Hetero Nanostructures Research Articles

Enhanced sensing performance of TiO2/Ag2V4O11 nanoheterostructures to ethanol gas

High performance sensor for gas species detection is a significant task not only for fundamental sciences but also for industries. In this study, a new type of ethanol gas sensor based on one-dimensional TiO2/Ag2V4O11 nanoheterostructures (NHSs) is reported. The sensitivity of the NHSs to ethanol is much higher than those of pure TiO2 and Ag2V4O11. By regulating the content of TiO2 and Ag2V4O11, it is found that TiO2/Ag2V4O11 NHSs with T/A (TiO2/Ag2V4O11) molar ratio of 2:1 exhibit excellent sensing performances to ethanol. The sensitivity at 300 °C to 100 ppm ethanol is 25.6, about 6 times and 3 times higher than TiO2 and Ag2V4O11, respectively, and the sensor also possesses good selectivity to ethanol gas. Specifically, the NHSs exhibit efficient sensitivity (4.2–100 ppm ethanol gas) and excellent stability at room temperature. High-depth mechanism study reveals that besides the contribution of the fast electron transfer properties of the Ag2V4O11, the formation of nanoheterojunctions and the rich surface interfaces rooting from the hybridization of nanoparticles (NPs) and nanowires (NWs) can significantly enhance the sensing performance of the NHSs.

Development of 2D nano heterostructures based on g-C[formula omitted]N[formula omitted] and flower shaped MoS[formula omitted] as electrode in symmetric supercapacitor device

g-C3N4 with plenty of lone pair electrons on the two dimensional (2D) lamellar structures have attracted remarkable attention as an electrical double layer (EDLC) supercapacitor electrodes due to their surface polarity and wettability with electrolyte molecule. However, the agglomeration of the exfoliated g-C3N4 sheets during the electrochemical process curtails their accessible electroactive surface area so that specific capacitance get reduces considerably. Here in for the first time in the literature, we report a 2D nanohybrid structure of g-C3N4/MoS2 having attractive electrochemical properties than bare g-C3N4 and MoS2, owing to the wonderful flower shaped morphology of the synthesized pseudocapacitive semiconducting MoS2 phase which acts as spacers in between the layers of g-C3N4. The specific capacitance of bare g-C3N4 and MoS2is 10 Fg−1 and 14 Fg−1 respectively however hybrid material g-C3N4/MoS2 exhibits a specific capacitance value of 45.5 Fg−1. This remarkable hike in specific capacitance can be attributed to the synergistic effect of both faradaic and non-faradaic process of energy storage.

Nanoheterostructures (NHS) and Their Applications in Nanomedicine: Focusing on In Vivo Studies.

Inorganic nanoparticles have great potential for application in many fields, including nanomedicine. Within this class of materials, inorganic nanoheterostructures (NHS) look particularly promising as they can be formulated as the combination of different domains; this can lead to nanosystems with different functional properties, which, therefore, can perform different functions at the same time. This review reports on the latest development in the synthesis of advanced NHS for biomedicine and on the tests of their functional properties in in vivo studies. The literature discussed here focuses on the diagnostic and therapeutic applications with special emphasis on cancer. Considering the diagnostics, a description of the NHS for cancer imaging and multimodal imaging is reported; more specifically, NHS for magnetic resonance, computed tomography and luminescence imaging are considered. As for the therapeutics, NHS employed in magnetic hyperthermia or photothermal therapies are reported. Examples of NHS for cancer theranostics are also presented, emphasizing their dual usability in vivo, as imaging and therapeutic tools. Overall, NHS show a great potential for biomedicine application; further studies, however, are necessary regarding the safety associated to their use.

Rapid microwave-assisted synthesis of gold loaded hydroxyapatite collagen nano-bio materials for drug delivery and tissue engineering application

A rapid microwave assisted facile synthetic technique was adopted to load gold nanoparticles (Au) on hydroxyapatite (HAp) surface. HAp nanoparticles were primarily synthesized by wet precipitation technique and further used for gold loading and successive collagen coating for biomedical applications. The microwave-assisted controlled synthesis technique with three heating cycles allows the very fast growing of Au seeds over HAp facets. Different sophisticated analytical techniques and spectroscopic characterization were employed to confirm the structural, chemical, and morphological features. The synthesized different concentration “Au” loaded hetero nanostructures coated with collagen (Au–HAp–Col) optimized for drug (Doxorubicin: DOX) loading and releasing purposes for biomedical applications. The maximum drug-loading efficiency of ~58.22% and a pH responsive releasing of ~53% (at pH 4.5) was obtained for 0.1 wt% Au–HAp–Col nanoparticles. To study the cytotoxic effects from the hetero nanostructures, MG-63 osteoblast-like cells were exposed to different concentration ranges on Au–HAp, Au–HAp–Col, and DOX loaded Au–HAp–Col nanoparticles. The non-toxic and bioactive properties of the synthesized nanoparticle-fabricated scaffold promotes cellular attachment, growth, and proliferation. These results indicated that optimized Au–HAp–Col nanoparticles may be promising drug delivery and scaffold materials for multifunctional biomedical applications.

