Metal-semiconductor Nanocomposites Research Articles

Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite Thin Films through Metallic CoTe2 Integration.

Metal-semiconductor nanocomposites have emerged as a viable strategy for concurrently tailoring both thermal and electronic transport properties of established thermoelectric materials, ultimately achieving synergistic performance. In this investigation, a series of nanocomposite thin films were synthesized, embedding metallic cobalt telluride (CoTe2) nanophase within the nanocrystalline ternary skutterudite (Co(Ge1.22Sb0.22)Te1.58 or CGST) matrix. Our approach harnessed composition fluctuation-induced phase separation and in situ growth during thermal annealing to seamlessly integrate the metallic phase. The distinctive band structures of both materials have developed an ohmic-type contact characteristic at the interface, which raised carrier density considerably yet negligibly affected the mobility counterpart, leading to a substantial improvement in electrical conductivity. The intricate balance in transport properties is further influenced by the metallic CoTe2 phase's role in diminishing lattice thermal conductivity. The presence of the metallic phase instigates enhanced phonon scattering at the interface boundaries. Consequently, a 2-fold enhancement in the thermoelectric figure of merit (zT ∼ 1.30) is attained with CGST-7 wt. % CoTe2 nanocomposite film at 655 K compared to that of pristine CGST.

Synthesis and Characterization of Hierarchical Structure Au/ZnO Nanocomposites for Possible Photocatalytic Applications

Semiconductor-metal nanocomposites are actively investigated for their diverse applications in emerging fields such as photocatalysis, photovoltaics, and chemical sensing. In this study, we synthesized ZnO semiconductor nanoparticles using a chemical bath deposition method with ZnSO4·7H2O and controlled NH4OH concentrations, facilitated by an anionic surfactant to enable the attachment of Au metal nanoparticles. Au nanoparticles were prepared from HAuCl4 using citrate as a reducing agent, and metal oxide was rapidly introduced to ensure a well-defined nanocomposite with a fixed 75 w/v% composition. Fast Fourier transform spectroscopy (FTIR) and Ultra-visible (UV-Vis) spectroscopy were used to provide clear evidence of Au/ZnO nanocomposite formation through the presence of distinctive peaks around 359nm and 518nm, with Dynamic Light Scattering (DLS) revealing contrasting average sizes for ZnO and Au, highlighting the significant size difference in the Au/ZnO nanocomposites. Additionally, the scanning electron microscopy – energy dispersive x-ray (SEM-EDS) analysis confirmed the successful presence of ZnO nanoparticles. These findings offer insights into the potential applications and unique properties of Au/ZnO nanocomposites for possible photocatalytic applications.

In situ synthesis of metal (Bi0)–semiconductor [BiOX (X = Cl, Br, and I)] nanocomposites as a highly effective catalyst for the reduction of 4-nitrophenol to 4-aminophenol

The BiOX (X = Cl, Br, and I) catalysts demonstrate significant catalytic activity for 4-nitrophenol reduction due to in situ formation of metal-semiconductor (Bi0–BiOX) nanocomposites in the presence of NaBH4.

Facile One‐Pot Synthesis of Uniquely Designed Au−Cu2O Nanocomposites for Effective Catalytic Degradation of Azo Dyes

AbstractIn the study of metal–semiconductor nanocomposites, the Au−Cu2O system is of significant interest because it can give rise to a variety of hybrid designs with pronounced activity for catalytic applications. In this work, a facile one‐pot synthetic strategy was developed to prepare Au−Cu2O nanocomposites with a unique core–shell nanoflower configuration, where a cluster of tiny Au nanoparticles constitutes the core, while larger cube‐like Cu2O nanoparticles surround this core in a petal‐like arrangement. Unlike previously published procedures that rely on two‐pot synthesis routes to generate the Au−Cu2O hybrid, the one‐pot synthesis protocol presented in this work is a more straightforward and less laborious approach that does not require a separate pre‐synthesis step. Furthermore, the synthesis can be conveniently performed at ambient conditions using nontoxic reagents. When tested as catalysts, the uniquely designed Au@Cu2O nanoflowers were found to effectively catalyze the borohydride‐mediated degradation of synthetic azo dyes (methyl orange and congo red). The hybrid exhibited superior catalytic activity relative to pristine Cu2O, underscoring the significance of creating a nanocomposite.

