Nanojunction System Research Articles

Rational design of a novel quaternary ZnO@ZnS/Ag@Ag2S nanojunction system for enhanced photocatalytic H2 production

A novel ZnO@ZnS/Ag@Ag2S quaternary nanojunction photocatalyst has been designed for efficient solar water splitting.

Bi2WO6/TiO2/Pt nanojunction system: A UV–vis light responsive photocatalyst with high photocatalytic performance

Abstract Aiming at enhancing photocatalysis through increasing light harvesting and improving quantum efficiency, a new Bi 2 WO 6 /TiO 2 /Pt composite photocatalyst was fabricated. Morphology characterization demonstrated that anatase TiO 2 and metal Pt were orderly incorporated with Bi 2 WO 6 nanosheets. UV–vis diffuse reflectance spectra and photocurrent measurements displayed that Bi 2 WO 6 /TiO 2 /Pt composite catalyst exhibited enlarged photoresponse range and improved photocurrent density. In the photodegradation experiments of Rhodamine B and bisphenol A under simulated sunlight (320 nm λ 2 WO 6 /TiO 2 /Pt composite presented the highest photocatalytic activity compared to the photocatalysts containing one-component (TiO 2 , Bi 2 WO 6 ) or two-component (TiO 2 /Pt, Bi 2 WO 6 /Pt). The enhanced photocatalysis benefited from the increased light harvesting owing to the excitation of both TiO 2 and Bi 2 WO 6 and the high quantum efficiency due to the heterojunction between Bi 2 WO 6 and TiO 2 and the Schottky junction between TiO 2 and Pt. The photocatalyitc mechanism analysis revealed that the superoxide radical originated from the electroreduction of dissolved oxygen with photogenerated electrons was the primary oxidant in Bi 2 WO 6 /TiO 2 /Pt photocatalysis, and the hydroxyl radical derived from the reaction of holes and H 2 O was also responsible for pollutant degradation.

Spin wave ballistic transport properties of [formula omitted] nanojunctions between Co leads

The spin wave (SW) ballistic transport properties are investigated for nanojunction systems composed of thin [Co1−cGdc]ℓ′[Co]ℓ[Co1−cGdc]ℓ′ layered nanostructures between cobalt leads. The nanojunction is considered as a homogeneous random alloy of concentrations c on an hcp crystal lattice. ℓ corresponds to the numbers of the hcp (0001) atomic planes per given layer. The phase field matching theory (PFMT) is used to investigate the spin dynamics of the nanojunction system in the virtual crystal approximation (VCA), valid in particular for submicroscopic SW wavelengths. The model calculations yield the spin modes localized on the nanojunction, normal to its plane, in their propagating and resonant forms. The eigenvectors of these modes are calculated for certain cases to illustrate the spin precession configurations on the nanojunction. The VCA-PFMT approach yields a general model, and is used to calculate the SW ballistic scattering and transport across the nanojunction for spin waves incident from the Co leads onto the nanojunction. The results demonstrate resonance Fano assisted maxima in the SW transmission spectra due to interactions between incident lead spin waves and localized spin resonances on the nanojunction. It is shown that these maxima change with nanojunction thickness and alloy concentration. The spectral transmission results for low frequency SWs are of specific interest, in particular they correspond to submicroscopic wavelengths which present an interest for current research of magnonic devices.

ZnWO4 nanorods decorated with Ag/AgBr nanoparticles as highly efficient visible-light-responsive photocatalyst for dye AR18 photodegradation

A novel Ag-AgBr/ZnWO4 nanorod heterostructure composite was prepared via a facile deposition–precipitation method with ZnWO4 nanorods as the substrate, and characterized by XRD, SEM-EDX, TEM, XPS, and DRS to confirm its structure, morphology, composition, and optical property. The composite was used as a photocatalyst to destroy azo dye Acid Red 18 (AR18) under visible light irradiation. The effects of catalyst composition, solution pH, catalyst loading, and initial dye concentration on photocatalytic degradation rate and efficiency were examined. It was revealed that the photocatalytic activity of Ag-AgBr/ZnWO4 nanojunction system was higher than that of the single ZnWO4 or Ag-AgBr for AR18 degradation under visible light irradiation. The optimal content of Ag-AgBr in Ag-AgBr/ZnWO4 composite was 0.58:1 of Ag/W molar ratio using in the catalyst preparation. Acid pH and decreasing dye initial concentration were favorable to AR18 photodegradation, but the catalyst loading had an optimal value. The catalyst was stable and recyclable, after five successive cycles the photoactivity was fully maintained and the XRD patterns of AgBr displayed no evident change. Photoluminescence spectra revealed the enhanced photocatalytic activity and stability were closely related to the efficient separation of photogenerated carriers in Ag-AgBr/ZnWO4 nanojunction system. Superoxide radicals and holes were found to be main active species for AR18 photodegradation. Finally, the possible mechanism for AR18 degradation over Ag-AgBr/ZnWO4 nanorods under visible light irradiation was proposed as well.