Biexciton states in nanoheterostructures of dielectric quantum dots

It has been found that the formation of a biexciton in a nanoheterostructures (NHS) made up of aluminum oxide quantum dots (QD) synthesized in a dielectric matrix is of threshold character and can occur in a nanosystem where the distance D between the surfaces of QD is given by the condition Dc(1)≤D≤Dc(2). We have shown that in such a NHS acting as “exciton molecules” (biexcitons consisting of spatially separated electrons and holes) are the quantum dots of aluminum oxide with excitons localizing over their surfaces. The position of the biexciton state energy band depends both on the mean radius of the quantum dots, and the distance between their surfaces, which enables one to purposefully control it by varying these parameters of the nanostructure.

Fabrication of One Dimensional MnO2‐TiO2 Nano‐Heterostructures for Enhanced Hole Mediated Oxidation of As(III) in Potable Water

AbstractThe conversion of the toxic As(III) from drinking water is a challenging task and it becomes more difficult when As(III) is present in low concentrations (50–200 ppb). Considering this, the present article demonstrates an easy and cost effective wet chemical synthesis of MnO2−TiO2 nanoheterostructures (NHs) and its application as the electrode for the oxidation and subsequent conversion of the comparatively low concentration of As(III) from drinking water. The MnO2−TiO2 NHs have been employed as the anode to enhance the hole mediated fast and effective oxidation and subsequent conversion of As(III) from water under the applied bias of 1 V vs. Ag/AgCl at room temperature (30 °C) with the water pH ∼7 in a three‐electrode electrochemical cell. The nano‐interfacial electronic band engineering at MnO2‐TiO2 heterointerface is found to be very effective to boost the hole mediated oxidation of As(III). The same NHs also exhibit enhanced photo‐electrochemical oxidation of As(III) under the illumination of low‐intensity white light. The photo‐oxidation in assistance with the applied bias has considerably improved the overall conversion efficiency of As(III) to As(V) in water with a treatment time of just five minutes. The study shows that the material and the method described here is an easy and effective strategy for the enhanced preoxidation and subsequent elimination of As(III) from the drinking water with a low arsenic concentration in the typical weather of Indian subcontinent.

Cation Exchange-Mediated Synthesis of Library of Plasmomagnetic Nanoheterostructures: Transformation of 2-Dimensional-Shaped Fe7S8 Nanoplates to Cu–Fe–S-Based Ternary Compound

Cation exchange mediated synthesis of nanoheterostructures (NHSs), core–shell structure or segmented nanostructures are gaining high interest in nanoscience research as the process gives a wide win...

Template-Guided Programmable Janus Heteronanostructure Arrays for Efficient Plasmonic Photocatalysis.

Janus heteronanostructures (HNs), as an important class of anisotropic nanomaterials, could facilitate synergistic coupling of diverse functions inherited by their comprised nanocomponents. Nowadays, synthesizing deterministically targeted Janus HNs remains a challenge. Here, a general yet scalable technique is utilized to fabricate an array of programmable Janus HNs based on anodic aluminum oxide binary-pore templates. By designing and employing an overetching process to partially expose four-edges of one set of nanocomponents in a binary-pore template, selective deposition and interfacing of the other set of nanocomponents is successfully achieved along the exposed four-edges to form a densely packed array of Janus HNs on a large scale. In combination with an upgraded two-step anodization, the synthesis provides high degrees of freedom for both nanocomponents of the Janus HNs, including morphologies, compositions, dimensions, and interfacial junctions. Arrays of TiO2-Au and TiO2/Pt NPs-Au Janus HNs are designed, fabricated, and demonstrated about 2.2 times photocurrent density and 4.6 times H2 evolution rate of that obtained from their TiO2 counterparts. The enhancement was mainly determined as a result of localized surface plasmon resonance induced direct hot electron injection and strong plasmon resonance energy transfer near the interfaces of TiO2 nanotubes and Au nanorods. This study may represent a promising step forward to pursue customized Janus HNs, leading to novel physicochemical effects and device applications.

