A facile one step synthesis of SnO<Subscript>2</Subscript>/CuO and CuO/SnO<Subscript>2</Subscript> nanocomposites: photocatalytic application

Here novel photocatalysts, SnO₂/CuO and CuO/SnO₂ nanocomposites were successfully synthesized by chemical method at room temperature. X-ray Diffraction (XRD), transmission electron microscopy (TEM), Fourier transform Infrared (FT-IR), UV–Visible (UV–Vis) and photoluminescence (PL) spectroscopy were utilized for characterization of the nanocomposites. The photocatalytic activity of the nanocomposites was investigated. The hybrid nanocomposites exhibited high photocatalytic activity as evident from the degradation of methylene blue (MB) dye. The result revealed substantial degradation of the MB dye (92 and 69.5% degradation of SnO₂/CuO and CuO/SnO₂, respectively) under visible light illumination with short period of 30 min. Their large conduction band potential difference and the inner electrostatic field formed in the p–n heterojunction provide a strong driving force for the photogenerated electrons to move from Cu₂O to SnO₂ under visible light illumination. The excellent photodegradation of methylene blue suggested that the heterostructured SnO₂/CuO nanocomposite possessed higher charge separation and photodegradation abilities than CuO/SnO₂ nanocomposite under visible light irradiation.     

The preparation of Cu<Subscript>2</Subscript>O@Au yolk/shell structures for efficient photocatalytic activity with a self-generated acid etching method

Cu₂O@Au yolk/shell structures were successfully prepared with a facile self-generated acid etching method at room temperature. The morphology is controllable by adding different amount of HAuCl₄·4H₂O. Scanning electron microscopy and transmission electron microscopy images showed that Au nanoparticles self-assembled into a porous shell around Cu₂O core while the produced etching agent etched the core gradually and formed the cavity. The photocatalytic property of Cu₂O@Au yolk/shell structures was studied by degrading MO under the irradiation of visible light at room temperature. Benefiting from the synergistic effect of cavity micro-reactor and electron transfer, the photocatalytic performance of the as-prepared Cu₂O@Au yolk/shell structures was much better than that of pure Cu₂O. The possible photocatalytic mechanism of the Cu₂O@Au yolk/shell catalysts was proposed and elaborated in this study. It is certified that Yolk/shell structures have potential applications in photocatalysis for its active sites on the large specific area.     

Enhanced visible light photocatalytic activity for g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/SnO<Subscript>2</Subscript>:Sb composites induced by Sb doping

In this paper, g-C₃N₄/SnO₂:Sb composite photocatalysts were fabricated by in situ loading Sb-doped SnO₂ (SnO₂:Sb) nanoparticles on graphitic carbon nitride (g-C₃N₄) nanosheets via a facile hydrothermal method. The synthesized g-C₃N₄/SnO₂:Sb composites delivered enhanced visible light photocatalytic performance for degradation of rhodamine B in comparison with g-C₃N₄/SnO₂ composites without doping Sb. Various techniques including XRD, SEM, TEM, FTIR, XPS, PL and electrochemical method were employed to demonstrate the successful fabrication of g-C₃N₄/SnO₂:Sb composite and to investigate the enhanced mechanism of photocatalytic activity. The improvement of visible light absorption and the promotion of separation efficiency and interfacial transfer of photogenerated carriers induced by Sb doping were responsible for the enhancement of photocatalytic activity. This study provides a simple and convenient method to synthesize a visible light responsive catalyst with promising performance for the potential application in environmental protection.     

Visible-light activities of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>/BiVO<Subscript>4</Subscript> composite photocatalysts

Gd₂O₃/BiVO₄ composite photocatalysts were hydrothermal synthesized and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and UV–vis diffusion reflectance spectra; all the composite photocatalysts exhibited enhanced photocatalytic activities than the pure BiVO₄ for degradation of methyl orange under visible-light irradiation. The improved activity of composites was discussed and ascribed to the electron-scavenging effect of dopants.     

