Seed-induced growth of flower-like Au-Ni-ZnO metal-semiconductor hybrid nanocrystals for photocatalytic applications

Bismuth quantum dots anchored one-dimensional CdS as plasmonic photocatalyst for pharmaceutical tetracycline hydrochloride pollutant degradation

Earth abundant metal based plasmonic photocatalysis is one of the most proficient approaches to degrade the emergent organic pollutants in contaminated water. Here, we report that using one-dimensional CdS/zero-dimensional Bi quantum dot (QD) heterostructures (1D/0D CdS/Bi HSs) were obtained via a simple solvothermal reaction. The results specified that the Bi QDs were grown onto CdS NRs through the reduction of Bi³⁺ ions. The Bi modified CdS HSs were employed as a photocatalyst for pharmaceutical pollutant tetracycline degradation and the optimized sample showed the maximum photocatalytic degradation activity of 90% under visible light radiation within 60 min, which is greater than the pure CdS (52%) under identical conditions. Based on the structural characterizations and degradation efficiency, the obtained CdS/Bi is a promising photocatalyst for the treatment of wastewater which contains emerging pollutants such as organic dyes and pharmaceutical antibiotics during the industrial processes. The boosted photocatalytic degradation efficiency is credited to the doped Bi³⁺ species; surface plasmon resonance effect that raised from metallic Bi QDs and proficient photoinduced charge carriers separation.

Low-Frequency Broadband Absorbing Coatings Based on MOFs: Design, Fabrication, Microstructure and Properties

Although most microwave absorbing materials (MAMs) have good absorption ability above 8 GHz, they perform poorly in the low-frequency range (1–8 GHz). Metal–organic frameworks (MOFs) derived carbon-based composites have been highly sought after in electromagnetic materials and functional devices, due to their high specific area, high porosity, high thermal stability, low reflection loss, and adjustable composition. In this review, we first introduce the three loss types of MAMs and argue that composite materials are effective ways to achieve broadband absorption. Secondly, the absorbing properties of traditional materials and MOF materials in the literature are compared, followed by a discussion of the promising strategies for designing MAMs with broadband absorption in low frequencies based on the recent progress. Finally, the main problems, fabrication methods, and applications are discussed for their future prospects.

Synthetic Approaches to Colloidal Nanocrystal Heterostructures Based on Metal and Metal-Oxide Materials

Composite inorganic nanoarchitectures, based on combinations of distinct materials, represent advanced solid-state constructs, where coexistence and synergistic interactions among nonhomologous optical, magnetic, chemical, and catalytic properties lay a basis for the engineering of enhanced or even unconventional functionalities. Such systems thus hold relevance for both theoretical and applied nanotechnology-based research in diverse areas, spanning optics, electronics, energy management, (photo)catalysis, biomedicine, and environmental remediation. Wet-chemical colloidal synthetic techniques have now been refined to the point of allowing the fabrication of solution free-standing and easily processable multicomponent nanocrystals with sophisticated modular heterostructure, built upon a programmed spatial distribution of the crystal phase, composition, and anchored surface moieties. Such last-generation breeds of nanocrystals are thus composed of nanoscale domains of different materials, assembled controllably into core/shell or heteromer-type configurations through bonding epitaxial heterojunctions. This review offers a critical overview of achievements made in the design and synthetic elaboration of colloidal nanocrystal heterostructures based on diverse associations of transition metals (with emphasis on plasmonic metals) and transition-metal oxides. Synthetic strategies, all leveraging on the basic seed-mediated approach, are described and discussed with reference to the most credited mechanisms underpinning regioselective heteroepitaxial deposition. The unique properties and advanced applications allowed by such brand-new nanomaterials are also mentioned.

Synthesis of hybrid Au-Ag2S-Cu2-xS nanocrystals with disparate interfacial features

Hybrid nanocrystals (NCs) with multiple components and junctions have attracted considerable attention due to their promising synergistic properties. In particular, great attention has been paid to the manipulation of buried multijunction heterointerfaces because they are closely related to the surface energy and carrier transfer of NCs. However, heterointerfaced NCs are usually constructed by sequential step-by-step pathways, and buried interfaces can only be formed along a given direction, resulting in the one and only spatial orientation of multiple interfaces. In this work, we demonstrate two types of Au-Ag₂S-Cu_2-xS NCs with disparate interfacial features. Specifically, the first type (Type I) is prepared through a routine two-step method and shows that Au domain close to the Ag₂S-Cu_2-xS interface; another type (Type II) is achieved by a facile one-pot synthesis procedure and contains Au domain with an interphase only with the Ag₂S domain, far from the Cu_2-xS domain. More importantly, type II NCs could not be formed through other traditional strategies and an underlying mechanism of formation is developed by monitoring the evolution process. Au@Ag core-shell NCs, metastable Au@Ag₂S NCs and Janus Au-Ag₂S NCs are formed successively before the Cu_2-xS domain appears. We speculate that the Au@Ag₂S intermediate plays an essential role in building the final complex nanostructure. We expect that such a simple and facile one-pot method will be used to fabricate additional asymmetric multicomponent NCs with distinctive interfacial features and promising potential applications.

