Semiconductor Nanocomposites Research Articles

Insights into the Recent Progress and Advanced Materials for Photocatalytic Nitrogen Fixation for Ammonia (NH3) Production

Ammonia (NH3) is one of the key agricultural fertilizers and to date, industries are using the conventional Haber-Bosh process for the synthesis of NH3 which requires high temperature and energy. To overcome such challenges and to find a sustainable alternative process, researchers are focusing on the photocatalytic nitrogen fixation process. Recently, the effective utilization of sunlight has been proposed via photocatalytic water splitting for producing green energy resource, hydrogen. Inspired by this phenomenon, the production of ammonia via nitrogen, water and sunlight has been attracted many efforts. Photocatalytic N2 fixation presents a green and sustainable ammonia synthesis pathway. Currently, the strategies for development of efficient photocatalyst for nitrogen fixation is primarily concentrated on creating active sites or loading transition metal to facilitate the charge separation and weaken the N–N triple bond. In this investigation, we review the literature knowledge about the photocatalysis phenomena and the most recent developments on the semiconductor nanocomposites for nitrogen fixation, following by a detailed discussion of each type of mechanism.

Two-Step Facile Preparation of MoS2·ZnO Nanocomposite as Efficient Photocatalyst for Methylene Blue (Dye) Degradation

In this work, we report the synthesis of binary semiconductor nanocomposite (NC) comprising spherical ZnO nanoparticles stacked with two-dimensional MoS2 nanosheets, utilizing a facile microwave assisted synthesis technique. The fabricated product was characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy instrument, scanning electron microscopy, Raman spectroscopy, energy-dispersive X-ray spectroscopy (EDAX), inductively coupled plasma analysis and Fourier transform infrared spectroscopy to distinguish the structure and morphology of arranged NC. Ultraviolet–visible spectroscopy was used to understand the optical properties of MoS2·ZnO NC. Optical transmission spectra gave a distinct red shift in the band gap of ZnO after making composition with MoS2 nanosheets which eventually shows higher retention of visible light. This occurs due to effective separation of photogenerated charge carriers and rapid charge transfer to reactions sites of conduction band potentials of both ZnO and MoS2 both. We plot that MoS2·ZnO NC has a band gap of 2.73 eV which is fundamentally a long way from the band gap of ZnO (~ 3.3 eV). The outcomes recommended the effective fading out of methylene blue (more than 95%) in 1 h on the illumination of visible light. Besides, the association of MoS2 prevents photo-corrosion of the ZnO bringing about upgraded photostability of the catalyst during the reaction. Moreover, we presented a recyclability test of the photocatalyst for five subsequent times to get the efficient dye degradation.

Photocatalytic study of ZnS-Ag2S nanocomposites-effect of thioglycerol

Nanocomposites (NCs) of different band gap semiconductors provide better photocatalytic activity as compared to that of monolithic semiconductor nanoparticles (NPs). With the aim to investigate the effect of organic capping agent (thioglycerol; TG in the present study) on photocatalytic activity, ZnS-Ag2S NCs have been synthesized in the presence of TG using simple chemical precipitation route. For comparative studies, NCs have been synthesized under same synthesis conditions without TG. Structural studies were done using X-Ray diffraction (XRD) technique. Morphological features of as prepared samples were recorded by high resolution transmission electron microscopy (HRTEM). UV–Vis and photoluminescence studies were carried out to study the optical properties of synthesized samples. Photocatalytic studies of as-synthesized NCs have been carried out by selecting crystal violet (CV) as a model organic pollutant. It is observed that NCs (synthesized in absence of TG) exhibit better photocatalytic activity as compared to the TG capped NCs. The results of the present study may helpful in practical application of these composites in the area of photocatalysis and other related optical applications.

X-ray peak profile analysis of Sb2O3-doped ZnO nanocomposite semiconductor

In the present work, nanostructured ZnO doped with (2, 4, 6, 8 and 10 ) is prepared by conventional solid state reaction method. X-ray diffraction peak intensities are sharp and narrow, confirming that the sample is of high quality with good crystallinity. The intensity and full width at half-maximum of x-ray diffraction peaks of (100) and (101) decreases with the increase of dopant in ZnO. X-ray peak profile analysis was used to evaluate the crystallite size and lattice strain by the Williamson-Hall (W-H) method. Using the models namely uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM) of W-H method, the physical parameters such as strain, stress, and energy density values were calculated. The surface morphology and elemental composition of the samples were characterized by scanning electron microscope and energy dispersive spectroscopy.