Surface Enhanced Raman Spectroscopic Studies on Surface Plasmon Resonance Catalytic Activity of TiO<sub>2</sub>-Metal Nanocomposites

The rapid recombination of carriers on plasmon metal nanoparticles leads to relatively low efficiency of traditional photocatalysts. The combination of a metal and a semiconductor allows to the separation of hot electrons and holes to improve photocatalytic efficiency. In this study, Au nanoparticles were integrated with semiconductor TiO2 nanoparticles of different sizes to improve the photocatalytic activity. Various techniques have been developed to study the mechanism of catalytic activity, the significance of band bending in the space-charge region within metal–semiconductor nanocomposites, and the built-in electric field. The results provide theoretical and experimental evidence for the design of a high-performance surface plasmon resonance (SPR) photocatalyst. To reveal the interface band structure, surface-enhanced Raman spectroscopy (SERS) was employed to analyze the band structure of the TiO2–metal composites. This approach was based on the electrochemical Stark effect and a molecular probe strategy, combined with X-ray photoelectron spectroscopy (XPS), Electrochemical impedance spectroscopy (EIS), and other techniques at the molecular level. The results demonstrated that charge transfer occurred spontaneously between the Au nanoparticles and TiO2, and that the TiO2–metal interface constitutes a Schottky barrier. Moreover, the size of the TiO2 nanoparticles affects the degree of band bending. Optimal state matching was achieved with TiO2 (60 nm)–Au, improving the photocatalytic activity of the nanocomposite. The photocatalytic coupling reaction of p-aminothiophenol (PATP) acted as a probe to study the catalytic performance of TiO2–metal nanocomposites. The results revealed that the introduction of TiO2 improves the SPR catalytic activity of Au, mainly through the efficient separation of electrons and holes at the TiO2–metal interface.

Nanocomposites of Cu2O with plasmonic metals (Au, Ag): design, synthesis, and photocatalytic applications.

Metal-semiconductor nanocomposites have been utilized in a multitude of applications in a wide array of fields, prompting substantial interest from different scientific sectors. Of particular interest are semiconductors paired with plasmonic metals due to the unique optical properties that arise from the individual interactions of these materials with light and the intercomponent movement of charge carriers in their heterostructure. This review focuses on the pairing of Cu2O semiconductor with strongly plasmonic metals, particularly Au and Ag. The design and synthesis of Au-Cu2O and Ag-Cu2O nanostructures, along with ternary nanostructures composed of the three components, are described, with in-depth discussion on the synthesis techniques and tunable parameters. The effects of compositing on the optical and electronic properties of the nanocomposites in the context of photocatalysis are discussed as well. Concluding remarks and potential areas for exploration are presented in the last section.

Anchoring branched Ag nano-islands on Au@CuxO mesoporous nanospheres as dual plasmonic absorbers for efficient photothermal conversion

Plasmonic semiconductor nanomaterials have been widely accepted as promising candidates for photothermal conversion, while the efficiency is yet to optimize. Herein, we report a facile synthesis of Au@CuxO mesoporous nanospheres anchored with branched Ag nano-islands on the surface and explore their applications as photothermal conversion agent. Due to the intimate hybridization of two materials, the Au@CuxO-Ag hybrid nanocomposites display a unique dual-plasmonic absorption that covers the visible-NIR range, benefiting the utilization efficiency of light energy. The synthesis is realized by reacting Au@CuxO with Ag+, the galvanic replacement reaction between them enables a preferential depletion of Cu phase, leaving Ag and Cu2O as dominate crystal phases. The resulting hybrid nanocomposites are featured with a core-shell structure but incomplete coverage, as well as the mesoporous interior and dendritic outer shell. In addition to the enhanced photothermal conversion efficiency, the current nano-hybrids show excellent structural stability and no decay in conversion after five successive rounds of measurement. The advantages in both morphological and electronic structure aspects are discussed. The present study validates the promising synergetic use of distinct hot charge carriers originating from metal and semiconductor that are photoexcited in the same hybrid nanoparticle for photothermal conversion, shedding light on rational design of photothermal materials based on metal-semiconductor hybrid nanocomposites.