CdS sensitized TiO[formula omitted] nano heterostructures as sunlight driven photocatalyst

Sunlight harvesting nano heterostructure materials with excellent photocatalytic activity has received considerable attention in recent years. Here we meticulously investigated the effect of CdS nano crystal loading on the light absorption capacity and the photocatalytic activity of TiO2 nanomaterials by assembling TiO2-CdS heterostructures. A distinct heterostructure was established in the presently reported hybrid system with 10 wt% CdS incorporation into TiO2 and the photocatalytic study showed that TiO2-CdS10 has 3.5 times higher catalytic activity than bare TiO2. This superior photocatalytic performance is attributed to the excellent light absorption, high surface area and the slow rate of recombination of photogenerated charge carriers of TiO2-CdS10 hetero structures. A mechanism was also proposed for the CdS sensitized sunlight driven photocatalytic degradation of methyl orange dye in presence of CdS–TiO2 nano heterostructure.

Microstructure evolution determined by the crystalline phases competition in self-assembled WO3-BiVO4 hetero nanostructures

A series of self-assembled WO3–BiVO4 nanostructured thin films were grown on the (001) yttria-stabilized zirconia (YSZ) substrate at the substrate temperatures of 400 °C, 500 °C, 550 °C, 600 °C, 650 °C and 700 °C by a pulsed laser deposition method. The microstructures including crystalline phases, epitaxial relationships, surface morphologies and interface structures were investigated by a combination of x-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The sample grown at 400 °C was amorphous due to the low driving forces for nucleation and diffusion. For the samples made at 500 °C, 550 °C and 600 °C, the monoclinic BiVO4 matrix epitaxially grew on YSZ, forming the matrix, where the WO3 nanopillars were embedded in with a specific orientation relationship among BiVO4, WO3 and YSZ. However, in thin films deposited at 650 °C and 700 °C, the WO3 grains randomly grew on the YSZ substrate, which dominated the microstructures of the resultant thin films. Quantitative analyses of the microstructures revealed that the lateral grain sizes of BiVO4 and WO3 increased and the volume fraction of BiVO4 in the thin films decreased with the increase of the deposition temperature. A three-regime growth mechanism of the WO3–BiVO4 composite thin film was proposed based on the growth dynamics determined by the competition between BiVO4 and WO3.

Recent Advances in Colloidal IV–VI Core/Shell Heterostructured Nanocrystals

Colloidal nanocrystals (NCs) have been at the forefront of scientific research and technological applications since their emergence in the 1980s. The limitations of single component NCs and the growing demand for wide electronic tunability switched the attention to core/shell nanoheterostructures (NHs). The NHs consist of at least two semiconductor compounds, exhibiting improved surface passivation of the cores and surplus electronic tunability beyond that gained by size confinement. Several synthetic approaches have been developed through the years for the formation of core/shell structures. This article discusses two recent synthetic approaches, cation exchange and the Kirkendall effect, for the preparation of core/shell NHs, focusing on IV–VI semiconductor compounds. Both cation exchange and the Kirkendall effect are postsynthetic routes which offer an indirect way to synthesize complex core/shell NHs, that are difficult to synthesize by other methods. Overall, the produced core/shell NCs show enhanced...

Yolk Type Asymmetric Ag–Cu2O Hybrid Nanoparticles on Graphene Substrate as Efficient Electrode Material for Hybrid Supercapacitors

Abstract Yolk type asymmetric Ag–Cu2O hybrid nanostructures are in situ synthesized on reduced graphene oxide (RGO) sheets for the first time under one pot hydrothermal mild reaction condition. The co-reduction method provides a facile and straight forward approach to metal/metal oxide hybrid NPs growth on graphene nanosheets and the nano heterostructures are found to be homogeneously distributed over graphene sheets with unique yolk type morphology forming Ag–Cu2O/RGO nanocomposite (NC). The supercapacitor performances of the NCs are evaluated in aqueous 6.0 M KOH by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD) in two electrode cell assembly using Ag-Cu2O/RGO as electrode material. The ternary NCs exhibit excellent hybrid capacitance behavior having ~812 Fg−1 specific capacitance value with high energy density 27.2 Wh kg−1 and power density 285 W kg−1, respectively, at current density of 0.5 Ag−1 that suits for potential applications in hybrid capacitor. The high capacitance property of ternary NCs without use of binder can be attributed to excellent electronic/ionic conductivity due to presence of highly conductive graphene sheets in addition of noble Ag metal and unique yolk type morphology which causes faster electronic conduction among different components of the electrode material.