Fabrication of plate-on-plate Z-scheme SnS<Subscript>2</Subscript>/Bi<Subscript>2</Subscript>MoO<Subscript>6</Subscript> heterojunction photocatalysts with enhanced photocatalytic activity

A class of direct plate-on-plate Z-scheme heterojunction SnS₂/Bi₂MoO₆ photocatalysts was synthesized via a two-step hydrothermal method. The materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectra, Fourier transform infrared photoluminescence emission spectra, and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity was estimated via the degradation of crystal violet (CV) and ciprofloxacin (CIP). The experimental results indicated that the 5 wt% SnS₂/Bi₂MoO₆ composites exhibited significantly enhanced performance in contrast to pure Bi₂MoO₆ or SnS₂ nanoflakes, and were also superior to the popular TiO₂ (P25). The degradation reaction accorded well with the first-order reaction kinetics equation; the rate constant of CV using a SnS₂ content of 5 wt% photocatalyst was ~?3.6 times that of the Bi₂MoO₆ and 2.4 times that of SnS₂. Furthermore, a SnS₂ content of 5 wt% exhibited a 1.7 times higher photocatalytic activity of CIP than that of pure Bi₂MoO₆, and 1.3 times that of pure SnS₂. Radical trapping experiments and an electron spin resonance technique indicated that h⁺ and ·OH were the dominant active species involved in the degradation process. A plasmonic Z-scheme photocatalytic mechanism was proposed to explain the superior photocatalytic activities and efficient separation of photogenerated electrons and holes.     

Interface-level thermodynamic stability diagram for in situ internal oxidation of Ag(SnO<Subscript>2</Subscript>)<Subscript>p</Subscript> composites

We present a combined experimental and theoretical study on interfacial structure and thermodynamics in internally oxidized Ag(SnO₂)_p composites. The orientation relation between in situ formed SnO₂ particles and the silver matrix was characterized using high-resolution transmission electron microscopy techniques. First-principles energetic calculations were then performed to predict the equilibrium interface structures and corresponding adhesion properties as functions of temperature and oxygen partial pressure. All results were combined to construct the interface-level thermodynamic stability diagram, for guiding the optimal design of internal oxidation parameters.     

Reduced graphene oxide/Cu<Subscript>2</Subscript>O nanostructure composite films as an effective and stable hydrogen evolution photocathode for water splitting

An efficient photocathode consisting of reduced graphene oxide/Cu₂O/Cu (rGO/Cu₂O/Cu) has been successfully prepared in this work via a facile two step method, consisting of chemical oxidation of a copper foil in alkaline solution using (NH₄)₂S₂O₈ as the oxidizing agent, dipping the prepared samples in graphene oxide (GO) solution and calcination at vacuum to form a rGO layer onto Cu₂O/Cu photocathode, which acts as a protective layer. The products were composed of a thin Cu₂O layer topped with a thin rGO film as the protective coating. The chemical composition and rGO amount in the composite materials were easily controlled by changing the immersion time to enhance PEC performance. UV–Vis spectroscopy, Raman spectroscopy, XRD, SEM, TEM and FTIR spectroscopy were used in the optical and morphological characterization of the graphene oxide and prepared photocathodes. Distinct patches of GO film are formed on the Cu(OH)₂ nanostructure surface, as shown by SEM results. Linear sweep voltammetry and chronoamperometry analysis have been applied in the photoelectrochemical characterizations in the dark and under illumination conditions. Photocurrent density provided by rGO/Cu₂O/Cu photocathode ??2.54 mA cm^??2 is three times greater than that of bare Cu₂O/Cu photocathode ??0.82 mA cm^??2 at 0 V vs. RHE under illumination. Low photostability of 42% is exhibited by bare Cu₂O/Cu photocathode after 200 s irradiation whereas rGO/Cu₂O/Cu photocathode shows approximately 98% of the initial photocurrent density. Therefore, a strategy has been developed in this work for the synthesis of this new photocathode using Cu₂O/Cu as an effective photocathode for photoelectrochemical (PEC) water splitting.     

Fabrication of TiO<Subscript>2</Subscript>/ZnO composite nanofibers with enhanced photocatalytic activity

TiO₂/ZnO composite nanofibers have been successfully prepared by electrospinning technique. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, Raman spectrum, X-ray photoelectron spectroscopy and UV–Vis diffuse reflectance spectroscopy, were used to characterize the as-synthesized nanofibers. The photocatalytic studies revealed that the TiO₂/ZnO nanofibers exhibited enhanced photocatalytic efficiency of photodegradation. Additionally, the recycling experiment of TiO₂/ZnO nanofibers had been done, demonstrating that TiO₂/ZnO nanofibers have high efficiency and stability.     