Biaxially Stretchable Fully Elastic Transistors Based on Rubbery Semiconductor Nanocomposites

AbstractA transistor that can be stretchable biaxially is a basic and indispensable component for many emerging applications ranging from wearables to organ implants and to soft robotics. A general approach to enable mechanical stretchability in transistors from existing nonstretchable materials is to create certain mechanical architectures such as in‐plane serpentines, out‐of‐plane wavy structures, kirigami structures, and the hybridization of elastic interconnectors and rigid components. Different from general stretchable transistors, the development of elastic transistors based on rubbery semiconductors nanocomposite of poly(3‐hexylthiophene‐2,5‐diyl) nanofibrils percolated in the silicone rubber matrix is reported. The transistor is fully with elastic materials and manufactured all by solution process. The transistor exhibits a field‐effect mobility of 3.3 cm2 V−1 s−1. The elastic transistor can be stretched biaxially with 50% linear strain and 125% areal strain and it retains its electrical performances. The exhibited reliable electrical functions upon mechanically poked or expanded as a skin for pneumatically actuated soft robots illustrate some practical applications of such biaxially stretchable transistors.

Nanocomposites of Chalcogenide and their Applications

Recently, matrix such as polymer, graphene and carbon nanotubes (CNTs) for the semiconductor nanoparticles plays a promising role due to their better structural, functional properties and broad range of applications in every field. This chapter reviews the metal chalcogenide semiconductor nanocomposites, their properties and applications. Furthermore, the importance of aforementioned matrix and their role in superior properties of metal chalcogenide nano composites have been discussed.

Chemical Synthesis and Characterization of ZnO–TiO2 Semiconductor Nanocomposites: Tentative Mechanism of Particle Formation

The compounds of ZnO–TiO2 can combine the characteristics of the individual oxides which has allowed them to be used as photocatalysts in general, photodegradants in the degradation of dyes, photocatalytic oxidation of NOx, antimicrobial, among other applications. In this study, ZnO–TiO2 semiconductor nanocomposites were synthesized in a controlled way at low temperature. These samples of ZnO–TiO2 were characterized using thermal analysis (TDA/TGA), IR and UV–Vis absorption spectroscopies, X-ray diffraction, and scanning electron microscopy. The primary particles showed a nanometric size (< 100 nm) and spheroidal morphology. All samples presented zincite as the main crystalline phase. When Ti4+ was added, the peaks of the diffractograms shifted slightly with respect to pure ZnO. This indicates the formation of a solid solution. Zn2TiO4 was observed in doped ZnO samples treated at 700 °C. The UV–Vis absorption spectra showed a band in the range between 350 and 425 nm, with a maximum around 375 nm (3.31 eV). With the addition of Ti4+, the nanocomposites showed a better absorbance in the visible range. Considering the nature of the synthesis process used, a mechanism was proposed to explanation of the formation of Nanocomposites.

Construction of a Z-scheme core–shell g-C3N4/MCNTs/BiOI nanocomposite semiconductor with enhanced visible-light photocatalytic activity

An S–C–S Z-scheme core–shell g-C3N4/MCNTs/BiOI nanocomposite semiconductor with enhanced photocatalytic activity was designed and fabricated.

Photocatalytic Activity of Graphene – Titania Nanocomposite

In the past few years, carbon-based semiconductor nanocomposites have attracted great attention due to their unique combinations of chemical and physical properties. Incessant research interest has been devoted on preparing graphene-based TiO2 nanocomposites for photocatalytic application. The present study aims to examine the photocatalytic activity of graphene-titania nanocomposite prepared via hydrothermal method. For a comparison, the photocatalytic activity of pure titania was also investigated. The prepared systems are well characterized using XRD analysis, FTIR spectroscopy, UV-VIS diffuse reflectance spectroscopy, Transmission Electron Microscopy, Photoluminescense study and Surface area analysis by BET method. The Photocatalytic activity of the composite was studied by measuring the degradation of aqueous solution of Crystal Violet (CV) dye under UV and Visible light. Modification with graphene has commendably increased the photocatalytic activity of titania.