Efficient carbon dioxide electroreduction over rationally designed heterogeneous Ag2S-Au nanocomposites

Electrochemical carbon dioxide reduction reaction (CO2RR) is regarded as an effective strategy to store abundant renewable energy and build a carbon neutral society. Gold (Au) and silver (Ag)-based catalysts for the effective electrochemical transformation of CO2 to CO emerge as promising candidates. Heterogeneous nanocomposites composed of noble metals and semiconductors exhibit great potential for electrocatalytic CO2 reduction through the electronic coupling effect at coherent interfaces. Herein, we successfully synthesize heterogeneous Ag2S-Au composite nanoparticles (NPs) as effective catalysts for CO production through CO2RR. At −0.8 V vs RHE, the heterogeneous Ag2S-Au nanocatalysts display a considerable CO Faradaic efficiency of 94.5%, and an appreciable CO partial current density of 9.17 mA cm−2. Moreover, they exhibit good stability for 30 h without obvious decrease. On the basis of density functional theory (DFT) calculations, it can be made clear that the heterogeneous Ag2S-Au interface is energetically more beneficial to the generation of COOH* intermediate for CO2RR. This study provides a new application for noble metal–semiconductor nanocomposites.

Photoexcitation and radiation regulation mechanism of Ag anchoring WSe2 heterojunction with plasma coupling effect

The noble metal silver (Ag) combined with tungsten selenide (WSe2) was used to solve the problems of the narrow absorption band range, low luminescence quantum yield, and nonlinear transmittance of WSe2 base materials. Ag/WSe2 films and core–shell Ag@WSe2 heterojunction were designed and fabricated by the two-step magnetron sputtering and hydrothermal/magnetron sputtering method, respectively. X-ray diffraction, scanning electron microscopy and X-ray photoelectric spectroscopy results confirmed that the successful preparation of Ag/WSe2 and Ag@WSe2. Raman results demonstrate the presence of interfacial stress between Ag and WSe2. Based on quantum particle coupling in metal–semiconductor nanocomposites, the adsorbed silver particles provide electrons and through charge transfer, which increases the density of electronic states in conduction band of the WSe2 and thus increases the spontaneous emission rate. Electron-hole pairs generated in the semiconductor through resonant coupling between surface plasmas of the Ag and WSe2 interface will provide strongly enhanced radiative recombination. The absorption and emission of WSe2 nanosheets in the visible light range and linear-nonlinear optical properties depend on the regulation the sputtering power and pressure of Ag particles. Our research results demonstrate that Ag&WSe2 have excellent optical and photoelectric properties, indicating that Ag&WSe2 have a wide application potential in photoelectric functional and optoelectronic devices.

Domestic microwave assisted one-step co-precipitation of Ag–CuO nanocomposite of Cu/Ag ratio optimized for photocatalysis and comparison with blending CuO with Ag nanoparticles

The Ag–CuO metal–semiconductor nanocomposite (NC) is an important component in various nanomaterial-based applications. Several approaches have been studied to facilitate its synthesis. However, most of them encounter some drawbacks. In the present work, we show the synthesis of Ag–CuO NCs through one-pot co-precipitation with the aid of simple starting chemicals and measures including metal nitrates, hexamine, agar, and domestic microwave heating. Photocatalyzed degradation of Congo Red in addition to the structural and optical characteristics show that this method is successful in production of the Schottky barrier in Ag–CuO NCs with improved photocatalytic activity (PCA). Changing the Cu content shows that the NC is not successfully formed at low Cu mol%. Consequently, the PCA of Ag–CuO of low Cu (2%–6%) lies within 4.5 × 10−4 – 5.1 × 10−4 min−1, which is even lower than those of plain Ag and CuO nanoparticles (6.0 × 10−4 – 8.1 × 10−4 min−1, respectively). 60 mol% was the optimum Cu content with the highest PCA (18.8 × 10−4 min−1). Blending plain Ag and CuO nanoparticles to mimic the co-precipitated 60 mol% Ag–CuO showed very low PCA, even lower than the plain Ag and CuO, which once again confirms the efficiency of the simple one-pot co-precipitation approach in producing Ag–CuO with the Schottky barrier and promoted PCA.