Facile fabrication of highly efficient, reusable heterostructured Ag–ZnO–CdO and its twin applications of dye degradation under natural sunlight and self-cleaning

A metal doped coupled semiconductor oxide, Ag–ZnO–CdO was fabricated by a simple co-precipitation method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), elemental mapping, high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area measurement, UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). XRD and EDS reveal the presence of CdO and metallic Ag in the catalyst. FESEM shows a mixture of hexagonal nanosheets, nanoclusters and nanoparticles with a large number of cavities. HR-SEM and TEM images of the catalyst show that ZnO particles have pentagonal or hexagonal plate-like structure. Cadmium oxide and silver clusters are formed on the clear smooth surface of ZnO. Ag–ZnO–CdO has increased absorption in the UV and Visible region when compared to ZnO. This three component nanojunction system exhibited enhanced photocatalytic activity for the degradation of acid black 1 (AB 1) and acid violet 7 (AV 7) under sunlight far exceeding those of the single and two component systems. Ag–ZnO–CdO was found to be stable and reusable without appreciable loss of catalytic activity up to five runs. This metal doped coupled oxide shows increased hydrophobicity, when compared to CdO or ZnO. Our results provide new insights of the performance of a solar active photocatalyst with self-cleaning properties.

Surface decoration of Bi2WO6 superstructures with Bi2O3 nanoparticles: an efficient method to improve visible-light-driven photocatalytic activity

Bi2WO6 superstructures have attracted extensive attention in the photocatalytic field, but their practical application has been limited by drawbacks such as an unsatisfactory visible-light photoresponse range. To address these drawbacks, we have developed a simple strategy by surface decoration of Bi2WO6 superstructures with Bi2O3 nanoparticles through a dip-coating–anneal method. The characterization results confirm robust construction of nanojunctions in the Bi2WO6 superstructure decorated with Bi2O3 nanoparticles (abbreviated as: Bi2WO6 SS–D–Bi2O3 NP) nanojunction system. Interestingly, this Bi2WO6 SS–D–Bi2O3 NP nanojunction system exhibits a broad-spectrum photoabsorption from the UV to visible-light region with an edge at ca. 650 nm, indicating a red shift of photoabsorption range compared with that of Bi2WO6 superstructures (edge at ca. 450 nm), nanoscale Bi2O3 powder (ca. 470 nm) and Bi2O3–Bi2WO6 composite microspheres (ca. 440 nm) prepared through a one-step hydrothermal route. Furthermore, by using Bi2WO6 SS–D–Bi2O3 NP as visible-light-driven (VLD) photocatalyst, the photodegradation efficiency of Rhodamine B (RhB) reaches 86% which is about 2.7 times as that (32.3%) by Bi2WO6 SS and 1.3 times that (64.4%) by Bi2O3–Bi2WO6 composite microspheres, in 20 min of reaction. Besides that, this nanojunction can still efficiently degrade the colorless pollutant parachlorophenol. In particular, the photocatalytic activity of the nanojunction is superior to the sum of the activities of two individual photocatalysts with the same weight of components (Bi2WO6 SS and Bi2O3 NP). Based on the above results and energy band diagram, two possible reasons have been proposed for the higher photocatalytic activity of Bi2WO6 SS–D–Bi2O3 NP nanojunction: (1) substantial broadening of the photoabsorption range and (2) efficient separation of photogenerated electron–hole pairs. This work provides some insight into the design of novel and efficient nanojunction photocatalysts with broadened photoabsorption range for enhancing VLD photocatalytic activity.