Catching and killing of airborne SARS-CoV-2 to control spread of COVID-19 by a heated air disinfection system

Airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via air-conditioning systems poses a significant threat for the continued escalation of the current coronavirus disease (COVID-19) pandemic. Considering that SARS-CoV-2 cannot tolerate temperatures above 70 °C, here we designed and fabricated efficient filters based on heated nickel (Ni) foam to catch and kill SARS-CoV-2. Virus test results revealed that 99.8% of the aerosolized SARS-CoV-2 was caught and killed by a single pass through a novel Ni-foam-based filter when heated up to 200 °C. In addition, the same filter was also used to catch and kill 99.9% of Bacillus anthracis, an airborne spore. This study paves the way for preventing transmission of SARS-CoV-2 and other highly infectious airborne agents in closed environments.

Metal/semiconductor interfaces in nanoscale objects: synthesis, emerging properties and applications of hybrid nanostructures

Hybrid nanostructures, composed of multi-component crystals of various shapes, sizes and compositions are much sought-after functional materials. Pairing the ability to tune each material separately and controllably combine two (or more) domains with defined spatial orientation results in new properties. In this review, we discuss the various synthetic mechanisms for the formation of hybrid nanostructures of various complexities containing at least one metal/semiconductor interface, with a focus on colloidal chemistry. Different synthetic approaches, alongside the underlying kinetic and thermodynamic principles are discussed, and future advancement prospects are evaluated. Furthermore, the proved unique properties are reviewed with emphasis on the connection between the synthetic method and the resulting physical, chemical and optical properties with applications in fields such as photocatalysis.

Photocatalysis with Pt-Au-ZnO and Au-ZnO Hybrids: Effect of Charge Accumulation and Discharge Properties of Metal Nanoparticles

Metal-semiconductor hybrid nanomaterials are becoming increasingly popular for photocatalytic degradation of organic pollutants. Herein, a seed-assisted photodeposition approach is put forward for the site-specific growth of Pt on Au-ZnO particles (Pt-Au-ZnO). A similar approach was also utilized to enlarge the Au nanoparticles at epitaxial Au-ZnO particles (Au@Au-ZnO). An epitaxial connection at the Au-ZnO interface was found to be critical for the site-specific deposition of Pt or Au. Light on-off photocatalysis tests, utilizing a thiazine dye (toluidine blue) as a model organic compound, were conducted and confirmed the superior photodegradation properties of Pt-Au-ZnO hybrids compared to Au-ZnO. In contrast, Au-ZnO type hybrids were more effective toward photoreduction of toluidine blue to leuco-toluidine blue. It was deemed that photoexcited electrons of Au-ZnO (Au, ∼5 nm) possessed high reducing power owing to electron accumulation and negative shift in Fermi level/redox potential; however, exciton recombination due to possible Fermi-level equilibration slowed down the complete degradation of toluidine blue. In the case of Au@Au-ZnO (Au, ∼15 nm), the photodegradation efficiency was enhanced and the photoreduction rate reduced compared to Au-ZnO. Pt-Au-ZnO hybrids showed better photodegradation and mineralization properties compared to both Au-ZnO and Au@Au-ZnO owing to a fast electron discharge (i.e. better electron-hole seperation). However, photoexcited electrons lacked the reducing power for the photoreduction of toluidine blue. The ultimate photodegradation efficiencies of Pt-Au-ZnO, Au@Au-ZnO, and Au-ZnO were 84, 66, and 39%, respectively. In the interest of effective metal-semiconductor type photocatalysts, the present study points out the importance of choosing the right metal, depending on whether a photoreduction and/or photodegradation process is desired.

