can firstly precipitate from the amorphous matrix below glass transition temperature during annealing for 30 min. Moreover, the corrosion resistance of the as-quenched amorphous alloy is better than that of partial and full crystallization products. In addition, Zr plays a crucial role in enriching the passive film and enhancing corrosion resistance.     

One-pot synthesis of bifunctionalized TiO<Subscript>2</Subscript> mesoporous photocatalyst with visible light response

A series of Fe-doped SH/TiO₂ mesoporous photocatalysts have been firstly prepared by one-pot method using P123 as structure-directing agent. This bifunctionalized mesoporous TiO₂ possesses perfect anatase crystal structure and high surface area. The surface area of Fe-doped SH/TiO₂ mesoporous material is 4 times higher than that of P25. Based on the EPR results, it was found that trivalent Fe ions exist at low spin state and substitutes a part of Ti⁴⁺ ions into TiO₂ lattice. Fe-dropping in TiO₂ extends the adsorption band side of the resulting material to about 600 nm. Much high photocatalytic activity in the degradation of phenanthrene was obtained on the bifunctionalized mesoporous TiO₂ under visible light irradiation (λ > 420 nm), which is 6 times higher than that of pristine mesoporous TiO₂. The enhancement in the photocatalytic activity of bifunctionalized TiO₂ is ascribed to the extended absorption to visible light and strong interaction between SH-groups and PHE molecules.     

Mg(OH)<Subscript>2</Subscript> Films Prepared by Ink-Jet Printing and Their Photocatalytic Activity in CO<Subscript>2</Subscript> Reduction and H<Subscript>2</Subscript>O Conversion

Mg(OH)₂ films on Al substrates were fabricated by ink-jet printing, and they were applied as photocatalysts in solar fuels production (H₂ and CH₃OH) from CO₂ and H₂O conversion. The films were fabricated by means of a deposition of a solution composed of magnesium complex nanoparticles over aluminum foils, which were submitted to a heat treatment to promote the crystallization of Mg(OH)₂. The films were characterized by razing incidence X-ray diffraction (GZXD), Fourier-transform infrared spectroscopy (FTIR), Scanning electronic microscopy, X-ray photoelectron spectroscopy (XPS), and N₂ physisorption by BET method. The Mg(OH)₂ was detected in all the samples synthesized with 1 to 40 layers. According to XPS and FTIR analysis, it was detected the presence of carbonates related to Mg₃O(CO₃)₂ and Al⁰ and Al³⁺ due to the substrate. The highest photocatalytic activity was reached using 30 layers of Mg(OH)₂ for H₂ and CH₃OH generation, which it was 268 and 15 µmol g^??1h^??1, respectively. These results were associated to the presence of adequate amounts of MgO and Al₂O₃ that promote an efficient transfer of the photogenerated electrons between them. Furthermore, the formation of porous structures with high surface area and relative high roughness promoted an increase in the mass transport between the gas and liquid phase, which increase the effectiveness of the photocatalysts.