Natural pigment sensitized solar cells based on ZnO-TiO2-Fe2O3 nanocomposite in quasi-solid state electrolyte system

Nanocomposites of Zn-Ti-Fe oxide using zinc as a host with different ratios of precursor salts were prepared by co-precipitation method to use as semiconductors for dye sensitized solar cell (DSSC). The as-synthesized nanocomposites were characterized using XRD, SEM-EDX, TEM and UV-Vis spectrophotometer. DSSCs based on the new semiconductors and di-tetrabutylammoniumcis-bis(isothiocyanato)bis(2,2’-bipyridyl-4,4’-dicarboxylato)-ruthenium(II) (N719) dye has been constructed and characterized. Stability towards dissolution of deposited films of semiconductors in the acidic dye and conversion efficiency was obtained in the order of: ZnO(100%) &lt;ZnO(70%)-TiO2(30%) &lt;ZnO(70%)-Fe2O3(30%) &lt;ZnO(60%)-TiO2(20%)-Fe2O3(20%). Natural pigments were also extracted using ethanol and water as solvents from flowers of Guizotia scabra and Salvia leucantha plants. From UV-Vis spectra analysis all ethanol extracts of natural sensitizers absorb in the visible region. DSSCs were constructed using the natural pigments as sensitizers. The following best device parameter was achieved by the ethanol extract of Salvia leucantha and ZnO-TiO2-Fe2O3 nanocomposite semiconductor. When the potential is scanned: a Voc of 280 mV, Jsc of 0.01761 mAcm-2 at light intensity of 100 mWcm-2 were obtained; the maximum IPCE % was 1.7 and 25.7 for the N719 dye and Salvia luecantha, respectively. KEY WORDS: Nanocomposite, Co-precipitation method, Semiconductor, Dye sensitized solar cell, Natural pigments, Conversion efficiency Bull. Chem. Soc. Ethiop. 2017, 31(2), 263-279. DOI: http://dx.doi.org/10.4314/bcse.v31i2.8

Enhanced Field Emission Performance of MoO3 Nanorods and MoO3‐rGO Nanocomposite

AbstractThe graphene and semiconducting hybrid based nanostructures have emerged as a new class of multifunctional materials with improved performance in comparison to the pristine semiconductors. Here, as‐synthesized MoO3‐reduced graphene oxide (rGO) nanocomposite emitter exhibits enhanced field emission (FE) behavior as compared to the pristine 1D MoO3 nanorods. The hydrothermally synthesized 1D MoO3 nanorods (1D) are grafted on the rGO sheet (2D) using a simple room temperature sonochemical method. The morphological and structural analysis confirms the attachment of MoO3 nanorods with rGO and the improved conductivity of the sample indicates a strong electronic interaction between them. Furthermore, the FE studies of as‐synthesized MoO3 nanorods and MoO3‐rGO nanocomposite emitters, carried out at a base pressure ∼1×10−8 mbar, reveals the values of turn on field (required to draw an emission current density of 1 μA/cm2) as 1.6 and 1.4 V/μm, respectively. Interestingly, the maximum emission current density of 2810 μA/cm2 is achieved at a lower applied field of 2.7 V/μm from the MoO3‐rGO nanocomposite emitter. The enhancement in FE performance of MoO3‐rGO nanocomposite is attributed to the improved electrical conductivity, mechanical properties and higher concentration of protruding edges (emission sites). This observation can be extended to other graphene‐based 1D inorganic hybrid semiconductor nanocomposites, which can provide a valuable opportunity to explore novel hybrid materials for vacuum nano‐electronic devices.

Stable and Fast-Response Capacitive Humidity Sensors Based on a ZnO Nanopowder/PVP-RGO Multilayer.

In this paper, capacitive-type humidity sensors were prepared by sequentially drop-coating the aqueous suspensions of zinc oxide (ZnO) nanopowders and polyvinyl pyrrolidone–reduced graphene oxide (PVP-RGO) nanocomposites onto interdigitated electrodes. Significant improvements in both sensitivity and linearity were achieved for the ZnO/PVP-RGO sensors compared with the PVP-RGO/ZnO, PVP-RGO, and ZnO counterparts. Moreover, the produced ZnO/PVP-RGO sensors exhibited rather small hysteresis, fast response-recovery time, and long-term stability. Based on morphological and structural analyses, it can be inferred that the excellent humidity sensing properties of the ZnO/PVP-RGO sensors may be attributed to the high surface-to-volume ratio of the multilayer structure and the supporting roles of the PVP-RGO nanocomposites. The results in this work hence provide adequate guidelines for designing high-performance humidity sensors that make use of the multilayer structure of semiconductor oxide materials and PVP-RGO nanocomposites.