Self-sustainable and recyclable ternary Au@Cu2O\u2013Ag nanocomposites: application in ultrasensitive SERS detection and highly efficient photocatalysis of organic dyes under visible light

Ternary noble metal–semiconductor nanocomposites (NCs) with core–shell–satellite nanostructures have received widespread attention due to their outstanding performance in detecting pollutants through surface-enhanced Raman scattering (SERS) and photodegradation of organic pollutants. In this work, ternary Au@Cu2O–Ag NCs were designed and prepared by a galvanic replacement method. The effect of different amounts of Ag nanocrystals adsorbed on the surfaces of Au@Cu2O on the SERS activity was investigated based on the SERS detection of 4-mercaptobenzoic acid (4-MBA) reporter molecules. Based on electromagnetic field simulations and photoluminescence (PL) results, a possible SERS enhancement mechanism was proposed and discussed. Moreover, Au@Cu2O–Ag NCs served as SERS substrates, and highly sensitive SERS detection of malachite green (MG) with a detection limit as low as 10−9 M was achieved. In addition, Au@Cu2O–Ag NCs were recycled due to their superior self-cleaning ability and could catalyze the degradation of MG driven by visible light. This work demonstrates a wide range of possibilities for the integration of recyclable SERS detection and photodegradation of organic dyes and promotes the development of green testing techniques.

Ag-ZnO Nanocomposites Are Used for SERS Substrates and Promote the Coupling Reaction of PATP.

Noble metal-semiconductor nanocomposites have received extensive attention in Surface Enhanced Raman Scattering (SERS) due to their unique properties. In this paper, the Ag–ZnO nanocomposites are prepared by hydrothermal growth and simple chemical reduction immersion. The synthesized nanocomposite material simultaneously integrates the individual enhancement effects of the two materials in the SERS, such as the electromagnetic enhancement of silver nanoparticles and the chemical enhancement of ZnO semiconductor materials. Using this substrate, Rhodamine 6G molecules with a concentration as low as 10−8 M can be detected, and the coupling reaction of PATP can be effectively promoted. The nanocomposite materials prepared by selecting appropriate semiconductor materials and metal materials combined, could be potentially applied, as SERS substrates, in certain catalytic reactions.

Selective laser-induced preparation of metal-semiconductor nanocomposites and application for enhanced photocatalytic performance in the degradation of organic pollutants

By selective laser-induced in a liquid medium, the metal-semiconductor nanocomposites were prepared, and its photocatalytic performance in the degradation of organic pollutants was evaluated. During the preparation, silver (Ag) and zinc oxide (ZnO) nanoparticles were employed as an example to construct the colloidal precursors and selectively heated under a laser beam unfocused irradiation. After that, the structures, morphologies, optical properties of the prepared nanocomposites were characterized by the XRD, STEM, EDX, UV-Vis and PL instruments, respectively. The results showed that the Ag/ZnO nanocomposites were successfully prepared under the selective laser-induced in a liquid phase, and the composite interfaces of crystal lattice between Ag and ZnO were observed. In addition, the methylene blue (MB) water solution was employed as a model system to check the difference of photocatalytic performance for pure and laser-induced composite catalysts. The results indicated the photocatalytic performance for laser-induced preparation of Ag/ZnO nanocomposites was enhanced two times than the pure photocatalyst of ZnO in the degradation of MB water solution, with a higher rate constant of 0.04 min−1. The corresponding mechanism for enhanced photocatalytic performance can be obtained from the optical properties of nanocomposites, and originated from the laser-induced formation of heterojunction by contact and fusion of Ag and ZnO, with a high electron transfer efficiency and benefit for the degradation. The method and results reported here possess great potential in future application of environmental remedies and other catalysis fields.