Ultrathin Oxide Layer-Wrapped Noble Metal Nanoparticles via Colloidal Electrostatic Self-Assembly for Efficient and Reusable Surface Enhanced Raman Scattering Substrates

Controllable and flexible fabrication of ultrathin and uniform oxide layer-wrapped noble metal nanoparticles (NPs) has been expected. Here a new strategy is presented for them based on colloidal electrostatic attraction and self-assembly on the metal NPs via one-step laser ablation of noble metal targets in the hydrolysis-induced hydroxide sol solutions at room temperature. The Au NPs, with several tens of nanometers in size, are taken as core part and TiO₂ as shell-layer to demonstrate the validity of the presented strategy. It has been shown that the TiO₂ shell-wrapped Au NPs are obtained after laser ablation of Au target in the hydrolysis-induced Ti(OH)₄ sol solution. The Au NPs are about 35 nm in mean size, and the TiO₂ shell layers are amorphous in structure and about 2.5 nm in thickness. The shell thickness is nearly independent of the Au NPs' size. Further experiments have shown that the thickness and crystallinity of the shell-layer can be tuned and controlled via changing the temperature or pH value of the Ti(OH)₄ sol solution or prolonging the laser ablation duration. The formation of the TiO₂ shell-wrapped Au NPs is attributed to attachment and self-assembly of Ti(OH)₄ colloids on the laser-induced Au NPs due to the electrostatic attraction between them. Importantly, the presented strategy is universal and suitable for fabrication of many other ultrathin oxide-wrapped noble metal NPs. A series of oxide shell-wrapped noble metal NPs have been successfully fabricated, such as Au@oxides (Fe₂O₃, Al₂O₃, CuO, and ZnO) as well as Pt@TiO₂ and Pd@TiO₂, etc. Further, compared with the pure gold NPs-built film, the TiO₂-wrapped Au NPs-built film has exhibited much stronger surface enhanced Raman scattering (SERS) performance to the anions NO₃^-, which weakly interact with noble metals, and the good reusability for the SERS-based detection of 4-nitrophenol, which could be photodegraded by xenon lamp irradiation. This work provides a flexible and universal route to the ultrathin and uniform oxide layer-wrapped noble metal NPs.

Synthesis and photocatalytic activity of Pt-ZnO hybrid nanocomposite by solution plasma technology

In this paper, Pt-ZnO hybrid nanocomposites were prepared by solution plasma technology. X-ray diffraction (XRD) and energy dispersive x-ray analysis (EDX) were used to verify their chemical composition. The size and morphology of the Pt-ZnO hybrid nanocomposites were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These results indicate that about 2-3 nm Pt nanoparticles (NPs) were synthesized and dispersed on the pyramid-like ZnO (20-60 nm) surface. Photodegradation of Rhodamine B (RhB) demonstrates that the Pt (5 wt%)-ZnO hybrid nanocomposite has better photocatalytic activity than commercial P25 because Pt NPs restrain the photogenerated electron/hole recombination and increase the catalyst activity.

Seed-Mediated Growth of Colloidal Metal Nanocrystals

Seed-mediated growth is a powerful and versatile approach for the synthesis of colloidal metal nanocrystals. The vast allure of this approach mainly stems from the staggering degree of control one can achieve over the size, shape, composition, and structure of nanocrystals. These parameters not only control the properties of nanocrystals but also determine their relevance to, and performance in, various applications. The ingenuity and artistry inherent to seed-mediated growth offer extensive promise, enhancing a number of existing applications and opening the door to new developments. This Review demonstrates how the diversity of metal nanocrystals can be expanded with endless opportunities by using seeds with well-defined and controllable internal structures in conjunction with a proper combination of capping agent and reduction kinetics. New capabilities and future directions are also highlighted.

Metal-Particle-Decorated ZnO Nanocrystals: Photocatalysis and Charge Dynamics

Understanding of charge transfer processes is determinant to the performance optimization for semiconductor photocatalysts. As a representative model of composite photocatalysts, metal-particle-decorated ZnO has been widely employed for a great deal of photocatalytic applications; however, the dependence of charge carrier dynamics on the metal content and metal composition and their correlation with the photocatalytic properties have seldom been reported. Here, the interfacial charge dynamics for metal-decorated ZnO nanocrystals were investigated and their correspondence with the photocatalytic properties was evaluated. The samples were prepared with a delicate antisolvent approach, in which ZnO nanocrystals were grown along with metal particle decoration in a deep eutectic solvent. By modulating the experimental conditions, the metal content (from 0.6 to 2.3 at%) and metal composition (including Ag, Au, and Pd) in the resulting metal-decorated ZnO could be readily controlled. Time-resolved photoluminescence spectra showed that an optimal Au content of 1.3 at% could effectuate the largest electron transfer rate constant for Au-decorated ZnO nanocrystals, in conformity with the highest photocatalytic efficiency observed. The relevance of charge carrier dynamics to the metal composition was also inspected and realized in terms of the energy level difference between ZnO and metal. Among the three metal-decorated ZnO samples tested, ZnO-Pd displayed the highest photocatalytic activity, fundamentally according with the largest electron transfer rate constant deduced in carrier dynamics measurements. The current work was the first study to present the correlations among charge carrier dynamics, metal content, metal composition, and the resultant photocatalytic properties for semiconductor/metal heterostructures. The findings not only helped to resolve the standing issues regarding the mechanistic foundation of photocatalysis but also shed light on the intelligent design of semiconductor/metal composite systems to consolidate their utility in photocatalytic fields.