Hierarchical Composite of Ag/AgBr Nanoparticles Supported on Bi2MoO6 Hollow Spheres for Enhanced Visible‐Light Photocatalytic Performance

AbstractThe fabrication of multicomponent composite systems may provide benefits in terms of charge separation and the retardation of charge pair recombination. For this purpose, a hierarchical Ag/AgBr/Bi2MoO6 composite was fabricated by using prepared hierarchical floriated Bi2MoO6 hollow spheres as a supporting material. The interleaved nanoflakes assembled in the hierarchical floriated Bi2MoO6 hollow spheres contributed to the stable deposition of Ag/AgBr nanoparticles and the formation of effective nanojunctions, which led to the low recombination rates of the photoinduced electron–hole pairs. The presence of double visible‐light‐active components in the Ag/AgBr/Bi2MoO6 nanojunction system further broadened the visible‐light photoresponse range. As a result, the hierarchical Ag/AgBr/Bi2MoO6 composite exhibited a higher photocatalytic activity than both photocatalysts containing single visible‐light‐active components and crushed Ag/AgBr/Bi2MoO6 nanoparticles for the degradation of alizarin red S (ARS) and phenol. X‐ray photoelectron spectroscopy (XPS) analyses indicated that both AgBr and Ag0 components coexist in the system, and the as‐prepared composite is relatively stable. The improved photoinduced charge‐transfer properties of the hierarchical Ag/AgBr/Bi2MoO6 composite were investigated by using the transient photovoltage (TPV) technique.

Enhanced visible light photocatalytic activity of novel Pt/C-doped TiO2/PtCl4 three-component nanojunction system for degradation of toluene in air

C-doped TiO2 nanoparticles prepared by partial oxidation of TiC were modified with Pt species by impregnation–calcination method in order to enhance the visible light photocatalytic activity. The physicochemical properties of as-prepared samples were characterized by various techniques in detail. The results indicated that a novel Pt/C-doped TiO2/PtCl4 three-component nanojunction system was formed, where C-doped TiO2 and PtCl4 behaved as two visible light responsive components, and Pt metal as electron-transfer system. The three-component nanojunctioned photocatalyst system exhibited six times higher visible light activity than that of the pristine C-doped TiO2 in degradation of toluene in air. The dramatically enhanced activity can be attributed to the increased utilization of visible light, the enhanced charge carrier separation and transfer process. Further more, the band structure and photocatalysis mechanism over the three-component nanojunction system was proposed and discussed. This work may provide new insights into the design of novel multi-component photocatalyst system with efficient visible light activity.

Effect of Noble Metal in CdS/M/TiO2 for Photocatalytic Degradation of Methylene Blue under Visible Light

ABSTRACT The CdS/M/TiO2 (M = Ag, Ru, Au, Pd, and Pt) three-component nanojunction systems were constructed using a two-step photodeposition method, and evaluated for their photocatalytic activities through the degradation of methylene blue in aqueous solution under visible light irradiation. The authors found that the photocatalytic activity of CdS/M/TiO2 (M = Ag, Ru, Au, Pd, Pt) three-component nanojunctions was superior to that of CdS/TiO2 two-component system. Moreover, the photocatalytic activity of the three-component nanojunction system was found to be dependent significantly on the type of the noble metals. The results can be explained by the influence of charge transfer on the basis of the work functions of different noble metals.

Effective Photocatalytic Disinfection of E. coli K-12 Using AgBr−Ag−Bi2WO6 Nanojunction System Irradiated by Visible Light: The Role of Diffusing Hydroxyl Radicals

Urgent development of effective and low-cost disinfecting technologies is needed to address the problems caused by an outbreak of harmful microorganisms. In this work, we report an effective photocatalytic disinfection of E. coli K-12 by using a AgBr-Ag-Bi(2)WO(6) nanojunction system as a catalyst under visible light (lambda >or= 400 nm) irradiation. The visible-light-driven (VLD) AgBr-Ag-Bi(2)WO(6) nanojunction could completely inactivate 5 x 10(7) cfu mL(-1) E. coli K-12 within 15 min, which was superior to other VLD photocatalysts such as Bi(2)WO(6) superstructure, Ag-Bi(2)WO(6) and AgBr-Ag-TiO(2) composite. Moreover, the photochemical mechanism of bactericidal action for the AgBr-Ag-Bi(2)WO(6) nanojunction was investigated by using different scavengers. It was found that the diffusing hydroxyl radicals generated both by the oxidative pathway and the reductive pathway play an important role in the photocatalytic disinfection. Moreover, direct contact between the AgBr-Ag-Bi(2)WO(6) nanojunction and bacterial cells was not necessary for the photocatalytic disinfection of E. coli K-12. Finally, the photocatalytic destruction of the bacterial cells was directly observed by TEM images and further confirmed by the determination of potassium ion (K(+)) leakage from the killed bacteria. This work provides a potential effective VLD photocatalyst to disinfect the bacterial cells, even to destruct the biofilm that can provide shelter and substratum for microorganisms and resist to disinfection.