Degradation of organic dyes using spray deposited nanocrystalline stratified WO3/TiO2 photoelectrodes under sunlight illumination

The need to utilize TiO2 based metal oxide hetero nanostructures for the degradation of environmental pollutants like Rhodamine B and reactive red 152 from the wastewater using stratified WO3/TiO2 catalyst under sunlight illumination. WO3, TiO2 and stratified WO3/TiO2 catalysts were prepared by a spray pyrolysis method. It was found that the stratified WO3/TiO2 heterostructure has high crystallinity, no mixed phase formation occurs, strong optical absorption in the visible region of the solar spectrum, and large surface area. The photocatalytic activity was tested for degradation of Rhodamine B (Rh B) and reactive red 152 in an aqueous medium. TiO2 layer in stratified WO3/TiO2 catalyst helps to extend its absorption spectrum in the solar light region. Rh B and Reactive red 152is eliminated up to 98 and 94% within the 30 and 40 min respectively at optimum experimental condition by stratified WO3/TiO2. Moreover, stratified WO3/TiO2 photoelectrode has good stability and reusability than individual TiO2 and WO3 thin film in the degradation of Rh B and reactive red 152. The photoelectrocatalytic experimental results indicate that stratified WO3/TiO2 photoelectrode is a promising material for dye removal.

Role of indium tin oxide electrode on the microstructure of self-assembled WO3-BiVO4 hetero nanostructures

Self-assembled WO3-BiVO4 nanostructured thin films were grown on a (001) yttrium stabilized zirconia (YSZ) substrate by the pulsed laser deposition method with and without the indium tin oxide (ITO) bottom electrode. Their microstructures including surface morphologies, crystalline phases, epitaxial relationships, interface structures, and composition distributions were investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray energy dispersive spectroscopy. In both samples, WO3 formed nanopillars embedded into the monoclinic BiVO4 matrix with specific orientation relationships. In the sample with the ITO bottom electrode, an atomically sharp BiVO4/ITO interface was formed and the orthorhombic WO3 nanopillars were grown on a relaxed BiVO4 buffer layer with a mixed orthorhombic and hexagonal WO3 transition layer. In contrast, a thin amorphous layer appears at the interfaces between the thin film and the YSZ substrate in the sample without the ITO electrode. In addition, orthorhombic Bi2WO6 lamellar nanopillars were formed between WO3 and BiVO4 due to interdiffusion. Such a WO3-Bi2WO6-BiVO4 double heterojunction photoanode may promote the photo-generated charge separation and further improve the photoelectrochemical water splitting properties.

Raman and photoluminescence spectra of ZnTe/CdSe and ZnTe/CdTe tetrapod shaped nano-hetero structures

In the present paper we report the Raman and photoluminescence characterization of two nano-hetero-structures of II-VI semiconductors, tetrapod shaped. The examined samples were constituted of a ZnTe core and either CdSe or CdTe arms. The main contributions to the Raman spectra were assigned to phonons from the arms of the structures, but the weak contribution from the ZnTe core was identified from the separate measurement of spectra of the seeds used for growing the arms. The simultaneously acquired photoluminescence spectra allowed identifying an intense band characteristic of a Type II band alignment at 920 nm for the ZnTe/CdSe nanostructures.

Fabrication of CdS-Ag3PO4 heteronanostructures for improved visible photocatalytic hydrogen evolution

Solar-driven photocatalytic water splitting is an ideal solution for clean and renewable fuels. The development of sustainable, low-cost, and efficient visible-light photocatalyst continues to be a serious challenge in this field. In this article, CdS−Ag3PO4 heteronanostructures (HNSs) were fabricated for the first time by a solvothermal and subsequent simple chemical reaction method. The as synthesized heterostructured photocatalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–visible spectroscopy. Their photocatalytic hydrogen production rate was evaluated by using an aqueous solution containing 10% methanol under visible light (λ > 420 nm). The resultant CdS-Ag3PO4 HNSs exhibit a higher photocatalytic hydrogen evolution rate than that of CdS NWs under visible light irradiation. The apparent H2 generation rate of CdS-Ag3PO4 HNSs is ∼2 times higher than that of bare CdS nanowires (NWs). The results show that the specially formed heterojunctions between CdS NWs and Ag3PO4 NPs favor the separation of photogenerated electron-hole pairs, which in turn produced the improved photocatalytic hydrogen evolution rate.