Embedding Au Quantum Dots in Rimous Cadmium Sulfide Nanospheres for Enhanced Photocatalytic Hydrogen Evolution

Rational design and development of new-generation photocatalysts with high hydrogen evolution activity is recognized as an effective strategy to settle energy crisis. To this regard, hybrid photocatalysts of Au quantum dots embedded in rimous cadmium sulfide nanospheres are synthesized by using a simple hydrothermal process followed by photoreduction. The rimous cadmium sulfide nanospheres with rough surface and irregular fissures greatly strengthen their adhesion and interaction with Au quantum dots, which effectively facilitates the separation, restrains the recombination, and accelerates the consumption of photoinduced electron-hole pairs. Impressively, the highest photocatalytic activity for hydrogen generation (601.2 μmol h^-1 g^-1 ) and organic pollutant degradation (100% degradation in 80 min) is obtained by adjusting the Au mass loading to achieve uniform distribution. This work paves new way to the exploitation of highly efficient metal/semiconductor hybrid photocatalysts for clean energy generation and environment restoration.

Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties

Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications. The utilization of low-cost non-noble metals to construct novel metal-semiconductor hybrid nanocrystals is important and meaningful for their large-scale applications. In this study, a facile solution approach is developed for the synthesis of Cu-ZnO hybrid nanocrystals with well-controlled morphologies, including nanomultipods, core-shell nanoparticles, nanopyramids and core-shell nanowires. In the synthetic strategy, Cu nanocrystals formed in situ serve as seeds for the heterogeneous nucleation and growth of ZnO, and it eventually forms various Cu-ZnO hetero-nanostructures under different reaction conditions. These hybrid nanocrystals possess well-defined and stable heterostructure junctions. The ultraviolet-visible-near infrared spectra reveal morphology-dependent surface plasmon resonance absorption of Cu and the band gap absorption of ZnO. Furthermore, we construct a novel Cu@CuNi-ZnO ternary hetero-nanostructure by incorporating the magnetic metal Ni into the pre-synthesized colloidal Cu nanocrystals. Such hybrid nanocrystals possess a magnetic Cu-Ni intermediate layer between the ZnO shell and the Cu core, and exhibit ferromagnetic/superparamagnetic properties which expand their functionalities. Finally, enhanced photocatalytic activities are observed in the as-prepared non-noble metal-ZnO hybrid nanocrystals. This study not only provides an economical way to prepare high-quality morphology-controlled Cu-ZnO hybrid nanocrystals for potential applications in the fields of photocatalysis and photovoltaic devices, but also opens up new opportunities in designing ternary non-noble metal-semiconductor hybrid nanocrystals with multifunctionalities.

Complete Au@ZnO core-shell nanoparticles with enhanced plasmonic absorption enabling significantly improved photocatalysis

Nanostructured ZnO exhibits high chemical stability and unique optical properties, representing a promising candidate among photocatalysts in the field of environmental remediation and solar energy conversion. However, ZnO only absorbs the UV light, which accounts for less than 5% of total solar irradiation, significantly limiting its applications. In this article, we report a facile and efficient approach to overcome the poor wettability between ZnO and Au by carefully modulating the surface charge density on Au nanoparticles (NPs), enabling rapid synthesis of Au@ZnO core-shell NPs at room temperature. The resulting Au@ZnO core-shell NPs exhibit a significantly enhanced plasmonic absorption in the visible range due to the Au NP cores. They also show a significantly improved photocatalytic performance in comparison with their single-component counterparts, i.e., the Au NPs and ZnO NPs. Moreover, the high catalytic activity of the as-synthesized Au@ZnO core-shell NPs can be maintained even after many cycles of photocatalytic reaction. Our results shed light on the fact that the Au@ZnO core-shell NPs represent a promising class of candidates for applications in plasmonics, surface-enhanced spectroscopy, light harvest devices, solar energy conversion, and degradation of organic pollutants.