AgBr-Ag-Bi 2WO 6 nanojunction system: A novel and efficient photocatalyst with double visible-light active components

A semiconductor-based photocatalyst system, consisting of two visible-light-driven (VLD) components and one electron-transfer system, has a great potential to efficiently photocatalytically degrade pollutants. In this paper, we have reported a simple strategy for constructing an all-solid-state AgBr-Ag-Bi 2WO 6 nanojunction by a facile deposition-precipitation method with Bi 2WO 6 as the substrate. Two visible-light active components (AgBr, Bi 2WO 6) and the electron-transfer system (Ag) are spatially fixed in this nanojunction system. Due to the presence of double visible-light active components, such a AgBr-Ag-Bi 2WO 6 nanojunction system has the broadened visible-light photo-response range, and it also exhibits higher photocatalytic activity than photocatalysts containing single visible-light active component, such as Bi 2WO 6, Ag-Bi 2WO 6 and AgBr-Ag-TiO 2 composite, for the degradation of the azo dye, Procion Red MX-5B and colorless pollutant pentachlorophenol. In addition, the initial dye concentration and pH value could greatly affect its photocatalytic activity, and the recycling experiments confirm that it is essentially stable during the photocatalytic process. In particular, the photocatalytic activity of AgBr-Ag-Bi 2WO 6 nanojunction is superior to the sum of the activities of two individual photocatalysts (AgBr-Ag-TiO 2 and Bi 2WO 6) that contain the same weight of AgBr or Bi 2WO 6, indicating the presence of a synergic effect between two visible-light active components in AgBr-Ag-Bi 2WO 6 nanojunction. On the basis of the photocatalytic results and energy band diagram, the photocatalytic process that may have occurred on the AgBr-Ag-Bi 2WO 6 nanojunction system is proposed; the vectorial electron transfer driven by the two-step excitation of both VLD components (AgBr and Bi 2WO 6) contributes to its high photocatalytic activity. Therefore, this work provides some insight into the design of novel and efficient photocatalysts with multi-visible-light active components for enhancing VLD photocatalytic activity.

Construction of Z-scheme type CdS–Au–TiO2 hollow nanorod arrays with enhanced photocatalytic activity

The Z-scheme type CdS–Au–TiO2 hollow nanorod arrays have been constructed on glass substrates by following these simple steps: firstly, highly ordered TiO2 hollow nanorod arrays (THNAs) were synthesized by liquid phase deposition (LPD) using ZnO nanorod arrays as templates; then both Au core and CdS shell nanoparticles were achieved on the THNAs by in situ photodeposition. The prepared three-component films were characterized by field-emission scanning electron microscopy (FSEM), high-resolution transmission electron microscope (HRTEM), Raman scattering and ultraviolet–visible absorption spectrum. The results showed that Au–CdS core–shell nanoparticles were well dispersed on wall of anatase THNAs from top to bottom. The three-component nanojunction system was evaluated for their photocatalytic activity through the degradation of methylene blue (MB) in aqueous solution. It was found that the CdS–Au–TiO2 three-component hollow nanorod arrays exhibited significantly enhanced photocatalytic activity compared with single (THNAs) and two components (Au-THNAs or CdS-THNAs) systems. Reasons for this enhanced photocatalytic activity were revealed by photoluminescence (PL) results of our samples.

All-solid-state Z-scheme in CdS–Au–TiO2 three-component nanojunction system

Natural photosynthesis, which achieves efficient solar energy conversion through the combined actions of many types of molecules ingeniously arranged in a nanospace, highlights the importance of a technique for site-selective coupling of different materials to realize artificial high-efficiency devices. In view of increasingly serious energy and environmental problems, semiconductor-based artificial photosynthetic systems consisting of isolated photochemical system 1 (PS1), PS2 and the electron-transfer system have recently been developed. However, the direct coupling of the components is crucial for retarding back reactions to increase the reaction efficiency. Here, we report a simple technique for forming an anisotropic CdS-Au-TiO2 nanojunction, in which PS1(CdS), PS2(TiO2) and the electron-transfer system (Au) are spatially fixed. This three-component system exhibits a high photocatalytic activity, far exceeding those of the single- and two-component systems, as a result of vectorial electron transfer driven by the two-step excitation of TiO2 and CdS.