Hybrid Ag/ZnO nanostructures for SERS detection of ammonium nitrate

Ag/ZnO composite nanostructures are produced by combined laser and ion implantation techniques. The ZnO layers are grown on SiO2 (001) and Al2O3 (r-cut) substrates by pulsed laser deposition (PLD) in vacuum and in oxygen ambient using a third-harmonic Nd:YAG laser. The ion implantation allows the introduction of Ag nanoparticles (NPs) in the surface of the ZnO matrix. These NPs are incorporated into the ZnO matrices to fabricate metal-semiconductor nanocomposites with the aim of manipulating their functionalities, exploiting the characteristics of both the matrix and the metal NPs. The composite samples are modified by laser annealing at 355 nm and 532 nm. The changes are investigated in the plasmon resonance absorption of the nanostructures before and after the annealing. The influence is explored of the different substrates used and the deposition conditions of ZnO growth on the properties of Ag/ZnO. The nanostructures obtained are efficient as SERS substrates for detection of ammonium nitrate under laser excitation at 633 nm. The SERS enhancement is attributed to the synergistic interactions between the plasmonic coupling among the surface embedded AgNPs and the enhanced charge transfer properties of the ZnO.

Synthesis and characterisation of green luminescent carbon dots from guava leaf extract

Carbon Dots (C-Dots) are carbon nanoparticles of very small size which has been a subject of intense study in the recent years due to their interesting properties and applications. This work reports green synthesis of C-Dots using guava leaf extract by a cost effective hydrothermal method with water and ethanol as solvents. TEM measurements revealed that the particles are below 10 nm in size. The optical properties of C-dots synthesized were characterised by absorbance and photoluminescence measurements. It was found that the C-dots show green emission and good stability to be used for various sensing and energy conversion applications. The carbon dot incorporated titanium dioxide showed good photocatalytic ability to degrade methylene blue (MB) dye similar to metal–semiconductor nanocomposites paving way for cost-effective nanomaterials for water purification.

Cu2O-Ag nanocomposites with tunable optical property

Semiconductor-metal nanocomposites were demonstrated to be great potential applications for their unique structures. In this work, Cu2O-Ag nanocomposites with tunable optical property were prepared by laser molecular beam epitaxy with an alternative deposition way. The growth process was characterized by in situ reflection high-energy electron diffraction and in situ x-ray photoelectron spectroscopy. Due to the surface plasmon resonance, the absorption peaks of Cu2O-Ag can be easily modulated from 618 nm to 650 nm by increasing Ag laser pulses. The corresponding band gap changed from 2.01 eV to 2.74 eV. The growth mechanism was also discussed in detail. The results provide a new route to control the optical absorption of semiconductor-metal oxide nanocomposites by an easy way.

Synergistical Tuning Interface Barrier and Phonon Propagation in Au-Sb2Te3 Nanoplate for Boosting Thermoelectric Performance.

Engineering of low-dimensional metal-semiconductor nanocomposites is expected to decouple electrical and thermal property, leading to substantially higher thermoelectric property. In this study, we rationally design a unique 0D-2D Au-Sb2Te3 architecture with beneficial interface barrier and strengthened phonon scattering, resulting in synergistically optimized electrical and thermal properties. In-situ growth of Au nanoparticles ∼10 nm on Sb2Te3 nanoplates enables better manipulation of electron and phonon transport compared to traditional bulks. The energy barrier between Au and Sb2Te3 effectively filters low-energy holes, while the Au nanoparticles competently hinder the propagation of midto-long wavelength phonons. As a result, this unique 0D-2D Au-Sb2Te3 composite exhibits a concurrent increase in electrical conductivity and Seebeck coefficient, and a decrease in lattice thermal conductivity, which allows a double of ZT value (∼0.8 at 523 K) for 1 mol % Au-Sb2Te3 composites with respect to the pristine Sb2Te3 (∼0.39 at 523 K). This self-assembled heterostructure provides a direction to design other low-dimensional metal-semiconductor nanoassemblies for thermoelectric application.

Titanate Nanowires as One-Dimensional Hot Spot Generators for Broadband Au-TiO2 Photocatalysis.