Infrared Absorption Enhancement by Charge Transfer in Ga-GaSb Metal-Semiconductor Nanohybrids

We fabricated Ga-GaSb nanohybrids by the droplet epitaxy method and precisely tuned the interaction between the metal and semiconductor parts. Selective absorption enhancement from 1.2 to 1.3 μm was confirmed via ultraviolet-visible-infrared absorption spectra in all of the nanohybrids, which shows size and component dependence. Valence band spectra of the samples indicate that carrier separation occurs at the interface at the Schottky junction and the high density of states near the Fermi level in a semiconductor controls the process of charge transfer. Thus, the enhanced selective absorption in the infrared region will open up a broad prospect for applications in infrared detection and thermophotovoltaic cells.

Synthesis of Sn(1−x)Fex@FeySn(1−y)Oznanohybrids via a simple programmed microfluidic process

Two kinds of nanohybrids were synthesized successfully by a microfluidic process through tuning just the temperature.

Au@ZnO core–shell nanostructures with plasmon-induced visible-light photocatalytic and photoelectrochemical properties

Au@ZnO core–shell nanostructures exhibit enhanced photocatalysis under both simulated sunlight and monochromatic LED light due to the synergistic effect between the plasmonic Au-nanosphere cores and the semiconducting ZnO shells.

Dual-ligand mediated one-pot self-assembly of Cu/ZnO core/shell structures for enhanced microwave absorption

A facile one-pot method has developed to assemble Cu/ZnO core/shell nanocrystals with different aspect ratios for enhanced microwave absorption. Besides, the one-pot method has shown the appreciable yields and no cumbersome multistep operations.

Synthesis of Ag/Ag2CO3 heterostructures with high length–diameter ratios for excellent photoactivity and anti-photocorrosion

Ag/Ag₂CO₃ heterostructures with high length–diameter ratios and superior photoactivity and stability are synthesized on a large scale by a simple one-pot method.

Controllable Synthesis and Surface Wettability of Flower-Shaped Silver Nanocube-Organosilica Hybrid Colloidal Nanoparticles

Synthesis of hybrid colloidal particles with complex and hierarchical structures is attracting much interest theoretically and technically in recent years, but still remains a tremendous challenge. Here, we present a mild and controllable wet-chemical method for the synthesis of silver nanocube (Ag NC)-organosilica hybrid particles with finely tuned numbers (with one, two, three, four, five, or six) and sizes of organosilica petals, by simply controlling the affinity with Ag NC/nature, amount, and prehydrolysis process of alkoxysilanes. The morphologies of hybrid colloidal particles have an obvious influence on the surface wettability of the hybrid particle-based films. More and larger organosilica petals can increase the surface hydrophobicity of the hybrid particle-based films.

Synthesis and photocatalytic properties of multi-morphological AuCu3-ZnO hybrid nanocrystals

Noble metal-semiconductor hybrid nanocrystals represent an important class of materials for many potential applications, especially for photocatalysis. The utilization of transition metals to form alloys with noble metals can not only reduce the preparation costs, but may also offer tunable optical and catalytic properties for a broader range of applications. In this study, we report on the solution synthesis of AuCu3-ZnO hybrid nanocrystals with three interesting morphologies, including urchin-like, flower-like and multipod-like nanocrystals. In the synthetic strategy, Au-Cu bimetallic alloy seeds formed in situ are used to induce the heteroepitaxial growth of ZnO nanocrystals on the surface of bimetallic alloy cores; thus different types of morphologies can be achieved by controlling the reaction conditions. Through high-resolution transmission electron microscopy observations, well-defined interfaces between ZnO and AuCu3 are observed, which indicate that ZnO has a (0001) orientation and prefers to grow on AuCu3 {111} facets. The as-prepared hybrid nanocrystals demonstrate morphology- and composition-dependent surface plasmon resonance (SPR) absorption bands. In addition, much higher photocatalytic efficiency than pure ZnO nanocrystals is observed for the hybrid nanocrystals in the degradation of methylene blue. In particular, the multipod-like AuCu3-ZnO hybrid nanocrystals show the highest catalytic performance, as well as more than three times higher photocurrent density than the pure ZnO sample. The reported synthetic strategy provides a facile route to the effective combination of a plasmonic alloy with semiconductor components at the nanoscale in a controlled manner.

ZnO nanorod/nickel phthalocyanine hierarchical hetero-nanostructures with superior visible light photocatalytic properties assisted by H2O2

ZnO-NR/TPNiPc hierarchical hetero-nanostructure arrays exhibited superior visible light photocatalytic activities in degradation of Rhodamine B assisted by H₂O₂.

Low-temperature synthesis of WO3 nanolamella and their sensing properties for xylene

Tungsten trioxides (WO₃) are an important class of n-type semiconductor oxide materials with a wide band-gap.