Microstructure evolution with composition ratio in self-assembled WO3–BiVO4 hetero nanostructures for water splitting

Abstract

TiO2 nanofibers coated with rGO and Ag2O for promoting visible light photocatalytic performance

Due to the increase in environmental pollution, highly efficient photocatalysts with enhanced visible light photocatalytic activity have attracted considerable attention. In this work, TiO2/reduced graphene oxide (rGO)/Ag2O nanoheterostructures (NHs) based photocatalysts are successfully synthesized and a markedly higher visible light photocatalytic activity is achieved, of which at least 96% of Rhodamine B (RhB) molecules are decomposed by the TiO2/rGO/Ag2O NHs after 120 min visible light irradiation, but only 30% of RhB molecules are decomposed by pure TiO2 nanofibers (NFs). Furthermore, the influence of rGO volume ratio in TiO2/rGO/Ag2O NHs photocatalysts on visible light photocatalysis is studied, and the result shows that the sample with 5 vol% rGO exhibits the highest visible light photocatalytic activity. The much enhanced visible light photocatalytic performance of the ternary TiO2/rGO/Ag2O NHs can be ascribed to the intense visible light absorption of Ag2O, the excellent electron conductivity of 2D rGO and the matched energy level of TiO2, Ag2O, and rGO, for efficient boost of the photogenerated charge carriers transfer and separation at the interface of hierarchical TiO2/rGO/Ag2O NHs.

Biexciton in nanoheterostructures of dielectric quantum dots

It has been found that the formation of a biexciton in a nanoheterostructures (NHS) made up of aluminum oxide quantum dots (QDs) synthesized in a dielectric matrix is of threshold character and can occur in a nanosystem, where the distance D between the surfaces of QD is given by the condition Dc(1)≤D≤Dc(2). We have shown that with such an NHS acting as “exciton molecules” (biexcitons consisting of spatially separated electrons and holes) are the QDs of aluminum oxide with excitons localizing over their surfaces. The position of the biexciton state energy band depends both on the mean radius of the QDs, and the distance between their surfaces, which enables one to purposefully control it by varying these parameters of the nanostructure.

Unique Nano-Architecture Electrodes for High-Performance Energy Storage

Unique core/shell type nano-architecture electrodes based on of transition metal/transition metal oxides are designed and fabricated by the simple electrochemical and chemical routes. The high-performance pseudo-capacitors based on the metal core and NiO, Co3O4, MnO2, mixed transition metal oxides and surface modified transition metal oxides shell nano-heterostructures electrode is demonstrated. Various nano-architectures based on those provide enhanced effective surface area, better electronic charge transport and high specific capacitance. For example, a unique 1D Co-Ni/Co3O4-NiO core/shell type arrays of nano-heterostructures (NHs) are designed and fabricated by a facile electrochemical template assisted route, for the first time to the best of our knowledge. Co3O4-NiO shell layer is developed on the Co-Ni nanowires cores (Fig. 1). It is found that the nano-heterostructures electrode exhibits high specific capacitance of 2013 F g-1 at a current density of 2.5 A g-1. The electrode also shows high energy and power density (23 Wh kg-1 and 5.5 kW kg-1, at the high discharge current density of 20.8 A g-1). Along with these the NHs electrode also provides good capacitance retention and long cyclicality ideal for applications in pseudocapacitors devices. The remarkable electrochemical property of the NHs electrode as pseudocapacitor is demonstrated based on the effective nano-architectural design having large surface area of the 1D nano-heterostructures. Moreover, the 1D Co-Ni/Co3O4-NiO core/shell nano-heterostructures have two different highly redox active transition metal oxides at the surface, which take part in the Faradic reactions in this electrode. The thin (few nm) mixed-oxide layer also provides the short ion transport path, whereas the metal alloy core will act as the ‘highway’ for the fast electron conduction to the current collector. In another work novel 1D core/shell Ni/NiO nano-architecture electrode has been fabricated and employed as a pseudocapacitor, where significantly improved capacitive performance has been achieved through hydrogenation (Fig. 1). The specific capacitance of the asprepared 1D core/shell Ni/NiO nanoheterostructure (717 Fg−1 at a scan rate of 2 mVs−1) is nearly 1635 Fg−1 after the hydrogenation. The improved pseudocapacitive properties of hydrogenated Ni/NiO nano-heterostructures (NHs) are attributed to the incorporation of the hydroxyl groups on the NiO surface due to hydrogenation, where the metallic Ni NWs core of this unique 1D core/shell NH serves as the efficient channel for the fast electron conduction to the current collector. The H–Ni/NiO NHs exhibit good rate capability (retaining nearly 60% of their initial charge) and good long-term cycling stability with an excellent specific energy and power density of 49.35 W h kg−1 and 7.9 kW kg−1, respectively, at a current density of 15.1 Ag−1. However, the remarkable electrochemical property of the large surface area nano-heterostructures is demonstrated based on the novel nano-architectural design of the electrode with the coexistence of the highly redox active materials at the surface supported by highly conducting metal alloy channel/highway at the core for faster charge transport.