Metal–semiconductor nanocomposites have become interesting materials for the development of new photocatalytic hybrids. Along these lines, plasmonic nanoparticles have proven to be particularly efficient photosensitizers due to their ability to transfer plasmonic hot electrons onto large bandgap semiconductors such as TiO2, thus extending the activity of the latter into a broader range of the electromagnetic spectrum. The extent of this photosensitization process can be substantially enhanced in those geometries in which high electromagnetic fields are created at the metal–semiconductor interface. In this manner, the formation of plasmonic hot spots can be used as a versatile tool to engineer the photosensitization process in this family of hybrid materials. Herein, we introduce the use of titanate nanowires as ideal substrates for the assembly of Au nanorods and TiO2 nanoparticles, leading to the formation of robust hybrids with improved photocatalytic properties. Our approach shows that the correct choice of the individual units together with their rational assembly are of paramount importance in the development of complex nanostructures with advanced functionalities.

Tea-phytochemicals functionalized Ag modified ZnO nanocomposites for visible light driven photocatalytic removal of organic water pollutants

Biogenic synthesis of semiconductor nanoparticles (NPs) as well as metal-semiconductor nanocomposites (NCs) has become a subject of comprehensive interest and research due to its cost-effective and eco-friendly synthesis approach. In this regard, the current work focuses on the biosynthesis of Zinc oxide (ZnO) NPs and Silver-Zinc oxide (Ag-ZnO) NCs using the leaves extract of tea plant (Camellia sinensis). The as-synthesized samples were characterized by various optical, structural and elemental characterization techniques. The successful capping of tea-phytochemicals were confirmed from the bonding information through Fourier Transform Infrared Spectroscopic analysis, while the formation of ZnO NPs and Ag-ZnO NCs were established using x-ray Diffraction, Energy Dispersive x-ray and x-ray photoelectron spectroscopic techniques. Optical absorbance of ZnO NPs revealed the formation of smaller particle size (∼5.2 nm) as compared to bulk ZnO, while the absorbance of Ag-ZnO NCs depicted the presence of metallic Ag in the sample through surface plasmon resonance. The potential of as-synthesized samples were then tested through the photocatalytic and catalytic degradation of organic water pollutants, such as Methylene blue, Paracetamol drug and para-Nitro phenol. The results indicated that Ag deposition on ZnO nanostructure was beneficial in terms of both catalytic as well as photocatalytic degradation under dark condition and visible light irradiation, respectively. A commercially available light source was used for photodegradation process instead of solar irradiation. In addition, an attempt has also been made to explain the plausible pathway of Ag-ZnO NCs formation by the functionalization of tea-phytochemicals. To the best of Authors’ understanding, this is the first attempt so-far reporting a cost-effective biosynthesis process of Ag-ZnO NCs using tea-extracts and its photocatalytic activity under visible light for the degradation of common organic pollutants.

Plasmon-promoted electrocatalytic water splitting on metal-semiconductor nanocomposites: the interfacial charge transfer and the real catalytic sites.

Plasmonic metal nanoparticles (NPs) have emerged as promising visible light harvesters to facilitate solar-to-chemical energy conversion via the generation of hot electrons by non-radiative decay of plasmons. As one of the most promising renewable energy production methods for the future, electrocatalytic water splitting is an ideal chemical reaction in which plasmonic NPs can be utilized for direct solar-to-fuel conversion. Due to the rapid carrier recombination on plasmonic NPs, hybrid photocatalysts integrating metals and semiconductors are usually employed to separate the hot electrons and holes. However, an understanding of the catalytic mechanism, which is critical for rational design of plasmonic electrocatalysts, including the interfacial charge transfer pathway and real reactive sites, has been lacking. Herein, we report on the combination of plasmonic Au NPs and semiconductors (Ni and/or Co hydroxides) for plasmon-promoted electrocatalytic water splitting. By using surface-enhanced Raman spectroscopy (SERS), we find a strong spontaneous interfacial charge transfer between Au and NiCo layered double hydroxide (LDH), which facilitates both the oxygen and hydrogen evolution reactions. The real catalytic sites on the hybrid material are confirmed by selective blocking of the metal surface with a thiol molecular monolayer. It is found that the plasmon-promoted oxygen evolution occurs on the LDH semiconductor but surprisingly, the hydrogen evolution sites are mainly located on the Au NP surface. This work demonstrates the critical role of interfacial charge transfer in hot electron-driven water splitting and paves the way for rational design of high-performance plasmonic electrocatalysts.