Atomistic Explanation for Interlayer Charge Transfer in Metal-Semiconductor Nanocomposites: The Case of Silver and Anatase.

A concerted theoretical and experimental investigation of the silver/anatase hybrid nanocomposite, a very promising material for advanced sensing applications, is presented. We measure its exceptional electrochemical virtues in terms of current densities and reproducibility, providing their explanation at the atomic-scale level and demonstrating how and why silver acts as a positive electrode. Using periodic plane-wave DFT calculations, we estimate the overall amount of electron transfer toward the semiconductor side of the interface at equilibrium. Suitably designed (photo)electrochemical experiments strictly agree, both qualitatively and quantitatively, with the theoretical charge transfer estimates. The unique permanent charge separation occurring in the device is possible because of the favorable synergy of Ag and TiO2, which exploits in a favorable band alignment, while the electron–hole recombination rate and carrier mobility decrease when electrons cross the metal–semiconductor interface. Finally, the hybrid material is proven to be extremely robust against aging, showing complete regeneration, even after 1 year.

Ultraviolet light-induced photochemical reaction for controlled fabrication of Ag nano-islands on ZnO nanosheets: an advanced inexpensive substrate for ultrasensitive surface-enhanced Raman scattering analysis

The fascinating nanocomposites of semiconductors coupled with noble metals have a promising potential to develop a low-cost substrate for surface-enhanced Raman scattering (SERS) applications. Herein, the controlled construction of Ag nano-islands on ZnO nanosheets (Ag@ZnO nanocomposites) was successfully achieved by a green and effective strategy based on ultraviolet light induced-photochemical reaction. It was found that the Ag content in Ag@ZnO nanocomposites linearly increases to 4.62% by simply increasing the irradiation time (0~10 min). More importantly, increasing the Ag content (0~4.62%) in the nanocomposites results in enhanced SERS activities with an enhancement factor up to 107 and a detection limit as low as 10−9 M. Compared with the complete noble metal substrate, the novel Ag@ZnO nanocomposites (<5% Ag compositions) were cost-effective and possessed high biocompatible properties; which can be established as an advanced inexpensive substrate for ultrasensitive SERS analysis, particularly for food safety and biomedical applications.

Plasmon-Enhanced Photoelectrochemical Current and Hydrogen Production of (MoS2-TiO2)/Au Hybrids

Three component hybrid (MoS2-TiO2)/Au substrate is fabricated by loading plasmonic Au nanorods on the MoS2 nanosheets coated TiO2 nanorod arrays. It is used for photoelectrochemical (PEC) cell and photocatalyst for hydrogen generation. Owing to the charge transfer between the MoS2-TiO2 hetero-structure, the PEC current density and hydrogen generation of TiO2 nanoarrays are enhanced 2.8 and 2.6 times. The broadband photochemical properties are further enhanced after Au nanorods loading. The plasmon resonance of Au nanorods provides more effective light-harvesting, induces hot-electron injection, and accelerates photo-excited charges separation. The results have suggested a route to construct nanohybrid by combining one-dimensional arrays and two-dimensional nanosheets, meanwhile have successfully utilized plasmonic nanorods as a sensitizer to improve the photochemical properties of the semiconductor nanocomposite.

Dynamic magnetic permeability of the heterogeneous nanosystems based on (Co41Fe39B20) x (SiO2)100 – x composites

Thin films of (Co41Fe39B20) x (SiO2)100 – x nanocomposites and hybrid nanocomposite–semiconductor [(Co41Fe39B20) x (SiO2)100 – x /C]50 multilayers are synthesized by ion-beam deposition at various contents x of ferromagnetic metallic Co41Fe39B2O nanogranules in an SiO2 matrix and at various carbon layer thicknesses h < 2 nm. Their magnetic and electrical properties, high-frequency magnetic permeability, magnetooptical spectra, and FMR spectra are studied. It is found that both the single-layer nanocomposites and the multilayers with carbon interlayers are superparamagnetic at x < x per, where x per is the electric conduction percolation threshold: a hysteresis at room temperature is absent, and the blocking temperature determined in quasi-static measurements does not exceed 20–30 K and weakly depends on the carbon layer thickness. At a carbon layer thickness h = 1.2–1.8 nm, the real and imaginary parts of complex magnetic permeability at 50 MHz and room temperature are substantially higher than those of the nanocomposites without carbon layers: their values are typical of ferromagnets. This dependence points to an exchange interaction between nanogranules in layers through a carbon interlayer. The influence of a conducting layer on the static and dynamic magnetic properties of a system of interacting superparamagnetic particles is discussed.