Morphological and humidity sensing characteristics of SnO<Subscript>2</Subscript>-CuO,SnO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and SnO<Subscript>2</Subscript>-SbO<Subscript>2</Subscript> nanocooxides

This paper reports the synthesis of SnO₂-CuO, SnO₂-Fe₂O₃ and SnO₂-SbO₂ composites of nano oxides and comparative study of humidity sensing on their electrical resistances. CuO, Fe₂O₃ and SbO₂ were added within base material SnO₂ in the ratio 1: 0.25, 1: 0.50 and 1: 1. Characterizations of materials were done using SEM and XRD. SEM images show the surface morphology and X-ray diffraction reveals the nanostructure of sensing materials. The pellets were annealed at 200, 400 and 600°C respectively for 3 h and after each step of annealing, observations were carried out. It was observed that as relative humidity (%RH) increases, there was decrease in the resistance of pellet for the entire range of RH. Results were found reproducible. SnO₂-SbO₂ shows maximum sensitivity for humidity (12 MΩ/%RH) among other composites.     

SnO<Subscript>2</Subscript>-based thin films with excellent photocatalytic performance

SnO₂ semiconductor is a new-typed promising photocatalyst, but wide application of SnO₂-based photocatalytic technology has been restricted by low visible light utilization efficiency and rapid recombination of photogenerated electrons–holes. To overcome these drawbacks, we prepared B/Fe codoped SnO₂–ZnO thin films on glass substrates through a simple sol–gel method. The photocatalytic activities of the films were evaluated by degradation of organic pollutants including acid naphthol red (ANR) and formaldehyde. UV–Vis absorption spectroscopy and photoluminescence (PL) spectra results revealed that the B/Fe codoped SnO₂–ZnO film not only enhanced optical absorption properties but also improved lifetime of the charge carriers. X-ray diffraction (XRD) results indicated that the nanocrystalline SnO₂ was a single crystal type of rutile. Field emission scanning electron microscopy (FE-SEM) results showed that the B/Fe codoped SnO2–ZnO film without cracks was composed of smaller nanoparticles or aggregates compared to pure SnO2 film. Brunauer–Emmett–Teller (BET) surface area results showed that the specific surface area of the B/Fe codoped SnO₂–ZnO was 85.2 m² g^?1, while that of the pure SnO₂ was 20.7 m² g^?1. Experimental results exhibited that the B/Fe codoped SnO₂–ZnO film had the best photocatalytic activity compared to a pure SnO₂ or singly-modified SnO₂ film.     

Role of Ti diffusion on the formation of phases in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> brazed interface

Diffusivities of Ti, Cu, Al and Ag in the interface of Al₂O₃–Al₂O₃ braze joints using Ag–Cu–Ti active filler alloy, have been calculated by Matano–Boltzman method. The Matano plane has been identified for each elemental diffusion at various brazing temperatures. The diffusivities of Ag, Cu and Al are almost insignificant on formation of interface during brazing, whereas the diffusivity of Ti changes significantly with the brazing temperature and controls the formation of different reaction product in the interface. Presence of TiO and Ti₃Cu₃O phases in the interface has been confirmed by transmission electron microscopy (TEM).     

Band gap narrowing and photocatalytic studies of Nd<Superscript>3+</Superscript> ion-doped SnO<Subscript>2</Subscript> nanoparticles using solar energy

Pure and Nd³⁺-doped tin oxide (SnO₂) nanoparticles have been prepared by the sol–gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive spectroscopy and UV–visible spectroscopy. The XRD patterns of all the samples are identified as tetragonal rutile-type SnO₂ phase which is further confirmed by TEM analysis. Neodymium doping introduces band gap narrowing in the prepared samples and enhances their absorption towards the visible-light region. The photocatalytic activity of all the samples was evaluated by monitoring the degradation of methylene blue solution under day light illumination and it was found that the photocatalytic activity significantly increases for the samples calcined at 600 than 400°C, which is due to the effective charge separation of photogenerated electron–hole pairs. The efficiency of photocatalysts was found to be related to neodymium doping percentage and calcination temperature.     

Facile fabrication of hierarchical BiVO<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> heterostructures for enhanced photocatalytic activities under visible-light irradiation

BiVO₄/TiO₂ nanocomposites were fabricated by a facile wet-chemical process, followed by the synthesis of TiO₂ hierarchical spheres via hydrothermal method. The BiVO₄/TiO₂ nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The results showed that prepared TiO₂ presented hierarchical spherical morphology self-assembled by nanoparticles and an anatase–brookite mixed crystal phase. The introduction of monoclinic BiVO₄ components retained the hierarchical structures and expanded the light response to around 510 nm. Type II BiVO₄/TiO₂ heterostructured nanocomposites exhibited improved photocatalytic degradation towards methylene blue under visible-light irradiation, especially for the composite photocatalysts with atomic Ti/Bi?=?10, which showed double degradation rate than that of pure BiVO₄. The enhanced photocatalytic mechanism of the heterostructured BiVO₄/TiO₂ nanocomposites was discussed as well.     

<Emphasis Type="Italic">In situ</Emphasis> loading of Cu<Subscript>2</Subscript>O nanoparticles on a hydroxyl group rich TiO<Subscript>2</Subscript> precursor as an excellent catalyst for the Ullmann reaction

An in situ method has been used to load Cu₂O nanoparticles on the surface of a hydroxyl group rich TiO₂ precursor. Cu₂O nanoparticles are formed by in situ reduction of Cu(OH)₂ with Sn²⁺ ions linked to the surface of the TiO₂ precursor. The initial Cu₂O nanoparticles serve as seeds for subsequent particle growth. The resulting Cu₂O nanoparticles are evenly dispersed on the surface of the TiO₂ precursor, and are heat and air stable. The as-prepared composite is an excellent catalyst for Ullmann type cross coupling reactions of aryl halides with phenol. The composite catalyst also showed good stability, remaining highly active after five consecutive runs.     

Popcorn like morphology and absence of room temperature ferromagnetism in Ni doped SnO<Subscript>2</Subscript> nanoparticles

Ni-doped SnO₂ nanoparticles were synthesized by the microwave oven assisted solvothermal method. The structural characterization was done by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy. The outcomes confirmed that Ni-doped SnO₂ nanoparticles have a pure rutile-type tetragonal phase of SnO₂ structures with a high degree of crystallization and a crystallite size of 10–14 nm. Popcorn like SEM morphology of the nickel doped sample is shown. Optical characterization was done by UV–Vis spectrometer, fluorescence spectroscopy and electron paramagnetic resonance spectroscopy. Magnetic characterization was done by vibrating sample magnetometer (VSM). The VSM measurements revealed that the Ni doped SnO₂ powder samples were diamagnetic at room temperature. This diamagnetic result is in contradiction to earlier published results.     

Rapid preparation and photocatalytic properties of octahedral Cu2O@Cu powders

To improve the photocatalytic properties of Cu₂O, octahedral Cu₂O@Cu powders were prepared by a convenient and rapid two-step liquid phase reduction method. Glucose (C₆H₁₂O₆) and thiourea dioxide (CH₄N₂O₂S, TD for short) were used as pre-reductant and secondary-reductant separately. The microstructure and composition of the products obtained after the reduction processes were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). With the increasing of TD content, the secondary reduced products changed from solid octahedral Cu₂O to octahedral Cu₂O@Cu composites and finally hollow octahedral Cu₂O/Cu composites. The corresponding calculated mass of Cu increased from 6.2 wt% to 80.2 wt%. The photocatalytic behavior of the reduced particles were analyzed by monitoring the degradation of methyl orange solution (MO for short) and electrochemical tests. Photocatalytic performance tests showed that octahedral Cu₂O@Cu powders had an excellent photocatalytic activity. The MO degradation rate was improved from 1.4% for photocatalysts without CuNPs to 92.9% after introducing 13.4 wt% CuNPs under visible light irradiation for 60 min. This simple and rapid synthesis process allowed for the fabrication of octahedral Cu₂O@Cu material with photocatalytic performance superior to pure octahedral Cu₂O and hollow octahedral Cu₂O/Cu materials.     