Effect of TiO2 morphology on structure of TiO2-graphene oxide nanocomposite synthesized via a one-step hydrothermal method

Titanium dioxide-graphene oxide (TiO2-GO) nanocomposites with different TiO2 morphologies were successfully fabricated by a facile, one-step hydrothermal method. The GO synthesized by the modified Hummer's method was employed as the base in composition with TiO2 using in-situ hydrothermal method. The nanowire (NW) and nanoparticle (NP) morphologies of TiO2 were grown up on the surface of the GO sheets, which was confirmed by FE-SEM and HR-TEM characterization techniques. XRD and Raman spectroscopy were revealed formation of the TiO2-GO nanocomposites with tetragonal structure and of the covalent bonds between the TiO2 nanostructures and GO sheets. The best photodegradation rate of methylene blue was found for the TiO2 NW-GO nanocomposite. The present results indicated that the graphene-based semiconductor nanocomposites can be successfully synthesized by the low cost, one-step hydrothermal approach.

Probing interfacial energetics and charge transfer kinetics in semiconductor nanocomposites: New insights into heterostructured TiO2/BiVO4 photoanodes

Heterostructured nanocomposites offer promise for creating systems exhibiting functional properties that exceed those of the isolated components. For solar energy conversion, such combinations of semiconducting nanomaterials can be used to direct charge transfer along pathways that reduce recombination and promote efficient charge extraction. However, interfacial energetics and associated kinetic pathways often differ significantly from predictions derived from the characteristics of pure component materials, particularly at the nanoscale. Here, the emergent properties of TiO2/BiVO4 nanocomposite photoanodes are explored using a combination of X-ray and optical spectroscopies, together with photoelectrochemical (PEC) characterization. Application of these methods to both the pure components and the fully assembled nanocomposites reveals unpredicted interfacial energetic alignment, which promotes ultrafast injection of electrons from BiVO4 into TiO2. Physical charge separation yields extremely long-lived photoexcited states and correspondingly enhanced photoelectrochemical functionality. This work highlights the importance of probing emergent interfacial energetic alignment and kinetic processes for understanding mechanisms of solar energy conversion in complex nanocomposites.

Hydrothermal synthesis of graphene/TiO2/CdS nanocomposites as efficient visible-light-driven photocatalysts

The construction of semiconductor nanocomposites has been considered as one of the efficient methods to improve photocatalytic activity. Herein, we have prepared the ternary reduced graphene oxide (rGO)-TiO2-CdS nanocomposites by firstly hydrolyzing tetrabutyl titanate in GO solution to prepare GO-TiO2 precursor, and then hydrothermally treating GO-TiO2/Cd(NO3)2/l-cysteine solution. Typically, rGO-TiO2-0.55CdS (Cd/Ti molar ratio: 0.55/1) consists of TiO2 spheres (∼1μm) and rGO framework, whose surfaces were uniformly decorated with CdS nanoparticles (∼30nm). Under the illumination of visible-light, rGO-TiO2-0.55CdS can degrade 90.3% methylene blue (MB) dye and 65.3% parachlorophenol (4-CP) in 60min, which are higher than those (55.9% for MB and 28.4% for 4-CP) by the binary rGO-TiO2. In addition, the recycling experiment confirms that rGO-TiO2-0.55CdS nanocomposite is essentially stable. Therefore, rGO-TiO2-CdS nanocomposites have great potential as effective and stable visible-light-driven photocatalysts.

Construction of semiconductor nanocomposite on porous silicon using chemical method

Porous silicon (PSi) samples fabricated by electrochemical etching method at current density (40) mA/cm2 with different etching time (3, 3:30, 4, 4:30) min where ZnO, TiO2 and 70% ZnO:30% TiO2 deposited by chemical spray pyrolysis to be applied for gas sensors, these sample have been investigated scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. XRD measurement has confirmed the crystallinity with Nanopores were produced on the PSi layer. The (FE-SEM) photographs revealed the highly porous structure which proved ideal for the performance as gas sensing element. AFM confirms the nanometric size.