Synthesis of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> composites with core/shell/shell nano-structure and evaluation of their photo-catalytic efficiency for degradation of methylene blue

The SrFe₁₂O₁₉/SiO₂/TiO₂ nanostructures with hard magnetic core were successfully synthesized through the facile and efficient wet chemical processes. At first, nanocrystalline strontium hexaferrite (SrFe₁₂O₁₉) powder was prepared using a new co-precipitation route in ethanol/water media. In the next step, SrFe₁₂O₁₉/SiO₂ composites were produced by well-known Stöber method using tetraethyl orthosilicate as precursor. Finally titania was coated on SrFe₁₂O₁₉/SiO₂ composite particles using titanium n-butoxide precursor. The core/shell/shell nanostructures have been characterized by means of X-ray diffraction, vibrating sample magnetometer, Fourier transform infrared spectra, field emission scanning electron microscopy, and transmission electron microscopy equipped with an energy-dispersive X-ray spectroscopy detector. The catalytic activity of SrFe₁₂O₁₉/SiO₂/TiO₂ composites has been investigated in the degradation of methylene blue dye under UV illumination. The results indicated that the obtained SrFe₁₂O₁₉/SiO₂/TiO₂ composite has photo-catalytic properties and can be retrieved by magnetic separation. The photo-degradation of methylene blue dye was about 80% in the presence of photo-catalyst powder at irradiation time of 180 min. Recycled composite particles could be used again.     

Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>/TiC composites prepared by PDS

Synthesis of composite materials with improved mechanical properties is considered. Pulse discharge sintering (PDS) technique was utilized for consolidation and synthesis of double phase Ti₃SiC₂/TiC composites from the initial powders TiH₂/SiC/TiC. Scanning electron microscopy with energy-dispersive spectrometry (SEM with EDS) and X-ray diffractometry (XRD) were exploited for the analysis of the microstructure and composition of the sintered specimens. Mechanical tests showed high bending and compression strength and low Vickers hardness of Ti₃SiC₂-rich specimens. The reasons of this behaviour are in the features of the textured microstructure of Ti₃SiC₂ phase.     

Photocatalytic degradation of pendimethalin over Cu2O/SnO2/graphene and SnO2/graphene nanocomposite photocatalysts under visible light irradiation

The Cu₂O/SnO₂/graphene (CSG) and SnO₂/graphene (SG) nanocomposite photocatalysts were prepared by simple sol-gel growth method, and characterized by Fourier transform infrared spectra (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) measurements, respectively. The photocatalytic efficiency of catalysts were evaluated by degradation of pendimethalin under visible light irradiation (λ > 420 nm), which conformed that CSG and SG exhibited better photocatalytic activity than SnO₂ or graphene alone. An effort has been made to correlate the photoelectro-chemical behavior of these samples to the rate of photocatalytic degradation of pendimethalin.     

Fabrication of Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript>-AgBr-PTh composite loaded on Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript> with enhanced visible-light photocatalytic activity

A novel Ag₃PO₄-AgBr-PTh composite loaded on Na₂SiO₃ was synthesized for enhanced visible-light photocatalytic activity. The photocatalytic activity of the samples was evaluated by photodegrading rhodamine B (RhB) under visible light irradiation. The main reactive species and possible photocatalytic mechanism were also discussed. As a result, the Ag₃PO₄-AgBr-PTh composite loaded on Na₂SiO₃ exhibited enhanced photocatalytic activity for RhB compared with Ag₃PO₄ under visible-light irradiation. Additionally, it was demonstrated that the hole (h⁺) and superoxide radical (?O ₂ ^? ) were the major reactive species involving in the RhB degradation. PTh played vital role for the enhanced photocatalytic activity of Ag₃PO₄-AgBr-PTh-Na₂SiO₃ composite, which offered an electron transfer expressway and accelerated the transfer of the electrons from the CB of AgBr into Ag₃PO₄. This work could provide a new perspective for the synthesis of Ag₃PO₄-based composites and the improvement of photocatalytic activity of Ag₃PO₄.